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rfc:rfc5546

Network Working Group C. Daboo, Ed. Request for Comments: 5546 Apple Inc. Obsoletes: 2446 December 2009 Updates: 5545 Category: Standards Track

  iCalendar Transport-Independent Interoperability Protocol (iTIP)

Abstract

 This document specifies a protocol that uses the iCalendar object
 specification to provide scheduling interoperability between
 different calendaring systems.  This is done without reference to a
 specific transport protocol so as to allow multiple methods of
 communication between systems.  Subsequent documents will define
 profiles of this protocol that use specific, interoperable methods of
 communication between systems.
 The iCalendar Transport-Independent Interoperability Protocol (iTIP)
 complements the iCalendar object specification by adding semantics
 for group scheduling methods commonly available in current
 calendaring systems.  These scheduling methods permit two or more
 calendaring systems to perform transactions such as publishing,
 scheduling, rescheduling, responding to scheduling requests,
 negotiating changes, or canceling.

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must

Daboo Standards Track [Page 1] RFC 5546 iTIP December 2009

 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction and Overview .......................................5
    1.1. Formatting Conventions .....................................5
    1.2. Related Documents ..........................................6
    1.3. Roles ......................................................6
    1.4. Methods ....................................................7
 2. Interoperability Models .........................................9
    2.1. Application Protocol ......................................10
         2.1.1. Scheduling State ...................................10
         2.1.2. Delegation .........................................10
         2.1.3. Acting on Behalf of Other Calendar Users ...........11
         2.1.4. Component Revisions ................................11
         2.1.5. Message Sequencing .................................12
 3. Application Protocol Elements ..................................13
    3.1. Common Component Restriction Tables .......................15
         3.1.1. VCALENDAR ..........................................15
         3.1.2. VTIMEZONE ..........................................15
         3.1.3. VALARM .............................................17
    3.2. Methods for VEVENT Calendar Components ....................17
         3.2.1. PUBLISH ............................................18
         3.2.2. REQUEST ............................................20
         3.2.3. REPLY ..............................................25
         3.2.4. ADD ................................................27
         3.2.5. CANCEL .............................................29
         3.2.6. REFRESH ............................................31
         3.2.7. COUNTER ............................................33
         3.2.8. DECLINECOUNTER .....................................35
    3.3. Methods for VFREEBUSY Components ..........................37
         3.3.1. PUBLISH ............................................37
         3.3.2. REQUEST ............................................40
         3.3.3. REPLY ..............................................42

Daboo Standards Track [Page 2] RFC 5546 iTIP December 2009

    3.4. Methods for VTODO Components ..............................44
         3.4.1. PUBLISH ............................................44
         3.4.2. REQUEST ............................................46
         3.4.3. REPLY ..............................................51
         3.4.4. ADD ................................................53
         3.4.5. CANCEL .............................................55
         3.4.6. REFRESH ............................................57
         3.4.7. COUNTER ............................................59
         3.4.8. DECLINECOUNTER .....................................61
    3.5. Methods for VJOURNAL Components ...........................62
         3.5.1. PUBLISH ............................................63
         3.5.2. ADD ................................................64
         3.5.3. CANCEL .............................................66
    3.6. Status Replies ............................................68
    3.7. Implementation Considerations .............................77
         3.7.1. Working With Recurrence Instances ..................77
         3.7.2. Attendee Property Considerations ...................78
         3.7.3. Extension Tokens ...................................79
 4. Examples .......................................................79
    4.1. Published Event Examples ..................................79
         4.1.1. A Minimal Published Event ..........................80
         4.1.2. Changing a Published Event .........................80
         4.1.3. Canceling a Published Event ........................81
         4.1.4. A Rich Published Event .............................81
         4.1.5. Anniversaries or Events Attached to Entire Days ....83
    4.2. Group Event Examples ......................................83
         4.2.1. A Group Event Request ..............................84
         4.2.2. Reply to a Group Event Request .....................85
         4.2.3. Update an Event ....................................85
         4.2.4. Countering an Event Proposal .......................86
         4.2.5. Delegating an Event ................................88
         4.2.6. Delegate Accepts the Meeting .......................90
         4.2.7. Delegate Declines the Meeting ......................91
         4.2.8. Forwarding an Event Request ........................92
         4.2.9. Cancel a Group Event ...............................92
         4.2.10. Removing Attendees ................................93
         4.2.11. Replacing the Organizer ...........................95
    4.3. Busy Time Examples ........................................96
         4.3.1. Publish Busy Time ..................................96
         4.3.2. Request Busy Time ..................................96
         4.3.3. Reply to a Busy Time Request .......................97
    4.4. Recurring Event and Time Zone Examples ....................98
         4.4.1. A Recurring Event Spanning Time Zones ..............98
         4.4.2. Modify a Recurring Instance ........................99
         4.4.3. Cancel an Instance ................................101
         4.4.4. Cancel a Recurring Event ..........................101
         4.4.5. Change All Future Instances .......................102
         4.4.6. Add a New Instance to a Recurring Event ...........102

Daboo Standards Track [Page 3] RFC 5546 iTIP December 2009

         4.4.7. Add a New Series of Instances to a
                Recurring Event ...................................103
         4.4.8. Refreshing a Recurring Event ......................104
         4.4.9. Counter an Instance of a Recurring Event ..........106
         4.4.10. Error Reply to a Request .........................107
    4.5. Group To-Do Examples .....................................108
         4.5.1. A VTODO Request ...................................109
         4.5.2. A VTODO Reply .....................................110
         4.5.3. A VTODO Request for Updated Status ................110
         4.5.4. A Reply: Percent-Complete .........................111
         4.5.5. A Reply: Completed ................................111
         4.5.6. An Updated VTODO Request ..........................112
         4.5.7. Recurring VTODOs ..................................112
    4.6. Journal Examples .........................................113
    4.7. Other Examples ...........................................114
         4.7.1. Event Refresh .....................................114
         4.7.2. Bad RECURRENCE-ID .................................114
 5. Application Protocol Fallbacks ................................116
    5.1. Partial Implementation ...................................116
         5.1.1. Event-Related Fallbacks ...........................117
         5.1.2. Free/Busy-Related Fallbacks .......................119
         5.1.3. To-Do-Related Fallbacks ...........................120
         5.1.4. Journal-Related Fallbacks .........................122
    5.2. Latency Issues ...........................................123
         5.2.1. Cancellation of an Unknown Calendar Component .....123
         5.2.2. Unexpected Reply from an Unknown Delegate .........124
    5.3. Sequence Number ..........................................124
 6. Security Considerations .......................................124
    6.1. Security Threats .........................................124
         6.1.1. Spoofing the Organizer ............................124
         6.1.2. Spoofing the Attendee .............................124
         6.1.3. Unauthorized Replacement of the Organizer .........125
         6.1.4. Eavesdropping and Data Integrity ..................125
         6.1.5. Flooding a Calendar ...............................125
         6.1.6. Unauthorized REFRESH Requests .....................125
    6.2. Recommendations ..........................................125
         6.2.1. Securing iTIP transactions ........................125
         6.2.2. Implementation Controls ...........................126
         6.2.3. Access Controls and Filtering .....................126
    6.3. Privacy Issues ...........................................126
 7. IANA Considerations ...........................................127
    7.1. Registration Template for REQUEST-STATUS Values ..........127
    7.2. Additions to iCalendar METHOD Registry ...................127
    7.3. REQUEST-STATUS Value Registry ............................129
 8. Acknowledgments ...............................................130
 9. References ....................................................131
    9.1. Normative References .....................................131
    9.2. Informative References ...................................131

Daboo Standards Track [Page 4] RFC 5546 iTIP December 2009

 Appendix A.  Differences from RFC 2446 ...........................132
   A.1.  Changed Restrictions .....................................132
   A.2.  Deprecated Features ......................................133

1. Introduction and Overview

 This document specifies how calendaring systems use iCalendar
 [RFC5545] objects to interoperate with other calendaring systems.  In
 particular, it specifies how to schedule events, to-dos, or daily
 journal entries.  It further specifies how to search for available
 busy time information.  It does so in a general way, without
 specifying how communication between different systems actually takes
 place.  Subsequent documents will specify transport bindings between
 systems that use this protocol.
 This protocol is based on messages sent from an originator to one or
 more recipients.  For certain types of messages, a recipient may
 reply in order to update their status and may also return
 transaction/request status information.  The protocol supports the
 ability for the message originator to modify or cancel the original
 message.  The protocol also supports the ability for recipients to
 suggest changes to the originator of a message.  The elements of the
 protocol also define the user roles for its transactions.
 This specification obsoletes RFC 2446 - a list of important changes
 is provided in Appendix A.

1.1. Formatting Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 Calendaring and scheduling roles are referred to in quoted-strings of
 text with the first character of each word in upper case.  For
 example, "Organizer" refers to a role of a "Calendar User" (CU)
 within the scheduling protocol.
 Calendar components defined by [RFC5545] are referred to with
 capitalized, quoted-strings of text.  All calendar components start
 with the letter "V".  For example, "VEVENT" refers to the event
 calendar component, "VTODO" refers to the to-do calendar component,
 and "VJOURNAL" refers to the daily journal calendar component.

Daboo Standards Track [Page 5] RFC 5546 iTIP December 2009

 Scheduling methods are referred to with capitalized, quoted-strings
 of text.  For example, "REQUEST" refers to the method for requesting
 a scheduling calendar component be created or modified; "REPLY"
 refers to the method a recipient of a request uses to update their
 status with the "Organizer" of the calendar component.
 Properties defined by [RFC5545] are referred to with capitalized,
 quoted-strings of text, followed by the word "property".  For
 example, "ATTENDEE" property refers to the iCalendar property used to
 convey the calendar address of a "Calendar User".
 Property parameters defined by this specification are referred to
 with capitalized, quoted-strings of text, followed by the word
 "parameter".  For example, "VALUE" parameter refers to the iCalendar
 property parameter used to override the default data type for a
 property value.
 Enumerated values defined by this specification are referred to with
 capitalized text, either alone or followed by the word "value".
 In tables, the quoted-string text is specified without quotes in
 order to minimize the table length.

1.2. Related Documents

 Implementers will need to be familiar with several other
 specifications that, along with this one, describe the Internet
 calendaring and scheduling standards.  The related documents are:
    [RFC5545] - specifies the objects, data types, properties, and
    property parameters used in the protocols, along with the methods
    for representing and encoding them.
    [iMIP] - specifies an Internet email binding for iTIP.
 This specification does not attempt to repeat the concepts or
 definitions from these other specifications.  Where possible,
 explicit references are made to the other specifications.

1.3. Roles

 Exchanges of iCalendar objects for the purposes of group calendaring
 and scheduling occur between "Calendar Users" (CUs).  CUs take on
 several roles in iTIP:

Daboo Standards Track [Page 6] RFC 5546 iTIP December 2009

 +-----------+-------------------------------------------------------+
 | Role      | Description                                           |
 +-----------+-------------------------------------------------------+
 | Organizer | The CU who initiates an exchange takes on the role of |
 |           | Organizer.  For example, the CU who proposes a group  |
 |           | meeting is the Organizer.                             |
 |           |                                                       |
 | Attendee  | CUs who are included in the scheduling message as     |
 |           | possible recipients of that scheduling message.  For  |
 |           | example, the CUs asked to participate in a group      |
 |           | meeting by the Organizer take on the role of          |
 |           | Attendee.                                             |
 |           |                                                       |
 | Other CU  | A CU that is not explicitly included in a scheduling  |
 |           | message, i.e., not the Organizer or an Attendee.      |
 +-----------+-------------------------------------------------------+
 Note that "ROLE" is also a descriptive parameter to the iCalendar
 "ATTENDEE" property.  Its use is to convey descriptive context about
 an "Attendee" -- such as "chair", "required participant", or "non-
 required participant" -- and has nothing to do with the calendaring
 workflow.

1.4. Methods

 The iTIP methods are listed below and their usage and semantics are
 defined in Section 3 of this document.

Daboo Standards Track [Page 7] RFC 5546 iTIP December 2009

 +----------------+--------------------------------------------------+
 | Method         | Description                                      |
 +----------------+--------------------------------------------------+
 | PUBLISH        | Used to publish an iCalendar object to one or    |
 |                | more "Calendar Users".  There is no              |
 |                | interactivity between the publisher and any      |
 |                | other "Calendar User".  An example might include |
 |                | a baseball team publishing its schedule to the   |
 |                | public.                                          |
 |                |                                                  |
 | REQUEST        | Used to schedule an iCalendar object with other  |
 |                | "Calendar Users".  Requests are interactive in   |
 |                | that they require the receiver to respond using  |
 |                | the reply methods.  Meeting requests, busy-time  |
 |                | requests, and the assignment of tasks to other   |
 |                | "Calendar Users" are all examples.  Requests are |
 |                | also used by the Organizer to update the status  |
 |                | of an iCalendar object.                          |
 |                |                                                  |
 | REPLY          | A reply is used in response to a request to      |
 |                | convey Attendee status to the Organizer.         |
 |                | Replies are commonly used to respond to meeting  |
 |                | and task requests.                               |
 |                |                                                  |
 | ADD            | Add one or more new instances to an existing     |
 |                | recurring iCalendar object.                      |
 |                |                                                  |
 | CANCEL         | Cancel one or more instances of an existing      |
 |                | iCalendar object.                                |
 |                |                                                  |
 | REFRESH        | Used by an Attendee to request the latest        |
 |                | version of an iCalendar object.                  |
 |                |                                                  |
 | COUNTER        | Used by an Attendee to negotiate a change in an  |
 |                | iCalendar object.  Examples include the request  |
 |                | to change a proposed event time or change the    |
 |                | due date for a task.                             |
 |                |                                                  |
 | DECLINECOUNTER | Used by the Organizer to decline the proposed    |
 |                | counter proposal.                                |
 +----------------+--------------------------------------------------+

Daboo Standards Track [Page 8] RFC 5546 iTIP December 2009

 Group scheduling in iTIP is accomplished using the set of "request"
 and "response" methods described above.  The following table shows
 the methods broken down by who can send them.
 +------------+------------------------------------------------------+
 | Originator | Methods                                              |
 +------------+------------------------------------------------------+
 | Organizer  | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER        |
 |            |                                                      |
 | Attendee   | REPLY, REFRESH, COUNTER, REQUEST (only when          |
 |            | delegating)                                          |
 +------------+------------------------------------------------------+
 Note that for some calendar component types, the allowable methods
 are a subset of the above set.  In addition, apart from "VTIMEZONE"
 iCalendar components, only one component type is allowed in a single
 iTIP message.

2. Interoperability Models

 There are two distinct protocols relevant to interoperability: an
 "application protocol" and a "transport protocol".  The application
 protocol defines the content of the iCalendar objects sent between
 sender and receiver to accomplish the scheduling transactions listed
 above.  The transport protocol defines how the iCalendar objects are
 sent between the sender and receiver.  This document focuses on the
 application protocol.  Binding documents such as [iMIP] focus on the
 transport protocol.
 The connection between sender and receiver in the diagram below
 refers to the application protocol.  The iCalendar objects passed
 from the sender to the receiver are presented in Section 3,
 "Application Protocol Elements".
         +----------+                +----------+
         |          |      iTIP      |          |
         |  Sender  |<-------------->| Receiver |
         |          |                |          |
         +----------+                +----------+
 There are several variations of this diagram in which the sender and
 receiver take on various roles of a "Calendar User Agent" (CUA) or a
 "Calendar Service" (CS).
 The architecture of iTIP is depicted in the diagram below.  An
 application written to this specification may work with bindings for
 the store-and-forward transport, the real-time transport, or both.
 Also note that iTIP could be bound to other transports.

Daboo Standards Track [Page 9] RFC 5546 iTIP December 2009

    +--------------------------------------------------------+
    |                     iTIP Protocol                      |
    +--------------------------------------------------------+
    |                       Transport                        |
    +  -  -  -  -  -  +  -  -  -  -  -  -  +  -  -  -  -  -  +
    | Real-Time       | Store-and-Forward  | Others          |
    +-----------------+--------------------+-----------------+

2.1. Application Protocol

 In the iTIP model, an iCalendar object is created and managed by an
 "Organizer".  The "Organizer" interacts with other CUs by sending one
 or more of the iTIP messages listed above.  "Attendees" use the
 "REPLY" method to communicate their status.  "Attendees" do not make
 direct changes to the master iCalendar object.  They can, however,
 use the "COUNTER" method to suggest changes to the "Organizer".  In
 any case, the "Organizer" has complete control over the master
 iCalendar object.

2.1.1. Scheduling State

 There are two distinct states relevant to iCalendar objects used in
 scheduling: the overall state of the iCalendar object and the state
 associated with an "Attendee" in that iCalendar object.
 The state of an iCalendar object is defined by the "STATUS" property
 and is controlled by the "Organizer."  There is no default value for
 the "STATUS" property.  The "Organizer" sets the "STATUS" property to
 the appropriate value for each iCalendar object.
 The state of a particular "Attendee" relative to an iCalendar object
 used for scheduling is defined by the "PARTSTAT" parameter in the
 "ATTENDEE" property for each "Attendee".  When an "Organizer" issues
 the initial iCalendar object, "Attendee" status is typically unknown.
 The "Organizer" specifies this by setting the "PARTSTAT" parameter to
 "NEEDS-ACTION".  Each "Attendee" modifies their "ATTENDEE" property
 "PARTSTAT" parameter to an appropriate value as part of a "REPLY"
 message sent back to the "Organizer".

2.1.2. Delegation

 Delegation is defined as the process by which an "Attendee" grants
 another CU (or several CUs) the right to attend on their behalf.  The
 "Organizer" is made aware of this change because the delegating
 "Attendee" informs the "Organizer".  These steps are detailed in the
 "REQUEST" method sections for the appropriate components.

Daboo Standards Track [Page 10] RFC 5546 iTIP December 2009

2.1.3. Acting on Behalf of Other Calendar Users

 In many organizations, one user will act on behalf of another to
 organize and/or respond to meeting requests. iTIP provides two
 mechanisms that support these activities.
 First, the "Organizer" is treated as a special entity, separate from
 "Attendees".  All responses from "Attendees" flow to the "Organizer",
 making it easy to separate a "Calendar User" organizing a meeting
 from "Calendar Users" attending the meeting.  Additionally, iCalendar
 provides descriptive roles for each "Attendee".  For instance, a role
 of "chair" may be ascribed to one or more "Attendees".  The "chair"
 and the "Organizer" may or may not be the same "Calendar User".  This
 maps well to scenarios where an assistant may manage meeting
 logistics for another individual who chairs a meeting.
 Second, a "SENT-BY" parameter may be specified in either the
 "Organizer" or "Attendee" properties.  When specified, the "SENT-BY"
 parameter indicates that the responding CU acted on behalf of the
 specified "Attendee" or "Organizer".

2.1.4. Component Revisions

 The "SEQUENCE" property is used by the "Organizer" to indicate
 revisions to the calendar component.  When the "Organizer" makes
 changes to one of the following properties, the sequence number MUST
 be incremented:
 o  "DTSTART"
 o  "DTEND"
 o  "DURATION"
 o  "DUE"
 o  "RRULE"
 o  "RDATE"
 o  "EXDATE"
 o  "STATUS"
 In addition, changes made by the "Organizer" to other properties MAY
 also require the sequence number to be incremented.  The "Organizer"
 CUA MUST increment the sequence number whenever it makes changes to
 properties in the calendar component that the "Organizer" deems will

Daboo Standards Track [Page 11] RFC 5546 iTIP December 2009

 jeopardize the validity of the participation status of the
 "Attendees".  For example, changing the location of a meeting from
 one location to another distant location could effectively impact the
 participation status of the "Attendees".
 Depending on the "METHOD", the "SEQUENCE" property MUST follow these
 rules in the context of iTIP:
 o  For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
    value is incremented according to the rules stated above.
 o  The "SEQUENCE" property value MUST be incremented each time the
    "Organizer" uses the "ADD" or "CANCEL" methods.
 o  The "SEQUENCE" property value MUST NOT be incremented when using
    "REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
    delegation "REQUEST".
 In some circumstances, the "Organizer" may not have received
 responses to the final revision sent out.  In this situation, the
 "Organizer" may wish to send an update "REQUEST" and set "RSVP=TRUE"
 for all "Attendees" so that current responses can be collected.
 The value of the "SEQUENCE" property contained in a response from an
 "Attendee" may not always match the "Organizer's" revision.
 Implementations may choose to have the CUA indicate to the CU that
 the response is to an iCalendar object that has been revised, and
 allow the CU to decide whether or not to accept the response.
 Whilst a change in sequence number is indicative of a significant
 change to a previously scheduled item, "Attendee" CUAs SHOULD NOT
 rely solely on a change in sequence number as a means of detecting a
 significant change.  Instead, CUAs SHOULD compare the old and new
 versions of the calendar components, determine the exact nature of
 the changes, and make decisions -- possibly based on "Calendar User"
 preferences -- as to whether the user needs to be explicitly informed
 of the change.

2.1.5. Message Sequencing

 CUAs that handle the iTIP application protocol must often correlate a
 component in a calendar store with a component received in the iTIP
 message.  For example, an event may be updated with a later revision
 of the same event.  To accomplish this, a CUA must correlate the
 version of the event already in its calendar store with the version
 sent in the iTIP message.  In addition to this correlation, there are
 several factors that can cause iTIP messages to arrive in an
 unexpected order.  That is, an "Organizer" could receive a reply to

Daboo Standards Track [Page 12] RFC 5546 iTIP December 2009

 an earlier revision of a component after receiving a reply to a later
 revision.
 To maximize interoperability and to handle messages that arrive in an
 unexpected order, use the following rules:
 1.  The primary key for referencing a particular iCalendar component
     is the "UID" property value.  To reference an instance of a
     recurring component, the primary key is composed of the "UID" and
     the "RECURRENCE-ID" properties.
 2.  The secondary key for referencing a component is the "SEQUENCE"
     property value.  For components where the "UID" and
     "RECURRENCE-ID" property values are the same, the component with
     the highest numeric value for the "SEQUENCE" property obsoletes
     all other revisions of the component with lower values.
 3.  "Attendees" send "REPLY" messages to the "Organizer".  For
     replies where the "UID" and "RECURRENCE-ID" property values are
     the same, the value of the "SEQUENCE" property indicates the
     revision of the component to which the "Attendee" is replying.
     The reply with the highest numeric value for the "SEQUENCE"
     property obsoletes all other replies with lower values.
 4.  In situations where the "UID", "RECURRENCE-ID", and "SEQUENCE"
     property values match, the "DTSTAMP" property is used as the tie-
     breaker.  The component with the latest "DTSTAMP" overrides all
     others.  Similarly, for "Attendee" responses where the "UID",
     "RECURRENCE-ID", and "SEQUENCE" property values match, the
     response with the latest "DTSTAMP" overrides all others.
 Hence, CUAs will need to persist the following component properties
 in order to correctly process iTIP messages: "UID", "RECURRENCE-ID",
 "SEQUENCE", and "DTSTAMP".  Furthermore, for each "ATTENDEE" property
 of a component, "Organizer" CUAs will need to persist the "SEQUENCE"
 and "DTSTAMP" property values associated with the "Attendee's" last
 response, so that any earlier responses from an "Attendee" that are
 received out of order (e.g., due to a delay in the transport) can be
 correctly discarded.

3. Application Protocol Elements

 iTIP messages are "text/calendar" MIME entities that contain
 calendaring and scheduling information.  The particular type of
 iCalendar message is referred to as the "method type".  Each method
 type is identified by a "METHOD" property specified as part of the
 "text/calendar" content type.  The table below shows various

Daboo Standards Track [Page 13] RFC 5546 iTIP December 2009

 combinations of calendar components and the method types that this
 specification supports.
      +----------------+--------+-------+----------+-----------+
      |                | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
      +----------------+--------+-------+----------+-----------+
      | PUBLISH        | Yes    | Yes   | Yes      | Yes       |
      | REQUEST        | Yes    | Yes   | No       | Yes       |
      | REFRESH        | Yes    | Yes   | No       | No        |
      | CANCEL         | Yes    | Yes   | Yes      | No        |
      | ADD            | Yes    | Yes   | Yes      | No        |
      | REPLY          | Yes    | Yes   | No       | Yes       |
      | COUNTER        | Yes    | Yes   | No       | No        |
      | DECLINECOUNTER | Yes    | Yes   | No       | No        |
      +----------------+--------+-------+----------+-----------+
 Each method type is defined in terms of its associated components and
 properties.  Some components and properties are required, some are
 optional, and others are excluded.  The restrictions are expressed in
 this document using a simple "restriction table".  The first column
 indicates the name of a component or property.  Properties of the
 iCalendar object are not indented.  Properties of a component are
 indented.  The second column (the "Presence" column) indicates
 whether or not a component or property should be present and, if
 present, how many times it can occur.  The third column contains
 comments for further clarification.
 The presence column uses the following values to assert whether a
 property is required or optional, and the number of times it may
 appear in the iCalendar object.
 +----------------+--------------------------------------------------+
 | Presence Value | Description                                      |
 +----------------+--------------------------------------------------+
 | 1              | One instance MUST be present.                    |
 | 1+             | At least one instance MUST be present.           |
 | 0              | Instances of this property MUST NOT be present.  |
 | 0+             | Multiple instances MAY be present.               |
 | 0 or 1         | Up to 1 instance of this property MAY be         |
 |                | present.                                         |
 +----------------+--------------------------------------------------+
 The tables also call out "IANA-PROPERTY", "X-PROPERTY", "IANA-
 COMPONENT", and "X-COMPONENT" to show where registered and
 experimental property and component extensions can appear.  The
 tables do not lay out the restrictions of property parameters.  Those
 restrictions are defined in [RFC5545].

Daboo Standards Track [Page 14] RFC 5546 iTIP December 2009

3.1. Common Component Restriction Tables

3.1.1. VCALENDAR

 The restriction table below applies to properties of the iCalendar
 object.  That is, the properties at the outermost scope.
        +-----------------------------------------------------+
        | Constraints for Properties in a VCALENDAR Component |
        +-----------------------------------------------------+
        +--------------------+----------+--------------------+
        | Component/Property | Presence | Comment            |
        +--------------------+----------+--------------------+
        | CALSCALE           | 0 or 1   |                    |
        | PRODID             | 1        |                    |
        | VERSION            | 1        | Value MUST be 2.0. |
        | IANA-PROPERTY      | 0+       |                    |
        | X-PROPERTY         | 0+       |                    |
        +--------------------+----------+--------------------+

3.1.2. VTIMEZONE

 "VTIMEZONE" components may be referred to by other components via a
 "TZID" parameter on a "DATETIME" value type.  The property
 restrictions in the table below apply to any "VTIMEZONE" component in
 an iTIP message.
               +--------------------------------------+
               | Constraints for VTIMEZONE Components |
               +--------------------------------------+

Daboo Standards Track [Page 15] RFC 5546 iTIP December 2009

 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to timezone.               |
 |   DAYLIGHT         | 0+       | MUST be one or more of either     |
 |                    |          | STANDARD or DAYLIGHT.             |
 |     COMMENT        | 0+       |                                   |
 |     DTSTART        | 1        | MUST be local time format.        |
 |     RDATE          | 0+       |                                   |
 |     RRULE          | 0 or 1   |                                   |
 |     TZNAME         | 0+       |                                   |
 |     TZOFFSETFROM   | 1        |                                   |
 |     TZOFFSETTO     | 1        |                                   |
 |     IANA-PROPERTY  | 0+       |                                   |
 |     X-PROPERTY     | 0+       |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   STANDARD         | 0+       | MUST be one or more of either     |
 |                    |          | STANDARD or DAYLIGHT.             |
 |     COMMENT        | 0+       |                                   |
 |     DTSTART        | 1        | MUST be local time format.        |
 |     RDATE          | 0+       | If present, RRULE MUST NOT be     |
 |                    |          | present.                          |
 |     RRULE          | 0 or 1   | If present, RDATE MUST NOT be     |
 |                    |          | present.                          |
 |     TZNAME         | 0+       |                                   |
 |     TZOFFSETFROM   | 1        |                                   |
 |     TZOFFSETTO     | 1        |                                   |
 |     IANA-PROPERTY  | 0+       |                                   |
 |     X-PROPERTY     | 0+       |                                   |
 |   TZID             | 1        |                                   |
 |   TZURL            | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 16] RFC 5546 iTIP December 2009

3.1.3. VALARM

 The property restrictions in the table below apply to any "VALARM"
 component in an iTIP message.
                 +-----------------------------------+
                 | Constraints for VALARM Components |
                 +-----------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | VALARM             | 0+       |                                   |
 |   ACTION           | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   ATTENDEE         | 0+       |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DURATION         | 0 or 1   | If present, REPEAT MUST be        |
 |                    |          | present.                          |
 |   REPEAT           | 0 or 1   | If present, DURATION MUST be      |
 |                    |          | present.                          |
 |   SUMMARY          | 0 or 1   |                                   |
 |   TRIGGER          | 1        |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 +--------------------+----------+-----------------------------------+

3.2. Methods for VEVENT Calendar Components

 This section defines the property set restrictions for the method
 types that are applicable to the "VEVENT" calendar component.  Each
 method is defined using a table that clarifies the property
 constraints that define the particular method.
 The following summarizes the methods that are defined for the
 "VEVENT" calendar component.

Daboo Standards Track [Page 17] RFC 5546 iTIP December 2009

 +----------------+--------------------------------------------------+
 | Method         | Description                                      |
 +----------------+--------------------------------------------------+
 | PUBLISH        | Post notification of an event.  Used primarily   |
 |                | as a method of advertising the existence of an   |
 |                | event.                                           |
 |                |                                                  |
 | REQUEST        | Make a request for an event.  This is an         |
 |                | explicit invitation to one or more Attendees.    |
 |                | Event requests are also used to update or change |
 |                | an existing event.  Clients that cannot handle   |
 |                | REQUEST MAY degrade the event to view it as a    |
 |                | PUBLISH.                                         |
 |                |                                                  |
 | REPLY          | Reply to an event request.  Clients may set      |
 |                | their status (PARTSTAT) to ACCEPTED, DECLINED,   |
 |                | TENTATIVE, or DELEGATED.                         |
 |                |                                                  |
 | ADD            | Add one or more instances to an existing event.  |
 |                |                                                  |
 | CANCEL         | Cancel one or more instances of an existing      |
 |                | event.                                           |
 |                |                                                  |
 | REFRESH        | A request is sent to an Organizer by an Attendee |
 |                | asking for the latest version of an event to be  |
 |                | resent to the requester.                         |
 |                |                                                  |
 | COUNTER        | Counter a REQUEST with an alternative proposal.  |
 |                | Sent by an Attendee to the Organizer.            |
 |                |                                                  |
 | DECLINECOUNTER | Decline a counter proposal.  Sent to an Attendee |
 |                | by the Organizer.                                |
 +----------------+--------------------------------------------------+

3.2.1. PUBLISH

 The "PUBLISH" method in a "VEVENT" calendar component is an
 unsolicited posting of an iCalendar object.  Any CU may add published
 components to their calendar.  The "Organizer" MUST be present in a
 published iCalendar component.  "Attendees" MUST NOT be present.  Its
 expected usage is for encapsulating an arbitrary event as an
 iCalendar object.  The "Organizer" may subsequently update (with
 another "PUBLISH" method), add instances to (with an "ADD" method),
 or cancel (with a "CANCEL" method) a previously published "VEVENT"
 calendar component.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 18] RFC 5546 iTIP December 2009

           +----------------------------------------------+
           | Constraints for a METHOD:PUBLISH of a VEVENT |
           +----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST equal PUBLISH.               |
 |                    |          |                                   |
 | VEVENT             | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
 |                    |          | greater than 0; MAY be present if |
 |                    |          | 0.                                |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0 or 1   |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | TENTATIVE/CONFIRMED/CANCELLED.    |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |

Daboo Standards Track [Page 19] RFC 5546 iTIP December 2009

 |   ATTENDEE         | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 +--------------------+----------+-----------------------------------+

3.2.2. REQUEST

 The "REQUEST" method in a "VEVENT" component provides the following
 scheduling functions:
 o  Invite "Attendees" to an event.
 o  Reschedule an existing event.
 o  Response to a "REFRESH" request.
 o  Update the details of an existing event, without rescheduling it.
 o  Update the status of "Attendees" of an existing event, without
    rescheduling it.
 o  Reconfirm an existing event, without rescheduling it.
 o  Forward a "VEVENT" to another uninvited CU.
 o  For an existing "VEVENT" calendar component, delegate the role of
    "Attendee" to another CU.
 o  For an existing "VEVENT" calendar component, change the role of
    "Organizer" to another CU.
 The "Organizer" originates the "REQUEST".  The recipients of the
 "REQUEST" method are the CUs invited to the event, the "Attendees".
 "Attendees" use the "REPLY" method to convey attendance status to the
 "Organizer".

Daboo Standards Track [Page 20] RFC 5546 iTIP December 2009

 The "UID" and "SEQUENCE" properties are used to distinguish the
 various uses of the "REQUEST" method.  If the "UID" property value in
 the "REQUEST" is not found on the recipient's calendar, then the
 "REQUEST" is for a new "VEVENT" calendar component.  If the "UID"
 property value is found on the recipient's calendar, then the
 "REQUEST" is for a rescheduling, an update, or a reconfirmation of
 the "VEVENT" calendar component.
 For the "REQUEST" method, multiple "VEVENT" components in a single
 iCalendar object are only permitted for components with the same
 "UID" property.  That is, a series of recurring events may have
 instance-specific information.  In this case, multiple "VEVENT"
 components are needed to express the entire series.
 This method type is an iCalendar object that conforms to the
 following property constraints:
           +----------------------------------------------+
           | Constraints for a METHOD:REQUEST of a VEVENT |
           +----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REQUEST.                  |
 |                    |          |                                   |
 | VEVENT             | 1+       | All components MUST have the same |
 |                    |          | UID.                              |
 |   ATTENDEE         | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
 |                    |          | greater than 0; MAY be present if |
 |                    |          | 0.                                |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |

Daboo Standards Track [Page 21] RFC 5546 iTIP December 2009

 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | TENTATIVE/CONFIRMED.              |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.2.1. Rescheduling an Event

 The "REQUEST" method may be used to reschedule an event.  A
 rescheduled event involves a change to the existing event in terms of
 its time or recurrence intervals and possibly the location or
 description.  If the recipient CUA of a "REQUEST" method finds that
 the "UID" property value already exists on the calendar but that the
 "SEQUENCE" (or "DTSTAMP") property value in the "REQUEST" method is
 greater than the value for the existing event, then the "REQUEST"
 method describes a rescheduling of the event.

Daboo Standards Track [Page 22] RFC 5546 iTIP December 2009

3.2.2.2. Updating or Reconfirmation of an Event

 The "REQUEST" method may be used to update or reconfirm an event.  An
 update to an existing event does not involve changes to the time or
 recurrence intervals, and might not involve a change to the location
 or description for the event.  If the recipient CUA of a "REQUEST"
 method finds that the "UID" property value already exists on the
 calendar and that the "SEQUENCE" property value in the "REQUEST" is
 the same as the value for the existing event, then the "REQUEST"
 method describes an update of the event details, but not a
 rescheduling of the event.
 The update "REQUEST" method is the appropriate response to a
 "REFRESH" method sent from an "Attendee" to the "Organizer" of an
 event.
 The "Organizer" of an event may also send unsolicited "REQUEST"
 methods.  The unsolicited "REQUEST" methods may be used to update the
 details of the event without rescheduling it, to update the
 "PARTSTAT" parameter of "Attendees", or to reconfirm the event.

3.2.2.3. Delegating an Event to Another CU

 Some calendar and scheduling systems allow "Attendees" to delegate
 their presence at an event to another "Calendar User". iTIP supports
 this concept using the following workflow.  Any "Attendee" may
 delegate their right to participate in a calendar "VEVENT" to another
 CU.  The implication is that the delegate participates in lieu of the
 original "Attendee", NOT in addition to the "Attendee".  The
 delegator MUST notify the "Organizer" of this action using the steps
 outlined below.  Implementations may support or restrict delegation
 as they see fit.  For instance, some implementations may restrict a
 delegate from delegating a "REQUEST" to another CU.
 The "Delegator" of an event forwards the existing "REQUEST" to the
 "Delegate".  The "REQUEST" method MUST include an "ATTENDEE" property
 with the calendar address of the "Delegate".  The "Delegator" MUST
 also send a "REPLY" method to the "Organizer" with the "Delegator's"
 "ATTENDEE" property "PARTSTAT" parameter value set to "DELEGATED".
 In addition, the "DELEGATED-TO" parameter MUST be included with the
 calendar address of the "Delegate".  Also, a new "ATTENDEE" property
 for the "Delegate" MUST be included and must specify the calendar
 user address set in the "DELEGATED-TO" parameter, as above.
 In response to the request, the "Delegate" MUST send a "REPLY" method
 to the "Organizer", and optionally to the "Delegator".  The "REPLY"
 method SHOULD include the "ATTENDEE" property with the "DELEGATED-
 FROM" parameter value of the "Delegator's" calendar address.

Daboo Standards Track [Page 23] RFC 5546 iTIP December 2009

 The "Delegator" may continue to receive updates to the event even
 though they will not be attending.  This is accomplished by the
 "Delegator" setting their "role" attribute to "NON-PARTICIPANT" in
 the "REPLY" to the "Organizer".

3.2.2.4. Changing the Organizer

 The situation may arise where the "Organizer" of a "VEVENT" is no
 longer able to perform the "Organizer" role and abdicates without
 passing on the "Organizer" role to someone else.  When this occurs,
 the "Attendees" of the "VEVENT" may use out-of-band mechanisms to
 communicate the situation and agree upon a new "Organizer".  The new
 "Organizer" should then send out a new "REQUEST" with a modified
 version of the "VEVENT" in which the "SEQUENCE" number has been
 incremented and the "ORGANIZER" property has been changed to the new
 "Organizer".

3.2.2.5. Sending on Behalf of the Organizer

 There are a number of scenarios that support the need for a "Calendar
 User" to act on behalf of the "Organizer" without explicit role
 changing.  This might be the case if the CU designated as "Organizer"
 is sick or unable to perform duties associated with that function.
 In these cases, iTIP supports the notion of one CU acting on behalf
 of another.  Using the "SENT-BY" parameter, a "Calendar User" could
 send an updated "VEVENT" "REQUEST".  In the case where one CU sends
 on behalf of another CU, the "Attendee" responses are still directed
 back towards the CU designated as "Organizer".

3.2.2.6. Forwarding to an Uninvited CU

 An "Attendee" invited to a "VEVENT" calendar component may send the
 "VEVENT" calendar component to another new CU not previously
 associated with the "VEVENT" calendar component.  The current
 "Attendee" invited to the "VEVENT" calendar component does this by
 forwarding the original "REQUEST" method to the new CU.  The new CU
 can send a "REPLY" to the "Organizer" of the "VEVENT" calendar
 component.  The reply contains an "ATTENDEE" property for the new CU.
 The "Organizer" ultimately decides whether or not the new CU becomes
 part of the event and is not obligated to do anything with a "REPLY"
 from a new (uninvited) CU.  If the "Organizer" does not want the new
 CU to be part of the event, the new "ATTENDEE" property is not added
 to the "VEVENT" calendar component.  The "Organizer" MAY send the CU
 a "CANCEL" message to indicate that they will not be added to the
 event.  If the "Organizer" decides to add the new CU, the new
 "ATTENDEE" property is added to the "VEVENT" calendar component.
 Furthermore, the "Organizer" is free to change any "ATTENDEE"

Daboo Standards Track [Page 24] RFC 5546 iTIP December 2009

 property parameter from the values supplied by the new CU to
 something the "Organizer" considers appropriate.  The "Organizer"
 SHOULD send the new CU a "REQUEST" message to inform them that they
 have been added.
 When forwarding a "REQUEST" to another CU, the forwarding "Attendee"
 MUST NOT make changes to the original message.

3.2.2.7. Updating Attendee Status

 The "Organizer" of an event may also request updated status from one
 or more "Attendees".  The "Organizer" sends a "REQUEST" method to the
 "Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter.  The
 "SEQUENCE" property for the event is not changed from its previous
 value.  A recipient will determine that the only change in the
 "REQUEST" is that their "RSVP" property parameter indicates a request
 for updated status.  The recipient SHOULD respond with a "REPLY"
 method indicating their current status with respect to the "REQUEST".

3.2.3. REPLY

 The "REPLY" method in a "VEVENT" calendar component is used to
 respond (e.g., accept or decline) to a "REQUEST" or to reply to a
 delegation "REQUEST".  When used to provide a delegation response,
 the "Delegator" SHOULD include the calendar address of the "Delegate"
 on the "DELEGATED-TO" property parameter of the "Delegator's"
 "ATTENDEE" property.  The "Delegate" SHOULD include the calendar
 address of the "Delegator" on the "DELEGATED-FROM" property parameter
 of the "Delegate's" "ATTENDEE" property.
 The "REPLY" method is also used when processing of a "REQUEST" fails.
 Depending on the value of the "REQUEST-STATUS" property, no
 scheduling action may have been performed.
 The "Organizer" of an event may receive the "REPLY" method from a CU
 not in the original "REQUEST".  For example, a "REPLY" may be
 received from a "Delegate" to an event.  In addition, the "REPLY"
 method may be received from an unknown CU (a "Party Crasher").  This
 uninvited "Attendee" may be accepted, or the "Organizer" may cancel
 the event for the uninvited "Attendee" by sending a "CANCEL" method
 to the uninvited "Attendee".
 An "Attendee" MAY include a message to the "Organizer" using the
 "COMMENT" property.  For example, if the user indicates tentative
 acceptance and wants to let the "Organizer" know why, the reason can
 be expressed in the "COMMENT" property value.

Daboo Standards Track [Page 25] RFC 5546 iTIP December 2009

 The "Organizer" may also receive a "REPLY" from one CU on behalf of
 another.  Like the scenario enumerated above for the "Organizer",
 "Attendees" may have another CU respond on their behalf.  This is
 done using the "SENT-BY" parameter.
 The optional properties listed in the table below (those listed as
 "0+" or "0 or 1") MUST NOT be changed from those of the original
 request.  If property changes are desired, the "COUNTER" message must
 be used.
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +--------------------------------------------+
            | Constraints for a METHOD:REPLY of a VEVENT |
            +--------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REPLY.                    |
 |                    |          |                                   |
 | VEVENT             | 1+       | All components MUST have the same |
 |                    |          | UID.                              |
 |   ATTENDEE         | 1        | MUST be the address of the        |
 |                    |          | Attendee replying.                |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   UID              | 1        | MUST be the UID of the original   |
 |                    |          | REQUEST.                          |
 |   SEQUENCE         | 0 or 1   | If non-zero, MUST be the sequence |
 |                    |          | number of the original REQUEST.   |
 |                    |          | MAY be present if 0.              |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DTSTART          | 0 or 1   |                                   |

Daboo Standards Track [Page 26] RFC 5546 iTIP December 2009

 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   |                                   |
 |   SUMMARY          | 0 or 1   |                                   |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.4. ADD

 The "ADD" method allows the "Organizer" to add one or more new
 instances to an existing "VEVENT" using a single iTIP message without
 having to send the entire "VEVENT" with all the existing instance
 data, as it would have to do if the "REQUEST" method were used.
 The "UID" must be that of the existing event.  If the "UID" property
 value in the "ADD" is not found on the recipient's calendar, then the
 recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
 updated with the latest version of the "VEVENT".  If an "Attendee"
 implementation does not support the "ADD" method, it should respond
 with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".

Daboo Standards Track [Page 27] RFC 5546 iTIP December 2009

 When handling an "ADD" message, the "Attendee" treats each component
 in the "ADD" message as if it were referenced via an "RDATE" in the
 main component.
 This method type is an iCalendar object that conforms to the
 following property constraints:
             +------------------------------------------+
             | Constraints for a METHOD:ADD of a VEVENT |
             +------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be ADD.                      |
 |                    |          |                                   |
 | VEVENT             | 1        |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        | MUST be greater than 0.           |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        | MUST match that of the original   |
 |                    |          | event.                            |
 |   ATTACH           | 0+       |                                   |
 |   ATTENDEE         | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | TENTATIVE/CONFIRMED.              |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |

Daboo Standards Track [Page 28] RFC 5546 iTIP December 2009

 |   EXDATE           | 0        |                                   |
 |   RECURRENCE-ID    | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RDATE            | 0        |                                   |
 |   RRULE            | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.5. CANCEL

 The "CANCEL" method in a "VEVENT" calendar component is used to send
 a cancellation notice of an existing event request to the affected
 "Attendees".  The message is sent by the "Organizer" of the event.
 For a recurring event, either the whole event or instances of an
 event may be cancelled.  To cancel the complete range of a recurring
 event, the "UID" property value for the event MUST be specified and a
 "RECURRENCE-ID" MUST NOT be specified in the "CANCEL" method.  In
 order to cancel an individual instance of the event, the
 "RECURRENCE-ID" property value for the event MUST be specified in the
 "CANCEL" method.
 There are two options for canceling a sequence of instances of a
 recurring "VEVENT" calendar component:
 a.  The "RECURRENCE-ID" property for an instance in the sequence MUST
     be specified with the "RANGE" property parameter value of
     "THISANDFUTURE" to indicate cancellation of the specified
     "VEVENT" calendar component and all instances after.
 b.  Individual recurrence instances may be cancelled by specifying
     multiple "VEVENT" components each with a "RECURRENCE-ID" property
     corresponding to one of the instances to be cancelled.

Daboo Standards Track [Page 29] RFC 5546 iTIP December 2009

 The "Organizer" MUST send a "CANCEL" message to each "Attendee"
 affected by the cancellation.  This can be done using a single
 "CANCEL" message for all "Attendees" or by using multiple messages
 with different subsets of the affected "Attendees" in each.
 When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be
 incremented as described in Section 2.1.4.
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +---------------------------------------------+
            | Constraints for a METHOD:CANCEL of a VEVENT |
            +---------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be CANCEL.                   |
 |                    |          |                                   |
 | VEVENT             | 1+       | All must have the same UID.       |
 |   ATTENDEE         | 0+       | MUST include some or all          |
 |                    |          | Attendees being removed from the  |
 |                    |          | event.  MUST include some or all  |
 |                    |          | Attendees if the entire event is  |
 |                    |          | cancelled.                        |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        |                                   |
 |   UID              | 1        | MUST be the UID of the original   |
 |                    |          | REQUEST.                          |
 |   COMMENT          | 0+       |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DTSTART          | 0 or 1   |                                   |
 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |

Daboo Standards Track [Page 30] RFC 5546 iTIP December 2009

 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MUST be set to CANCELLED to       |
 |                    |          | cancel the entire event.  If      |
 |                    |          | uninviting specific Attendees,    |
 |                    |          | then MUST NOT be included.        |
 |   SUMMARY          | 0 or 1   |                                   |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.6. REFRESH

 The "REFRESH" method in a "VEVENT" calendar component is used by
 "Attendees" of an existing event to request an updated description
 from the event "Organizer".  The "REFRESH" method must specify the
 "UID" property of the event to update.  A recurrence instance of an
 event may be requested by specifying the "RECURRENCE-ID" property
 corresponding to the associated event.  The "Organizer" responds with
 the latest description and version of the event.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 31] RFC 5546 iTIP December 2009

           +----------------------------------------------+
           | Constraints for a METHOD:REFRESH of a VEVENT |
           +----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REFRESH.                  |
 |                    |          |                                   |
 | VEVENT             | 1        |                                   |
 |   ATTENDEE         | 1        | MUST be the address of requester. |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   UID              | 1        | MUST be the UID associated with   |
 |                    |          | original REQUEST.                 |
 |   COMMENT          | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   ATTACH           | 0        |                                   |
 |   CATEGORIES       | 0        |                                   |
 |   CLASS            | 0        |                                   |
 |   CONTACT          | 0        |                                   |
 |   CREATED          | 0        |                                   |
 |   DESCRIPTION      | 0        |                                   |
 |   DTEND            | 0        |                                   |
 |   DTSTART          | 0        |                                   |
 |   DURATION         | 0        |                                   |
 |   EXDATE           | 0        |                                   |
 |   GEO              | 0        |                                   |
 |   LAST-MODIFIED    | 0        |                                   |
 |   LOCATION         | 0        |                                   |
 |   PRIORITY         | 0        |                                   |
 |   RDATE            | 0        |                                   |
 |   RELATED-TO       | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RESOURCES        | 0        |                                   |
 |   RRULE            | 0        |                                   |
 |   SEQUENCE         | 0        |                                   |
 |   STATUS           | 0        |                                   |
 |   SUMMARY          | 0        |                                   |
 |   TRANSP           | 0        |                                   |
 |   URL              | 0        |                                   |
 |                    |          |                                   |

Daboo Standards Track [Page 32] RFC 5546 iTIP December 2009

 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       |                                   |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.7. COUNTER

 The "COUNTER" method for a "VEVENT" calendar component is used by an
 "Attendee" of an existing event to submit to the "Organizer" a
 counter proposal to the event.  The "Attendee" sends this message to
 the "Organizer" of the event.
 The counter proposal is an iCalendar object consisting of a "VEVENT"
 calendar component that provides the complete description of the
 alternate event.
 The "Organizer" rejects the counter proposal by sending the
 "Attendee" a "DECLINECOUNTER" method.  The "Organizer" accepts the
 counter proposal by rescheduling the event as described in
 Section 3.2.2.1, "Rescheduling an Event".  The "Organizer's" CUA
 SHOULD send a "REQUEST" message to all "Attendees" affected by any
 change triggered by an accepted "COUNTER".
 This method type is an iCalendar object that conforms to the
 following property constraints:
           +----------------------------------------------+
           | Constraints for a METHOD:COUNTER of a VEVENT |
           +----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be COUNTER.                  |
 |                    |          |                                   |
 | VEVENT             | 1        |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |

Daboo Standards Track [Page 33] RFC 5546 iTIP December 2009

 |   ORGANIZER        | 1        | MUST be the Organizer of the      |
 |                    |          | original event.                   |
 |   SEQUENCE         | 1        | MUST echo the original SEQUENCE   |
 |                    |          | number.  MUST be present if       |
 |                    |          | non-zero.  MAY be present if      |
 |                    |          | zero.                             |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        | MUST be the UID associated with   |
 |                    |          | the REQUEST being countered.      |
 |   ATTACH           | 0+       |                                   |
 |   ATTENDEE         | 0+       | Can also be used to propose other |
 |                    |          | Attendees.                        |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | Value must be one of              |
 |                    |          | CONFIRMED/TENATIVE/CANCELLED.     |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |

Daboo Standards Track [Page 34] RFC 5546 iTIP December 2009

 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.2.8. DECLINECOUNTER

 The "DECLINECOUNTER" method in a "VEVENT" calendar component is used
 by the "Organizer" of an event to reject a counter proposal submitted
 by an "Attendee".  The "Organizer" must send the "DECLINECOUNTER"
 message to the "Attendee" that sent the "COUNTER" method to the
 "Organizer".
 This method type is an iCalendar object that conforms to the
 following property constraints:
        +-----------------------------------------------------+
        | Constraints for a METHOD:DECLINECOUNTER of a VEVENT |
        +-----------------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be DECLINECOUNTER.           |
 |                    |          |                                   |
 | VEVENT             | 1+       | All components MUST have the same |
 |                    |          | UID.                              |
 |   ATTENDEE         | 1+       | MUST for all Attendees.           |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        | MUST echo the original SEQUENCE   |
 |                    |          | number.                           |
 |   UID              | 1        | MUST echo original UID.           |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTSTART          | 0 or 1   |                                   |
 |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |

Daboo Standards Track [Page 35] RFC 5546 iTIP December 2009

 |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | TENTATIVE/CONFIRMED.              |
 |   SUMMARY          | 0 or 1   | Can be null.                      |
 |   TRANSP           | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 36] RFC 5546 iTIP December 2009

3.3. Methods for VFREEBUSY Components

 This section defines the property set for the methods that are
 applicable to the "VFREEBUSY" calendar component.  Each of the
 methods is defined using a restriction table.
 This document only addresses the transfer of busy time information.
 Applications desiring free time information MUST infer this from
 available busy time information.
 The "FREEBUSY" property value MAY include a list of values, separated
 by the COMMA character (US-ASCII decimal 44).  Alternately, multiple
 busy time periods MAY be specified with multiple instances of the
 "FREEBUSY" property.  Both forms MUST be supported by implementations
 conforming to this document.  Duplicate busy time periods SHOULD NOT
 be specified in an iCalendar object.  However, two different busy
 time periods MAY overlap.
 "FREEBUSY" properties SHOULD be sorted such that their values are in
 ascending order, based on the start time and then the end time, with
 the earliest periods first.  For example, today's busy time
 information should appear after yesterday's busy time information.
 And the busy time for this half-hour should appear after the busy
 time for earlier today.  Busy time periods can also span a day
 boundary.
 The following summarizes the methods that are defined for the
 "VFREEBUSY" calendar component.
           +---------+-------------------------------------+
           | Method  | Description                         |
           +---------+-------------------------------------+
           | PUBLISH | Publish unsolicited busy time data. |
           |         |                                     |
           | REQUEST | Request busy time data.             |
           |         |                                     |
           | REPLY   | Reply to a busy time request.       |
           +---------+-------------------------------------+

3.3.1. PUBLISH

 The "PUBLISH" method in a "VFREEBUSY" calendar component is used to
 publish busy time data.  The method may be sent from one CU to any
 other.  The purpose of the method is to provide a way to send
 unsolicited busy time data.  That is, the busy time data is not being
 sent as a "REPLY" to the receipt of a "REQUEST" method.

Daboo Standards Track [Page 37] RFC 5546 iTIP December 2009

 The "ORGANIZER" property MUST be specified in the busy time
 information.  The value is the CU address of the originator of the
 busy time information.
 The busy time information within the iCalendar object MAY be grouped
 into more than one "VFREEBUSY" calendar component.  This capability
 allows busy time periods to be grouped according to some common
 periodicity, such as a calendar week, month, or year.  In this case,
 each "VFREEBUSY" calendar component MUST include the "ORGANIZER",
 "DTSTART", and "DTEND" properties in order to specify the source of
 the busy time information and the date and time interval over which
 the busy time information covers.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 38] RFC 5546 iTIP December 2009

          +-------------------------------------------------+
          | Constraints for a METHOD:PUBLISH of a VFREEBUSY |
          +-------------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be PUBLISH.                  |
 |                    |          |                                   |
 | VFREEBUSY          | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        | DateTime values must be in UTC.   |
 |   DTEND            | 1        | DateTime values must be in UTC.   |
 |   FREEBUSY         | 0+       | MUST be BUSYTIME.  Multiple       |
 |                    |          | instances are allowed.  Multiple  |
 |                    |          | instances SHOULD be sorted in     |
 |                    |          | ascending order.                  |
 |   ORGANIZER        | 1        | MUST contain the address of       |
 |                    |          | originator of busy time data.     |
 |   UID              | 1        |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   URL              | 0 or 1   | Specifies busy time URL.          |
 |   ATTENDEE         | 0        |                                   |
 |   DURATION         | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 39] RFC 5546 iTIP December 2009

3.3.2. REQUEST

 The "REQUEST" method in a "VFREEBUSY" calendar component is used to
 ask a "Calendar User" for their busy time information.  The request
 may be for a busy time information bounded by a specific date and
 time interval.
 This message only permits requests for busy time information.  The
 message is sent from a "Calendar User" requesting the busy time
 information of one or more intended recipients.
 If the originator of the "REQUEST" method is not authorized to make a
 busy time request on the recipient's calendar system, then an
 exception message SHOULD be returned in a "REPLY" method, but no busy
 time data need be returned.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 40] RFC 5546 iTIP December 2009

          +-------------------------------------------------+
          | Constraints for a METHOD:REQUEST of a VFREEBUSY |
          +-------------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REQUEST.                  |
 |                    |          |                                   |
 | VFREEBUSY          | 1        |                                   |
 |   ATTENDEE         | 1+       | Contains the calendar user        |
 |                    |          | addresses of the "Calendar Users" |
 |                    |          | whose freebusy is being           |
 |                    |          | requested.                        |
 |   DTEND            | 1        | DateTime values must be in UTC.   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        | DateTime values must be in UTC.   |
 |   ORGANIZER        | 1        | MUST be the request originator's  |
 |                    |          | address.                          |
 |   UID              | 1        |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   FREEBUSY         | 0        |                                   |
 |   DURATION         | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   URL              | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 41] RFC 5546 iTIP December 2009

3.3.3. REPLY

 The "REPLY" method in a "VFREEBUSY" calendar component is used to
 respond to a busy time request.  The method is sent by the recipient
 of a busy time request to the originator of the request.
 The "REPLY" method may also be used to respond to an unsuccessful
 "REQUEST" method.  Depending on the "REQUEST-STATUS" value, no busy
 time information may be returned.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 42] RFC 5546 iTIP December 2009

           +-----------------------------------------------+
           | Constraints for a METHOD:REPLY of a VFREEBUSY |
           +-----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REPLY.                    |
 |                    |          |                                   |
 | VFREEBUSY          | 1        |                                   |
 |   ATTENDEE         | 1        | MUST be the address of the        |
 |                    |          | Attendee replying.                |
 |   DTSTAMP          | 1        |                                   |
 |   DTEND            | 1        | DateTime values must be in UTC.   |
 |   DTSTART          | 1        | DateTime values must be in UTC.   |
 |   FREEBUSY         | 0+       | MUST be BUSYTIME.  Multiple       |
 |                    |          | instances are allowed.  Multiple  |
 |                    |          | instances SHOULD be sorted in     |
 |                    |          | ascending order.                  |
 |   ORGANIZER        | 1        | MUST be the request originator's  |
 |                    |          | address.                          |
 |   UID              | 1        | MUST be the UID of the original   |
 |                    |          | REQUEST.                          |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0 or 1   |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   URL              | 0 or 1   | Specifies busy time URL.          |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   DURATION         | 0        |                                   |
 |   SEQUENCE         | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 43] RFC 5546 iTIP December 2009

3.4. Methods for VTODO Components

 This section defines the property set for the methods that are
 applicable to the "VTODO" calendar component.  Each of the methods is
 defined using a restriction table that specifies the property
 constraints that define the particular method.
 The following summarizes the methods that are defined for the "VTODO"
 calendar component.
 +----------------+--------------------------------------------------+
 | Method         | Description                                      |
 +----------------+--------------------------------------------------+
 | PUBLISH        | Post notification of a VTODO.  Used primarily as |
 |                | a method of advertising the existence of a       |
 |                | VTODO.                                           |
 |                |                                                  |
 | REQUEST        | Assign a VTODO.  This is an explicit assignment  |
 |                | to one or more Calendar Users.  The REQUEST      |
 |                | method is also used to update or change an       |
 |                | existing VTODO.  Clients that cannot handle      |
 |                | REQUEST MAY degrade the method to treat it as a  |
 |                | PUBLISH.                                         |
 |                |                                                  |
 | REPLY          | Reply to a VTODO request.  Attendees MAY set     |
 |                | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE,       |
 |                | DELEGATED, PARTIAL, and COMPLETED.               |
 |                |                                                  |
 | ADD            | Add one or more instances to an existing to-do.  |
 |                |                                                  |
 | CANCEL         | Cancel one or more instances of an existing      |
 |                | to-do.                                           |
 |                |                                                  |
 | REFRESH        | A request sent to a VTODO Organizer asking for   |
 |                | the latest version of a VTODO.                   |
 |                |                                                  |
 | COUNTER        | Counter a REQUEST with an alternative proposal.  |
 |                |                                                  |
 | DECLINECOUNTER | Decline a counter proposal by an Attendee.       |
 +----------------+--------------------------------------------------+

3.4.1. PUBLISH

 The "PUBLISH" method in a "VTODO" calendar component has no
 associated response.  It is simply a posting of an iCalendar object
 that may be added to a calendar.  It MUST have an "Organizer".  It
 MUST NOT have "Attendees".  Its expected usage is for encapsulating
 an arbitrary "VTODO" calendar component as an iCalendar object.  The

Daboo Standards Track [Page 44] RFC 5546 iTIP December 2009

 "Organizer" MAY subsequently update (with another "PUBLISH" method),
 add instances to (with an "ADD" method), or cancel (with a "CANCEL"
 method) a previously published "VTODO" calendar component.
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +---------------------------------------------+
            | Constraints for a METHOD:PUBLISH of a VTODO |
            +---------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be PUBLISH.                  |
 |                    |          |                                   |
 | VTODO              | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   PRIORITY         | 1        |                                   |
 |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
 |                    |          | greater than 0; MAY be present if |
 |                    |          | 0.                                |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |

Daboo Standards Track [Page 45] RFC 5546 iTIP December 2009

 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | COMPLETED/NEEDS-ACTION/           |
 |                    |          | IN-PROCESS/CANCELLED.             |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   ATTENDEE         | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.2. REQUEST

 The "REQUEST" method in a "VTODO" calendar component provides the
 following scheduling functions:
 o  Assign a to-do to one or more "Calendar Users".
 o  Reschedule an existing to-do.
 o  Update the details of an existing to-do, without rescheduling it.
 o  Update the completion status of "Attendees" of an existing to-do,
    without rescheduling it.
 o  Reconfirm an existing to-do, without rescheduling it.
 o  Delegate/reassign an existing to-do to another "Calendar User".
 The assigned "Calendar Users" are identified in the "VTODO" calendar
 component by individual "ATTENDEE;ROLE=REQ-PARTICIPANT" property
 value sequences.

Daboo Standards Track [Page 46] RFC 5546 iTIP December 2009

 Typically, the originator of a "REQUEST" is the "Organizer" of the
 to-do, and the recipient of a "REQUEST" is the "Calendar User"
 assigned the to-do.  The "Attendee" uses the "REPLY" method to convey
 their acceptance and completion status to the "Organizer" of the
 "REQUEST".
 The "UID", "SEQUENCE", and "DTSTAMP" properties are used to
 distinguish the various uses of the "REQUEST" method.  If the "UID"
 property value in the "REQUEST" is not found on the recipient's
 calendar, then the "REQUEST" is for a new to-do.  If the "UID"
 property value is found on the recipient's calendar, then the
 "REQUEST" is a rescheduling, an update, or a reconfirmation of the
 "VTODO" calendar object.
 If the "Organizer" of the "REQUEST" method is not authorized to make
 a to-do request on the "Attendee's" calendar system, then an
 exception is returned in the "REQUEST-STATUS" property of a
 subsequent "REPLY" method, but no scheduling action is performed.
 For the "REQUEST" method, multiple "VTODO" components in a single
 iCalendar object are only permitted for components with the same
 "UID" property.  That is, a series of recurring events may have
 instance-specific information.  In this case, multiple "VTODO"
 components are needed to express the entire series.
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +---------------------------------------------+
            | Constraints for a METHOD:REQUEST of a VTODO |
            +---------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REQUEST.                  |
 |                    |          |                                   |
 | VTODO              | 1+       | All components must have the same |
 |                    |          | UID.                              |
 |   ATTENDEE         | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   PRIORITY         | 1        |                                   |
 |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
 |                    |          | greater than 0; MAY be present if |
 |                    |          | 0.                                |
 |   SUMMARY          | 1        | Can be null.                      |

Daboo Standards Track [Page 47] RFC 5546 iTIP December 2009

 |   UID              | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null                       |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | COMPLETED/NEEDS-ACTION/           |
 |                    |          | IN-PROCESS.                       |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 +--------------------+----------+-----------------------------------+

Daboo Standards Track [Page 48] RFC 5546 iTIP December 2009

3.4.2.1. REQUEST for Rescheduling a VTODO

 The "REQUEST" method may be used to reschedule a "VTODO" calendar
 component.
 Rescheduling a "VTODO" calendar component involves a change to the
 existing "VTODO" calendar component in terms of its start or due
 time, recurrence intervals, and possibly the description.  If the
 recipient CUA of a "REQUEST" method finds that the "UID" property
 value already exists on the calendar but that the "SEQUENCE" property
 value in the "REQUEST" is greater than the value for the existing
 "VTODO", then the "REQUEST" method describes a rescheduling of the
 "VTODO" calendar component.

3.4.2.2. REQUEST for Update or Reconfirmation of a VTODO

 The "REQUEST" method may be used to update or reconfirm a "VTODO"
 calendar component.  Reconfirmation is merely an update of "Attendee"
 completion status or overall "VTODO" calendar component status.
 An update to an existing "VTODO" calendar component does not involve
 changes to the start or due time, recurrence intervals, or
 (generally) the description for the "VTODO" calendar component.  If
 the recipient CUA of a "REQUEST" method finds that the "UID" property
 value already exists on the calendar and that the "SEQUENCE" property
 value in the "REQUEST" is the same as the value for the existing
 event, then the "REQUEST" method describes an update of the "VTODO"
 calendar component details, but not a rescheduling of the "VTODO"
 calendar component.
 The update "REQUEST" is the appropriate response to a "REFRESH"
 method sent from an "Attendee" to the "Organizer" of a "VTODO"
 calendar component.
 Unsolicited "REQUEST" methods MAY be sent by the "Organizer" of a
 "VTODO" calendar component.  The unsolicited "REQUEST" methods are
 used to update the details of the "VTODO" (without rescheduling it or
 updating the completion status of "Attendees") or the "VTODO"
 calendar component itself (i.e., reconfirm the "VTODO").

3.4.2.3. REQUEST for Delegating a VTODO

 The "REQUEST" method is also used to delegate or reassign ownership
 of a "VTODO" calendar component to another "Calendar User".  For
 example, it may be used to delegate an "Attendee's" role (i.e.,
 "chair" or "participant") for a "VTODO" calendar component.  The
 "REQUEST" method is sent by one of the "Attendees" of an existing
 "VTODO" calendar component to some other individual.

Daboo Standards Track [Page 49] RFC 5546 iTIP December 2009

 For the purposes of this description, the "Attendee" delegating the
 "VTODO" calendar component is referred to as the "Delegator".  The
 "Attendee" receiving the delegation request is referred to as the
 "Delegate".
 The "Delegator" of a "VTODO" calendar component MUST forward the
 existing "REQUEST" method for a "VTODO" calendar component to the
 "Delegate".  The "VTODO" calendar component description MUST include
 the "Delegator's" up-to-date "VTODO" calendar component definition.
 The "REQUEST" method MUST also include an "ATTENDEE" property with
 the calendar address of the "Delegate".  The "Delegator" MUST also
 send a "REPLY" method back to the "Organizer" with the "Delegator's"
 "Attendee" property "PARTSTAT" parameter value set to "DELEGATED".
 In addition, the "DELEGATED-TO" parameter MUST be included with the
 calendar address of the "Delegate".  A response to the delegation
 "REQUEST" is sent from the "Delegate" to the "Organizer", and
 optionally to the "Delegator".  The "REPLY" method from the
 "Delegate" SHOULD include the "ATTENDEE" property with their calendar
 address and the "DELEGATED-FROM" parameter with the value of the
 "Delegator's" calendar address.
 The delegation "REQUEST" method MUST assign a value for the "RSVP"
 property parameter associated with the "Delegator's" "Attendee"
 property to that of the "Delegate's" "ATTENDEE" property.  For
 example, if the "Delegator's" "ATTENDEE" property specifies
 "RSVP=TRUE", then the "Delegate's" "ATTENDEE" property MUST specify
 "RSVP=TRUE".

3.4.2.4. REQUEST Forwarded to an Uninvited Calendar User

 An "Attendee" assigned a "VTODO" calendar component may send the
 "VTODO" calendar component to another new CU not previously
 associated with the "VTODO" calendar component.  The current
 "Attendee" assigned the "VTODO" calendar component does this by
 forwarding the original "REQUEST" method to the new CU.  The new CU
 can send a "REPLY" to the "Organizer" of the "VTODO" calendar
 component.  The reply contains an "ATTENDEE" property for the new CU.
 The "Organizer" ultimately decides whether or not the new CU becomes
 part of the to-do and is not obligated to do anything with a "REPLY"
 from a new (uninvited) CU.  If the "Organizer" does not want the new
 CU to be part of the to-do, the new "ATTENDEE" property is not added
 to the "VTODO" calendar component.  The "Organizer" MAY send the CU a
 "CANCEL" message to indicate that they will not be added to the to-
 do.  If the "Organizer" decides to add the new CU, the new "ATTENDEE"
 property is added to the "VTODO" calendar component.  Furthermore,
 the "Organizer" is free to change any "ATTENDEE" property parameter
 from the values supplied by the new CU to something the "Organizer"

Daboo Standards Track [Page 50] RFC 5546 iTIP December 2009

 considers appropriate.  The "Organizer" SHOULD send the new
 "Attendee" a "REQUEST" message to inform them that they have been
 added.
 When forwarding a "REQUEST" to another CU, the forwarding "Attendee"
 MUST NOT make changes to the original message.

3.4.2.5. REQUEST Updated Attendee Status

 An "Organizer" of a "VTODO" may request an updated status from one or
 more "Attendees".  The "Organizer" sends a "REQUEST" method to the
 "Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence.  The
 "SEQUENCE" property for the "VTODO" is not changed from its previous
 value.  A recipient determines that the only change in the "REQUEST"
 is that their "RSVP" property parameter indicates a request for an
 updated status.  The recipient SHOULD respond with a "REPLY" method
 indicating their current status with respect to the "REQUEST".

3.4.3. REPLY

 The "REPLY" method in a "VTODO" calendar component is used to respond
 (e.g., accept or decline) to a request or to reply to a delegation
 request.  It is also used by an "Attendee" to update their completion
 status.  When used to provide a delegation response, the "Delegator"
 MUST include the calendar address of the "Delegate" in the
 "DELEGATED-TO" parameter of the "Delegator's" "ATTENDEE" property.
 The "Delegate" MUST include the calendar address of the "Delegator"
 on the "DELEGATED-FROM" parameter of the "Delegate's" "ATTENDEE"
 property.
 The "REPLY" method MAY also be used to respond to an unsuccessful
 "VTODO" calendar component "REQUEST" method.  Depending on the
 "REQUEST-STATUS" value, no scheduling action may have been performed.
 The "Organizer" of a "VTODO" calendar component MAY receive a "REPLY"
 method from a "Calendar User" not in the original "REQUEST".  For
 example, a "REPLY" method MAY be received from a "Delegate" of a
 "VTODO" calendar component.  In addition, the "REPLY" method MAY be
 received from an unknown "Calendar User" who has been forwarded the
 "REQUEST" by an original "Attendee" of the "VTODO" calendar
 component.  This uninvited "Attendee" MAY be accepted or the
 "Organizer" MAY cancel the "VTODO" calendar component for the
 uninvited "Attendee" by sending them a "CANCEL" method.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 51] RFC 5546 iTIP December 2009

             +-------------------------------------------+
             | Constraints for a METHOD:REPLY of a VTODO |
             +-------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REPLY.                    |
 |                    |          |                                   |
 | VTODO              | 1+       | All components MUST have the same |
 |                    |          | UID.                              |
 |   ATTENDEE         | 1        | MUST be the address of the        |
 |                    |          | Attendee replying.                |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   UID              | 1        | MUST be the UID of the original   |
 |                    |          | REQUEST.                          |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTSTART          | 0 or 1   |                                   |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   SEQUENCE         | 0 or 1   | MUST be the sequence number of    |
 |                    |          | the original REQUEST if greater   |
 |                    |          | than 0.  MAY be present if 0.     |

Daboo Standards Track [Page 52] RFC 5546 iTIP December 2009

 |   STATUS           | 0 or 1   |                                   |
 |   SUMMARY          | 0 or 1   | Can be null.                      |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.4. ADD

 The "ADD" method allows the "Organizer" to add one or more new
 instances to an existing "VTODO" using a single iTIP message without
 having to send the entire "VTODO" with all the existing instance
 data, as it would have to do if the "REQUEST" method were used.
 The "UID" must be that of the existing to-do.  If the "UID" property
 value in the "ADD" is not found on the recipient's calendar, then the
 recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
 updated with the latest version of the "VTODO".  If an "Attendee"
 implementation does not support the "ADD" method, it should respond
 with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".
 When handling an "ADD" message, the "Attendee" treats each component
 in the "ADD" message as if it were referenced via an "RDATE" in the
 main component.
 The "SEQUENCE" property value is incremented since the sequence of
 to-dos has changed.
 This method type is an iCalendar object that conforms to the
 following property constraints:

Daboo Standards Track [Page 53] RFC 5546 iTIP December 2009

              +-----------------------------------------+
              | Constraints for a METHOD:ADD of a VTODO |
              +-----------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be ADD.                      |
 |                    |          |                                   |
 | VTODO              | 1        |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   PRIORITY         | 1        |                                   |
 |   SEQUENCE         | 1        | MUST be greater than 0.           |
 |   SUMMARY          | 1        | Can be null.                      |
 |   UID              | 1        | MUST match that of the original   |
 |                    |          | to-do.                            |
 |   ATTACH           | 0+       |                                   |
 |   ATTENDEE         | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTSTART          | 0 or 1   |                                   |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | COMPLETED/NEEDS-ACTION/           |
 |                    |          | IN-PROCESS.                       |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   EXDATE           | 0        |                                   |
 |   RECURRENCE-ID    | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RDATE            | 0        |                                   |
 |   RRULE            | 0        |                                   |

Daboo Standards Track [Page 54] RFC 5546 iTIP December 2009

 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VJOURNAL           | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.5. CANCEL

 The "CANCEL" method in a "VTODO" calendar component is used to send a
 cancellation notice of an existing "VTODO" calendar request to the
 affected "Attendees".  The message is sent by the "Organizer" of a
 "VTODO" calendar component to the "Attendees" of the "VTODO" calendar
 component.  For a recurring "VTODO" calendar component, either the
 whole "VTODO" calendar component or instances of a "VTODO" calendar
 component may be cancelled.  To cancel the complete range of a
 recurring "VTODO" calendar component, the "UID" property value for
 the "VTODO" calendar component MUST be specified and a "RECURRENCE-
 ID" MUST NOT be specified in the "CANCEL" method.  In order to cancel
 an individual instance of a recurring "VTODO" calendar component, the
 "RECURRENCE-ID" property value for the "VTODO" calendar component
 MUST be specified in the "CANCEL" method.
 There are two options for canceling a sequence of instances of a
 recurring "VTODO" calendar component:
 a.  The "RECURRENCE-ID" property for an instance in the sequence MUST
     be specified with the "RANGE" property parameter value of
     "THISANDFUTURE" to indicate cancellation of the specified "VTODO"
     calendar component and all instances after.
 b.  Individual recurrence instances may be cancelled by specifying
     multiple "VTODO" components each with a "RECURRENCE-ID" property
     corresponding to one of the instances to be cancelled.
 The "Organizer" MUST send a "CANCEL" message to each "Attendee"
 affected by the cancellation.  This can be done by using either a
 single "CANCEL" message for all "Attendees" or multiple messages with
 different subsets of the affected "Attendees" in each.

Daboo Standards Track [Page 55] RFC 5546 iTIP December 2009

 When a "VTODO" is cancelled, the "SEQUENCE" property value MUST be
 incremented as described in Section 2.1.4.
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +--------------------------------------------+
            | Constraints for a METHOD:CANCEL of a VTODO |
            +--------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be CANCEL.                   |
 |                    |          |                                   |
 | VTODO              | 1+       |                                   |
 |   ATTENDEE         | 0+       | MUST include some or all          |
 |                    |          | Attendees being removed from the  |
 |                    |          | to-do.  MUST include some or all  |
 |                    |          | Attendees if the entire to-do is  |
 |                    |          | cancelled.                        |
 |   UID              | 1        | MUST echo original UID.           |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTSTART          | 0 or 1   |                                   |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |

Daboo Standards Track [Page 56] RFC 5546 iTIP December 2009

 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MUST be set to CANCELLED to       |
 |                    |          | cancel the entire VTODO.  If      |
 |                    |          | removing specific Attendees, then |
 |                    |          | MUST NOT be included.             |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.6. REFRESH

 The "REFRESH" method in a "VTODO" calendar component is used by
 "Attendees" of an existing "VTODO" calendar component to request an
 updated description from the "Organizer" of the "VTODO" calendar
 component.  The "Organizer" of the "VTODO" calendar component MAY use
 this method to request an updated status from the "Attendees".  The
 "REFRESH" method MUST specify the "UID" property corresponding to the
 "VTODO" calendar component needing update.
 A refresh of a recurrence instance of a "VTODO" calendar component
 may be requested by specifying the "RECURRENCE-ID" property
 corresponding to the associated "VTODO" calendar component.  The
 "Organizer" responds with the latest description and rendition of the
 "VTODO" calendar component.  In most cases, this will be a "REQUEST"
 unless the "VTODO" has been cancelled, in which case the "Organizer"
 MUST send a "CANCEL".  This method is intended to facilitate machine
 processing of requests for updates to a "VTODO" calendar component.

Daboo Standards Track [Page 57] RFC 5546 iTIP December 2009

 This method type is an iCalendar object that conforms to the
 following property constraints:
            +---------------------------------------------+
            | Constraints for a METHOD:REFRESH of a VTODO |
            +---------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be REFRESH.                  |
 |                    |          |                                   |
 | VTODO              | 1        |                                   |
 |   ATTENDEE         | 1        |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   UID              | 1        | MUST echo original UID.           |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   ATTACH           | 0        |                                   |
 |   CATEGORIES       | 0        |                                   |
 |   CLASS            | 0        |                                   |
 |   COMMENT          | 0        |                                   |
 |   COMPLETED        | 0        |                                   |
 |   CONTACT          | 0        |                                   |
 |   CREATED          | 0        |                                   |
 |   DESCRIPTION      | 0        |                                   |
 |   DTSTART          | 0        |                                   |
 |   DUE              | 0        |                                   |
 |   DURATION         | 0        |                                   |
 |   EXDATE           | 0        |                                   |
 |   GEO              | 0        |                                   |
 |   LAST-MODIFIED    | 0        |                                   |
 |   LOCATION         | 0        |                                   |
 |   ORGANIZER        | 0        |                                   |
 |   PERCENT-COMPLETE | 0        |                                   |
 |   PRIORITY         | 0        |                                   |
 |   RDATE            | 0        |                                   |
 |   RELATED-TO       | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RESOURCES        | 0        |                                   |
 |   RRULE            | 0        |                                   |
 |   SEQUENCE         | 0        |                                   |
 |   STATUS           | 0        |                                   |
 |   URL              | 0        |                                   |

Daboo Standards Track [Page 58] RFC 5546 iTIP December 2009

 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       |                                   |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.7. COUNTER

 The "COUNTER" method in a "VTODO" calendar component is used by an
 "Attendee" of an existing "VTODO" calendar component to submit to the
 "Organizer" a counter proposal for the "VTODO" calendar component.
 The counter proposal is an iCalendar object consisting of a "VTODO"
 calendar component that provides the complete description of the
 alternate "VTODO" calendar component.
 The "Organizer" rejects the counter proposal by sending the
 "Attendee" a "DECLINECOUNTER" method.  The "Organizer" accepts the
 counter proposal by rescheduling the to-do as described in
 Section 3.4.2.1, "REQUEST for Rescheduling a To-Do".  The
 "Organizer's" CUA SHOULD send a "REQUEST" message to all "Attendees"
 affected by any change triggered by an accepted "COUNTER".
 This method type is an iCalendar object that conforms to the
 following property constraints:
            +---------------------------------------------+
            | Constraints for a METHOD:COUNTER of a VTODO |
            +---------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be COUNTER.                  |
 |                    |          |                                   |
 | VTODO              | 1        |                                   |
 |   ATTENDEE         | 1+       |                                   |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   PRIORITY         | 1        |                                   |
 |   SUMMARY          | 1        | Can be null.                      |

Daboo Standards Track [Page 59] RFC 5546 iTIP December 2009

 |   UID              | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   | Can be null.                      |
 |   DTSTART          | 0 or 1   |                                   |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   SEQUENCE         | 0 or 1   | MUST echo the original SEQUENCE   |
 |                    |          | number.  MUST be present if       |
 |                    |          | non-zero.  MAY be present if      |
 |                    |          | zero.                             |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | COMPLETED/NEEDS-ACTION/           |
 |                    |          | IN-PROCESS/CANCELLED.             |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |

Daboo Standards Track [Page 60] RFC 5546 iTIP December 2009

 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.4.8. DECLINECOUNTER

 The "DECLINECOUNTER" method in a "VTODO" calendar component is used
 by an "Organizer" of the "VTODO" calendar component to reject a
 counter proposal offered by one of the "Attendees".  The "Organizer"
 sends the message to the "Attendee" that sent the "COUNTER" method to
 the "Organizer".
 This method type is an iCalendar object that conforms to the
 following property constraints:
        +----------------------------------------------------+
        | Constraints for a METHOD:DECLINECOUNTER of a VTODO |
        +----------------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be DECLINECOUNTER.           |
 |                    |          |                                   |
 | VTODO              | 1        |                                   |
 |   ATTENDEE         | 1+       | MUST for all ATTENDEEs.           |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        | MUST echo the original SEQUENCE   |
 |                    |          | number.                           |
 |   UID              | 1        | MUST echo original UID.           |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   COMPLETED        | 0 or 1   |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTSTART          | 0 or 1   |                                   |
 |   DUE              | 0 or 1   | If present, DURATION MUST NOT be  |
 |                    |          | present.                          |
 |   DURATION         | 0 or 1   | If present, DUE MUST NOT be       |
 |                    |          | present.                          |
 |   EXDATE           | 0+       |                                   |
 |   GEO              | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |

Daboo Standards Track [Page 61] RFC 5546 iTIP December 2009

 |   LOCATION         | 0 or 1   |                                   |
 |   PERCENT-COMPLETE | 0 or 1   |                                   |
 |   PRIORITY         | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   REQUEST-STATUS   | 0+       |                                   |
 |   RESOURCES        | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | COMPLETED/NEEDS-ACTION/           |
 |                    |          | IN-PROCESS.                       |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.5. Methods for VJOURNAL Components

 This section defines the property set for the methods that are
 applicable to the "VJOURNAL" calendar component.
 The following summarizes the methods that are defined for the
 "VJOURNAL" calendar component.

Daboo Standards Track [Page 62] RFC 5546 iTIP December 2009

 +---------+---------------------------------------------------------+
 | Method  | Description                                             |
 +---------+---------------------------------------------------------+
 | PUBLISH | Post a journal entry.  Used primarily as a method of    |
 |         | advertising the existence of a journal entry.           |
 |         |                                                         |
 | ADD     | Add one or more instances to an existing journal entry. |
 |         |                                                         |
 | CANCEL  | Cancel one or more instances of an existing journal     |
 |         | entry.                                                  |
 +---------+---------------------------------------------------------+

3.5.1. PUBLISH

 The "PUBLISH" method in a "VJOURNAL" calendar component has no
 associated response.  It is simply a posting of an iCalendar object
 that may be added to a calendar.  It MUST have an "Organizer".  It
 MUST NOT have "Attendees".  The expected usage is for encapsulating
 an arbitrary journal entry as an iCalendar object.  The "Organizer"
 MAY subsequently update (with another "PUBLISH" method) or cancel
 (with a "CANCEL" method) a previously published journal entry.
 This method type is an iCalendar object that conforms to the
 following property constraints:
          +------------------------------------------------+
          | Constraints for a METHOD:PUBLISH of a VJOURNAL |
          +------------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be PUBLISH.                  |
 |                    |          |                                   |
 | VJOURNAL           | 1+       |                                   |
 |   DESCRIPTION      | 1        | Can be null.                      |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   UID              | 1        |                                   |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   EXDATE           | 0+       |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |

Daboo Standards Track [Page 63] RFC 5546 iTIP December 2009

 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   SEQUENCE         | 0 or 1   | MUST be present if non-zero.  MAY |
 |                    |          | be present if zero.               |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | DRAFT/FINAL/CANCELLED.            |
 |   SUMMARY          | 0 or 1   | Can be null.                      |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   ATTENDEE         | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |
 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.5.2. ADD

 The "ADD" method allows the "Organizer" to add one or more new
 instances to an existing "VJOURNAL" using a single iTIP message
 without having to send the entire "VJOURNAL" with all the existing
 instance data, as it would have to do if the "REQUEST" method were
 used.
 The "UID" must be that of the existing journal entry.  If the "UID"
 property value in the "ADD" is not found on the recipient's calendar,
 then the recipient MAY treat the "ADD" as a "PUBLISH".
 When handling an "ADD" message, the "Attendee" treats each component
 in the "ADD" message as if it were referenced via an "RDATE" in the
 main component.  There is no response to the "Organizer".

Daboo Standards Track [Page 64] RFC 5546 iTIP December 2009

 This method type is an iCalendar object that conforms to the
 following property constraints:
            +--------------------------------------------+
            | Constraints for a METHOD:ADD of a VJOURNAL |
            +--------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be ADD.                      |
 |                    |          |                                   |
 | VJOURNAL           | 1        |                                   |
 |   DESCRIPTION      | 1        | Can be null.                      |
 |   DTSTAMP          | 1        |                                   |
 |   DTSTART          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        | MUST be greater than 0.           |
 |   UID              | 1        | MUST match that of the original   |
 |                    |          | journal.                          |
 |   ATTACH           | 0+       |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   RELATED-TO       | 0+       |                                   |
 |   STATUS           | 0 or 1   | MAY be one of                     |
 |                    |          | DRAFT/FINAL/CANCELLED.            |
 |   SUMMARY          | 0 or 1   | Can be null.                      |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   ATTENDEE         | 0        |                                   |
 |   EXDATE           | 0        |                                   |
 |   RECURRENCE-ID    | 0        |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |   RDATE            | 0        |                                   |
 |   RRULE            | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0+       |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |

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 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.5.3. CANCEL

 The "CANCEL" method in a "VJOURNAL" calendar component is used to
 send a cancellation notice of an existing journal entry.  The message
 is sent by the "Organizer" of a journal entry.  For a recurring
 journal entry, either the whole journal entry or instances of a
 journal entry may be cancelled.  To cancel the complete range of a
 recurring journal entry, the "UID" property value for the journal
 entry MUST be specified and a "RECURRENCE-ID" property MUST NOT be
 specified in the "CANCEL" method.  In order to cancel an individual
 instance of the journal entry, the "RECURRENCE-ID" property value for
 the journal entry MUST be specified in the "CANCEL" method.
 There are two options for canceling a sequence of instances of a
 recurring "VJOURNAL" calendar component:
 a.  The "RECURRENCE-ID" property for an instance in the sequence MUST
     be specified with the "RANGE" property parameter value of
     "THISANDFUTURE" to indicate cancellation of the specified
     "VJOURNAL" calendar component and all instances after.
 b.  Individual recurrence instances may be cancelled by specifying
     multiple "VJOURNAL" components each with a "RECURRENCE-ID"
     property corresponding to one of the instances to be cancelled.
 When a "VJOURNAL" is cancelled, the "SEQUENCE" property value MUST be
 incremented as described in Section 2.1.4.
 This method type is an iCalendar object that conforms to the
 following property constraints:

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           +-----------------------------------------------+
           | Constraints for a METHOD:CANCEL of a VJOURNAL |
           +-----------------------------------------------+
 +--------------------+----------+-----------------------------------+
 | Component/Property | Presence | Comment                           |
 +--------------------+----------+-----------------------------------+
 | METHOD             | 1        | MUST be CANCEL.                   |
 |                    |          |                                   |
 | VJOURNAL           | 1+       | All MUST have the same UID.       |
 |   DTSTAMP          | 1        |                                   |
 |   ORGANIZER        | 1        |                                   |
 |   SEQUENCE         | 1        |                                   |
 |   UID              | 1        | MUST be the UID of the original   |
 |                    |          | REQUEST.                          |
 |   ATTACH           | 0+       |                                   |
 |   ATTENDEE         | 0        |                                   |
 |   CATEGORIES       | 0+       |                                   |
 |   CLASS            | 0 or 1   |                                   |
 |   COMMENT          | 0+       |                                   |
 |   CONTACT          | 0+       |                                   |
 |   CREATED          | 0 or 1   |                                   |
 |   DESCRIPTION      | 0 or 1   |                                   |
 |   DTSTART          | 0 or 1   |                                   |
 |   EXDATE           | 0+       |                                   |
 |   LAST-MODIFIED    | 0 or 1   |                                   |
 |   RDATE            | 0+       |                                   |
 |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
 |                    |          | of a recurring calendar           |
 |                    |          | component.  Otherwise, it MUST    |
 |                    |          | NOT be present.                   |
 |   RELATED-TO       | 0+       |                                   |
 |   RRULE            | 0 or 1   |                                   |
 |   STATUS           | 0 or 1   | MAY be present; MUST be CANCELLED |
 |                    |          | if present.                       |
 |   SUMMARY          | 0 or 1   |                                   |
 |   URL              | 0 or 1   |                                   |
 |   IANA-PROPERTY    | 0+       |                                   |
 |   X-PROPERTY       | 0+       |                                   |
 |   REQUEST-STATUS   | 0        |                                   |
 |                    |          |                                   |
 |   VALARM           | 0        |                                   |
 |                    |          |                                   |
 | VTIMEZONE          | 0+       | MUST be present if any date/time  |
 |                    |          | refers to a timezone.             |
 |                    |          |                                   |
 | IANA-COMPONENT     | 0+       |                                   |
 | X-COMPONENT        | 0+       |                                   |

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 |                    |          |                                   |
 | VEVENT             | 0        |                                   |
 |                    |          |                                   |
 | VFREEBUSY          | 0        |                                   |
 |                    |          |                                   |
 | VTODO              | 0        |                                   |
 +--------------------+----------+-----------------------------------+

3.6. Status Replies

 The "REQUEST-STATUS" property is used to convey status information
 about a "REPLY", "COUNTER", or "DECLINECOUNTER" iTIP message.  The
 codes listed in the table below SHOULD be used.  If the "REQUEST-
 STATUS" property is not present in one of these iTIP messages, then a
 status code of "2.0" (success) MUST be assumed.
 This specification adds a new IANA registry for "REQUEST-STATUS"
 property values, as defined in Section 7, which includes a new
 registration template for defining the specific components of the
 "REQUEST-STATUS" property value.  Additional codes MAY be used,
 provided the process described in Section 8.2.1 of [RFC5545] is used
 to register them.
 This specification allows for multiple "REQUEST-STATUS" properties to
 be returned in iCalendar components in the appropriate iTIP messages.
 When multiple "REQUEST-STATUS" properties are present, the following
 restrictions apply:
 1.  Within any one component, the "top-level" numeric value of the
     "short return status code" MUST be the same for all "REQUEST-
     STATUS" properties, i.e., there cannot be a mixture of, e.g.,
     2.xx and 5.xx codes within a single component.
 2.  Across all components in the iTIP message, the following applies:
     A.  If any one component would have a 5.xx code, then either all
         components MUST have a code in that range or "REQUEST-STATUS"
         MUST NOT be present in the other components if a 5.xx code is
         not appropriate for those components.
     B.  Otherwise, if any one component would have a 3.xx code, then
         either all components MUST have a code in that range or
         "REQUEST-STATUS" MUST NOT be present in the other components
         if a 3.xx code is not appropriate for those components.
     C.  2.xx and 4.xx codes can be used in different components,
         provided that each component follows the restriction in (1)
         above.

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 The following "REQUEST-STATUS" codes are defined (any "Offending
 Data" MAY be specified in the "REQUEST-STATUS" value as the extdata
 field):

3.6.1. Status Code 2.0

 Status Code:  2.0
 Status Description:  Success.
 Status Exception Data:  None.
 Description:  iTIP operation succeeded.

3.6.2. Status Code 2.1

 Status Code:  2.1
 Status Description:  Success, but fallback taken on one or more
    property values.
 Status Exception Data:  Property name and value MAY be specified.
 Description:  iTIP operation succeeded with fallback on one or more
    property values.

3.6.3. Status Code 2.2

 Status Code:  2.2
 Status Description:  Success; invalid property ignored.
 Status Exception Data:  Property name MAY be specified.
 Description:  iTIP operation succeeded but a property was ignored.

3.6.4. Status Code 2.3

 Status Code:  2.3
 Status Description:  Success; invalid property parameter ignored.
 Status Exception Data:  Property parameter name and value MAY be
    specified.
 Description:  iTIP operation succeeded but a property parameter was
    ignored because it was invalid.

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3.6.5. Status Code 2.4

 Status Code:  2.4
 Status Description:  Success; unknown, non-standard property ignored.
 Status Exception Data:  Non-standard property name MAY be specified.
 Description:  iTIP operation succeeded but a property parameter was
    ignored because it was unknown.

3.6.6. Status Code 2.5

 Status Code:  2.5
 Status Description:  Success; unknown, non-standard property value
    ignored.
 Status Exception Data:  Property and non-standard value MAY be
    specified.
 Description:  iTIP operation succeeded but a property was ignored
    because its value was unknown.

3.6.7. Status Code 2.6

 Status Code:  2.6
 Status Description:  Success; invalid calendar component ignored.
 Status Exception Data:  Calendar component sentinel (e.g., BEGIN:
    ALARM) MAY be specified.
 Description:  iTIP operation succeeded but a component was ignored
    because it was invalid.

3.6.8. Status Code 2.7

 Status Code:  2.7
 Status Description:  Success; request forwarded to Calendar User.
 Status Exception Data:  Original and forwarded calendar user
    addresses MAY be specified.
 Description:  iTIP operation succeeded, and the request was forwarded
    to another Calendar User.

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3.6.9. Status Code 2.8

 Status Code:  2.8
 Status Description:  Success; repeating event ignored.  Scheduled as
    a single component.
 Status Exception Data:  RRULE or RDATE property name and value MAY be
    specified.
 Description:  iTIP operation succeeded but a repeating event was
    truncated to a single instance.

3.6.10. Status Code 2.9

 Status Code:  2.9
 Status Description:  Success; truncated end date time to date
    boundary.
 Status Exception Data:  DTEND property value MAY be specified.
 Description:  iTIP operation succeeded but the end time was truncated
    to a date boundary.

3.6.11. Status Code 2.10

 Status Code:  2.10
 Status Description:  Success; repeating VTODO ignored.  Scheduled as
    a single VTODO.
 Status Exception Data:  RRULE or RDATE property name and value MAY be
    specified.
 Description:  iTIP operation succeeded but a repeating to-do was
    truncated to a single instance.

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3.6.12. Status Code 2.11

 Status Code:  2.11
 Status Description:  Success; unbounded RRULE clipped at some finite
    number of instances.
 Status Exception Data:  RRULE property name and value MAY be
    specified.  Number of instances MAY also be specified.
 Description:  iTIP operation succeeded but an unbounded repeating
    object was clipped to a finite number of instances.

3.6.13. Status Code 3.0

 Status Code:  3.0
 Status Description:  Invalid property name.
 Status Exception Data:  Property name MAY be specified.
 Description:  iTIP operation failed because of an invalid property
    name.

3.6.14. Status Code 3.1

 Status Code:  3.1
 Status Description:  Invalid property value.
 Status Exception Data:  Property name and value MAY be specified.
 Description:  iTIP operation failed because of an invalid property
    value.

3.6.15. Status Code 3.2

 Status Code:  3.2
 Status Description:  Invalid property parameter.
 Status Exception Data:  Property parameter name and value MAY be
    specified.
 Description:  iTIP operation failed because of an invalid property
    parameter.

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3.6.16. Status Code 3.3

 Status Code:  3.3
 Status Description:  Invalid property parameter value.
 Status Exception Data:  Property parameter name and value MAY be
    specified.
 Description:  iTIP operation failed because of an invalid property
    parameter value.

3.6.17. Status Code 3.4

 Status Code:  3.4
 Status Description:  Invalid calendar component sequence.
 Status Exception Data:  Calendar component sentinel MAY be specified
    (e.g., BEGIN:VTIMEZONE).
 Description:  iTIP operation failed because of an invalid component.

3.6.18. Status Code 3.5

 Status Code:  3.5
 Status Description:  Invalid date or time.
 Status Exception Data:  Date/time value(s) MAY be specified.
 Description:  iTIP operation failed because of an invalid date or
    time property.

3.6.19. Status Code 3.6

 Status Code:  3.6
 Status Description:  Invalid rule.
 Status Exception Data:  RRULE property value MAY be specified.
 Description:  iTIP operation failed because of an invalid rule
    property.

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3.6.20. Status Code 3.7

 Status Code:  3.7
 Status Description:  Invalid Calendar User.
 Status Exception Data:  ATTENDEE property value MAY be specified.
 Description:  iTIP operation failed because of an invalid ATTENDEE
    property.

3.6.21. Status Code 3.8

 Status Code:  3.8
 Status Description:  No authority.
 Status Exception Data:  METHOD and ATTENDEE property values MAY be
    specified.
 Description:  iTIP operation failed because an Attendee does not have
    suitable privileges for the operation.

3.6.22. Status Code 3.9

 Status Code:  3.9
 Status Description:  Unsupported version.
 Status Exception Data:  VERSION property name and value MAY be
    specified.
 Description:  iTIP operation failed because the calendar data version
    is not supported.

3.6.23. Status Code 3.10

 Status Code:  3.10
 Status Description:  Request entity too large.
 Status Exception Data:  None.
 Description:  iTIP operation failed because the calendar data was too
    large.

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3.6.24. Status Code 3.11

 Status Code:  3.11
 Status Description:  Required component or property missing.
 Status Exception Data:  Component or property name MAY be specified.
 Description:  iTIP operation failed because the calendar data did not
    contain a required property or component.

3.6.25. Status Code 3.12

 Status Code:  3.12
 Status Description:  Unknown component or property found.
 Status Exception Data:  Component or property name MAY be specified.
 Description:  iTIP operation failed because the calendar data
    contained an unknown property or component.

3.6.26. Status Code 3.13

 Status Code:  3.13
 Status Description:  Unsupported component or property found.
 Status Exception Data:  Component or property name MAY be specified.
 Description:  iTIP operation failed because the calendar data
    contained an unsupported property or component.

3.6.27. Status Code 3.14

 Status Code:  3.14
 Status Description:  Unsupported capability.
 Status Exception Data:  METHOD or action MAY be specified.
 Description:  iTIP operation failed because the operation is not
    supported.

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3.6.28. Status Code 4.0

 Status Code:  4.0
 Status Description:  Event conflict.  Date/time is busy.
 Status Exception Data:  DTSTART and DTEND property names and values
    MAY be specified.
 Description:  iTIP operation failed because the event overlaps the
    date and time of another event.

3.6.29. Status Code 5.0

 Status Code:  5.0
 Status Description:  Request not supported.
 Status Exception Data:  METHOD property value MAY be specified.
 Description:  iTIP operation failed because the operation is not
    supported.

3.6.30. Status Code 5.1

 Status Code:  5.1
 Status Description:  Service unavailable.
 Status Exception Data:  ATTENDEE property value MAY be specified.
 Description:  iTIP operation failed because scheduling is not active.

3.6.31. Status Code 5.2

 Status Code:  5.2
 Status Description:  Invalid calendar service.
 Status Exception Data:  ATTENDEE property value MAY be specified.
 Description:  iTIP operation failed because there is no scheduling
    capability.

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3.6.32. Status Code 5.3

 Status Code:  5.3
 Status Description:  No scheduling support for user.
 Status Exception Data:  ATTENDEE property value MAY be specified.
 Description:  iTIP operation failed because scheduling is not enabled
    for an Attendee.

3.7. Implementation Considerations

3.7.1. Working With Recurrence Instances

 iCalendar includes a recurrence grammar to represent recurring
 events.  The benefit of such a grammar is the ability to represent a
 number of events in a single object.  However, while this simplifies
 creation of a recurring event, meeting instances still need to be
 referenced.  For instance, an "Attendee" may decline the third
 instance of a recurring Friday event.  Similarly, the "Organizer" may
 change the time or location to a single instance of the recurring
 event.
 Since implementations may elect to store recurring events as either a
 single event object or a collection of discrete, related event
 objects, the protocol is designed so that each recurring instance may
 be both referenced and versioned.  Hence, implementations that choose
 to maintain per-instance properties (such as "ATTENDEE" property
 "PARTSTAT" parameter) may do so.  However, the protocol does not
 require per-instance recognition unless the instance itself must be
 renegotiated.
 The scenarios for recurrence instance referencing are listed below.
 For purposes of simplification, a change to an event refers to a
 "trigger property."  That is, a property that has a substantive
 effect on the meeting itself, such as start time, location, due date
 (for "VTODO" calendar components), and possibly description.
 "Organizer"-initiated actions:
 o  deletes or changes a single instance of a recurring event
 o  makes changes that affect all future instances
 o  makes changes that affect all previous instances
 o  deletes or modifies a previously changed instance

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 "Attendee"-initiated actions:
 o  changes status for a particular recurrence instance
 o  sends a "COUNTER" for a particular recurrence instance
 An instance of a recurring event is assigned a unique identification,
 "RECURRENCE-ID" property, when that instance is renegotiated.
 Negotiation may be necessary when a substantive change to the event
 or to-do has been made (such as changing the start time, end time,
 due date, or location).  The "Organizer" can identify a specific
 recurrence instance using the "RECURRENCE-ID" property.  The property
 value is equal to the date/time of the instance.  If the "Organizer"
 wishes to change the "DTSTART", the original, unmodified "DTSTART"
 value of the instance is used as the value "RECURRENCE-ID" property,
 and the new "DTSTART" and "DTEND" values reflect the change.

3.7.2. Attendee Property Considerations

 The "ORGANIZER" property is required on published events, to-dos, and
 journal entries for two reasons.  First, only the "Organizer" is
 allowed to update and redistribute an event or to-do component.  It
 follows that the "ORGANIZER" property MUST be present in the event,
 to-do, or journal entry component so that the CUA has a basis for
 authorizing an update.  Second, it is prudent to provide a point of
 contact for anyone who receives a published component, in case of
 problems.
 Email addresses that correspond to groups of "Calendar Users" could
 be specified as a mailto: URI [RFC2368] calendar user address.
 Sending email to such an address results in email being sent to
 multiple recipients.  Such an address may be used as the value of an
 "ATTENDEE" property.  Thus, it is possible that the recipient of a
 "REQUEST" does not appear explicitly in the list.
 It is recommended that the general approach to finding a "Calendar
 User" in an "Attendee" list be as follows:
 1.  Search for the "Calendar User" in the "Attendee" list where
     "CUTYPE=INDIVIDUAL"
 2.  Failing (1), look for "Attendees" where "CUTYPE=GROUP" or
     "CUTYPE=UNKNOWN".  The CUA then determines if the "Calendar User"
     is a member of one of these groups.  If so, the "REPLY" method
     sent to the "Organizer" MUST contain a new "ATTENDEE" property in
     which:
  • the "TYPE" property parameter is set to INDIVIDUAL

Daboo Standards Track [Page 78] RFC 5546 iTIP December 2009

  • the "MEMBER" property parameter is set to the name of the

group

 3.  Failing (2), the CUA MAY ignore or accept the request as the
     "Calendar User" wishes.

3.7.3. Extension Tokens

 To make iCalendar objects extensible, new component, property, or
 property parameters can be used.  Two types of extensions are defined
 by [RFC5545]: IANA-registered tokens ("iana-token") and experimental
 use tokens ("x-name").  A client SHOULD save "iana-token's" and MAY
 use them in replies.  A client MAY save "x-name's" and MAY use them
 in replies.  When delegating or forwarding messages to other CUs, a
 client SHOULD include "iana-token's" and "x-names's".

4. Examples

4.1. Published Event Examples

 In the calendaring and scheduling context, publication refers to the
 one-way transfer of event information.  Consumers of published events
 simply incorporate the event into a calendar.  No reply is expected.
 Individual "A" publishes an event.  Individual "B" reads the event
 and incorporates it into their calendar.  Events are published in
 several ways, including embedding the event as an object in a web
 page, emailing the event to a distribution list, or posting the event
 to a newsgroup.
 The table below illustrates the sequence of events between the
 publisher and the consumers of a published event.
 +----------------+-----------------------+--------------------------+
 | Action         | Organizer             | Receiver                 |
 +----------------+-----------------------+--------------------------+
 | Publish an     | "A" sends or posts a  | "B" reads a published    |
 | event          | PUBLISH message.      | event.                   |
 |                |                       |                          |
 | Publish an     | "A" sends or posts a  | "B" reads the updated    |
 | updated event  | PUBLISH message.      | event.                   |
 |                |                       |                          |
 | Cancel a       | "A" sends or posts a  | "B" reads the canceled   |
 | published      | CANCEL message.       | event publication.       |
 | event          |                       |                          |
 +----------------+-----------------------+--------------------------+

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4.1.1. A Minimal Published Event

 The iCalendar object below describes a single event that begins on
 July 1, 1997 at 20:00 UTC.  This event contains the minimum set of
 properties for a "PUBLISH" for a "VEVENT" calendar component.
    BEGIN:VCALENDAR
    METHOD:PUBLISH
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    DTSTART:19970701T200000Z
    DTSTAMP:19970611T190000Z
    SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
    UID:0981234-1234234-23@example.com
    END:VEVENT
    END:VCALENDAR

4.1.2. Changing a Published Event

 The iCalendar object below describes an update to the event described
 in Section 4.1.1; the time has been changed, an end time has been
 added, and the sequence number has been adjusted.
    BEGIN:VCALENDAR
    METHOD:PUBLISH
    VERSION:2.0
    PRODID:-//Example/ExampleCalendarClient//EN
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    DTSTAMP:19970612T190000Z
    DTSTART:19970701T210000Z
    DTEND:19970701T230000Z
    SEQUENCE:1
    UID:0981234-1234234-23@example.com
    SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
    END:VEVENT
    END:VCALENDAR
 The "UID" property is used by the client to identify the event.  The
 "SEQUENCE" property indicates that this is a change to the event.
 The event with a matching "UID" and sequence number 0 is superseded
 by this event.
 The "SEQUENCE" property provides a reliable way to distinguish
 different versions of the same event.  Each time an event is
 published, its sequence number is incremented.  If a client receives

Daboo Standards Track [Page 80] RFC 5546 iTIP December 2009

 an event with a sequence number 5 and finds it has the same event
 with sequence number 2, the event SHOULD be updated.  However, if the
 client received an event with sequence number 2 and finds it already
 has sequence number 5 of the same event, the event MUST NOT be
 updated.

4.1.3. Canceling a Published Event

 The iCalendar object below cancels the event described in
 Section 4.1.1.  This cancels the event with "SEQUENCE" property of 0,
 1, and 2.
    BEGIN:VCALENDAR
    METHOD:CANCEL
    VERSION:2.0
    PRODID:-//Example/ExampleCalendarClient//EN
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    COMMENT:DUKES forfeit the game
    SEQUENCE:2
    UID:0981234-1234234-23@example.com
    DTSTAMP:19970613T190000Z
    END:VEVENT
    END:VCALENDAR

4.1.4. A Rich Published Event

 This example describes the same event as in Section 4.1.1, but in
 much greater detail.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:PUBLISH
    SCALE:GREGORIAN
    VERSION:2.0
    BEGIN:VTIMEZONE
    TZID:America-Chicago
    TZURL:http://example.com/tz/America-Chicago
    BEGIN:STANDARD
    DTSTART:19671029T020000
    RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
    TZOFFSETFROM:-0500
    TZOFFSETTO:-0600
    TZNAME:CST
    END:STANDARD
    BEGIN:DAYLIGHT
    DTSTART:19870405T020000
    RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4

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    TZOFFSETFROM:-0600
    TZOFFSETTO:-0500
    TZNAME:CDT
    END:DAYLIGHT
    END:VTIMEZONE
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTACH:http://www.example.com/
    CATEGORIES:SPORTS EVENT,ENTERTAINMENT
    CLASS:PRIVATE
    DESCRIPTION:MIDWAY STADIUM\n
     Big time game.  MUST see.\n
     Expected duration:2 hours\n
    DTEND;TZID=America-Chicago:19970701T180000
    DTSTART;TZID=America-Chicago:19970702T160000
    DTSTAMP:19970614T190000Z
    STATUS:CONFIRMED
    LOCATION;VALUE=URI:http://stadium.example.com/
    PRIORITY:2
    RESOURCES:SCOREBOARD
    SEQUENCE:3
    SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
    UID:0981234-1234234-23@example.com
    RELATED-TO:0981234-1234234-14@example.com
    BEGIN:VALARM
    TRIGGER:-PT2H
    ACTION:DISPLAY
    DESCRIPTION:You should be leaving for the game now.
    END:VALARM
    BEGIN:VALARM
    TRIGGER:-PT30M
    ACTION:AUDIO
    END:VALARM
    END:VEVENT
    END:VCALENDAR
 The "RELATED-TO" field contains the "UID" property of a related
 calendar event.  The "SEQUENCE" property 3 indicates that this event
 supersedes versions 0, 1, and 2.

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4.1.5. Anniversaries or Events Attached to Entire Days

 This example demonstrates the use of the "VALUE" parameter to tie a
 "VEVENT" to a day rather than a specific time.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:PUBLISH
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    DTSTAMP:19970614T190000Z
    UID:0981234-1234234-23@example.com
    DTSTART;VALUE=DATE:19970714
    RRULE:FREQ=YEARLY;INTERVAL=1
    SUMMARY: Bastille Day
    END:VEVENT
    END:VCALENDAR

4.2. Group Event Examples

 Group events are distinguished from published events in that they
 have "Attendees" and there is interaction between the "Attendees" and
 the "Organizer" with respect to the event.  Individual "A" requests a
 meeting between individuals "A", "B", "C", and "D".  Individual "B"
 confirms attendance to the meeting.  Individual "C" declines
 attendance.  Individual "D" tentatively confirms attendance.  The
 following table illustrates the message flow between these
 individuals.  "A", the CU scheduling the meeting, is referenced as
 the "Organizer".

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 +--------------+-----------------------+----------------------------+
 | Action       | "Organizer"           | Attendee                   |
 +--------------+-----------------------+----------------------------+
 | Initiate a   | "A" sends a REQUEST   |                            |
 | meeting      | message to "B", "C",  |                            |
 | request      | and "D".              |                            |
 |              |                       |                            |
 | Accept the   |                       | "B" sends a REPLY message  |
 | meeting      |                       | to "A" with its ATTENDEE   |
 | request      |                       | PARTSTAT parameter set to  |
 |              |                       | ACCEPTED.                  |
 |              |                       |                            |
 | Decline the  |                       | "C" sends a REPLY message  |
 | meeting      |                       | to "A" with its ATTENDEE   |
 | request      |                       | PARTSTAT parameter set to  |
 |              |                       | DECLINED.                  |
 |              |                       |                            |
 | Tentatively  |                       | "D" sends a REPLY message  |
 | accept the   |                       | to "A" with its ATTENDEE   |
 | meeting      |                       | PARTSTAT parameter set to  |
 | request      |                       | TENTATIVE.                 |
 |              |                       |                            |
 | Confirm      | "A" sends a REQUEST   |                            |
 | meeting      | message to "B" and    |                            |
 | status with  | "D" with updated      |                            |
 | Attendees    | information.          |                            |
 +--------------+-----------------------+----------------------------+

4.2.1. A Group Event Request

 A sample meeting request is sent from "A" to "B", "C", and "D".  "E"
 is also sent a copy of the request but is not expected to attend and
 need not reply.  "E" illustrates how CUAs might implement an "FYI"-
 type feature.  Note the use of the "ROLE" parameter.  The default
 value for the "ROLE" parameter is "REQ-PARTICIPANT" and it need not
 be enumerated.  In this case, we are using the value "NON-
 PARTICIPANT" to indicate "E" is a non-attending CU.  The parameter is
 not needed on other "Attendees" since "PARTICIPANT" is the default
 value.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;CN=A:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=B:mailto:b@example.com

Daboo Standards Track [Page 84] RFC 5546 iTIP December 2009

    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=C:mailto:c@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=Hal:mailto:d@example.com
    ATTENDEE;RSVP=FALSE;CUTYPE=ROOM:conf_big@example.com
    ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:mailto:e@example.com
    DTSTAMP:19970611T190000Z
    DTSTART:19970701T200000Z
    DTEND:19970701T2100000Z
    SUMMARY:Conference
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.2.2. Reply to a Group Event Request

 "Attendee" "B" accepts the meeting.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VEVENT
    ATTENDEE;PARTSTAT=ACCEPTED:mailto:b@example.com
    ORGANIZER:mailto:a@example.com
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    REQUEST-STATUS:2.0;Success
    DTSTAMP:19970612T190000Z
    END:VEVENT
    END:VCALENDAR
 "B" could have declined the meeting or indicated tentative acceptance
 by setting the "ATTENDEE" "PARTSTAT" parameter to "DECLINED" or
 "TENTATIVE", respectively.  Also, "REQUEST-STATUS" is not required in
 successful transactions.

4.2.3. Update an Event

 The event is moved to a different time.  The combination of the "UID"
 property (unchanged) and the "SEQUENCE" (bumped to 1) properties
 indicate the update.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT

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    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=Hal:mailto:d@example.com
    ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE;
     CUTYPE=ROOM:mailto:conf@example.com
    ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:mailto:e@example.com
    DTSTART:19970701T180000Z
    DTEND:19970701T190000Z
    SUMMARY:Phone Conference
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:1
    DTSTAMP:19970613T190000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.2.4. Countering an Event Proposal

 "A" sends a "REQUEST" to "B" and "C".  "B" makes a counter proposal
 to "A" to change the time and location.
 "A" sends the following "REQUEST":
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    DTSTART:19970701T190000Z
    DTEND:19970701T200000Z
    SUMMARY:Discuss the Merits of the election results
    LOCATION:Green Conference Room
    UID:calsrv.example.com-873970198738777a@example.com
    SEQUENCE:0
    DTSTAMP:19970611T190000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

Daboo Standards Track [Page 86] RFC 5546 iTIP December 2009

 "B" sends "COUNTER" to "A", requesting changes to time and place.
 "B" uses the "COMMENT" property to communicate a rationale for the
 change.  Note that the "SEQUENCE" property is not incremented on a
 "COUNTER".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:COUNTER
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    DTSTART:19970701T160000Z
    DTEND:19970701T170000Z
    DTSTAMP:19970612T190000Z
    SUMMARY:Discuss the Merits of the election results
    LOCATION:Blue Conference Room
    COMMENT:This time works much better and I think the big conference
     room is too big
    UID:calsrv.example.com-873970198738777a@example.com
    SEQUENCE:0
    END:VEVENT
    END:VCALENDAR
 "A" accepts the changes from "B".  To accept a counter proposal, the
 "Organizer" sends a new event "REQUEST" with an incremented sequence
 number.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    DTSTAMP:19970613T190000Z
    DTSTART:19970701T160000Z
    DTEND:19970701T170000Z
    SUMMARY:Discuss the Merits of the election results - changed to
     meet B's schedule
    LOCATION:Blue Conference Room
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:1
    STATUS:CONFIRMED

Daboo Standards Track [Page 87] RFC 5546 iTIP December 2009

    END:VEVENT
    END:VCALENDAR
 Instead, "A" rejects "B's" counter proposal.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:DECLINECOUNTER
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    COMMENT:Sorry, I cannot change this meeting time
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    DTSTAMP:19970614T190000Z
    END:VEVENT
    END:VCALENDAR

4.2.5. Delegating an Event

 When delegating an event request to another "Calendar User", the
 "Delegator" must both update the "Organizer" with a "REPLY" and send
 a request to the "Delegate".  There is currently no protocol
 limitation to delegation depth.  It is possible for the original
 delegate to delegate the meeting to someone else, and so on.  When a
 request is delegated from one CUA to another, there are a number of
 responsibilities required of the "Delegator".  The "Delegator" MUST:
 o  Send a "REPLY" to the "Organizer" with the following updates:
    A.  The "Delegator's" "ATTENDEE" property "PARTSTAT" parameter is
        set to "DELEGATED" and the "DELEGATED-TO" parameter is set to
        the address of the "Delegate".
    B.  Add an additional "ATTENDEE" property for the "Delegate" with
        the "DELEGATED-FROM" property parameter set to the
        "Delegator".
    C.  Indicate whether they want to continue to receive updates when
        the "Organizer" sends out updated versions of the event.
        Setting the "RSVP" property parameter to "TRUE" will cause the
        updates to be sent; setting it to "FALSE" causes no further
        updates to be sent.  Note that in either case, if the
        "Delegate" declines the invitation, the "Delegator" will be
        notified.

Daboo Standards Track [Page 88] RFC 5546 iTIP December 2009

 o  The "Delegator" MUST also send a copy of the original "REQUEST"
    method to the "Delegate", with changes (A) and (B), as detailed
    above applied.
 If the "Delegate" declines the meeting, the "Organizer" MUST send an
 update "REQUEST" to the "Delegator" so that the "Delegator" may elect
 to delegate the "REQUEST" to another CUA.
 +----------------+-----------------+--------------------------------+
 | Action         | "Organizer"     | Attendee                       |
 +----------------+-----------------+--------------------------------+
 | Initiate a     | "A" sends a     |                                |
 | meeting        | REQUEST message |                                |
 | request        | to "B" and "C". |                                |
 |                |                 |                                |
 | Delegate: "C"  |                 | "C" sends a REPLY to "A" with  |
 | delegates to   |                 | the ATTENDEE PARTSTAT          |
 | "E"            |                 | parameter set to DELEGATED and |
 |                |                 | with a new ATTENDEE property   |
 |                |                 | for "E".  "E's" ATTENDEE       |
 |                |                 | DELEGATED-FROM parameter is    |
 |                |                 | set to "C".  "C's" ATTENDEE    |
 |                |                 | DELEGATED-TO parameter is set  |
 |                |                 | to "E".  "C" sends REQUEST     |
 |                |                 | message to "E" with the        |
 |                |                 | original meeting request       |
 |                |                 | information.  The PARTSTAT     |
 |                |                 | property parameter for "C" is  |
 |                |                 | set to DELEGATED and the       |
 |                |                 | DELEGATED-TO parameter is set  |
 |                |                 | to the address of "E".  An     |
 |                |                 | ATTENDEE property is added for |
 |                |                 | "E" and the DELEGATED-FROM     |
 |                |                 | parameter is set to the        |
 |                |                 | address of "C".                |
 |                |                 |                                |
 | Confirm        |                 | "E" sends REPLY message to     |
 | meeting        |                 | "A", and optionally to "C",    |
 | attendance     |                 | with its PARTSTAT property     |
 |                |                 | parameter set to ACCEPTED.     |
 |                |                 |                                |
 | Optional:      | "A" sends       |                                |
 | Redistribute   | REQUEST message |                                |
 | meeting to     | to "B", "C",    |                                |
 | Attendees      | and "E".        |                                |
 +----------------+-----------------+--------------------------------+

Daboo Standards Track [Page 89] RFC 5546 iTIP December 2009

 "C" responds to the "Organizer".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
     TO="mailto:e@example.com":mailto:c@example.com
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    REQUEST-STATUS:2.0;Success
    DTSTAMP:19970611T190000Z
    END:VEVENT
    END:VCALENDAR
 "Attendee" "C" delegates presence at the meeting to "E".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
     TO="mailto:e@example.com":mailto:c@example.com
    ATTENDEE;RSVP=TRUE;
     DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com
    DTSTART:19970701T180000Z
    DTEND:19970701T200000Z
    SUMMARY:Phone Conference
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    STATUS:CONFIRMED
    DTSTAMP:19970611T190000Z
    END:VEVENT
    END:VCALENDAR

4.2.6. Delegate Accepts the Meeting

 To accept a delegated meeting, the delegate, "E", sends the following
 message to "A" and "C".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0

Daboo Standards Track [Page 90] RFC 5546 iTIP December 2009

    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=ACCEPTED;DELEGATED-
     FROM="mailto:c@example.com":mailto:e@example.com
    ATTENDEE;PARTSTAT=DELEGATED;
     DELEGATED-TO="mailto:e@example.com":mailto:c@example.com
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    REQUEST-STATUS:2.0;Success
    DTSTAMP:19970614T190000Z
    END:VEVENT
    END:VCALENDAR

4.2.7. Delegate Declines the Meeting

 In this example, the "Delegate" declines the meeting request and sets
 the "ATTENDEE" property "PARTSTAT" parameter to "DECLINED".  The
 "Organizer" SHOULD resend the "REQUEST" to "C" with the "PARTSTAT"
 parameter of the "Delegate" set to "DECLINED".  This lets the
 "Delegator" know that the "Delegate" has declined and provides an
 opportunity to the "Delegator" to either accept the request or
 delegate it to another CU.
 "E" responds to "A" and "C".  Note the use of the "COMMENT" property
 "E" uses to indicate why the delegation was declined.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=DELEGATED;
     DELEGATED-TO="mailto:e@example.com":mailto:c@example.com
    ATTENDEE;PARTSTAT=DECLINED;
     DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com
    COMMENT:Sorry, I will be out of town at that time.
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    REQUEST-STATUS:2.0;Success
    DTSTAMP:19970614T190000Z
    END:VEVENT
    END:VCALENDAR
 "A" resends the "REQUEST" method to "C".  "A" may also wish to
 express the fact that the item was delegated in the "COMMENT"
 property.

Daboo Standards Track [Page 91] RFC 5546 iTIP December 2009

    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=DECLINED;
     DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:0
    SUMMARY:Phone Conference
    DTSTART:19970701T180000Z
    DTEND:19970701T200000Z
    DTSTAMP:19970614T200000Z
    COMMENT:DELEGATE (ATTENDEE mailto:e@example.com) DECLINED YOUR
     INVITATION
    END:VEVENT
    END:VCALENDAR

4.2.8. Forwarding an Event Request

 The protocol does not prevent an "Attendee" from "forwarding" a
 "VEVENT" calendar component to other "Calendar Users".  Forwarding
 differs from delegation in that the forwarded "Calendar User" (often
 referred to as a "Party Crasher") does not replace the forwarding
 "Calendar User".  Implementations are not required to add the "Party
 Crasher" to the "Attendee" list, and hence there is no guarantee that
 a "Party Crasher" will receive additional updates to the event.  The
 forwarding "Calendar User" SHOULD NOT add the "Party Crasher" to the
 "Attendee" list.  The "Organizer" MAY add the forwarded "Calendar
 User" to the "Attendee" list.

4.2.9. Cancel a Group Event

 Individual "A" requests a meeting between individuals "A", "B", "C",
 and "D".  Individual "B" declines attendance to the meeting.
 Individual "A" decides to cancel the meeting.  The following table
 illustrates the sequence of messages that would be exchanged between
 these individuals.
 Messages related to a previously canceled event ("SEQUENCE" property
 value is less than the "SEQUENCE" property value of the "CANCEL"
 message) MUST be ignored.

Daboo Standards Track [Page 92] RFC 5546 iTIP December 2009

 +-------------+---------------------+-------------------------------+
 | Action      | Organizer           | Attendee                      |
 +-------------+---------------------+-------------------------------+
 | Initiate a  | "A" sends a REQUEST |                               |
 | meeting     | message to "B",     |                               |
 | request     | "C", and "D".       |                               |
 |             |                     |                               |
 | Decline the |                     | "B" sends a REPLY message to  |
 | meeting     |                     | "A" with its PARTSTAT         |
 | request     |                     | parameter set to DECLINED.    |
 |             |                     |                               |
 | Cancel the  | "A" sends a CANCEL  |                               |
 | meeting     | message to "B",     |                               |
 |             | "C", and "D".       |                               |
 +-------------+---------------------+-------------------------------+
 This example shows how "A" cancels the event.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:CANCEL
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL;mailto:a@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com
    COMMENT:Mr. B cannot attend.  It's raining.  Lets cancel.
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:1
    STATUS:CANCELLED
    DTSTAMP:19970613T190000Z
    END:VEVENT
    END:VCALENDAR

4.2.10. Removing Attendees

 "A" wants to remove "B" from a meeting.  This is done by sending a
 "CANCEL" to "B" and removing "B" from the "Attendee" list in the
 master copy of the event.

Daboo Standards Track [Page 93] RFC 5546 iTIP December 2009

 +--------------------+-----------------------------------+----------+
 | Action             | Organizer                         | Attendee |
 +--------------------+-----------------------------------+----------+
 | Remove "B" as an   | "A" sends a CANCEL message to     |          |
 | Attendee           | "B".                              |          |
 |                    |                                   |          |
 | Update the master  | "A" optionally sends the updated  |          |
 | copy of the event  | event to the remaining Attendees. |          |
 +--------------------+-----------------------------------+----------+
 The original meeting includes "A", "B", "C", and "D".  The example
 below shows the "CANCEL" that "A" sends to "B".  Note that in the
 example below, the "STATUS" property is omitted.  This is used when
 the meeting itself is cancelled and not when the intent is to remove
 an "Attendee" from the event.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:CANCEL
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    COMMENT:You're off the hook for this meeting
    UID:calsrv.example.com-873970198738777@example.com
    DTSTAMP:19970613T193000Z
    SEQUENCE:1
    END:VEVENT
    END:VCALENDAR
 The updated master copy of the event is shown below.  The "Organizer"
 MAY resend the updated event to the remaining "Attendees".  Note that
 "B" has been removed.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com
    ATTENDEE;CUTYPE=ROOM:mailto:cr_big@example.com
    ATTENDEE;ROLE=NON-PARTICIPANT;
     RSVP=FALSE:mailto:e@example.com
    DTSTAMP:19970611T190000Z
    DTSTART:19970701T200000Z

Daboo Standards Track [Page 94] RFC 5546 iTIP December 2009

    DTEND:19970701T203000Z
    SUMMARY:Phone Conference
    UID:calsrv.example.com-873970198738777@example.com
    SEQUENCE:2
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.2.11. Replacing the Organizer

 The scenario for this example begins with "A" as the "Organizer" for
 a recurring meeting with "B", "C", and "D".  "A" receives a new job
 offer in another country and drops out of touch.  "A" left no
 forwarding address or way to be reached.  Using out-of-band
 communication, the other "Attendees" eventually learn what has
 happened and reach an agreement that "B" should become the new
 "Organizer" for the meeting.  To do this, "B" sends out a new version
 of the event and the other "Attendees" agree to accept "B" as the new
 "Organizer".  "B" also removes "A" from the event.
 When the "Organizer" is replaced, the "SEQUENCE" property value MUST
 be incremented.
 This is the message "B" sends to "C" and "D".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:b@example.com
    ATTENDEE;ROLE=CHAIR;STATUS=ACCEPTED:mailto:b@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com
    ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com
    DTSTAMP:19970611T190000Z
    DTSTART:19970701T200000Z
    DTEND:19970701T203000Z
    RRULE:FREQ=WEEKLY
    SUMMARY:Phone Conference
    UID:123456@example.com
    SEQUENCE:1
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

Daboo Standards Track [Page 95] RFC 5546 iTIP December 2009

4.3. Busy Time Examples

 Busy time objects can be used in several ways.  First, a CU may
 request busy time from another CU for a specific range of time.  That
 request can be answered with a busy time "REPLY".  Additionally, a CU
 may simply publish their busy time for a given interval and point
 other CUs to the published location.  The following examples outline
 both scenarios.

4.3.1. Publish Busy Time

 Individual "A" publishes busy time for one week.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    METHOD:PUBLISH
    BEGIN:VFREEBUSY
    DTSTAMP:19980101T124100Z
    ORGANIZER:mailto:a@example.com
    DTSTART:19980101T124200Z
    DTEND:19980108T124200Z
    FREEBUSY:19980101T180000Z/19980101T190000Z
    FREEBUSY:19980103T020000Z/19980103T050000Z
    FREEBUSY:19980107T020000Z/19980107T050000Z
    FREEBUSY:19980113T000000Z/19980113T010000Z
    FREEBUSY:19980115T190000Z/19980115T200000Z
    FREEBUSY:19980115T220000Z/19980115T230000Z
    FREEBUSY:19980116T013000Z/19980116T043000Z
    END:VFREEBUSY
    END:VCALENDAR

4.3.2. Request Busy Time

 Individual "A" requests busy time from individuals "B" and "C".
 Individuals "B" and "C" reply with busy time data to individual "A".
 The following table illustrates the sequence of messages that would
 be exchanged between these individuals.

Daboo Standards Track [Page 96] RFC 5546 iTIP December 2009

 +---------------------+--------------------+------------------------+
 | Action              | Organizer          | Attendee               |
 +---------------------+--------------------+------------------------+
 | Initiate a busy     | "A" sends REQUEST  |                        |
 | time request        | message to "B" and |                        |
 |                     | "C".               |                        |
 |                     |                    |                        |
 | Reply to the BUSY   |                    | "B" sends a REPLY      |
 | request with BUSY   |                    | message to "A" with    |
 | time data           |                    | busy time data.        |
 +---------------------+--------------------+------------------------+
 "A" sends a "REQUEST" to "B" and "C" for busy time.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VFREEBUSY
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    DTSTAMP:19970613T190000Z
    DTSTART:19970701T080000Z
    DTEND:19970701T200000
    UID:calsrv.example.com-873970198738777@example.com
    END:VFREEBUSY
    END:VCALENDAR

4.3.3. Reply to a Busy Time Request

 "B" sends a "REPLY" method type of a "VFREEBUSY" calendar component
 to "A".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VFREEBUSY
    ORGANIZER:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    DTSTART:19970701T080000Z
    DTEND:19970701T200000Z
    UID:calsrv.example.com-873970198738777@example.com
    FREEBUSY:19970701T090000Z/PT1H,19970701T140000Z/PT30M
    DTSTAMP:19970613T190030Z
    END:VFREEBUSY

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    END:VCALENDAR
 "B" is busy from 09:00 to 10:00 and from 14:00 to 14:30.

4.4. Recurring Event and Time Zone Examples

4.4.1. A Recurring Event Spanning Time Zones

 This event describes a weekly phone conference.  The "Attendees" are
 each in a different time zone.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VTIMEZONE
    TZID:America-SanJose
    TZURL:http://example.com/tz/America-SanJose
    BEGIN:STANDARD
    DTSTART:19671029T020000
    RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
    TZOFFSETFROM:-0700
    TZOFFSETTO:-0800
    TZNAME:PST
    END:STANDARD
    BEGIN:DAYLIGHT
    DTSTART:19870405T020000
    RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
    TZOFFSETFROM:-0800
    TZOFFSETTO:-0700
    TZNAME:PDT
    END:DAYLIGHT
    END:VTIMEZONE
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;
     CUTYPE=INDIVIDUAL:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:b@example.fr
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:c@example.jp
    DTSTAMP:19970613T190030Z
    DTSTART;TZID=America-SanJose:19970701T140000
    DTEND;TZID=America-SanJose:19970701T150000
    RRULE:FREQ=WEEKLY;COUNT=20;WKST=SU;BYDAY=TU
    RDATE;TZID=America-SanJose:19970910T140000
    EXDATE;TZID=America-SanJose:19970909T140000
    EXDATE;TZID=America-SanJose:19971028T140000
    SUMMARY:Weekly Phone Conference
    UID:calsrv.example.com-873970198738777@example.com

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    SEQUENCE:0
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR
 The first component of this iCalendar object is the time zone
 component.  The "DTSTART" date coincides with the first instance of
 the "RRULE" property.
 The recurring meeting is defined in a particular time zone,
 presumably that of the originator.  The client for each "Attendee"
 has the responsibility of determining the recurrence time in the
 "Attendee's" time zone.
 The repeating event starts on Tuesday, July 1, 1997 at 2:00pm PDT
 (UTC-7).  "Attendee" B@example.fr is in France, where the local time
 on this date is 9 hours ahead of PDT, or 23:00 CEST (UTC+2).
 "Attendee" C@example.jp is in Japan, where local time is 16 hours
 ahead of PDT, or Wednesday, July 2 at 06:00 JST (UTC+9).  The event
 repeats weekly on Tuesdays (in PST/PDT).  The "RRULE" property
 results in 20 instances.  The last instance falls on Tuesday,
 November 11, 1997 2:00pm PST.  The "RDATE" property adds another
 instance: WED, 10-SEP-1997 2:00 PM PDT.
 There are also two exception dates to the recurrence rule.  The first
 one is:
 o  TUE, 09-SEP-1997 14:00 PDT (UTC-7)
 o  TUE, 09-SEP-1997 23:00 CEST (UTC+2)
 o  WED, 10-SEP-1997 06:00 JST (UTC+9)
 and the second is:
 o  TUE, 28-OCT-1997 14:00 PST (UTC-8)
 o  TUE, 28-OCT-1997 23:00 CET (UTC+1)
 o  WED, 29-OCT-1997 07:00 JST (UTC+9)

4.4.2. Modify a Recurring Instance

 In this example, the "Organizer" issues a recurring meeting.  Later,
 the "Organizer" changes an instance of the event by changing the
 "DTSTART" property.  Note the use of "RECURRENCE-ID" property and
 "SEQUENCE" property in the second request.

Daboo Standards Track [Page 99] RFC 5546 iTIP December 2009

 Original Request:
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    SEQUENCE:0
    RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    ATTENDEE:mailto:d@example.com
    DESCRIPTION:IETF-C&S Conference Call
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970601T210000Z
    DTEND:19970601T220000Z
    LOCATION:Conference Call
    DTSTAMP:19970526T083000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR
 The event request below is to change the time of a specific instance.
 This changes the July 1st instance to July 3rd.
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    RECURRENCE-ID:19970701T210000Z
    SEQUENCE:1
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    ATTENDEE:mailto:d@example.com
    DESCRIPTION:IETF-C&S Conference Call
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970703T210000Z
    DTEND:19970703T220000Z
    LOCATION:Conference Call

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    DTSTAMP:19970626T093000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.4.3. Cancel an Instance

 In this example, the "Organizer" of a recurring event deletes the
 August 1st instance.
    BEGIN:VCALENDAR
    METHOD:CANCEL
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    ATTENDEE:mailto:d@example.com
    RECURRENCE-ID:19970801T210000Z
    SEQUENCE:2
    STATUS:CANCELLED
    DTSTAMP:19970721T093000Z
    END:VEVENT
    END:VCALENDAR

4.4.4. Cancel a Recurring Event

 In this example, the "Organizer" wishes to cancel the entire
 recurring event and any exceptions.
    BEGIN:VCALENDAR
    METHOD:CANCEL
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    ATTENDEE:mailto:d@example.com
    DTSTAMP:19970721T103000Z
    STATUS:CANCELLED
    SEQUENCE:3
    END:VEVENT

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    END:VCALENDAR

4.4.5. Change All Future Instances

 This example changes the meeting location from a conference call to
 Seattle, starting September 1 and extending to all future instances.
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    RECURRENCE-ID;THISANDFUTURE:19970901T210000Z
    SEQUENCE:3
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    ATTENDEE;RSVP=TRUE:mailto:d@example.com
    DESCRIPTION:IETF-C&S Discussion
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970901T210000Z
    DTEND:19970901T220000Z
    LOCATION:Building 32, Microsoft, Seattle, WA
    DTSTAMP:19970526T083000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.4.6. Add a New Instance to a Recurring Event

 This example adds a one-time additional instance to the recurring
 event.  "Organizer" adds a second July meeting on the 15th.
    BEGIN:VCALENDAR
    METHOD:ADD
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:4
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    ATTENDEE;RSVP=TRUE:mailto:d@example.com

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    DESCRIPTION:IETF-C&S Conference Call
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970715T210000Z
    DTEND:19970715T220000Z
    LOCATION:Conference Call
    DTSTAMP:19970629T093000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.4.7. Add a New Series of Instances to a Recurring Event

 The scenario for this example involves an ongoing meeting, originally
 set up to occur every Tuesday.  The "Organizer" later decides that
 the meetings need to be on Tuesdays and Thursdays.
 The original event:
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:0
    RRULE:WKST=SU;BYDAY=TU;FREQ=WEEKLY
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980303T210000Z
    DTEND:19980303T220000Z
    LOCATION:The White Room
    DTSTAMP:19980301T093000Z
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR
 The entire event can be rescheduled using a "REQUEST".  This is done
 by using the "UID" of the event to reschedule and including the
 modified "RRULE".  Note that since this is an entire rescheduling of
 the event, any instance-specific information will be lost, unless
 explicitly included with the update "REQUEST".
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN

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    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:7
    RRULE:WKST=SU;BYDAY=TU,TH;FREQ=WEEKLY
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980303T210000Z
    DTEND:19980303T220000Z
    DTSTAMP:19980303T193000Z
    LOCATION:The White Room
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.4.8. Refreshing a Recurring Event

 The next series of examples illustrate how an "Organizer" would
 respond to a "REFRESH" submitted by an "Attendee" after a series of
 instance-specific modifications.  To convey all instance-specific
 changes, the "Organizer" must provide the latest event description
 and the relevant instances.  The first three examples show the
 history, including the initial "VEVENT" request and subsequent
 instance changes, and finally the "REFRESH".
 Original Request:
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:0
    RDATE:19980304T180000Z
    RDATE:19980311T180000Z
    RDATE:19980318T180000Z
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980304T180000Z
    DTEND:19980304T200000Z
    DTSTAMP:19980303T193000Z
    LOCATION:Conference Room A
    STATUS:CONFIRMED

Daboo Standards Track [Page 104] RFC 5546 iTIP December 2009

    END:VEVENT
    END:VCALENDAR
 Organizer changes 2nd instance location and time:
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:1
    RECURRENCE-ID:19980311T180000Z
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980311T160000Z
    DTEND:19980311T180000Z
    DTSTAMP:19980306T193000Z
    LOCATION:The Small conference room
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR
 Organizer adds a 4th instance of the meeting using the "ADD" method.
    BEGIN:VCALENDAR
    METHOD:ADD
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:2
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980315T180000Z
    DTEND:19980315T200000Z
    DTSTAMP:19980307T193000Z
    LOCATION:Conference Room A
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

Daboo Standards Track [Page 105] RFC 5546 iTIP December 2009

 If "B" requests a "REFRESH", "A" responds with the following to
 capture all instance-specific data.  In this case, both the initial
 request and an additional "VEVENT" that specifies the instance-
 specific data are included.  Because these are both of the same type
 (they are both "VEVENTS"), they can be conveyed in the same iCalendar
 object.
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:123456789@example.com
    SEQUENCE:2
    RDATE:19980304T180000Z
    RDATE:19980311T160000Z
    RDATE:19980315T180000Z
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980304T180000Z
    DTEND:19980304T200000Z
    DTSTAMP:19980303T193000Z
    LOCATION:Conference Room A
    STATUS:CONFIRMED
    END:VEVENT
    BEGIN:VEVENT
    SEQUENCE:2
    UID:123456789@example.com
    RECURRENCE-ID:19980311T160000Z
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    SUMMARY:Review Accounts
    DTSTART:19980311T160000Z
    DTEND:19980304T180000Z
    DTSTAMP:19980306T193000Z
    LOCATION:The Small conference room
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR

4.4.9. Counter an Instance of a Recurring Event

 In this example, one of the "Attendees" counters the "DTSTART"
 property of the proposed second July meeting.

Daboo Standards Track [Page 106] RFC 5546 iTIP December 2009

    BEGIN:VCALENDAR
    METHOD:COUNTER
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    RECURRENCE-ID:19970715T210000Z
    SEQUENCE:4
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;RSVP=TRUE:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    ATTENDEE;RSVP=TRUE:mailto:d@example.com
    DESCRIPTION:IETF-C&S Conference Call
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970715T220000Z
    DTEND:19970715T230000Z
    LOCATION:Conference Call
    COMMENT:May we bump this by an hour? I have a conflict
    DTSTAMP:19970629T094000Z
    END:VEVENT
    END:VCALENDAR

4.4.10. Error Reply to a Request

 The following example illustrates a scenario where a meeting is
 proposed containing an unsupported property and a bad property.
 Original Request:
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:guid-1@example.com
    SEQUENCE:0
    RRULE:FREQ=MONTHLY;BYMONTHDAY=1
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    ATTENDEE;RSVP=TRUE:mailto:d@example.com
    DESCRIPTION:IETF-C&S Conference Call
    CLASS:PUBLIC
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970601T210000Z

Daboo Standards Track [Page 107] RFC 5546 iTIP December 2009

    DTEND:19970601T220000Z
    DTSTAMP:19970602T094000Z
    LOCATION:Conference Call
    STATUS:CONFIRMED
    FOO:BAR
    END:VEVENT
    END:VCALENDAR
 "B" responds to indicate that "RRULE" is not supported and that an
 unrecognized property was encountered.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    REQUEST-STATUS:3.0;Invalid Property Name;FOO
    UID:guid-1@example.com
    SEQUENCE:0
    DTSTAMP:19970603T094000Z
    END:VEVENT
    END:VCALENDAR

4.5. Group To-Do Examples

 Individual "A" creates a group task in which individuals "A", "B",
 "C", and "D" will participate.  Individual "B" confirms acceptance of
 the task.  Individual "C" declines the task.  Individual "D"
 tentatively accepts the task.  The following table illustrates the
 sequence of messages that would be exchanged between these
 individuals.  Individual "A" then issues a "REQUEST" method to obtain
 the status of the to-do from each participant.  The response
 indicates the individual "Attendee's" completion status.  The table
 below illustrates the message flow.

Daboo Standards Track [Page 108] RFC 5546 iTIP December 2009

 +--------------+------------------------+---------------------------+
 | Action       | Organizer              | Attendee                  |
 +--------------+------------------------+---------------------------+
 | Initiate a   | "A" sends a REQUEST    |                           |
 | to-do        | message to "B", "C",   |                           |
 | request      | and "D".               |                           |
 |              |                        |                           |
 | Accept the   |                        | "B" sends a REPLY message |
 | to-do        |                        | to "A" with its PARTSTAT  |
 | request      |                        | parameter set to          |
 |              |                        | ACCEPTED.                 |
 |              |                        |                           |
 | Decline the  |                        | "C" sends a REPLY message |
 | to-do        |                        | to "A" with its PARTSTAT  |
 | request      |                        | parameter set to          |
 |              |                        | DECLINED.                 |
 |              |                        |                           |
 | Tentatively  |                        | "D" sends a REPLY message |
 | accept the   |                        | to "A" with its PARTSTAT  |
 | to-do        |                        | parameter set to          |
 | request      |                        | TENTATIVE.                |
 |              |                        |                           |
 | Check        | "A" sends a REQUEST    |                           |
 | Attendee     | message to "B" and "D" |                           |
 | completion   | with current           |                           |
 | status       | information.           |                           |
 |              |                        |                           |
 | Attendee     |                        | "B" sends a REPLY message |
 | indicates    |                        | indicating percent        |
 | percent      |                        | complete.                 |
 | complete     |                        |                           |
 |              |                        |                           |
 | Attendee     |                        | "D" sends a REPLY message |
 | indicates    |                        | indicating completion.    |
 | completion   |                        |                           |
 +--------------+------------------------+---------------------------+

4.5.1. A VTODO Request

 A sample "REQUEST" for a "VTODO" calendar component that "A" sends to
 "B", "C", and "D".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com

Daboo Standards Track [Page 109] RFC 5546 iTIP December 2009

    ATTENDEE;ROLE=CHAIR:mailto:a@example.com
    ATTENDEE;RSVP=TRUE:mailto:b@example.com
    ATTENDEE;RSVP=TRUE:mailto:c@example.com
    ATTENDEE;RSVP=TRUE:mailto:d@example.com
    DTSTART:19970701T170000Z
    DUE:19970722T170000Z
    PRIORITY:1
    SUMMARY:Create the requirements document
    UID:calsrv.example.com-873970198738777-00@example.com
    SEQUENCE:0
    DTSTAMP:19970717T200000Z
    STATUS:NEEDS-ACTION
    END:VTODO
    END:VCALENDAR

4.5.2. A VTODO Reply

 "B" accepts the to-do.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=ACCEPTED:mailto:b@example.com
    UID:calsrv.example.com-873970198738777-00@example.com
    COMMENT:I'll send you my input by email
    SEQUENCE:0
    DTSTAMP:19970717T203000Z
    REQUEST-STATUS:2.0;Success
    END:VTODO
    END:VCALENDAR
 "B" could have declined the "VTODO" or indicated tentative acceptance
 by setting the "PARTSTAT" property parameter sequence to "DECLINED"
 or "TENTATIVE", respectively.

4.5.3. A VTODO Request for Updated Status

 "A" requests status from all "Attendees".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com

Daboo Standards Track [Page 110] RFC 5546 iTIP December 2009

    ATTENDEE;ROLE=CHAIR:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:d@example.com
    UID:calsrv.example.com-873970198738777-00@example.com
    SUMMARY:Create the requirements document
    PRIORITY:1
    SEQUENCE:0
    STATUS:IN-PROCESS
    DTSTART:19970701T170000Z
    DTSTAMP:19970717T230000Z
    END:VTODO
    END:VCALENDAR

4.5.4. A Reply: Percent-Complete

 A reply indicating the task being worked on and that "B" is 75%
 complete with "B's" part of the assignment.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=IN-PROCESS:mailto:b@example.com
    PERCENT-COMPLETE:75
    UID:calsrv.example.com-873970198738777-00@example.com
    DTSTAMP:19970717T233000Z
    SEQUENCE:0
    END:VTODO
    END:VCALENDAR

4.5.5. A Reply: Completed

 A reply indicating that "D" completed "D's" part of the assignment.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com
    ATTENDEE;PARTSTAT=COMPLETED:mailto:d@example.com
    UID:calsrv.example.com-873970198738777-00@example.com
    DTSTAMP:19970717T233000Z
    SEQUENCE:0
    END:VTODO
    END:VCALENDAR

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4.5.6. An Updated VTODO Request

 "Organizer" "A" resends the "VTODO" calendar component.  "A" sets the
 overall completion for the to-do at 40%.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE;PARTSTAT=ACCEPTED;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;PARTSTAT=COMPLETED;CUTYPE=INDIVIDUAL:mailto:d@example.com
    DTSTART:19970701T170000Z
    DUE:19970722T170000Z
    PRIORITY:1
    SUMMARY:Create the requirements document
    UID:calsrv.example.com-873970198738777-00@example.com
    SEQUENCE:1
    DTSTAMP:19970718T100000Z
    STATUS:IN-PROCESS
    PERCENT-COMPLETE:40
    END:VTODO
    END:VCALENDAR

4.5.7. Recurring VTODOs

 The following examples relate to recurring "VTODO" calendar
 components.

4.5.7.1. Request for a Recurring VTODO

 In this example, "A" sends a recurring "VTODO" calendar component to
 "B" and "D".
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REQUEST
    VERSION:2.0
    BEGIN:VTODO
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR:mailto:a@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com
    ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:d@example.com
    RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
    DTSTART:19980101T100000Z
    DUE:19980103T100000Z

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    SUMMARY:Send Status Reports to Area Managers
    UID:calsrv.example.com-873970198738777-00@example.com
    SEQUENCE:0
    DTSTAMP:19970717T200000Z
    STATUS:NEEDS-ACTION
    PRIORITY:1
    END:VTODO
    END:VCALENDAR

4.5.7.2. Replying to an Instance of a Recurring VTODO

 In this example, "B" updates "A" on a single instance of the "VTODO"
 calendar component.
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VTODO
    ATTENDEE;PARTSTAT=IN-PROCESS:mailto:b@example.com
    PERCENT-COMPLETE:75
    UID:calsrv.example.com-873970198738777-00@example.com
    DTSTAMP:19970717T233000Z
    RECURRENCE-ID:19980101T170000Z
    SEQUENCE:1
    END:VTODO
    END:VCALENDAR

4.6. Journal Examples

 The iCalendar object below describes a single journal entry for
 October 2, 1997.  The "RELATED-TO" property references the phone
 conference event for which minutes were taken.
    BEGIN:VCALENDAR
    METHOD:PUBLISH
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VJOURNAL
    DTSTART:19971002T200000Z
    DTSTAMP:19970717T233100Z
    ORGANIZER:mailto:a@example.com
    SUMMARY:Phone conference minutes
    DESCRIPTION:The editors meeting was held on October 1, 1997.
     Details are in the attached document.
    UID:0981234-1234234-2410@example.com
    RELATED-TO:0981234-1234234-2402-35@example.com
    ATTACH:ftp://ftp.example.com/pub/ed/minutes100197.txt

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    END:VJOURNAL
    END:VCALENDAR

4.7. Other Examples

4.7.1. Event Refresh

 Refresh the event with a "UID" property value of
 "guid-1-12345@example.com":
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REFRESH
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    ATTENDEE:mailto:c@example.com
    ATTENDEE:mailto:d@example.com
    UID:guid-1-12345@example.com
    DTSTAMP:19970603T094000
    END:VEVENT
    END:VCALENDAR

4.7.2. Bad RECURRENCE-ID

 Component instances are identified by the combination of "UID",
 "RECURRENCE-ID", and "SEQUENCE".  When an "Organizer" sends an iTIP
 message to an "Attendee", there are three cases in which an instance
 cannot be found.  They are:
 1.  The component with the referenced "UID" and "RECURRENCE-ID" has
     been found but the "SEQUENCE" number in the calendar store does
     not match that of the iTIP message.
 2.  The component with the referenced "UID" has been found, the
     "SEQUENCE" numbers match, but the "RECURRENCE-ID" cannot be
     found.
 3.  The "UID" and "SEQUENCE" numbers are found but the CUA does not
     support recurrences.
 In case (1), two things can happen.  If the "SEQUENCE" number of the
 "Attendee's" instance is larger than that in the "Organizer's"
 message, then the "Attendee" is receiving an out-of-sequence message
 and MUST ignore it.  If the "SEQUENCE" number of the "Attendee's"
 instance is smaller, then the "Organizer" is sending out a newer

Daboo Standards Track [Page 114] RFC 5546 iTIP December 2009

 version of the component and the "Attendee's" version needs to be
 updated.  Since one or more updates have been missed, the "Attendee"
 SHOULD send a "REFRESH" message to the "Organizer" to get an updated
 version of the event.
 In case (2), something has gone wrong.  Both the "Organizer" and the
 "Attendee" should have the same instances, but the "Attendee" does
 not have the referenced instance.  In this case, the "Attendee"
 SHOULD send a "REFRESH" to the "Organizer" to get an updated version
 of the event.
 In case (3), the limitations of the "Attendee's" CUA makes it
 impossible to match an instance other than the single instance
 scheduled.  In this case, the "Attendee" need not send a "REFRESH" to
 the "Organizer".
 The example below shows a sequence in which an "Attendee" sends a
 "REFRESH" to the "Organizer".
 +-------------------------+--------------------+--------------------+
 | Action                  | Organizer          | Attendee           |
 +-------------------------+--------------------+--------------------+
 | Update an instance      | "A" sends REQUEST  |                    |
 | request                 | message to "B".    |                    |
 |                         |                    |                    |
 | Attendee requests       |                    | "B" sends a        |
 | refresh because         |                    | REFRESH message to |
 | RECURRENCE-ID was not   |                    | "A".               |
 | found                   |                    |                    |
 |                         |                    |                    |
 | Refresh the entire      | "A" sends the      |                    |
 | event                   | latest copy of the |                    |
 |                         | event to "B"       |                    |
 |                         |                    |                    |
 | Attendee handles the    |                    | "B" updates to the |
 | request and updates the |                    | latest copy of the |
 | instance                |                    | meeting.           |
 +-------------------------+--------------------+--------------------+
 Request from "A":
    BEGIN:VCALENDAR
    METHOD:REQUEST
    PRODID:-//Example/ExampleCalendarClient//EN
    VERSION:2.0
    BEGIN:VEVENT
    UID:example-12345@example.com
    SEQUENCE:3

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    RRULE:FREQ=WEEKLY
    RDATE;VALUE=PERIOD:19970819T210000Z/199700819T220000Z
    ORGANIZER:mailto:a@example.com
    ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    DESCRIPTION:IETF-C&S Conference Call
    SUMMARY:IETF Calendaring Working Group Meeting
    DTSTART:19970801T210000Z
    DTEND:19970801T220000Z
    RECURRENCE-ID:19970809T210000Z
    DTSTAMP:19970726T083000
    STATUS:CONFIRMED
    END:VEVENT
    END:VCALENDAR
 "B" has the event with "UID" property "example-12345@example.com",
 but "B's" "SEQUENCE" property value is "1" and the event does not
 have an instance at the specified recurrence time.  This means that
 "B" has missed at least one update and needs a new copy of the event.
 "B" requests the latest copy of the event with the following refresh
 message:
    BEGIN:VCALENDAR
    PRODID:-//Example/ExampleCalendarClient//EN
    METHOD:REFRESH
    VERSION:2.0
    BEGIN:VEVENT
    ORGANIZER:mailto:a@example.com
    ATTENDEE:mailto:b@example.com
    UID:example-12345@example.com
    DTSTAMP:19970603T094000
    END:VEVENT
    END:VCALENDAR

5. Application Protocol Fallbacks

5.1. Partial Implementation

 Applications that support this specification are not required to
 support the entire protocol.  The following describes how methods and
 properties SHOULD "fallback" in applications that do not support the
 complete protocol.  If a method or property is not addressed in this
 section, it may be ignored.

Daboo Standards Track [Page 116] RFC 5546 iTIP December 2009

5.1.1. Event-Related Fallbacks

 +----------------+--------------------------------------------------+
 | Method         | Fallback                                         |
 +----------------+--------------------------------------------------+
 | PUBLISH        | Required                                         |
 | REQUEST        | PUBLISH                                          |
 | REPLY          | Required                                         |
 | ADD            | Required if recurrences supported; otherwise,    |
 |                | reply with a REQUEST-STATUS "2.8; Success,       |
 |                | repeating event ignored.  Scheduled as a single  |
 |                | component", and schedule as a single component.  |
 | CANCEL         | Required                                         |
 | REFRESH        | Required                                         |
 | COUNTER        | Reply with "Not Supported".                      |
 | DECLINECOUNTER | Required if COUNTER is implemented for VEVENTs;  |
 |                | otherwise, reply with "Not Supported".           |
 +----------------+--------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | iCalendar       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | CALSCALE        | Ignore - assume GREGORIAN.                      |
 | PRODID          | Ignore                                          |
 | METHOD          | Required as described in the Method list above. |
 | VERSION         | Ignore                                          |
 +-----------------+-------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | Event-Related   | Fallback                                        |
 | Components      |                                                 |
 +-----------------+-------------------------------------------------+
 | VALARM          | Reply with "Not Supported".                     |
 | VTIMEZONE       | Required if any DateTime value refers to a time |
 |                 | zone.                                           |
 +-----------------+-------------------------------------------------+

Daboo Standards Track [Page 117] RFC 5546 iTIP December 2009

 +-----------------+-------------------------------------------------+
 | Component       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | ATTACH          | Ignore                                          |
 | ATTENDEE        | Required if METHOD is REQUEST; otherwise,       |
 |                 | ignore.                                         |
 | CATEGORIES      | Ignore                                          |
 | CLASS           | Ignore                                          |
 | COMMENT         | Ignore                                          |
 | COMPLETED       | Ignore                                          |
 | CONTACT         | Ignore                                          |
 | CREATED         | Ignore                                          |
 | DESCRIPTION     | Ignore                                          |
 | DURATION        | Required                                        |
 | DTSTAMP         | Required                                        |
 | DTSTART         | Required                                        |
 | DTEND           | Required                                        |
 | EXDATE          | Ignore                                          |
 | GEO             | Ignore                                          |
 | LAST-MODIFIED   | Ignore                                          |
 | LOCATION        | Required                                        |
 | ORGANIZER       | Required if METHOD is REQUEST; otherwise,       |
 |                 | ignore.                                         |
 | PRIORITY        | Ignore                                          |
 | RELATED-TO      | Ignore                                          |
 | RDATE           | Ignore                                          |
 | RRULE           | Ignore - assume the first instance occurs on    |
 |                 | the DTSTART property.  If implemented,          |
 |                 | VTIMEZONE MUST also be implemented.             |
 | RECURRENCE-ID   | Required if RRULE is implemented; otherwise,    |
 |                 | ignore.                                         |
 | REQUEST-STATUS  | Required                                        |
 | RESOURCES       | Ignore                                          |
 | SEQUENCE        | Required                                        |
 | STATUS          | Ignore                                          |
 | SUMMARY         | Ignore                                          |
 | TRANSP          | Required if FREEBUSY is implemented; otherwise, |
 |                 | ignore.                                         |
 | URL             | Ignore                                          |
 | UID             | Required                                        |
 | X-              | Ignore                                          |
 +-----------------+-------------------------------------------------+

Daboo Standards Track [Page 118] RFC 5546 iTIP December 2009

5.1.2. Free/Busy-Related Fallbacks

 +---------+---------------------------------------------------------+
 | Method  | Fallback                                                |
 +---------+---------------------------------------------------------+
 | PUBLISH | Required if freebusy lookups are supported; otherwise,  |
 |         | reply with a REQUEST-STATUS "3.14; Unsupported          |
 |         | capability".                                            |
 | REQUEST | Required if freebusy lookups are supported; otherwise,  |
 |         | reply with a REQUEST-STATUS "3.14; Unsupported          |
 |         | capability".                                            |
 | REPLY   | Required if freebusy lookups are supported; otherwise,  |
 |         | reply with a REQUEST-STATUS "3.14; Unsupported          |
 |         | capability".                                            |
 +---------+---------------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | iCalendar       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | CALSCALE        | Ignore - assume GREGORIAN.                      |
 | PRODID          | Ignore                                          |
 | METHOD          | Required as described in the Method list above. |
 | VERSION         | Ignore                                          |
 +-----------------+-------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | Component       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | ATTENDEE        | Required if METHOD is REQUEST; otherwise,       |
 |                 | ignore.                                         |
 | COMMENT         | Ignore                                          |
 | CONTACT         | Ignore                                          |
 | DTEND           | Required                                        |
 | DTSTAMP         | Required                                        |
 | DTSTART         | Required                                        |
 | DURATION        | Ignore                                          |
 | FREEBUSY        | Required                                        |
 | ORGANIZER       | Required if METHOD is REQUEST; otherwise,       |
 |                 | ignore.                                         |
 | REQUEST-STATUS  | Ignore                                          |
 | UID             | Required                                        |
 | URL             | Ignore                                          |
 | X-              | Ignore                                          |
 +-----------------+-------------------------------------------------+

Daboo Standards Track [Page 119] RFC 5546 iTIP December 2009

5.1.3. To-Do-Related Fallbacks

 +----------------+--------------------------------------------------+
 | Method         | Fallback                                         |
 +----------------+--------------------------------------------------+
 | PUBLISH        | Required                                         |
 | REQUEST        | PUBLISH                                          |
 | REPLY          | Required                                         |
 | ADD            | Required if recurrences supported; otherwise,    |
 |                | reply with a REQUEST-STATUS "2.8; Success,       |
 |                | repeating event ignored.  Scheduled as a single  |
 |                | component", and schedule as a single component.  |
 | CANCEL         | Required                                         |
 | REFRESH        | Required                                         |
 | COUNTER        | Reply with "Not Supported".                      |
 | DECLINECOUNTER | Required if COUNTER for VTODOs is implemented;   |
 |                | otherwise, reply with "Not Supported".           |
 +----------------+--------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | iCalendar       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | CALSCALE        | Ignore - assume GREGORIAN.                      |
 | PRODID          | Ignore                                          |
 | METHOD          | Required as described in the Method list above. |
 | VERSION         | Ignore                                          |
 +-----------------+-------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | To-Do-Related   | Fallback                                        |
 | Components      |                                                 |
 +-----------------+-------------------------------------------------+
 | VALARM          | Reply with "Not Supported".                     |
 | VTIMEZONE       | Required if any DateTime value refers to a time |
 |                 | zone.                                           |
 +-----------------+-------------------------------------------------+

Daboo Standards Track [Page 120] RFC 5546 iTIP December 2009

 +------------------+------------------------------------------------+
 | Component        | Fallback                                       |
 | Property         |                                                |
 +------------------+------------------------------------------------+
 | ATTACH           | Ignore                                         |
 | ATTENDEE         | Required if METHOD is REQUEST; otherwise,      |
 |                  | ignore.                                        |
 | CATEGORIES       | Ignore                                         |
 | CLASS            | Ignore                                         |
 | COMMENT          | Ignore                                         |
 | COMPLETED        | Required                                       |
 | CONTACT          | Ignore                                         |
 | CREATED          | Ignore                                         |
 | DESCRIPTION      | Required if METHOD is REQUEST; otherwise,      |
 |                  | ignore.                                        |
 | DUE              | Required                                       |
 | DURATION         | Required                                       |
 | DTSTAMP          | Required                                       |
 | DTSTART          | Required                                       |
 | EXDATE           | Ignore - reply with "Not Supported".           |
 | LAST-MODIFIED    | Ignore                                         |
 | LOCATION         | Ignore                                         |
 | ORGANIZER        | Required if METHOD is REQUEST; otherwise,      |
 |                  | ignore.                                        |
 | PERCENT-COMPLETE | Ignore                                         |
 | PRIORITY         | Required                                       |
 | RECURRENCE-ID    | Required if RRULE is implemented; otherwise,   |
 |                  | ignore.                                        |
 | RELATED-TO       | Ignore                                         |
 | REQUEST-STATUS   | Ignore                                         |
 | RDATE            | Ignore                                         |
 | RRULE            | Ignore - assume the first instance occurs on   |
 |                  | the DTSTART property.  If implemented,         |
 |                  | VTIMEZONE MUST also be implemented.            |
 | RESOURCES        | Ignore                                         |
 | SEQUENCE         | Required                                       |
 | STATUS           | Required                                       |
 | SUMMARY          | Ignore                                         |
 | URL              | Ignore                                         |
 | UID              | Required                                       |
 | X-               | Ignore                                         |
 +------------------+------------------------------------------------+

Daboo Standards Track [Page 121] RFC 5546 iTIP December 2009

5.1.4. Journal-Related Fallbacks

 +---------+---------------------------------------------------------+
 | Method  | Fallback                                                |
 +---------+---------------------------------------------------------+
 | PUBLISH | Implementations MAY ignore the METHOD type.  The        |
 |         | REQUEST-STATUS "3.14; Unsupported capability" MUST be   |
 |         | returned.                                               |
 | ADD     | Implementations MAY ignore the METHOD type.  The        |
 |         | REQUEST-STATUS "3.14; Unsupported capability" MUST be   |
 |         | returned.                                               |
 | CANCEL  | Implementations MAY ignore the METHOD type.  The        |
 |         | REQUEST-STATUS "3.14; Unsupported capability" MUST be   |
 |         | returned.                                               |
 +---------+---------------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | iCalendar       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | CALSCALE        | Ignore - assume GREGORIAN.                      |
 | PRODID          | Ignore                                          |
 | METHOD          | Required as described in the Method list above. |
 | VERSION         | Ignore                                          |
 +-----------------+-------------------------------------------------+
 +-----------------+-------------------------------------------------+
 | Journal-Related | Fallback                                        |
 | Components      |                                                 |
 +-----------------+-------------------------------------------------+
 | VTIMEZONE       | Required if any DateTime value refers to a time |
 |                 | zone.                                           |
 +-----------------+-------------------------------------------------+

Daboo Standards Track [Page 122] RFC 5546 iTIP December 2009

 +-----------------+-------------------------------------------------+
 | Component       | Fallback                                        |
 | Property        |                                                 |
 +-----------------+-------------------------------------------------+
 | ATTACH          | Ignore                                          |
 | ATTENDEE        | Ignore                                          |
 | CATEGORIES      | Ignore                                          |
 | CLASS           | Ignore                                          |
 | COMMENT         | Ignore                                          |
 | CONTACT         | Ignore                                          |
 | CREATED         | Ignore                                          |
 | DESCRIPTION     | Ignore                                          |
 | DTSTAMP         | Required                                        |
 | DTSTART         | Required                                        |
 | EXDATE          | Ignore                                          |
 | LAST-MODIFIED   | Ignore                                          |
 | ORGANIZER       | Ignore                                          |
 | RECURRENCE-ID   | Required if RRULE is implemented; otherwise,    |
 |                 | ignore.                                         |
 | RELATED-TO      | Ignore                                          |
 | RDATE           | Ignore                                          |
 | RRULE           | Ignore - assume the first instance occurs on    |
 |                 | the DTSTART property.  If implemented,          |
 |                 | VTIMEZONE MUST also be implemented.             |
 | SEQUENCE        | Required                                        |
 | STATUS          | Ignore                                          |
 | SUMMARY         | Required                                        |
 | URL             | Ignore                                          |
 | UID             | Required                                        |
 | X-              | Ignore                                          |
 +-----------------+-------------------------------------------------+

5.2. Latency Issues

 With a store-and-forward transport, it is possible for events to
 arrive out of sequence.  That is, a "CANCEL" method may be received
 prior to receiving the associated "REQUEST" for the calendar
 component.  This section discusses a few of these scenarios.

5.2.1. Cancellation of an Unknown Calendar Component

 When a "CANCEL" method is received before the original "REQUEST"
 method, the calendar will be unable to correlate the "UID" property
 of the cancellation with an existing calendar component.  It is
 suggested that messages that cannot be correlated and that also
 contain non-zero sequence numbers be held and not discarded.
 Implementations MAY age them out if no other messages arrive with the
 same "UID" property value and a lower sequence number.

Daboo Standards Track [Page 123] RFC 5546 iTIP December 2009

5.2.2. Unexpected Reply from an Unknown Delegate

 When an "Attendee" delegates an item to another CU, they MUST send a
 "REPLY" method to the "Organizer" using the "ATTENDEE" properties to
 indicate that the request was delegated and to whom.  Hence, it is
 possible for an "Organizer" to receive a "REPLY" from a CU not listed
 as one of the original "Attendees".  The resolution is left to the
 implementation, but it is expected that the calendaring software will
 either accept the reply or hold it until the related "REPLY" method
 is received from the "Delegator".  If the version of the "REPLY"
 method is out of date, the "Organizer" SHOULD treat the message as a
 "REFRESH" message and update the "Delegate" with the correct version,
 provided that delegation to that delegate is acceptable.

5.3. Sequence Number

 Under some conditions, a CUA may receive requests and replies with
 the same "SEQUENCE" property value.  The "DTSTAMP" property is
 utilized as a tie-breaker when two items with the same "SEQUENCE"
 property value are evaluated.

6. Security Considerations

 iTIP is an abstract transport protocol that will be bound to a real-
 time transport, a store-and-forward transport, and perhaps other
 transports.  The transport protocol will be responsible for providing
 facilities for authentication and encryption using standard Internet
 mechanisms that are mutually understood between the sender and
 receiver.

6.1. Security Threats

6.1.1. Spoofing the Organizer

 In iTIP, the "Organizer" (or someone working on the "Organizer's"
 behalf) is the only person authorized to make changes to an existing
 "VEVENT", "VTODO", or "VJOURNAL" calendar component and republish it
 or redistribute updates to the "Attendees".  An iCalendar object that
 maliciously changes or cancels an existing "VEVENT", "VTODO", or
 "VJOURNAL" calendar component may be constructed by someone other
 than the "Organizer" and republished or sent to the "Attendees".

6.1.2. Spoofing the Attendee

 In iTIP, an "Attendee" of a "VEVENT" or "VTODO" calendar component
 (or someone working on the "Attendee's" behalf) is the only person
 authorized to update any parameter associated with their "ATTENDEE"

Daboo Standards Track [Page 124] RFC 5546 iTIP December 2009

 property and send it to the "Organizer".  An iCalendar object that
 maliciously changes the "ATTENDEE" parameters may be constructed by
 someone other than the real "Attendee" and sent to the "Organizer".

6.1.3. Unauthorized Replacement of the Organizer

 There will be circumstances when "Attendees" of an event or to-do
 decide, using out-of-band mechanisms, that the "Organizer" must be
 replaced.  When the new "Organizer" sends out the updated "VEVENT" or
 "VTODO", the "Attendee's" CUA will detect that the "Organizer" has
 been changed, but it has no way of knowing whether or not the change
 was mutually agreed upon.

6.1.4. Eavesdropping and Data Integrity

 The iCalendar object is constructed with human-readable clear text.
 Any information contained in an iCalendar object may be read and/or
 changed by unauthorized persons while the object is in transit.

6.1.5. Flooding a Calendar

 Implementations could provide a means to automatically incorporate
 "REQUEST" methods into a calendar.  This presents the opportunity for
 a calendar to be flooded with requests, which effectively blocks all
 the calendar's free time.

6.1.6. Unauthorized REFRESH Requests

 It is possible for an "Organizer" to receive a "REFRESH" request from
 someone who is not an "Attendee" of an event or to-do.  Only
 "Attendees" of an event or to-do are authorized to receive replies to
 "REFRESH" requests.  Replying to such requests to anyone who is not
 an "Attendee" may be a security problem.

6.2. Recommendations

 For an application where the information is sensitive or critical and
 the network is subject to a high probability of attack, iTIP
 transactions SHOULD be encrypted and authenticated.  This helps
 mitigate the threats of spoofing, eavesdropping, and malicious
 changes in transit.

6.2.1. Securing iTIP transactions

 iTIP transport bindings MUST provide a mechanism to enable
 authentication of the sender's identity as well as privacy and
 integrity of the data being transmitted.  This allows the receiver of
 a signed iCalendar object to verify the identity of the sender.  This

Daboo Standards Track [Page 125] RFC 5546 iTIP December 2009

 sender may then be correlated to an "ATTENDEE" property in the
 iCalendar object.  If the correlation is made and the sender is
 authorized to make the requested change or update, then the operation
 may proceed.  It also allows the message to be encrypted to prevent
 unauthorized reading of the message contents in transit. iTIP
 transport binding documents describe this process in detail.

6.2.2. Implementation Controls

 The threat of unauthorized replacement of the "Organizer" SHOULD be
 mitigated by a calendar system that uses this protocol by providing
 controls or alerts that make "Calendar Users" aware of such
 "Organizer" changes and allowing them to decide whether or not the
 request should be honored.
 The threat of flooding a calendar SHOULD be mitigated by a calendar
 system that uses this protocol by providing controls that may be used
 to limit the acceptable sources for iTIP transactions, and perhaps
 the size of messages and volume of traffic, by source.
 The threat of unauthorized "REFRESH" requests SHOULD be mitigated by
 a calendar system that uses this protocol by providing controls or
 alerts that allow "Calendar Users" to decide whether or not the
 request should be honored.  An implementation MAY decide to maintain,
 for audit or historical purposes, "Calendar Users" who were part of
 an "Attendee" list and who were subsequently uninvited.  Similar
 controls or alerts should be provided when a "REFRESH" request is
 received from these "Calendar Users" as well.

6.2.3. Access Controls and Filtering

 In many environments, there could be restrictions on who is allowed
 to schedule with whom and who the allowed delegates are for
 particular "Calendar Users".
 iTIP transport bindings SHOULD provide mechanisms for implementing
 access controls or filtering to ensure iTIP transactions only take
 place between authorized "Calendar Users".  That would include
 preventing one "Calendar User" from scheduling with another or one
 "Calendar User" delegating to another.

6.3. Privacy Issues

 The "Organizer" might want to keep "Attendees" from knowing which
 other "Attendees" are participating in an event or to-do.  The
 "Organizer" has the choice of sending single iTIP messages with a
 full list of "Attendees" or sending iTIP messages to each "Attendee"
 with only that "Attendee" listed.

Daboo Standards Track [Page 126] RFC 5546 iTIP December 2009

7. IANA Considerations

7.1. Registration Template for REQUEST-STATUS Values

 This specification updates [RFC5545] by adding a "REQUEST-STATUS"
 value registry to the iCalendar Elements registry.
 A "REQUEST-STATUS" value is defined by completing the following
 template.
    Status Code:  Hierarchical, numeric return status code, following
       the rules defined in Section 3.8.8.3 of [RFC5545].
    Status Description:  Textual status description.  A short but
       clear description of the error.
    Status Exception Data:  Textual exception data.  A short but clear
       description of what might appear in this field.
    Description:  Describe the underlying cause for this status code
       value.

7.2. Additions to iCalendar METHOD Registry

 This document defines the following values for the iCalendar "METHOD"
 property, using the values template from Section 8.2.6 of [RFC5545].
 These should be added to the Methods Registry defined in Section
 8.3.12 of [RFC5545]:

7.2.1. METHOD:PUBLISH

 Value:  PUBLISH
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.2.2. METHOD:REQUEST

 Value:  REQUEST
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

Daboo Standards Track [Page 127] RFC 5546 iTIP December 2009

7.2.3. METHOD:REPLY

 Value:  REPLY
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.2.4. METHOD:ADD

 Value:  ADD
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.2.5. METHOD:CANCEL

 Value:  CANCEL
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.2.6. METHOD:REFRESH

 Value:  REFRESH
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.2.7. METHOD:COUNTER

 Value:  COUNTER
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.

Daboo Standards Track [Page 128] RFC 5546 iTIP December 2009

 Examples:  See this RFC.

7.2.8. METHOD:DECLINECOUNTER

 Value:  DECLINECOUNTER
 Purpose:  Standard iTIP "METHOD" value.
 Conformance:  Only used with the "METHOD" property.
 Examples:  See this RFC.

7.3. REQUEST-STATUS Value Registry

 New "REQUEST-STATUS" values can be registered using the process
 described in Section 8.2.1 of [RFC5545].
 The following table is to be used to initialize the "REQUEST-STATUS"
 value registry.

Daboo Standards Track [Page 129] RFC 5546 iTIP December 2009

         +-------------+---------+--------------------------+
         | Status Code | Status  | Reference                |
         +-------------+---------+--------------------------+
         | 2.0         | Current | RFC 5546, Section 3.6.1  |
         | 2.1         | Current | RFC 5546, Section 3.6.2  |
         | 2.2         | Current | RFC 5546, Section 3.6.3  |
         | 2.3         | Current | RFC 5546, Section 3.6.4  |
         | 2.4         | Current | RFC 5546, Section 3.6.5  |
         | 2.5         | Current | RFC 5546, Section 3.6.6  |
         | 2.6         | Current | RFC 5546, Section 3.6.7  |
         | 2.7         | Current | RFC 5546, Section 3.6.8  |
         | 2.8         | Current | RFC 5546, Section 3.6.9  |
         | 2.9         | Current | RFC 5546, Section 3.6.10 |
         | 2.10        | Current | RFC 5546, Section 3.6.11 |
         | 2.11        | Current | RFC 5546, Section 3.6.12 |
         | 3.0         | Current | RFC 5546, Section 3.6.13 |
         | 3.1         | Current | RFC 5546, Section 3.6.14 |
         | 3.2         | Current | RFC 5546, Section 3.6.15 |
         | 3.3         | Current | RFC 5546, Section 3.6.16 |
         | 3.4         | Current | RFC 5546, Section 3.6.17 |
         | 3.5         | Current | RFC 5546, Section 3.6.18 |
         | 3.6         | Current | RFC 5546, Section 3.6.19 |
         | 3.7         | Current | RFC 5546, Section 3.6.20 |
         | 3.8         | Current | RFC 5546, Section 3.6.21 |
         | 3.9         | Current | RFC 5546, Section 3.6.22 |
         | 3.10        | Current | RFC 5546, Section 3.6.23 |
         | 3.11        | Current | RFC 5546, Section 3.6.24 |
         | 3.12        | Current | RFC 5546, Section 3.6.25 |
         | 3.13        | Current | RFC 5546, Section 3.6.26 |
         | 3.14        | Current | RFC 5546, Section 3.6.27 |
         | 4.0         | Current | RFC 5546, Section 3.6.28 |
         | 5.0         | Current | RFC 5546, Section 3.6.29 |
         | 5.1         | Current | RFC 5546, Section 3.6.30 |
         | 5.2         | Current | RFC 5546, Section 3.6.31 |
         | 5.3         | Current | RFC 5546, Section 3.6.32 |
         +-------------+---------+--------------------------+

8. Acknowledgments

 This is an update to the original iTIP document authored by S.
 Silverberg, S. Mansour, F. Dawson, and R. Hopson.
 This revision is the product of the Calsify IETF Working Group, and
 several participants have made important contributions to this
 specification, including Oliver Block, Bernard Desruisseaux, Mike
 Douglass, Tim Hare, Ciny Joy, Bruce Kahn, Reinhold Kainhofer, Eliot
 Lear, Jonathan Lennox, Andy Mabbett, Aki Niemi, John W. Noerenberg
 II, Robert Ransdell, and Caleb Richardson.

Daboo Standards Track [Page 130] RFC 5546 iTIP December 2009

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2368]  Hoffman, P., Masinter, L., and J. Zawinski, "The mailto
            URL scheme", RFC 2368, July 1998.
 [RFC5545]  Desruisseaux, B., "Internet Calendaring and Scheduling
            Core Object Specification (iCalendar)", RFC 5545,
            September 2009.

9.2. Informative References

 [iMIP]     Melnikov, A., Ed., "iCalendar Message-Based
            Interoperability Protocol (iMIP)", Work in Progress,
            October 2009.

Daboo Standards Track [Page 131] RFC 5546 iTIP December 2009

Appendix A. Differences from RFC 2446

A.1. Changed Restrictions

 This specification now defines an allowed combination of "REQUEST-
 STATUS" codes when multiple iCalendar components are included in an
 iTIP message.
 This specification now restricts "RECURRENCE-ID" to only a single
 occurrence in any one iCalendar component in an iTIP message, as
 required by [RFC5545].
 Changed the "RECURRENCE-ID" entry in the component restriction table
 to "0 or 1" from "0+", to fall in line with [RFC5545].
 Changed the "FREEBUSY" entry in the "VFREEBUSY", "PUBLISH", and
 "REPLY" restriction tables to "0+" from "1+", to fall in line with
 [RFC5545].
 Changed the "FREEBUSY" description in the "VFREEBUSY" and "REPLY"
 restriction tables to indicate that different "FBTYPE" ranges MUST
 NOT overlap.
 Changed the "TZNAME" entry in the "VTIMEZONE" restriction table to
 "0+" from "0 or 1", to fall in line with [RFC5545].
 Changed the "COMMENT" entry in the component restriction tables to
 "0+" from "0 or 1", to fall in line with [RFC5545].
 Added the "ATTENDEE" entry in the "VALARM" restriction table to match
 the email alarm type in [RFC5545].
 Changed the "CATEGORIES" entry in the component restriction tables to
 "0+" from "0 or 1", to fall in line with [RFC5545].
 Changed the "RESOURCES" entry in the component restriction tables to
 "0+" from "0 or 1", to fall in line with [RFC5545].
 Changed the "CONTACT" entry in the "VFREEBUSY" restriction table to
 "0 or 1" from "0+", to fall in line with [RFC5545].
 Changed the "UID" entry in the "VFREEBUSY" and "PUBLISH" restriction
 tables to "1" from "0", to fall in line with [RFC5545].
 Added the "COMPLETED" entry in the "VTODO" restriction tables to fall
 in line with [RFC5545].

Daboo Standards Track [Page 132] RFC 5546 iTIP December 2009

 Added the "REQUEST-STATUS" entry in the "VJOURNAL" restriction tables
 to fall in line with [RFC5545].

A.2. Deprecated Features

 The "EXRULE" property was removed in [RFC5545] and references to that
 have been removed in this document too.
 The "PROCEDURE" value for the "ACTION" property was removed in
 [RFC5545] and references to that have been removed in this document
 too.
 The "THISANDPRIOR" option for the "RANGE" parameter was removed in
 [RFC5545] and references to that have been removed in this document
 too.

Author's Address

 Cyrus Daboo (editor)
 Apple Inc.
 1 Infinite Loop
 Cupertino, CA  95014
 USA
 EMail: cyrus@daboo.name
 URI:   http://www.apple.com/

Daboo Standards Track [Page 133]

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