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rfc:rfc3842

Network Working Group R. Mahy Request for Comments: 3842 Cisco Systems, Inc. Category: Standards Track August 2004

 A Message Summary and Message Waiting Indication Event Package for
               the Session Initiation Protocol (SIP)

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) The Internet Society (2004).

Abstract

 This document describes a Session Initiation Protocol (SIP) event
 package to carry message waiting status and message summaries from a
 messaging system to an interested User Agent.

Mahy Standards Track [Page 1] RFC 3842 SIP Message Waiting August 2004

Table of Contents

 1.   Conventions  . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.   Background and Appropriateness . . . . . . . . . . . . . . .   3
 3.   Event Package Formal Definition  . . . . . . . . . . . . . .   4
      3.1.  Event Package Name . . . . . . . . . . . . . . . . . .   4
      3.2.  Event Package Parameters . . . . . . . . . . . . . . .   4
      3.3.  SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . .   4
      3.4.  Subscription Duration. . . . . . . . . . . . . . . . .   4
      3.5.  NOTIFY Bodies. . . . . . . . . . . . . . . . . . . . .   4
      3.6.  Subscriber Generation of SUBSCRIBE Requests. . . . . .   6
      3.7.  Notifier Processing of SUBSCRIBE Requests. . . . . . .   6
      3.8.  Notifier Generation of NOTIFY Requests . . . . . . . .   7
      3.9.  Subscriber Processing of NOTIFY Requests . . . . . . .   7
      3.10. Handling of Forked Requests. . . . . . . . . . . . . .   7
      3.11. Rate of Notifications. . . . . . . . . . . . . . . . .   7
      3.12. State Agents and Lists . . . . . . . . . . . . . . . .   8
      3.13. Behavior of a Proxy Server . . . . . . . . . . . . . .   8
 4.   Examples of Usage  . . . . . . . . . . . . . . . . . . . . .   8
      4.1.  Example Message Flow . . . . . . . . . . . . . . . . .   8
      4.2.  Example Usage with Callee Capabilities and Caller
            Preferences. . . . . . . . . . . . . . . . . . . . . .  14
 5.   Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . .  14
      5.1.  New Event-Package Definition . . . . . . . . . . . . .  15
      5.2.  Body Format Syntax . . . . . . . . . . . . . . . . . .  15
 6.   Security Considerations  . . . . . . . . . . . . . . . . . .  15
 7.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  16
      7.1.  SIP Event Package Registration for message-summary . .  16
      7.2.  MIME Registration for application/
            simple-message-summary . . . . . . . . . . . . . . . .  16
 8.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  17
 9.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  17
 10.  References . . . . . . . . . . . . . . . . . . . . . . . . .  17
      10.1. Normative References . . . . . . . . . . . . . . . . .  17
      10.2. Informational References . . . . . . . . . . . . . . .  18
 11.  Author's Address . . . . . . . . . . . . . . . . . . . . . .  18
 12.  Full Copyright Statement . . . . . . . . . . . . . . . . . .  19

1. 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 BCP 14, RFC 2119 [3].

Mahy Standards Track [Page 2] RFC 3842 SIP Message Waiting August 2004

2. Background and Appropriateness

 Message Waiting Indication is a common feature of telephone networks.
 It typically involves an audible or visible indication that messages
 are waiting, such as playing a special dial tone (which in telephone
 networks is called message-waiting dial tone), lighting a light or
 indicator on the phone, displaying icons or text, or some
 combination.
    Message-waiting dial tone is similar to but distinct from stutter
    dial tone.  Both are defined in GR-506 [11].
 The methods in the SIP [1] base specification were only designed to
 solve the problem of session initiation for multimedia sessions, and
 rendezvous.  Since Message Waiting Indication is really status
 information orthogonal to a session, it was not clear how an IP
 telephone acting as a SIP User Agent would implement comparable
 functionality.  Members of the telephony community viewed this as a
 shortcoming of SIP.
 Users want the useful parts of the functionality they have using
 traditional analog, mobile, and PBX telephones.  It is also desirable
 to provide comparable functionality in a flexible way that allows for
 more customization and new features.  SIP Specific Event Notification
 (RFC 3265 -- SIP Events) [2] is an appropriate mechanism to use in
 this environment, as it preserves the user mobility and rendezvous
 features which SIP provides.
 Using SIP-Specific Event Notification, a Subscriber User Agent
 (typically an IP phone or SIP software User Agent) subscribes to the
 status of their messages.  A SIP User Agent acting on behalf of the
 user's messaging system then notifies the Subscriber each time the
 messaging account's messages have changed.  (This Notifier could be
 composed with a User Agent that provides a real-time media interface
 to send or receive messages, or it could be a stand-alone entity.)
 The Notifier sends a message summary in the body of a NOTIFY, encoded
 in a new MIME type defined later in this document.  A User Agent can
 also explicitly fetch the current status.
 A SIP User Agent MAY subscribe to multiple accounts (distinguished by
 the Request URI).  Multiple SIP User Agents MAY subscribe to the same
 account.
 Before any subscriptions or notifications are sent, each interested
 User Agent must be made aware of its messaging notifier(s).  This MAY
 be manually configured on interested User Agents, manually configured
 on an appropriate SIP Proxy, or dynamically discovered based on

Mahy Standards Track [Page 3] RFC 3842 SIP Message Waiting August 2004

 requested caller preferences [4] and registered callee capabilities
 [5].  (For more information on usage with callee capabilities, see
 Section 4.2)

3. Event Package Formal Definition

3.1. Event Package Name

 This document defines a SIP Event Package as defined in RFC 3265 [2].
 The event-package token name for this package is:
    "message-summary"

3.2. Event Package Parameters

 This package does not define any event package parameters.

3.3. SUBSCRIBE Bodies

 This package does not define any SUBSCRIBE bodies.

3.4. Subscription Duration

 Subscriptions to this event package MAY range from minutes to weeks.
 Subscriptions in hours or days are more typical and are RECOMMENDED.
 The default subscription duration for this event package is one hour.

3.5. NOTIFY Bodies

 A simple text-based format is proposed to prevent an undue burden on
 low-end user agents, for example, inexpensive IP phones with no
 display.  Although this format is text-based, it is intended for
 machine consumption only.
 A future extension MAY define other NOTIFY bodies.  If no "Accept"
 header is present in the SUBSCRIBE, the body type defined in this
 document MUST be assumed.
 The format specified in this proposal attempts to separate orthogonal
 attributes of messages as much as possible.  Messages are separated
 by message-context-class (for example: voice-message, fax-message,
 pager-message, multimedia-message, text-message, and none), by
 message status (new and old), and urgent and non-urgent type.
 The text format begins with a simple status line, and optionally a
 summary line per message-context-class.  Message-context-classes are
 defined in [7].  For each message-context-class, the total number of
 new and old messages is reported in the new and old fields.

Mahy Standards Track [Page 4] RFC 3842 SIP Message Waiting August 2004

 In some cases, detailed message summaries are not available.  The
 status line allows messaging systems or messaging gateways to provide
 the traditional boolean message waiting notification.
    Messages-Waiting: yes
 If the Request-URI or To header in a message-summary subscription
 corresponds to a group or collection of individual messaging
 accounts, the notifier MUST specify to which account the message-
 summary body corresponds.  Note that the account URI MUST NOT be
 delimited with angle brackets ("<" and ">").
    Message-Account: sip:alice@example.com
 In the example that follows, more than boolean message summary
 information is available to the User Agent.  There are two new and
 four old fax messages.
    Fax-Message: 2/4
 After the summary, the format can optionally list a summary count of
 urgent messages.  In the next example there are one new and three old
 voice messages, none of the new messages are urgent, but one of the
 old messages is.  All counters have a maximum value of 4,294,967,295
 ((2^32) - 1).  Notifiers MUST NOT generate a request with a larger
 value.  Subscribers MUST treat a larger value as 2^32-1.
    Voice-Message: 1/3 (0/1)
 Optionally, after the summary counts, the messaging systems MAY
 append RFC 2822 style message headers [9], which further describe
 newly added messages.  Message headers MUST NOT be included in an
 initial NOTIFY, as new messages could be essentially unbounded in
 size.  Message headers included in subsequent notifications MUST only
 correspond to messages added since the previous notification for that
 subscription.  A messaging system which includes message headers in a
 NOTIFY MUST provide an administrator configurable mechanism to select
 which headers are sent.  Headers likely for inclusion are To, From,
 Date, Subject, and Message-ID.  Note that the formatting of these
 headers in this body is identical to that of SIP extension-headers,
 not the (similar) format defined in RFC 2822.
 Implementations which generate large notifications are reminded to
 follow the message size restrictions for unreliable transports
 articulated in Section 18.1.1 of SIP [1].
 Mapping local message state to new/old message status and urgency is
 an implementation issue of the messaging system.  However, the

Mahy Standards Track [Page 5] RFC 3842 SIP Message Waiting August 2004

 messaging notifier MUST NOT consider a message "old" merely because
 it generated a notification, as this could prevent another
 subscription from accurately receiving message-summary notifications.
 Likewise, the messaging system MAY use any suitable algorithm to
 determine that a message is "urgent".
 Messaging systems MAY use any algorithm for determining the
 appropriate message-context-class for a specific message.  Systems
 which use Internet Mail SHOULD use the contents of the Message-
 Context header [7] (defined in RFC 3458) if present as a hint to make
 a context determination.  Note that a composed messaging system does
 not need to support a given context in order to generate
 notifications identified with that context.

3.6. Subscriber Generation of SUBSCRIBE Requests

 Subscriber User Agents will typically SUBSCRIBE to message summary
 information for a period of hours or days, and automatically attempt
 to re-SUBSCRIBE well before the subscription is completely expired.
 If re-subscription fails, the Subscriber SHOULD periodically retry
 again until a subscription is successful, taking care to backoff to
 avoid network congestion.  If a subscription has expired, new re-
 subscriptions MUST use a new Call-ID.
 The Subscriber SHOULD SUBSCRIBE to that user's message summaries
 whenever a new user becomes associated with the device (a new login).
 The Subscriber MAY also explicitly fetch the current status at any
 time.  The subscriber SHOULD renew its subscription immediately after
 a reboot, or when the subscriber's network connectivity has just been
 re-established.
 The Subscriber MUST be prepared to receive and process a NOTIFY with
 new state immediately after sending a new SUBSCRIBE, a SUBSCRIBE
 renewal, an unsubscribe, a fetch, or at any other time during the
 subscription.
 When a user de-registers from a device (logoff, power down of a
 mobile device, etc.), subscribers SHOULD unsubscribe by sending a
 SUBSCRIBE message with an Expires header of zero.

3.7. Notifier Processing of SUBSCRIBE Requests

 When a SIP Messaging System receives SUBSCRIBE messages with the
 message-summary event-type, it SHOULD authenticate the subscription
 request.  If authentication is successful, the Notifier MAY limit the
 duration of the subscription to an administrator defined amount of
 time as described in SIP Events [2].

Mahy Standards Track [Page 6] RFC 3842 SIP Message Waiting August 2004

3.8. Notifier Generation of NOTIFY Requests

 Immediately after a subscription is accepted, the Notifier MUST send
 a NOTIFY with the current message summary information.  This allows
 the Subscriber to resynchronize its state.  This initial
 synchronization NOTIFY MUST NOT include the optional RFC 2822 style
 message headers [8].
 When the status of the messages changes sufficiently for a messaging
 account to change the number of new or old messages, the Notifier
 SHOULD send a NOTIFY message to all active subscribers of that
 account.  NOTIFY messages sent to subscribers of a group or alias,
 MUST contain the message account name in the notification body.
 A Messaging System MAY send a NOTIFY with an "Expires" header of "0"
 and a "Subscription-State" header of "terminated" before a graceful
 shutdown.

3.9. Subscriber Processing of NOTIFY Requests

 Upon receipt of a valid NOTIFY request, the subscriber SHOULD
 immediately render the message status and summary information to the
 end user in an implementation specific way.
 The Subscriber MUST be prepared to receive NOTIFYs from different
 Contacts corresponding to the same SUBSCRIBE.  (The SUBSCRIBE may
 have been forked).

3.10. Handling of Forked Requests

 Forked requests are allowed for this event type and may install
 multiple subscriptions.  The Subscriber MAY render multiple summaries
 corresponding to the same account directly to the user, or MAY merge
 them as described below.
 If any of the "Messages-Waiting" status lines report "yes", then the
 merged state is "yes"; otherwise the merged state is "no".
 The Subscriber MAY merge summary lines in an implementation-specific
 way if all notifications contain at least one msg-summary line.

3.11. Rate of Notifications

 A Notifier MAY choose to hold NOTIFY requests in "quarantine" for a
 short administrator-defined period (seconds or minutes) when the
 message status is changing rapidly.  Requests in the quarantine which
 become invalid are replaced by newer notifications, thus reducing the
 total volume of notifications.  This behavior is encouraged for

Mahy Standards Track [Page 7] RFC 3842 SIP Message Waiting August 2004

 implementations with heavy interactive use.  Note that timely
 notification resulting in a change of overall state (messages waiting
 or not) and notification of newly added messages is probably more
 significant to the end user than a notification of newly deleted
 messages which do not affect the overall message waiting state (e.g.,
 there are still new messages).
 Notifiers SHOULD NOT generate NOTIFY requests more frequently than
 once per second.

3.12. State Agents and Lists

 A Subscriber MAY use an "alias" or "group" in the Request-URI of a
 subscription if that name is significant to the messaging system.
 Implementers MAY create a service which consolidates and summarizes
 NOTIFYs from many Contacts.  This document does not preclude
 implementations from building state agents which support this event
 package.  One way to implement such a service is with the event list
 extension [10].

3.13. Behavior of a Proxy Server

 There are no additional requirements on a SIP Proxy, other than to
 transparently forward the SUBSCRIBE and NOTIFY methods as required in
 SIP.  However, Proxies SHOULD allow non-SIP URLs.  Proxies and
 Redirect servers SHOULD be able to direct the SUBSCRIBE request to an
 appropriate messaging notifier User Agent.

4. Examples of Usage

4.1. Example Message Flow

 The examples shown below are for informational purposes only.  For a
 normative description of the event package, please see sections 3 and
 5 of this document.
 In the example call flow below, Alice's IP phone subscribes to the
 status of Alice's messages.  Via headers are omitted for clarity.

Mahy Standards Track [Page 8] RFC 3842 SIP Message Waiting August 2004

    Subscriber              Notifier
        |                       |
        |  A1: SUBSCRIBE (new)  |
        |---------------------->|
        |  A2: 200 OK           |
        |<----------------------|
        |                       |
        |  A3: NOTIFY (sync)    |
        |<----------------------|
        |  A4: 200 OK           |
        |---------------------->|
        |                       |
        |                       |
        |  A5: NOTIFY (change)  |
        |<----------------------|
        |  A6: 200 OK           |
        |---------------------->|
        |                       |
        |                       |
        |  A7: (re)SUBSCRIBE    |
        |---------------------->|
        |  A8: 200 OK           |
        |<----------------------|
        |                       |
        |  A9: NOTIFY (sync)    |
        |<----------------------|
        |  A10: 200 OK          |
        |---------------------->|
        |                       |
        |                       |
        |  A11: (un)SUBSCRIBE   |
        |---------------------->|
        |  A12: 200 OK          |
        |<----------------------|
        |                       |
        |  A13: NOTIFY (sync)   |
        |<----------------------|
        |  A14: 200 OK          |
        |---------------------->|
    A1: Subscriber (Alice's phone) ->
        Notifier (Alice's voicemail gateway)
        Subscribe to Alice's message summary status for 1 day.
    SUBSCRIBE sip:alice@vmail.example.com SIP/2.0
    To: <sip:alice@example.com>
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 03:55:06 GMT

Mahy Standards Track [Page 9] RFC 3842 SIP Message Waiting August 2004

    Call-Id: 1349882@alice-phone.example.com
    CSeq: 4 SUBSCRIBE
    Contact: <sip:alice@alice-phone.example.com>
    Event: message-summary
    Expires: 86400
    Accept: application/simple-message-summary
    Content-Length: 0
        A2: Notifier -> Subscriber
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=4442
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 03:55:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 4 SUBSCRIBE
    Expires: 86400
    Content-Length: 0
        A3: Notifier -> Subscriber
        (immediate synchronization of current state:
         2 new and 8 old [2 urgent] messages)
    NOTIFY sip:alice@alice-phone.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 03:55:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 20 NOTIFY
    Contact: <sip:alice@vmail.example.com>
    Event: message-summary
    Subscription-State: active
    Content-Type: application/simple-message-summary
    Content-Length: 99
    Messages-Waiting: yes
    Message-Account: sip:alice@vmail.example.com
    Voice-Message: 2/8 (0/2)
        A4: Subscriber -> Notifier
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 03:55:08 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 20 NOTIFY
    Content-Length: 0

Mahy Standards Track [Page 10] RFC 3842 SIP Message Waiting August 2004

        A5: Notifier -> Subscriber
        This is a notification of new messages.
        Some headers from each of the new messages are appended.
    NOTIFY sip:alice@alice-phone.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 04:28:53 GMT
    Contact: <sip:alice@vmail.example.com>
    Call-ID: 1349882@alice-phone.example.com
    CSeq: 31 NOTIFY
    Event: message-summary
    Subscription-State: active
    Content-Type: application/simple-message-summary
    Content-Length: 503
    Messages-Waiting: yes
    Message-Account: sip:alice@vmail.example.com
    Voice-Message: 4/8 (1/2)
    To: <alice@atlanta.example.com>
    From: <bob@biloxi.example.com>
    Subject: carpool tomorrow?
    Date: Sun, 09 Jul 2000 21:23:01 -0700
    Priority: normal
    Message-ID: 13784434989@vmail.example.com
    To: <alice@example.com>
    From: <cathy-the-bob@example.com>
    Subject: HELP! at home ill, present for me please
    Date: Sun, 09 Jul 2000 21:25:12 -0700
    Priority: urgent
    Message-ID: 13684434990@vmail.example.com
        A6: Subscriber -> Notifier
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 04:28:53 GMT
    Call-ID: 1349882@alice-phone.example.com
    CSeq: 31 NOTIFY
    Content-Length: 0
        A7: Subscriber  ->  Notifier
        Refresh subscription.

Mahy Standards Track [Page 11] RFC 3842 SIP Message Waiting August 2004

    SUBSCRIBE sip:alice@vmail.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=4442
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 15:55:06 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 8 SUBSCRIBE
    Contact: <sip:alice@alice-phone.example.com>
    Event: message-summary
    Expires: 86400
    Accept: application/simple-message-summary
    Content-Length: 0
        A8: Notifier -> Subscriber
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=4442
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 15:55:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 8 SUBSCRIBE
    Contact: <sip:alice@alice-phone.example.com>
    Expires: 86400
    Content-Length: 0
        A9: Notifier -> Subscriber
        (immediate synchronization of current state)
    NOTIFY sip:alice@alice-phone.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 15:55:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 47 NOTIFY
    Contact: <sip:alice@vmail.example.com>
    Event: message-summary
    Subscription-State: active
    Content-Type: application/simple-message-summary
    Content-Length: 99
    Messages-Waiting: yes
    Message-Account: sip:alice@vmail.example.com
    Voice-Message: 4/8 (1/2)
        A10: Subscriber -> Notifier
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442

Mahy Standards Track [Page 12] RFC 3842 SIP Message Waiting August 2004

    Date: Mon, 10 Jul 2000 15:55:08 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 47 NOTIFY
    Contact: <sip:alice@vmail.example.com>
        A11: Subscriber  ->  Notifier
        Un-subscribe after "alice" logs out.
    SUBSCRIBE sip:alice@vmail.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=4442
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 19:35:06 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 17 SUBSCRIBE
    Contact: <sip:alice@alice-phone.example.com>
    Event: message-summary
    Expires: 0
    Accept: application/simple-message-summary
    Content-Length: 0
        A12: Notifier -> Subscriber
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=4442
    From: <sip:alice@example.com>;tag=78923
    Date: Mon, 10 Jul 2000 19:35:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 17 SUBSCRIBE
    Contact: <sip:alice@alice-phone.example.com>
    Expires: 0
    Content-Length: 0
        A13: Notifier -> Subscriber
       (immediate synchronization of current state,
        which the subscriber can now ignore)
    NOTIFY sip:alice@alice-phone.example.com SIP/2.0
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 19:35:07 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 56 NOTIFY
    Contact: <sip:alice@vmail.example.com>
    Event: message-summary
    Subscription-State: terminated;reason=timeout
    Content-Type: application/simple-message-summary
    Content-Length: 99

Mahy Standards Track [Page 13] RFC 3842 SIP Message Waiting August 2004

    Messages-Waiting: yes
    Message-Account: sip:alice@vmail.example.com
    Voice-Message: 4/8 (1/2)
        A14: Subscriber -> Notifier
    SIP/2.0 200 OK
    To: <sip:alice@example.com>;tag=78923
    From: <sip:alice@example.com>;tag=4442
    Date: Mon, 10 Jul 2000 19:35:08 GMT
    Call-Id: 1349882@alice-phone.example.com
    CSeq: 56 NOTIFY
    Event: message-summary
    Content-Length: 0

4.2. Example Usage with Callee Capabilities and Caller Preferences

 The use of callee capabilities is optional but encouraged.  If callee
 capabilities are used, a messaging notifier MAY REGISTER a Contact
 with an appropriate methods and events tag as shown in the example
 below.  To further distinguish itself, the messaging notifier MAY
 also REGISTER as a Contact with the actor="msg-taker" tag.  An
 example of this kind of registration follows below.
     REGISTER sip:sip3-sj.example.com SIP/2.0
     To: <sip:alice@example.com>
     From: <sip:alice@example.com>;tag=4442
     ...
     Contact: <sip:alice@vm13-sj.example.com>
      ;actor="msg-taker";methods="SUBSCRIBE"
      ;automata;events="message-summary"
 The following SUBSCRIBE message would find the Contact which
 registered in the example above.
     SUBSCRIBE sip:alice@example.com SIP/2.0
     ...
     Accept: application/simple-message-summary
     Event: message-summary
     Accept-Contact: *;automata;actor="msg-taker"

5. Formal Syntax

 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) as described in RFC 2234 [6].

Mahy Standards Track [Page 14] RFC 3842 SIP Message Waiting August 2004

5.1. New Event-Package Definition

 This document defines a new event-package with the package name:
    message-summary

5.2. Body Format Syntax

 The formal syntax for the application/simple-message-summary MIME
 type is described below.  The message-context-class production is
 defined in Section 6.2 of RFC 3458 [7].  Note that all productions
 described here are case insensitive.
 message-summary = msg-status-line CRLF
                    [msg-account CRLF]
                    [*(msg-summary-line CRLF)]
                    [ *opt-msg-headers ]
 msg-status-line  = "Messages-Waiting" HCOLON msg-status
 msg-status = "yes" / "no"
 msg-account = "Message-Account" HCOLON Account-URI
 Account-URI = SIP-URI / SIPS-URI / absoluteURI
 msg-summary-line = message-context-class HCOLON newmsgs SLASH oldmsgs
                 [ LPAREN new-urgentmsgs SLASH old-urgentmsgs RPAREN ]
 opt-msg-headers = CRLF 1*(extension-header CRLF)
 newmsgs = msgcount
 oldmsgs = msgcount
 new-urgentmsgs = msgcount
 old-urgentmsgs  = msgcount
 msgcount = 1*DIGIT   ; MUST NOT exceed 2^32-1

6. Security Considerations

 Message summaries and optional message bodies contain information
 which is typically very privacy sensitive.  At a minimum,
 subscriptions to this event package SHOULD be authenticated and
 properly authorized.  Furthermore, notifications SHOULD be encrypted
 and integrity protected using either end-to-end mechanisms, or the
 hop-by-hop protection afforded messages sent to SIPS URIs.
 Additional and privacy security considerations are discussed in
 detail in SIP [1] and SIP Events [2].

Mahy Standards Track [Page 15] RFC 3842 SIP Message Waiting August 2004

7. IANA Considerations

7.1. SIP Event Package Registration for message-summary

 Package name: message-summary
 Type: package
 Contact: [Mahy]
 Published Specification: This document.

7.2. MIME Registration for application/simple-message-summary

 MIME media type name: application
 MIME subtype name: simple-message-summary
 Required parameters: none.
 Optional parameters: none.
 Encoding considerations:   This MIME type was designed for
   use with protocols which can carry binary-encoded data.
   Although the format of this MIME type is similar to RFC 2822,
   it is not identical.  (Specifically, line folding rules are
   SIP-specific and included URIs can contain non-ASCII
   characters.)  Protocols which do not carry binary data
   (which have line length or character-set restrictions
   for example) MUST use a reversible transfer encoding
   (such as base64) to carry this MIME type.
 Security considerations: See the "Security Considerations"
   section in this document.
 Interoperability considerations: none
 Published specification: This document.
 Applications which use this media: The simple-message-summary
 application subtype supports the exchange of message waiting and
 message summary information in SIP networks.

Mahy Standards Track [Page 16] RFC 3842 SIP Message Waiting August 2004

       Additional information:
            1. Magic number(s): N/A
            2. File extension(s): N/A
            3. Macintosh file type code: N/A

8. Contributors

 Ilya Slain came up with the initial format of the text body contained
 in this document.  He was previously listed as a co-author, however,
 he is no longer reachable.

9. Acknowledgments

 Thanks to Dan Wing, Dave Oran, Bill Foster, Steve Levy, Denise
 Caballero-McCann, Jeff Michel, Priti Patil, Satyender Khatter, Bich
 Nguyen, Manoj Bhatia, David Williams, and Bryan Byerly of Cisco,
 Jonathan Rosenberg and Adam Roach of Dynamicsoft, Eric Burger of
 Snowshore, Nir Chen of Comverse, and Eric Tremblay of Mediatrix.

10. References

10.1. Normative References

 [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
      Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
      Session Initiation Protocol", RFC 3261, June 2002.
 [2]  Roach, A.B., "Session Initiation Protocol (SIP)-Specific Event
      Notification", RFC 3265, June 2002.
 [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [4]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
      Preferences for the Session Initiation Protocol (SIP)", RFC
      3841, August 2004.
 [5]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User
      Agent Capabilities in the Session Initiation Protocol (SIP)",
      RFC 3840, August 2004.
 [6]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, November 1997.

Mahy Standards Track [Page 17] RFC 3842 SIP Message Waiting August 2004

 [7]  Burger, E., Candell, E., Eliot, C., and G. Klyne, "Message
      Context for Internet Mail", RFC 3458, January 2003.

10.2. Informational References

 [8]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
      Extensions (MIME) Part Two: Media Types", RFC 2046, November
      1996.
 [9] Resnick, P., Ed., "Internet Message Format", RFC 2822, April
      2001.
 [10] Rosenberg, J., Roach, A.B., and B. Campbell, "A Session
      Initiation Protocol (SIP) Event Notification Extension for
      Resource Lists", Work in Progress, June 2003.
 [11] Telcordia, "GR-506: Signaling for Analog Interfaces, Issue 1,
      Revision 1", Nov 1996.

11. Author's Address

 Rohan Mahy
 Cisco Systems, Inc.
 5617 Scotts Valley Drive, Suite 200
 Scotts Valley, CA 95066
 USA
 EMail: rohan@cisco.com

Mahy Standards Track [Page 18] RFC 3842 SIP Message Waiting August 2004

12. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  This document is subject
 to the rights, licenses and restrictions contained in BCP 78, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 pertain to the implementation or use of the technology described in
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 might or might not be available; nor does it represent that it has
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 Copies of IPR disclosures made to the IETF Secretariat and any
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 The IETF invites any interested party to bring to its attention any
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Mahy Standards Track [Page 19]

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