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rfc:rfc3859

Network Working Group J. Peterson Request for Comments: 3859 NeuStar Category: Standards Track August 2004

                 Common Profile for Presence (CPP)

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

 At the time this document was written, numerous presence protocols
 were in use (largely as components of commercial instant messaging
 services), and little interoperability between services based on
 these protocols has been achieved.  This specification defines common
 semantics and data formats for presence to facilitate the creation of
 gateways between presence services.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
 3.  Abstract Presence Service  . . . . . . . . . . . . . . . . . .  4
     3.1.  Overview of the Presence Service . . . . . . . . . . . .  4
     3.2.  Identification of PRESENTITIES and WATCHERS  . . . . . .  6
           3.2.1.  Address Resolution . . . . . . . . . . . . . . .  6
     3.3.  Format of Presence Information . . . . . . . . . . . . .  6
     3.4.  The Presence Service . . . . . . . . . . . . . . . . . .  7
           3.4.1.  The Subscribe Operation  . . . . . . . . . . . .  7
           3.4.2.  The Notify Operation . . . . . . . . . . . . . .  8
           3.4.3.  Subscribe Operation (with Zero Duration) . . . .  8
 4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
 5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  The PRES URI Scheme  . . . . . . . . . . . . . . . . . .  9
 6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
 7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . 11

Peterson Standards Track [Page 1] RFC 3859 Common Profile for Presence August 2004

 A.  PRES URI IANA Registration Template  . . . . . . . . . . . . . 12
     A.1.  URI Scheme Name  . . . . . . . . . . . . . . . . . . . . 12
     A.2.  URI Scheme Syntax  . . . . . . . . . . . . . . . . . . . 12
     A.3.  Character Encoding Considerations  . . . . . . . . . . . 12
     A.4.  Intended Usage . . . . . . . . . . . . . . . . . . . . . 12
     A.5.  Applications and/or Protocols which use this URI Scheme
           Name . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     A.6.  Interoperability Considerations  . . . . . . . . . . . . 13
     A.7.  Security Considerations  . . . . . . . . . . . . . . . . 13
     A.8.  Relevant Publications  . . . . . . . . . . . . . . . . . 13
     A.9.  Person & Email Address to Contact for Further
           Information. . . . . . . . . . . . . . . . . . . . . . . 13
     A.10. Author/Change Controller . . . . . . . . . . . . . . . . 13
     A.11. Applications and/or Protocols which use this URI Scheme
           Name . . . . . . . . . . . . . . . . . . . . . . . . . . 13
 B.  Issues of Interest . . . . . . . . . . . . . . . . . . . . . . 13
     B.1.  Address Mapping  . . . . . . . . . . . . . . . . . . . . 13
     B.2.  Source-Route Mapping . . . . . . . . . . . . . . . . . . 13
 C.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 15

1. Introduction

 Presence is defined in RFC2778 [5].  At the time this document was
 written, numerous presence protocols are in use (largely as
 components of commercial instant messaging services), and little
 interoperability between services based on these protocols has been
 achieved.  This specification defines semantics and data formats for
 common services of presence to facilitate the creation of gateways
 between presence services: a common profile for presence (CPP).
 Service behavior is described abstractly in terms of operations
 invoked between the consumer and provider of a service.  Accordingly,
 each presence service must specify how this behavior is mapped onto
 its own protocol interactions.  The choice of strategy is a local
 matter, providing that there is a clear relation between the abstract
 behaviors of the service (as specified in this memo) and how it is
 faithfully realized by a particular presence service.   For example,
 one strategy might transmit presence information as key/value pairs,
 another might use a compact binary representation, and a third might
 use nested containers.
 The parameters for each operation are defined using an abstract
 syntax.  Although the syntax specifies the range of possible data
 values, each presence service must specify how well-formed instances
 of the abstract representation are encoded as a concrete series of
 bits.

Peterson Standards Track [Page 2] RFC 3859 Common Profile for Presence August 2004

 In order to provide a means for the preservation of end-to-end
 features (especially security) to pass through presence
 interoperability gateways, this specification also provides
 recommendations for presence document formats that could be employed
 by presence protocols.

2. Terminology

 In this document, the key words "MUST", "MUST NOT", "REQUIRED",
 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
 described in BCP 14, RFC 2119 [1] and indicate requirement levels for
 compliant implementations.
 This memos makes use of the vocabulary defined in RFC 2778 [5].
 Terms such as CLOSED, INSTANT INBOX, PRESENCE, and OPEN are used in
 the same meaning as defined therein.
 The term 'gateway' used in this document denotes a network element
 responsible for interworking between diverse presence protocols.
 Although the presence protocols themselves are diverse, under the
 model in this document these protocols can carry a common payload
 that is relayed by the gateway.  Whether these interworking
 intermediaries should be called 'gateways' or 'relays' is therefore
 somewhat debatable; for the purposes of this document, they are
 called 'CPP gateways'.
 The term 'presence service' also derives from RFC 2778, but its
 meaning changes slightly due to the existence of gateways in the CPP
 model.  When a client sends an operation to a presence service, that
 service might either be an endpoint or an intermediary such as a CPP
 gateway - in fact, the client should not have to be aware which it is
 addressing, as responses from either will appear the same.
 This document defines operations and attributes of an abstract
 presence protocol.  In order for a compliant protocol to interface
 with a presence gateway, it must support all of the operations
 described in this document (i.e., the presence protocol must have
 some message or capability that provides the function described by
 all given operations).  Similarly, the attributes defined for these
 operations must correspond to information available in the presence
 protocol in order for the protocol to interface with gateways defined
 by this specification.  Note that these attributes provide only the
 minimum possible information that needs to be specified for
 interoperability - the functions in a presence protocol that
 correspond to the operations described in this document can contain
 additional information that will not be mapped by CPP.

Peterson Standards Track [Page 3] RFC 3859 Common Profile for Presence August 2004

3. Abstract Presence Service

3.1. Overview of the Presence Service

 When an application wants to subscriber to the presence information
 associated with a PRESENTITY (in order to receive periodic
 notifications of presence information), it invokes the subscribe
 operation, e.g.,
           +-------+                    +-------+
           |       |                    |       |
           | appl. | -- subscribe ----> | pres. |
           |       |                    | svc.  |
           +-------+                    +-------+
 The subscribe operation has the following attributes: watcher,
 target, duration, SubscriptID and TransID.  The 'watcher' and
 'target' identify the WATCHER and PRESENTITY, respectively, using the
 identifiers described in Section 3.2.  The duration specifies the
 maximum number of seconds that the SUBSCRIPTION should be active
 (which may be zero, in which case this is a one-time request for
 presence information).  The SubscriptID creates a reference to the
 SUBSCRIPTION that is used when unsubscribing.  The TransID is a
 unique identifier used to correlate the subscribe operation with a
 response operation.  Gateways should be capable of handling TransIDs
 and SubscriptIDs up to 40 bytes in length.
 Upon receiving a subscribe operation, the service immediately
 responds by invoking the response operation containing the same
 TransID, e.g.,
           +-------+                    +-------+
           |       |                    |       |
           | appl. | <----- response -- | pres. |
           |       |                    | svc.  |
           +-------+                    +-------+
 The response operation has the following attributes: status, TransID,
 and duration.  'status' indicates whether the subscribe operation has
 succeeded or failed.  The TransID of the response operation
 corresponds to the TransID of the subscription operation to which it
 is responding.  The 'duration' attribute specifies the number of
 seconds for which the subscription will be active (which may differ
 from the value requested in the subscribe operation).

Peterson Standards Track [Page 4] RFC 3859 Common Profile for Presence August 2004

 If the response operation indicates success, the service immediately
 invokes the notify operation to communicate the presence information
 to the WATCHER, e.g.,
           +-------+                    +-------+
           |       |                    |       |
           | appl. | <------- notify -- | pres. |
           |       |                    | svc.  |
           +-------+                    +-------+
 The notify operation has the following attributes: watcher, target,
 and TransID.  The values of 'watcher' and 'target' are identical to
 those given in the subscribe operation that triggered this notify
 operation.  The TransID is a unique identifier for this notification.
 The notify operation also has content, namely PRESENCE INFORMATION.
 Content details are specified in Section 3.3.
 If the duration parameter is non-zero, then for up to the specified
 duration, the service invokes the notify operation whenever there are
 any changes to the PRESENTITY's presence information.  Otherwise,
 exactly one notify operation is invoked, achieving a one-time poll of
 the presence information.  Regardless, there is no application
 response to the notify operation (i.e., the application does not
 invoke a response operation when a notify operation occurs) defined
 in CPP.
 The application may prematurely cancel a subscription by re-invoking
 the subscribe operation (as described above) with a duration of 0 and
 the same SubscriptID as the original subscribe operation , e.g.,
           +-------+                    +-------+
           |       |                    |       |
           | appl. | -- subscribe 0 --> | pres. |
           |       |                    | svc.  |
           +-------+                    +-------+
 Note that a notify operation will be invoked when a subscription is
 prematurely canceled in this fashion; this notification may be
 discarded by the watcher.

Peterson Standards Track [Page 5] RFC 3859 Common Profile for Presence August 2004

 The service immediately responds by invoking the response operation
 containing the same TransID; e.g.,
           +-------+                    +-------+
           |       |                    |       |
           | appl. | <----- response -- | pres. |
           |       |                    | svc.  |
           +-------+                    +-------+
 Note that this specification assumes that CPP-compliant presence
 protocols provide reliable message delivery; there are no
 application-layer message delivery assurance provisions in this
 specification.

3.2. Identification of PRESENTITIES and WATCHERS

 A PRESENTITY is specified using the PRES URI scheme, which is further
 described in Appendix A.  An example would be:
 "pres:fred@example.com"
 WATCHERs identify themselves in the same manner as PRESENTITIES; that
 is, with a pres URI.

3.2.1. Address Resolution

 A presence service client determines the next hop to forward an
 operation to by resolving the domain name portion of the service
 destination.  Compliant implementations SHOULD follow the guidelines
 for dereferencing URIs given in [2].

3.3. Format of Presence Information

 This specification defines an abstract interoperability mechanism for
 presence protocols; the message content definition given here
 pertains to semantics rather than syntax.  However, some important
 properties for interoperability can only be provided if a common
 end-to-end format for presence is employed by the interoperating
 presence protocols, especially with respect to security.  In order to
 maintain end-to-end security properties, applications that send
 notification operations through a CPP gateway MUST support the format
 defined in PIDF [4].  Applications MAY support other content formats.
 CPP gateways MUST be capable of relaying the body of a notification
 operation between supported presence protocols without needing to
 modify or inspect the content.

Peterson Standards Track [Page 6] RFC 3859 Common Profile for Presence August 2004

3.4. The Presence Service

 An implementation of the service must maintain information about both
 presence information and continual operations (like periodic
 notification) in persistent storage.
 Note that the subscription-identifier attribute used by the subscribe
 operation is potentially long-lived.  Accordingly, the values
 generated for this parameter should be unique across a significant
 duration of time.  The SubscriptID parameter should be intrinsically
 globally unique over time, not merely unique among operations sent to
 or from a particular WATCHER and PRESENTITY.

3.4.1. The Subscribe Operation

 When an application wants to subscribe to the presence information
 associated with a PRESENTITY, it invokes the subscribe operation.
 When the service is informed of the subscribe operation, it performs
 these steps:
 1.  If the watcher or target parameter does not refer to a valid
     PRESENTITY, a response operation having status "failure" is
     invoked.
 2.  If access control does not permit the application to request this
     operation, a response operation having status "failure" is
     invoked.
 3.  If the duration parameter is non-zero, and if the watcher and
     target parameters refer to an in-progress subscribe operation for
     the application, a response operation having status "failure" is
     invoked.
 4.  Otherwise, if the service is able to successfully deliver the
     message:
       A response operation having status "success" is immediately
       invoked.  (If the service chooses a different duration for the
       subscription then it conveys this information in the response
       operation.)
       A notify operation, corresponding to the target's presence
       information, is immediately invoked for the watcher.

Peterson Standards Track [Page 7] RFC 3859 Common Profile for Presence August 2004

       For up to the amount of time indicated by the duration
       parameter of the notify operation (measured from the time that
       the subscribe operation was received), if the target's presence
       information changes, and if access control allows, a notify
       operation is invoked for the watcher.
 Note that if the duration parameter is zero-valued, then the
 subscribe operation is making a one-time poll of the presence
 information.  Accordingly, the final step above (continued
 notifications for the duration of the subscription) does not occur.
 When the service invokes a response operation as a result of this
 processing, the transID parameter is identical to the value found in
 the subscribe operation invoked by the application.

3.4.2. The Notify Operation

 The service invokes the notify operation whenever the presence
 information associated with a PRESENTITY changes and there are
 subscribers requesting notifications for that PRESENTITY.
 There is no application response to the notify operation.

3.4.3. Subscribe Operation (with Zero Duration)

 When an application wants to terminate a subscription, it issues a
 SUBSCRIBE 0 with the SubscriptID of an existing subscription.  Note
 that a notify operation will be invoked by the presentity when a
 subscription is canceled in this fashion; this notification can be
 discarded by the watcher.  There is no independent UNSUBSCRIBE
 operation.
 When an application wants to directly request presence information to
 be supplied immediately without initiating any persistent
 subscription, it issues a SUBSCRIBE 0 with a new SubscriptID.  There
 is no independent FETCH operation.

4. Security Considerations

 Detailed security considerations for presence protocols given in RFC
 2779 [6] (in particular, requirements are given in sections 5.1
 through 5.3 with some motivating discussion in 8.2).
 CPP defines an interoperability function that is employed by gateways
 between presence protocols.  CPP gateways MUST be compliant with the
 minimum security requirements of the presence protocols with which
 they interface.

Peterson Standards Track [Page 8] RFC 3859 Common Profile for Presence August 2004

 The introduction of gateways to the security model of presence in RFC
 2779 also introduces some new risks.  End-to-end security properties
 (especially confidentiality and integrity) between presentities and
 watchers that interface through a CPP gateway can only be provided if
 a common presence format (such as the format described in [4]) is
 supported by the protocols interfacing with the CPP gateway.
 When end-to-end security is required, the notify operation MUST use
 PIDF, and MUST secure the PIDF MIME body with S/MIME [8], with
 encryption (CMS EnvelopeData) and/or S/MIME signatures (CMS
 SignedData).
 The S/MIME algorithms are set by CMS [9].  The AES [11] algorithm
 should be preferred, as it is expected that AES best suits the
 capabilities of many platforms.  Implementations MAY use AES as an
 encryption algorithm, but are REQUIRED to support only the baseline
 algorithms mandated by S/MIME and CMS.
 When PRES URIs are used in presence protocols, they convey the
 identity of watchers and/or presentities.  Certificates that are used
 for S/MIME presence operations SHOULD, for the purposes of reference
 integrity, contain a subjectAltName field containing the PRES URI of
 their subject.  Note that such certificates may also contain other
 identifiers, including those specific to particular presence
 protocols.  In order to further facilitate interoperability of secure
 presence services through CPP gateways, users and service providers
 are encouraged to employ trust anchors for certificates that are
 widely accepted rather than trust anchors specific to any particular
 presence service or provider.
 In some cases, anonymous presence services may be desired.  Such a
 capability is beyond the scope of this specification.

5. IANA Considerations

 The IANA has assigned the "pres" URI scheme.

5.1. The PRES URI Scheme

 The Presence (PRES) URI scheme designates an Internet resource,
 namely a PRESENTITY or WATCHER.
 The syntax of a PRES URI is given in Appendix A.

Peterson Standards Track [Page 9] RFC 3859 Common Profile for Presence August 2004

6. Contributors

 Dave Crocker edited earlier versions of this document.
 The following individuals made substantial textual contributions to
 this document:
    Athanassios Diacakis (thanos.diacakis@openwave.com)
    Florencio Mazzoldi (flo@networkprojects.com)
    Christian Huitema (huitema@microsoft.com)
    Graham Klyne (gk@ninebynine.org)
    Jonathan Rosenberg (jdrosen@dynamicsoft.com)
    Robert Sparks (rsparks@dynamicsoft.com)
    Hiroyasu Sugano (suga@flab.fujitsu.co.jp)

7. References

7.1. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to indicate requirement
      levels", BCP 14, RFC 2119, March 1997.
 [2]  Peterson, J., "Address Resolution for Instant Messaging and
      Presence", RFC 3861, August 2004.
 [3]  Resnick, P., "Internet Message Format", STD 11, RFC 2822, April
      2001.
 [4]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
      J. Peterson, "Presence Information Data Format (PIDF)", RFC
      3863, August 2004.
 [5]  Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and
      Instant Messaging", RFC 2778, February 2000.
 [6]  Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging /
      Presence Protocol Requirements", RFC 2779, February 2000.
 [7]  Allocchio, C., "GSTN Address Element Extensions in Email
      Services", RFC 2846, June 2000.

Peterson Standards Track [Page 10] RFC 3859 Common Profile for Presence August 2004

 [8]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
      (S/MIME) Version 3.1 Message Specification", RFC 3851, July
      2004.
 [9]  Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852,
      July 2004.
 [10] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
      Resource Identifiers (URI): Generic Syntax", RFC 2396, August
      1998.

7.2. Informative References

 [11] Schaad, J., "Use of the Advanced Encryption Standard (AES)
      Encryption Algorithm and in Cryptographic Message Syntax (CMS)",
      RFC 3565, July 2003.

Peterson Standards Track [Page 11] RFC 3859 Common Profile for Presence August 2004

Appendix A. PRES URI IANA Registration Template

 This section provides the information to register the pres: presence
 URI .

A.1. URI Scheme Name

 pres

A.2. URI Scheme Syntax

 The syntax follows the existing mailto: URI syntax specified in RFC
 2368.  The ABNF is:
 PRES-URI         = "pres:" [ to ] [ headers ]
 to             =  mailbox
 headers        =  "?" header *( "&" header )
 header         =  hname "=" hvalue
 hname          =  *uric
 hvalue         =  *uric
 Here the symbol "mailbox" represents an encoded mailbox name as
 defined in RFC 2822 [3], and the symbol "uric" denotes any character
 that is valid in a URL (defined in RFC 2396 [10]).

A.3. Character Encoding Considerations

 Representation of non-ASCII character sets in local-part strings is
 limited to the standard methods provided as extensions to RFC 2822
 [3].

A.4. Intended Usage

 Use of the pres: URI follows closely usage of the mailto: URI.  That
 is, invocation of an PRES URI will cause the user's instant messaging
 application to start, with destination address and message headers
 fill-in according to the information supplied in the URI.

A.5. Applications and/or Protocols which use this URI Scheme Name

 It is anticipated that protocols compliant with RFC 2779, and meeting
 the interoperability requirements specified here, will make use of
 this URI scheme name.

Peterson Standards Track [Page 12] RFC 3859 Common Profile for Presence August 2004

A.6. Interoperability Considerations

 The underlying exchange protocol used to send an instant message may
 vary from service to service.  Therefore complete, Internet-scale
 interoperability cannot be guaranteed.  However, a service conforming
 to this specification permits gateways to achieve interoperability
 sufficient to the requirements of RFC 2779.

A.7. Security Considerations

 See Section 4.

A.8. Relevant Publications

 RFC 2779, RFC 2778

A.9. Person & Email Address to Contact for Further Information

 Jon Peterson [mailto:jon.peterson@neustar.biz]

A.10. Author/Change Controller

 This scheme is registered under the IETF tree.  As such, IETF
 maintains change control.

A.11. Applications and/or Protocols which use this URI Scheme Name

 Instant messaging service; presence service

Appendix B. Issues of Interest

 This appendix briefly discusses issues that may be of interest when
 designing an interoperation gateway.

B.1. Address Mapping

 When mapping the service described in this memo, mappings that place
 special information into the im: address local-part MUST use the
 meta-syntax defined in RFC2846 [7].

B.2. Source-Route Mapping

 The easiest mapping technique is a form of source-routing and usually
 is the least friendly to humans having to type the string.  Source-
 routing also has a history of operational problems.

Peterson Standards Track [Page 13] RFC 3859 Common Profile for Presence August 2004

 Use of source-routing for exchanges between different services is by
 a transformation that places the entire, original address string into
 the im: address local part and names the gateway in the domain part.
 For example, if the destination INSTANT INBOX is "pepp://example.com/
 fred", then, after performing the necessary character conversions,
 the resulting mapping is:
           im:pepp=example.com/fred@relay-domain
 where "relay-domain" is derived from local configuration information.
 Experience shows that it is vastly preferable to hide this mapping
 from end-users - if possible, the underlying software should perform
 the mapping automatically.

Appendix C. Acknowledgments

 The author would like to acknowledge John Ramsdell for his comments,
 suggestions and enthusiasm.  Thanks to Derek Atkins for editorial
 fixes.

Author's Address

 Jon Peterson
 NeuStar, Inc.
 1800 Sutter St
 Suite 570
 Concord, CA  94520
 US
 Phone: +1 925/363-8720
 EMail: jon.peterson@neustar.biz

Peterson Standards Track [Page 14] RFC 3859 Common Profile for Presence August 2004

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
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement

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

Peterson Standards Track [Page 15]

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