SIMPLE WG M. Lonnfors Internet-Draft A. Niemi Expires: August 25, 2005 Nokia Research Center E. Leppanen Nokia February 21, 2005 Partial Publication of Presence Information draft-ietf-simple-partial-publish-02 Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 25, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract Session Initiation Protocol (SIP) Extension for Event State Publication describes a mechanism with which a presence user agent is able to publish presence information to a presence agent. Using the Presence Information Data Format (PIDF), each presence publication Lonnfors, et al. Expires August 25, 2005 [Page 1] Internet-Draft Partial Publication February 2005 contains full state, regardless of how much of that information has actually changed since the previous update. As a consequence, updating a sizeable presence document with small changes bear a considerable overhead and is therefore inefficient. Especially with low bandwidth and high latency links, this can constitue a considerable burden to the system. This memo defines a solution that aids in reducing the impact of those constraints and increases transport efficiency by introducing a mechanism that allows for publication of partial presence information. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions and Document Conventions . . . . . . . . . . . . . 3 3. Overall Operation . . . . . . . . . . . . . . . . . . . . . . 3 3.1 Presence Publication . . . . . . . . . . . . . . . . . . . 4 3.2 Partial Presence Publication . . . . . . . . . . . . . . . 4 4. Client and Server Operation . . . . . . . . . . . . . . . . . 5 4.1 Content-type for Partial Publications . . . . . . . . . . 5 4.2 Generation of Partial Publications . . . . . . . . . . . . 5 4.3 Processing of Partial Publications . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1 Normative references . . . . . . . . . . . . . . . . . . . 7 7.2 Informative references . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Lonnfors, et al. Expires August 25, 2005 [Page 2] Internet-Draft Partial Publication February 2005 1. Introduction Session Initiation Protocol (SIP) Extension for Event State Publication [2] allows Presence User Agents ('PUA') to publish presence information of a user ('presentity'). The Presence Agent ('PA') collects publications from one or several presence user agents, and generates the composite event state of the presentity. The baseline format for presence information is defined in the Presence Information Data Format (PIDF) [3] and is by default used in presence publication. The PIDF uses Extensible Markup Language (XML) [12], and groups data into elements called tuples. In addition, [8], [9], [10], and [11] define extension elements that provide various additional features to PIDF. Presence publication by default uses the PIDF document format, and each publication contains full state regardless of how much of the presence information has actually changed since the previous update. As a consequence, updating a sizeable presence document especially with small changes bears a considerable overhead and is therefore inefficient. Publication of information over low bandwidth and high latency links further exacerbates this inefficiency. This memo specifies a mechanism with which the PUA is able to publish only those parts of the presence document that have changed since the previous update. This is accomplished using the partial PIDF format [5]. 2. Definitions and Document Conventions In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [1]and indicate requirement levels for compliant implementations. This document makes use of the vocabulary defined in RFC 2778 [6], the Event State Publication Extension to SIP [2], and PIDF Extension for Partial Presence [5]. 3. Overall Operation This section introduces the baseline functionality for presence publication, and gives an overview of the partial publication mechanism. This section is informational in nature. It does not contain any normative statements. Lonnfors, et al. Expires August 25, 2005 [Page 3] Internet-Draft Partial Publication February 2005 3.1 Presence Publication Event state publication is specified in [2]. The publication of presence information consists of a presence user agent sending a PUBLISH request targeted to the address-of-record of the presentity, and serviced by a presence agent or compositor. The body of the PUBLISH request carries full event state in the form of a presence document. The compositor processes the PUBLISH request and stores the presence information. It also assigns an entity-tag that is used to identify the publication. This entity-tag is returned to the PUA in the response to the PUBLISH request. The PUA uses the entity-tag in the following PUBLISH request for identifying the publication that the request is meant to refresh, modify or remove. Presence information is stored in an initial publication, and maintained using the refreshing and modifying publications. Presence information disappears either by expilicitly removing it or when it meets its expiration time. 3.2 Partial Presence Publication The partial publication mechanism enables the PUA to update only parts of its presence information, namely those sections of the presence document that have changed. The initial publication always carries full state. However, modifying publications that update the initial presence state only carry partial state. Versioning of the partial publications guarantees that the changes are applied in the correct order. Even though the PUBLISH mechanism in itself already accomplishes this using entity-tags, versioning is important in case the updates traverse a gateway into a system without such guarantees. To initialize its publications, the PUA first publishes a full state initial publication using the PIDF document format. The consequent updates result in the publication of partial presence state, using the 'application/pidf-partial+xml' content type [5]. The partial state may contain operations for adding new elements or attributes ( elements), replacing elements or attributes whose content has changed ( elements) , and it may also indicate removal of certain elements or attributes ( elements). The PUA is free to decide the granularity in which changes in presence information are reported to the composer. When the presence composer receives a partial publication it performs the included operations in sequence. The resulting changed presence document is then submitted to the composition logic in the same Lonnfors, et al. Expires August 25, 2005 [Page 4] Internet-Draft Partial Publication February 2005 manner as with a full state presence publication. 4. Client and Server Operation Unless otherwise specified in this document, the presence user agent and presence agent behavior are as defined in the Event State Publication Extension to SIP [2]. 4.1 Content-type for Partial Publications The entities supporting the partial publication extension described in this document MUST support the 'application/pidf-diff+xml' content type defined in the partial PIDF format [5] in addition to the baseline 'application/pidf+xml' content type defined in [3]. 4.2 Generation of Partial Publications Whenever a PUA decides to begin publication of presence information, it first needs to make an initial publication. After the initial publication, presence information can be updated using modifying publications, using the partial presence document format [5]. Finally, the publication can be terminated by explicit removal, or by expiration. To construct an initial publication, the PUA uses the following logic: o The Content-Type header field in the PUBLISH request MUST be set to the value 'application/pidf+xml' o The body of the request is populated with a PIDF document containing the full state of which the PUA is aware. o The version number local to the PUA MUST be initialized, i.e., set to zero. To construct a modifying PUBLISH request the following logic is followed: o The Content-Type header field in the PUBLISH request MUST be set to the value 'application/pidf-diff+xml' o The local version value MUST be incremented by one, and the "version" attribute is set to that value. o The "entity" attribute MUST be set to the same value as in the initial publication. Lonnfors, et al. Expires August 25, 2005 [Page 5] Internet-Draft Partial Publication February 2005 o The changes to the presentity's presence information MUST be constructed into operations in sequence, as defined in the partial PIDF format [5]. The PUA is free to decide the granularity by which changes in the presentity's presence information are reported to the presence compositor. In order to reduce unnecessary network traffic, the PUA SHOULD be able to batch several partial publications together. For example, a reasonable granularity would be to batch events related to a single UI event together in a single PUBLISH request. If a modifying publication carrying partial presence information is not understood by the presence composer, it will reject the request with a 415 (Unsupported Media Type). If the PUA receives a 415 reponse, it MUST fall back to full state presence updates. To find out whether a specific presence compositor supports partial presence publication, the PUA MAY use the OPTIONS method, as described in [4]. 4.3 Processing of Partial Publications Processing of publications generally follows the guidelines set in [2]. In addition, processing modifying PUBLISH requests, the following logic is followed: o If the value of the Content-Type header field is 'application/pidf-diff+xml', the publication is partial, and the next steps apply. o The compositor MUST apply the partial publication operations in sequence against its locally stored presence information. o If any errors are encountered before the entire partial publication is completely processed, including all of the operations in the 'application/pidf-diff+xml' body, the compositor MUST reject the request with a 500 (Server Internal Error) response, and revert back to its original, locally stored presence information. 5. Security Considerations This specification relies on protocol behavior defined in [2]. General event state publication related security considerations are extensively discussed in that specification and all the identified security considerations apply to this document in entirety. In addition, this specification adds no new security considerations. Lonnfors, et al. Expires August 25, 2005 [Page 6] Internet-Draft Partial Publication February 2005 6. Acknowledgements The authors would like to thank Atle Monrad, Christian Schmidt and George Foti for review comments. 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] Niemi, A., "Session Initiation Protocol (SIP) Extension for Event State Publication", RFC 3903, October 2004. [3] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004. [4] 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. [5] Lonnfors, M., Leppanen, E., Khartabil, H. and J. Urpalainen, "Presence Information Data format (PIDF) Extension for Partial Presence", Internet-Draft draft-ietf-simple-partial-pidf-format-03, February 2005. 7.2 Informative references [6] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [7] Campbell, B., "SIMPLE Presence Publication Requirements", Internet-Draft draft-ietf-simple-publish-reqs-00, February 2003. [8] Rosenberg, J., "A Data Model for Presence", Internet-Draft draft-ietf-simple-presence-data-model-01, October 2004. [9] Schulzrinne, H., Gurbani, V., Kyzivat, P. and J. Rosenberg, "RPID: Rich Presence: Extensions to the Presence Information Data Format (PIDF)", Internet-Draft draft-ietf-simple-rpid-04, October 2004. [10] Schulzrinne, H., "CIPID: Contact Information in Presence Lonnfors, et al. Expires August 25, 2005 [Page 7] Internet-Draft Partial Publication February 2005 Information Data Format", Internet-Draft draft-ietf-simple-cipid-03, July 2004. [11] Lonnfors, M. and K. Kiss, "User Agent Capability Extension to Presence Information Data Format(PIDF)", Internet-Draft draft-ietf-simple-prescaps-ext-02, October 2004. [12] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml, October 2000, . Authors' Addresses Mikko Lonnfors Nokia Research Center Itamerenkatu 11-13 Helsinki Finland Phone: +358 71 8008000 Email: mikko.lonnfors@nokia.com Aki Niemi Nokia Research Center P.O. Box 407 NOKIA GROUP, FIN 00045 Finland Phone: +358 50 389 1644 Email: aki.niemi@nokia.com Eva Leppanen Nokia P.O BOX 785 Tampere Finland Email: eva-maria.leppanen@nokia.com Lonnfors, et al. 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