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SIMPLE                                                       B. Campbell
Internet-Draft                                               dynamicsoft
Expires: August 28, 2003                                        S. Olson
                                                               Microsoft
                                                             J. Peterson
                                                           NeuStar, Inc.
                                                            J. Rosenberg
                                                             dynamicsoft
                                                              B. Stucker
                                                   Nortel Networks, Inc.
                                                       February 27, 2003


                 SIMPLE Presence Publication Mechanism
                     draft-olson-simple-publish-02

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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 28, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes an extension to the Session Initiation
   Protocol (SIP) for publishing event state used within the framework
   for SIP Event Notification.  The first application of this extension
   is targeted at the publication of presence information.



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   The method described in this document allows event information to be
   published to a presence agent on behalf of a user.  This method can
   be extended to support publication of other event state, but it is
   not intended to be a general-purpose mechanism for transport of
   arbitrary data as there are better suited mechanisms for this purpose
   (ftp, http, etc.) This method is intended to be a simple,
   light-weight mechanism that employs SIP in order to support SIMPLE
   services.

Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   3
   2.     Terminology  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.     Constructing the PUBLISH Request . . . . . . . . . . . . .   6
   4.     Requirements of the body of a PUBLISH request  . . . . . .   8
   5.     Creating Initial Publication Soft-State  . . . . . . . . .   9
   6.     Setting the Expiration Interval of Event State . . . . . .  10
   7.     Removing Event State . . . . . . . . . . . . . . . . . . .  11
   8.     Querying the Current Event State . . . . . . . . . . . . .  12
   9.     Refreshing Event State . . . . . . . . . . . . . . . . . .  13
   10.    Processing PUBLISH Requests  . . . . . . . . . . . . . . .  14
   11.    Syntax . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   11.1   New Method . . . . . . . . . . . . . . . . . . . . . . . .  17
   11.2   New Response Code  . . . . . . . . . . . . . . . . . . . .  18
   11.2.1 "494 Out Of Sync" Response Code  . . . . . . . . . . . . .  19
   12.    Examples . . . . . . . . . . . . . . . . . . . . . . . . .  20
   13.    IANA Considerations  . . . . . . . . . . . . . . . . . . .  28
   14.    Security Considerations  . . . . . . . . . . . . . . . . .  29
   15.    Open Issues  . . . . . . . . . . . . . . . . . . . . . . .  30
          Normative References . . . . . . . . . . . . . . . . . . .  31
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  31
          Intellectual Property and Copyright Statements . . . . . .  33



















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1. Introduction

   The focus of this specification is to provide a framework for the
   publication of event state from a UA to a entity that is responsible
   for compositing this event state and distributing that state to
   interested parties through the SUBSCRIBE/NOTIFY mechanism.  This
   specification fills a current gap in the event notification framework
   to allow for a client to push its state to the state agent that acts
   on its behalf.  It is the intention of this framework to allow any
   event state for which there is an appropriate event package (as
   defined in RFC 3265 [2]) to be published.

   The first application of this mechanism is the publication of
   presence state by a PUA to a presence compositor which has a tightly
   coupled relationship to the PA.  The requirements and model for
   presence publication are documented in [4].  This specification will
   address each of these requirments.

   To accomplish this task a new SIP method, PUBLISH, is defined.
   PUBLISH is analogous to REGISTER in that it allows a UA to add,
   modify, and remove state in another entity which manages this state
   on behalf of a user.  The user may in turn have multiple UAs or
   endpoints.  Each endpoint may publish its own unique state and
   through a subscription to that event discover the event state of the
   other endpoints for a user.  PUBLISH is defined to create soft-state
   in the state agent; this state has a defined lifetime and will expire
   after a negotiated amount of time.  Local policy at the compositor
   may in turn define hard-state for this event package.  That is, the
   steady-state of this event package in the absence of any other
   soft-state provided through the PUBLISH method.  In the generic
   sense, a UAC which publishes event state is labelled an Event
   Publication Agent (EPA).  For presence in particular, this is the
   familiar PUA role as defined in [7].  The entity which processes the
   PUBLISH request is known as a Event State Compositor (ESC).  For
   presence in particular, this is the familiar PA role.

   Event state publication inherently involves at least two parties: the
   source of the publication and the target of the publication.  The
   source of the publication is naturally represented as an
   address-of-record (AOR).  For some types of event state, namely
   presence, the target of the publication may not sufficiently be
   represented by an address-of-record (AOR) alone.  Rather, the target
   is a combination of both an AOR and a unique identifier which acts to
   represent one of N possible sections of an overall event state for
   that AOR.  In this specification, these sections are referred to as
   event state segments.  In the context of presence publication, the
   event state segment is nothing more than the presence tuple
   associated with the presentity (AOR).  It is the role of the



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   compositor to aggregate these segments into a complete event state
   which is presented to the subscribers of that event state.  This
   composition logic is a matter of local policy.  For some event
   packages, there is no natural decomposition of event state into these
   segments and for these packages, an AOR is sufficient to identify the
   target of the publish.













































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2. Terminology

   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 RFC 2119 [3].

   In addition to the terminology of RFC 3265 [2], this document
   introduces some new concepts:

      Event Publication Agent (EPA): The UAC which issues a PUBLISH
      request to publish event state.

      Event State Compositor (ESC): The UAS which processes PUBLISH
      requests and composites the event state.  It is assumed that there
      is a tight coupling between the ESC which receives the PUBLISH
      requests and the state agent which issues appropriate NOTIFY
      requests based on this change in event state.  The interface
      between these two components is out-of-scope for this
      specification.

      Event State Segment: The EPA may publish event state that is
      divided into individual segments.  For the presence publication
      case, these segments are the individual tuples in the presence
      document.  In the generic case, this document will refer to these
      segments as event state segments.


























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3. Constructing the PUBLISH Request

   PUBLISH requests create, remove, and modify event state.  A PUBLISH
   request can create new event state in the state agent, associating
   this event state with an address-of-record and optionally with a
   unique identifier for segments of event state being published.
   Publication on behalf of a particular address-of-record may also be
   performed by a suitably authorized third party.  To determine the
   current published state for a particular address-of-record, the
   client MAY create a subscription for this address-of-record and event
   package using the SUBSCRIBE/NOTIFY mechanism of RFC3265.

   Note that in the case the event state is segmented, each segment
   logically represents an independent publication that may be added,
   removed, modified, and expired separately.  For presence publication,
   this means each tuple in the PIDF document in the PUBLISH request is
   logically a separate publication that may be manipulated
   independently even though they are grouped together in the same PIDF
   document initially.

   Except as noted, the construction of the PUBLISH request and the
   behavior of clients sending a PUBLISH request is identical to the
   general UAC behavior described in Section 8.1 and Section 17.1 of RFC
   3261 [1].

   A PUBLISH request does not establish a dialog.  A UAC MAY include a
   Route header field in a PUBLISH request based on a pre-existing route
   set as described in Section 8.1 of RFC3261.  The Record-Route header
   field has no meaning in PUBLISH requests or responses, and MUST be
   ignored if present.  In particular, the UAC MUST NOT create a new
   route set based on the presence or absence of a Record-Route header
   field in any response to a PUBLISH request.  The PUBLISH request MUST
   NOT contain a Contact header.

   The following header fields MUST be included in a PUBLISH request:

   Request-URI: The Request-URI initially contains the address-of-record
      whose publication is to be created, removed, or modified.  Unlike
      the REGISTER request, the Request-URI SHOULD contain a SIP(S) URI
      with a username.  The address-of-record MUST be a SIP URI or SIPS
      URI.

   To: The To header field contains the address of record whose
      publication is to be created, removed, or modified.  The To header
      field and the Request-URI field are typically the same.  This
      address-of-record MUST be a SIP URI or SIPS URI.





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   From: The From header field contains the address-of-record of the
      person responsible for the publication.  The value is the same as
      the To header field unless the request is a third- party
      publication.

   Call-ID: All publications from an EPA MAY use the same Call-ID header
      field value for publications sent to a particular state agent.

   CSeq: An EPA MUST increment the CSeq value by one for each PUBLISH
      request with the same Call-ID.  Unlike REGISTER requests, the
      Call-ID and CSeq are not directly used for ordering of PUBLISH
      requests.

   Event: PUBLISH requests MUST contain a single Event header field.
      This value indicates the event package which this request is
      publishing state for.

   Expires: PUBLISH requests SHOULD contain a single Expires header
      field.  This value indicates the lifetime of the event state being
      published by this request.  A special value of "0" indicates the
      removal of any prior soft-state established by a prior PUBLISH
      request from this UAC.

   The body of the PUBLISH request contains the event state that the
   client wishes to publish.  The content format and semantics are
   dependent on the event package identified in the Event header.  Any
   event package which makes use of the PUBLISH mechanism MUST describe
   these semantics and MUST prescribe a default, mandatory to implement
   format.  This document defines the semantics of the presence
   publication requests (event package "presence") when the CPIM PIDF
   [5] presence document format is used.




















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4. Requirements of the body of a PUBLISH request

   In order to satisfy the requirements of [4], the body of the PUBLISH
   request must fulfill several requirements as well.  Any application
   of the PUBLISH mechanism for a given event package MUST support a
   Content-Type which fulfills these requirements.  For presence
   publication, it will be demonstrated how these requirements may be
   fulfilled using the CPIM PIDF presence format in [5] within a PUBLISH
   request.  A PUA which uses PUBLISH to publish presence state to the
   PA MUST support the CPIM PIDF presence format.

      The content type MUST provide a way to indicate an ordering of
      publication requests.  For example, the timestamp element in PIDF
      provides a temporal ordering of presence state changes that allows
      the Event State Compositor (ESC) to properly order PUBLISH
      requests.  When used as the content of a PUBLISH request, the PUA
      MUST supply a timestamp element for every presence tuple present
      in the PIDF document.

      The content type MUST provide a way to publish partial state for
      an event package.  The intention is to allow each device or client
      for an address-of-record to publish event state independently.  To
      accomplish this, the event state that is published by these
      devices must be allowed to be only a portion of the complete state
      that the state agent advertises for that AOR.  For example, a PUA
      can publish presence state for just a subset of the tuples that
      may be composited into the presence document that watchers receive
      in a NOTIFY.  The mechanism by which the ESC aggregates this
      information is a matter of local policy.

      If the content type allows for event state segments to be
      represented, the content type MUST provide a means to uniquely
      identify each unique segment.  For example, the CPIM PIDF presence
      document provides a tuple ID to distinguish the segments of the
      presence document associated with the encompassing presentity.

   As with any other SIP message, the PUBLISH mechanism MAY use the
   content indirection mechanism defined in [6].  There are no
   additional requirements or restrictions on content indirection as
   applied to the PUBLISH request.  Content indirection is a useful
   mechanism for communicating large event state information that cannot
   be carried directly within the SIP signaling (PUBLISH request).









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5. Creating Initial Publication Soft-State

   The PUBLISH request created by the EPA and sent to the Event State
   Compositor (ESC) establishes soft-state in the state agent for the
   event package indicated in the request and bound to the
   address-of-record in the To header of the request.  Additionally, the
   PUBLISH request may publish event state that is further sub-divided
   into segments of event state that may be manipulated independently.
   As an example, presence publication using the CPIM PIDF format may
   manipulate individual tuples related to a common presentity.

   Once the initial PUBLISH request has been processed by the ESC, the
   EPA MAY send subsequent PUBLISH requests to refresh, modify, or
   delete the publication state established by the first PUBLISH
   request.  These operations will be described in subsequent sections.

   EPAs MUST NOT send a new PUBLISH request (not a re-transmission)
   until they have received a final response from the state agent for
   the previous one or the previous PUBLISH request has timed out.
































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6. Setting the Expiration Interval of Event State

   When a client sends a PUBLISH request, it SHOULD suggest an
   expiration interval that indicates how long the client would like the
   publication to be valid.  The actual duration of the soft state is
   defined by local policy at the ESC.  The expiration value is
   presented in the Expires header of the PUBLISH request.  If an
   Expires header is not present, the client is indicating its desire
   for the server to choose.  It is RECOMMENDED that the PA use a value
   of 3600 seconds (1 hour) for this default expiration value in the
   case of presence publication.  The default value is generally event
   package specific.







































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7. Removing Event State

   PUBLISH establishes soft state which expires unless refreshed.  This
   event state may also be explicitly removed.  A UA requests the
   immediate removal of event state by specifying an Expires value of
   "0" in the PUBLISH request.  Such a request SHOULD NOT contain any
   body.  UAs which support PUBLISH SHOULD support this mechanism for
   explicitly removing event state.











































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8. Querying the Current Event State

   The response to a PUBLISH request indicates whether the request was
   successful or not.  In general, the body of a such response will be
   empty unless the event package defines explicit meaning for such a
   body.  There is no such meaning for a response to a presence
   publication when the document format used is CPIM PIDF.

   To query the event state that the state agent in fact publishes, the
   client may SUBSCRIBE to the event package for which it has sent a
   PUBLISH, indicating the same address-of-record in the To header.  An
   Expires header value of "0" may be used in this SUBSCRIBE request to
   do a one-time fetch of this event state as defined in RFC3265.






































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9. Refreshing Event State

   Each EPA is responsible for refreshing the publications that it has
   previously established.  An EPA MAY choose to refresh the publication
   established by another EPA for the same address-of-record.  The
   authorization policy of the ESC.

   The 200 (OK) response from the state agent MUST contain an Expires
   header indicating the expiration time interval for the publication.
   The EPA then issues a PUBLISH request for each of its publications
   before the expiration interval has elapsed.

   If an EPA receives a 423 (Interval Too Brief) response to a PUBLISH
   request, it MAY retry the publication after changing the expiration
   interval in the Expires header to be equal to or greater than the
   expiration interval within the Min-Expires header field of the
   423(Interval Too Brief) response.


































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10. Processing PUBLISH Requests

   The Event State Compositor (ESC) is a UAS that responds to PUBLISH
   requests and maintains a list of publications for a given
   address-of-record.  The ESC MUST ignore the Record-Route header field
   if it is included in a PUBLISH request.  The ESC MUST NOT include a
   Record-Route header field in any response to a PUBLISH request.

   The ESC has to know (for example, through configuration) the set of
   domain(s) for which it maintains event state.  PUBLISH requests MUST
   be processed in the order that they are received.  PUBLISH requests
   MUST also be processed atomically, meaning that a particular PUBLISH
   request is either processed completely or not at all.

   When receiving a PUBLISH request, the ESC follows these steps:

   1.  The ESC inspects the Request-URI to determine whether this
       request is for a domain supported by the ESC.  If not, the ESC
       SHOULD proxy the request to the addressed domain.

   2.  To guarantee that the ESC supports any necessary extensions, the
       ESC MUST process the Require header field values as described for
       UASs in Section 8.2.2 of RFC3261.

   3.  An ESC SHOULD authenticate the UAC.  Mechanisms for the
       authentication of SIP user agents are described in Section 22 of
       RFC3261.

   4.  The ESC SHOULD determine if the authenticated user is authorized
       to publish for this address-of-record.  If the authenticated user
       is not authorized to publish, the ESC MUST return a 403
       (Forbidden).  This authorization may take into account 3rd party
       publication of event state.

   5.  The ESC extracts the address-of-record from the To header field
       of the request.  If the address-of-record is not valid for the
       domain in the Request-URI, the ESC MUST send a 404 (Not Found)
       response and skip the remaining steps.  The URI MUST then be
       converted to a canonical form.  To do that, all URI parameters
       MUST be removed (including the user-param), and any escaped
       characters MUST be converted to their unescaped form.  The result
       serves as an index into the list of publications.

   6.  The ESC examines the Event header of the PUBLISH request.  If the
       Event header is missing or contains an event package which the
       ESC does not support, the ESC MUST respond to the PUBLISH request
       with a 489 (Bad Event) response.




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   7.  The ESC now processes the Expires header value from the PUBLISH
       request.

       *  If the request has an Expires header field, that value MUST be
          taken as the requested expiration.

       *  Else, a locally-configured default value MUST be taken as the
          requested expiration.

       *  The ESC MAY choose an expiration less than the requested
          expiration interval.  If and only if the requested expiration
          interval is greater than zero AND less than a ESC-configured
          minimum, the ESC MAY reject the publication with a response of
          423 (Interval Too Brief).  This response MUST contain a
          Min-Expires header field that states the minimum expiration
          interval the ESC is willing to honor.  It then skips the
          remaining steps.

   8.  The ESC may then process the body of the PUBLISH request (the
       actual event state)

       *  For each publication, the ESC will record the target of the
          publication (To URI), the source of the publication (From
          URI), and the version of the publication.  This version
          information must be present in the body of the PUBLISH
          request.  In the presence publication application, this
          information will come from the timestamp element associated
          with each presence tuple.

       *  If the version of the event state present in the PUBLISH
          request is older than the current version known by the ESC,
          the ESC MUST return a 494 (Out of Sync) response and MUST NOT
          update the event state for this AOR.  This is to handle
          out-of-order or stale PUBLISH requests.  To recover from this
          error, the client SHOULD determine the current version of the
          event state at the server by sending a SUBSCRIBE request to
          the server and re-issue the PUBLISH request if the event state
          changes again.

       *  The processing of the PUBLISH request must be atomic.  If
          internal errors (such as the inability to access a back-end
          database) occur before processing is complete, no portion of
          the PUBLISH document must be published and the ESC MUST fail
          with a 500 (Server Error) response.

   9.  The ESC returns a 200 (OK) response.  The response MUST contain
       an Expires header indicating the expiration interval chosen by
       the ESC.  The state agent associated with this ESC may then issue



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       appropriate NOTIFY requests to any watchers of this event state.
       The timing between the receipt of the PUBLISH request and the
       issuance of NOTIFY requests is implementation dependent and may
       vary according to throttling policies at the state agent.















































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11. Syntax

11.1 New Method

   The following is the BNF definition for the PUBLISH method.  As with
   all other SIP methods, the method name is case sensitive.


         PUBLISHm = %x50.55.42.4C.49.53.48 ; PUBLISH in caps.


   Tables 1 and 2 extend Tables 2 and 3 of RFC 3261 [1] by adding an
   additional column, defining the header fields that can be used in
   PUBLISH requests and responses.



                      Header Field       where  proxy  PUBLISH
                      __________________________________________
                      Accept               R              -
                      Accept              2xx             -
                      Accept              415             m*
                      Accept-Encoding      R              -
                      Accept-Encoding     2xx             -
                      Accept-Encoding     415             m*
                      Accept-Language      R              -
                      Accept-Language     2xx             -
                      Accept-Language     415             m*
                      Alert-Info           R              -
                      Alert-Info          180             -
                      Allow                R              o
                      Allow               2xx             o
                      Allow                r              o
                      Allow               405             m
                      Authentication-Info 2xx             o
                      Authorization        R              o
                      Call-ID              c      r       m
                      Call-Info                  ar       o
                      Contact              R              -
                      Contact             1xx             -
                      Contact             2xx             -
                      Contact             3xx             o
                      Contact             485             o
                      Content-Disposition                 o
                      Content-Encoding                    o
                      Content-Language                    o
                      Content-Length             ar       t
                      Content-Type                        *



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                      CSeq                c       r       m
                      Date                        a       o
                      Event               a       m
                      Error-Info       300-699    a       o
                      Expires                             o
                      From                c       r       m
                      In-Reply-To         R               o
                      Max-Forwards        R      amr      m
                      Organization               ar       o

                      Table 1: Summary of header fields, A--O



                      Header Field       where  proxy    PUBLISH
                   __________________________________________

                      Priority             R     ar         o
                      Proxy-Authenticate  407    ar         m
                      Proxy-Authenticate  401    ar         o
                      Proxy-Authorization  R     dr         o
                      Proxy-Require        R     ar         o
                      Record-Route               ar         -
                      Reply-To                              o
                      Require                    ar         c
                      Retry-After   404,413,480,486         o
                                        500,503             o
                                        600,603             o
                      Route                R     adr        o
                      Server               r                o
                      Subject              R                o
                      Timestamp                             o
                      To                 c(1)     r         m
                      Unsupported         420               o
                      User-Agent                            o
                      Via                  R     amr        m
                      Via                 rc     dr         m
                      Warning              r                o
                      WWW-Authenticate    401    ar         m
                      WWW-Authenticate    407    ar         o

                      Table 2: Summary of header fields, P--Z



11.2 New Response Code





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11.2.1 "494 Out Of Sync" Response Code

   The 494 event response is added to the "Client-Error" header field
   definition.  "494 Out of Sync" is used to indicate that the server
   detected that the event state that the client is trying to publish is
   out of sync (stale) relative to the event state that the server has.
   The version information in the PUBLISH body is older than the version
   information that the server maintains for the corresponding event and
   AOR.










































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12. Examples

   The following section shows an example of the usage of the PUBLISH
   method in the case of publishing the presence document from a
   presence user agent to a presence agent.  The watcher in this case is
   watching the PUA's presentity.  The PUA will SUBSCRIBE to its own
   presence to see the composite presence state exposed by the PA.  This
   is an optional but likely step for the PUA.




       PUA                     PA                      WATCHER
      (EPA)                   (ESC)
        |                       |                         |
        |                       | <---- M1: SUBSCRIBE --- |
        |                       |                         |
        |                       | ----- M2: 200 OK -----> |
        |                       |                         |
        |                       | ----- M3: NOTIFY -----> |
        |                       |                         |
        |                       | <---- M4: 200 OK ------ |
        |                       |                         |
        | --- M5: SUBSCRIBE --> |                         |
        |                       |                         |
        |<--- M6: 200 OK    --> |                         |
        |                       |                         |
        |<--- M7: NOTIFY  ----- |                         |
        |                       |                         |
        | --- M8: 200 OK    --> |                         |
        |                       |                         |
        | --- M9: PUBLISH ----> |                         |
        |                       |                         |
        | <-- M10: 200 OK ----  |                         |
        |                       |                         |
        |                       | ----- M11: NOTIFY ----> |
        |                       |                         |
        |                       | <---- M12: 200 OK ----- |
        |                       |                         |
        |                       |                         |
        |<---- M13: NOTIFY ---- |                         |
        |                       |                         |
        |----- M14: 200 OK  --> |                         |
        |                       |                         |



   Message flow:



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   M1: The watcher initiates a new subscription to the
      presentity@domain.com's presence agent.




   SUBSCRIBE sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP 10.0.0.1:5060;branch=z9hG4bKnashds7
   To: <sip:presentity@domain.com>
   From: <sip:watcher@domain.com>;tag=12341234
   Call-ID: 12345678@10.0.0.1
   CSeq: 1 SUBSCRIBE
   Expires: 3600
   Event: presence
   Contact: <sip:watcher@domain.com>
   Content-Length: 0


   M2: The presence agent for presentity@domain.com processes the
      subscription request and creates a new subscription.  A 200 (OK)
      response is sent to confirm the subscription.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 10.0.0.1:5060;branch=z9hG4bKnashds7
   To: <sip:presentity@domain.com>;tag=abcd1234
   From: <sip:watcher@domain.com>;tag=12341234
   Call-ID: 12345678@10.0.0.1
   CSeq: 1 SUBSCRIBE
   Contact: <sip:pa@domain.com>
   Expires: 3600
   Content-Length: 0


   M3: In order to complete the process, the presence agent sends the
      watcher a NOTIFY with the current presence state of the
      presentity.












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   NOTIFY sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdf2
   To: <sip:watcher@domain.com>;tag=12341234
   From: <sip:presentity@domain.com>;tag=abcd1234
   Call-ID: 12345678@10.0.0.1
   CSeq: 1 NOTIFY
   Event: presence
   Subscription-State: active; expires=3599
   Content-Type: application/cpim-pidf+xml
   Content-Length: ...

   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
             entity="pres:presentity@domain.com">
      <tuple id="mobile-phone">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T16:49:29Z</timestamp>
      </tuple>
      <tuple id="desktop">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T12:21:29Z</timestamp>
      </tuple>
   </presence>


   M4: The watcher confirms receipt of the NOTIFY request.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdf2
   To: <sip:watcher@domain.com>;tag=12341234
   From: <sip:presentity@domain.com>;tag=abcd1234
   Call-ID: 12345678@10.0.0.1
   CSeq: 1 NOTIFY
   Contact: <sip:watcher@domain.com>


   M5: To view its composite presence state, the PUA issues a SUBSCRIBE
      to the PA for itself.






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   SUBSCRIBE sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bKjjsdfj
   To: <sip:presentity@domain.com>
   From: <sip:presentity@domain.com>;tag=43214321
   Call-ID: 87654321@10.0.0.2
   CSeq: 1 SUBSCRIBE
   Expires: 3600
   Event: presence
   Contact: <sip:pua@domain.com>
   Content-Length: 0


   M6: The presence agent for presentity@domain.com processes the
      subscription request and creates a new subscription.  A 200 (OK)
      response is sent to confirm the subscription.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bKjjsdfj
   To: <sip:presentity@domain.com>;tag=abcd1235
   From: <sip:watcher@domain.com>;tag=43214321
   Call-ID: 87654321@10.0.0.2
   CSeq: 1 SUBSCRIBE
   Contact: <sip:pa@domain.com>
   Expires: 3600
   Content-Length: 0


   M7: In order to complete the process, the presence agent sends the
      PUA a NOTIFY with the current presence state of the presentity.
















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   NOTIFY sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdfk
   To: <sip:watcher@domain.com>;tag=abcd1235
   From: <sip:presentity@domain.com>;tag=43214321
   Call-ID: 87654321@10.0.0.2
   CSeq: 1 NOTIFY
   Event: presence
   Subscription-State: active; expires=3599
   Content-Type: application/cpim-pidf+xml
   Content-Length: ...

   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
             entity="pres:presentity@domain.com">
      <tuple id="mobile-phone">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T16:49:29Z</timestamp>
      </tuple>
      <tuple id="desktop">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T12:21:29Z</timestamp>
      </tuple>
   </presence>



   M9: A presence user agent for the presentity detects a change in the
      user's presence state.  It initiates a PUBLISH to the presentity's
      presence agent in order to update it with the new presence
      information.  The timestamp element is updated to indicate the
      time of the change.  The Expires header indicates the desired
      duration of this soft-state.  The "entity" attribute of the
      presence element in the PIDF document matches the To AOR.














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   PUBLISH sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP pua.domain.com;branch=z9hG4bK652hsge
   To: <sip:presentity@domain.com>;tag=1a2b3c4d
   From: <sip:presentity@domain.com>;tag=1234wxyz
   Call-ID: 81818181@pua.domain.com
   CSeq: 1 PUBLISH
   Expires: 3600
   Event: presence
   Content-Type: application/cpim-pidf+xml
   Content-Length: ...

   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
             entity="pres:presentity@domain.com">
      <tuple id="mobile-phone">
         <status>
            <basic>closed</basic>
         </status>
         <timestamp>2003-02-01T17:00:19Z</timestamp>
      </tuple>
   </presence>


   M10: The presence agent receives, and accepts the presence
      information.  The published data is incorporated into the
      presentity's presence document.  A 200 (OK) response is sent to
      confirm the publication.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP pua.domain.com;branch=z9hG4bK652hsge
   To: <sip:presentity@domain.com>;tag=1a2b3c4d
   From: <sip:presentity@domain.com>;tag=1234wxyz
   Call-ID: 81818181@pua.domain.com
   CSeq: 1 PUBLISH
   Expires: 1800


   M11: The presence agent determines that a reportable change has been
      made to the presentity's presence document, and sends another
      notification to those watching the presentity to update their
      information regarding the presentity's current presence status.







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   NOTIFY sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42a
   To: <sip:watcher@domain.com>;tag=12341234
   From: <sip:presentity@domain.com>;tag=abcd1234
   Call-ID: 12345678@10.0.0.1
   CSeq: 2 NOTIFY
   Event: presence
   Subscription-State: active; expires=3400
   Content-Type: application/cpim-pidf+xml
   Content-Length: ...

   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
             entity="pres:presentity@domain.com">
      <tuple id="mobile-phone">
         <status>
            <basic>closed</basic>
         </status>
         <timestamp>2003-02-01T17:00:19Z</timestamp>
      </tuple>
      <tuple id="desktop">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T12:21:29Z</timestamp>
      </tuple>
   </presence>


   M12: The watcher confirms receipt of the NOTIFY request.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42a
   To: <sip:watcher@domain.com>;tag=12341234
   From: <sip:presentity@domain.com>;tag=abcd1234
   Call-ID: 12345678@10.0.0.1
   CSeq: 2 NOTIFY
   Content-Length: 0


   M13: The presence agent also sends a NOTIFY to the PUA.







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   NOTIFY sip:presentity@domain.com SIP/2.0
   Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42b
   To: <sip:watcher@domain.com>;tag=abcd1235
   From: <sip:presentity@domain.com>;tag=43214321
   Call-ID: 87654321@10.0.0.2
   CSeq: 2 NOTIFY
   Event: presence
   Subscription-State: active; expires=3400
   Content-Type: application/cpim-pidf+xml
   Content-Length: ...

   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
             entity="pres:presentity@domain.com">
      <tuple id="mobile-phone">
         <status>
            <basic>closed</basic>
         </status>
         <timestamp>2003-02-01T17:00:19Z</timestamp>
      </tuple>
      <tuple id="desktop">
         <status>
            <basic>open</basic>
         </status>
         <timestamp>2003-02-01T12:21:29Z</timestamp>
      </tuple>
   </presence>


   M14: The PUA confirms receipt of the NOTIFY request.




   SIP/2.0 200 OK
   Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42b
   To: <sip:watcher@domain.com>;tag=abcd1235
   From: <sip:presentity@domain.com>;tag=43214321
   Call-ID: 87654321@10.0.0.2
   CSeq: 2 NOTIFY











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13. IANA Considerations

   This document registers a new response code.  This response code is
   defined by the following information, which is to be added to the
   method and response-code sub-registry under http://www.iana.org/
   assignments/sip-parameters.  Response Code Number:   494 Default
   Reason Phrase:  Out Of Sync












































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14. Security Considerations

   The state agent SHOULD authenticate the Event Publication Agent
   (EPA), and SHOULD apply authorization policies.  The composition
   model makes no assumptions that all input sources for a compositor
   (ESC) are on the same network, or in the same administrative domain.

   The ESC should throttle incoming publications and the corresponding
   notifications resulting from the changes in event state.  As a first
   step, careful selection of default Expires: values for the supported
   event packages at a ESC can help limit refreshes of event state.
   Additional throttling and debounce logic at the ESC is advisable to
   further reduce the notification traffic produced as a result of a
   PUBLISH method.

   Integrity protection and privacy of the PUBLISH requests can be
   ensured using the S/MIME mechanisms outlined in section 23 of
   RFC3261.  Integrity protection of the To, From, Call-ID, CSeq, Event,
   Route, and Expires headers should be done at a minimum.

   If the ESC receives a PUBLISH request which is integrity protected
   using a security association that is not with the ESC (for example,
   end-to-end S/MIME integrity protection), the state agent coupled with
   the ESC MUST NOT modify the event state before exposing it to the
   watchers of this event state in a NOTIFY request(s).  This is to
   preserve the end-to-end integrity of the event state.

























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15. Open Issues

   o  Should the version information of the publication request be
      carried explicitly in a header of the request, or is sufficient to
      rely on the body for this information?

   o  Should the segments of event state (presence tuples) be sent in
      separate PUBLISH requests or is it enough to treat these as
      implicitly separate publication requests?

   o  Should the PUBLISH mechanism be overloaded to publish
      authorization information (ACLs) for the event state as well?

   o  Does end-to-end S/MIME integrity protection make sense when an
      event compositor is used?




































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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., "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]  Campbell, Olson, Peterson, Rosenberg and Stucker, "SIMPLE
        Presence Publication Requirements",
        draft-ietf-simple-publish-reqs-00 (work in progress), February
        2003.

   [5]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A. and W. Carr,
        "Common Presence and Instant Messaging (CPIM) Presence
        Information Data Format", draft-ietf-impp-cpim-pidf-07 (work in
        progress), May 2002.

   [6]  Olson, "A Mechanism for Content Indirection in SIP Messages",
        draft-olson-sip-content-indirect-mech-01 (work in progress),
        August 2002.

   [7]  Rosenberg, "A Presence Event Package for the Session Initiation
        Protocol (SIP)", draft-ietf-simple-presence-10 (work in
        progress), January 2003.


Authors' Addresses

   Ben Campbell
   dynamicsoft
   5100 Tennyson Parkway
   Suite 1200
   Plano, TX  75025
   US

   EMail: bcampbell@dynamicsoft.com










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   Sean Olson
   Microsoft
   One Microsoft Way
   Redmond, WA  98052
   US

   Phone: +1-425-707-2846
   EMail: seanol@microsoft.com
   URI:   http://www.microsoft.com/rtc


   Jon Peterson
   NeuStar, Inc.
   1800 Sutter St
   Suite 570
   Concord, CA  94520
   US

   Phone: +1-925-363-8720
   EMail: jon.peterson@neustar.biz
   URI:   http://www.neustar.biz


   Jonathan Rosenberg
   dynamicsoft
   72 Eagle Rock Avenue
   First Floor
   East Hanover, NJ  07936
   US

   EMail: jdrosen@dynamicsoft.com


   Brian Stucker
   Nortel Networks, Inc.
   2380 Performance Drive
   Richardson, TX  75082
   US

   EMail: bstucker@nortelnetworks.com











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Intellectual Property Statement

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Full Copyright Statement

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   This document and translations of it may be copied and furnished to
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

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











































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