SIPPING                                                     J. Rosenberg
Internet-Draft                                               dynamicsoft
Expires: April 26, August 15, 2004                                  H. Schulzrinne
                                                     Columbia University
                                                           O. Levin, Ed.
                                                   Microsoft Corporation
                                                        October 27, 2003
                                                       February 15, 2004

    A Session Initiation Protocol (SIP) Event Package for Conference

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
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   This Internet-Draft will expire on April 26, August 15, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). (2004). All Rights Reserved.


   This document defines a conference event package for the Session
   Initiation Protocol (SIP) Events framework, along with a data format
   used in notifications for this package. The conference package allows
   users to subscribe to a conference URI. Notifications are sent about
   changes in the membership of this conference, the status of users'
   participation in the conference, and the sidebars in the conference.

Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
   2.      Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   3.      Conference Event Package . . . . . . . . . . . . . . . . .  5
   3.1     Event Package Name . . . . . . . . . . . . . . . . . . . .  5
   3.2     SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . .  5
   3.3     Subscription Duration  . . . . . . . . . . . . . . . . . .  5
   3.4     NOTIFY Bodies  . . . . . . . . . . . . . . . . . . . . . .  5  6
   3.5     Notifier Processing of SUBSCRIBE Requests  . . . . . . . .  6
   3.6     Notifier Generation of NOTIFY Requests . . . . . . . . . .  6
   3.7     Subscriber Processing of NOTIFY Requests . . . . . . . . .  6  7
   3.8     Handling of Forked Requests  . . . . . . . . . . . . . . .  7
   3.9     Rate of Notifications  . . . . . . . . . . . . . . . . . .  7
   3.10    State Agents . . . . . . . . . . . . . . . . . . . . . . .  7
   4.      Conference Data Format . . . . . . . . . . . . . . . . . .  8
   4.1     Conference Information . . . . . . . . . . . . . . . . . .  8
   4.1.1   User Element . . . . . . . . . . . . . . . . . . . . . . .  8  9 User Statuses  . . . . . . . . . . . . . . . . . . . . . .  9 Media Stream Information . . . . . . . . . . . . . . . . .  9 10
   4.1.2   Sidebar  . . . . . . . . . . . . . . . . . . . . . . . . . 10 11
   4.1.3   Additional Conference Identifiers  . . . . . . . . . . . . 11
   4.1.4   Policy URIs  . . . . . . . . . . . . . . . . . . . . . . . 11
   4.2     Constructing Coherent State  . . . . . . . . . . . . . . . 10 11
   4.3     Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 11 12
   4.4     Example  . . . . . . . . . . . . . . . . . . . . . . . . . 13 15
   5.      Security Considerations  . . . . . . . . . . . . . . . . . 15 16
   6.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 16 17
   6.1     conference Event Package Registration  . . . . . . . . . . 16 17
   6.2     application/conference-info+xml MIME Registration  . . . . 16 17
   6.3     URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:conference-info . . . . . . . . . . 17 18
   6.4     XML Schema Registration  . . . . . . . . . . . . . . . . . 18 19
   7.      Acknowledgements . . . . . . . . . . . . . . . . . . . . . 19 20
   8.      Changes since -02  . . . . . . . . . . . . . . . . . . . . 21
   9.      Changes since -01  . . . . . . . . . . . . . . . . . . . . 20 22
           Normative References . . . . . . . . . . . . . . . . . . . 21 23
           Informative References . . . . . . . . . . . . . . . . . . 22 24
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 22 24
           Intellectual Property and Copyright Statements . . . . . . 23 26

1. Introduction

   The Session Initiation Protocol (SIP) [3] Events framework [2]
   defines general mechanisms for subscribing to, and receiving
   notifications of, events within SIP networks. It introduces the
   notion of a package, which is a specific "instantiation" of the
   events framework for a well-defined set of events. Here, we define an
   event package for SIP conferences. This package provides the
   conference notification service as outlined in the SIP conferencing
   framework [9]. As described there, subscriptions to a conference URI
   are routed to the focus that is handling the conference. It acts as
   the notifer, and provides clients with updates on conference state.

   The information provided by this package is comprised of conference
   identifier(s), conference participants (optionally with their
   statuses and media types) and conference sidebars.

2. Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

3. Conference Event Package

   The conference event package allows a user to subscribe to a
   conference. In SIP, conferences are represented by URIs. These URIs
   route to a SIP user agent, called a focus, that is responsible for
   ensuring that all users in the conference can communicate with each
   other [9]. The focus has sufficient information about the state of
   the conference to inform subscribers about it.

   It is possible a participant in the conference may in fact be another
   focus.  In order to provide a more complete participant list, the
   focus MAY subscribe to the conference package of the other focus to
   discover the participant list in the cascaded conference.  This
   information can then be included in notifications by using of the
   "cascaded-focus" attribute as specified by this package.

   This section provides the details for defining a SIP Events package,
   as specified by [2].

3.1 Event Package Name

   The name of this event package is "conference". This package name is
   carried in the Event and Allow-Events header, as defined in [2].

3.2 SUBSCRIBE Bodies

   A SUBSCRIBE for a dialog conference package MAY contain a body. This body
   defines a filter to apply to the subscription. Filter documents are
   not specified in this document, and at the time of writing, are
   expected to be the subject of future standardization activity.

   A SUBSCRIBE for a dialog conference package MAY be sent without a body. This
   implies the default subscription filtering policy. The default policy

   o  Notifications are generated every time there is any change in the
      state of the conference.

   o  Notifications do not normally contain full state; rather, they
      only indicate the state that has changed. The exception is a
      NOTIFY sent in response to a SUBSCRIBE. These NOTIFYs contain the
      full state of the information requested by the subscriber.

3.3 Subscription Duration

   The default expiration time for a subscription to a conference is one
   hour. Once the conference ends, all subscriptions to that particular
   conference are terminated, with a reason of "noresource" [2].

3.4 NOTIFY Bodies

   As described in RFC 3265 [2], the NOTIFY message will contain bodies
   that describe the state of the subscribed resource. This body is in a
   format listed in the Accept header field of the SUBSCRIBE, or a
   package-specific default if the Accept header field was omitted from

   In this event package, the body of the notification contains a
   conference information document. This document describes the state of
   a conference. All subscribers and notifiers  MUST support the
   "application/conference-info+xml" data format described in Section 4.
   The subscribe request MAY contain an Accept header field. If no such
   header field is present, it has a default value of "application/
   conference-info+xml". If the header field is present, it MUST include
   "application/conference-info+xml", and MAY include any other types
   capable of representing dialog state.

   Of course, the notifications generated by the server MUST be in one
   of the formats specified in the Accept header field in the SUBSCRIBE

3.5 Notifier Processing of SUBSCRIBE Requests

   The conference information contains very sensitive information.
   Therefore, all subscriptions SHOULD be authenticated and then
   authorized before approval. Authorization policy is at the discretion
   of the administrator, as always. However, a few recommendations can
   be made.

   It is RECOMMENDED that all users in the conference be allowed to
   subscribe to the conference.

3.6 Notifier Generation of NOTIFY Requests

   Notifications SHOULD be generated for the conference whenever there
   is a change in the state in any of the information delivered to the

   The changes generally occur when a new participant joins, a
   participant leaves, or a participant is put on-hold. Subject to a
   local focus policy, changes in media types and other optional media
   attributes MAY be reported by the focus. In addition, creation and
   deletion of sidebars together with their rosters MAY be reported by
   the focus, subject to its local policy.

3.7 Subscriber Processing of NOTIFY Requests

   The SIP Events framework expects packages to specify how a subscriber
   processes NOTIFY requests in any package specific ways, and in
   particular, how it uses the NOTIFY requests to contruct a coherent
   view of the state of the subscribed resource.

   Typically, the NOTIFY for the conference package will only contain
   information about those users whose state in the conference has
   changed. To construct a coherent view of the total state of all
   users, a subscriber to the dialog conference package will need to combine
   NOTIFYs received over time.

   Notifications within this package can convey partial information;
   that is, they can indicate information about a subset of the state
   associated with the subscription. This means that an explicit
   algorithm needs to be defined in order to construct coherent and
   consistent state. The details of this mechanism are specific to the
   particular document type. See Section 4.2 for information on
   constructing coherent information from an application/
   conference-info+xml document.

3.8 Handling of Forked Requests

   By their nature, the conferences supported by this package are
   centralized. Therefore, SUBSCRIBE requests for a conference should
   not generally fork. Users of this package MUST NOT install more than
   a single subscription as a result of a single SUBSCRIBE request.

3.9 Rate of Notifications

   For reasons of congestion control, it is important that the rate of
   notifications not become excessive. As a result, it is RECOMMENDED
   that the server not generate notifications for a single subscriber at
   a rate faster than once every 5 seconds.

3.10 State Agents

   Conference state is ideally maintained in the element in which the
   conference resides. Therefore, the elements that maintain the
   conference are the ones best suited to handle subscriptions to it.
   Therefore, the usage of state agents is NOT RECOMMENDED for this

4. Conference Data Format

   Conference information is an XML document that MUST be well-formed
   and SHOULD be valid. Dialog information documents MUST be based on
   XML 1.0 and MUST be encoded using UTF-8. This specification makes use
   of XML namespaces for identifying dialog information documents and
   document fragments. The namespace URI for elements defined by this
   specification is a URN [4], using the namespace identifier 'ietf'
   defined by [5] and extended by [6]. This URN is:


   A conference information document begins with the root element tag

4.1 Conference Information

   Conference information begins with the top level element
   "conference-info". This element has three mandatory and one optional

   version: This mandatory attribute allows the recipient of conference
      information documents to properly order them. Versions start at 0
      and increment by one for each new document sent to a subscriber.
      Versions are scoped within a subscription. Versions MUST be
      represented using a 32 bit integer.

   state: This mandatory attribute indicates whether the document
      contains the full conference information, or whether it contains
      only the information that has changed since the previous document

   entity: This mandatory attribute contains the conference URI that
      identifies the conference being described in the document.

   recording: This optional attribute indicates whether the conference
      is being recorded at this moment ("on") or not ("off").

   The "conference-info" element has zero or more "user" sub-elements
   which contain information on the users in the conference. This is
   followed by zero or more "sidebar" sub-elements which contain
   information on the sidebars in the conference. This is followed by
   zero or more "conf-uri" sub-elements which contain information on
   additional URIs that the conference can be accessed by. This is
   followed by zero or more "policy-uri" sub-elements which contain
   information on additional URIs that the conference policies can be
   accessed by.

4.1.1 User Element

   The user element has one mandatory attribute, "uri" that indicates
   the URI for the user in the conference. This is a logical identifier,
   not a machine specific one (i.e., it's taken from the authenticated
   identity of the participant). The optional attribute "display-name"
   contains a display name for the user. The standard "xml:lang"
   language attribute can also be present to indicate the language of
   the display-name. User Statuses


   The optional status elements attribute "cascaded-focus" contains a conference URI
   (different from the main conference URI) for users that are defined: activity-status and history
   status. "Activity-status" provides information about user's current
   level of participation in connected
   to the main conference as a result of focus cascading. In accordance
   with the SIP conferencing framework [9], this defined package allows
   for representation of peer-to-peer (i.e. "flat") focus cascading
   only. The actual cascading graph is not explicitly expressed in this
   package because most applications do not care about the actual
   topology of the cascaded focuses as long as the information about
   their participants is available. In addition, an advanced application
   can construct the graph by subscribing to both this package and the
   Dialog Package [10] of the involved focuses and correlating the
   required information. User Statuses

   Three optional status elements are defined: status, joining-mode, and

   o  "status": provides information about user's current level of
      participation in the conference. "History-status",

   o  "joining-mode": if present, provides information about the way the
      user joined or left the conference. Additional optional indication "is-on-dial-out-list"
   completes the

   o  "disconnection-reason": if present, provides information about the
      way the user membership in left the conference.

   The following statuses are defined for the activity-status "status" element:

   connected: The user is a participant in the conference. Depending on
      the media policies, he/she can send and receive media to and from
      other participants.

   disconnected: The user is not a participant in the conference and no
      active dialog exists between the user and the focus.

   on-hold: Active SIP dialog exists between a user and a focus, but
      user is "on-hold" for this conference, i.e. neither he/she is
      "hearing" the conference mix, nor is his/her media being mixed in
      the conference. As an example, the user has asked to join the
      conference using SIP, but his/her participation is pending based
      on moderator approval. In the meantime he/she is hearing
      music-on-hold or some other kind of related content.

   muted-by-focus: Active SIP dialog exists between a user and a focus
      and the user can "listen" to the conference, but user's media is
      not being mixed into the conference.

   The following statuses are defined for the history-status "joining-mode" element:

   dialed-in: The user dialed into the conference, i.e. sent INVITE to
      the focus, which resulted in successful dialog establishment.

   dialed-out: The focus has brought the user into the conference by
      sending a successful INVITE to the user.

   focus-owner: The user is the focus itself for this conference.

   The following statuses are defined for the disconnection-reason

   departed: The user sent a BYE, thus leaving the conference.

   booted: The user was sent a BYE by the focus, booting him/her out of
      the conference. Alternatively, the user tried to dial into to
      conference without success because was rejected by the focus
      according to local policy decisions.

   failed: The server tried to bring the user into the conference, but
      its attempt to contact the specific user resulted in a non-200
      class final response. Alternatively, the user tried to dial into
      the conference without success due to technical reasons. Media Stream Information

   Each user has zero or more "media-stream" sub-elements.

   Each "media-stream" element indicates the media stream that the user
   is currently connected to. Here, "connected to" implies that a user
   has a media line in their SDP [10]. [12]. With this definition, a user is
   connected to a media stream even if they are not sending any media.

   The "media-stream" element has a mandatory "media-type" attribute
   which identifies the media type (e.g. audio, video, message and
   application) and MUST have one of the values registered for "media"
   of SDP [10]. [12].

   The "media-stream" element has also an optional "proto" sub-element,
   which MUST has the value registered for "proto" of SDP [10]). [12]).

   An optional "ssrc" sub-element, if present, carries the value of SSRC
   (RTP/RTCP [8]) as generated by the user for the stream it sends.

   When an RTP mixer generates a CSRC list according to RTP/RTCP [8], it
   inserts a list of the SSRC identifiers of the sources that
   contributed to the generation of a particular packet into the RTP
   header of that packet. "An example application is audio conferencing
   where a mixer indicates all the talkers whose speech was combined to
   produce the outgoing packet, allowing the receiver to indicate the
   current talker, even though all the audio packets contain the same
   SSRC identifier (that of the mixer)."

4.1.2 Sidebar

   The sidebar element has one attribute - "entity" that indicates the
   URI which identifiers the sidebar. A sidebar has zero or more users
   that are of type "user-type" as the users of the main conference are.

4.1.3 Additional Conference Identifiers

   In addition to the Conference URI present in the "entity" attribute,
   a conference MAY have additional URIs of various types. Connecting to
   these URIs will result in joining to the same conference.

4.1.4 Policy URIs

   A policy URI specifies where and how a certain policy pertaining to
   the conference can be accessed. The actual policy name and usage is
   deduced from the URI schema name.

   An example for the "policy-uri" usage is inclusion of the URI of the
   CPCP [11]. A subscriber to the Conference package can use the Policy
   URI to access and modify the conference policy.

4.2 Constructing Coherent State

   The conference information subscriber maintains a table for the list
   of users in the conference. The table contains a row for each user.
   Each row is indexed by a URI, present in the "uri" attribute of the
   "user" element. The contents of each row contain the state of that
   user as conveyed in the document.

   The table is associated with a version number. The version number
   MUST be initialized with the value of the "version" attribute from
   the "conference-info" element in the first document received. Each
   time a new document is received, the value of the local version
   number, and the "version" attribute in the new document, are
   compared. If the value in the new document is one higher than the
   local version number, the local version number is increased by one,
   and the document is processed. If the value in the document is more
   than one higher than the local version number, the local version
   number is set to the value in the new document, the document is
   processed, and the subscriber SHOULD generate a refresh request to
   trigger a full state notification. If the value in the document is
   less than the local version, the document is discarded without

   The processing of the conference information document depends on
   whether it contains full or partial state. If it contains full state,
   indicated by the value of the "state" attribute in the
   "conference-info" element, the contents of the table is flushed. It
   is repopulated from the document. A new row in the user table is
   created for each "user" element. If the document contains partial
   state, as indicated by the value of the "state" attribute in the
   "conference-info" element, the document is used to update the table.
   For each "user" element in the document, the subscriber checks to see
   whether a row exists for that user in the user table. This check is
   done by comparing the URI in the "uri" attribute of the "user"
   element with the URI associated with the row. If the user doesn't
   exist in the table, a row is added, and its state is set to the
   information from that "user" element. If the user does exist, its
   state is updated to be the information from that "user" element. If a
   row is updated or created, such that its state is now disconnected,
   booted, failed or departed, that entry MAY be removed from the table
   at any time.

4.3 Schema

   <?xml version="1.0" encoding="UTF-8" ?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:conference-info" xmlns:tns="urn:ietf:params:xml:ns:conference-info" xmlns:xs="" xmlns="urn:ietf:params:xml:ns:conference-info" elementFormDefault="qualified" attributeFormDefault="unqualified">
    This import brings in the XML language attribute xml:lang
     <xs:import namespace="" schemaLocation="" />

   <xs:element name="conference-info">

     <xs:element name="user" type="user-type" minOccurs="0" maxOccurs="unbounded" />
     <xs:element name="sidebar" type="sidebar-type" minOccurs="0" maxOccurs="unbounded" />
     <xs:element name="conf-uri" type="xs:anyURI" minOccurs="0" maxOccurs="unbounded" />
     <xs:element name="policy-uri" type="xs:anyURI" minOccurs="0" maxOccurs="unbounded" />
     <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />

     <xs:attribute name="version" type="xs:nonNegativeInteger" use="required" />
     <xs:attribute name="state" use="required">
        <xs:restriction base="xs:string">
           <xs:enumeration value="full" />
           <xs:enumeration value="partial" />

     <xs:attribute name="entity" type="xs:anyURI" use="required" />
     <xs:attribute name="recording" type="tns:recording-type" use="optional" />

     <xs:anyAttribute />


   <xs:complexType name="user-type">
     <xs:element name="activity-status" type="tns:activity-status-type" name="status" type="tns:status-type" minOccurs="0" />
     <xs:element name="history-status" type="tns:history-status-type" name="joining-mode" type="tns:joining-mode-type" minOccurs="0" />
     <xs:element name="is-on-dial-out-list" type="xs:boolean" name="disconnection-reason" type="tns:disconnection-reason-type" minOccurs="0" />
     <xs:element name="media-stream" type="tns:media-stream-type" minOccurs="0" maxOccurs="unbounded" />
     <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />

     <xs:attribute name="uri" type="xs:anyURI" use="required" />
     <xs:attribute name="display-name" type="xs:string" use="optional" />
     <xs:attribute ref="xml:lang" use="optional" />
     <xs:attribute name="cascaded-focus" type="xs:anyURI" use="optional" />
     <xs:anyAttribute />


   <xs:complexType name="sidebar-type">
     <xs:element name="user" type="user-type" minOccurs="0" maxOccurs="unbounded" />
     <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />

     <xs:attribute name="entity" type="xs:anyURI" use="required" />

   <xs:complexType name="media-stream-type">
     <xs:element name="proto" type="xs:string" minOccurs="0" />
     <xs:element name="ssrc" type="xs:nonNegativeInteger" minOccurs="0" />
     <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />

     <xs:attribute name="media" type="xs:string" use="required" />

   <xs:simpleType name="activity-status-type"> name="status-type">
    <xs:restriction base="xs:string">
     <xs:enumeration value="connected" />
     <xs:enumeration value="disconnected" />
     <xs:enumeration value="on-hold" />
     <xs:enumeration value="muted-by-focus" />

   <xs:simpleType name="history-status-type"> name="joining-mode-type">
    <xs:restriction base="xs:string">
     <xs:enumeration value="dialed-in" />
     <xs:enumeration value="dialed-out" />
     <xs:enumeration value="focus-owner" />

   <xs:simpleType name="disconnection-reason-type">
    <xs:restriction base="xs:string">
     <xs:enumeration value="departed" />
     <xs:enumeration value="booted" />
     <xs:enumeration value="failed" />

   <xs:simpleType name="recording-type">
    <xs:restriction base="xs:string">
     <xs:enumeration value="on" />
     <xs:enumeration value="off" />


4.4 Example

   The following is an example conference information document:

   <conference-info version="0" state="full" entity=""> entity="" recording="on">

     <user uri="" display-name="Bob Jones">
       <media-stream media-type="audio" media-type="audio">
          <proto> RTP/AVP <proto> </proto>
          <ssrc> 583398 <ssrc> </ssrc>

     <user uri="" display-name="Barbara Jones">

     <user uri="" display-name="Bill Minelli">

     <sidebar entity="">
       <user uri="">
       <user uri="">



   This document describes a conference with currently has three users, two of which are in a
   sidebar conversation. The conference is being recorded. There are
   additional means to join the conference either by phone using tel URI
   [14] or by H.323 protocol using h323 URL [13].

5. Security Considerations

   Subscriptions to conference state can reveal very sensitive
   information. For this reason, the document recommends authentication
   and authorization, and provides guidelines on sensible authorization

   Since the data in notifications is sensitive as well, end-to-end SIP
   encryption mechanisms using S/MIME SHOULD be used to protect it.

6. IANA Considerations

   This document registers a SIP event package, a new MIME type,
   application/conference-info+xml, a new XML namespace, and a new XML

6.1 conference Event Package Registration

   This specification registers an event package, based on the
   registration procedures defined in RFC 3265 [2]. The following is the
   information required for such a registration:

   Package Name: conference

   Package or Template-Package: This is a package.

   Published Document: RFC XXXX (Note to RFC Editor: Please fill in XXXX
      with the RFC number of this specification).

   Person to Contact: Jonathan Rosenberg,

6.2 application/conference-info+xml MIME Registration

   MIME media type name: application

   MIME subtype name: conference-info+xml

   Mandatory parameters: none

   Optional parameters: Same as charset parameter application/xml as
      specified in RFC 3023 [7].

   Encoding considerations: Same as encoding considerations of
      application/xml as specified in RFC 3023 [7].

   Security considerations: See Section 10 of RFC 3023 [7] and Section 5
      of this specification.

   Interoperability considerations: none.

   Published specification: This document.

   Applications which use this media type: This document type has been
      used to support SIP conferencing applications.

   Additional Information:

      Magic Number: None

      File Extension: .cif or .xml

      Macintosh file type code: "TEXT"

   Personal and email address for further information: Jonathan
      Rosenberg, <>

   Intended usage: COMMON

   Author/Change controller: The IETF.

6.3 URN Sub-Namespace Registration for

   This section registers a new XML namespace, as per the guidelines in

   URI: The URI for this namespace is

   Registrant Contact: IETF, SIPPING working group, <>,
      Jonathan Rosenberg <>.


   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
   <html xmlns="">
     <meta http-equiv="content-type"
     <title>Conference Information Namespace</title>
     <h1>Namespace for Conference Information</h1>
     <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>

6.4 XML Schema Registration

   This specification registers a schema, as per the guidelines in in

      URI: please assign.

      Registrant Contact: IETF, SIPPING Working Group
      (, Jonathan Rosenberg (

      XML: The XML can be found as the sole content of Section 4.3.

7. Acknowledgements

   The authors would like to thank Dan Petrie and Petrie, Sean Olson Olson, and Alan
   Johnston for their comments.

8. Changes since -02

   o  State "muted-by-focus" is added to user's status.

   o  Optional conference attribute "recording" is added.

   o  Policy URI placeholder (i.e. element "policy-uri") is created.

   o  Example∆s syntax is corrected.

   o  Optional attribute "cascaded-focus" URI per user is added.

   o  Optional additional conference identifiers (i.e. element
      "conf-uri") are added.

   o  In order to cover all possible cases, participant's status is
      expressed using three optional statuses: "status", "joining-mode"
      and "disconnection-reason". That is instead of "activity-status",
      "history-status" and "is-on-dial-out-list".

9. Changes since -01

   o  Package parameters are removed. Decision about performing
      "recursive" membership algorithm is perceived as a focus local

   o  General information (i.e. pointers to additional available
      services) is removed. The defined XML schema can be extended in
      future to include those when XCON work matures.

   o  Dialog information is removed. It can be obtained by direct
      subscription to a dialog package of a participant.

   o  Media stream information is aligned with SDP definitions (media
      and proto) and SSRC attribute is added.

   o  Participant's status is expressed using two optional statuses:
      "activity" and "history". Optional "is-on-a-dial-out-list"
      indication is added.

   o  Normative references to XCON work are removed.

   o  Optional sidebar rosters are added.

Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
        Notification", RFC 3265, June 2002.

   [3]  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.

   [4]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [5]  Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
        August 1999.

   [6]  Mealling, M., "The IETF XML Registry",
        draft-mealling-iana-xmlns-registry-05 (work in progress), June

   [7]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
        3023, January 2001.

   [8]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", RFC
        3550, July 2003.

Informative References

   [9]   Rosenberg, J., "A Framework for Conferencing with the Session
         Initiation Protocol",
         draft-ietf-sipping-conferencing-framework-01 (work in
         progress), May October 2003.

   [10]  Rosenberg, J. and H. Schulzrinne, "An INVITE Inititiated Dialog
         Event Package for the Session Initiation  Protocol (SIP)",
         draft-ietf-sipping-dialog-package-03 (work in progress),
         October 2003.

   [11]  Koskelainen, P., "Requirements for Conference Policy Control
         Protocol", draft-ietf-xcon-cpcp-reqs-02 (work in progress),
         February 2004.

   [12]  Handley, M. and V. Jacobson, "SDP: Session Description
         Protocol", RFC 2327, April 1998.

   [13]  Levin, O., "H.323 Uniform Resource Locator (URL) Scheme
         Registration", RFC 3508, April 2003.

   [14]  Schulzrinne, H., "The tel URI for Telephone Numbers",
         draft-ietf-iptel-tel-rfc2806bis-03 (work in progress), February

Authors' Addresses

   Jonathan Rosenberg
   600 Lanidex Plaza
   Parsippany, NJ  07054

   Phone: +1 973 952-5000
   Henning Schulzrinne
   Columbia University
   M/S 0401
   1214 Amsterdam Ave.
   New York, NY  10027


   Orit Levin (editor)
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052


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