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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 4575

SIPPING                                                     J. Rosenberg
Internet-Draft                                             Cisco Systems
Expires: January 2, 2006                                  H. Schulzrinne
                                                     Columbia University
                                                           O. Levin, Ed.
                                                   Microsoft Corporation
                                                            July 1, 2005


 A Session Initiation Protocol (SIP) Event Package for Conference State
                draft-ietf-sipping-conference-package-12

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   This Internet-Draft will expire on January 2, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines a conference event package for tightly coupled
   conferences using 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



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   membership of this conference and optionally about changes in the
   state of additional conference components.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Conference Event Package . . . . . . . . . . . . . . . . . . .  4
     3.1   Event Package Name . . . . . . . . . . . . . . . . . . . .  5
     3.2   Filtering  . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3   Subscription Duration  . . . . . . . . . . . . . . . . . .  5
     3.4   NOTIFY Bodies  . . . . . . . . . . . . . . . . . . . . . .  5
     3.5   Notifier Processing of SUBSCRIBE Requests  . . . . . . . .  6
     3.6   Notifier Generation of NOTIFY Requests . . . . . . . . . .  6
     3.7   Subscriber Processing of NOTIFY Requests . . . . . . . . .  6
     3.8   Handling of Forked Requests  . . . . . . . . . . . . . . .  7
     3.9   Rate of Notifications  . . . . . . . . . . . . . . . . . .  7
     3.10  State Agents . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Conference Document  . . . . . . . . . . . . . . . . . . . . .  7
     4.1   Format . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2   Namespace  . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.3   Versioning . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.4   Partial Notifications Mechanism  . . . . . . . . . . . . .  8
     4.5   Element Keys . . . . . . . . . . . . . . . . . . . . . . .  9
     4.6   Constructing Coherent State Procedure  . . . . . . . . . .  9
   5.  Conference Data  . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.2   <conference-info>  . . . . . . . . . . . . . . . . . . . . 13
     5.3   <conference-description> . . . . . . . . . . . . . . . . . 14
       5.3.1   <conf-uris>  . . . . . . . . . . . . . . . . . . . . . 14
       5.3.2   <service-uris> . . . . . . . . . . . . . . . . . . . . 15
       5.3.3   <maximum-user-count> . . . . . . . . . . . . . . . . . 16
       5.3.4   <available-media>  . . . . . . . . . . . . . . . . . . 16
     5.4   <host-info>  . . . . . . . . . . . . . . . . . . . . . . . 17
       5.4.1   <display-text> . . . . . . . . . . . . . . . . . . . . 17
       5.4.2   <web-page> . . . . . . . . . . . . . . . . . . . . . . 17
       5.4.3   <uris> . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.5   <conference-state> . . . . . . . . . . . . . . . . . . . . 17
       5.5.1   <user-count> . . . . . . . . . . . . . . . . . . . . . 17
       5.5.2   <active> . . . . . . . . . . . . . . . . . . . . . . . 17
       5.5.3   <locked> . . . . . . . . . . . . . . . . . . . . . . . 18
     5.6   <users> and its <user> sub-elements  . . . . . . . . . . . 18
       5.6.1   <display-text> . . . . . . . . . . . . . . . . . . . . 19
       5.6.2   <associated-aors>  . . . . . . . . . . . . . . . . . . 19
       5.6.3   <roles>  . . . . . . . . . . . . . . . . . . . . . . . 19
       5.6.4   <languages>  . . . . . . . . . . . . . . . . . . . . . 19
       5.6.5   <cascaded-focus> . . . . . . . . . . . . . . . . . . . 19
       5.6.6   <endpoint> . . . . . . . . . . . . . . . . . . . . . . 19



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     5.7   <endpoint> . . . . . . . . . . . . . . . . . . . . . . . . 20
       5.7.1   <display-text> . . . . . . . . . . . . . . . . . . . . 20
       5.7.2   <referred> . . . . . . . . . . . . . . . . . . . . . . 20
       5.7.3   <status> . . . . . . . . . . . . . . . . . . . . . . . 21
       5.7.4   <joining-method> . . . . . . . . . . . . . . . . . . . 22
       5.7.5   <joining-info> . . . . . . . . . . . . . . . . . . . . 22
       5.7.6   <disconnection-method> . . . . . . . . . . . . . . . . 23
       5.7.7   <disconnection-info> . . . . . . . . . . . . . . . . . 23
       5.7.8   <media>  . . . . . . . . . . . . . . . . . . . . . . . 24
       5.7.9   <call-info>  . . . . . . . . . . . . . . . . . . . . . 24
     5.8   <media>  . . . . . . . . . . . . . . . . . . . . . . . . . 24
       5.8.1   <display-text> . . . . . . . . . . . . . . . . . . . . 25
       5.8.2   <type> . . . . . . . . . . . . . . . . . . . . . . . . 25
       5.8.3   <label>  . . . . . . . . . . . . . . . . . . . . . . . 25
       5.8.4   <src-id> . . . . . . . . . . . . . . . . . . . . . . . 25
       5.8.5   <status> . . . . . . . . . . . . . . . . . . . . . . . 26
     5.9   Sidebars . . . . . . . . . . . . . . . . . . . . . . . . . 26
       5.9.1   <sidebars-by-ref>  . . . . . . . . . . . . . . . . . . 26
       5.9.2   <sidebar-by-val> . . . . . . . . . . . . . . . . . . . 26
   6.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 26
   7.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     7.1   Basic Example  . . . . . . . . . . . . . . . . . . . . . . 35
     7.2   Rich Example . . . . . . . . . . . . . . . . . . . . . . . 36
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 40
     8.1   Connection Security  . . . . . . . . . . . . . . . . . . . 40
     8.2   Authorization Considerations . . . . . . . . . . . . . . . 41
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 41
     9.1   conference Event Package Registration  . . . . . . . . . . 41
     9.2   application/conference-info+xml MIME Registration  . . . . 42
     9.3   URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:conference-info . . . . . . . . . . 42
     9.4   XML Schema Registration  . . . . . . . . . . . . . . . . . 43
     9.5   URI Purposes Sub-registry Establishment  . . . . . . . . . 43
   10.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44
   11.   References . . . . . . . . . . . . . . . . . . . . . . . . . 45
     11.1  Normative References . . . . . . . . . . . . . . . . . . . 45
     11.2  Informative References . . . . . . . . . . . . . . . . . . 46
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 47
       Intellectual Property and Copyright Statements . . . . . . . . 48












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1.  Introduction

   The Session Initiation Protocol (SIP) Events Framework [10] 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 a SIP event
   package for tightly coupled conferences.  This package can be used by
   the conference notification service as outlined in the SIP
   conferencing framework [16].  As described there, subscriptions to a
   conference URI are routed to the focus that is handling the
   conference.  It acts as the notifier, 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 description), conference sidebars, conference
   service URIs, etc.

2.  Terminology

   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 uses the conferencing terminology defined in
   Conferencing Framework [16].  In addition, the "roster" term is used
   to collectively refer to participants in a conference or a sub-
   conference.

3.  Conference Event Package

   The conference event package allows a user to subscribe to the
   information relating to a conference.  In SIP, conferences are
   represented by URIs.  These URIs identify a SIP user agent, called a
   focus, that is responsible for ensuring that all users in the
   conference can communicate with each other, as described in
   Conferencing Framework [16].  The focus has sufficient information
   about the state of the conference to inform subscribers about it.

   It is possible that 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 use of the
   <cascaded-focus> element as specified by this package.




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   This section provides the details for defining a SIP-specific event
   notification package, as specified by RFC 3265 [10].

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 RFC 3265
   [10].

3.2  Filtering

   Filters, which can be applied to conference subscriptions, are a
   desirable feature and can be considered as a subject of future
   standardization activities.  This document does not define the
   filters for the conference package to be included in the SUBSCRIBE
   body.

   A SUBSCRIBE for a conference package, being sent without a body,
   implies the default subscription filtering policy.  The default
   policy is:
   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" as defined
   in RFC 3265 [10].

3.4  NOTIFY Bodies

   According to RFC 3265 [10], 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
   the SUBSCRIBE.

   In this event package, the body of the notification contains a
   conference information document that describes the state of a
   conference.  All subscribers and notifiers MUST support the
   "application/conference-info+xml" data format described in Section 5.
   By default, i.e. if no Accept header is specified to a SUBSCRIBE
   request, the NOTIFY will contain a body in the "application/



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   conference-info+xml" data format.  If the Accept header field is
   present, it MUST include "application/conference-info+xml" and MAY
   include any other types.

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, it is RECOMMENDED that all users in the conference be
   allowed to subscribe to the conference event package.

3.6  Notifier Generation of NOTIFY Requests

   Notifications SHOULD be generated for the conference state when a new
   participant joins (i.e. gets "connected" to) or a participant leaves
   (i.e. gets "disconnected" from) the conference.

   Subject to a local focus policy, additional changes in participants'
   status, changes in their media types, and other optional information
   MAY be reported by the focus.

   Changes in sidebar rosters SHOULD be reported by the focus to their
   participants and MAY be reported to others, subject to local policy.

   Changes in conference identifiers and service URIs SHOULD be reported
   by the focus to the Conference package subscribers.

   Changes in other conference state information MAY be reported by the
   focus to the Conference package subscribers.

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 construct 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 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



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   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 4.6 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.  If forking happens in the network, subscribers
   to this package MUST NOT establish more than a single SIP dialog as a
   result of a single SUBSCRIBE request.  In the foci cascading case,
   detailed conference information can be retrieved by establishing an
   individual SUBSCRIBE dialog with each participating focus.

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 doesn't 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, a conference focus is the best suited
   element to handle subscriptions to it.  Cascaded foci MAY implement
   state agents (as defined in RFC 3265 [10]) for this package.

4.  Conference Document

4.1  Format

   Conference information is an XML document that MUST be well-formed
   and valid.  It MUST be based on Extensible Markup Language (XML) 1.0
   and MUST be encoded using UTF-8 [14].

4.2  Namespace

   This specification makes use of XML namespaces for identifying
   conference information documents and document fragments.  The
   namespace URI for elements defined by this specification is a URN
   [2], using the namespace identifier 'ietf' defined by [6] and
   extended by RFC 3688 [21].  This URN is:

   urn:ietf:params:xml:ns:conference-info



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4.3  Versioning

   The conference information is described by a hierarchal XML structure
   with the root element <conference-info>.  The root element is the
   only element in the schema that carries meaningful version number for
   all the elements in the document.  The whole conference information
   is associated with this version number.

   The 'version' attribute MUST be included in the root <conference-
   info> element.

4.4  Partial Notifications Mechanism

   This specification defines a basic partial notifications mechanism by
   using a 'state' attribute as described below.  This mechanism MUST be
   supported by all subscribing clients.  Additional general partial
   notifications mechanisms can be defined and applied to this package
   in the future.

   All sub-elements in the <conference-info> hierarchal XML structure
   can be classified in two groups: permissible for partial
   notifications or not.  Elements that carry a substantial amount of
   data that is subject to frequent changes are permissible for partial
   notifications and have a 'state' attribute attached to them.  All
   future extensions to this schema MUST define which extension elements
   can also use this mechanism.  All other elements can be updated as
   atomic pieces of data only.

   Below is the complete list of elements permissible to use the partial
   notifications mechanism defined in this specification.  (Note that
   future partial notifications mechanisms can potentially be applicable
   to additional elements.)

   o  Element <conference-info>
   o  Element <users>
   o  Element <user>
   o  Element <endpoint>
   o  Element <sidebars-by-val>
   o  Element <sidebars-by-ref>

   The 'state' attribute value indicates whether the reported
   information about the element is "full", "partial" or the element is
   "deleted" from the conference state document.  The default value of
   any 'state' attribute is "full".

   A 'state' attribute of a child element in the document MUST be
   consistent with its parent 'state'.  This means that if the parent's
   'state' is "full", the state of its children MUST be "full".  If the



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   parent's 'state' is "partial", the state of its children MAY be
   either "partial", "full", or "deleted".  A parent element with
   "deleted" 'state' SHOULD NOT contain child elements.  Any information
   provided for child elements of a "deleted" parent MUST be ignored by
   the package subscriber.

4.5  Element Keys

   The defined XML schema has a property of unique identification among
   sub-elements of a common parent, which makes it possible to use the
   partial notifications mechanism defined in this document.  This
   property is achieved by defining a key to each sub-element that can
   appear multiple times under the common parent.

   In the context of this specification, the element key is the set of
   mandatory attributes or sub-elements of an element.  The key value
   MUST be unique for the element among its siblings of the same type.

   In the context of this specification, two keys of type xs:anyURI are
   considered to be equal if the UTF-8 representations of the keys
   (including all URI parameters that can be included with the URI) are
   identical.  Consequently, it is NOT RECOMMENDED using relative URIs
   and lexical white space in these keys.

   Below is the list of elements (subject to partial notifications of
   their parent elements) with their keys as defined by this
   specification:

   o  Element <user> uses as the key 'entity'
   o  Element <endpoint> uses as the key 'entity'
   o  Element <media> uses as the key 'id'
   o  Element <entry> (child to <sidebars-by-val>) uses as the key
      'entity'
   o  Element <sidebars-by-ref> uses as the key <uri>

4.6  Constructing Coherent State Procedure

   This section describes the algorithm for constructing a coherent
   conference state by a subscriber to the conference package.  Using
   software programming abstraction, the subscriber maintains a single
   local version number for the whole conference document and a local
   element instance for each element in the schema.  Also, for each
   element with keys (as defined above), the subscriber maintains a
   virtual table with a row for each existing key value.

   The first time a NOTIFY with a "full" document is received (as
   indicated by the value of the 'state' attribute in the <conference-
   info> element), the conference package subscriber MUST set the local



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   'version' number to the value of the 'version' attribute from the
   received <conference-info> and populate local data with the received
   information.

   Each time a new NOTIFY is received, the value of the local version
   number and the value of the 'version' attribute in the new received
   document are compared.  If the value in the document is equal or less
   than the local version, the document is discarded without processing.

   Otherwise, if the received NOTIFY contains a "full" or "deleted"
   state, the conference package subscriber MUST set the local 'version'
   number to the value of the 'version' attribute from the received
   <conference-info> and replace the local information with the received
   document.  Receiving "deleted" state for the <conference-info>
   element means that the conference has ceased to exist and the
   subscriber SHOULD terminate the subscription by sending the SUBSCRIBE
   with Expires = 0.

   Otherwise (i.e. if the received NOTIFY contains "partial" state), if
   the 'version' number in the received document is more than one number
   higher than the previous local version number, the subscriber MUST
   generate a subscription refresh request to trigger a full state
   notification.  If the 'version' number in the document is one higher
   than the local version number, the local version number is updated
   accordingly and the document is used to update the local content as
   described below.

   For each sub-element of the <conference-info> element in the received
   document,

   1.  If the element contains "full" state, the whole local element
   content is flushed and repopulated from the document.

   2.  Otherwise, if the element contains "deleted" state, the whole
   element MUST be removed from the local content.

   3.  Otherwise, if the element contains "partial" state:

   3.1 For elements with keys, the subscriber compares the keys received
   in the update with the keys in the local tables.

   3.1.1 If a key does not exist in the local table, a row is added, and
   its content is set to the element information from the update.

   3.1.2 Otherwise, if a key of the same value does exist, for each sub-
   element in the row the algorithm is applied from step 3.2.

   3.2 For each atomic element received in the schema, the element is



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   replaced with the new information as a whole.  For each non-atomic
   element received in the schema with either no 'state' attribute
   included or the state attribute is set to "full", the element is
   replaced with the new information as a whole.  Also, for each element
   with the state attribute set to "deleted", the whole element is
   removed from the local content.

   3.3 For each non-atomic element with the state attribute set to
   "partial", the algorithm is applied recursively starting from step
   3.1.

5.  Conference Data

5.1  Overview

   The <conference-info> document format is designed to convey
   information about the conference and about participation in the
   conference.  The following non-normative diagram gives an example of
   the overall hierarchy used in this format.  Conferences contain users
   who can be represented by multiple endpoints, each of which can have
   multiple media streams.  Conferences can also include or reference
   "sidebar conferences".  When sidebar information is incorporated into
   a conference information document in a <sidebar-by-value> element,
   each <entry> element represents a sidebar and can include any sub-
   elements permitted in the <conference-info> top-level element.


























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   conference-info
     |
     |-- conference-description
     |
     |-- host-info
     |
     |-- conference-state
     |
     |-- users
     |    |-- user
     |    |    |-- endpoint
     |    |    |    |-- media
     |    |    |    |-- media
     |    |    |    |-- call-info
     |    |    |
     |    |    |-- endpoint
     |    |         |-- media
     |    |-- user
     |         |-- endpoint
     |              |-- media
     |

     |-- sidebars-by-ref
     |    |-- entry
     |    |-- entry
     |
     |-- sidebars-by-val
          |-- entry
          |    |-- users
          |         |-- user
          |         |-- user
          |-- entry
               |-- users
                    |-- user
                    |-- user
                    |-- user

   In most cases, this document doesn't mandate how the information,
   presented through the conference document to the subscribers, is
   obtained by the focus.  In many cases, the information can be
   dynamically learned from the call signaling and also be manually
   populated by an administrator - all subject to local policies.  This
   document specifies what the XML elements mean in order to allow the
   subscribers to appropriately interpret it.  Some portions of the
   information are intended for processing by automata, others are for
   human consumption only.  For example, the <display-text> sub-elements
   of elements <conf-uris>, <service-uris>, <available-media>, <host-
   info>, <endpoint>, and <media> are intended for display to human



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   subscribers only.

   Although in multiple places this document states that specific
   information "SHOULD" be communicated to the subscribers, note that
   particular conference package subscribers (e.g. representing a
   moderator, an administrator, or a cascaded focus) rely on accuracy of
   this information for their proper operation.  Therefore, a
   conferencing server MUST ensure that all critical changes (stated
   as "SHOULD") are communicated to these specific subscribers,
   otherwise these changes MUST be communicated to all subscribers to
   the conference information.

   Following sections describe the XML schema in more details.

5.2  <conference-info>

   A conference information document begins with the root element tag
   <conference-info> of conference-type.

   The following attributes are defined for <conference-info>:

   entity: This attribute contains the conference URI that identifies
      the conference being described in the document.  This is the SIP
      URI that an interested entity needs to SUBSCRIBE to in order to
      get the conference package information.  Note that this URI can be
      listed as one of the URIs to be used in order to access the
      conference by SIP means and in accordance with  Section 5.3.1
      below.

   state: This attribute indicates whether the document contains the
      whole conference information ("full"), only the information that
      has changed since the previous document ("partial"), or the
      conference ceased to exist ("deleted").  For more detail see
      Section 4.

   version: This attribute allows the recipient of conference
      information documents to properly order the received notifications
      and it MUST be used with the root <conference-info> element.
      Version number is a 32 bit monotonically increasing integer scoped
      within a subscription.  A server MUST increment the version number
      for each notification (full, partial, and deleted) being sent to a
      subscriber and reporting a change in the conference document
      state.  For each partial notification, the version number MUST be
      increased by one. Note that a partial notification and a
      subsequent full notification over the same dialog MAY contain the
      same version number if no change in the conference state occurred
      in between.




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   The <conference-info> element is comprised of <conference-
   description>, <host-info>, <conference-state>, <users>, <sidebar-by-
   ref> and <sidebars-by-val> child elements.  A "full" conference
   document MUST at least include the <conference-description> and
   <users> child elements.

   Following sections describe these elements in detail.  The full XML
   schema is provided in Section 6.

5.3  <conference-description>

   The <conference-description> element describes the conference as a
   whole.

   The child elements <display-text>, <subject>, <free-text>, and
   <keywords> are used to describe the conference content:

   <display-text>: Contains descriptive text suitable for human
      consumption, for example, listing in a directory

   <subject>: Contains the subject of the conference

   <free-text>: Contains an additional longer description of the
      conference

   <keywords>: Contains a list of space-separated string tokens that can
      be used by search engines to better classify the conference

   Additional child elements <conf-uris> and <service-uris> are used to
   describe the conference-related URIs; <maximum-user-count> and
   <available-media> are used to describe the overall characteristics.

   This information is typically derived from the system conference
   policies, is set before the conference activation, and is rarely
   changed during the conference lifetime.

   The following sections describe the remaining elements in more
   detail.  Other sub-elements can extend <conference-description> in
   the future.

5.3.1  <conf-uris>

   This element contains a sequence of <entry> child elements - each
   containing the URI to be used in order to access the conference by
   different signaling means.  The value of the URI MUST be unique in
   the conference context and is included in the <uri> sub-element.

   Each <entry> MAY contain additional information useful to the



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   participant when accessing the conference.

   An <entry> element MAY contain the <display-text> sub-element that
   provides a textual description meant for human consumption.

   Each <entry> element SHOULD contain a <purpose> sub-element that
   describes what happens when accessing the URI.  The currently defined
   <purpose> values to be used with the <conf-uris> are:

   participation: Accessing a URI with this <purpose> will bring the
      party into the conference
   streaming: Accessing a URI with this <purpose> will commence
      streaming the conference, but not allow active participation

   Examples of suitable URI schemes include sip: and sips: [8], xmpp:
   [22], h323: [20], and tel: [19] URIs.  The rtsp [18] URI is suitable
   for streaming.

   Future extensions to this schema may define new values and register
   them with IANA under the registry established by this specification.

5.3.2  <service-uris>

   This element describes auxiliary services available for the
   conference.  Like <conference-uris>, this element contains a set of
   <entry> child elements - each containing the URI to be used in order
   to access different services available for the particular conference.
   The value of the URI MUST be unique in the conference context and is
   included in the <uri> sub-element.

   An <entry> element MAY contain the <display-text> sub-element that
   provides a textual description meant for user consumption.

   Each <entry> element SHOULD contain a <purpose> sub-element.  The
   currently defined <purpose> values to be used with the <service-uris>
   are:

   web-page: Indicates the web page containing the additional
      information about the conference
   recording: Indicates the link at which the recorded conference
      context can be retrieved
   event: Indicates the URI at which a subscription to the conference
      event package may be requested.  This would typically be the
      conference URI of the main conference

   Future extensions to this schema may define new values and register
   them with IANA under the registry established by this specification.




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5.3.3  <maximum-user-count>

   The value of this element provides a hint to the recipient of the
   conference document about the number of users that can be invited to
   the conference.  Typically, this value represents the overall number
   of users allowed to join the conference by different means as
   published through the conference document in <conf-uris>.  Note that
   this value is set by an administrator and can reflect any local
   policies combination such as network consumption, CPU processing
   power, and licensing rules.

5.3.4  <available-media>

   This element contains a sequence of <entry> child elements of
   conference-medium-type, each being indexed by the attribute 'label'.

   The 'label' attribute is the media stream identifier assigned by the
   conferencing server: its value will be unique in the <conference-
   info> context.  The value of this attribute will typically correspond
   to the Session Description Protocol (SDP) "label" media attribute
   defined in [17].

   Each <entry> describes a single media stream available to the
   participants in the conference and contains the following
   information:

   <display-text> This element contains the display text for the media
      stream.

   <type> This element contains the media type of the media stream.  The
      value of this element MUST be one of the values registered for
      "media" of SDP [3] and its later revision(s).  For example:
      "audio", "video", "text", and "message".

   <status> This element indicates the available status of the media
      stream available to the conference participants.  For example,
      this would be the status of the media stream, which would be
      offered by the focus, in a 'dial-out' scenario.  Using normal SIP
      offer answer mechanisms (being defined in RFC 3264 [9])in both
      dial-in and dial-out scenarios, a participant can of course
      establish only a subset of the available stream (i.e., request or
      accept the stream in one direction only, if both directions are
      available).  The valid values are "sendrecv", "sendonly",
      "recvonly", or "inactive" as defined in SDP [3] and its later
      revision(s).  (Note that the value specifies the direction from
      the participants' point of view.)





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5.4  <host-info>

   This element contains information about the entity hosting the
   conference.  This information is set before the conference
   activation, and is rarely changed during the conference lifetime,
   unless the whole conference is moved to be hosted by another entity.
   The host information is comprised of the following elements:

5.4.1  <display-text>

   This element contains display text describing the entity hosting the
   conference.

5.4.2  <web-page>

   This element contains HTTP: or HTTPS: URI of a web page describing
   either the conference service or the user hosting the conference.

5.4.3  <uris>

   This element contains a set of <entry> child elements, each
   containing the URI value and optionally its description.

5.5  <conference-state>

   By including this element in the conference document, the server can
   inform the subscribers about the changes in the overall conference
   information.  The <conference-state> child elements are described
   below.

5.5.1  <user-count>

   The value of this element tells the recipient of the conference
   document the overall number of users participating in the conference
   at a certain moment.  Typically this value represents the overall
   number of users who joined the conference by different means as
   published through the conference document in <conf-uris>.  Note that
   this number does not necessarily need to match and MAY exceed the
   number of the entries in the <users> container.  For example, in
   lecturing scenario a large conference notifications may not include
   every participant in the <users> element, but instead report only the
   panelists or the speakers.

5.5.2  <active>

   This Boolean element indicates whether the conference is currently
   active or not.  A conference is active if calling one of the <conf-
   uris> by an authorized client results in successful establishment of



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   a signaling session between the client and the focus and a successful
   joining of the conference.

5.5.3  <locked>

   This Boolean element says whether the conference is currently locked
   or not.  In this context, "locked" means that the conference roster
   can not be added to (although participants may leave or be removed
   from the conference).

5.6  <users> and its <user> sub-elements

   The <users> element is a container of <user> child elements, each
   describing a single participant in the conference.

   The following attributes are defined for <user> element:

   entity: This attribute contains the URI for the user in the
      conference.  This is a logical identifier, which corresponds to
      the call signaling authenticated identity of the participant.  The
      'entity' value MUST be unique among all participants in the
      conference.  If for some participants, the focus decides to not
      reveal this information (due to local policies or security
      reasons, for example), the host portion of the user URI MUST use
      the .invalid top level domain (TLD) according to definitions of
      RFC 2606 [5].  The focus also MUST construct the user portion of
      the URI so that the URI is unique among all participants of the
      same domain.  For example, the convention

          "AnonymousX" <sip:anonymousX@anonymous.invalid>

      SHOULD be used for a participant requesting privacy in accordance
      with the guidelines for generating anonymous URIs of RFC 3323
      [11].  Note that in a different case, such as when used in
      conjunction with Enhancements for Authenticated Identity
      Management in SIP [25], the following convention can be used:

          "AnonymousX" <sip:anonymousX@example.com>


   state: This attribute indicates whether the document contains the
      whole user information ("full"), only the information that has
      changed since the previous document ("partial"), or the user was
      removed from the conference ("deleted").

   The following child elements are defined for <user> element:





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5.6.1  <display-text>

   This element is used to display the user friendly name in the
   conference.

5.6.2  <associated-aors>

   This element contains additional (to the 'entity') URIs being
   associated with the <user>.  Typically, this information will be
   manually provided by an administrator showing the logical association
   between signaling entities otherwise independent.  For example, if
   the 'entity' of a <user> contains a GRUU Globally Routable User URI
   [24] or tel: URI RFC 3966 [19], it would be useful to populate this
   field with the Address of Record (AOR) of the person, who uses these
   devices, each represented as an independent <user>.

5.6.3  <roles>

   This element MAY contain a set of human readable strings describing
   the roles of the user in the conference.  Note that this information
   is applicable for human consumption only.  This specification doesn't
   define the set of possible conferencing roles nor the semantics
   associated with each.  It is expected that future conferencing
   specifications will define these and the corresponding schema
   extensions, as appropriate.

5.6.4  <languages>

   This element contains a list of tokens, separated by spaces, each
   containing a language understood by the user.  This information can
   be automatically learned via call signaling or be manually set per
   participant.

5.6.5  <cascaded-focus>

   This element contains a conference URI (different from the main
   conference URI) for users that are connected to the main conference
   as a result of focus cascading.  In accordance with the SIP
   conferencing framework [16], this package allows for representation
   of peer-to-peer (i.e. "flat") focus cascading only.  The actual
   cascading graph can not be deduced from the information provided in
   the package alone.  Advanced applications can construct the graph by
   subscribing to both this package and the Dialog Package [23] of each
   cascaded focus and correlating the relevant information.

5.6.6  <endpoint>

   By including one or more <endpoint> elements under a parent <user>



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   element, the server can provide the desired level of detail
   (including the state, media streams, and access information) about
   the user's devices and signaling sessions taking part in the
   conference.

   In a conferencing system where authentication is performed per
   endpoint (rather than per user), the focus can be unaware of the
   logical association of multiple endpoints under a common user.  In
   this case, each endpoint will appear as a separate <user> with its
   own <endpoint> sub-element(s) in the conference document.

   In a different case, the focus may choose to shield the information
   about the participant's multiple endpoints and signaling sessions
   from other subscribers altogether (due to privacy policies, for
   example).  To do so, the focus MAY aggregate the multiple signaling
   sessions' information under a single <endpoint> element.  Note that
   in this case, the detailed call signaling information (represented by
   <call-info> sub-element) will not be included.

5.7  <endpoint>

   This section describes the <endpoint> element in more detail.

   The following attributes are defined for <endpoint> element:

   entity: The server MUST generate the 'entity' key for each <endpoint>
      element included under the parent <user>, such as its value is
      unique in the user context.  In SIP terms, this can be the Contact
      URI, GRUU, etc.

   state: This attribute indicates whether the element contains the
      whole endpoint information ("full"), only the information that has
      changed since the previous document ("partial"), or the endpoint
      has been removed from the conference ("deleted").

   The following child elements are defined for <endpoint> element:

5.7.1  <display-text>

   This element contains the display text for the endpoint.

5.7.2  <referred>

   This element contains information about the user whose action
   resulted in this endpoint being brought into the conference (e.g. the
   SIP user identified by this URI sent a REFER to the focus).  It MAY
   contain the following sub-elements:




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   when: This element of the XML dateTime type contains the date and
      time that the endpoint was referred to the conference and SHOULD
      be expressed in Coordinated Universal Time (UTC) format.  For
      example,

        <when>2005-03-04T20:00:00Z</when>


   reason: This element contains the reason the endpoint was referred to
      the conference.  It is RECOMMENDED to include the information in
      the format defined by RFC 3326 [12].  For example,

   <reason>Reason: SIP;text="Ad-hoc Invitation"</reason>


   by: This element contains the URI of the entity which caused the
      endpoint to be referred to the conference.  In SIP case, it will
      be populated from the Referred-By header defined in RFC 3892 [15].

5.7.3  <status>

   This element contains the status of the endpoint, and can assume the
   following values:

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

   on-hold: Active signaling dialog exists between an endpoint and a
      focus, but endpoint is "on-hold" for this conference, i.e. he/she
      is neither "hearing" the conference mix, nor is his/her media
      being mixed in the conference.  As an example, the endpoint 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-via-focus: Active signaling dialog exists between an endpoint
      and a focus and the endpoint can "listen" to the conference, but
      endpoint's media is not being mixed into the conference.  Note
      that sometimes a subset of endpoint media streams can be muted by
      focus (such as poor quality video) while others (such as voice or
      IM) can still be active.  In this case, it is RECOMMENDED that the
      "aggregated" endpoint connectivity <status> reflects the status of
      the most active media.




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   pending: Endpoint is not yet in the session, but it is anticipated
      that he/she will join in the near future.

   alerting: A PSTN ALERTING or SIP 180 Ringing was returned for the
      outbound call, endpoint is being alerted.

   dialing-in: Endpoint is dialing into the conference, not yet in the
      roster (probably being authenticated).

   dialing-out: Focus has dialed out to connect the endpoint to the
      conference, but the endpoint is not yet in the roster (probably
      being authenticated).

   disconnecting: Focus is in the process of disconnecting the endpoint
      (e.g., in SIP a DISCONNECT or BYE was sent to the endpoint).

   Note that the defined transient statuses (e.g., disconnecting,
   alerting, etc.) could generate a lot of traffic.  Therefore
   implementations MAY choose to generate notifications on these
   statuses to certain participants only or not generate them at all,
   subject to local policy.

5.7.4  <joining-method>

   This element contains the method by which the endpoint joined the
   conference, and can assume the following values:

   dialed-in: The endpoint dialed into the conference (e.g., in SIP sent
      INVITE to the focus), which resulted in successful dialog
      establishment.

   dialed-out: The focus has brought the endpoint into the
      conference(e.g., in SIP the focus sent a successful INVITE to the
      endpoint).

   focus-owner: The endpoint is the focus for this conference.  This
      status is used only when a participant's UA acts as a conference
      focus.

5.7.5  <joining-info>

   This element contains information about how the endpoint joined and
   MAY contain the following sub-elements:







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   when: This element of the XML dateTime type contains the date and
      time that the endpoint joined the conference and SHOULD be
      expressed in Coordinated Universal Time (UTC).

   reason: This element contains the reason the endpoint joined the
      conference.  It is RECOMMENDED to include the information in the
      format defined by RFC 3326 [12].  For example,

   <reason>Reason: SIP;text="Ad-hoc Invitation"</reason>


   by: This element contains the URI of the entity which caused the
      endpoint to join the conference.

5.7.6  <disconnection-method>

   This element contains the method by which the endpoint departed the
   conference, and can assume the following values:

   departed: In SIP, the endpoint sent a BYE, thus leaving the
      conference.

   booted: In SIP, the endpoint was sent a BYE by the focus, ejecting
      him/her out of the conference.  Alternatively, the endpoint tried
      to dial into to conference but was rejected by the focus due to
      local policy.

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

   busy: In SIP, the server tried to bring the endpoint into the
      conference, but its attempt to contact the specific endpoint
      resulted in 486 "Busy Here" final response.  Alternatively, the
      endpoint tried to dial into the conference but the focus responded
      with 486 response.

5.7.7  <disconnection-info>

   This element contains information about the endpoint's departure from
   the conference and MAY contain the following sub-elements:








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   when: This element of the XML dateTime type contains the date and
      time that the endpoint departed the conference and SHOULD be
      expressed in Coordinated Universal Time (UTC).

   reason: This element contains the reason the endpoint departed the
      conference.  When known and meaningful, it is RECOMMENDED to
      include the information as conveyed/reported by the call signaling
      in the format defined by RFC 3326 [12].  For example,


   <reason>Reason: SIP;cause=415;text="Unsupported Media Type"</reason>


   by: This element contains the URI of the entity which caused the
      endpoint to depart the conference.

5.7.8  <media>

   This element contains information about a single media stream and is
   included for each media stream being established between the focus
   and the <endpoint>.  The media stream definition can be found in SDP
   [3].

   Note that if the <call-info> sub-element of the endpoint is not
   included in the document by the server, it is possible that the media
   streams listed under the common <endpoint> were established by
   separate signaling sessions.

5.7.9  <call-info>

   The <call-info> element provides detailed call signaling information
   for a call being maintained between the participant and the focus.
   Privacy policies MUST be consulted before revealing this information
   to other participants.

   The <sip> sub-element contains the SIP dialog identifier of the
   endpoint's dialog with the focus.  The element includes sub-elements
   <display-text>, <call-id>, <to-tag>, <from-tag>.

   In future, the <call-info> element can be expanded to include call
   signaling protocol information for other protocols besides SIP.

5.8  <media>

   This section describes the <media> element in more detail.

   A single 'id' attribute is defined for this element.  This is the
   media stream identifier being generated by the server such as its



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   value is unique in the endpoint context.  This attribute is the key
   to refer to a particular media stream in the conference document.

   The following child elements are defined for <media>:

5.8.1  <display-text>

   This element contains the display text for the media stream.  The
   value of this element corresponds to the SDP description media
   attribute ("i") defined in SDP [3].

5.8.2  <type>

   This element contains the media type for the media stream.  The value
   of this element MUST be one of the values registered for "media" of
   SDP [3] and its later revision(s).

5.8.3  <label>

   The <label> element carries a unique identifier for this stream among
   all streams in the conference and is assigned by the focus.  The
   value of this element will typically correspond to the SDP "label"
   media attribute defined in [17] and is exchanged between a
   participant and a focus over the signaling connection between them.

   If the <available-media> information (described in Section 5.3.4) is
   included in the conference document, the value of this element MUST
   be equal to the 'label' value of the corresponding media stream
   <entry> in the <available-media> container.

5.8.4  <src-id>

   The <src-id> element, if applicable, carries the information about
   the actual source of the media.  For example, for Real-Time Transport
   Protocol (RTP) / Real-Time Control Protocol (RTCP) [13] media
   streams, the value MUST contain the synchronization source (SSRC)
   identifier value generated by the endpoint for the stream it sends.

   When an RTP mixer generates a contributing source (CSRC) identifiers'
   list according to RTP/RTCP [13], 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.  A quote from
   RFC 3550: "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)."




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   If an RTP mixer compliant to the above is used, participants can
   perform an SSRC to user mapping and identify "a current speaker".

5.8.5  <status>

   The element <status> indicates the status in both directions of the
   media stream and has the values "sendrecv", "sendonly", "recvonly",
   or "inactive" as defined in SDP [3] and its later revision(s).  Note
   that value specifies the direction from the participant's point of
   view.  For example, a muted participant's stream will have the value
   of "recvonly".

5.9  Sidebars

   If a participant in the main conference joins a sidebar, a new <user>
   element representing the user is created either as a part of a
   separate sub-conference referenced from the <sidebars-by-ref> element
   or under one of the <sidebar-by-val> elements as described below.

   Note that the <user> in the main roster is not being deleted, but its
   media statuses can be updated to reflect the effect being caused by
   his/her participation in the sidebar.  The display of this
   information can vary among subscribers to the same conference
   information, subject to local policies and to the subscriber role
   both in the sidebar and in the main conference.

5.9.1  <sidebars-by-ref>

   This element contains a set of <entry> child elements each containing
   a sidebar conference URI.  The recipient of the information can then
   subscribe to sidebar information independently from the main
   conference package subscription.

5.9.2  <sidebar-by-val>

   This element contains a set of <entry> child elements each containing
   information about a single sidebar.  By using this element of
   conference-type, the server can include a full or a partial
   description of each sidebar (as a sub-conference) in the body of the
   main conference document.

6.  XML 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"



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   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:conference-info"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified">
   <!--
     This imports the xml:language definition
   -->
      <xs:import namespace="http://www.w3.org/XML/1998/namespace"
       schemaLocation="http://www.w3.org/2001/03/xml.xsd"/>
   <!--
     CONFERENCE ELEMENT
   -->
      <xs:element name="conference-info" type="conference-type"/>
      <!--
         CONFERENCE TYPE
      -->
      <xs:complexType name="conference-type">
       <xs:sequence>
        <xs:element name="conference-description"
         type="conference-description-type" minOccurs="0"/>
        <xs:element name="host-info"
         type="host-type" minOccurs="0"/>
        <xs:element name="conference-state"
         type="conference-state-type" minOccurs="0"/>
        <xs:element name="users"
         type="users-type" minOccurs="0"/>
        <xs:element name="sidebars-by-ref"
         type="uris-type" minOccurs="0"/>
        <xs:element name="sidebars-by-val"
         type="sidebars-by-val-type" minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="entity"
        type="xs:anyURI" use="required"/>
       <xs:attribute name="state"
        type="state-type" use="optional" default="full"/>
       <xs:attribute name="version"
        type="xs:unsignedInt" use="optional"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         STATE TYPE
      -->
      <xs:simpleType name="state-type">
       <xs:restriction base="xs:string">
        <xs:enumeration value="full"/>
        <xs:enumeration value="partial"/>



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        <xs:enumeration value="deleted"/>
       </xs:restriction>
      </xs:simpleType>
      <!--
         CONFERENCE DESCRIPTION TYPE
      -->
      <xs:complexType name="conference-description-type">
       <xs:sequence>
        <xs:element name="display-text"
         type="xs:string" minOccurs="0"/>
        <xs:element name="subject"
         type="xs:string" minOccurs="0"/>
        <xs:element name="free-text"
         type="xs:string" minOccurs="0"/>
        <xs:element name="keywords"
         type="keywords-type" minOccurs="0"/>
        <xs:element name="conf-uris"
         type="uris-type" minOccurs="0"/>
        <xs:element name="service-uris"
         type="uris-type" minOccurs="0"/>
        <xs:element name="maximum-user-count"
         type="xs:unsignedInt" minOccurs="0"/>
        <xs:element name="available-media"
         type="conference-media-type" minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         HOST TYPE
      -->
      <xs:complexType name="host-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="web-page" type="xs:anyURI"
         minOccurs="0"/>
        <xs:element name="uris" type="uris-type"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         CONFERENCE STATE TYPE
      -->



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      <xs:complexType name="conference-state-type">
       <xs:sequence>
        <xs:element name="user-count" type="xs:unsignedInt"
         minOccurs="0"/>
        <xs:element name="active" type="xs:boolean"
         minOccurs="0"/>
        <xs:element name="locked" type="xs:boolean"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         CONFERENCE MEDIA TYPE
      -->
      <xs:complexType name="conference-media-type">
       <xs:sequence>
        <xs:element name="entry" type="conference-medium-type"
         maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         CONFERENCE MEDIUM TYPE
      -->
      <xs:complexType name="conference-medium-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="type" type="xs:string"/>
        <xs:element name="status" type="media-status-type"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="label" type="xs:string"
        use="required"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         URIs TYPE
      -->
      <xs:complexType name="uris-type">
       <xs:sequence>
        <xs:element name="entry" type="uri-type"
         maxOccurs="unbounded"/>
       </xs:sequence>



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       <xs:attribute name="state" type="state-type"
        use="optional" default="full"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         URI TYPE
      -->
      <xs:complexType name="uri-type">
       <xs:sequence>
        <xs:element name="uri" type="xs:anyURI"/>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="purpose" type="xs:string"
         minOccurs="0"/>
        <xs:element name="modified" type="execution-type"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         KEWORDS TYPE
      -->
      <xs:simpleType name="keywords-type">
       <xs:list itemType="xs:string"/>
      </xs:simpleType>
      <!--
         USERS TYPE
      -->
      <xs:complexType name="users-type">
       <xs:sequence>
        <xs:element name="user" type="user-type"
         minOccurs="0" maxOccurs="unbounded"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="state" type="state-type"
        use="optional" default="full"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         USER TYPE
      -->
      <xs:complexType name="user-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>



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        <xs:element name="associated-aors" type="uris-type"
         minOccurs="0"/>
        <xs:element name="roles" type="user-roles-type"
         minOccurs="0"/>
        <xs:element name="languages" type="user-languages-type"
         minOccurs="0"/>
        <xs:element name="cascaded-focus" type="xs:anyURI"
         minOccurs="0"/>
        <xs:element name="endpoint" type="endpoint-type"
         minOccurs="0" maxOccurs="unbounded"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="entity" type="xs:anyURI"/>
       <xs:attribute name="state" type="state-type"
        use="optional" default="full"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         USER ROLES TYPE
      -->
      <xs:complexType name="user-roles-type">
       <xs:sequence>
        <xs:element name="entry" type="xs:string"
         maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         USER LANGUAGES TYPE
      -->
      <xs:simpleType name="user-languages-type">
       <xs:list itemType="xs:language"/>
      </xs:simpleType>
      <!--
         ENDPOINT TYPE
      -->
      <xs:complexType name="endpoint-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="referred" type="execution-type"
         minOccurs="0"/>
        <xs:element name="status" type="endpoint-status-type"
         minOccurs="0"/>
        <xs:element name="joining-method" type="joining-type"
         minOccurs="0"/>
        <xs:element name="joining-info"



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         type="execution-type"
         minOccurs="0"/>
        <xs:element name="disconnection-method"
         type="disconnection-type"
         minOccurs="0"/>
        <xs:element name="disconnection-info"
         type="execution-type"
         minOccurs="0"/>
        <xs:element name="media" type="media-type"
         minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="call-info" type="call-type"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="entity" type="xs:string"/>
       <xs:attribute name="state" type="state-type"
        use="optional" default="full"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         ENDPOINT STATUS TYPE
      -->
      <xs:simpleType name="endpoint-status-type">
       <xs:restriction base="xs:string">
        <xs:enumeration value="pending"/>
        <xs:enumeration value="dialing-out"/>
        <xs:enumeration value="dialing-in"/>
        <xs:enumeration value="alerting"/>
        <xs:enumeration value="on-hold"/>
        <xs:enumeration value="connected"/>
        <xs:enumeration value="muted-via-focus"/>
        <xs:enumeration value="disconnecting"/>
        <xs:enumeration value="disconnected"/>
       </xs:restriction>
      </xs:simpleType>
      <!--
         JOINING TYPE
      -->
      <xs:simpleType name="joining-type">
       <xs:restriction base="xs:string">
        <xs:enumeration value="dialed-in"/>
        <xs:enumeration value="dialed-out"/>
        <xs:enumeration value="focus-owner"/>
       </xs:restriction>
      </xs:simpleType>
      <!--
         DISCONNECTION TYPE



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      -->
      <xs:simpleType name="disconnection-type">
       <xs:restriction base="xs:string">
        <xs:enumeration value="departed"/>
        <xs:enumeration value="booted"/>
        <xs:enumeration value="failed"/>
        <xs:enumeration value="busy"/>
       </xs:restriction>
      </xs:simpleType>
      <!--
         EXECUTION TYPE
      -->
      <xs:complexType name="execution-type">
       <xs:sequence>
        <xs:element name="when" type="xs:dateTime"
         minOccurs="0"/>
        <xs:element name="reason" type="xs:string"
         minOccurs="0"/>
        <xs:element name="by" type="xs:anyURI"
         minOccurs="0"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
     <!--
         CALL TYPE
      -->
      <xs:complexType name="call-type">
       <xs:choice>
        <xs:element name="sip" type="sip-dialog-id-type"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:choice>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         SIP DIALOG ID TYPE
      -->
      <xs:complexType name="sip-dialog-id-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="call-id" type="xs:string"/>
        <xs:element name="from-tag" type="xs:string"/>
        <xs:element name="to-tag" type="xs:string"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:anyAttribute namespace="##other" processContents="lax"/>



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      </xs:complexType>
      <!--
         MEDIA TYPE
      -->
      <xs:complexType name="media-type">
       <xs:sequence>
        <xs:element name="display-text" type="xs:string"
         minOccurs="0"/>
        <xs:element name="type" type="xs:string"
         minOccurs="0"/>
        <xs:element name="label" type="xs:string"
         minOccurs="0"/>
        <xs:element name="src-id" type="xs:string"
         minOccurs="0"/>
        <xs:element name="status" type="media-status-type"
         minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
         minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="id" type="xs:string"
        use="required"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:complexType>
      <!--
         MEDIA STATUS TYPE
      -->
      <xs:simpleType name="media-status-type">
       <xs:restriction base="xs:string">
        <xs:enumeration value="recvonly"/>
        <xs:enumeration value="sendonly"/>
        <xs:enumeration value="sendrecv"/>
        <xs:enumeration value="inactive"/>
       </xs:restriction>
      </xs:simpleType>
       <!--
         SIDEBARS BY VAL TYPE
       -->
       <xs:complexType name="sidebars-by-val-type">
        <xs:sequence>
         <xs:element name="entry" type="conference-type"
          minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="state" type="state-type"
         use="optional" default="full"/>
        <xs:anyAttribute namespace="##other" processContents="lax"/>
       </xs:complexType>
      </xs:schema>




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7.  Examples

7.1  Basic Example

   The following is an example of a full conference information
   document:


   <?xml version="1.0" encoding="UTF-8"?>
   <conference-info
    xmlns="urn:ietf:params:xml:ns:conference-info"
    entity="sips:conf233@example.com"
    state="full" version="1">
   <!--
     CONFERENCE INFO
   -->
    <conference-description>
     <subject>Agenda: This month's goals</subject>
      <service-uris>
       <entry>
        <uri>http://sharepoint/salesgroup/</uri>
        <purpose>web-page</purpose>
       </entry>
      </service-uris>
     </conference-description>
   <!--
      CONFERENCE STATE
   -->
    <conference-state>
     <user-count>33</user-count>
    </conference-state>
   <!--
     USERS
   -->
    <users>
     <user entity="sip:bob@example.com" state="full">
      <display-text>Bob Hoskins</display-text>
   <!--
     ENDPOINTS
   -->
      <endpoint entity="sip:bob@pc33.example.com">
       <display-text>Bob's Laptop</display-text>
       <status>disconnected</status>
       <disconnection-method>departed</disconnection-method>
       <disconnection-info>
        <when>2005-03-04T20:00:00Z</when>
        <reason>bad voice quality</reason>
        <by>sip:mike@example.com</by>



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       </disconnection-info>
   <!--
     MEDIA
   -->
       <media id="1">
        <display-text>main audio</display-text>
        <type>audio</type>
        <label>34567</label>
        <src-id>432424</src-id>
        <status>sendrecv</status>
       </media>
      </endpoint>
     </user>
   <!--
     USER
   -->
     <user entity="sip:alice@example.com" state="full">
      <display-text>Alice</display-text>
   <!--
     ENDPOINTS
   -->
      <endpoint entity="sip:4kfk4j392jsu@example.com;grid=433kj4j3u">
       <status>connected</status>
       <joining-method>dialed-out</joining-method>
       <joining-info>
        <when>2005-03-04T20:00:00Z</when>
        <by>sip:mike@example.com</by>
       </joining-info>
   <!--
     MEDIA
   -->
       <media id="1">
        <display-text>main audio</display-text>
        <type>audio</type>
        <label>34567</label>
        <src-id>534232</src-id>
        <status>sendrecv</status>
       </media>
      </endpoint>
     </user>
    </users>
   </conference-info>


7.2  Rich Example

   The following is an example of a partial conference information
   document.  In this example, there are 32 participants in a voice



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   conference.  The user Bob has been ejected from the conference by
   Mike due to bad voice quality.  Note that there are three sidebars in
   the conference, two are referenced just by their sidebar URIs and
   information about the third sidebar is included in this notification.
   Also note that while this conference offers both audio and video
   capabilities, only audio is currently in use.


   <?xml version="1.0" encoding="UTF-8"?>
   <conference-info
    xmlns="urn:ietf:params:xml:ns:conference-info"
    entity="sips:conf233@example.com"
    state="partial" version="5">
   <!--
     CONFERENCE INFO
   -->
    <conference-description>
     <display-text>Weekly Sales Meeting</display-text>
     <subject>Agenda: This month's goals</subject>
     <free-text>We will start strict on time</free-text>
     <keywords>sales meeting weekly</keywords>
     <conf-uris>
      <entry>
       <uri>tel:+18005671234</uri>
       <display-text>TTI Bridge</display-text>
       <purpose>participation</purpose>
      </entry>
      <entry>
       <uri>h323:conf545@h323.example.com</uri>
       <purpose>participation</purpose>
      </entry>
      <entry>
       <uri>http://real.streaming.com/54634/live.ram</uri>
       <purpose>streaming</purpose>
      </entry>
     </conf-uris>
     <service-uris>
      <entry>
       <uri>http://sharepoint/salesgroup/</uri>
       <purpose>web-page</purpose>
      </entry>
      <entry>
       <uri>http://quicktime.com/54634/recording.mov</uri>
       <display-text>Quicktime</display-text>
       <purpose>recording</purpose>
      </entry>
     </service-uris>
     <maximum-user-count>100</maximum-user-count>



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     <available-media>
      <entry label="34567">
       <display-text>main audio</display-text>
       <type>audio</type>
       <status>sendrecv</status>
      </entry>
      <entry label="34569">
       <display-text>main video</display-text>
       <type>video</type>
       <status>inactive</status>
      </entry>
     </available-media>
    </conference-description>
   <!--
     HOST INFO
   -->
    <host-info>
     <display-text>Sales Host</display-text>
     <web-page>http://sharepoint/salesgroup/hosts/</web-page>
     <uris>
      <entry>
       <uri>sip:sales@example.com</uri>
      </entry>
     </uris>
    </host-info>
   <!--
     CONFERENCE STATE
   -->
    <conference-state>
     <user-count>32</user-count>
     <active>true</active>
     <locked>false</locked>
    </conference-state>
   <!--
     USERS
   -->
    <users>
     <user entity="sip:bob@example.com">
      <display-text>Bob Hoskins</display-text>
      <associated-aors>
       <entry>
        <uri>mailto:bob@example.com</uri>
        <display-text>email</display-text>
       </entry>
      </associated-aors>
      <roles>
      <entry>participant</entry>
      </roles>



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      <languages>en</languages>
   <!--
     ENDPOINTS
   -->
      <endpoint entity="sip:bob@pc33.example.com">
       <display-text>Bob's Laptop</display-text>
       <referred>
        <when>2005-03-04T20:00:00Z</when>
        <reason>expert required</reason>
        <by>sip:mike@example.com</by>
       </referred>
       <status>disconnecting</status>
       <joining-method>dialed-out</joining-method>
       <joining-info>
        <when>2005-03-04T20:00:00Z</when>
        <reason>invitation</reason>
        <by>sip:mike@example.com</by>
       </joining-info>
       <disconnection-method>booted</disconnection-method>
       <disconnection-info>

        <when>2005-03-04T20:00:00Z</when>
        <reason>bad voice quality</reason>
        <by>sip:mike@example.com</by>
       </disconnection-info>
   <!--
     MEDIA
   -->
       <media id="1">
        <display-text>main audio</display-text>
        <type>audio</type>
        <label>34567</label>
        <src-id>432424</src-id>
        <status>sendrecv</status>
       </media>
   <!--
     CALL INFO
   -->
       <call-info>
        <sip>
         <display-text>full info</display-text>
           <call-id>hsjh8980vhsb78</call-id>
           <from-tag>vav738dvbs</from-tag>
           <to-tag>8954jgjg8432</to-tag>
        </sip>
       </call-info>
      </endpoint>
     </user>



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    </users>
   <!--
     SIDEBARS BY REFERENCE
   -->
    <sidebars-by-ref state="partial">
     <entry>
      <uri>sips:conf233@example.com;grid=45</uri>
      <display-text>sidebar with Carol</display-text>
     </entry>
     <entry>
      <uri>sips:conf233@example.com;grid=21</uri>
      <display-text>private with Peter</display-text>
     </entry>
    </sidebars-by-ref>
   <!--
     SIDEBARS BY VALUE
   -->
    <sidebars-by-val state="partial">
     <entry entity="sips:conf233@example.com;grid=77"

      state="partial">
      <users>
       <user entity="sip:bob@example.com"/>
       <user entity="sip:mark@example.com"/>
       <user entity="sip:dan@example.com"/>
      </users>
     </entry>
    </sidebars-by-val>
   </conference-info>


8.  Security Considerations

   Subscriptions to conference state information can reveal very
   sensitive information.  For this reason, it is RECOMMENDED a focus
   use a strong means for authentication, conference information
   protection, and apply comprehensive authorization rules when using
   the conference notification mechanism defined in this document.  The
   following sections will discuss each of these aspects in more detail.

8.1  Connection Security

   It is RECOMMENDED that a focus authenticate a conference package
   subscriber using the normal SIP authentication mechanisms, such as
   Digest as defined in Section 22 of RFC 3261 [8].

   The mechanism used for conveying the conference information MUST
   ensure integrity and SHOULD ensure confidentially of the information.



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   In order to achieve these, an end-to-end SIP encryption mechanism,
   such as S/MIME described in Section 26.2.4 of RFC 3261 [8], SHOULD be
   used.

   If strong end-to-end security means (such as above) is not available,
   it is RECOMMENDED that a focus use mutual hop-by-hop TLS
   authentication and encryption mechanisms described in Section 26.2.2
   "SIPS URI Scheme" and Section 26.3.2.2 "Interdomain Requests" of RFC
   3261 [8].

8.2  Authorization Considerations

   Generally speaking, conference applications are very concerned about
   authorization decisions.  Mechanisms for establishing and enforcing
   such authorization rules are a central concept throughout the SIP
   conferencing framework [16].  Because most of the information about a
   conference can be presented using the conference package, many of the
   authorization rules directly apply to this specification.  As a
   result, a notification server MUST be capable of generating distinct
   conference information views to different subscribers, subject to a
   subscriber's role in a conference, personal access rights, etc. - all
   subject to local authorization policies and rules.

   Since a focus provides participant identity information using this
   event package, participant privacy needs to be taken into account.  A
   focus MUST support requests by participants for privacy.  Privacy can
   be indicated by the conference policy - for every participant or
   select participants.  It can also be indicated in the session
   signaling.  In SIP this can be done using the Privacy header field
   described in RFC 3323 [11].  For a participant requesting privacy, no
   identity information SHOULD be revealed by the focus in any included
   URI (e.g. the Address of Record, Contact, or GRUU).  For these cases,
   the anonymous URI generation method outlined in Section 5.6 of this
   document MUST be followed.

9.  IANA Considerations

   This document registers a SIP event package, a new MIME type,
   application/conference-info+xml, a new XML namespace, a new XML
   schema, and creates a  sub-registry "URI purposes" under the
   existing registry: http://www.iana.org/assignments/sip-parameters.

9.1  conference Event Package Registration

   This specification registers an event package, based on the
   registration procedures defined in RFC 3265 [10].  The following is
   the information required for such a registration:




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   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: IETF SIPPING Working Group <sipping@ietf.org>, as
      designated by the IESG <iesg@ietf.org>

9.2  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 8
      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: .xml
      Macintosh file type code: "TEXT"
   Personal and email address for further information: IETF SIPPING
      Working Group <sipping@ietf.org>, as designated by the IESG
      <iesg@ietf.org>
   Intended usage: COMMON
   Author/Change controller: IETF SIPPING Working Group
      <sipping@ietf.org>, as designated by the IESG <iesg@ietf.org>

9.3  URN Sub-Namespace Registration for
     urn:ietf:params:xml:ns:conference-info

   This section registers a new XML namespace, as per the guidelines in
   RFC 3688 [21].

   URI: The URI for this namespace is
      urn:ietf:params:xml:ns:conference-info
   Registrant Contact: IETF SIPPING Working Group <sipping@ietf.org>, as
      designated by the IESG <iesg@ietf.org>
   XML:








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   BEGIN
   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
             "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
   <html xmlns="http://www.w3.org/1999/xhtml">
   <head>
     <meta http-equiv="content-type"
        content="text/html;charset=iso-8859-1"/>
     <title>Conference Information Namespace</title>

   </head
   <body>
     <h1>Namespace for Conference Information</h1>
     <h2>urn:ietf:params:xml:ns:conference-info</h2>
     <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
   </body>
   </html>
   END


9.4  XML Schema Registration

   This specification registers a schema, as per the guidelines in RFC
   3688 [21].
      URI: please assign
      Registrant Contact: IETF SIPPING Working Group <sipping@ietf.org>,
      as designated by the IESG <iesg@ietf.org>
      XML: The XML can be found as the sole content of Section 6

9.5  URI Purposes Sub-registry Establishment

   This document instructs the IANA to create a new sub-registry "URI
   purposes" under the already existing registry:
   http://www.iana.org/assignments/sip-parameters.

   The purpose of a URI is an XML element, encoded in the conference
   event package [RFC XXXX - substitute with the number assigned to this
   draft].  The value of the <purpose> element indicates the intended
   usage of the URI in the context of the conference event package and
   is defined in sections Section 5.3.1 and Section 5.3.2 of this
   specification.

   This sub-registry is defined as a table that contains the following
   three columns:







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   Value: The token under registration
   Description: A descriptive text defining the intended usage of the
      URI
   Document: A reference to the document defining the registration

   This specification instructs IANA to create the table with the
   initial content as defined below:


   Value         Description                         Document
   -------       ----------------------------------  ----------

   participation The URI can be used to join the     [RFC XXXX]
                 conference

   streaming     The URI can be used to access the   [RFC XXXX]
                 streamed conference data

   event         The URI can be used to subscribe    [RFC XXXX]
                 to the conference event package

   recording     The URI can be used to access the   [RFC XXXX]
                 recorded conference data

   web-page      The URI can be used to access a     [RFC XXXX]
                 web page that contains additional
                 information of the conference


   New values of the "URI purposes" are registered by the IANA and are
   specification required according to the definition of RFC 2434 [4].
   The IANA Considerations section of the specification MUST include the
   following information:

   Value: The value of the <purpose> element to be registered
   Description: A short description of the intended usage of the URI

10.  Acknowledgements

   The authors would like to thank Dan Petrie, Sean Olson, Alan
   Johnston, Rohan Mahy, Cullen Jennings, Brian Rosen, Roni Even, and
   Miguel Garcia for their comments and inputs.

11.  References







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11.1  Normative References

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

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

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

   [4]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434,
         October 1998.

   [5]   Eastlake, D. and A. Panitz, "Reserved Top Level DNS Names",
         BCP 32, RFC 2606, June 1999.

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

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

   [8]   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.

   [9]   Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
         Session Description Protocol (SDP)", RFC 3264, June 2002.

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

   [11]  Peterson, J., "A Privacy Mechanism for the Session Initiation
         Protocol (SIP)", RFC 3323, November 2002.

   [12]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason Header
         Field for the Session Initiation Protocol (SIP)", RFC 3326,
         December 2002.

   [13]  Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
         "RTP: A Transport Protocol for Real-Time Applications", STD 64,
         RFC 3550, July 2003.

   [14]  Yergeau, F., "UTF-8, a transformation format of ISO 10646",
         STD 63, RFC 3629, November 2003.

   [15]  Sparks, R., "The Session Initiation Protocol (SIP) Referred-By



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         Mechanism", RFC 3892, September 2004.

   [16]  Rosenberg, J., "A Framework for Conferencing with the Session
         Initiation Protocol",
         draft-ietf-sipping-conferencing-framework-05 (work in
         progress), May 2005.

   [17]  Levin, O. and G. Camarillo, "The SDP (Session Description
         Protocol) Label Attribute",
         draft-ietf-mmusic-sdp-media-label-01 (work in progress),
         January 2005.

11.2  Informative References

   [18]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
         Protocol (RTSP)", RFC 2326, April 1998.

   [19]  Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
         December 2004.

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

   [21]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
         January 2004.

   [22]  Saint-Andre, P., "A Uniform Resource Identifier (URI) Scheme
         for the Extensible Messaging and  Presence Protocol (XMPP)",
         draft-saintandre-xmpp-uri-08 (work in progress), December 2004.

   [23]  Rosenberg, J., "An INVITE Inititiated Dialog Event Package for
         the Session Initiation  Protocol (SIP)",
         draft-ietf-sipping-dialog-package-06 (work in progress),
         April 2005.

   [24]  Rosenberg, J., "Obtaining and Using Globally Routable User
         Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
         (SIP)", draft-ietf-sip-gruu-03 (work in progress),
         February 2005.

   [25]  Peterson, J. and C. Jennings, "Enhancements for Authenticated
         Identity Management in the Session Initiation  Protocol (SIP)",
         draft-ietf-sip-identity-05 (work in progress), May 2005.








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Authors' Addresses

   Jonathan Rosenberg
   Cisco Systems
   600 Lanidex Plaza
   Parsippany, NJ  07054
   US

   Phone: +1 973 952-5000
   Email: jdrosen@cisco.com
   URI:   http://www.jdrosen.net


   Henning Schulzrinne
   Columbia University
   M/S 0401
   1214 Amsterdam Ave.
   New York, NY  10027
   US

   Email: schulzrinne@cs.columbia.edu
   URI:   http://www.cs.columbia.edu/~hgs


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

   Email: oritl@microsoft.com




















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Copyright Statement

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