    Network Working Group                                       J. Rosenberg
    Request for Comments: 4575                                 Cisco Systems
    Category: Standards Track                                 H. Schulzrinne
                                                         Columbia University
                                                               O. Levin, Ed.
                                                       Microsoft Corporation
                                                                 August 2006

                      A Session Initiation Protocol (SIP)
                       Event Package for Conference State

    Status of This Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (2006).

    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 Uniform Resource Identifier (URI).  Notifications are sent
       about changes in the membership of this conference and optionally
       about changes in the state of additional conference components.

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    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> ...........................................18
               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> .........................................20
          5.7. <endpoint> ................................................20
               5.7.1. <display-text> .....................................20
               5.7.2. <referred> .........................................21

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               5.7.3. <status> ...........................................21
               5.7.4. <joining-method> ...................................22
               5.7.5. <joining-info> .....................................23
               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 ........................43
          9.4. XML Schema Registration ...................................43
          9.5. URI Purposes Sub-registry Establishment ...................44
       10. Acknowledgements ..............................................45
       11. References ....................................................45
          11.1. Normative References .....................................45
          11.2. Informative References ...................................46

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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 (UA),
       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 as follows:

       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 Sections 9

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       and 5.  By default, i.e., if no Accept header is specified to a
       SUBSCRIBE request, the NOTIFY will contain a body in the
       "application/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.

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       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 4.6 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 does 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, 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 Uniform
       Resource Namespace (URN) [2], using the namespace identifier 'ietf'

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       defined by [6] and extended by RFC 3688 [21].  This URN is as
       follows:

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

    4.3.  Versioning

       The conference information is described by a hierarchical XML
       structure with the root element <conference-info>.  The root element
       is the only element in the schema that carries a 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> hierarchical 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>

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       The 'state' attribute value indicates whether the reported
       information about the element is "full" or "partial", or whether the
       element has been "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
       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, using relative URIs and lexical white space
       in these keys is NOT RECOMMENDED.

       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

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       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 '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 to 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:

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          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 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 <sidebars-by-val> 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 does not 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 can 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>,

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       <host-info>, <endpoint>, and <media> are intended for display to
       human 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 detail.

    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") or only the information that
          has changed since the previous document ("partial"), or whether
          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>,
       <sidebars-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.

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       Each <entry> MAY contain additional information useful to the
       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 the following:

       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 the following:

       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.

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

    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

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          revision(s).  (Note that the value specifies the direction from
          the participants' point of view.)

    5.4.  <host-info>

       This element contains information about the entity hosting the
       conference.  This information is set before the conference
       activation, and it 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 a
       lecturing scenario, large conference notifications may not include
       every participant in the <users> element, but instead report only the
       panelists or the speakers.

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    5.5.2.  <active>

       This Boolean element indicates whether the conference is currently
       active.  A conference is active if calling one of the <conf-uris> by
       an authorized client results in successful establishment of 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.
       In this context, "locked" means that the conference roster cannot 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 not to
          reveal this information (e.g., due to local policies or security
          reasons), 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") or only the information that has
          changed since the previous document ("partial"), or whether the
          user was removed from the conference ("deleted").

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

    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 Globally Routable User URI (GRUU)
       [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 does
       not define the set of possible conferencing roles or 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 cannot 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.

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    5.6.6.  <endpoint>

       By including one or more <endpoint> elements under a parent <user>
       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 (e.g., due to privacy policies).
       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 the <endpoint> element:

       entity:  The server MUST generate the 'entity' key for each
          <endpoint> element included under the parent <user>, such that 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") or only the information that
          has changed since the previous document ("partial"), or whether
          the endpoint has been removed from the conference ("deleted").

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

    5.7.1.  <display-text>

       This element contains the display text for the endpoint.

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    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:

       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.  Including the information in the format
          defined by RFC 3326 [12] is RECOMMENDED.  For example,

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

       by:  This element contains the URI of the entity that caused the
          endpoint to be referred to the conference.  In the case of SIP, 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
          the endpoint's media is not being mixed into the conference.  Note

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          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.

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

       alerting:  A Public Switched Telephone Network (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 a 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.

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    5.7.5.  <joining-info>

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

       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.  Including the information in the format defined by
          RFC 3326 [12] is RECOMMENDED.  For example,

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

       by:  This element contains the URI of the entity that 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 the 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 a 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, including the information
          as conveyed/reported by the call signaling in the format defined
          by RFC 3326 [12] is RECOMMENDED.  For example,

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

       by:  This element contains the URI of the entity that 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 that 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) / RTP 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 [13] explains as follows: "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 <sidebars-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.  <sidebars-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 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"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"

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       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"/>
            <xs:enumeration value="deleted"/>

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           </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
          -->
          <xs:complexType name="conference-state-type">

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           <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>
           <xs:attribute name="state" type="state-type"

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            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>
          <!--
             KEYWORDS 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"/>
            <xs:element name="associated-aors" type="uris-type"

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             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"
             type="execution-type"

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             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"/>
          </xs:complexType>

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          <!--
             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>
           </disconnection-info>

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       <!--
         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
       conference.  The user Bob has been ejected from the conference by
       Mike due to bad voice quality.  Note that there are three sidebars in

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    RFC 4575                   Conference Package                August 2006

       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>
         <available-media>
          <entry label="34567">
           <display-text>main audio</display-text>

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           <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>
          <languages>en</languages>
       <!--
         ENDPOINTS

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       -->
          <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>
        </users>
       <!--
         SIDEBARS BY REFERENCE

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       -->
        <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 that a
       focus use a strong means for authentication and conference
       information protection and that it 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.
       In order to achieve these, an end-to-end SIP encryption mechanism,

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       such as S/MIME described in Section 26.2.4 of RFC 3261 [8], SHOULD be
       used.

       If a strong end-to-end security means (such as above) is not
       available, it is RECOMMENDED that a focus use mutual hop-by-hop
       Transport Layer Security (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, and 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 4575

       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

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       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:

       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="http://www.rfc-editor.org/rfc/rfc4575.txt">
            RFC4575</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.

    Rosenberg, et al.           Standards Track                    [Page 43]

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    9.5.  URI Purposes Sub-registry Establishment

       The IANA has created 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 4575.  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 5.3.1 and 5.3.2 of this
       specification.

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

       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

       The IANA has created the table with the initial content as defined
       below:

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

       participation The URI can be used to join the     [RFC 4575]
                     conference

       streaming     The URI can be used to access the   [RFC 4575]
                     streamed conference data

       event         The URI can be used to subscribe    [RFC 4575]
                     to the conference event package

       recording     The URI can be used to access the   [RFC 4575]
                     recorded conference data

       web-page      The URI can be used to access a     [RFC 4575]
                     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:

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    RFC 4575                   Conference Package                August 2006

       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

    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., Jacobson, V. and C. Perkins, "SDP: Session
             Description Protocol", RFC 4566, July 2006.

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

       [5]   Eastlake 3rd, 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.B., "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.

    Rosenberg, et al.           Standards Track                    [Page 45]

    RFC 4575                   Conference Package                August 2006

       [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
             Mechanism", RFC 3892, September 2004.

       [16]  Rosenberg, J., "A Framework for Conferencing with the Session
             Initiation Protocol (SIP)", RFC 4353, February 2006.

       [17]  Levin, O. and G. Camarillo, "The Session Description Protocol
             (SDP) Label Attribute", RFC 4574, August 2006.

    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)",
             Work in Progress, December 2004.

       [23]  Rosenberg, J., Schulzrinne, H., and R. Mahy, "An INVITE-
             Initiated Dialog Event Package for the Session Initiation
             Protocol (SIP)", RFC 4235, November 2005.

       [24]  Rosenberg, J., "Obtaining and Using Globally Routable User
             Agent (UA) URIs (GRUU) in the Session Initiation Protocol
             (SIP)", Work in Progress, May 2006.

    Rosenberg, et al.           Standards Track                    [Page 46]

    RFC 4575                   Conference Package                August 2006

       [25]  Peterson, J. and C. Jennings, "Enhancements for Authenticated
             Identity Management in the Session Initiation Protocol (SIP)",
             RFC 4474, August 2006.

    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

    Rosenberg, et al.           Standards Track                    [Page 47]

    RFC 4575                   Conference Package                August 2006

    Full Copyright Statement

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    Acknowledgement

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