SIPPING J. Rosenberg
Internet-Draft dynamicsoft
Expires: April 26, 2004 H. Schulzrinne
Columbia University
O. Levin, Ed.
Microsoft Corporation
October 27, 2003
A Session Initiation Protocol (SIP) Event Package for Conference
State
draft-ietf-sipping-conference-package-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on April 26, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines a conference event package for the Session
Initiation Protocol (SIP) Events framework, along with a data format
used in notifications for this package. The conference package allows
users to subscribe to a conference URI. Notifications are sent about
changes in the membership of this conference, the status of users'
participation in the conference, and the sidebars in the conference.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conference Event Package . . . . . . . . . . . . . . . . . 5
3.1 Event Package Name . . . . . . . . . . . . . . . . . . . . 5
3.2 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 5
3.3 Subscription Duration . . . . . . . . . . . . . . . . . . 5
3.4 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 5
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 Data Format . . . . . . . . . . . . . . . . . . 8
4.1 Conference Information . . . . . . . . . . . . . . . . . . 8
4.1.1 User Element . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1.1 User Statuses . . . . . . . . . . . . . . . . . . . . . . 9
4.1.1.2 Media Stream Information . . . . . . . . . . . . . . . . . 9
4.1.2 Sidebar . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Constructing Coherent State . . . . . . . . . . . . . . . 10
4.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4 Example . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . 16
6.1 conference Event Package Registration . . . . . . . . . . 16
6.2 application/conference-info+xml MIME Registration . . . . 16
6.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:conference-info . . . . . . . . . . 17
6.4 XML Schema Registration . . . . . . . . . . . . . . . . . 18
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 19
8. Changes since -01 . . . . . . . . . . . . . . . . . . . . 20
Normative References . . . . . . . . . . . . . . . . . . . 21
Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . 23
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1. Introduction
The Session Initiation Protocol (SIP) [3] Events framework [2]
defines general mechanisms for subscribing to, and receiving
notifications of, events within SIP networks. It introduces the
notion of a package, which is a specific "instantiation" of the
events framework for a well-defined set of events. Here, we define an
event package for SIP conferences. This package provides the
conference notification service as outlined in the SIP conferencing
framework [9]. As described there, subscriptions to a conference URI
are routed to the focus that is handling the conference. It acts as
the notifer, and provides clients with updates on conference state.
The information provided by this package is comprised of conference
identifier, conference participants (optionally with their statuses
and media types) and conference sidebars.
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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.
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3. Conference Event Package
The conference event package allows a user to subscribe to a
conference. In SIP, conferences are represented by URIs. These URIs
route to a SIP user agent, called a focus, that is responsible for
ensuring that all users in the conference can communicate with each
other [9]. The focus has sufficient information about the state of
the conference to inform subscribers about it.
This section provides the details for defining a SIP Events package,
as specified by [2].
3.1 Event Package Name
The name of this event package is "conference". This package name is
carried in the Event and Allow-Events header, as defined in [2].
3.2 SUBSCRIBE Bodies
A SUBSCRIBE for a dialog package MAY contain a body. This body
defines a filter to apply to the subscription. Filter documents are
not specified in this document, and at the time of writing, are
expected to be the subject of future standardization activity.
A SUBSCRIBE for a dialog package MAY be sent without a body. This
implies the default subscription filtering policy. The default policy
is:
o Notifications are generated every time there is any change in the
state of the conference.
o Notifications do not normally contain full state; rather, they
only indicate the state that has changed. The exception is a
NOTIFY sent in response to a SUBSCRIBE. These NOTIFYs contain the
full state of the information requested by the subscriber.
3.3 Subscription Duration
The default expiration time for a subscription to a conference is one
hour. Once the conference ends, all subscriptions to that particular
conference are terminated, with a reason of "noresource" [2].
3.4 NOTIFY Bodies
As described in RFC 3265 [2], the NOTIFY message will contain bodies
that describe the state of the subscribed resource. This body is in a
format listed in the Accept header field of the SUBSCRIBE, or a
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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. This document describes the state of
a conference. All subscribers and notifiers MUST support the
"application/conference-info+xml" data format described in Section 4.
The subscribe request MAY contain an Accept header field. If no such
header field is present, it has a default value of "application/
conference-info+xml". If the header field is present, it MUST include
"application/conference-info+xml", and MAY include any other types
capable of representing dialog state.
Of course, the notifications generated by the server MUST be in one
of the formats specified in the Accept header field in the SUBSCRIBE
request.
3.5 Notifier Processing of SUBSCRIBE Requests
The conference information contains very sensitive information.
Therefore, all subscriptions SHOULD be authenticated and then
authorized before approval. Authorization policy is at the discretion
of the administrator, as always. However, a few recommendations can
be made.
It is RECOMMENDED that all users in the conference be allowed to
subscribe to the conference.
3.6 Notifier Generation of NOTIFY Requests
Notifications SHOULD be generated for the conference whenever there
is a change in the state in any of the information delivered to the
subscriber.
The changes generally occur when a new participant joins, a
participant leaves, or a participant is put on-hold. Subject to a
local focus policy, changes in media types and other optional media
attributes MAY be reported by the focus. In addition, creation and
deletion of sidebars together with their rosters MAY be reported by
the focus, subject to its local policy.
3.7 Subscriber Processing of NOTIFY Requests
The SIP Events framework expects packages to specify how a subscriber
processes NOTIFY requests in any package specific ways, and in
particular, how it uses the NOTIFY requests to contruct a coherent
view of the state of the subscribed resource.
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Typically, the NOTIFY for the conference package will only contain
information about those users whose state in the conference has
changed. To construct a coherent view of the total state of all
users, a subscriber to the dialog package will need to combine
NOTIFYs received over time.
Notifications within this package can convey partial information;
that is, they can indicate information about a subset of the state
associated with the subscription. This means that an explicit
algorithm needs to be defined in order to construct coherent and
consistent state. The details of this mechanism are specific to the
particular document type. See Section 4.2 for information on
constructing coherent information from an application/
conference-info+xml document.
3.8 Handling of Forked Requests
By their nature, the conferences supported by this package are
centralized. Therefore, SUBSCRIBE requests for a conference should
not generally fork. Users of this package MUST NOT install more than
a single subscription as a result of a single SUBSCRIBE request.
3.9 Rate of Notifications
For reasons of congestion control, it is important that the rate of
notifications not become excessive. As a result, it is RECOMMENDED
that the server not generate notifications for a single subscriber at
a rate faster than once every 5 seconds.
3.10 State Agents
Conference state is ideally maintained in the element in which the
conference resides. Therefore, the elements that maintain the
conference are the ones best suited to handle subscriptions to it.
Therefore, the usage of state agents is NOT RECOMMENDED for this
package.
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4. Conference Data Format
Conference information is an XML document that MUST be well-formed
and SHOULD be valid. Dialog information documents MUST be based on
XML 1.0 and MUST be encoded using UTF-8. This specification makes use
of XML namespaces for identifying dialog information documents and
document fragments. The namespace URI for elements defined by this
specification is a URN [4], using the namespace identifier 'ietf'
defined by [5] and extended by [6]. This URN is:
urn:ietf:params:xml:ns:conference-info
A conference information document begins with the root element tag
"conference-info".
4.1 Conference Information
Conference information begins with the top level element
"conference-info". This element has three mandatory attributes:
version: This attribute allows the recipient of conference
information documents to properly order them. Versions start at 0
and increment by one for each new document sent to a subscriber.
Versions are scoped within a subscription. Versions MUST be
represented using a 32 bit integer.
state: This attribute indicates whether the document contains the
full conference information, or whether it contains only the
information that has changed since the previous document
(partial).
entity: This attribute contains the conference URI that identifies
the conference being described in the document.
The "conference-info" element has zero or more "user" sub-elements
which contain information on the users in the conference. This is
followed by zero or more "sidebar" sub-elements which contain
information on the sidebars in the conference.
4.1.1 User Element
The user element has one mandatory attribute, "uri" that indicates
the URI for the user in the conference. This is a logical identifier,
not a machine specific one (i.e., it's taken from the authenticated
identity of the participant). The optional attribute "display-name"
contains a display name for the user. The standard "xml:lang"
language attribute can also be present to indicate the language of
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the display-name.
4.1.1.1 User Statuses
Two optional status elements are defined: activity-status and history
status. "Activity-status" provides information about user's current
level of participation in the conference. "History-status", if
present, provides information about the way the user joined or left
the conference. Additional optional indication "is-on-dial-out-list"
completes the information about the user membership in the
conference.
The following statuses are defined for the activity-status element:
connected: The user is a participant in the conference. Depending on
the media policies, he/she can send and receive media to and from
other participants.
disconnected: The user is not a participant in the conference and no
active dialog exists between the user and the focus.
on-hold: Active SIP dialog exists between a user and a focus, but
user is "on-hold" for this conference. As an example, the user has
asked to join the conference using SIP, but his/her participation
is pending based on moderator approval. In the meantime he/she is
hearing music-on-hold or some other kind of related content.
The following statuses are defined for the history-status element:
dialed-in: The user dialed into the conference, i.e. sent INVITE to
the focus, which resulted in successful dialog establishment.
dialed-out: The focus has brought the user into the conference by
sending a successful INVITE to the user.
departed: The user sent a BYE, thus leaving the conference.
booted: The user was sent a BYE by the focus, booting him/her out of
the conference.
failed: The server tried to bring the user into the conference, but
its attempt to contact the specific user resulted in a non-200
class final response.
4.1.1.2 Media Stream Information
Each user has zero or more "media-stream" sub-elements.
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Each "media-stream" element indicates the media stream that the user
is currently connected to. Here, "connected to" implies that a user
has a media line in their SDP [10]. With this definition, a user is
connected to a media stream even if they are not sending any media.
The "media-stream" element has a mandatory "media-type" attribute
which identifies the media type (e.g. audio, video, message and
application) and MUST have one of the values registered for "media"
of SDP [10].
The "media-stream" element has also an optional "proto" sub-element,
which MUST has the value registered for "proto" of SDP [10]).
An optional "ssrc" sub-element, if present, carries the value of SSRC
(RTP/RTCP [8]) as generated by the user for the stream it sends.
When an RTP mixer generates a CSRC list according to RTP/RTCP [8], it
inserts a list of the SSRC identifiers of the sources that
contributed to the generation of a particular packet into the RTP
header of that packet. "An example application is audio conferencing
where a mixer indicates all the talkers whose speech was combined to
produce the outgoing packet, allowing the receiver to indicate the
current talker, even though all the audio packets contain the same
SSRC identifier (that of the mixer)."
4.1.2 Sidebar
The sidebar element has one attribute - "entity" that indicates the
URI which identifiers the sidebar. A sidebar has zero or more users
that are of type "user-type" as the users of the main conference are.
4.2 Constructing Coherent State
The conference information subscriber maintains a table for the list
of users in the conference. The table contains a row for each user.
Each row is indexed by a URI, present in the "uri" attribute of the
"user" element. The contents of each row contain the state of that
user as conveyed in the document.
The table is associated with a version number. The version number
MUST be initialized with the value of the "version" attribute from
the "conference-info" element in the first document received. Each
time a new document is received, the value of the local version
number, and the "version" attribute in the new document, are
compared. If the value in the new document is one higher than the
local version number, the local version number is increased by one,
and the document is processed. If the value in the document is more
than one higher than the local version number, the local version
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number is set to the value in the new document, the document is
processed, and the subscriber SHOULD generate a refresh request to
trigger a full state notification. If the value in the document is
less than the local version, the document is discarded without
processing.
The processing of the conference information document depends on
whether it contains full or partial state. If it contains full state,
indicated by the value of the "state" attribute in the
"conference-info" element, the contents of the table is flushed. It
is repopulated from the document. A new row in the user table is
created for each "user" element. If the document contains partial
state, as indicated by the value of the "state" attribute in the
"conference-info" element, the document is used to update the table.
For each "user" element in the document, the subscriber checks to see
whether a row exists for that user in the user table. This check is
done by comparing the URI in the "uri" attribute of the "user"
element with the URI associated with the row. If the user doesn't
exist in the table, a row is added, and its state is set to the
information from that "user" element. If the user does exist, its
state is updated to be the information from that "user" element. If a
row is updated or created, such that its state is now disconnected,
booted, failed or departed, that entry MAY be removed from the table
at any time.
4.3 Schema
<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:conference-info" xmlns:tns="urn:ietf:params:xml:ns:conference-info" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:ietf:params:xml:ns:conference-info" elementFormDefault="qualified" attributeFormDefault="unqualified">
<!--
This import brings in the XML language attribute xml:lang
-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/03/xml.xsd" />
<xs:element name="conference-info">
<xs:complexType>
<xs:sequence>
<xs:element name="user" type="user-type" minOccurs="0" maxOccurs="unbounded" />
<xs:element name="sidebar" type="sidebar-type" minOccurs="0" maxOccurs="unbounded" />
<xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
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<xs:attribute name="version" type="xs:nonNegativeInteger" use="required" />
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="full" />
<xs:enumeration value="partial" />
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="entity" type="xs:anyURI" use="required" />
</xs:complexType>
</xs:element>
<xs:complexType name="user-type">
<xs:sequence>
<xs:element name="activity-status" type="tns:activity-status-type" minOccurs="0" />
<xs:element name="history-status" type="tns:history-status-type" minOccurs="0" />
<xs:element name="is-on-dial-out-list" type="xs:boolean" minOccurs="0" />
<xs:element name="media-stream" type="tns:media-stream-type" minOccurs="0" maxOccurs="unbounded" />
<xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
<xs:attribute name="uri" type="xs:anyURI" use="required" />
<xs:attribute name="display-name" type="xs:string" use="optional" />
<xs:attribute ref="xml:lang" use="optional" />
</xs:complexType>
<xs:complexType name="sidebar-type">
<xs:sequence>
<xs:element name="user" type="user-type" minOccurs="0" maxOccurs="unbounded" />
<xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
<xs:attribute name="entity" type="xs:anyURI" use="required" />
</xs:complexType>
<xs:complexType name="media-stream-type">
<xs:sequence>
<xs:element name="proto" type="xs:string" minOccurs="0" />
<xs:element name="ssrc" type="xs:nonNegativeInteger" minOccurs="0" />
<xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
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<xs:attribute name="media" type="xs:string" use="required" />
</xs:complexType>
<xs:simpleType name="activity-status-type">
<xs:restriction base="xs:string">
<xs:enumeration value="connected" />
<xs:enumeration value="disconnected" />
<xs:enumeration value="on-hold" />
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="history-status-type">
<xs:restriction base="xs:string">
<xs:enumeration value="dialed-in" />
<xs:enumeration value="dialed-out" />
<xs:enumeration value="departed" />
<xs:enumeration value="booted" />
<xs:enumeration value="failed" />
</xs:restriction>
</xs:simpleType>
</xs:schema>
4.4 Example
The following is an example conference information document:
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<conference-info version="0" state="full" entity="sip:conf233@example.com">
<user uri="sip:bob@example.com" display-name="Bob Jones">
<activity-status>connected</activity-status>
<history-status>dialed-in</history-status>
<media-stream media-type="audio"
<proto> RTP/AVP <proto>
<ssrc> 583398 <ssrc>
</media-stream>
</user>
<user uri="sip:barbara@example.com" display-name="Barbara Jones">
<activity-status>on-hold</activity-status>
</user>
<user uri="sip:bill@example.com" display-name="Bill Minelli">
<activity-status>on-hold</activity-status>
</user>
<sidebar entity="sip:conf233.1@example.com">
<user>uri="sip:barbara@example.com"</user>
<user>uri="sip:bill@example.com"</user>
</sidebar>
</conference-info>
This document describes a conference with three users, two of which
are in a sidebar conversation.
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5. Security Considerations
Subscriptions to conference state can reveal very sensitive
information. For this reason, the document recommends authentication
and authorization, and provides guidelines on sensible authorization
policies.
Since the data in notifications is sensitive as well, end-to-end SIP
encryption mechanisms using S/MIME SHOULD be used to protect it.
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6. IANA Considerations
This document registers a SIP event package, a new MIME type,
application/conference-info+xml, a new XML namespace, and a new XML
schema.
6.1 conference Event Package Registration
This specification registers an event package, based on the
registration procedures defined in RFC 3265 [2]. The following is the
information required for such a registration:
Package Name: conference
Package or Template-Package: This is a package.
Published Document: RFC XXXX (Note to RFC Editor: Please fill in XXXX
with the RFC number of this specification).
Person to Contact: Jonathan Rosenberg, jdrosen@jdrosen.net.
6.2 application/conference-info+xml MIME Registration
MIME media type name: application
MIME subtype name: conference-info+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [7].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [7].
Security considerations: See Section 10 of RFC 3023 [7] and Section 5
of this specification.
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has been
used to support SIP conferencing applications.
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Additional Information:
Magic Number: None
File Extension: .cif or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Jonathan
Rosenberg, <jdrosen@jdrosen.net>
Intended usage: COMMON
Author/Change controller: The IETF.
6.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:conference-info
This section registers a new XML namespace, as per the guidelines in
[6].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:conference-info.
Registrant Contact: IETF, SIPPING working group, <sipping@ietf.org>,
Jonathan Rosenberg <jdrosen@jdrosen.net>.
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="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
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6.4 XML Schema Registration
This specification registers a schema, as per the guidelines in in
[6].
URI: please assign.
Registrant Contact: IETF, SIPPING Working Group
(sipping@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net).
XML: The XML can be found as the sole content of Section 4.3.
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7. Acknowledgements
The authors would like to thank Dan Petrie and Sean Olson for their
comments.
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8. Changes since -01
o Package parameters are removed. Decision about performing
"recursive" membership algorithm is perceived as a focus local
policy.
o General information (i.e. pointers to additional available
services) is removed. The defined XML schema can be extended in
future to include those when XCON work matures.
o Dialog information is removed. It can be obtained by direct
subscription to a dialog package of a participant.
o Media stream information is aligned with SDP definitions (media
and proto) and SSRC attribute is added.
o Participant's status is expressed using two optional statuses:
"activity" and "history". Optional "is-on-a-dial-out-list"
indication is added.
o Normative references to XCON work are removed.
o Optional sidebar rosters are added.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[4] Moats, R., "URN Syntax", RFC 2141, May 1997.
[5] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[6] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-05 (work in progress), June
2003.
[7] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[8] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", RFC
3550, July 2003.
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Informative References
[9] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol",
draft-ietf-sipping-conferencing-framework-00 (work in
progress), May 2003.
[10] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
Authors' Addresses
Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07054
US
Phone: +1 973 952-5000
EMail: jdrosen@dynamicsoft.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
USA
EMail: oritl@microsoft.com
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