SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: May 28, 2005 A. Johnston
MCI
November 27, 2004
Conference Establishment Using Request-Contained Lists in the Session
Initiation Protocol (SIP)
draft-ietf-sipping-uri-list-conferencing-02.txt
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Copyright (C) The Internet Society (2004).
Abstract
This document describes how to create a conference using SIP URI-list
services. In particular, we describe a mechanism that allows a
client to provide a conference server with the initial list of
participants using an INVITE-contained URI-list.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Providing a Conference Server with a URI-List . . . . . . . . 3
4. URI List Format . . . . . . . . . . . . . . . . . . . . . . . 3
5. Conference Server Behavior . . . . . . . . . . . . . . . . . . 4
6. Re-INVITEs . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1 Normative References . . . . . . . . . . . . . . . . . . . . 7
10.2 Informational References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 9
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1. Introduction
Section 4.5 of [3] describes how to create a conference using ad-hoc
SIP [2] methods. The client sends an INVITE request to a conference
factory URI, and receives the actual conference URI, which contains
the "isfocus" feature tag, in the Contact header field of a response
(typically a 200 OK).
Once the client obtains the conference URI, it can add participants
to the newly created conference in several ways, which are described
in [3].
Some environments have tough requirements regarding conference
establishment time. So, they require the client to be able to
request the creation of an ad-hoc conference and to provide the
server with the initial set of participants in a single operation.
This document describes how to meet this requirement using the
mechanism to transport URI lists in SIP messages described in [4].
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Providing a Conference Server with a URI-List
A client that wants to include the set of initial participants in its
initial INVITE to create an ad-hoc conference, adds a body whose
disposition type is recipient-list, as defined in [4], with a
URI-list that contains the participants that the client wants the
server to INVITE. The client sends this INVITE to the conference
factory URI.
4. URI List Format
As described in [4], specifications of individual URI-list services,
like the conferencing service described here, need to specify a
default format for recipient-list bodies used within the particular
service.
The default format for recipient-list bodies for conferencing UAs
(User Agents) and servers is the resource list format defined in [5].
So, conferencing UAs and servers handling recipient-list bodies MUST
support this format and MAY support other formats.
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Nevertheless, the Extensible Markup Language (XML) Configuration
Access Protocol (XCAP) resource list document provides features, such
as hierarchical lists and the ability to include entries by reference
relative to the XCAP root URI, that are not needed by the
conferencing service defined in this document, which only needs to
transfer a flat list of URIs between a UA and the conference server.
Therefore, when using the default resource list document,
conferencing UAs SHOULD use flat lists (i.e., no hierarchical lists)
and SHOULD NOT use <entry-ref> elements.
A conference factory application receiving a URI-list with more
information than what has just been described MAY discard all the
extra information.
Figure 1 shows an example of a flat list that follows the resource
list document.
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list>
<entry uri="sip:bill@example.com" />
<entry uri="sip:joe@example.org" />
<entry uri="sip:ted@example.net" />
</list>
</resource-lists>
Figure 1: URI List
5. Conference Server Behavior
On reception of an INVITE with a recipient-list body as described in
Section 3, a conference server MUST follow the rules described in [3]
to create ad-hoc conferences. Once the ad-hoc conference is created,
the conference server SHOULD attempt to add the participants in the
URI-list to the conference as if their addition had been requested
using any of the methods described in [3] (e.g., using CPCP [6]).
Once the conference server has created the ad-hoc conference and has
attempted to add the initial set of participants, the conference
server behaves as a regular conference server and MUST follow the
rules in [3].
Note that the status code in the response to the INVITE does not
provide any information about whether or not the conference server
was able to bring the users in the URI-list into the conference.
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That is, a 200 (OK) means that the conference was created
successfully, that the client that generated the INVITE is in the
conference, and that the server understood the URI-list. If the
client wishes to obtain information about the status of other users
in the conference it SHOULD use general conference mechanisms, such
as the conference package [7].
6. Re-INVITEs
The previous Sections have specified how to include a URI-list in an
initial INVITE request to a conference server. Once the
INVITE-initiated dialog between the client and the conference server
has been established, the client may need to send subsequent INVITE
requests (typically referred to as re-INVITEs) to the conference
server to, for example, modify the characteristics of the media
exchanged with the server.
At this point, there are no semantics associated with resource-list
bodies in re-INVITEs (although future extensions may define them).
Therefore, clients SHOULD NOT include resource-list bodies in
re-INVITEs sent to a conference server.
A conference server receiving a re-INVITE with a resource-list body,
following standard SIP procedures, rejects it with a 415 (Unsupported
Media Type) response.
Note that a difference between an initial INVITE request and a
re-INVITE is that while the initial INVITE is sent to the
conference factory URI, the re-INVITE is sent to the URI provided
by the server in a Contact header field when the dialog was
established. Therefore, from the client's point of view, the
resource identified by the former URI supports recipient-list
bodies while the resource identified by the latter does not
support them.
7. Example
The following is an example of an INVITE request, which carries a URI
list in a recipient-list body part, sent by a UA to a conference
factory application. Note that since the INVITE carries an SDP
description as well, it contains a multipart body.
INVITE sip:conf-fact@example.com SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: Conf Factory <sip:conf-fact@example.com>
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From: Carol <sip:carol@chicago.example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 1 INVITE
Contact: <sip:carol@client.chicago.example.com>
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
SUBSCRIBE, NOTIFY
Allow-Events: dialog
Accept: application/sdp, message/sipfrag
Conten-Type: multipart/mixed;boundary="boundary1"
Content-Length: 690
--boundary1
Content-Type: application/sdp
v=0
o=carol 2890844526 2890842807 IN IP4 chicago.example.com
s=-
c=IN IP4 192.0.2.1
t=0 0
m=audio 20000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
m=video 20002 RTP/AVP 31
a=rtpmap:31 H261/90000
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list>
<entry uri="sip:bill@example.com" />
<entry uri="sip:joe@example.org" />
<entry uri="sip:ted@example.net" />
</list>
</resource-lists>
--boundary1--
Figure 2: INVITE request
8. Security Considerations
This document discusses setup of SIP conferences using a
request-contained URI-list. Both conferencing and URI-lists services
have specific security requirements which will be summarized here.
Conferences generally have authorization rules about who may or may
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not join a conference, what type of media may or may not be used,
etc. This information is used by the focus to admit or deny
participation in a conference. It is RECOMMENDED that these types of
authorization rules be used to provide security for a SIP conference.
For this authorization information to be used, the focus needs to be
able to authenticate potential participants. Normal SIP mechanisms
including Digest authentication and certificates can be used. These
conference specific security requirements are discussed further in
the requirements and framework documents.
For conference creation using a list, there are some additional
security considerations. The Framework and Security Considerations
for SIP URI-List Services [4] discusses issues related to SIP
URI-list services. Given that a conference server sending INVITEs to
a set of users acts as an URI-list service, implementations of
conference servers that handle lists MUST follow the security-related
rules in [4]. These rules include mandatory authentication and
authorization of clients, and opt-in lists.
9. Acknowledges
Cullen Jennings, Hisham Khartabil, and Jonathan Rosenberg provided
useful comments on this document.
10. References
10.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] Johnston, A. and O. Levin, "Session Initiation Protocol Call
Control - Conferencing for User Agents",
draft-ietf-sipping-cc-conferencing-05 (work in progress),
October 2004.
[4] Camarillo, G., "Requirements and Framework for Session
Initiation Protocol (SIP)Uniform Resource Identifier (URI)-List
Services", draft-ietf-sipping-uri-services-01 (work in
progress), October 2004.
[5] Rosenberg, J., "Extensible Markup Language (XML) Formats for
Representing Resource Lists",
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draft-ietf-simple-xcap-list-usage-04 (work in progress), October
2004.
10.2 Informational References
[6] Koskelainen, P. and H. Khartabil, "An Extensible Markup Language
(XML) Configuration Access Protocol (XCAP) Usage for Conference
Policy Manipulation", draft-koskelainen-xcon-xcap-cpcp-usage-02
(work in progress), February 2004.
[7] Rosenberg, J. and H. Schulzrinne, "A Session Initiation Protocol
(SIP) Event Package for Conference State",
draft-ietf-sipping-conference-package-06 (work in progress),
October 2004.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
Alan Johnston
MCI
100 South 4th Street
St. Louis, MO 63102
USA
EMail: alan.johnston@mci.com
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