SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: January 5, 2005 A. Johnston
MCI
July 7, 2004
Conference Establishment Using Request-Contained Lists in the Session
Initiation Protocol (SIP)
draft-ietf-sipping-uri-list-conferencing-00.txt
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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. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 6
9.2 Informational References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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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 uri-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], the default format for URI lists in SIP is the
XCAP resource list format [5]. Still, specific services need to
describe which information clients should include in their URI lists,
as described in [4].
Conferencing UAs SHOULD use flat lists (i.e., no hierarchical lists),
SHOULD NOT use any entry's attributes but "uri", and SHOULD NOT
include any elements inside entries but "display-name" elements.
A conference factory application receiving a URI list with more
information than what we have just described SHOULD discard all the
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extra information.
5. Conference Server Behavior
On reception of an INVITE with a uri-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 [7]).
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. 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 [8].
6. Example
The following is an example of an INVITE request, which carries a URI
list in a uri-list body, sent by a UA to a conference factory
application.
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>
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: 635
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--boundary1
Content-Type: application/sdp
v=0
o=carol 2890844526 2890842807 IN IP4 chicago.example.com
s=Example Subject
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: uri-list
<?xml version="1.0" encoding="UTF-8"?>
<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 1: INVITE request
7. 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
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
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security considerations. The Security Considerations Section of the
Requirements and Framework for SIP URI-List Services [6] 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 [6]. These rules include mandatory
authentication and authorization of clients, and opt-in lists.
8. Acknowledges
Cullen Jennings provided useful comments on this document.
9. References
9.1 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-03 (work in progress),
February 2004.
[4] Camarillo, G., "Providing a Session Initiation Protocol (SIP)
Application Server with a List of URIs",
draft-camarillo-sipping-uri-list-01 (work in progress), February
2004.
[5] Rosenberg, J., "An Extensible Markup Language (XML)
Configuration Access Protocol (XCAP) Usage for Presence Lists",
draft-ietf-simple-xcap-list-usage-02 (work in progress),
February 2004.
[6] Camarillo, G., "Requirements for Session Initiation Protocol
(SIP) Exploder Invocation", draft-camarillo-sipping-exploders-02
(work in progress), February 2004.
9.2 Informational References
[7] 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.
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[8] Rosenberg, J. and H. Schulzrinne, "A Session Initiation Protocol
(SIP) Event Package for Conference State",
draft-ietf-sipping-conference-package-03 (work in progress),
February 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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