SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: July 30, 2007 A. Johnston
Avaya
January 26, 2007
Conference Establishment Using Request-Contained Lists in the Session
Initiation Protocol (SIP)
draft-ietf-sip-uri-list-conferencing-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document describes how to create a conference using SIP URI-list
services. In particular, it describes a mechanism that allows a user
agent 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. User Agent Client Procedures . . . . . . . . . . . . . . . . . 3
3.1. Response Handling . . . . . . . . . . . . . . . . . . . . 3
3.2. Re-INVITE Request Generation . . . . . . . . . . . . . . . 4
4. URI-List Document Format . . . . . . . . . . . . . . . . . . . 4
5. Conference Server Procedures . . . . . . . . . . . . . . . . . 6
5.1. Re-INVITE Request Handling . . . . . . . . . . . . . . . . 6
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
Section 5.4 of RFC 4579 [5] describes how to create a conference
using ad-hoc SIP (which is specified in RFC 3261 [4]) 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) response.
Once the UAC (User Agent Client) obtains the conference URI, it can
add participants to the newly created conference in several ways,
which are described in RFC 4579 [5].
Some environments have tough requirements regarding conference
establishment time. They require the UAC to be able to request the
creation of an ad-hoc conference and to provide the conference 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 RFC xxxx [6].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
3. User Agent Client Procedures
A UAC that wants to include the set of initial participants in its
initial INVITE request to create an ad-hoc conference, adds a body
whose disposition type is 'recipient-list', as defined in RFC xxxx
[6], with a URI-list that contains the participants that the UAC
wants the conference server to invite. Additionally, the UAC MUST
include the 'recipient-list-invite' option-tag, which is registered
with the IANA in Section 8 in a Require header field. The UAC sends
this INVITE request to the conference factory URI.
3.1. Response Handling
The status code in the response to the INVITE request 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) response means that the conference was created
successfully, that the UAC that generated the INVITE request is in
the conference, and that the server understood the URI-list. If the
UAC wishes to obtain information about the status of other users in
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the conference it SHOULD use general conference mechanisms, such as
the conference package, which is defined in RFC 4575 [9].
3.2. Re-INVITE Request Generation
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 UAC and the conference server has been
established, the UAC can send subsequent INVITE requests (typically
referred to as re-INVITE requests) 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-INVITE requests (although future extensions may define
them). Therefore, UACs SHOULD NOT include resource-list bodies in
re-INVITE requests sent to a conference server.
Note that a difference between an initial INVITE request and a re-
INVITE request is that while the initial INVITE request is sent to
the conference factory URI, the re-INVITE request is sent to the
URI provided by the server in a Contact header field when the
dialog was established. Therefore, from the UAC'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.
4. URI-List Document Format
As described in RFC xxxx [6], 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) is the XML resource list format (which is specified in
RFC xxxx [7]) extended with the XML Format Extension for Representing
Copy Control Attributes in Resource Lists (which is specified in RFC
xxxx [8]). Consequently, conferencing UACs generating 'recipient-
list' bodies MUST support both of these formats and MAY support other
formats. Conferencing servers able to handle 'recipient-list' bodies
MUST support both of these formats and MAY support other formats.
As described in the XML Format Extension for Representing Copy
Control Attributes in Resource Lists (which is specified in RFC xxxx
[8]), each URI can be tagged with a 'copyControl' attribute set to
either "to", "cc", or "bcc", indicating the role in which the
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recipient will get the INVITE request. Additionally, URIs can be
tagged with the 'anonymize' attribute to prevent that the conference
server discloses the target URI in a URI-list.
In addition, the XML Format Extension for Representing Copy Control
Attributes in Resource Lists (which is specified in RFC xxxx [8])
defines a 'recipient-list-history' body that contains the list of
recipients. The default format for 'recipient-list-history' bodies
for conferencing UAs is also the XML resource list document format
specified in RFC xxxx [7] extended with the XML Format Extension for
Representing Copy Control Attributes in Resource Lists specified in
[8]. Consequently, conferencing UACs able to generate 'recipient-
list-history' bodies MUST support these formats and MAY support
others. Conferencing UAs able to understand 'recipient-list-history'
MUST support these formats and MAY support others. Conferencing
servers able to handle 'recipient-list-history' bodies MUST support
these formats and MAY support others.
Nevertheless, the XML resource list document specified in RFC xxxx
[7] 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 (User
Agent) 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 XML
resource list document (specified in RFC xxxx [7]) extended with the
XML Format Extension for Representing Copy Control Attributes in
Resource Lists (specified in RFC xxxx [8]).
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:cp="urn:ietf:params:xml:ns:copycontrol">
<list>
<entry uri="sip:bill@example.com" cp:copyControl="to" />
<entry uri="sip:joe@example.org" cp:copyControl="cc" />
<entry uri="sip:ted@example.net" cp:copyControl="bcc" />
</list>
</resource-lists>
Figure 1: URI-List
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5. Conference Server Procedures
Conference servers that are able to receive and process INVITE
requests with a 'recipient-list' body SHOULD include a 'recipient-
list-invite' option-tag in a Supported header field when responding
to OPTIONS requests.
On reception of an INVITE request containing a 'recipient-list' body
as described in Section 3, a conference server MUST follow the rules
described in RFC 4579 [5] 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 RFC
4579 [5].
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 RFC 4579 [5].
The incoming INVITE request will contain a URI-list body or reference
(as specified in RFC xxxx [6]) with the actual list of recipients.
If this URI-list includes resources tagged with the 'copyControl'
attribute set to a value of "to" or "cc", the conference server
SHOULD include a URI-list in each of the outgoing INVITE requests.
This list SHOULD be formatted according to the XML format for
representing resource lists (specified in RFC xxxx [7]) and the
copyControl extension specified in RFC xxxx [8]. The URI-list
service MUST follow the procedures specified in RFC xxxx [8] with
respect to the handling of the 'anonymize', 'count' and 'copyControl'
attributes.
If the conference server includes a URI-list in an outgoing INVITE
request, it MUST include a Content-Disposition header field (which is
specified in RFC 2183 [2]) with the value set to 'recipient-list-
history' and a 'handling' parameter (as specified in RFC 3204 [3])
set to "optional".
5.1. Re-INVITE Request Handling
At this point, there are no semantics associated with resource-list
bodies in re-INVITE requests (although future extensions may define
them). Therefore, a conference server receiving a re-INVITE request
with a resource-list body and, consequently, a 'recipient-list-
invite' option-tag, following standard SIP procedures, rejects it
with a 420 (Bad Extension), which carries an Unsupported header field
listing the 'recipient-list-invite' option-tag.
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This is because the resource identified by the conference URI does
not actually support this extension. On the other hand, the
resource identified by the conference factory URI does support
this extension and, consequently, would include the 'recipient-
list-invite' option-tag in, for example, responses to OPTIONS
requests.
6. Example
Figure 2 shows an example of operation. A UAC sends an INVITE
request (F1) that contains an SDP body and a URI-list to the
conference server. The conference server answers with a 200 (OK)
response and generates an INVITE request to each of the UASs (USer
Agent Servers) identifies by the URIs included in the URI-list. The
conference server includes SDP and a manipulated URI-list in each of
the outgoing INVITE requests.
+--------+ +---------+ +--------+ +--------+ +--------+
|SIP UAC | | confer. | |SIP UAS | |SIP UAS | |SIP UAS |
| | | server | | 1 | | 2 | | n |
+--------+ +---------+ +--------+ +--------+ +--------+
| | | | |
| F1. INVITE | | | |
| ---------------->| | | |
| F2. 200 OK | | | |
|<---------------- | F3. INVITE | | |
| | ------------->| | |
| | F4. INVITE | | |
| | ------------------------>| |
| | F5. INVITE | | |
| | ----------------------------------->|
| | F6. 200 OK | | |
| |<------------- | | |
| | F7. 200 OK | | |
| |<------------------------ | |
| | F8. 200 OK | | |
| |<----------------------------------- |
| | | | |
| | | | |
| | | | |
Figure 2: Example of operation
Figure 3 shows an example of the INVITE request F1, which carries a
multipart/mixed body composed of two other bodies: an application/sdp
body that describes the session and an application/resource-lists+xml
body that contains the list of target URIs.
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INVITE sip:conf-fact@example.com SIP/2.0
Via: SIP/2.0/TCP atlanta.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: "Conf Factory" <sip:conf-fact@example.com>
From: Alice <sip:alice@example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 1 INVITE
Contact: <sip:alice@atlanta.example.com>
Allow: INVITE, ACK, CANCEL, BYE, REFER
Allow-Events: dialog
Accept: application/sdp, message/sipfrag
Require: recipient-list-invite
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: 690
--boundary1
Content-Type: application/sdp
v=0
o=alice 2890844526 2890842807 IN IP4 atlanta.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:cp="urn:ietf:params:xml:ns:copyControl">
<list>
<entry uri="sip:bill@example.com" cp:copyControl="to" />
<entry uri="sip:randy@example.net" cp:copyControl="to"
cp:anonymize="true"/>
<entry uri="sip:eddy@example.com" cp:copyControl="to"
cp:anonymize="true"/>
<entry uri="sip:joe@example.org" cp:copyControl="cc" />
<entry uri="sip:carol@example.net" cp:copyControl="cc"
cp:anonymize="true"/>
<entry uri="sip:ted@example.net" cp:copyControl="bcc" />
<entry uri="sip:andy@example.com" cp:copyControl="bcc" />
</list>
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</resource-lists>
--boundary1--
Figure 3: INVITE request received at the conference server
The INVITE requests F3, F4, and F5 are similar in nature. All those
INVITE requests contain a multipart/mixed body which is composed of
two other bodies: an application/sdp body describing the session and
an application/resource-lists+xml containing the list of recipients.
The application/resource-lists+xml bodies are not equal to the
application/resource-lists+xml included in the received INVITE
request F1, because the conference server has anonymized those URIs
tagged with the 'anonymize' attribute and has removed those URIs
tagged with a "bcc" 'copyControl' attribute. Figure 4 shows an
example of the message F3.
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INVITE sip:bill@example.com SIP/2.0
Via: SIP/2.0/TCP conference.example.com
;branch=z9hG4bKhjhs8as454
Max-Forwards: 70
To: <sip:bill@example.com>
From: Conference Server <sip:conf34@example.com>;tag=234332
Call-ID: 389sn189dasdf
CSeq: 1 INVITE
Contact: <sip:conf34@conference.example.com>;isfocus
Allow: INVITE, ACK, CANCEL, BYE, REFER
Allow-Events: dialog, conference
Accept: application/sdp, message/sipfrag
Require: recipient-list-invite
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: 690
--boundary1
Content-Type: application/sdp
v=0
o=conf 2890844343 2890844343 IN IP4 conference.example.com
s=-
c=IN IP4 192.0.2.5
t=0 0
m=audio 40000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
m=video 40002 RTP/AVP 31
a=rtpmap:31 H261/90000
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list-history; handling=optional
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:cp="urn:ietf:params:xml:ns:copycontrol">
<list>
<entry uri="sip:bill@example.com" cp:copyControl="to" />
<entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="to"
cp:count="2"/>
<entry uri="sip:joe@example.org" cp:copyControl="cc" />
<entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="cc"
cp:count="1"/>
</list>
</resource-lists>
--boundary1--
Figure 4: INVITE request sent by the conference server
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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 can or
cannot join a conference, what type of media can or cannot 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 (which is documented in RFC xxxx [6])
discusses issues related to SIP URI-list services. Given that a
conference server sending INVITE requests 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 RFC xxxx [6].
These rules include mandatory authentication and authorization of
clients, and opt-in lists.
8. IANA Considerations
This document defines the 'recipient-list-invite' SIP option-tag. It
should be registered in the Option Tags subregistry under the SIP
parameter registry. The following is the description to be used in
the registration.
+------------------------+------------------------------+-----------+
| Name | Description | Reference |
+------------------------+------------------------------+-----------+
| recipient-list-invite | The body contains a list of | [RFCXXXX] |
| | URIs that indicates the | |
| | recipients of the SIP INVITE | |
| | request | |
+------------------------+------------------------------+-----------+
Table 1: Registration of the 'recipient-list-invite' Option-Tag in
SIP
Note to IANA and the RFC editor: replace RFCXXXX above with the RFC
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number of this specification.
9. Acknowledges
Cullen Jennings, Hisham Khartabil, Jonathan Rosenberg, and Keith
Drage provided useful comments on this document. Miguel Garcia-
Martin assembled the dependencies to the 'copyControl' attribute
extension.
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] Troost, R., Dorner, S., and K. Moore, "Communicating
Presentation Information in Internet Messages: The Content-
Disposition Header Field", RFC 2183, August 1997.
[3] Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F.,
Watson, M., and M. Zonoun, "MIME media types for ISUP and QSIG
Objects", RFC 3204, December 2001.
[4] 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.
[5] Johnston, A. and O. Levin, "Session Initiation Protocol (SIP)
Call Control - Conferencing for User Agents", BCP 119, RFC 4579,
August 2006.
[6] Camarillo, G. and A. Roach, "Framework and Security
Considerations for Session Initiation Protocol (SIP) Uniform
Resource Identifier (URI)-List Services",
draft-ietf-sipping-uri-services-06 (work in progress),
September 2006.
[7] Rosenberg, J., "Extensible Markup Language (XML) Formats for
Representing Resource Lists",
draft-ietf-simple-xcap-list-usage-05 (work in progress),
February 2005.
[8] Garcia-Martin, M. and G. Camarillo, "Extensible Markup Language
(XML) Format Extension for Representing Copy Control Attributes
in Resource Lists", draft-ietf-sipping-capacity-attribute-03
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(work in progress), December 2006.
10.2. Informative References
[9] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference State",
RFC 4575, August 2006.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Alan Johnston
Avaya
St. Louis, MO 63124
USA
Email: alan@sipstation.com
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