SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: August 6, 2004 A. Niemi
H. Khartabil
M. Isomaki
Nokia
February 6, 2004
Refering to Multiple Resources in the Session Initiation Protocol
(SIP)
draft-camarillo-sipping-multiple-refer-00.txt
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines extensions to the SIP REFER method so that this
method can be used to refer to multiple resources. These extensions
include the use of pointers to URI-lists in the Refer-To header
field, the use of bodies to describe the requests to be sent by the
server, and the use of a new event package to report the state of
several transactions.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Carrying Multiple Destinations . . . . . . . . . . . . . . . . 3
4. The Transaction State Event Package . . . . . . . . . . . . . 4
5. The Multiple-Refer SIP Option-Tag . . . . . . . . . . . . . . 5
6. The Template Disposition-Type . . . . . . . . . . . . . . . . 6
7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
Normative References . . . . . . . . . . . . . . . . . . . . . 8
Informational References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 10
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1. Introduction
The need for exploders in SIP [2] is described in [6]. Mechanisms to
invoke exploders in SIP need to meet the requirements listed there.
The SIP REFER method [4] allows a user agent to request a server to
send a request to a third party. Still, a number of applications need
to request a server to initiate transactions towards a set of
destinations. We define several extensions to REFER so that REFER can
be used to refer to multiple destinations (e.g., a user agent
requesting a conferencing server to INVITE several new participants).
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.
We define the following three new terms:
REFER-Issuer: the UA issuing the REFER request.
REFER-Recipient: the UA receiving the REFER request.
REFER-Target: the UA designated in the Refer-To URI.
3. Carrying Multiple Destinations
We represent the multiple REFER-Targets of a REFER using a URI list.
We use the Refer-To header field to carry a pointer to that URI-list.
draft-camarillo-sipping-uri-list provides rules to carry a pointer to
a URI list in a URI parameter called list. Refer-To header fields
carring a pointer to a URI-list follow the same rules. That is, the
Refer-To header field of REFER with multiple REFER-Targets MUST
contain a URI that points to a URI list. The XCAP resource list
format [5] MUST be supported; any other URI list formats MAY be
supported.
The following is an example of a REFER with a Refer-To header field
that points to a URI list which is carried in the message body. The
option-tag "multiple-refer" in the Require header, which is defined
in Section 5, ensures that the REFER-Recipient understands Refer-To
header fields with pointers to URI lists.
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REFER sip:b@atlanta.example.com SIP/2.0
Via: SIP/2.0/UDP agenta.atlanta.example.com;branch=z9hG4bK2293
To: <sip:b@atlanta.example.com>
From: <sip:a@atlanta.example.com>;tag=193402342
Call-ID: 898234234@agenta.atlanta.example.com
CSeq: 1 REFER
Max-Forwards: 70
Require: multiple-refer
Refer-To: cid:cn35t8jf02@example.com
Contact: sip:a@atlanta.example.com
Accept: application/sdp, message/sipfrag,
application/transaction-info+xml
Content-Type: application/resource-lists+xml
Content-Length: xxx
Content-ID: <cn35t8jf02@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list name="ad-hoc-1">
<entry name="1" uri="sip:bill@example.com" />
<entry name="2" uri="sip:joe@example.com" />
<entry name="3" uri="sip:ted@example.com" />
<entry name="4" uri="sip:bob@example.com" />
</list>
</resource-lists>
Figure 1
4. The Transaction State Event Package
REFER requests establish an implicit subscription to the "refer"
event package, defined in [4]. The data format used in this event
package is message/sipfrag, which is defined in [3]. The REFER
specification says the following about the NOTIFIES triggered by the
REFER's implicit subscription:
Each NOTIFY MUST contain an Event header field with a value of
refer and possibly an id parameter.
Each NOTIFY MUST contain a body of type "message/sipfrag".
We keep the first statement, but relax the second statement (about
the body format) so that the refer event package is aligned with any
other event package. That is, the notifier can choose any format that
is applicable to the event package and that appears in the Accept
header field of the request that created the subscription (the REFER,
in our case). The resulting normative statement is the following:
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The notifications generated by the server MUST be in one of the
formats specified in the Accept header field in the REFER request.
The default format, which MUST be supported by all UAs that generate
REFERs with the option-tag "multiple-refer" in a Require header
field, is "application/transaction-info+xml", as defined in
(draft-camarillo-sipping-transac-package).
The following is an example of the body of a NOTIFY generated by the
REFER-Recipient of the REFER in Figure 1.
<?xml version="1.0"?>
<transaction-info xmlns="urn:ietf:params:xml:ns:transaction-info"
version="0"
state="full"
entity="sip:b@atlanta.example.com">
<transaction id="frgd870th87" r-uri="sip:bill@example.com">
<state code="200">complete</state>
</transaction>
<transaction id="234f12345" r-uri="sip:joe@example.com">
<state code="404">complete</state>
</transaction>
<transaction id="fghd2345" r-uri="sip:ted@example.com">
<state code="200">complete</state>
</transaction>
<transaction id="12dvg2345" r-uri="sip:bob@example.com">
<state code="200">complete</state>
</transaction>
</transaction-info>
Figure 2
5. The Multiple-Refer SIP Option-Tag
We define a new SIP option-tag for the Require and Supported header
fields: multiple-refer.
A UA including the multiple-refer option-tag in a Supported header
understands Refer-To header fields that point to URI lists and
understands the "application/transaction-info+xml" body type.
A UA generating a REFER with a pointer to a URI-list in its Refer-To
header field MUST include the multiple-refer option-tag in the
Require header field of the REFER.
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6. The Template Disposition-Type
When using REFER, the new request to be sent is described using URI
parameters. For example, the following Refer-To header field contains
the values of the Accept-Contact and Call-ID header fields of the new
request.
Refer-To: <sip:bob@biloxi.example.net?Accept-Contact=sip:bobsdesk.
biloxi.example.net&Call-ID%3D55432%40alicepc.atlanta.example.com>
REFERs with multiple REFER-Targets usually request that the
REFER-Recipient sends a set of similar requests. Describing a set of
similar requests by adding the same URI parameters to all the URIs in
the definition of the URI list is not an efficient way to encode that
information.
We define a new disposition-type: template. Bodies of this
disposition-type (typically sipfrag bodies as defined in RFC 3420
[3]) provide the server with a template for the messages to be sent.
The following example shows a body whose disposition-type is
template. It indicates that the requests to be sent should be
MESSAGEs carrying the text "Hello world."
Content-Disposition: template;handling=required
Content-type: message/sipfrag
Content-Length: xxx
MESSAGE sip:whoever.invalid SIP/2.0
Content-Type: text/plain
Content-Length: 12
Hello World.
If any of the URIs defining the REFER-Targets has a URI parameter
indicating a different value for a header field than the one
indicated in the template, the exploder MUST use the value in the URI
parameter.
Note that in order to include the method in a sipfrag body, it is
necessary to include the Request-URI as well (the whole Request-line
needs to be included as specified in RFC 3420 [3]. If the REFER
request contains a single REFER-Target, the URI of the Request-Target
SHOULD be placed in the Request-URI of the template body. Otherwise,
it is RECOMMENDED that the Request-URI in the template body is an
invalid URI.
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OPEN ISSUE: we may want to define an option-tag for this
disposition-type, or to include support for this disposition type in
the multiple-refer option tag.
7. Example
We need to add the whole call flow.
REFER sip:b@atlanta.example.com SIP/2.0
Via: SIP/2.0/UDP agenta.atlanta.example.com;branch=z9hG4bK2293
To: <sip:b@atlanta.example.com>
From: <sip:a@atlanta.example.com>;tag=193402342
Call-ID: 898234234@agenta.atlanta.example.com
CSeq: 1 REFER
Max-Forwards: 70
Require: multiple-refer
Refer-To: cid:cn35t8jf02@example.com
Contact: sip:a@atlanta.example.com
Accept: application/sdp, message/sipfrag,
application/transaction-info+xml
Conten-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx
--boundary1
Content-Disposition: template;handing=required
Content-type: message/sipfrag
Content-Length: xxx
MESSAGE sip:whoever.invalid SIP/2.0
Content-Type: text/plain
Content-Length: 12
Hello World.
--boundary1
Content-Type: application/resource-lists+xml
Content-Length: xxx
Content-ID: <cn35t8jf02@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list name="ad-hoc-1">
<entry name="1" uri="sip:bill@example.com" />
<entry name="2" uri="sip:joe@example.com" />
<entry name="3" uri="sip:ted@example.com" />
<entry name="4" uri="sip:bob@example.com" />
</list>
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</resource-lists>
--boundary1--
8. Security Considerations
TBD
9. IANA Considerations
TBD: we need to register the multiple-refer option-tag and the
template disposition type.
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] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
November 2002.
[4] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[5] Rosenberg, J., "An Extensible Markup Language (XML)
Configuration Access Protocol (XCAP) Usage for Presence Lists",
draft-ietf-simple-xcap-list-usage-01 (work in progress), October
2003.
Informational References
[6] Camarillo, G., "Requirements for Session Initiation Protocol
(SIP) Exploder Invocation", draft-camarillo-sipping-exploders-01
(work in progress), November 2003.
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Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
Aki Niemi
Nokia
P.O. Box 321
NOKIA GROUP, FIN 00045
Finland
EMail: Aki.Niemi@nokia.com
Hisham Khartabil
Nokia
P.O. Box 321
NOKIA GROUP, FIN 00045
Finland
EMail: Hisham.Khartabil@nokia.com
Markus Isomaki
Nokia
Itamerenkatu 11-13
Helsinki 00180
Finland
EMail: Markus.Isomaki@nokia.com
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