One document matched: draft-camarillo-sipping-uri-list-02.txt
Differences from draft-camarillo-sipping-uri-list-01.txt
SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: September 25, 2004 A. Roach
dynamicsoft
March 27, 2004
Providing a Session Initiation Protocol (SIP) Application Server with
a List of URIs
draft-camarillo-uri-list-02.txt
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes how a user agent can provide an application
server with a list of URIs. The way the application server uses the
URIs in the list is method specific.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Procedures at the User Agent . . . . . . . . . . . . . . . . . 4
5. URI List Format . . . . . . . . . . . . . . . . . . . . . . . 4
6. The SIP and SIPS URI List Parameter . . . . . . . . . . . . . 5
7. The Content-ID SIP Header Field . . . . . . . . . . . . . . . 5
8. Pointing to External URI Lists . . . . . . . . . . . . . . . . 6
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
12. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 8
Normative References . . . . . . . . . . . . . . . . . . . . . 8
Informational References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
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1. Introduction
Some services require a SIP UA to provide an application server with
a set of URIs. For example, a UA creating a conference needs to
provide the conference server with the participants. The same way, a
UA requesting presence information from a set of users needs to
provide the resource list server with the URIs of the users that
belong to the list.
These lists are typically configured using out-of-band methods. For
instance, a UA can use XCAP [7] to create a list of URIs and to
associate this list with a SIP URI (e.g., sip:myfriends@example.com).
It can, then, send a SIP request (an INVITE or a SUBSCRIBE in our
previous examples) to that SIP URI.
Still, there is a need to create lists of URIs in an ad-hoc way and
send them directly in a SIP message. Transporting the URI list in the
SIP message that triggers the service usually helps reduce the
service establishment time, and is useful for UAs that do not have
access to a server to host their list (and they cannot act as a
server themselves).
In any case, the way the application server interprets the URI list
received in the request is method specific.
A UA creating a SIP request that needs to carry a URI list proceeds
this way. It places the URI list (e.g., an XCAP resource list [4]) in
a body part, and constructs a pointer to that body part (i.e., a
Content-ID URL [2] that points to the body part that carries the URI
list). Then, the UA places the pointer in a "list" URI parameter. The
way the application server interprets the URI list received in the
request is method specific.
2. Scope
This document specifies how to associate a URI list with a SIP or
SIPS URI using the "list" parameter. The base URI identifies, as
usual, a resource (generally a service), which is further described
by the associated URI list.
SIP transport of URI lists that are not associated with a SIP or SIPS
URI is outside the scope of this document. Note, in any case, that
the syntax of a number of already defined SIP header fields (e.g.,
Alert-Info, Call-Info, Contact, etc) allows them to carry a set of
URIs.
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3. 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.
4. Procedures at the User Agent
A UA creating a SIP request that needs to carry a SIP or SIPS URI
with an associated URI list MUST place the URI list in a body part,
and MUST construct a pointer to that body part (i.e., a Content-ID
URL [2] that points to the body part that carries the URI list).
Then, the UA MUST place the pointer in a "list" URI parameter (which
is defined in Section 6) of the SIP or SIPS URI.
The following is an example of a Content-ID URL:
cid:cn35t8jf02@example.com
The body the previous Content-ID URI points to would be described by,
among other header fields, the following Content-ID header field:
Content-ID: <cn35t8jf02@example.com>
Further procedures are method specific and are defined in separate
documents. For example, the use of lists and the INVITE method is
described in (draft-camarillo-sipping-adhoc-conferencing-00.txt), and
the use of lists and SUBSCRIBE is defined in
(draft-camarillo-sipping-adhoc-simple-00.txt).
As for any other SIP request, the size of requests carrying URI lists
MUST NOT exceed 1300 bytes, unless the user agent client has positive
knowledge that the message will not traverse a congestion-unsafe link
at any hop, or that the message size is at least 200 bytes less than
the lowest MTU value found en route to the server.
5. URI List Format
The default URI list format for SIP entities is the XCAP resource
list format defined in [4]. So, SIP entities handling URI lists MUST
support this format.
Nevertheless, the XCAP resource list format provides features such as
hierarchical lists and list's attributes that are not needed by many
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services, which only need to transfer a flat list of URIs from a
client to a server. The amount of information that a URI list needs
to carry between a client and a server is method specific.
Additionally, the way a client and a server negotiate the amount of
information needed for a particular service is method specific as
well.
A client invoking a particular service SHOULD NOT include more
information in its URI list than the service requires. A server
providing a particular service MAY discard any extra information
which is received in a URI list from the client.
The following is an example of a flat list without attributes.
<?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.com" />
<entry uri="sip:ted@example.com" />
<entry uri="sip:bob@example.com" />
</list>
</resource-lists>
Figure 1: URI List
6. The SIP and SIPS URI List Parameter
SIP and SIPS URIs that need to reference a URI list MUST carry a
pointer to the URI list, as described in Section 4, in a "list" SIP
and SIPS URI parameter. We define the "list" parameter for SIP and
SIPS URIs so that it MUST contain a Content-ID URL [2] that points to
a URI list. The ABNF of the "list" parameter is:
list-param = "list=" absoluteURI
The following is an example of a SIP URI with a list parameter
pointing to a body part using a Content-ID URL [2]:
sip:group@example.com;list=cid:cn35t8jf02@example.com
7. The Content-ID SIP Header Field
The Content-ID MIME header field is defined in RFC 2045 [6]. We
define here the same header field to be used in SIP messages. Without
this definition, SIP messages with a single body could not reference
it using Content-ID URLs (messages with multiple bodies use the
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definition RFC 2045 [6]). The ABNF of the SIP Content-ID header field
is:
Content-ID = "Content-ID" HCOLON msg-id
RFC 2822 [3] defines msg-id in Section 3.6.4.
The Content-ID value is used to uniquely identify a body. The
Content-ID header field MAY appear in any SIP request or response
that contains a body.
8. Pointing to External URI Lists
UAs that want to use an external URI list, instead of sending it as a
body part, SHOULD use the content indirection mechanism defined in
[5]. Indirected body parts are equivalent and have the same treatment
as in-line body parts.
The content indirection mechanism has certain security properties,
such as allowing the UA to provide a hash of the contents of the
external list, that could not be provided if "list" parameters could
point directly to external lists (e.g., using an HTTP URI).
9. Examples
The following is an example of an INVITE request that carries a URI
list in its body. The Request-URI of this INVITE contains a pointer
to the body part carrying the list.
INVITE sip:ad-hoc@example.com;list=cid:cn35t8jf02@example.com SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: <sip:ad-hoc@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,
application/resource-lists+xml
Conten-Type: multipart/mixed;boundary="boundary1"
Content-Length: 679
--boundary1
Content-Type: application/sdp
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Content-Length: 160
v=0
o=carol 2890844526 2890842807 IN IP4 chicago.example.com
s=Example Subject
c=IN IP4 192.0.0.1
t=0 0
m=audio 20000 RTP/AVP 0
m=video 20002 RTP/AVP 31
--boundary1
Content-Type: application/resource-lists+xml
Content-Length: 315
Content-ID: <cn35t8jf02@example.com>
<?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.com" />
<entry uri="sip:ted@example.com" />
<entry uri="sip:bob@example.com" />
</list>
</resource-lists>
--boundary1--
Figure 2: INVITE request
Refer to (draft-camarillo-sipping-adhoc-conferencing-00.txt) for the
normative details on how a list can be used with the INVITE method.
10. Security Considerations
This document discusses how to carry URI lists in SIP messages. In
some cases, the URIs in the lists may need to be kept private. It is
RECOMMENDED that S/MIME is used to prevent a third party from viewing
this information.
Some application servers, on reception of a SIP message with a URI
list, send SIP requests to the URIs in the list. Such an application
server may have policies that limit the number of URIs in the list,
as a very long list could be used in a denial of service attack to
place a large burden on the application server to send a large number
of SIP requests. In addition, it is RECOMMENDED that S/MIME is used
to integrity protect the list contents to keep attackers from adding
URIs to a list.
An application server MUST authenticate and authorize any user that
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requests the application server to send requests to a list of URIs.
Otherwise, a malicious client could use the application server to
perform a denial of service attack. In any event, this risk also
exists when a client sets up a URI list using out-of-band methods
(e.g., XCAP) and sends a request to that list. Application servers
MUST use authentication and authorization mechanisms with equivalent
security properties when sending requests to URI lists created using
out-of-band and in-band methods.
11. IANA Considerations
This document registers the "list" SIP and SIPS URI parameter, which
is described in Section 6. This parameter is to be added to the SIP
and SIPS URI parameter registry under http://www.iana.org/ TBD.
This document registers the Content-ID SIP header field, which is
described in Section 7. This header field is to be added to the
header field registry under http://www.iana.org/assignments/
sip-parameters.
Header Name: Content-ID
Compact Form: (none)
12. Acknowledges
Alan Johnston, Orit Levin, and Cullen Jennings provided useful
comments on this document.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
[3] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[4] 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.
[5] Olson, S., "A Mechanism for Content Indirection in Session
Initiation Protocol (SIP) Messages",
draft-ietf-sip-content-indirect-mech-03 (work in progress), June
2003.
Informational References
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[6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[7] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-02
(work in progress), February 2004.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
Adam Roach
dynamicsoft
5100 Tennyson Pkwy
Suite 1200
Plano, TX 75024
US
EMail: adam@dynamicsoft.com
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