SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: October 10, 2005 A. Roach
Estacado Systems
O. Levin
Microsoft Corporation
April 8, 2005
Subscriptions to Request-Contained Resource Lists in the Session
Initiation Protocol (SIP)
draft-ietf-sipping-uri-list-subscribe-03.txt
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Copyright (C) The Internet Society (2005).
Abstract
This document specifies a way to create subscription to a list of
resources in SIP. This is achieved by including the list of
resources in the body of a SUBSCRIBE. Instead of having a subscriber
send a SUBSCRIBE for each resource individually, the subscriber
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defines the resource list, subscribes to it, and gets notifications
about changes in the resources' state using a single SUBSCRIBE
dialog.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Providing a Resource List Server with a URI-List . . . . . . . 3
4. URI-List Format . . . . . . . . . . . . . . . . . . . . . . . 3
5. Resource List Server Behavior . . . . . . . . . . . . . . . . 4
6. Subsequent SUBSCRIBEs . . . . . . . . . . . . . . . . . . . . 4
7. Option-tag . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Providing a URI to Manipulate a Resource List . . . . . . . . 5
9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . 6
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
12. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . 7
13. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 9
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1. Introduction
RFC xxxx [4] specifies how to establish subscriptions to a
homogeneous resource list in SIP [2] and defines the procedures for
getting notifications about changes in the state of the associated
resources. Yet, list creation is outside the scope of [4].
This document specifies a way to create a list with a set of
resources and subscribe to it using a single SIP request. This is
achieved by including the list of resources (as defined in [5]) in
the body of the SUBSCRIBE request.
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 Resource List Server with a URI-List
A client that wants to create a resource list and subscribe to it,
using the mechanism described in this document, constructs a
SUBSCRIBE with at least one body, whose disposition is type
"recipient-list" as defined in [5], containing the URI-list. The
client MUST build the remaining of the SUBSCRIBE request following
the rules in RFC 3265 [3].
The client MUST support the "rlmi+xml" format defined in [4] and
signal this by including "rlmi+xml" in the Accept header. The client
MAY support additional formats and include them in the Accept header
field of the SUBSCRIBE.
4. URI-List Format
The [5] mandates that each URI-list services specification, such as
the subscription service defined here, specifies the default format
for the recipient-list bodies used within the particular service.
The default format for the recipient-list bodies for the subscription
service defined in this document is the resource list format defined
in [6]. UAs (User Agents) and resource list servers handling
recipient-list bodies MUST support this format and MAY support other
formats.
The Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) resource list document provides features, such as hierarchical
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lists and the ability to include entries by reference relative to the
XCAP root URI, that are not needed by the subscription service
defined here, which only needs to transfer a flat list of URIs
between a UA and the resource list server. Therefore, when using the
default resource list document, UAs SHOULD use flat lists (i.e., no
hierarchical lists) and SHOULD NOT use <entry-ref> elements.
A resource list server 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. Resource List Server Behavior
On reception of a SUBSCRIBE with a URI-list, a resource list server,
which chooses to accept the "rlmi+xml" format, MUST comply with [4]
for creating the subscription and reporting the changes in the
resources within the created dialog.
Note that the status code in the response to the SUBSCRIBE does not
provide any information about whether or not the resource list server
was able to successfully subscribe to the URIs in the URI-list. The
client obtains this information in the notifications sent by the
server.
6. Subsequent SUBSCRIBEs
The previous Sections have specified how to include a URI-list in an
initial SUBSCRIBE request to a resource list server in order to
subscribe to the state of a set of resources. Once the subscription
has been created and a dialog between the client and the resource
list server has been established, the client may need to send
subsequent SUBSCRIBE requests to, for example, extend the duration of
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the subscription.
At this point, there are no semantics associated with resource-list
bodies in subsequent SUBSCRIBE requests (although future extensions
may define them). Therefore, clients SHOULD NOT include resource-
list bodies in subsequent SUBSCRIBE requests to a resource list
server.
A resource list server receiving a subsequent SUBSCRIBE request 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 SUBSCRIBE request and
subsequent ones is that while the initial request is sent to the
public URI of the resource list, subsequent ones are sent to the
URI provided by the server 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. Option-tag
This document defines the 'recipient-list-subscribe' option-tag for
use in the Require and Supported SIP header fields.
User agent clients generating a SUBSCRIBE with a recipient-list body,
as described in previous sections, MUST include this option-tag in a
Require header field. User agents that are able to receive and
process SUBSCRIBEs with a recipient-list body, as described in
previous sections, SHOULD include this option-tag in a Supported
header field when responding to OPTIONS requests.
8. Providing a URI to Manipulate a Resource List
A client may need to manipulate a resource list at a resource list
server. The resource list server MAY provide a URI to manipulate the
resource list associated with a subscription using the Call-Info
header field in the NOTIFY that establishes the subscription. The
"purpose" parameter of the Call-Info header field MUST have a value
of 'list-management', which we register with the IANA in Section 11.
The following is an example of such a header field.
Call-Info: <http://xcap.example.com/your-list.xml>
;purpose=list-management
The life-time of a resource list to be manipulated by the URI
provided by the server is blundled to the life-time of the
subscription. That is, the resource list SHOULD be destroyed when
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the subscription expires or is otherwise terminated.
9. Example
The following is an example of a SUBSCRIBE request, which carries a
URI-list in its body, sent by a UA to a resource list server.
SUBSCRIBE sip:rls@example.com SIP/2.0
Via: SIP/2.0/TCP terminal.example.com;branch=z9hG4bKwYb6QREiCL
Max-Forwards: 70
To: RLS <sip:rls@example.com>
From: <sip:adam@example.com>;tag=ie4hbb8t
Call-ID: cdB34qLToC@terminal.example.com
CSeq: 1 SUBSCRIBE
Contact: <sip:terminal.example.com>
Event: presence
Expires: 7200
Require: recipient-list-subscribe
Supported: eventlist
Accept: application/cpim-pidf+xml
Accept: application/rlmi+xml
Accept: multipart/related
Accept: multipart/signed
Accept: multipart/encrypted
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
Content-Length: 337
<?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 2: SUBSCRIBE request
10. Security Considerations
The Security Considerations Section of [4] discusses security issues
related to resource list servers. Resource list servers accepting
request-contained URI-lists MUST also follow the security guidelines
given in [4].
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The Framework and Security Considerations for SIP URI-List Services
[5] discusses issues related to SIP URI-list services. Given that a
resource list server sending SUBSCRIBEs to a set of users acts as a
URI-list service, implementations of resource list servers that
handle request-contained URI-lists MUST follow the security-related
rules in [5]. These rules include mandatory authentication and
authorization of clients, and opt-in lists.
11. IANA Considerations
The document defines the 'list-management' value for the purpose
parameter of the Call-Info header field. A reference to this RFC (in
double brackets) needs to be added to the purpose Call-Info parameter
entry in the SIP Parameters registry.
This document defines the 'recipient-list-subscribe' SIP option-tag
in Section 7. 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.
This option-tag is used to ensure that a server can process the
'recipient-list' body used in a SUBSCRIBE request.
12. Acknowledges
Cullen Jennings and Jonathan Rosenberg provided useful comments on
this document.
13. 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] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[4] Roach, A., Rosenberg, J., and B. Campbell, "A Session Initiation
Protocol (SIP) Event Notification Extension for Resource
Lists", draft-ietf-simple-event-list-07 (work in progress),
January 2005.
[5] Camarillo, G. and A. Roach, "Requirements and Framework for
Session Initiation Protocol (SIP)Uniform Resource Identifier
(URI)-List Services", draft-ietf-sipping-uri-services-02 (work
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in progress), December 2004.
[6] Rosenberg, J., "Extensible Markup Language (XML) Formats for
Representing Resource Lists",
draft-ietf-simple-xcap-list-usage-05 (work in progress),
February 2005.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Adam Roach
Estacado Systems
Email: adam@estacado.net
Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Email: oritl@microsoft.com
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