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rfc:rfc5367

Network Working Group G. Camarillo Request for Comments: 5367 Ericsson Updates: 3265 A.B. Roach Category: Standards Track Tekelec

                                                              O. Levin
                                                 Microsoft Corporation
                                                          October 2008
         Subscriptions to Request-Contained Resource Lists
              in the Session Initiation Protocol (SIP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

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 request.  Instead of having a
 subscriber send a SUBSCRIBE request for each resource individually,
 the subscriber defines the resource list, subscribes to it, and gets
 notifications about changes in the resources' states using a single
 SUBSCRIBE dialog.

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................2
 3. User Agent Client Procedures ....................................2
    3.1. Response Handling ..........................................2
    3.2. Subsequent SUBSCRIBE Requests ..............................3
 4. URI-List Document Format ........................................3
 5. Resource List Server Behavior ...................................4
    5.1. Subsequent SUBSCRIBE Requests ..............................4
 6. Providing a URI to Manipulate a Resource List ...................4
 7. Example .........................................................5
 8. Security Considerations .........................................6
 9. IANA Considerations .............................................6
    9.1. List-Management Purpose Parameter Value ....................6
    9.2. recipient-list-subscribe Option-Tag ........................7
 10. Acknowledgments ................................................7
 11. Normative References ...........................................7

Camarillo Standards Track [Page 1] RFC 5367 SUBSCRIBE-Contained Lists October 2008

1. Introduction

 [RFC4662] specifies how to establish subscriptions to a homogeneous
 resource list in SIP (which is specified in [RFC3261]) and defines
 the procedures for getting notifications about changes in the state
 of the associated resources.  Yet, list creation is outside the scope
 of [RFC4662].
 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 [RFC5363])
 in the body of the SUBSCRIBE request.

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 [RFC2119].

3. User Agent Client Procedures

 A UAC (User Agent Client) that wants to create a resource list and
 subscribe to it using the mechanism described in this document
 constructs a SUBSCRIBE request with at least one body, whose
 disposition is type "recipient-list" as defined in [RFC5363], that
 contains the URI list.  Additionally, the UAC MUST include the
 'recipient-list-subscribe' option-tag (which is registered with the
 IANA in Section 9) in a Require header field.  The UAC MUST build the
 rest of the SUBSCRIBE request following the rules in [RFC3265].
 The UAC MUST support the "rlmi+xml" format defined in [RFC4662] and
 signal this by including "rlmi+xml" in the Accept header.  The UAC
 MAY support additional formats and include them in the Accept header
 field of the SUBSCRIBE request.

3.1. Response Handling

 The status code in the response to the SUBSCRIBE request 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
 UAC obtains this information in the notifications sent by the server.

Camarillo Standards Track [Page 2] RFC 5367 SUBSCRIBE-Contained Lists October 2008

3.2. Subsequent SUBSCRIBE Requests

 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 UAC and the resource list
 server has been established, the UAC can send subsequent SUBSCRIBE
 requests to, for example, extend the duration of the subscription.
 At this point, there are no semantics associated with resource-list
 bodies in subsequent SUBSCRIBE requests (although future extensions
 can define them).  Therefore, UACs SHOULD NOT include resource-list
 bodies in subsequent SUBSCRIBE requests to a resource list server.
    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 is 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

 [RFC5363] 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 [RFC4826].  UAs (User Agents) generating recipient-list bodies
 MUST support this format and MAY support other formats.  Resource
 list servers able to handle 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
 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.

Camarillo Standards Track [Page 3] RFC 5367 SUBSCRIBE-Contained Lists October 2008

 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

 Resource list servers that are able to receive and process SUBSCRIBE
 requests with a recipient-list body SHOULD include a 'recipient-list-
 subscribe' option-tag in a Supported header field when responding to
 OPTIONS requests.
 On reception of a SUBSCRIBE request with a URI list, a resource list
 server that chooses to accept the "rlmi+xml" format MUST comply with
 [RFC4662] for creating the subscription and reporting the changes in
 the resources within the created dialog.

5.1. Subsequent SUBSCRIBE Requests

 At this point, there are no semantics associated with resource-list
 bodies in subsequent SUBSCRIBE requests (although future extensions
 may define them).  Therefore, 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.

6. Providing a URI to Manipulate a Resource List

 A UAC can 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 request 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 9.
 The following is an example of such a header field.
 Call-Info: <http://xcap.example.com/your-list.xml>
            ;purpose=list-management

Camarillo Standards Track [Page 4] RFC 5367 SUBSCRIBE-Contained Lists October 2008

 The lifetime of a resource list to be manipulated by the URI provided
 by the server is bundled to the lifetime of the subscription.  That
 is, the resource list SHOULD be destroyed when the subscription
 expires or is otherwise terminated.
 Section 7.1 of [RFC3265] does not list the Call-Info header field in
 the table of header fields that NOTIFY requests can carry.  This
 document updates that table so that the Call-Info header field can be
 optionally included in NOTIFY requests.

7. Example

 The following is an example of a SUBSCRIBE request, which carries a
 URI list in its body, sent by a UAC 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

Camarillo Standards Track [Page 5] RFC 5367 SUBSCRIBE-Contained Lists October 2008

8. Security Considerations

 The Security Considerations section of [RFC4662] discusses security
 issues related to resource list servers.  Resource list servers
 accepting request-contained URI lists MUST also follow the security
 guidelines given in [RFC4662].
 "Framework and Security Considerations for Session Initiation
 Protocol (SIP) URI-List Services" [RFC5363] discusses issues related
 to SIP URI-list services.  Given that a resource list server sending
 SUBSCRIBE requests 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
 [RFC5363].  These rules include opt-in lists and mandatory
 authentication and authorization of clients.

9. IANA Considerations

 The following sections describe the IANA registration of the 'list-
 management' value for the "purpose" parameter of the Call-Info header
 field and the 'recipient-list-subscribe' SIP option-tag.

9.1. List-Management Purpose Parameter Value

 This document defines the 'list-management' value for the "purpose"
 parameter of the Call-Info header field.  A reference to this RFC (in
 double brackets) has been added to the existing "purpose" Call-Info
 parameter entry in the SIP Parameters registry, which currently looks
 as follows:
                                                Predefined
 Header Field                  Parameter Name     Values     Reference
 ----------------------------  ---------------   ---------   ---------
 Call-Info                     purpose             Yes       [RFC3261]

Camarillo Standards Track [Page 6] RFC 5367 SUBSCRIBE-Contained Lists October 2008

9.2. recipient-list-subscribe Option-Tag

 This document defines the SIP option tag "recipient-list-subscribe".
 The following row has been added to the "Option Tags" section of the
 SIP Parameter Registry:
 +--------------------------+----------------------------+-----------+
 | Name                     | Description                | Reference |
 +--------------------------+----------------------------+-----------+
 | recipient-list-subscribe | This option tag is used to | [RFC5367] |
 |                          | ensure that a server can   |           |
 |                          | process the recipient-list |           |
 |                          | body used in a SUBSCRIBE   |           |
 |                          | request.                   |           |
 +-------------------------------------------------------+-----------+

10. Acknowledgments

 Cullen Jennings and Jonathan Rosenberg provided useful comments on
 this document.

11. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3261]  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.
 [RFC3265]  Roach, A.B., "Session Initiation Protocol (SIP)-Specific
            Event Notification", RFC 3265, June 2002.
 [RFC4662]  Roach, A.B., Campbell, B., and J. Rosenberg, "A Session
            Initiation Protocol (SIP) Event Notification Extension for
            Resource Lists", RFC 4662, August 2006.
 [RFC4826]  Rosenberg, J., "Extensible Markup Language (XML) Formats
            for Representing Resource Lists", RFC 4826, May 2007.
 [RFC5363]  Camarillo, G. and A.B. Roach, "Framework and Security
            Considerations for Session Initiation Protocol (SIP) URI-
            List Services", RFC 5363, October 2008.

Camarillo Standards Track [Page 7] RFC 5367 SUBSCRIBE-Contained Lists October 2008

Authors' Addresses

 Gonzalo Camarillo
 Ericsson
 Hirsalantie 11
 Jorvas  02420
 Finland
 EMail: Gonzalo.Camarillo@ericsson.com
 Adam Roach
 Tekelec
 17210 Campbell Rd Ste 250
 Dallas, TX  75252
 USA
 EMail: Adam.Roach@tekelec.com
 Orit Levin
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA  98052
 EMail: oritl@microsoft.com

Camarillo Standards Track [Page 8] RFC 5367 SUBSCRIBE-Contained Lists October 2008

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 contained in BCP 78, and except as set forth therein, the authors
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Camarillo Standards Track [Page 9]

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