





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



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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.










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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.






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   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



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   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




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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]

















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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.






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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

























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