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Versions: 00                                                            
SIPPING Working Group                                   M. Garcia-Martin
Internet-Draft                                                     Nokia
Expires: November 9, 2004                                   G. Camarillo
                                                                Ericsson
                                                            May 11, 2004


     Multiple recipient MESSAGE requests in the Session Initiation
                             Protocol (SIP)
              draft-garcia-sipping-message-exploder-00.txt

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document specifies how to request a MESSAGE exploder to send a
   copy of a MESSAGE to a set of destinations.  The client sends a SIP
   MESSAGE request with a URI list to the MESSAGE exploder, which sends
   a similar MESSAGE request to each of URIs included in the list.






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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Procedures at the UAC  . . . . . . . . . . . . . . . . . . . .  4
   4.  Procedures at the MESSAGE exploder . . . . . . . . . . . . . .  5
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Change control . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1   Changes from
           draft-garcia-simple-message-exploder-00.txt to
           draft-garcia-sipping-message-exploder-00.txt . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   9.1   Normative References . . . . . . . . . . . . . . . . . . . .  9
   9.2   Informational References . . . . . . . . . . . . . . . . . . 10
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
       Intellectual Property and Copyright Statements . . . . . . . . 11

































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1.  Introduction

   SIP [2] can carry instant messages in MESSAGE [3] requests.  The
   Advanced Instant Messaging Requirements for SIP [6] mentions the need
   for sending a MESSAGE request to multiple receipients:

   "REQ-GROUP-3: It MUST be possible for a user to send to an ad-hoc
   group, where the identities of the recipients are carried in the
   message itself."

   To meet this requirement, we allow SIP MESSAGE requests carry an URI
   list as specified in [4].  The Request-URI of the MESSAGE request
   contains a "list" URI parameter that points to a body part that
   carries the URI list.  A specialized application server receives the
   request and sends a similar MESSAGE request to each of the URIs in
   the list.  Each of these MESSAGE requests contains a copy of the body
   included in the original MESSAGE request.

   The UAC needs to be configured with the SIP URI of the application
   server that provides the functionality.  Discovering and provisioning
   of this URI to the UAC is outside the scope of this document.

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.

   'MESSAGE exploder': SIP application server that receives a MESSAGE
   request with a URI list and sends a similar MESSAGE request to each
   URI in the list.  MESSAGE exploders behave effectively as specialised
   B2BUAs (Back-To-Back-User-Agents).  A MESSAGE exploder can be
   modelled as a fractional function of a B2BUA that can offer other
   exploder functionality (e.g., for other SIP methods), although that
   other exploder functionality is outside the scope of this document.
   In this document we only discuss the explosion of SIP MESSAGE
   requests.

   'Incoming MESSAGE request': A SIP MESSAGE request that a UAC creates
   and addresses to a SIP MESSAGE exploder.  Besides the regular instant
   message payload, an incoming MESSAGE request contains a URI list.

   'Outgoing MESSAGE request': A SIP MESSAGE request that a MESSAGE
   exploder creates and addresses to a UAS.  It contains the regular
   instant message payload.




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3.  Procedures at the UAC

   A client that wants to create a multiple recipient MESSAGE request
   SHOULD add a "list" parameter (specified in [4]) to the MESSAGE
   exploder's URI and MUST place the resulting URI in the Request-URI of
   the MESSAGE request.  The "list" parameter MUST contain a pointer to
   a URI list that contains the recipients of the MESSAGE.  The
   following is an example of a Request-URI with a "list" parameter.

   sip:message-exploder.example.com;list=cid:cn35t8jf@uac.example.com

   Multiple recipient MESSAGE requests will typically contain a
   multiparty body that contains the body carrying the list and the
   actual instant message payload.  In some cases, the MESSAGE request
   will contain bodies other than the text and the list bodies, for
   instance, when the request is protected with S/MIME.

   Typically the MESSAGE exploder will copy all the significant header
   fields in the exploded MESSAGE request.  However, there might be
   cases where the SIP UA wants the MESSAGE exploder to add a particular
   header field with a particular value, when the header field wasn't
   present in the MESSAGE request sent by the UAC.  In this case the UAC
   MAY use the "?" mechanism described in Section 19.1.1 of RFC 3261 [2]
   to encode extra information in any URI in the list.  However, the UAC
   MUST NOT use the special "body" hname (see Section 19.1.1 of RFC 3261
   [2]) to encode a body, since the body is present in the MESSAGE
   request itself.

   The following is an example of a URI that uses the "?" mechanism:

   sip:message-exploder.example.com;list=cid:cn35t8jf@uac.example.com?
   Accept-Contact=*%3bmobility%3d%22mobile%22

   The previous URI requests the MESSAGE exploder to add the following
   header field to a MESSAGE request:

   Accept-Contact: *;mobility="mobile"

   As described in [4], the default format for URI lists in SIP is the
   XCAP resource list format [5].  User Agents compliant to this
   specification MUST support the XCAP resource list format  [5] and MAY
   support other formats.

   UAs generating multiple recipient MESSAGEs SHOULD use flat lists
   (i.e., no hierarchical lists), SHOULD NOT use any entry's attributes
   but "uri", and SHOULD NOT include any elements inside entries but
   "display-name" elements.




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4.  Procedures at the MESSAGE exploder

   On receiving a MESSAGE request that contains a "list" parameter in
   the Request-URI as described in [4], a MESSAGE exploder SHOULD answer
   to the UAC with a 202 Accepted response.  Note that the status code
   in the response to the MESSAGE does not provide any information about
   whether or not the MESSAGEs generated by the exploder were
   successfully delivered to the URIs in the list.  That is, a 202
   Accepted means that the MESSAGE exploder has received the MESSAGE and
   that it will try to send a similar MESSAGE to the URIs in the list.
   Designing a mechanism to inform a client about the delivery status of
   an instant message is outside the scope of this document.

   On receiving a MESSAGE request that contains a "list" parameter in
   the Request-URI as described [4], a MESSAGE exploder SHOULD create as
   many new MESSAGE requests as URIs the list contains, except when two
   of those URIs are equivalent (section 19.1.4 of RFC 3261 [2] defines
   equivalent URIs), in which case the MESSAGE exploder SHOULD create
   only one outgoing MESSAGE request per URI.

   The Request-URI of each of the outgoing MESSAGE requests MUST NOT
   include any "list" parameters.  This avoids loops in exploding
   MESSAGE requests.  It also avoids the implementation a MESSAGE
   exploder functionality in the UAS, that otherwise, would be required.

   On creating the body of each of the outgoing MESSAGE requests, the
   MESSAGE exploder tries to keep the relevant bodies of the incoming
   MESSAGE request and copies them to the outgoing MESSAGE request.  The
   following guidelines are provided:

   o  The incoming MESSAGE request typically contains a URI list body
      [4] with the actual list of recipients.  The MESSAGE exploder need
      not copy the URI list body to the outgoing MESSAGE request,
      although it MAY do it.
      NOTE: This document does not provide any semantics associated to a
         URI list body included in an outgoing MESSAGE request.  Future
         extensions can indicate actions at a UAS when it receives that
         body.
   o  The MESSAGE exploder MUST NOT copy any security body (such as an
      S/MIME signed body) addressed to the MESSAGE exploder to the
      outgoing MESSAGE request.  This includes, e.g., security bodies
      signed with the public key of the exploder.
   o  The MESSAGE exploder SHOULD copy all the rest of the message
      bodies (e.g., text messages, images, etc.) to the outgoing MESSAGE
      request.
   o  If there is only one body left, the MESSAGE exploder MUST remove
      the multipart/mixed wrapper in the outgoing MESSAGE request.




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   The rest of the MESSAGE request corresponding to a given URI in the
   list MUST be created following the rules in Section 19.1.5 "Forming
   Requests from a URI" of RFC 3261 [2].  In particular, Section 19.1.5
   of RFC 3261 [2] states:

   "An implementation SHOULD treat the presence of any headers or body
   parts in the URI as a desire to include them in the message, and
   choose to honor the request on a per-component basis."

   SIP allows to append a "method" parameter to a URI.  Therefore, it is
   legitimate that an the "uri" attribute of the "entry" element in the
   XCAP resource list contains a "method" parameter.  MESSAGE exploders
   MUST generate only MESSAGE requests, regardless of the "method"
   parameter that the URIs in the list indicate.  Effectively, MESSAGE
   exploders MUST ignore the "method" parameter in each of the URIs
   present in the URI list.

   It is RECOMMENDED that the MESSAGE exploder copies the value From
   header field of the incoming MESSAGE into the outgoing MESSAGE
   requests (note that this need not apply to the "tag" parameter).  The
   MESSAGE exploder SHOULD also copy to the outgoing MESSAGE request any
   P-Asserted-Identity header fields that can be present in the incoming
   MESSAGE request.

   On each given outgoing MESSAGE request, the MESSAGE exploder SHOULD
   generate a new To header field value which, according to the
   procedures of RFC 3261 Section 8.1.1.1, should be equal to the
   Request-URI of the outgoing MESSAGE request.

   On each given outgoing MESSAGE request, the MESSAGE exploder SHOULD
   initialize the values of the Call-ID, CSeq and Max-Forwards header
   fields.  The MESSAGE exploder should also include its own value in
   the Via header field.

   A MESSAGE exploder receiving a URI list with more information than
   what we have just described SHOULD discard all the extra information.

   As described in [4], the default format for URI lists in SIP is the
   XCAP resource list format [5].  MESSAGE exploders compliant to this
   specification MUST support the XCAP resource list format [5] and MAY
   support other formats.

5.  Examples

   The following is an example of an incoming MESSAGE request which
   carries a URI list in its body.

   MESSAGE sip:exploder.example.com;list=cid:cn35t8jf@uac.example.com



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           SIP/2.0
   Via: SIP/2.0/TCP uac.example.com
       ;branch=z9hG4bKhjhs8ass83
   Max-Forwards: 70
   To: MESSAGE Exploder <sip:exploder.example.com>
   From: Carol <sip:carol@example.com>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 1 MESSAGE
   Content-Type: multipart/mixed;boundary="boundary1"
   Content-Length: xxx

   --boundary1
   Content-Type: text/plain
   Content-Length: 13

   Hello World!

   --boundary1
   Content-Type: application/resource-lists+xml
   Content-Length: 315
   Content-ID: <cn35t8jf@uac.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 4: Multiple recipient incoming MESSAGE request

   The following is an example of one of the outgoing MESSAGE requests
   that the MESSAGE exploder creates.














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   MESSAGE sip:bill@example.com SIP/2.0
   Via: SIP/2.0/TCP exploder.example.com
       ;branch=z9hG4bKhjhs8as34sc
   Max-Forwards: 70
   To: <sip:bill@example.com>
   From: Carol <sip:carol@uac.example.com>;tag=210342
   Call-ID: 39s02sdsl20d9sj2l
   CSeq: 1 MESSAGE
   Content-Type: text/plain
   Content-Length: 13

   Hello World!

                   Figure 5: Outgoing MESSAGE request


6.  Security Considerations

   If MESSAGE exploders are not implemented properly, they could  become
   a SPAM amplification tool.  The SPAMMER would have the exploder,
   which will generally have a higher access bandwidth and more
   processing power, send a SPAM message to a large set of destinations.
   This section provides guidelines to prevent SPAM amplifications in
   particular, and DoS attacks in general.  In addition, we describe how
   to provide content confidentiality and integrity.

   MESSAGE exploders MUST authenticate and authorize any user agent
   sending a multiple recipient MESSAGE.  Additionally, MESSAGE
   exploders MAY have policies that limit the number of URIs in the
   list, as a very long list could be used in a DoS attack to place a
   large burden on the exploder to send a large number of MESSAGEs or to
   perform an amplification attack.

   In case an exploder is used to send unsolicited instant messages
   (i.e., SPAM), it should be possible to track down the sender of such
   messages.  To do that, MESSAGE exploders MAY provide information
   about the identity of the original sender of the MESSAGE in their
   outgoing MESSAGE requests.  Exploders can use Authenticated Identity
   Bodies (AIB) [7] or P-Asserted-Identity header fields [8] to provide
   this information.  Furthermore, it is RECOMMENDED that MESSAGE
   exploders keep a log of all the transactions they handle (for a
   reasonable period of time), so that SPAMMERS can be tracked down.

   It is RECOMMENDED that user agents using MESSAGE exploders integrity
   protect the contents of their instant messages and the list of
   recipients using S/MIME.  If the contents of the instant message or
   the list of recipients needs to be kept private, the user agent
   SHOULD also use S/MIME to prevent a third party from viewing this



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   information.

7.  Acknowledgements

   Duncan Mills supported the idea of having 1 to n MESSAGEs.  Ben
   Campbell and Paul Kyzivat provided helpful comments.

8.  Change control

8.1  Changes from draft-garcia-simple-message-exploder-00.txt to
    draft-garcia-sipping-message-exploder-00.txt

   The MESSAGE exploder may or may not copy the URI list body to the
   outgoing MESSAGE request.  This allows to extend the mechanism with a
   Reply-to-all feature.

   It is clarified that the MESSAGE exploder must not include a list in
   the outgoing MESSAGE requests.  This avoids loops or requires a
   MESSAGE exploder functionality in the next hop.

   The MESSAGE exploder must remove the multipart/mixed wrapper if there
   is only one body left in the outgoing MESSAGE request.

   Filename changed due to focus on the SIPPING WG.

9.  References

9.1  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]  Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D.
        Gurle, "Session Initiation Protocol (SIP) Extension for Instant
        Messaging", RFC 3428, December 2002.

   [4]  Camarillo, G., "Providing a Session Initiation Protocol (SIP)
        Application Server with a  List of URIs",
        draft-camarillo-sipping-uri-list-00 (work in progress), November
        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



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        2003.

9.2  Informational References

   [6]  Rosenberg, J., "Advanced Instant Messaging Requirements for the
        Session Initiation Protocol  (SIP)",
        draft-rosenberg-simple-messaging-requirements-00 (work in
        progress), December 2002.

   [7]  Peterson, J., "SIP Authenticated Identity Body (AIB) Format",
        draft-ietf-sip-authid-body-02 (work in progress), July 2003.

   [8]  Jennings, C., Peterson, J. and M. Watson, "Private Extensions to
        the Session Initiation Protocol (SIP) for Asserted Identity
        within Trusted Networks", RFC 3325, November 2002.


Authors' Addresses

   Miguel A. Garcia-Martin
   Nokia
   P.O.Box 407
   NOKIA GROUP, FIN  00045
   Finland

   EMail: miguel.an.garcia@nokia.com


   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: Gonzalo.Camarillo@ericsson.com
















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