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Versions: 00 01 02 03 04 05 06 07 08 draft-ietf-sip-uri-list-message

SIPPING Working Group                                   M. Garcia-Martin
Internet-Draft                                                     Nokia
Expires: April 24, 2006                                     G. Camarillo
                                                                Ericsson
                                                        October 21, 2005


 Multiple-Recipient MESSAGE Requests in the Session Initiation Protocol
                                 (SIP)
               draft-ietf-sipping-uri-list-message-04.txt

Status of this Memo

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   This Internet-Draft will expire on April 24, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies how to request a SIP URI-list service 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 URI-list service,
   which sends a similar MESSAGE request to each of the URIs included in
   the list.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  URI-List document  . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Extension to the resource lists data format  . . . . . . .  6
     4.2.  URI-list example . . . . . . . . . . . . . . . . . . . . .  7
   5.  Option-tag . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Procedures at the User Agent Client  . . . . . . . . . . . . .  8
   7.  Procedures at the MESSAGE URI-List Service . . . . . . . . . .  9
     7.1.  Determining the intended recipient . . . . . . . . . . . .  9
     7.2.  Creating an outgoing MESSAGE request . . . . . . . . . . .  9
     7.3.  Composing bodies in the outgoing MESSAGE request . . . . . 10
   8.  Procedures at the UAS  . . . . . . . . . . . . . . . . . . . . 12
   9.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Disposition Type Registration  . . . . . . . . . . . . . . 16
     11.2. Option-Tag Registration  . . . . . . . . . . . . . . . . . 16
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   13. Change control . . . . . . . . . . . . . . . . . . . . . . . . 16
     13.1. Changes from draft-ietf-sipping-uri-list-message-02.txt  . 17
     13.2. Changes from draft-ietf-sipping-uri-list-message-01.txt  . 17
     13.3. Changes from draft-ietf-sipping-uri-list-message-00.txt  . 17
     13.4. Changes from
           draft-ietf-sipping-message-exploder-00.txt to
           draft-ietf-sipping-uri-list-message-00.txt . . . . . . . . 17
     13.5. Changes from
           draft-garcia-simple-message-exploder-00.txt to
           draft-garcia-sipping-message-exploder-00.txt . . . . . . . 18
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     14.2. Informational References . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
   Intellectual Property and Copyright Statements . . . . . . . . . . 21















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1.  Introduction

   SIP [6] can carry instant messages in MESSAGE [9] requests.  The
   Advanced Instant Messaging Requirements for SIP [13] mentions the
   need for sending a MESSAGE request to multiple recipients:

      "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."

   One possibility to fulfill the above requirement is to establish a
   session of instant messages with an instant messaging conference
   server.  While this option seems to be reasonable in many cases, in
   other situations the sending user just want to send a small page-mode
   instant message to an ad-hoc group, without entering the burden of
   setting up a session.  This document focuses on sending a page-mode
   instant message to a number of intended recipients.

   To meet the requirement with a page-mode instant message, we allow
   SIP MESSAGE requests carry URI-lists in body parts whose Content-
   Disposition [2] is 'recipient-list', as specified in the Framework
   and Security Considerations for SIP URI-List Services [12].  A SIP
   MESSAGE URI-list service, which is a specialized application service,
   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 Advanced Instant Messaging Requirements for SIP [13] also
   includes a requirement that allows to provide a "Reply-to-All"
   functionality:

      "REQ-GROUP-4: It MUST be possible for the recipient of a group IM
      to send a message to all other participants that received the same
      group IM (i.e., Reply-To-All)."

   To meet this requirement, we provide a mechanism whereby the MESSAGE
   URI-list service can include the received URI-list along the instant
   message payload in each of the instant messages sent to the
   recipients.

   The UAC (User Agent Client) that sends a MESSAGE request to a MESSAGE
   URI-list service needs to be configured with the SIP URI of the
   service that provides the functionality.  Discovering and
   provisioning of this URI to the UAC is outside the scope of this
   document.






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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 URI-list service: SIP application service that receives a
      MESSAGE request with a URI-list and sends a similar MESSAGE
      request to each URI in the list.  In this context, similar
      indicates that some SIP header fields can change, but the MESSAGE
      URI-list service will not change the instant message payload.
      MESSAGE URI-list services behave effectively as specialised B2BUAs
      (Back-To-Back-User-Agents).  A server providing MESSAGE URI-list
      services can also offer URI-list services for other methods,
      although this functionality is outside the scope of this document.
      In this document we only discuss MESSAGE URI-list services.

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

   Outgoing MESSAGE request: A SIP MESSAGE request that a MESSAGE URI-
      list service creates and addresses to a UAS (User Agent Server).
      It contains the regular instant message payload.

   Intended recipient: The intended final recipient of the request to be
      generated by MESSAGE URI-list service.



3.  Overview

   A UAC creates a MESSAGE request that contains a multipart body
   including a list of URIs (intended recipients) and an instant
   message.  The UAC sends this MESSAGE request to the MESSAGE URI-List
   service.  On reception of this incoming MESSAGE request, the MESSAGE
   URI-list service creates a MESSAGE request per intended recipient
   (listed in the URI-list) and copies the instant message payload to
   each of those MESSAGES.  Then the MESSAGE URI-list service sends each
   of the created outgoing MESSAGE request to the respective receiver.

   The mechanism reuses the XML format for representing resource lists
   [10] to include the list of intended recipients.  We define an
   extension to that list to indicate the capacity of each resource,
   which can be To, Cc or Bcc (in an analogy to e-mail).  The MESSAGE



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   URI-list service can include a resource list in the outgoing MESSAGE
   request that contain those resources tagged with a To or Cc
   capacities (and not Bcc capacities).  This allows the creator of the
   incoming MESSAGE request to identify if a resource should be
   receiving a copy of the MESSAGE request as a capacity of recipient
   (to), carbon copy (cc) or blind carbon copy (bcc).  It also allows
   some the intended recipients to reply to the initial sender and all
   the visible recipients of the MESSAGE request.


4.  URI-List document

   As described in the Framework and Security Considerations for SIP
   URI-List Services [12], specifications of individual URI-list
   services, like the MESSAGE URI-list service described here, need to
   specify a default format for 'recipient-list' bodies used within the
   particular service.

   The default format for recipient-list bodies for MESSAGE URI-list
   services is the resource list document format [10] .  UAs (User
   Agents) and servers handling recipient-list bodies MUST support this
   format and MAY support other formats.

   Nevertheless, 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 MESSAGE
   URI-list service defined in this document, which only needs to
   transfer a flat list of URIs between a UA and the 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.

   Section 4.1 defines an extension to the XML format for representing
   resource lists [10].  This extension allows us to characterize a
   resource with a 'capacity' attribute.  UACs (User Agent Clients) and
   MESSAGE URI-list services handling 'recipient-list' bodies MUST
   support 'capacity' extension.

   A MESSAGE URI-list service receiving a URI-list with more information
   than what has just been described MAY discard all the extra
   information.

   Additionally, this document defines a new mail disposition type value
   to be included in a Content-Disposition [2] header field of a SIP
   MESSAGE request.  The value of this new disposition type is
   'recipient-list-history' and its purpose is to indicate a list of
   recipients that a MESSAGE was sent to.  A body whose Content-



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   Disposition type is 'recipient-list-history' contains a URI-list with
   the visible recipients of the MESSAGE.  The <entry> element in the
   URI-list MAY also include a 'capacity' attribute, as specified in
   Section 4.1.  MESSAGE URI-list services MUST implement support for
   this Content-Disposition type.  User Agent Servers (UAS) MAY
   implement support for the resource-list document format [10] and the
   'recipient-list-history' Content-Disposition type.

4.1.  Extension to the resource lists data format

   This document defines an extension to indicate the capacity of a
   resource.  We define a new 'capacity' attribute to the <entry>
   element.  The 'capacity' attribute has similar semantics to the type
   of destination address in e-mail systems.  It can take the values
   "to", "cc" and "bcc".  A "to" value of the 'capacity' attribute
   indicates that the resource is considered the recipient of the
   MESSAGE request.  A "cc" value indicates that the resource receives a
   carbon copy of the MESSAGE request.  A "bcc" value indicates that the
   resource receives a blind carbon copy of the MESSAGE request.  The
   default 'capacity' value is "bcc", that is, the absence of a
   'capacity' attribute MUST be treated as if the 'capacity' was set to
   "bcc".

   The 'capacity' attribute SHOULD be included as a modifier of any of
   the child elements included in the <list> element of a resource list
   (e.g., an attribute of the <entry> or <external> elements).

   Figure 1 describes the format of the 'capacity' attribute.
   Implementations according to this specification MUST support this XML
   Schema.





















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   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:capacity"
       xmlns="urn:ietf:params:xml:ns:capacity"
       xmlns:rls="urn:ietf:params:xml:ns:resource-lists"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"
       elementFormDefault="qualified"
       attributeFormDefault="unqualified">

       <xs:annotation>
         <xs:documentation xml:lang="en">
            Adds the capacity attribute to URIs included
            in a resource list.
         </xs:documentation>
       </xs:annotation>

       <xs:attribute name="capacity">
          <xs:simpleType>
             <xs:restriction base="xs:string">
                <xs:enumeration value="to"/>
                <xs:enumeration value="cc"/>
                <xs:enumeration value="bcc"/>
             </xs:restriction>
          </xs:simpleType>
       </xs:attribute>
   </xs:schema>

   Figure 1: Extension to the resource lists data format

4.2.  URI-list example

   Figure 2 shows an example of a flat list that follows the resource
   list data format.  Each resource indicates the capacity of a
   resource.


   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:capacity"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <list>
       <entry uri="sip:bill@example.com" cp:capacity="to" />
       <entry uri="sip:joe@example.org" cp:capacity="cc" />
       <entry uri="sip:ted@example.net" cp:capacity="bcc" />
     </list>
   </resource-lists>

   Figure 2: URI-List




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5.  Option-tag

   This document defines the 'recipient-list-message' option-tag for use
   in the Require and Supported SIP header fields.

   User agent clients generating a MESSAGE 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 MESSAGEs 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.


6.  Procedures at the User Agent Client

   A UAC that wants to create a multiple-recipient MESSAGE request MUST
   create a MESSAGE request according to RFC 3428 [9] Section 4.  The
   UAC SHOULD populate the Request-URI with the SIP or SIPS URI of the
   MESSAGE URI-list service.  In addition to the regular instant message
   body, the UAC SHOULD add a URI-list body whose Content-Disposition
   type is 'recipient-list', specifed in the Framework and Security
   Considerations for SIP URI-list Services [12].  This body contains a
   URI-list with the recipients of the MESSAGE.  The URI-list body MAY
   also include the 'capacity' extension to the URI-list specified in
   Section 4.1.  The UAC MUST also include the 'recipient-list-message'
   option-tag, defined in Section 5, in a Require header field.

   Multiple-recipient MESSAGE requests contain a multipart body that
   contains the body carrying the list and the actual instant message
   payload.  In some cases, the MESSAGE request may contain bodies other
   than the text and the list bodies (e.g., when the request is
   protected with S/MIME [11]).

   Typically, the MESSAGE URI-list service will copy all the significant
   header fields in the outgoing MESSAGE request.  However, there might
   be cases where the SIP UA wants the MESSAGE URI-list service to add a
   particular header field with a particular value, even if 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 [6] 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 [6]) 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:bob@example.com?Accept-Contact=*%3bmobility%3d%22mobile%22




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   The previous URI requests the MESSAGE URI-list service to add the
   following header field to a MESSAGE request to be sent to
   bob@example.com:

   Accept-Contact: *;mobility="mobile"


7.  Procedures at the MESSAGE URI-List Service

   On reception of a MESSAGE request with a URI-list, a MESSAGE URI-list
   service 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
   URI-list service were successfully delivered to the URIs in the list.
   That is, a 202 Accepted means that the MESSAGE URI-list service 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.

7.1.  Determining the intended recipient

   On reception of a MESSAGE request with a URI-list, a MESSAGE URI-list
   service SHOULD determine the list of intended recipients, by
   inspecting the URI-list contained in the body.  In case two of those
   URIs are equivalent (section 19.1.4 of RFC 3261 [6] defines
   equivalent URIs), the MESSAGE URI-list SHOULD consider a single
   intended recipient.

7.2.  Creating an outgoing MESSAGE request

   Since the MESSAGE URI-list behaves as a UAC for outgoing MESSAGE
   requests, for each of the intended recipients, the MESSAGE URI-list
   service creates a new MESSAGE request according to the procedures
   described in Section 4 of RFC 3428 [9] and the following procedures:

   o  A MESSAGE URI-list service MUST include a From header field whose
      value is the same as the From header field included in the
      incoming MESSAGE request, subject to the privacy requirements (see
      RFC 3323 [7] and RFC 3325 [8]) expressed in the incoming MESSAGE
      request.  Note that this does not apply to the "tag" parameter.
   o  A MESSAGE URI-list service SHOULD generate a new To header field
      value set to the intended recipient URI.  According to the
      procedures of RFC 3261 Section 8.1.1.1, this value should also be
      equal to the Request-URI of the outgoing MESSAGE request.
   o  A MESSAGE URI-list service SHOULD create a new Call-ID header
      field value.




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   o  If a P-Asserted-Identity header field was present in the incoming
      MESSAGE request and the request was received from a trusted
      source, as specified in RFC 3325 [8], and the first hop of the
      outgoing MESSAGE request is also trusted, a MESSAGE URI-list
      service MUST include a P-Asserted-Identity header field in the
      outgoing MESSAGE request with the same received value.  However,
      if the first hop of the outgoing MESSAGE request is not trusted
      and the incoming MESSAGE request included a Privacy header field
      with a value different than 'none', the MESSAGE URI-list service
      MUST NOT include a P-Asserted-Identity header field in the
      outgoing MESSAGE request.
   o  If a MESSAGE URI-list service is able to assert the identity of a
      user (e.g., using HTTP Digest authentication scheme [4], S/MIME
      [11], etc.) and the service implements a mechanism where it can
      map that authentication scheme to a user's SIP or SIPS URI, and
      subject to the privacy requirements expressed in the incoming
      MESSAGE request (see RFC 3323 [7], the MESSAGE URI-list MAY insert
      a P-Asserted-Identity header with the value of the user's asserted
      URI.
   o  If the incoming MESSAGE request contains an Authorization or
      Proxy-Authorization header fields whose realm is set to the
      MESSAGE URI-list server's realm, then the MESSAGE URI-list service
      SHOULD NOT copy it to the outgoing MESSAGE request; otherwise
      (i.e., if the Authorization or Proxy-Authorization header field of
      incoming MESSAGE request contains a different realm), the MESSAGE
      URI-list service MUST copy the value to the respective header
      field of the outgoing MESSAGE request.
   o  A MESSAGE URI-list service SHOULD create a separate count for the
      CSeq header field of the outgoing MESSAGE request.
   o  A MESSAGE URI-list service SHOULD initialize the value of the Max-
      Forward header field of the outgoing MESSAGE request.
   o  A MESSAGE URI-list service MUST include its own value in the Via
      header field.
   o  A MESSAGE URI-list service SHOULD include any other header field
      expressed with the "?" mechanism described in Section 19.1.1 of
      RFC 3261 [6] and encoded in the intended recipient URI of the URI-
      list.
   o  A MESSAGE URI-list service SHOULD preserve to the outgoing MESSAGE
      request any other header field not explicitly indicated in the
      above paragraphs.

7.3.  Composing bodies in the outgoing MESSAGE request

   When creating the body of each of the outgoing MESSAGE requests, the
   MESSAGE URI-list service tries to keep the relevant bodies of the
   incoming MESSAGE request and copies them to the outgoing MESSAGE
   request.  The following guidelines are provided:




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   o  A MESSAGE request received at a MESSAGE URI-list service can
      contain one or more security bodies (e.g., S/MIME [11]) encrypted
      with the public key of the MESSAGE URI-list service.  These bodies
      are deemed to be read by the URI-list service rather than the
      recipient of the outgoing MESSAGE request (which will not be able
      to decrypt them).  Therefore, a MESSAGE URI-list service MUST NOT
      copy any security body (such as an S/MIME [11] encrypted body)
      addressed to the MESSAGE URI-list service to the outgoing MESSAGE
      request.  This includes bodies encrypted with the public key of
      the URI-list service.
   o  If the URI-list of the incoming MESSAGE request include resources
      tagged with the 'capacity' attribute set with a value of "to" or
      "cc", the URI-list service SHOULD include a URI-list in each of
      the outgoing MESSAGE requests.  The format of such list SHOULD BE
      according to the XML format for representing resource lists [10]
      and the capacity extension specified in Section 4.1.  This
      resource list MUST contain those elements categorized with the
      "to" or "cc" capacity attribute and MUST NOT contain those
      resources categorized with the "bcc" or lacking the capacity
      attribute.
   o  If the MESSAGE URI-list service includes a URI-list in an outgoing
      MESSAGE request, it MUST include a Content-Disposition header
      field [2] with the value set to 'recipient-list-history' and a
      'handling' parameter [5] set to "optional".
   o  If a MESSAGE URI-list service includes a URI-list in an outgoing
      MESSAGE request, it SHOULD use S/MIME [11] to encrypt the URI-list
      with the public key of the receiver.
   o  The incoming MESSAGE request typically contains a URI-list body or
      reference [12] with the actual list of recipients.  Section 7.2
      contains procedures that determine when the MESSAGE URI-list
      service should include a URI-list body in the outgoing MESSAGE
      request.
   o  The MESSAGE URI-list service 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 URI-list service MUST
      remove the multipart/mixed wrapper in the outgoing MESSAGE
      request.

   The rest of the MESSAGE request corresponding to a given URI in the
   URI-list MUST be created following the rules in Section 19.1.5
   "Forming Requests from a URI" of RFC 3261 [6].  In particular,
   Section 19.1.5 of RFC 3261 [6] 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."




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   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 URI-list
   services MUST generate only MESSAGE requests, regardless of the
   'method' parameter that the URIs in the list indicate.  Effectively,
   MESSAGE URI-list services MUST ignore the 'method' parameter in each
   of the URIs present in the URI-list.


8.  Procedures at the UAS

   A UAS (in this specification, also known as intended recipient UAS)
   that receives a MESSAGE request from the URI-list service behaves as
   specified in RFC 3428 [9] Section 7.

   If the UAS supports this specification and the MESSAGE request
   contains a body with a Content-Disposition header field [2] set to
   'recipient-list-history', then the UAS will be able to determine who
   are the other intended visible recipients of the MESSAGE request.
   This allows the user to create a reply request (e.g., MESSAGE,
   INVITE) to the sender and the rest of the visible recipients.


9.  Examples

   Figure 3 shows an example of operation.  A SIP UAC issuer sends a
   MESSAGE request.  The MESSAGE URI-list service answers with a 202
   Accepted message and sends a MESSAGE request to each of the intended
   recipients.






















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   +--------+        +---------+      +--------+ +--------+ +--------+
   |SIP UAC |        | MESSAGE |      |intended| |intended| |intended|
   | issuer |        | URI-list|      | recip. | | recip. | | recip. |
   |        |        | service |      |   1    | |   2    | |   3    |
   +--------+        +---------+      +--------+ +--------+ +--------+
       |                  |               |          |          |
       | F1. MESSAGE      |               |          |          |
       | ---------------->|               |          |          |
       | F2. 202 Accepted |               |          |          |
       |<---------------- |  F3. MESSAGE  |          |          |
       |                  | ------------->|          |          |
       |                  |  F4. MESSAGE  |          |          |
       |                  | ------------------------>|          |
       |                  |  F5. MESSAGE  |          |          |
       |                  | ----------------------------------->|
       |                  |  F6. 200 OK   |          |          |
       |                  |<------------- |          |          |
       |                  |  F7. 200 OK   |          |          |
       |                  |<------------------------ |          |
       |                  |  F8. 200 OK   |          |          |
       |                  |<----------------------------------- |
       |                  |               |          |          |
       |                  |               |          |          |
       |                  |               |          |          |

   Figure 3: Example of operation

   The MESSAGE request F1 is as follows:























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   MESSAGE sip:list-service.example.com SIP/2.0
   Via: SIP/2.0/TCP uac.example.com
       ;branch=z9hG4bKhjhs8ass83
   Max-Forwards: 70
   To: MESSAGE URI-list Service <sip:list-service.example.com>
   From: Carol <sip:carol@example.com>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 1 MESSAGE
   Require: recipient-list-message
   Content-Type: multipart/mixed;boundary="boundary1"
   Content-Length: 501

   --boundary1
   Content-Type: text/plain

   Hello World!

   --boundary1
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:capacity"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <list>
       <entry uri="sip:bill@example.com" cp:capacity="to" />
       <entry uri="sip:joe@example.org" cp:capacity="cc" />
       <entry uri="sip:ted@example.net" cp:capacity="bcc" />
     </list>
   </resource-lists>
   --boundary1--

   Messages F3, F4 and F5 are similar in nature.  Especially the bodies
   are exactly the same for all of them, since they include the instant
   message payload and a URI-list that contains the resources tagged
   with the "to" and "cc" capacity attribute.  We show an example of F3:














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   MESSAGE sip:bill@example.com SIP/2.0
   Via: SIP/2.0/TCP list-service.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: multipart/mixed;boundary="boundary1"
   Content-Length: 501

   --boundary1
   Content-Type: text/plain

   Hello World!

   --boundary1
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list-history; handling=optional

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:capacity"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <list>
       <entry uri="sip:bill@example.com" cp:capacity="to" />
       <entry uri="sip:joe@example.org" cp:capacity="cc" />
     </list>
   </resource-lists>
   --boundary1--


10.  Security Considerations

   The Framework and Security Considerations for SIP URI-List Services
   [12] discusses issues related to SIP URI-list services.
   Implementations of MESSAGE URI-list services MUST follow the
   security-related rules in the Framework and Security Considerations
   for SIP URI-List Services [12].  These rules include mandatory
   authentication and authorization of clients, and opt-in lists.

   If the contents of the instant message needs to be kept private, the
   user agent client SHOULD use S/MIME [11] to prevent a third party
   from viewing this information.  In this case, the user agent client
   SHOULD encrypt the instant message body with a content encryption
   key.  Then, for each receiver in the list, the UAC SHOULD encrypt the
   content encryption key with the public key of the receiver, and
   attach it to the MESSAGE request.



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11.  IANA Considerations

   The following sections instruct the IANA to register a new
   disposition type and a new SIP option-tag.

11.1.  Disposition Type Registration

   Section 4 defines a new 'recipient-list-history' value of the Mail
   Content Disposition Values registry.  This value should be registered
   in the IANA registry of Mail Content Disposition Values with the
   following registration data:

   +------------------------+------------------------------+-----------+
   | Name                   | Description                  | Reference |
   +------------------------+------------------------------+-----------+
   | recipient-list-history | the body contains a list of  | [RFCXXXX] |
   |                        | URIs that indicates the      |           |
   |                        | recipients of the message    |           |
   +------------------------+------------------------------+-----------+

    Table 1: Registration of the 'recipient-list-history' Mail Content
                             Disposition Value

   Note to IANA and the RFC editor: replace RFCXXXX above with the RFC
   number of this specification.

11.2.  Option-Tag Registration

   This document defines the 'recipient-list-message' SIP option-tag in
   Section 5.  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 MESSAGE request.


12.  Acknowledgements

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


13.  Change control






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13.1.  Changes from draft-ietf-sipping-uri-list-message-02.txt

   Typos fixed.

   'recipient-list-message' option-tag defined and registered with the
   IANA.

13.2.  Changes from draft-ietf-sipping-uri-list-message-01.txt

   Added a reference to missing REQ-GROUP-4 in the Advanced Instant
   Messaging Requirements for SIP document.

   Since the resource list allows now attribute extensibility, the
   former <capacity> element has been replaced by a 'capacity'
   attribute, which allows a more compact representation of the URI.

   Added a new Content-Disposition disposition type 'recipient-list-
   history'.  It is used in the MESSAGE request that the MESSAGE URI-
   list service sends to each of the recipients.  This allows the UAS to
   differentiate it from a 'recipient-list', which has a separate
   meaning.

13.3.  Changes from draft-ietf-sipping-uri-list-message-00.txt

   Revision of the treatment of headers the MESSAGE URI-list service, on
   a header by header basis.

   Added an overview section.

   Added functionality that allows the sender of the incoming MESSAGE
   request to tag each of the intended recipients with the "to", "cc",
   or "bcc" capacity.  If there are resources tagged as "to" or "cc",
   the URI-list service will include a URI-list in each of the outgoing
   MESSAGE request including those resources.

   Procedures at the UAS included.

   Better example including a flow.

13.4.  Changes from draft-ietf-sipping-message-exploder-00.txt to
       draft-ietf-sipping-uri-list-message-00.txt

   Clarified that the MESSAGE exploder should not distribute a body that
   has been encrypted with the public key of the exploder.  The
   exception is the URI-list, which can be distributed by the exploder,
   providing that is encrypted with the public key of the receiver.

   The security considerations section describes how to encrypt the list



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   and how to encrypt the instant message payload.

   Terminology aligned with the requirements and the framework for URI-
   list services (e.g., the term "exploder" has been deprecated).

13.5.  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.


14.  References

14.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Troost, R., Dorner, S., and K. Moore, "Communicating
         Presentation Information in Internet Messages: The Content-
         Disposition Header Field", RFC 2183, August 1997.

   [3]   Levinson, E., "Content-ID and Message-ID Uniform Resource
         Locators", RFC 2392, August 1998.

   [4]   Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
         Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
         Basic and Digest Access Authentication", RFC 2617, June 1999.

   [5]   Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F.,
         Watson, M., and M. Zonoun, "MIME media types for ISUP and QSIG
         Objects", RFC 3204, December 2001.

   [6]   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.




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   [7]   Peterson, J., "A Privacy Mechanism for the Session Initiation
         Protocol (SIP)", RFC 3323, November 2002.

   [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.

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

   [10]  Rosenberg, J., "Extensible Markup Language (XML) Formats for
         Representing Resource Lists",
         draft-ietf-simple-xcap-list-usage-05 (work in progress),
         February 2005.

   [11]  Ramsdell, B., "S/MIME Version 3.1 Message Specification",
         draft-ietf-smime-rfc2633bis-09 (work in progress), April 2004.

   [12]  Camarillo, G. and A. Roach, "Requirements and Framework for
         Session Initiation Protocol (SIP)Uniform  Resource Identifier
         (URI)-List Services", draft-ietf-sipping-uri-services-03 (work
         in progress), April 2005.

14.2.  Informational References

   [13]  Rosenberg, J., "Advanced Instant Messaging Requirements for the
         Session Initiation Protocol  (SIP)",
         draft-rosenberg-simple-messaging-requirements-01 (work in
         progress), February 2004.

   [14]  Peterson, J., "Session Initiation Protocol (SIP) Authenticated
         Identity Body (AIB) Format", RFC 3893, September 2004.


















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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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