SIPPING Working Group                                   M. Garcia-Martin
Internet-Draft                                                     Nokia
Expires: March 22, 2007                                     G. Camarillo
                                                                Ericsson
                                                      September 18, 2006


 Multiple-Recipient MESSAGE Requests in the Session Initiation Protocol
                                 (SIP)
                 draft-ietf-sip-uri-list-message-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document specifies a mechanism that allows a SIP User Agent
   Client (UAC) to request a SIP URI-list (Uniform Resource Identifier
   list) service to send a SIP MESSAGE request to a set of destinations.
   The client sends a SIP MESSAGE request that includes the payload
   along with the 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
   5.  Option-tag . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Procedures at the User Agent Client  . . . . . . . . . . . . .  6
   7.  Procedures at the MESSAGE URI-List Service . . . . . . . . . .  7
     7.1.  Determining the intended recipient . . . . . . . . . . . .  8
     7.2.  Creating an outgoing MESSAGE request . . . . . . . . . . .  8
     7.3.  Composing bodies in the outgoing MESSAGE request . . . . .  9
   8.  Procedures at the UAS  . . . . . . . . . . . . . . . . . . . . 11
   9.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     13.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 18





























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1.  Introduction

   SIP [5] can carry instant messages in MESSAGE [8] 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 wants to send a small page-
   mode instant message to an ad-hoc group without 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 [11].  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 also includes a URI-list in body parts whose
   Content-Disposition [2] is 'recipient-list-history', as specified in
   the Extensible Markup Language (XML) Format Extension for
   Representing Copy Control Attributes in Resource Lists [12].  The
   'recipient-list-history' body is sent along with the instant message
   payload in each of the instant messages sent to the recipients.

   The User Agent Client (UAC) 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 list of URIs is formatted according to the XML resource
   list [10] and extended with the attributes defined in [12].  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.  The MESSAGE URI-list service also manipulates the XML
   resource list according to the procedures indicated in [12], and
   attaches the result to each of the MESSAGE requests, along with the
   instant message payload.  Then the MESSAGE URI-list service sends
   each of the created outgoing MESSAGE request to the respective



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   receiver.

   The MESSAGE URI-list mechanism allows a sender to specify multiple
   targets for a MESSAGE request by including an XML resource list [10]
   in the body of the MESSAGE request extended with the attributes
   defined in the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [12].  This resource list, whose
   Content-Disposition [2] is 'recipient-list', as specified in the
   Framework and Security Considerations for SIP URI-List Services [11],
   includes the URIs of the targets.  Each target URI may also be marked
   to indicate in what role the URI-list service will place the target
   (e.g., "to", "cc", or "bcc"), and whether the target URI should be
   anonymized or not, according to the procedures described in [12].
   When the MESSAGE URI-list server expands the MESSAGE request to each
   recipient, it includes (along with the instant message payload) a new
   URI-list (based on the received one), whose Content-Disposition [2]
   is 'recipient-list-history', as specified in the XML Format Extension
   for Representing Copy Control Attributes in Resource Lists [12].
   This new URI-list includes the list of non-anonymous "to" and "cc"
   targets, allowing recipients to both get knowledge of other
   recipients and reply to them.


4.  URI-List document

   As described in the Framework and Security Considerations for SIP
   URI-List Services [11], 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 XML resource list document format [10] extended with
   the XML Format Extension for Representing Copy Control Attributes in
   Resource Lists [12].  UACs and MESSAGE URI-list services handling
   'recipient-list' bodies MUST support both of these formats and MAY
   support other formats.

   As described in the XML Format Extension for Representing Copy
   Control Attributes in Resource Lists [12], each URI can be tagged
   with a 'copyControl' attribute set to either "to", "cc", or "bcc",
   indicating the role in which the recipient will get the MESSAGE
   request.  Additionally, URIs can be tagged with the 'anonymize'
   attribute to prevent that the MESSAGE URI-list server discloses the
   target URI in a URI-list.

   Additionally, the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [12] defines a 'recipient-list-history'



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   body that contains the list of intended recipients.  The default
   format for 'recipient-list-history' bodies for MESSAGE URI-list
   services is also the XML resource list document format [10] extended
   with the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [12].  MESSAGE URI-list services MUST
   support both of these formats; UASes MAY support these formats.
   MESSAGE URI-list servers and UASes MAY support other formats.

   Nevertheless, the XML resource list document [10] 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 (User Agent) and the
   MESSAGE URI-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 MESSAGE URI-list service receiving a URI-list with more information
   than what has just been described MAY discard all the extra
   information.


5.  Option-tag

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

      This option-tag is used to ensure that a server can process the
      'recipient-list' body used in a MESSAGE request.  It also provides
      a mechanism to discover the capability of the server in responses
      to OPTIONS requests.

   UACs generating MESSAGE request that carry recipient-list bodies, as
   described in previous sections, MUST include this option-tag in a
   Require header field.  UAs 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
   creates a MESSAGE request that MUST be formatted according to RFC
   3428 [8] Section 4.  The UAC populates 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 adds a URI-list body whose
   Content-Disposition type is 'recipient-list', specified in the



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   Framework and Security Considerations for SIP URI-list Services [11].
   This body contains a URI-list with the recipients of the MESSAGE.
   Target URIs in this body MAY also be tagged with the 'copyControl'
   and 'anonymize' attributes specified in the XML Format Extension for
   Representing Copy Control Attributes in Resource Lists [12].  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 [9]).

   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 [5] 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 [5]) 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

   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, the MESSAGE URI-
   list service answers 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) response 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.



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7.1.  Determining the intended recipient

   On reception of a MESSAGE request with a URI-list, a MESSAGE URI-list
   service determines 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 [5] defines equivalent URIs),
   the MESSAGE URI-list SHOULD consider a single intended recipient
   rather than sending multiple copies of the MESSAGE to the same
   destination.

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 [8] 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 [6] and RFC 3325 [7]) expressed in the incoming MESSAGE
      request.  Note that this does not apply to the "tag" parameter.
         Failing to copy the From header field of the sender would
         prevent the recipient to get a hint of the sender's identity.
         Note also that this requirement does not intend to contradict
         requirements for additional services running on the same
         physical node.  Specifically, a privacy service (see RFC 3323
         [6]) can be co-located with the MESSAGE URI-list service, in
         which case, the privacy service has precedence over the MESSAGE
         URI-list service.
   o  A MESSAGE URI-list service SHOULD generate a new To header field
      value set to the intended recipient's URI.  According to the
      procedures of RFC 3261 [5] Section 8.1.1.1, this value should also
      be equal to the Request-URI of the outgoing MESSAGE request.
         The MESSAGE URI-list service behaves as a User Agent Client,
         thus, the To header field should be populated with the
         recipient's URI.
   o  A MESSAGE URI-list service SHOULD create a new Call-ID header
      field value.
         A Call-ID header field might contain addressing information
         that the sender wants to remain private.  Since there is no
         need to keep the same Call-ID on both sides of the MESSAGE URI-
         list service, and since the MESSAGE URI-list service behaves as
         a User Agent Client, it is recommended to create a new Call-ID
         header field value according to the regular SIP procedures.
   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 [7], and the first hop of the



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      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 [3], S/MIME
      [9], 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 [6], 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 [5] 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:

   o  A MESSAGE request received at a MESSAGE URI-list service can
      contain one or more security bodies (e.g., S/MIME [9]) encrypted
      with the public key of the MESSAGE URI-list service.  These bodies



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      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 [9] 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  The incoming MESSAGE request typically contains a URI-list body or
      reference [11] with the actual list of recipients.  If this URI-
      list includes resources tagged with the 'copyControl' attribute
      set to a value of "to" or "cc", the URI-list service SHOULD
      include a URI-list in each of the outgoing MESSAGE requests.  This
      list SHOULD be formatted according to the XML format for
      representing resource lists [10] and the copyControl extension
      specified in [12].  The URI-list service MUST follow the
      procedures specified in XML format for representing resource lists
      [12] with respect handling of the 'anonymize', 'count' and
      'copyControl' attributes.
   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 [4] set to "optional".
   o  If a MESSAGE URI-list service includes a URI-list in an outgoing
      MESSAGE request, it SHOULD use S/MIME [9] to encrypt the URI-list
      with the public key of the receiver.
   o  The MESSAGE URI-list service SHOULD copy all the remaining message
      bodies (e.g., text messages, images, etc.) of the incoming MESSAGE
      request 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 [5].  In particular,
   Section 19.1.5 of RFC 3261 [5] 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
   XML 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.



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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 [8] 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 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 recipients included in the URI-list.


9.  Examples

   Figure 1 shows an example of operation.  A SIP UAC issuer sends a
   MESSAGE request.  The MESSAGE URI-list service answers with a 202
   (Accepted) response and sends a MESSAGE request to each of the
   intended recipients.

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

   Figure 1: Example of operation




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   The MESSAGE request F1 (shown in Figure 2) contains a multipart/mixed
   body that is composed of two bodies: a text/plain body containing the
   instant message payload and an application/resource-lists+xml body
   containing the list of recipients.

   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: Alice <sip:alice@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:copycontrol">
     <list>
       <entry uri="sip:bill@example.com" cp:copyControl="to" />
       <entry uri="sip:randy@example.net" cp:copyControl="to"
                                          cp:anonymize="true"/>
       <entry uri="sip:eddy@example.com" cp:copyControl="to"
                                         cp:anonymize="true"/>
       <entry uri="sip:joe@example.org" cp:copyControl="cc" />
       <entry uri="sip:carol@example.net" cp:copyControl="cc"
                                          cp:anonymize="true"/>
       <entry uri="sip:ted@example.net" cp:copyControl="bcc" />
       <entry uri="sip:andy@example.com" cp:copyControl="bcc" />
     </list>
   </resource-lists>
   --boundary1--

   Figure 2: MESSAGE request received at the MESSAGE URI-list server

   The MESSAGE requests F3, F4 and F5 are similar in nature.  All those
   MESSAGE requests contain a multipart/mixed body which is composed of



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   two other bodies: a text/plain body containing the instant message
   payload and an application/resource-lists+xml containing the list of
   recipients.  Unlike the text/plain body the application/
   resource-lists+xml body is not equal to the application/
   resource-lists+xml included in the incoming MESSAGE request F1,
   because the URI-list service has anonymized those URIs tagged with
   the 'anonymize' attribute and has removed those URIs tagged with a
   "bcc" 'copyControl' attribute.  Figure 3 shows an examples of the
   message F3.

   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: Alice <sip:alice@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:copycontrol">
     <list>
       <entry uri="sip:bill@example.com" cp:copyControl="to" />
       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="to"
                                                    cp:count="2"/>
       <entry uri="sip:joe@example.org" cp:copyControl="cc" />
       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="cc"
                                                    cp:count="1"/>
     </list>
   </resource-lists>
   --boundary1--

   Figure 3: MESSAGE request sent by the MESSAGE URI-list server






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10.  Security Considerations

   The Framework and Security Considerations for SIP URI-List Services
   [11] 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 [11].  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 [9] 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.


11.  IANA Considerations

   This document defines the 'recipient-list-message' SIP option-tag in
   Section 5.  IANA should register this option-tag in the Option Tags
   subregistry under the IANA registry of SIP parameters, with the
   following registration data:

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

    Table 1: Registration of the 'recipient-list-message' Option-Tag in
                                    SIP

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


12.  Acknowledgements

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





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13.  References

13.1.  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]   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.

   [4]   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.

   [5]   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.

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

   [7]   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.

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

   [9]   Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
         (S/MIME) Version 3.1 Message Specification", RFC 3851,
         July 2004.

   [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]  Camarillo, G. and A. Roach, "Framework and Security
         Considerations for Session Initiation Protocol (SIP)  Uniform
         Resource Identifier (URI)-List Services",
         draft-ietf-sipping-uri-services-05 (work in progress),
         January 2006.



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   [12]  Garcia-Martin, M. and G. Camarillo, "Extensible Markup Language
         (XML) Format Extension for Representing Capacity  Attributes in
         Resource Lists", draft-ietf-sipping-capacity-attribute-01 (work
         in progress), September 2006.

13.2.  Informative References

   [13]  Rosenberg, J. and M. Isomaki, "Advanced Instant Messaging
         Requirements for the Session Initiation Protocol  (SIP)",
         draft-ietf-simple-messaging-requirements-00 (work in progress),
         June 2006.








































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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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