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Versions: (draft-saintandre-sip-xmpp-groupchat) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7702

Network Working Group                                     P. Saint-Andre
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                               S. Ibarra
Expires: April 1, 2014                                       AG Projects
                                                               S. Loreto
                                                                Ericsson
                                                      September 28, 2013


   Interworking between the Session Initiation Protocol (SIP) and the
      Extensible Messaging and Presence Protocol (XMPP): Groupchat
                      draft-ietf-stox-groupchat-01

Abstract

   This document defines a bidirectional protocol mapping for the
   exchange of instant messages in the context of a multiparty chat
   session among users of the Session Initiation Protocol (SIP) and
   users of the Extensible Messaging and Presence Protocol (XMPP).
   Specifically, this document defines a mapping between the SIP-based
   Message Session Relay Protocol (MSRP) and the XMPP Multi-User Chat
   (MUC) extension.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 1, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  XMPP MUC to MSRP Multi-party Messaging Session . . . . . . . .  3
     3.1.  Enter Room . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Set Nickname . . . . . . . . . . . . . . . . . . . . . . .  8
     3.3.  Conference Subscription  . . . . . . . . . . . . . . . . .  8
     3.4.  Presence Broadcast . . . . . . . . . . . . . . . . . . . .  9
     3.5.  Exchange Messages  . . . . . . . . . . . . . . . . . . . . 12
       3.5.1.  Send a Message to All Occupants  . . . . . . . . . . . 12
       3.5.2.  Send a Private Message . . . . . . . . . . . . . . . . 14
     3.6.  Change Nickname  . . . . . . . . . . . . . . . . . . . . . 15
     3.7.  Invite Another User to a Room  . . . . . . . . . . . . . . 16
     3.8.  Exit Room  . . . . . . . . . . . . . . . . . . . . . . . . 18
   4.  MSRP Multi-party Messaging Session to XMPP MUC . . . . . . . . 18
     4.1.  Enter Room (Includes Set Nickname) . . . . . . . . . . . . 20
     4.2.  Presence Broadcast . . . . . . . . . . . . . . . . . . . . 23
     4.3.  Exchange Messages  . . . . . . . . . . . . . . . . . . . . 26
       4.3.1.  Send a Message to All Occupants  . . . . . . . . . . . 26
       4.3.2.  Send a Private Message . . . . . . . . . . . . . . . . 27
     4.4.  Change Nickname  . . . . . . . . . . . . . . . . . . . . . 29
     4.5.  Invite Another User to a Room  . . . . . . . . . . . . . . 30
     4.6.  Exit Room  . . . . . . . . . . . . . . . . . . . . . . . . 31
   5.  Handling of Nicknames and Display Names  . . . . . . . . . . . 31
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 32
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 32
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 33
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 34
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34











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1.  Introduction

   Both the Session Initiation Protocol (SIP) [RFC3261] and the
   Extensible Messaging and Presence Protocol (XMPP) [RFC6120] can be
   used for the purpose of multiparty text chat over the Internet.  To
   ensure interworking between these technologies, it is important to
   define bidirectional protocol mappings.

   The architectural assumptions underlying such protocol mappings are
   provided in [I-D.ietf-stox-core], including mapping of addresses and
   error conditions.  This document specifies mappings for multiparty
   text chat sessions (often called "groupchat"); specifically, this
   document defines a mapping between the XMPP Multi-User Chat (MUC)
   extension [XEP-0045] and SIP-based multiparty chat using Message
   Session Relay Protocol [RFC4975] as specified in
   [I-D.ietf-simple-chat].

   Both MUC and MSRP contain a large set of features, such as the
   ability to administer rooms, kick and ban users, reserve a nickname
   within a room, change room subject, enable room moderation, and
   destroy the room.  This document covers only a basic subset of
   groupchat features: joining a room, establishing or changing (but not
   permanently registering) a room nickname, modifying presence
   information within the room, sending a message to all participants,
   sending a private message to a single participant, inviting another
   user to the room, and leaving the room.  Future documents might
   define mappings for additional features beyond this set.

   The discussion venue for this document is the mailing list of the
   STOX WG; visit https://www.ietf.org/mailman/listinfo/stox for
   subscription information and discussion archives.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   A number of technical terms used here are defined in [RFC3261],
   [RFC4975], [RFC6120], and [XEP-0045].  The term "JID" is short for
   "Jabber ID".


3.  XMPP MUC to MSRP Multi-party Messaging Session

   This section describes how to map an XMPP MUC session to an MSRP



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   Multi-party Messaging session.  The following diagram outlines the
   overall protocol flow of a sample session, which includes some
   optional exchanges (such as sending messages, changing nickname, and
   inviting another user).

   XMPP User                   Gateway               MSRP Conference
       |                          |                          |
       |(X1) (XMPP) Enter room    |                          |
       |------------------------->|                          |
       |                          |(X2) (SIP) INVITE         |
       |                          |------------------------->|
       |                          |(X3) (SIP) 200 OK         |
       |                          |<-------------------------|
       |                          |(X4) (SIP) ACK            |
       |                          |------------------------->|
       |                          |(X5) (MSRP) NICKNAME      |
       |                          |------------------------->|
       |                          |(X6) (MSRP) 200 OK        |
       |                          |<-------------------------|
       |                          |(X7) (SIP) SUBSCRIBE      |
       |                          |------------------------->|
       |                          |     Event:conference     |
       |                          |                          |
       |                          |(X8) (SIP) 200 OK         |
       |                          |<-------------------------|
       |                          |(X9) (SIP) NOTIFY         |
       |                          |<-------------------------|
       |                          |(X10) (SIP) 200 OK        |
       |                          |------------------------->|
       |(X11) (XMPP) Presence     |                          |
       |<-------------------------|                          |
       |(X12) (XMPP) Subject      |                          |
       |<-------------------------|                          |
       |                          |                          |
       |(X13) (XMPP) Groupchat message                       |
       |------------------------->|                          |
       |                          |(X14) (MSRP) SEND         |
       |                          |------------------------->|
       |                          |(X15) (MSRP) 200 OK       |
       |                          |<-------------------------|
       |(X16) (XMPP) Groupchat message                       |
       |<-------------------------|                          |
       |                          |                          |
       |(X17) (XMPP) Private message                         |
       |------------------------->|                          |
       |                          |(X18) (MSRP) SEND         |
       |                          |------------------------->|
       |                          |(X19) (MSRP) 200 OK       |



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       |                          |<-------------------------|
       |                          |                          |
       |(X20) (XMPP) Change nick  |                          |
       |------------------------->|                          |
       |                          |(X21) (MSRP) NICKNAME     |
       |                          |------------------------->|
       |                          |(X22) (MSRP) 425 Error    |
       |                          |<-------------------------|
       |                          |                          |
       |(X23) (XMPP) Presence Error
       |<-------------------------|                          |
       |                          |                          |
       |(X24) (XMPP) Message stanza to invite participant    |
       |------------------------->|                          |
       |                          |(X25) (SIP) REFER         |
       |                          |------------------------->|
       |                          |(X26) (SIP) 200 OK        |
       |                          |<-------------------------|
       |                          |(X27) (SIP) NOTIFY        |
       |                          |<-------------------------|
       .                          .                          .
       .                          .                          .
       |(X28) (XMPP) Exit room    |                          |
       |------------------------->|                          |
       |                          |(X29) (SIP) BYE           |
       |                          |------------------------->|
       |                          |(X30) (SIP) 200 OK        |
       |                          |<-------------------------|
       |(X31) (XMPP) Presence unavailable
       |<-------------------------|                          |

   Detailed protocol flows and mappings are provided in the following
   sections.

3.1.  Enter Room

   As defined in the XMPP Multi-User Chat (MUC) specification
   [XEP-0045], when an XMPP user (say, "juliet@example.com") wants to
   join a groupchat room (say, "verona@chat.example.org"), she sends a
   directed <presence/> stanza [RFC6121] to that chat room.  In her
   request she also specifies the nickname she wants to use within the
   room (say, "JuliC"); in XMPP this room nickname is the resourcepart
   of an occupant JID (thus "verona@chat.example.org/JuliC").  The
   joining client signals its ability to speak the multi-user chat
   protocol by including in the initial presence stanza an empty <x/>
   element qualified by the 'http://jabber.org/protocol/muc' namespace.





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   Example 1: Juliet enters room (X1)

   |  <presence from='juliet@example.com/balcony'
   |            to='verona@chat.example.org/JuliC'>
   |    <x xmlns='http='http://jabber.org/protocol/muc'/>
   |  </presence>

   Upon receiving such a presence stanza, the XMPP server to which
   Juliet has connected needs to determine the identity of the
   domainpart in the 'to' address, which it does by following the
   procedures discussed in [I-D.ietf-stox-core].  Here we assume that
   the XMPP server has determined the domain is serviced by a SIMPLE
   server, that it contains or has available to it an XMPP-SIMPLE
   gateway or connection manager (which enables it to speak natively to
   SIMPLE servers), and that it hands off the presence stanza to the
   XMPP-SIMPLE gateway.

   Because a multi-user chat service accepts the presence stanza shown
   above as a request to enter a room, the XMPP-to-SIP gateway
   transforms it into a SIP INVITE request.

   Example 2: SIP mapping of room join (X2)

   |  INVITE sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>
   |  From: "Juliet" <sip:juliet@example.com>
   |  Contact: <sip:juliet@example.com>;gr=balcony
   |  Call-ID: 711609sa
   |  Content-Type: application/sdp
   |  Content-Length: 182
   |
   |  c=IN IP4 x2s.example.org
   |  m=message 7654 TCP/MSRP *
   |  a=accept-types:text/cpim
   |  a=accept-wrapped-types:text/plain text/html
   |  a=path:msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  a=chatroom

   Here the Session Description Protocol offer specifies the MSRP-aware
   XMPP-to-SIP gateway on the XMPP side as well as other particulars of
   the session.

      There is no direct mapping for the MSRP URIs.  In fact MSRP URIs
      identify a session of instant messages at a particular device;
      they are ephemeral and have no meaning outside the scope of that
      session.  The authority component of the MSRP URI MUST contain the
      XMPP-to-SIP gateway hostname or numeric IP address and an explicit
      port number.



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   As specified in [I-D.ietf-stox-core], the mapping of XMPP syntax
   elements to SIP and [RFC4566] syntax elements is as shown in the
   following table.

   Table 1: Message syntax mapping from XMPP to SIP/SDP

       +-----------------------------+-----------------------------+
       |  XMPP Element or Attribute  |  SIP Header or SDP Contents |
       +-----------------------------+-----------------------------+
       |  from                       |  From                       |
       |  <thread/>                  |  Call-ID                    |
       |  to (without the /nick)     |  To                         |
       +-----------------------------+-----------------------------+

   Here we assume that the MSRP conference server accepts the session
   establishment.  It includes the 'isfocus' and other relevant feature
   tags in the Contact header field of the response.  The MSRP
   conference server also includes an answer session description that
   acknowledges the choice of media and contains the extensions
   specified in [I-D.ietf-simple-chat].

   Example 3: Chat room accepts session establishment (X3)

   |  SIP/2.0 200 OK
   |  From: <sip:verona@chat.example.org>
   |  To: "Juliet" <sip:juliet@example.com>;tag=786
   |  Call-ID: 711609sa
   |  Contact: <sip:verona@chat.example.org;transport=tcp>;isfocus
   |  Content-Type: application/sdp
   |  Content-Length: 214
   |
   |  c=IN IP4 example.org
   |  m=message 12763 TCP/MSRP *
   |  a=chatroom:nickname private-messages
   |  a=accept-types:message/cpim
   |  a=accept-wrapped-types:text/plain text/html
   |  a=path:msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp

   Upon receiving such a response, the SIMPLE server or associated SIP-
   to-XMPP gateway sends a SIP ACK to the MSRP conference server on
   behalf of the joining user.

   Example 4: Gateway sends ACK to MSRP conference server (X4)

   |  ACK sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>;tag=087js
   |  From: "Juliet" <sip:juliet@example.com>;tag=786
   |  Call-ID: 711609sa



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3.2.  Set Nickname

   If the chat room server accepted the session, the SIMPLE server or
   associated SIP-to-XMPP gateway MUST set up the nickname as received
   in the presence stanza (i.e., the resourcepart of the 'to' address,
   such "JuliC" in "verona@chat.example.org/JuliC").  The nickname is
   set up using the extension specified in [I-D.ietf-simple-chat].

   Example 5: Gateway sets up nickname (X5)

   |  MSRP a786hjs2 NICKNAME
   |  To-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  From-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  Use-Nickname: "JuliC"
   |  -------a786hjs2

   The MSRP conference server analyzes the existing allocation of
   nicknames, accepts the nickname proposal, and answers with a 200
   response.

   Example 6: MSRP conference accepts nickname proposal (X6)

   |  MSRP a786hjs2 200 OK
   |  To-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  From-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  -------a786hjs2

   This section assumes that the nickname request is successful.  The
   error flow resulting from a nickname conflict is described under
   Section 3.6.

3.3.  Conference Subscription

   If the nickname request is successful, the XMPP-to-SIP gateway then
   formally subscribes to the MSRP conference on behalf of the XMPP
   user.















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   Example 7: Gateway subscribes to the MSRP conference (X7)

   |  SUBSCRIBE sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>
   |  From: "Juliet" <sip:juliet@example.com>
   |  Contact: <sip:juliet@example.com>;gr=balcony
   |  Call-ID: hsuKZGkjQewg6IJI8.PD5rRAvbuTYLR-
   |  Event: conference
   |  Expires: 600
   |  Accept: application/conference-info+xml
   |  Allow-Events: conference
   |  Content-Length: 0

   The conference server will accept or reject the request based on
   local policy.

   Example 8: MSRP conference server accepts subscription request (X8)

   |  SIP/2.0 200 OK
   |  To: <sip:verona@chat.example.org>
   |  From: "Juliet" <sip:juliet@example.com>
   |  Call-ID: hsuKZGkjQewg6IJI8.PD5rRAvbuTYLR-
   |  Contact: <sip:verona@chat.example.org;transport=tcp>;isfocus
   |  Allow: SUBSCRIBE, NOTIFY, PRACK, INVITE, ACK, BYE,
   |         CANCEL, UPDATE, MESSAGE, REFER
   |  Expires: 600
   |  Content-Length: 0

3.4.  Presence Broadcast

   If the MSRP conference service accepts the request to enter a room,
   the XMPP user expects to receive back presence information from all
   the existing occupants of the room.  So the XMPP-to-SIP gateway MUST
   subscribe to the Conference Event package [RFC4575] on the MSRP
   conference server.  When the subscription is completed the MSRP
   conference server sends to the XMPP-to-SIP gateway a NOTIFY
   containing the presence information of all the existing occupants,
   represented using the [RFC4575] format.













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   Example 9: MSRP conference sends presence information (X9)

   |  NOTIFY sip:verona@chat.example.org SIP/2.0
   |  To: "Juliet" <sip:juliet@example.com>;gr=balcony
   |  From: <sip:verona@chat.example.org>;tag=a3343df32
   |  Call-ID: k3l43id034ksereree
   |  Event: conference
   |  Subscription-State: active;expires=3600
   |  Content-Type: application/conference-info+xml
   |  Content-Length: ...
   |
   |  <conference-info version="0" state="full"
   |      entity="sip:3402934234@chat.example.org">
   |    <conference-description>
   |      <subject>Today in Verona</subject>
   |      <conf-uris>
   |        <entry>
   |          <uri>tel:+18882934234</uri>
   |        </entry>
   |      </conf-uris>
   |    </conference-description>
   |    <users>
   |      <user entity="sip:verona@chat.example.org;gr=Romeo"
   |            state="full">
   |        <display-text>Romeo</display-text>
   |        <roles>
   |          <entry>participant</entry>
   |        </roles>
   |      </user>
   |      <user entity="sip:verona@chat.example.org;gr=Ben"
   |            state="full">
   |        <display-text>Ben</display-text>
   |        <roles>
   |          <entry>participant</entry>
   |        </roles>
   |      </user>
   |      <user entity="sip:verona@chat.example.org;gr=JuliC"
   |            state="full">
   |        <display-text>JuliC</display-text>
   |        <roles>
   |          <entry>participant</entry>
   |        </roles>
   |      </user>
   |    </users>
   |  </conference-info>

   The following table shows the syntax mapping from the RFC 4575
   payload to the XMPP participant list.  (Mappings for elements not



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   mentioned are undefined.)

   Table 2: Participant list mapping

       +--------------------------------+-----------------------------+
       |  RFC 4575 Element              |  XMPP Element or Attribute  |
       +--------------------------------+-----------------------------+
       |  conference-info entity        |  room JID                   |
       |  conference subject            |  room subject               |
       |  user entity                   |  participant bare JID       |
       |  user display-text / nickname  |  participant nickname       |
       |  endpoint entity               |  participant full JID       |
       +--------------------------------+-----------------------------+

   Upon receiving such a response, the SIP-to-XMPP gateway MUST send a
   200 OK to the MSRP conference server and translate the participant
   list into a series of XMPP presence stanzas.

   Example 10: XMPP mapping of chatroom presence (F11)

   |  <presence from='verona@chat.example.org/Romeo'
   |            to='juliet@example.com/balcony'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |    </x>
   |  </presence>

   |  <presence from='verona@chat.example.org/Ben'
   |            to='juliet@example.com/balcony'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |    </x>
   |  </presence>

   |  <presence from='verona@chat.example.org/JuliC'
   |            to='juliet@example.com/balcony'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |      <status code='110'/>
   |    </x>
   |  </presence>

   If the NOTIFY included a subject, the gateway converts that into a
   separate XMPP message.







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   Example 11: XMPP mapping of chatroom subject (F12)

   |  <message from='verona@chat.example.com/mayor'
   |           to='juliet@example.com/balcony'
   |           id='mbh2vd68'>
   |    <subject>Today in Verona</subject>
   |  </message>

   The mapping of SIP and [RFC4575] payload syntax elements to XMPP
   syntax elements is as shown in the following table.  (Mappings for
   elements not mentioned are undefined.)

   Table 3: Message syntax mapping from SIP to XMPP

       +---------------------------------+-----------------------------+
       | SIP Header or RFC4575 Contents  | XMPP Element or Attribute   |
       +---------------------------------+-----------------------------+
       |  <user entity=...>              |  from                       |
       |  Call-ID                        |  thread                     |
       |  To + / <display-text>          |  to                         |
       |  roles                          |  role                       |
       |  'none'                         |  affiliation                |
       +---------------------------------+-----------------------------+

3.5.  Exchange Messages

   Once the user has joined the chatroom, the user can exchange an
   unbounded number of messages, both public and private.

   The mapping of XMPP syntax elements to MSRP syntax elements is as
   shown in the following table.  (Mappings for elements not mentioned
   are undefined.)

   Table 4: Message syntax mapping from XMPP Message to MSRP

       +-----------------------------+-----------------------------+
       |  XMPP Element or Attribute  |  CPIM Header                |
       +-----------------------------+-----------------------------+
       |  to                         |  To                         |
       |  from                       |  From                       |
       |  <body/>                    |  body of the SEND request   |
       +-----------------------------+-----------------------------+

3.5.1.  Send a Message to All Occupants

   When Juliet wants to sends a message to all other occupants in the
   room, she sends a message of type "groupchat" to the <room@service>
   itself (in our example, <verona@chat.example.org>).



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   The following examples show an exchange of a public message.

   Example 12: Juliet sends message to all occupants (X13)

   |  <message from='juliet@example.com/balcony'
   |           to='verona@chat.example.org'
   |           type='groupchat'
   |           id='lzfed24s'>
   |        <body>Who knows where Romeo is?</body>
   |  </message>

   Upon receiving such a message, the XMPP-to-SIP gateway MUST translate
   it into an MSRP SEND message.

   Example 13: Gateway maps XMPP message to MSRP (X14)

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  From-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  Message-ID: 87652491
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:verona@chat.example.org>
   |  From: "Juliet" <sip:juliet@example.com>
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  Who knows where Romeo is?
   |  -------a786hjs2$

   Upon receiving the SEND request, if the request either contains a
   Failure-Report header field value of "yes" or does not contain a
   Failure-Report header at all, the MSRP conference server MUST
   immediately generate and send a response.

   Example 14: MSRP conference returns 200 OK (X15)

   |  MSRP d93kswow 200 OK
   |  To-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  From-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  -------d93kswow$

   Since an XMPP MUC room could be moderated and an XMPP user cannot be
   sure whether her message has been accepted or not without receiving
   it back from the server, [XEP-0045] states that the sender needs to
   receive the same message it has generated.  So in this scenario the
   XMPP-to-SIP gateway has to reflect the message back to the sender.



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   This prodedure only applies to XMPP endpoints.

   Example 15: Gateway reflects message to XMPP user (X16)

   |  <message from='verona@chat.example.org/JuliC'
   |           to='verona@chat.example.org'
   |           type='groupchat'
   |           id='ix51z73m'>
   |        <body>Who knows where Romeo is?</body>
   |  </message>

3.5.2.  Send a Private Message

   Since each occupant has a unique JID, Juliet can send a "private
   message" to a selected occupant through the service by sending a
   message to the user's occupant JID.  The XMPP message type SHOULD be
   "chat" and MUST NOT be "groupchat", but MAY be left unspecified.

   If the XMPP-to-SIP gateway has support for private messaging it MUST
   advertise that fact by adding a "private-messages" value to the
   a=chatroom SDP attribute it sends to the MSRP conference server, as
   specified in [I-D.ietf-simple-chat].

   |  a=chatroom:nickname private-messages

   The following examples show an exchange of a private message.

   Example 16: Juliet sends private message (X17)

   |  <message from='juliet@example.com/balcony'
   |           to='verona@chat.example.org/Romeo'
   |           type='chat'
   |           id='6sfln45q'>
   |        <body>O Romeo, Romeo! wherefore art thou Romeo?</body>
   |  </message>

   Upon receiving such a message, the XMPP-to-SIP gateway MUST translate
   it into an MSRP SEND message.













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   Example 17: Gateway maps private message from XMPP to MSRP (X18)

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  From-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  Message-ID: 87652491
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:verona@chat.example.org>;gr=Romeo
   |  From: <sip:juliet@example.org>;gr=balcony
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  O Romeo, Romeo! wherefore art thou Romeo?
   |  -------a786hjs2$

   After acknowledging the message by sending a SIP 200 OK (step X19,
   not shown), the MSRP conference server is responsible for sending the
   message to the intended recipient (not shown in the protocol flow).
   When doing so, it MUST modify the "From" header to the sender's
   address within the chatroom.

   Example 18: MSRP conference sends private message to SIP user

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  From-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  Message-ID: 87652491
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:romeo@example.com>
   |  From: <sip:verona@chat.example.com>;gr=JuliC
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  O Romeo, Romeo! wherefore art thou Romeo?
   |  -------a786hjs2$

3.6.  Change Nickname

   The XMPP user might want to change her nickname.  She can do so by
   sending an updated presence stanza to the room, containing a new
   nickname.






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   Example 19: Juliet changes her nickname (X20)

   |  <presence from='juliet@example.com/balcony'
   |            to='verona@chat.example.org/CapuletGirl'/>

   So far we have assumed that the requested nickname did not conflict
   with any existing nicknames.  The following text describes the
   handling of a nickname conflict.

   The MSRP conference server analyzes the existing allocation of
   nicknames, and detects that the nickname proposal is already provided
   to another participant.  In this case the MSRP conference server
   answers with a 425 response.

   Example 20: MSRP conference does not accept nickname proposal (X22)

   |  MSRP a786hjs2 425 Nickname usage failed
   |  To-Path: msrp://x2s.example.com:7654/jshA7weztas;tcp
   |  From-Path: msrp://s2x.example.org:12763/kjhd37s2s20w2a;tcp
   |  -------a786hjs2

   Upon receiving such a response, the SIP-to-XMPP gateway SHOULD
   translate it into an XMPP presence stanza of type "error" specifying
   a <conflict/> error condition (which implies that the XMPP client
   will then need to choose another nickname and repeat the process of
   joining).

   Example 21: Conflict error for nickname (X23)

   |  <presence from='verona@chat.example.org/JuliC'
   |            to='juliet@example.com/balcony'
   |            type='error'>
   |    <x xmlns='http='http://jabber.org/protocol/muc'/>
   |    <error type='cancel' by='verona@chat.example.org'>
   |      <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
   |    </error>
   |  </presence>

   Alternatively, the gateway might generate a new nickname request on
   behalf of the XMPP user, thus shielding the XMPP client from handling
   the conflict error.

3.7.  Invite Another User to a Room

   In XMPP there are two methods for inviting another user to a room:
   direct invitations [XEP-0249] (sent directly from the user's real JID
   outside the room to the invitee's real JID) and mediated invitations
   (sent through the room from the user's occupant JID to the invitee's



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   JID).  In this document we cover mediated invitations only.

   For example, if Juliet decides to invite Benvolio to the room, she
   sends a message stanza with an invite and Benvolio's JID (which could
   be his real JID or an occupant JID in another room).

   Example 22: Juliet invites Benvolio to the room (X24)

   |  <message from='juliet@example.com/balcony'
   |           id='nzd143v8'
   |           to='verona@chat.example.org'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <invite to='benvolio@example.com'/>
   |    </x>
   |  </message>

   The SIP-to-XMPP gateway then sends a SIP REFER request to the MSRP
   conference server indicating who needs to be invited in the Refer-To
   header, as per [RFC4579] (sec 5.5)

   Example 23: SIP mapping of invite (X25)

   |  REFER sip:verona@chat.example.com SIP/2.0
   |  To: <sip:verona@chat.example.com>
   |  From: "Juliet" <sip:juliet@example.com>;tag=5534562
   |  Call-ID: 849392fklgl43
   |  Contact: <sip:juliet@example.com>;gr=balcony
   |  Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
   |  Accept: message/sipfrag
   |  Refer-To: <sip:benvolio@example.com>
   |  Supported: replaces
   |  Content-Length: 0

   The MSRP conference server then acknowledges the SIP REFER request
   with a 200 OK response (step X25, not shown).

   The progress of the invitation will be tracked by the received NOTIFY
   requests as per [RFC3515].













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   Example 24: Progress notification for invitation (X27)

   |  NOTIFY sip:juliet@example.com SIP/2.0
   |  To: <sip:juliet@example.com>;tag=5534562
   |  From: <sip:verona@chat.example.com>;tag=18747389
   |  Call-ID: 849392fklgl43
   |  Max-Forwards: 70
   |  Event: refer
   |  Subscription-State: active;expires=60
   |  Contact: <sip:verona@chat.example.com;transport=tcp>;isfocus
   |  Content-Type: message/sipfrag;version=2.0
   |  Content-Length: ...

3.8.  Exit Room

   If Juliet decides to exit the chatroom, her client sends a directed
   presence stanza of type "unavailable" to the occupant JID she is
   currently using in the room (here <verona@chat.example.org/JuliC>).

   Example 25: Juliet exits room (X28)

   |  <presence from='juliet@example.com/balcony'
   |            to='verona@chat.example.org/JuliC'
   |            type='unavailable'/>

   Upon receiving such a stanza, the XMPP-to-SIP gateway terminates the
   SIP session by sending a SIP BYE to the MSRP conference server and
   the MSRP conference server responds with a 200 OK (steps X29 and X30,
   not shown).

   Juliet MAY include a custom exit message in the presence stanza of
   type "unavailable", in which case it SHOULD be broadcasted to other
   participants using the methods described above.

   Example 26: Juliet exits the chatroom (F31)

   |  <presence from='juliet@example.com/balcony'
   |            to='verona@chat.example.org/JuliC'
   |            type='unavailable'>
   |    <status>Time to go!</status>
   |  </presence>


4.  MSRP Multi-party Messaging Session to XMPP MUC

   This section describes how to map a Multi-party Instant Message (IM)
   MSRP session to an XMPP Multi-User Chat (MUC) session.  As before,
   the following diagram outlines the overall protocol flow of a sample



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   session, which includes some optional exchanges (such as sending
   messages, changing nickname, and inviting another user).

   SIP User                  Gateway                   XMPP MUC
      |                         |                           |
      |(S1)(SIP) INVITE         |                           |
      |------------------------>|                           |
      |(S2) (SIP) 200 OK        |                           |
      |<------------------------|                           |
      |(S3) (SIP) ACK           |                           |
      |------------------------>|                           |
      |(S4) (MSRP) NICKNAME     |                           |
      |------------------------>|                           |
      |                         |(S5)(XMPP) Enter room      |
      |                         |-------------------------->|
      |(S6) (MSRP) 200 OK       |                           |
      |<------------------------|                           |
      |                         |(S7)(XMPP) (XMPP) Presence |
      |                         |<--------------------------|
      |                         |                           |
      |(S8)(SIP) SUBSCRIBE      |                           |
      |------------------------>|                           |
      |     Event:conference    |                           |
      |                         |                           |
      |(S9) (SIP) 200 OK        |                           |
      |<------------------------|                           |
      |(S10) (SIP) NOTIFY       |                           |
      |<------------------------|                           |
      |(S11) (SIP) 200 OK       |                           |
      |------------------------>|                           |
      |                         |(S12)(XMPP) (XMPP) Subject |
      |                         |<--------------------------|
      |                         |                           |
      |(S13)(MSRP) SEND         |                           |
      |------------------------>|                           |
      |                         |(S14)(XMPP) Chat message   |
      |(S15)(MSRP) 200 OK       |-------------------------->|
      |<------------------------|(S16)(XMPP) Chat message   |
      |                         |<--------------------------|
      |(S17)(MSRP) SEND         |                           |
      |<------------------------|                           |
      |(S18)(MSRP) 200 OK       |                           |
      |------------------------>|                           |
      |                         |                           |
      |(S19)(MSRP) SEND         |                           |
      |------------------------>|                           |
      |                         |(S20)(XMPP) Private message|
      |                         |-------------------------->|



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      |(S21)(MSRP) 200 OK       |                           |
      |<------------------------|                           |
      |                         |                           |
      |(S22)(MSRP) NICKNAME     |                           |
      |------------------------>|(S24)(XMPP) Presence       |
      |                         |-------------------------->|
      |                         |(S25)(XMPP) Presence Error |
      |                         |<--------------------------|
      |(S26)(MSRP) 425 Error    |                           |
      |<------------------------|                           |
      |                         |                           |
      |(S27)(SIP) REFER         |                           |
      |------------------------>|                           |
      |                         |                           |
      |(S28)(SIP) 200 OK        |                           |
      |<------------------------|                           |
      |                         |                           |
      |(S29)(SIP) NOTIFY        |                           |
      |<------------------------|                           |
      |                         |                           |
      |                         |(S30)(XMPP) Message stanza |
      |                         | to invite participant     |
      |                         |-------------------------->|
      .                         .                           .
      .                         .                           .
      |                         |                           |
      |(S31)(SIP) BYE           |                           |
      |------------------------>|                           |
      |                         |(S32)(XMPP) Exiting a room |
      |                         |-------------------------->|
      |(S33)(SIP) 200 OK        |                           |
      |<------------------------|                           |

   If the XMPP presence stanza is received before the SIP SUBSCRIBE
   dialog is established for the "conference" event, then the server
   SHOULD cache the participant list until the subscription is
   established and delivered in a SIP NOTIFY request.

4.1.  Enter Room (Includes Set Nickname)

   When the SIP user ("Romeo") wants to join a groupchat room
   ("Verona"), he first has to start the SIP session by sending out a
   SIP INVITE request containing an offered session description that
   includes an MSRP media line accompanied by a mandatory "path" and
   "chatroom" attributes.  The MSRP media line is also accompanied by an
   "accept-types" attribute specifing support for a Message/CPIM top
   level wrapper for the MSRP message.




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   Example 27: SIP user starts session (S1)

   |  INVITE sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>
   |  Contact: <sip:romeo@example.com>;gr=orchard
   |  Call-ID: 742510no
   |  Content-Type: application/sdp
   |  Content-Length: 163
   |
   |  c=IN IP4 s2x.example.net
   |  m=message 7313 TCP/MSRP *
   |  a=accept-types:message/cpim text/plain text/html
   |  a=accept-wrapped-types:text/plain text/html
   |  a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  a=chatroom

   Upon receiving the INVITE, the SIP-to-XMPP gateway needs to determine
   the identity of the remote domain, which it does by following the
   procedures discussed in [I-D.ietf-stox-core].  Here we assume that
   the gateway server has determined that the remote domain is serviced
   by an XMPP server, that it contains or has available to it a SIP-to-
   XMPP gateway or connection manager (which enables it to speak
   natively to XMPP servers), and that it hands off the message to the
   gateway.  If this succeeds, the gateway SHOULD answer successfuly
   with a SIP 200 OK (S2, not shown).

   Implementations MAY wait until the nickname is set with an MSRP
   NICKNAME chunk before joining the XMPP MUC or MAY choose a temporary
   nickname (such as the SIP From header display name) and use it to
   join the room.

   Example 28: SIP user acks session (S3)

   |  SIP/2.0 200 OK
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>
   |  Contact: <sip:x2s.example.com;transport=tcp>;isfocus
   |  Call-ID: 742510no
   |  Content-Type: application/sdp
   |
   |  c=IN IP4 x2s.example.com
   |  m=message 8763 TCP/MSRP *
   |  a=accept-types:message/cpim text/plain text/html
   |  a=accept-wrapped-types:text/plain text/html
   |  a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  a=chatroom:nickname private-messages




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   The SIP user then requests a nickname.

   Example 29: MSRP user sets up nickname (S4)

   |  MSRP a786hjs2 NICKNAME
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  Use-Nickname: "Romeo"
   |  -------a786hjs2

   Upon receiving the MSRP NICKNAME request, the SIP-to-XMPP gateway is
   responsible for generating an XMPP presence stanza and sending it to
   the chatroom.

   Example 30: Romeo enters XMPP chatroom (S5)

   |  <presence from='romeo@example.com'
   |            to='verona@chat.example.org/Romeo'>
   |    <x xmlns='http='http://jabber.org/protocol/muc'/>
   |  </presence>

   If the room does not already contain another user with the requested
   nickname, the service accepts the access request.  Thus if the
   gateway does not receive any stanza of type "error" specifying a
   <conflict/> error condition within a reasonable amount of time (e.g.,
   5 seconds), it MUST answer the MSRP nickname proposal with a 200 OK
   response (S6).

   Example 31: Acknowledgement of join (S6)

   |  MSRP a786hjs2 200 OK
   |  To-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  From-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  -------a786hjs2

   Once the nickname has been set the user subscribes to the conference
   event.














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   Example 32: User subscribes to the conference event (S8)

   |  SUBSCRIBE sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>
   |  Contact: <sip:romeo@example.com>;gr=orchard
   |  Call-ID: hsuKZGkjQewg6IJI8.PD5rRAvbuTYLR-
   |  Event: conference
   |  Expires: 600
   |  Accept: application/conference-info+xml
   |  Allow-Events: conference
   |  Content-Length: 0

   The gateway will accept or reject the request based on local policy.

   Example 33: Gateway accepts subscription (S9)

   |  SIP/2.0 200 OK
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>
   |  Call-ID: hsuKZGkjQewg6IJI8.PD5rRAvbuTYLR-
   |  Contact: <sip:verona@chat.example.org;transport=tcp>;isfocus
   |  Allow: SUBSCRIBE, NOTIFY, PRACK, INVITE, ACK, BYE,
   |         CANCEL, UPDATE, MESSAGE, REFER
   |  Expires: 600
   |  Content-Length: 0

4.2.  Presence Broadcast

   If the multi-user chat service is able to add the SIP user to the
   room, it sends presence from all the existing occupants' room JIDs to
   the new occupant's full JID, including extended presence information
   about roles in an <x/> element.


















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   Example 34: XMPP service sends presence from existing occupants to
   new occupant (S7)

   |  <presence from='verona@chat.example.org/Romeo'
   |            to='romeo@example.com'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |      <status='110'/>
   |    </x>
   |  </presence>

   |  <presence from='verona@chat.example.org/Ben'
   |            to='romeo@example.com'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |    </x>
   |  </presence>

   |  <presence from='verona@chat.example.org/JuliC'
   |            to='romeo@example.com'>
   |    <x xmlns='http://jabber.org/protocol/muc#user'>
   |      <item affiliation='none' role='participant'/>
   |    </x>
   |  </presence>

   Upon receiving these presence stanzas, if the MSRP conference server
   has already completed the subscription to the Conference Event
   package [RFC4575], the XMPP-to-SIP gateway MUST translate them into a
   SIP NOTIFY request containing the participant list (represented in
   the conference-info format specified in [RFC4575]).





















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   Example 35: MSRP mapping of XMPP participant presence (S10)

   |  NOTIFY sip:romeo@example.com SIP/2.0
   |  To: <sip:romeo@example.com>;tag=43524545
   |  From: <sip:verona@chat.example.org>;tag=a3343df32
   |  Call-ID: k3l43id034ksererff
   |  Event: conference
   |  Subscription-State: active;expires=3600
   |  Content-Type: application/conference-info+xml
   |  Content-Length: ...
   |
   |  <conference-info version="0" state="full"
   |      entity="sip:verona@chat.example.org">
   |    <conference-description>
   |      <subject>Today in Verona</subject>
   |      <conf-uris>
   |        <entry>
   |          <uri>tel:+18882934234</uri>
   |          <uri>sip:verona@chat.example.org</uri>
   |        </entry>
   |      </conf-uris>
   |   </conference-description>
   |   <users>
   |     <user entity="sip:verona@chat.example.org;gr=JuliC"
   |           state="full">
   |       <display-text>JuliC</display-text>
   |       <roles>
   |         <entry>participant</entry>
   |       </roles>
   |     </user>
   |     <user entity="sip:verona@chat.example.org;gr=Ben"
   |           state="full">
   |       <display-text>Ben</display-text>
   |       <roles>
   |         <entry>participant</entry>
   |       </roles>
   |   </users>
   |  </conference-info>

   Because the "room roster" is communicated in XMPP by means of
   multiple presence stanzas (one for each participant) whereas the
   participant list is communicated in SIP by means of a single
   conference-info document, the SIP-to-XMPP gateway will need to keep
   track of the user's SIP URI and the mapping of that URI into an XMPP
   address; then, based on that mapping, it will need to determine when
   it has received a complete room roster from the MUC room, i.e., when
   it has received the in-room presence of the SIP user (which according
   to XEP-0045 is the last presence stanza received in the initial batch



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   sent after joining).  Once that happens, the SIP-to-XMPP gateway can
   construct the conference-info document containing the complete
   participant list and send that to the SIP user.

4.3.  Exchange Messages

   Once the user has joined the chat room, the user can exchange an
   unbounded number of messages, both public and private.

   The mapping of MSRP syntax elements to XMPP syntax elements SHOULD be
   as shown in the following table.  (Mappings for elements not
   mentioned are undefined.)

   Table 5: Message syntax mapping from MSRP Message to XMPP

       +-----------------------------+-----------------------------+
       |  CPIM Header                |XMPP Element or Attribute    |
       +-----------------------------+-----------------------------+
       |  To                         |  to                         |
       |  From                       |  from                       |
       |  body of the SEND request   |  <body/>                    |
       +-----------------------------+-----------------------------+

4.3.1.  Send a Message to All Occupants

   When Romeo wants to send a message to all other occupants in the
   room, he sends an MSRP SEND request to <room@service> itself (i.e.,
   <verona@chat.example.org> in our example).

   The following examples show an exchange of a public message.

   Example 36: Romeo sends a message to the chat room (S13)

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  Message-ID: 87652492
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>;gr=orchard
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  Romeo is here!
   |  -------a786hjs2$




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   Upon receiving the SEND request, if the request either contains a
   Failure-Report header field value of "yes" or does not contain a
   Failure-Report header at all, the SIP-to-XMPP gateway MUST
   immediately translate it into an XMPP message stanza (S14) and then
   generate and send an MSRP response (S15).

   Example 37: XMPP mapping of message (S14)

   |  <message from='romeo@example.com/orchard'
   |           to='verona@chat.example.org'
   |           type='groupchat'
   |           id='8gbx1g4p'>
   |    <body>Romeo is here!</body>
   |  </message>

   Example 38: MSRP response to public message (S15)

   |  MSRP d93kswow 200 OK
   |  To-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  From-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  -------d93kswow$

   Note well that the XMPP MUC room will reflect the sender's message
   back to all users, including the sender.  In MSRP this reflected
   message is unnecessary.  Therefore gateways are advised to maintain a
   cache and if the same stanza is received within a reasonable amount
   of time, assume is the reflected message and ignore it.

4.3.2.  Send a Private Message

   Romeo can send a "private message" to a selected occupant via the
   chat room service by sending a message to the occupant's room
   nickname.

   The following examples show an exchange of a private message.
















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   Example 39: Romeo sends a private message (S19)

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  Message-ID: 87652492
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:verona@chat.example.org>;gr=JuliC
   |  From: "Romeo" <sip:romeo@example.com>;gr=orchard
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  I am here!!!
   |  -------a786hjs2$

   The MSRP conference is responsible for transforming the "From"
   address into an in-room address.

   Example 40: MSRP handling of private message

   |  MSRP a786hjs2 SEND
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  Message-ID: 87652492
   |  Byte-Range: 1-*/*
   |  Content-Type: message/cpim
   |
   |  To: <sip:verona@chat.example.org>;gr=JuliC
   |  From: <sip:verona@chat.example.org>;gr=Romeo
   |  DateTime: 2008-10-15T15:02:31-03:00
   |  Content-Type: text/plain
   |
   |  I am here!!!
   |  -------a786hjs2$

   Once the MSRP conference sends that message to the gateway, the
   gateway is responsible for translating it into XMPP syntax.

   Example 41: XMPP mapping of private message (S20)

   |  <message from='verona@chat.example.org/Romeo'
   |           to='verona@chat.example.org/JuliC'
   |           type='chat'
   |           id='rg2ca9k7'/>
   |    <body>I am here!!!</body>
   |  </message>



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4.4.  Change Nickname

   If Romeo decides to change his nickname within the room, he MUST send
   a new MSRP NICKNAME request.  In fact modification of the nickname in
   MSRP is not different from the initial reservation and usage of a
   nickname.

   Example 42: MSRP user changes nickname (S22)

   |  MSRP a786hjs2 NICKNAME
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
   |  Use-Nickname: "montecchi"
   |  -------a786hjs2

   Upon receiving such a message, the SIP-to-XMPP gateway MUST translate
   it into an XMPP presence stanza.

   Example 43: XMPP mapping of nickname change (S24)

   |  <presence from='romeo@example.com'
   |            to='verona@chat.example.org/montecchi'/>

   The XMPP server will analyze the nickname allocation and determine if
   the requested nickname is available.  In case the nickname is not
   available or not usable, the server will generate a presence stanza
   of type "error" specifying a <conflict/> error condition.

   Example 44: XMPP conflict error for nickname (S25)

   |  <presence from='verona@chat.example.org/Romeo'
   |            to='romeo@example.com/orchard'
   |            type='error'>
   |    <x xmlns='http='http://jabber.org/protocol/muc'/>
   |    <error type='cancel' by='verona@chat.example.org'>
   |      <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
   |    </error>
   |  </presence>

   Upon receiving this stanza, the XMPP-SIP gateway will reply to the
   NICKNAME request with code 425

   Example 45: Gateway translates XMPP nickname conflict to MSRP error
   code (S26)

   |  MSRP a786hjs2 425 Nickname usage failed
   |  To-Path: msrp://s2x.example.net:7313/ansp71weztas;tcp
   |  From-Path: msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp



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   |  -------a786hjs2

4.5.  Invite Another User to a Room

   If a SIP user wants to invite another user to join the conference he
   will send a REFER request indicating who needs to be invited in the
   Refer-To header, as per Section 5.5 of [RFC4579].

   Example 46: Inviting a XMPP participant (S27)

   |  REFER sip:verona@chat.example.org SIP/2.0
   |  To: <sip:verona@chat.example.org>
   |  From: "Romeo" <sip:romeo@example.com>;tag=5534562
   |  Call-ID: 849392fklgl43
   |  Contact: <sip:romeo@example.com>;gr=orchard
   |  Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
   |  Accept: message/sipfrag
   |  Refer-To: <sip:benvolio@example.com>
   |  Supported: replaces
   |  Content-Length: 0

   The XMPP-SIP gateway then acknowledges the SIP REFER request with a
   200 OK response (step S28, not shown).

   The gateway will then send a NOTIFY requests as per [RFC3515]
   indicating that the invitation is is progress.  Since there is no way
   know the progress of the invitation until the user has joined,
   implementations are advised to terminate the REFER dialog
   subscription with the first NOTIFY, with a status code of 100 Trying.

   Example 47: Progress notification for invitation (S29)

   |  NOTIFY sip:romeo@example.com SIP/2.0
   |  To: <sip:romeo@example.com>;tag=5534562
   |  From: <sip:verona@chat.example.org>;tag=18747389
   |  Call-ID: 849392fklgl43
   |  Event: refer
   |  Subscription-State: terminated;reason=noresource
   |  Contact: <sip:verona@chat.example.com;transport=tcp>;isfocus
   |  Content-Type: message/sipfrag;version=2.0
   |  Content-Length: 20
   |
   |  SIP/2.0 100 Trying








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4.6.  Exit Room

   If Romeo decides to exit the chat room, his client sends a SIP BYE to
   the <verona@chat.example.org> chat room.

   Example 48: Romeo terminates session (S27)

   |  BYE sip:verona@chat.example.org SIP/2.0
   |  Max-Forwards: 70
   |  From: "Romeo" <sip:romeo@example.net>;tag=786
   |  To: <sip:verona@chat.example.org>;tag=534
   |  Call-ID: 742510no
   |  Cseq: 1 BYE
   |  Content-Length: 0

   Upon receiving the SIP BYE, the SIP-to-XMPP gateway translates it
   into a presence stanza (F19) and sends it to the XMPP MUC room
   service.  Then the SIP-to-XMPP gateway responds with a 200 OK to the
   MSRP user.

   Example 49: Romeo exits chatroom (S28)

   |  <presence from='romeo@example.com'
   |            to='verona@chat.example.org/Romeo'
   |            type='unavailable'/>


5.  Handling of Nicknames and Display Names

   Fundamental rules for mapping addresses between XMPP and SIP are
   provided in [I-D.ietf-stox-core].  However, chatrooms include a more
   specialized, unique identifier for each participant in a room, called
   a nickname.  Implementations are strongly encouraged to apply the
   rules for preparation and comparison of nicknames specified in
   [I-D.ietf-precis-nickname].

   In addition to nicknames, some groupchat implementations also include
   display names (which might or might not be different from users'
   nicknames).  A display name need not be unique within the context of
   a room but instead simply provides a user-friendly name for a
   participant.

   In SIP, the nickname is the value of the XCON 'nickname' attribute of
   the <user/> element [RFC6501] and the display name is the XML
   character data of the conference-info <display-text/> element
   [RFC4575].  In XMPP, the nickname is the value of the resourcepart of
   the occupant JID [XEP-0045] and the display name is the XML character
   data of the <nick/> element [XEP-0172].



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   In practice, the <display-text/> element is treated as canonical in
   SIP implementations, and the <nick/> element is rarely used in XMPP
   implementations.  Therefore, for display purposes SIP implementations
   ought to use the <display-text/> element (not the XCON 'nickname'
   attribute) and XMPP implementations ought to use the resourcepart of
   the occupant JID (not the character data of the <nick/> element).

   If there is a conflict between the SIP nickname and the XMPP
   nickname, the SIP-to-XMPP or XMPP-to-SIP gateway is responsible for
   adjusting the nickname to avoid the conflict and for informing the
   SIP or XMPP client of the unique nickname used to join the chatroom.


6.  IANA Considerations

   This document requests no actions of the IANA.


7.  Security Considerations

   The security considerations of [RFC3261], [RFC4975], [RFC6120],
   [I-D.ietf-stox-core], [I-D.ietf-simple-chat], and [XEP-0045] apply.


8.  References

8.1.  Normative References

   [I-D.ietf-precis-nickname]
              Saint-Andre, P., "Preparation and Comparison of
              Nicknames", draft-ietf-precis-nickname-06 (work in
              progress), July 2013.

   [I-D.ietf-simple-chat]
              Niemi, A., Garcia-Martin, M., and G. Sandbakken, "Multi-
              party Instant Message (IM) Sessions Using the Message
              Session Relay  Protocol (MSRP)", draft-ietf-simple-chat-18
              (work in progress), January 2013.

   [I-D.ietf-stox-core]
              Saint-Andre, P., Houri, A., and J. Hildebrand,
              "Interworking between the Session Initiation Protocol
              (SIP) and the Extensible Messaging and Presence Protocol
              (XMPP): Core", draft-ietf-stox-core-05 (work in progress),
              September 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC4579]  Johnston, A. and O. Levin, "Session Initiation Protocol
              (SIP) Call Control - Conferencing for User Agents",
              RFC 4579, August 2006.

   [RFC4975]  Campbell, B., Mahy, R., and C. Jennings, "The Message
              Session Relay Protocol (MSRP)", RFC 4975, September 2007.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 6121, March 2011.

   [XEP-0045]
              Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
              July 2008.

8.2.  Informative References

   [RFC3515]  Sparks, R., "The Session Initiation Protocol (SIP) Refer
              Method", RFC 3515, April 2003.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4575]  Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
              Initiation Protocol (SIP) Event Package for Conference
              State", RFC 4575, August 2006.

   [RFC6501]  Novo, O., Camarillo, G., Morgan, D., and J. Urpalainen,
              "Conference Information Data Model for Centralized
              Conferencing (XCON)", RFC 6501, March 2012.

   [XEP-0172]
              Saint-Andre, P. and V. Mercier, "User Nickname", XSF
              XEP 0172, March 2012.

   [XEP-0249]
              Saint-Andre, P., "Direct MUC Invitations", XSF XEP 0249,
              September 2011.





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Appendix A.  Acknowledgements

   Special thanks to Fabio Forno for his co-authorship of an early
   version of this document.

   Thanks also to Philipp Hancke for his detailed feedback.

   Some text in this document was borrowed from [I-D.ietf-stox-core] and
   from [XEP-0045].


Authors' Addresses

   Peter Saint-Andre
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3282
   Email: psaintan@cisco.com


   Saul Ibarra Corretge
   AG Projects
   Dr. Leijdsstraat 92
   Haarlem  2021RK
   The Netherlands

   Email: saul@ag-projects.com


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Salvatore.Loreto@ericsson.com












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