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In: MissingRef
Network Working Group                                           A. Niemi
Internet-Draft                                                     Nokia
Intended status: Standards Track                        M. Garcia-Martin
Expires: August 7, 2008                           Nokia Siemens Networks
                                                           G. Sandbakken
                                                                TANDBERG
                                                        February 4, 2008


  Multi-party Instant Message (IM) Sessions Using the Message Session
                         Relay Protocol (MSRP)
                       draft-ietf-simple-chat-02

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 7, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   The Message Session Relay Protocol (MSRP) defines a mechanism for
   sending instant messages within a peer-to-peer session, negotiated
   using the Session Initiation Protocol (SIP) and the Session
   Description Protocol (SDP).  This document defines the necessary



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   tools for establishing multi-party instant messaging (IM) sessions,
   or chat rooms, with MSRP.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Motivations and Requirements . . . . . . . . . . . . . . . . .  5
   4.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  6
   5.  Creating, Joining, and Deleting a Chat Room  . . . . . . . . .  8
     5.1.  Creating a Chat Room . . . . . . . . . . . . . . . . . . .  8
     5.2.  Joining a Chat Room  . . . . . . . . . . . . . . . . . . .  8
     5.3.  Deleting a Chat Room . . . . . . . . . . . . . . . . . . .  9
   6.  Sending and Receiving Instant Messages . . . . . . . . . . . .  9
     6.1.  Regular Messages . . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Private Messages . . . . . . . . . . . . . . . . . . . . . 11
   7.  Nicknames  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Using Nicknames within a Conference  . . . . . . . . . . . 13
     7.2.  Modifying a Nickname . . . . . . . . . . . . . . . . . . . 14
     7.3.  Nicknames in the Conference Event Package  . . . . . . . . 14
     7.4.  Nicknames not supported nor allowed  . . . . . . . . . . . 15
   8.  The SDP 'chatroom' attribute . . . . . . . . . . . . . . . . . 15
   9.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Joining a chat room  . . . . . . . . . . . . . . . . . . . 16
     9.2.  Setting up a nickname  . . . . . . . . . . . . . . . . . . 18
     9.3.  Sending a regular message to the chat room . . . . . . . . 20
     9.4.  Sending a private message to a participant . . . . . . . . 21
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23
   13. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 24
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 24
     14.2. Informative References . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 27














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1.  Introduction

   The Message Session Relay Protocol (MSRP) [RFC4975] defines a
   mechanism for sending a series of instant messages within a session.
   The Session Initiation Protocol (SIP) [RFC3261] in combination with
   the Session Description Protocol (SDP) [RFC3264] allows for two peers
   to establish and manage such sessions.

   In another application of SIP, a user agent can join in a multi-party
   conversation called a conference that is hosted by a specialized user
   agent called a focus [RFC4353].  Such a conference can naturally
   involve an MSRP session as one of possibly many media components.  It
   is the responsibility of an entity handling the media to relay
   instant messages received from one participant to the rest of the
   participants in the conference.

   Several such systems already exist in the Internet.  Participants in
   a chat room can be identified with a pseudonym or nickname, and
   decide whether their real identity is disclosed to other
   participants.  Participants can also use a rich set of features such
   as the ability to send private instant messages to other
   participants.  They also allow combining instant messaging with other
   media components, such as voice, video, white boarding, screen
   sharing, and file transfer.

   Similar conferences are already available today with other
   technologies different than MSRP.  For example, Internet Relay Chat
   (IRC) [RFC2810], Extensible Messaging and Presence Protocol [RFC3920]
   based chat rooms, and many other proprietary systems provide this
   kind of functionality.  It makes sense to specify equivalent
   functionality for MSRP-based systems to both provide competitive
   features as well as enable interworking between the systems.

   This document defines requirements, conventions, and extensions for
   providing private messages and nickname management in centralized
   conferences with MSRP.  This document, however, does not specify
   functionality that can be used in conference with media different
   than MSRP.  This memo uses the SIP Conferencing Framework [RFC4353]
   as a design basis.  It also aims to be compatible with the
   Centralized Conferencing Framework [I-D.ietf-xcon-framework].  It is
   expected that future mechanisms will be developed for providing
   similar functionality in generic conferences, i.e., where the media
   is not only restricted to MSRP.  The mechanisms described in this
   document provide a future compatible short-term solution for MSRP
   centralized conferences.






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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119, BCP 14
   [RFC2119], and indicate requirement levels for compliant
   implementations.

   This memo deals with a particular case of tightly coupled SIP
   conferences where the media exchanged consist of session-based
   instant messaging.  Unless otherwise noted, we use the terminology
   defined in the SIP Conferencing Framework [RFC4353] applied to the
   scope of this document.  In addition to that terminology, we
   introduce some new terms:

   Nickname:   a pseudonym or descriptive name associated to a
      participant.  See Section 7 for details

   Session-based Instant Messaging Conference:   an instance of a
      tightly coupled conference, in which the media exchanged between
      the participants consist of (among others) MSRP based instant
      messages.  Also known as a chat room.

   Chat Room:   a synonym for session-based instant messaging
      conference.

   Chat Room URI:   a URI that identifies a particular chat room.  Since
      a chat room is a specialized conference of instant messages, in
      the context of this document, a chat room URI is a synonym of a
      conference URI.

   Sender:   the conference participant that originally created an
      instant message and sent it to the chat room for delivery.

   Recipient:   the destination conference participant(s).  This
      defaults to the full conference participant list, minus the IM
      Sender.

   MSRP switch:   a media level entity that receives MSRP messages and
      delivers them to the other conference participants.  An MSRP
      switch has a similar role to a conference mixer with the exception
      that an MSRP switch does not actually "mix" together different
      input media streams; it merely relays the messages between
      participants.







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   Private Instant Message:   an instant message sent in a chat room
      whose intended to a single participant.  A private IM is usually
      rendered distinctly from the rest of the IMs, as to indicate that
      the message was a private communication.

   Replacement URI:  an anonymous URI that is routable and unique inside
      the scope of the focus.  It is used by the MSRP switch to send and
      receive anonymous messages replacing the participant's SIP AOR.


3.  Motivations and Requirements

   Although conference frameworks describing many types of conferencing
   applications already exist, such as the Framework and Data Model for
   Centralized Conferencing [I-D.ietf-xcon-framework] and the SIP
   Conferencing Framework [RFC4353], the exact details of session-based
   instant messaging conferences are not well-defined at the moment.

   To allow interoperable chat implementations, for both conference-
   aware, and conference-unaware user agents, certain conventions for
   MSRP conferences need to be defined.  It also seems beneficial to
   provide a set of features that enhance the baseline multiparty MSRP
   in order to be able to create systems that have functionality on par
   with existing chat systems, as well as enable building interworking
   gateways to these existing chat systems.

   We define the following requirements:

   REQ-1:   A basic requirement is the existence of a multiparty
            conference, where participants can join and leave the
            conference and get instant messages exchanged to the rest of
            the participants.

   REQ-2:   The conference must have the ability to host other media in
            addition to MSRP, as well as multiple streams of MSRP.

   REQ-3:   A conference participant must be able to determine the
            identities of the sender and recipient of the received IMs.

   REQ-4:   A conference participant must be able to determine the
            recipient of the received message.  For instance, the
            recipient of the message might be the entire conference or a
            single participant of the conference (i.e., a private
            message).







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   REQ-5:   It must be possible to send a message to a single
            participant within the conference (i.e., a private instant
            message).

   REQ-6:   A conference participant may have a nickname or pseudonym
            associated with their real identity.

   REQ-7:   It must be possible for a participant to change their
            nickname during the progress of the conference.

   REQ-8:   It must be possible that a participant is only known by
            their nickname and not their real identity to the rest of
            the conference.

   REQ-9:   It must be possible for the MSRP switch itself to send IMs
            to the conference (e.g. message of the day, welcome
            messages, server is shutting down, etc.)

   REQ-10:  It must be possible for participants to learn the
            capabilities support of the features described in this
            document (and perhaps others).


4.  Overview of Operation

   In order to set up a conference, one must first be created.  Users
   wishing to host a conference themselves can of course do just that;
   their user agents simply morph from an ordinary user agent into a
   special purpose one called a conference focus.  Another, commonly
   used setup is one where a dedicated node in the network functions as
   a conference focus.

   Each chat room has an identity of its own: a SIP URI that
   participants use to join the conference, e.g. by sending an INVITE
   request.  The conference focus processes the invitations, and as
   such, maintains SIP dialogs with each participant.  In an instant
   messaging conference, or chat room, MSRP is one of the established
   media streams.  Each conference participant establishes an MSRP
   session with an MSRP switch, which is a special purpose MSRP
   application.  The MSRP switch is similar to a conference mixer in
   that it handles media sessions with each of the participants and
   bridges these streams together.  However, unlike a conference mixer,
   the MSRP switch merely relays messages between participants but
   doesn't actually mix the streams in any way.  The system is
   illustrated in Figure 1.






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                               +------+
                               | MSRP |
                               |Client|
             +------+          +--.---+          +------+
             | MSRP |             |              | MSRP |
             |Client|             |             _|Client|
             +------._            |           ,' +------+
                      `._         |         ,'
                         `.. +----------+ ,'
                            `|          |'
                             |   MSRP   |
                             |  Switch  |
                            ,|          |_
                       _,-'' +----------+ ``-._
             +------.-'            |           `--+------+
             | MSRP |              |              | MSRP |
             |Client|              |              |Client|
             +------+              |              +------+
                               +---'--+
                               | MSRP |
                               |Client|
                               +------+

           Figure 1: Multiparty MSRP in a Centralized Conference

   Typically conference participants also subscribe to the conference
   event package [RFC4575] to gather information about the conference
   roster in the form of conference state notifications.  For example,
   participants can learn about other participants' identities.

   All messages in the chat room use the 'Message/CPIM' wrapper content
   type [RFC3862], so that it is possible to distinguish between private
   and regular messages.  When a participant wants to send an instant
   message to the conference, it constructs an MSRP SEND request and
   submits it to the MSRP switch including a regular payload (e.g. a
   Message/CPIM message that contains a text, html, an image, etc.).
   The Message/CPIM To header is set to the chat room URI.  The switch
   then fans out the SEND request to all of the other participants using
   their existing MSRP sessions.

   A participant can also send a private instant message addressed to a
   participants whose identity has been learned, e.g. via a notification
   from the conference event package [RFC4575].  In this case the sender
   creates an MSRP SEND request with a Message/CPIM body whose To header
   contains not the chat room URI but the recipient's URI.  The MSRP
   switch then forwards the SEND request to the recipient.

   We extend the current MSRP negotiation that takes place in SDP



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   [RFC4566] to allow participants to learn whether the chat room
   supports and is willing to accept (e.g. due to local policy
   restrictions) certain MSRP functions defined in this memo, such as
   nicknames or private messaging.

   Naturally, when a participant wishes to leave a chat room, it sends a
   SIP BYE request to the conference focus and disconnects.


5.  Creating, Joining, and Deleting a Chat Room

5.1.  Creating a Chat Room

   Since we consider a chat room a particular type of conference where
   one of the offered media happens to be MSRP, the methods defined by
   the SIP Conference Framework [RFC4353] for creating conferences are
   directly applicable to a chat room.

   Once a chat room is created, it is identified by a SIP URI, like any
   other conference.

5.2.  Joining a Chat Room

   Participants usually join the conference by sending an INVITE request
   to the conference URI.  As long as the conference policy allows, the
   INVITE request is accepted by the focus and the user is brought into
   the conference.  Participants are aware that the peer is a focus due
   to the presence of the "isfocus" feature tag [RFC3840] in the Contact
   header field of the 200-class response to the INVITE request.
   Participants are also aware that the mixer is an MSRP switch due to
   the presence of an additional 'message' media type and either TCP/
   MSRP or TCP/TLS/MSRP as the protocol field in the SDP [RFC4566]
   media-line.

   If the participant wants to remain anonymous to the rest of the
   participants, the participant can issue privacy by using the Privacy
   header [RFC3323] when sending the INVITE request to the conference
   URI.  If a Privacy header with a priv-value different form 'none' is
   present and the focus allows anonymous participants, the focus MUST
   provide the participant with a replacement URI.  The creation of the
   replacement URI SHOULD follow the recommendations of RFC 4575 section 
   5.6 [RFC4575], and distributed as described in the event notification
   package.  The MSRP switch MUST keep a mapping between the URI of
   which the participant is known to the focus and the provided
   replacement URI.  This allows the MSRP switch to route messages to
   and from anonymous participants.

   The conference focus of a chat room MUST include support for a



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   Message/CPIM [RFC3862] top-level wrapper for the MSRP messages by
   setting the 'accept-types' MSRP media line attribute in the SDP offer
   or answer to include 'Message/CPIM'.

      Note that the 'Message/CPIM' wrapper is used to carry the sender
      information that, otherwise, it will not be available to the
      recipient.  Additionally, 'Message/CPIM' wrapper carries the
      recipient information (e.g.  To and Cc: headers).

   The conference focus of a chat room MUST learn the chat room
   capabilities of each participant that joins the chat room, and MUST
   inform the MSRP switch of such support.  This is to prevent that the
   MSRP switch distributes private messages to participants who do not
   support private messaging.

5.3.  Deleting a Chat Room

   As with creating a conference, the methods defined by the SIP
   Conference Framework [RFC4353] for deleting a conference are directly
   applicable to a chat room.

   Deleting a chat room is an action that heavily depends on the policy
   of the chat room.  The policy can determine that the chat room is
   deleted when the creator leaves the conference, or with any out of
   band mechanism.


6.  Sending and Receiving Instant Messages

6.1.  Regular Messages

   This section describes the conventions used to send and receive
   instant messages that are addressed to all the participants in the
   chat room.  These are sent over a regular MSRP SEND request that
   contains a Message/CPIM wrapper [RFC3862] that in turn contains the
   desired payload (e.g. text, image, video-clip, etc.).

   When a chat room participant wishes to send an instant message to all
   the other participants in the chat room, he constructs an MSRP SEND
   request that MUST contain a top-level wrapper of type 'Message/CPIM'
   [RFC3862].  The actual instant message payload inside 'Message/CPIM'
   MAY be of any type negotiated in the SDP 'accepted-types' attribute
   according to the MSRP rules.

   The sender SHOULD populate the From header of the Message/CPIM
   wrapper with a proper identity by which the user is recognized in the
   conference.  Identities that can be used (among others) are:




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   o  A SIP URI [RFC3261] representing the participant's address-of-
      record

   o  A tel URI [RFC3966] representing the participant's telephone
      number

   o  An IM URI [RFC3860] representing the participant's instant
      messaging address

   An MSRP switch that receives a SEND request from a participant SHOULD
   first verify that the From header field of the Message/CPIM wrapper
   is correctly populated with a valid URI as indicated earlier.  If the
   URI included in the From header field of the Message/CPIM wrapper is
   not valid (e.g, because it does not "belong" to the user), then the
   MSRP switch MUST generate a 403 response and MUST NOT forward the
   SEND request to any of the participants.  Otherwise, the MSRP switch
   SHOULD generate a 200 response according to the MSRP rules for
   response generation.  If the participant has requested privacy when
   joining (Section 5.2) , the MSRP switch MUST replace the From header
   field of the Message/CPIM wrapper with the replacement URI provided
   to the sender

   Then the MSRP switch should inspect the To header field of the
   Message/CPIM wrapper.  If the To header field of the Message/CPIM
   wrapper contains the chat room URI, the MSRP switch can generate a
   copy of the SEND request to each of the participants in the
   conference except the sender.  The MSRP switch MUST NOT modify any of
   the bodies included in the received SEND request.  Note that the MSRP
   switch does not need to wait for the reception of the complete MSRP
   chunk or MSRP message before it starts the distribution to the rest
   of the participants.  Instead, once the MSRP switch has received the
   headers of the Message/CPIM body it SHOULD start the distribution
   process.

   An MSRP endpoint that receives a SEND request from an MSRP switch
   containing a Message/CPIM wrapper SHOULD first inspect the To header
   field of the Message/CPIM body.  If the To header field is set to the
   chat room URI, then it is a regular message that has been distributed
   to all the participants in the conference.  Then the MSRP endpoint
   SHOULD inspect the From header field of the Message/CPIM body to
   identify the sender.  The From header field will include a URI that
   identifies the sender.  The endpoint might have also received further
   identity information through a subscription to the SIP conference
   event package [RFC4575].







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6.2.  Private Messages

   This section describes the conventions used to send and receive
   private instant messages, i.e., instant messages that are addressed
   to one participant of the chat room rather to all of them.  A chat
   room can signal support for private messages using the chatroom-
   attribute (see Section 8 for details).

   When a chat room participant wishes to send a private instant message
   to a participant the chat room, he constructs an MSRP SEND request
   that MUST contain a top-level wrapper of type 'Message/CPIM'
   [RFC3862].  The actual instant message payload inside 'Message/CPIM'
   MAY be of any type negotiated in the SDP 'accepted-types' attribute
   according to the MSRP rules (e.g. text, image, video-clip etc.)

   The sender SHOULD populate the From header of the Message/CPIM
   wrapper with a proper identity by which the user is recognized in the
   conference as indicated for regular instant messages.  Then the
   sender MUST populate the To header field with the identity of
   intended recipient.  The identity can be SIP, TEL, and IM URIs
   typically learned from the information received in notifications of
   the conference event package [RFC4575].

   As for regular messages, an MSRP switch that receives a SEND request
   from a participant SHOULD first verify that the From header field of
   the Message/CPIM wrapper is correctly populated with a valid URI.  If
   the URI included in the From header field of the Message/CPIM wrapper
   is not valid (e.g, because it does not "belong" to the user), then
   the MSRP switch MUST generate a 403 response and MUST NOT forward the
   SEND request to any of the participants.  Otherwise, the MSRP switch
   SHOULD generate a 200 response according to the MSRP rules for
   response generation.

   Then the MSRP switch MUST inspect the To header field of the Message/
   CPIM wrapper.  If the To header field of the Message/CPIM wrapper
   does not contain the chat room URI, it must check if it contains a
   participant or replacement URI.  If the URI in the To header can not
   be resolved (e.g. cased by a mistyped URI or that the recipient has
   abandoned the chat room), and the Failure-Report header field of the
   SEND request was either not present in the original request, or had a
   value of "yes", the MSRP switch MUST generate a REPORT request to the
   sender.  The status header field MUST be set to 427.  The new 427
   status code indicates a failure to resolve the recipient URI in the
   To header field.  If the recipient is valid, but the recipient does
   not support private messages, and the Failure-Report header field of
   the SEND request was either not present in the original request, or
   had a value of "yes", the MSRP switch MUST send a REPORT request
   having the status code of 428.  The new response 428 indicate that



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   the recipient does not support private messages.  In either case the
   REPORT request MUST include a Message/CPIM wrapper, with the original
   From header field included in the SEND request, and the To header
   field of the original message.  The message MUST not be forwarded to
   the recipient if above conditions applies.

   The MSRP switch should search it's mapping table to find the MSRP
   session established towards the recipient.  If a match is found the
   MSRP switch MUST create a SEND request and MUST copy the contents of
   the sender's message to it.  If the sender has requested privacy when
   joining (Section 5.2) the conference, the MSRP switch MUST put the
   replacement URI in the From header.  If no privacy is requested, the
   URI of which the sender is known to the focus will be used.  The To
   header field in the Message/CPIM wrapper MUST be set to the URI of
   which the recipient is known to the focus.  If a replacement URI is
   present in the sender's message, it MUST use the mapping and replaced
   it with the URI for which the recipient is known to the focus.

   An MSRP endpoint that receives a SEND request from an MSRP switch
   containing a Message/CPIM wrapper SHOULD first inspect the To header
   field of the Message/CPIM body.  If the To header field is not set to
   the chat room URI, then it is a private message.  Then the MSRP
   endpoint SHOULD inspect the From header field of the Message/CPIM
   body to identify the sender.  The From header field will include a
   URI that identifies the sender.  The endpoint might have also
   received further identity information through a subscription to the
   SIP conference event package [RFC4575].

   It is possible that a participant, identified by a SIP Address of
   Record, joins a conference of instant messages from two or more
   different SIP UAs.  It is RECOMMENDED that the an MSRP switch can map
   a participant or replacement URI for two or more MSRP sessions.  If
   the policy of the server allows for this, the MSRP switch MUST copy
   all messages intended for the recipient through each MSRP session.


7.  Nicknames

   A common characteristic of existing chat room services is that
   participants have the ability to identify themselves with a nickname
   to the rest of the participants of the conference.  It is used for
   easy reference of participants in the chat room, and can also provide
   anonymous participants with a meaningful descriptive name.

   Nicknames are a useful construct in many use cases, of which MSRP
   chat is but one example.  Nicknames are an alternate form of
   identity, associated with a URI of which the participant is known to
   the focus.  It is not a 'display-name', but it is used somewhat like



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   a display name.  A main difference is that a nickname is unique
   inside a chat room to allow an unambiguou reference to a participant
   in the chat.  Nicknames may be long lived, or may be temporary.
   Users also need to reserve a nickname prior to its utilization.

   This memo specifies the nickname as a string.  The nickname string
   MUST be unambiguous within the scope of the chat room (conference
   instance).  This scope is similar to having a nickname unique inside
   a chat room from Extensible Messaging  and Presence Protocol
   [RFC3920].  The chat room may have policies associated with
   nicknames.  It may not accept nickname strings at all, or a it may
   provide a wider unambiguous scope like a domain or server, similar to
   Internet Relay Chat (IRC) [RFC2810].

7.1.  Using Nicknames within a Conference

   This memo provides a mechanism to reserve a nickname for a
   participant for as long as the participants is logged into the chat
   room.  The mechanism is based on a NICKNAME MSRP method (see below)
   and a new "Use-Nickname" header.  Note that other mechanisms may
   exists (for example, a web page reservation system), although they
   are outside the scope of this document.

   A conference participant who has established an MSRP session with an
   MSRP switch, where the MSRP switch has indicated the support and
   availability of nicknames with the 'nicknames' token in the
   'chatroom' SDP attribute, MAY send a NICKNAME request to the MSRP
   switch.  The NICKNAME request MUST include a new Use-Nickname header
   that contains the nickname string that the participant wants to
   reserve.

   An MSRP switch that receives a NICKNAME request containing a nickname
   in the Use-Nickname header field SHOULD first verify whether the
   policy of the chat room allows the nickname functionality.  If is not
   allowed, the MSRP switch MUST answer with a 501 response.

   If the policy of the chat room allows the usage of nicknames, the
   MSRP switch SHOULD validate that the SIP AOR is entitled to reserve
   the nickname.  The participant's authenticated identity can be
   derived after a successful HTTP Digest Authentication, included in a
   trusted SIP P-Asserted-Identity header field, included in a valid SIP
   Identity header field, or derived from any other present or future
   SIP authentication mechanism.  Once the MSRP switch has validated
   that the participant is entitled to reserve the nickname, the MSRP
   switch answers to the MSRP NICKNAME request with a 200 response.

   The reservation of a nickname can fail, e.g. if the NICKNAME request
   contains a malformed or non-existent Use-Nickname header field, or if



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   the same nickname has already been reserved by another participant in
   the conference.  The validation can also fail where the SIP AOR is
   not entitled to reserve the nickname.  In any of these cases the MSRP
   switch MUST answer with a newly defined 423 response.  The semantics
   of the 423 response are: "Nickname usage failed; the nickname is not
   allocated to this user".

   As indicated earlier, this specification defines a new MSRP header
   field: "Use-Nickname".  The Use-Nickname header field carries a
   nickname string, and SHOULD be included in the NICKNAME requests.

   The syntax of the NICKNAME method and the "Use-Nickname" header field
   is built upon the MSRP formal syntax [RFC4975]

               ext-method =/ NICKNAMEm
               NICKNAMEm = %x4E.49.43.4B.4E.41.4D.45 ; NICKNAME in caps
               ext-header =/ Use-Nickname
               ; ext-header is specified in RFC 4975
               Use-Nickname = "Use-Nickname" ":" nickname
               nickname = quoted-string

7.2.  Modifying a Nickname

   Typically participants will reserve a nickname as soon as they join
   the chat room.  But it is also possible for participants to modify
   their own nicknames and replace them it a new one at any time during
   the duration of the MSRP session.  Modification of the nickname is
   not different from the initial reservation and usage of a nickname,
   thus the NICKNAME method is used as described in Section 7.1.

   If a NICKNAME request that attempts to modify the current nickname of
   the user for some reason fails, the current nickname stays in effect.
   A new nickname comes into effect and the old one is released only
   after a NICKNAME request is accepted with a 200 response.

7.3.  Nicknames in the Conference Event Package

   Typically the conference focus acts as a notifier of the SIP
   conference event package [RFC4575].  The conference focus MAY notify
   subscribers of the nickname reserved by a given participant.  We
   define an extension to the conference event package to include
   nicknames.  The extension adds a <nickname-text> attribute to the
   <user> containing the nickname string.








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      TO BE DONE: include a formal definition of the <nickname>
      extension to the conference event package.

7.4.  Nicknames not supported nor allowed

   The participants SHOULD be notified of the URIs associated with the
   other participants of the conference even if nicknames are provided.
   The entity attribute in event notification framework being an SIP AOR
   or a replacement URI.  A client not supporting the extensions of this
   memo will not render nicknames and can therefore can not be referred
   to using nickname inside the chat room.  The same would apply where a
   chat room do not allow nicknames to be used.


8.  The SDP 'chatroom' attribute

   There are a handful of use cases where a participant would like to
   learn the chat room capabilities supported by the MSRP switch and the
   chat room.  For example, a participant would like to learn if the
   MSRP switch supports private messaging, otherwise, the participant
   may send what he believes is a private instant message addressed to a
   participant, but since the MSRP switch does not support the functions
   specified in this memo, the message gets eventually distributed to
   all the participants of the chat room.

   The reverse case also exists.  A participant, say Alice, whose user
   agent does not support the extensions defined by this document joins
   the chat room.  The MSRP switch learns that Alice application does
   not support private messaging nor nicknames.  If another participant,
   say Bob, sends a private message to Alice, the MSRP switch does not
   distribute it to Alice, because Alice is not able to differentiate it
   from a regular message sent to the whole roster.  Further more, if
   Alice replied to this message, she would do it to the whole roster.
   Because of this, the MSRP switch keeps also track of users who do not
   support the extensions defined in this document.

   In another scenario, the policy of a chat room may indicate that
   certain functions are not allowed.  For example, the policy may
   indicate that nicknames or private messages are not allowed.

   In order to provide the user with a good chat room experience, we
   define a new 'chatroom' SDP attribute.  The 'chatroom' attribute is a
   media-level attribute that MAY be included in conjunction with and
   MSRP media stream (i.e., when an m= line in SDP indicates "TCP/MSRP"
   or "TCP/TLS/MSRP").  The 'chatroom' attribute indicates the
   intersection of support and chat room local policy allowance for a
   number of functions specified in this document.  Specifically, we
   provide the means for indicating support to use nicknames and private



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   messaging.

   The 'chatroom' SDP attribute has the following syntax:

             chatroom = chatroom-label ":" chat-token *(SP chat-token)
             chatroom-label = "chatroom"
             chat-token = (nicknames-token | private-msg-token | token)
             nicknames-token = "nicknames"
             private-msg-token = "private-messages"

   A conference focus that includes the 'nicknames' token in the session
   description is signaling that the MSRP switch supports and the chat
   room allows to use the procedures specified in Section 7.  A
   conference focus that includes the 'private-messages' in the SDP
   description is signaling that the MSRP switch supports and the chat
   room allows to use the procedures specified in Section 6.2.

   Example of the 'chatroom' attribute for an MSRP media stream that
   indicates the acceptance of nicknames and private messages:

             a=chatroom:nickname private-messages


9.  Examples

9.1.  Joining a chat room

   Figure 5 presents a flow diagram where Alice joins a chat room by
   sending an INVITE request.  This INVITE request contains a session
   description that includes the chatroom extensions defined in this
   document.

                    Alice               Conference focus
                      |                        |
                      |(1) (SIP) INVITE        |
                      |----------------------->|
                      |(2) (SIP) 200 OK        |
                      |<-----------------------|
                      |(3) (SIP) ACK           |
                      |----------------------->|
                      |                        |

           Figure 5: Flow diagram of a user joining a chat room

   F1: Alice constructs an SDP description that includes an MSRP media
   stream.  She also indicates her support for the chatroom extensions
   defined in this document.  She sends the INVITE request to the chat
   room server.



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   INVITE sip:chatroom22@chat.example.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Chatroom 22 <sip:chatroom22@chat.example.com>
   Call-ID: 3848276298220188511@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: [length]

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 atlanta.example.com
   m=message 7654 TCP/MSRP *
   a=accept-types:message/cpim text/plain text/html
   a=path:msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   a=chatroom:nickname private-messages

      Figure 6: INVITE request containing an SDP offer with chat room
                                extensions

   F2: The chat room server accepts the session establishment.  It
   includes the 'isfocus' and other relevant feature tags in the Contact
   header field of the response.  The chat room server also builds an
   SDP answer that also that forces the reception of messages wrapped in
   message/cpim envelops.  It also includes the the chatroom attribute
   with the allowed extensions.






















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   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Chatroom 22 <sip:chatroom22@chat.example.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:chatroom22@chat.example.com;transport=tcp> \
             ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL,SUBSCRIBE,NOTIFY" \
             ;automata;isfocus;message;event="conference"
   Content-Type: application/sdp
   Content-Length: [length]

   v=0
   o=chat 2890844527 2890844527 IN IP4 chat.example.com
   s=-
   c=IN IP4 chat.example.com
   m=message 12763 TCP/MSRP *
   a=accept-types:message/cpim
   a=accept-wrapped-types:text/plain text/html *
   a=path:msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   a=chatroom:nickname private-messages

        Figure 7: 200 (OK) response including chat room extensions

   F3: The session established is acknowledged (details not shown).

9.2.  Setting up a nickname

   Figure 8 shows an example of Alice setting up a nickname using the
   conference as provider.  Her first proposal is not accepted because
   the proposed nickname is already in use.  Her second proposal is
   accepted.

                     Alice                  MSRP switch
                       |                        |
                       |(1) (MSRP) NICKNAME     |
                       |----------------------->|
                       |(2) (MSRP) 423          |
                       |<-----------------------|
                       |(3) (MSRP) NICKNAME     |
                       |----------------------->|
                       |(4) (MSRP) 200          |
                       |<-----------------------|
                       |                        |

         Figure 8: Flow diagram of a user setting up her nickname




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   F1: Alice sends an MSRP NICKNAME request that contains her proposed
   nicknames in the Set-Nickname header field.

   MSRP d93kswow NICKNAME
   To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   Use-Nickname: "Alice the great"
   -------d93kswow$

     Figure 9: MSRP NICKNAME request with an initial nickname proposal

   F2: The MSRP switch analyzes the existing allocation of nicknames and
   detects that the nickname "Alice is great" is already provided to
   another participant by the conference.  The MSRP switch answers with
   a 423 response.

   MSRP d93kswow 423 Nickname usage failed
   To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   -------d93kswow$

                       Figure 10: MSRP 423 response

   F3: Alice receives the response.  She proposes a new nickname in a
   second NICKNAME request.

   MSRP 09swk2d NICKNAME
   To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   Use-Nickname: "Alice in wonderland"
   -------09swk2d$

     Figure 11: MSRP NICKNAME request with a second nickname proposal

   F4: The MSRP switch accepts the nickname proposal and answers with a
   200 response.

   MSRP 09swk2d 200 OK
   To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   -------09swk2d$

                     Figure 12: MSRP NICKNAME request








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9.3.  Sending a regular message to the chat room

   Figure 13 depicts a flow diagram where Alice is sending a regular
   message addressed to the chat room.  The MSRP switch distributes the
   message to the rest of the participants.

      Alice               MSRP switch                   Bob   Charlie
        |                      |                        |       |
        | (1) (MSRP) SEND      |                        |       |
        |--------------------->|  (3) (MSRP) SEND       |       |
        | (2) (MSRP) 200       |----------------------->|       |
        |<---------------------|  (4) (MSRP) SEND       |       |
        |                      |------------------------------->|
        |                      |  (5) (MSRP) 200 OK     |       |
        |                      |<-----------------------|       |
        |                      |  (6) (MSRP) 200 OK     |       |
        |                      |<------------------------------ |
        |                      |                        |       |
        |                      |                        |       |

           Figure 13: Sending a regular message to the chat room

   F1: Alice builds a text message and wraps it in a CPIM message.  She
   addresses the CPIM message to the chat room.  She encloses the result
   in an MSRP SEND request and sends it to the MSRP switch via the
   existing TCP connection.

   MSRP 3490visdm SEND
   To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   Message-ID: 99s9s2
   Byte-Range: 1-*/*
   Content-Type: message/cpim

   To: <sip:chatroom22@chat.example.com;transport=tcp>
   From: <sip:alice@atlanta.example.com>
   DateTime: 2007-03-02T15:02:31-03:00
   Content-Type: text/plain

   Hello guys, how are you today?
   -------3490visdm$

   Figure 14: Instant message addressed to all participants in the chat
                                   room

   F2: The MSRP switch acknowledges the reception of the SEND request
   with a 200 (OK) response.




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   MSRP 3490visdm 200 OK
   To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   Message-ID: 99s9s2
   Byte-Range: 1-*/*
   -------3490visdm$

                       Figure 15: 200 (OK) response

   F3: The MSRP switch creates a new MSRP SEND request that contains the
   received message/cpim body and sends it to Bob.

   MSRP 490ej23 SEND
   To-Path: msrp://client.biloxi.example.com:4923/49dufdje2;tcp
   From-Path: msrp://chat.example.com:5678/jofofo3;tcp
   Message-ID: 304sse2
   Byte-Range: 1-*/*
   Content-Type: message/cpim

   To: <sip:chatroom22@chat.example.com;transport=tcp>
   From: <sip:alice@atlanta.example.com>
   DateTime: 2007-03-02T15:02:31-03:00
   Content-Type: text/plain

   Hello guys, how are you today?
   -------490ej23$

            Figure 16: Instant message sent to all participants

   The rest of the message flows are analogous to the previous.  They
   are not shown here.

9.4.  Sending a private message to a participant

   Figure 17 depicts a flow diagram where Alice is sending a private
   message addressed to Bob's SIP AOR.  The MSRP switch distributes the
   message only to Bob.

      Alice               MSRP switch                   Bob   Charlie
        |                      |                        |       |
        | (1) (MSRP) SEND      |                        |       |
        |--------------------->|  (3) (MSRP) SEND       |       |
        | (2) (MSRP) 200       |----------------------->|       |
        |<---------------------|  (4) (MSRP) SEND       |       |
        |                      |------------------------------->|
        |                      |                        |       |
        |                      |                        |       |




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                Figure 17: Sending a private message to Bob

   F1: Alice builds a text message and wraps it in a CPIM message.  She
   addresses the CPIM message to the Bob's nickname, which she learned
   from a notification in the conference event package.  She encloses
   the result in an MSRP SEND request and sends it to the MSRP switch
   via the existing TCP connection.

   MSRP 6959ssdf SEND
   To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   Message-ID: okj3kw
   Byte-Range: 1-*/*
   Content-Type: message/cpim

   To: <sip:Bob%20the%20great@example.com>
   From: <sip:Alice%20in%20wonderland@example.com>
   DateTime: 2007-03-02T15:02:31-03:00
   Content-Type: text/plain

   Hello Bob.
   -------6959ssdf$

      Figure 18: Private instant message addressed to one participant

   F2: The MSRP switch acknowledges the reception of the SEND request
   with a 200 (OK) response.

   MSRP 6959ssdfm 200 OK
   To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
   From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
   Message-ID: okj3kw
   Byte-Range: 1-*/*
   -------6959ssdfm$

                       Figure 19: 200 (OK) response

   F3: The MSRP switch creates a new MSRP SEND request that contains the
   received message/cpim body and sends it only to Bob. Bob can
   distinguish the sender in the From header of the CPIM message.  He
   also identifies this as a private message due to the To CPIM header.










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   MSRP 9v9s2 SEND
   To-Path: msrp://client.biloxi.example.com:4923/49dufdje2;tcp
   From-Path: msrp://chat.example.com:5678/jofofo3;tcp
   Message-ID: d9fghe982
   Byte-Range: 1-*/*
   Content-Type: message/cpim

   To: <sip:Bob%20the%20great@example.com>
   From: <sip:alice@atlanta.example.com>
   DateTime: 2007-03-02T15:02:31-03:00
   Content-Type: text/plain

   Hello Bob.
   -------9v9s2$

              Figure 20: Private instant message sent to Bob

   Flow F4 is not shown.


10.  IANA Considerations

   TBD.


11.  Security Considerations

   This document proposes extensions to the Message Session Relay
   Protocol [RFC4975].  Therefore, the security considerations of such
   document apply to this document as well.

   In general, messages sent to a multi-party session based messaging
   focus are not deem to expose any security threat.  Nevertheless, if a
   participant wants to avoid eavesdropping from non authorized
   entities, it should send those messages a TLS [RFC4346] transport
   connection, as allowed by MSRP.


12.  Contributors

   This work would have never been possible without the fruitful
   discussions in the SIMPLE WG mailing list, specially with Brian Rosen
   (Neustar) and Paul Kyzivat (Cisco), who provided extensive review and
   improvements throughout the document.







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13.  Acknowledgments

   The authors want to thank Eva Leppanen, Adamu Haruna, Adam Roach and
   Matt Lepinski for providing comments.


14.  References

14.1.  Normative References

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

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

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323, November 2002.

   [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
              "Indicating User Agent Capabilities in the Session
              Initiation Protocol (SIP)", RFC 3840, August 2004.

   [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, August 2004.

   [RFC3862]  Klyne, G. and D. Atkins, "Common Presence and Instant
              Messaging (CPIM): Message Format", RFC 3862, August 2004.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [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.

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

14.2.  Informative References

   [RFC2810]  Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
              April 2000.



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   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3920]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [RFC3966]  Schulzrinne, H., "The tel URI for Telephone Numbers",
              RFC 3966, December 2004.

   [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
              Session Initiation Protocol (SIP)", RFC 4353,
              February 2006.

   [I-D.ietf-xcon-framework]
              Barnes, M., Boulton, C., and O. Levin, "A Framework for
              Centralized Conferencing", draft-ietf-xcon-framework-10
              (work in progress), November 2007.


Authors' Addresses

   Aki Niemi
   Nokia
   P.O. Box 407
   NOKIA GROUP, FIN  00045
   Finland

   Phone: +358 50 389 1644
   Email: aki.niemi@nokia.com


   Miguel A. Garcia-Martin
   Nokia Siemens Networks
   P.O.Box 6
   Nokia Siemens Networks, FIN  02022
   Finland

   Email: miguel.garcia@nsn.com












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   Geir A. Sandbakken
   TANDBERG
   N-1366 Lysaker
   Norway

   Phone: +47 67 125 125
   Email: geir.sandbakken@tandberg.com
   URI:   http://www.tandberg.com











































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Full Copyright Statement

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