Network Working Group A. Niemi
Internet-Draft M. Garcia-Martin
Expires: August 17, 2006 Nokia Research Center
February 13, 2006
Multi-party Instant Message (IM) Sessions Using the Message Session
Relay Protocol (MSRP)
draft-niemi-simple-chat-04
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 17, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
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
tools for establishing multi-party instant messaging (IM) sessions,
or chat rooms, using the centralized conferencing model.
Niemi & Garcia-Martin Expires August 17, 2006 [Page 1]
Internet-Draft Multiparty MSRP February 2006
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. The SDP 'chatroom' attribute . . . . . . . . . . . . . . . 9
5.4. Deleting a Chat Room . . . . . . . . . . . . . . . . . . . 10
6. Nicknames . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Provisioning Nicknames . . . . . . . . . . . . . . . . . . 12
6.2. Modifying a Nickname . . . . . . . . . . . . . . . . . . . 14
6.3. Mapping Nicknames to Other Identities . . . . . . . . . . 14
7. Sending and Receiving Instant Messages . . . . . . . . . . . . 15
7.1. Regular Messages . . . . . . . . . . . . . . . . . . . . . 15
7.2. Private Messages . . . . . . . . . . . . . . . . . . . . . 16
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . . . 21
Niemi & Garcia-Martin Expires August 17, 2006 [Page 2]
Internet-Draft Multiparty MSRP February 2006
1. Introduction
The Message Session Relay Protocol (MSRP)
[I-D.ietf-simple-message-sessions] 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
session or conference that is hosted by a specialized user agent
called a conference 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 one or more
participants, and the ability to establish sub-conferences with one
or more of the participants within the existing conference. They
also allow combining instant messaging with other media components,
such as voice, video, whiteboarding, screen sharing, and file
transfer.
Such 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.
The aim of this document is to define requirements, conventions and
extensions for enabling features similar to many of these existing
systems in the Internet, namely the Internet Relay Chat (IRC)
[RFC2810] and Extensible Messaging and Presence Protocol [RFC3920]
based multi-party chats.
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].
Niemi & Garcia-Martin Expires August 17, 2006 [Page 3]
Internet-Draft Multiparty MSRP February 2006
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 descriptive name associated to a participant.
Nickname URI: A SIP URI that includes a nickname in the user part.
See more information in Section 6.
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 in a
conference server. 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.
Conference Server: a (possibly decomposed) server that provides
multipart text conference services. It is also the combination of
a conference focus and an MSRP switch.
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
Niemi & Garcia-Martin Expires August 17, 2006 [Page 4]
Internet-Draft Multiparty MSRP February 2006
input media streams; it merely relays the messages between
participants.
Private Instant Message: an instant message sent in a chat room
whose intended recipient is something other than the default. The
recipient of a private IM can either be one specific conference
participant, or a subset of the full participant list. A private
IM is usually rendered distinctly from the rest of the IMs, as to
indicate that the message was a private communication.
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.
A number of requirements that enrich the session based messaging
conferences have already been described in Requirements for Instant
Messaging in 3GPP Wireless Systems
[I-D.niemi-simple-im-wireless-reqs] or the Advanced Instant Messaging
Requirements for the Session Initiation Protocol
[I-D.rosenberg-simple-messaging-requirements].
In addition, we define the following requirements:
REQ-1: The conference must have the ability to host other media in
addition to MSRP, as well as multiple streams of MSRP.
REQ-2: A conference participant must be able to determine the
identities of the sender and recipient of the received IMs.
REQ-3: 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, a
conference sidebar or a single participant of the conference
(i.e., a private message).
Niemi & Garcia-Martin Expires August 17, 2006 [Page 5]
Internet-Draft Multiparty MSRP February 2006
REQ-4: It must be possible to send a message to a single
participant, or a subset of the conference participants
(i.e., a private instant message).
REQ-5: It must be possible to set up a sidebar session with one or
more participants of the chat room.
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.
OPEN ISSUE: This requirement, and the one above it, are
not strictly an IM conference issue. In principle,
participants of any conferences should be able to use a
nickname, and change their nickname in the course 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: A chat room, or a chat room sidebar must be able to be
characterized with a topic whose purpose is to identify the
subject of conversation.
REQ-11: A user with the appropriate privileges must be able to set
and/or modify the topic of the chat room, or chat room
sidebar.
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
Niemi & Garcia-Martin Expires August 17, 2006 [Page 6]
Internet-Draft Multiparty MSRP February 2006
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.
+------+
| 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 [I-D.ietf-sipping-conference-package] 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 'multipart/mixed' MIME type to
accommodate a 'Message/CPIM' wrapper content type [RFC3862] .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
Niemi & Garcia-Martin Expires August 17, 2006 [Page 7]
Internet-Draft Multiparty MSRP February 2006
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
one or more conference participants whose identities have been
learnt, e.g., via a notification from the conference event package
[I-D.ietf-sipping-conference-package]. In this case the sender
creates an MSRP SEND request with a Message/CPIM body whose To or Cc
headers contain not the chat room URI but one or more nickname or
participant URIs. The MSRP switch then fans out the SEND request to
each of the participants listed in the To or Cc headers of the
Message/CPIM body.
We extend the current MSRP negotiation that takes place in SDP
[RFC2327] 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 [RFC2327]
media-line.
Niemi & Garcia-Martin Expires August 17, 2006 [Page 8]
Internet-Draft Multiparty MSRP February 2006
The conference focus of a chat room MUST include support for a
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).
5.3. The SDP 'chatroom' attribute
There are a handful of use cases where a participant would like to
learn the chatroom 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
few participants, 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.
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 chatroom 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 chatroom 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
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 signalling that the MSRP switch supports and the
chatroom allows to use the procedures specified in Section 6. A
conference focus that includes the 'private-messages' in the SDP
description is signalling that the MSRP switch supports and the
Niemi & Garcia-Martin Expires August 17, 2006 [Page 9]
Internet-Draft Multiparty MSRP February 2006
chatroom allows to use the procedures specified in Section 7.2.
Example of the 'chatroom' attribute for an MSRP media stream that
indicates the acceptance of nicknames and private messages:
a=chatroom:nickname private-messages
5.4. 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. 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. This provides a
layer of anonymity, whereby the conference server authenticates the
participant, but still allows the participant to keep anonymity of
his SIP URI towards the rest of the participants without downgrading
his services. Specifically, anonymous participants are able to
receive private instant messages from other participants without
revealing their SIP URI.
One option to satisfy an aspect of nicknames would be using the
display name with a real identity as the URI. A nickname in the
display name offers a pseudonym that anyone can map to a real
identity, thus not satisfying the anonymity requirements.
Another option would be to use a nicknaming service, that allows
allocating nickname URIs to users. Using such a URI in a conference
in effect anonymizes the user, but still allows the user to be
reached outside the chat room using the same identity. However,
defining such nicknaming service machinery is out of the scope of
this specification.
Instead, we take the approach of defining a nickname as the
combination of an optional quoted display name followed by a nickname
URI. A nickname URI is a SIP URI formed from the chat room URI that
embeds a nickname identifier. A nickname URI does not resolve to the
user himself, but to the particular chat room where the user has
Niemi & Garcia-Martin Expires August 17, 2006 [Page 10]
Internet-Draft Multiparty MSRP February 2006
joined.
In other words, a nickname is simply a username that is scoped for a
particular chat room. Such nicknames are allocated on a first-come
first-served policy, meaning they can also be "stolen". It is out of
the scope of this specification to define nickname retention schemes,
or nickaming services as discussed above.
Note that for some hosted chat rooms, this feature of nicknames
may be too much to tolerate. For such chat rooms, it may be more
desirable to disallow nicknames altogether, and have chat room
participants be identified with their own full SIP URI instead (or
any other URI scheme they used to join the room).
Based on the above discussion, we define a nickname as follows:
Nickname = [Display-Name] (nickname URI)
An example of a nickname is:
"Alice in wonderland" <sip:alice%40wonderland@chat.example.com>
The display name of a nickname is used only for displaying purposes.
The nickname URI is used for routing. In particular, the conference
server maintains a mapping table between nickname URIs, SIP URIs and
MSRP sessions pertaining to a participant.
Nickname URIs are scoped to a chatroom. Therefore, a nickname
identifier MUST be unique within a chatroom, and SHOULD be unique
within a conference server or administrative domain. This way, two
different users can't have the same nickname in different rooms on
the same chat server, unless there are valid reasons for allowing
this. E.g., some chat rooms might need to assign some well-known
nickname to a secretary, which of course might be a different user in
different rooms.
However, it is still possible that the same user is using different
nicknames in different chat rooms hosted by the same conference
server.
In order to maintain high compatibility with existing SIP User
Agents, we define a convention for creating a nickname URI. The
convention consist on prepending an escaped nickname identifier and a
possible escaped '@' sign to the existing username part of the chat
room URI.
Let us take a look at an example. Assume the chat room URI allocated
to a given chat room is 'sip:room34@example.com'. A user whose
Niemi & Garcia-Martin Expires August 17, 2006 [Page 11]
Internet-Draft Multiparty MSRP February 2006
nickname identifier is set to 'nordicguy' is represented with the
nickname URI: 'sip:nordicguy%40room34@example.com'.
In another example the chat room URI does not include a username
part. For example, the chat room URI is 'sip:chat34.example.com'.
In this context a user whose nickname is 'nordicguy' gets represented
with a nickname URI of 'sip:nordicguy@chat34.example.com'.
An interesting property of this approach is that nickname URIs do not
really resolve to the SIP UA or real identity of the user. Instead,
they resolve to the conference server. Only the conference server
and the owner of the nickname are able to map a nickname URI to the
SIP URI of the user. Other participants can use the conference
server as an intermediary for delivery of private messages addressed
to any of the nickname URIs of the chat room.
As a consequence of the structure of the nickname URI, if a user has
the same nickname identifier in two different chat rooms, the
nickname URI will be different (because the chat room URIs are
different). For example, the nickname URIs of 'nordicguy' in two
different chat rooms would be 'sip:nordicguy%40conf12@example.com'
and 'sip:nordicguy%40conf34@example.com'. Each one is used within
its own chat room.
6.1. Provisioning Nicknames
Since nicknames are scoped within a chat room (and usually also
within a chat server or administrative domain), we provide a
mechanism for requesting and reserving a nickname for the user's
disposal for the duration the user is logged into the chat room. The
mechanism is based on the definition of the NICKNAME MSRP method (see
below). Note that other mechanisms may exists (for example, a web
page reservation system), although they are outside the scope of this
document. Further more, the mechanism that we specify in this memo
is able to reserve a nickname for the user's disposal for the time
the user is logged into the chat room. Other mechanisms that provide
persistent nicknames or nickname reservation across multiple chat
rooms or conference servers are outside the scope of this memo.
A participant in a chat room MAY send a NICKNAME method to the MSRP
switch to request the reservation of a nickname for the user's
disposal for the duration of the session (i.e., while the participant
is joined to the chat room) at any time once the MSRP session has
been established and authenticated. Typically users will reserve a
nickname as soon as the join the chat room, prior to sending any
messages.
We additionally define two new header fields "Set-Nickname" and
Niemi & Garcia-Martin Expires August 17, 2006 [Page 12]
Internet-Draft Multiparty MSRP February 2006
"Proposed-Nickname" that carry one or more nickname URIs. Set-
Nickname headefr field MUST only be included in a NICKNAME request.
The Proposed-Nickname header fields MUST only be included a 423
responses to NICKNAME requests. URIs included in the Set-Nickname
and Proposed-Nickname header fields MUST be formatted according to
the conventions for nickname URIs.
The syntax of the NICKNAME method and the "Proposed-Nickname" header
field is built upon the MSRP formal syntax
[I-D.ietf-simple-message-sessions] and the SIP formal syntax
[RFC3261]:
ext-method =/ NICKNAMEm
NICKNAMEm = %x4E.49.43.4B.4E.41.4D.45 ; NICKNAME in caps
ext-header =/ Set-Nickname
; ext-header is specified in RFC XXXX
; name-addr is specified in RFC 3261
Set-Nickname = "Set-Nickname" ":" name-addr
ext-header =/ Proposed-Nickname
Proposed-Nickname = "Proposed-Nickname" ":" name-addr
*(COMMA name-addr)
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 MSRP NICKNAME request MUST contain a Set-Nickname header
field that includes one nickname URI that the user would like to be
known as. URIs included in the Set-Nickname header field MUST be
formatted as nickname URIs.
An MSRP switch that receives a NICKNAME request containing a proposed
nickname in the Set-Nickname header field SHOULD verify first 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 conference participants to
negotiate and use their nicknames, the MSRP switch then examines
nickname contained in the Set-Nickname header field. If the URI
included in the Set-Nickname header field is not formatted as a
nickname URI (e.g., the chat room URI is not used), then the MSRP
switch discards that proposal and moves to the next one. For every
valid nickname URI the MSRP switch finds if the proposed nickname URI
is already in use or matches the local policy otherwise. If the
proposal is not acceptable for any reason, the MSRP switch discards
the proposal and moves to the next one. Note that the MSRP switch
bases its decision on the nickname URI only, and it does not use the
display name for this validation. If a proposed nickname URI is
Niemi & Garcia-Martin Expires August 17, 2006 [Page 13]
Internet-Draft Multiparty MSRP February 2006
valid and not already used, the MSRP switch inserts the entry into
its mapping table, associated to the user's SIP URI and MSRP session,
and generates a 200 response to the NICKNAME request. The 200
response MUST include a Proposed-Nickname header field that contains
the selected nickname.
If the MSRP NICKNAME request does not contain a Proposed-Nickname
header field, or if it contains such header, but all the proposed
nicknames are not acceptable (e.g., because they are already taken),
the MSRP switch generates a 423 response. The 423 response SHOULD
contain a Proposed-Nickname header field that contains one or more
nickname URIs proposed by the MSRP switch.
The sender of an MSRP NICKNAME request can receive a 200 response
that contains a Proposed-Nickname header field containing the
nickname URI that the user has been granted for the duration of the
session. If the response is a 423, then none of the proposals of the
NICKNAME request were accepted. The 423 response includes a
Proposed-Nickname header field that contains the MSRP switch
proposals. The MSRP endpoint MAY send a new NICKNAME request that
includes a new nickname proposal.
6.2. Modifying a Nickname
At any time during the session the MSRP endpoint may want to modify
his nickname. Modification of the nickname is not different from the
initial provision of a nickname, thus the NICKNAME method is used as
described in Section 6.1.
If a NICKNAME method that attempts to modify the current nickname of
the user for some reason fails, the current nickname stays in effect.
The new nickname comes into effect and the old one is released only
after a NICKNAME method is accepted and receives a 200-class
repsonse.
6.3. Mapping Nicknames to Other Identities
The MSRP switch maintains a mapping table that correlates, for a
given user, his nickname, SIP URI, and MSRP session ID. This
correlation is valid for the duration of the session (unless
mechanisms specified elsewhere exists to provide long-lasting
nicknames). Thus, at the dismissal of the session the MSRP switch
should dispose the nickname and make it available to other
participants.
Typically the conference focus acts as a notifier of the SIP
conference event package [I-D.ietf-sipping-conference-package]. The
conference focus MAY notify subscribers of the nickname allocated to
Niemi & Garcia-Martin Expires August 17, 2006 [Page 14]
Internet-Draft Multiparty MSRP February 2006
a given participant. We define an extension to the conference event
package to include nicknames. [NOTE: To be done: defining an
extension to the conference event package
[I-D.ietf-sipping-conference-package] to include nicknames].
7. Sending and Receiving Instant Messages
7.1. 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] and 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:
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
o A nickname URI formatted according to the rules indicated in
Section 6 and allocated for the user.
If the sender of the message wants to remain anonymous to the rest of
the participants, and providing that the policy of the conference
allows anonymous participation, the creator SHOULD populate the From
header of the Message/CPIM body with an anonymous identity, e.g.,
using the "anonymous" SIP URI as described in RFC 3261 [RFC3261]
Section 8.1.1.3. or using a nickname URI (see Section 6) that has
been allocated to the user.
The sender MUST populate the To header field of the Message/CPIM body
Niemi & Garcia-Martin Expires August 17, 2006 [Page 15]
Internet-Draft Multiparty MSRP February 2006
with the chat room URI.
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.
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 [I-D.ietf-sipping-conference-package].
7.2. Private Messages
This section describes the conventions used to send and receive
private instant messages, i.e., instant messages that are address to
one or more selected participants of the chat room rather to all of
them. A private instant message is sent over a regular MSRP SEND
request that contains a Message/CPIM wrapper [RFC3862] and the
desired payload (e.g., text, image, video-clip, etc.).
When a chat room participant wishes to send a private instant message
to one or more 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/
Niemi & Garcia-Martin Expires August 17, 2006 [Page 16]
Internet-Draft Multiparty MSRP February 2006
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 as indicated for regular instant messages. Then the
sender MUST populate the To header field and MAY populate the Cc
header field of the Message/CPIM with the identity of intended
recipients. These identities include SIP, TEL, and IM URIs, and
nickname URIs (see Section 6) typically learnt from the information
received in notifications of the conference event package
[I-D.ietf-sipping-conference-package].
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 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.
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 chatroom URI the MSRP switch inspects the URIs
included in both the To and Cc headers. For each URI found there,
the MSRP switch searches in its mapping table to find the MSRP
session established towards the user's MSRP endpoint. Once a match
is found the MSRP switch MUST create a SEND request on that MSRP
session and MUST copy the contents (e.g., the whole Message/CPIM
wrapper and its bodies) to a SEND request and send it over that MSRP
session.
There might be situations where one or more URIs included in the To
or Cc headers of the Message/CPIM wrapper cannot resolve to existing
MSRP sessions, e.g., due to a mistyped URI or because the recipient
has abandoned the chat room. In this case it might be benefitial for
the sender to become aware of which recipients the MSRP switch failed
to resolve. To support this case we define a new MSRP response code
427. This response code is not used in MSRP responses, but as part
of the REPORT status code. Note that the 427 status code in a REPORT
request merely indicates a failure in resolving a URI to an active
MSRP session, and it does not indicate whether the SEND request was
successfully received by any of the recipients (it might be still
possible that a URI resolves to an active MSRP session but the SEND
request cannot be delivered due to congestion, failure of the TCP
connection, or any failure at the recipient's MSRP endpoint).
Niemi & Garcia-Martin Expires August 17, 2006 [Page 17]
Internet-Draft Multiparty MSRP February 2006
If the MSRP switch cannot resolve any of the URIs included in the To
or Cc headers, 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 REPORT
request MUST include a Message/CPIM wrapper, with the original From
header field included in the SEND request, and the To and Cc header
fields containing the subset of failed-to-resolve URIs included in
the To and Cc header fields of original Message/CPIM wrapper,
respectively.
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 that has been
distributed to only selected participants in the conference
(addressed in the To and Cc headers of the Message/CPIM body). 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
[I-D.ietf-sipping-conference-package].
8. Examples
TBD.
9. IANA Considerations
TBD.
10. Security Considerations
This document proposes extensions to the Message Session Relay
Protocol [I-D.ietf-simple-message-sessions]. 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 [RFC2246] transport
connection, as allowed by MSRP.
Niemi & Garcia-Martin Expires August 17, 2006 [Page 18]
Internet-Draft Multiparty MSRP February 2006
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[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.
[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.
[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., "A Framework and Data Model for Centralized
Conferencing", draft-ietf-xcon-framework-02 (work in
progress), October 2005.
[I-D.ietf-simple-message-sessions]
Campbell, B., "The Message Session Relay Protocol",
draft-ietf-simple-message-sessions-13 (work in progress),
December 2005.
Niemi & Garcia-Martin Expires August 17, 2006 [Page 19]
Internet-Draft Multiparty MSRP February 2006
11.2. Informative References
[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.
[RFC2810] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
April 2000.
[I-D.niemi-simple-im-wireless-reqs]
Niemi, A., "Requirements for Instant Messaging in 3GPP
Wireless Systems", draft-niemi-simple-im-wireless-reqs-02
(work in progress), October 2003.
[I-D.rosenberg-simple-messaging-requirements]
Rosenberg, J., "Advanced Instant Messaging Requirements
for the Session Initiation Protocol (SIP)",
draft-rosenberg-simple-messaging-requirements-01 (work in
progress), February 2004.
[I-D.ietf-sipping-conference-package]
Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Conference State",
draft-ietf-sipping-conference-package-12 (work in
progress), July 2005.
Authors' Addresses
Aki Niemi
Nokia Research Center
P.O. Box 407
NOKIA GROUP, FIN 00045
Finland
Phone: +358 50 389 1644
Email: aki.niemi@nokia.com
Niemi & Garcia-Martin Expires August 17, 2006 [Page 20]
Internet-Draft Multiparty MSRP February 2006
Miguel A. Garcia-Martin
Nokia Research Center
P.O. Box 407
NOKIA GROUP, FIN 00045
Finland
Phone: +358 50 480 4586
Email: miguel.an.garcia@nokia.com
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
Niemi & Garcia-Martin Expires August 17, 2006 [Page 21]
Internet-Draft Multiparty MSRP February 2006
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Niemi & Garcia-Martin Expires August 17, 2006 [Page 22]