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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
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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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