Multi-party Chat
Using the Message Session Relay Protocol (MSRP)NokiaP.O. Box 407NOKIA GROUPFIN00045Finland+358 50 389 1644aki.niemi@nokia.comEricssonCalle Via de los Poblados 13MadridES28033Spainmiguel.a.garcia@ericsson.comTANDBERGPhilip Pedersens vei 20N-1366 LysakerNorway+47 67 125 125geir.sandbakken@tandberg.comhttp://www.tandberg.com
General
I-DInternet-Draftmessagingmessage sessionsmulti-partyThe 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
chat sessions, or chat rooms, using MSRP.
The Message Session Relay Protocol (MSRP)
defines a mechanism for sending a series of instant
messages within a session. The
Session Initiation Protocol (SIP) in
combination with the Session Description
Protocol (SDP) 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
. 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),
Extensible Messaging and Presence Protocol
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 as a design
basis. It also aims to be compatible with the
Centralized Conferencing
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. 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, 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
applied to the scope of this document. In
addition to that terminology, we introduce some new terms:
a pseudonym or descriptive name associated to a
participant. See for details
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. a synonym for a multi-party chat 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. the conference participant that
originally created an instant message and sent it to the chat room for
delivery. the destination conference
participant(s). This defaults to the full conference participant
list, minus the IM Sender. 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. 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. a temporary GRUU that can be registered
with the conference focus to conceal a participant's SIP AOR
from the other participants in the a conference.
Although conference frameworks describing many types of
conferencing applications already exist, such as the
Framework and Data Model for
Centralized Conferencing and the
SIP Conferencing
Framework, 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
multi-party 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:
A basic requirement is the existence of a multi-party
conference, where participants can join and leave the conference
and get instant messages exchanged to the rest of the participants.
The conference must have the ability to host other media in
addition to MSRP, as well as multiple streams of MSRP.
A conference participant must be able to determine the
identities of the sender and recipient of the received IMs.
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).
It must be possible to send a message to a single
participant within the conference (i.e., a private instant message).
A conference participant may have a nickname or pseudonym
associated with their real identity.
It must be possible for a participant to change their nickname
during the progress of the conference.
It must be possible that a participant is only known by
their nickname and not their real identity to the rest of the
conference.
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.)
It must be possible for participants to learn the capabilities
support of the features described in this document (and perhaps
others).
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
multi-party chat, 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
.
Typically conference participants also subscribe to the
conference event 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
'Message/CPIM' wrapper content type,
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. 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 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.
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 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.
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 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 media-line.
The conference focus of a chat room MUST include support for
a Message/CPIM 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).
If a participant wants to remain anonymous to the rest of the
participants in the conference, the participant's UA can
register or acquire by other means a temporary GRUU
with the conference focus. The procedure SHOULD follow
the recommendation of
draft-ietf-sip-gruu.
The temporary GRUU can be used in the From and To header in
the 'Message/CPIM' wrapper concealing the participant's SIP AOR
from the other participants in the conference.
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.
As with creating a conference, the methods defined by the
SIP Conference Framework
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.
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
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'. 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:A SIP URI representing the
participant's address-of-recordA tel URI representing the
participant's telephone numberAn IM URI representing the
participant's instant messaging address An temporary GRUU
representing the anonymous URI associated with the sender.
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.
The valid URI can be the SIP AOR of the participant, or a temporary
GRUU registered with the focus associated with an anonymous participant.
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.
The MSRP SHALL follow the success report and failure report
handling described in section 7 of when it
receives a SEND request with a Message/CPIM
wrapper having the To header field set to the chat room URI.
The MSRP switch MAY use any report model in the copies
of the SEND request intended for the recipients, but
any received reports MUST NOT be forwarded to the originator of
the original SEND request. The report model for handling private messages
is different from SEND requests to the chat room
(see for details)
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 .
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
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'. 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 .
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 participants URI associated with
a participant. If the URI in the To header can not be resolved
(e.g. cased by a mistyped URI or that the recipient has abandoned
he 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" or "partial", 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" or "partial", the MSRP switch
MUST send a REPORT request having the status code of 428.
The new response 428 indicate that 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 original SEND request contained a Success-report header field
with the value of "yes" it MUST be added to the SEND request intended
for the recipient. If the MSRP switch receives an success report from
the recipient of the private message, and the original request had
the Success-report header field present with a value of "yes",
the MSRP switch MUST create a success REPORT and MUST copy the contents
of the recipient's report to it. The REPORT MUST be sent to the
originator of the original SEND request. If the original SEND request
contained the Success-report header field with the value of "no", it
may be added to the SEND request intended for the recipient; but
any received reports from the recipient MUST NOT be forwarded to the
originator of the original SEND request.
If the original SEND request contained a Failure-report header field
with the value of "yes" or "partial" it MUST be added to the SEND
request intended for the recipient. The MSRP switch MUST follow the
Failure-Report handling described in section 7.1.1 of
If the MSRP switch receives a failure report from the recipient of the
private message, and the original SEND request had the Failure-report
header field present with the value of "yes" or "partial", the
MSRP switch MUST create a failure REPORT and MUST copy the
contents of the recipient's report to it. The REPORT MUST be sent
to the originator of the original SEND request. If the original SEND
request contained a Failure-report header field
with the value of "no", it may be added to the SEND request intended
for the recipient; but any received reports from the recipient
MUST NOT be forwarded to the originator of the original SEND request.
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 .
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 anonymous 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.
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 a display name.
A main difference is that a nickname is unique inside a chat
room to allow an unambiguous 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. 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).
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&nbhy;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&nbhy;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&nbhy;Nickname header
field, or if 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&nbhy;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
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
.
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.
If the participant no longer wants to be known by a nickname
in the conference, the participant can follow the method
described in .
The nickname element of the Use&nbhy;Nickname header MUST be
set to an empty quoted string.
Typically the conference focus acts as a notifier of the
SIP conference event package . 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> attribute to the <user> containing the
nickname string.
]]> 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 anonymous 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.
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 messaging.
The 'chatroom' SDP attribute has the following syntax:
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
. 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 .
Example of the 'chatroom' attribute for an MSRP media stream
that indicates the acceptance of nicknames and private
messages:
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.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.
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.
F3: The session established is acknowledged (details not
shown).
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.F1: Alice sends an MSRP NICKNAME request that contains her
proposed nicknames in the Set-Nickname header field.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.F3: Alice receives the response. She proposes a new
nickname in a second NICKNAME request.F4: The MSRP switch accepts the nickname proposal and
answers with a 200 response. 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.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.F2: The MSRP switch acknowledges the reception of the SEND
request with a 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.The rest of the message flows are analogous to the
previous. They are not shown here. 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.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.F2: The MSRP switch acknowledges the reception of the SEND
request with a 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. presents a flow diagram where
Alice registers her SIP AOR with the conference focus. The response will
contain a temp-gruu which can be used as an anonymous URI when joining the conference.
The temp-gruu is also used to send anonymous MSRP messages to and from the MSRP switch.F1: Alice constructs an REGISTER including an instance id in
her Contact header defined in
draft-ietf-sip-gruu.
F2: The chat room server accepts the registration
returning a "pub-gruu" and a "temp-gruu".
depicts a flow
diagram where Alice is utilizing the temporary GRUU when sending a
private message to BobF1: Alice builds a text message adding her registered temp-gruu
to the From header of the CPIM messageF2: The MSRP switch inspects the From header field and verifies
that the temp-gruuu in registered to Alice. If the temporary gruu
is valid, the MSRP acknowledges the reception of SEND request with
a 200 (OK) responseFlow F3 is not shown This specification defines a new MSRP method to be added to the
Methods sub-registry under the MSRP Parameter registry: NICKNAME.
See section for details.
This specification defines a new MSRP header to be added to
the header-field sub registry under the MSRP Parameter registry:
Use&nbhy;Nickname. See section for details.
This specification defines three new MSRP status codes to be added
to the Status-Code sub-registry under MSRP parameters.
The 427 status code indicates the failure to resolve the
recipient URI in the To header field of the Message/CPIM wrapper in the
SEND request. See section for details.
The 428 status code indicates that the recipient of a SEND request does
not support private messages. See section for details.
The 423 response indicates that the requested nickname is not allocated
to the user requesting it. See section for details.
This specification defines a new media level attribute in the
Session Description Protocol (SDP) Parameters registry: chatroom.
See section for details.
This document proposes extensions to the
Message Session Relay
Protocol . 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 transport
connection, as allowed by MSRP.
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.
The authors want to thank Eva Leppanen, Adamu Haruna,
Adam Roach and Matt Lepinski for providing comments.