Internet DRAFT - draft-ietf-simple-chat
draft-ietf-simple-chat
Network Working Group A. Niemi
Internet-Draft
Intended status: Standards Track M. Garcia-Martin
Expires: July 15, 2013 Ericsson
G. Sandbakken
Cisco Systems
January 11, 2013
Multi-party Chat Using the Message Session Relay Protocol (MSRP)
draft-ietf-simple-chat-18
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 chat sessions, or chat rooms,
using MSRP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on July 15, 2013.
Copyright Notice
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivations and Requirements . . . . . . . . . . . . . . . . . 6
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
4.1. Policy Attributes of the Chat Room . . . . . . . . . . . . 10
5. Creating, Joining, and Deleting a Chat Room . . . . . . . . . 11
5.1. Creating a Chat Room . . . . . . . . . . . . . . . . . . . 11
5.2. Joining a Chat Room . . . . . . . . . . . . . . . . . . . 12
5.3. Deleting a Chat Room . . . . . . . . . . . . . . . . . . . 14
6. Sending and Receiving Instant Messages . . . . . . . . . . . . 14
6.1. Regular Messages . . . . . . . . . . . . . . . . . . . . . 14
6.2. Private Messages . . . . . . . . . . . . . . . . . . . . . 17
6.3. MSRP reports and responses . . . . . . . . . . . . . . . . 19
6.4. Congestion Avoidance . . . . . . . . . . . . . . . . . . . 20
7. Nicknames . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. Using Nicknames within a Chat Room . . . . . . . . . . . . 22
7.2. Modifying a Nickname . . . . . . . . . . . . . . . . . . . 24
7.3. Removing a Nickname . . . . . . . . . . . . . . . . . . . 24
7.4. Nicknames in Conference Event Packages . . . . . . . . . . 25
8. The SDP 'chatroom' attribute . . . . . . . . . . . . . . . . . 25
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Joining a chat room . . . . . . . . . . . . . . . . . . . 27
9.2. Setting up a nickname . . . . . . . . . . . . . . . . . . 29
9.3. Sending a regular message to the chat room . . . . . . . . 30
9.4. Sending a private message to a participant . . . . . . . . 32
9.5. Chunked private message . . . . . . . . . . . . . . . . . 34
9.6. Nickname in a conference information document . . . . . . 34
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
10.1. New MSRP Method . . . . . . . . . . . . . . . . . . . . . 36
10.2. New MSRP Header . . . . . . . . . . . . . . . . . . . . . 36
10.3. New MSRP Status Codes . . . . . . . . . . . . . . . . . . 36
10.4. New SDP Attribute . . . . . . . . . . . . . . . . . . . . 37
11. Security Considerations . . . . . . . . . . . . . . . . . . . 37
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 39
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
14.1. Normative References . . . . . . . . . . . . . . . . . . . 40
14.2. Informative References . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
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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) [RFC4566] 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 MSRP sessions. 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 identifier 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.
Similar conferences supporting chat rooms are already available
today. For example, Internet Relay Chat (IRC) [RFC2810], Extensible
Messaging and Presence Protocol (XMPP): Core [RFC6120] based chat
rooms, and many other proprietary systems provide chat room
functionality. Specifying equivalent functionality for MSRP-based
systems eases interworking between these systems.
This document defines requirements, conventions, and extensions for
providing private messages and nickname management in centralized
chat rooms with MSRP. Participants in a chat room can be identified
by a pseudonym, and decide if their real identifier is disclosed to
other participants. This memo uses the SIP Conferencing Framework
[RFC4353] as a design basis. It also aims to be compatible with the
A Framework for Centralized Conferencing [RFC5239]. Should
requirements arise, future mechanisms for providing similar
functionality in generic conferences might be developed, for example,
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 chat rooms.
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
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[RFC2119], and indicate requirement levels for compliant
implementations.
This memo deals with tightly coupled SIP conferences defined in SIP
Conferencing Framework [RFC4353] and adopts the terminology from that
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.
Multi-party chat: an instance of a tightly coupled conference, in
which the media exchanged between the participants consist of MSRP
based instant messages. Also known as a chat room.
Chat Room: a synonym for a multi-party chat.
Chat Room URI: a URI that identifies a particular chat room, and is
a synonym of a Conference URI defined in RFC 4353 [RFC4353].
Sender: the chat room participant who originally created an instant
message and sent it to the chat room server for further delivery.
Recipient: the destination chat room participant(s). This defaults
to the full conference participant list minus the Instant Message
(IM) Sender.
MSRP switch: a media level entity that is a MSRP endpoint. It is a
special MSRP endpoint that receives MSRP messages and delivers
them to the other chat room participants. The MSRP switch has a
similar role to a conference mixer with the exception that the
MSRP switch does not actually "mix" together different input media
streams; it merely relays the messages between chat room
participants.
Private Instant Message: an instant message sent in a chat room
intended for a single participant. Generally speaking, a private
IM is seen by the MSRP switch, in addition to the sender and
recipient. A private IM is usually rendered distinctly from the
rest of the IMs, indicating that the message was a private
communication.
Anonymous URI: a URI concealing the participant's SIP AOR from the
other participants in the chat room. The allocation of such a URI
is out of scope of this specification. An anonymous URI must be
valid for the length of the chat room session and will be utilized
by the MSRP switch to forward messages to and from anonymous
participants. Privacy and anonymity are discussed in greater
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detail in RFC 3323 [RFC3323] and RFC 3325 [RFC3325].
Conference Event Package: a notification mechanism that allows
conference participants to learn conference information including
roster and state changes in a conference. This would typically be
A Session Initiation Protocol (SIP) Event Package for Conference
State [RFC4575] or Conference Event Package Data Format Extension
for Centralized Conferencing [RFC6502].
Identifier: a string used to recognize or establish as being a
particular user.
To log in: to enter identifying data, as a name or password, into a
chat room, so as to be able to do work with the chat room.
3. Motivations and Requirements
Although conference frameworks describing many types of conferencing
applications already exist, such as the Framework for Centralized
Conferencing [RFC5239] and the SIP Conferencing Framework [RFC4353],
the exact details of session-based instant messaging conferences
(chat rooms) 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 chat rooms 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:
REQ-1: A basic requirement is the existence of a chat room, where
participants can join and leave the chat room and get instant
messages exchanged to the rest of the participants.
REQ-2: A recipient of an instant message in a chat room must be able
to determine the identifier of the sender of the message.
Note that the actual identifier depends on the one which was
used by the sender when they joined the chat room.
REQ-3: A recipient of an instant message in a chat room must be able
to determine the identifier of the recipient of received
messages. For instance, the recipient of the message might
be the entire chat room or a single participant (i.e., a
private message). Note that the actual identifier may depend
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on the one which was used by the recipient when he or she
joined the chat room.
REQ-4: It must be possible to send a message to a single participant
within the chat room (i.e., a private instant message).
REQ-5: A chat room participant may have a nickname or pseudonym
associated with their real identifier.
REQ-6: It must be possible for a participant to change their
nickname during the progress of the chat room session.
REQ-7: It must be possible that a participant is only known by an
anonymous identifier and not their real identifier to the
rest of the chat room.
REQ-8: It must be possible for chat room participants to learn the
chat room capabilities described in this document.
4. Overview of Operation
Before a chat room can be entered, it must be created. Users wishing
to host a chat room themselves can of course do just that; their User
Agent (UA) simply morphs from an ordinary UA into a special purpose
one called a Focus UA. Another, commonly used setup is one where a
dedicated node in the network functions as a Focus UA.
Each chat room has an identifier of its own: a SIP URI that
participants use to join the chat room, e.g. by sending an INVITE
request to it. The conference focus processes the invitations, and
as such, maintains SIP dialogs with each participant. In a multi-
party chat, or chat room, MSRP is one of the established media
streams. Each chat room participant establishes an MSRP session with
the MSRP switch, which is a special purpose MSRP application. The
MSRP sessions can be relayed by one or more MSRP relays, which are
specified in RFC 4976 [RFC4976]. This is illustrated in Figure 1.
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MSRP Sessions
+--------------------------+
| |
+---+--+ +---+--+ |
| SIP | | SIP | |
| MSRP | | MSRP | +-----+-----+
|Client| |Client| | MSRP |
+---+--+ ++--+--+ | Relay |
| | \ +-----+-----+
SIP Dialogs | / +----+ |
| | \ | MSRP Sessions
+----+------+--+ | |
| | +-+-----+-----+
| Conference | | MSRP |
| Focus UA |........| Switch |
| | | |
+----+-------+-+ +-+-----+-----+
| \ | |
SIP Dialogs | | +------+ | MSRP Sessions
| \ / |
+---+--+ +-+--+-+ +-----+-----+
| SIP | | SIP | | MSRP |
| MSRP | | MSRP | | Relay |
|Client| |Client| +-----+-----+
+---+--+ +------+ |
| |
+--------------------------+
MSRP sessions
Figure 1: Multi-party chat overview shown with MSRP Relays and a
conference Focus UA
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 forwards messages between participants but doesn't
actually mix the streams in any way. The system is illustrated in
Figure 2.
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+------+
| MSRP |
|Client|
+------+ +--.---+ +------+
| MSRP | | | MSRP |
|Client| | _|Client|
+------._ | ,' +------+
`._ | ,'
`.. +----------+ ,'
`| |'
| MSRP |
| Switch |
,| |_
_,-'' +----------+ ``-._
+------.-' | `--+------+
| MSRP | | | MSRP |
|Client| | |Client|
+------+ | +------+
+---'--+
| MSRP |
|Client|
+------+
Figure 2: Multi-party chat in a Centralized Chat Room
Typically chat room participants also subscribe to a 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' identifiers, including their
nicknames.
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 chat room, 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 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
participant whose identifier has been learned, e.g. via a conference
event package. In this case the sender creates an MSRP SEND request
with a Message/CPIM wrapper whose To header contains not the chat
room URI but the recipient's URI. The MSRP switch then forwards the
SEND request to that recipient. This specification supports the
sending of private messages to one and only one recipient. However,
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if the recipient is logged in from different endpoints, the MSRP
switch will distribute the private message to each endpoint the
recipient is logged in.
We extend the current MSRP negotiation that takes place in SDP
[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. This is achieved by a new 'chatroom'
attribute in SDP (please refer to Section 8 for a detailed
description).
Naturally, when a participant wishes to leave a chat room, it sends a
SIP BYE request to the Focus UA and terminates the SIP dialog with
the focus and MSRP sessions with the MSRP switch.
This document assumes that each chat room is allocated its own SIP
URI. A user joining a chat room sends an INVITE request to that SIP
URI, and as a result, a new MSRP session is established between the
user and the MSRP switch. It is assumed that an MSRP session is
mapped to a chat room. If a user wants to join a second chat room,
he creates a different INVITE request, through a different SIP
dialog, which leads to the creation of a second MSRP session between
the user and the MSRP switch. Notice that these two MSRP sessions
can still be multiplexed over the same TCP connection as per regular
MSRP procedures. However, each chat room is associated to a unique
MSRP session and a unique SIP dialog.
4.1. Policy Attributes of the Chat Room
The Conference Framework with SIP [RFC4353] introduces the notion of
a Conference Policy as a complete set of rules governing a particular
conference. In the case of chat rooms, since they are a specialized
type of conferences, the notion of a Conference Policy exists and it
is sometimes extended with new chat-specific rules. This section
lists all the Conference Policy attributes used by the present
document and refers to sections in the document where the usage of
these attributes are described in greater detail.
Nicknames: Whether the chat room accepts users to be recognized
with a nickname. See Section 7, Section 7.1, and Section 8 for
details. Also, the scope of uniqueness of the nickname: the chat
room (conference instance), a realm or domain, a server, etc.
Nickname quarantine: The quarantine to be imposed to a nickname
once it is not currently in use (e.g., because the participant
holding this nickname abandons the chat room), prior to the wide
availability of this nickname to other users. This allows the
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initial holder of the nickname to join the chat room during the
quarantine period and claim the same nickname they were previously
using. See Section 11 for details.
Private messaging: Whether the chat room accepts users to send
private messages to other users of the chat room through the MSRP
switch. See Section 6.2 and Section 8 for details.
Deletion of the chat room: Whether the chat room can be deleted
when the creator leaves the chat room or through an out of band
mechanism. See Section 5.3 for details.
Simultaneous access: Whether a user can log from different
endpoints using the same identity. See Section 6.1 and
Section 6.2 for details.
Force TLS transport: Whether the MSRP switch accepts only TLS as an
MSRP transport, in an effort to guarantee confidentiality and
privacy. See Section 11 for details.
Maximum message size in congested MSRP sessions: The maximum size
of messages that can be distributed to a user over a congested
MSRP session. See Section 6.4 for details.
Chunk reception timer: The value of a time that controls the
maximum time that the MSRP switch is waiting for the reception of
different chunks belonging to the same message. If the timer
expires, the MSRP switch will discard the associated message
state. See Section 6.1 for details.
Supported wrapped media types: The list of media types that the
MSRP switch accepts in Message/CPIM wrappers sent from
participants. This list is included in the 'accept-wrapped-types'
attribute of the MSRP message media line in SDP. If the MSRP
switch accepts additional media types than those explicitly
listed, a "*" is added to the list. A single "*" indicates that
the chat room accepts any wrapped media type.
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 having
MSRP media, the methods defined by the SIP Conference Framework
[RFC4353] for creating conferences are directly applicable to a chat
room.
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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 chat room by sending an INVITE request
to the chat room URI. The chat room then uses regular SIP mechanisms
to authenticate the participant. This may include, e.g., client
certificates, SIP Digest authentication [RFC3261], asserted network
identity [RFC3325], SIP Identity header field [RFC4474], etc. As
long as the user is authenticated, the INVITE request is accepted by
the focus and the user is brought into the actual chat room.
This specification requires all instant messages to be wrapped in a
Message/CPIM wrapper [RFC3862]. Therefore, the 'accept-types'
attribute for the MSRP message media in both the SDP offer and answer
need to include at least the value 'Message/CPIM' (Notice that RFC
4575 [RFC4575] mandates this 'accept-types' attribute in SDP). If
the 'accept-types' attribute does not contain the value 'Message/
CPIM', the conference focus will reject the request. The actual
instant message payload type is negotiated in the 'accept-wrapped-
types' attribute in SDP (see RFC 4975 [RFC4975] for details). There
is no default wrapped type. Typical wrapped type values can include:
text/plain, text/html, image/jpeg, image/png, audio/mp3, etc. It is
RECOMMENDED that participant endpoints add an 'accept-wrapped-types'
attribute to the MSRP 'message' media line in SDP, where the
supported wrapped types are declared, as per RFC 4975 procedures
[RFC4975].
The MSRP switch needs to be aware of the URIs of the participant
(SIP, Tel, or IM URIs) in order to validate messages sent from this
participant prior to their forwarding. This information is known to
the focus of the conference. Therefore an interface between the
focus and the MSRP switch is assumed. However, the interface between
the focus and the MSRP switch is outside the scope of this document.
Conference-aware participants will detect 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.
Conference-unaware participants will not notice it is a focus, and
can not apply the additional mechanisms defined in this document.
Participants are also aware that the mixer is an MSRP switch due to
the presence of a 'message' media type and either TCP/MSRP or TCP/
TLS/MSRP as the protocol field in the media line of SDP [RFC4566].
The conference focus of a chat room MUST only use a Message/CPIM
[RFC3862] top-level wrapper as a payload of MSRP messages, and the
focus MUST declare it in the SDP offer or answer as per regular RFC
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4975 procedures [RFC4975]. This implies that if the conference focus
receives from a participant's endpoint an SDP offer that does not
include the value 'Message/CPIM' in the 'accept-types' attribute for
the MSRP message media line, the conference focus SHOULD either
reject the MSRP message media stream or the complete SDP offer by
using regular SIP or SDP procedures (e.g., creating an SDP answer
that sets to zero the port of the MSRP message media line, responding
the INVITE with a 488 response, etc.).
If the conference focus accepts the participant's SDP offer, when the
conference focus generates the SDP answer, it MUST set the 'accept-
types' attribute for the MSRP message media line to a value of
'Message/CPIM'. This specification requires all instant messages to
be wrapped in a Message/CPIM wrapper, therefore, the 'accept-types'
attribute in this SDP body contains a single value of 'Message/CPIM'.
The actual instant message payload type is negotiated in the 'accept-
wrapped-types' attribute in SDP (see RFC 4975 [RFC4975] for details).
The conference focus MAY also add an 'accept-wrapped-types' attribute
to the MSRP message media line in SDP containing the supported
wrapped types, according to the supported wrapped media types policy.
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 the user agent supports anonymous participation and the user
chooses to use it, the participant's UA SHOULD do at least one of
these options:
(a) provide an anonymous URI in SIP headers that otherwise reveal
identifiers. Please refer to RFC 3323 [RFC3323] for a detailed
description of which headers are subject to reveal identifiers
and how to populate them; or
(b) trust the conference focus and request privacy of their URI,
e.g, by means of the SIP Privacy header field [RFC3323], Network
asserted identity [RFC3325], or similar privacy mechanism.
If the participant has requested privacy, the conference focus MUST
expose a participant's anonymous URI through the conference event
package [RFC4575].
The conference focus of a chat room learns the supported chat room
capabilities in the endpoint by means of the 'chatroom' attribute
exchanged in the SDP offer/answer (please refer to Section 8 for a
detailed description). The conference focus MUST inform the MSRP
switch of the chat room capabilities of each participant that joins
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the chat room (note that the interface defined between the conference
focus and the MSRP switch is outside the scope of this
specification). This information allows the MSRP switch, e.g., to
avoid the distribution of private messages to participants whose
endpoints 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. The MSRP switch will terminate the MSRP
sessions with all the participants.
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 chat room, 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, it constructs an MSRP SEND
request according to the procedures specified in RFC 4975 [RFC4975].
The sender MAY choose the desired MSRP report model (e.g., populate
the Success-Report and Failure-Report MSRP header fields).
On sending a regular message the sender MUST populate the To header
of the Message/CPIM wrapper with the URI of the chat room. The
sender MUST also populate the From header of the Message/CPIM wrapper
with a proper identifier by which the user is recognized in the chat
room. Identifiers 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
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o An IM URI [RFC3860] representing the participant's instant
messaging address
o An Anonymous URI representing the participant's anonymous address
If the participant wants to remain anonymous, the participant's
endpoint MUST populate an anonymous URI in the From header of the
'Message/CPIM' wrapper. Other participants of the chat room will use
this anonymous URI in the To header of the 'Message/CPIM' wrapper
when sending private messages. Notice that in order for the
anonymity mechanism to work, the anonymous URI MUST NOT reveal the
participant's SIP AOR. The mechanism for acquiring an anonymous URI
is outside the scope of this specification.
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 of a participant. This
imposes a requirement for the focus of the conference to inform the
MSRP switch of the URIs by which the participant is known, in order
for the MSRP switch to validate messages. Section 6.3 provides
further information with the actions to be taken in case this
validation fails.
Then the MSRP switch should inspect the To header field of the
Message/CPIM wrapper. If the MSRP switch receives a message
containing several To header fields in the Message/CPIM wrapper the
MSRP switch MUST reject the MSRP SEND request with a 403 response, as
per procedures in RFC 4975 [RFC4975]. Then, if the To header field
of the Message/CPIM wrapper contains the chat room URI and there are
no other To header fields, the MSRP switch can generate a copy of the
SEND request to each of the participants in the chat room except the
sender. The MSRP switch MUST NOT modify the content received in the
SEND request. However, the MSRP switch MAY re-chunk any of the
outbound MSRP SEND requests.
When generating a copy of the SEND request to each participant in the
chat room, the MSRP switch MUST evaluate the wrapped media types that
the recipient is able to accept. This was learned through the
'accept-wrapped-types' attribute of the MSRP message media line in
SDP. If the MSRP switch is aware that the media type of the wrapped
content is not acceptable to the recipient, the MSRP switch SHOULD
NOT forward this message to that endpoint. Note that this version of
the specification does not require the MSRP switch to notify the
sender about this failure. Extensions to this specification may
improve handling of unknown media types.
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
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distribution to the rest of the participants. Instead, once the MSRP
switch has received the headers of the Message/CPIM wrapper it SHOULD
start the distribution process. But bear in mind that still the MSRP
switch SHOULD implement some sanity checking. Please refer to the
security considerations in Section 11 for further details.
When forwarding chunked messages as soon as they are received, the
Message/CPIM wrapper is only present at the beginning of the message,
typically within the first chunk. Subsequent chunks will contain the
rest of the message, but not the Message/CPIM headers. Therefore, an
MSRP switch that receives a subsequent message may face challenges in
determining the correct list of recipients of the message. An MSRP
switch that uses this fast forwarding procedure MUST temporarily
store the Message-Id of the MSRP message to correlate the different
chunks, as well as it MUST temporarily store the list of recipients
to which the initial chunks were delivered. The MSRP switch SHOULD
forward subsequent chunks only to those recipients who were sent the
initial chunks, except if the MSRP switch has knowledge that one of
the recipients of the initial chunks has dropped from the chat room.
This behavior also avoids new participants who joined the chat room
when the first chunk has been distributed to receive subsequent
chunks that would otherwise need to be discarded.
Once the MSRP switch receives the last chunk of a message, and that
chunk is successfully sent to each of the recipients, the MSRP switch
discards the temporary storage of MSRP Message-ID and the associated
list of recipients.
In some occasions, a sender might suffer a transport error condition
(such as loss of connectivity or depletion of battery) that makes the
sending of a message incomplete, e.g., some chunks were received by
the MSRP switch, but not all of them. This is a behavior already
considered in the core MSRP specification (see RFC 4975 [RFC4975]
Section 5.4). The problem in the context of a chat room lies with
the usage of temporary storage for fast forwarding. In order to
prevent attacks related to the exhaustion of temporary storage of
chunked messages, on receiving a first chunk of a message, where the
MSRP switch is using the fast forward method, the MSRP switch MUST
set a chunk reception timer for controlling the reception of the
remaining chunks.
This chunk reception timer can be re-set every time a new chunk of
the same message is received. When this timer fires, the MSRP switch
MUST consider that the sending of the message was aborted, and MAY
discard all the message state associated to it, including the
Message-ID and the list of recipients. Additionally, if this chunk
reception timer fires, the MSRP switch MAY choose to send an abort
chunk (i.e., one with the "#" flag set) to each to the recipients.
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This is just an optimization, since MSRP endpoints need to be able to
handle incomplete messages as per regular MSRP.
The specific value of this chunk reception timer is not standardized;
it is subject of local policy. However, it is recommended not to be
a short value. For example a time interval on the order of a normal
TCP timeout (i.e., around 540 seconds) would be reasonable. A value
on the order of a few seconds would not.
An MSRP endpoint that receives a SEND request from the MSRP switch
containing a Message/CPIM wrapper SHOULD first inspect the To header
field of the Message/CPIM wrapper. If the To header field is set to
the chat room URI, it should render it as a regular message that has
been distributed to all the participants in the chat room. Then the
MSRP endpoint SHOULD inspect the From header field of the Message/
CPIM wrapper to identify the sender. The From header field will
include a URI that identifies the sender. The endpoint might have
also received further identifier information through a subscription
to a conference event package.
It is possible that a participant, identified by a SIP Address of
Record or other valid URI, joins a chat room simultaneously from two
or more different SIP UAs. It is recommended that the MSRP switch
implements means to map a URI to two or more MSRP sessions. If the
policy of the chat room allows simultaneous access, the MSRP switch
MUST copy all regular messages intended to the recipient through each
MSRP session mapped to the recipient's URI.
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. The chat
room has local policy that determines whether private messages are
supported or not. A chat room can signal support for private
messages using the 'chatroom' attribute in SDP (please refer to
Section 8 for a detailed description).
When a chat room participant wishes to send a private instant message
to a participant in the chat room, it follows the same procedures for
creating a SEND request as for regular messages (Section 6.1). The
only difference is that the MSRP endpoint MUST populate a single To
header of the Message/CPIM wrapper with the identifier of the
intended recipient. The identifier can be SIP, TEL, and IM URIs
typically learned from the information received in notifications of a
conference event package.
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This version of the specification does not support sending a
private message to multiple recipients, i.e., the presence of
multiple To headers in the Message/CPIM wrapper of the MSRP SEND
request. This is due to added complexity, for example, with the
need to determine whether a message was not deliver to some of the
intended recipients. Implementations that still want to recreate
this function can send a series of single private messages, one
private message per intended recipient. The endpoint can
correlate this series of messages and create the effect of a
private message addressed to multiple recipients.
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
(i.e., the URI is a participant of this chat room). Section 6.3
provides further information with the actions to be taken in case
this validation fails.
Then the MSRP switch inspects the To header field of the Message/CPIM
wrapper. If the MSRP switch receives a message containing several To
header fields in the Message/CPIM wrapper the MSRP switch MUST reject
the MSRP SEND request with a 403 response, as per procedures in RFC
4975 [RFC4975]. Then the MSRP switch verifies that the To header of
the Message/CPIM wrapper matches the URI of a participant of the chat
room. If this To header field does not contain the URI of a
participant of the chat room or if the To header field cannot be
resolved (e.g., caused by a mistyped URI), the MSRP switch MUST
reject the request with a 404 response. This new 404 status code
indicates a failure to resolve the recipient URI in the To header
field of the Message/CPIM wrapper.
Notice the importance of the From and To headers in the Message/
CPIM wrapper. If an intermediary modifies these values, the MSRP
switch might not be able to identify the source or intended
destination of the message, resulting in a rejection of the
message.
Finally, the MSRP switch verifies that the recipient supports private
messages. If the recipient does not support private messages, the
MSRP switch MUST reject the request with a 428 response. This new
response 428 indicates that the recipient does not support private
messages. Any potential REPORT request that the MSRP switch sends to
the sender MUST include a Message/CPIM wrapper containing the
original From header field included in the SEND request and the To
header field of the original Message/CPIM wrapper. The MSRP switch
MUST NOT forward private messages to a recipient that does not
support private messaging.
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If successful, the MSRP switch should search its mapping table to
find the MSRP sessions established toward 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.
An MSRP endpoint that receives a SEND request from the MSRP switch
does the same validations as for regular messages (Section 6.1). If
the To header field is different from the chat room URI, the MSRP
endpoints knows that this is a private message. The endpoint should
render who it is from based on the value of the From header of the
Message/CPIM wrapper. The endpoint can also use the sender's
nickname, possibly learned via a conference event package, to render
such nickname rather than the sender's actual URI.
As with regular messages, if the policy of the chat room allows
simultaneous access, the MSRP switch MUST copy all private messages
intended to the recipient through each MSRP session mapped to the
recipient's URI.
6.3. MSRP reports and responses
This section discusses the common procedures for regular and private
messages with respect to MSRP reports and responses. Any particular
procedure affecting only regular messages or only private messages is
discussed in the previous Section 6.1 or Section 6.2, respectively.
MSRP switches MUST follow the success report and failure report
handling described in section 7 of RFC 4975 [RFC4975], complemented
with the procedures described in this section. The MSRP switch MUST
act as an MSRP endpoint receiver of the request according to section
5.3 of RFC 4975 [RFC4975].
If the MSRP switch receives an MSRP SEND request that does not
contain a Message/CPIM wrapper, the MSRP switch MUST reject the
request with a 415 response (specified in RFC 4975 [RFC4975]).
If the MSRP switch receives an MSRP SEND request where 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 sender of the
message or is not a valid participant of the chat room), the MSRP
switch MUST reject the request with a 403 response. In non-error
cases, the MSRP switch MUST construct responses according to section
7.2 of RFC 4975 [RFC4975].
When the MSRP switch forwards a SEND request, it MAY use any report
model in the copies intended for the recipients. The receiver
reports from the recipients MUST NOT be forwarded to the originator
of the original SEND request. This could lead to having the sender
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receiving multiple reports for a single MSRP request.
6.4. Congestion Avoidance
Congestion can occur when multiple heterogeneous interfaces are used
by a diversity of users who are participating in a chat room, and, in
particular, when paths become overloaded by any application. Some of
these users might have fast path capable of high throughputs while
other users might be slow paths with constrained throughputs. Some
paths might become congested only by the chat application; other
paths gets congested by other applications different than the chat
one. It is therefore possible that a subset of the participants of
the chat room are able to send and receive a large number of messages
in a short time or with large contents (e.g., pictures), whereas
others are not able to keep the pace.
Additionally, since MSRP uses a connection-oriented transport
protocol such as TCP, it is expected that TCP congestion control
mechanisms are activated if congestion occurs. Details on congestion
control are specified in RFC 5681 [RFC5681].
While this document does not mandate a particular MSRP-specific
mechanism to avoid congestion in any of the paths, something that is
deemed outside the scope of this document, this document provides
some recommendations for implementors to consider.
It is RECOMMENDED that MSRP switches implement one or more MSRP-
specific strategies to detect and avoid congestion. Possible
strategies (but definitely not a comprehensive list) include:
o If the MSRP switch is writing data to a send buffer and detects
that the send buffer associated to that TCP connection is getting
full (e.g., close to 80% of its capacity), the MSRP switch marks
the associated MSRP sessions making use of that TCP connection as
"congested".
o Prior to sending a new MSRP message to a user, the MSRP switch
verifies the congested flag associated to that MSRP session. If
the MSRP session is marked as congested, the MSRP switch can apply
a congestion avoidance mechanism, such as:
* The MSRP switch MAY discard regular MSRP messages sent to that
user while the congestion flag is raised for the user's TCP
connection. In order to inform the user of the congestion, the
MSRP switch MAY send a regular MSRP message to the user whose
congestion flag is raised. This message indicates that some
other messages are being discarded due to network congestion.
However, it should be noted that this message can get stuck at
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MSRP switch, if the path is fully congested, i.e., it may not
be delivered anyhow.
* The MSRP can implement a temporary policy to disallow the
distribution of messages larger than a certain size to MSRP
sessions marked as congested. Similarly, the user should be
informed of this fact by the MSRP switch sending a regular MSRP
message indicating this condition.
o If the MSRP switch determines that the congestion flag associated
to a given TCP connection has been raised for quite some time (on
the order of a few minutes), or if the interface is down, this may
be considered as an indication that the TCP connection has not
been able to recover from a congestion state. The MSRP switch MAY
close this congested TCP connection, as well as the MSRP session
and SIP session.
7. Nicknames
A common characteristic of existing chat room services is that
participants have the ability to present themselves with a nickname
to the rest of the participants of the chat room. It is used for
easy reference of participants in the chat room, and can also provide
anonymous participants with a meaningful descriptive name.
A nickname is a useful construct in many use cases, of which MSRP
chat is but one example. It is associated with a URI of which the
participant is known to the focus. Therefore, if a user joins the
chat room under the same URI from multiple devices, he or she may
request the same nickname across all these devices.
A nickname is a user selectable appearance of which the participant
wants to be known to the other participants. 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 unambiguously be associated to a single user in the scope of the
chat room (conference instance). This scope is similar to having a
nickname unique per user inside a chat room from Extensible Messaging
and Presence Protocol [RFC6120]. 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].
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7.1. Using Nicknames within a Chat Room
This memo provides a mechanism to reserve a nickname for a
participant for as long as the participant 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
exist (for example, a web page reservation system), although they are
outside the scope of this document.
A chat room participant who has established an MSRP session with the
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. This nickname string MUST NOT be zero octets in length and
MUST NOT be more than 1023 octets in length. Last, MSRP NICKNAME
requests MUST NOT include Success-Report or Failure-Report header
fields.
Bear in mind that nickname strings, like the rest of the MSRP
message, use the UTF-8 transformation format [RFC3629].
Therefore, a character may result encoded in more than one octet.
An MSRP switch that receives a NICKNAME request containing a
Use-Nickname header field SHOULD first verify whether the policy of
the chat room allows the nickname functionality. If not allowed, the
MSRP switch MUST reject the request with a 403 response, as per RFC
4975 [RFC4975].
If the policy of the chat room allows the usage of nicknames, any new
nickname requested MUST be prepared and compared with nicknames
already in use or reserved following the rules defined in Preparation
and Comparison of Nicknames [I-D.ietf-precis-nickname].
This mitigates the problem of nickname duplication, but it does not
solve a problem whereby users can choose similar (but different)
characters to represent two different nicknames. For example, "BOY"
and "B0Y" are different nicknames which can mislead users. The
former uses the capital letter "O" while the latter uses the number
zero "0". In many fonts the letter "O" and the number zero "0" might
be quite similar, and difficult to be perceived as different
characters. Chat rooms MAY provide a mechanism to mitigate
confusable nicknames.
In addition to preparing and comparing following the rules above, the
MSRP switch SHOULD only allow the reservation of an already used
nickname, if the same user (e.g., identified by the SIP AOR) that is
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currently using the nickname is making this subsequent request. This
may include, e.g., allowing that the participant's URI may use the
same nickname when the participant has joined the chat room from
different devices under the same URI. The participant's
authenticated identifier can be derived after a successful SIP Digest
Authentication [RFC3261], be included in a trusted SIP P-Asserted-
Identity header field [RFC3325], be included in a valid SIP Identity
header field [RFC4474], or be derived from any other present or
future SIP authentication mechanism. Once the MSRP switch has
validated that the participant is entitled to reserve the requested
nickname, the MSRP switch verifies if the suggested nickname can be
accepted (see below).
The reservation of a nickname can fail in several cases. If the
NICKNAME request contains a malformed value in the Use-Nickname
header field, the MSRP switch MUST answer the NICKNAME request with a
424 response code. This can be the case when the value of the
Use-Nickname header field does not conform to the syntax.
The reservation of a nickname can also fail if the value of the
Use-Nickname header field of the NICKNAME request is a reserved word
(not to be used as a nickname by any user) or that particular value
is already in use by another user. In this case the MSRP switch MUST
answer the NICKNAME request with a 425 response code.
In both error conditions (receiving a 424 or 425 response code), the
nickname usage is considered failed; the nickname is not allocated to
this user. The user can select a different nickname and retry
another NICKNAME request.
If the MSRP switch is able to accept the suggested nickname to be
used by this user, the MSRP switch MUST answer the NICKNAME request
with a 200 response as per regular MSRP procedures.
As indicated earlier, this specification defines a new MSRP header
field: "Use-Nickname". The Use-Nickname header field carries a
nickname string. This specification defines the usage of the
Use-Nickname header field in NICKNAME requests. If need arises,
usages of the Use-Nickname header field in other MSRP methods should
be specified separately.
According to RFC 4975 [RFC4975], MSRP uses the UTF-8 transformation
format [RFC3629]. The syntax of the MSRP NICKNAME method and the
"Use-Nickname" header field is built upon the MSRP formal syntax
[RFC4975] using the Augmented Backus-Naur Form (ABNF) [RFC5234].
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ext-method =/ NICKNAMEm
NICKNAMEm = %x4E.49.43.4B.4E.41.4D.45 ; NICKNAME in caps
ext-header =/ Use-Nickname
; ext-header defined in RFC 4975
Use-Nickname = "Use-Nickname:" SP nickname
nickname = DQUOTE 1*1023(qdtext / qd-esc) DQUOTE
; qdtext and qd-esc defined in RFC 4975
Note that, according to RFC 4975 [RFC4975], "quoted-string" admits a
subset of UTF-8 characters [RFC3629]. Please refer to Section 9 of
RFC 4975 [RFC4975] for more details.
Once the MSRP switch has reserved a nickname and has bound it to a
URI (e.g., a SIP Address-of-Record), the MSRP server MAY allow the
usage of the same nickname by the same user (identified by the same
URI, such as a SIP AoR) over a second MSRP session. This might be
the case if the user joins the same chat room from a different SIP
User Agent. In this case, the user MAY request the same or a
different nickname than that used in conjunction with the first MSRP
session; the MSRP server MAY accept the usage of the same nickname by
the same user. The MSRP switch MUST NOT automatically assign the
same nickname to more than one MSRP session established from the same
URI, because this can create confusion to the user as whether the
same nickname is bound to the second MSRP session.
7.2. Modifying a Nickname
Typically a participant will reserve a nickname as soon as the
participant joins the chat room. But it is also possible for a
participant to modify his/her own nickname and replace it with 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. Removing a Nickname
If the participant no longer wants to be known by a nickname in the
chat room, the participant can follow the method described in
Section 7.2. The nickname element of the Use-Nickname header MUST be
set to an empty quoted string.
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7.4. Nicknames in Conference Event Packages
Typically the conference focus acts as a notifier of the conference
event package, RFC 4575 [RFC4575]. It is RECOMMENDED that conference
foci and endpoints support RFC 6502 [RFC6502] for providing
information regarding the conference, and in particular, supplying
information of the roaster of the conference. It is also RECOMMENDED
that conference foci and endpoints support RFC 6501 [RFC6501], which
extends the <user> element originally specified in RFC 4575 [RFC4575]
with a new 'nickname' attribute. This allows endpoints to learn the
nicknames of participants of the chat room.
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 local policy of 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's 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. Furthermore, if
Alice replied to this message, she would do it to the whole roster.
Because of this, the MSRP switch also keeps 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 value attribute [RFC4566] that MAY be included in
conjunction with an MSRP media stream (i.e., when an m= line in SDP
indicates "TCP/MSRP" or "TCP/TLS/MSRP"). The 'chatroom' attribute
without further modifiers (e.g., chat-tokens) indicates that the
endpoint supports the procedures described in this document for
transferring MSRP messages to/from a chat room. The 'chatroom'
attribute can be complemented with additional modifiers that further
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indicate the intersection of support and 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' attribute merely indicates the capabilities supported
and allowed by the local policy. This attribute is not a negotiation
subject to the SDP offer/answer model [RFC3264], but instead a
declaration. Therefore, a 'chatroom' attribute included in an SDP
answer does not need to be a subset of the values included in the
'chatroom' attribute of its corresponding SDP offer. Consequently,
an SDP answer MAY contain a 'chatroom' attribute even if its
corresponding SDP offer did not include it.
On doing subsequent SDP offer/answer [RFC3264] exchanges pertaining
to the same session, the 'chatroom' attribute MAY be modified with
respect an earlier SDP offer/answer exchange. The new value of this
attribute indicate the current support and local policy, meaning that
some restrictions can apply now or might have been removed. If the
'chatroom' attribute is not included in a subsequent SDP offer/
answer, but is corresponding MSRP stream is still in place, it
indicates that support for the procedures indicated in this document
are disabled.
The 'chatroom' SDP attribute has the following Augmented BNF (ABNF)
[RFC5234] syntax:
attribute =/ chatroom-attr
; attribute defined in RFC 4566
chatroom-attr = chatroom-label [":" chat-token
*(SP chat-token)]
chatroom-label = "chatroom"
chat-token = (nicknames-token / private-msg-token /
ext-token)
nicknames-token = "nickname"
private-msg-token = "private-messages"
ext-token = private-token / standard-token
private-token = toplabel "." *(domainlabel ".") token
; toplabel defined in RFC 3261
; domainlabel defined in RFC 3261
; token defined in RFC 3261
standard-token = token
A given 'chat-token' value MUST NOT appear more than once in a
'chatroom' attribute.
A conference focus that includes the 'nicknames' token in the session
description is signaling that the MSRP switch supports and the chat
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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
An example of a 'chatroom' attribute for an MSRP media stream where
the endpoint, e.g., an MSRP switch, does not allow either nicknames
nor private messages.
a=chatroom
The 'chatroom' attribute allows extensibility with the addition of
new tokens. No IANA registry is provided at this time, since no
extensions are expected at the time of this writing. Extensions to
the 'chatroom' attribute can be defined in IETF documents or as
private vendor extensions.
Extensions defined in IETF document MUST follow the 'standard-token'
ABNF previously defined. In this type of extensions, care must be
taken in the selection of the token to avoid a clash with any of the
tokens previously defined.
Private extensions MUST follow the 'private-token' ABNF previously
defined. The 'private-token' MUST include the DNS name of the
vendor. Then the token is reversed in order to avoid clashes of
tokens. The following is an example of a extension named "foo.chat"
by a vendor "example.com"
a=chatroom:nickname private-messages com.example.chat.foo
Note that feature names created by different organizations are not
intended to have the same semantics or even interoperate.
9. Examples
9.1. Joining a chat room
Figure 3 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.
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Alice Conference focus
| |
|F1: (SIP) INVITE |
|----------------------->|
|F2: (SIP) 200 OK |
|<-----------------------|
|F3: (SIP) ACK |
|----------------------->|
| |
Figure 3: 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.
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: 290
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 client.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
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 forces the reception of messages wrapped in Message/
CPIM wrappers. It also includes 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: 290
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
F3: The session established is acknowledged (details not shown).
9.2. Setting up a nickname
Figure 4 shows an example of Alice setting up a nickname using the
chat room as provider. Her first proposal is not accepted because
that proposed nickname is already in use. Then, she makes a second
proposal with a new nickname. This second proposal is accepted.
Alice MSRP switch
| |
|F1: (MSRP) NICKNAME |
|----------------------->|
|F2: (MSRP) 425 |
|<-----------------------|
|F3: (MSRP) NICKNAME |
|----------------------->|
|F4: (MSRP) 200 |
|<-----------------------|
| |
Figure 4: Flow diagram of a user setting up her nickname
F1: Alice sends an MSRP NICKNAME request that contains her proposed
nicknames in the Use-Nickname header field.
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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$
F2: The MSRP switch analyzes the existing allocation of nicknames and
detects that the nickname "Alice the great" is already provided to
another participant in the chat room. The MSRP switch answers with a
425 response.
MSRP d93kswow 425 Nickname reserved or already in use
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
-------d93kswow$
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$
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$
9.3. Sending a regular message to the chat room
Figure 5 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.
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Alice MSRP switch Bob Charlie
| | | |
| F1: (MSRP) SEND | | |
|--------------------->| F3: (MSRP) SEND | |
| F2: (MSRP) 200 |----------------------->| |
|<---------------------| F4: (MSRP) SEND | |
| |------------------------------->|
| | F5: (MSRP) 200 OK | |
| |<-----------------------| |
| | F6: (MSRP) 200 OK | |
| |<------------------------------ |
| | | |
| | | |
Figure 5: Sending a regular message to the chat room
F1: Alice builds a text message and wraps it in a Message/CPIM
wrapper. She addresses the message to the chat room. She encloses
the resulting Message/CPIM wrapper 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: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello guys, how are you today?
-------3490visdm$
F2: The MSRP switch acknowledges the reception of the SEND request
with a 200 (OK) response.
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
-------3490visdm$
F3: The MSRP switch creates a new MSRP SEND request that contains the
received Message/CPIM wrapper and sends it to Bob.
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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: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello guys, how are you today?
-------490ej23$
Since the received message is addressed to the chat room URI in the
From header of the Message/CPIM header, Bob knows that this is a
regular message distributed all participants in the chat room, rather
that a private message addressed to him.
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 6 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
| | |
| F1: (MSRP) SEND | |
|--------------------->| F3: (MSRP) SEND |
| F2: (MSRP) 200 |----------------------->|
|<---------------------| F4: (MSRP) 200 |
| |<-----------------------|
| | |
Figure 6: Sending a private message to Bob
F1: Alice builds a text message and wraps it in a Message/CPIM
wrapper. She addresses the message to Bob's URI, which she learned
from a notification in the conference event package. She encloses
the resulting Message/CPIM wrapper in an MSRP SEND request and sends
it to the MSRP switch via the existing TCP connection.
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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@example.com>
From: <sip:alice@example.com>
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob.
-------6959ssdf$
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
-------6959ssdfm$
F3: The MSRP switch creates a new MSRP SEND request that contains the
received Message/CPIM wrapper and sends it only to Bob. Bob can
distinguish the sender in the From header of the Message/CPIM
wrapper. He also identifies this as a private message due to the
presence of his own SIP AOR in the To header field of the Message/
CPIM wrapper.
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@example.com>
From: <sip:alice@atlanta.example.com>
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob.
-------9v9s2$
F4: Bob acknowledges the reception of the SEND request with a 200
(OK) response.
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MSRP 9v9s2 200 OK
To-Path: msrp://chat.example.com:5678/jofofo3;tcp
From-Path: msrp://client.biloxi.example.com:4923/49dufdje2;tcp
Message-ID: d9fghe982
-------9v9s2$
9.5. Chunked private message
The MSRP message below depicts the example of the same private
message described in Section 9.4, but now the message is split in two
chunks. The MSRP switch must wait for the complete set of Message/
CPIM headers before distributing the messages.
MSRP 7443ruls SEND
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Message-ID: aft4to
Byte-Range: 1-*/174
Content-Type: message/cpim
To: <sip:bob@example.com>
From: <sip:alice@example.com>
-------7443ruls$
MSRP 7443ruls SEND
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Message-ID: aft4to
Byte-Range: 68-174/174
Content-Type: message/cpim
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob
-------7443ruls$
9.6. Nickname in a conference information document
Figure 7 depicts an XML Conference Information Document received in a
SIP NOTIFY request as a notification to the XCON Conference Event
Package, RFC 6502 [RFC6502]. The Conference Information Document
follows the XCON Data Model specified in RFC 6501 [RFC6501].
The Conference Information Document of Figure 7 presents information
of two users who are participating in the conference (see each of the
<user> elements). Each participant is bound to a nickname, shown in
the 'nickname' attribute of the <user> element.
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NOTE: The purpose of Figure 7 is to show the user-to-nickname
relation. It is believed that the example is correct, according
to RFC 6501 [RFC6501]. In case of contradictions between this
specification and RFC 6501 [RFC6501], the latter has precedence
over this one.
<?xml version="1.0" encoding="UTF-8"?>
<conference-info
xmlns="urn:ietf:params:xml:ns:conference-info"
xmlns:xcon="urn:ietf:params:xml:ns:xcon-conference-info"
entity="sip:chatroom22@chat.example.com"
state="full" version="1">
<!--
CONFERENCE INFO
-->
<conference-description>
<subject>MSRP nickname example</subject>
</conference-description>
<!--
CONFERENCE STATE
-->
<conference-state>
<user-count>2</user-count>
</conference-state>
<!--
USERS
-->
<users>
<user entity="sip:bob@example.com"
state="full"
xcon:nickname="Dopey Donkey">
<display-text>Bob Hoskins</display-text>
</user>
<!--
USER
-->
<user entity="sip:alice@atlanta.example.com"
state="full"
xcon:nickname="Alice the great">
<display-text>Alice Kay</display-text>
</user>
</users>
</conference-info>
Figure 7: Nickname in a conference information document
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10. IANA Considerations
10.1. New MSRP Method
This specification defines a new MSRP method to be added to the
Methods sub-registry of the Message Session Relay Protocol (MSRP)
Parameters registry:
NICKNAME
See section Section 7 for details.
10.2. New MSRP Header
This specification defines a new MSRP header to be added to the
Header Field sub-registry of the Message Session Relay Protocol
(MSRP) Parameters registry:
Use-Nickname
See Section 7 for details.
10.3. New MSRP Status Codes
This specification defines three new MSRP status codes to be added to
the Status-Code sub-registry of the Message Session Relay Protocol
(MSRP) parameters registry.
The 404 status code indicates the failure to resolve the recipient's
URI in the To header field of the Message/CPIM wrapper in the SEND
request, e.g, due to an unknown recipient. See Section 6.2 for
details.
The 424 status code indicates a failure in allocating the requested
nickname due to a malformed syntax in the Use-Nickname header field.
See Section 7 for details.
The 425 status code indicates a failure in allocating the requested
nickname because the requested nickname in the Use-Nickname header
field is reserved or is already in use by another user. See
Section 7 for details.
The 428 status code indicates that the recipient of a SEND request
does not support private messages. See Section 6.2 for details.
Table 1 summarizes the IANA registration data with respect to new
MSRP status codes:
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+-------+-------------------------------------+-----------+
| Value | Description | Reference |
+-------+-------------------------------------+-----------+
| 404 | Failure to resolve recipient's URI | RFC XXXX |
| 424 | Malformed nickname | RFC XXXX |
| 425 | Nickname reserved or already in use | RFC XXXX |
| 428 | Private messages not supported | RFC XXXX |
+-------+-------------------------------------+-----------+
Table 1: New status codes
10.4. New SDP Attribute
This specification defines a new media-level attribute in the Session
Description Protocol (SDP) Parameters registry. The registration
data is as follows:
Contact: Miguel Garcia <miguel.a.garcia@ericsson.com>
Phone: +34 91 339 1000
Attribute name: chatroom
Long-form attribute name: Chat Room
Type of attribute: media level only
This attribute is not subject to the charset attribute
Description: This attribute identifies support and local policy
allowance for a number of chat room related functions
Specification: RFC XXXX
See section Section 8 for details.
11. Security Considerations
This document proposes extensions to the Message Session Relay
Protocol [RFC4975]. Therefore, the security considerations of that
document apply to this document as well.
A chat room is by its nature a potential Denial-of-Service (DoS)
accellerator as it takes a message from one entity and sends that to
many. Implementers of both UAs and switches need to carefully
consider the set of anti-DoS measures that are appropriate for this
application and switch implementations in particular ought to include
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appropriate anti-DoS features. The details of what is appropriate
will vary over time and will also depend on the specific needs of the
implementation and so cannot be specified here.
If the participant's SIP user agent does not understand the "isfocus"
feature tag [RFC3840], it will not know that it is connected to a
conference instance. The participant might not be notified that the
participant's MSRP client will try to send messages to the MSRP
switch having potentially multiple recipients. If the participant's
MSRP client does not support the extensions of this specification, it
is unlikely that it will try to send a message using 'Message/CPIM'
wrapper content type [RFC3862], and the MSRP switch will reject the
request with a 415 response [RFC4975]. Still if a participant's MSRP
client does create a message with a valid 'Message/CPIM' wrapper
content type [RFC3862] having the To header set to the URI of the
chat room and the From header set to the URI of which the participant
is known to the chat room, the participant might be unaware that the
message can be forwarded to multiple recipients. Equally if the To
header is set to a valid URI of a recipient known to the chat room,
the message can be forwarded as a private message without the
participant knowing.
To mitigate these problems, when the chat room detects that a user
agent does not support the procedures of this document (i.e., when
the SIP User Agent is not chat room aware), the MSRP switch SHOULD
send a regular MSRP message indicating that the SIP User Agent is
actually part of a chat room, and that all the messages that the user
sends correctly formated will be distributed to a number of
participants. Additionally, the MSRP switch SHOULD also send a
regular MSRP text message including the list of participants in the
chat room, so that the user becomes aware of the roster.
If a participant wants to avoid security concerns on the path between
himself and the MSRP switch (e.g., being eavesdropped, faked packet
injection, or packet corruption), the participant's user agent can
force the usage of MSRP over a TLS [RFC5246] transport connection.
This is negotiated in the SDP offer/answer exchange as per regular
RFC 4975 [RFC4975] procedures. This negotiation will result in both
endpoints establishing a TLS [RFC5246] transport connection that is
used to exchange MSRP messages. The MSRP switch may also have local
policy that forces the usage of TLS transport for all MSRP sessions,
something that is also negotiated in SDP as per regular RFC 4975
[RFC4975] procedures.
Nicknames are used to show the appearance of the participants of the
chat room. A successful take over of a nickname from a participant
might lead to private messages to be sent to the wrong destination.
The recipient's URI will be different from the URI associated to the
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original owner of the nickname, but the sender might not notice this.
To avoid takeovers the MSRP switch MUST make sure that a nickname is
unique inside a chat room. Also the security consideration for any
authenticated identity mechanisms used to validate the SIP AOR will
apply to this document as well. The chat room has a policy that
determines the time that a nickname is still reserved to its holder,
once it is no longer in used. This allows, e.g., a user that
accidentally looses its connectivity, to re-connect to the chat room
and keep on using the same nickname. It is up to the policy of the
chat room to determine if a nickname that has been previously used by
another participant of the chat room can be reserved or not.
Section 7.1 discusses the problem of similar but different nicknames
(e.g., thanks to the use of similar characters), and chat rooms MAY
provide a mechanism to mitigate confusable nicknames.
Recipients of instant messages should be cautious with the rendering
of content, which can be malicious in nature. This includes, but it
is not only restricted to, the reception of HTML and Javascript
scripts, executable code, phishing attempts, etc. Endpoints SHOULD
always request permission from the user before executing one of these
actions.
It must be noted that endpoints using TLS client side certificate
with real names in the certificates will not be anonymous to the MSRP
switch they connect to. While the name in the certificate might not
be used by MSRP, the server will have a certificate with the actual
name in it.
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 (Huawei), who provided extensive review
and improvements throughout the document.
13. Acknowledgments
The authors want to thank Eva Leppanen, Adamu Haruna, Adam Roach,
Matt Lepinski, Mary Barnes, Ben Campbell, Paul Kyzivat, Adrian
Georgescu, Nancy Greene, Cullen Jennings, Flemming Andreasen, Suresh
Krishnan, Christer Holmberg, Saul Ibarra, Enrico Marocco, Alexey
Melnikov, Peter Saint-Andre, Stephen Farrel, and Martin Stiemerling
for providing comments.
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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.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[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.
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 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.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
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September 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for
Centralized Conferencing", RFC 5239, June 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, September 2009.
[RFC6501] Novo, O., Camarillo, G., Morgan, D., and J. Urpalainen,
"Conference Information Data Model for Centralized
Conferencing (XCON)", RFC 6501, March 2012.
[RFC6502] Camarillo, G., Srinivasan, S., Even, R., and J.
Urpalainen, "Conference Event Package Data Format
Extension for Centralized Conferencing (XCON)", RFC 6502,
March 2012.
[I-D.ietf-precis-nickname]
Saint-Andre, P., "Preparation and Comparison of
Nicknames", draft-ietf-precis-nickname-05 (work in
progress), November 2012.
14.2. Informative References
[RFC2810] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
April 2000.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
Niemi, et al. Expires July 15, 2013 [Page 41]
Internet-Draft Multi-party Chat MSRP January 2013
Authors' Addresses
Aki Niemi
Email: aki.niemi@iki.fi
Miguel A. Garcia-Martin
Ericsson
Calle Via de los Poblados 13
Madrid, ES 28033
Spain
Email: miguel.a.garcia@ericsson.com
Geir A. Sandbakken
Cisco Systems
Philip Pedersens vei 20
N-1366 Lysaker
Norway
Phone: +47 67 125 125
Email: geirsand@cisco.com
URI: http://www.cisco.com
Niemi, et al. Expires July 15, 2013 [Page 42]
