SIMPLE WG B. Campbell, Ed.
Internet-Draft Estacado Systems
Expires: August 24, 2005 R. Mahy, Ed.
Airespace
C. Jennings, Ed.
Cisco Systems, Inc.
February 20, 2005
The Message Session Relay Protocol
draft-ietf-simple-message-sessions-10.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 24, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes the Message Session Relay Protocol (MSRP), a
protocol for transmitting a series of related instant messages in the
context of a session. Message sessions are treated like any other
Campbell, et al. Expires August 24, 2005 [Page 1]
Internet-Draft MSRP February 2005
media stream when setup via a rendezvous or session setup protocol
such as the Session Initiation Protocol (SIP).
Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction and Background . . . . . . . . . . . . . . . . 4
3. Applicability of MSRP . . . . . . . . . . . . . . . . . . . 5
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 6
5. Key Concepts . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 MSRP Framing and Message Chunking . . . . . . . . . . . . 8
5.2 MSRP Addressing . . . . . . . . . . . . . . . . . . . . . 9
5.3 MSRP Transaction and Report Model . . . . . . . . . . . . 10
5.4 MSRP Connection Model . . . . . . . . . . . . . . . . . . 11
6. MSRP URLs . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1 MSRP URL Comparison . . . . . . . . . . . . . . . . . . . 14
6.2 Resolving MSRP Host Device . . . . . . . . . . . . . . . . 14
7. Method-Specific Behavior . . . . . . . . . . . . . . . . . . 15
7.1 Constructing Requests . . . . . . . . . . . . . . . . . . 15
7.1.1 Delivering SEND requests . . . . . . . . . . . . . . . 16
7.1.2 Sending REPORT requests . . . . . . . . . . . . . . . 18
7.1.3 Failure REPORT Generation . . . . . . . . . . . . . . 19
7.2 Constructing Responses . . . . . . . . . . . . . . . . . . 20
7.3 Receiving Requests . . . . . . . . . . . . . . . . . . . . 21
7.3.1 Receiving SEND requests . . . . . . . . . . . . . . . 21
7.3.2 Receiving REPORT requests . . . . . . . . . . . . . . 22
8. Using MSRP with SIP . . . . . . . . . . . . . . . . . . . . 23
8.1 SDP Offer-Answer Exchanges for MSRP Sessions . . . . . . . 23
8.1.1 URL Negotiations . . . . . . . . . . . . . . . . . . . 25
8.1.2 Path Attributes with Multiple URLs . . . . . . . . . . 26
8.1.3 SDP Connection and Media Lines . . . . . . . . . . . . 27
8.1.4 Updated SDP Offers . . . . . . . . . . . . . . . . . . 28
8.1.5 Example SDP Exchange . . . . . . . . . . . . . . . . . 28
8.1.6 Connection Negotiation . . . . . . . . . . . . . . . . 29
8.2 MSRP User Experience with SIP . . . . . . . . . . . . . . 29
9. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 30
10. Response Code Descriptions . . . . . . . . . . . . . . . . . 32
10.1 200 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.2 400 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.3 403 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.4 408 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.5 413 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.6 415 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.7 423 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.8 426 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.9 481 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.10 501 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.11 506 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Campbell, et al. Expires August 24, 2005 [Page 2]
Internet-Draft MSRP February 2005
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 34
11.1 Basic IM session . . . . . . . . . . . . . . . . . . . . 34
11.2 Message with XHTML Content . . . . . . . . . . . . . . . 36
11.3 Chunked Message . . . . . . . . . . . . . . . . . . . . 36
11.4 System Message . . . . . . . . . . . . . . . . . . . . . 36
11.5 Positive Report . . . . . . . . . . . . . . . . . . . . 37
11.6 Forked IM . . . . . . . . . . . . . . . . . . . . . . . 37
12. Extensibility . . . . . . . . . . . . . . . . . . . . . . . 40
13. CPIM compatibility . . . . . . . . . . . . . . . . . . . . . 40
14. Security Considerations . . . . . . . . . . . . . . . . . . 41
14.1 Transport Level Protection . . . . . . . . . . . . . . . 42
14.2 S/MIME . . . . . . . . . . . . . . . . . . . . . . . . . 43
14.3 Other Security Concerns . . . . . . . . . . . . . . . . 44
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 45
15.1 MSRP Port . . . . . . . . . . . . . . . . . . . . . . . 45
15.2 MSRP URL Schemes . . . . . . . . . . . . . . . . . . . . 45
15.3 SDP Transport Protocol . . . . . . . . . . . . . . . . . 46
15.4 SDP Attribute Names . . . . . . . . . . . . . . . . . . 46
15.4.1 Accept Types . . . . . . . . . . . . . . . . . . . . 46
15.4.2 Wrapped Types . . . . . . . . . . . . . . . . . . . 46
15.4.3 Max Size . . . . . . . . . . . . . . . . . . . . . . 47
15.4.4 Path . . . . . . . . . . . . . . . . . . . . . . . . 47
16. Change History . . . . . . . . . . . . . . . . . . . . . . . 47
16.1 draft-ietf-simple-message-sessions-10 . . . . . . . . . 47
16.2 draft-ietf-simple-message-sessions-09 . . . . . . . . . 48
16.3 draft-ietf-simple-message-sessions-08 . . . . . . . . . 48
16.4 draft-ietf-simple-message-sessions-07 . . . . . . . . . 49
16.5 draft-ietf-simple-message-sessions-06 . . . . . . . . . 49
16.6 draft-ietf-simple-message-sessions-05 . . . . . . . . . 50
16.7 draft-ietf-simple-message-sessions-04 . . . . . . . . . 50
16.8 draft-ietf-simple-message-sessions-03 . . . . . . . . . 50
16.9 draft-ietf-simple-message-sessions-02 . . . . . . . . . 51
16.10 draft-ietf-simple-message-sessions-01 . . . . . . . . . 51
16.11 draft-ietf-simple-message-sessions-00 . . . . . . . . . 51
16.12 draft-campbell-simple-im-sessions-01 . . . . . . . . . . 52
17. Contributors and Acknowledgments . . . . . . . . . . . . . . 52
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
18.1 Normative References . . . . . . . . . . . . . . . . . . 52
18.2 Informational References . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 55
Intellectual Property and Copyright Statements . . . . . . . 56
Campbell, et al. Expires August 24, 2005 [Page 3]
Internet-Draft MSRP February 2005
1. Conventions
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 [5].
This document consistently refers to a "message" as a complete unit
of MIME or text content. In some cases a message is split and
delivered in more than one MSRP request. Each of these portions of
the complete message is called a "chunk".
2. Introduction and Background
A series of related instant messages between two or more parties can
be viewed as part of a "message session", that is, a conversational
exchange of messages with a definite beginning and end. This is in
contrast to individual messages each sent completely independently.
The SIMPLE Working Group describes messaging schemes that only track
individual messages as "page-mode" messages, whereas messaging that
is part of a "session" with a definite start and end is called
"session-mode" messaging.
Page-mode messaging is enabled in SIMPLE via the SIP [4]MESSAGE
method [18]. Session-mode messaging has a number of benefits [19]
over page-mode messaging however, such as explicit rendezvous,
tighter integration with other media types, direct client-to-client
operation, and brokered privacy and security.
This document defines a session-oriented instant message transport
protocol called the Message Session Relay Protocol (MSRP), whose
sessions can be included in an offer or answer [3] using the Session
Description Protocol(SDP [2]). The exchange is carried by some
signaling protocol, such as the Session Initiation Protocol (SIP
[4]). This allows a communication user agent to offer a messaging
session as one of the possible media types in a session. For
instance, Alice may want to communicate with Bob. Alice doesn't know
at the moment whether Bob has his phone or his IM client handy, but
she's willing to use either. She sends an invitation to a session to
the address of record she has for Bob, sip:bob@example.com. Her
invitation offers both voice and an IM session. The SIP services at
example.com forward the invitation to Bob at his currently registered
clients. Bob accepts the invitation at his IM client and they begin
a threaded chat conversation.
When a user uses an IM URL, other documents define how DNS can be
used to map this to a particular protocol to establish the session
such as SIP. SIP can use an offer answer model to transport the MSRP
URLs for the media in SDP. This document defines how the
Campbell, et al. Expires August 24, 2005 [Page 4]
Internet-Draft MSRP February 2005
offer-answer exchange works to establish MSRP connections and how
messages are sent across the MSRP protocol but it does not deal with
the issues of mapping an IM URL to a session establishment protocol.
This session model allows message sessions to be integrated into
advanced communications applications with little to no additional
protocol development. For example, during the above chat session,
Bob decides Alice really needs to be talking to Carol. Bob can
transfer [17] Alice to Carol, introducing them into their own
messaging session. Messaging sessions can then be easily integrated
into call-center and dispatch environments utilizing third-party call
control [16] and conferencing [15] applications.
3. Applicability of MSRP
MSRP is not designed for use as a standalone protocol. MSRP MUST be
used only in the context of a rendezvous mechanism meeting the
following requirements:
The rendezvous mechanism MUST provide both MSRP URLs associated
with an MSRP session to each of the participating endpoints. The
rendezvous mechanism MUST implement mechanisms to provide these
URLs securely - they MUST NOT be made available to an untrusted
third party or be easily discoverable.
The rendezvous mechanism MUST provide mechanisms for the
negotiation of any supported MSRP extensions that are not
backwards compatible.
The rendezvous mechanism MUST be able to natively transport im:
URIs or automatically translate im: URIs [24] into the addressing
identifiers of the rendezvous protocol.
To use a rendezvous mechanism with MSRP, an RFC must be prepared
describing how it exchanges MSRP URIs and meets these requirements
listed here. This document provides such a description for the use
of MSRP in the context of SIP and SDP.
SIP meets these requirements for a rendezvous mechanism. The MSRP
URLs are exchanged using SDP in an offer/answer exchange via SIP.
The exchanged SDP can also be used to negotiate MSRP extensions.
This SDP can be secured using any of the mechanisms available in SIP,
including using the sips mechanism to ensure transport security
across intermediaries and S/MIME for end-to-end protection of the SDP
entity. SIP can carry arbitrary URIs (including im: URIs) in the
Request-URI, and procedures are available to map im: URIs to sip: or
sips: URIs. It is expected that initial deployments of MSRP will use
SIP as its rendezvous mechanism.
Campbell, et al. Expires August 24, 2005 [Page 5]
Internet-Draft MSRP February 2005
4. Protocol Overview
MSRP is a text-based, connection-oriented protocol for exchanging
arbitrary (binary) MIME content, especially instant messages. This
section is a non-normative overview of how MSRP works and how it is
used with SIP.
MSRP sessions are typically arranged using SIP the same way a session
of audio or video media is setup. One SIP user agent (Alice) sends
the other (Bob) a SIP invitation containing an offered
session-description which includes a session of MSRP. The receiving
SIP user agent can accept the invitation and include an answer
session-description which acknowledges the choice of media. Alice's
session description contains an MSRP URL that describes where she is
willing to receive MSRP requests from Bob, and vice-versa. (Note:
Some lines in the examples are removed for clarity and brevity.)
Alice sends to Bob:
INVITE sip:alice@atlanta.example.com SIP/2.0
To: <sip:bob@biloxi.example.com>
From: <sip:alice@atlanta.example.com>;tag=786
Call-ID: 3413an89KU
Content-Type: application/sdp
c=IN IP4 atlanta.example.com
m=message 7654 msrp/tcp *
a=accept-types:text/plain
a=path:msrp://atlanta.example.com:7654/jshA7we;tcp
Bob sends to Alice:
SIP/2.0 200 OK
To: <sip:bob@biloxi.example.com>;tag=087js
From: <sip:alice@atlanta.example.com>;tag=786
Call-ID: 3413an89KU
Content-Type: application/sdp
c=IN IP4 biloxi.example.com
m=message 12763 msrp/tcp *
a=accept-types:text/plain
a=path:msrp://biloxi.example.com:12763/kjhd37s2s2;tcp
Alice sends to Bob:
ACK sip:alice@atlanta.example.com SIP/2.0
To: <sip:bob@biloxi.example.com>;tag=087js
From: <sip:alice@atlanta.example.com>;tag=786
Campbell, et al. Expires August 24, 2005 [Page 6]
Internet-Draft MSRP February 2005
Call-ID: 3413an89KU
MSRP defines two request types, or methods. SEND requests are used
to deliver a complete message or a chunk (a portion of a complete
message), while REPORT requests report on the status of an earlier
SEND request. When Alice receives Bob's answer, she checks to see if
she has an existing connection to Bob. If not, she opens a new
connection to Bob using the URL he provided in the SDP. Alice then
delivers a SEND request to Bob with her initial message, and Bob
replies indicating that Alice's request was received successfully.
MSRP a786hjs2 SEND
To-Path: msrp://biloxi.example.com:12763/kjhd37s2s2;tcp
From-Path: msrp://atlanta.example.com:7654/jshA7we;tcp
Message-ID: 87652
Byte-Range: 1-25/25
Content-Type: text/plain
Hey Bob, are you there?
-------a786hjs2$
MSRP a786hjs2 200 OK
To-Path: msrp://atlanta.example.com:7654/jshA7we;tcp
From-Path: msrp://biloxi.example.com:12763/kjhd37s2s2;tcp
Message-ID: 87652
Byte-Range: 1-25/25
-------a786hjs2$
Alice's request begins with the MSRP start line, which contains a
transaction identifier that is also used as a final boundary marker.
Next she includes the path of URLs to the destination in the To-Path
header, and her own URL in the From-Path header. In this typical
case there is just one "hop", so there is only one URL in each path
header field. She also includes a message ID which she can use to
correlate responses and status reports with the original message.
Next she puts the actual content. Finally she closes the request
with an end line: seven hyphens, the transaction identifier /
boundary marker and a "$" to indicate this request contains the end
of a complete message.
If Alice wants to deliver a very large message, she can split the
message into chunks and deliver each chunk in a separate SEND
request. The message ID corresponds to the whole message, so the
receiver can also use it to reassemble the message and tell which
chunks belong with which message. Chunking is described in more
detail in Section 5.1. The Byte-Range header identifies the portion
of the message carried in this chunk and the total size of the
Campbell, et al. Expires August 24, 2005 [Page 7]
Internet-Draft MSRP February 2005
message.
Alice can also specify what type of reporting she would like in
response to her request. If Alice requests positive acknowledgments,
Bob sends a REPORT request to Alice confirming the delivery of her
complete message. This is especially useful if Alice sent a series
of SEND request containing chunks of a single message. More on
requesting types of reports and errors is described in Section 5.3.
Alice and Bob generally choose their MSRP URLs in such a way that is
difficult to guess the exact URL. Alice and Bob can reject requests
to URLs they are not expecting to service, and can correlate the
specific URL with the probable sender. Alice and Bob can also use
TLS [1] to provide channel security over this hop. To receive MSRP
requests over a TLS protected connection, Alice or Bob could
advertise URLs with the "msrps" scheme instead of "msrp."
This document specifies MSRP behavior only for peer-to-peer sessions,
that is, sessions crossing only a single hop. However, work to
specify behavior for MSRP relay devices [20] (referred to herein as
"relays") is occurring as a separate effort. MSRP is designed with
the expectation that MSRP can carry URLs for nodes on the far side of
such relays. For this reason, a URL with the "msrps" scheme makes no
assertion about the security properties of other hops, just the next
hop. The user agent knows the URL for each hop, so it can verify
that each URL has the desired security properties.
MSRP URLs are discussed in more detail in Section 6.
An adjacent pair of busy MSRP nodes (for example two relays) can
easily have several sessions, and exchange traffic for several
simultaneous users. The nodes can use existing connections to carry
new traffic with the same destination host, port, transport protocol,
and scheme. MSRP nodes can keep track of how many sessions are using
a particular connection and close these connections when no sessions
have used them for some period of time. Connection management is
discussed in more detail in Section 5.4.
5. Key Concepts
5.1 MSRP Framing and Message Chunking
Messages sent using MSRP can be very large and can be delivered in
several SEND requests, where each SEND request contains one chunk of
the overall message. Long chunks may be interrupted in
mid-transmission to ensure fairness across shared transport
connections. To support this, MSRP uses a boundary based framing
mechanism. The start line of an MSRP request contains a unique
Campbell, et al. Expires August 24, 2005 [Page 8]
Internet-Draft MSRP February 2005
boundary string that is used to indicate the end of the request.
Following the boundary string at the end of the body data, there is a
flag that indicates whether this is the last chunk of data for this
message or whether the message will be continued in a subsequent
chunk. There is also a Byte-Range header in the request that
indicates the overall position of this chunk inside the complete
message.
For example, the following snippet of two SEND requests demonstrates
a message that contains the text "abcdEFGH" being sent as two chunks.
MSRP dkei38sd SEND
Message-ID: 456
Byte-Range: 1-4/8
Content-Type: text/plain
abcd
-------dkei38sd+
MSRP dkei38ia SEND
Message-ID: 456
Byte-Range: 5-8/8
Content-Type: text/plain
EFGH
-------dkei38ia$
This chunking mechanism allows a sender to interrupt a chunk part of
the way through sending it. The ability to interrupt messages allows
multiple sessions to share a TCP connection, and for large messages
to be sent efficiently while not blocking other messages that share
the same connection. Any chunk that is larger than 2048 octets MUST
be interruptible. While MSRP would be simpler to implement if each
MSRP session used its own TCP connection, that approach would
circumvent the congestion avoidance features of TCP.
5.2 MSRP Addressing
MSRP entities are addressed using URLs. The MSRP URL schemes are
defined in Section 6. The syntax of the To-Path and From-Path
headers each allow for a list of URLs. This was done to allow the
protocol to work with gateways or relays defined in the future, to
provide a complete path to the end recipient. When two MSRP nodes
communicate directly they need only one URL in the To-Path list and
one URL in the From-Path list.
Campbell, et al. Expires August 24, 2005 [Page 9]
Internet-Draft MSRP February 2005
5.3 MSRP Transaction and Report Model
A sender sends MSRP requests to a receiver. The receiver MUST
quickly accept or reject the request. If the receiver initially
accepted the request, it still may then do things that take
significant time to succeed or fail. For example, if the receiver is
an MSRP to XMPP [28] gateway, it may forward the message over XMPP.
The XMPP side may later indicate that the request did not work. At
this point, the MSRP receiver may need to indicate that the request
did not succeed. There are two important concepts here: first, the
hop by hop delivery of the request may succeed or fail; second, the
end result of the request may be successfully processed or not. The
first type of status is referred to as "transaction status" and may
be returned in response to a request. The second type of status is
referred to as "request status" and may be returned in a REPORT
transaction.
The original sender of a request can indicate if they wish to receive
reports for requests that fail, and can independently indicate if
they wish to receive reports for requests that succeed. A receiver
only sends a success REPORT if it knows that the request succeeded,
and the sender requested a success report. A receiver only sends a
failure REPORT if the request failed and the sender requested failure
reports.
This document describes the behavior of MSRP endpoints. MSRP
relays or gateways are likely to have additional conditions that
indicate a failure REPORT should be sent, such as the failure to
receive a positive response from the next hop.
Two header fields control the sender's desire to receive reports.
The header "Success-Report" can have a value of "yes" or "no" and the
"Failure-Report" header can have a value of "yes", "no", or
"partial".
The combinations of reporting are needed to meet the various
scenarios of currently deployed IM systems. Success-Report might be
"no" in many public systems to reduce load but is used in some
current enterprise systems, such as systems used for securities
trading. A Failure-Report value of "no" is useful for sending system
messages such as "the system is going down in 5 minutes" without
causing a response explosion to the sender. A Failure-Report of
"yes" is used by many systems that wish to notify the user if the
message failed. A Failure-Report of "partial" is a way to report
errors except timeouts. The timeout error reporting requires the
sending hop to run a timer and that receiving hop to send an
acknowledgment to stop the timer. Some systems don't want the
overhead of doing this so choose not to but still allow error
Campbell, et al. Expires August 24, 2005 [Page 10]
Internet-Draft MSRP February 2005
responses to be sent in many cases and these systems can use
"partial".
5.4 MSRP Connection Model
When MSRP wishes to send a request to a peer identified by an MSRP
URL, it first needs a transport connection, with the appropriate
security properties, to the host specified in the URL. If the sender
already has such a connection, that is, one associated with the same
host, port, and URL scheme, then it SHOULD reuse that connection.
When a new MSRP session is created, the offerer MUST act as the
"active" endpoint, meaning that it is responsible for opening the
transport connection to the answerer, if a new connection is
required. However, this requirement MAY be weakened if standardized
mechanisms for negotiating the connection direction become available,
and is implemented by both parties to the connection.
Likewise, the active endpoint MUST immediately issue a SEND request.
This initial SEND request MAY have a empty body, or MAY carry
content.
When an element needs to form a new connection, it looks at the URL
to decide on the type of connection (TLS, TCP, etc.) then connects to
the host indicated by the URL, following the URL resolution rules in
Section 6.2. Connections using the msrps: scheme MUST use TLS. The
SubjectAltName in the received certificate MUST match the hostname
part of the URL and the certificate MUST be valid, including having a
date that is valid and being signed by an acceptable certificate
authority. At this point the device that initiated the connection
can assume that this connection is with the correct host.
If the connection used mutual TLS authentication, and the TLS client
presented a valid certificate, then the element accepting the
connection can immediately know the identity of the connecting host.
When mutual TLS authentication is not used, the listening device MUST
wait until it receives a request on the connection, at which it
infers the identity of the connecting device from the associated
session description.
When the first request arrives, its To-Path header field should
contain a URL that the listening element handed out in the SDP for a
session. The element that accepted the connection looks up the URL
in the received request, and determines which session it matches. If
a match exists, the node MUST assume that the host that formed the
connection is the host to which this URL was given. If no match
exists, the node MUST reject the request with a 481 response. The
node MUST also check to make sure the session is not already in use
Campbell, et al. Expires August 24, 2005 [Page 11]
Internet-Draft MSRP February 2005
on another connection. If the session is already in use, it MUST
reject the request with a 506 response.
If it were legal to have multiple connections associated with the
same session, a security problem would exist. If the initial SEND
request is not protected, an eavesdropper might learn the URL, and
use it to insert messages into the session via a different
connection.
If a connection fails for any reason, then an MSRP endpoint MUST
consider any sessions associated with the connection as also having
failed. When an endpoint notices such a failure, it MAY attempt to
re-create any such sessions. If it chooses to do so, it MUST use new
SDP exchange, for example, in a SIP re-INVITE or UPDATE [11] request.
If a replacement session is successfully created, endpoints MAY
attempt to resend any content for which delivery on the original
session could not be confirmed. If it does this, the Message-ID
values for the resent messages MUST match those used in the initial
attempts. If the receiving endpoint receives more than one message
with the same Message-ID. It SHOULD assume that the messages are
duplicates. It MAY take any action based on that knowledge, but
SHOULD NOT present the duplicate messages to the user without warning
of the duplication.
In this situation, the endpoint MUST ensure that the Message-ID of
each distinct (i.e. non-duplicate) message is unique in the context
of both the original session and the replacement session.
When endpoints create a new session in this fashion, the chunks for a
given logical message MAY be split across the sessions. However,
endpoints SHOULD NOT split chunks between sessions under non-failure
circumstances.
If an endpoint attempts to re-create a failed session in this manner,
it MUST NOT assume that the MSRP URLs in the SDP will be the same as
the old ones.
A connection SHOULD not be closed while there are sessions associated
with it.
6. MSRP URLs
URLs using the MSRP and MSRPS schema are used to identify a session
of instant messages at a particular MSRP device. MSRP URLs are
ephemeral; an MSRP device will generally use a different MSRP URL for
each distinct session. An MSRP URL generally has no meaning outside
of the associated session.
Campbell, et al. Expires August 24, 2005 [Page 12]
Internet-Draft MSRP February 2005
An MSRP URL follows a subset of the URL syntax in Appendix A of
RFC2396bis [9], with a scheme of "msrp" or "msrps". The syntax is
described in Section 9.
The constructions for "userinfo", and "unreserved" are detailed in
RFC2396bis [9]. In order to allow IPV6 addressing, the construction
for hostport is that used for SIP in RFC3261. URLs designating MSRP
over TCP MUST include the "tcp" transport parameter.
Since this document only specifies MSRP over TCP, all MSRP URLs
herein use the "tcp" transport parameter. Documents that provide
bindings on other transports should define respective parameters
for those transports.
An MSRP URL hostport field identifies a participant in a particular
MSRP session. If the hostport contains a numeric IP address, it MUST
also contain a port. The session-id part identifies a particular
session of the participant. The absence of the session-id part
indicates a reference to an MSRP host device, but does not
specifically refer to a particular session.
A scheme of "msrps" indicates the underlying connection MUST be
protected with TLS.
MSRP has an IANA registered recommended port defined in Section 15.1.
This value is not a default, as the URL negotiation process described
herein will always include explicit port numbers. However, the URLs
SHOULD be configured so that the recommended port is used whenever
appropriate. This makes life easier for network administrators who
need to manage firewall policy for MSRP.
The server part will typically not contain a userinfo component, but
MAY do so to indicate a user account for which the session is valid.
Note that this is not the same thing as identifying the session
itself. If a userinfo component exists, it MUST be constructed only
from "unreserved" characters, to avoid a need for escape processing.
Escaping MUST NOT be used in an MSRP URL. Furthermore, a userinfo
part MUST NOT contain password information.
The limitation of userinfo to unreserved characters is an
additional restriction to the userinfo definition in RFC2396bis.
That version allows reserved characters. The additional
restriction is to avoid the need for escaping.
The following is an example of a typical MSRP URL:
msrp://host.example.com:8493/asfd34;tcp
Campbell, et al. Expires August 24, 2005 [Page 13]
Internet-Draft MSRP February 2005
6.1 MSRP URL Comparison
MSRP URL comparisons MUST be performed according to the following
rules:
1. The scheme must match. Scheme comparison is case insensitive.
2. If the hostpart contains an explicit IP address, and/or port,
these are compared for address and port equivalency. Otherwise,
hostpart is compared as a case insensitive character string.
3. If the port exists explicitly in either URL, then it must match
exactly. An URL with an explicit port is never equivalent to
another with no port specified.
4. The session-id part is compared as case sensitive. A URL without
a session-id part is never equivalent to one that includes one.
5. URLs with different "transport" parameters never match. Two URLs
that are identical except for transport are not equivalent. The
transport parameter is case-insensitive.
6. Userinfo parts are not considered for URL comparison.
Path normalization is not relevant for MSRP URLs. Escape
normalization is not required due to character restrictions in the
formal syntax.
6.2 Resolving MSRP Host Device
An MSRP host device is identified by the server part of an MSRP URL.
If the server part contains a numeric IP address and port, they MUST
be used as listed.
If the server part contains a host name and a port, the connecting
device MUST determine a host address by doing an A or AAAA DNS query,
and use the port as listed.
If a connection attempt fails, the device SHOULD attempt to connect
to the addresses returned in any additional A or AAAA records, in the
order the records were presented.
This process assumes that the connection port is always known
prior to resolution. This is always true for the MSRP URL uses
described in this document, that is, URLs exchanged in the SDP
offer and answer. The introduction of relays may create
situations where this is not the case. For example, the MSRP URL
Campbell, et al. Expires August 24, 2005 [Page 14]
Internet-Draft MSRP February 2005
that a user enters into a client to configure it to use a relay
may be intended to be easily remembered and communicated by
humans, and therefore is likely to omit the port. Therefore, the
relay specification [20] may describe additional steps to resolve
the port number.
MSRP devices MAY use other methods for discovering other such
devices, when appropriate. For example, MSRP endpoints may use other
mechanisms to discover relays, which are beyond the scope of this
document.
7. Method-Specific Behavior
7.1 Constructing Requests
To form a new request, the sender creates a unique transaction
identifier and uses this and the method name to create an MSRP
request start line. Next, the sender places the target path in a
To-Path header, and the sender's URL in a From-Path header. If
multiple URLs are present in the To-Path, the leftmost is the first
URL visited; the rightmost URL is the last URL visited. The
processing then becomes method specific. Additional method-specific
headers are added as described in the following sections.
After any method-specific headers are added, processing continues to
handle a body, if present. A body in a Non-SEND request MUST NOT be
longer than 2048 octets. If the request has a body, it must contain
a Content-Type header field. It may contain other MIME specific
headers. The Content-Type header MUST be the last header line. The
body MUST be separated from the headers with an extra CRLF. Note
that, if no body is present, no blank line will be present between
the headers and the boundary marker below.
The boundary marker that terminates the body MUST be preceded by a
CRLF that is not part of the body and then seven "-" (minus sign)
characters. After the boundary marker, there MUST be a flag
character. If the chunk represents the data that forms the end of
the complete message, the flag value MUST be a "$". If sender is
abandoning an incomplete message, and intends to send no further
chunks in that message, it MUST be a "#". Otherwise it MUST be a
"+".
If the request contains a body, the sender MUST ensure that the
closing sequence (a CRLF, seven hyphens, and the transaction
identifier) is not present in the body. If the closing sequence is
present in the body, the sender MUST choose a new transaction
identifier that is not present in the body, and add the closing
sequence, including the "$", "#", or "+" character, and a final CRLF.
Campbell, et al. Expires August 24, 2005 [Page 15]
Internet-Draft MSRP February 2005
Some implementations may choose to implement this such that if they
find the closing sequence in the body of the message they are
sending, simply interrupting the message at that point and starting a
new transaction with a different transaction identifier to carry the
rest of the body. Other implementation may choose to scan the data
an ensure that the body does not contain the transaction identifier
before they start sending the transaction.
Finally, requests which have no body MUST NOT contain a Content-Type
header or any other MIME specific header. Requests without bodies
MUST contain a closing sequence after the final header.
Once a request is ready for delivery, the sender follows the
connection management (Section 5.4) rules to forward the request over
an existing open connection or create a new connection.
7.1.1 Delivering SEND requests
When an endpoint has a message to deliver, it first generates a new
unique Message-ID. This ID MUST be unique within the scope of the
session. If necessary, it breaks the message into chunks. It then
generates a SEND request for each chunk, following the procedures for
constructing requests (Section 7.1).
Each chunk MUST contain a Message-ID header field containing the
Message-ID. If the sender wishes non-default status reporting, it
MUST insert a Failure-Report and/or Success-Report header field with
an appropriate value. All chunks of the same message MUST use the
same Failure-Report and Success-Report values in their SEND requests.
If success reports are requested, i.e. the value of the
Success-Report header is "yes", the sending device MAY wish to run a
timer of some value that makes sense for its application and take
action if a success Report is not received in this time. There is no
universal value for this timer. For many IM applications, it may be
2 minutes while for some trading systems it may be under a second.
Regardless of whether such a timer is used, if the success report has
not been received by the time the session is ended, the device SHOULD
inform the user.
If the value of "Failure-Report" is set to "yes", then the sender of
the request runs a timer. If a 200 response to the transaction is
not received within 30 seconds from the time the last byte of the
transaction is sent, the element MUST inform the user that the
request probably failed. If the value is set to "partial", then the
element sending the transaction does not have to run a timer, but
MUST inform the user if receives a non-recoverable error response to
the transaction.
Campbell, et al. Expires August 24, 2005 [Page 16]
Internet-Draft MSRP February 2005
If no Success-Report header is present in a SEND request, it MUST be
treated the same as a Success-Report header with value of "no". If
no Failure-Report header is present, it MUST be treated the same as a
Failure-Report header with value of "yes". REPORT requests MUST have
the same Message-ID header value as the request they are reporting
on. They MAY also have the Byte-Range of the chunk they are
reporting on. If an MSRP endpoint receives a REPORT for a Message-ID
it does not recognize, it SHOULD silently ignore the REPORT.
Success-Report and Failure-Report MUST NOT be present for any method
other than SEND. MSRP nodes MUST NOT send REPORT requests in
response to report requests. MSRP Nodes MUST NOT send MSRP responses
to REPORT requests.
The Byte-Range header value contains a starting value (range-start)
followed by a "-", an ending value (range-end) followed by a "/", and
finally the total length. The first octet in the message has a
position of one, rather than a zero.
The first chunk of the message SHOULD, and all subsequent chunks MUST
include a Byte-Range header field. The range-start field MUST
indicate the position of the first byte in the body in the overall
message (for the first chunk this field will have a value of one).
The range-end field SHOULD indicate the position of the last byte in
the body, if known. It MUST take the value of "*" if the position is
unknown, or if the request needs to be interruptible. The total
field SHOULD contain the total size of the message, if known. The
total field MAY contain a "*" if the total size of the message is not
known in advance. The sender MUST send all chunks in Byte-Range
order. (However, the receiver cannot assume the requests will be
delivered in order, as intervening relays may have changed the
order.)
To ensure fairness over a connection, senders MUST NOT send chunks
with a body larger than 2048 octets unless they are prepared to
interrupt them (meaning that any chunk with a body of greater than
2048 octets will have a "*" character in the range-end field). A
sender can use one of the following two strategies to satisfy this
requirement. The sender is STRONGLY RECOMMENDED to send messages
larger than 2048 octets using as few chunks as possible, interrupting
chunks (at least 2048 octets long) only when other traffic is waiting
to use the same connection. Alternatively, the sender MAY simply
send chunks in 2048 octet increments until the final chunk. Note
that the former strategy results in markedly more efficient use of
the connection. All MSRP nodes MUST be able to receive chunks of any
size from zero octets to the maximum number of octets they can
receive for a complete message. Senders SHOULD NOT break messages
into chunks smaller than 2048 octets, except for the final chunk of a
Campbell, et al. Expires August 24, 2005 [Page 17]
Internet-Draft MSRP February 2005
complete message.
A SEND request is interrupted while a body is in the process of being
written to the connection by simply noting how much of the message
has already been written to the connection, then writing out the
boundary string to end the chunk. It can then be resumed in a
another chunk with the same Message-ID and a Byte-Range header range
start field containing the position of the first byte after the
interruption occurred.
SEND requests larger than 2048 octets MUST be interrupted to send
pending responses or REPORT requests. If multiple SEND requests from
different sessions are concurrently being sent over the same
connection, the device SHOULD implement some scheme to alternate
between them such that each concurrent request gets a chance to send
some fair portion of data at regular intervals suitable to the
application.
The sender MUST NOT assume that a message is received by the peer
with the same chunk allocation with which it was sent. An
intervening relay could possibly break SEND requests into smaller
chunks, or aggregate multiple chunks into larger ones.
The default disposition of bodies is "render". If the sender wants
different disposition, it MAY insert a Content-Disposition header.
Since MSRP is a binary protocol, transfer encoding is always
"binary", and transfer-encoding paramaters MUST NOT be present.
7.1.2 Sending REPORT requests
REPORT requests are similar to SEND requests, except that report
requests MUST NOT include Success-Report or Failure-Report header
fields, and MUST contain a Status header field. REPORT requests MUST
contain the Message-ID header from the original SEND request.
If an MSRP element receives a REPORT for a Message-ID it does not
recognize, it SHOULD silently ignore the REPORT.
An MSRP endpoint MUST be able to generate success REPORT requests.
REPORT requests will normally not include a body, as the REPORT
request header fields can carry sufficient information in most cases.
However, REPORT requests MAY include a body containing additional
information about the status of the associated SEND request. Such a
body is informational only, and the sender of the REPORT request
SHOULD NOT assume that the recipient pays any attention to the body.
Since REPORT requests are not interruptible, the size of such a body
MUST NOT exceed 2048 octets.
Campbell, et al. Expires August 24, 2005 [Page 18]
Internet-Draft MSRP February 2005
An endpoint MUST send a success report if it successfully receives a
SEND request which contained a Success-Report value of "yes" and
either contains a complete message, or contains the last chunk needed
to complete the message. This request is sent following the normal
procedures (Section 7.1), with a few additional requirements.
The endpoint inserts a To-Path header field containing the From-Path
value from the original request, and a From-Path header containing
the URL identifying itself in the session. The endpoint then inserts
a Status header field with a namespace of "000", a short-status of
"200" and a relevant Reason phrase, and a Message-ID header field
containing the value from the original request.
The namespace field denotes the context the short-status field.
The namespace value of "000" means the short-status should be
interpreted in the same way as the matching MSRP transaction
response code. If a future specification uses the short-status
field for some other purpose, it MUST define a new namespace field
value.
The endpoint MUST NOT send a success report for a SEND request that
either contained no Success-Report header field, or contained such a
field with a value of "no". That is, if no Success-Report header
field is present, it is treated identically to one with a value of
"no."
7.1.3 Failure REPORT Generation
If an MSRP endpoint receives a SEND request that it cannot process
for some reason, and the Failure-Report header either was not present
in the original request, or had a value of "yes", it SHOULD simply
include the appropriate error code in the transaction response.
However, there may be situations where the error cannot be determined
quickly, such as when the endpoint is a gateway that must wait for a
downstream network to indicate an error. In this situation, it MAY
send a 200 OK response to the request, and then send a failure REPORT
request when the error is detected.
If the endpoint receives a SEND request with a Failure-Report header
field value of "no", then it MUST NOT send a failure REPORT request,
and MUST NOT send a transaction response. If the value is "partial",
it MUST NOT send a 200 transaction response to the request, but
SHOULD send an appropriate non-200 class response if a failure
occurs.
As stated above, if no Failure-Report header is present, it MUST be
treated the same as a Failure-Report header with value of "yes".
Campbell, et al. Expires August 24, 2005 [Page 19]
Internet-Draft MSRP February 2005
Construction of failure REPORT requests is identical to that for
success reports, except the Status header code and reason fields MUST
contain appropriate error codes. Any error response code defined in
this specification MAY also be used in failure reports.
If a failure report is sent in response to a SEND request that
contained a chunk, it MUST include a Byte-Range header indicating the
actual range being reported on. It can take the range-start and
total values from the original SEND request, but MUST calculate the
range-end field from the actual body data.
Endpoints SHOULD NOT send REPORT requests if they have reason to
believe the request will not be delivered. For example, they SHOULD
NOT send a REPORT request on a session that is no longer valid.
This section only describes failure report generation behavior for
MSRP endpoints. Relay behavior is beyond the scope of this
document, and will be considered in a separate document. We
expect failure reports to be more commonly generated by relays
than by endpoints.
7.2 Constructing Responses
If an MSRP endpoint receives a request that either contains a
Failure-Report header value of "yes", or does not contain a
Failure-Report header field at all, it MUST immediately generate a
response. Likewise, if an MSRP endpoint receives a request that
contains a Failure-Report header value of "partial", and the receiver
is unable to process the request, it SHOULD immediately generate a
response.
To construct the response, the endpoint first creates the response
start-line, inserting appropriate response code and reason fields.
The transaction identifier in the response start line MUST match the
transaction identifier from the original request.
The endpoint then inserts an appropriate To-Path header field. If
the request triggering the response was a SEND request, the To-Path
header field is formed by copying the last (right-most) URL in the
From-Path header field of the request. (Responses to SEND requests
are returned only to the previous hop.) For responses to all other
request methods, the To-Path header field contains the full path back
to the original sender. This full path is generated by taking the
list of URLs from the From-Path of the original request, reversing
the list, and writing the reversed list into the To-Path of the
response. (Legal REPORT requests do not request responses, so this
specification doesn't exercise the behavior described above, however
we expect that extensions for gateways and relays will need such
Campbell, et al. Expires August 24, 2005 [Page 20]
Internet-Draft MSRP February 2005
behavior.)
Finally, the endpoint inserts a From-Path header field containing the
URL that identifies it in the context of the session, followed by the
closing sequence after the last header field. The response MUST be
transmitted back on the same connection on which the original request
arrived.
7.3 Receiving Requests
The receiving endpoint must first check the URL in the To-Path to
make sure the request belongs to an existing session. When the
request is received, the To-Path will have exactly one URL, which
MUST map to an existing session that is associated with the
connection on which the request arrived. If this is not true then
the receiver MUST generate an 481 error and ignore the request. Note
that if the Failure-Report header had a value of "no", then no error
report would be sent.
Further request processing by the receiver is method specific.
7.3.1 Receiving SEND requests
When the receiving endpoint receives a SEND request, it first
determines if it contains a complete message, or a chunk from a
larger message. If the request contains no Byte-Range header, or
contains one with a range-start value of "1", and the closing line
continuation flag has a value of "$", then the request contained the
entire message. Otherwise, the receiver looks at the Message-ID
value to associate chunks together into the original message. It
forms a virtual buffer to receive the message, keeping track of which
bytes have been received and which are missing. The receiver takes
the data from the request and places it in the appropriate place in
the buffer. The receiver SHOULD determine the actual length of each
chunk by inspecting the payload itself; it is possible the body is
shorter than the range-end field indicates. This can occur if the
sender interrupted a SEND request unexpectedly. It is worth nothing
that the chunk that has a termination character of "$" defines the
total length of the message.
It is technically illegal for the sender to prematurely interrupt
a request that had anything other "*" in the last-byte position of
the Byte-Range header. But having the receiver calculate a chunk
length based on actual content adds resilience in the face of
sender errors. Since this should never happen with compliant
senders, this only has a SHOULD strength.
Receivers MUST not assume the chunks will be delivered in order or
Campbell, et al. Expires August 24, 2005 [Page 21]
Internet-Draft MSRP February 2005
that they will receive all the chunks with "+" flags before they
receive the chunk with the "$" flag. In certain cases of connection
failure, it is possible for information to be duplicated. If chunk
data is received that overlaps already received data for the same
message, the last chunk received takes precedence (even though this
may not have been the last chunk transmitted). For example, if bytes
1 to 100 was received and a chunk arrives that contains bytes 50 to
150, this second chunk will overwrite bytes 50 to 100 of the data
that had already been received. Although other schemes work, this is
the easiest for the receiver and results in consistent behavior
between clients.
The seven "-" before the boundary are used so that the receiver can
search for the value "----", 32 bits at a time to find the probable
location of the boundary. This allows most processors to locate the
boundaries and copy the memory at the same rate that a normal memory
copy could be done. This approach results in a system that is as
fast as framing based on specifying the body length in the headers of
the request, but also allows for the interruption of messages.
What is done with the body is outside the scope of MSRP and largely
determined by the MIME Content-Type and Content-Disposition. The
body MAY be rendered after the whole message is received or partially
rendered as it is being received.
If the SEND request contained a Content-Type header field indicating
an unsupported MIME type, the receiver MUST generate a failure report
with a 415 error code. Note that this failure report will not be
sent if the Report-Failure header contains a value of "no". All MSRP
endpoints MUST be able to receive the multipart/mixed and
multipart/alternative MIME types.
If the Success-Report header was set to "yes", then when a complete
message has been received, the receiver MUST send a success REPORT
with a byte range covering the whole message. If the Success-Report
header is not set to "no", then the receiver MAY generate incremental
success REPORTs as the chunks are received. These can be sent
periodically and cover all the bytes that have been received so far
or they can be sent after a chunk arrives and cover just the part
from that chunk.
7.3.2 Receiving REPORT requests
When an endpoint receives a REPORT request, it correlates it to the
original SEND request using the Message-ID and the Byte-Range, if
present. If it requested success reports, then it SHOULD keep enough
state about each outstanding sent message so that it can correlate
REPORT requests to the original messages.
Campbell, et al. Expires August 24, 2005 [Page 22]
Internet-Draft MSRP February 2005
An endpoint that receives a REPORT request containing a Status header
with a namespace field of "000", MUST interpret the report in exactly
the same way it would interpret an MSRP transaction response with a
response code matching the short-code field.
It is possible to receive a failure report or a failure transaction
response for a chunk that is currently being delivered. In this case
the entire message corresponding to that chunk should be aborted, by
including the "#" character in the continuation field of the closing
sequence.
It is possible that an endpoint will receive a REPORT request on a
session that is no longer valid. The endpoint's behavior if this
happens is a matter of local policy. The endpoint is not required to
take any steps to facilitate such late delivery, i.e. it is not
expected to keep a connection active in case late REPORTs might
arrive.
When a device that sent a SEND request receives a failure REPORT
indicating that a particular byte range was not received, it MUST
treat the session as failed. If it wishes to recover, it MUST first
re-negotiate the URLs at the signaling level then resend that range
of bytes of the message on the resulting new session.
MSRP Modes MUST NOT send a MSRP REPORT in responses to REPORT
requests.
8. Using MSRP with SIP
8.1 SDP Offer-Answer Exchanges for MSRP Sessions
MSRP sessions will typically be initiated using the Session
Description Protocol (SDP) [2] via the SIP offer-answer mechanism
[3].
This document defines a handful of new SDP parameters to setup MSRP
sessions. These are detailed below and in the IANA Considerations
section.
An MSRP media-line in the session description is always accompanied
by a mandatory "path" attribute. This attribute contains a space
separated list of URLs that must be visited to contact the user agent
advertising this session-description. If more than one URL is
present, the leftmost URL is the first URL that must be visited to
reach the target resource. (The path list can contain multiple URLs
to allow for the deployment of gateways or relays in the future.)
MSRP implementations which can accept incoming connections will
typically only provide a single URL here.
Campbell, et al. Expires August 24, 2005 [Page 23]
Internet-Draft MSRP February 2005
An MSRP medialine MUST also be accompanied by an "accept-types"
attribute. This attribute contains a list of MIME types which are
acceptable to the endpoint.
A "*" entry in the accept-types attribute indicates that the sender
may attempt to send content with media types that have not been
explicitly listed. Likewise, an entry with an explicit type and a
"*" character as the subtype indicates that the sender may attempt to
send content with any subtype of that type. If the receiver receives
an MSRP request and is able to process the media type, it does so.
If not, it will respond with a 415 response. Note that all explicit
entries SHOULD be considered preferred over any non-listed types.
This feature is needed as, otherwise, the list of formats for rich IM
devices may be prohibitively large.
The accept-types attribute may include container types, that is, MIME
formats that contain other types internally. If compound types are
used, the types listed in the accept-types attribute may be used both
as the root payload, or may be wrapped in a listed container type.
Any container types MUST also be listed in the accept-types
attribute.
Occasionally an endpoint will need to specify a MIME body type that
can only be used if wrapped inside a listed container type.
Endpoints MAY specify MIME types that are only allowed when wrapped
inside compound types using the "accept-wrapped-types" attribute in
an SDP a-line.
The semantics for accept-wrapped-types are identical to those of the
accept-types attribute, with the exception that the specified types
may only be used when wrapped inside containers. Only types listed
in the accept-types attribute may be used as the "root" type for the
entire body. Since any type listed in accept-types may be used both
as a root body, and wrapped in other bodies, format entries from
accept-types SHOULD NOT be repeated in this attribute.
This approach does not allow for specifying distinct lists of
acceptable wrapped types for different types of containers. If an
endpoint understands a MIME type in the context of one wrapper, it is
assumed to understand it in the context of any other acceptable
wrappers, subject to any constraints defined by the wrapper types
themselves.
The approach of specifying types that are only allowed inside of
containers separately from the primary payload types allows an
endpoint to force the use of certain wrappers. For example, a
CPIM [12] gateway device may require all messages to be wrapped
Campbell, et al. Expires August 24, 2005 [Page 24]
Internet-Draft MSRP February 2005
inside message/cpim bodies, but may allow several content types
inside the wrapper. If the gateway were to specify the wrapped
types in the accept-types attribute, its peer might attempt to use
those types without the wrapper.
If the recipient of an offer does not understand any of the payload
types indicated in the offered SDP, it SHOULD indicate that using the
appropriate mechanism of the rendezvous protocol. For example, in
SIP, it SHOULD return a SIP 488 response.
An endpoint MAY indicate the maximum size message they wish to
receive using the max-size a-line attribute. Max-size refers to the
complete message in octets, not the size of any one chunk. Senders
SHOULD NOT exceed the max-size limit for any message sent in the
resulting session. However, the receiver should consider max-size
value as a hint.
The formal syntax for these attributes are as follows:
accept-types = accept-types-label ":" format-list
accept-types-label = "accept-types"
accept-wrapped-types = wrapped-types-label ":" format-list
wrapped-types-label = "accept-wrapped-types"
format-list = format-entry *( SP format-entry)
format-entry = (type "/" subtype) / (type "/" "*") / ("*")
type = token
subtype = token
max-size = max-size-label ":" max-size-value
max-size-label = "max-size"
max-size-value = 1*(DIGIT) ;max size in octets
8.1.1 URL Negotiations
Each endpoint in an MSRP session is identified by a URL. These URLs
are negotiated in the SDP exchange. Each SDP offer or answer MUST
contain one or more MSRP URL in a path attribute. This attribute has
the following syntax:
"a=path:" MSRP-URL *(SP MSRP-URL)
where MSRP-URL is an msrp: or msrps: URL as defined in Section 6.
MSRP URLs included in an SDP offer or answer MUST include explicit
port numbers.
An MSRP device uses the URL to determine a host address, port,
transport, and protection level when connecting, and to identify the
Campbell, et al. Expires August 24, 2005 [Page 25]
Internet-Draft MSRP February 2005
target when sending requests and responses.
The offerer and answerer each selects a URL to represent itself, and
send it to the peer device in the SDP document. Each device stores
the path value received from the peer, and uses that value as the
target for requests inside the resulting session. If the path
attribute received from the peer contains more than one URL, then the
target URL is the rightmost, while the leftmost entry represents the
adjacent hop. If only one entry is present, then it is both the peer
and adjacent hop URL. The target path is the entire path attribute
value received from the peer.
The following example shows an SDP offer with a session URL of
"msrp://alice.example.com:7394/2s93i;tcp"
v=0
o=alice 2890844526 2890844527 IN IP4 alice.example.com
s=
c=IN IP4 alice.example.com
m=message 7394 msrp/tcp *
a=accept-types:text/plain
a=path:msrp://alice.example.com:7394/2s93i;tcp
The rightmost URL in the path attribute MUST identify the endpoint
that generated the SDP document, or some other location where that
endpoint wishes to receive requests associated with the session. It
MUST be assigned for this particular session, and MUST NOT duplicate
any URL in use for any other session in which the endpoint is
currently participating. It SHOULD be hard to guess, and protected
from eavesdroppers. This is discussed in more detail in Section 14.
8.1.2 Path Attributes with Multiple URLs
As mentioned previously, this document describes MSRP for
peer-to-peer scenarios, that is, when no relays are used. However,
we expect a separate document to describe the use of relays. In
order to allow an MSRP device that only implements the core
specification to interoperate with devices that use relays, this
document must include a few assumptions about how relays work.
An endpoint that uses one or more relays will indicate that by
putting a URL for each device in the relay chain into the SDP path
attribute. The final entry would point to the endpoint itself. The
other entries would indicate each proposed relay, in order. The
first entry would point to the first relay in the chain from the
perspective of the peer; that is, the relay to which the peer device,
or a relay operating on its behalf, should connect.
Campbell, et al. Expires August 24, 2005 [Page 26]
Internet-Draft MSRP February 2005
Endpoints that do not wish to insert a relay, including those that do
not support relays at all, will put exactly one URL into the path
attribute. This URL represents both the endpoint for the session,
and the connection point.
Even though endpoints that implement only this specification will
never introduce a relay, they need to be able to interoperate with
other endpoints that do use relays. Therefore, they MUST be prepared
to receive more than one URL in the SDP path attribute. When an
endpoint receives more than one URL in a path header, only the first
entry is relevant for purposes of resolving the address and port, and
establishing the network connection, as it describes the first
adjacent hop.
If an endpoint puts more than one URL in a path attribute, the final
URL in the path (the peer URL) attribute MUST exhibit the uniqueness
properties described above. Uniqueness requirements for other
entries in the attribute are out of scope for this document.
8.1.3 SDP Connection and Media Lines
The format of an SDP connection-line takes the following format:
c=<network type> <address type> <connection address>
The network type and address type fields are used as normal for SDP.
The connection address field MUST be set to the IP address or fully
qualified domain name from MSRP URL identifying the endpoint in its
PATH attribute.
The general format of an SDP media-line is:
m=<media> <port> <protocol> <format list>
An offered or accepted media-line for MSRP over TCP MUST include a
protocol field value of "msrp/tcp". The media field value MUST be
"message". The format list field MUST be set to "*".
The port field value MUST match the port value used in the endpoint's
MSRP URL in the PATH attribute, except that, as described in [3], a
user agent that wishes to accept an offer, but not a specific
media-line MUST set the port number of that media-line to zero (0) in
the response.) Since MSRP allows multiple sessions to share the same
TCP connection, multiple m-lines in a single SDP document may share
the same port field value; MSRP devices MUST NOT assume any
particular relationship between m-lines on the sole basis that they
have matching port field values.
Campbell, et al. Expires August 24, 2005 [Page 27]
Internet-Draft MSRP February 2005
MSRP devices do not use the c-line address field, or the m-line
port and format list fields to determine where to connect.
Rather, they use the attributes defined in this specification.
The connection information is copied to the c-line and m-line for
purposes of backwards compatibility with conventional SDP usages.
While MSRP could theoretically carry any media type, "message" is
appropriate.
8.1.4 Updated SDP Offers
MSRP endpoints may sometimes need to send additional SDP exchanges
for an existing session. They may need to send periodic exchanges
with no change to refresh state in the network, for example, SIP
Session Timers. They may need to change some other stream in a
session without affecting the MSRP stream, or they may need to change
an MSRP stream without affecting some other stream.
Either peer may initiate an updated exchange at any time. The
endpoint that sends the new offer assumes the role of offerer for all
purposes. The answerer MUST respond with a path attribute that
represents a valid path to itself at the time of the updated
exchange. This new path may be the same as its previous path, but
may be different. The new offerer MUST NOT assume that the peer will
answer with the same path it used previously.
If either party wishes to send an SDP document that changes nothing
at all, then it MUST have the same o-line as in the previous
exchange.
8.1.5 Example SDP Exchange
Endpoint A wishes to invite Endpoint B to a MSRP session. A offers
the following session description:
v=0
o=usera 2890844526 2890844527 IN IP4 alice.example.com
s=
c=IN IP4 alice.example.com
t=0 0
m=message 7394 msrp/tcp *
a=accept-types: message/cpim text/plain text/html
a=path:msrp://alice.example.com:7394/2s93i9;tcp
B responds with its own URL:
Campbell, et al. Expires August 24, 2005 [Page 28]
Internet-Draft MSRP February 2005
v=0
o=userb 2890844530 2890844532 IN IP4 bob.example.com
s=
c=IN IP4 bob.example.com
t=0 0
m=message 8493 msrp/tcp *
a=accept-types:message/cpim text/plain
a=path:msrp://bob.example.com:8493/si438ds;tcp
8.1.6 Connection Negotiation
Previous versions of this document included a mechanism to negotiate
the direction for any required TCP connection. The mechanism was
loosely based on the COMEDIA [23] work being done in the MMUSIC
working group. The primary motivation was to allow MSRP sessions to
succeed in situations where the offerer could not accept connections
but the answerer could. For example, the offerer might be behind a
NAT, while the answerer might have a globally routable address.
The SIMPLE working group chose to remove that mechanism from MSRP, as
it added a great deal of complexity to connection management.
Instead, MSRP now specifies a default connection direction. Namely,
the party that sent the original offer
8.2 MSRP User Experience with SIP
In typical SIP applications, when an endpoint receives an INVITE
request, it alerts the user, and waits for user input before
responding. This is analogous to the typical telephone user
experience, where the callee "answers" the call.
In contrast, the typical user experience for instant messaging
applications is that the initial received message is immediately
displayed to the user, without waiting for the user to "join" the
conversation. Therefore, the principle of least surprise would
suggest that MSRP endpoints using SIP signaling SHOULD allow a mode
where the endpoint quietly accepts the session, and begins displaying
messages.
SIP INVITE requests may be forked by a SIP proxy, resulting in more
than one endpoint receiving the same INVITE. SIP early media [27]
techniques can be used to establish a preliminary session with each
endpoint, and canceling the INVITE transaction for any endpoints that
do not send MSRP traffic after some period of time.
Campbell, et al. Expires August 24, 2005 [Page 29]
Internet-Draft MSRP February 2005
9. Formal Syntax
MSRP is a text protocol that uses the UTF-8 [14] transformation
format.
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC-2234 [6].
msrp-req-or-resp = msrp-request / msrp-response
msrp-request = req-start headers [content-stuff] end-line
msrp-response = resp-start headers end-line
req-start = pMSRP SP transact-id SP method CRLF
resp-start = pMSRP SP transact-id SP status-code [SP phrase] CRLF
phrase = utf8text
pMSRP = %x4D.53.52.50 ; MSRP in caps
transact-id = ident
method = mSEND / mREPORT / other-method
mSEND = %x53.45.4e.44 ; SEND in caps
mREPORT = %x52.45.50.4f.52.54; REPORT in caps
other-method = 1*UPALPHA
status-code = 3DIGIT ; any code defined in this document
; or an extension document
MSRP-URL = msrp-scheme "://" [userinfo "@"] hostport
["/" session-id] ";" transport
; userinfo as defined in RFC2396, except
; limited to unreserved.
; hostport as defined in RFC3261
; [Todo: update with RFC number for 2396bis]
msrp-scheme = "msrp" / "msrps"
session-id = 1*( unreserved / "+" / "=" / "/" )
; unreserved as defined in RFC2396
transport = "tcp" / ALPHANUM
headers = To-Path CRLF From-Path CRLF 1*( header CRLF )
header = Message-ID
/ Success-Report
/ Failure-Report
/ Byte-Range
/ Status
/ ext-header
Campbell, et al. Expires August 24, 2005 [Page 30]
Internet-Draft MSRP February 2005
To-Path = "To-Path:" SP MSRP-URL *( SP MSRP-URL )
From-Path = "From-Path:" SP MSRP-URL *( SP MSRP-URL )
Message-ID = "Message-ID:" SP ident
Success-Report = "Success-Report:" SP ("yes" / "no" )
Failure-Report = "Failure-Report:" SP ("yes" / "no" / "partial" )
Byte-Range = "Byte-Range:" SP range-start "-" range-end "/" total
range-start = 1*DIGIT
range-end = 1*DIGIT / "*"
total = 1*DIGIT / "*"
Status = "Status:" SP namespace SP status-code [SP text-reason]
namespace = "000"
text-reason = utf8text
ident = alphanum 3*31ident-char
ident-char = alphanum / "." / "-" / "+" / "%" / "="
content-stuff = *(Other-Mime-Header CRLF)
Content-Type 2CRLF data CRLF
Content-Type = "Content-Type:" SP media-type
media-type = type "/" subtype *( ";" gen-param )
type = token
subtype = token
gen-param = pname [ "=" pval ]
pname = token
pval = token / quoted-string
token = 1*(%x21 / %x23-27 / %x2A-2B / %x2D-2E
/ %x30-39 / %x41-5A / %x5E-7E)
; token is compared case-insensitive
quoted-string = DQUOTE *(qdtext / qd-esc) DQUOTE
qdtext = SP / HTAB / %x21 / %x23-5B / %x5D-7E
/ UTF8-NONASCII
qd-esc = (BACKSLASH BACKSLASH) / (BACKSLASH DQUOTE)
BACKSLASH = "\"
UPALPHA = %x41-5A
ALPHANUM = ALPHA / DIGIT
Other-Mime-Header = (Content-ID
/ Content-Description
/ Content-Disposition
/ mime-extension-field);
Campbell, et al. Expires August 24, 2005 [Page 31]
Internet-Draft MSRP February 2005
; Content-ID, and Content-Description are defined in RFC2045.
; Content-Disposition is defined in RFC2183
; MIME-extension-field indicates additional MIME extension
; headers as described in RFC2045
data = *OCTET
end-line = "-------" transact-id continuation-flag CRLF
continuation-flag = "+" / "$" / "#"
ext-header = hname ":" SP hval CRLF
hname = ALPHA *token
hval = utf8text
utf8text = *(HTAB / %x20-7E / UTF8-NONASCII)
UTF8-NONASCII = %xC0-DF 1UTF8-CONT
/ %xE0-EF 2UTF8-CONT
/ %xF0-F7 3UTF8-CONT
/ %xF8-Fb 4UTF8-CONT
/ %xFC-FD 5UTF8-CONT
UTF8-CONT = %x80-BF
10. Response Code Descriptions
This section summarizes the semantics of various response codes that
may be used in MSRP transaction responses. These codes may also be
used in the Status header in REPORT requests.
10.1 200
The 200 response code indicates a successful transaction.
10.2 400
A 400 response indicates a request was unintelligible.
10.3 403
The action is not allowed.
10.4 408
A 408 response indicates that a downstream transaction did not
complete in the alloted time. It is never sent by any elements
described in this specification. However, 408 is used in the MSRP
Campbell, et al. Expires August 24, 2005 [Page 32]
Internet-Draft MSRP February 2005
Relay extension; therefore MSRP endpoints may receive it. An
endpoint MUST treat a 408 response in the same manner as it would
treat a local timeout.
10.5 413
A 413 response indicates that the receiver wishes the sender to stop
sending the particular message. Typically, a 413 is sent in response
to a chunk of an undesired message.
If a message sender receives a 413 in a response, or in a REPORT
request, it MUST NOT send any further chunks in the message, that is,
any further chunks with the same Message-ID value. If the sender
receives the 413 while in the process of sending a chunk, and the
chunk is interruptible, the sender MUST abort sending the chunk.
10.6 415
A 415 response indicates the SEND request contained a MIME
content-type that is not understood by the receiver.
10.7 423
A 423 response indicates that one of the requested parameters is out
of bounds. It is used by the relay extensions to this document.
10.8 426
A 426 response indicates that the request is only allowed over TLS
protected connections.
10.9 481
A 481 response indicates that the indicated session does not exist.
10.10 501
A 501 response indicates that the recipient does not understand the
request method.
The 501 response code exists to allow some degree of method
extensibility. It is not intended as a license to ignore methods
defined in this document; rather it is a mechanism to report lack
of support of extension methods.
10.11 506
A 506 response indicates that a request arrived on a session which is
Campbell, et al. Expires August 24, 2005 [Page 33]
Internet-Draft MSRP February 2005
already bound to another network connection.
11. Examples
11.1 Basic IM session
This section shows an example flow for the most common scenario. The
example assumes SIP is used to transport the SDP exchange. Details
of the SIP messages and SIP proxy infrastructure are omitted for the
sake of brevity. In the example, assume the offerer is
sip:alice@example.com and the answerer is sip:bob@example.com.
Alice Bob
| |
| |
|(1) (SIP) INVITE |
|----------------------->|
|(2) (SIP) 200 OK |
|<-----------------------|
|(3) (SIP) ACK |
|----------------------->|
|(4) (MSRP) SEND |
|----------------------->|
|(5) (MSRP) 200 OK |
|<-----------------------|
|(6) (MSRP) SEND |
|<-----------------------|
|(7) (MSRP) 200 OK |
|----------------------->|
|(8) (SIP) BYE |
|----------------------->|
|(9) (SIP) 200 OK |
|<-----------------------|
| |
| |
1. Alice constructs a local URL of
msrp://alicepc.example.com:7777/iau39;tcp .
Alice->Bob (SIP): INVITE sip:bob@example.com
v=0
o=alice 2890844557 2890844559 IN IP4 alicepc.example.com
s=
c=IN IP4 alicepc.example.com
t=0 0
m=message 7777 msrp/tcp *
a=accept-types:text/plain
Campbell, et al. Expires August 24, 2005 [Page 34]
Internet-Draft MSRP February 2005
a=path:msrp://alicepc.example.com:7777/iau39;tcp
2. Bob listens on port 8888, and sends the following response:
Bob->Alice (SIP): 200 OK
v=0
o=bob 2890844612 2890844616 IN IP4 bob.example.com
s=
c=IN IP4 bob.example.com
t=0 0
m=message 8888 msrp/tcp *
a=accept-types:text/plain
a=path:msrp://bob.example.com:8888/9di4ea;tcp
3. Alice->Bob (SIP): ACK
4. (Alice opens connection to Bob.) Alice->Bob (MSRP):
MSRP d93kswow SEND
To-Path:msrp://bob.example.com:8888/9di4ea;tcp
From-Path:msrp://alicepc.example.com:7777/iau39;tcp
Message-ID: 12339sdqwer
Content-Type: text/plain
Hi, I'm Alice!
-------d93kswow$
5. Bob->Alice (MSRP):
MSRP d93kswow 200 OK
To-Path:msrp://bob.example.com:8888/9di4ea;tcp
From-Path:msrp://alicepc.example.com:7777/iau39;tcp
-------d93kswow$
6. Bob->Alice (MSRP):
MSRP dkei38sd SEND
To-Path:msrp://alice.example.com:7777/iau39;tcp
From-Path:msrp://bob.example.com:8888/9di4ea;tcp
Message-ID: 456
Content-Type: text/plain
Hi, Alice! I'm Bob!
-------dkei38sd$
7. Alice->Bob (MSRP):
Campbell, et al. Expires August 24, 2005 [Page 35]
Internet-Draft MSRP February 2005
MSRP dkei38sd 200 OK
To-Path:msrp://alice.example.com:7777/iau39;tcp
From-Path:msrp://bob.example.com:8888/9di4ea;tcp
-------dkei38sd$
8. Alice->Bob (SIP): BYE
Alice invalidates local session state.
9. Bob invalidates local state for the session.
Bob->Alice (SIP): 200 OK
11.2 Message with XHTML Content
MSRP dsdfoe38sd SEND
To-Path:msrp://alice.atlanta.com:7777/iau39;tcp
From-Path:msrp://bob.atlanta.com:8888/9di4ea;tcp
Message-ID: 456
Content-Type:application/xhtml+xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"_http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd_">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>FY2005 Results</title>
</head>
<body>
<p>See the results at<a
href="http://example.org/">example.org</a>.</p>
</body>
</html>
-------dsdfoe38sd$
11.3 Chunked Message
For an example of a chunked message, see the example in Section 5.1.
11.4 System Message
Sysadmin->Alice (MSRP):
MSRP d93kswow SEND
To-Path:msrp://alicepc.example.com:8888/9di4ea;tcp
From-Path:msrp://example.com:7777/iau39;tcp
Message-ID: 12339sdqwer
Campbell, et al. Expires August 24, 2005 [Page 36]
Internet-Draft MSRP February 2005
Failure-Report: no
Success-Report: no
Content-Type: text/plain
This conference will end in 5 minutes
-------d93kswow$
11.5 Positive Report
Alice->Bob (MSRP):
MSRP d93kswow SEND
To-Path:msrp://bob.example.com:8888/9di4ea;tcp
From-Path:msrp://alicepc.example.com:7777/iau39;tcp
Message-ID: 12339sdqwer
Success-Report: yes
Content-Type: text/html
<html><body>
<p>Here is that important link...
<a href="www.example.com/foobar">foobar</a>
</p>
</body></html>
-------d93kswow$
Bob->Alice (MSRP):
MSRP d93kswow 200 OK
To-Path:msrp://alicepc.example.com:7777/iau39;tcp
From-Path:msrp://bob.example.com:8888/9di4ea;tcp
-------d93kswow$
Bob->Alice (MSRP):
MSRP dkei38sd REPORT
To-Path:msrp://alicepc.example.com:7777/iau39;tcp
From-Path:msrp://bob.example.com:8888/9di4ea;tcp
Message-ID: 12339sdqwer
Status: 000 200 OK
-------dkei38sd$
11.6 Forked IM
Traditional IM systems generally do a poor job of handling multiple
simultaneous IM clients online for the same person. While some do a
better job than many existing systems, handling of multiple clients
Campbell, et al. Expires August 24, 2005 [Page 37]
Internet-Draft MSRP February 2005
is fairly crude. This becomes a much more significant issue when
always-on mobile devices are available, but when it is desirable to
use them only if another IM client is not available.
Using SIP makes rendezvous decisions explicit, deterministic, and
very flexible; instead "pager-mode" IM systems use implicit
implementation-specific decisions which IM clients cannot influence.
With SIP session mode messaging rendezvous decisions can be under
control of the client in a predictable, interoperable way for any
host that implements callee capabilities [29]. As a result,
rendezvous policy is managed consistently for each address of record.
The following example shows Juliet with several IM clients where she
can be reached. Each of these has a unique SIP Contact and MSRP
session. The example takes advantage of SIP's capability to "fork"
an invitation to several Contacts in parallel, in sequence, or in
combination. Juliet has registered from her chamber, the balcony,
her PDA, and as a last resort, you can leave a message with her
Nurse. Juliet's contacts are listed below. The q-values express
relative preference (q=1.0 is the highest preference).
The example uses REGISTER to learn of Juliet's registered
contacts. This does not constitute an endorsement of that
approach; it is used here to avoid cluttering the example with too
many SIP details. A more realistic application would be the use a
SIP proxy or redirect server for this purpose.
We query for a list of Juliet's contacts by sending a REGISTER:
REGISTER sip:thecapulets.example.com SIP/2.0
To: Juliet <sip:juliet@thecapulets.example.com>
From: Juliet <sip:juliet@thecapulets.example.com>;tag=12345
Call-ID: 09887877
CSeq: 772 REGISTER
The Response contains her Contacts:
SIP/2.0 200 OK
To: Juliet <sip:juliet@thecapulets.example.com>
From: Juliet <sip:juliet@thecapulets.example.com>;tag=12345
Call-ID: 09887877
CSeq: 772 REGISTER
Contact: <sip:juliet@balcony.thecapulets.example.com>
;q=0.9;expires=3600
Contact: <sip:juliet@chamber.thecapulets.example.com>
;q=1.0;expires=3600
Contact: <sip:jcapulet@veronamobile.example.net>;q=0.4;expires=3600
Campbell, et al. Expires August 24, 2005 [Page 38]
Internet-Draft MSRP February 2005
Contact: <sip:nurse@thecapulets.example.com>;q=0.1;expires=3600
When Romeo opens his IM program, he selects Juliet and types the
message "art thou hither?" (instead of "you there?"). His client
sends a SIP invitation to sip:juliet@thecapulets.example.com. The
Proxy there tries first the balcony and the chamber simultaneously.
A client is running on both those systems, both of which setup early
sessions of MSRP with Romeo's client. The client automatically sends
the message over the MSRPS to the two MSRP URIs involved. After a
delay of a several seconds with no reply or activity from Juliet, the
proxy cancels the invitation at her first two contacts, and forwards
the invitation on to Juliet's PDA. Since her father is talking to
her about her wedding, she selects "Do Not Disturb" on her PDA, which
sends a "Busy Here" response. The proxy then tries the Nurse, who
answers and tells Romeo what is going on.
Romeo Juliet's Juliet/ Juliet/ Juliet/ Nurse
Proxy balcony chamber PDA
| | | | | |
|--INVITE--->| | | | |
| |--INVITE--->| | | |
| |<----180----| | | |
|<----180----| | | | |
|---PRACK---------------->| | | |
|<----200-----------------| | | |
|<===Early MSRP Session==>| art thou hither? | |
| | | | | |
| |--INVITE---------------->| | |
| |<----180-----------------| | |
|<----180----| | | | |
|---PRACK----------------------------->| | |
|<----200------------------------------| | |
|<========Early MSRP Session==========>| art thou hither? |
| | | | | |
| | | | | |
| | .... Time Passes .... | | |
| | | | | |
| | | | | |
| |--CANCEL--->| | | |
| |<---200-----| | | |
| |<---487-----| | | |
| |----ACK---->| | | |
| |--CANCEL---------------->| | |
| |<---200------------------| | |
| |<---487------------------| | |
| |----ACK----------------->| | |
Campbell, et al. Expires August 24, 2005 [Page 39]
Internet-Draft MSRP February 2005
| |--INVITE---------------------------->| romeo wants
| | | | | to IM w/ you
| |<---486 Busy Here--------------------| |
| |----ACK----------------------------->| |
| | | | | |
| |--INVITE---------------------------------------->|
| |<---200 OK---------------------------------------|
|<--200 OK---| | | | |
|---ACK------------------------------------------------------->|
|<================MSRP Session================================>|
| | | | | |
| Hi Romeo, Juliet is |
| with her father now |
| can i take a message?|
| |
| Tell her to go to confession tomorrow.... |
12. Extensibility
MSRP was designed to be only minimally extensible. New MSRP Methods,
Headers, and status codes can be defined in standards track RFCs.
There is no registry of headers, methods, or status codes, since the
number of new elements and total extensions is expected to be very
small. MSRP does not contain a version number or any negotiation
mechanism to require or discover new features. If a
non-interoperable update or extension occurs in the future, it will
be treated as a new protocol, and must describe how its use will be
signaled.
In order to allow extension header fields without breaking
interoperability, if an MSRP device receives a request or response
containing a header field that it does not understand, it MUST ignore
the header field and process the request or response as if the header
field was not present. If an MSRP device receives a request with an
unknown method, it MUST return a 501 response.
MSRP was designed to use lists of URLs instead of a single URL in the
To-Path and From-Path headers in anticipation of relay or gateway
functionality being added. In addition, msrp: and msrps: URLs can
contain parameters which are extensible.
13. CPIM compatibility
MSRP sessions may go to a gateway to other CPIM [24] compatible
protocols. If this occurs, the gateway MUST maintain session state,
and MUST translate between the MSRP session semantics and CPIM
Campbell, et al. Expires August 24, 2005 [Page 40]
Internet-Draft MSRP February 2005
semantics, which do not include a concept of sessions. Furthermore,
when one endpoint of the session is a CPIM gateway, instant messages
SHOULD be wrapped in "message/cpim" [12] bodies. Such a gateway MUST
include "message/cpim" as the first entry in its SDP accept-types
attribute. MSRP endpoints sending instant messages to a peer that
has included 'message/cpim" as the first entry in the accept-types
attribute SHOULD encapsulate all instant message bodies in
"message/cpim" wrappers. All MSRP endpoints MUST support the
message/cpim type, and SHOULD support the S/MIME features of that
format.
If a message is to be wrapped in a message/cpim envelope, the
wrapping MUST be done prior to breaking the message into chunks, if
needed.
All MSRP endpoints MUST recognize the From, To, DateTime, and Require
headers as defined in RFC3862. Such applications SHOULD recognize
the CC header, and MAY recognize the Subject header. Any MSRP
application that recognizes any message/cpim header MUST understand
the NS (name space) header.
All message/cpim body parts sent by an MSRP endpoint MUST include the
From and To headers. If the message/cpim body part is protected
using S/MIME, then it MUST also include the DateTime header.
The NS, To, and CC headers may occur multiple times. Other headers
defined in RFC3862 MUST NOT occur more than once in a given
message/cpim body part in an MSRP message. The Require header MAY
include multiple values. The NS header MAY occur zero or more times,
depending on how many name spaces are being referenced.
Extension headers MAY occur more than once, depending on the
definition of such headers.
Using message/cpim envelopes are also useful if an MSRP device
wishes to send a message on behalf of some other identity. The
device may add a message/cpim envelope with the appropriate From
header value.
14. Security Considerations
Instant Messaging systems are used to exchange a variety of sensitive
information ranging from personal conversations, to corporate
confidential information, to account numbers and other financial
trading information. IM is used by individuals, corporations, and
governments for communicating important information. Like many
communications systems, the properties of Integrity and
Confidentiality of the exchanged information, along with the
Campbell, et al. Expires August 24, 2005 [Page 41]
Internet-Draft MSRP February 2005
possibility of Anonymous communications, and knowing you are
communicating with the correct other party are required. MSRP pushes
many of the hard problems to SIP when SIP sets up the session, but
some of the problems remain. Spam and DoS attacks are also very
relevant to IM systems.
MSRP needs to provide confidentiality and integrity for the messages
it transfers. It also needs to provide assurances the connected host
is the host that it meant to connect to and that the connection has
not been hijacked.
14.1 Transport Level Protection
When using only TCP connections, MSRP security is fairly weak. If
host A is contacting B, B passes its hostname and a secret to A using
a rendezvous protocol. Although MSRP requires the use of a
rendezvous protocol with the ability to protect this exchange, there
is no guarantee that the protection will be used all the time. If
such protection is not used, anyone can see this secret. A then
connects to the provided host name and passes the secret in the clear
across the connection to B. A assumes that it is talking to B based
on where it sent the SYN packet and then delivers the secret in plain
text across the connections. B assumes it is talking to A because
the host on the other end of the connection delivered the secret. An
attacker that could ACK the SYN packet could insert itself as a man
in the middle in the connection.
When using TLS connections, the security is significantly improved.
We assume that the host accepting the connection has a certificate
from a well know certificate authority. Furthermore, we assume that
the signaling to set up the session is protected by the rendezvous
protocol. In this case, when host A contacts host B, the secret is
passed through a confidential channel to A. A connects with TLS to
B. B presents a valid certificate, so A knows it really is connected
to B. A then delivers the secret provided by B, so that B can verify
it is connected to A. In this case, a rogue SIP Proxy can see the
secret in the SIP signaling traffic and could potentially insert
itself as a man-in-the-middle.
Realistically, using TLS is difficult for peer to peer connections,
as the types of hosts that end clients use for sending instant
messages are unlikely to have long term stable IP addresses or DNS
names that certificate can bind to. In addition, the cost of server
certificates from well known certificate authorities is currently
expensive enough to discourage their use for each client. While not
in scope for this document, using TLS with a DH profile is possible.
TLS becomes much more practical when some form of relay is
Campbell, et al. Expires August 24, 2005 [Page 42]
Internet-Draft MSRP February 2005
introduced. Clients can then form TLS connections to relays, which
are much more likely to have TLS certificates. While this
specification does not address such relays, they are described by a
companion document [20]. That document makes extensive use of TLS to
protect traffic between clients and relays, and between one relay and
another.
TLS is used to authenticate devices and to provide integrity and
confidentiality for the headers being transported. MSRP elements
MUST implement TLS and MUST also implement the TLS
ClientExtendedHello extended hello information for server name
indication as described in [10]. A TLS cipher-suite of
TLS_RSA_WITH_AES_128_CBC_SHA [13] MUST be supported (other
cipher-suites MAY also be supported).
14.2 S/MIME
The only strong security for non-TLS connections is achieved using
S/MIME.
Since MSRP carries arbitrary MIME content, it can trivially carry
S/MIME protected messages as well. All MSRP implementations MUST
support the multipart/signed MIME type even if they do not support
S/MIME. Since SIP can carry a session key, S/MIME messages in the
context of a session could also be protected using a key-wrapped
shared secret [25] provided in the session setup. MSRP is a binary
protocol and MIME bodies MUST be transfered with a transfer encoding
of binary. If a message is both signed and encrypted, it SHOULD be
signed first, then encrypted. If S/MIME is supported, SHA-1, RSA,
and AES-128 MUST be supported.
This does not actually require the endpoint to have certificates from
a well known certificate authority. When MSRP is used with SIP, the
Identity [21] and Certificates [22] mechanism provides S/MIME based
delivery of a secret between A and B. No SIP intermediary except the
explicitly trusted authentication service (one per user) can see the
secret. The S/MIME encryption of the SDP can also be used by SIP to
exchange keying material that can be used in MRSP. The MSRP session
can then use S/MIME with this keying material to encrypt and sign
messages sent over MSRP. The connection can still be hijacked since
the secret is sent in clear text to the other end of the TCP
connection, but the consequences are mitigated if all the MSRP
content is encrypted and signed with S/MIME. It is out of scope for
this document but there is nothing stopping the SIP negotiation of
MSRP session from negotiating symmetric keying material that is used
with S/MIME for integrity and privacy.
Campbell, et al. Expires August 24, 2005 [Page 43]
Internet-Draft MSRP February 2005
14.3 Other Security Concerns
MSRP can not be used as an amplifier for DoS attacks, but it can be
used to form a distributed attack to consume TCP connection resource
on servers. The attacker, Eve, sends a SIP INVITE with no offer to
Alice. Alice returns a 200 with an offer and Eve returns an answer
with the SDP that indicates that her MSRP address is the address of
Tom. Since Alice sent the offer, Alice will initiate a connection to
Tom using up resources on Tom's server. Given the huge number of IM
clients, and the relatively few TCP connections that most servers
support, this is a fairly straightforward attack.
SIP is attempting to address issues in dealing with spam. The spam
issue is probably best dealt with at the SIP level when an MSRP
session is initiated and not at the MSRP level.
If a sender chooses to employ S/MIME to protect a message, all S/MIME
operations MUST occur prior to breaking the message into chunks, if
needed.
The signaling will have set up the session to or from some specific
URLs that will often have "im:" or "sip:" URI schemes. When the
signaling has been set up to a specific end users, and S/MIME is
implemented, then the client needs to verify that the name in the
SubjectAltName of the certificate contains an entry that matches the
URI that was used for the other end in the signaling. There are some
cases, such as IM conferencing, where the S/MIME certificate name and
the signaled identity will not match. In these cases the client
should ensure that the user is informed that the message came from
the user identified in the certificate and does not assume that the
message came from the party they signaled.
In some cases, a sending device may need to attribute a message to
some other identity, and may use different identities for different
messages in the same session. For example, a conference server may
send messages on behalf of multiple users on the same session.
Rather than add additional headers to MSRP for this purpose, MSRP
relies on the message/cpim format for this purpose. The sender may
envelope such a message in a message/cpim body, and place the actual
sender identity in the From field. The trustworthiness of such an
attribution is affected by the security properties of the session in
the same way that the trustworthiness of the identity of the actual
peer is affected, with the additional issue of determining whether
the recipient trusts the sender to assert the identity.
This approach can result in nesting of message/cpim envelopes. For
example, a message originates from a CPIM gateway, and is then
forwarded by a conference server onto a new session. Both the
Campbell, et al. Expires August 24, 2005 [Page 44]
Internet-Draft MSRP February 2005
gateway and the conference server introduce envelopes. In this case,
the recipient client SHOULD indicate the chain of identity assertions
to the user, rather than allow the user to assume that either the
gateway or the conference server originated the message.
It is possible that a recipient might receive messages that are
attributed to the same sender via different MSRP sessions. For
example, Alice might be in a conversation with Bob via an MSRP
session over a TLS protected channel. Alice might then receive a
different message from Bob over a different session, perhaps with a
conference server that asserts Bob's identity in a message/cpim
envelope signed by the server.
MSRP does not prohibit multiple simultaneous sessions between the
same pair of identities. Nor does it prohibit an endpoint sending a
message on behalf of another identity, such as may be the case for a
conference server. The recipient's endpoint should determine its
level of trust of the authenticity of the sender independently for
each session. The fact that an endpoint trusts the authenticity of
the sender on any given session should not affect the level of trust
it assigns for apparently the same sender on a different session.
When MSRP clients form or acquire a certificate, they SHOULD ensure
that the subjectAltName has a GeneralName entry of type
uniformResourceIdentifier for each URL corresponding to this client
and should always include an "im:" URI. It is fine if the
certificate contains other URIs such as an "sip:" or "xmpp:" URIs.
MSRP implementors should be aware of a potential attack on MSRP
devices that involves placing very large values in the byte-range
header field, potentially causing the device to allocate very large
memory buffers to hold the message. Implementations SHOULD apply
some degree of sanity checking on byte-range values before allocating
such buffers.
15. IANA Considerations
15.1 MSRP Port
MSRP uses TCP port XYX, to be determined by IANA after this document
is approved for publication. Usage of this value is described in
Section 6
15.2 MSRP URL Schemes
This document defines the URL schemes of "msrp" and "msrps".
Campbell, et al. Expires August 24, 2005 [Page 45]
Internet-Draft MSRP February 2005
Syntax: See Section 6.
Character Encoding: See Section 6.
Intended Usage: See Section 6.
Protocols: The Message Session Relay Protocol (MSRP).
Security Considerations: See Section 14.
Relevant Publications: RFCXXXX
[Note to RFC Editor: Please replace RFCXXXX in the above
paragraph with the actual number assigned to this document.
15.3 SDP Transport Protocol
MSRP defines the a new SDP protocol field value "msrp/tcp", which
should be registered in the sdp-parameters registry under "proto".
This value indicates the MSRP protocol when TCP is used as an
underlying transport.
Specifications defining new protocol values must define the rules for
the associated media format namespace. The "msrp/tcp" protocol value
allows only one value in the format field (fmt), which is a single
occurrence of "*". Actual format determination is made using the
"accept-types" and "accept-wrapped-types" attributes.
15.4 SDP Attribute Names
This document registers the following SDP attribute parameter names
in the sdp-parameters registry. These names are to be used in the
SDP att-name field.
15.4.1 Accept Types
Contact Information: Ben Campbell (ben@estacado.net)
Attribute-name: accept-types
Long-form Attribute Name: Acceptable MIME Types
Type: Media level
Subject to Charset Attribute: No
Purpose and Appropriate Values: The "accept-types" attribute contains
a list of MIME content-types that the endpoint is willing to
receive. It may contain zero or more registered MIME types, or
"*" in a space delimited string.
15.4.2 Wrapped Types
Contact Information: Ben Campbell (ben@estacado.net)
Attribute-name: accept-wrapped-types
Long-form Attribute Name: Acceptable MIME Types Inside Wrappers
Campbell, et al. Expires August 24, 2005 [Page 46]
Internet-Draft MSRP February 2005
Type: Media level
Subject to Charset Attribute: No
Purpose and Appropriate Values: The "accept-wrapped-types" attribute
contains a list of MIME content-types that the endpoint is willing
to receive in an MSRP message with multipart content, but may not
be used as the outermost type of the message. It may contain zero
or more registered MIME types, or "*" in a space delimited string.
15.4.3 Max Size
Contact Information: Ben Campbell (ben@estacado.net)
Attribute-name: max-size
Long-form Attribute Name: Maximum message size.
Type: Media level
Subject to Charset Attribute: No
Purpose and Appropriate Values: The "max-size" attribute indicates
the largest message an endpoint wishes to accept. It may take any
numeric value, specified in octets.
15.4.4 Path
Contact Information: Ben Campbell (ben@estacado.net)
Attribute-name: path
Long-form Attribute Name: MSRP URL Path
Type: Media level
Subject to Charset Attribute: No
Purpose and Appropriate Values: The "path" attribute indicates a
series of MSRP devices that must be visited by messages sent in
the session, including the final endpoint. The attribute contains
one or more MSRP URIs, delimited by the space character.
16. Change History
16.1 draft-ietf-simple-message-sessions-10
Changed SDP m-line protocol field to "msrp/tcp". Added
requirement to copy the MSRP address and port from the path to the
c and m lines as a courtesy to legacy SDP devices. The path
attribute is still used as previousl specificed.
Changed SDP reference to point to SDP-New draft.
Relaxed the URL session-id syntax to allow (unreserved / "+" / "="
/ "/" ), to make it easier to embed base64 encoded information.
Updated example in overview to have Byte-Range header.
Added 413 response code.
Changed report-failure and report-success to failure-report and
success-report, respectively. Change made to increase parsing
efficiency.
Campbell, et al. Expires August 24, 2005 [Page 47]
Internet-Draft MSRP February 2005
Refined the iana registration section.
Added registration of "msrp" as an sdp proto field value in iana
section.
Moved 408 and 423 from relays document to this draft.
Expanded security considerations to include more discussion of the
difficulties of peer-to-peer TLS, and how relays can help make
that better.
16.2 draft-ietf-simple-message-sessions-09
o Updated retransmission when receiving a failure report.
o Added applicability statement.
o Added CPIM application considerations.
o Added language to security considerations about receiving messages
from the same sender over different sessions.
o Added 501 response code.
o Various scrubbing of the ABNF
o Change resource construction name to session-id in MSRP syntax.
o Added language to define the purpose of msrp URLs.
o Change RFC2396 reference to 2396bis
o Clarify that max-size is in octets.
o Clarify that userinfo is restricted to unreserved characters,
which is an additional restriction over the RFC2396 version.
o Consolidated the ABNF for the MSRP URL into the formal syntax
section.
o Clarified that if an MSRP endpoint receives and SDP offer and does
not understand any of the media types, it SHOULD return a SIP 488
response, or whatever is appropriate for the rendezvous protocol.
o Added more text around using message/cpim for identity
attribution.
16.3 draft-ietf-simple-message-sessions-08
o Removed DSN section. Removed statements that an error report
SHOULD contain a body. REPORT requests may now contain
informational bodies no larger than 2K, but the recipient is free
to ignore them.
o Added the "#" value for the continuation-flag to indicate the last
chunk of an abandoned message.
o Added direction that s/mime and cpim envelops must be applied
before chunking.
o Added direction to set the last-byte field in byte-range to "*" if
there is any chance of interrupting a SEND request.
o Changed to refer to entire message, instead of a particular MIME
content-type
o Added requirement for the use of UTF-8, and reference to RFC3629
o Added requirement to ignore unknown headers.
Campbell, et al. Expires August 24, 2005 [Page 48]
Internet-Draft MSRP February 2005
o Several ABNF fixes
o Removed redundant material between normative sections.
o Numerous editorial fixes.
16.4 draft-ietf-simple-message-sessions-07
o Significant re-write to attempt to improve readability.
o Added maximum size parameter in accept-types
o Changed the Boundary field to be part of the start-line rather
than a header field.
o Removed the TR-ID header, and changed request-response matching to
be based on the Boundary field value. Responses still contain the
TR-ID header, which must match the Boundary from the request.
o Removed transport selection from URL scheme and added the "tcp"
parameter.
o Added description of the "simple" mode with no transaction
responses, and made mode selection dependent on the reporting
level requested for a give message.
o Changed the DSN section to reflect separate request of success and
failure reports. Enhanced REPORT method to be useful even without
a payload.
o removed SRV usage for URL resolution. This is only used for relay
discovery, and therefore should be moved to the relay draft.
o Added discussion about late REPORT handling. Asserted that REPORT
requests are always sent in simple mode.
o Removed the dependency on multipart/byteranges for fragmentation.
Incorporated the Byte-Range header into the base MSRP header set.
o Removed the VISIT method. Change to use SEND to serve the purpose
formerly reserved to VISIT.
16.5 draft-ietf-simple-message-sessions-06
o Changed To and From header names to To-Path and From-Path. Added
more clarification to path handling, and commentary on how it
enables relay usage.
o Changed mechanism for signaling transport and TLS protection into
the MSRP URL, rather than the SDP M-Line.
o Removed length field from start line and added Boundary header
field and Closing field.
o Added recommendation to fragment any content over 2k.
o Added Rohan's proposal to make offerer connect to answerer. (With
open issue for more discussion.)
o Changed To-Path and From-Path usage in responses to indicate the
destination and source of the response, rather than merely copy
from the associated request.
o Updated DSN section. Added text on field usage.
o Fixed change TR-ID header from version 05 were erroneously
attributed to 04.
Campbell, et al. Expires August 24, 2005 [Page 49]
Internet-Draft MSRP February 2005
16.6 draft-ietf-simple-message-sessions-05
o Changed the use of session URLs. Instead of a single session URL,
each endpoint is identified by a distinct URL. MSRP requests will
put the destination URL in a To header, and the sender URL in a
From header.
o Changed the SDP exchange of MSRP URLs to handle the URL for each
endpoint. Further, changed the SDP attribute to support a list of
URLs in each direction. This may be used with relays to exchange
paths, rather than single URLs. MSRP endpoints must be able to
intelligently process such a list if received. This document does
not, however, describe how to generate such a list.
o Added section for Delivery Status Notification handling, and added
associated entries into the syntax definition.
o Added content fragmentation section.
o Removed recommendation to start separate session for large
transfers.
o Corrected some mistakes in the syntax definitions.
o Added Chris Boulton as a co-author for his contribution of the DSN
text.
16.7 draft-ietf-simple-message-sessions-04
o Removed the direction attribute. Rather than using a comedia
styled direction negotiation, we just state that the answerer
opens any needed connection.
16.8 draft-ietf-simple-message-sessions-03
o Removed all specification of relays, and all features specific to
the use of relays. The working group has chosen to move relay
work into a separate effort, in order to advance the base
specification. (The MSRP acronym is unchanged for the sake of
convenience.) This included removal of the BIND method, all
response codes specific to BIND, Digest Authentication, and the
inactivity timeout.
o Removed text indicating that an endpoint could retry failed
requests on the same connection. Rather, the endpoint should
consider the connection dead, and either signal a reconnection or
end the session.
o Added text describing subsequent SDP exchanges. Added mandatory
"count" parameter to the direction attribute to allow explicit
signaling of the need to reconnect.
o Added text to describe the use of send and receive only indicators
in SDP for one-way transfer of large content.
o Added text requiring unique port field values if multiple M-line's
exist.
Campbell, et al. Expires August 24, 2005 [Page 50]
Internet-Draft MSRP February 2005
o Corrected a number of editorial mistakes.
16.9 draft-ietf-simple-message-sessions-02
o Moved all content type negotiation from the "m"-line format list
into "a"-line attributes. Added the accept-types attribute. This
is due to the fact that the sdp format-list syntax is not
conducive to encoding MIME content types values.
o Added "other-method" construction to the message syntax to allow
for extensible methods.
o Consolidated all syntax definitions into the same section.
Cleaned up ABNF for digest challenge and response syntax.
o Changed the session inactivity timeout to 12 minutes.
o Required support for the SHA1 algorithm.
o Required support for the message/cpim format.
o Fixed lots of editorial issues.
o Documented a number of open issues from recent list discussions.
16.10 draft-ietf-simple-message-sessions-01
o Abstract rewritten.
o Added architectural considerations section.
o The m-line format list now only describes the root body part for a
request. Contained body part types may be described in the
"accept-wrapped-types" a-line attribute.
o Added a standard dummy value for the m-line port field. Clarified
that a zero in this field has normal SDP meaning.
o Clarified that an endpoint is globally configured as to whether or
not to use a relay. There is no relay discovery mechanism
intrinsic to MSRP.
o Changed digest algorithm to SHA1. Added TR-ID and S-URI to the
hash for digest authentication.
o CMS usage replaced with S/MIME.
o TLS and msrps: usage clarified.
o Session state timeout is now based on SEND activity, rather than
BIND and VISIT refreshes.
o Default port added.
o Added sequence diagrams to the example message flows.
o Added discussion of self-signed certificates in the security
considerations section.
16.11 draft-ietf-simple-message-sessions-00
o Name changed to reflect status as a work group item.
o This version no longer supports the use of multiple sessions
across a single TCP session. This has several related changes:
There is now a single session URL, rather than a separate one for
each endpoint. The session URL is not required to be in requests
Campbell, et al. Expires August 24, 2005 [Page 51]
Internet-Draft MSRP February 2005
other than BIND and VISIT, as the session can be determined based
on the connection on which it arrives.
o BIND and VISIT now create soft state, eliminating the need for the
RELEASE and LEAVE methods.
o The MSRP URL format was changed to better reflect generic URL
standards. URL comparison and resolution rules were added. SRV
usage added.
o Determination of host and visitor roles now uses a direction
attribute much like the one used in COMEDIA.
o Format list negotiation expanded to allow a "prefer these formats
but try anything" semantic
o Clarified handling of direction notification failures.
o Clarified signaling associated with session failure due to dropped
connections.
o Clarified security related motivations for MSRP.
o Removed MIKEY dependency for session key exchange. Simple usage
of k-lines in SDP, where the SDP exchange is protected end-to-end
seems sufficient.
16.12 draft-campbell-simple-im-sessions-01
Version 01 is a significant re-write. References to COMEDIA were
removed, as it was determined that COMEDIA would not allow
connections to be used bidirectional in the presence of NATs.
Significantly more discussion of a concrete mechanism has been added
to make up for no longer using COMEDIA. Additionally, this draft and
draft-campbell-cpimmsg-sessions (which would have also changed
drastically) have now been combined into this single draft.
17. Contributors and Acknowledgments
In addition to the editors, The following people contributed
extensive work to this document: Chris Boulton, Paul Kyzivat, Orit
Levin, Adam Roach, Jonathan Rosenberg, and Robert Sparks.
The following people contributed substantial discussion and feedback
to this ongoing effort: Eric Burger, Allison Mankin, Jon Peterson,
Brian Rosen, Dean Willis, Aki Niemi, Hisham Khartabil, Pekka Pessi,
Miguel Garcia, Peter Ridler, and Sam Hartman.
18. References
18.1 Normative References
[1] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[2] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session
Campbell, et al. Expires August 24, 2005 [Page 52]
Internet-Draft MSRP February 2005
Description Protocol",
Internet-Draft draft-ietf-mmusic-sdp-new-23, December 2004.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[4] 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.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[8] Troost, R., Dorner, S. and K. Moore, "Communicating
Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, August 1997.
[9] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax",
internet-draft draft-fielding-uri-rfc2396bis-07, September
2004.
[10] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J. and
T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 3546, June 2003.
[11] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002.
[12] Klyne, G. and D. Atkins, "Common Presence and Instant Messaging
(CPIM): Message Format", RFC 3862, August 2004.
[13] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
Transport Layer Secur ity (TLS)", RFC 3268, June 2002.
[14] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 3629, November 2003.
18.2 Informational References
[15] Johnston, A. and O. Levin, "Session Initiation Protocol Call
Campbell, et al. Expires August 24, 2005 [Page 53]
Internet-Draft MSRP February 2005
Control - Conferencing for User Agents",
Internet-Draft draft-ietf-sipping-cc-conferencing-05, October
2004.
[16] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo,
"Best Current Practices for Third Party Call Control in the
Session Initiation Protocol", rfc 3725, April 2004.
[17] Sparks, R. and A. Johnston, "Session Initiation Protocol Call
Control - Transfer",
Internet-Draft draft-ietf-sipping-cc-transfer-03, October 2004.
[18] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging", RFC 3428, December 2002.
[19] Mahy, R., "Benefits and Motivation for Session Mode Instant
Messaging",
Internet-Draft draft-mahy-simple-why-session-mode-01, February
2004.
[20] Jennings, C. and R. Mahy, "Relay Extensions for Message
Sessions Relay Protocol (MSRP)",
Internet-Draft draft-ietf-simple-msrp-relays-03, February 2005.
[21] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
Internet-Draft draft-ietf-sip-identity-03 , September 2004.
[22] Jennings, C. and J. Peterson, "Certificate Management Service
for SIP", Internet-Draft draft-ietf-sipping-certs-00, October
2004.
[23] Yon, D., "Connection-Oriented Media Transport in SDP",
Internet-Draft draft-ietf-mmusic-sdp-comedia-09, September
2004.
[24] Peterson, J., "A Common Profile for Instant Messaging (CPIM)",
rfc 3860, August 2004.
[25] Housley, R., "Triple-DES and RC2 Key Wrapping", RFC 3217,
December 2001.
[26] Ramsdell, B., "S/MIME Version 3 Message Specification",
RFC 2633, June 1999.
[27] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing Tone
Generation in the Session Initiation Protocol (SIP)",
Campbell, et al. Expires August 24, 2005 [Page 54]
Internet-Draft MSRP February 2005
Internet-Draft draft-ietf-sipping-early-media-02, June 2004.
[28] Saint-Andre, P., "Extensible Messaging and Presence Protocol
(XMPP): Instant Messaging and Presence", rfc 3921, October
2004.
[29] Rosenberg, J., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)", rfc 3840, August 2004.
Authors' Addresses
Ben Campbell (editor)
Estacado Systems
Email: ben@estacado.net
Rohan Mahy (editor)
Airespace
110 Nortech Parkway
San Jose, CA 95134
USA
Email: rohan@ekabal.com
Cullen Jennings (editor)
Cisco Systems, Inc.
170 West Tasman Dr.
MS: SJC-21/2
San Jose, CA 95134
USA
Phone: +1 408 421-9990
Email: fluffy@cisco.com
Campbell, et al. Expires August 24, 2005 [Page 55]
Internet-Draft MSRP February 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Campbell, et al. Expires August 24, 2005 [Page 56]