SIMPLE WG B. Campbell, Ed.
Internet-Draft Estacado Systems
Expires: February 23, 2005 R. Mahy, Ed.
C. Jennings, Ed.
Cisco Systems, Inc.
August 25, 2004
The Message Session Relay Protocol
draft-ietf-simple-message-sessions-08.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
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
media stream when setup via a rendezvous or session setup protocol
such as the Session Initiation Protocol (SIP).
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Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction and Background . . . . . . . . . . . . . . . . 4
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 5
4. Key Concepts . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 MSRP Framing and Message Chunking . . . . . . . . . . . . 8
4.2 MSRP Addressing . . . . . . . . . . . . . . . . . . . . . 9
4.3 MSRP Transaction and Report Model . . . . . . . . . . . . 9
4.4 MSRP Connection Model . . . . . . . . . . . . . . . . . . 10
5. MSRP URLs . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1 MSRP URL Comparison . . . . . . . . . . . . . . . . . . . 13
5.2 Resolving MSRP Host Device . . . . . . . . . . . . . . . . 14
6. Method-Specific Behavior . . . . . . . . . . . . . . . . . . 14
6.1 Constructing Requests . . . . . . . . . . . . . . . . . . 14
6.1.1 Delivering SEND requests . . . . . . . . . . . . . . . 15
6.1.2 Sending REPORT requests . . . . . . . . . . . . . . . 18
6.1.3 Failure REPORT Generation . . . . . . . . . . . . . . 18
6.2 Constructing Responses . . . . . . . . . . . . . . . . . . 19
6.3 Receiving Requests . . . . . . . . . . . . . . . . . . . . 20
6.3.1 Receiving SEND requests . . . . . . . . . . . . . . . 20
6.3.2 Receiving REPORT requests . . . . . . . . . . . . . . 21
7. Using MSRP with SIP . . . . . . . . . . . . . . . . . . . . 22
7.1 SDP Offer-Answer Exchanges for MSRP Sessions . . . . . . . 22
7.1.1 URL Negotiations . . . . . . . . . . . . . . . . . . . 24
7.1.2 Path Attributes with Multiple URLs . . . . . . . . . . 25
7.1.3 Updated SDP Offers . . . . . . . . . . . . . . . . . . 26
7.1.4 Example SDP Exchange . . . . . . . . . . . . . . . . . 26
7.1.5 Connection Negotiation . . . . . . . . . . . . . . . . 27
7.2 MSRP User Experience with SIP . . . . . . . . . . . . . . 27
8. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 28
9. Response Code Descriptions . . . . . . . . . . . . . . . . . 30
9.1 200 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2 400 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.3 403 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.4 415 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.5 426 . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.6 481 . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.7 506 . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 31
10.1 Basic IM session . . . . . . . . . . . . . . . . . . . . 31
10.2 Chunked Message . . . . . . . . . . . . . . . . . . . . 33
10.3 System Message . . . . . . . . . . . . . . . . . . . . . 33
10.4 Positive Report . . . . . . . . . . . . . . . . . . . . 34
10.5 Forked IM . . . . . . . . . . . . . . . . . . . . . . . 34
11. Extensibility . . . . . . . . . . . . . . . . . . . . . . . 37
12. CPIM compatibility . . . . . . . . . . . . . . . . . . . . . 37
13. Security Considerations . . . . . . . . . . . . . . . . . . 38
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14. IANA Considerations . . . . . . . . . . . . . . . . . . . . 40
14.1 MSRP Port . . . . . . . . . . . . . . . . . . . . . . . 40
14.2 MSRP URL Schemes . . . . . . . . . . . . . . . . . . . . 40
14.3 SDP Parameters . . . . . . . . . . . . . . . . . . . . . 40
14.3.1 Accept Types . . . . . . . . . . . . . . . . . . . . 40
14.3.2 Wrapped Types . . . . . . . . . . . . . . . . . . . 40
14.3.3 Max Size . . . . . . . . . . . . . . . . . . . . . . 41
14.3.4 Path . . . . . . . . . . . . . . . . . . . . . . . . 41
15. Change History . . . . . . . . . . . . . . . . . . . . . . . 41
15.1 draft-ietf-simple-message-sessions-08 . . . . . . . . . 41
15.2 draft-ietf-simple-message-sessions-07 . . . . . . . . . 41
15.3 draft-ietf-simple-message-sessions-06 . . . . . . . . . 42
15.4 draft-ietf-simple-message-sessions-05 . . . . . . . . . 42
15.5 draft-ietf-simple-message-sessions-04 . . . . . . . . . 43
15.6 draft-ietf-simple-message-sessions-03 . . . . . . . . . 43
15.7 draft-ietf-simple-message-sessions-02 . . . . . . . . . 43
15.8 draft-ietf-simple-message-sessions-01 . . . . . . . . . 44
15.9 draft-ietf-simple-message-sessions-00 . . . . . . . . . 44
15.10 draft-campbell-simple-im-sessions-01 . . . . . . . . . . 45
16. Contributors and Acknowledgments . . . . . . . . . . . . . . 45
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
17.1 Normative References . . . . . . . . . . . . . . . . . . . 45
17.2 Informational References . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 48
Intellectual Property and Copyright Statements . . . . . . . 49
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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 textual messages between two or more parties can
be viewed as part of a session with a definite start 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 [19]. Session-mode messaging has a number of benefits [20]
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 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.
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 [18] Alice to Carol, introducing them into their own
messaging session. Messaging sessions can then be easily integrated
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into call-center and dispatch environments utilizing third-party call
control [17] and conferencing [16] applications.
3. 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 offer
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.)
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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 10.1.1.1
m=message 9 msrp *
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 10.2.2.2
m=message 9 msrp *
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
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.
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MSRP a786hjs2 SEND
To-Path: msrp://biloxi.example.com:12763/kjhd37s2s2;tcp
From-Path: msrp://atlanta.example.com:7654/jshA7we;tcp
Message-ID: 87652
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
-------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 4.1.
Alice can also specify what type of reporting she would like in
response to her request. If Alice requests positive
acknowledgements, 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 4.3.
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
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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 peer-to-peer session, that
is, for a single hop. But is designed with the expectation that MSRP
can carry URLs for nodes on the far side of gateways or relays. For
this reason, a URL with the "msrps" scheme makes no assertion about
the security properties of other hops, just the next hop.
MSRP URLs are discussed in more detail in Section 5.
An adjacent pair of busy MSRP nodes (for example two gateways) 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 4.4.
4. Key Concepts
4.1 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. To support this, MSRP uses a boundary based
framing mechanism. The header of an MSRP request contains a unique
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.
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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 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.
The ability to interrupt messages is needed so that TCP connections
can be shared. Connection sharing is necessary for "fair" allocation
of bandwidth in congestion situations and for allowing MSRP network
elements that have a very large number of concurrent connections to
different users.
4.2 MSRP Addressing
MSRP entities are addressed using URLs. The MSRP URL schemes are
defined in Section 5. The syntax of the To-Path and From-Path
headers 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.
4.3 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 [29] 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
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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 "Report-Success" can have a value of "yes" or "no" and the
"Report-Failure" 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. Report-Success 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 Report-Failure 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 Report-Failure of
"yes" is used by many systems that wish to notify the user if the
message failed but some other systems choose to use a value of
"partial" to reduce the load on the servers caused by 200 OK
responses, but still allow error responses to be sent in many cases.
4.4 MSRP Connection Model
When MSRP wishes to send a request to a peer identified by an MSRP
URL, it first needs a 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 convention is that the
element that sent the SDP offer MUST immediately issue a SEND request
to the answerer. This request MAY have a empty body, or MAY carry
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content.
When a new connection needs to be formed, the element 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 5.2. For connections using the msrps:
scheme, 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 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 to determine the identity of
the connecting device.
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 that this URL was given to. 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
on another connection. If so, 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 failed any sessions associated with the connection as well.
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. 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
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without warning of the duplicates.
In this situation, the endpoint MUST choose Message-ID values so that
they are 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 normal
circumstances.
If a connection fails, the sender SHOULD attempt to re-setup the URL
path using a new offer, for example, in a SIP re-invite or update
[12]. It MUST not assume that the new URLs in the SDP will be the
same as the old ones. A connection SHOULD not be closed while there
are sessions that are using this connection.
5. MSRP URLs
An MSRP URL follows a subset of the URL syntax in Appendix A of
RFC2396 [10], with a scheme of "msrp" or "msrps":
MSRP_urls = msrp-scheme "://" [userinfo "@"] hostport ["/"
resource] ";" transport
msrp-scheme = "msrp" / "msrps"
resource = 1*unreserved
transport = "tcp" / ALPHANUM
The constructions for "userinfo", "hostport", and "unreserved" are
detailed in RFC2396 [10]. URLs designating MSRP over TCP MUST
include the "tcp" parameter. If some other transport is used, the
"tcp" parameter MUST NOT be present.
Since this document only specifies MSRP over TCP, all MSRP URLs
herein use the "tcp" parameter. Documents that provide bindings
on other transports should define respective parameters for those
transports.
An MSRP URL hostport field identifies a participant in an MSRP
session. If the hostport contains a numeric IP address, it MUST also
contain a port. The resource part identifies a particular session
the participant. The absence of the resource part indicates a
reference to an MSRP host device, but does not specifically refer to
a particular session resource.
A scheme of "msrps" indicates the underlying connection MUST be
protected with TLS.
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MSRP has an IANA registered recommended port defined in Section 14.1.
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 following is an example of a typical MSRP URL:
msrp://host.example.com:8493/asfd34;tcp
5.1 MSRP URL Comparison
MSRP URL comparisons MUST be performed according to the following
rules:
1. The scheme must match exactly.
2. If the hostpart contains an eplicit IP address, and/or port,
these are compared numerically. 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 resource part is compared as case sensitive. A URL without a
resource part is never equivalent to one that includes a resource
part.
5. URLs with different "transport" parameters never match. Two URLs
that are identical except for transport are not equivalent.
6. Userinfo parts are not considered for URL comparison.
Path normalization is not relevant for MSRP URLs. Escape
normalization is not required, since the relevant parts are limited
to unreserved characters.
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5.2 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 always created and
consumed by automata, rather than by humans. The introduction of
relays may create situations where this is not the case. For
example, the MSRP URL 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 [21] 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.
6. Method-Specific Behavior
6.1 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
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headers. The Content-Type header MUST be the last header line. The
body MUST be separated from the headers with an extra CRLF.
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 that is a "$" (for the last chunk of the complete
message), "#" (for the last chunk of an aborted message), or "+" (for
chunks other than the last). If the chunk represents the data that
forms the end of the complete message, the flag value MUST be a "$".
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 check the body to
insure 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.
Finally, requests which have no body MUST NOT contain a Content-Type
header or any other MIME specific header. Bodiless requests MUST
contain a closing sequence after the final header.
Once a request is ready for delivery, the sender follows the
connection management (Section 4.4) rules to forward the request over
an existing open connection or create a new connection.
6.1.1 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 the message is larger than 2048 octets in length, it
either generates an interruptible chunk (which is RECOMMENDED), or it
MAY break the complete message into chunks of 2048 octets. It then
generates a SEND request for each chunk, following the procedures
for constructing requests (Section 6.1).
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 Report-Failure and/or Report-Success header field with
an appropriate value. All chunks of the same message MUST use the
same Report-Failure and Report-Success values in their SEND requests.
If success reports are requested, i.e. the value of the
Report-Success header is "yes", the sending device MAY wish to run a
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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 "Report-Failure" 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.
If no Report-Success header is present in a SEND request, it MUST be
treated the same as a Report-Success header with value of "no". If
no Report-Failure header is present, it MUST be treated the same as a
Report-Failure 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 element receives a REPORT for a Message-ID
it does not recognize, it SHOULD silently ignore the REPORT.
Report-Success and Report-Failure 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 byte in the message is indicated
by a 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 (that is, 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. All
chunks other than the last MUST include a "+" character in the
continuation field of the closing line. The final chunk MUST use a
"$" character if it completes the message, or a "#" if the sender is
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aborting the message. The sender MUST send all chunks in Byte-Range
order. (However, the receiver cannot assume the requests will be
delivered in order, as an intervening relay may have changed the
order.)
To insure fairness over a connection, senders MUST NOT send chunks
with a body larger than 2048 octets unless they are prepared to
interrupt them. 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) 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 0 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 complete message.
A SEND request is interruptible if it either has no Byte-Range header
field, or has such a field with a "*" in the last-byte sub-field.
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 2k MUST be interrupted to send pending
response 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 it was sent with. An intervening
relay could possibly break SEND requests into smaller chunks, or
aggregate multiple chunks into larger ones.
The default disposition of body is "render". If the sender wants
different disposition, it MAY insert a Content-Disposition header.
Since MSRP is a binary protocol, transfer encoding MUST be "binary".
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6.1.2 Sending REPORT requests
REPORT requests are similar to SEND requests, except that report
requests MUST NOT include Report-Success or Report-Failure 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 assocated 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 2 kilobytes.
An endpoint MUST send a success report if it successfully receives a
SEND request which contained a Report-Success 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 6.1), 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 endpoint MUST NOT send a success report for a SEND request that
either contained no Report-Success header field, or contained such a
field with a value of "no". That is, if no Report-Success header
field is present, it is treated identically to one with a value of
"no."
6.1.3 Failure REPORT Generation
If an MSRP endpoint receives a SEND request that it cannot process
for some reason, and the Report-Failure header either was not present
in the original request, or had a value of "yes", it SHOULD simply
include the appopriate error code in the transaction respons.
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
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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 Report-Failure header
field value of "no", then it MUST NOT send a failure REPORT request,
and SHOULD NOT send an MSRP response. If the value is "partial", it
SHOULD NOT send a 200 response to the request, but SHOULD send a
non-200 class response if appropriate.
As stated above, if no Report-Failure header is present, it MUST be
treated the same as a Report-Failure header with value of "yes".
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.
6.2 Constructing Responses
If an MSRP endpoint receives a request that either contains a
Report-Failure header value of "yes", or does not contain a
Report-Failure header field at all, it MUST immediately generate a
response. Likewise, if an MSRP endpoint receives a request that
contains a Report-Failure 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.
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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) URI in the
From-Path header field of the request. (Unlike other methods,
responses to SEND requests are returned only to the previous hop.)
For responses to all other requests, 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 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.
6.3 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, and
the request contained a Report-Failure header value of "no", then the
receiver SHOULD quietly ignore the request. If the Report-Failure
header is not present, or had any other value, then the receiver MUST
return a 481 response.
Further request processing by the receiver is method specific.
6.3.1 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 "$", then the request contained the
entire message. Otherwise, the receiver looks at the Message-ID
value to associate chunks together into the original message. It
forms a virtual buffer to receive the message, keeping track of which
bytes have been received and which are missing. The receiver takes
the data from the request and places it in the appropriate place in
the buffer. The receiver MUST determine the actual length of each
chunk by inspecting the payload itself; it is possible the body is
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shorter than the range-end field indicates. This can occur if the
sender interrupted a SEND request unexpectedly. It is worth nothing
that the chunk that has a termination character of "$" defines the
total length of the message.
Receivers MUST not assume the chunks will be delivered in order or
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 chunks
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 SHOULD send a 415 response, if
allowed by the Report-Failure header field. All MSRP endpoints MUST
be able to receive the multipart/mixed and multipart/alternative MIME
types.
6.3.2 Receiving REPORT requests
When an endpoint receives a REPORT request, it may correlate 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.
An endpoint that receives a REPORT request containing a Status header
with a namespace field of "000", it SHOULD interpret the report in
exactly the same way it would interpret an MSRP transaction response
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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.
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.
MSRP Modes MUST NOT send MSRP responses to REPORT requests.
7. Using MSRP with SIP
7.1 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.
The general format of an SDP media-line is:
m=<media> <port> <protocol> <format list>
An offered or accepted MSRP media-line MUST have the following value
exactly, with the exception that the port field MAY be set to zero.
(According to [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).)
m=message 9 msrp *
While MSRP could theoretically carry any media type, "message" is
appropriate. For MSRP, the port number is always ignored--the
actual port number is provided in an MSRP URL. Instead a dummy
value is used, which is always ignored if non-zero. The protocol
is always "msrp", and the value of the format list is always a
single asterisk character ("*").
An MSRP media-line is always accompanied by a mandatory "path"
attribute. This attribute contains a space separated list of URLs
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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.
MSRP media lines 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
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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 [13] gateway device may require all messages to be wrapped
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.
An endpoint MAY indicate the maximim size message they wish to
receive using the max-size a-line attribute Max-size refers to the
complete message, 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.
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)
7.1.1 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 5.
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
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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://a.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 9 msrp *
a=accept-types:text/plain
a=path:msrp://a.example.com:7394/2s93i;tcp
The rightmost URI 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 URI 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 13.
7.1.2 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; that is, the
relay to which the peer device, or a relay operation on its behalf,
should connect.
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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.
While endpoints that implement only this specification will never
introduce a relay, they will 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.
7.1.3 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.
7.1.4 Example SDP Exchange
Endpoint A wishes to invite Endpoint B to a MSRP session. A offers
the following session description:
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v=0
o=usera 2890844526 2890844527 IN IP4 alice.example.com
s=
c=IN IP4 alice.example.com
t=0 0
m=message 9 msrp *
a=accept-types: message/cpim text/plain text/html
a=path:msrp://alice.example.com:7394/2s93i9;tcp
B responds with its own URL:
v=0
o=userb 2890844530 2890844532 IN IP4 bob.example.com
s=
c=IN IP4 bob.example.com
t=0 0
m=message 9 msrp *
a=accept-types:message/cpim text/plain
a=path:msrp://bob.example.com:8493/si438ds;tcp
7.1.5 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 [24] 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.
7.2 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
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messages.
SIP INVITE requests may be forked by a SIP proxy, resulting in more
than one endpoint receiving the same INVITE. SIP early media [28]
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.
8. Formal Syntax
MSRP is a text protocol that uses the UTF-8 [15] 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 = %53.45.4e.44 ; SEND in caps
mREPORT = %52.45.50.4f.52.54; REPORT in caps
other-method = 1*UPALPHA
status-code = 3DIGIT
headers = 1*( header CRLF )
header = ( To-Path
/ From-Path
/ Message-ID
/ Report-Success
/ Report-Failure
/ Byte-Range
/ Status
/ ext-header )
To-Path = "To-Path:" SP URL *( SP URL )
From-Path = "From-Path:" SP URL *( SP URL )
Message-ID = "Message-ID:" SP ident
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Report-Success = "Report-Success:" SP ("yes" / "no" )
Report-Failure = "Report-Failure:" 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 / "*"
dUmMy= "Status:" SP namespace SP short-status [SP text-reason]
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 / %xx23-27 / %x2A-2B / %x2D-2E
/ %x30-39 / %x41-5A / %x5E-7E)
quoted-string = DQUOTE *(qdtext / qd-esc) DQUOTE
qdtext = SP / HT / %x21 / %x23-5B / %x5D-7E
/ UTF8-NONASCII
qd-esc = (BACKSLASH BACKSLASH) / (BACKSLASH DQUOTE)
BACKSLASH = "\"
DQUOTE = %x22
CRLF = %x0D.0A
HT = %x09
SP = %x20
UPALPHA = %x41-5A
LOWALPHA = %x61-7A
DIGIT = %x30-39
ALPHANUM = LOWALPHA / UPALPHA / DIGIT
Other-Mime-Header = (Content-ID
/ Content-Description
/ Content-Disposition
/ mime-extension-field);
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; 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 = *(HT / %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
9. 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.
9.1 200
The 200 response code indicates a successful transaction.
9.2 400
A 400 response indicates a request was unintelligible.
9.3 403
The action is not allowed
9.4 415
A 415 response indicates the SEND request contained a MIME
content-type that is not understood by the receiver.
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9.5 426
A 426 response indicates that the request is only allowed over TLS
protected connections.
9.6 481
A 481 response indicates that no session exists for the connection.
9.7 506
A 506 response indicates that a request arrived on a session which is
already bound to another network connection.
10. Examples
10.1 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 |
|<-----------------------|
| |
| |
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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 9 msrp *
a=accept-types:text/plain
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 9 msrp *
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):
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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):
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
10.2 Chunked Message
For an example of a chunked message, see the example in Section 4.1.
10.3 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
Report-Failure: no
Report-Success: no
Content-Type:text/plain
This conference will end in 5 minutes
-------d93kswow$
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10.4 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
Report-Success: 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$
10.5 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
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.
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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 [30]. 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).
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
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
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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----------------->| | |
| |--INVITE---------------------------->| romeo wants
| | | | | to IM w/ you
| |<---486 Busy Here--------------------| |
| |----ACK----------------------------->| |
| | | | | |
| |--INVITE---------------------------------------->|
| |<---200 OK---------------------------------------|
|<--200 OK---| | | | |
|---ACK------------------------------------------------------->|
|<================MSRP Session================================>|
| | | | | |
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| Hi Romeo, Juliet is |
| with her father now |
| can i take a message?|
| |
| Tell her to go to confession tommorrow.... |
11. 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
interoperablility, 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.
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.
12. CPIM compatibility
MSRP sessions may be gatewayed to other CPIM [25]compatible
protocols. If this occurs, the gateway MUST maintain session state,
and MUST translate between the MSRP session semantics and CPIM
semantics that 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" [7] 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 chuncks, if
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needed.
13. 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
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.
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
SIP. If the SIP offer or answer is not TLS or S/MIME [27] protected,
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 SIP signaling to set up the session is protected with TLS (using
sips). In this case, when host A contacts host B, the secret is
passed through a SIP 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 only feasible when connecting to gateways
or relays , as the types of hosts that end clients use for sending
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instant messages are unlikely to have a long term stable IP address
or a stable DNS name that a certificate can bind to. In addition,
the cost of server certificates from well known certificate
authorities is currently too high for the vast majority of end users
to even consider getting one for each client.
The only real security for connections without relays is achieved
using S/MIME. This does not require the actual endpoint to have
certificates from a well known certificate authority. The Identity
[22] and Certificates [23] mechanism with SIP 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 this risk is mitigated if all the MSRP content is
encrypted and signed with S/MIME.
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 an 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.
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 [11]. A TLS cipher-suite of
TLS_RSA_WITH_AES_128_CBC_SHA [14] MUST be supported (other
cipher-suites MAY also be supported).
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 [26] provided in the session setup.
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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.
14. IANA Considerations
14.1 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 5
14.2 MSRP URL Schemes
This document defines the URL schemes of "msrp" and "msrps".
Syntax See Section 5.
Character Encoding See Section 5.
Intended Usage See Section 5.
Protocols The Message Session Relay Protocol (MSRP).
Security Considerations See Section 13.
Relevant Publications RFCXXXX
[Note to RFC Editor: Please replace RFCXXXX in the above
paragraph with the actual number assigned to this document.
14.3 SDP Parameters
This document registers the following SDP parameters in the
sdp-parameters registry:
14.3.1 Accept Types
Attribute-name: accept-types
Long-form Attribute Name Acceptable MIME Types
Type: Media level
Subject to Charset Attribute No
Purpose and Appropriate Values See Section 7.1.
14.3.2 Wrapped Types
Attribute-name: accept-wrapped-types
Long-form Attribute Name Acceptable MIME Types Inside Wrappers
Type: Media level
Subject to Charset Attribute No
Purpose and Appropriate Values See Section 7.1.
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14.3.3 Max Size
Attribute-name: max-size
Long-form Attribute Name Maximum message size.
Type: Media level
Subject to Charset Attribute No
Purpose and Appropriate Values See Section 7.1.
14.3.4 Path
Attribute-name: path
Long-form Attribute Name MSRP URL Path
Type: Media level
Subject to Charset Attribute No
Purpose and Appropriate Values See Section 7.1.1.
15. Change History
15.1 draft-ietf-simple-message-sessions-08
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.
Added the "#" value for the continuation-flag to indicate the last
chunk of an abandoned message.
Added direction that s/mime and cpim envelops must be applied
before chunking.
Added direction to set the last-byte field in byte-range to "*" if
there is any chance of interrupting a SEND request.
Changed max-size to refer to entire message, instead of a
particular MIME content-type
Added requirent for the use of UTF-8, and reference to RFC3629
Added requrement to ignore unknown headers.
Several ABNF fixes
Removed redundant material between normative sections.
Numerous editorial fixes.
15.2 draft-ietf-simple-message-sessions-07
Significant re-write to attempt to improve readability.
Added maximum size parameter in accept-types
Changed the Boundary field to be part of the start-line rather
than a header field.
Removed the TR-IDheader, 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.
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Removed transport selection from URL scheme and added the "tcp"
parameter.
Added description of the "simple" mode with no transaction
responses, and made mode selection dependent on the reporting
level requested for a give message.
Changed the DSN section to reflect separate request of success and
failure reports. Enhanced REPORT method to be useful even without
a payload.
removed SRV usage for URL resolution. This is only used for relay
discovery, and therefore should be moved to the relay draft.
Added discussion about late REPORT handling. Asserted that REPORT
requests are always sent in simple mode.
Removed the dependency on multipart/byteranges for fragmentation.
Incorporated the Byte-Range header into the base MSRP header set.
Removed the VISIT method. Change to use SEND to serve the purpose
formerly reserved to VISIT.
15.3 draft-ietf-simple-message-sessions-06
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.
Changed mechanism for signaling transport and TLS protection into
the MSRP URL, rather than the SDP M-Line.
Removed length field from start line and added Boundary header
field and Closing field.
Added recommendation to fragment any content over 2k.
Added Rohan's proposal to make offerer connect to answerer. (With
open issue for more discussion.)
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.
Updated DSN section. Added text on field usage.
Fixed change TR-ID header from version 05 were erroneously
attributed to 04.
15.4 draft-ietf-simple-message-sessions-05
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.
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.
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Added section for Delivery Status Notification handling, and added
associated entries into the syntax definition.
Added content fragmentation section.
Removed recommendation to start separate session for large
transfers.
Corrected some mistakes in the syntax definitions.
Added Chris Boulton as a co-author for his contribution of the DSN
text.
15.5 draft-ietf-simple-message-sessions-04
Removed the direction attribute. Rather than using a comedia
styled direction negotiation, we just state that the answerer
opens any needed connection.
15.6 draft-ietf-simple-message-sessions-03
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.
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.
Added text describing subsequent SDP exchanges. Added mandatory
"count" parameter to the direction attribute to allow explicit
signaling of the need to reconnect.
Added text to describe the use of send and receive only indicators
in SDP for one-way transfer of large content.
Added text requiring unique port field values if multiple M-line's
exist.
Corrected a number of editorial mistakes.
15.7 draft-ietf-simple-message-sessions-02
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.
Added "other-method" construction to the message syntax to allow
for extensible methods.
Consolidated all syntax definitions into the same section.
Cleaned up ABNF for digest challenge and response syntax.
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Changed the session inactivity timeout to 12 minutes.
Required support for the SHA1 algorithm.
Required support for the message/cpim format.
Fixed lots of editorial issues.
Documented a number of open issues from recent list discussions.
15.8 draft-ietf-simple-message-sessions-01
Abstract rewritten.
Added architectural considerations section.
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.
Added a standard dummy value for the m-line port field. Clarified
that a zero in this field has normal SDP meaning.
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.
Changed digest algorithm to SHA1. Added TR-ID and S-URI to the
hash for digest authentication.
CMS usage replaced with S/MIME.
TLS and msrps: usage clarified.
Session state timeout is now based on SEND activity, rather than
BIND and VISIT refreshes.
Default port added.
Added sequence diagrams to the example message flows.
Added discussion of self-signed certificates in the security
considerations section.
15.9 draft-ietf-simple-message-sessions-00
Name changed to reflect status as a work group item.
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 URI, rather than a separate one for
each endpoint. The session URI is not required to be in requests
other than BIND and VISIT, as the session can be determined based
on the connection on which it arrives.
BIND and VISIT now create soft state, eliminating the need for the
RELEASE and LEAVE methods.
The MSRP URL format was changed to better reflect generic URL
standards. URL comparison and resolution rules were added. SRV
usage added.
Determination of host and visitor roles now uses a direction
attribute much like the one used in COMEDIA.
Format list negotiation expanded to allow a "prefer these formats
but try anything" semantic
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Clarified handling of direction notification failures.
Clarified signaling associated with session failure due to dropped
connections.
Clarified security related motivations for MSRP.
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.
15.10 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.
16. 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,
and Orit Levin.
17. References
17.1 Normative References
[1] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.
[2] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[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.
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[6] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[7] Atkins, D. and G. Klyne, "Common Presence and Instant Messaging
Message Format", draft-ietf-impp-cpim-msgfmt-08 (work in
progress), January 2003.
[8] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[9] Troost, R., Dorner, S. and K. Moore, "Communicating
Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, August 1997.
[10] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[11] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J. and
T. Wright, "Transport Layer Security (TLS) Extensions", RFC
3546, June 2003.
[12] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002.
[13] Atkins, D. and G. Klyne, "Common Presence and Instant
Messaging: Message Format", draft-ietf-impp-cpim-msgfmt-08
(work in progress), January 2003.
[14] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
Transport Layer Secur ity (TLS)", RFC 3268, June 2002.
[15] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
3269, November 2003.
17.2 Informational References
[16] Johnston, A. and O. Levin, "Session Initiation Protocol Call
Control - Conferencing for User Agents",
draft-ietf-sipping-cc-conferencing-03 (work in progress),
February 2004.
[17] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo,
"Best Current Practices for Third Party Call Control in the
Session Initiation Protocol", draft-ietf-sipping-3pcc-06 (work
in progress), January 2004.
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[18] Sparks, R. and A. Johnston, "Session Initiation Protocol Call
Control - Transfer", draft-ietf-sipping-cc-transfer-02 (work in
progress), February 2004.
[19] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging", RFC 3428, December 2002.
[20] Mahy, R., "Benefits and Motivation for Session Mode Instant
Messaging", draft-mahy-simple-why-session-mode-00 (work in
progress), February 2004.
[21] Mahy, R. and C. Jennings, "Relays for the Message Session Relay
Protocol (MSRP)", draft-ietf-simple-msrp-relays-01.txt (work in
progress), July 2004.
[22] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
draft-ietf-sip-identity-02 (work in progress), May 2004.
[23] Jennings, C. and J. Peterson, "Certificate Management Service
for SIP", draft-jennings-sipping-certs-03 (work in progress),
May 2004.
[24] Yon, D., "Connection-Oriented Media Transport in SDP",
draft-ietf-mmusic-sdp-comedia-05 (work in progress), March
2003.
[25] Peterson, J., "A Common Profile for Instant Messaging (CPIM)",
draft-ietf-impp-im-04 (work in progress), August 2003.
[26] Housley, R., "Triple-DES and RC2 Key Wrapping", RFC 3217,
December 2001.
[27] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
2633, June 1999.
[28] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing Tone
Generation in the Session Initiation Protocol (SIP)",
draft-ietf-sipping-early-media-02 (work in progress), June
2004.
[29] Saint-Andre, P., "Extensible Messaging and Presence Protocol
(XMPP): Instant Messaging and Presence", draft-ietf-xmpp-im-22
(work in progress), April 2004.
[30] Rosenberg, J., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)",
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draft-ietf-sip-callee-caps-03 (work in progress), January 2004.
Authors' Addresses
Ben Campbell (editor)
Estacado Systems
EMail: ben@nostrum.com
Rohan Mahy (editor)
Cisco Systems, Inc.
5617 Scotts Valley Drive, Suite 200
Scotts Valley, CA 95066
USA
EMail: rohan@cisco.com
Cullen Jennings (editor)
Cisco Systems, Inc.
170 West Tasman Dr.
MS: SJC-21/2
San Jose, CA 95134
USA
EMail: fluffy@cisco.com
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Campbell, et al. Expires February 23, 2005 [Page 49]
