Internet Engineering Task Force J. Rosenberg
Internet-Draft D. Willis
Expires: May 2, 2002 R. Sparks
B. Campbell
dynamicsoft
H. Schulzrinne
J. Lennox
Columbia University
C. Huitema
B. Aboba
D. Gurle
Microsoft Corporation
D. Oran
Cisco Systems
Nov. 2001
SIP Extensions for Instant Messaging
draft-ietf-sip-message-00
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 2, 2002.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
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Abstract
This document defines a SIP extension (a single new method) that
supports Instant Messaging (IM).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Changed Introduced in draft-ietf-sip-message-00 . . . . . . 3
3. Changes Introduced in draft-ietf-simple-im-01 . . . . . . . 4
4. Changes Introduced in draft-ietf-simple-im-00 . . . . . . . 4
5. Changes Introduced in draft-rosenberg-impp-im-01 . . . . . . 4
6. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Overview of Operation . . . . . . . . . . . . . . . . . . . 5
8. The MESSAGE request . . . . . . . . . . . . . . . . . . . . 6
8.1 Method Definition . . . . . . . . . . . . . . . . . . . . . 6
8.2 UAC processing of MESSAGE request . . . . . . . . . . . . . 8
8.3 Finding the next hop . . . . . . . . . . . . . . . . . . . . 9
8.4 Proxy processing of MESSAGE requests . . . . . . . . . . . . 9
8.5 UAS processing of MESSAGE requests . . . . . . . . . . . . . 10
8.6 UAS processing of MESSAGE response . . . . . . . . . . . . . 10
9. Caller Preferences . . . . . . . . . . . . . . . . . . . . . 11
10. Mapping to CPIM . . . . . . . . . . . . . . . . . . . . . . 11
10.1 Mapping SIP Requests to CPIM . . . . . . . . . . . . . . . . 11
10.2 Mapping CPIM Responses to SIP . . . . . . . . . . . . . . . 12
10.3 Mapping CPIM operations to SIP . . . . . . . . . . . . . . . 12
10.4 Mapping SIP responses to CPIM . . . . . . . . . . . . . . . 12
10.5 URL Scheme Mapping . . . . . . . . . . . . . . . . . . . . . 12
11. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1 Privacy . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.2 Outbound authentication . . . . . . . . . . . . . . . . . . 13
11.3 Replay Prevention . . . . . . . . . . . . . . . . . . . . . 13
12. Congestion Control . . . . . . . . . . . . . . . . . . . . . 14
13. Example Messages . . . . . . . . . . . . . . . . . . . . . . 14
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 16
References . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
A. Requirements Evaluation . . . . . . . . . . . . . . . . . . 19
Full Copyright Statement . . . . . . . . . . . . . . . . . . 24
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1. Introduction
This document defines an extension to SIP (RFC2543 [2]) to support
Instant Messaging.
Instant messaging is defined as the exchange of content between a
set of participants in real time. Generally, the content is short
textual messages, although that need not be the case. Generally, the
messages that are exchanged are not stored, but this also need not
be the case. IM differs from email in common usage in that instant
messages are usually grouped together into brief live conversations,
consisting of numerous small messages sent back and forth.
Instant messaging as a service has been in existence within
intranets and IP networks for quite some time. Early implementations
include zephyr [1], the unix talk application, and IRC. More
recently, IM has been used as a service coupled with presence and
buddy lists; that is, when a friend comes online, a user can be made
aware of this and have the option of sending the friend an instant
message. The protocols for accomplishing this are all proprietary,
which has seriously hampered interoperability. Furthermore, most of
these protocols tightly couple presence and IM, due to the way in
which the service is offered.
Despite the popularity of presence coupled IM services, IM is a
separate application from presence. There are many ways to use IM
outside of presence (for example, as part of a voice communications
session). Another example are interactive games (possibly
established with SIP - SIP can establish any type of session, not
just voice or video); IM is already a common component of
multiplayer online games. Keeping it apart from presence means it
can be used in such ways. Furthermore, keeping them separate allows
separate providers for IM and for presence service. Of course, it
can always be offered by the same provider, with both protocols
implemented into a single client application.
Along a similar vein, the mechanisms needed in an IM protocol are
very similar to those needed to establish an interactive session -
rapid delivery of small content to a user at their current location,
which may, in general, be dynamically changing as the user moves.
The similarity of needed function implies that existing solutions
for initiation of sessions (namely, the Session Initiation Protocol
(SIP) [2]) is an ideal base on which to build an IM protocol.
2. Changed Introduced in draft-ietf-sip-message-00
The draft name changed (again) due to its move to the SIP working
group.
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The draft now clarifies that, while MESSAGE requests do not
establish dialogs, user agents may group messages into conversation
threads.
The draft clarifies the intend that all implementations must handle
message/cpim body parts.
References to PGP encryption in SIP have been removed.
Open Issue concerning mapping between URL schemes at a CPIM
compliant gateway device has been closed. This draft treats such
mapping as a matter of local policy.
Added text for the congestion control section and removed related
open issues.
3. Changes Introduced in draft-ietf-simple-im-01
This version removes the idea of implicit sessions created by
MESSAGE requests. MESSAGE requests are now completely stateless in
themselves.
The version also some open issues: Bodies are not allowed in
responses; an Accept header on a 415 response includes body types
nested inside message/cpim bodies, all IM UAs MUST be able to
receive message/cpim.
This draft introduces a new section for CPIM mapping. The authors
expect this section will need further work to complete.
4. Changes Introduced in draft-ietf-simple-im-00
The draft name changed to reflect its status as a SIMPLE working
group item. This version introduces no other changes.
5. Changes Introduced in draft-rosenberg-impp-im-01
This submission serves to track transition of the work on a SIP
implementation of IM to the newly formed SIMPLE working group. It
endeavors to capture the progress made in IMPP since the original
submission (in particular, including the im: URL and the
message/cpim body) and detail a set of open issues for the SIMPLE
working group to address.
To support those goals, a great deal of the background and
motivation material in the original text has been shortened or
removed.
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6. Terminology
Most of the terminology used here is defined in RFC2778 [4].
However, we duplicate some of the terminology from SIP in order to
clarify this document:
User Agent (UA): A UA is a piece of software which is capable of
initiating requests, and of responding to requests.
User Agent Server (UAS): A UAS is the component of a UA which
receives requests, and responds to them.
User Agent Client (UAC): A UAC is the component of a UA which sends
requests, and receives responses.
Registrar: A registrar is a SIP server which can receive and
process REGISTER requests. These requests are used to construct
address bindings.
7. Overview of Operation
When one user wishes to send an instant message to another, the
sender formulates and issues a SIP request using the new MESSAGE
method defined by this document. The request URI of this request
will normally be the im: URL of the party to whom the message is
directed (see CPIM [15]), but can also be a normal SIP URL. The body
of the request will contain the message to be delivered. This body
can be of any MIME type, including "message/cpim" [16].
The request may traverse a set of SIP proxies using a variety of
transport mechanism (UDP, TCP, even SCTP [5]) before reaching its
destination. The destination for each hop is located using the
address resolution rules detailed in the CPIM and SIP specifications
(see Section 8 for more detail). During traversal, each proxy may
rewrite the request URI based on available routing information.
Provisional and final responses to the request will be returned to
the sender as with any other SIP request. Normally, a 200 OK
response will be generated by the user agent of the request's final
recipient. Note that this indicates that the user agent accepted the
message, not that the user has seen it.
MESSAGE requests do not create any implied session. They do not in
themselves establish a call leg, or any concept of call state. SIP
proxies may not record-route MESSAGE requests. User Agents may use
Call-ID values and/or In-Reply-To headers to indicate conversation
threading to the end user. Any such threading has no meaning at the
protocol level.
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8. The MESSAGE request
This section defines the syntax and semantics of this extension.
8.1 Method Definition
This specification defines a new SIP method, MESSAGE. The BNF for
this method is:
Message = "MESSAGE"
As with all other methods, the MESSAGE method name is case
sensitive.
Tables 1 and 2 extend Tables 4 and 5 of SIP by adding an additional
column, defining the headers that can be used in MESSAGE requests
and responses.
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where enc. e-e MESSAGE
__________________________________________
Accept R e -
Accept 415 e o
Accept-Encoding R e o
Accept-Encoding 415 e o
Accept-Language R e o
Accept-Language 415 e o
Allow 200 e o
Allow 405 e m
Authorization R e o
Authorization r e o
Call-ID gc n e m
Contact R e -
Contact 2xx e -
Contact 3xx e o
Contact 485 e o
Content-Encoding e e o
Content-Length e e m
Content-Type e e *
CSeq gc n e m
Date g e o
Encryption g n e o
Expires g e o
From gc n e m
Hide R n h o
In-Reply-To R e o
Max-Forwards R n e o
Organization g c h o
Table 1: Summary of header fields, A--O
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where enc. e-e MESSAGE
________________________________________________________
Priority R c e o
Proxy-Authenticate 407 n h o
Proxy-Authorization R n h o
Proxy-Require R n h o
Record-Route R h -
Record-Route 2xx,401,484 h -
Require R e o
Retry-After R c e -
Retry-After 404,413,480,486 c e o
500,503 c e o
600,603 c e o
Response-Key R c e o
Route R h o
Server r c e o
Subject R c e o
Timestamp g e o
To gc(1) n e m
Unsupported 420 e o
User-Agent g c e o
Via gc(2) n e m
Warning r e o
WWW-Authenticate R c e o
WWW-Authenticate 401 c e o
(1): copied with possible addition of tag
(2): UAS removes first Via header field
Table 2: Summary of header fields, P--Z
A MESSAGE request MAY contain a body, using the standard MIME
headers to identify the content.
Unless stated otherwise in this document, the protocol for emitting
and responding to a MESSAGE request is identical to that for a BYE
request as defined in [2]. The behavior of SIP entities not
implementing the MESSAGE (or any other unknown) method is explicitly
defined in [2].
8.2 UAC processing of MESSAGE request
A MESSAGE request MUST contain a To, From, Call-ID, CSeq, Via, and
Content-Length, formatted as specified in [2].
All UAs MUST be prepared to send and receive MESSAGE requests with a
body of type text/plain. They MUST be prepared to receive and
interpret message/cpim body types, and MAY choose to send
message/cpim body types.
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A UAC MAY send a MESSAGE request within an existing SIP call,
established with an INVITE. In this case, the MESSAGE request is
processed identically to the INFO method [9]. The only difference is
that a MESSAGE request is assumed to be for the purpose of instant
messaging as part of the call, whereas INFO is less specific.
MESSAGE requests do not imply any sort of association or session on
their own. User Agents MUST not insert contact headers into MESSAGE
requests.
A UA MAY associate MESSAGE requests that share the same To, From,
and Call-Id values into conversation threads, using increasing CSeq
values to provide ordering. A UA MAY also use In-Reply-To headers to
provide more precise coversation theading, where two MESSAGE
requests are in the same thread if there exists an In-Reply-To value
chain that connects them. The In-Reply-To approach is more useful
when there are more than two participants in a thread. Such
associations are meaningful at the user interface presentation level
only, and have no meaning whatsoever at the protocol level.
8.3 Finding the next hop
The mechanism used to determine the next hop destination for a SIP
MESSAGE request is detailed in [15] and [2]. Briefly, for the URL
im:user@host,
1. The UA makes a DNS SRV [12] query for _im._sip.host. If any RRs
are returned, they determine the next hop. Otherwise:
2. The UA makes a DNS SRV query for _sip.host. If any RRs are
returned, they determine the next hop. Otherwise:
3. The UA makes a DNS A query for host. If any records are
returned, they determine the address of the next hop. The
destination port is determined from the input URL (if the input
was an im: URL, the request is sent to the default SIP port of
5060).
For sip: URLs, the UA starts at step 2.
8.4 Proxy processing of MESSAGE requests
Proxies route requests with method MESSAGE the same as they would
any other SIP request (proxy routing in SIP does not depend on the
method). Note that the MESSAGE request MAY fork; this allows for
delivery of the message to several possible terminals where the user
might be.
Proxies MUST NOT create call state based on MESSAGE requests alone.
Proxies MUST NOT insert record-route headers. If a route header is
present in the request, a proxy MUST honor it.
If a MESSAGE request hits a proxy that uses registrations to route
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requests, but no registration exists for the target user in the
request-URI, the request is rejected with a 404 (Not Found).
Proxies MAY have access rules which prohibit the transmission of
instant messages based on certain criteria. Typically, this criteria
will be based on the identity of the sender of the instant messages.
Establishment of this criteria in the proxy is outside the scope of
this extension. We anticipate that such access controls will often
be controlled through web pages accessible by users, mitigating the
need for standardization of a protocol for defining access rules.
8.5 UAS processing of MESSAGE requests
As specified in RFC 2543, if a UAS receives a request with a body of
type it does not understand, it MUST respond with a 415 (Unsupported
Media Type) containing an Accept header listing those types which
are acceptable. This list SHOULD also include types acceptable
nested within a message/cpim body.
Servers MAY reject requests (using a 413 response code) that are too
long, where too long is a matter of local configuration. All servers
MUST accept requests which are up to 1184 bytes in length.
1184 = minimum IPv6 guaranteed length (1280 bytes) minus UDP (8
bytes) minus IPSEC (48 bytes) minus layer one encapsulation (40
bytes).
A UAS receiving a MESSAGE request SHOULD respond with a final
response immediately. A 200 OK is sent if the request is acceptable.
Note, however, that the UAS is not obliged to display the message to
the user either before or after responding with a 200 OK. A 200
class response to a MESSAGE request MUST NOT contain a body.
Like any other SIP request, a MESSAGE request MAY be redirected, or
otherwise responded to with any SIP response code. Note that a 200
OK response to a MESSAGE request does not mean the user has read the
message.
A UAS which is, in fact, a message relay, storing the message and
forwarding it later on, or forwarding it into a non-SIP domain,
SHOULD return a 202 (Accepted) response indicating that the message
was accepted, but end to end delivery has not been guaranteed.
8.6 UAS processing of MESSAGE response
A 400 or 500 class response indicates that the message was not
delivered successfully. A 600 response means it was delivered
successfully, but refused.
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A UAS MUST NOT insert a contact header into a 200 class response.
9. Caller Preferences
User agents SHOULD add the "methods" tag defined in the caller
preference specification [8] to Contact headers with SIP URLs placed
in REGISTER requests, indicating support for the MESSAGE method.
Other elements of caller preferences MAY be supported. For example:
REGISTER sip:dynamicsoft.com SIP/2.0
Via: SIP/2.0/UDP mypc.dynamicsoft.com
To: sip:jdrosen@dynamicsoft.com
From: sip:jdrosen@dynamicsoft.com
Call-ID: asidhasd@1.2.3.4
CSeq: 39 REGISTER
Contact: sip:jdrosen@im-pc.dynamicsoft.com;methods="MESSAGE"
Content-Length: 0
Registrar/proxies which wish to offer IM service SHOULD implement
the proxy processing defined in the caller preferences specification
[8].
10. Mapping to CPIM
10.1 Mapping SIP Requests to CPIM
The CPIM draft[15] describes an abstract set of Instant Messaging
operations that all instant messaging services must map to to insure
interoperability. This section describes the mapping between SIP
instant messaging and CPIM.
The SIP MESSAGE request maps to the CPIM message operation, which
requires the parameters of source, destination, transID, and the
message to be sent.
The From header maps to the source parameter, in the case of
unauthenticated MESSAGE requests. However, a CPIM compliant gateway
SHOULD authenticate the message request. If the request is in fact
authenticated, then the source parameter MUST be the authenticated
credentials of the sender.
The requestURI maps to the destination parameter.
The transID maps to the SIP transaction identifiers (combination of
To, From, Call-ID, and CSeq.) gateway must maintain sufficient
transaction state to build a proper response to the SIP request.
The message to be sent maps to the body of the MESSAGE request. If
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the body has a MIME type of message/cpim, it SHOULD be sent as is.
Any other mime-types MUST be embedded into a message/cpim body part.
If a gateway UAS cannot determine the results of the message
operation in a short time, it MUST return a 202 accepted response.
10.2 Mapping CPIM Responses to SIP
CPIM specifies the response types of success, failure, and
indeterminate. A success response maps to a 200 OK message. An
indeterminate response maps to a 202 Accepted response.
10.3 Mapping CPIM operations to SIP
When a gateway maps a CPIM message operation to SIP, it MUST
generate a MESSAGE request. The request URI and the To header MUST
both contain the URL from the CPIM destination parameter. The From
header SHOULD contain the URL from the source parameter. The message
MUST copied into the body unchanged. Otherwise, the MESSAGE request
is generated using normal SIP. The gateway UAC MUST keep enough
transaction state to be able to determine the transID from the SIP
response.
10.4 Mapping SIP responses to CPIM
Then the gateway UAC receives a response to a MESSAGE request, it
determines the CPIM response according to the following rules: A 202
response maps to "undetermined." Any other 200 class response maps
to "success." Any 400, 500, and 600 class response maps to
"failure". 100 class responses MUST be consumed by the gateway UAC.
300 class responses SHOULD be acted upon by the gateway UAC
according to normal SIP rules.
10.5 URL Scheme Mapping
Mapping of URLs between URL schemes is a matter of the local policy
of a SIP/CPIM gateway. Such mapping is beyond the scope of this
document.
11. Security
End-to-end security concerns for instant messaging were a primary
driving force behind the creation of message/cpim [16]. Applications
needing end-to-end security should study that work carefully.
SIP provides numerous security mechanisms which can be utilized in
addition to those made available through the use of message/cpim.
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11.1 Privacy
In order to enhance privacy of instant messages, it is RECOMMENDED
that between network servers (proxies to proxies, proxies to
redirect servers), transport mode ESP [6] or TLS is used to encrypt
all traffic. Coupled with persistent connections, this makes it
impossible for eavesdroppers on non-UA connections to determine when
a particular user has even sent an IM, let alone what the content
is. Of course, the content of unencrypted IMs are exposed to
proxies.
Between a UAC and its local proxy, TLS [11] is RECOMMENDED.
Similarly, TLS SHOULD be used between a proxy and the UAS receiving
the IM. The proxy can determine whether TLS is supported by the
receiving client based on the transport parameter in the Contact
header of its registration. If that registration contains the token
"tls" as transport, it implies that the UAS supports TLS.
11.2 Outbound authentication
When local proxies are used for transmission of outbound messages,
proxy authentication is RECOMMENDED. This is useful to verify the
identity of the originator, and prevent spoofing and spamming at the
originating network.
11.3 Replay Prevention
To prevent the replay of old SIP requests, all signed MESSAGE
requests and responses SHOULD contain a Date header covered by the
message signature. Any message with a date older than several
minutes in the past, or which is more than several minutes in the
future, SHOULD be answered with a 400 (Incorrect Date or Time)
message, unless such messages arrive repeatedly from the same
source, in which case they MAY be discarded without sending a
response. Obviously, this replay attack prevention mechanism does
not work for devices without clocks.
Furthermore, all signed SIP MESSAGE requests MUST contain a Call-ID
and CSeq header covered by the message signature. A user agent MAY
store a list of Call-ID values, and for each, the highest CSeq seen
within that Call-ID. Any message that arrives for a Call-ID that
exists, whose CSeq is lower than the highest seen so far, is
discarded.
Finally, challenge-response authentication MAY be used to prevent
replay protection.
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12. Congestion Control
Existing IM services have a history of very high volume usage. There
is potential that when a SIP infrastructure is shared between call
signalling and instant messaging, the IM traffic will interfere with
call signalling traffic. Congestion control in general is an issue
that should be addressed at the SIP specification level rather than
for an individual method. But since the traffic patterns are likely
to be different for MESSAGE than for most other methods, it makes
sense to give MESSAGE special consideration.
Whenever possible, MESSAGE requests SHOULD be sent over transports
that implement end-to-end congestion control, such as TCP or SCTP.
13. Example Messages
An example message flow is shown in Figure 1. The message flow shows
an initial IM sent from User 1 to User 2, both users in the same
domain, "domain", through a single proxy.
| F1 MESSAGE | |
|--------------------> | F2 MESSAGE |
| | ----------------------->|
| | |
| | F3 200 OK |
| | <-----------------------|
| F4 200 OK | |
|<-------------------- | |
| | |
| | |
| | |
User 1 Proxy User 2
Figure 1: Example Message Flow
Message F1 looks like:
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MESSAGE im:user2@domain.com SIP/2.0
Via: SIP/2.0/UDP user1pc.domain.com
From: im:user1@domain.com
To: im:user2@domain.com
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Content-Type: text/plain
Content-Length: 18
Watson, come here.
User1 forwards this message to the server for domain.com (discovered
through the combination of SRV and A record processing described in
Section 8.3 , using UDP. The proxy receives this request, and
recognizes that it is the server for domain.com. It looks up user2
in its database (built up through registrations), and finds a
binding from im:user2@domain.com to sip:user2@user2pc.domain.com. It
forwards the request to user2. The resulting message, F2, looks
like:
MESSAGE sip:user2@domain.com SIP/2.0
Via: SIP/2.0/UDP proxy.domain.com
Via: SIP/2.0/UDP user1pc.domain.com
From: im:user1@domain.com
To: im:user2@domain.com
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Content-Type: text/plain
Content-Length: 18
Watson, come here.
The message is received by user2, displayed, and a response is
generated, message F3, and sent to the proxy:
SIP/2.0 200 OK
Via: SIP/2.0/UDP proxy.domain.com
Via: SIP/2.0/UDP user1pc.domain.com
From: im:user1@domain.com
To: im:user2@domain.com;tag=ab8asdasd9
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Content-Length: 0
Note that most of the header fields are simply reflected in the
response. The proxy receives this response, strips off the top Via,
and forwards to the address in the next Via, user1pc.domain.com, the
result being message F4:
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SIP/2.0 200 OK
Via: SIP/2.0/UDP user1pc.domain.com
From: im:user1@domain.com
To: im:user2@domain.com;tag=ab8asdasd9
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Content-Length: 0
14. Acknowledgments
The authors would like to thank the following people for their
support of the concept of SIP for IM, support for this work, and for
their useful comments and insights:
Jon Peterson Neustar
Sean Olson Ericsson
Adam Roach Ericsson
Billy Biggs University of Waterloo
Stuart Barkley UUNet
Mauricio Arango SUN
Richard Shockey Neustar
Jorgen Bjorker Hotsip
Henry Sinnreich MCI Worldcom
Ronald Akers Motorola
References
[1] DellaFera, C. A., Eichin, M. W., French, R. S., Jedlinski, D.
C., Kohl, J. T. and W. E. Sommerfeld, "The Zephyr notification
service", in USENIX Winter Conference (Dallas, Texas), Feb.
1988.
[2] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
"SIP: Session Initiation Protocol", RFC 2543, March 1999.
[3] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[4] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence
and Instant Messaging", RFC 2778, February 2000.
[5] Rosenberg, J. and H. Schulzrinne, "SCTP as a transport for
SIP", draft-rosenberg-sip-sctp-00 (work in progress), June
2000.
[6] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
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[7] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[8] Rosenberg, J. and H. Schulzrinne, "SIP caller preferences and
callee capabilities", draft-ietf-sip-callerprefs-03 (work in
progress), November 2000.
[9] Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.
[10] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
"SIP: Session Initiation Protocol", RFC 2543, March 1999.
[11] Dierks, T., Allen, C., Treese, W., Karlton, P. L., Freier, A.
O. and P. C. Kocher, "The TLS Protocol Version 1.0", RFC 2246,
January 1999.
[12] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[13] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[14] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[15] Crocker, D., Diacakis, A., Mazzoldi, F., Huitema, C., Klyne,
G., Rose, M., Rosenberg, J., Sparks, R. and H. Sugano, "A
Common Profile for Instant Messaging (CPIM)",
draft-ietf-impp-cpim-01 (work in progress), February 2001.
[16] Atkins, D. and G. Klyne, "Common Presence and Instant
Messaging Message Format", draft-ietf-impp-cpim-msgfmt-00
(work in progress), February 2001.
Authors' Addresses
Jonathan Rosenberg
dynamicsoft
72 Eagle Rock Avenue
First Floor
East Hanover, NJ 07936
email: jdrosen@dynamicsoft.com
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Dean Willis
dynamicsoft
5100 Tennyson Parkway
Suite 1200
Plano, TX 75024
email: dwillis@dynamicsoft.com
Robert J. Sparks
dynamicsoft
5100 Tennyson Parkway
Suite 1200
Plano, TX 75024
email: rsparks@dynamicsoft.com
Ben Campbell
dynamicsoft
5100 Tennyson Parkway
Suite 1200
Plano, TX 75024
email: bcampbell@dynamicsoft.com
Henning Schulzrinne
Columbia University
M/S 0401
1214 Amsterdam Ave.
New York, NY 10027-7003
email: schulzrinne@cs.columbia.edu
Jonathan Lennox
Columbia University
M/S 0401
1214 Amsterdam Ave.
New York, NY 10027-7003
email: lennox@cs.columbia.edu
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Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
email: huitema@microsoft.com
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
email: bernarda@microsoft.com
David Gurle
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
email: dgurle@microsoft.com
David Oran
Cisco Systems
170 West Tasman Dr.
San Jose, CA 95134
email: oran@cisco.com
Appendix A. Requirements Evaluation
This section was moved forward verbatim from -00.
RFC 2779 [3] outlines requirements for IM and presence protocols.
The document describes both shared requirements and IM and presence
specific requirements. Examining each of the IM requirements in
turn, we also observe that they are met by this proposal:
"Requirement 2.1.1: The protocols MUST allow a PRESENCE SERVICE to
be available independent of whether an INSTANT MESSAGE SERVICE is
available, and vice-versa." This requirement is met by the
separation of presence and IM which we propose here.
"Requirement 2.1.2. The protocols must not assume that an INSTANT
INBOX is necessarily reached by the same IDENTIFIER as that of a
PRESENTITY. Specifically, the protocols must assume that some
INSTANT INBOXes may have no associated PRESENTITIES, and vice
versa." This requirement is also easily met by any architecture
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which completely separates IM and presence as we propose.
"Requirement 2.1.3. The protocols MUST also allow an INSTANT INBOX
to be reached via the same IDENTIFIER as the IDENTIFIER of some
PRESENTITY." Same as above.
"Requirement 2.1.4. The administration and naming of ENTITIES
within a given DOMAIN MUST be able to operate independently of
actions in any other DOMAIN." This requirement is met by SIP. SIP
uses email-like identifiers which consist of a user name at a
domain. Administration of user names is done completely within
the domain, and these user names have no defined rules or
organization that needs to be known outside of the domain in
order for SIP to operate.
"Requirement 2.1.5. The protocol MUST allow for an arbitrary number
of DOMAINS within the NAMESPACE." This requirement is met by SIP.
SIP uses standard DNS domains, which are not restricted in
number.
"Requirement 2.2.1. It MUST be possible for ENTITIES in one DOMAIN
to interoperate with ENTITIES in another DOMAIN, without the
DOMAINS having previously been aware of each other." This
requirement is met by SIP, as it is essential for establishing
sessions as well. DNS SRV records are used to discover servers
for a particular service within a domain. They are a
generalization of MX records, used for email routing. SIP defines
procedures for usage of DNS records to find servers in another
domains, which include SRV lookups. This allows domains to
communicate without prior setup.
"Requirement 2.2.2: The protocol MUST be capable of meeting its
other functional and performance requirements even when there are
millions of ENTITIES within a single DOMAIN." Whilst it is hard
to judge whether this can be met by examining the architecture of
a protocol, SIP has numerous mechanisms for achieving large
scales of users within a domain. It allows hierarchies of
servers, whereby the namespace can be partitioned among servers.
Servers near the top of the hierarchy, used solely for routing,
can be stateless, providing excellent scale.
"Requirement 2.2.3: The protocol MUST be capable of meeting its
other functional and performance requirements when there are
millions of DOMAINS within the single NAMESPACE." The usage of
DNS for dividing the namespace into domains provides the same
scale as todays email systems, which support millions of DOMAINS.
"Requirement 2.3.5: The PRINCIPAL controlling an INSTANT INBOX MUST
be able to control which other PRINCIPALS, if any, can send
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INSTANT MESSAGES to that INSTANT INBOX." This is provided by
access control mechanisms, outside the scope of this extension.
"Requirement 2.3.6: The PRINCIPAL controlling an INSTANT INBOX MUST
be able to control which other PRINCIPALS, if any, can read
INSTANT MESSAGES from that INSTANT INBOX." This is accomplished
through authenticated registration requests. Registrations are
used to determine which user gets delivered an instant message.
Policy in proxies can allow only certain users to register
contact address for a particular inbox (an inbox is defined by
the address-of- record in the To field in the registration).
"Requirement 2.4.3: The protocol MUST allow the sending of an
INSTANT MESSAGE both directly and via intermediaries, such as
PROXIES." This is fundamental to the operation of SIP.
"Requirement 2.4.4: The protocol proxying facilities and transport
practices MUST allow ADMINISTRATORS ways to enable and disable
protocol activity through existing and commonly-deployed
FIREWALLS. The protocol MUST specify how it can be effectively
filtered by such FIREWALLS." Although SIP itself runs on port
5060 by default, any other port can be used. It is simple to
specify that IM should run on a different port, if so desired.
"Requirement 2.5.1. The protocol MUST provide means to ensure
confidence that a received message (NOTIFICATION or INSTANT
MESSAGE) has not been corrupted or tampered with." This is
supported by the end-to-end signature mechanism in message/cpim.
"Requirement 2.5.2. The protocol MUST provide means to ensure
confidence that a received message (NOTIFICATION or INSTANT
MESSAGE) has not been recorded and played back by an adversary."
This is provided by SIP's challenge response authentication
mechanisms, through timestamp-based replay prevention, or through
stateful storage of previous transaction identifiers (the
combination of To, From, Call-ID, CSeq).
"Requirement 2.5.3. The protocol MUST provide means to ensure that
a sent message (NOTIFICATION or INSTANT MESSAGE) is only readable
by ENTITIES that the sender allows." This is supported through
SIPs and message/cpim's end to end and hop by hop encryption
mechanisms.
"Requirement 2.5.4. The protocol MUST allow any client to use the
means to ensure non-corruption, non-playback, and privacy, but
the protocol MUST NOT require that all clients use these means at
all times." All algorithms for security in SIP are optional.
"Requirement 4.1.1. All ENTITIES sending and receiving INSTANT
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MESSAGES MUST implement at least a common base format for INSTANT
MESSAGES." We specify text/plain and message/cpim here.
"Requirement 4.1.2. The common base format for an INSTANT MESSAGE
MUST identify the sender and intended recipient." This is
accomplished with the To and From fields in SIP.
"Requirement 4.1.3. The common message format MUST include a return
address for the receiver to reply to the sender with another
INSTANT MESSAGE." This is done through the Contact headers
defined in SIP.
"Requirement 4.1.4. The common message format SHOULD include
standard forms of addresses or contact means for media other than
INSTANT MESSAGES, such as telephone numbers or email addresses."
SIP supports any URL format in the Contact headers. Furthermore,
the body of a MESSAGE request can be multipart, and contain
things like vCards.
"Requirement 4.1.5. The common message format MUST permit the
encoding and identification of the message payload to allow for
non-ASCII or encrypted content." MIME content labeling is used in
SIP.
"Requirement 4.1.6. The protocol must reflect best current
practices related to internationalization." SIP uses UTF-8 and is
completely internationalized.
"Requirement 4.1.7. The protocol must reflect best current
practices related to accessibility." Additional requirements are
needed on what is required for accessibility.
"Requirement 4.1.9. The working group MUST determine whether the
common message format includes fields for numbering or
identifying messages. If there are such fields, the working group
MUST define the scope within which such identifiers are unique
and the acceptable means of generating such identifiers." This is
done with the combination of Call-ID and CSeq. The mechanisms for
guaranteeing uniqueness are specified in SIP.
"Requirement 4.1.10. The common message format SHOULD be based on
IETF-standard MIME (RFC 2045)[14]." SIP uses MIME.
"Requirement 4.2.1. The protocol MUST include mechanisms so that a
sender can be informed of the SUCCESSFUL DELIVERY of an INSTANT
MESSAGE or reasons for failure. The working group must determine
what mechanisms apply when final delivery status is unknown, such
as when a message is relayed to non-IMPP systems." SIP specifies
notification of successful delivery through 200 OK. When delivery
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of requests through gateways, success can be indicated only
through the SIP component (if the gateway acts as a UAS/UAC) or
through the entire system (if it acts like a proxy).
"Requirement 4.3.1. The transport of INSTANT MESSAGES MUST be
sufficiently rapid to allow for comfortable conversational
exchanges of short messages." The support for end to end
messaging (i.e., without intervening proxies) allows IMs to be
delivered as rapidly as possible. The UDP reliability mechanisms
also support fast recovery from loss.
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Full Copyright Statement
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Acknowledgement
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