SIPPING Working Group M. Garcia-Martin
Internet-Draft Nokia
Expires: September 28, 2004 G. Camarillo
Ericsson
March 30, 2004
Multiple recipient MESSAGE requests in the Session Initiation
Protocol (SIP)
draft-garcia-simple-message-exploder-00.txt
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Abstract
This document specifies how to request a MESSAGE exploder to send a
copy of a MESSAGE to a set of destinations. The client sends a SIP
MESSAGE request with a URI list to the MESSAGE exploder, which sends
a similar MESSAGE request to each of URIs included in the list.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Procedures at the UAC . . . . . . . . . . . . . . . . . . . . 3
4. Procedures at the MESSAGE Exploder . . . . . . . . . . . . . . 4
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
Normative References . . . . . . . . . . . . . . . . . . . . . 8
Informational References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
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1. Introduction
SIP [2] can carry instant messages in MESSAGE [3] requests. The
Advanced Instant Messaging Requirements for SIP [6] mention the need
for exploders for MESSAGE transactions:
"REQ-GROUP-3: It MUST be possible for a user to send to an ad-hoc
group, where the identities of the recipients are carried in the
message itself."
To meet this requirement, we allow SIP MESSAGE requests carry an URI
list as specified in [4]. The Request-URI of the MESSAGE request
contains a "list" URI parameter that points to a body part that
carries the URI list. On reception of such a request, the MESSAGE
exploder sends a similar MESSAGE request that includes a copy of the
body (except the list itself) to each URI in the list.
The UAC needs to be configured with the SIP URI of the MESSAGE
exploder. Provisioning of the MESSAGE exploder URI to the UAC is
outside the scope of this document.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
'MESSAGE exploder': SIP application server that receives a MESSAGE
request with a URI list and sends a similar MESSAGE request to each
URI in the list. MESSAGE exploders behave effectively as B2BUAs
(Back-To-Back-User-Agents).
'Incoming MESSAGE request': A SIP MESSAGE request that a UAC creates
and addresses to a SIP MESSAGE exploder. Besides the regular instant
message payload, an incoming MESSAGE request contains a URI list.
'Outgoing MESSAGE request': A SIP MESSAGE request that a MESSAGE
exploder and addresses to a UAS. It contains the regular instant
message payload.
3. Procedures at the UAC
A client that wants to create a multiple recipient MESSAGE request
SHOULD add a "list" parameter (specified in [4]) to the MESSAGE
exploder's URI and MUST place the resulting URI in the Request-URI of
the MESSAGE request. The "list" parameter MUST contain a pointer to a
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URI list that contains the recipients of the MESSAGE. The following
is an example of a Request-URI with a "list" parameter.
sip:message-exploder.example.com;list=cid:cn35t8jf@uac.example.com
Multiple recipient MESSAGE requests will typically contain a
multiparty body that contains the body carrying the list and the
actual instant message payload. In some cases, the MESSAGE request
will contain bodies other than the text and the list bodies, for
instance, when the request is protected with S/MIME.
Typically the MESSAGE exploder will copy all the significant header
fields in the exploded MESSAGE request. However, there might be cases
where the SIP UA wants the MESSAGE exploder to add a particular
header field with a particular value, when the header field wasn't
present in the MESSAGE request sent by the UAC. In this case the UAC
MAY use the "?" mechanism described in Section 19.1.1 of RFC 3261 [2]
to encode extra information in any URI in the list. However, the UAC
MUST NOT use the special "body" hname (see Section 19.1.1 of RFC 3261
[2]) to encode a body, since the body is present in the MESSAGE
request itself.
The following is an example of a URI that uses the "?" mechanisms:
sip:message-exploder.example.com;list=cid:cn35t8jf@uac.example.com?
Accept-Contact=*%3bmobility%3d%22mobile%22
The previous URI requests the exploder to add the following header
field to a MESSAGE request:
Accept-Contact: *;mobility="mobile"
As described in [4], the default format for URI lists in SIP is the
XCAP resource list format [5]. User Agents compliant to this
specification MUST support the XCAP resource list format [5] and MAY
support other formats.
UAs generating multiple recipient MESSAGEs SHOULD use flat lists
(i.e., no hierarchical lists), SHOULD NOT use any entry's attributes
but "uri", and SHOULD NOT include any elements inside entries but
"display-name" elements.
4. Procedures at the MESSAGE Exploder
On receiving a MESSAGE request that contains a "list" parameter in
the Request-URI as described in [4], a MESSAGE exploder SHOULD answer
to the UAC with a 202 Accepted response. Note that the status code in
the response to the MESSAGE does not provide any information about
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whether or not the MESSAGEs generated by the exploder were
successfully delivered to the URIs in the list. That is, a 202
Accepted means that the MESSAGE exploder has received the MESSAGE and
that it will try to send a similar MESSAGE to the URIs in the list.
Designing a mechanism to inform a client about the delivery status of
an instant message is outside the scope of this document.
On receiving a MESSAGE request that contains a "list" parameter in
the Request-URI as described [4], a MESSAGE exploder SHOULD create as
many new MESSAGEs as URIs the list contains. The body of these new
MESSAGEs SHOULD contain the same bodies as the incoming MESSAGE
carried, except the body carrying the list, which MUST NOT be present
in the outgoing MESSAGE request. This behaviour allows the MESSAGE
exploder to transfer all the relevant bodies included in the request,
e.g., text message, images, etc.
The rest of the MESSAGE request corresponding to a given URI in the
list MUST be created following the rules in Section 19.1.5 "Forming
Requests from a URI" of RFC 3261 [2]. In particular, Section 19.1.5
of RFC 3261 [2] states:
"An implementation SHOULD treat the presence of any headers or body
parts in the URI as a desire to include them in the message, and
choose to honor the request on a per-component basis."
SIP allows to append a "method" parameter to a URI. Therefore, it is
legitimate that an the "uri" attribute of the "entry" element in the
XCAP resource list contains a "method" parameter. MESSAGE exploders
MUST generate only MESSAGE requests, regardless of the "method"
parameter that the URIs in the list indicate. Effectively, MESSAGE
exploders MUST ignore the "method" parameter in each of the URIs
present in the URI list.
It is RECOMMENDED that the MESSAGE exploder copies the value From
header field of the incoming MESSAGE into the outgoing MESSAGE
requests (note that this need not apply to the "tag" parameter). The
MESSAGE exploder SHOULD also copy to the outgoing MESSAGE request any
P-Asserted-Identity header fields that can be present in the incoming
MESSAGE request.
OPEN ISSUE: What should the exploder do with a possible
P-Asserted-Identity? Copying the contents of the incoming MESSAGE
request or generate a new "unasserted" value to the outgoing
MESSAGE request?
On each given outgoing MESSAGE request, the MESSAGE exploder SHOULD
generate a new To header field value which, according to the
procedures of RFC 3261 Section 8.1.1.1, should be equal to the
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Request-URI of the outgoing MESSAGE request.
On each given outgoing MESSAGE request, the MESSAGE exploder SHOULD
initialize the values of the Call-ID, CSeq and Max-Forwards header
fields. The MESSAGE exploder should also include its own value in the
Via header field.
A MESSAGE exploder receiving a URI list with more information than
what we have just described SHOULD discard all the extra information.
As described in [4], the default format for URI lists in SIP is the
XCAP resource list format [5]. MESSAGE exploders compliant to this
specification MUST support the XCAP resource list format [5] and MAY
support other formats.
5. Examples
The following is an example of an incoming MESSAGE request which
carries a URI list in its body.
MESSAGE sip:exploder.example.com;list=cid:cn35t8jf@uac.example.com
SIP/2.0
Via: SIP/2.0/TCP uac.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: MESSAGE Exploder <sip:exploder.example.com>
From: Carol <sip:carol@example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 1 MESSAGE
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx
--boundary1
Content-Type: text/plain
Content-Length: 13
Hello World!
--boundary1
Content-Type: application/resource-lists+xml
Content-Length: 315
Content-ID: <cn35t8jf@uac.example.com>
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list>
<entry uri="sip:bill@example.com" />
<entry uri="sip:joe@example.com" />
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<entry uri="sip:ted@example.com" />
<entry uri="sip:bob@example.com" />
</list>
</resource-lists>
--boundary1--
Figure 4: Multiple recipient incoming MESSAGE request
The following is an example of one of the outgoing MESSAGE requests
that the MESSAGE exploder creates.
MESSAGE sip:bill@example.com SIP/2.0
Via: SIP/2.0/TCP exploder.example.com
;branch=z9hG4bKhjhs8as34sc
Max-Forwards: 70
To: <sip:bill@example.com>
From: Carol <sip:carol@uac.example.com>;tag=210342
Call-ID: 39s02sdsl20d9sj2l
CSeq: 1 MESSAGE
Content-Type: text/plain
Content-Length: 13
Hello World!
Figure 5: Outgoing MESSAGE request
6. Security Considerations
If MESSAGE exploders are not implemented properly, they could become
a SPAM amplification tool. The SPAMMER would have the exploder, which
will generally have a higher access bandwidth and more processing
power, send a SPAM message to a large set of destinations. This
section provides guidelines to prevent SPAM amplifications in
particular, and DoS attacks in general. In addition, we describe how
to provide content confidentiality and integrity.
MESSAGE exploders MUST authenticate and authorize any user agent
sending a multiple recipient MESSAGE. Additionally, MESSAGE exploders
MAY have policies that limit the number of URIs in the list, as a
very long list could be used in a DoS attack to place a large burden
on the exploder to send a large number of MESSAGEs or to perform an
amplification attack.
In case an exploder is used to send unsolicited instant messages
(i.e., SPAM), it should be possible to track down the sender of such
messages. To do that, MESSAGE exploders MAY provide information about
the identity of the original sender of the MESSAGE in their outgoing
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MESSAGE requests. Exploders can use Authenticated Identity Bodies
(AIB) [7] or P-Asserted-Identity header fields [8] to provide this
information. Furthermore, it is RECOMMENDED that MESSAGE exploders
keep a log of all the transactions they handle (for a reasonable
period of time), so that SPAMMERS can be tracked down.
It is RECOMMENDED that user agents using MESSAGE exploders integrity
protect the contents of their instant messages and the list of
recipients using S/MIME. If the contents of the instant message or
the list of recipients needs to be kept private, the user agent
SHOULD also use S/MIME to prevent a third party from viewing this
information.
7. Acknowledgements
Duncan Mills supported the idea of having 1 to n MESSAGEs.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D.
Gurle, "Session Initiation Protocol (SIP) Extension for Instant
Messaging", RFC 3428, December 2002.
[4] Camarillo, G., "Providing a Session Initiation Protocol (SIP)
Application Server with a List of URIs",
draft-camarillo-sipping-uri-list-00 (work in progress), November
2003.
[5] Rosenberg, J., "An Extensible Markup Language (XML)
Configuration Access Protocol (XCAP) Usage for Presence Lists",
draft-ietf-simple-xcap-list-usage-01 (work in progress), October
2003.
Informational References
[6] Rosenberg, J., "Advanced Instant Messaging Requirements for the
Session Initiation Protocol (SIP)",
draft-rosenberg-simple-messaging-requirements-00 (work in
progress), December 2002.
[7] Peterson, J., "SIP Authenticated Identity Body (AIB) Format",
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draft-ietf-sip-authid-body-02 (work in progress), July 2003.
[8] Jennings, C., Peterson, J. and M. Watson, "Private Extensions to
the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", RFC 3325, November 2002.
Authors' Addresses
Miguel A. Garcia-Martin
Nokia
P.O.Box 407
NOKIA GROUP, FIN 00045
Finland
EMail: miguel.an.garcia@nokia.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
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