Network Working Group Q. Sun
Internet-Draft L. Tian
Expires: April 14, 2008 D. Ren
Huawei Technologies
October 12, 2007
Multiple Reply to MESSAGE requests in the Session Initiation Protocol
(SIP)
draft-sun-sipping-multiple-reply-01
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Copyright (C) The IETF Trust (2007).
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Abstract
This document defines a multiple target address extension to the
Reply-To header field for the SIP MESSAGE method. The extension
includes the use of a pointer to a Uniform Resource Identifier (URI)-
list in the Reply-To header field.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. URI-List Document Format . . . . . . . . . . . . . . . . . . . 6
4. Procedures at the Reply-Issuer . . . . . . . . . . . . . . . . 8
5. Procedures at the Reply-Recipient . . . . . . . . . . . . . . 9
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Reply-Recipient uses MESSAGE URI-List service to send
reply MESSAGE requests . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
RFC 3261 [2] defines a Reply-To header field containing a logical
return URI that may be different from the From header field. For
example, the URI MAY be used to return missed calls or unestablished
sessions.
RFC 3428 [3] further defines the Reply-To as an optional header field
that can be used and present in MESSAGE requests and responses. This
allows a Reply-Issuer to provide the Reply-Recipient with one User
Agent (UA) as the target of a reply MESSAGE request.
However, in some scenarios, the Reply-Issuer may want the Reply-
Recipient to send reply MESSAGE requests to a list of UAs, as opposed
to just one UA. For example, a manager sends a message to request a
secretary to prepare meeting arrangements. In the message, the
manager provides a list of meeting attendees. When the secretary
schedules the meeting, the secretary sends the meeting information in
a reply MESSAGE to the list of attendees. Another use case may be
for an application to send a notification to a user to respond with
certain information, such as a project report, to a list of users.
As with the previous example, the original message itself is not
meaningful for the intended recipients.
At present, there is no mechanism to convey a list of users to which
a UAC can respond. This specification extends the Reply-To mechanism
to fulfill the requirement by defining the use of a URI-List in the
Reply-to header. With this specification, the Reply-Issuer sends to
a Reply-Recipient a MESSAGE request with a Reply-To header pointing
to a Uniform Resource List (URI-list) containing the targets of a
reply MESSAGE request. Another possible solution is to define a new
SIP header field e.g. "Addtional-Reply-To" which is able to carry
mutiple reply targets. This seems much simpler, but can not indicate
more elaborate intention e.g. "bcc".
The Reply-Recipient can create a reply MESSAGE request for each entry
in the URI-List and send them respectively, or can send a reply
MESSAGE to a MESSAGE URI-list service [9] to distribute the reply
MESSAGE requests. The Reply-Recipient may modify the provided list
to add or remove recipients.
The requirements to support Multiple Reply to MESSAGE requests may be
summarized as follows:
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REQ-1: It MUST be possible for a Reply-Issuer to specify multiple
reply targets in a MESSAGE request, where the identities of the
reply targets are carried in the request itself.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
This document defines the following new terms:
Reply-Issuer: the user agent issuing the SIP request with Reply-To
header field.
Reply-Recipient: the user agent receiving the SIP request with
Reply-To header field.
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3. URI-List Document Format
As described in the Framework and Security Considerations for SIP
URI-List Services [4] , specifications of individual URI-list
services, need to specify a default format for 'recipient-list'
bodies used within the particular service.
The default format for 'recipient-list' bodies for multiple reply is
XML Resource Lists [7] extended with Copy Control Attribute [8] .
Reply-Issuer and Reply-Recipient MUST support both these formats and
MAY support other formats.
As described in Copy Control Attribute [8] , each URI can be tagged
with a 'copyControl' attribute set to either "to", "cc", or "bcc",
indicating the role in which the recipient will receive the reply
MESSAGE request. Additionally, URIs can be tagged with the
'anonymize' attribute to prevent that the Reply-Recipient (UAS) from
disclosing the target URI in a URI-list.
In addition, the XML Resource Lists [7] defines a 'recipient-list-
history' body that contains the list of recipients. The default
format for 'recipient-list-history' bodies for UAs is also the XML
Resource Lists [7] extended with the Copy Control Attribute [8] . If
the Reply-Recipient sends reply MESSAGE requests to each entry in the
URI-List, it may provide a 'recipient-list-history' body in the reply
MESSAGE requests. In this case the Reply-Recipient MAY support these
formats and MAY support others. If the Reply-Recipient sends a reply
MESSAGE request to a MESSAGE URI-list service [9] , it does not need
to support these formats. UAs able to understand 'recipient-list-
history' MUST support these formats and MAY support others.
The XML Resource Lists [7] provides features, such as hierarchical
lists and the ability to include entries by reference relative to the
XCAP root URI or by external reference; however, these are not needed
by the reply mechanism defined in this specification. The reply
mechanism defined herein only needs to transfer a flat list of URIs
between the Reply-Issuer and the Reply-Recipient. Therefore, when
using the default resource list document, UAs SHOULD use flat lists
(i.e., no hierarchical lists) and SHOULD NOT use references. A
Reply-Recipient receiving a URI-list with more information than what
has just been described MAY discard the additional information.
Figure 1 shows an example of a flat URI-List that follows XML
Resource Lists [7] extended with Copy Control Attribute [8] ).
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Figure 1: Example for XML Resource List Document
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4. Procedures at the Reply-Issuer
A Reply-Issuer that wants to specify multiple reply addresses MUST
use formatting according to Section 4 of RFC 3428 [3] . The Reply-
Issuer populates the Request-URI of the MESSAGE request with the SIP
or SIPS URI of the Reply-Recipient. In addition to the regular
MESSAGE request body, the Reply-Issuer adds a recipient-list body
whose Content-Disposition type is 'recipient-list' as defined in
Framework and Security Considerations for SIP URI-List Services [4] .
This body contains a URI-list with the recipients of the reply
MESSAGE request from the Reply-Recipient. Target URIs in this body
MAY also be tagged with the 'copyControl' and 'anonymize' attributes
specified in the Copy Control Attribute [8] . The Reply-Issuer MUST
provide an appropriate Content-ID for the recipient-list body and
populates the Reply-To with the value of Content-ID that identifies
the list of intended recipient of the reply MESSAGE requests.
The Reply-Issuer MAY use the "?" mechanism described in Section
19.1.1 of RFC 3261 [2] to encode extra information in any URI of the
list. The following is an example of a URI that uses the "?"
mechanism:
sip:bob@example.com?Accept-Contact=*%3bmobility%3d%22mobile%22
The previous URI requests the Reply-Recipient to add the following
header field to a reply MESSAGE request to be sent to
bob@example.com: Accept-Contact: *;mobility="mobile"
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5. Procedures at the Reply-Recipient
A Reply-Recipient that receives a MESSAGE request with a Reply-To
header field and 'recipient-list' body processes it and responds
following the procedure in section 7 of RFC 3428 [3]
There are two possibilities for a Reply-Recipient to send reply
MESSAGE requests to intended recipients:
o The Reply-Recipient creates a reply MESSAGE request for each entry
in the URI-List and sends them respectively. If it supports the
'recipient-list-history' Content-Disposition type, it MAY provide
a 'recipient-list-history' body in the reply MESSAGE requests for
each intended recipient following the procedure defined in Copy
Control Attribute [8] .
o The Reply-Recipient sends a reply MESSAGE request that includes
the payload along with the URI-list to a MESSAGE URI-list service
[9] to distribute simliar reply MESSAGE requests to each of the
URIs included in the list. The Reply-Recipient MAY modify the
URI-list from the Reply-Issuer so as to add or remove recipients.
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6. Examples
6.1. Reply-Recipient uses MESSAGE URI-List service to send reply
MESSAGE requests
Figure 1 shows an example flow where a Reply-Issuer sends a MESSAGE
request with Reply-To header field pointing to a URI list to a Reply-
Recipient. The Reply-Recipient sends a reply MESSAGE with the URI
list to MESSAGE URI-list service.
+--------+ +--------+ +---------+ +--------+ +--------+
| Reply- | | Reply- | | MESSAGE | | reply | | reply |
| Issuer | | Recip. | | URI-List| | target | | target |
| | | | | server | | 1 | | 2 |
+--------+ +--------+ +---------+ +--------+ +--------+
| | | | |
| F1:MESSAGE with Reply-To pointing to a URI-List |
|------------>| | | |
| F2:200 OK | | | |
|<------------| | | |
| | F3:MESSAGE | | |
| |-------------->| | |
| | F4:202 Accepted | |
| |<--------------| | |
| | | F5:MESSAGE | |
| | | --------------->| |
| | | F6:MESSAGE | |
| | | -------------------------->|
| | | F8:200 OK | |
| | |<--------------- | |
| | | F9:200 OK | |
| | |<-------------------------- |
| | | | |
Figure 1: Example flow for Reply-To pointing to multiple addresses
Figure 2 shows an example of the MESSAGE request F1, which carries a
'multipart/mixed' body composed of two other bodies:
o 'text/plain' body: contains the instant message payload;
o 'application/resource-lists+xml' body: contains the intended
recipients receiving the reply MESSAGE request from Reply-
Recipient.
The Reply-To header field has the same value of Content-ID pointing
to the URI-List which contains the intended recipients.
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MESSAGE sip:tom@example.com SIP/2.0
Via: SIP/2.0/TCP uac1.example.com
;branch=z9hG4bKhjhs8as34sc
Max-Forwards: 70
To:
From: Alice ;tag=210342
Call-ID: 39s02sdsl20d9sj2l
CSeq: 1 MESSAGE
Reply-To:
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx
--boundary1
Content-Type: text/plain
Please reply the team with the deadline!
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
Content-ID:
--boundary1--
Figure 2: MESSAGE with Reply-To header field pointing to a URI list
Figure 3 shows an example of the MESSAGE request F3, which carries a
'multipart/mixed' body composed of two other bodies:
o 'text/plain' body: contains the instant message payload;
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o 'application/resource-lists+xml' body: contains the list of
recipients. This list is the same with F1.
MESSAGE sip:list-service.example.com SIP/2.0
Via: SIP/2.0/TCP uac1.example.com
;branch=z9hG4bKhjhs8as34sc
Max-Forwards: 70
To: MESSAGE URI-list Service
From: Alice ;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 1 MESSAGE
Content-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx
--boundary1
Content-Type: text/plain
The deadline is 14:00 GMT October 10, 2007.
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
--boundary1--
Figure 3: MESSAGE request received at the MESSAGE URI-list server
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7. Security Considerations
URI-lists may contain private information, such as SIP URIs. It is,
therefore, not desirable that these URI-lists are known by third
parties. Eavesdroppers are able to watch URI-lists contained in SIP
MESSAGE requests unless the MESSAGE requests are sent over a secured
channel, by using any of the available SIP mechanisms, such as
Transport Layer Security (TLS) [5] , or unless the URI-list body
itself is encrypted with, e.g., S/MIME [6] . Therefore, it is
RECOMMENDED that URI-list bodies are encrypted with S/MIME [6] or
that the SIP request is encrypted with TLS [5] or any other suitable
encryption mechanism.
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8. IANA Considerations
There are no IANA considerations.
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9. Acknowledgements
The authors would like to thank Tom Hiller, Henning Schulzrinne,
Jonathan Rosenberg and Spencer Dawkins for their valuable comments
and contributions.
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10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", 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. and A. Roach, "Framework and Security
Considerations for Session Initiation Protocol (SIP) Uniform
Resource Identifier (URI)-List Services",
draft-ietf-sipping-uri-services-06.txt (work in progress),
September 2006.
[5] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.1", RFC 4346, April 2006.
[6] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 4346, January
1999.
[7] Rosenberg, J., "Extensible Markup Language (XML) Formats for
Representing Resource Lists", RFC 4826, May 2007.
[8] Garcia-Martin, M. and G. Camarillo, "Extensible Markup Language
(XML) Format Extension for Representing Copy Control Attributes
in Resource Lists",
draft-ietf-sipping-capacity-attribute-04.txt (work in
progress), March 2007.
10.2. Informative References
[9] Garcia-Martin, M. and G. Camarillo, "Multiple-Recipient MESSAGE
Requests in the Session Initiation Protocol (SIP)",
draft-ietf-sip-uri-list-message-01.txt (work in progress),
January 2007.
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Authors' Addresses
Qian Sun
Huawei Technologies
Bantian Longgang
Shenzhen, Guandong 518129
P.R China
Phone: +86 755 28780808
Email: sunqian@huawei.com
Linyi Tian
Huawei Technologies
Bantian Longgang
Shenzhen, Guandong 518129
P.R China
Phone: +86 755 28780808
Email: tianlinyi@huawei.com
Daqi Ren
Huawei Technologies
Bantian Longgang
Shenzhen, Guandong 518129
P.R China
Phone: +86 755 28780808
Email: dren@huawei.com
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