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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 April 14, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Sun, et al. Expires April 14, 2008 [Page 1] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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 Sun, et al. Expires April 14, 2008 [Page 2] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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: Sun, et al. Expires April 14, 2008 [Page 3] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 4] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 5] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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] ). Sun, et al. Expires April 14, 2008 [Page 6] Internet-Draft Multiple Reply to MESSAGE requests October 2007 Figure 1: Example for XML Resource List Document Sun, et al. Expires April 14, 2008 [Page 7] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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" Sun, et al. Expires April 14, 2008 [Page 8] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 9] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 10] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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; Sun, et al. Expires April 14, 2008 [Page 11] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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 Sun, et al. Expires April 14, 2008 [Page 12] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 13] Internet-Draft Multiple Reply to MESSAGE requests October 2007 8. IANA Considerations There are no IANA considerations. Sun, et al. Expires April 14, 2008 [Page 14] Internet-Draft Multiple Reply to MESSAGE requests October 2007 9. Acknowledgements The authors would like to thank Tom Hiller, Henning Schulzrinne, Jonathan Rosenberg and Spencer Dawkins for their valuable comments and contributions. Sun, et al. Expires April 14, 2008 [Page 15] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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. Sun, et al. Expires April 14, 2008 [Page 16] Internet-Draft Multiple Reply to MESSAGE requests October 2007 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 Sun, et al. Expires April 14, 2008 [Page 17] Internet-Draft Multiple Reply to MESSAGE requests October 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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