Internet Draft M. Barnes Document: draft-barnes-sipping-history-info-00.txt M. Watson Category: Standards Track Nortel Networks Cullen Jennings Cisco Expires: April, 2003 October 2002 An Extension to the Session Initiation Protocol for Request History Information 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. Abstract This draft defines a standard mechanism for capturing the history information associated with a SIP request. This capability enables many enhanced services by providing the information as to how and why a call arrives at a specific application or user. This draft defines a new optional SIP header, History-Info, for capturing the history information in requests. A new option tag, HistInfo, to be included in the Supported header is defined to allow UAs to indicate whether the HistInfo should be returned in responses to a request which has captured the history information. The draft suggests the use of a secure transport mechanism such as TLS and the use of S/MIME for ensuring the security of the HistInfo. Table of Contents 1 Request History Information Description........................3 2 Request History Information Protocol Details...................4 2.1 Protocol Structure of History-Info........................4 2.2 Protocol Examples.........................................5 2.3 Protocol usage............................................5 2.4 Security for History-Info.................................6 2.5 Example Applications using History-Info...................7 3 Security Considerations........................................8 References.......................................................9 Appendix A û Forking Scenarios..................................10 A.1 Sequentially forking (Hist-Info in Response).............10 A.2 Sequential Forking (with Success)........................11 Appendix B û Voicemail..........................................12 Barnes Expires - April 2003 [Page 1] SIP Request History Information October 2002 Appendix C û Automatic Call Distribution Example................16 Appendix D û Solution options analysis..........................16 Full Copyright Statement........................................18 Overview This document provides the solution for the Request History requirements as defined in [1]. The fundamental functionality provided by the request history information is the ability to inform proxies and UAs involved in processing a request about the history or progress of that request. This functionality provides a standard mechanism for capturing the request history information to enable a wide variety of services for networks and end users, without prescribing the operation of those services. Section 1 provides an overall description of the solution, providing references to the appropriate requirements met by each aspect of the solution. For background, further detail on some aspects of the solution with regards to optionality and the detailed protocol requirements is provided in Appendix D. Section 2 provides the details of the additions to the SIP protocol, which are required to capture the Request History information. An example use of the request history information is included in Section 2, with additional scenarios included in the Appendix. It is anticipated that these would be moved and progressed in the Service examples draft [2] or individual informational drafts describing these specific services. Individual drafts would be particularly useful for documenting services for which there are multiple solutions (i.e. the use of the request history information isnÆt prescriptive). Conventions used in this document 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 [7]. In order to provide a cross reference of the solution description to the requirements defined in [1] without reiterating the entirety of the requirements in this document, the requirements are referenced as [REQNAME-req] following the text or paragraph which explicitly satisfies the requirement. Definitions The following terminology is used in this document: Retarget (as defined in [1]): The process of a Proxy Server/UAC changing a URI in a request and thus changing the target of the request. Retargeted: past of Retarget. Retargeted-from-URI: The URI or address from which the request was retargeted. Barnes Expires - April 2003 [Page 2] SIP Request History Information October 2002 Retargeted-to-URI: The new URI or address to which the request is in the process of being retargeted. 1 Request History Information Description The fundamental functionality provided by the request history information is the ability to inform proxies and UAs involved in processing a request about the history or progress of that request [CAPABILITY-req]. The solution for the capture of the Request History Information defines a new header for SIP messages: History- Info [CONTENT-req]. The Request History Information can appear in any request not associated with an established dialog, which includes INVITE, REGISTER, MESSAGE and OPTIONS [REQUEST-VALIDITY-req] and any valid response to these requests.[ISSUER-req] Request History Information is captured when a request is retargeted. In some scenarios, it might be possible for more than one instance of retargeting to occur within the same Proxy. A proxy SHOULD also generate request history information for the 'internal retargeting'. An entity (UA or proxy) retargeting in response to a redirect or REFER SHOULD include any Request History information from the redirect/REFER in the new request [GENERATION- req, FORWARDS-req]. The Request History Information is optional in that neither UAs nor Proxies are required to support it. The requirement for Request History information to be returned in Responses is indicated using a new Supported header: HistInfo [BACKWARDS-req]. In addition, local policy can define whether or not the information is captured by the retargeting entity for any request, or a specific Request- URI, being retargeted. In many instances, it is likely that this could restrict the applicability of services which make us of the Request History Information to be limited to retargeting within domain(s) controlled by the same local policy, or between domain(s) which negotiate policies with other domains to ensure support of the given policy, or services for which "complete" History Information isnÆt required to provide the service. [OPTIONALITY- req] Thus, it is highly recommended that all applications making use of the request history information clearly define the impact of the information not being available and specify the processing of such a request. This draft defines a new header for SIP and builds on the security model as defined in [4]. However, The Request History information is being inserted by an entity retargeting a Request, resulting in a slightly different problem than the basic SIP header or Identity problem. It is primarily the Request-URIs that are the security concern, since they can reflect some aspect of a userÆs identity and service routing. Thus, the primary objective of the security solution is to ensure that the information being captured is protected from being accessed or manipulated by non-authorized entities, with the fundamental assumption that retargeting entities are implicitly authorized. The draft suggests the use of a secure transport mechanism such as TLS [SEC-req-4]. The use of S/MIME in a manner similar to that used for the Authenticated Identity Body defined in [5] is recommended to protect the Request History Information from being manipulated by a rogue application. Further details of the use of this proposed mechanism to satisfy the Barnes Expires - April 2003 [Page 3] SIP Request History Information October 2002 security requirements are provided in section 2.4. The security associated with the Request History Information is optional and depends upon local policy and the impact on specific applications of having the information compromised. Since, the Request History Information itself is also optional and it has been recommended that applications document the impact of the information not being available, it is also suggested that the impact of not supporting the security recommendations also be documented to ensure that it is sufficiently addressed by the application. In order to satisfy the requirements of ensuring that the privacy associated with a retargeted request URI is maintained by the retargeting entity [PRIV-req-1] and by the receiving entity [PRIV- req-2], the retargeting entity must determine if there is any privacy associated with a request URI being retargeted. In some scenarios, the Privacy header would indicate whether a field in a message should be privacy protected. However, the basic assumption is that local policy would be used to determine whether a specific request URI should have its privacy maintained and whether maintaining that privacy means that the request URI would NOT be captured or that it would be appropriately Privacy protected if it were captured. The proposal for ensuring that the privacy is protected is to assume the use of a Privacy Service as defined by [6]. [EditorÆs note: Do we really want to solve the problem this way OR assume that if there is any level of privacy for the request URI, to just NOT capture it? Or, should this also be a local policy thing? ] It is recognized that meeting the privacy requirements can impact the functionality of this solution by overriding the request to generate the information. As with the optionality and security requirements, applications making use of History-Info should address any impact this may have. 2 Request History Information Protocol Details This section contains the details and usage of the proposed new SIP protocol elements. It also discusses the security aspects of the solution and provides some examples. 2.1 Protocol Structure of History-Info History-Info is a header field as defined by [4]. It can appear in any request not associated with an established dialog, which includes INVITE, REGISTER, MESSAGE and OPTIONS and any valid response to these requests. It carries the following information: History-Info = ("History-Info" / "h") HCOLON HI-retargeted-from-uri HI-retargeted-to-uri *( SEMI HI-param ) HI-retargeted-from-uri = name-addr HI-retargeted-to-uri= name-addr HI-param = HI-reason / HI-reason-cause / HI-reason-text / HI-extension Barnes Expires - April 2003 [Page 4] SIP Request History Information October 2002 HI-reason = "HI-reason" EQUAL HI-reason-protocol HI-reason-protocol = "SIP" / "Q.850" / token HI-reason-cause = "cause" EQUAL 1*DIGIT HI-reason-text = "text" EQUAL quoted-string HI-extension = generic-param 2.2 Protocol Examples History-Info: ; HI-reason=SIP;cause=302;text="Moved Temporarily"; foo=bar History-Info: ; HI-reason=SIP;cause=486;text="Busy Here" 2.3 Protocol usage This section describes the processing specific to UAs and Proxies for the History-Info and the HistInfo option tag. [EditorÆs note: Once the Security solution is fully fleshed out, it may be reasonable to move this section 2.3 after section 2.4 and provide the detailed security related processing prior to this section, so that security aspects can be highlighted in this section, as well.] 2.3.1 UAC Behavior The UAC SHOULD include the HistInfo option tag in the Supported header in any request not associated with an established dialog for which the UAC would like the History-Info in the Response. The processing of the History-Info received in the response is application specific and outside the scope of this draft. 2.3.2 UAS Behavior The processing of History-Info by a UAS in a Request depends upon local policy and specific applications at the UAS which might make use of the information. If the HistInfo option tag is received in a request, the UAS should include any History-Info received in the request in the subsequent response. 2.3.3 Proxy Behavior The use of History-Info does not alter the fundamental processing of proxies for determining request targets as defined in section 16.5 of [4]. Whether a proxy captures the History-Info depends upon local policy and whether the Request contains the HistInfo option tag in the Supported header. The following are further Barnes Expires - April 2003 [Page 5] SIP Request History Information October 2002 considerations for refinement of a local policy supporting History- Info: o Whether retargets within a Proxy are captured o Whether the History-Info captured for a proxy/domain should go outside that domain (e.g. a Proxy knows that the information is potentially useful within that domain, however, policies (for privacy, user and network security, etc.) prohibit the exposure of that information outside that domain). Each application making use of History-Info should address the applicability and impacts of the local policies. Consistent with basic SIP processing of optional headers, proxies should maintain History-Info captured by other domains, received in Requests which they forward, independent of whether local policy supports History-Info. If the proxy supports History-Info, the proxy SHOULD add any History-Info collected as a result of a retarget to a Request as it is forwarded. The History-Info SHOULD be added following any History-Info received in the request being forwarded to preserve the relative order of the information. A proxy that receives a Request with the HistInfo option tag in the Supported header and depending upon a local policy which supports the capturing of History-Info SHOULD return captured History-Info in subsequent responses to the Request. Parallel forking, as with basic SIP processing, does introduce somewhat of a special case. In the case of parallel forking, the proxy SHOULD capture each of the Request-URIs to which the Request is forked. Since, the forking is parallel, the order in which the entries would be included in a response or subsequent non-forked request would be up to local policy. Logically, with the information in the History-Info, the end application would not necessarily be able to determine that parallel forking occurred, but rather would be able to reconstruct the tree of requests and responses associated with the forking. 2.4 Security for History-Info As discussed in Section 1, the security requirements are met through the use of S/MIME to protect the Request History Information from being manipulated by a rogue application. The solution proposes the definition of an authenticated identity for the retargeted-URI using S/MIME similar to the Authenticated Identity Body defined in [5]. As defined in [1], there are 3 fundamental security requirements associated with the History-Info: 1) Determination of whether any of the previously added History- Info headers have been altered [SEC-req-1]. 2) Preserving the chronological order of each History-Info header content [SEC-req-2]. 3) Ability to authenticate the identity represented by HI- retargeted-from-URI and HI-retargeted-to-URI in the History-Info [SEC-req-3] Barnes Expires - April 2003 [Page 6] SIP Request History Information October 2002 The third requirement can be satisfied by defining an authenticated identity for the HI-retargeted-from-URI and HI-retargeted-to-URI similar to the Authenticated Identity Body defined in [5]. In addition to the mandatory fields specified in [5] for inclusion in the Authenticated Identity body, HI-reason should also be included. The second requirement can be met by signing the entirety of the History-Info that is forwarded or returned in a response. There are some slight differences between the Authentication Service required for the History-Info and the Authentication Service defined in [5]: o The authenticated identity body relates to a History-Info header field rather than the From field of the Request. o The authenticated identity body is being requested to be authenticated by the retargeting entity and NOT by the user associated with the identity (i.e. the retargeted entity). o There may be multiple History-Info headers in a message, thus this may require multiple authenticated identity bodies. 2.4.1 Security examples [EditorÆs Note: Need to add some protocol details based on the use of S/MIME for protecting History-Info]. 2.5 Example Applications using History-Info This scenario highlights an example where the History-Info in the response is primarily of use in not retrying routes that have already been tried by another proxy. Note, that this is just an example and that there may be valid reasons why a Proxy would want to retry the routes and thus, this would like be a local proxy or even user specific policy. UA 1 sends a call to "Bob" to proxy 1. Proxy 1 forwards the request to Proxy 2. Proxy 2 parallel forks and tries several places (UA2, UA3 and UA4) before sending a response to Proxy 1 that all the places are busy. Proxy 1, without the History-Info, would try several of the same places (UA3 and UA4)based upon registered contacts for "Bob", before completing at UA5. However, with the History-Info, Proxy 1 determines that UA3 and UA4 have already received the invite, thus the INVITE goes directly to UA5. UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | |-INVITE->| | | | | Supported: HistInfo History-Info: | | | | | | | | | |-INVITE>| | | | History-Info: History-Info: | | | | | | | | | |-----INVITE ---->| | | History-Info: History-Info: Barnes Expires - April 2003 [Page 7] SIP Request History Information October 2002 | | | | | | | | | |-------INVITE------------>| | History-Info: History-Info: /* All Responses from the INVITEs indicate Busy. */ | | | | | | | | |<-486 ---| | | | | History-Info: History-Info: History-Info: History-Info: | | | | | | | /* Upon receipt of the response, P1 determines another route for the INVITE, but finds that it matches some routes already attempted (e.g. UA2 and UA3, thus the INVITE is only forwarded to UA5, where the session is successfully established */ | | | | | | | | |----------------INVITE --------------------->| History-Info: History-Info: History-Info: History-Info: History-Info: | | | | | | | | |<-----200 OK---------------------------------| |<--200 OK---| | | | | | | | | | | | | |--ACK --------------------------------------------------->| Additional detailed scenarios are available in the appendix. 3 Security Considerations This draft provides a proposal for addressing the Security requirements identified in [1] in sections 1 and 2.4 of this draft by proposing the use of TLS between entities and the use of S/MIME to protect the History-Info based upon the SIP Authenticated Identity model defined in [5]. 4 IANA Considerations (Note to RFC Editor: Please fill in all occurrences of XXXX in this section with the RFC number of this specification). This document defines a new SIP header field name with a compact form: History-Info and h respectively, and a new option tag: HistInfo. The following changes should be made to http:///www.iana.org/ assignments/sip-parameters The following row should be added to the header field section: Header Name Compact Form Reference History-Info h [RFCXXXX] Barnes Expires - April 2003 [Page 8] SIP Request History Information October 2002 The following should be added to the Options Tags section: Name Description Reference HistInfo When used with the Supported header, [RFCXXXX] this option tag indicates support for the History Information to be captured for requests and returned in subsequent responses. This tag is not used in a Proxy-Require or Requires header field since support of History-Info is optional. References [1] M. Barnes, M. Watson, C. Jennings, J. Peterson, "SIP Generic Request History Capability û Requirements", draft-ietf-sipping-req- history-00.txt, August, 2002. [2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service- examples-02.txt, June, 2002. [3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field for the Session Initiation Protocol", draft-ietf-sip-reason-01.txt, th May 14 , 2002. [4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC 3261, June, 2002. [5] J. Peterson, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft- peterson-sip-identity-01.txt, July 1, 2002. [6] J. Peterson, "A Privacy Mechanism for the Session Initiation Protocol (SIP)", draft-ietf-sip-privacy-general-01.txt, June, 2002. [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. Acknowledgements The authors would like to acknowledge the constructive feedback provided by Robert Sparks, Scott Orton, Jayshree Bharatia, Anthony Brown and Francois Audet. AuthorsÆ Addresses Mary Barnes Nortel Networks 2380 Performance Drive Phone: 1-972-684-5432 Richardson, TX USA Email: mbarnes@nortelnetworks.com Cullen Jennings Cisco Systems 170 West Tasman Dr Tel: +1 408 527 9132 MS: SJC-21/3 Email: fluffy@cisco.com Mark Watson Barnes Expires - April 2003 [Page 9] SIP Request History Information October 2002 Nortel Networks (UK) Maidenhead Office Park (Bray House) Westacott Way Maidenhead, Berkshire Tel: +44 (0)1628-434456 England Email: mwatson@nortelnetworks.com Appendix A û Forking Scenarios A.1 Sequentially forking (Hist-Info in Response) This scenario highlights an example where the History-Info in the response is useful to an application or user that originated the request. UA 1 sends a call to "Bob" via proxy 1. Proxy 1 sequentially tries several places (UA2, UA3 and UA4) unsuccessfully before sending a response to UA1. This scenario is provided to show that by providing the History- Info to UA1, the end user or an application at UA1 could make a decision on how best to attempt finding "Bob". Without this mechanism UA1 might well attempt UA3 (and thus UA4) and then re- rd attempt UA4 on a 3 manual attempting at reaching "Bob". With this mechanism, either the end user or application could know that "Bob" is busy on his home phone and is physically not in the office. If there were an alternative address for "Bob" known to this end user or application, that hasnÆt been attempted, then either the application or the end user could attempt that. The intent here is to highlight an example of the flexibility of this mechanism that enables applications well beyond SIP as it is certainly well beyond the scope of this draft to prescribe detailed applications. UA1 Proxy1 UA2 UA3 UA4 | | | | | |--INVITE -->| | | | | | | | | | |--INVITE -------->| | | |<--100 -----| | | | | |<-302 ------------| | | | | | | | | |-------INVITE ------------>| | | | | | | | |<-------180 ---------------| | |<---180 ----| | | | | . . |-------INVITE------------->| | | | timeout | | | | | | | | | |------INVITE ---------------------->| |<--100 -----| | | | | | | | | | |<-486 ------------------------------| | | | | | | |-- ACK ---------------------------->| |<--486------| | | | | | | | | |--ACK ----->| | | | | | | | | Barnes Expires - April 2003 [Page 10] SIP Request History Information October 2002 [EditorÆs Note: Need to detail the message flow.] A.2 Sequential Forking (with Success) This scenario highlights an example where the History-Info in the request is primarily of use in not retrying routes that have already been tried by another proxy. Note, that this is just an example and that there may be valid reasons why a Proxy would want to retry the routes and thus, this would like be a local proxy or even user specific policy. UA 1 sends a call to "Bob" to proxy 1. Proxy 1 sequentially tries several places (UA2, UA3 and UA4) before retargeting the call to Proxy 2. Proxy 2, without the History-Info, would try several of the same places (UA3 and UA4)based upon registered contacts for "Bob", before completing at UA5. However, with the History-Info, Proxy 2 determines that UA3 and UA4 have already received the invite, thus the INVITE goes directly to UA5. UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | | | | | | | | |--INVITE -------->| | | | |<--100 -----| | | | | | | |<-302 ------------| | | | | | | | | | | | |-------INVITE ------------>| | | | | | | | | | | |<-------180 ---------------| | | |<---180 ----| | | | | | | . . |-------INVITE------------->| | | | | timeout | | | | | | | | | | | | |------INVITE ---------------------->| | |<--100 -----| | | | | | | |<-302 ------------------------------| | | | | | | | | | |-INVITE->| | | | | | | | | | | | | | | | | | | | | |------INVITE --------------------->| | | | | | | | | | |<-----200 OK---------------------->| |<--200 OK-------------| | | | | | | | | | | | |--ACK --------------------------------------------------->| [EditorÆs Note: Need to add the details of the messages here.] Barnes Expires - April 2003 [Page 11] SIP Request History Information October 2002 Appendix B û Voicemail This scenario highlights an example where the History-Info in the request is primarily of use by an edge service (e.g. Voicemail Server). UA 1 called UA A which had been forwarded to UA B which forwarded to a UA VM (voicemail server). Based upon the retargeted URIs and Reasons in the INVITE, the VM server makes a policy decision about what mailbox to use, which greeting to play etc. UA1 Proxy UA-A UA-B UA-VM | | | | | |--INVITE F1-->| | | | | | | | | | |--INVITE F2-->| | | |<--100 F3-----| | | | | |<-302 F4------| | | | | | | | | |--------INVITE F5---------->| | | | | | | | |<--------180 F6-------------| | |<---180 F7----| | | | | . . . | | | | | |------retransmit INVITE-----|--------->| | . . . | | | | | | (timeout) | | | | | | | | |-------INVITE F8---------------------->| | | | | | | |<-200 F9-------------------------------| | | | | | |<-200 F10-----| | | | | | | | | |--ACK F11-------------------------------------------->| Message Details INVITE F1 UA1->Proxy INVITE sip:UserA@nortelnetworks.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: BigGuy Content-Type: application/sdp Content-Length: v=0 o=UserA 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 100.101.102.103 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 /*Client for UA1 prepares to receive data on port 49170 Barnes Expires - April 2003 [Page 12] SIP Request History Information October 2002 from the network. */ INVITE F2 Proxy->UA-A INVITE sip:UserA@ims.nortelnetworks.com SIP/2.0 Via: SIP/2.0/UDPims.nortelnetworks.com:5060;branch=1 Via: SIP/2.0/UDP here.com:5060 Record-Route: From: BigGuy To: LittleGuy Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: BigGuy Content-Type: application/sdp Content-Length: v=0 o=UserA 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 100.101.102.103 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 100 Trying F3 Proxy->UA1 SIP/2.0 100 Trying Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-Id: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 302 Moved Temporarily F4 UserA->Proxy SIP/2.0 302 Moved Temporarily Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=1 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: Content-Length: 0 INVITE F5 Proxy-> UA-B INVITE sip:UserB@nortelnetworks.com SIP/2.0 Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=2 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-Id: 12345600@here.com History-Info: ; HI-reason=SIP; cause=302; text="Moved Temporarily" CSeq: 1 INVITE Barnes Expires - April 2003 [Page 13] SIP Request History Information October 2002 Contact: BigGuy Content-Type: application/sdp Content-Length: v=0 o=User1 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 100.101.102.103 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 180 Ringing F6 UA-B ->Proxy SIP/2.0 180 Ringing Via: SIP/2.0/UDP there.com:5060 From: BigGuy To: LittleGuy ;tag=5 Call-ID: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 180 Ringing F7 Proxy-> UA1 SIP/2.0 180 Ringing SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-Id: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 /* User B is not available. INVITE is sent multiple times until it times out. */ /* The proxy forwards the INVITE to UA-VM after adding the additional History Information entry. */ INVITE F8 Proxy-> UA-VM INVITE sip:VM@nortelnetworks.com SIP/2.0 Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-Id: 12345600@here.com History-Info: ; HI-reason=SIP;cause=302;text="Moved Temporarily" History-Info: ; HI-reason=SIP;cause=480;text="Temporarily Unavailable" CSeq: 1 INVITE Contact: BigGuy Content-Type: application/sdp Content-Length: v=0 o=User1 2890844526 2890844526 IN IP4 client.here.com Barnes Expires - April 2003 [Page 14] SIP Request History Information October 2002 s=Session SDP c=IN IP4 100.101.102.103 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 200 OK F9 SIP/2.0 200 OK UA-VM->Proxy Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: TheVoiceMail Content-Type: application/sdp Content-Length: v=0 o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com s=Session SDP c=IN IP4 110.111.112.114 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 200 OK F10 Proxy->UA1 SIP/2.0 200 OK Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: TheVoiceMail Content-Type: application/sdp Content-Length: v=0 o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com s=Session SDP c=IN IP4 110.111.112.114 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 ACK F11 UA1-> UA-VM ACK sip:VM@nortelnetworks.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy;tag=3 Call-Id: 12345600@here.com CSeq: 1 ACK Content-Length: 0 Barnes Expires - April 2003 [Page 15] SIP Request History Information October 2002 /* RTP streams are established between UA1 and UA-VM. UA-VM starts announcement for UA1 */ Appendix C û Automatic Call Distribution Example Appendix D û Solution options analysis This section is included to capture some background analysis which formed the basis for the solution proposed in this document. This section can be deleted from a subsequent version once the content of this document is sufficiently developed and well understood. D.1 Optionality Requirements. In many cases, it is anticipated that whether the history is added to the Request would be a local policy decision enforced by the specific application, thus no specific protocol element is needed. However, due to the capability being "optional" from the SIP protocol perspective, the impact to an application of not having the "Request History" must be described. For example, in a scenario where there is sequential forking and retargeting, some of the destinations previously tried could be retried. The impact of not having the "Request History" information for this sample application is that routing is inefficient. However, another scenario involving a voicemail application, the impact of not having the "Request History" information would be the service could not operate without having the information as to why the call was retargeted and the initial target for the call. Thus, the expectation would be that the policy in a system that intended to support this voicemail application would have to require the entities within its domain which are capable of retargeting to capture "Request History" information. Thus, there are several aspects to the optionality requirement: o Optionality with regards to whether the History Information is to be included in responses to the original Request. o Optionality with regards to whether a particular retargeting entity records the History Information. o Due to the Privacy requirement, the information MUST not be captured for Request URIs that have indicated a requirement for privacy. The optionality mechanisms also depends upon whether the need for the "Request History" is based upon an end user based service (e.g. a GUI that provides the list of tried entities for an unsuccessful call setup, thus ensuring that the caller doesnÆt re-attempt an entity in that list or attendant services) or a network based service whose use of the "Request History" would likely be transparent to the UA (e.g. the Voicemail example). The Supported header is the chosen mechanism for a UAC to indicate that the information should be included in subsequent responses. Whether a server processing the request supports the mechanism would be based upon local policy for that domain. Barnes Expires - April 2003 [Page 16] SIP Request History Information October 2002 D.2 Content-req The Content-req specifies the following: Retargeted-to-URI Retargeted-from-URI Reason Chronological ordering The following summarizes the solution considerations for each of these content requirements: D.2.1 Is the Retargeted-to-URI required when it can be derived at the next hop, which would capture this as the Retargeted-from-URI for subsequent retargeting? In a series of Request History Information, the Retargeted-to-URI becomes the Retargeted-from-URI for the next occurrence of retargeting, thus it would be possible in a scenario where the Request History functionality is supported by each of the retargeting entities to derive a complete set of Retargeted-to and Retargeted-from URIs from the sequence of History Information rather than including both Retargeted-to and Retargeting-from URI in each occurrence of History Information. However, for the scenario where a particular proxy retargets, but local policy does not support the Request History Information, this approach could result in a potential loss of information. In addition, the support of the BACKWARDS-Req does require that the retargeted-to URI also be captured to ensure completeness of information (to the extent possible based on policies, privacy, etc.) in Responses. D.2.2 Reason The Reason header field [3] seems like a possible solution for carrying the Reason associated with the Retargeting, however, this header field is limited to a single instance for a particular protocol in a given request within a dialog. In addition, most instances of the retargeting are anticipated to be based upon the Status-Code in SIP Responses. Thus, Request History Information defines its own reason field based on the reason-value format defined in [3]. D.2.3 Chronological ordering The Chronological ordering requirement should not require a specific protocol element if the History-Info entries are recommended to be added in the order they are generated and collected. Certainly, an explicit counter or index would seem to facilitate and maintain the order, however, a simple counter would have problems with parallel forking. The following were considered as alternatives for maintaining the logical order of the parallel forking: o Indexing using a dot delimiter to indicate hops and forking (e.g. 1.1.1, 1.1.2 would indicate 2 hops with 2 retargeted nd URIs at the 2 hop.) o ABNF reflecting the nesting/hops (whether this is even feasible was not determined). Barnes Expires - April 2003 [Page 17] SIP Request History Information October 2002 o Allowing the same value for the count/index (i.e. not worrying about duplicates as the value indicates only relative order). However it was decided to remove the count/index altogether, as logically the application that is concerned about knowing something about forking can generate the tree by using the Retargeted-to and Retargeted-from URIs in the History-Info. ItÆs not possible to determine the exact time order in which the requests were forked, but this requirement would be well beyond the scope of the intent of the History-Info (i.e. History-Info is not intended to be a realtime trace, but rather to provide some logical information as to the entities which received a particular request and reasons as to why a request would have been retargeted). Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Barnes Expires - April 2003 [Page 18]