Internet Draft M. Barnes Document: draft-ietf-sip-history-info-01.txt Editor Category: Standards Track Nortel Networks Expires: April, 2004 October, 2003 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. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. 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 History-Info should be returned in responses to a request which has captured the history information. Table of Contents 1 Request History Information Description.........................3 1.1 Optionality of History-Info................................4 1.2 Securing History-Info......................................4 Barnes Expires April 2004 [Page 1] SIP Request History Information October 2003 1.3 Ensuring the Privacy of History-Info.......................5 2 Request History Information Protocol Details....................5 2.1 Protocol Structure of History-Info.........................5 2.2 Protocol Examples..........................................6 2.3 Protocol usage.............................................7 2.4 Security for History-Info.................................10 2.5 Example Applications using History-Info...................11 3. Security Considerations.......................................13 References.......................................................14 Appendix A Forking Scenarios....................................16 A.1 Sequentially forking (Hist-Info in Response)..............16 A.2 Sequential Forking (with Success).........................17 Appendix B Voicemail............................................18 Appendix C Automatic Call Distribution Example..................23 Full Copyright Statement.........................................25 Overview This document defines a solution for the Request History requirements as defined in [1], providing the capability to inform proxies and UAs involved in processing a request about the history or progress of that request. This draft defines a new SIP header, History-Info, to provide a standard mechanism for capturing the request history information to enable a wide variety of services for networks and end users. The History-Info header provides a building block for development of new services. Section 1 provides an overall description of the solution, providing references to the appropriate requirements. Section 2 provides the details of the additions to the SIP protocol. An example use of the new header is included in Section 2, with additional scenarios included in the Appendix. It is anticipated that these would be moved and progressed in a general Service examples draft such as [2] or individual informational drafts describing these specific services, since the History-Info header is just one of the building blocks for implementing these services. Individual drafts would be particularly useful for documenting services for which there are multiple solutions, since the use of the request history information isn't prescriptive. As well, as these example applications, the History-Info header can be used to enhance basic SIP functionality by providing additional diagnostic information. In addition, the inclusion of the History-Info header in messages strengthens the overall SIP security solution. When the History-Info header is secured as described in section 2.4, it provides an additional means by which the initiator of a request can be assured that the forwarding and any retargeting of that request was valid. Barnes Expires April 2004 [Page 2] SIP Request History Information October 2003 Section 3 summarizes the security solution as described in section 2.4. 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. 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 is to capture the Request-URIs as a request is forwarded in a new header for SIP messages: History-Info [CONTENT-req]. This allows for the capturing of the history of a request that would be lost with the normal SIP processing involved in the subsequent forwarding of the request. This solution proposes no changes in the fundamental determination of request targets or in the request forwarding as defined in sections 16.5 and 16.6 of the SIP protocol specification [4]. The History-Info header can appear in any request not associated with an established dialog, which includes INVITE, REGISTER, MESSAGE, REFER and OPTIONS [REQUEST-VALIDITY-req] and any valid response to these requests.[ISSUER-req] The History-Info header is added to a Request when a new request is created by a UAC or Proxy, or when the target of a request is changed. The term 'retarget' was introduced in [1] to refer to this changing of the target of a request and the subsequent forwarding of that request. It should be noted that retargeting only occurs when the Request-URI indicates a domain for which the processing entity is responsible. In terms of the SIP protocol, the processing associated with retargeting is described in sections 16.5, and 16.6 of [4]. As described in section 16.5 of [4], it is possible for the target of a request to be changed by the same proxy multiple times (referred to as 'internal retargeting' in [1]), as the proxy MAY add targets to the target set after beginning Request Forwarding. Section 16.6 of [1] describes Request Forwarding. It is during this process of Barnes Expires April 2004 [Page 3] SIP Request History Information October 2003 Request Forwarding, that the History Information is captured as an optional, additional header field. Thus, the addition of the History- Info header does not impact fundamental SIP Request Forwarding. An entity (UA or proxy) changing the target of a request in response to a redirect or REFER SHOULD also propagate any History-Info header from the initial Request in the new request [GENERATION-req, FORWARDS-req]. 1.1 Optionality of History-Info The History-Info header is optional in that neither UAs nor Proxies are required to support it. A new Supported header, Histinfo, is included in the Request to indicate whether the History-Info header is returned in Responses [BACKWARDS-req]. In addition to the Histinfo Supported header, local policy determines whether or not the header is added to any request, or for a specific Request-URI, being retargeted. It is possible that this could restrict the applicability of services which make use 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 isn't required to provide the service. [OPTIONALITY-req] All applications making use of the History-info header MUST clearly define the impact of the information not being available and specify the processing of such a request. 1.2 Securing History-Info This draft defines a new header for SIP. The draft does RECOMMEND the use of a secure transport mechanism such as TLS to ensure the overall confidentiality of the History-Info headers[SEC-req-4]. However, the problem is slightly different than the hop by hop security problem solved by TLS, as each hop is not required to add the History-Info header. Since the History-Info header is being inserted by an entity as it targets and forwards a Request, the resulting security requirements also introduce a slightly different problem than the basic SIP header or Identity [8] problem, which are focused on securing the information in the initial request end to end. For the History-Info header, the general requirement is to secure a header that is inserted by an intermediary and then subsequently referenced, by other intermediaries to build the next header entry, or by an end application using the information to provide a service. Thus, the general requirement takes the form of a middle to middle and middle to end security solution, which is addressed in a separate draft [5]. The use of the middle-to-end security solution discussed in [5] allows the integrity of the History-Info to be ascertained as it traverses the intermediaries. Thus, including the History-Info header in SIP Requests and securing in this manner adds an additional level of security end to end, assuring the initiator of a Request Barnes Expires April 2004 [Page 4] SIP Request History Information October 2003 that it has indeed reached the intended recipient. Further discussion of the security mechanism for History-Info is provided in section 2.4. 1.3 Ensuring the Privacy of History-Info Since the History-Info header can inadvertently reveal information about the requestor as described in [6], the Privacy header SHOULD be used to determine whether an intermediary can include the History- Info header in a Request that it receives and forwards [PRIV-req-2] or that it retargets [PRIV-req-1]. Thus, the History-Info header SHOULD not be included in Requests where the requestor has indicated a priv-value of Session or Header level privacy. In addition, the History-Info header can reveal general routing information, which may be viewed by a specific intermediary or network, to be subject to privacy restrictions. Thus, local policy MAY also be used to determine whether to include the History-Info header, or if it would only be included in the Request as it is retargeted within a specific domain. It is recognized that satisfying 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, REFER and OPTIONS and any valid response to these requests. It carries the following information: o Targeted-to-URI: the Request URI captured as the Request is forwarded. o Index: A mandatory parameter for History-Info reflecting the chronological order of the information, indexed to also reflect the forking and nesting of requests. The format for this Barnes Expires April 2004 [Page 5] SIP Request History Information October 2003 parameter is a string of digits, separated by dots to indicate the number of forward hops and retargets. This results in a tree representation of the history of the request, with the lowest level index reflecting a branch of the tree. By including the index and securing the header, the ordering of the History-info headers in the request is assured.[SEC-req-2] o Reason: An optional parameter for History-info. The reason for the retargeting is captured by including the Reason Header [3] associated with the Request URI being retargeted. Thus, a reason is not included for a Request URI when it is first added in a History-info header, but rather is added when that particular Request-URI is retargeted. Note, that this does appear to complicate the security problem, however, retargeting only occurs when the Request-URI indicates a domain for which the processing entity is responsible, thus it would be the same processing entity that initially added the Request-URI to the header that would be updating it with the Reason. The following summarizes the syntax of the History-Info header, based upon the standard SIP syntax [4]: History-Info = ("History-Info" / "h") HCOLON hist-info *(COMMA hist-info) hist-info = hi-targeted-to-uri *( SEMI hi-param ) hi-targeted-to-uri= name-addr hi-param = hi-index / hi-extension hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT) hi-extension = generic-param 2.2 Protocol Examples History-Info:; index=1; foo=bar History-Info: ; index=1.1, ;index=1.2, ; index=1.3 Barnes Expires April 2004 [Page 6] SIP Request History Information October 2003 [Editor's note: need to insert row for Table 2]. 2.3 Protocol usage This section describes the processing specific to UAs and Proxies for the History-Info header and the Histinfo option tag. As discussed in section 1, the fundamental objective is to capture the target Request-URIs as a request is forwarded. This allows for the capturing of the history of a request that would be lost due to subsequent (re)targeting and forwarding. To accomplish this for the entire history of a request, either the UAC must capture the Request- URI in the initial request or a proxy must add History-Info headers for both the Request-URI in the initial request and the target Request-URI as the request is forwarded. The basic processing is for each entity forwarding a request to add a History-Info header for the target Request-URI, updating the index and adding the Reason as appropriate for any retargeted Request-URI. [Editor's 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 detailed 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. In addition, the UAC SHOULD initiate the capturing of the History Information by adding a History-Info header using the Request-URI of the request as the hi-targeted-to-uri and initializing the index to 1 in the History-Info header The processing of the History-Info header received in the Response is application specific and outside the scope of this draft. However, the validity of the information SHOULD be ensured prior to any application usage. [Editor's note: Further detail to be provided once the security solution is available.] 2.3.2 UAS Behavior The processing of the History-Info header by a UAS in a Request depends upon local policy and specific applications at the UAS which might make use of the information. Prior to any application usage of the information, the validity SHOULD be ascertained. [Editor's note: Further detail to be provided once the security solution is available.] Barnes Expires April 2004 [Page 7] SIP Request History Information October 2003 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 inclusion of the History-Info header in a Request does not alter the fundamental processing of proxies for determining request targets as defined in section 16.5 of [4]. Whether a proxy adds the the History-Info header as it forwards a Request depends upon local policy, with the following being considerations in the definition of that policy: o Whether the Request contains the Histinfo option tag in the Supported header. o Whether the proxy supports the History-Info header. o Whether any History-Info header added for a proxy/domain should go outside that domain. An example being the use of the History-Info header within the specific domain in which it is retargeted, however, policies (for privacy, user and network security, etc.) prohibit the exposure of that information outside that domain. An example of such an application is provided in Appendix C. o Whether the History-Info header is added for a specific Request URI due to local privacy policy considerations. An example policy would be a proxy that only adds the History-Info header if the Histinfo option tag is in the Supported header. Other proxies may have a policy that they always add the header, but never forward it outside a particular domain. Each application making use of the History-Info header SHOULD address the impacts of the local policies on the specific application (e.g. what specification of local policy is optimally required for a specific application and any potential limitations imposed by local policy decisions). Consistent with basic SIP processing of optional headers, proxies SHOULD maintain History-Info headers, received in messages being forwarded, independent of whether local policy supports History-Info. The specific processing by proxies for adding the History-Info headers in Requests and Responses is described in detail in the following sections. 2.3.3.1 Adding the History-Info header to Requests Barnes Expires April 2004 [Page 8] SIP Request History Information October 2003 If the proxy supports the History-Info header, the proxy SHOULD add a History-Info header as it forwards a Request. Section 16.6 of [4] defines the steps to be followed as the proxy forwards a Request. Step 5 prescribes the addition of optional headers. Although, this would seem the appropriate step for adding the History-info header, the interaction with Step 6 "Postprocess routing information" and the impact of a strict route in the Route header could result in the Request-URI being changed, thus adding the History-info header between steps 8 and 9 is RECOMMENDED. Note, that in the case of loose routing, the Request-URI does not change during the forwarding of a Request, thus the capturing of History-Info for such a request would result in duplicate Request-URIs with different indices. The History- Info header SHOULD be added following any History-Info header received in the request being forwarded. Additionally, if a request is received that doesn't include a History-Info header, the proxy MAY add an additional History-Info header preceding the one being added for the current request being forwarded. The index for this entry is RECOMMENDED to start at 1. For retargets that are the result of an explicit SIP response, the SIP Response Code that triggered the retargeting MUST be included in the Reason header field of the Request URI that has been retargeted. For retargets as a result of timeouts or internal events, a Reason MAY be included in the Reason header field of the Request URI that has been retargeted. In order to maintain ordering and accurately reflect the nesting and retargeting of the request, an index MUST be included along with the Targeted-to-URI being captured. Per the ABNF in section 2.1, the index consists of a dot delimited series of digits (e.g. 1.1.2), with each dot reflecting the number of hops or level of nesting of the request. Thus, the indexing results in a logical tree representation for the history of the Request. It is recommended that for each level of indexing, the index start at 1. For retargets within a proxy, the proxy MUST maintain the current level of nesting by incrementing the lowest/last digit of the index for each instance of retargeting, thus reflecting the number of retargets within the proxy. The basic rules for adding the index are summarized as follows: 1. If the Request-URI in the original request indicates a resource for which this proxy is responsible, then the proxy reads the value from the History-Info header in the received request, if available, and adds another level of indexing. For example, if the index in the last History-Info header field in the received request is 1.1, this proxy would initialize its index to 1.1.1. For each subsequent target that is forwarded by the same proxy, a new index is used by incrementing the last/lowest digit. Barnes Expires April 2004 [Page 9] SIP Request History Information October 2003 2. If the Request-URI indicates a resource that this proxy is not responsible for, then the lowest/last digit of the index is incremented (i.e. a new level is not created). For example, if the index in the History-Info header of the received request was 1, then the index in the History-Info header field added by this proxy would be 2. If the request forwarding is done in parallel, the proxy MUST capture each of the Request-URIs to which the Request is forwarded in the manner previously described per rule 1 above. The index MUST be captured for each forked request per the rules above, with each new Request having a unique index. The proxy builds the subsequent requests and responses using the amalgamated information associated with each of those requests and including the header entries in the order indicated by the indexing. Section 2.5 provides an example of a parallel request scenario, highlighting this indexing mechanism. 2.3.3.2 Processing History-Info in Responses A proxy that receives a Request with the Histinfo option tag in the Supported header, and depending upon a local policy supporting the capture of History-Info, SHOULD return captured History-Info in subsequent, provisional and final responses to the Request. It should be noted that local policy considerations, for network and intermediary privacy, MAY restrict the sending of the History-Info headers added by the intermediary in subsequent responses. Thus, in such cases, the proxy MAY remove from these responses the History- Info headers which it inserted in the original forwarded request. 2.3.4 Redirect Server Behavior A redirect server SHOULD NOT add any new History-Info, as that would be done by the entity receiving the 3xx response. However, a redirect server MAY include History-Info in responses by adding any History- Info headers received in a request to a subsequent response. 2.4 Security for History-Info As discussed in Section 1, the security requirements are partially met by recommending the use of TLS (a basic SIP requirement per [4]) for hop by hop security. In addition, the use of the middle-to-end security solution discussed in [5] allows the integrity of the History-Info to be ascertained as it traverses the intermediaries. For the History-Info header, the general requirement is to secure a header that is inserted by an intermediary and then subsequently referenced, by other intermediaries to build the next header entry or by an end application using the information to provide a service. In terms of exactly what is being secured, it is primarily the captured Barnes Expires April 2004 [Page 10] SIP Request History Information October 2003 Request-URIs that are the security concern, since they can reflect some aspect of a user's identity and service routing. However, the indices are also important in that they can be used to determine if specific Request-URIs have been removed from the header. Thus, the primary objective of the security solution is to ensure that the entire History-Info header is protected from being accessed or manipulated by non-authorized entities, with the fundamental assumption that retargeting entities are implicitly authorized. 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 by the application to ensure that the impacts have been sufficiently addressed by the application. 2.4.1 Security examples [Editor's Note: Need to add some protocol details for protecting History-Info once [5] is further along]. 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 sends the requests in parallel 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 -->| | | | | | Barnes Expires April 2004 [Page 11] SIP Request History Information October 2003 | |-INVITE->| | | | | Supported: Histinfo History-Info: ;index=1, ; index=2 | | | | | | | | | |-INVITE>| | | | History-Info: ;index=1, ; index=2, ; index=2.1 | | | | | | | | | |-----INVITE ---->| | | History-Info: ;index=1, ; index=2, ; index=2.2 | | | | | | | | | |-------INVITE------------>| | History-Info: ;index=1, ; index=2, ; index=2.3 /* All Responses from the INVITEs indicate non-success/non- availability*/ | | | | | | | | |<-480 ---| | | | | History-Info: ;index=1, ; index=2, ;index=2.1, ; index=2.2, ; index=2.3 | | | | | | | /* 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: ;index=1, ; index=2, ;index=2.1, ; index=2.2, ; index=2.3 Barnes Expires April 2004 [Page 12] SIP Request History Information October 2003 ;index=1.1 | | | | | | | | |<-----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 1.2 and 2.4 of this draft by proposing the use of TLS between entities, and by securing the History-Info headers added by proxies as described 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] 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 Require header field since support of History-Info is optional. 5. Changes since last version Barnes Expires April 2004 [Page 13] SIP Request History Information October 2003 Changes from the û00 to the û01 version: o Attempted to be more explicit about the fundamental processing associated with the header. Removed definitions of new terms, only referencing the terms from the requirements in the context of the fundamental SIP processing implied by the terms. o Attempted to clarify the Index and the related processing. o Added more detail addressing the privacy requirements. o Added a bit more detail on security. The security solution remains in a separate document and this document will need updating once that is completed. o Updated the examples (in section 2.5 and appendix) and clarified the definition and the maintenance of the Index in sections 2.1 and 2.3.3.1. o Clarified the Reason description in section 2.1. There had been an error in the description of the processing that was a remnant of the change to include only a single URI for each History-Info header. o Miscellaneous editorial changes (i.e. HistInfo -> Histinfo, etc.) Changes from individual draft-barnes-sipping-history-info-02 to the û 00 WG version: o Updated references and added reference to Security solution draft. o Removed appendix D which included background on analysis of solution options. o Cleaned up the document format per rfc2223bis. o Strengthened the inclusion of the INDEX as a MUST (per discussion at IETF-56). o Added text around the capturing of the Reason (SHOULD be captured for SIP responses and MAY be captured for other things such as timeouts). o Clarified the response processing 2.3.3.2 to include provisional responses and the sending of a 183 to convey History-Info. o Added section 2.3.4 to address Redirect Server behavior. References [1] M. Barnes, M. Watson, C. Jennings, J. Peterson, "SIP Generic Request History Capability Requirements", draft-ietf-sipping-req- history-04.txt, June, 2003. [2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service- examples-05.txt, November, 2002. [3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field for the Session Initiation Protocol", RFC 3326, December, 2002. Barnes Expires April 2004 [Page 14] SIP Request History Information October 2003 [4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC 3261, June, 2002. [5] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October, 2003. [6] J. Peterson, "A Privacy Mechanism for the Session Initiation Protocol (SIP)", RFC 3323, November, 2002. [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [8] J. Peterson, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity- 01.txt, February, 2003. [9] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. Acknowledgements The editor would like to acknowledge the constructive feedback provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell, Nir Chen, Francois Audet, Palash Jain, Brian Stucker, Norma Ng, Anthony Brown, and Jayshree Bharatia. The editor would like to acknowledge the significant input from Rohan Mahy on some of the normative aspects of the ABNF, particularly around the need for and format of the index and around the enhanced SIP security aspects enabled by this draft Contributors' Addresses Cullen and Mark provided substantial input in the form of email discussion in the development of the initial version of this individual solution document. Cullen Jennings Cisco Systems 170 West Tasman Dr MS: SJC-21/3 Tel: +1 408 527 9132 Email: fluffy@cisco.com Barnes Expires April 2004 [Page 15] SIP Request History Information October 2003 Mark Watson Nortel Networks (UK) Maidenhead Office Park (Bray House) Westacott Way Maidenhead, Berkshire England Tel: +44 (0)1628-434456 Email: mwatson@nortelnetworks.com Author's Address Mary Barnes Nortel Networks 2380 Performance Drive Richardson, TX USA Phone: 1-972-684-5432 Email: mary.barnes@nortelnetworks.com Appendix A Forking Scenarios A.1 Sequentially forking (History-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-attempt UA4 on a rd 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 hasn't 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. Barnes Expires April 2004 [Page 16] SIP Request History Information October 2003 UA1 Proxy1 UA2 UA3 UA4 | | | | | |--INVITE -->| | | | | | | | | | |--INVITE -------->| | | |<--100 -----| | | | | |<-302 ------------| | | | | | | | | |-------INVITE ------------>| | | | | | | | |<-------180 ---------------| | |<---180 ----| | | | | . . |-------INVITE------------->| | | | timeout | | | | | | | | | |------INVITE ---------------------->| |<--100 -----| | | | | | | | | | |<-486 ------------------------------| | | | | | | |-- ACK ---------------------------->| |<--486------| | | | | | | | | |--ACK ----->| | | | | | | | | [Editor's 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. Barnes Expires April 2004 [Page 17] SIP Request History Information October 2003 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 --------------------------------------------------->| [Editor's Note: Need to add the details of the messages here.] Appendix B 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). It should be noted that this isn't intended to be a complete specification for this specific edge service as it is quite likely that additional information is need by the edge service. History-Info is just one building block that this service makes use of. 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 (and other information) in the INVITE, the VM server makes a Barnes Expires April 2004 [Page 18] SIP Request History Information October 2003 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 Barnes Expires April 2004 [Page 19] SIP Request History Information October 2003 a=rtpmap:0 PCMU/8000 /*Client for UA1 prepares to receive data on port 49170 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 History-Info: ; index=1 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 Barnes Expires April 2004 [Page 20] SIP Request History Information October 2003 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: ; index=1, ;index=2 CSeq: 1 INVITE 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. */ Barnes Expires April 2004 [Page 21] SIP Request History Information October 2003 /* 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: ;index=1, ;index=2, ;index=3 CSeq: 1 INVITE 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 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 Barnes Expires April 2004 [Page 22] SIP Request History Information October 2003 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 /* RTP streams are established between UA1 and UA-VM. UA-VM starts announcement for UA1 */ Appendix C Automatic Call Distribution Example This scenario highlights an example of an Automatic Call Distribution service, where the agents are divided into groups based upon the type of customers they handle. In this example, the Gold customers are given higher priority than Silver customers, so a Gold call would get serviced even if all the agents servicing the Gold group (ACDGRP1) were busy, by retargeting the request to the Silver Group. Upon Barnes Expires April 2004 [Page 23] SIP Request History Information October 2003 receipt of the call at the agent assigned to handle the incoming call, based upon the History-Info header in the message, the application at the agent can provide an indication that this is a Gold call, from how many groups it might have overflowed before reaching the agent, etc. and thus can be handled appropriately by the agent. For scenarios whereby calls might overflow from the Silver to the Gold, clearly the alternate group identification, internal routing or actual agent that handles the call SHOULD not be sent to UA1, thus for this scenario, one would expect that the Proxy would not support the sending of the History-Info in the response, even if requested by the calling UA. As with the other examples, this is not prescriptive of how one would do this type of service but an example of a subset of processing that might be associated with such a service. In addition, this example is not addressing any aspects of Agent availability, which might also be done via a SIP interface. UA1 Proxy ACDGRP1 Svr ACDGRP2 Svr UA2-ACDGRP2 | | | | | |--INVITE F1-->| | | | Supported:Histinfo | | | | | | |--INVITE F2-->| | | Supported:Histinfo History-Info: ; index=1 History-Info: ; index=1.1 | | | | | | |<-302 F3------| | | Contact: | | | | | | |--------INVITE F4---------->| | History-Info: ; index=1 History-Info: ; index=1.1 History-Info: ; index=1.2 | | | | | | | | | | | | | |INVITE F5>| History-Info: ; index=1 History-Info: ; index=1.1 History-Info: ; index=1.2 | | | | | | | | |<-200 F6--| | | | | | Barnes Expires April 2004 [Page 24] SIP Request History Information October 2003 | |<-200 F7--------------------| | History-Info: ; index=1 History-Info: ; index=1.1 History-Info: ; index=1.2 |<-200 F8------| | | | No History-Info included in the response due to Local Policy> | | | | | |--ACK F9--------------------------------------------->| Message Details [To be completed] Full Copyright Statement Copyright (C) The Internet Society (2003). 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 2004 [Page 25]