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Versions: 00 01 02

 Internet Draft                                               M. Barnes
 Document: draft-barnes-sipping-history-info-02.txt           M. Watson
 Category: Standards Track                              Nortel Networks
                                                        Cullen Jennings
                                                                  Cisco
 Expires: August, 2003                                   February 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.
 
 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.
 
 Table of Contents
 
    1 Request History Information Description........................3
       1.1 Optionality of History-Info...............................3
       1.2 Securing History-Info.....................................3
       1.3 Ensuring the Privacy of History-Info......................4
    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.................................7
       2.5 Example Applications using History-Info...................8
    3 Security Considerations........................................9
    References.......................................................9
    Appendix A  Forking Scenarios...................................10
       A.1 Sequentially forking (Hist-Info in Response).............10
       A.2 Sequential Forking (with Success)........................11
    Appendix B  Voicemail...........................................12
 
 
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    Appendix C  Automatic Call Distribution Example.................16
    Appendix D  Solution options analysis...........................18
    Full Copyright Statement........................................20
 
 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, since
    History-Info 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.
 
  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.
 
 
 
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    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].
 
 1.1 Optionality of History-Info
 
    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 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]  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.
 
 1.2 Securing History-Info
 
    This draft defines a new header for SIP.  Since, the Request
    History information is being inserted by an entity as it targets a
    Request, the resulting security requirements introduce a slightly
    different problem than the basic SIP header or Identity problem.
    For History-Info, the general requirement is to secure information
    that is inserted by a proxy.  It is primarily the captured Request-
    URIs that are the security concern, since they can reflect some
    aspect of a user's 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
 
 
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    assumption that retargeting entities are implicitly authorized.
    The draft does suggest the use of a secure transport mechanism such
    as TLS to ensure the overall confidentiality of the History-
    Info[SEC-req-4].  However, the complete security solution for
    History-Info depends upon a general solution for protecting the
    captured information. This will be addressed in a separate solution
    draft [TBD]. Details of the use of this proposed mechanism to
    satisfy the 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.
 
 1.3 Ensuring the Privacy of History-Info
 
    In order to satisfy the requirements of ensuring that the privacy
    associated with a retargeted request 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 being retargeted. In some
    scenarios, the Privacy header would indicate whether the headers in
    a message should be privacy protected. However, the basic
    assumption is that local policy would be used to determine whether
    a specific request should have its privacy maintained and whether
    maintaining that privacy means that a specific 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 recommend the use of a Privacy Service as defined
    by [6] for headers.
 
    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:
 
       o Targeted-to-URI: the Request URI captured as the Request is
         targeted. By capturing a copy of the Request URI in the
 
 
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         initial request, the Retargeted-from-URI is already captured
         when a request is retargeted and the Retargeted-to-URI is
         being captured.
 
       o Reason: An optional parameter for History-info. The reason for
         the retargeting is captured by including the Reason Header [3]
         as part of the captured Request URI.
 
       o Index: An optional parameter for History-Info reflecting the
         chronological order of the information, indexed to also
         reflect the forking and nesting of requests.
 
    The semantics of the captured Targeted-to-URIs are derived from the
    current context of the request as follows:
 
       o Retargeted-from-URI: this is the Request URI that is being
         changed due to the retargeting. It is the Targeted-to-URI in
         the request received by the retargeting entity.  If it was not
         explicitly captured by the original sender/forwarder of the
         request, it would be captured and added to the request prior
         to the Targeted-to-URI currently being captured.  If the
         sender/forwarder supported History-Info, it would have been
         added prior to sending/forwarding the Request.
 
       o Retargeted-to-URI: this is the Targeted-to-URI being captured
         in the request being retargeted.
 
    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:<sip:UserA@ims.nortelnetworks.com?Reason=SIP;
    cause=302;text=öMoved Temporarilyö>; foo=bar
 
    History-Info: <sip:45432@vm.nortelnetworks.com?
    Reason=SIP;cause=486;text="Busy Here"> ; index=1.1.2
 
 
 2.3 Protocol usage
 
    This section describes the processing specific to UAs and Proxies
    for the History-Info and the HistInfo option tag.
 
 
 
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    [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 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.  In
    addition, the UAC should initiate the capturing of the History
    Information by capturing the Request-URI as the hi-targeted-to-uri
    and initializing the index to 1.
 
    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 several factors:
         o Whether the Request contains the HistInfo option tag in the
           Supported header.
         o Local Policy
           The following are further considerations for refinement of a
           local policy supporting History-Info:
              o Whether retargeting within a Proxy is 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
    messages which they forward, independent of whether local policy
    supports History-Info.
 
    The specific processing by proxies for capturing the History-Info
    in Requests and Responses is described in detail in the following
    sections.
 
    2.3.3.1 Capturing History-Info in Requests
 
 
 
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    If the proxy supports History-Info, the proxy SHOULD add any
    History-Info collected as it retargets a Request. The SIP Response
    Code should be included in the Reason header of the Targeted-to-
    URI. The History-Info SHOULD be added following any History-Info
    received in the request being forwarded. Additionally, if a request
    is received that doesn't include a captured Request URI from the
    previous entity, the proxy MAY add an additional entry, effectively
    capturing the retargeted-from-URI in the Request.
 
    In order to maintain ordering and accurately reflect the nesting
    and retargeting of the request, it is recommended that an index be
    included along with the Targeted-to-URI being captured. The basic
    rule for adding the index are to read the value from the previous
    History-Info, if available, and capture the index.n as the index
    for the History-Info being captured, where n would typically be 1
    for a forwarded request. Thus, the level of nesting of the index
    reflects the number of hops. 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.  If there is no previous History-Info entry, or index in the
    previous entry, an index MAY be included for the current entry,
    with the index starting at 1.  An index SHOULD NOT be added in the
    scenario whereby the received request had no History-Info header
    and the retargeted-from-URI is being captured for completeness.
 
    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 in the manner previously described. However, since the
    forking is parallel, it's recommended that rather than attempt to
    send the logical order of the requests being sent, that the
    information for subsequent requests or responses is built upon
    receipt of the initial response to ensure that the series of any
    subsequent forking and retargeting of any of the forked requests
    accurately reflects the logical sequence.  Again, it is recommended
    that the index be captured for each forked request following a
    similar model as that previously described, with each new Request
    having a unique index.  The lack of Reason headers in the captured
    Request-URIs should be indicative of the parallel nature of forking
    (i.e the Request-URIs are not the result of retargets, but are
    rather all simultaneous Targeted-To URIs.)
 
    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.
 
 
 2.4 Security for History-Info
 
    As discussed in Section 1, the security requirements are met by
    recommending the use of TLS (a basic SIP requirement per [4]) and
    through the use of the security solution defined in [TBD].
 
    2.4.1 Security examples
 
 
 
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    [Editor's Note: Need to add some protocol details based on the use
    of S/MIME for protecting History-Info once [TBD] 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 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: <sip:Bob@P1>, <sip:Bob@P2>; index=1
    |            |         |        |        |        |        |
    |            |         |-INVITE>|        |        |        |
                   History-Info: <sip:Bob@P1>, <sip:Bob@P2>; index=1,
                                 <sip:User2@UA2>; index=1.1
    |            |         |        |        |        |        |
    |            |         |-----INVITE ---->|        |        |
                   History-Info: <sip:Bob@P1 >, <sip:Bob@P2 >; index=1,
                                 <sip:User3@UA3>; index=1.2
    |            |         |        |        |        |        |
    |            |         |-------INVITE------------>|        |
                   History-Info: <sip:Bob@P1 >, <sip:Bob@P2 >; index=1,
                                 <sip:User4@UA4 >; index=1.3
 
    /* All Responses from the INVITEs indicate Busy.   */
    |            |         |        |        |        |        |
    |            |<-486 ---|        |        |        |        |
                   History-Info: <sip:Bob@P1 >, <sip:Bob@P2 >; index=1,
                                 <sip:User2@UA2>; index=1.1,
                                 <sip:User3@UA3>; index=1.2,
                                 <sip:User4@UA4>; index=1.3
    |            |         |        |        |        |        |
   /* 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: <sip:Bob@P1>, <sip:Bob@P2>; index=1,
                                 <sip:User2@UA2>; index=1.1,
                                 <sip:User3@UA3>; index=1.2,
 
 
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                                 <sip:User4@UA4>; index=1.3,
                                 <sip:User5@UA5?Reason=SIP;cause=486>
    |            |         |        |        |        |        |
    |            |<-----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. The protection
    of the History-Info is dependent upon a general solution for
    securing headers added by proxies. This general solution is
    described in [TBD] [Editor's note: Assumed to be based upon the SIP
    Authenticated Identity body 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]
 
    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-02.txt, February, 2003.
 
    [2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service-
    examples-03.txt, November, 2002.
 
 
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    [3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field
    for the Session Initiation Protocol", RFC 3326, December, 2002.
 
    [4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
    3261, June, 2002.
 
    [5] J. Peterson, " SIP Authenticated Identity Body (AIB) Format",
    draft-ietf-sip-authid-body-00.txt, October, 2002.
 
    [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-00.txt, October, 2002.
 
    [9] Crocker, D. and P. Overell, "Augmented BNF for Syntax
    Specifications: ABNF", RFC 2234, November 1997.
 
 
 Acknowledgements
 
    The authors would like to acknowledge the constructive feedback
    provided by Robert Sparks, Rohan Mahy, Paul Kyzivat, Scott Orton,
    John Elwell, Francois Audet, Anthony Brown, and Jayshree Bharatia.
 
 Authors' 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
    Nortel Networks (UK)
    Maidenhead Office Park (Bray House)
    Westacott Way
    Maidenhead,
    Berkshire                      Tel: +44 (0)1628-434456
    England                        Email:  mwatson@nortelnetworks.com
 
 Appendix A  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.
 
 
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    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 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.
 
 
    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.
 
 
 
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                    SIP Request History Information     February 2003
 
 
    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 --------------------------------------------------->|
 
   [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 policy decision about what mailbox to use, which greeting to play
    etc.
 
    UA1          Proxy           UA-A         UA-B        UA-VM
 
 
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                    SIP Request History Information     February 2003
 
 
 
    |              |              |             |          |
    |--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 <sip:User1@here.com>
   To: LittleGuy <sip:UserA@nortelnetworks.com>
   Call-Id: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:User1@here.com>
   Content-Type: application/sdp
   Content-Length: <appropriate value>
 
    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
    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: <sip:UserA@nortelnetworks.com>
    From: BigGuy <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>
    Call-Id: 12345600@here.com
    CSeq: 1 INVITE
 
 
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                    SIP Request History Information     February 2003
 
 
    History-Info: <sip:UserA@ims.nortelnetworks.com>; index=1
    Contact: BigGuy <sip:User1@here.com>
    Content-Type: application/sdp
    Content-Length: <appropriate value>
 
    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 <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>
    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 <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
    Call-Id: 12345600@here.com
    CSeq: 1 INVITE
    Contact: <sip:UserB@nortelnetworks.com>
    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 <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>
    Call-Id: 12345600@here.com
    History-Info: <sip:UserA@ims.nortelnetworks.com>; index=1,
    <sip:UserB@nortelnetworks.com?Reason=SIP; cause=302; text="Moved
    Temporarily">;index=2
    CSeq: 1 INVITE
    Contact: BigGuy <sip:User1@here.com>
    Content-Type: application/sdp
    Content-Length: <appropriate value>
 
    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
 
 
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                    SIP Request History Information     February 2003
 
 
 
    180 Ringing F6  UA-B ->Proxy
 
    SIP/2.0 180 Ringing
    Via: SIP/2.0/UDP there.com:5060
    From: BigGuy <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>;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 <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>
    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 <sip:User1@here.com>
       To: LittleGuy <sip:UserA@nortelnetworks.com>
    Call-Id: 12345600@here.com
    History-Info: <sip:UserA@ims.nortelnetworks.com>;index=1,
    <sip:UserB@nortelnetworks.com?Reason=SIP; cause=302; text="Moved
    Temporarily">;index=2,
    <sip:VM@nortelnetworks.com?Reason=SIP;cause=480;text="Temporarily
    Unavailable">;index=3
    CSeq: 1 INVITE
    Contact: BigGuy <sip:User1@here.com>
    Content-Type: application/sdp
    Content-Length: <appropriate value>
 
    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
 
 
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                    SIP Request History Information     February 2003
 
 
    Via: SIP/2.0/UDP here.com:5060
    From: BigGuy <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
    Call-Id: 12345600@here.com
    CSeq: 1 INVITE
    Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
    Content-Type: application/sdp
    Content-Length: <appropriate value>
 
    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 <sip:User1@here.com>
    To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
    Call-Id: 12345600@here.com
    CSeq: 1 INVITE
    Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
    Content-Type: application/sdp
    Content-Length: <appropriate value>
 
    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 <sip:User1@here.com>
    To: LittleGuy<sip:UserA@nortelnetworks.com>;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
 
 
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                    SIP Request History Information     February 2003
 
 
    Gold group (ACDGRP1) were busy, by retargeting the request to the
    Silver Group.  Upon receipt of the call at the agent assigned to
    handle the incoming call, based upon the History-Info 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. 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: <sip:Gold@ACD.com>; index=1
                     History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
    |              |              |             |          |
    |              |<-302 F3------|             |          |
                     Contact: <sip:ACDGRP2@ACD.com>
    |              |              |             |          |
    |              |--------INVITE F4---------->|          |
                     History-Info: <sip:Gold@ACD.com>; index=1
                     History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
                     History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
    |              |              |             |          |
    |              |              |             |          |
    |              |              |             |INVITE F5>|
                     History-Info: <sip:Gold@ACD.com>; index=1
                     History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
                     History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
    |              |              |             |          |
    |              |              |             |<-200 F6--|
    |              |              |             |          |
    |              |<-200 F7--------------------|          |
                     History-Info: <sip:Gold@ACD.com>; index=1
                     History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
                     History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
    |<-200 F8------|              |             |          |
 < No History-Info included in the response due to Local Policy>
    |              |              |             |          |
    |--ACK F9--------------------------------------------->|
 
    Message Details
 
 
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                    SIP Request History Information     February 2003
 
 
 
    [To be completed]
 
 Appendix D  Solution options analysis
 
    This section is included to capture some background analysis
    forming 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 doesn't 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.
 
 
    D.2 Content-req
 
    The Content-req specifies the following:
    Retargeted-to-URI
    Retargeted-from-URI
    Reason
 
 
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                    SIP Request History Information     February 2003
 
 
    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.
 
    Another option put forth was capture only one URI, but to actually
    capture the initial targeted-to-URI which then becomes a
    retargeted-from-URI when the request is retargeted, with the
    retargeted-to-URI captured as the next targeted-to-URI.  This would
    require that a UA wanting to make use of History-Info in responses
    would actually capture the first targeted-to-URI.  In addition, a
    proxy that supports History-Info would need to capture two
    targeted-to URIs IF one was not included in the initial Request.
    This processing could appear to be in conflict with the privacy and
    optionality requirements, however, since a Request-URI is only
    retargeted if it indicates a resource that a proxy is responsible
    for, this isn't an issue. What this does mean is that a request
    that is only forwarded by a proxy would NOT capture the retargeted-
    from URI, but could capture the retargeted-to URI.
 
 
    D.2.2 Reason
 
    The Reason header field [3] seems like a possible solution for
    carrying the Reason associated with the Retargeting.  It is
    proposed to include this header as an optional escaped part of the
    targeted-to-URI.
 
    D.2.3 Chronological ordering
 
    The following were considered as options for satisfying this
    requirement:
       o No explicit count/index.  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.
    If a count/index is included, the following were considered as
    alternatives for maintaining the logical order of the parallel
    forking:
 
 
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                    SIP Request History Information     February 2003
 
 
       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).
       o Allowing the same value for the count/index (i.e. not worrying
         about duplicates as the value indicates only relative order).
       o Including a count and an additional branch parameter for the
         forking (e.g. n=1, br=1.1, n=1, br=1.2).
 
 
 
 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
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    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
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