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Versions: 00 01 02 03 04 05 06 RFC 4244

Internet Draft                                               M. Barnes
Document: draft-ietf-sip-history-info-00.txt                    Editor
Category: Standards Track                              Nortel Networks

Expires: December, 2003                                     June 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
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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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 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................................4
      1.2 Securing History-Info......................................4


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      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.............................................6
      2.4 Security for History-Info..................................9
      2.5 Example Applications using History-Info...................10
   3. Security Considerations.......................................11
   References.......................................................12
   Appendix A  Forking Scenarios....................................14
      A.1 Sequentially forking (Hist-Info in Response)..............14
      A.2 Sequential Forking (with Success).........................15
   Appendix B  Voicemail............................................16
   Appendix C  Automatic Call Distribution Example..................21
   Full Copyright Statement.........................................22

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.

   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





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   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.

   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].



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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 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, which is addressed
   in a separate solution draft [5]. 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.


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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 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.



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     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. [SEC-req-2]

   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="Moved Temporarily">; foo=bar

   History-Info: <sip:45432@vm.nortelnetworks.com?
   Reason=SIP;cause=486;text="Busy Here"> ; index=1.1.2


2.3 Protocol usage




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   This section describes the processing specific to UAs and Proxies for
   the History-Info and the HistInfo option tag.

   [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).


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          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

   If the proxy supports History-Info, the proxy SHOULD add any History-
   Info collected as it retargets a Request. 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 of
   the Targeted-to-URI. For retargets as a result of timeouts or
   internal events, a Reason header MAY 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, an index MUST 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, the
   index included for the current entry is RECOMMENDED to start at 1,
   indicating a new thread of History-Info.  An index MUST 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.  This allows the entities making use of the History-
   Info to detect any gaps in History-Info captured in the request.

   Parallel forking, as with basic SIP processing, does introduce
   somewhat of a special case. In the case of parallel forking, the
   proxy SHOULD capture each of the Request-URIs to which the Request is
   forked in the manner previously described. However, since the forking


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   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.  A 183
   response MAY be sent explicitly for the purposes of conveying
   History-Info prior to the final response.

   2.3.4 Redirect Server Behavior

   It MAY be advantageous for redirect servers to support the receipt of
   History-Info in requests. By receiving it in the request, the
   Redirect Server MAY be able to optimize the information it sends in
   responses by looking at the already targeted-to-URIs.  However, a
   redirect server SHOULD NOT add any new History-Info, as that would be
   done by the entity receiving the 3xx response. Thus, a redirect
   server SHOULD have local policy defined such that History-Info is not
   captured, which should be the default.  However, a redirect server
   MAY include History-Info in responses to reflect retargets that have
   already taken place by including any History-Info received in a
   request in a subsequent response.


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 [5].

   2.4.1 Security examples

   [Editor's Note: Need to add some protocol details for protecting
   History-Info once [5] is further along].




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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
   |            |         |        |        |        |        |



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  /* 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,
                                <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 [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


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   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.

5. Changes since last version

Changes from individual draft-barnes-sipping-history-info-02 to the รป00
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-03.txt, November, 2002.

   [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] M. Barnes, "A Mechanism to Secure SIP Identity Headers Inserted
   by Intermediaries", draft-barnes-sipping-inserted-info-00.txt, June,
   2003.

   [6] J. Peterson, "A Privacy Mechanism for the Session Initiation
   Protocol (SIP)", RFC 3323, November, 2002.



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   [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, 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.

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

   Mark Watson
   Nortel Networks (UK)
   Maidenhead Office Park (Bray House)
   Westacott Way
   Maidenhead,
   Berkshire
   England

   Tel: +44 (0)1628-434456
   Email:  mwatson@nortelnetworks.com

Authors' Address

   Mary Barnes


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   Nortel Networks
   2380 Performance Drive
   Richardson, TX USA

   Phone:  1-972-684-5432
   Email:  mbarnes@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.

   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.


   UA1        Proxy1              UA2      UA3      UA4
   |            |                  |        |        |
   |--INVITE -->|                  |        |        |
   |            |                  |        |        |
   |            |--INVITE -------->|        |        |
   |<--100 -----|                  |        |        |
   |            |<-302 ------------|        |        |
   |            |                  |        |        |
   |            |-------INVITE ------------>|        |
   |            |                  |        |        |
   |            |<-------180 ---------------|        |
   |<---180 ----|                  |        |        |
   |  . .       |-------INVITE------------->|        |


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   |            |       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.



   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

   |            |         |        |        |        |        |
   |--INVITE -->|         |        |        |        |        |
   |            |         |        |        |        |        |
   |            |--INVITE -------->|        |        |        |
   |<--100 -----|         |        |        |        |        |
   |            |<-302 ------------|        |        |        |
   |            |         |        |        |        |        |
   |            |-------INVITE ------------>|        |        |
   |            |         |        |        |        |        |
   |            |<-------180 ---------------|        |        |


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   |<---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

   |              |              |             |          |
   |--INVITE F1-->|              |             |          |
   |              |              |             |          |
   |              |--INVITE F2-->|             |          |
   |<--100 F3-----|              |             |          |
   |              |<-302 F4------|             |          |
   |              |              |             |          |
   |              |--------INVITE F5---------->|          |
   |              |              |             |          |
   |              |<--------180 F6-------------|          |
   |<---180 F7----|              |             |          |


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   |  . . .       |              |             |          |
   |              |------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
   History-Info: <sip:UserA@ims.nortelnetworks.com>; index=1


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   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>


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   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

   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,


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   <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
   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>


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   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 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


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   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

   [To be completed]


Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.


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   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."






























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