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Versions: 00 01 02 03 04 05 06 RFC 4244

Internet Draft                                              M. Barnes
Document: draft-ietf-sip-history-info-01.txt                   Editor
Category: Standards Track                             Nortel Networks

Expires: April, 2004                                 October,  2003

    An Extension to the Session Initiation Protocol for Request History
                                Information

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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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 History-Info should be returned in responses to a request which
   has captured the history information.

Table of Contents

   1 Request History Information Description.........................3
      1.1 Optionality of History-Info................................4
      1.2 Securing History-Info......................................4


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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.............................................7
      2.4 Security for History-Info.................................10
      2.5 Example Applications using History-Info...................11
   3. Security Considerations.......................................13
   References.......................................................14
   Appendix A  Forking Scenarios....................................16
      A.1 Sequentially forking (Hist-Info in Response)..............16
      A.2 Sequential Forking (with Success).........................17
   Appendix B  Voicemail............................................18
   Appendix C  Automatic Call Distribution Example..................23
   Full Copyright Statement.........................................25

Overview

   This document defines a solution for the Request History requirements
   as defined in [1], providing the capability to inform proxies and UAs
   involved in processing a request about the history or progress of
   that request. This draft defines a new SIP header, History-Info, to
   provide a standard mechanism for capturing the request history
   information to enable a wide variety of services for networks and end
   users.  The History-Info header provides a building block for
   development of new services.

   Section 1 provides an overall description of the solution, providing
   references to the appropriate requirements.

   Section 2 provides the details of the additions to the SIP protocol.
   An example use of the new header is included in Section 2, with
   additional scenarios included in the Appendix. It is anticipated that
   these would be moved and progressed in a general Service examples
   draft such as [2] or individual informational drafts describing these
   specific services, since the History-Info header is just one of the
   building blocks for implementing these services. Individual drafts
   would be particularly useful for documenting services for which there
   are multiple solutions, since the use of the request history
   information isn't prescriptive.   As well, as these example
   applications, the History-Info header can be used to enhance basic
   SIP functionality by providing additional diagnostic information.  In
   addition, the inclusion of the History-Info header in messages
   strengthens the overall SIP security solution.  When the History-Info
   header is secured as described in section 2.4, it provides an
   additional means by which the initiator of a request can be assured
   that the forwarding and any retargeting of that request was valid.




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   Section 3 summarizes the security solution as described in section
   2.4.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [7].

   In order to provide a cross reference of the solution description to
   the requirements defined in [1] without reiterating the entirety of
   the requirements in this document, the requirements are referenced as
   [REQNAME-req] following the text or paragraph which explicitly
   satisfies the requirement.



1 Request History Information Description

   The fundamental functionality provided by the request history
   information is the ability to inform proxies and UAs involved in
   processing a request about the history or progress of that request
   [CAPABILITY-req].  The solution is to capture the Request-URIs as a
   request is forwarded in a new header for SIP messages: History-Info
   [CONTENT-req].  This allows for the capturing of the history of a
   request that would be lost with the normal SIP processing involved in
   the subsequent forwarding of the request. This solution proposes no
   changes in the fundamental determination of request targets or in the
   request forwarding as defined in sections 16.5 and 16.6 of the SIP
   protocol specification [4].

   The History-Info header can appear in any request not associated with
   an established dialog, which includes INVITE, REGISTER, MESSAGE,
   REFER and OPTIONS [REQUEST-VALIDITY-req] and any valid response to
   these requests.[ISSUER-req]

   The History-Info header is added to a Request when a new request is
   created by a UAC or Proxy, or when the target of a request is
   changed. The term 'retarget' was introduced in [1] to refer to this
   changing of the target of a request and the subsequent forwarding of
   that request. It should be noted that retargeting only occurs when
   the Request-URI indicates a domain for which the processing entity is
   responsible.  In terms of the SIP protocol, the processing associated
   with retargeting is described in sections 16.5, and 16.6 of [4].  As
   described in section 16.5 of [4], it is possible for the target of a
   request to be changed by the same proxy multiple times (referred to
   as 'internal retargeting' in [1]), as the proxy MAY add targets to
   the target set after beginning Request Forwarding. Section 16.6 of
   [1] describes Request Forwarding. It is during this process of


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   Request Forwarding, that the History Information is captured as an
   optional, additional header field. Thus, the addition of the History-
   Info header does not impact fundamental SIP Request Forwarding. An
   entity (UA or proxy) changing the target of a request in response to
   a redirect or REFER SHOULD also propagate any History-Info header
   from the initial Request in the new request [GENERATION-req,
   FORWARDS-req].

1.1 Optionality of History-Info

   The History-Info header is optional in that neither UAs nor Proxies
   are required to support it.  A new Supported header, Histinfo, is
   included in the Request to indicate whether the History-Info header
   is returned in Responses [BACKWARDS-req]. In addition to the Histinfo
   Supported header, local policy determines whether or not the header
   is added to any request, or for a specific Request-URI, being
   retargeted. It is possible that this could restrict the applicability
   of services which make use of the Request History Information to be
   limited to retargeting within domain(s) controlled by the same local
   policy, or between domain(s) which negotiate policies with other
   domains to ensure support of the given policy, or services for which
   "complete" History Information isn't required to provide the service.
   [OPTIONALITY-req]  All applications making use of the History-info
   header MUST clearly define the impact of the information not being
   available and specify the processing of such a request.

1.2 Securing History-Info

   This draft defines a new header for SIP. The draft does RECOMMEND the
   use of a secure transport mechanism such as TLS to ensure the overall
   confidentiality of the History-Info headers[SEC-req-4]. However, the
   problem is slightly different than the hop by hop security problem
   solved by TLS, as each hop is not required to add the History-Info
   header.  Since the History-Info header is being inserted by an entity
   as it targets and forwards a Request, the resulting security
   requirements also introduce a slightly different problem than the
   basic SIP header or Identity [8] problem, which are focused on
   securing the information in the initial request end to end. For the
   History-Info header, the general requirement is to secure a header
   that is inserted by an intermediary and then subsequently referenced,
   by other intermediaries to build the next header entry, or by an end
   application using the information to provide a service. Thus, the
   general requirement takes the form of a middle to middle and middle
   to end security solution, which is addressed in a separate draft [5].
   The use of the middle-to-end security solution discussed in [5]
   allows the integrity of the History-Info to be ascertained as it
   traverses the intermediaries.  Thus, including the History-Info
   header in SIP Requests and securing in this manner adds an additional
   level of security end to end, assuring the initiator of a Request


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   that it has indeed reached the intended recipient.  Further
   discussion of the security mechanism for History-Info is provided in
   section 2.4.


1.3 Ensuring the Privacy of History-Info

   Since the History-Info header can inadvertently reveal information
   about the requestor as described in [6], the Privacy header SHOULD be
   used to determine whether an intermediary can include the History-
   Info header in a Request that it receives and forwards [PRIV-req-2]
   or that it retargets [PRIV-req-1]. Thus, the History-Info header
   SHOULD not be included in Requests where the requestor has indicated
   a priv-value of Session or Header level privacy.

   In addition, the History-Info header can reveal general routing
   information, which may be viewed by a specific intermediary or
   network, to be subject to privacy restrictions.  Thus, local policy
   MAY also be used to determine whether to include the History-Info
   header, or if it would only be included in the Request as it is
   retargeted within a specific domain.

   It is recognized that satisfying the privacy requirements can impact
   the functionality of this solution by overriding the request to
   generate the information. As with the optionality and security
   requirements, applications making use of History-Info SHOULD address
   any impact this may have.

2 Request History Information Protocol Details

   This section contains the details and usage of the proposed new SIP
   protocol elements.  It also discusses the security aspects of the
   solution and provides some examples.

2.1 Protocol Structure of History-Info

   History-Info is a header field as defined by [4].  It can appear in
   any request not associated with an established dialog, which includes
   INVITE, REGISTER, MESSAGE, REFER and OPTIONS and any valid response
   to these requests.

   It carries the following information:

     o Targeted-to-URI: the Request URI captured as the Request is
        forwarded.

     o Index: A mandatory parameter for History-Info reflecting the
        chronological order of the information, indexed to also reflect
        the forking and nesting of requests. The format for this


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        parameter is a string of digits, separated by dots to indicate
        the number of forward hops and retargets. This results in a tree
        representation of the history of the request, with the lowest
        level index reflecting a branch of the tree. By including the
        index and securing the header, the ordering of the History-info
        headers in the request is assured.[SEC-req-2]

     o Reason: An optional parameter for History-info. The reason for
        the retargeting is captured by including the Reason Header [3]
        associated with the Request URI being retargeted.  Thus, a
        reason is not included for a Request URI when it is first added
        in a History-info header, but rather is added when that
        particular Request-URI is retargeted.  Note, that this does
        appear to complicate the security problem, however, retargeting
        only occurs when the Request-URI indicates a domain for which
        the processing entity is responsible, thus it would be the same
        processing entity that initially added the Request-URI to the
        header that would be updating it with the Reason.


   The following summarizes the syntax of the History-Info header, based
   upon the standard SIP syntax [4]:

          History-Info = ("History-Info" / "h") HCOLON

                            hist-info *(COMMA hist-info)

          hist-info = hi-targeted-to-uri *( SEMI hi-param )

          hi-targeted-to-uri= name-addr

          hi-param = hi-index / hi-extension

           hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT)

          hi-extension = generic-param


2.2 Protocol Examples

   History-Info:<sip:UserA@ims.nortelnetworks.com?Reason=SIP;
   cause=302;text="Moved Temporarily">; index=1; foo=bar

   History-Info: <sip:UserA@ims.nortelnetworks.com?Reason=SIP;
   cause=302; text="Moved Temporarily">; index=1.1,
   <sip:UserB@nortelnetworks.com? Reason=SIP;cause=486;
   text="Busy Here">;index=1.2,
   <sip:45432@vm.nortelnetworks.com> ; index=1.3



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   [Editor's note: need to insert row for Table 2].

2.3 Protocol usage

   This section describes the processing specific to UAs and Proxies for
   the History-Info header and the Histinfo option tag. As discussed in
   section 1, the fundamental objective is to capture the target
   Request-URIs as a request is forwarded.  This allows for the
   capturing of the history of a request that would be lost due to
   subsequent (re)targeting and forwarding.  To accomplish this for the
   entire history of a request, either the UAC must capture the Request-
   URI in the initial request or a proxy must add History-Info headers
   for both the Request-URI in the initial request and the target
   Request-URI as the request is forwarded.  The basic processing is for
   each entity forwarding a request to add a History-Info header for the
   target Request-URI, updating the index and adding the Reason as
   appropriate for any retargeted Request-URI.

   [Editor's note: Once the Security solution is fully fleshed out, it
   may be reasonable to move this section 2.3 after section 2.4 and
   provide the detailed security related processing prior to this
   section, so that security aspects can be detailed in this section, as
   well.]

   2.3.1 UAC Behavior

   The UAC SHOULD include the Histinfo option tag in the Supported
   header in any request not associated with an established dialog for
   which the UAC would like the History-Info in the Response.  In
   addition, the UAC SHOULD initiate the capturing of the History
   Information by adding a History-Info header using the Request-URI of
   the request as the hi-targeted-to-uri and initializing the index to 1
   in the History-Info header

   The processing of the History-Info header received in the Response is
   application specific and outside the scope of this draft. However,
   the validity of the information SHOULD be ensured prior to any
   application usage. [Editor's note: Further detail to be provided once
   the security solution is available.]


   2.3.2 UAS Behavior

   The processing of the History-Info header by a UAS in a Request
   depends upon local policy and specific applications at the UAS which
   might make use of the information.  Prior to any application usage of
   the information, the validity SHOULD be ascertained.  [Editor's note:
   Further detail to be provided once the security solution is
   available.]


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   If the Histinfo option tag is received in a request, the UAS should
   include any History-Info received in the request in the subsequent
   response.


   2.3.3 Proxy Behavior

   The inclusion of the History-Info header in a Request does not alter
   the fundamental processing of proxies for determining request targets
   as defined in section 16.5 of [4].  Whether a proxy adds the the
   History-Info header as it forwards a Request depends upon local
   policy, with the following being considerations in the definition of
   that policy:
       o Whether the Request contains the Histinfo option tag in the
          Supported header.
       o Whether the proxy supports the History-Info header.
       o Whether any History-Info header added for a proxy/domain
          should go outside that domain.  An example being the use of
          the History-Info header within the specific domain in which
          it is retargeted, however, policies (for privacy, user and
          network security, etc.) prohibit the exposure of that
          information outside that domain.  An example of such an
          application is provided in Appendix C.
       o Whether the History-Info header is added for a specific
          Request URI due to local privacy policy considerations.

   An example policy would be a proxy that only adds the History-Info
   header if the Histinfo option tag is in the Supported header.  Other
   proxies may have a policy that they always add the header, but never
   forward it outside a particular domain.

   Each application making use of the History-Info header SHOULD address
   the impacts of the local policies on the specific application (e.g.
   what specification of local policy is optimally required for a
   specific application and any potential limitations imposed by local
   policy decisions).

   Consistent with basic SIP processing of optional headers, proxies
   SHOULD maintain History-Info headers, received in messages being
   forwarded, independent of whether local policy supports History-Info.

   The specific processing by proxies for adding the History-Info
   headers in Requests and Responses is described in detail in the
   following sections.

   2.3.3.1 Adding the History-Info header to Requests




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   If the proxy supports the History-Info header, the proxy SHOULD add a
   History-Info header as it forwards a Request. Section 16.6 of [4]
   defines the steps to be followed as the proxy forwards a Request.
   Step 5 prescribes the addition of optional headers.  Although, this
   would seem the appropriate step for adding the History-info header,
   the interaction with Step 6 "Postprocess routing information" and the
   impact of a strict route in the Route header could result in the
   Request-URI being changed, thus adding the History-info header
   between steps 8 and 9 is RECOMMENDED. Note, that in the case of loose
   routing, the Request-URI does not change during the forwarding of a
   Request, thus the capturing of History-Info for such a request would
   result in duplicate Request-URIs with different indices. The History-
   Info header SHOULD be added following any History-Info header
   received in the request being forwarded.  Additionally, if a request
   is received that doesn't include a History-Info header, the proxy MAY
   add an additional History-Info header preceding the one being added
   for the current request being forwarded.  The index for this entry is
   RECOMMENDED to start at 1.

   For retargets that are the result of an explicit SIP response, the
   SIP Response Code that triggered the retargeting MUST be included in
   the Reason header field of the Request URI that has been retargeted.
   For retargets as a result of timeouts or internal events, a Reason
   MAY be included in the Reason header field of the Request URI that
   has been retargeted.

   In order to maintain ordering and accurately reflect the nesting and
   retargeting of the request, an index MUST be included along with the
   Targeted-to-URI being captured. Per the ABNF in section 2.1, the
   index consists of a dot delimited series of digits (e.g. 1.1.2), with
   each dot reflecting the number of hops or level of nesting of the
   request.  Thus, the indexing results in a logical tree representation
   for the history of the Request. It is recommended that for each level
   of indexing, the index start at 1.  For retargets within a proxy, the
   proxy MUST maintain the current level of nesting by incrementing the
   lowest/last digit of the index for each instance of retargeting, thus
   reflecting the number of retargets within the proxy.

   The basic rules for adding the index are summarized as follows:

     1. If the Request-URI in the original request indicates a resource
     for which this proxy is responsible, then the proxy reads the value
     from the History-Info header in the received request, if available,
     and adds another level of indexing. For example, if the index in
     the last History-Info header field in the received request is 1.1,
     this proxy would initialize its index to 1.1.1.  For each
     subsequent target that is forwarded by the same proxy, a new index
     is used by incrementing the last/lowest digit.



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     2. If the Request-URI indicates a resource that this proxy is not
     responsible for, then the lowest/last digit of the index is
     incremented (i.e. a new level is not created).  For example, if the
     index in the History-Info header of the received request was 1,
     then the index in the History-Info header field added by this proxy
     would be 2.

   If the request forwarding is done in parallel, the proxy MUST capture
   each of the Request-URIs to which the Request is forwarded in the
   manner previously described per rule 1 above. The index MUST be
   captured for each forked request per the rules above, with each new
   Request having a unique index. The proxy builds the subsequent
   requests and responses using the amalgamated information associated
   with each of those requests and including the header entries in the
   order indicated by the indexing.  Section 2.5 provides an example of
   a parallel request scenario, highlighting this indexing mechanism.

   2.3.3.2 Processing History-Info in Responses

   A proxy that receives a Request with the Histinfo option tag in the
   Supported header, and depending upon a local policy supporting the
   capture of History-Info, SHOULD return captured History-Info in
   subsequent, provisional and final responses to the Request.

   It should be noted that local policy considerations, for network and
   intermediary privacy, MAY restrict the sending of the History-Info
   headers added by the intermediary in subsequent responses.  Thus, in
   such cases, the proxy MAY remove from these responses the History-
   Info headers which it inserted in the original forwarded request.

   2.3.4 Redirect Server Behavior

   A redirect server SHOULD NOT add any new History-Info, as that would
   be done by the entity receiving the 3xx response. However, a redirect
   server MAY include History-Info in responses by adding any History-
   Info headers received in a request to a subsequent response.

   2.4 Security for History-Info

   As discussed in Section 1, the security requirements are partially
   met by recommending the use of TLS (a basic SIP requirement per [4])
   for hop by hop security.   In addition, the use of the middle-to-end
   security solution discussed in [5] allows the integrity of the
   History-Info to be ascertained as it traverses the intermediaries.
   For the History-Info header, the general requirement is to secure a
   header that is inserted by an intermediary and then subsequently
   referenced, by other intermediaries to build the next header entry or
   by an end application using the information to provide a service. In
   terms of exactly what is being secured, it is primarily the captured


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   Request-URIs that are the security concern, since they can reflect
   some aspect of a user's identity and service routing. However, the
   indices are also important in that they can be used to determine if
   specific Request-URIs have been removed from the header. Thus, the
   primary objective of the security solution is to ensure that the
   entire History-Info header is protected from being accessed or
   manipulated by non-authorized entities, with the fundamental
   assumption that retargeting entities are implicitly authorized.

   The security associated with the Request History Information is
   optional and depends upon local policy and the impact on specific
   applications of having the information compromised.  Since, the
   Request History Information itself is also optional and it has been
   recommended that applications document the impact of the information
   not being available, it is also suggested that the impact of not
   supporting the security recommendations also be documented by the
   application to ensure that the impacts have been sufficiently
   addressed by the application.


   2.4.1 Security examples

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

2.5 Example Applications using History-Info

   This scenario highlights an example where the History-Info in the
   response is primarily of use in not retrying routes that have already
   been tried by another proxy. Note, that this is just an example and
   that there may be valid reasons why a Proxy would want to retry the
   routes and thus, this would like be a local proxy or even user
   specific policy.

   UA 1 sends a call to "Bob" to proxy 1. Proxy 1 forwards the request
   to Proxy 2.  Proxy 2 sends the requests in parallel and tries several
   places (UA2, UA3 and UA4) before sending a response to Proxy 1 that
   all the places are busy.   Proxy 1, without the History-Info, would
   try several of the same places (UA3 and UA4) based upon registered
   contacts for "Bob", before completing at UA5. However, with the
   History-Info, Proxy 1 determines that UA3 and UA4 have already
   received the invite, thus the INVITE goes directly to UA5.



   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

   |            |         |        |        |        |        |
   |--INVITE -->|         |        |        |        |        |


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   |            |-INVITE->|        |        |        |        |
                 Supported: Histinfo
                 History-Info: <sip:Bob@P1>;index=1,
                               <sip:Bob@P2>; index=2
   |            |         |        |        |        |        |
   |            |         |-INVITE>|        |        |        |
                  History-Info: <sip:Bob@P1>;index=1,
                                <sip:Bob@P2>; index=2,
                                <sip:User2@UA2>; index=2.1
   |            |         |        |        |        |        |
   |            |         |-----INVITE ---->|        |        |
                  History-Info: <sip:Bob@P1>;index=1,
                                <sip:Bob@P2 >; index=2,
                                <sip:User3@UA3>; index=2.2
   |            |         |        |        |        |        |
   |            |         |-------INVITE------------>|        |
                  History-Info: <sip:Bob@P1>;index=1,
                                <sip:Bob@P2 >; index=2,
                                <sip:User4@UA4 >; index=2.3

   /* All Responses from the INVITEs indicate non-success/non-
   availability*/
  |            |         |        |        |        |        |
  |            |<-480 ---|        |        |        |        |
               History-Info: <sip:Bob@P1>;index=1,
                  <sip:Bob@P2>; index=2,
                  <sip:User2@UA2?Reason:SIP;
                   cause=408;text="RequestTimeout">;index=2.1,
                  <sip:User3@UA3?Reason:SIP;
                   cause=487;text="Request Terminated">; index=2.2,
                  <sip:User4@UA4?Reason:SIP;
                   cause=603;text="Decline">; index=2.3


  |            |         |        |        |        |        |
 /* Upon receipt of the response, P1 determines another route for the
  INVITE, but finds that it matches some routes already attempted
 (e.g. UA2 and UA3, thus the INVITE is only forwarded to UA5, where
  the session is successfully established  */
  |            |         |        |        |        |        |
   |            |----------------INVITE --------------------->|
                History-Info: <sip:Bob@P1>;index=1,
                   <sip:Bob@P2>; index=2,
                   <sip:User2@UA2?Reason:SIP;cause=408;
                    text="RequestTimeout">;index=2.1,
                   <sip:User3@UA3?Reason:SIP;cause=487;
                    text="Request Terminated">; index=2.2,
                   <sip:User4@UA4?Reason:SIP;cause=603;
                    text="Decline">; index=2.3


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                  <sip:User5@UA5>;index=1.1
  |            |         |        |        |        |        |
   |            |<-----200 OK---------------------------------|
  |<--200 OK---|         |        |        |        |        |
  |            |         |        |        |        |        |
  |--ACK --------------------------------------------------->|


   Additional detailed scenarios are available in the appendix.


3. Security Considerations

   This draft provides a proposal for addressing the Security
   requirements identified in [1] in sections 1.2 and 2.4 of this draft
   by proposing the use of TLS between entities, and by securing the
   History-Info headers added by proxies as described in [5].

4. IANA Considerations

   (Note to RFC Editor: Please fill in all occurrences of XXXX in this
   section with the RFC number of this specification).

   This document defines a new SIP header field name with a compact
   form: History-Info and h respectively, and a new option tag:
   Histinfo.

   The following changes should be made to
   http:///www.iana.org/assignments/sip-parameters

   The following row should be added to the header field section:

   Header Name             Compact Form               Reference
   History-Info                  h                    [RFCXXXX]

  The following should be added to the Options Tags section:

  Name          Description                          Reference
  Histinfo      When used with the Supported header, [RFCXXXX]
                this option tag indicates support
                for the History Information to be
                captured for requests and returned in
                subsequent responses. This tag is not
                used in a Proxy-Require or Require
                header field since support of
                History-Info is optional.

5. Changes since last version



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   Changes from the û00 to the û01 version:

     o Attempted to be more explicit about the fundamental processing
        associated with the header.  Removed definitions of new terms,
        only referencing the terms from the requirements in the context
        of the fundamental SIP processing implied by the terms.
     o Attempted to clarify the Index and the related processing.
     o Added more detail addressing the privacy requirements.
     o Added a bit more detail on security. The security solution
        remains in a separate document and this document will need
        updating once that is completed.
     o Updated the examples (in section 2.5 and appendix) and clarified
        the definition and the maintenance of the Index in sections 2.1
        and 2.3.3.1.
     o Clarified the Reason description in section 2.1.  There had been
        an error in the description of the processing that was a remnant
        of the change to include only a single URI for each History-Info
        header.
     o Miscellaneous editorial changes (i.e. HistInfo -> Histinfo,
        etc.)

   Changes from individual draft-barnes-sipping-history-info-02 to the û
   00 WG version:
        o Updated references and added reference to Security solution
          draft.
        o Removed appendix D which included background on analysis of
          solution options.
        o Cleaned up the document format per rfc2223bis.
        o Strengthened the inclusion of the INDEX as a MUST (per
          discussion at IETF-56).
        o Added text around the capturing of the Reason (SHOULD be
          captured for SIP responses and MAY be captured for other
          things such as timeouts).
        o Clarified the response processing 2.3.3.2 to include
          provisional responses and the sending of a 183 to convey
          History-Info.
        o Added section 2.3.4 to address Redirect Server behavior.

References

   [1] M. Barnes, M. Watson, C. Jennings, J. Peterson, "SIP Generic
   Request History Capability Requirements", draft-ietf-sipping-req-
   history-04.txt, June, 2003.

   [2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service-
   examples-05.txt, November, 2002.

   [3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field
   for the Session Initiation Protocol", RFC 3326, December, 2002.


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   [4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC 3261,
   June, 2002.

   [5] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by
   Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October,
   2003.

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

   [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
   Levels", RFC 2119, March 1997.

   [8] J. Peterson, "Enhancements for Authenticated Identity Management
   in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity-
   01.txt, February, 2003.

   [9] Crocker, D. and P. Overell, "Augmented BNF for Syntax
   Specifications: ABNF", RFC 2234, November 1997.




Acknowledgements

   The editor would like to acknowledge the constructive feedback
   provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell,
   Nir Chen, Francois Audet, Palash Jain, Brian Stucker, Norma Ng,
   Anthony Brown, and Jayshree Bharatia.

   The editor would like to acknowledge the significant input from
   Rohan Mahy on some of the normative aspects of the ABNF, particularly
   around the need for and format of the index and around the enhanced
   SIP security aspects enabled by this draft

Contributors' Addresses

   Cullen and Mark provided substantial input in the form of email
   discussion in the development of the initial version of this
   individual solution document.

   Cullen Jennings
   Cisco Systems
   170 West Tasman Dr
   MS: SJC-21/3

   Tel: +1 408 527 9132
   Email: fluffy@cisco.com


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

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

Author's Address

   Mary Barnes
   Nortel Networks
   2380 Performance Drive
   Richardson, TX USA

   Phone:  1-972-684-5432
   Email:  mary.barnes@nortelnetworks.com



Appendix A  Forking Scenarios

A.1 Sequentially forking (History-Info in Response)

   This scenario highlights an example where the History-Info in the
   response is useful to an application or user that originated the
   request.

   UA 1 sends a call to "Bob" via proxy 1. Proxy 1 sequentially tries
   several places (UA2, UA3 and UA4) unsuccessfully before sending a
   response to UA1.

   This scenario is provided to show that by providing the History-Info
   to UA1, the end user or an application at UA1 could make a decision
   on how best to attempt finding "Bob".  Without this mechanism UA1
   might well attempt UA3 (and thus UA4) and then re-attempt UA4 on a     rd   3   manual attempting at reaching "Bob". With this mechanism, either
   the end user or application could know that "Bob" is busy on his home
   phone and is physically not in the office. If there were an
   alternative address for "Bob" known to this end user or application,
   that hasn't been attempted, then either the application or the end
   user could attempt that. The intent here is to highlight an example
   of the flexibility of this mechanism that enables applications well
   beyond SIP as it is certainly well beyond the scope of this draft to
   prescribe detailed applications.


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   UA1        Proxy1              UA2      UA3      UA4
   |            |                  |        |        |
   |--INVITE -->|                  |        |        |
   |            |                  |        |        |
   |            |--INVITE -------->|        |        |
   |<--100 -----|                  |        |        |
   |            |<-302 ------------|        |        |
   |            |                  |        |        |
   |            |-------INVITE ------------>|        |
   |            |                  |        |        |
   |            |<-------180 ---------------|        |
   |<---180 ----|                  |        |        |
   |  . .       |-------INVITE------------->|        |
   |            |       timeout    |        |        |
   |            |                  |        |        |
   |            |------INVITE ---------------------->|
  |<--100 -----|                  |        |        |
   |            |                  |        |        |
   |            |<-486 ------------------------------|
   |            |                  |        |        |
   |            |-- ACK ---------------------------->|
  |<--486------|                  |        |        |
  |            |                  |        |        |
  |--ACK ----->|                  |        |        |
  |            |                  |        |        |


   [Editor's Note: Need to detail the message flow.]



A.2 Sequential Forking (with Success)

   This scenario highlights an example where the History-Info in the
   request is primarily of use in not retrying routes that have already
   been tried by another proxy. Note, that this is just an example and
   that there may be valid reasons why a Proxy would want to retry the
   routes and thus, this would like be a local proxy or even user
   specific policy.

   UA 1 sends a call to "Bob" to proxy 1. Proxy 1 sequentially tries
   several places (UA2, UA3 and UA4) before retargeting the call to
   Proxy 2.  Proxy 2, without the History-Info, would try several of the
   same places (UA3 and UA4)based upon registered contacts for "Bob",
   before completing at UA5. However, with the History-Info, Proxy 2
   determines that UA3 and UA4 have already received the invite, thus
   the INVITE goes directly to UA5.


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   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



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   policy decision about what mailbox to use, which greeting to play
   etc.

   UA1          Proxy           UA-A         UA-B        UA-VM

   |              |              |             |          |
   |--INVITE F1-->|              |             |          |
   |              |              |             |          |
   |              |--INVITE F2-->|             |          |
   |<--100 F3-----|              |             |          |
   |              |<-302 F4------|             |          |
   |              |              |             |          |
   |              |--------INVITE F5---------->|          |
   |              |              |             |          |
   |              |<--------180 F6-------------|          |
   |<---180 F7----|              |             |          |
  |  . . .       |              |             |          |
   |              |------retransmit INVITE---->|          |
  |  . . .       |              |             |          |
   |              |       (timeout)            |          |
   |              |              |             |          |
   |              |-------INVITE F8---------------------->|
   |              |              |             |          |
   |              |<-200 F9-------------------------------|
   |              |              |             |          |
   |<-200 F10-----|              |             |          |
   |              |              |             |          |
   |--ACK F11-------------------------------------------->|

   Message Details

 INVITE F1   UA1->Proxy

 INVITE sip:UserA@nortelnetworks.com SIP/2.0
 Via: SIP/2.0/UDP here.com:5060
 From: BigGuy <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


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   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
  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


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   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?Reason=SIP;
   cause=302; text="Moved Temporarily">; index=1,
   <sip:UserB@nortelnetworks.com>;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

  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. */


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     /* 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?Reason=SIP;
   cause=302; text="Moved Temporarily">;index=1,
   <sip:UserB@nortelnetworks.com?Reason=SIP;cause=480;text="Temporarily
   Unavailable" >;index=2,
   <sip:VM@nortelnetworks.com>;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


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   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 Gold group (ACDGRP1)
   were busy, by retargeting the request to the Silver Group.  Upon


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   receipt of the call at the agent assigned to handle the incoming
   call, based upon the History-Info header in the message, the
   application at the agent can provide an indication that this is a
   Gold call, from how many groups it might have overflowed before
   reaching the agent, etc. and thus can be handled appropriately by the
   agent.

   For scenarios whereby calls might overflow from the Silver to the
   Gold, clearly the alternate group identification, internal routing or
   actual agent that handles the call SHOULD not be sent to UA1, thus
   for this scenario, one would expect that the Proxy would not support
   the sending of the History-Info in the response, even if requested by
   the calling UA.

   As with the other examples, this is not prescriptive of how one would
   do this type of service but an example of a subset of processing that
   might be associated with such a service.  In addition, this example
   is not addressing any aspects of Agent availability, which might also
   be done via a SIP interface.



   UA1          Proxy        ACDGRP1 Svr   ACDGRP2 Svr UA2-ACDGRP2

   |              |              |             |          |
   |--INVITE F1-->|              |             |          |
    Supported:Histinfo
   |              |              |             |          |
   |              |--INVITE F2-->|             |          |
                    Supported:Histinfo
                    History-Info: <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--|
   |              |              |             |          |


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   |              |<-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.

   This document and translations of it may be copied and furnished to
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