[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 RFC 4244

 INTERNET-DRAFT                                              M. Barnes
 Document: draft-ietf-sip-history-info-03.txt                   Editor
 Category: Standards Track                             Nortel Networks

 Expires: January 8, 2005                               July 8,  2004

    An Extension to the Session Initiation Protocol for Request History
                                Information

 Status of this Memo

     By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 8th, 2005.

 Copyright Notice

   Copyright (C) The Internet Society (2004).  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. A new priv-value, history, is



 Barnes                Expires January 8, 2005               [Page 1]

                   SIP Request History Information       July 8, 2004


   added to the Privacy header to allow for privacy handling of the
   History-Info header.

 Table of Contents

   1.Background:  Why define a Generic "Request History" capability?.3
   2. "Request History" Requirements.................................4
      2.1 Security Requirements......................................6
      2.2 Privacy Requirements.......................................7
   3. Request History Information Description........................7
      3.1 Optionality of History-Info................................8
      3.2 Securing History-Info......................................8
      3.3 Ensuring the Privacy of History-Info.......................9
   4 Request History Information Protocol Details...................10
      4.1 Protocol Structure of History-Info........................10
      4.2 Protocol Examples.........................................12
      4.3 Protocol usage............................................12
      4.4 Security for History-Info.................................17
      4.5 Example Applications using History-Info...................18
   5. Application Considerations....................................22
   6. Security Considerations.......................................23
   7. IANA Considerations...........................................23
   Normative References.............................................26
   Informational References.........................................27
   Appendix A  Forking Scenarios....................................28
      A.1 Sequentially forking (History-Info in Response)...........28
      A.2 Sequential Forking (with Success).........................30
   Appendix B  Voicemail............................................31
   Appendix C  Automatic Call Distribution Example..................36
   Appendix D Session via Redirect and Proxy Servers................37
   Full Copyright Statement.........................................40

 Overview

   Many services that SIP is anticipated to support require the ability
   to determine why and how the call arrived at a specific application.
   Examples of such services include (but are not limited to) sessions
   initiated to call centers via "click to talk" SIP URLs on a web page,
   "call history/logging" style services within intelligent "call
   management" software for SIP UAs and calls to voicemail servers and
   call centers.  While SIP implicitly provides the redirect/retarget
   capabilities that enable calls to be routed to chosen applications,
   there is currently no standard mechanism within SIP for communicating
   the history of such a request. This "request history" information
   allows the receiving application to determine hints about how and why
   the call arrived at the application/user. 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



 Barnes                Expires January 8, 2005               [Page 2]

                   SIP Request History Information       July 8, 2004


   services for networks and end users.  The History-Info header
   provides a building block for development of new services.

   Section 1 provides additional background motivation for the Request
   History capability.  Section 2 identifies the requirements for a
   solution, with Section 3 providing an overall description of the
   solution.

   Section 4 provides the details of the additions to the SIP protocol.
   Example uses of the new header are included in Section 4.5, 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 [SIPSVCEX] 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, as it is not the
   intent, nor is it within the scope, of this draft to prescribe a
   complete solution for any of these applications.

   Section 5 summarizes the application considerations identified in the
   previous sections. Section 6 summarizes the security solution.

 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 [RFC2119].

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


 1.Background:  Why define a Generic "Request History" capability?

   SIP implicitly provides redirect/retarget capabilities that enable
   calls to be routed to specific applications as defined in [RFC3261].
   The term retarget will be used henceforth in this draft to refer to
   the process of a Proxy Server/UAC changing a URI in a request and
   thus changing the target of the request.  This term is chosen to
   avoid associating this request history only with the specific SIP
   Redirect Server capability that provides for a response to be sent
   back to a UAC requesting that the UAC should retarget the original
   request to an alternate URI.  The rules for determining request
   targets as described in section 16.5 of [RFC3261] are consistent with
   the use of the retarget term in this draft.



 Barnes                Expires January 8, 2005               [Page 3]

                   SIP Request History Information       July 8, 2004


   The motivation for the request history is that in the process of
   retargeting old routing information can be forever lost. This lost
   information may be important history that allows elements to which
   the call is retargeted to process the call in a locally defined,
   application specific manner. The proposal in this draft is to provide
   a mechanism for transporting the request history.  It is not
   proposing any application specific behavior for a Proxy or UA upon
   receipt of the information. Indeed, such behavior should be a local
   decision for the recipient application.

   Current network applications provide the ability for elements
   involved with the call to exchange additional information relating to
   how and why the call was routed to a particular destination.  The
   following are examples of such applications:

  1. Web "referral" applications, whereby an application residing
     within a web server determines that a visitor to a website has
     arrived at the site via an "associate" site which will receive
     some "referral" commission for generating this traffic,

  2. Email forwarding whereby the forwarded-to user obtains a "history"
     of who sent the email to whom and at what time

  3. Traditional telephony services such as Voicemail, call-center
     "automatic call distribution", and "follow-me" style services.


   Several of the aforementioned applications currently define
   application specific mechanisms through which it is possible to
   obtain the necessary history information.

   In addition, request history information could be used to enhance
   basic SIP functionality by providing the following:

  4. Some diagnostic information for debugging SIP requests.

  5. A stronger security solution for SIP. A side effect is that each
     proxy which captures the "request history" information in a secure
     manner provides an additional means (without requiring signed keys)
     for the original requestor to be assured that the request was
     properly retargeted.


 2. "Request History" Requirements

   The following list constitutes a set of requirements for a "Request
   History" capability.




 Barnes                Expires January 8, 2005               [Page 4]

                   SIP Request History Information       July 8, 2004


   1) CAPABILITY-req:  The "Request History" capability provides a
   capability to inform proxies and UAs involved in processing a request
   about the history/progress of that request. While this is inherently
   provided when the retarget is in response to a SIP redirect, it is
   deemed useful for non-redirect retargeting scenarios, as well.

   2) OPTIONALITY-req: The "Request History" information is optional.

   2.1) In many cases, it is anticipated that whether the history is
   added to the Request would be a local policy decision enforced by the
   specific application, thus no specific protocol element is needed.

   2.2) Due to the capability being "optional" from the SIP protocol
   perspective, the impact to an application of not having the "Request
   History" must be described. Applicability guidelines to be addressed
   by applications using this capability must be provided as part of the
   solution to these requirements.


   3) GENERATION-req: "Request History" information is generated when
   the request is retargeted.

   3.1) 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'.

   3.2) 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.


   4) ISSUER-req: "Request History" information can be generated by a UA
   or proxy. It can be passed in both requests and responses.


   5) CONTENT-req:  The "Request History" information for each
   occurrence of retargeting, shall include the following:

     5.1) The new URI or address to which the request is in the process
     of being retargeted,

     5.2) The URI or address from which the request was retargeted,

     5.3) The reason for the Request-URI or address modification,

     5.4) Chronological ordering of the Request History information.




 Barnes                Expires January 8, 2005               [Page 5]

                   SIP Request History Information       July 8, 2004


   6) REQUEST-VALIDITY-req:  Request-History is applicable to requests
   not sent within an established dialog. (i.e. INVITE, REGISTER,
   MESSAGE, and OPTIONS).

   7) BACKWARDS-req: Request-History information may be passed from the
   generating entity backwards towards the UAC. This is needed to enable
   services that inform the calling party about the dialog establishment
   attempts.

   8) FORWARDS-req:  Request-History information may also be included by
   the generating entity in the request, if it is forwarded onwards.

 2.1 Security Requirements

   The Request History information is being inserted by a network
   element retargeting a Request, resulting in a slightly different
   problem than the basic SIP header problem, thus requiring specific
   consideration.  It is recognized that these security requirements can
   be generalized to a basic requirement of being able to secure
   information that is inserted by proxies.

   The potential security problems include the following:
   1) A rogue application could insert a bogus Request History entry
   either by adding an additional entry as a result of retargeting or
   entering invalid information.

   2) A rogue application could re-arrange the Request History
   information to change the nature of the end application or to mislead
   the receiver of the information.

   Thus, a security solution for "Request History" must meet the
   following requirements:

   1) SEC-req-1: The entity receiving the Request History must be able
   to determine whether any of the previously added Request History
   content has been altered.

   2) SEC-req-2: The ordering of the Request History information must be
   preserved at each instance of retargeting.

   3) SEC-req-3: The entity receiving the information conveyed by the
   Request History must be able to authenticate the source of the
   information.

   4) SEC-req-4: To ensure the confidentiality of the Request History
   information, only entities which process the request should have
   visibility to the information.




 Barnes                Expires January 8, 2005               [Page 6]

                   SIP Request History Information       July 8, 2004


   It should be noted that these security requirements apply to any
   entity making use of the Request History information, either by
   retargeting and capturing the information, or as an application
   making use of the information received in either a Request or
   Response.

 2.2 Privacy Requirements

   Since the Request URI that is captured could inadvertently reveal
   information about the originator, there are general privacy
   requirements that MUST be met:

   1) PRIV-req-1: The entity retargeting the Request must ensure that it
   maintains the network-provided privacy (as described in [RFC3323])
   associated with the Request as it is retargeted.

   2) PRIV-req-2: The entity receiving the Request History must maintain
   the privacy associated with the information.

   In addition, local policy at a proxy may identify privacy
   requirements associated with the Request URI being captured in the
   Request History information.

   3) PRIV-req-3: Request History information subject to privacy
   requirements shall not be included in outgoing messages unless it is
   protected as described in [RFC3323].



 3. 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 [RFC3261].

   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]




 Barnes                Expires January 8, 2005               [Page 7]

                   SIP Request History Information       July 8, 2004


   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' is introduced 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
   [RFC3261].  As described in section 16.5 of [RFC3261], it is possible
   for the target of a request to be changed by the same proxy multiple
   times (referred to as 'internal retargeting' in section 2), as the
   proxy MAY add targets to the target set after beginning Request
   Forwarding. Section 16.6 of [RFC3261] describes Request Forwarding.
   It is during this process of 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].

 3.1 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.

 3.2 Securing History-Info

   This draft defines a new header for SIP. The draft RECOMMENDs the use
   of TLS as a mandatory mechanism to ensure the overall confidentiality
   of the History-Info headers [SEC-req-4]. This results in History-Info
   having at least the same level of security as other headers in SIP
   which are inserted by intermediaries. With the level of security
   provided by TLS [SEC-req-3], the information in the History-Info
   header can thus be evaluated to determine if information has been
   removed by evaluating the indices for gaps [SEC-req-1, SEC-req-2].


 Barnes                Expires January 8, 2005               [Page 8]

                   SIP Request History Information       July 8, 2004


   It would be up to the application to define whether it can make use
   of the information in the case of missing entries.

   A more robust security solution would need to consider the aspects of
   the problem that are different than the hop by hop security problem
   solved by TLS, as each hop is not required to add the History-Info
   header.  History-Info also introduces a slightly different problem
   than the basic SIP header or Identity [SIPATHID] problems, which is
   focused on securing the information in the initial request end to
   end. The History-Info header is being inserted by an entity as it
   targets and forwards a Request, thus the requirements for the
   security solution are similar to the Via and Record-Route headers.
   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 for a more robust security solution for
   SIP takes the form of a middle to middle and middle to end security
   solution, which is addressed in a separate document [SIPIISEC]. The
   use of the middle-to-end security solution discussed in [SIPIISEC]
   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 would add an
   additional level of security end to end, assuring the initiator of a
   Request that it has indeed reached the intended recipient.

 3.3 Ensuring the Privacy of History-Info

   Since the History-Info header can inadvertently reveal information
   about the requestor as described in [RFC3323], 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 at all, whether to capture a specific Request-URI in the
   header, or whether it be included only in the Request as it is
   retargeted within a specific domain. [PRIV-req-3]  This is
   accomplished by adding a new priv-value to the Privacy header [RFC
   3323] indicating whether any or a specific History-Info header(s)
   SHOULD be forwarded.




 Barnes                Expires January 8, 2005               [Page 9]

                   SIP Request History Information       July 8, 2004


   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.

 4 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.

 4.1 Protocol Structure of History-Info

   History-Info is a header field as defined by [RFC3261].  It is an
   optional header field and MAY appear in any request or response not
   associated with a dialog or which starts a dialog. For example,
   History-Info MAY appear in INVITE, REGISTER, MESSAGE, REFER and
   OPTIONS and any valid responses, plus NOTIFY requests which initiate
   a dialog.

   The History-Info header carries the following information, with the
   mandatory parameters REQUIRED when the header is included a request
   or response:

     o Targeted-to-URI (hi-targeted-to-uri): A mandatory parameter for
        capturing the Request URI for the specific Request as it is
        forwarded.

     o Index (hi-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 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]  In addition,
        applications MAY extract a variety of metrics (total number of
        retargets, total number of retargets from a specific branch,
        etc.) based upon the index values.

     o Reason: An optional parameter for History-info, reflected in the
        History-Info header by including the Reason Header [RFC3326]
        escaped in the Request URI being retargeted.  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


 Barnes                Expires January 8, 2005              [Page 10]

                   SIP Request History Information       July 8, 2004


        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.

     o Privacy: An optional parameter for History-info, reflected in
        the History-Info header by including the Privacy Header
        [RFC3323] with a priv-value of "history" escaped in the Request
        URI or by adding the Privacy header with a priv-value of
        "history" to the Request.  The use of the Privacy Header with a
        priv-value of "history" indicates whether a specific or all
        History-Info headers SHOULD NOT be forwarded.

     o  Extension (hi-extension): An optional parameter to allow for
       future optional extensions.  As per the [RFC3261], any
       implementation not understanding an extension SHOULD ignore it.

   The following summarizes the syntax of the History-Info header, based
   upon the standard SIP syntax [RFC3261]:

          History-Info = "History-Info" 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


    This document adds the following entry to Table 2 of [RFC3261].
   Additions to this table are also provided for extension methods
   at the time of publication of this document.  This is provided as a
   courtesy to the reader and is not normative in any way.

      Header field    where   proxy   ACK  BYE  CAN  INV  OPT  REG  MSG
      ------------    -----   -----   ---  ---  ---  ---  ---  ---  ---
      History-Info            amdr     -    -    -    o    o    o    o


                                      SUB  NOT  REF  INF  UPD  PRA  PUB
                                      ---  ---  ---  ---  ---  ---  ---
      History-Info            amdr     -    o    o    -    -    -    -



 Barnes                Expires January 8, 2005              [Page 11]

                   SIP Request History Information       July 8, 2004




 4.2 Protocol Examples

   The following provides some examples of the History-Info header. Note
   that the backslash, CRLF, and spacing between the fields in the
   examples below are for readability purposes only.


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

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

 4.3 Protocol usage

   This section describes the processing specific to UAs and Proxies for
   the History-Info header, the Histinfo option tag and the priv-value
   of "history". 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.

   4.3.1 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
   the RECOMMENDED value of 1 in the History-Info header.

   In the case where the request is routed to a redirect server and the
   UAC receives a 3xx response with a Contact header, the UAC MAY
   maintain the previous History-Info entry(-ies) in the request. A new
   History-Info entry MAY then be added for the URI from the Contact
   header (which will become the new Request-URI). In this case, the


 Barnes                Expires January 8, 2005              [Page 12]

                   SIP Request History Information       July 8, 2004


   index is created by reading and incrementing the value of the index
   from the previous history entry, thus following the same rules as
   those prescribed for a proxy in retargeting, described in section
   4.3.3.1.3. An example of this scenario can be found in Appendix D.

   A UAC that does not want History-Info headers added due to privacy
   considerations SHOULD include a Privacy header with a priv-value(s)
   of "session", "header" or "history" in the request.

   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.  For example, the entries MAY be evaluated to
   determine gaps in indices, which could indicate that an entry has
   been maliciously removed or removed for privacy reasons.  Either way,
   an application MAY want to be notified of potentially missing
   information.


   4.3.2 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.  For example,
   the entries MAY be evaluated to determine gaps in indices, which
   could indicate that an entry has been maliciously removed or removed
   for privacy reasons.  Either way, an application MAY want to be
   notified of potentially missing 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.


   4.3.3 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 [RFC3261].  Whether a proxy adds the
   the History-Info header as it forwards a Request depends upon the
   following considerations:
       1. Whether the Request contains the Histinfo option tag in the
          Supported header.
       2. Whether the proxy supports the History-Info header.
       3. Whether the Request contains a Privacy header with a priv-
          value of "session", "header" or "history".
       4. Whether any History-Info header added for a proxy/domain
          should go outside that domain.  An example being the use of


 Barnes                Expires January 8, 2005              [Page 13]

                   SIP Request History Information       July 8, 2004


          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.  A proxy MAY insert the
          Privacy header with a priv-value of "history" to indicate
          this. An example of such an application is provided in
          Appendix C.
       5. Whether the History-Info header is added for a specific
          Request URI due to local privacy policy considerations.  A
          proxy MAY add the Privacy header with a priv-value of
          "history" associated with the specific hi-targeted-to-uri.

   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, accomplishing this by adding
   a Privacy header with a priv-value of "history" to allow the
   information to be collected for internal retargeting only.

   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.

   4.3.3.1 Adding the History-Info header to Requests

   Upon evaluation of the considerations under which the History-Info
   header is to be included in requests (e.g. no Privacy header
   overriding inclusion, local policy supports, etc.), detailed in
   section 4.3.3, a 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
   (adding Via header) and 9 (adding Content-Length) 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


 Barnes                Expires January 8, 2005              [Page 14]

                   SIP Request History Information       July 8, 2004


   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. The following subsections define the details of creating
   the information associated with and in the History-Info header.

   4.3.3.1.1 Privacy in the History-Info header

   If the proxy's local policies, per consideration 4 in section 4.3.3,
   indicate that this History-Info entry and any entries added due to
   subsequent retargeting should not be forwarded beyond the domain for
   which this intermediary is responsible, then a Privacy header with a
   priv-value of "history" SHOULD be added to the request, if there is
   not already one, provided the request is being forwarded to a
   specific URI associated with the domain(s) for which this entity is
   responsible.

   If a request is being forwarded to a Request URI associated with a
   domain for which the proxy is not responsible, the proxy needs to
   determine if there are any entries to be removed prior to forwarding.
   Any headers associated with the domain(s) for which this proxy is
   responsible SHOULD be removed prior to forwarding.

   If through local policy, there is knowledge of privacy associated
   with a specific URI being captured as the hi-targeted-to-uri, a
   Privacy header with a priv-value of "history" SHOULD be associated
   with this specific URI as the request is forwarded, if it is being
   forwarded to a Request URI associated with a domain for which the
   processing entity is responsible.

   If a request is being forwarded to a Request URI, for which the
   processing entity is not responsible, the proxy needs to determine if
   there are any entries, that need to be removed prior to forwarding.
   The proxy needs to determine if any of the specific URIs that have
   been captured in the History-Info entries, associated with the
   domain(s) for which it is responsible, have a priv-value of
   "history".  Each of these header entries SHOULD be removed from the
   Request prior to forwarding.

   4.3.3.1.2 Reason in the History-Info header

   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.
   This should occur prior to the forwarding of the request, as it


 Barnes                Expires January 8, 2005              [Page 15]

                   SIP Request History Information       July 8, 2004


   associated with the previous hi-targeted-to-uri, since it reflects
   the reason why the Request to that specific URI was not successful.

   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.

   4.3.3.1.3 Indexing in the History-Info header

   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 4.1, 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. Within each level, the number reflects the number of peer
   entities to which the request has been routed.  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.  It is recommended that an increment of 1 is used for
   advancing to a new branch.  For retargets within a proxy, the proxy
   MUST maintain the current level of nesting by incrementing by 1 the
   lowest/last digit of the index for each instance of retargeting, thus
   reflecting the number of retargets (branches) within the proxy.

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

     1. Basic Forwarding:  In the case of a Request that is being
     forwarded, the index is determined by adding another level of
     indexing since the depth/length of the branch is increasing. To
     accomplish this, the proxy reads the value from the History-Info
     header in the received request, if available, and adds another
     level of indexing by appending the DOT delimiter followed by an
     initial index for the new level RECOMMENDED to be  1.  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 and
     forward the request.

     2. Retargeting within a Proxy - 1st instance:  For the first
     instance of retargeting within a Proxy, the calculation of the
     index follows that prescribed for basic forwarding.

     3. Retargeting within a Proxy - subsequent instance: For each
     subsequent retargeting of a request by the same proxy, another
     branch is added.  With the index for each new branch calculated by
     incrementing the last/lowest digit at the current level, thus the
     index in the next request forwarded by this same proxy, following
     the example above, would be 1.1.2.




 Barnes                Expires January 8, 2005              [Page 16]

                   SIP Request History Information       July 8, 2004


     4. Retargeting based upon a Response:  In the case of retargeting
     due to a specific response (e.g. 302), the index would be
     calculated per rule 3.  That is, the lowest/last digit of the index
     is incremented (i.e. a new branch is created), with the increment
     RECOMMENDED to be 1.  For example, if the index in the History-Info
     header of the received request was 1.2, then the index in the
     History-Info header field for the new hi-targeted-to-URI would be
     1.3.

     5. Retargeting the request in parallel: If the request forwarding
     is done in parallel, the index MUST be captured for each forked
     request per the rules above, with each new Request having a unique
     index. The only difference in the messaging for this scenario and
     the messaging produced per basic proxy retargeting in rules 2 and 3
     is these forwarded requests do not have History-Info entries
     associated with their peers.  The proxy builds the subsequent
     response (or request) using the amalgamated information associated
     with each of those requests and including the header entries in the
     order indicated by the indexing.  Section 4.5 provides an example
     of a parallel request scenario, highlighting this indexing
     mechanism.

   4.3.3.2 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.

   4.3.4 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.

   4.4 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
   [RFC3261]) for hop by hop security.   In addition, the use of the
   middle-to-end security solution discussed in [SIPIISEC] allows the



 Barnes                Expires January 8, 2005              [Page 17]

                   SIP Request History Information       July 8, 2004


   integrity of the History-Info to be ascertained as it traverses the
   intermediaries.

 4.5 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 likely 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 some of the same places (e.g. UA3) based upon registered
   contacts for "Bob", before completing at UA5. However, with the
   History-Info, Proxy 1 determines that UA3 has already received the
   invite, thus the INVITE goes directly to UA5.

   Section 4.5.1 provides this same scenario using one of the privacy
   mechanism, with Proxy2 adding the Privacy header indicating that the
   History-Info header is not to be propagated outside P2's domain. This
   scenario highlights the potential functionality lost with the use of
   "history" privacy in the Privacy header for the entire request and
   the need for careful consideration on the use of privacy for History-
   Info.

   Section 4.5.2 also provides the same scenario using one of the
   privacy mechanisms, however, due to local policy at Proxy2, only one
   of the Request-URIs (UA4) in the History-Info contains a priv-value
   of "history", thus allowing some optimized functionality in the
   routing of the request, but still maintaining privacy for specific
   URIs.

   Additional detailed scenarios are available in the appendix.


   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

   |            |         |        |        |        |        |
   |--INVITE -->|         |        |        |        |        |
   |            |-INVITE->|        |        |        |        |
                 Supported: Histinfo
                 History-Info: <sip:Bob@P1.example.com>;index=1,
                               <sip:Bob@P2.example.com>; index=2
   |            |         |        |        |        |        |
   |            |         |-INVITE>|        |        |        |


 Barnes                Expires January 8, 2005              [Page 18]

                   SIP Request History Information       July 8, 2004


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

   /* All Responses from the INVITEs indicate non-success/non-
   availability*/
   |            |         |        |        |        |        |
   |            |<-480 ---|        |        |        |        |
                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2,
                   <sip:User2@UA2.example.com?Reason=SIP;\
                    cause=480;text="RequestTimeout">;index=2.1,
                   <sip:User3@UA3.example.com?Reason=SIP; \
                    cause=487;text="Request Terminated">; index=2.2,
                   <sip:User4@UA4.example.com?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 a route already attempted
  (e.g. UA3, thus the INVITE is only forwarded to UA5, where
   the session is successfully established  */
   |            |         |        |        |        |        |
   |            |----------------INVITE --------------------->|
                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2,
                   <sip:User2@UA2.example.com?Reason=SIP;cause=480;\
                    text="RequestTimeout">;index=2.1,
                   <sip:User3@UA3.example.com?Reason=SIP;cause=487;\
                    text="Request Terminated">; index=2.2,
                   <sip:User4@UA4.example.com?Reason=SIP;cause=603;\
                    text="Decline">; index=2.3
                   <sip:User5@UA5.example.com>;index=1.1
   |            |         |        |        |        |        |
   |            |<-----200 OK---------------------------------|
   |<--200 OK---|         |        |        |        |        |
   |            |         |        |        |        |        |
   |--ACK --------------------------------------------------->|




 Barnes                Expires January 8, 2005              [Page 19]

                   SIP Request History Information       July 8, 2004


   4.5.1 Example with Privacy header for entire request at Proxy2

   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

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

   /* All Responses from the INVITEs indicate non-success/non-
   availability and only the initial, received History-Info entries
   are NOT returned to P1 due to the Privacy header value.*/
   |            |         |        |        |        |        |
   |            |<-480 ---|        |        |        |        |
                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2
   |            |         |        |        |        |        |
   /* Upon receipt of the response, P1 determines another route for the
   INVITE, including UA3 which was attempted by P2, but due to
   Privacy P1 is not aware of this, so UA3 is re-attempted prior to
   forwarding the INVITE to UA5, where the session is successfully
   established  */
   |            |         |        |        |        |        |
   |            |--------------INVITE ----->|        |        |
                  History-Info: <sip:Bob@P1.example.com>;index=1,
                                <sip:Bob@P2.example.com>; index=2,
                                <sip:User3@UA3.example.com>; index=1.1
   |            |         |        |        |        |        |
   |            |<-- 486 -------------------|        |        |


 Barnes                Expires January 8, 2005              [Page 20]

                   SIP Request History Information       July 8, 2004


                  History-Info: <sip:Bob@P1.example.com>;index=1,
                                <sip:Bob@P2.example.com>; index=2,
                                <sip:User3@UA3.example.com>; index=1.1
   |            |         |        |        |        |        |
   |            |----------------INVITE --------------------->|
                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2,
                   <sip:User3@UA3.example.com?Reason=SIP;cause=486;\
                    text=Busy Here">;index=1.1,
                   <sip:User5@UA5.example.com>;index=1.2
   |            |         |        |        |        |        |
   |            |<-----200 OK---------------------------------|
   |<--200 OK---|         |        |        |        |        |
   |            |         |        |        |        |        |
   |--ACK --------------------------------------------------->|


   4.5.2 Example with Privacy header for specific URI (UA4) at Proxy2

   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

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

   /* All Responses from the INVITEs indicate non-success/non-
   availability.  The History-Info associated with UA4 is not returned
   in the response due to the privacy header associated with that URI */
   |            |         |        |        |        |        |
   |            |<-480 ---|        |        |        |        |


 Barnes                Expires January 8, 2005              [Page 21]

                   SIP Request History Information       July 8, 2004


                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2,
                   <sip:User2@UA2.example.com?Reason=SIP;\
                    cause=480;text="RequestTimeout">;index=2.1,
                   <sip:User3@UA3.example.com?Reason=SIP; \
                    cause=487;text="Request Terminated">; index=2.2,
   |            |         |        |        |        |        |
  /* Upon receipt of the response, P1 determines another route for the
   INVITE, but finds that it matches a route already attempted
  (e.g. UA3), thus the INVITE is only forwarded to UA5, where
   the session is successfully established  */
   |            |         |        |        |        |        |
   |            |----------------INVITE --------------------->|
                History-Info: <sip:Bob@P1.example.com>;index=1,
                   <sip:Bob@P2.example.com>; index=2,
                   <sip:User2@UA2.example.com?Reason=SIP;cause=480;\
                    text="RequestTimeout">;index=2.1,
                   <sip:User3@UA3.example.com?Reason=SIP;cause=487;\
                    text="Request Terminated">; index=2.2,
                   <sip:User5@UA5.example.com>;index=1.1
   |            |         |        |        |        |        |
   |            |<-----200 OK---------------------------------|
   |<--200 OK---|         |        |        |        |        |
   |            |         |        |        |        |        |
   |--ACK --------------------------------------------------->|


 5. Application Considerations

   As seen by the example scenarios in the appendix, History-Info
   provides a very flexible building block that can be used by
   intermediaries and UAs for a variety of services.  As such, any
   services making use of History-Info must be designed with the
   following considerations:
   1) History-Info is optional, thus a service should define default
      behavior for requests and responses not containing History-Info
      headers.
   2) History-Info may be impacted by privacy considerations.
      Applications requiring History-Info need to be aware that if
      Header, Session or History level privacy is requested by a UA (or
      imposed by an intermediary) that History-Info may not be
      available in a request or response.  This would be addressed by
      an application in the same manner as the previous consideration
      by ensuring there is reasonable default behavior should the
      information not be available.
   3) History-Info may be impacted by local policy. 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


 Barnes                Expires January 8, 2005              [Page 22]

                   SIP Request History Information       July 8, 2004


      specific application and any potential limitations imposed by
      local policy decisions). Note, that this is related to the
      optionality and privacy considerations identified in 1 and 2
      above, but goes beyond that. For example, due to the optionality
      and privacy considerations, an entity may receive only partial
      History-Info entries; will this suffice? Note, that this would be
      a limitation for debugging purposes, but might be perfectly
      satisfactory for some models whereby only the information from a
      specific intermediary is required.
   4) The security associated with the Request History Information is
      optional. Whether there is security applied to the entries
      depends upon local policy. The impact of lack of having the
      information compromised depends upon the nature of the specific
      application (e.g. is the information something that appears on a
      display or is it processed by automata which could have negative
      impacts on the subsequent processing of a request?).   It is
      suggested that the impact of an intermediary not supporting the
      security recommendations should be evaluated by the application
      to ensure that the impacts have been sufficiently addressed by
      the application.

 6. Security Considerations

   This draft provides a proposal in sections 3.2 and 4.4 for addressing
   the Security requirements identified in section 2.1 by mandating the
   use of TLS between entities.  With TLS, History-Info headers are no
   less, nor no more, secure than other SIP headers, which generally
   have even more impact on the subsequent processing of SIP sessions
   than the History-Info header.  A more robust security solution, which
   would secure headers added by proxies, SHOULD be used for History-
   Info implementations once there is a solution to the requirements
   identified in [SIPIISEC].

 7. IANA Considerations

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

   7.1 Registration of new SIP History-Info header

   This document defines a new SIP header field name: History-Info 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


 Barnes                Expires January 8, 2005              [Page 23]

                   SIP Request History Information       July 8, 2004


   -----------             ------------               ---------
   History-Info               none                    [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.


   7.2 Registration of "history" for SIP Privacy header

   This document defines a new priv-value for the SIP Privacy header:
   history

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


   The following should be added to the registration for the SIP
   Privacy header:

   Name      Description               Registrant   Reference
   ----      -----------               ----------   ---------
   history   Privacy requested for     Mary Barnes  [RFCXXXX]
             History-Info header(s)    mary.barnes@nortelnetworks.com


 Changes since last version

   Changes from the û02 to the û03 version:
      o Editorial changes: Updating to the new template to reflect new
        IPR guidelines, ensuring that the normative text is complete
        and accurate in section 4.1, removing "Editor's Notes", etc.
      o Section 4.5: Fixed error in cause (408 -> 480).
      o Examples: changed the domain to "example.com", IP addresses to
        the 192.0.2.0/24 range, changed  occurrences of "Reason:" to
        "Reason=", added use of Privacy header to examples.
      o Added text to reflect WG consensus on Issue-1: Privacy
        indication for History-Info entries.  Proposed an extension to
        the priv-values defined in RFC 3323 in abstract and section
        3.3, impacting the protocol structure in section 4.1 and


 Barnes                Expires January 8, 2005              [Page 24]

                   SIP Request History Information       July 8, 2004


        processing in 4.3.3 (and 4.3.3.1 and 4.3.3.2).  In addition,
        the new priv-value needs to be registered with IANA, per
        section 7.
      o Removed Open Issues section. For Issue-2, there was not WG
        consensus to define an algorithm for bounding the number of
        History-Info entries, but rather that is left as an
        implementation decision.
      o Updated Security discussions to reflect WG consensus that TLS
        is mandatory and sufficient for general History-Info
        implementation. The e2m and m2m security solutions can be
        applied to History-Info when they become available to provide a
        more robust SIP solution.
      o Section 4.1: Added additional text to ensure that all the
        information in the History-Info header is appropriately and
        normatively described (in text).
      o Added text in section 4.3.1 and an example to the appendices to
        address the UAC having added multiple History-Info headers for
        the case where the 3xx response goes back to the UAC and it's
        the UAC that retargets the INVITE request.
      o Clarified the addition of the Reason header in section
        4.3.3.1.2.
      o Further delineated the basic rules in section 4.3.3.1.3 for
        calculating the index for various scenarios, as this was still
        causing some confusion.

   Changes from the û01 to the û02 version:

      o Merged the SIPPING WG requirements draft into this document.
        Note that this increments the section references in the
        remainder of the document by 2 (and by 3 for Security and IANA
        considerations due to new section added). Also, removed
        redirect server from ISSUER-req since the solution identified
        this as not being required (or desirable).
      o Added an explicit privacy requirement (PRIV-req-3) for the
        proxy's role in recognizing and maintaining privacy associated
        with a Request-URI being captured in History-Info due to local
        policy. (Note, that the text was already there, it just wasn't
        highlighted as an explicit requirement).
      o Clarified the use of CRLF and spacing in the example headers in
        section 4.2.
      o Removed the compact form for the header since unknown headers
        with multiple entries would not be recognized (i.e. this may
        cause parsing problems).
      o Added a summary of Application Considerations to address
        concerns about the optional usage of History-Info.
      o Converted the references from numbers to labels to avoid the
        continual problem of renumbering.
      o Minor editorial changes (per NITS highlighted by Rohan and Eric
        and some minor rewording for clarity).


 Barnes                Expires January 8, 2005              [Page 25]

                   SIP Request History Information       July 8, 2004





   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.

 Normative References

   [RFC3261] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
   3261, June, 2002.

   [RFC3326] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header
   Field for the Session Initiation Protocol", RFC 3326, December, 2002.



 Barnes                Expires January 8, 2005              [Page 26]

                   SIP Request History Information       July 8, 2004


   [RFC3323] J. Peterson, "A Privacy Mechanism for the Session
   Initiation Protocol (SIP)", RFC 3323, November, 2002.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, March 1997.

   [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
   Specifications: ABNF", RFC 2234, November 1997.

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


 Informational References

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

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

   [RFC3665] A. Johnson et al, "SIP Basic Call Flow Examples", RFC 3665,
   BCP 75, December, 2003.



 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, Jayshree Bharatia, Jonathan Rosenberg, Eric Burger and
   Martin Dolly.

   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, Mark and Jon contributed to the development of the initial
   requirements.

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


 Barnes                Expires January 8, 2005              [Page 27]

                   SIP Request History Information       July 8, 2004



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

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

   Jon Peterson
   NeuStar, Inc.
   1800 Sutter Street, Suite 570
   Concord, CA  94520
   USA

   Phone: +1 925-363-8720
   EMail: Jon.Peterson@NeuStar.biz

   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.




 Barnes                Expires January 8, 2005              [Page 28]

                   SIP Request History Information       July 8, 2004



   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
   third manual attempt at reaching "Bob". With this mechanism, either
   the end user or application could know that "Bob" is busy on his home
   phone and is physically not in the office. If there were an
   alternative address for "Bob" known to this end user or application,
   that hasn't been attempted, then either the application or the end
   user could attempt that. The intent here is to highlight an example
   of the flexibility of this mechanism that enables applications well
   beyond SIP as it is certainly well beyond the scope of this draft to
   prescribe detailed applications.


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


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



 Barnes                Expires January 8, 2005              [Page 29]

                   SIP Request History Information       July 8, 2004





 A.2 Sequential Forking (with Success)

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

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



   UA1        Proxy1  Proxy2     UA2      UA3      UA4      UA5

   |            |         |        |        |        |        |
   |--INVITE -->|         |        |        |        |        |
   |            |         |        |        |        |        |
   |            |--INVITE -------->|        |        |        |
   |<--100 -----|         |        |        |        |        |
   |            |<-302 ------------|        |        |        |
   |            |         |        |        |        |        |
   |            |-------INVITE ------------>|        |        |
   |            |         |        |        |        |        |
   |            |<-------180 ---------------|        |        |
   |<---180 ----|         |        |        |        |        |
   |  . .       |-------INVITE------------->|        |        |
   |            |       timeout    |        |        |        |
   |            |         |        |        |        |        |
   |            |------INVITE ---------------------->|        |
   |<--100 -----|         |        |        |        |        |
   |            |<-302 ------------------------------|        |
   |            |         |        |        |        |        |
   |            |-INVITE->|        |        |        |        |
   |            |         |        |        |        |        |
   |            |         |        |        |        |        |
   |            |         |------INVITE --------------------->|
   |            |         |        |        |        |        |
   |            |         |<-----200 OK---------------------->|
   |<--200 OK-------------|        |        |        |        |


 Barnes                Expires January 8, 2005              [Page 30]

                   SIP Request History Information       July 8, 2004


   |            |         |        |        |        |        |
   |--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----|              |             |          |
   |  . . .       |              |             |          |
   |              |------retransmit INVITE---->|          |
   |  . . .       |              |             |          |
   |              |       (timeout)            |          |
   |              |              |             |          |
   |              |-------INVITE F8---------------------->|
   |              |              |             |          |
   |              |<-200 F9-------------------------------|
   |              |              |             |          |
   |<-200 F10-----|              |             |          |
   |              |              |             |          |
   |--ACK F11-------------------------------------------->|

   Message Details



 Barnes                Expires January 8, 2005              [Page 31]

                   SIP Request History Information       July 8, 2004


  INVITE F1   UA1->Proxy

  INVITE sip:UserA@example.com SIP/2.0
  Via: SIP/2.0/UDP here.com:5060
  From: BigGuy <sip:User1@here.com>
  To: LittleGuy <sip:UserA@example.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 192.0.2.3
   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.example.com SIP/2.0
   Via: SIP/2.0/UDPims.example.com:5060;branch=1
     Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserA@example.com>
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.com>
   Call-Id: 12345600@here.com
   CSeq: 1 INVITE
   History-Info: <sip:UserA@ims.example.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 192.0.2.3
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   100 Trying F3 Proxy->UA1

   SIP/2.0 100 Trying


 Barnes                Expires January 8, 2005              [Page 32]

                   SIP Request History Information       July 8, 2004


   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.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.example.com:5060;branch=1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.com>;tag=3
   Call-Id: 12345600@here.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@example.com>
   Content-Length: 0



   INVITE F5 Proxy-> UA-B

   INVITE sip:UserB@example.com SIP/2.0
   Via: SIP/2.0/UDP ims.example.com:5060;branch=2
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.com>
   Call-Id: 12345600@here.com
   History-Info: <sip:UserA@ims.example.com?Reason=SIP;\ cause=302;
   text="Moved Temporarily">; index=1,
   <sip:UserB@example.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 192.0.2.3
   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


 Barnes                Expires January 8, 2005              [Page 33]

                   SIP Request History Information       July 8, 2004


   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.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@example.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@example.com SIP/2.0
   Via: SIP/2.0/UDP ims.example.com:5060;branch=3
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
      To: LittleGuy <sip:UserA@example.com>
   Call-Id: 12345600@here.com
   History-Info:<sip:UserA@ims.example.com?Reason=SIP;\ cause=302;
   text="Moved Temporarily">;index=1,
   <sip:UserB@example.com?Reason=SIP;cause=480;\
   text="Temporarily Unavailable" >;index=2,
   <sip:VM@example.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 192.0.2.3
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000



 Barnes                Expires January 8, 2005              [Page 34]

                   SIP Request History Information       July 8, 2004



   200 OK F9

   SIP/2.0 200 OK UA-VM->Proxy

   Via: SIP/2.0/UDP ims.example.com:5060;branch=3
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.com>;tag=3
   Call-Id: 12345600@here.com
   CSeq: 1 INVITE
   Contact: TheVoiceMail <sip:VM@example.com>
   Content-Type: application/sdp
   Content-Length: <appropriate value>

   v=0
   o=UserA 2890844527 2890844527 IN IP4 vm.example.com
   s=Session SDP
   c=IN IP4 192.0.2.4
   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.example.com:5060;branch=3
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:User1@here.com>
   To: LittleGuy <sip:UserA@example.com>;tag=3
   Call-Id: 12345600@here.com
   CSeq: 1 INVITE
   Contact: TheVoiceMail <sip:VM@example.com>
   Content-Type: application/sdp
   Content-Length: <appropriate value>

   v=0
   o=UserA 2890844527 2890844527 IN IP4 vm.example.com
   s=Session SDP
   c=IN IP4 192.0.2.4
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   ACK F11 UA1-> UA-VM

   ACK sip:VM@example.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060


 Barnes                Expires January 8, 2005              [Page 35]

                   SIP Request History Information       July 8, 2004


   From: BigGuy <sip:User1@here.com>
   To: LittleGuy<sip:UserA@example.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 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


 Barnes                Expires January 8, 2005              [Page 36]

                   SIP Request History Information       July 8, 2004


                    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]


 Appendix D Session via Redirect and Proxy Servers

   In this scenario, Alice places a call to Bob using first a Redirect
   server then a Proxy Server.  The INVITE message is first sent to the
   Redirect Server.  The Server returns a 302 Moved Temporarily response
   (F2) containing a Contact header with Bob's current SIP address.
   Alice then generates a new INVITE with Bob's current SIP address
   included in another History-Info entry.  The INVITE is then sent to
   Bob via the Proxy Server, with Bob receiving the complete History
   information; the call then proceeds normally.  The complete call flow
   for this scenario, without the use of History-Info is described in
   the SIP Basic Call Flow Examples [RFC3665].


   Alice        Redirect Server     Proxy 3             Bob
     |                |                |                |
     |   INVITE F1    |                |                |


 Barnes                Expires January 8, 2005              [Page 37]

                   SIP Request History Information       July 8, 2004


     |--------------->|                |                |
     |     302 F2     |                |                |
     |<---------------|                |                |
     |     ACK F3     |                |                |
     |--------------->|                |                |
     |     INVITE F4                   |                |
     |-------------------------------->|    INVITE F5   |
     |             100  F6             |--------------->|



   Message Details

   F1 INVITE Alice -> Redirect Server

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   History-Info: <sip:bob@biloxi.example.com>; index=1
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Length: 0


   F2 302 Moved Temporarily Redirect Proxy -> Alice

   SIP/2.0 302 Moved Temporarily
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
    ;received=192.0.2.1
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   History-Info: <sip:bob@biloxi.example.com>; index=1
   Contact: <sip:bob@chicago.example.com;transport=tcp>
   Content-Length: 0


   F3 ACK Alice -> Redirect Server

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com


 Barnes                Expires January 8, 2005              [Page 38]

                   SIP Request History Information       July 8, 2004


   CSeq: 1 ACK
   Content-Length: 0


   F4 INVITE Alice -> Proxy 3

   INVITE sip:bob@chicago.example.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 2 INVITE
   History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\
                  text="Moved Temporarily">; index=1,
                 <sip:bob@chicago.example.com>; index=2
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
   Content-Length: 0


   F5 INVITE Proxy 3 -> Bob

   INVITE sip:bob@client.chicago.example.com SIP/2.0
   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.1
   Max-Forwards: 69
   Record-Route: <sip:ss3.chicago.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 2 INVITE
   History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\
                  text="Moved Temporarily">; index=1,
                 <sip:bob@chicago.example.com>; index=2,
                 <sip:bob@client.chicago.example.com>; index=2.1
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
   Content-Length: 0

   Detailed Call Flow continues per section 6.3 in [RFC 3665].


 Intellectual Property Statement

     The IETF takes no position regarding the validity or scope of any
     intellectual property or other rights that might be claimed to
     pertain to the implementation or use of the technology described
     in this document or the extent to which any license under such
     rights might or might not be available; neither does it represent


 Barnes                Expires January 8, 2005              [Page 39]

                   SIP Request History Information       July 8, 2004


     that it has made any effort to identify any such rights.
     Information on the IETF's procedures with respect to rights in
     IETF Documents can be found in BCP 78 and 79.

     Copies of IPR disclosures made to the IETF Secretariat and any
     assurances of licenses to be made available, or the result of an
     attempt made to obtain a general license or permission for the use
     of such proprietary rights by implementers or users of this
     specification can be obtained from the IETF on-line IPR repository
     at http://www.ietf.org/ipr.

     The IETF invites any interested party to bring to its attention
     any copyrights, patents or patent applications, or other
     proprietary rights which may cover technology that may be required
     to implement this standard. Please address the information to the
     IETF at ietf-ipr.org.

 Disclaimer of Validity

     This document and the information contained herein are provided on
     an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
     REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
     THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

 Full Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


















 Barnes                Expires January 8, 2005              [Page 40]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/