Internet DRAFT - draft-ietf-sip-history-info

draft-ietf-sip-history-info




 INTERNET-DRAFT                                              M. Barnes 
 Document: draft-ietf-sip-history-info-06.txt                   Editor 
 Category: Standards Track                             Nortel Networks 
                                                                       
 Expires: July 17th, 2005                              Jan 17th, 2005 
 
    An Extension to the Session Initiation Protocol for Request History 
                                Information  
     
 Status of this Memo  
      
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   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.  
          
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   This Internet-Draft will expire on July 17th, 2005. 
  
 Copyright Notice 
    
   Copyright (C) The Internet Society (2005).  All Rights Reserved. 
    
 Abstract  
    
   This document 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 document 
   defines a new optional SIP header, History-Info, for capturing the 
   history information in requests.  
 



 
 
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 Table of Contents 
    
   1.Background:  Why define a Generic "Request History" capability?.3 
   2. "Request History" Requirements.................................4 
      2.1 Security Requirements......................................5 
      2.2 Privacy Requirements.......................................6 
   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.......................8 
   4 Request History Information Protocol Details....................9 
      4.1 Protocol Structure of History-Info.........................9 
      4.2 Protocol Examples.........................................11 
      4.3 Protocol usage............................................11 
      4.4 Security for History-Info.................................18 
      4.5 Example Applications using History-Info...................18 
   5. Application Considerations....................................23 
   6. Security Considerations.......................................24 
   7. IANA Considerations...........................................24 
   Normative References.............................................25 
   Informational References.........................................25 
   Appendix. Example Scenarios......................................27 
   Appendix A. Sequentially forking (History-Info in Response)......27 
   Appendix B.  Voicemail...........................................32 
   Appendix C.  Automatic Call Distribution Example.................38 
   Appendix D. Session via Redirect and Proxy Servers...............39 
       
 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 Uniform Resource 
   Locators (URLs) on a web page, "call history/logging" style services 
   within intelligent "call management" software for SIP User Agents 
   (UAs) and calls to voicemail servers.  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 document defines a new SIP header, History-Info, to provide a 
   standard mechanism for capturing the request history information to 
   enable a wide variety of services for networks and end users.  The 
   History-Info header provides a building block for development of new 
   services.   
   

 
 
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   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.    
    
   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]. 
 
 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 document to refer 
   to the process of a Proxy Server/User Agent Client (UAC) changing a 
   Uniform Resource Identifier(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 document. 
    
   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 document 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:  
    

 
 
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  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: 
    
   o Some diagnostic information for debugging SIP requests. 
   
   o 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.  
    
   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 

 
 
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   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.   
    
   6) REQUEST-VALIDITY-req:  Request-History is applicable to requests 
   not sent within an established dialog. (e.g. 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 
 
 
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   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.   
 
   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. 
    

 
 
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   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 (e.g. INVITE, REGISTER, MESSAGE, REFER and 
   OPTIONS, PUBLISH and SUBSCRIBE, etc.) (REQUEST-VALIDITY-req) and any 
   valid response to these requests. (ISSUER-req) 
    
   The History-Info header is added to a Request when a new request is 
   created by a UAC or forwarded by a 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) 
 
 
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   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 document defines a new header for SIP. The document strongly 
   RECOMMENDs the use of the Transport Layer Security (TLS) protocol 
   [RFC2246] 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. If TLS is not 
   available for the connection over which the request is being 
   forwarded, then the request MUST not include the History-Info header 
   or the request MUST be redirected to the client, including the 
   History-Info header, so that the request can be retargeted by the 
   client.  
 
   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).  It would be up to the application 
   to define whether it can make use of the information in the case of 
   missing entries.  
    
 
 
 3.3 Ensuring the Privacy of History-Info 
    

 
 
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   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).  In the latter 
   case, this is accomplished by adding a new priv-value, history, to 
   the Privacy header [RFC 3323] indicating whether any or a specific 
   History-Info header(s) SHOULD be forwarded. 
    
   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 or MUST explain why it does not impact the 
   application. 
 
 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, OPTIONS, 
   SUBSCRIBE and PUBLISH and any valid responses, plus NOTIFY requests 
   which initiate a dialog.   
    
   This document adds the following entry to Table 2 of [RFC3261]. The 
   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 
 
 
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                                      SUB  NOT  REF  INF  UPD  PRA  PUB 
                                      ---  ---  ---  ---  ---  ---  --- 
      History-Info            amdr     o    o    o    -    -    -    o 
 
    
   The History-Info header carries the following information, with the 
   mandatory parameters required when the header is included in 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 adding 
        the new entries in order (i.e. following existing entries per 
        the details in section 4.3.3.1), 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 hi-targeted-to-uri. A reason is not included for 
        a hi-targeted-to-uri when it is first added in a History-info 
        header, but rather is added when the retargeting actually 
        occurs.  Note, that this does appear to complicate the security 
        problem, however, retargeting only occurs when the hi-targeted-
        to-uri indicates a domain for which the processing entity is 
        responsible, thus it would be the same processing entity that 
        initially added the hi-targeted-to-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 field values by including the Privacy 
        Header [RFC3323] with a priv-value of "history" escaped in the 
        hi-targeted-to-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. 
 
 
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     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  
    
                            hi-entry *(COMMA hi-entry) 
    
          hi-entry = 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 
    
    
    
 4.2 Protocol Examples 
    
   The following provides some examples of the History-Info header. Note 
   that the backslash and CRLF between the fields in the examples below 
   are for readability purposes only. 
    
    
      History-Info:<sip:UserA@ims.example.com?Reason=SIP%3B\ 
        cause%3D302>;index=1;foo=bar 
    
      History-Info: <sip:UserA@ims.example.com?Reason=SIP%3B \  
         cause%3D302>; index=1.1,       
         <sip:UserB@example.com?Privacy=history&Reason=SIP%3B\ 
         cause%3D486>;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 
 
 
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   the Request-URI in a History-Info header in the initial request or a 
   proxy must add a History-Info header with both an hi-entry for the 
   Request-URI in the initial request and an hi-entry for the target 
   Request-URI as the request is forwarded.  The basic processing is for 
   each entity forwarding a request to add an hi-entry for the target 
   Request-URI, updating the index and adding the Reason as appropriate 
   for any retargeted Request-URI.  
 
   4.3.1 User Agent Client (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 header 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 hi-entry.   
    
   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 hi-entry(s) in the request. In this case, the 
   reason header SHOULD be associated with the hi-targeted-to-uri in the 
   previous (last) hi-entry, as described in section 4.3.3.1.2. A new 
   hi-entry MAY then be added for the URI from the Contact header (which 
   becomes the new Request-URI). In this case, the index is created by 
   reading and incrementing the value of the index from the previous hi-
   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 the History-Info header added due to privacy 
   considerations SHOULD include a Privacy header with a priv-value(s) 
   of "session", "header" or "history" in the request.  
    
   With the exception of the processing of a 3xx response described 
   above, the processing of the History-Info header received in the 
   Response is application specific and outside the scope of this 
   document. 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 aware of potentially 
   missing information.  
    
    
   4.3.2 User Agent Server (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 
 
 
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   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 aware 
   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 
   History-Info header or a new hi-entry 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 
          the History-Info header within the specific domain in which 
          it is retargeted, however, policies (for privacy, user and 
          network security, etc.) would prohibit the exposure of that 
          information outside that domain.  To accommodate such a 
          scenario, a proxy MAY insert the Privacy header with a priv-
          value of "history" when the request is being forwarded within 
          the same domain. An example of such an application is 
          provided in Appendix C. 
       5. Whether an hi-entry 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 each hi-
   entry 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. 
 
 
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   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 the History-Info header(s), 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, to accommodate the considerations 
   outlined above, 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 an hi-entry as it forwards a 
   Request. Section 16.6 of [RFC3261] 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 History-Info for such 
   a request would result in duplicate Request-URIs with different 
   indices. The hi-entry MUST be added following any hi-entry received 
   in the request being forwarded.  Additionally, if a request is 
   received that doesn't include a History-Info header, the proxy MAY 
   add a History-Info header with an hi-entry preceding the one being 
   added for the current request being forwarded.  The index for this 
   hi-entry is RECOMMENDED to start at 1. The following subsections 
   define the details of creating the information associated with each 
   hi-entry. 
    
   4.3.3.1.1 Privacy in the History-Info header 
    
   If there is a Privacy header in the request with a priv-value of 
   "session", "header" or "history", an hi-entry MAY be added, if the 
   request is being forwarded to a Request URI associated with a domain 
   for which the processing entity is responsible (and provided local 
   policy supports the History-Info header, etc.).  If a request is 
   being forwarded to a Request URI associated with a domain for which 
   the proxy is not responsible and there is a Privacy header in the 
   request with a priv-value of "session", "header" or "history", the 
 
 
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   proxy SHOULD remove any hi-entry(s) prior to forwarding, depending 
   upon local policy and whether the proxy might know a priori that it 
   can rely on a downstream privacy service to apply the requested 
   privacy.   
    
   For the scenario where there is no Privacy header in the request and 
   the request is being forwarded to a Request URI associated with the 
   domain(s) for which this entity is responsible, there are several 
   additional considerations:  
     o If there is no local policy associated with privacy, then an hi-
       entry MAY be added to the Request.   
      
     o If the proxy's local policies, per consideration 4 in section 
       4.3.3, indicate that the History-Info header 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 associated with each hi-entry added by that 
       proxy in this scenario.  
      
     o If the proxy's policy per consideration 5 in section 4.3.3, 
       indicates that History-Info for a specific Request URI 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 associated with the specific hi-entry, for 
       that specific hi-targeted-to-uri, added by that proxy in this 
       scenario.   
      
   If a request is being forwarded to a Request URI associated with a 
   domain for which the proxy is not responsible and local policy 
   requires privacy associated with any, or with specific hi-entries it 
   has added, any hi-entry with a priv-value of "history" SHOULD be 
   removed 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, a 
   Reason MUST be associated with the hi-targeted-to-uri.  If the SIP 
   response does not include a Reason header, the SIP Response Code that 
   triggered the retargeting MUST be included as the Reason associated 
   with the hi-targeted-to-uri that has been retargeted.  If the 
   response contains a non-SIP Reason header (e.g. Q.850), it MUST be 
   captured as an additional Reason associated with the hi-targeted-to-
   uri that has been retargeted, along with the SIP Response Code.  If 
   the Reason header is a SIP reason, then it MUST be used as the Reason 
   associated with the hi-targeted-to-uri rather than the SIP response 
   code.   
    


 
 
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   For retargets as a result of timeouts or internal events, a Reason 
   MAY be associated with the hi-targeted-to-uri that has been 
   retargeted. 
    
   The addition of the Reason should occur prior to the forwarding of 
   the request (which may add a new hi-entry with a new hi-targeted-to-
   uri) as it is associated with the hi-targeted-to-uri that has been 
   retargeted, since it reflects the reason why the Request to that 
   specific URI was not successful. 
    
    
   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). Each 
   dot reflects a hop or level of nesting, thus the number of hops is 
   determined by the total number of dots. Within each level, the 
   integer 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.   
    
   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.   
      
 
 
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     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 (forking): 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 aggregated information 
     associated with each of those requests and including the header 
     entries in the order indicated by the indexing.  Responses are 
     processed as described in section 16.7 of [RFC3261] with the 
     aggregated History-Info entries processed similar to step 7 
     "Aggregate Authentication Header Field Values". 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, subject 
   to the following considerations for privacy: 
    
     o If the response is being forwarded to a Request URI associated 
       with a domain for which the proxy is not responsible and there 
       was a Privacy header, in the request received by the proxy, with 
       a priv-value of "session", "header" or "history", the proxy MUST 
       remove the History-Info header (i.e. all hi-entries) prior to 
       forwarding.  
    
     o If a request is being forwarded to a Request URI associated with 
       a domain for which the proxy is not responsible and local policy 
       requires privacy associated with any or all hi-entry(s) it has 
       added, any hi-entry with a priv-value of "history" MUST be 
       removed prior to forwarding. 
    
     o If a proxy receives a response, from another intermediary 
       associated with a domain for which it is responsible, including 
       hi-entry(s) with privacy headers and that response is to be 
 
 
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       forwarded to a domain for which it is not responsible, then 
       those hi-entry(s) MUST be removed.    
    
   The processing of History-Info in responses follows the methodology 
   described in section 16.7 of [RFC3261], with the processing of 
   History-Info headers adding an additional step, just before step 9 
   "Forwarding the Response".   
    
    
   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 3, the security requirements are met by 
   recommending the use of TLS (a basic SIP requirement per [RFC3261]) 
   for hop by hop security.  If TLS is not available on the connection 
   over which a request, containing a History-Info header, is being 
   forwarded, then either of the following two options MUST be 
   implemented: 
     o The History-Info header MUST be removed prior to forwarding the 
       request, or 
     o The request MUST be redirected, including the History-Info header 
       in the response, to allow the UAC to securely issue the request, 
       including the History-Info header.  
 
  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.  
    

 
 
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   Section 4.5.1 provides this same scenario using one of the privacy 
   mechanisms, 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=1.1 
   |            |         |        |        |        |        | 
   |            |         |-INVITE>|        |        |        | 
                 History-Info: <sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>;index=1.1, 
                               <sip:User2@UA2.example.com>;index=1.1.1 
   |            |         |        |        |        |        | 
   |            |         |-----INVITE ---->|        |        | 
                  History-Info:<sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>; index=1.1, 
                               <sip:User3@UA3.example.com>;index=1.1.2 
   |            |         |        |        |        |        | 
   |            |         |-------INVITE------------>|        |  
                  History-Info:<sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>;index=1.1, 
                               <sip:User4@UA4.example.com>;index=1.1.3 
    
   /* 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=1.1,   
                   <sip:User2@UA2.example.com?Reason=SIP;\ 
 
 
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                    cause=408;text="RequestTimeout">;index=1.1.1,                  
                   <sip:User3@UA3.example.com?Reason=SIP; \        
                    cause=487;text="Request Terminated">; index=1.1.2, 
                   <sip:User4@UA4.example.com?Reason=SIP;\         
                    cause=603;text="Decline">; index=1.1.3                           
   |            |         |        |        |        |        | 
  /* 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=1.1,  
                   <sip:User2@UA2.example.com?Reason=SIP;cause=408;\ 
                    text="RequestTimeout">;index=1.1.1,                      
                   <sip:User3@UA3.example.com?Reason=SIP;cause=487;\ 
                    text="Request Terminated">; index=1.1.2, 
                   <sip:User4@UA4.example.com?Reason=SIP;cause=603;\ 
                    text="Decline">; index=1.1.3 
                   <sip:User5@UA5.example.com>;index=1.2 
   |            |         |        |        |        |        | 
   |            |<-----200 OK---------------------------------| 
   |<--200 OK---|         |        |        |        |        | 
   |            |         |        |        |        |        |  
   |--ACK --------------------------------------------------->| 
 
    
   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=1.1 
   |            |         |        |        |        |        | 
   |            |         |-INVITE>|        |        |        | 
                 Privacy: history 
                 History-Info:<sip:Bob@P1.example.com>;index=1,  
                              <sip:Bob@P2.example.com>;index=1.1, 
                              <sip:User2@UA2.example.com>;index=1.1.1 
   |            |         |        |        |        |        | 
   |            |         |-----INVITE ---->|        |        | 
                  Privacy: history 
                  History-Info:<sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>; index=1.1, 
 
 
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                               <sip:User3@UA3.example.com>;index=1.1.2 
   |            |         |        |        |        |        | 
   |            |         |-------INVITE------------>|        |  
                  Privacy: history 
                  History-Info:<sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>;index=1.1, 
                               <sip:User4@UA4.example.com>;index=1.1.3 
    
   /* 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=1.1                            
   |            |         |        |        |        |        | 
   /* 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=1.1, 
                                <sip:User3@UA3.example.com>; index=1.2 
   |            |         |        |        |        |        | 
   |            |<-- 486 -------------------|        |        | 
                  History-Info: <sip:Bob@P1.example.com>;index=1,  
                                <sip:Bob@P2.example.com>; index=1.1, 
                                <sip:User3@UA3.example.com>; index=1.2 
   |            |         |        |        |        |        | 
   |            |----------------INVITE --------------------->| 
                History-Info: <sip:Bob@P1.example.com>;index=1, 
                   <sip:Bob@P2.example.com>; index=1.1,  
                   <sip:User3@UA3.example.com?Reason=SIP;cause=486;\ 
                    text="Busy Here">;index=1.2, 
                   <sip:User5@UA5.example.com>;index=1.3 
   |            |         |        |        |        |        | 
   |            |<-----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 
                
 
 
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   |            |         |        |        |        |        | 
   |--INVITE -->|         |        |        |        |        | 
   |            |-INVITE->|        |        |        |        | 
                 Supported: histinfo 
                 History-Info: <sip:Bob@P1.example.com>;index=1, 
                               <sip:Bob@P2.example.com>; index=1.1 
   |            |         |        |        |        |        | 
   |            |         |-INVITE>|        |        |        | 
                 History-Info:<sip:Bob@P1.example.com>;index=1,  
                              <sip:Bob@P2.example.com>;index=1.1, 
                              <sip:User2@UA2.example.com>;index=1.1.1 
   |            |         |        |        |        |        | 
   |            |         |-----INVITE ---->|        |        | 
                  History-Info:<sip:Bob@P1.example.com>;index=1,  
                               <sip:Bob@P2.example.com>;index=1.1, 
                               <sip:User3@UA3.example.com>;index=1.1.2 
   |            |         |        |        |        |        | 
   |            |         |-------INVITE------------>|        |  
                  History-Info: <sip:Bob@P1.example.com>;index=1,  
                                <sip:Bob@P2.example.com>;index=1.1, 
                                <sip:User4@UA4.example.com?\   
                                 Privacy=history>; index=1.1.3 
    
   /* 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 ---|        |        |        |        | 
                History-Info: <sip:Bob@P1.example.com>;index=1,  
                   <sip:Bob@P2.example.com>; index=1.1,   
                   <sip:User2@UA2.example.com?Reason=SIP;\ 
                    cause=408;text="RequestTimeout">;index=1.1.1,                  
                   <sip:User3@UA3.example.com?Reason=SIP; \        
                    cause=487;text="Request Terminated">; index=1.1.2, 
   |            |         |        |        |        |        | 
  /* 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=1.1,  
                   <sip:User2@UA2.example.com?Reason=SIP;cause=408;\ 
                    text="RequestTimeout">;index=1.1.1,                      
                   <sip:User3@UA3.example.com?Reason=SIP;cause=487;\ 
                    text="Request Terminated">; index=1.1.2, 
                   <sip:User5@UA5.example.com>;index=1.2  
   |            |         |        |        |        |        | 
 
 
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   |            |<-----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 MUST 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 
      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 History-Info header requires the 
      use of TLS. In the case of TLS not being available for a 
      connection over which a request is being forwarded, the History-
      Info header may be removed from a request. The impact of lack of 
      having the information 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.   
 
 
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 6. Security Considerations  
    
   The threat model and related security and privacy requirements for 
   the History-Info header are described in section 2.1 and 2.2 of this 
   document.  Sections 3.2, 3.3 and 4.4 provide normative 
   recommendations related to security and privacy fulfilling these 
   requirements.  The use of TLS is mandated between the entities (i.e. 
   UAC to Proxy, Proxy to Proxy, and Proxy to UAS) which use the 
   History-Info header.  The appropriate handling of a request in the 
   case that TLS is not available for a specific connection is described 
   in section 5.  
    
   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.   
    
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 
   -----------             ------------               --------- 
   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.       
 
 
 
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   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 
                  
   
 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. 
 
   [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. 
    
   [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", 
   RFC 2246, January 1999. 
 
    
 Informational References 
 
   [SIPSVCEX] A. Johnson, "SIP Service Examples", draft-ietf-sipping-
   service-examples-07.txt, July, 2004. 
    
   [RFC3665] A. Johnson et al, "SIP Basic Call Flow Examples", RFC 3665, 
   BCP 75, December, 2003.  
 
 
 
 
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 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, 
   Martin Dolly, Roland Jesske, Takuya Sawada, Sebastien Prouvost and 
   Sebastien Garcin. 
    
   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 security 
   aspects. 
    
 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.   
 
   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 
 
 
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   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. Example Scenarios  
 
   The scenarios in Appendix A-D provide sample use cases for the 
   History-Info header for informational purposes only.  They are not 
   intended to be normative and the formatting is for visual purposes, 
   thus the headers in the URI are not shown properly formatted for 
   escaping. Refer to section 4.2 examples with the proper formatting.  
    
 Appendix A. 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. 
 
   "Alice" at UA 1sends a call to "Bob" via proxy 1. Proxy 1 
   sequentially tries several places (UA2, UA3 and UA4) unsuccessfully 
   before sending a response to "Alice".   
 
   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 document 
   to prescribe detailed applications.   
    
   UA1      Proxy1                UA2      UA3      UA4                   
   |            |                  |        |        |         
   |-INVITE F1->|                  |        |        |         
 
 
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   |            |                  |        |        |         
   |            |--INVITE F2------>|        |        |         
   |<--100 F3---|                  |        |        |         
   |            |<-302 F4----------|        |        |         
   |            |                  |        |        |         
   |            |-------INVITE F5 --------->|        |         
   |            |                  |        |        |         
   |            |<-------180 F6 ------------|        |         
   |<---180 F7--|                  |        |        |         
   |  . .       |---retransmit INVITE ----->|        |  
   |            |                  |        |        |        
   |            |      ( timeout ) |        |        |         
   |            |                  |        |        |         
   |            |------INVITE F8 ------------------->|         
   |<--100 F9 --|                  |        |        |         
   |            |                  |        |        |         
   |            |<-486 F10 --------------------------|         
   |            |                  |        |        |         
   |            |-- ACK F11------------------------->|                 
   |<--486 F12--|                  |        |        |         
   |            |                  |        |        |          
   |--ACK F13-->|                  |        |        |         
   |            |                  |        |        |          
   
   
   Message Details  
       
      F1 INVITE UA1 ->Proxy1  
      
      INVITE sip:UserA@example.com SIP/2.0  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      Contact: Alice <sip:User1@example.net>  
      Content-Type: application/sdp  
      Content-Length: <appropriate value>  
        
      v=0  
      o=UserA 2890844526 2890844526 IN IP4 client.example.net  
      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. */  
 
 
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      F2 INVITE  Proxy1 ->UA2       
       
      INVITE sip:UserA@ims.example.com SIP/2.0     
      Via: SIP/2.0/UDP ims.example.com:5060;branch=1   
        Via: SIP/2.0/UDP example.net:5060  
      Record-Route: <sip:UserA@example.com>  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      History-Info: <sip:UserA@ims.example.com>; index=1 
      Contact: Alice <sip:User1@example.net>  
      Content-Type: application/sdp  
      Content-Length: <appropriate value>  
        
      v=0  
      o=UserA 2890844526 2890844526 IN IP4 client.example.net  
      s=Session SDP  
      c=IN IP4 192.0.2.3 
      t=0 0  
      m=audio 49170 RTP/AVP 0  
      a=rtpmap:0 PCMU/8000  
        
      F3 100 Trying Proxy1 ->UA1     
       
      SIP/2.0 100 Trying  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      Content-Length: 0  
        
        
      F4 302 Moved Temporarily UA2 ->Proxy1  
        
      SIP/2.0 302 Moved Temporarily  
      Via: SIP/2.0/UDP ims.example.com:5060;branch=1  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>;tag=3  
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      Contact: <sip:UserB@example.com> 
      Content-Length: 0  
        
                         
      F5 INVITE Proxy1 -> UA3       
 
 
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      INVITE sip:UserB@example.com SIP/2.0  
      Via: SIP/2.0/UDP ims.example.com:5060;branch=2  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      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: Alice <sip:User1@example.net> 
      Content-Type: application/sdp  
      Content-Length: <appropriate value>  
        
      v=0  
      o=User1 2890844526 2890844526 IN IP4 client.example.net  
      s=Session SDP  
      c=IN IP4 192.0.2.3 
      t=0 0  
      m=audio 49170 RTP/AVP 0  
      a=rtpmap:0 PCMU/8000  
        
      F6 180 Ringing UA3 ->Proxy1  
        
      SIP/2.0 180 Ringing  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>;tag=5  
      Call-ID: 12345600@example.net  
      CSeq: 1 INVITE  
      Content-Length: 0  
        
      F7 180 Ringing Proxy1 -> UA1   
             
      SIP/2.0 180 Ringing  
      SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      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 UA4 after adding the 
      additional History Information entry. */ 
       
 
 
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      F8 INVITE Proxy1 -> UA4      
         
      INVITE sip:UserC@example.com SIP/2.0  
      Via: SIP/2.0/UDP ims.example.com:5060;branch=3  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com> 
      Call-Id: 12345600@example.net  
      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:UserC@example.com>;index=3 
      CSeq: 1 INVITE  
      Contact: Alice <sip:User1@example.net>  
      Content-Type: application/sdp  
      Content-Length: <appropriate value>  
        
      v=0  
      o=User1 2890844526 2890844526 IN IP4 client.example.net  
      s=Session SDP  
      c=IN IP4 192.0.2.3 
      t=0 0  
      m=audio 49170 RTP/AVP 0  
      a=rtpmap:0 PCMU/8000  
         
       
      F9 100 Trying Proxy1 ->UA1     
       
      SIP/2.0 100 Trying  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com>  
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      Content-Length: 0  
       
       
      F10 486 Busy Here UA4 -> Proxy1 
    
      SIP/2.0  486 Busy Here 
      Via: SIP/2.0/UDP ims.example.com:5060;branch=3  
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com> 
      Call-Id: 12345600@example.net  
      CSeq: 1 INVITE  
      Content-Length: 0 
 
 
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      F11 ACK Proxy1 -> UA4 
    
      ACK sip:UserC@example.com SIP/2.0 
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com> 
      Call-Id: 12345600@example.net  
      CSeq: 1 ACK  
      Content-Length: 0 
    
    
       /* The proxy forwards the 486 to Alice after adding the 
          associated History Information entries from the series of  
          INVITES */ 
       
      F12 486 Busy Here Proxy1 -> UA1 
    
      SIP/2.0  486 Busy Here 
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com> 
      Call-Id: 12345600@example.net  
      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:UserC@example.com>;index=3 
      CSeq: 1 INVITE  
      Content-Length: 0 
    
      F13 ACK Alice -> Proxy 1 
    
      ACK sip:UserA@example.com SIP/2.0 
      Via: SIP/2.0/UDP example.net:5060  
      From: Alice <sip:User1@example.net>  
      To: Bob <sip:UserA@example.com> 
      Call-Id: 12345600@example.net 
      CSeq: 1 ACK 
      Content-Length: 0 
    
    
 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 
 
 
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   that additional information is needed 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  
       
  INVITE F1   UA1->Proxy  
      
  INVITE sip:UserA@example.com SIP/2.0  
  Via: SIP/2.0/UDP example.net:5060  
  From: BigGuy <sip:User1@example.net>  
  To: LittleGuy <sip:UserA@example.com>  
  Call-Id: 12345600@example.net  
  CSeq: 1 INVITE  
  Contact: BigGuy <sip:User1@example.net>  
  Content-Type: application/sdp  
  Content-Length: <appropriate value>  
     
 
 
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   v=0  
   o=UserA 2890844526 2890844526 IN IP4 client.example.net  
   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 example.net:5060  
   Record-Route: <sip:UserA@example.com>  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>  
   Call-Id: 12345600@example.net  
   CSeq: 1 INVITE  
   History-Info: <sip:UserA@ims.example.com>; index=1 
   Contact: BigGuy <sip:User1@example.net>  
   Content-Type: application/sdp  
   Content-Length: <appropriate value>  
     
   v=0  
   o=UserA 2890844526 2890844526 IN IP4 client.example.net  
   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  
   Via: SIP/2.0/UDP example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>  
   Call-Id: 12345600@example.net  
   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 example.net:5060  
 
 
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   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy<sip:UserA@example.com>;tag=3  
   Call-Id: 12345600@example.net  
   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 example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>  
   Call-Id: 12345600@example.net  
   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@example.net> 
   Content-Type: application/sdp  
   Content-Length: <appropriate value>  
     
   v=0  
   o=User1 2890844526 2890844526 IN IP4 client.example.net  
   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 example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>;tag=5  
   Call-ID: 12345600@example.net  
   CSeq: 1 INVITE  
   Content-Length: 0  
     
   180 Ringing F7  Proxy-> UA1   
          
   SIP/2.0 180 Ringing  
   SIP/2.0/UDP example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>  
   Call-Id: 12345600@example.net  
 
 
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   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 example.net:5060  
   From: BigGuy <sip:User1@example.net>  
      To: LittleGuy <sip:UserA@example.com> 
   Call-Id: 12345600@example.net  
   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@example.net>  
   Content-Type: application/sdp  
   Content-Length: <appropriate value>  
     
   v=0  
   o=User1 2890844526 2890844526 IN IP4 client.example.net  
   s=Session SDP  
   c=IN IP4 192.0.2.3 
   t=0 0  
   m=audio 49170 RTP/AVP 0  
   a=rtpmap:0 PCMU/8000  
      
      
   200 OK F9     
    
   SIP/2.0 200 OK UA-VM->Proxy 
         
   Via: SIP/2.0/UDP ims.example.com:5060;branch=3  
   Via: SIP/2.0/UDP example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>;tag=3  
   Call-Id: 12345600@example.net  
   CSeq: 1 INVITE  
   Contact: TheVoiceMail <sip:VM@example.com>  
   Content-Type: application/sdp  
 
 
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   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 example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy <sip:UserA@example.com>;tag=3  
   Call-Id: 12345600@example.net              
   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 example.net:5060  
   From: BigGuy <sip:User1@example.net>  
   To: LittleGuy<sip:UserA@example.com>;tag=3  
   Call-Id: 12345600@example.net  
   CSeq: 1 ACK  
   Content-Length: 0  
     
   /* RTP streams are established between UA1 and  
   UA-VM. UA-VM starts announcement for UA1 */ 





 
 
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 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@example.com>; index=1  
                    History-Info: <sip:ACDGRP1@example.com>; index=1.1 
   |              |              |             |          |  
   |              |<-302 F3------|             |          | 
                    Contact: <sip:ACDGRP2@ACD.com>                  
   |              |              |             |          | 
   |              |--------INVITE F4---------->|          | 
                    History-Info: <sip:Gold@example.com>; index=1  
                    History-Info: <sip:ACDGRP1@example.com>; index=1.1 
 
 
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                    History-Info: <sip:ACDGRP2@example.com>; index=1.2               
   |              |              |             |          |         
   |              |              |             |          | 
   |              |              |             |INVITE F5>| 
                    History-Info: <sip:Gold@example.com>; index=1  
                    History-Info: <sip:ACDGRP1@example.com>; index=1.1 
                    History-Info: <sip:ACDGRP2@example.com>; index=1.2                
   |              |              |             |          | 
   |              |              |             |<-200 F6--|                 
   |              |              |             |          | 
   |              |<-200 F7--------------------|          |  
                    History-Info: <sip:Gold@example.com>; index=1  
                    History-Info: <sip:ACDGRP1@example.com>; index=1.1 
                    History-Info: <sip:ACDGRP2@example.com>; index=1.2                
   |<-200 F8------|              |             |          | 
   < No History-Info included in the response due to Local Policy> 
   |              |              |             |          | 
   |--ACK F9--------------------------------------------->| 
 
    
    
 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 
   section 3.6 of the SIP Basic Call Flow Examples [RFC3665].  
 
 
   Alice        Redirect Server     Proxy 3             Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|                |                | 
     |     302 F2     |                |                | 
     |<---------------|                |                | 
     |     ACK F3     |                |                | 
     |--------------->|                |                | 
     |     INVITE F4                   |                | 
     |-------------------------------->|    INVITE F5   | 
     |             100  F6             |--------------->| 
       
      
    
 
 
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   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 
   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> 
 
 
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   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]. 
      
      
Appendix E. Changelog 
 
   NOTE TO THE RFC-Editor: Please remove this section prior to 
   publication as an RFC. 
    
   Changes from the 05 to 06 version: 
    
     o General changes to tidy document: 
          o  Change the term "this draft" to "this document". 
          o  Spell out first use of acronyms (ex: UA, UAC, UAS, URI, 
             URL, TLS) 
          o  Change Histinfo to "histinfo"  
    
     o Abstract: delete last 2 sentences in Abstract 
    
     o Overview:  
          o Insert paragraph break just before "This draft defined a new 
             SIP header..." 
 
 
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          o 2nd to last paragraph of Overview, delete all but first 
             sentence." (the other stuff on where examples would be 
             further documented isn't really relevant to what this draft 
             does and had been there for purposes of WG discussion 
             during development of document).  
    
     o Background: Put "retarget" in single quotes when the term is 
       introduced in the second sentence (consistent with reference in 
       section 3. 
        
     o Section 3, 2nd para, add SUBSCRIBE and PUBLISH as appropriate 
       methods (consistent with section 4.1) 
    
     o Section 3.2:  Changed "RECOMMENDs the use of TLS" to "strongly 
       RECOMMENDS the use of TLS". 
    
     o Section 4.1, Privacy bullet item, clarified the first reference 
        of "History-Info header" as "History-Info header field values". 
    
     o Section 4.2: 
        oFor clarity in the examples, removed the text phrases escaped 
          into the URI.  
        oChange capitalized "Cause" to LC "cause".  
      
      o Section 6 (Security): deleted the last two paragraphs (on AIB, 
        Body additions, Security of Inserted Info since those are not 
        relevant to the security solution required for History-Info), 
        and restated what security mechanisms are mandatory to 
        implement, including references to the sections of the document 
        dealing with those mechanisms.  
    
      o References: Updated references: Added TLS and removed body-add, 
        AIB, and sec-inserted. 
    
   Changes from the 04 to 05 version: 
    
     o Section 3, 3rd paragraph:  Clarified that the Proxy does not 
       create the requests, but rather forwards. (SP - individual email 
       Nov. 18) 
    
     o Section 4.3.1:   
          - 2nd paragraph: Added text for handling the reason, referring 
             to section 4.3.3.1.2 for details(JRE-individual email Nov. 
             15) 
          - last paragraph: Clarified that with the exception of 3xx 
             responses, handling of responses is application specific.  
    
     o Section 4.3.3.1.1, lst paragraph, last statment:  changed "...the 
       proxy MUST remove any hi-entry(s) prior to forwarding." 
 
 
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       to: 
       "...the proxy SHOULD remove any hi-entry(s) prior to forwarding, 
       depending upon local policy and whether the proxy might know 
       apriori that it can rely on a downstream privacy service to 
       apply the requested privacy." (WG mailing list - conclusion 
       posted on Nov. 17) 
    
     o Section 4.3.3.1.2, last paragraph : a "is" has been added 
        between "it" and "associated" in the phrase "as it associated 
        with the hi-targeted-to-uri ..."  (SP - individual email Nov. 
        18) 
    
     o Section 4.5 examples:  
          o  Fixed indexing (2 should have been 1.1, which affects the 
             whole series). (WG mailing list response to TS posted on 
             Nov. 3rd) 
          o  Fixed the 480 "timeouts" which should be 408s (note this 
             error was introduced with changes made in this section in 
             the 03 version. (NC-individual email Oct 31) 
          o  Fixed missing " on the "Busy Here" on the INVITE to UA5 in 
             4.5.1. (NC-individual email Oct 31) 
    
 
   Changes from the 03 to the 04 version: 
     o Editorial nits:  
          o Removed second reference to "call center" in Overview 
            section. (EB) 
          o Changed square brackets on references to requirements to 
            parenthesis so they wouldn't appear to be external 
            references. (EB) 
          o Moved the updates to table 2 in section 4.1, so that it 
            appears right after the paragraph discussing in which 
            messages the header can appear. (RM) 
     o Section 3.2: 
          o Moved discussion of new security solution proposals per 
            updated identity draft and rohan's body addition to section 
            6 as they're not relevant to the solution in this document 
            (per (JRE-1)).  
          o Per IETF-60 discussion and Rohan's input, added a statement 
            that if TLS isn't available on the connection over which 
            the History-info is being forwarded, either a redirection 
            (per identity document) is required or the History-info is 
            not forwarded.  
     o Section 3.3:  
          o 2nd paragraph: adding clarification text "In the latter 
            case,.." to the last sentence. (JRE-2) 
          o Last paragraph: Clarified in the last sentence that if there 
            is no impact on the application due to privacy 

 
 
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            considerations, why that is so MUST also be explained by 
            that application. (EB) 
     o Section 4.1: 
          o Added SUBSCRIBE and PUBLISH to the list of messages in which 
            History-Info header may appear. (JRE-3/10) 
          o Changed the wording in the text descriptions of the fields 
            to be non-normative (i.e. not caps for the reserved words 
            in RFC 2119). (KD) 
          o In the text description for the Index, clarified that the 
            entries are added in a specific order, with the indexing to 
            ensure the proper ordering. (JRE-4) 
          o In the text descriptions for the Reason and Privacy 
            parameters, changed the references of "Request URI" to "hi-
            targeted-to-uri" to explicitly refer to the field in the 
            header entry. (JRE-5) 
          o In the ABNF syntax, changed the "hist-info" field name to 
            "hi-entry".  This is then used throughout the remainder of 
            the document to refer to a "History-Info header entry". 
            (Note, this impacted the text primarily in section 4.3 - 
            specifically )(JRE-8/9) 
     o Section 4.2: Added appropriate hex characters for the escaped 
       headers in the example (e.g. for ", = and ;). (LIST 10/15) 
     o Section 4.3.1: changed "notified" to "aware" in terms of 
       application interface to be less specific about interface to 
       application  (consistent with 4.3.2) 
     o Section 4.3.2: same change as in 4.3.1.  Capitalized "should" in 
       last sentence. (EB) 
     o Section 4.3.3: Clarified item 4 to be specific that the privacy 
       header may be used when the request is being forwarded within 
       the same domain (accomodating the scenario which allows 
       information to only be forwarded within the domain in which it 
       was retargeted). (JRE-11) 
     o Section 4.3.3.1: rewording to include explicit references to hi-
       entry [JRE-8/9] and changed the "header should be added 
       following..." to "the hi-entry MUST be added following..." (JRE-
       4) 
     o Section 4.3.3.1.1: Reworded privacy section for clarity.  
       Basically, need to tag each of the entires with 
       "privacy=history" for retargeting within the domain and strip 
       out the entries when leaving the domain IF the request has a 
       privacy header of Session, Header or History or local policy 
       requires.  (JRE-13) 
     o Section 4.3.3.1.2: Added the use of a Reason header in a 
       response, as the Reason field associated with a retargeted URI. 
       (LIST-10/5) 
     o Section 4.3.3.1.3:  
          o Clarified that the number of hops is reflected by the total 
            number of dots (and not the value of the digits) (JRE-14.1) 

 
 
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          o Deleted last sentence of 1st paragraph as that was a 
            holdover from a previous version. (JRE-14.2) 
          o Item 5: clarified that the referenced scenario is forking 
            and that the response consists of the aggregated (rather 
            than the word "amalgamated") information. (JRE-15) 
     o Section 4.3.3.2:  
          o Clarified that response processing for History-Info follows 
            the general processing described in section 16.7 of 
            RFC3261.  (related to JRE-15) 
          o More detail added on the processing of responses with 
            Privacy header. (LIST-8/18)  
     o Section 4.4: Added text addressing the security when TLS is not 
       available, per Rohan's comment above.  
     o Section 5:  
          o Changed the "should" to a "MUST" in the 1st application 
            consideration in terms of the requirement to define default 
            behavior should the information not be available, due to 
            History-Info being an optional header. (EB) 
          o Updated the 5th consideration for security to reflect the 
            lack of information due to potential TLS inavailability for 
            a connection, thus the potential for no History-Info header 
            (per Rohan's comment).  
     oSection 6:  
          o Updated security considerations per TLS issue (Rohan) and to 
            reference the new security solution proposals.  
          o Added discussion of new security solution proposals per 
            updated identity document and rohan's body addition.  
     oAppendix:  
          o Added overview clarifying that flows are informational and 
            not normative. 
          o Changed domains to appropriate example.com and example.net 
            ones.  
          o A.1 Added message details 
          o A.2 Removed as this is redundant since this example is what 
            is now in section 4.2. 
 
   Changes from the 02 to the 03 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 
        processing in 4.3.3 (and 4.3.3.1 and 4.3.3.2).  In addition, 
 
 
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        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 01 to the 02 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).  
 
 
 
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   Changes from the 00 to the 01 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 
   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. 
     Added section 2.3.4 to address Redirect Server behavior. 
      
 Intellectual Property Statement  
          
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     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 
     that it has made any effort to identify any such rights. 

 
 
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     Information on the IETF's procedures with respect to rights in 
     IETF Documents can be found in BCP 78 and 79.   
          
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