INTERNET-DRAFT M. Barnes Document: draft-ietf-sip-history-info-03.txt Editor Category: Standards Track Nortel Networks Expires: January 8, 2005 July 8, 2004 An Extension to the Session Initiation Protocol for Request History Information Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 8th, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This draft defines a standard mechanism for capturing the history information associated with a SIP request. This capability enables many enhanced services by providing the information as to how and why a call arrives at a specific application or user. This draft defines a new optional SIP header, History-Info, for capturing the history information in requests. A new option tag, Histinfo, to be included in the Supported header, is defined to allow UAs to indicate whether the History-Info should be returned in responses to a request which has captured the history information. A new priv-value, history, is Barnes Expires January 8, 2005 [Page 1]
SIP Request History Information July 8, 2004 added to the Privacy header to allow for privacy handling of the History-Info header. Table of Contents 1.Background: Why define a Generic "Request History" capability?.3 2. "Request History" Requirements.................................4 2.1 Security Requirements......................................6 2.2 Privacy Requirements.......................................7 3. Request History Information Description........................7 3.1 Optionality of History-Info................................8 3.2 Securing History-Info......................................8 3.3 Ensuring the Privacy of History-Info.......................9 4 Request History Information Protocol Details...................10 4.1 Protocol Structure of History-Info........................10 4.2 Protocol Examples.........................................12 4.3 Protocol usage............................................12 4.4 Security for History-Info.................................17 4.5 Example Applications using History-Info...................18 5. Application Considerations....................................22 6. Security Considerations.......................................23 7. IANA Considerations...........................................23 Normative References.............................................26 Informational References.........................................27 Appendix A Forking Scenarios....................................28 A.1 Sequentially forking (History-Info in Response)...........28 A.2 Sequential Forking (with Success).........................30 Appendix B Voicemail............................................31 Appendix C Automatic Call Distribution Example..................36 Appendix D Session via Redirect and Proxy Servers................37 Full Copyright Statement.........................................40 Overview Many services that SIP is anticipated to support require the ability to determine why and how the call arrived at a specific application. Examples of such services include (but are not limited to) sessions initiated to call centers via "click to talk" SIP URLs on a web page, "call history/logging" style services within intelligent "call management" software for SIP UAs and calls to voicemail servers and call centers. While SIP implicitly provides the redirect/retarget capabilities that enable calls to be routed to chosen applications, there is currently no standard mechanism within SIP for communicating the history of such a request. This "request history" information allows the receiving application to determine hints about how and why the call arrived at the application/user. This draft defines a new SIP header, History-Info, to provide a standard mechanism for capturing the request history information to enable a wide variety of Barnes Expires January 8, 2005 [Page 2]
SIP Request History Information July 8, 2004 services for networks and end users. The History-Info header provides a building block for development of new services. Section 1 provides additional background motivation for the Request History capability. Section 2 identifies the requirements for a solution, with Section 3 providing an overall description of the solution. Section 4 provides the details of the additions to the SIP protocol. Example uses of the new header are included in Section 4.5, with additional scenarios included in the Appendix. It is anticipated that these would be moved and progressed in a general Service examples draft such as [SIPSVCEX] or individual informational drafts describing these specific services, since the History-Info header is just one of the building blocks for implementing these services. Individual drafts would be particularly useful for documenting services for which there are multiple solutions, as it is not the intent, nor is it within the scope, of this draft to prescribe a complete solution for any of these applications. Section 5 summarizes the application considerations identified in the previous sections. Section 6 summarizes the security solution. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. In order to provide a cross reference of the solution description to the requirements without reiterating the entirety of the requirements inline, the requirements are referenced as [REQNAME-req] following the text or paragraph which explicitly satisfies the requirement. 1.Background: Why define a Generic "Request History" capability? SIP implicitly provides redirect/retarget capabilities that enable calls to be routed to specific applications as defined in [RFC3261]. The term retarget will be used henceforth in this draft to refer to the process of a Proxy Server/UAC changing a URI in a request and thus changing the target of the request. This term is chosen to avoid associating this request history only with the specific SIP Redirect Server capability that provides for a response to be sent back to a UAC requesting that the UAC should retarget the original request to an alternate URI. The rules for determining request targets as described in section 16.5 of [RFC3261] are consistent with the use of the retarget term in this draft. Barnes Expires January 8, 2005 [Page 3]
SIP Request History Information July 8, 2004 The motivation for the request history is that in the process of retargeting old routing information can be forever lost. This lost information may be important history that allows elements to which the call is retargeted to process the call in a locally defined, application specific manner. The proposal in this draft is to provide a mechanism for transporting the request history. It is not proposing any application specific behavior for a Proxy or UA upon receipt of the information. Indeed, such behavior should be a local decision for the recipient application. Current network applications provide the ability for elements involved with the call to exchange additional information relating to how and why the call was routed to a particular destination. The following are examples of such applications: 1. Web "referral" applications, whereby an application residing within a web server determines that a visitor to a website has arrived at the site via an "associate" site which will receive some "referral" commission for generating this traffic, 2. Email forwarding whereby the forwarded-to user obtains a "history" of who sent the email to whom and at what time 3. Traditional telephony services such as Voicemail, call-center "automatic call distribution", and "follow-me" style services. Several of the aforementioned applications currently define application specific mechanisms through which it is possible to obtain the necessary history information. In addition, request history information could be used to enhance basic SIP functionality by providing the following: 4. Some diagnostic information for debugging SIP requests. 5. A stronger security solution for SIP. A side effect is that each proxy which captures the "request history" information in a secure manner provides an additional means (without requiring signed keys) for the original requestor to be assured that the request was properly retargeted. 2. "Request History" Requirements The following list constitutes a set of requirements for a "Request History" capability. Barnes Expires January 8, 2005 [Page 4]
SIP Request History Information July 8, 2004 1) CAPABILITY-req: The "Request History" capability provides a capability to inform proxies and UAs involved in processing a request about the history/progress of that request. While this is inherently provided when the retarget is in response to a SIP redirect, it is deemed useful for non-redirect retargeting scenarios, as well. 2) OPTIONALITY-req: The "Request History" information is optional. 2.1) In many cases, it is anticipated that whether the history is added to the Request would be a local policy decision enforced by the specific application, thus no specific protocol element is needed. 2.2) Due to the capability being "optional" from the SIP protocol perspective, the impact to an application of not having the "Request History" must be described. Applicability guidelines to be addressed by applications using this capability must be provided as part of the solution to these requirements. 3) GENERATION-req: "Request History" information is generated when the request is retargeted. 3.1) In some scenarios, it might be possible for more than one instance of retargeting to occur within the same Proxy. A proxy should also generate Request History information for the 'internal retargeting'. 3.2) An entity (UA or proxy) retargeting in response to a redirect or REFER should include any Request History information from the redirect/REFER in the new request. 4) ISSUER-req: "Request History" information can be generated by a UA or proxy. It can be passed in both requests and responses. 5) CONTENT-req: The "Request History" information for each occurrence of retargeting, shall include the following: 5.1) The new URI or address to which the request is in the process of being retargeted, 5.2) The URI or address from which the request was retargeted, 5.3) The reason for the Request-URI or address modification, 5.4) Chronological ordering of the Request History information. Barnes Expires January 8, 2005 [Page 5]
SIP Request History Information July 8, 2004 6) REQUEST-VALIDITY-req: Request-History is applicable to requests not sent within an established dialog. (i.e. INVITE, REGISTER, MESSAGE, and OPTIONS). 7) BACKWARDS-req: Request-History information may be passed from the generating entity backwards towards the UAC. This is needed to enable services that inform the calling party about the dialog establishment attempts. 8) FORWARDS-req: Request-History information may also be included by the generating entity in the request, if it is forwarded onwards. 2.1 Security Requirements The Request History information is being inserted by a network element retargeting a Request, resulting in a slightly different problem than the basic SIP header problem, thus requiring specific consideration. It is recognized that these security requirements can be generalized to a basic requirement of being able to secure information that is inserted by proxies. The potential security problems include the following: 1) A rogue application could insert a bogus Request History entry either by adding an additional entry as a result of retargeting or entering invalid information. 2) A rogue application could re-arrange the Request History information to change the nature of the end application or to mislead the receiver of the information. Thus, a security solution for "Request History" must meet the following requirements: 1) SEC-req-1: The entity receiving the Request History must be able to determine whether any of the previously added Request History content has been altered. 2) SEC-req-2: The ordering of the Request History information must be preserved at each instance of retargeting. 3) SEC-req-3: The entity receiving the information conveyed by the Request History must be able to authenticate the source of the information. 4) SEC-req-4: To ensure the confidentiality of the Request History information, only entities which process the request should have visibility to the information. Barnes Expires January 8, 2005 [Page 6]
SIP Request History Information July 8, 2004 It should be noted that these security requirements apply to any entity making use of the Request History information, either by retargeting and capturing the information, or as an application making use of the information received in either a Request or Response. 2.2 Privacy Requirements Since the Request URI that is captured could inadvertently reveal information about the originator, there are general privacy requirements that MUST be met: 1) PRIV-req-1: The entity retargeting the Request must ensure that it maintains the network-provided privacy (as described in [RFC3323]) associated with the Request as it is retargeted. 2) PRIV-req-2: The entity receiving the Request History must maintain the privacy associated with the information. In addition, local policy at a proxy may identify privacy requirements associated with the Request URI being captured in the Request History information. 3) PRIV-req-3: Request History information subject to privacy requirements shall not be included in outgoing messages unless it is protected as described in [RFC3323]. 3. Request History Information Description The fundamental functionality provided by the request history information is the ability to inform proxies and UAs involved in processing a request about the history or progress of that request [CAPABILITY-req]. The solution is to capture the Request-URIs as a request is forwarded in a new header for SIP messages: History-Info [CONTENT-req]. This allows for the capturing of the history of a request that would be lost with the normal SIP processing involved in the subsequent forwarding of the request. This solution proposes no changes in the fundamental determination of request targets or in the request forwarding as defined in sections 16.5 and 16.6 of the SIP protocol specification [RFC3261]. The History-Info header can appear in any request not associated with an established dialog, which includes INVITE, REGISTER, MESSAGE, REFER and OPTIONS [REQUEST-VALIDITY-req] and any valid response to these requests.[ISSUER-req] Barnes Expires January 8, 2005 [Page 7]
SIP Request History Information July 8, 2004 The History-Info header is added to a Request when a new request is created by a UAC or Proxy, or when the target of a request is changed. The term 'retarget' is introduced to refer to this changing of the target of a request and the subsequent forwarding of that request. It should be noted that retargeting only occurs when the Request-URI indicates a domain for which the processing entity is responsible. In terms of the SIP protocol, the processing associated with retargeting is described in sections 16.5, and 16.6 of [RFC3261]. As described in section 16.5 of [RFC3261], it is possible for the target of a request to be changed by the same proxy multiple times (referred to as 'internal retargeting' in section 2), as the proxy MAY add targets to the target set after beginning Request Forwarding. Section 16.6 of [RFC3261] describes Request Forwarding. It is during this process of Request Forwarding, that the History Information is captured as an optional, additional header field. Thus, the addition of the History-Info header does not impact fundamental SIP Request Forwarding. An entity (UA or proxy) changing the target of a request in response to a redirect or REFER SHOULD also propagate any History-Info header from the initial Request in the new request [GENERATION-req, FORWARDS-req]. 3.1 Optionality of History-Info The History-Info header is optional in that neither UAs nor Proxies are required to support it. A new Supported header, Histinfo, is included in the Request to indicate whether the History-Info header is returned in Responses [BACKWARDS-req]. In addition to the Histinfo Supported header, local policy determines whether or not the header is added to any request, or for a specific Request-URI, being retargeted. It is possible that this could restrict the applicability of services which make use of the Request History Information to be limited to retargeting within domain(s) controlled by the same local policy, or between domain(s) which negotiate policies with other domains to ensure support of the given policy, or services for which "complete" History Information isn't required to provide the service. [OPTIONALITY-req] All applications making use of the History-info header MUST clearly define the impact of the information not being available and specify the processing of such a request. 3.2 Securing History-Info This draft defines a new header for SIP. The draft RECOMMENDs the use of TLS as a mandatory mechanism to ensure the overall confidentiality of the History-Info headers [SEC-req-4]. This results in History-Info having at least the same level of security as other headers in SIP which are inserted by intermediaries. With the level of security provided by TLS [SEC-req-3], the information in the History-Info header can thus be evaluated to determine if information has been removed by evaluating the indices for gaps [SEC-req-1, SEC-req-2]. Barnes Expires January 8, 2005 [Page 8]
SIP Request History Information July 8, 2004 It would be up to the application to define whether it can make use of the information in the case of missing entries. A more robust security solution would need to consider the aspects of the problem that are different than the hop by hop security problem solved by TLS, as each hop is not required to add the History-Info header. History-Info also introduces a slightly different problem than the basic SIP header or Identity [SIPATHID] problems, which is focused on securing the information in the initial request end to end. The History-Info header is being inserted by an entity as it targets and forwards a Request, thus the requirements for the security solution are similar to the Via and Record-Route headers. For the History-Info header, the general requirement is to secure a header that is inserted by an intermediary and then subsequently referenced, by other intermediaries to build the next header entry, or by an end application using the information to provide a service. Thus, the general requirement for a more robust security solution for SIP takes the form of a middle to middle and middle to end security solution, which is addressed in a separate document [SIPIISEC]. The use of the middle-to-end security solution discussed in [SIPIISEC] allows the integrity of the History-Info to be ascertained as it traverses the intermediaries. Thus, including the History-Info header in SIP Requests and securing in this manner would add an additional level of security end to end, assuring the initiator of a Request that it has indeed reached the intended recipient. 3.3 Ensuring the Privacy of History-Info Since the History-Info header can inadvertently reveal information about the requestor as described in [RFC3323], the Privacy header SHOULD be used to determine whether an intermediary can include the History-Info header in a Request that it receives and forwards [PRIV- req-2] or that it retargets [PRIV-req-1]. Thus, the History-Info header SHOULD not be included in Requests where the requestor has indicated a priv-value of Session or Header level privacy. In addition, the History-Info header can reveal general routing information, which may be viewed by a specific intermediary or network, to be subject to privacy restrictions. Thus, local policy MAY also be used to determine whether to include the History-Info header at all, whether to capture a specific Request-URI in the header, or whether it be included only in the Request as it is retargeted within a specific domain. [PRIV-req-3] This is accomplished by adding a new priv-value to the Privacy header [RFC 3323] indicating whether any or a specific History-Info header(s) SHOULD be forwarded. Barnes Expires January 8, 2005 [Page 9]
SIP Request History Information July 8, 2004 It is recognized that satisfying the privacy requirements can impact the functionality of this solution by overriding the request to generate the information. As with the optionality and security requirements, applications making use of History-Info SHOULD address any impact this may have. 4 Request History Information Protocol Details This section contains the details and usage of the proposed new SIP protocol elements. It also discusses the security aspects of the solution. 4.1 Protocol Structure of History-Info History-Info is a header field as defined by [RFC3261]. It is an optional header field and MAY appear in any request or response not associated with a dialog or which starts a dialog. For example, History-Info MAY appear in INVITE, REGISTER, MESSAGE, REFER and OPTIONS and any valid responses, plus NOTIFY requests which initiate a dialog. The History-Info header carries the following information, with the mandatory parameters REQUIRED when the header is included a request or response: o Targeted-to-URI (hi-targeted-to-uri): A mandatory parameter for capturing the Request URI for the specific Request as it is forwarded. o Index (hi-index): A mandatory parameter for History-Info reflecting the chronological order of the information, indexed to also reflect the forking and nesting of requests. The format for this parameter is a string of digits, separated by dots to indicate the number of forward hops and retargets. This results in a tree representation of the history of the request, with the lowest level index reflecting a branch of the tree. By including the index and securing the header, the ordering of the History- info headers in the request is assured.[SEC-req-2] In addition, applications MAY extract a variety of metrics (total number of retargets, total number of retargets from a specific branch, etc.) based upon the index values. o Reason: An optional parameter for History-info, reflected in the History-Info header by including the Reason Header [RFC3326] escaped in the Request URI being retargeted. A reason is not included for a Request URI when it is first added in a History- info header, but rather is added when that particular Request- URI is retargeted. Note, that this does appear to complicate the security problem, however, retargeting only occurs when the Barnes Expires January 8, 2005 [Page 10]
SIP Request History Information July 8, 2004 Request-URI indicates a domain for which the processing entity is responsible, thus it would be the same processing entity that initially added the Request-URI to the header that would be updating it with the Reason. o Privacy: An optional parameter for History-info, reflected in the History-Info header by including the Privacy Header [RFC3323] with a priv-value of "history" escaped in the Request URI or by adding the Privacy header with a priv-value of "history" to the Request. The use of the Privacy Header with a priv-value of "history" indicates whether a specific or all History-Info headers SHOULD NOT be forwarded. o Extension (hi-extension): An optional parameter to allow for future optional extensions. As per the [RFC3261], any implementation not understanding an extension SHOULD ignore it. The following summarizes the syntax of the History-Info header, based upon the standard SIP syntax [RFC3261]: History-Info = "History-Info" HCOLON hist-info *(COMMA hist-info) hist-info = hi-targeted-to-uri *( SEMI hi-param ) hi-targeted-to-uri= name-addr hi-param = hi-index / hi-extension hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT) hi-extension = generic-param This document adds the following entry to Table 2 of [RFC3261]. Additions to this table are also provided for extension methods at the time of publication of this document. This is provided as a courtesy to the reader and is not normative in any way. Header field where proxy ACK BYE CAN INV OPT REG MSG ------------ ----- ----- --- --- --- --- --- --- --- History-Info amdr - - - o o o o SUB NOT REF INF UPD PRA PUB --- --- --- --- --- --- --- History-Info amdr - o o - - - - Barnes Expires January 8, 2005 [Page 11]
SIP Request History Information July 8, 2004 4.2 Protocol Examples The following provides some examples of the History-Info header. Note that the backslash, CRLF, and spacing between the fields in the examples below are for readability purposes only. History-Info:<sip:UserA@ims.example.com?Reason=SIP;\ cause=302;text="Moved Temporarily">; index=1; foo=bar History-Info: <sip:UserA@ims.example.com?Reason=SIP;\ cause=302; text="Moved Temporarily">; index=1.1, <sip:UserB@example.com?Privacy=history&Reason=SIP;cause=486;\ text="Busy Here">;index=1.2, <sip:45432@vm.example.com>;index=1.3 4.3 Protocol usage This section describes the processing specific to UAs and Proxies for the History-Info header, the Histinfo option tag and the priv-value of "history". As discussed in section 1, the fundamental objective is to capture the target Request-URIs as a request is forwarded. This allows for the capturing of the history of a request that would be lost due to subsequent (re)targeting and forwarding. To accomplish this for the entire history of a request, either the UAC must capture the Request-URI in the initial request or a proxy must add History- Info headers for both the Request-URI in the initial request and the target Request-URI as the request is forwarded. The basic processing is for each entity forwarding a request to add a History-Info header for the target Request-URI, updating the index and adding the Reason as appropriate for any retargeted Request-URI. 4.3.1 UAC Behavior The UAC SHOULD include the Histinfo option tag in the Supported header in any request not associated with an established dialog for which the UAC would like the History-Info in the Response. In addition, the UAC SHOULD initiate the capturing of the History Information by adding a History-Info header using the Request-URI of the request as the hi-targeted-to-uri and initializing the index to the RECOMMENDED value of 1 in the History-Info header. In the case where the request is routed to a redirect server and the UAC receives a 3xx response with a Contact header, the UAC MAY maintain the previous History-Info entry(-ies) in the request. A new History-Info entry MAY then be added for the URI from the Contact header (which will become the new Request-URI). In this case, the Barnes Expires January 8, 2005 [Page 12]
SIP Request History Information July 8, 2004 index is created by reading and incrementing the value of the index from the previous history entry, thus following the same rules as those prescribed for a proxy in retargeting, described in section 4.3.3.1.3. An example of this scenario can be found in Appendix D. A UAC that does not want History-Info headers added due to privacy considerations SHOULD include a Privacy header with a priv-value(s) of "session", "header" or "history" in the request. The processing of the History-Info header received in the Response is application specific and outside the scope of this draft. However, the validity of the information SHOULD be ensured prior to any application usage. For example, the entries MAY be evaluated to determine gaps in indices, which could indicate that an entry has been maliciously removed or removed for privacy reasons. Either way, an application MAY want to be notified of potentially missing information. 4.3.2 UAS Behavior The processing of the History-Info header by a UAS in a Request depends upon local policy and specific applications at the UAS which might make use of the information. Prior to any application usage of the information, the validity SHOULD be ascertained. For example, the entries MAY be evaluated to determine gaps in indices, which could indicate that an entry has been maliciously removed or removed for privacy reasons. Either way, an application MAY want to be notified of potentially missing information. If the Histinfo option tag is received in a request, the UAS should include any History-Info received in the request in the subsequent response. 4.3.3 Proxy Behavior The inclusion of the History-Info header in a Request does not alter the fundamental processing of proxies for determining request targets as defined in section 16.5 of [RFC3261]. Whether a proxy adds the the History-Info header as it forwards a Request depends upon the following considerations: 1. Whether the Request contains the Histinfo option tag in the Supported header. 2. Whether the proxy supports the History-Info header. 3. Whether the Request contains a Privacy header with a priv- value of "session", "header" or "history". 4. Whether any History-Info header added for a proxy/domain should go outside that domain. An example being the use of Barnes Expires January 8, 2005 [Page 13]
SIP Request History Information July 8, 2004 the History-Info header within the specific domain in which it is retargeted, however, policies (for privacy, user and network security, etc.) prohibit the exposure of that information outside that domain. A proxy MAY insert the Privacy header with a priv-value of "history" to indicate this. An example of such an application is provided in Appendix C. 5. Whether the History-Info header is added for a specific Request URI due to local privacy policy considerations. A proxy MAY add the Privacy header with a priv-value of "history" associated with the specific hi-targeted-to-uri. An example policy would be a proxy that only adds the History-Info header if the Histinfo option tag is in the Supported header. Other proxies may have a policy that they always add the header, but never forward it outside a particular domain, accomplishing this by adding a Privacy header with a priv-value of "history" to allow the information to be collected for internal retargeting only. Each application making use of the History-Info header SHOULD address the impacts of the local policies on the specific application (e.g. what specification of local policy is optimally required for a specific application and any potential limitations imposed by local policy decisions). Consistent with basic SIP processing of optional headers, proxies SHOULD maintain History-Info headers, received in messages being forwarded, independent of whether local policy supports History-Info. The specific processing by proxies for adding the History-Info headers in Requests and Responses is described in detail in the following sections. 4.3.3.1 Adding the History-Info header to Requests Upon evaluation of the considerations under which the History-Info header is to be included in requests (e.g. no Privacy header overriding inclusion, local policy supports, etc.), detailed in section 4.3.3, a proxy SHOULD add a History-Info header as it forwards a Request. Section 16.6 of [4] defines the steps to be followed as the proxy forwards a Request. Step 5 prescribes the addition of optional headers. Although, this would seem the appropriate step for adding the History-info header, the interaction with Step 6 "Postprocess routing information" and the impact of a strict route in the Route header could result in the Request-URI being changed, thus adding the History-info header between steps 8 (adding Via header) and 9 (adding Content-Length) is RECOMMENDED. Note, that in the case of loose routing, the Request-URI does not change during the forwarding of a Request, thus the capturing of Barnes Expires January 8, 2005 [Page 14]
SIP Request History Information July 8, 2004 History-Info for such a request would result in duplicate Request- URIs with different indices. The History-Info header SHOULD be added following any History-Info header received in the request being forwarded. Additionally, if a request is received that doesn't include a History-Info header, the proxy MAY add an additional History-Info header preceding the one being added for the current request being forwarded. The index for this entry is RECOMMENDED to start at 1. The following subsections define the details of creating the information associated with and in the History-Info header. 4.3.3.1.1 Privacy in the History-Info header If the proxy's local policies, per consideration 4 in section 4.3.3, indicate that this History-Info entry and any entries added due to subsequent retargeting should not be forwarded beyond the domain for which this intermediary is responsible, then a Privacy header with a priv-value of "history" SHOULD be added to the request, if there is not already one, provided the request is being forwarded to a specific URI associated with the domain(s) for which this entity is responsible. If a request is being forwarded to a Request URI associated with a domain for which the proxy is not responsible, the proxy needs to determine if there are any entries to be removed prior to forwarding. Any headers associated with the domain(s) for which this proxy is responsible SHOULD be removed prior to forwarding. If through local policy, there is knowledge of privacy associated with a specific URI being captured as the hi-targeted-to-uri, a Privacy header with a priv-value of "history" SHOULD be associated with this specific URI as the request is forwarded, if it is being forwarded to a Request URI associated with a domain for which the processing entity is responsible. If a request is being forwarded to a Request URI, for which the processing entity is not responsible, the proxy needs to determine if there are any entries, that need to be removed prior to forwarding. The proxy needs to determine if any of the specific URIs that have been captured in the History-Info entries, associated with the domain(s) for which it is responsible, have a priv-value of "history". Each of these header entries SHOULD be removed from the Request prior to forwarding. 4.3.3.1.2 Reason in the History-Info header For retargets that are the result of an explicit SIP response, the SIP Response Code that triggered the retargeting MUST be included in the Reason header field of the Request URI that has been retargeted. This should occur prior to the forwarding of the request, as it Barnes Expires January 8, 2005 [Page 15]
SIP Request History Information July 8, 2004 associated with the previous hi-targeted-to-uri, since it reflects the reason why the Request to that specific URI was not successful. For retargets as a result of timeouts or internal events, a Reason MAY be included in the Reason header field of the Request URI that has been retargeted. 4.3.3.1.3 Indexing in the History-Info header In order to maintain ordering and accurately reflect the nesting and retargeting of the request, an index MUST be included along with the Targeted-to-URI being captured. Per the ABNF in section 4.1, the index consists of a dot delimited series of digits (e.g. 1.1.2), with each dot reflecting the number of hops or level of nesting of the request. Within each level, the number reflects the number of peer entities to which the request has been routed. Thus, the indexing results in a logical tree representation for the history of the Request. It is recommended that for each level of indexing, the index start at 1. It is recommended that an increment of 1 is used for advancing to a new branch. For retargets within a proxy, the proxy MUST maintain the current level of nesting by incrementing by 1 the lowest/last digit of the index for each instance of retargeting, thus reflecting the number of retargets (branches) within the proxy. The basic rules for adding the index are summarized as follows: 1. Basic Forwarding: In the case of a Request that is being forwarded, the index is determined by adding another level of indexing since the depth/length of the branch is increasing. To accomplish this, the proxy reads the value from the History-Info header in the received request, if available, and adds another level of indexing by appending the DOT delimiter followed by an initial index for the new level RECOMMENDED to be 1. For example, if the index in the last History-Info header field in the received request is 1.1, this proxy would initialize its index to 1.1.1 and forward the request. 2. Retargeting within a Proxy - 1st instance: For the first instance of retargeting within a Proxy, the calculation of the index follows that prescribed for basic forwarding. 3. Retargeting within a Proxy - subsequent instance: For each subsequent retargeting of a request by the same proxy, another branch is added. With the index for each new branch calculated by incrementing the last/lowest digit at the current level, thus the index in the next request forwarded by this same proxy, following the example above, would be 1.1.2. Barnes Expires January 8, 2005 [Page 16]
SIP Request History Information July 8, 2004 4. Retargeting based upon a Response: In the case of retargeting due to a specific response (e.g. 302), the index would be calculated per rule 3. That is, the lowest/last digit of the index is incremented (i.e. a new branch is created), with the increment RECOMMENDED to be 1. For example, if the index in the History-Info header of the received request was 1.2, then the index in the History-Info header field for the new hi-targeted-to-URI would be 1.3. 5. Retargeting the request in parallel: If the request forwarding is done in parallel, the index MUST be captured for each forked request per the rules above, with each new Request having a unique index. The only difference in the messaging for this scenario and the messaging produced per basic proxy retargeting in rules 2 and 3 is these forwarded requests do not have History-Info entries associated with their peers. The proxy builds the subsequent response (or request) using the amalgamated information associated with each of those requests and including the header entries in the order indicated by the indexing. Section 4.5 provides an example of a parallel request scenario, highlighting this indexing mechanism. 4.3.3.2 Processing History-Info in Responses A proxy that receives a Request with the Histinfo option tag in the Supported header, and depending upon a local policy supporting the capture of History-Info, SHOULD return captured History-Info in subsequent, provisional and final responses to the Request. It should be noted that local policy considerations, for network and intermediary privacy, MAY restrict the sending of the History-Info headers added by the intermediary in subsequent responses. Thus, in such cases, the proxy MAY remove from these responses the History- Info headers which it inserted in the original forwarded request. 4.3.4 Redirect Server Behavior A redirect server SHOULD NOT add any new History-Info, as that would be done by the entity receiving the 3xx response. However, a redirect server MAY include History-Info in responses by adding any History- Info headers received in a request to a subsequent response. 4.4 Security for History-Info As discussed in Section 1, the security requirements are partially met by recommending the use of TLS (a basic SIP requirement per [RFC3261]) for hop by hop security. In addition, the use of the middle-to-end security solution discussed in [SIPIISEC] allows the Barnes Expires January 8, 2005 [Page 17]
SIP Request History Information July 8, 2004 integrity of the History-Info to be ascertained as it traverses the intermediaries. 4.5 Example Applications using History-Info This scenario highlights an example where the History-Info in the response is primarily of use in not retrying routes that have already been tried by another proxy. Note, that this is just an example and that there may be valid reasons why a Proxy would want to retry the routes and thus, this would likely be a local proxy or even user specific policy. UA 1 sends a call to "Bob" to proxy 1. Proxy 1 forwards the request to Proxy 2. Proxy 2 sends the requests in parallel and tries several places (UA2, UA3 and UA4) before sending a response to Proxy 1 that all the places are busy. Proxy 1, without the History-Info, would try several some of the same places (e.g. UA3) based upon registered contacts for "Bob", before completing at UA5. However, with the History-Info, Proxy 1 determines that UA3 has already received the invite, thus the INVITE goes directly to UA5. Section 4.5.1 provides this same scenario using one of the privacy mechanism, with Proxy2 adding the Privacy header indicating that the History-Info header is not to be propagated outside P2's domain. This scenario highlights the potential functionality lost with the use of "history" privacy in the Privacy header for the entire request and the need for careful consideration on the use of privacy for History- Info. Section 4.5.2 also provides the same scenario using one of the privacy mechanisms, however, due to local policy at Proxy2, only one of the Request-URIs (UA4) in the History-Info contains a priv-value of "history", thus allowing some optimized functionality in the routing of the request, but still maintaining privacy for specific URIs. Additional detailed scenarios are available in the appendix. UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | |-INVITE->| | | | | Supported: Histinfo History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2 | | | | | | | | | |-INVITE>| | | | Barnes Expires January 8, 2005 [Page 18]
SIP Request History Information July 8, 2004 History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>;index=2, <sip:User2@UA2.example.com>;index=2.1 | | | | | | | | | |-----INVITE ---->| | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com>; index=2.2 | | | | | | | | | |-------INVITE------------>| | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User4@UA4.example.com>; index=2.3 /* All Responses from the INVITEs indicate non-success/non- availability*/ | | | | | | | | |<-480 ---| | | | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User2@UA2.example.com?Reason=SIP;\ cause=480;text="RequestTimeout">;index=2.1, <sip:User3@UA3.example.com?Reason=SIP; \ cause=487;text="Request Terminated">; index=2.2, <sip:User4@UA4.example.com?Reason=SIP;\ cause=603;text="Decline">; index=2.3 | | | | | | | /* Upon receipt of the response, P1 determines another route for the INVITE, but finds that it matches a route already attempted (e.g. UA3, thus the INVITE is only forwarded to UA5, where the session is successfully established */ | | | | | | | | |----------------INVITE --------------------->| History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User2@UA2.example.com?Reason=SIP;cause=480;\ text="RequestTimeout">;index=2.1, <sip:User3@UA3.example.com?Reason=SIP;cause=487;\ text="Request Terminated">; index=2.2, <sip:User4@UA4.example.com?Reason=SIP;cause=603;\ text="Decline">; index=2.3 <sip:User5@UA5.example.com>;index=1.1 | | | | | | | | |<-----200 OK---------------------------------| |<--200 OK---| | | | | | | | | | | | | |--ACK --------------------------------------------------->| Barnes Expires January 8, 2005 [Page 19]
SIP Request History Information July 8, 2004 4.5.1 Example with Privacy header for entire request at Proxy2 UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | |-INVITE->| | | | | Supported: Histinfo History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2 | | | | | | | | | |-INVITE>| | | | Privacy: history History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>;index=2, <sip:User2@UA2.example.com>;index=2.1 | | | | | | | | | |-----INVITE ---->| | | Privacy: history History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com>; index=2.2 | | | | | | | | | |-------INVITE------------>| | Privacy: history History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User4@UA4.example.com>; index=2.3 /* All Responses from the INVITEs indicate non-success/non- availability and only the initial, received History-Info entries are NOT returned to P1 due to the Privacy header value.*/ | | | | | | | | |<-480 ---| | | | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2 | | | | | | | /* Upon receipt of the response, P1 determines another route for the INVITE, including UA3 which was attempted by P2, but due to Privacy P1 is not aware of this, so UA3 is re-attempted prior to forwarding the INVITE to UA5, where the session is successfully established */ | | | | | | | | |--------------INVITE ----->| | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com>; index=1.1 | | | | | | | | |<-- 486 -------------------| | | Barnes Expires January 8, 2005 [Page 20]
SIP Request History Information July 8, 2004 History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com>; index=1.1 | | | | | | | | |----------------INVITE --------------------->| History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com?Reason=SIP;cause=486;\ text=Busy Here">;index=1.1, <sip:User5@UA5.example.com>;index=1.2 | | | | | | | | |<-----200 OK---------------------------------| |<--200 OK---| | | | | | | | | | | | | |--ACK --------------------------------------------------->| 4.5.2 Example with Privacy header for specific URI (UA4) at Proxy2 UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | |-INVITE->| | | | | Supported: Histinfo History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2 | | | | | | | | | |-INVITE>| | | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>;index=2, <sip:User2@UA2.example.com>;index=2.1 | | | | | | | | | |-----INVITE ---->| | | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User3@UA3.example.com>; index=2.2 | | | | | | | | | |-------INVITE------------>| | History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User4@UA4.example.com?\ Privacy=history>; index=2.3 /* All Responses from the INVITEs indicate non-success/non- availability. The History-Info associated with UA4 is not returned in the response due to the privacy header associated with that URI */ | | | | | | | | |<-480 ---| | | | | Barnes Expires January 8, 2005 [Page 21]
SIP Request History Information July 8, 2004 History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User2@UA2.example.com?Reason=SIP;\ cause=480;text="RequestTimeout">;index=2.1, <sip:User3@UA3.example.com?Reason=SIP; \ cause=487;text="Request Terminated">; index=2.2, | | | | | | | /* Upon receipt of the response, P1 determines another route for the INVITE, but finds that it matches a route already attempted (e.g. UA3), thus the INVITE is only forwarded to UA5, where the session is successfully established */ | | | | | | | | |----------------INVITE --------------------->| History-Info: <sip:Bob@P1.example.com>;index=1, <sip:Bob@P2.example.com>; index=2, <sip:User2@UA2.example.com?Reason=SIP;cause=480;\ text="RequestTimeout">;index=2.1, <sip:User3@UA3.example.com?Reason=SIP;cause=487;\ text="Request Terminated">; index=2.2, <sip:User5@UA5.example.com>;index=1.1 | | | | | | | | |<-----200 OK---------------------------------| |<--200 OK---| | | | | | | | | | | | | |--ACK --------------------------------------------------->| 5. Application Considerations As seen by the example scenarios in the appendix, History-Info provides a very flexible building block that can be used by intermediaries and UAs for a variety of services. As such, any services making use of History-Info must be designed with the following considerations: 1) History-Info is optional, thus a service should define default behavior for requests and responses not containing History-Info headers. 2) History-Info may be impacted by privacy considerations. Applications requiring History-Info need to be aware that if Header, Session or History level privacy is requested by a UA (or imposed by an intermediary) that History-Info may not be available in a request or response. This would be addressed by an application in the same manner as the previous consideration by ensuring there is reasonable default behavior should the information not be available. 3) History-Info may be impacted by local policy. Each application making use of the History-Info header SHOULD address the impacts of the local policies on the specific application (e.g. what specification of local policy is optimally required for a Barnes Expires January 8, 2005 [Page 22]
SIP Request History Information July 8, 2004 specific application and any potential limitations imposed by local policy decisions). Note, that this is related to the optionality and privacy considerations identified in 1 and 2 above, but goes beyond that. For example, due to the optionality and privacy considerations, an entity may receive only partial History-Info entries; will this suffice? Note, that this would be a limitation for debugging purposes, but might be perfectly satisfactory for some models whereby only the information from a specific intermediary is required. 4) The security associated with the Request History Information is optional. Whether there is security applied to the entries depends upon local policy. The impact of lack of having the information compromised depends upon the nature of the specific application (e.g. is the information something that appears on a display or is it processed by automata which could have negative impacts on the subsequent processing of a request?). It is suggested that the impact of an intermediary not supporting the security recommendations should be evaluated by the application to ensure that the impacts have been sufficiently addressed by the application. 6. Security Considerations This draft provides a proposal in sections 3.2 and 4.4 for addressing the Security requirements identified in section 2.1 by mandating the use of TLS between entities. With TLS, History-Info headers are no less, nor no more, secure than other SIP headers, which generally have even more impact on the subsequent processing of SIP sessions than the History-Info header. A more robust security solution, which would secure headers added by proxies, SHOULD be used for History- Info implementations once there is a solution to the requirements identified in [SIPIISEC]. 7. IANA Considerations (Note to RFC Editor: Please fill in all occurrences of XXXX in this section with the RFC number of this specification). 7.1 Registration of new SIP History-Info header This document defines a new SIP header field name: History-Info and a new option tag: Histinfo. The following changes should be made to http:///www.iana.org/assignments/sip-parameters The following row should be added to the header field section: Header Name Compact Form Reference Barnes Expires January 8, 2005 [Page 23]
SIP Request History Information July 8, 2004 ----------- ------------ --------- History-Info none [RFCXXXX] The following should be added to the Options Tags section: Name Description Reference ---- ----------- --------- Histinfo When used with the Supported header, [RFCXXXX] this option tag indicates support for the History Information to be captured for requests and returned in subsequent responses. This tag is not used in a Proxy-Require or Require header field since support of History-Info is optional. 7.2 Registration of "history" for SIP Privacy header This document defines a new priv-value for the SIP Privacy header: history The following changes should be made to http://www.iana.org/assignments/sip-priv-values The following should be added to the registration for the SIP Privacy header: Name Description Registrant Reference ---- ----------- ---------- --------- history Privacy requested for Mary Barnes [RFCXXXX] History-Info header(s) mary.barnes@nortelnetworks.com Changes since last version Changes from the û02 to the û03 version: o Editorial changes: Updating to the new template to reflect new IPR guidelines, ensuring that the normative text is complete and accurate in section 4.1, removing "Editor's Notes", etc. o Section 4.5: Fixed error in cause (408 -> 480). o Examples: changed the domain to "example.com", IP addresses to the 192.0.2.0/24 range, changed occurrences of "Reason:" to "Reason=", added use of Privacy header to examples. o Added text to reflect WG consensus on Issue-1: Privacy indication for History-Info entries. Proposed an extension to the priv-values defined in RFC 3323 in abstract and section 3.3, impacting the protocol structure in section 4.1 and Barnes Expires January 8, 2005 [Page 24]
SIP Request History Information July 8, 2004 processing in 4.3.3 (and 4.3.3.1 and 4.3.3.2). In addition, the new priv-value needs to be registered with IANA, per section 7. o Removed Open Issues section. For Issue-2, there was not WG consensus to define an algorithm for bounding the number of History-Info entries, but rather that is left as an implementation decision. o Updated Security discussions to reflect WG consensus that TLS is mandatory and sufficient for general History-Info implementation. The e2m and m2m security solutions can be applied to History-Info when they become available to provide a more robust SIP solution. o Section 4.1: Added additional text to ensure that all the information in the History-Info header is appropriately and normatively described (in text). o Added text in section 4.3.1 and an example to the appendices to address the UAC having added multiple History-Info headers for the case where the 3xx response goes back to the UAC and it's the UAC that retargets the INVITE request. o Clarified the addition of the Reason header in section 4.3.3.1.2. o Further delineated the basic rules in section 4.3.3.1.3 for calculating the index for various scenarios, as this was still causing some confusion. Changes from the û01 to the û02 version: o Merged the SIPPING WG requirements draft into this document. Note that this increments the section references in the remainder of the document by 2 (and by 3 for Security and IANA considerations due to new section added). Also, removed redirect server from ISSUER-req since the solution identified this as not being required (or desirable). o Added an explicit privacy requirement (PRIV-req-3) for the proxy's role in recognizing and maintaining privacy associated with a Request-URI being captured in History-Info due to local policy. (Note, that the text was already there, it just wasn't highlighted as an explicit requirement). o Clarified the use of CRLF and spacing in the example headers in section 4.2. o Removed the compact form for the header since unknown headers with multiple entries would not be recognized (i.e. this may cause parsing problems). o Added a summary of Application Considerations to address concerns about the optional usage of History-Info. o Converted the references from numbers to labels to avoid the continual problem of renumbering. o Minor editorial changes (per NITS highlighted by Rohan and Eric and some minor rewording for clarity). Barnes Expires January 8, 2005 [Page 25]
SIP Request History Information July 8, 2004 Changes from the û00 to the û01 version: o Attempted to be more explicit about the fundamental processing associated with the header. Removed definitions of new terms, only referencing the terms from the requirements in the context of the fundamental SIP processing implied by the terms. o Attempted to clarify the Index and the related processing. o Added more detail addressing the privacy requirements. o Added a bit more detail on security. The security solution remains in a separate document and this document will need updating once that is completed. o Updated the examples (in section 2.5 and appendix) and clarified the definition and the maintenance of the Index in sections 2.1 and 2.3.3.1. o Clarified the Reason description in section 2.1. There had been an error in the description of the processing that was a remnant of the change to include only a single URI for each History-Info header. o Miscellaneous editorial changes (i.e. HistInfo -> Histinfo, etc.) Changes from individual draft-barnes-sipping-history-info-02 to the û 00 WG version: o Updated references and added reference to Security solution draft. o Removed appendix D which included background on analysis of solution options. o Cleaned up the document format per rfc2223bis. o Strengthened the inclusion of the INDEX as a MUST (per discussion at IETF-56). o Added text around the capturing of the Reason (SHOULD be captured for SIP responses and MAY be captured for other things such as timeouts). o Clarified the response processing 2.3.3.2 to include provisional responses and the sending of a 183 to convey History-Info. o Added section 2.3.4 to address Redirect Server behavior. Normative References [RFC3261] J. Rosenberg et al, "SIP: Session initiation protocol," RFC 3261, June, 2002. [RFC3326] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field for the Session Initiation Protocol", RFC 3326, December, 2002. Barnes Expires January 8, 2005 [Page 26]
SIP Request History Information July 8, 2004 [RFC3323] J. Peterson, "A Privacy Mechanism for the Session Initiation Protocol (SIP)", RFC 3323, November, 2002. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [SIPIISEC] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October, 2003. Informational References [SIPSVCEX] A. Johnson, "SIP Service Examples", draft-ietf-sipping- service-examples-05.txt, November, 2002. [SIPATHID] J. Peterson, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft-ietf-sip- identity-01.txt, February, 2003. [RFC3665] A. Johnson et al, "SIP Basic Call Flow Examples", RFC 3665, BCP 75, December, 2003. Acknowledgements The editor would like to acknowledge the constructive feedback provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell, Nir Chen, Francois Audet, Palash Jain, Brian Stucker, Norma Ng, Anthony Brown, Jayshree Bharatia, Jonathan Rosenberg, Eric Burger and Martin Dolly. The editor would like to acknowledge the significant input from Rohan Mahy on some of the normative aspects of the ABNF, particularly around the need for and format of the index and around the enhanced SIP security aspects enabled by this draft. Contributors' Addresses Cullen, Mark and Jon contributed to the development of the initial requirements. Cullen and Mark provided substantial input in the form of email discussion in the development of the initial version of the individual solution document. Barnes Expires January 8, 2005 [Page 27]
SIP Request History Information July 8, 2004 Cullen Jennings Cisco Systems 170 West Tasman Dr MS: SJC-21/3 Tel: +1 408 527 9132 Email: fluffy@cisco.com Jon Peterson NeuStar, Inc. 1800 Sutter Street, Suite 570 Concord, CA 94520 USA Phone: +1 925-363-8720 EMail: Jon.Peterson@NeuStar.biz Mark Watson Nortel Networks (UK) Maidenhead Office Park (Bray House) Westacott Way Maidenhead, Berkshire England Tel: +44 (0)1628-434456 Email: mwatson@nortelnetworks.com Author's Address Mary Barnes Nortel Networks 2380 Performance Drive Richardson, TX USA Phone: 1-972-684-5432 Email: mary.barnes@nortelnetworks.com Appendix A Forking Scenarios A.1 Sequentially forking (History-Info in Response) This scenario highlights an example where the History-Info in the response is useful to an application or user that originated the request. Barnes Expires January 8, 2005 [Page 28]
SIP Request History Information July 8, 2004 UA 1 sends a call to "Bob" via proxy 1. Proxy 1 sequentially tries several places (UA2, UA3 and UA4) unsuccessfully before sending a response to UA1. This scenario is provided to show that by providing the History-Info to UA1, the end user or an application at UA1 could make a decision on how best to attempt finding "Bob". Without this mechanism UA1 might well attempt UA3 (and thus UA4) and then re-attempt UA4 on a third manual attempt at reaching "Bob". With this mechanism, either the end user or application could know that "Bob" is busy on his home phone and is physically not in the office. If there were an alternative address for "Bob" known to this end user or application, that hasn't been attempted, then either the application or the end user could attempt that. The intent here is to highlight an example of the flexibility of this mechanism that enables applications well beyond SIP as it is certainly well beyond the scope of this draft to prescribe detailed applications. UA1 Proxy1 UA2 UA3 UA4 | | | | | |--INVITE -->| | | | | | | | | | |--INVITE -------->| | | |<--100 -----| | | | | |<-302 ------------| | | | | | | | | |-------INVITE ------------>| | | | | | | | |<-------180 ---------------| | |<---180 ----| | | | | . . |-------INVITE------------->| | | | timeout | | | | | | | | | |------INVITE ---------------------->| |<--100 -----| | | | | | | | | | |<-486 ------------------------------| | | | | | | |-- ACK ---------------------------->| |<--486------| | | | | | | | | |--ACK ----->| | | | | | | | | [Editor's Note: Need to detail the message flow.] Barnes Expires January 8, 2005 [Page 29]
SIP Request History Information July 8, 2004 A.2 Sequential Forking (with Success) This scenario highlights an example where the History-Info in the request is primarily of use in not retrying routes that have already been tried by another proxy. Note, that this is just an example and that there may be valid reasons why a Proxy would want to retry the routes and thus, this would like be a local proxy or even user specific policy. UA 1 sends a call to "Bob" to proxy 1. Proxy 1 sequentially tries several places (UA2, UA3 and UA4) before retargeting the call to Proxy 2. Proxy 2, without the History-Info, would try several of the same places (UA3 and UA4)based upon registered contacts for "Bob", before completing at UA5. However, with the History-Info, Proxy 2 determines that UA3 and UA4 have already received the invite, thus the INVITE goes directly to UA5. UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5 | | | | | | | |--INVITE -->| | | | | | | | | | | | | | |--INVITE -------->| | | | |<--100 -----| | | | | | | |<-302 ------------| | | | | | | | | | | | |-------INVITE ------------>| | | | | | | | | | | |<-------180 ---------------| | | |<---180 ----| | | | | | | . . |-------INVITE------------->| | | | | timeout | | | | | | | | | | | | |------INVITE ---------------------->| | |<--100 -----| | | | | | | |<-302 ------------------------------| | | | | | | | | | |-INVITE->| | | | | | | | | | | | | | | | | | | | | |------INVITE --------------------->| | | | | | | | | | |<-----200 OK---------------------->| |<--200 OK-------------| | | | | Barnes Expires January 8, 2005 [Page 30]
SIP Request History Information July 8, 2004 | | | | | | | |--ACK --------------------------------------------------->| [Editor's Note: Need to add the details of the messages here.] Appendix B Voicemail This scenario highlights an example where the History-Info in the request is primarily of use by an edge service (e.g. Voicemail Server). It should be noted that this isn't intended to be a complete specification for this specific edge service as it is quite likely that additional information is need by the edge service. History-Info is just one building block that this service makes use of. UA 1 called UA A which had been forwarded to UA B which forwarded to a UA VM (voicemail server). Based upon the retargeted URIs and Reasons (and other information) in the INVITE, the VM server makes a policy decision about what mailbox to use, which greeting to play etc. UA1 Proxy UA-A UA-B UA-VM | | | | | |--INVITE F1-->| | | | | | | | | | |--INVITE F2-->| | | |<--100 F3-----| | | | | |<-302 F4------| | | | | | | | | |--------INVITE F5---------->| | | | | | | | |<--------180 F6-------------| | |<---180 F7----| | | | | . . . | | | | | |------retransmit INVITE---->| | | . . . | | | | | | (timeout) | | | | | | | | |-------INVITE F8---------------------->| | | | | | | |<-200 F9-------------------------------| | | | | | |<-200 F10-----| | | | | | | | | |--ACK F11-------------------------------------------->| Message Details Barnes Expires January 8, 2005 [Page 31]
SIP Request History Information July 8, 2004 INVITE F1 UA1->Proxy INVITE sip:UserA@example.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: BigGuy <sip:User1@here.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=UserA 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 192.0.2.3 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 /*Client for UA1 prepares to receive data on port 49170 from the network. */ INVITE F2 Proxy->UA-A INVITE sip:UserA@ims.example.com SIP/2.0 Via: SIP/2.0/UDPims.example.com:5060;branch=1 Via: SIP/2.0/UDP here.com:5060 Record-Route: <sip:UserA@example.com> From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com CSeq: 1 INVITE History-Info: <sip:UserA@ims.example.com>; index=1 Contact: BigGuy <sip:User1@here.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=UserA 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 192.0.2.3 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 100 Trying F3 Proxy->UA1 SIP/2.0 100 Trying Barnes Expires January 8, 2005 [Page 32]
SIP Request History Information July 8, 2004 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 302 Moved Temporarily F4 UserA->Proxy SIP/2.0 302 Moved Temporarily Via: SIP/2.0/UDP ims.example.com:5060;branch=1 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com>;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: <sip:UserB@example.com> Content-Length: 0 INVITE F5 Proxy-> UA-B INVITE sip:UserB@example.com SIP/2.0 Via: SIP/2.0/UDP ims.example.com:5060;branch=2 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com History-Info: <sip:UserA@ims.example.com?Reason=SIP;\ cause=302; text="Moved Temporarily">; index=1, <sip:UserB@example.com>;index=2 CSeq: 1 INVITE Contact: BigGuy <sip:User1@here.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=User1 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 192.0.2.3 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 180 Ringing F6 UA-B ->Proxy SIP/2.0 180 Ringing Via: SIP/2.0/UDP there.com:5060 Barnes Expires January 8, 2005 [Page 33]
SIP Request History Information July 8, 2004 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com>;tag=5 Call-ID: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 180 Ringing F7 Proxy-> UA1 SIP/2.0 180 Ringing SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com CSeq: 1 INVITE Content-Length: 0 /* User B is not available. INVITE is sent multiple times until it times out. */ /* The proxy forwards the INVITE to UA-VM after adding the additional History Information entry. */ INVITE F8 Proxy-> UA-VM INVITE sip:VM@example.com SIP/2.0 Via: SIP/2.0/UDP ims.example.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com> Call-Id: 12345600@here.com History-Info:<sip:UserA@ims.example.com?Reason=SIP;\ cause=302; text="Moved Temporarily">;index=1, <sip:UserB@example.com?Reason=SIP;cause=480;\ text="Temporarily Unavailable" >;index=2, <sip:VM@example.com>;index=3 CSeq: 1 INVITE Contact: BigGuy <sip:User1@here.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=User1 2890844526 2890844526 IN IP4 client.here.com s=Session SDP c=IN IP4 192.0.2.3 t=0 0 m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000 Barnes Expires January 8, 2005 [Page 34]
SIP Request History Information July 8, 2004 200 OK F9 SIP/2.0 200 OK UA-VM->Proxy Via: SIP/2.0/UDP ims.example.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com>;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: TheVoiceMail <sip:VM@example.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=UserA 2890844527 2890844527 IN IP4 vm.example.com s=Session SDP c=IN IP4 192.0.2.4 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 200 OK F10 Proxy->UA1 SIP/2.0 200 OK Via: SIP/2.0/UDP ims.example.com:5060;branch=3 Via: SIP/2.0/UDP here.com:5060 From: BigGuy <sip:User1@here.com> To: LittleGuy <sip:UserA@example.com>;tag=3 Call-Id: 12345600@here.com CSeq: 1 INVITE Contact: TheVoiceMail <sip:VM@example.com> Content-Type: application/sdp Content-Length: <appropriate value> v=0 o=UserA 2890844527 2890844527 IN IP4 vm.example.com s=Session SDP c=IN IP4 192.0.2.4 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 ACK F11 UA1-> UA-VM ACK sip:VM@example.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 Barnes Expires January 8, 2005 [Page 35]
SIP Request History Information July 8, 2004 From: BigGuy <sip:User1@here.com> To: LittleGuy<sip:UserA@example.com>;tag=3 Call-Id: 12345600@here.com CSeq: 1 ACK Content-Length: 0 /* RTP streams are established between UA1 and UA-VM. UA-VM starts announcement for UA1 */ Appendix C Automatic Call Distribution Example This scenario highlights an example of an Automatic Call Distribution service, where the agents are divided into groups based upon the type of customers they handle. In this example, the Gold customers are given higher priority than Silver customers, so a Gold call would get serviced even if all the agents servicing the Gold group (ACDGRP1) were busy, by retargeting the request to the Silver Group. Upon receipt of the call at the agent assigned to handle the incoming call, based upon the History-Info header in the message, the application at the agent can provide an indication that this is a Gold call, from how many groups it might have overflowed before reaching the agent, etc. and thus can be handled appropriately by the agent. For scenarios whereby calls might overflow from the Silver to the Gold, clearly the alternate group identification, internal routing or actual agent that handles the call SHOULD not be sent to UA1, thus for this scenario, one would expect that the Proxy would not support the sending of the History-Info in the response, even if requested by the calling UA. As with the other examples, this is not prescriptive of how one would do this type of service but an example of a subset of processing that might be associated with such a service. In addition, this example is not addressing any aspects of Agent availability, which might also be done via a SIP interface. UA1 Proxy ACDGRP1 Svr ACDGRP2 Svr UA2-ACDGRP2 | | | | | |--INVITE F1-->| | | | Supported:Histinfo | | | | | | |--INVITE F2-->| | | Supported:Histinfo History-Info: <sip:Gold@ACD.com>; index=1 Barnes Expires January 8, 2005 [Page 36]
SIP Request History Information July 8, 2004 History-Info: <sip:ACDGRP1@ACD.com>; index=1.1 | | | | | | |<-302 F3------| | | Contact: <sip:ACDGRP2@ACD.com> | | | | | | |--------INVITE F4---------->| | History-Info: <sip:Gold@ACD.com>; index=1 History-Info: <sip:ACDGRP1@ACD.com>; index=1.1 History-Info: <sip:ACDGRP2@ACD.com>; index=1.2 | | | | | | | | | | | | | |INVITE F5>| History-Info: <sip:Gold@ACD.com>; index=1 History-Info: <sip:ACDGRP1@ACD.com>; index=1.1 History-Info: <sip:ACDGRP2@ACD.com>; index=1.2 | | | | | | | | |<-200 F6--| | | | | | | |<-200 F7--------------------| | History-Info: <sip:Gold@ACD.com>; index=1 History-Info: <sip:ACDGRP1@ACD.com>; index=1.1 History-Info: <sip:ACDGRP2@ACD.com>; index=1.2 |<-200 F8------| | | | < No History-Info included in the response due to Local Policy> | | | | | |--ACK F9--------------------------------------------->| Message Details [To be completed] Appendix D Session via Redirect and Proxy Servers In this scenario, Alice places a call to Bob using first a Redirect server then a Proxy Server. The INVITE message is first sent to the Redirect Server. The Server returns a 302 Moved Temporarily response (F2) containing a Contact header with Bob's current SIP address. Alice then generates a new INVITE with Bob's current SIP address included in another History-Info entry. The INVITE is then sent to Bob via the Proxy Server, with Bob receiving the complete History information; the call then proceeds normally. The complete call flow for this scenario, without the use of History-Info is described in the SIP Basic Call Flow Examples [RFC3665]. Alice Redirect Server Proxy 3 Bob | | | | | INVITE F1 | | | Barnes Expires January 8, 2005 [Page 37]
SIP Request History Information July 8, 2004 |--------------->| | | | 302 F2 | | | |<---------------| | | | ACK F3 | | | |--------------->| | | | INVITE F4 | | |-------------------------------->| INVITE F5 | | 100 F6 |--------------->| Message Details F1 INVITE Alice -> Redirect Server INVITE sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 Max-Forwards: 70 From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 1 INVITE History-Info: <sip:bob@biloxi.example.com>; index=1 Contact: <sip:alice@client.atlanta.example.com> Content-Length: 0 F2 302 Moved Temporarily Redirect Proxy -> Alice SIP/2.0 302 Moved Temporarily Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 ;received=192.0.2.1 From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2 Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 1 INVITE History-Info: <sip:bob@biloxi.example.com>; index=1 Contact: <sip:bob@chicago.example.com;transport=tcp> Content-Length: 0 F3 ACK Alice -> Redirect Server ACK sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 Max-Forwards: 70 From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2 Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com Barnes Expires January 8, 2005 [Page 38]
SIP Request History Information July 8, 2004 CSeq: 1 ACK Content-Length: 0 F4 INVITE Alice -> Proxy 3 INVITE sip:bob@chicago.example.com SIP/2.0 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 2 INVITE History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\ text="Moved Temporarily">; index=1, <sip:bob@chicago.example.com>; index=2 Contact: <sip:alice@client.atlanta.example.com;transport=tcp> Content-Length: 0 F5 INVITE Proxy 3 -> Bob INVITE sip:bob@client.chicago.example.com SIP/2.0 Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 ;received=192.0.2.1 Max-Forwards: 69 Record-Route: <sip:ss3.chicago.example.com;lr> From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 2 INVITE History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\ text="Moved Temporarily">; index=1, <sip:bob@chicago.example.com>; index=2, <sip:bob@client.chicago.example.com>; index=2.1 Contact: <sip:alice@client.atlanta.example.com;transport=tcp> Content-Length: 0 Detailed Call Flow continues per section 6.3 in [RFC 3665]. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent Barnes Expires January 8, 2005 [Page 39]
SIP Request History Information July 8, 2004 that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in IETF Documents can be found in BCP 78 and 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Full Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Barnes Expires January 8, 2005 [Page 40]
