Network Working Group M. Barnes Internet-Draft Polycom Obsoletes: 4244 (if approved) F. Audet Intended status: Standards Track Skype Expires: October 3, 2012 S. Schubert NTT J. van Elburg Detecon International Gmbh C. Holmberg Ericsson Apr 2012 An Extension to the Session Initiation Protocol (SIP) for Request History Information draft-ietf-sipcore-rfc4244bis-08.txt Abstract This document defines a standard mechanism for capturing the history information associated with a Session Initiation Protocol (SIP) request. This capability enables many enhanced services by providing the information as to how and why a SIP request arrives at a specific application or user. This document defines an optional SIP header field, History-Info, for capturing the history information in requests. The document also defines SIP header field parameters for the History-Info and Contact header fields to tag the method by which the target of a request is determined. In addition, this specification defines a value for the Privacy header field that directs the anonymization of values in the History-Info header field This document obsoletes RFC 4244. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on October 3, 2012. Barnes, et al. Expires October 3, 2012 [Page 1] Internet-Draft History-Info Apr 2012 Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Barnes, et al. Expires October 3, 2012 [Page 2] Internet-Draft History-Info Apr 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. History-Info Header Field Protocol Structure . . . . . . . . . 8 5.1. History-Info Header Field Example Scenario . . . . . . . . 11 6. User Agent Handling of the History-Info Header Field . . . . . 14 6.1. User Agent Client (UAC) Behavior . . . . . . . . . . . . . 14 6.2. User Agent Server (UAS) Behavior . . . . . . . . . . . . . 14 7. Proxy/Intermediary Handling of History-Info Header Fields . . 14 8. Redirect Server Handling of History-Info Header Fields . . . . 15 9. Handling of History-Info Header Fields in Requests and Responses . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Receiving a Request . . . . . . . . . . . . . . . . . . . 16 9.2. Sending a Request with History-Info . . . . . . . . . . . 16 9.3. Receiving a Response with History-Info or Request Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.4. Sending History-Info in Responses . . . . . . . . . . . . 17 10. Processing the History-Info Header Field . . . . . . . . . . . 18 10.1. Privacy in the History-Info Header Field . . . . . . . . . 18 10.1.1. Indicating Privacy . . . . . . . . . . . . . . . . . 18 10.1.2. Applying Privacy . . . . . . . . . . . . . . . . . . 19 10.2. Reason in the History-Info Header Field . . . . . . . . . 20 10.3. Indexing in the History-Info Header Field . . . . . . . . 20 10.4. Mechanism for Target Determination in the History-Info Header Field . . . . . . . . . . . . . . . . . . . . . . . 22 11. Application Considerations . . . . . . . . . . . . . . . . . . 23 12. Application Specific Usage . . . . . . . . . . . . . . . . . . 25 12.1. PBX Voicemail . . . . . . . . . . . . . . . . . . . . . . 25 12.2. Consumer Voicemail . . . . . . . . . . . . . . . . . . . . 26 13. Security Considerations . . . . . . . . . . . . . . . . . . . 26 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 14.1. Registration of New SIP History-Info Header Field . . . . 27 14.2. Registration of "history" for SIP Privacy Header Field . . 27 14.3. Registration of Header Field Parameters . . . . . . . . . 28 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 16. Changes from RFC 4244 . . . . . . . . . . . . . . . . . . . . 29 16.1. Backwards compatibility . . . . . . . . . . . . . . . . . 30 17. Changes since last Version . . . . . . . . . . . . . . . . . . 31 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38 18.1. Normative References . . . . . . . . . . . . . . . . . . . 38 18.2. Informative References . . . . . . . . . . . . . . . . . . 39 Appendix A. Request History Requirements . . . . . . . . . . . . 39 A.1. Security Requirements . . . . . . . . . . . . . . . . . . 40 A.2. Privacy Requirements . . . . . . . . . . . . . . . . . . . 41 Appendix B. Example call flows . . . . . . . . . . . . . . . . . 42 Barnes, et al. Expires October 3, 2012 [Page 3] Internet-Draft History-Info Apr 2012 B.1. PBX Voicemail call flow . . . . . . . . . . . . . . . . . 42 B.2. Consumer Voicemail example call flow . . . . . . . . . . . 46 B.3. Sequentially Forking (History-Info in Response) . . . . . 50 B.4. History-Info with Privacy Header Field . . . . . . . . . . 58 B.5. Privacy for a Specific History-Info Entry . . . . . . . . 62 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 66 Barnes, et al. Expires October 3, 2012 [Page 4] Internet-Draft History-Info Apr 2012 1. Introduction Many services that SIP is anticipated to support require the ability to determine why and how a SIP request 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. Although SIP implicitly provides the retarget capabilities that enable SIP requests to be routed to chosen applications, there is a need for a standard mechanism within SIP for communicating the retargeting history of the requests. This "request history" information allows the receiving application to obtain information about how and why the SIP request arrived at the application/user. This document defines a SIP header field, 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. SIP header field parameters are defined for the History-Info and Contact header fields to tag the method by which the target of a request is determined. In addition, this specification defines a value for the Privacy header field specific to the History-Info header. The History-Info header field provides a building block for development of SIP based applications and services. The requirements for the solution described in this specification are included in Appendix A. Example scenarios using the History-Info header field are included in Appendix B. 2. Conventions and Terminology 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 [RFC2119]. The term "retarget" is used in this specification to refer to the process of a SIP entity changing the request-URI [RFC3261, section 7.1] in a request based on the rules for determining request targets as described in Section 16.5 of [RFC3261] and of the subsequent forwarding of that request as described in step 2 in section 16.6 of [RFC3261]. This includes changing the Request-URI due to a location service lookup and redirect processing. This also includes internal (to a Proxy/SIP intermediary) changes of the URI prior to forwarding of the request. The terms "location service", "forward", "redirect" and "AOR" are Barnes, et al. Expires October 3, 2012 [Page 5] Internet-Draft History-Info Apr 2012 used consistent with the terminology in [RFC3261]. The terms "target user" is used in this specification as the human user associated with particular AoR or AoRs (in case the human user has multiple alias). The references to "domain for which the SIP entity/Proxy/Intermediary is responsible" are consistent with and intended to convey the same context as the usage of that terminology in [RFC3261]. The applicability of History-Info to architectures or models outside the context of [RFC3261] is outside the scope of this specification. 3. Background SIP implicitly provides retargeting capabilities that enable SIP requests to be routed to specific applications as defined in [RFC3261]. The motivation for capturing the request history is that in the process of retargeting a request, old routing information can be forever lost. This lost information may be important history that allows elements to which the request is retargeted to process the request in a locally defined, application-specific manner. This document defines a mechanism for transporting the request history. Application-specific behavior is outside the scope of this specification. Current network applications for other protocols provide the ability for elements involved with the request to obtain additional information relating to how and why the request 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 that will receive some "referral" commission for generating this traffic 2. Email forwarding whereby the forwarded-to user obtains a detailed "trace of the path" of the message from sender to receiver 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. Barnes, et al. Expires October 3, 2012 [Page 6] Internet-Draft History-Info Apr 2012 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 Capturing aliases and Globally Routable User Agent URIs (GRUUs) [RFC5627], which can be overwritten by a registrar or a "home proxy" (a proxy serving as the terminal point for routing an address-of-record) upon receipt of the initial request. o Facilitating the use of limited use addresses (minted on demand) and sub-addressing. o Preserving service specific URIs that can be overwritten by a downstream proxy, such as those defined in [RFC3087], and control of network announcements and IVR with SIP URI [RFC4240]. 4. Overview 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. The solution is to capture the Request-URIs as a request is retargeted, in a SIP header field: History-Info. This allows for the capturing of the history of a request that would be lost with the normal SIP processing involved in the subsequent retargeting of the request. The History-Info header field 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. It is possible for the target of a request to be changed by the same proxy/SIP intermediary multiple times (referred to as 'internal retargeting'). A SIP entity changing the target of a request in response to a redirect also propagates any History-Info header field from the initial request in the new request. The ABNF and detailed description of the History-Info header field parameters along with examples, is provided in Section 5. Section 6, Section 7 and Section 8 provide the detailed handling of the History-Info header field by SIP User Agents, Proxies and Redirect Servers respectively. This specification also defines three new SIP header field parameters, "rc", "mp" and "np", for the History-Info and Contact header fields, to tag the method by which the target of a request is determined. Further detail on the use of these header field parameters is provided in Section 10.4. Barnes, et al. Expires October 3, 2012 [Page 7] Internet-Draft History-Info Apr 2012 In addition, this specification defines a priv-value for the Privacy header, "history", that requires anonymization of all the History- Info header field entries in a Request or to a specific History-Info header field hi-entry as described above. Further detail is provided in Section 10.1. 5. History-Info Header Field Protocol Structure The History-Info header field defined in this specification defines the usage in out-of-dialog requests or initial requests for a dialog (e.g., INVITE, REGISTER, MESSAGE, REFER and OPTIONS, PUBLISH and SUBSCRIBE, etc.) and any non-100 provisional or final responses to these requests. The following provides details for the information that is captured in the History-Info header field entries for each target used for forwarding a request: o hi-targeted-to-uri: A mandatory parameter for capturing the Request-URI for the specific request as it is forwarded. o 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 sequance of nonnegative integers, 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 leaf. By adding the new entries in order (i.e., following existing entries per the details in Section 10.3), including the index and sending the messages using a secure transport, the ordering of the History-Info header fields in the request is assured. 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 hi-target-param: An optional parameter reflecting the mechanism by which the Request URI captured in the hi-targeted-to-uri in the History-Info header field value (hi-entry) was determined. This parameter is either an "rc", "mp" or "np" header field parameter, which is interpreted as follows: "rc": The hi-targeted-to-URI represents a change in Request-URI while the target user remains the same. This occurs for example when user has multiple AoRs as an alias. The "rc" header field parameter contains the value of the hi-index in the hi-entry with an hi-targeted-to-uri that reflects the Barnes, et al. Expires October 3, 2012 [Page 8] Internet-Draft History-Info Apr 2012 Request-URI that was retargeted "mp": The hi-targeted-to-URI represents a user other than the target user associated with the Request-URI in the incoming request that was retargeted. This occurs when a request is statically or dynamically retargeted to another user represented by an AoR unassociated with the AoR of the original target user. The "mp" header field parameter contains the value of the hi-index in the hi-entry with an hi-targeted-to- uri that reflects the Request-URI that was retargeted, thus identifying the "mapped from" target. "np": The hi-targeted-to-URI represents that there was no change in Request-URI. This would apply for example when a proxy merely forwards a request to a next hop proxy and loose routing is used. The "np" header field parameter contains the value of the hi-index in the hi-entry with an hi-targeted-to- uri that reflects the Request-URI that was copied unchanged into the request represented by this hi-entry. That value will usually be the hi-index of the parent hi-entry of this hi- entry. o Extension (hi-extension): A parameter to allow for future optional extensions. As per [RFC3261], any implementation not understanding an extension MUST ignore it. The ABNF syntax [RFC5234] for the History-Info header field and header field parameters is as follows: Barnes, et al. Expires October 3, 2012 [Page 9] Internet-Draft History-Info Apr 2012 History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry) hi-entry = hi-targeted-to-uri *(SEMI hi-param) hi-targeted-to-uri = addr-spec / name-addr hi-param = hi-index / hi-target-param / hi-extension hi-index = "index" EQUAL index-val index-val = number *("." number) number = [ %31-39 *DIGIT ] DIGIT hi-target-param = rc-param / mp-param / np-param rc-param = "rc" EQUAL index-val mp-param = "mp" EQUAL index-val np-param = "np" EQUAL index-val hi-extension = generic-param The ABNF definitions for "generic-param" and "name-addr" are from [RFC3261]. This document also extends the "contact-params" for the Contact header field as defined in [RFC3261] with the "rc", "mp" and "np" header field parameters defined above. In addition to the parameters defined by the ABNF, an hi-entry may also include a Reason header field and/or a Privacy header field, which are both included in the "headers" component of the hi- targeted-to-uri as described below: o Reason: An optional parameter for History-Info, reflected in the History-Info header field by including the Reason header field [RFC3326] included in the hi-targeted-to-uri. A reason is included in the hi-targeted-to-uri of an hi-entry to reflect information received in a response to the request sent to that URI. o Privacy: An optional parameter for History-Info, reflected in the History-Info header field values by including the Privacy Header [RFC3323] included in the hi- targeted-to-uri or by adding the Privacy header field to the request. The latter case indicates that the History-Info entries for all History-Info entries whose Barnes, et al. Expires October 3, 2012 [Page 10] Internet-Draft History-Info Apr 2012 hi-targeted-to-uri has the same domain as the domain for which the SIP entity processing the message is responsible MUST be anonymized prior to forwarding, whereas the use of the Privacy header field included in the hi-targeted-to-uri means that a specific hi-entry MUST be anonymized. Note that since both the Reason and Privacy parameters are included in the hi-targeted-to-uri, these fields will not be available in the case that the hi-targeted-to-uri is a Tel-URI [RFC3966]. The following provides examples of the format for the History-Info header field. Note that the backslash, CRLF and whitespace between the lines in the examples below are inserted for readability purposes only. (But History-Info can be broken into multiple lines due to the SWS that is part of HCOLON, COMMA and SEMI, and there can be multiple History-Info header fields due to the rule of section 7.3 [RFC3261].) History-Info: ;index=1;foo=bar History-Info: ;index=1.1,\ ;index=1.2;mp=1.1,\ ;index=1.3;rc=1.2 5.1. History-Info Header Field Example Scenario The following is an illustrative example of usage of History-Info. In this example, Alice (sip:alice@atlanta.example.com) calls Bob (sip:bob@biloxi.example.com). Alice's proxy in her home domain (sip: atlanta.example.com) forwards the request to Bob's proxy (sip: biloxi.example.com). When the request arrives at sip: biloxi.example.com, it does a location service lookup for bob@biloxi.example.com and changes the target of the request to Bob's Contact URIs provided as part of normal SIP registration. In this example, Bob is simultaneously contacted on a PC client and on a phone, and Bob answers on the PC client. One important thing illustrated by this call flow is that without History-Info, Bob would "lose" the original target information or the initial request-URI, including any parameters in the request URI. Bob can recover that information by locating the last hi-entry with an "rc" header field parameter. This "rc" header field parameter contains the index of the hi-entry containing the lost target information - i.e., the sip:bob@biloxi.example.com hi-entry with index=1.1. Note that in the 200 response to Alice, an hi-entry is Barnes, et al. Expires October 3, 2012 [Page 11] Internet-Draft History-Info Apr 2012 not included for the fork to sip:bob@192.0.2.7 (index 1.1.1) since biloxi.example.com had not received a response from that fork at the time it sent the 200 OK that ultimately reached Alice. Additional detailed scenarios are available in Appendix B. Note: This example uses loose routing procedures. Barnes, et al. Expires October 3, 2012 [Page 12] Internet-Draft History-Info Apr 2012 Alice atlanta.example.com biloxi.example.com Bob@pc Bob@phone | | | | | | INVITE sip:bob@biloxi.example.com;p=x | | |--------------->| | | | | Supported: histinfo | | | | | | | | | | INVITE sip:bob@biloxi.example.com;p=x | | |--------------->| | | | History-Info: ;index=1 | | History-Info: ;np=1;index=1.1 | | | | | | | | INVITE sip:bob@192.0.2.3| | | |--------------->| | | History-Info: ;index=1 | History-Info: ;np=1;index=1.1 | History-Info: ;index=1.1.1;rc=1.1 | | | | | | | | INVITE sip:bob@192.0.2.7| | | |-------------------------->| | History-Info: ;index=1 | History-Info: ;np=1;index=1.1 | History-Info: ;index=1.1.2;rc=1.1 | | | 200 | | | | |<---------------| | | History-Info: ;index=1 | History-Info: ;np=1;index=1.1 | History-Info: ;index=1.1.1;rc=1.1 | | | | | | | 200 | | | | |<---------------| | | | History-Info: ;index=1 | History-Info: ;np=1;index=1.1 | History-Info: ;index=1.1.1;rc=1.1 | | | | | | | | Proxy Cancels INVITE | | | |<=========================>| | | | | | | 200 | | | | |<---------------| | | | | History-Info: ;index=1 | History-Info: ;np=1;index=1.1 | History-Info: ;index=1.1.1;rc=1.1 | | | | | | ACK | | | | |--------------->| ACK | | | | |--------------->| ACK | | | | |--------------->| | Barnes, et al. Expires October 3, 2012 [Page 13] Internet-Draft History-Info Apr 2012 Figure 1: Basic Call 6. User Agent Handling of the History-Info Header Field A B2BUA MAY follow the behavior of a SIP intermediary as an alternative to following the behavior of a UAS per Section 6.2 and a UAC per Section 6.1. In behaving as an intermediary, a B2BUA carries forward hi-entries received in requests at the UAS to requests being forwarded by the UAC, as well as carrying forward hi-entries in responses received at the UAC to the responses forwarded by the UAS, subject to privacy considerations per Section 10.1. 6.1. User Agent Client (UAC) Behavior The UAC MUST include the "histinfo" option tag in the Supported header field in any out-of-dialog requests or initial requests for a dialog for which the UAC would like the History-Info header field in the response. When issuing a request, the UAC MUST follow the procedures in Section 9.2. In the case of an initial request, except where the UAC is part of a B2BUA, there is no cache of hi- entries with which to populate the History-Info header field and the hi-index is set to 1 per Section 10.3. When receiving a response the UAC MUST follow the procedures in Section 9.3. If the UAC generates further forks of the initial request (either due to acting on a 3xx response or internally-directed forking to multiple destinations), the successive requests will add hi-entries with hi-indexes of 2, 3, etc. 6.2. User Agent Server (UAS) Behavior When receiving a request, a UAS MUST follow the procedures defined in Section 9.1. When sending a response other than a 3xx response, a UAS MUST follows the procedures in Section 9.4. When sending a 3xx response, the UAS MUST follow the procedures defined for a redirect server per Section 8. An application at the UAS can make use of the cached hi-entries as described in Section 11. 7. Proxy/Intermediary Handling of History-Info Header Fields This section describes the procedures for proxies and other SIP intermediaries for the handling of the History-Info header fields for each of the following scenarios: Barnes, et al. Expires October 3, 2012 [Page 14] Internet-Draft History-Info Apr 2012 Receiving a Request: An intermediary MUST follow the procedures in Section 9.1 for the handling of hi-entries in incoming SIP requests. Sending a Request: For each outgoing request relating to a target in the target set, the intermediary MUST follow the procedures of Section 9.2. Receiving a Response or Timeout: An intermediary MUST follow the procedures of Section 9.3 when a SIP response is received or a request times out. Sending a Response: An intermediary MUST follow the procedures of Section 9.4 for the handling of the hi-entries when sending a SIP response. In some cases, an intermediary may retarget a request more than once before forwarding - i.e., a request is retargeted to a SIP entity that is "internal" to the intermediary before the same intermediary retargets the request to an external target . A typical example would be a proxy that retargets a request first to a different user (i.e., it maps to a different AOR) and then forwards to a registered contact bound to the same AOR. In this case, the intermediary MUST add a hi-entry for (each of) the internal target(s) per the procedures in Section 9.2. The intermediary MAY include a Reason header field in the hi-entry with the hi-targeted-to-uri that has been retargeted as shown in the INVITE (F6) in the example in Appendix B.3. 8. Redirect Server Handling of History-Info Header Fields A redirect server MUST follow the procedures in Section 9.1 when it receives a SIP Request. A redirect server MUST follow the procedures in Section 9.4 when it sends a SIP Response. When generating the Contact header field in a 3xx response, the redirect server MUST add the appropriate "mp", "np" or "rc" header field parameter to each Contact header field as described in Section 10.4, if applicable. 9. Handling of History-Info Header Fields in Requests and Responses This section describes the procedures for SIP entities for the handling of the History-Info header field in SIP requests and responses. Barnes, et al. Expires October 3, 2012 [Page 15] Internet-Draft History-Info Apr 2012 9.1. Receiving a Request When receiving a request, a SIP entity MUST create a cache containing the hi-entries associated with the request. The hi-entries MUST be added to the cache in the order in which they were received in the request. If the Request-URI of the incoming request does not match the hi- targeted-to-uri in the last hi-entry (i.e., the previous SIP entity that sent the request did not include a History-Info header field), the SIP entity MUST add a hi-entry to end of the cache, on behalf of the previous SIP entity, as follows: The SIP entity MUST set the hi-targeted-to-uri to the value of the Request-URI in the incoming request. If the Request-URI is a Tel- URI, it SHOULD be transformed into a SIP URI per section 19.1.6 of [RFC3261] before being added as a hi-targted-to-uri. If privacy is required, the SIP entity MUST follow the procedures of Section 10.1. The SIP entity MUST set the hi-index parameter as described in Section 10.3. The SIP entity MUST NOT include an "rc", "mp" or "np" header field parameter. 9.2. Sending a Request with History-Info When sending a request, a SIP entity MUST include all cached hi- entries in the request. In addition, the SIP entity MUST add a new hi-entry to the outgoing request, but the SIP entity MUST NOT add the hi-entry to the cache at this time. The hi-entries in the outgoing request's History-Info header field is the preorder of the tree of hi-entries, that is, by the lexicographic ordering of the hi-indexes. The new hi-entry is populated as follows: hi-targeted-to-uri: The hi-targeted-to-uri MUST be set to the value of the Request-URI of the current (outgoing) request. privacy: If privacy is required, the procedures of Section 10.1 MUST be followed. hi-index: The SIP entity MUST include an hi-index for the hi-entry as described in Section 10.3. Barnes, et al. Expires October 3, 2012 [Page 16] Internet-Draft History-Info Apr 2012 rc/mp/np: The SIP entity MUST include an "rc", "mp" or "np" header field parameter in the hi-entry, if applicable, per the procedures in Section 10.4. 9.3. Receiving a Response with History-Info or Request Timeouts When a SIP entity receives a non-100 response or a request times out, the SIP entity performs the following steps: Step 1: Add hi-entry to cache The SIP entity MUST add the hi-entry that was added to the request that received the non-100 response or timed out to the cache, if it was not already cached. The hi-entry MUST be added to the cache in ascending order as indicated by the values in the hi- index parameters of the hi-entries (e.g., 1.2.1 comes after 1.2 but before 1.2.2 or 1.3). Step 2: Add Reason header field The SIP entity adds one or more Reason header fields to the hi- targeted-to-uri in the (newly) cached hi-entry reflecting the SIP response code in the non-100 response, per the procedures of Section 10.2. Step 3: Add additional hi-entries The SIP entity MUST also add to the cache any hi-entries received in the response that are not already in the cache. This situation can occur when the entity that generated the non-100 response retargeted the request before generating the response. As per Step 1, the hi-entries MUST be added to the cache in ascending order as indicated by the values in the hi-index parameters of the hi-entries It is important to note that the cache does not contain hi-entries for requests that have not yet received a non-100 response, so there can be gaps in indices (e.g., 1.2 and 1.4 could but present but not 1.3). 9.4. Sending History-Info in Responses When sending a response other than a 100, a SIP entity MUST include all the cached hi-entries in the response, subject to the privacy consideration in Section 10.1.2, and with the following exception: If the received request contained no hi-entries and there is no "histinfo" option tag in the Supported header field, the SIP entity MUST NOT include History-Info in the response. Barnes, et al. Expires October 3, 2012 [Page 17] Internet-Draft History-Info Apr 2012 10. Processing the History-Info Header Field The following sections describe the procedures for processing the History-Info header field. These procedures are applicable to SIP entities such as Proxies/Intermediaries, Redirect Servers or User Agents. 10.1. Privacy in the History-Info Header Field The privacy requirements for this document are described in Appendix A.2. Section 10.1.1 describes the insertion of the Privacy header field defined in [RFC3323] to indicate the privacy to be applied to the History-Info header field entries. Section 10.1.2 describes how to apply privacy to a request or response that is being forwarded, based on the presence of the Privacy header field. 10.1.1. Indicating Privacy As with other SIP headers described in [RFC3323], the hi-targeted-to- uris in the History-Info header field can inadvertently reveal information about the initiator of the request. Thus, the UAC needs a mechanism to indicate that the hi-targeted-to-uris in the hi- entries need to be privacy protected. The Privacy header field is used by the UAC to indicate that privacy is to be applied to all the hi-entries in the request as follows: o If the UAC is including a Privacy header field with a priv-value of "header" in the request, then the UAC SHOULD NOT include a priv-value of "history" in the Privacy header field in the Request. o If the UAC is including any priv-values other than "header" in the Privacy header field, then the UAC MUST also include a priv-value of "history" in the Privacy header field in the Request. o If the UAC is not including any priv-values in the Privacy header field in the request, then the UAC MUST add a Privacy header field, with a priv-value of "history", to the request. The UAC MUST NOT include a priv-value of "critical" in the Privacy header field in the Request in this case. In addition, the History-Info header field can reveal general routing and diverting information within an intermediary, which the intermediary wants to privacy protect. In this case, the intermediary MUST construct a Privacy header field with the single priv-value of "history" and include the Privacy header field in the hi-targeted-to-uri, for each new hi-entry created by the intermediary whose hi-targeted-to-uri it wishes to privacy protect. Note that the Barnes, et al. Expires October 3, 2012 [Page 18] Internet-Draft History-Info Apr 2012 priv-value in the Privacy header for the incoming request does not necessarily influence whether the intermediary includes a Privacy header field in the hi-entries. For example, even if the Privacy header for the incoming request contained a priv-value of "none", the Proxy can still set a priv-value of "history" in the Privacy header field included in the hi-targeted-to-uri. Finally, the UAS may not want to reveal the final reached target to the originator. In this case, the UAS MUST include a Privacy header field with a priv-value of "history" in the hi-targeted-to-uri in the last hi-entry, in the response. As noted above, the UAS of the request MUST NOT use any other priv-values in the Privacy header field included in the hi-entry. 10.1.2. Applying Privacy When a SIP message is forwarded to a domain for which the SIP intermediary is not responsible, a Privacy Service at the boundary of the domain applies the appropriate privacy based on the value of the Privacy header field in the message header or in the "headers" component of the hi-targeted-to-uri in the individual hi-entries. If there is a Privacy header field in the message header of a request or response, with a priv-value of "header" or "history", then all the hi-targeted-to-uris in the hi-entries, associated with the domain for which the SIP intermediary is responsible, are anonymized by the Privacy Service. The Privacy Service MUST change any hi-targeted-to- uris in these hi-entries that have not been anonymized(evidenced by their domain not being "anonymous.invalid") to anonymous URIs containing a domain of anonymous.invalid (e.g., anonymous@anonymous.invalid). If there is a Privacy header field in the "headers" component of the hi-targeted-to-uri in the hi-entries, then the Privacy header field value MUST be removed from the hi- entry. Once all the appropriate hi-entries have been anonymized, the Privacy Service MUST remove the priv-value of "history" from the Privacy header field in the message header of the request or response. If there are no remaining priv-values in the Privacy header field, the Privacy Service MUST remove the Privacy header field from the request or response per [RFC3323]. If there is not a Privacy header field in the message header of the request or response that is being forwarded, but there is a Privacy header field with a priv-value of "history" in the "headers" component in any of the hi-targeted-uris in the hi-entries associated with the domain for which a SIP intermediary is responsible, then the Privacy Service MUST update those hi-targeted-to-uris as described above. Any other priv-values in the Privacy header field in the "headers" component of the hi-targeted-to-uris in the hi-entries MUST Barnes, et al. Expires October 3, 2012 [Page 19] Internet-Draft History-Info Apr 2012 be ignored. In any case, the Privacy Service MUST remove the Privacy header field from the "headers" compenent of the hi-targeted-to-uris in the hi-entries prior to forwarding. 10.2. Reason in the History-Info Header Field A Reason header field is added to the "headers" component in an hi- targeted-to-uri when the hi-entry is added to the cache based upon the receipt of a non-100 or non-2xx SIP response, as described in Section 9.3. If the Reason header field is being added due to receipt of an explicit SIP response and the response contains any Reason header fields (see [RFC3326]), then the SIP entity MUST include the Reason header fields in the "headers" component of the hi-targeted-to-uri in the last hi-entry added to the cache, unless the hi-targeted-to-uri is a Tel-URI. If the SIP response does not contain a Reason header field, the SIP entity MUST include a Reason header field, containing the SIP Response Code, in the "headers" component of the hi-targeted-to-uri in the last hi-entry added to the cache, unless the hi-targeted-to-uri is a Tel-URI. If a request has timed out (instead of being explicitly rejected), the SIP entity MUST update the cache as if the request received a SIP error response code of 408 "Request Timeout". A request can receive multiple non-100 non-2xx responses which carry or imply (for responses without Reason headers, and for timeouts) multiple, possibly duplicated, reason-values to be applied to an hi- targeted-to-uri. In these situations, the SIP entity creating History-Info header value would choose the appropriate Reason header field value. A SIP entity MAY also include a Reason header field in the "headers" component of an hi-targeted-to-uri containing the URI of a request that was retargeted as a result of internal retargeting. If additional Reason header field parameters are defined in the future per [RFC3326], the use of these Reason header field parameters for the History-Info header field MUST follow the same rules as described above. 10.3. Indexing in the History-Info Header Field In order to maintain ordering and accurately reflect the retargeting of the request, the SIP entity MUST add a hi-index to each hi-entry. Per the syntax in Section 5, the hi-index consists of a series of nonnegative integer separated by dots (e.g., 1.1.2). Each dot reflects a SIP forwarding hop. The nonnegative integer following each dot reflects the order in which a request was retargeted at the Barnes, et al. Expires October 3, 2012 [Page 20] Internet-Draft History-Info Apr 2012 hop. The highest nonnegative integer at each hop reflects the number of entities to which the request has been retargeted at the specific hop (i.e., the number of branches) at the time that the request represented by this hi-entry was generated. Thus, the indexing results in a logical tree representation for the history of the request and the hi-entries are given in the preorder of the tree. The first index in a series of History-Info entries MUST be set to 1. In the case that a SIP entity (intermediary or UAS) adds a first hi- entry on behalf of the previous hop, the hi-index MUST be set to 1. For each forward hop (i.e., each new level of indexing), the last integers of the hi-indexes of the new requests MUST be generated starting at 1 and incrementing by 1 for each additional request" The basic rules for adding the hi-index are summarized as follows: 1. Forwarding a request without changing the target: In the case of a request that is being forwarded without changing the target, the hi-index reflects the increasing length of the branch. In this case, the SIP entity MUST read the value from the History- Info header field in the received request and MUST add another level of indexing by appending the dot delimiter followed by an initial value of 1 for the new level. For example, if the hi- index in the last History-Info header field in the received request is 1.1, a proxy would add a hi-entry with an hi-index of 1.1.1 and forward the request. 2. Retargeting within a processing entity - 1st instance: For the first instance of retargeting within a processing entity, the SIP entity MUST calculate the hi-index as prescribed for basic forwarding. 3. Retargeting within a processing entity - subsequent instance: For each subsequent retargeting of a request by the same SIP entity, the SIP entity MUST calculate and add the hi-index for each new branch by incrementing the rightmost value from the hi-index in the last hi-entry. Per the example above, the hi-index in the next request forwarded by this same SIP entity would be 1.1.2. 4. Retargeting based upon a Response: In the case of retargeting due to a specific response (e.g., 302), the SIP entity MUST calculate the hi-index calculated per rule 3. That is, the rightmost value of the hi-index MUST be incremented (i.e., a new branch is created). For example, if the hi-index in the History-Info header field of the sent request is 1.2 and the response to the request is a 302, then the hi-index in the History-Info header field for the new hi-targeted-to-URI would be 1.3. Barnes, et al. Expires October 3, 2012 [Page 21] Internet-Draft History-Info Apr 2012 5. Forking requests: If the request forwarding is done in multiple forks (sequentially or in parallel), the SIP entity MUST set the hi-index for each hi-entry for each forked request per the rules above, with each new request having a unique index. Each index MUST be sequentially assigned. For example, if the index in the last History-Info header field in the received request is 1.1, this processing entity would initialize its index to 1.1.1 for the first fork, 1.1.2 for the second, and so forth (see Figure 1 for an example). Note, that in the case of parallel forking, only the hi-entry corresponding to the fork is included in the request because no response can yet have been received for any of the parallel forked requests. 6. Missing entity: If the request clearly has a gap in the hi-entry, the entity adding an hi-entry MUST add an index a nonnegative integer of "0" to the current index prior to adding appropriate index for the action to be taken. If the index of the last hi- entry in the request received was 1.1.2 and there was a missing hi-entry and the request was being forwarded to the next hop, the resulting index will be 1.1.2.0.1. 10.4. Mechanism for Target Determination in the History-Info Header Field This specification defines two header field parameters, "rc", "mp" and "np", indicating two mechanisms by which a new target for a request is determined. Both parameters contain an index whose value is the hi-index of the hi-entry with an hi-targeted-to-uri that represents the Request-URI that was retargeted. The SIP entity MUST determine the specific parameter field to be included in the hi-target-param, in the History-Info header field, as the targets are added to the target set per the procedures in section 16.5 of [RFC3261] or per section 8.1.3.4 [RFC3261] in the case of retargeting to a contact URI received in a 3xx response. In the latter case, the specific header field parameter in the Contact header field becomes the header field parameter that is used in the hi-entry when the request is retargeted. If the Contact header field does not contain an "rc", "mp" or "np" header field parameter, then the SIP entity MUST NOT include an "rc", "mp" or "np" header field parameter in the hi-target-param in the hi-entry when the request is retargeted to a contact URI received in a 3xx response.. The SIP entity (intermediary or redirect server) determines the specific header field parameter ("rc", "mp" or "np") to be used based on the following criteria: Barnes, et al. Expires October 3, 2012 [Page 22] Internet-Draft History-Info Apr 2012 o "rc": The Request-URI has changed while retaining the target user associated with the original Request-URI prior to retargeting. o "mp": The target was determined based on a mapping to a user other than the target user associated with the Request-URI being retargeted. o "np": The target hasn't changed and associated Request-URI remained the same. Note that there are two scenarios by which the "mp" header field parameter can be derived. o The mapping was done by the receiving entity on its own authority, in which case the mp-value is the parent index of the hi-entry's index. o The mapping was done due to receiving a 3xx response, in which case the mp-value is an earlier sibling or descendant of an earlier sibling of the hi-entry's index, that of the downstream request which received the 3xx response. 11. Application Considerations History-Info provides a very flexible building block that can be used by intermediaries and UAs for a variety of services. Prior to any application usage of the History-Info header field parameters, the SIP entity that processes the hi-entries MUST evaluate the hi- entries. The SIP entity MUST be prepared to process effectively messages whose hi-entries show evidence of "gaps", that is, situations that reveal that not all of the forks of the request have been recorded in the hi-entries. Gaps are possible if the request is forwarded through intermediaries that do not support the History-Info header field and are reflected by the existence of hi-entries with a nonnegative integer of "0" e.g. "1.1.0.1". Gaps are also possible in the case of parallel forking if there is an outstanding request at the time the SIP entity sends a message. Thus, if gaps are detected, the SIP entity MUST NOT treat this as an error, but SHOULD indicate to any applications that there are gaps. The interpretation of the information in the History-Info header field depends upon the specific application; an application might need to provide special handling in some cases where there are gaps. The following describes some categories of information that applications can use: Barnes, et al. Expires October 3, 2012 [Page 23] Internet-Draft History-Info Apr 2012 1. Complete history information - e.g., for debug or other operational and management aspects, optimization of determining targets to avoid retargeting to the same URI, etc. This information is relevant to proxies, UACs and UASs. 2. Hi-entry with the index that matches the value of the "rc" header field parameter in the last hi-entry with a "rc" header field parameter in the Request received by a UAS - i.e., the last AOR that was retargeted to a contact based on an AOR-to-contact binding. 3. Hi-entry with the index that matches the value of the "mp" header field parameter in the last hi-entry with a "mp" header field parameter in the hi-target-param in the Request received by a UAS - i.e., the last Request URI that was mapped to reach the destination. 4. Hi-entry with the index that matches the value of the "rc" header field parameter in the first hi-entry with a "rc" header field parameter in the Request received by a UAS. Note, this would be the original AoR if all the entities involved support the History-Info header field and there is absence of an "mp" header field parameter prior to the "rc" header field parameter in the hi-target-param in the History-Info header field. However, there is no guarantee that all entities will support History-Info, thus the hi-entry that matches the value of the "rc" header field parameter of the first hi-entry with an "rc" header field parameter in the hi-target-param within the domain associated with the target URI at the destination is more likely to be useful. 5. Hi-entry with the index that matches the value of "mp" header field parameter in the first hi-entry with an "mp" header field parameter in the Request received by a UAS. Note, this would be the original mapped URI if all entities supported the History- Info header field. However, there is no guarantee that all entities will support History-Info, thus the hi-entry that matches the value of the "mp" header field parameter of the first hi-entry with an "mp" header field parameter within the domain associated with the target URI at the destination is more likely to be useful. In many cases, applications are most interested in the information within a particular domain(s), thus only a subset of the information is required. Some applications may use multiple types of information. For example, an Automatic Call Distribution (ACD)/Call center application Barnes, et al. Expires October 3, 2012 [Page 24] Internet-Draft History-Info Apr 2012 that utilizes the hi-entry which index matches the value of the "mp" header field parameter of the first hi-entry with an "mp" header field parameter, may also display other agents, reflected by other hi-entries prior to entries with hi-target value of "rc" header field parameter, to whom the call was targeted prior to its arrival at the current agent. This could allow the agent the ability to decide how they might forward or reroute the call if necessary (avoiding agents that were not previously available for whatever reason, etc.). Since support for History-Info header field is optional, a service MUST define default behavior for requests and responses not containing History-Info header fields. For example, an entity may receive an incomplete set of hi-entries or hi-entries which are not tagged appropriately with an hi-target-param. This may not impact some applications (e.g., debug), however, it could require some applications to make some default assumptions in this case. For example, in an ACD scenario, the application could select the oldest hi-entry with the domain associated with the ACD system and display that as the original called party. Depending upon how and where the request may have been retargeted, the complete list of agents to whom the call was targeted may not be available. 12. Application Specific Usage Following are possible (non-normative) application-specific usages of History-Info. 12.1. PBX Voicemail A voicemail system typically requires the original called party information to determine the appropriate mailbox so an appropriate greeting can be provided and the appropriate party notified of the message. The original target is determined by finding the first hi-entry tagged with "rc" and using the hi-entry referenced by the index of "rc" header field parameter as the target for determining the appropriate mailbox. This hi-entry is used to populate the "target" URI parameter as defined in [RFC4458] The VMS can look at the last hi-entry and find the target of the mailbox by looking at the URI entry in the "target" URI parameter in the hi-entry. For example call flow please refer to the Appendix B.1. This example usage does not work properly in the presence of forwarding that takes place before the call reaches the company in that case not the first hi-entry with an rc value, but the first hi- entry with an rc value following an mp entry needs to be picked. Barnes, et al. Expires October 3, 2012 [Page 25] Internet-Draft History-Info Apr 2012 12.2. Consumer Voicemail The voicemail system in these environment typically requires the last called party information to determine the appropriate mailbox so an appropriate greeting can be provided and the appropriate party notified of the message. The last target is determined by finding the hi-entry referenced by the index of last hi-entry tagged with "rc" for determining the appropriate mailbox. This hi-entry is used to populate the "target" URI parameter as defined in [RFC4458]. The VMS can look at the last hi-entry and find the target of the mailbox by looking for the "target" URI parameter in the hi-entry. For example call flow please refer to the Appendix B.2. 13. Security Considerations The security requirements for this specification are specified in Appendix A.1. This document defines a header field for SIP. The use of the Transport Layer Security (TLS) protocol [RFC5246] as a mechanism to ensure the overall confidentiality of the History-Info header fields (SEC-req-4) is strongly RECOMMENDED. This results in History-Info having at least the same level of security as other headers in SIP that are inserted by intermediaries. With TLS, History-Info header fields are no less, nor no more, secure than other SIP header fields, which generally have even more impact on the subsequent processing of SIP sessions than the History-Info header field. Note that while using the SIPS scheme (as per [RFC5630]) protects History-Info from tampering by arbitrary parties outside the SIP message path, all the intermediaries on the path are trusted implicitly. A malicious intermediary could arbitrarily delete, rewrite, or modify History-Info. This specification does not attempt to prevent or detect attacks by malicious intermediaries. In terms of ensuring the privacy of hi-entries, the same security considerations as those described in [RFC3323] apply. Namely if the entity requesting privacy wants to ensure privacy is applied to the hi-entries, a Privacy Service that supports both [RFC3323] and this specification is REQUIRED in the entity's domain, so that the privacy can be applied, as described in Section 10.1.2, when a request or response leaves the domain. Barnes, et al. Expires October 3, 2012 [Page 26] Internet-Draft History-Info Apr 2012 14. IANA Considerations This document requires several IANA registrations detailed in the following sections. This document obsoletes [RFC4244] but uses the same SIP header field name and option tag. The IANA registry needs to update the references to [RFC4244] with [RFC XXXX]. 14.1. Registration of New SIP History-Info Header Field This document defines a SIP header field name: History-Info and an option tag: histinfo. The following changes have been made to http:///www.iana.org/assignments/sip-parameters The following row has been added to the header field section:. The following row has been added to the header field section: Header Name Compact Form Reference ----------- ------------ --------- History-Info none [RFC XXXX] The following has been added to the Options Tags section: Name Description Reference ---- ----------- --------- histinfo When used with the Supported header field, [RFC XXXX] this option tag indicates the UAC supports 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. Note to RFC Editor: Please replace RFC XXXX with the RFC number of this specification. 14.2. Registration of "history" for SIP Privacy Header Field This document defines a priv-value for the SIP Privacy header field: history The following changes have been made to http://www.iana.org/assignments/sip-priv-values The following has been added to the registration for the SIP Privacy header field: Barnes, et al. Expires October 3, 2012 [Page 27] Internet-Draft History-Info Apr 2012 Name Description Registrant Reference ---- ----------- ---------- --------- history Privacy requested for Mary Barnes [RFC XXXX] History-Info header mary.barnes@polycom.com fields(s) Note to RFC Editor: Please replace RFC XXXX with the RFC number of this specification. 14.3. Registration of Header Field Parameters This specification defines the following new SIP header field parameters in the SIP Header Field parameter sub-registry in the SIP Parameter Registry, http:/www.iana.org/assignments/sip-parameters. Header Field Parameter Name Predefined Reference Values _____________________________________________________________________ History-Info mp No [RFC xxxx] History-Info rc No [RFC xxxx] History-Info np No [RFC xxxx] Contact mp No [RFC xxxx] Contact rc No [RFC xxxx] Contact np No [RFC xxxx] Note to RFC Editor: Please replace RFC XXXX with the RFC number of this specification. 15. Acknowledgements Jonathan Rosenberg et al produced the document that provided additional use cases precipitating the requirement for the new header parameters to capture the method by which a Request URI is determined. The authors would like to acknowledge the constructive feedback provided by Ian Elz, Paul Kyzivat, John Elwell, Hadriel Kaplan and Dale Worley. John Elwell provided excellent suggestions in terms of document structure. Mark Watson, Cullen Jennings and Jon Peterson provided significant input into the initial work that resulted in the development of of [RFC4244]. The editor would like to acknowledge the constructive feedback provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell, Nir Chen, Palash Jain, Brian Stucker, Norma Ng, Anthony Brown, Jayshree Bharatia, Jonathan Rosenberg, Eric Burger, Martin Barnes, et al. Expires October 3, 2012 [Page 28] Internet-Draft History-Info Apr 2012 Dolly, Roland Jesske, Takuya Sawada, Sebastien Prouvost, and Sebastien Garcin in the development of [RFC4244]. The editor would like to acknowledge the significant input from Rohan Mahy on some of the normative aspects of the ABNF for [RFC4244], particularly around the need for and format of the index and around the security aspects. 16. Changes from RFC 4244 This RFC replaces [RFC4244]. Deployment experience with [RFC4244] over the years has shown a number of issues, warranting an update: o In order to make [RFC4244] work in "real life", one needs to make "assumptions" on how History-Info is used. For example, many implementations filter out many entries, and only leave specific entries corresponding, for example, to first and last redirection. Since vendors uses different rules, it causes significant interoperability issues. o [RFC4244] is overly permissive and evasive about recording entries, causing interoperability issues. o The examples in the call flows had errors, and confusing because they often assume "loose routing". o [RFC4244] has lots of repetitive and unclear text due to the combination of requirements with solution. o [RFC4244] gratuitously mandates the use of TLS on every hop. No existing implementation enforces this rule, and instead, the use of TLS or not is a general SIP issue, not an [RFC4244] issue per se. o [RFC4244] does not include clear procedures on how to deliver current target URI information to the UAS when the Request-URI is replaced with a contact. o [RFC4244] does not allow for marking History-Info entries for easy processing by User Agents. The following summarizes the functional changes between this specification and [RFC4244]: Barnes, et al. Expires October 3, 2012 [Page 29] Internet-Draft History-Info Apr 2012 1. Added header field parameters to capture the specific method by which a target is determined to facilitate processing by users of the History-Info header field entries. A specific header field parameter is captured for each of the target URIs as the target set is determined (per section 16.5 of [RFC3261]). The header field parameter is used in both the History-Info and the Contact header fields. 2. Rather than recommending that entries be removed in the case of certain values of the Privacy header field, the entries are anonymized. 3. Updated the security section to be equivalent to the security recommendations for other SIP header fields inserted by intermediaries. The first 2 changes are intended to facilitate application usage of the History-Info header field and eliminate the need to make assumptions based upon the order of the entries and ensure that the most complete set of information is available to the applications. In addition, editorial changes were done to both condense and clarify the text, moving the requirements to an appendix and removing the inline references to the requirements. The examples were simplified and updated to reflect the protocol changes. Several of the call flows in the appendix were removed and put into a separate document that includes additional use cases that require the new header field parameters. 16.1. Backwards compatibility This specification is backwards compatible since [RFC4244] allows for the addition of new optional parameters. This specification adds an optional SIP header field parameter to the History-Info and Contact header fields. Entities that have not implemented this specification will ignore these parameters, however, per [RFC4244] an entity will not remove this parameter from an hi-entry. As for the behavior of the entity followings have changed since the [RFC4244]. UAC behavior 1. Inclusion of option tag by UAC has changed from SHOULD to MUST. 2. Inclusion of hi-target-entry along with hi-index has changed from MAY/RECOMMEND to MUST/MUST. Barnes, et al. Expires October 3, 2012 [Page 30] Internet-Draft History-Info Apr 2012 3. Behavior surrounding the addition of hi-target-entry based on 3xx response has changed from MAY/SHOULD to MUST. None of the behavior changes would cause any backward compatibility issues. UAS behavior 1. Inclusion of hi-entry in response has changed from SHOULD to MUST. As the entity receiving response with hi-entry expected it with SHOULD, this change will not cause any backward compatibility issues. Proxy/Redirect Server behavior 1. Inclusion of H-I as forwarding the request has changed from SHOULD to MUST. 2. Association of Reason with time-out/internal reason has changed from MAY to MUST. 3. Inclusion of hi-index has changed from RECOMMENDED to MUST. 4. Inclusion of hi-entries in response has changed from SHOULD to MUST. None of the behavior changes will cause any backward compatibility issues as entity interacting with the updated code, expects the values set by the revised behavior anyway. 17. Changes since last Version NOTE TO THE RFC-Editor: Please remove this section prior to publication as an RFC. Changes from 04 to 05: 1. Lots of editorial corrections/clarifications per John Elwell's comment. 2. Updated Reason header section 10.2 to be consistent (i.e., removed references to retargeting) with section 9.3 (Receiving a response) where the hi-entries and reason header are added to the cache. Barnes, et al. Expires October 3, 2012 [Page 31] Internet-Draft History-Info Apr 2012 3. Updated section 9.3 (receiving responses) to also include timeouts and updated to reflect that we don't add the Reason header in the case of 2xx responses. 4. Added text in Security considerations with regards to needing a Privacy Service per RFC 3323 to ensure that the privacy is applied. Changes from 03 to 04: 1. Reorganization of sections per John Elwell's comments - i.e., a common section for building HI referenced by the UA, Intermediary and Redirect server sections. 2. Removing the use of "escape" when describing the handling of the Privacy and Reason header fields. 3. Clarification of TEL URIs in terms of not having a Privacy or Reason header field in the hi-targeted-to-uri. Changes from 02 to 03: 1. Lots of editorial: 2. A. Reorganized sections similar to the RFC 4244 order - i.e., introduce header field parameters and syntax first, then describe how the functional entities use the header field. This removes redundant (and often inconsistent) text describing the parameters. B. Expanded use of "header" to "header field" C. More precision in terms of "escaping" of the Privacy and Reason headers in the hi-targeted-to-uri (versus "adding"/"setting"/etc. them to the hi-entry). D. Consistent use of parameter names (i.e., hi-entry versus entry, hi-target versus target, etc.) E. Moved item 6 in the Index section to the section on Response handling F. Removed last remaining vestiges of inline references to requirements. Barnes, et al. Expires October 3, 2012 [Page 32] Internet-Draft History-Info Apr 2012 3. Clarifications of functionality/applicability including: 4. A. which messages may contain History-Info B. removing security text with regards to being able to figure out if there are missing entries when using TLS (issue #44) C. More complete information on the new header field parameters as they relate to the hi-target parameter. D. Changed wording from passive to active for normative statements in many cases and removed superfluous normative language. 5. Rewrite of the Privacy section to address issues and splitting into the setting of the Privacy header fields and the processing/ application of the privacy header field priv-values. 6. Rewrite of the Reason header field section - simplifying the text and adding back the RFC 4244 text with regards to the use of the Reason header field in cases of internal retargeting. Changes from 01 to 02: 1. Editorial nits/clarifications. [Issues: 1,6,17,18,21- 23,25,26,30-33,35-37,39,40] 2. Removing extraneous 4244 text - e.g., errors in flows, "stronger" security, "session" privacy. [Issues: 3,5,7,11 ] 3. Updated definition of "retarget" to be all encompassing - i.e., also includes internal changes of target URI. Clarified text for "internal retargeting" in proxy section. [Issues: 2,8,9] 4. Clarified that the processing for Proxies is equally applicable to other SIP intermediaries. [Issue: 9]. 5. Changed more SHOULDs to MUSTs. [Issue: 10] 6. Fixes to Application considerations section. [Issues: 12-15] 7. Changed language in the procedure for Indexing to normative language. 8. Clarifications for UAC processing: Barnes, et al. Expires October 3, 2012 [Page 33] Internet-Draft History-Info Apr 2012 * MUST add hi-entry. [Issue: 28] * Clarify applicability to B2BUA. [Issue: 29] * Fixed text for indexing for UAC in case of 3xx. 9. Changed "hit" URI parameter to header field parameters: [Issues: 4,40] * Added index to all target header parameters. [Issues: 41] * Updated all the relevant sections documenting setting and use of new header parameters. [Issue: 40] 10. Updated/clarified privacy handling. [Issue: 16] 11. Updated Redirect Server section to allow adding History-Info header fields. [Issue: 24 ] 12. Added text around restrictions for Tel-URIs - i.e., no privacy or reason. [Issues: 4, 12] 13. Updated text for forking - what goes in response. [Issues: 19,20] Changes from 00 to 01: 1. Moved examples (except first) in appendix to a new (informational) document. 2. Updated UAS and UAC sections to clarify and expand on the handling of the History-Info header field. 3. Updated the Application considerations section: o Included more detail with regards to how applications can make use of the information, in particular based on the new tags. o Removed privacy consideration (2nd bullet) since privacy is now accomplished by anonymizing rather than removal of entries. Changes from (individual) barnes-sipcore-4244bis-03 to (WG) ietf- sipcore-4244bis-00: 1. Added a new SIP/SIPS URI parameter to tag the URIs as they are added to the target list and those returned in the contact header in a 3xx response. Barnes, et al. Expires October 3, 2012 [Page 34] Internet-Draft History-Info Apr 2012 2. Updated description of "target" parameter to use the new URI parameter value in setting the value for the parameter. 3. Clarified privacy. 4. Changed handling at redirect server to include the use of the new URI parameter and to remove the functionality of adding the History-Info entries (basically reverting to core 4244 processing). 5. Additional text to clarify that a service such as voicemail can be done in multiple ways. 6. Editorial changes including removal of some vestiges of tagging all entries (including the "aor" tag). Changes from barnes-sipcore-4244bis-02 to 03: 1. Fixed problem with indices in example in voicemail example. 2. Removed oc and rt from the Hi-target parameter. 3. Removed aor tag 4. Added index parameter to "mp" 5. Added use-cases and call-flows from target-uri into appendix. Changes from barnes-sipcore-4244bis-01 to 02: 1. Added hi-aor parameter that gets marked on the "incoming" hi- entry. 2. Hi-target parameter defined to be either rc, oc, mp, rt, and now gets included when adding an hi-entry. 3. Added section on backwards compatibility, as well as added the recognition and handling of requests that do not support this specification in the appropriate sections. 4. Updated redirect server/3xx handling to support the new parameters - i.e., the redirecting entity must add the new hi- entry since the proxy does not have access to the information as to how the Contact was determined. 5. Added section on normative differences between this specification and RFC 4244. Barnes, et al. Expires October 3, 2012 [Page 35] Internet-Draft History-Info Apr 2012 6. Restructuring of document to be more in line with current IETF practices. 7. Moved Requirements section into an Appendix. 8. Fixed ABNF to remove unintended ordering requirement on hi-index that was introduced in attempting to illustrate it was a mandatory parameter. Changes from barnes-sipcore-4244bis-00 to 01 : 1. Clarified "retarget" definition. 2. Removed privacy discussion from optionality section - just refer to privacy section. 3. Removed extraneous text from target-parameter (leftover from sip- 4244bis). Changed the terminology from the "reason" to the "mechanism" to avoid ambiguity with parameter. 4. Various changes to clarify some of the text around privacy. 5. Reverted proxy response handling text to previous form - just changing the privacy aspects to anonymize, rather than remove. 6. Other editorial changes to condense and simplify. 7. Moved Privacy examples to Appendix. 8. Added forking to Basic call example. Changes from barnes-sipcore-4244bis-00 to 01 : 1. Clarified "retarget" definition. 2. Removed privacy discussion from optionality section - just refer to privacy section. 3. Removed extraneous text from target-parameter (leftover from sip- 4244bis). Changed the terminology from the "reason" to the "mechanism" to avoid ambiguity with parameter. 4. Various changes to clarify some of the text around privacy. 5. Reverted proxy response handling text to previous form - just changing the privacy aspects to anonymize, rather than remove. Barnes, et al. Expires October 3, 2012 [Page 36] Internet-Draft History-Info Apr 2012 6. Other editorial changes to condense and simplify. 7. Moved Privacy examples to Appendix. 8. Added forking to Basic call example. Changes from barnes-sip-4244bis-00 to barnes-sipcore-4244bis-00: 1. Added tags for each type of retargeting including proxy hops, etc. - i.e., a tag is defined for each specific mechanism by which the new Request-URI is determined. Note, this is extremely helpful in terms of backwards compatibility. 2. Fixed all the examples. Made sure loose routing was used in all of them. 3. Removed example where a proxy using strict routing is using History-Info for avoiding trying same route twice. 4. Remove redundant Redirect Server example. 5. Index is now mandated to start at "1" instead of recommended. 6. Updated 3xx behavior as the entity sending the 3XX response MUST add the hi-target attribute to the previous hi-entry to ensure that it is appropriately tagged (i.e., it's the only one that knows how the contact in the 3xx was determined.) 7. Removed lots of ambiguity by making many "MAYs" into "SHOULDs" and some "SHOULDs" into "MUSTs". 8. Privacy is now recommended to be done by anonymizing entries as per RFC 3323 instead of by removing or omitting hi-entry(s). 9. Requirement for TLS is now same level as per RFC 3261. 10. Clarified behavior for "Privacy" (i.e., that Privacy is for Hi- entries, not headers). 11. Removed "OPTIONALITY" as specific requirements, since it's rather superflous. 12. Other editorial changes to remove redundant text/sections. Changes from RFC4244 to barnes-sip-4244bis-00: 1. Clarified that HI captures both retargeting as well as cases of just forwarding a request. Barnes, et al. Expires October 3, 2012 [Page 37] Internet-Draft History-Info Apr 2012 2. Added descriptions of the usage of the terms "retarget", "forward" and "redirect" to the terminology section. 3. Added additional examples for the functionality provided by HI for core SIP. 4. Added hi-target parameter values to HI header to ABNF and protocol description, as well as defining proxy, UAC and UAS behavior for the parameter. 5. Simplified example call flow in section 4.5. Moved previous call flow to appendix. 6. Fixed ABNF per RFC4244 errata "dot" -> "." and added new parameter. 18. References 18.1. Normative References [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason Header Field for the Session Initiation Protocol (SIP)", RFC 3326, December 2002. [RFC3323] Peterson, J., "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", BCP 14, RFC 2119, March 1997. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC4244] Barnes, M., "An Extension to the Session Initiation Protocol (SIP) for Request History Information", RFC 4244, November 2005. Barnes, et al. Expires October 3, 2012 [Page 38] Internet-Draft History-Info Apr 2012 18.2. Informative References [RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User Agent URIs (GRUUs) in the Session Initiation Protocol (SIP)", RFC 5627, October 2009. [RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session Initiation Protocol (SIP)", RFC 5630, October 2009. [RFC3087] Campbell, B. and R. Sparks, "Control of Service Context using SIP Request-URI", RFC 3087, April 2001. [RFC4240] Burger, E., Van Dyke, J., and A. Spitzer, "Basic Network Media Services with SIP", RFC 4240, December 2005. [RFC3969] Camarillo, G., "The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)", BCP 99, RFC 3969, December 2004. [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004. [RFC4458] Jennings, C., Audet, F., and J. Elwell, "Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR)", RFC 4458, April 2006. Appendix A. 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. Although 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. GENERATION-req: "Request History" information is generated when the request is retargeted. A. In some scenarios, it might be possible for more than one instance of retargeting to occur within the same proxy. A proxy MUST also generate Request History information for the 'internal retargeting'. Barnes, et al. Expires October 3, 2012 [Page 39] Internet-Draft History-Info Apr 2012 B. An entity (UA or proxy) retargeting in response to a redirect or REFER MUST include any Request History information from the redirect/REFER in the new request. 3. ISSUER-req: "Request History" information can be generated by a UA or proxy. It can be passed in both requests and responses. 4. CONTENT-req: The "Request History" information for each occurrence of retargeting shall include the following: A. The new URI or address to which the request is in the process of being retargeted, B. The URI or address from which the request was retargeted, and whether the retarget URI was an AOR C. The mechanism by which the new URI or address was determined, D. The reason for the Request-URI or address modification, E. Chronological ordering of the Request History information. 5. REQUEST-VALIDITY-req: Request History is applicable to requests not sent within an early or established dialog (e.g., INVITE, REGISTER, MESSAGE, and OPTIONS). 6. 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. 7. FORWARDS-req: Request History information may also be included by the generating entity in the request, if it is forwarded onwards. A.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-Info entry either by adding an additional hi-entry as a result of retargeting or entering invalid information. Barnes, et al. Expires October 3, 2012 [Page 40] Internet-Draft History-Info Apr 2012 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. 3. A rogue application could delete some or all of the Request History 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 entity providing the request. 4. SEC-req-4: To ensure the confidentiality of the Request History information, only entities that 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. A.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 shall not be included in out going messages unless it is protected as described in [RFC3323]. Barnes, et al. Expires October 3, 2012 [Page 41] Internet-Draft History-Info Apr 2012 Appendix B. Example call flows The scenarios in this section provide sample use cases for the History-Info header field for informational purposes only. They are not intended to be normative. A basic forking use case is included, along with two use cases illustrating the use of the privacy. B.1. PBX Voicemail call flow In this example, Alice calls Bob, whose SIP client is forwarded to Carol. Carol does not answer the call, thus it is forwarded to a VM (voicemail) server (VMS). In order to determine the appropriate mailbox to use for this call, the VMS needs the original target for the request. The original target is determined by finding the first hi-entry tagged with "rc" and using the hi-entry referenced by the index of "rc" header field parameter as the target for determining the appropriate mailbox. This hi-entry is used to populate the "target" URI parameter as defined in [RFC4458]. The reason associated with the first hi-entry tagged with "rc" (i.e., 302) could be used to provide a customized voicemail greeting and is used to populate the "cause" URI parameter as defined in [RFC4458]. Note that some VMSs may also (or instead) use the information available in the History-Info headers for custom handling of the VM in terms of how and why the call arrived at the VMS. Furthermore it is the proxy forwarding the call to VMS that determines the target of the voicemail, it is the proxy that sets the target of voicemail which is also the entity that utilizes RFC4244bis to find the target which is usually based on local policy installed by the user or an administrator. Alice example.com Bob Carol VM | INVITE F1 | | | | |------------->| | | | | | INVITE F2 | | | | |------------->| | | | | | | | | 100 Trying | | | | |<-------------| 302 Moved Temporarily F3 | | | |<-------------| | | | | ACK | | | | |------------->| | | | | | | | | | INVITE F4 | | | | |--------------------------->| | | | | | | | | 180 Ringing F5 | | Barnes, et al. Expires October 3, 2012 [Page 42] Internet-Draft History-Info Apr 2012 | |<---------------------------| | | | | | | | 180 Ringing | | | | |<-------------| | | | | | | | | | | (timeout) | | | | | | | | | INVITE F6 | | | | |-------------------------------------->| | | | | | | | 200 OK F7 | | |<--------------------------------------| | 200 OK | | | | |<-------------| | | | | | | | | | ACK | | | | |------------->| ACK | | |-------------------------------------->| F1 INVITE Alice -> Example.com INVITE sip:bob@example.com Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Contact: Alice Content-Length: [SDP Not Shown] F2 INVITE Example.com -> Bob INVITE sip:bob@192.0.2.5 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Alice Barnes, et al. Expires October 3, 2012 [Page 43] Internet-Draft History-Info Apr 2012 Content-Type: application/sdp Content-Length: [SDP Not Shown] F3 302 Moved Temporarily Bob -> Example.com SIP/2.0 302 Moved Temporarily Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se ;received=192.0.2.112 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob ;tag=2hi-1nf Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Content-Type: application/sdp Content-Length: [SDP Not Shown] F4 INVITE Example.com -> Carol INVITE sip:carol@192.0.2.4 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK353s Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 Contact: Alice Content-Type: application/sdp Content-Length: [SDP Not Shown] F5 180 Ringing Carol -> Example.com Barnes, et al. Expires October 3, 2012 [Page 44] Internet-Draft History-Info Apr 2012 SIP/2.0 180 Ringing Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK353s ;received=192.0.2.113 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob ;tag=setss3x Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 Contact: Content-Type: application/sdp Content-Length: [SDP Not Shown] F6 INVITE Example.com -> VM INVITE sip:vm@192.0.2.6;target=sip:bob%40example.com;cause=408 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;\ index=1.2.1;rc=1.2 History-Info: ;\ index=1.3;mp=1.2 History-Info: ;\ index=1.3.1;rc=1.3 Contact: Alice Content-Type: application/sdp Content-Length: [SDP Not Shown] Barnes, et al. Expires October 3, 2012 [Page 45] Internet-Draft History-Info Apr 2012 F7 200 OK VM -> Example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 ;received=192.0.2.114 From: Alice ;tag=kkaz- To: Bob ;tag=3dweggs Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;\ index=1.2.1;rc=1.2 History-Info: ;\ index=1.3;mp=1.2 History-Info: ;\ index=1.3.1;rc=1.3 Contact: Content-Type: application/sdp Content-Length: [SDP Not Shown] B.2. Consumer Voicemail example call flow In this example, Alice calls the Bob but Bob has temporarily forwarded his phone to Carol because she is his wife. Carol does not answer the call, thus it is forwarded to a VM (voicemail) server (VMS). In order to determine the appropriate mailbox to use for this call, the VMS needs the appropriate target for the request. The last target is determined by finding the hi-entry referenced by the index of last hi-entry tagged with "rc" for determining the appropriate mailbox. This hi-entry is used to populate the "target" URI parameter as defined in [RFC4458]. Note that some VMSs may also (or instead) use the information available in the History-Info headers for custom handling of the VM in terms of how and why the called arrived at the VMS. Alice example.com Bob Carol VM Barnes, et al. Expires October 3, 2012 [Page 46] Internet-Draft History-Info Apr 2012 | INVITE F1 | | | | |------------->| | | | | | INVITE F2 | | | | |------------->| | | | | | | | | 100 Trying | | | | |<-------------| 302 Moved Temporarily F3 | | | |<-------------| | | | | ACK | | | | |------------->| | | | | | | | | | INVITE F5 | | | | |--------------------------->| | | | | | | | | 180 Ringing F6 | | | |<---------------------------| | | | | | | | 180 Ringing | | | | |<-------------| | | | | | | | | | | (timeout) | | | | | | | | | INVITE F7 | | | | |-------------------------------------->| | | | | | | | 200 OK F8 | | |<--------------------------------------| | 200 OK | | | | |<-------------| | | | | | | | | | ACK | | | | |------------->| ACK | | |-------------------------------------->| F1 INVITE Alice -> Example.com INVITE sip:bob@example.com Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Contact: Alice Content-Length: [SDP Not Shown] Barnes, et al. Expires October 3, 2012 [Page 47] Internet-Draft History-Info Apr 2012 F2 INVITE Example.com -> Bob INVITE sip:bob@192.0.2.5 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Alice Content-Type: application/sdp Content-Length: [SDP Not Shown] F3 302 Moved Temporarily Bob -> Example.com SIP/2.0 302 Moved Temporarily Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK12se ;received=192.0.2.111 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob ;tag=2hi1nfo Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Content-Type: application/sdp Content-Length: [SDP Not Shown] F4 INVITE Example.com -> Carol INVITE sip:carol@192.0.2.4 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKseb1 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Barnes, et al. Expires October 3, 2012 [Page 48] Internet-Draft History-Info Apr 2012 History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 Contact: Alice Content-Type: application/sdp Content-Length: [SDP Not Shown] F5 180 Ringing Carol -> Example.com SIP/2.0 180 Ringing Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKseb1 ;received=192.0.2.112 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob ;tag=setss3x Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 Contact: Carol Content-Type: application/sdp Content-Length: [SDP Not Shown] F6 INVITE Example.com -> VM INVITE sip:vm@192.0.2.6;target=sip:carol%40example.com Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKb3ss Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc History-Info: ;\ index=1.2;mp=1 Barnes, et al. Expires October 3, 2012 [Page 49] Internet-Draft History-Info Apr 2012 History-Info: ;index=1.2.1;rc=1.2 History-Info: ;\ index=1.3;mp=1.2 History-Info: ;\ index=1.3.1 Contact: Alice Content-Type: application/sdp Content-Length: [SDP Not Shown] F7 200 OK VM -> Example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKb3ss ;received=192.0.2.113 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=kkaz- To: Bob ;tag=3dweggs Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;\ index=1.1;rc History-Info: ;\ index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 History-Info: ;\ index=1.3;mp=1.2 History-Info: ;\ index=1.3.1 Contact: Content-Type: application/sdp Content-Length: [SDP Not Shown] The VMS can look at the last hi-entry and find the target of the mailbox by looking for the "target" URI parameter in the hi-entry. B.3. 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, et al. Expires October 3, 2012 [Page 50] Internet-Draft History-Info Apr 2012 Alice sends a call to Bob via sip:example.com. The proxy sip: example.com sequentially tries Bob on a SIP UA that has bound a contact with the sip:bob@example.com AOR, and then several alternate addresses (Office and Home) unsuccessfully before sending a response to Alice. The hi-entry containing the initial contact is the hi- entry just prior to the first hi-entry tagged with an "rc" header field parameter. In this example, the Office and Home are not the same AOR as sip:bob@example.com, but rather different AORs that have been configured as alternate addresses for Bob in the proxy. In other words, Office and Bob are not bound through SIP Registration with Bob's AOR. This type of arrangement is common for example when a "routing" rule to a PSTN number is manually configured in a proxy. These hi-entries are identified by the index contained in the hi- target-param "mp" header field parameter in the hi-entries. This scenario illustrates that by providing the History-Info to Alice, the end-user or an application at Alice could make a decision on how best to attempt finding Bob without sending multiple requests to the same destination. Upon receipt of the response containing the History-Info entries, the Request URIs for the History-Info entries tagged with "mp" header field parameter are extracted. Those Request-URIs can be compared to other URIs (if any) that might be attempted in order to establish the session with Bob. Thus, avoiding another INVITE to Bob's home phone. Without this mechanism, Alice might well attempt to reach Bob at his office phone, which would then retarget the request to Bob's home phone. When that attempt failed, then Alice might attempt to reach Bob directly at his home phone, unknowingly for a third time. Barnes, et al. Expires October 3, 2012 [Page 51] Internet-Draft History-Info Apr 2012 Alice example.com Bob Office Home | | | | | | INVITE F1 | | | | |----------->| INVITE F2 | | | | |----------------->| | | | 100 Trying F3 | | | |<-----------| 302 Move Temporarily F4 | | | |<-----------------| | | | | ACK F5 | | | | |----------------->| | | | | INVITE F6 | | | |-------------------------->| | | | 180 Ringing F7 | | | |<--------------------------| | | 180 Ringing F8 | | |<-----------| retransmit INVITE | | | |-------------------------->| | | | ( timeout ) | | | | INVITE F9 | | |----------------------------------->| | | 100 Trying F10 | | |<-----------------------------------| | | 486 Busy Here F11 | | |<-----------------------------------| | 486 Busy Here F12 | |<-----------| ACK F13 | | |----------------------------------->| | ACK F14 | | |----------->| | Message Details F1 INVITE alice -> example.com INVITE sip:bob@example.com SIP/2.0 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=sr3dds To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE History-Info: ;index=1 Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 52] Internet-Draft History-Info Apr 2012 F2 INVITE example.com -> Bob INVITE sip:bob@192.0.2.4 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=sr3dds To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Record-Route: History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Alice Content-Type: application/sdp Content-Length: F3 100 Trying example.com -> alice SIP/2.0 100 Trying Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=sr3dds To: Bob Call-Id: 12345600@example.com CSeq: 1 INVITE Content-Length: 0 F4 302 Moved Temporarily Bob -> example.com SIP/2.0 302 Moved Temporarily Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKrs22 ;received=192.0.2.111 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=sr3dds To: Bob ;tag=hi51nfo Call-Id: 12345600@example.com CSeq: 1 INVITE Record-Route: History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: ;mp=1 Barnes, et al. Expires October 3, 2012 [Page 53] Internet-Draft History-Info Apr 2012 Content-Length: 0 F5 ACK example.com -> Bob ACK sip:bob@example.com SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKrs22 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st From: Alice ;tag=sr3dds To: Bob ;tag=hi51nfo Call-Id: 12345600@example.com CSeq: 1 ACK Content-Length: 0 F6 INVITE example.com -> office INVITE sip:office@192.0.2.5 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKzeld Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob Supported: histinfo Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 CSeq: 1 INVITE Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 54] Internet-Draft History-Info Apr 2012 F7 180 Ringing office -> example.com SIP/2.0 180 Ringing Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKzeld ;received=192.0.2.113 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob ;tag=53rdds Supported: histinfo Call-ID: 12345600@example.com Record-Route: History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 CSeq: 1 INVITE Contact: Office Content-Length: 0 F8 180 Ringing example.com -> alice SIP/2.0 180 Ringing Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob ;tag=53rdds Supported: histinfo Call-Id: 12345600@example.com History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;index=1.2.1;rc=1.2 CSeq: 1 INVITE Contact: Office Content-Length: 0 Barnes, et al. Expires October 3, 2012 [Page 55] Internet-Draft History-Info Apr 2012 F9 INVITE example.com -> home INVITE sip:home@192.0.2.6 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob Supported: histinfo Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;\ index=1.2.1>;index=1.2.1;rc=1.2 History-Info: ;index=1.3;mp=1 History-Info: ;index=1.3.1;rc=1.3 CSeq: 1 INVITE Contact: Alice Content-Type: application/sdp Content-Length: F10 100 Trying home -> example.com SIP/2.0 100 Trying Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob Call-Id: 12345600@example.com CSeq: 1 INVITE Content-Length: 0 Barnes, et al. Expires October 3, 2012 [Page 56] Internet-Draft History-Info Apr 2012 F11 486 Busy Here home -> example.com SIP/2.0 486 Busy Here Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st ;received=192.0.2.114 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob ;tag=53rdds Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;\ index=1.2.1>;index=1.2.1;rc=1.2 History-Info: ;index=1.3;mp=1 History-Info: ;index=1.3.1;rc=1.3 CSeq: 1 INVITE Content-Length: 0 F12 486 Busy Here example.com -> alice SIP/2.0 486 Busy Here Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob ;tag=53rdds Call-Id: 12345600@example.com History-Info: ;index=1 History-Info: ;\ index=1.1;rc=1 History-Info: ;index=1.2;mp=1 History-Info: ;\ index=1.2.1>;index=1.2.1;rc=1.2 History-Info: ;index=1.3;mp=1 History-Info: ;index=1.3.1;rc=1.3 CSeq: 1 INVITE Content-Length: 0 Barnes, et al. Expires October 3, 2012 [Page 57] Internet-Draft History-Info Apr 2012 F13 ACK example.com -> home ACK sip:home@192.0.2.6 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx3st From: Alice ;tag=sr3dds>; To: Bob ;tag=53rdds Call-Id: 12345600@example.com CSeq: 1 ACK Content-Length: 0 F14 ACK alice -> example.com ACK sip:bob@example.com SIP/2.0 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bKbst2 From: Alice ;tag=sr3dds To: Bob ;tag=53rdds Call-Id: 12345600@example.com Route: CSeq: 1 ACK Content-Length: 0 B.4. History-Info with Privacy Header Field This example provides a basic call scenario without forking. Alice has indicated that she wants Privacy associated with the History-Info header field entries. In addition, sip:biloxi.example.com adds Privacy header fields indicating that the History-Info header field information is anonymized outside the biloxi.example.com domain. Note, that if the atlanta.example.com proxy had added privacy header fields to all its hi-entries, then all the hi-entries in the response would be anonymous. Barnes, et al. Expires October 3, 2012 [Page 58] Internet-Draft History-Info Apr 2012 Alice atlanta.example.com biloxi.example.com Bob | | | | | INVITE F1 | | | |--------------->| | | | | | | | | INVITE F2 | | | |--------------->| | | | | | | | | INVITE F3 | | | |--------------->| | | | | | | | 200 F4 | | | |<---------------| | | | | | | 200 F5 | | | |<---------------| | | | | | | 200 F6 | | | |<---------------| | | | | | | | ACK | | | |--------------->| ACK | | | |--------------->| ACK | | | |--------------->| Figure 2: Example with Privacy Header Fields Message Details F1 INVITE alice -> atlanta.example.com INVITE sip:bob@biloxi.example.com;p=x SIP/2.0 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Privacy: History Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 59] Internet-Draft History-Info Apr 2012 F2 INVITE atlanta.example.com -> biloxi.example.com INVITE sip:bob@biloxi.example.com;p=x SIP/2.0 Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Alice Content-Type: application/sdp Content-Length: F3 INVITE biloxi.example.com -> Bob INVITE sip:bob@192.0.1.11 SIP/2.0 Via: SIP/2.0/TCP proxy.biloxi.example.com:5060;branch=z9hG4bKtg3s Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.111 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 60] Internet-Draft History-Info Apr 2012 F4 200 OK Bob -> biloxi.example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.biloxi.example.com:5060;branch=z9hG4bKtg3s ;received=192.0.2.112 Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.111 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Bob Content-Type: application/sdp Content-Length: F5 200 OK biloxi.example.com -> atlanta.example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.111 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Bob Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 61] Internet-Draft History-Info Apr 2012 F6 200 OK atlanta.example.com -> Alice SIP/2.0 200 OK Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: Content-Type: application/sdp Content-Length: B.5. Privacy for a Specific History-Info Entry This example provides a basic call scenario similar to Appendix B.4, however, due to local policy at sip:biloxi.example.com, only the final hi-entry in the History-Info, which is Bob's local URI, contains a privacy header field with a priv-value of "history", thus providing Alice with some information about the history of the request, but anonymizing Bob's local URI. Barnes, et al. Expires October 3, 2012 [Page 62] Internet-Draft History-Info Apr 2012 Alice atlanta.example.com biloxi.example.com Bob | | | | | INVITE F1 | | | |--------------->| | | | | | | | | INVITE F2 | | | |--------------->| | | | | | | | | INVITE F3 | | | |--------------->| | | | | | | | 200 F4 | | | |<---------------| | | | | | | 200 F5 | | | |<---------------| | | | | | | 200 F6 | | | |<---------------| | | | | | | | ACK | | | |--------------->| ACK | | | |--------------->| ACK | | | |--------------->| Figure 3: Example with Privacy Header Field for Specific URI Message Details F1 INVITE alice -> atlanta.example.com INVITE sip:bob@biloxi.example.com;p=x SIP/2.0 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 63] Internet-Draft History-Info Apr 2012 F2 INVITE atlanta.example.com -> biloxi.example.com INVITE sip:bob@biloxi.example.com;p=x SIP/2.0 Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 Contact: Alice Content-Type: application/sdp Content-Length: F3 INVITE biloxi.example.com -> Bob INVITE sip:bob@192.0.1.11 SIP/2.0 Via: SIP/2.0/TCP proxy.biloxi.example.com:5060;branch=z9hG4bKeset Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.112 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 64] Internet-Draft History-Info Apr 2012 F4 200 OK Bob -> biloxi.example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.biloxi.example.com:5060;branch=z9hG4bKeset ;received=192.0.2.111 Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.112 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Bob Content-Type: application/sdp Content-Length: F5 200 OK biloxi.example.com -> atlanta.example.com SIP/2.0 200 OK Via: SIP/2.0/TCP proxy.atlanta.example.com:5060;branch=z9hG4bKbst2 ;received=192.0.2.112 Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Bob Content-Type: application/sdp Content-Length: Barnes, et al. Expires October 3, 2012 [Page 65] Internet-Draft History-Info Apr 2012 F6 200 OK atlanta.example.com -> Alice SIP/2.0 200 OK Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321 From: Alice ;tag=22 To: Bob ;tag=33 Supported: histinfo Call-Id: 12345600@atlanta.example.com CSeq: 1 INVITE History-Info: ;index=1 History-Info: ;index=1.1;rc=1 History-Info: ;index=1.1.1;rc=1.1 Contact: Bob Content-Type: application/sdp Content-Length: Authors' Addresses Mary Barnes Polycom TX US Email: mary.ietf.barnes@gmail.com Francois Audet Skype Email: francois.audet@skype.net Shida Schubert NTT Email: shida@ntt-at.com Barnes, et al. Expires October 3, 2012 [Page 66] Internet-Draft History-Info Apr 2012 Hans Erik van Elburg Detecon International Gmbh Oberkasseler str. 2 Bonn, Germany Email: ietf.hanserik@gmail.com Christer Holmberg Ericsson Hirsalantie 11, Jorvas Finland Email: christer.holmberg@ericsson.com Barnes, et al. Expires October 3, 2012 [Page 67]