Network Working Group M. Barnes, Ed. Internet-Draft F. Audet, Ed. Obsoletes: RFC4244 Nortel (if approved) J. van Elburg Intended status: Standards Track C. Holmberg Expires: January 14, 2010 Ericsson July 13, 2009 An Extension to the Session Initiation Protocol (SIP) for Request History Information draft-barnes-sipcore-rfc4244bis-02.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 14, 2010. Copyright Notice Barnes, et al. Expires January 14, 2010 [Page 1] Internet-Draft History-Info July 2009 Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. 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 call arrives at a specific application or user. This document defines an optional SIP header, History-Info, for capturing the history information in requests. Barnes, et al. Expires January 14, 2010 [Page 2] Internet-Draft History-Info July 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 3. Overview of Operations . . . . . . . . . . . . . . . . . . . . 5 4. General User Agent Behavior . . . . . . . . . . . . . . . . . 8 4.1. User Agent Client (UAC) Behavior . . . . . . . . . . . . . 8 4.2. User Agent Server (UAS) Behavior . . . . . . . . . . . . . 9 4.2.1. Redirect Server Behavior . . . . . . . . . . . . . . . 10 5. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 11 5.1. Adding the History-Info Header to Requests . . . . . . . . 11 5.1.1. Initial Request . . . . . . . . . . . . . . . . . . . 12 5.1.2. Re-sending based on failure response . . . . . . . . . 13 5.1.3. Re-sending based on redirection response . . . . . . . 13 5.2. Sending History-Info in Responses . . . . . . . . . . . . 14 6. The History-Info header field . . . . . . . . . . . . . . . . 14 6.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 18 6.3.1. Privacy in the History-Info Header . . . . . . . . . . 18 6.3.2. Reason in the History-Info Header . . . . . . . . . . 19 6.3.3. AOR Marking in the History-Info Header . . . . . . . . 19 6.3.4. Indexing in the History-Info Header . . . . . . . . . 20 6.3.5. Request Target in the History-Info Header . . . . . . 21 7. Application Considerations . . . . . . . . . . . . . . . . . . 22 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 9.1. Registration of New SIP History-Info Header . . . . . . . 23 9.2. Registration of "history" for SIP Privacy Header . . . . . 24 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 24 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25 12. Changes from RFC 4244 . . . . . . . . . . . . . . . . . . . . 25 12.1. Backwards compatibility . . . . . . . . . . . . . . . . . 26 13. Changes since last Version . . . . . . . . . . . . . . . . . . 26 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 14.1. Normative References . . . . . . . . . . . . . . . . . . . 29 14.2. Informative References . . . . . . . . . . . . . . . . . . 29 Appendix A. Request History Requirements . . . . . . . . . . . . 30 A.1. Security Requirements . . . . . . . . . . . . . . . . . . 31 A.2. Privacy Requirements . . . . . . . . . . . . . . . . . . . 32 Appendix B. Detailed call flows . . . . . . . . . . . . . . . . . 32 B.1. Sequentially Forking (History-Info in Response) . . . . . 33 B.2. Voicemail . . . . . . . . . . . . . . . . . . . . . . . . 40 B.3. Automatic Call Distribution . . . . . . . . . . . . . . . 42 B.4. History-Info with Privacy Header . . . . . . . . . . . . . 44 B.5. Privacy Header for a Specific History-Info Entry . . . . . 45 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 47 Barnes, et al. Expires January 14, 2010 [Page 3] Internet-Draft History-Info July 2009 1. Introduction Many services that SIP is anticipated to support require the ability to determine why and how the call arrived at a specific application. Examples of such services include (but are not limited to) sessions initiated to call centers via "click to talk" SIP Uniform Resource Locators (URLs) on a web page, "call history/logging" style services within intelligent "call management" software for SIP User Agents (UAs), and calls to voicemail servers. Although SIP implicitly provides the redirect/retarget capabilities that enable calls to be routed to chosen applications, there is a need for a standard mechanism within SIP for communicating the retargeting history of such a request. This "request history" information allows the receiving application to determine hints about how and why the call arrived at the application/user. This document defines a SIP header, History-Info, to provide a standard mechanism for capturing the request history information to enable a wide variety of services for networks and end-users. The History-Info header provides a building block for development of new services. The requirements for this document are described in Appendix A. 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 document to refer both to the process of a Proxy Server/User Agent Client (UAC) changing a Uniform Resource Identifier (URI) in a request based on the rules for determining request targets as described in Section 16.5 of [RFC3261] and the subsequent forwarding of that request as described in section 16.6 of [RFC3261]. The term "forward" is used consistent with the terminology in [RFC3261]. Noting that [RFC3261] uses the term "forwarding" to describe a proxy's handling of requests for domains for which is not responsible, as well as to describe the basic "forwarding" of a request (in section 16.6) once a target has been determined. However, the context of the usage is sufficient to differentiate the slightly different meanings. The terms "location service" and "redirect" are used consistent with the terminology in [RFC3261]. Barnes, et al. Expires January 14, 2010 [Page 4] Internet-Draft History-Info July 2009 3. Overview of Operations SIP implicitly provides retargeting capabilities that enable calls 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 call is retargeted to process the call 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 provide the ability for elements involved with the call to exchange additional information relating to how and why the call was routed to a particular destination. The following are examples of such applications: 1. Web "referral" applications, whereby an application residing within a web server determines that a visitor to a website has arrived at the site via an "associate" site that will receive some "referral" commission for generating this traffic 2. Email forwarding whereby the forwarded-to user obtains a "history" of who sent the email to whom and at what time 3. Traditional telephony services such as voicemail, call-center "automatic call distribution", and "follow-me" style services Several of the aforementioned applications currently define application-specific mechanisms through which it is possible to obtain the necessary history information. In addition, request history information could be used to enhance basic SIP functionality by providing the following: o Some diagnostic information for debugging SIP requests. (Note that the diagnostic utility of this mechanism is limited by the fact that its use by entities that retarget is optional.) o Capturing aliases and Globally Routable User Agent URIs (GRUUs) [I-D.ietf-sip-gruu], which can be overwritten by a home proxy 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 Barnes, et al. Expires January 14, 2010 [Page 5] Internet-Draft History-Info July 2009 of network announcements and IVR with SIP URI [RFC4240]. o A stronger security solution for SIP. A side effect is that each proxy that captures the "request history" information in a secure manner provides an additional means (without requiring signed keys) for the original requestor to be assured that the request was properly retargeted. The fundamental functionality provided by the request history information is the ability to inform proxies and UAs involved in processing a request about the history or progress of that request (CAPABILITY-req, see Appendix A). The solution is to capture the Request-URIs as a request is retargeted, in a new header for SIP messages: History-Info (CONTENT-req, see Appendix A). 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. This solution proposes no changes in the fundamental determination of request targets or in the request forwarding as defined in Sections 16.5 and 16.6 of the SIP protocol specification [RFC3261]. The History-Info header can appear in any request not associated with an established dialog (e.g., INVITE, REGISTER, MESSAGE, REFER and OPTIONS, PUBLISH and SUBSCRIBE, etc.) (REQUEST-VALIDITY-req, seeAppendix A) and any valid response to these requests (ISSUER-req, seeAppendix A). This specification defines parameters (see Section 6.1) for carrying the following information in the History-Info header: o Targeted-to-URI: The targeted-to-URI entry captures the Request- URI for the specific Request as it is forwarded. o Index: The index reflects the chronological order of the information, indexed to also reflect the forking and nesting of requests. o Reason: Reason describes why an entry was retargeted. o Privacy: Privacy is used to request that entries be anonymized. o AOR indicator: The AOR indicator is to mark an URI entry as being an Address Of Record. o Target: The target parameter indicates the mechanism by which the new target is determined, i.e., a "registered contact", an "implicitly contact obtained through means other than SIP registration", a "mapped URI", or just "normal routing." Barnes, et al. Expires January 14, 2010 [Page 6] Internet-Draft History-Info July 2009 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 home proxy (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 target information, including any parameters in the request URI. Bob can now recover that information by looking for the last hi-entry marked as "aor." The formatting in this scenario is for visual purposes; thus, backslash and CRLF are used between the fields for readability and the headers in the URI are not shown properly formatted for escaping. Refer to Section 6.2 for the proper formatting. Additional detailed scenarios are available in the Appendix B. Note: This example uses loose routing procedures. 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: ;index=1.1;rt | | | | | | | | INVITE sip:bob@192.0.2.3 | | |--------------->| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | | | INVITE sip:bob@192.0.2.7 | | |-------------------------->| | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.2;rc Barnes, et al. Expires January 14, 2010 [Page 7] Internet-Draft History-Info July 2009 | | | 200 | | | | |<---------------| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | | |<===Proxy cancels INVITE==>| | | 200 | | | | |<---------------| | | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | History-Info: ;\ | index=1.1.2;rc | | | | | | 200 | | | | |<---------------| | | | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;\ | index=1.1.2;rc | | | | | | ACK | | | | |--------------->| ACK | | | | |--------------->| ACK | | | | |--------------->| | Figure 1: Basic Call 4. General User Agent Behavior This section describes the processing specific to UAs for the History-Info header. 4.1. User Agent Client (UAC) Behavior The UAC SHOULD include the "histinfo" option tag in the Supported header in any request not associated with an established dialog for which the UAC would like the History-Info header in the response. In addition, the UAC MAY add a History-Info header, using the Request- URI of the request as the hi-target-to-uri, in which case the index MUST be set to a value of 1 in the hi-entry. As a result, intermediaries and the UAS will know at least the original Request- URI, and if the Request-URI was modified by a previous hop. Normally, UACs are not expected to include a History-Info header in Barnes, et al. Expires January 14, 2010 [Page 8] Internet-Draft History-Info July 2009 an initial request as it is more of a Proxy function; the main reason it is allowed is for B2BUAs who are performing proxy-like functions like routing. A UAC that does not want an hi-entry added due to privacy considerations MUST include a Privacy header with a priv-value(s) of "header" or "history." A UAC that wants to ensure that privacy not be applied to its identity MUST include a Privacy header with a priv- value of "none." In the case where a UAC receives a 3xx response with a Contact header and sends a new request in response to it, the UAC MUST include in the outgoing request the previous hi-entry(s) received in the response. The UAC MUST evaluate the last hi-entry in the 3xx response and verify that they are the same (as per the procedures in section Section 4.2.1); if the hi-entry is not the same as the value in contact, hi-entry MUST be added using the value of Contact. If the hi-entry for the redirection is not included in the 3xx response, then an hi-entry MUST be added to the outgoing request. In this case, the index MUST be created by reading and incrementing the value of the index from the previous hi-entry, thus following the same rules as those prescribed for a proxy in retargeting, described in Section 6.3.4. The reason MUST be added per Section 6.3.2. The hi-target and hi-aor attributes MUST NOT be added to this hi-entry since there is no way to know the mechanism by which the redirecting entity determined the URI in the Contact header nor whether the previous hi-targeted-to-uri was an AOR. If no hi-entry for redirection were included at all in the 3xx response, and multiple redirection occurs, the UAC MAY attempt to synthetise the missing hi-entrie(s) before inserting the last one (as per the previous step). At a minimum, the last entry (as per the previous step) MUST be included. With the exception of the processing of a 3xx response described above, the processing of the History-Info header received in the Response is application specific and outside the scope of this document. 4.2. User Agent Server (UAS) Behavior Once the request terminates at the UAS, the processing of the information in the History-Info header by a UAS in a Request depends upon local policy and specific applications at the UAS that might make use of the information. Prior to any application usage of the information, the validity SHOULD be ascertained. For example, the entries MAY be evaluated to determine gaps in indices, which could Barnes, et al. Expires January 14, 2010 [Page 9] Internet-Draft History-Info July 2009 indicate that an entry has been maliciously removed or removed for privacy reasons. Either way, an application MAY want to be aware of potentially missing information. If the "histinfo" option tag is received in a request, the UAS MUST include any History-Info received in the request in the subsequent response. If privacy is required, entries MUST be anonymized using [RFC3323]. The UAS MUST follow the rules for a redirect server per Section 4.2.1 in generating a 3xx response. The processing of History-Info in responses follows the methodology described in Section 16.7 of [RFC3261], with the processing of History-Info headers adding an additional step, just before Step 9, "Forwarding the Response". 4.2.1. Redirect Server Behavior A redirect server MUST include the History-Info headers received in the request in the 3XX response that it sends, and it MUST perform the following steps: Step 1: Adding Entries on Behalf of Previous Hops If an incoming request does not already have a History-Info header field (e.g., the UAC does not include any History-Info header and no proxies in between support History-Info), or if the Request-URI of the incoming request does not match the last hi-entry (e.g., the last hop proxy does not support History-Info), the redirect server MUST insert an hi-entry. The redirect server MUST set the hi-targeted-to-uri to the value of Request URI in the incoming request, unless privacy is required. If privacy is required, the procedures of Section 6.3.1 MUST be used. The proxy MUST NOT include a hi-target attribute. The proxy MUST include an hi-index attribute as described in Section 6.3.4. Step 2: Tagging the Last Incoming Entry The redirect server then examines the last hi-entry of the History-Info header resulting from the previous step. If the redirect server recognizes the hi-targeted-to-uri as being an AOR that is under its domain, then the redirect server MUST add an hi- aor parameter set to "aor" to that entry (see Section 6.3.3). If privacy is required for this entry, the procedures of Section 6.3.1 MUST be used for that entry. The Reason header MUST be added to that entry as per the procedures of Section 6.3.2, and must be set to the proper SIP 3XX response. Barnes, et al. Expires January 14, 2010 [Page 10] Internet-Draft History-Info July 2009 Step 3: Generating New Entries for the Response The redirect servert MUST add a new hi-entry for each of the Contact header URIs, which becomes the new Request-URIs when the recipient forwards the new Request. The index is created as described in Section 6.3.4. If privacy is required, the procedures of Section 6.3.1 MUST be used. A hi-target parameter MUST be included for each entry indicating the mechanism by which it is routed as per the procedures of Section 6.3.5. Redirection is an iterative process, i.e., a redirect server may redirect "internally " more than one time. A typical example would be a redirect server that redirects a request first to a different user (i.e., it maps to a different AOR), and then redirects again to a registered contact bound to that new AOR. A redirect server that uses such mechamism SHOULD add multiple hi-entry fields to provide a logical description of retargeting process (e.g., bob@example.com to office@example.com to office@192.0.2.5). Seethe example inAppendix B.1) for an example. 5. Proxy Behavior The specific processing by proxies for adding the History-Info headers in Requests and Responses is described in this section for the following cases: o Forwarding of initial request (see Section 5.1.1) o Resending based on failure response (see Section 5.1.2) o Resending based on redirection response (see Section 5.1.3) 5.1. Adding the History-Info Header to Requests This section describes the process of adding the History-Info Header to Requests. Retargeting is an iterative process, i.e., a proxy may redirect "internally " more than one time. A typical example would be a proxy that redirects a request first to a different user (i.e., it maps to a different AOR), and then forwards to a registered contact bound to that new AOR. A proxy that uses such mechamism SHOULD add multiple hi-entry fields to provide a logical description of the retargeting process. Barnes, et al. Expires January 14, 2010 [Page 11] Internet-Draft History-Info July 2009 5.1.1. Initial Request Upon receipt of an initial request for a dialog, or a standalone request, a proxy forwarding the request MUST perform the following steps. Note that those steps below do not apply if the request is being re-sent as a result of failure (i.e., timeout, reception of an error response), or redirection caused by receipt of a 3XX message). Step 1: Adding Entries on Behalf of Previous Hops If an incoming request does not already have a History-Info header field (e.g., the UAC does not include any History-Info header and no proxies in between support History-Info), or if the Request-URI of the incoming request does not match the last hi-entry (e.g., the last proxy does not support History-Info), the proxy MUST insert an hi-entry. The proxy MUST set the hi-targeted-to-uri based to the value of Request URI in the incoming request, unless privacy is required. If privacy is required, the procedures of Section 6.3.1 MUST be used. The proxy MUST NOT include a hi- target attribute. The proxy MUST include an hi-index attribute as described in Section 6.3.4. Step 2: Tagging the Last Incoming Entry The proxy then examines the last hi-entry of the History-Info header resulting from the previous step. If the proxy recognizes the hi-targeted-to-uri as being an AOR that is under its domain, then the proxy MUST add an hi-aor parameter set to "aor" to that entry (see Section 6.3.3). If privacy is required for this entry, the procedures of Section 6.3.1 MUST be used for that entry. Step 3: Generating New Entries for Each Outgoing Requests The proxy then proceeds to determining the request targets as per 16.5/[RFC3261] and request forwarding as per 16.6/[RFC3261]. The proxy MUST add a separate hi-entry in each separate outgoing request for each of the current (outgoing) targets in the target set. The proxy MUST set the hi-targeted-to-uri in those separate hi-entry(s) to the value of the Request-URI of the current (outgoing) request, unless privacy is required. If privacy is required, the procedures of Section 6.3.1 MUST be used. The proxy MUST include a hi-target attribute for each of the separate entry(s) as described in Section 6.3.5. The proxy MUST include an hi-index for each of the separate hi-entry(s) as described in Section 6.3.4. Barnes, et al. Expires January 14, 2010 [Page 12] Internet-Draft History-Info July 2009 5.1.2. Re-sending based on failure response When re-sending a request as a result of retargeting because of failure (i.e., either reception of error responses or a timeout which is considered to be an implicit 487 error response), the proxy MUST perform the following steps: Step 1: Including the Entries from Error Responses & Timeouts The proxy MUST build the History-Info header field(s) sent in the outgoing request using the aggregate information associated with the received error responses(s) and timeout(s) for all the branches that are generating failures, including the header entries in the order indicated by the indexing (see Section 6.3.4). If the received error response did not include any History-Info header fields, the proxy MUST use the same History-Info header fields that were sent in the outgoing request that failed to build the outgoing request. Step 2: Tagging the Last Entries The proxy then examines the last hi-entry of the History-Info that was just generated in Step 1 for each one of the branches that generated failures or timeouts and MUST add a Reason header for each one of those entries as per the procedures of Section 6.3.2. Step 3: Generating New Entries for Each Outgoing Requests Same as per Step 3 above for the normal forwarding case. 5.1.3. Re-sending based on redirection response When re-sending a request as a result of retargeting because of redirection (i.e., receipt of a 3XX response), the following steps apply: Step 1: Including Previous Entries If the received 3XX response does not include any History-Info header fields, the proxy MUST include the History-Info header fields that were sent in the outgoing request that is being redirected. The proxy MUST then perform Steps 2 and 3. If the 3XX response contains a History-Info Header field, but the last entries does not correspond to the current target (i.e., they do not correspond to the Contact(s) in the 3XX), the proxy MUST include in the outgoing request the same History-Info header fields that were received in the 3XX response. The proxy MUST Barnes, et al. Expires January 14, 2010 [Page 13] Internet-Draft History-Info July 2009 then perform Steps 2 and 3. If the 3XX response contains a History-Info Header field and the last entries correspond to the current target (i.e., they correspond to the Contact(s) in the 3XX), the proxy MUST include in the outgoing request the same History-Info header fields that were received in the 3XX response. No other entries need to be added as this is the complete set: the proxy MUST NOT perform Steps 2 and 3. Step 2: Tagging the Last Entry The proxy then examines the last hi-entry of the History-Info that was just generated in Step 1 and MUST add a Reason header this entry as per the procedures of Section 6.3.2. Step 3: Generating New Entries for Each Outgoing Requests Same as per Step 3 above for the normal forwarding case, except that the hi-target parameter MUST NOT be set when the proxy receiving the 3xx does not know the mechanism by which this target was determined. For example, the proxy can not determine the hi- target mechanism when the domain of the Contact is not under the control of the proxy. However, if it under the control of the proxy, then it may be able to determine the mechanism (e.g., Bob can deflect a call to his SIP PC client to his cell phone). 5.2. Sending History-Info in Responses A proxy that receives a Request with the "histinfo" option tag in the Supported header, SHOULD forward captured History-Info in subsequent, provisional, and final responses to the Request sent by the ultimate UAS (see Section 4.2). A proxy MAY anonymize any hi-entry whose domain corresponds to a domain for which it is responsible (as per [RFC3323]). For example, anonymity may be required when responses are forwarded to a domain for which it is not responsible. The processing of History-Info in responses follows the methodology described in Section 16.7 of [RFC3261], with the processing of History-Info headers adding an additional step, just before Step 9, "Forwarding the Response". 6. The History-Info header field Barnes, et al. Expires January 14, 2010 [Page 14] Internet-Draft History-Info July 2009 6.1. Definition History-Info is a header field as defined by [RFC3261]. "It may appear in any initial request for a dialog, standalone request or responses associated with these requests. For example, History-Info may appear in INVITE, REGISTER, MESSAGE, REFER, OPTIONS, SUBSCRIBE, and PUBLISH and any valid responses, plus NOTIFY requests that initiate a dialog. The History-Info header carries the following information, with the mandatory parameters required when the header is included in a request or response: o Targeted-to-URI (hi-targeted-to-uri): A mandatory parameter for capturing the Request-URI for the specific Request as it is forwarded. o Index (hi-index): A mandatory parameter for History-Info reflecting the chronological order of the information, indexed to also reflect the forking and nesting of requests. The format for this parameter is a string of digits, separated by dots to indicate the number of forward hops and retargets. This results in a tree representation of the history of the request, with the lowest-level index reflecting a branch of the tree. By adding the new entries in order (i.e., following existing entries per the details in Section 5.1), including the index and securing the header, the ordering of the History-Info headers in the request is assured (SEC-req-2, see Appendix A.1). In addition, applications may extract a variety of metrics (total number of retargets, total number of retargets from a specific branch, etc.) based upon the index values. o Reason: An optional parameter for History-Info, reflected in the History-Info header by including the Reason Header [RFC3326] escaped in the hi-targeted-to-uri. A reason is included for the hi-targeted-to-uri that was retargeted as opposed to the hi- targeted-to-uri to which it was retargeted. o Privacy: An optional parameter for History-Info, reflected in the History-Info header field values by including the Privacy Header [RFC3323] escaped in the hi- targeted-to-uri or by adding the Privacy header to the Request. The latter case indicates that the History-Info entries for the domain MUST be anonymized prior to forwarding, whereas the use of the Privacy header escaped in the hi-targeted-to-uri means that a specific hi-entry MUST be anonymized. Barnes, et al. Expires January 14, 2010 [Page 15] Internet-Draft History-Info July 2009 o AOR indicator (hi-aor): An optional parameter for the History-Info indicating that the hi-targeted-to-uri is an Address Of Record (as defined in section 6/[RFC3261]) . The hi-aor parameter is added by a proxy or redirect server to a hi-entry when it recognizes the URI in the last entry as a URI in its abstract location service (and then it can be routed accordingly). Therefore, the hi-aor parameter (i.e., "aor") is not added for a hi-entry when it is first added in a History-Info header field, but rather is added when the retargeting actually occurs - i.e., the parameter indicates that the specific hi-targeted-to-uri that was retargeted was an AOR and thus the previous information in the request-URI may be "lost". Upon receipt of a request or response containing the History-Info header, a UA can determine a "lost" target AOR for a request by traversing the HI entries in reverse order to find the first one tagged with a specific hi-aor parameter. o Target (hi-target): A mandatory parameter for the History-Info indicating the mechanism by which the new target is determined, based on the procedures of 16.5 [RFC3261]. The hi-target is added for a hi-entry when it is first added in a History-Info header field, and only one value is permitted. Upon receipt of a request or response containing the History-Info header, a UA can determine the nature of the target. The following values are defined for this parameter: * "rc": The entry is a contact that is bound to an AOR in an abstract location service. The AOR-to-contact binding has been placed into the location service by a SIP Registrar that received a SIP REGISTER request. * "cc": The entry is a contact that is bound to an AOR in an abstract location service. The AOR-to-contact binding has been placed into the location service implicitly through a means other than a SIP Registrar acting on a REGISTER request, e.g., the user may be currently logged into a Web Portal that implements a Presence and IM service, or it could be manually configured. * "mp": The entry is a URI that represents another user. This occurs in cases where a request is statically or dynamically retargeted to another user. * "rt": The entry is "routed", i.e., it is either a no-op like a proxy forwarding, predetermined by a maddr in the Request-URI, or the Request-URI is changed to a new URI that represents the same user, and is not a contact in a SIP Registrar. Barnes, et al. Expires January 14, 2010 [Page 16] Internet-Draft History-Info July 2009 o Extension (hi-extension): A parameter to allow for future optional extensions. As per [RFC3261], any implementation not understanding an extension should ignore it. The following summarizes the syntax of the History-Info header, based upon the standard SIP syntax [RFC3261]: History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry) hi-entry = hi-targeted-to-uri *(SEMI hi-param) hi-targeted-to-uri = name-addr hi-param = hi-index / hi-target / hi-aor / hi-extension hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT) hi-target = "rc" / "cc" / "mp" / "rt" hi-aor = "aor" hi-extension = generic-param The following rules apply: o There MUST exactly 1 hi-index parameter per hi-entry. o There MUST be no more than 1 hi-target parameter. o There MUST be no more than 1 hi-aor parameter. o They MAY be any number of hi-extension parameters. o The ABNF definitions for "generic-param" and "name-addr" are from [RFC3261]. 6.2. Examples The following provides some examples of the History-Info header. Note that the backslash and CRLF between the fields in the examples below are for readability purposes only. Barnes, et al. Expires January 14, 2010 [Page 17] Internet-Draft History-Info July 2009 History-Info: ;index=1;aor;foo=bar History-Info: ;index=1.1;mp;aor,\ ;index=1.2;mp;aor,\ ;index=1.3;rc 6.3. Procedures The following sections defines procedures for different parameters in the History-Info header. These procedures may be applicable to "processing entities" such as Proxies, Redirect Servers or User Agents. 6.3.1. Privacy in the History-Info Header The privacy requirements for this document are described in Appendix A.2. Since the History-Info header can inadvertently reveal information about the requestor as described in [RFC3323], the Privacy header can be used to determine whether an intermediary can include the Request- URI in a Request that it receives (PRIV-req-2, see Appendix A.2) or that it retargets (PRIV-req-1, see Appendix A.2) as an entry in a History-Info header. Thus, the History- Info entry for that identity can be anonymized where the requestor has indicated a priv-value of Session- or Header-level privacy. Privacy is associated with a specific history information entry, and perhaps any entry that corresponds to that same user, and not the History-Info header itself. This allows for anonymizing some entries, but not others, as required. For example, if Alice sends a request to Bob without any privacy, and Bob redirects to Carol with privacy setup for himself, Carol should receive a request where Alice's history information is present, but Bob's has been anonymized. In addition, the History-Info header can reveal general routing information which may be viewed by a specific intermediary or network. Thus, a proxy can use local policy to determine whether the History-Info header entries for it's whole domain are private or not when exiting the domain through retargeting (PRIV-req-3). This is accomplished by adding a new priv-value, history, to the Privacy header [RFC3323] indicating that a specific History-Info header entry can not be forwarded outside the domain. It is recognized that satisfying the privacy requirements can impact Barnes, et al. Expires January 14, 2010 [Page 18] Internet-Draft History-Info July 2009 the functionality of this solution by overriding the request to generate the information. If there is a Privacy header in the request with a priv-value of "session", "header", or "history", an hi-entry SHOULD be added if the request is being retargeted to a URI associated with a domain for which the processing entity is responsible. If there is no Privacy header, but the processing entity's local policies indicate that the hi-entry(s) cannot be forwarded beyond the domain for which this intermediary is responsible, then a Privacy header with a priv-value of "history" SHOULD be associated with each hi-entry added by the proxy as the request is forwarded within the domain. If a request is being retargeted to a URI associated with a domain for which the processing identity is not responsible and there is a Privacy header in the request with a priv-value of "session", "header", or "history", the processing entity MUST anonymize hi- entry(s) as per [RFC3323] prior to forwarding, unless the processing entity knows a priori that it can rely on a downstream processing entity within its domain to apply the requested privacy or local policy allows the forwarding. 6.3.2. Reason in the History-Info Header For retargets that are the result of an explicit SIP response, a Reason MUST be associated with the hi-targeted-to-uri. If the SIP response does not include a Reason header (see [RFC3326]), the SIP Response Code that triggered the retargeting MUST be included as the Reason associated with the hi-targeted-to-uri that has been retargeted. If the response contains a Reason header for a protocol that is not SIP (e.g., Q.850), it MUST be captured as an additional Reason associated with the hi-targeted-to- uri that has been retargeted, along with the SIP Response Code. If the Reason header is a SIP reason, then it MUST be used as the Reason associated with the hi-targeted-to-uri rather than the SIP response code. If a request has timed out (instead of being explicitly rejected), it SHOULD be treated as if a 487 "Request Terminated" error response code was received. 6.3.3. AOR Marking in the History-Info Header If the processing entity (Redirect Server or Proxy) is responsible for the domain of the Request-URI of the incoming request, and will treat it as an AOR as per section 16.5 of [RFC3261], the processing entity MUST set the hi-aor parameter for the hi-entry that represents the Request-URI of the incoming request to "aor." Barnes, et al. Expires January 14, 2010 [Page 19] Internet-Draft History-Info July 2009 6.3.4. Indexing in the History-Info Header In order to maintain ordering and accurately reflect the nesting and retargeting of the request, an index MUST be included along with the Targeted-to-URI being captured. Per the syntax in Section 6, the index consists of a dot-delimited series of digits (e.g., 1.1.2). Each dot reflects a hop or level of nesting; thus, the number of hops is determined by the total number of dots. Within each level, the integer reflects the number of peer entities to which the request has been routed. Thus, the indexing results in a logical tree representation for the history of the Request. For each level of indexing, the index MUST start at 1. An increment of 1 MUST be used for advancing to a new branch. The first entry MUST be set to 1. The basic rules for adding the index are summarized as follows: 1. Basic Forwarding: In the case of a Request that is being forwarded, the index is determined by adding another sub-level of indexing since the depth/length of the branch is increasing. To accomplish this, the processing entity reads the value from the History-Info header in the received request, if available, and adds another level of indexing by appending the dot delimiter followed by an initial index for the new level of 1. For example, if the index in the last History-Info header field in the received request is 1.1, this proxy would initialize its index to 1.1.1 and forward the request. 2. Retargeting within a processing entity - 1st instance: For the first instance of retargeting within a processing entity, the calculation of the index follows that prescribed for basic forwarding. 3. Retargeting within a processing entity - subsequent instance: For each subsequent retargeting of a request by the same processing entity, another branch is added. With the index for each new branch calculated by incrementing the last/lowest digit at the current level, the index in the next request forwarded by this same processing entity, following the example above, 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 index would be calculated per rule 3. That is, the lowest/last digit of the index is incremented (i.e., a new branch is created), with the increment of 1. For example, if the index in the History-Info header of the received request was 1.2, then the index in the History-Info header field for the new hi-targeted- to-URI would be 1.3. Barnes, et al. Expires January 14, 2010 [Page 20] Internet-Draft History-Info July 2009 5. Forking requests: If the request forwarding is done in multiple forks (sequentially or in parallel), the index MUST be captured for each forked request per the rules above, with each new Request having a unique index. Each index are 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 for each individual fork, only the entry corresponding that that fork is included (e.g., the entry for fork 1.1.1 is not included in the request sent to fork 1.1.2, and vice-versa). 6. When a response is built and it represents the aggregate of multiple forks (e.g., multiple forks that fail), the processing entity builds the subsequent response using the aggregated information associated with each of those forks and including the header entries in the order indicated by the indexing. For example, if a procesing entity received failure responses for forks 1.1.1 and 1.1.2, it would forward both the 1.1.1 and 1.1.2 entries to 1.1. See Appendix B.1 for an example. Responses are processed as described in Section 16.7 of [RFC3261] with the aggregated History-Info entries processed similar to Step 7 "Aggregate Authentication Header Field Values". 6.3.5. Request Target in the History-Info Header The value for the hi-target attribute is based upon the mechanism by which the new target has been determined per the procedures described in 16.5/[RFC3261]. The following describes how the specific values for the hi-target attribute are determined: o If the Request-URI is a contact that is bound to an AOR in an abstract location service for the domain for which the processing entity is responsible, and the AOR-to-contact binding has been placed into the location service by a SIP Registrar that received a REGISTER request, the hi-target attribute MUST be added to the hi-entry with a value of "rc." o If the Request-URI is a contact that is bound to an AOR in an abstract location service for the domain for which the processing entity is responsible, and the AOR-to-contact binding has been placed into the location service through a means other than a SIP Registrar acontin on a REGISTER request (e.g., throug configuration), the hi-target attribute MUST be added to the hi- entry with a value of "oc." o If the Request-URI is a URI that represents another user than the one indicated by the incoming Request-URI, as this would occur in Barnes, et al. Expires January 14, 2010 [Page 21] Internet-Draft History-Info July 2009 cases where a request is statically or dynamically retargeted to another user, the hi-target attribute MUST be added to the hi- entry with a value of "mp." o If the Request-URI represent normal SIP routing, i.e., it is either a no-op like a proxy forwarding, predertermined by a maddr in the Request-URI, or the Request-URI is changed to a new URI that represents the same user, and is not a contact in a SIP Registrar, the hi-target attribute MUST be added to the hi-entry with a value of "mp." 7. Application Considerations As seen by the example scenarios in the Appendix B, History-Info provides a very flexible building block that can be used by intermediaries and UAs for a variety of services. As such, any services making use of History-Info must be designed with the following considerations: 1. History-Info is optional; thus, a service MUST define default behavior for requests and responses not containing History-Info headers. 2. History-Info may be impacted by privacy considerations. Applications requiring History-Info need to be aware that if Header-, Session-, or History-level privacy is requested by a UA (or imposed by an intermediary) that History-Info may not be available in a request or response. This would be addressed by an application in the same manner as the previous consideration by ensuring there is reasonable default behavior should the information not be available. 3. History-Info may be impacted by local policy. Each application making use of the History-Info header SHOULD address the impacts of the local policies on the specific application (e.g., what specification of local policy is optimally required for a specific application and any potential limitations imposed by local policy decisions). Note that this is related to the optionality and privacy considerations identified in 1 and 2 above, but goes beyond that. For example, due to the optionality and privacy considerations, an entity may receive only partial History-Info entries; will this suffice? Note that this would be a limitation for debugging purposes, but might be perfectly satisfactory for some models whereby only the information from a specific intermediary is required. Barnes, et al. Expires January 14, 2010 [Page 22] Internet-Draft History-Info July 2009 8. Security Considerations The security requirements for this document are specified in Appendix A.1. This document defines a header for SIP. The use of the Transport Layer Security (TLS) protocol [RFC5246] as a mechanism to ensure the overall confidentiality of the History-Info headers (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 headers are no less, nor no more, secure than other SIP headers, which generally have even more impact on the subsequent processing of SIP sessions than the History-Info header. With the level of security provided by TLS (SEC-req-3), the information in the History-Info header can thus be evaluated to determine if information has been removed by evaluating the indices for gaps (SEC-req-1, SEC-req-2). It would be up to the application to define whether it can make use of the information in the case of missing entries. Note that while using the SIPS scheme (as per [I-D.ietf-sip-sips]) 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. 9. IANA Considerations This document requires several IANA registrations detailed in the following sections. This document updates [RFC4244] but uses the same SIP header field name and option tag. The IANA registry needs to update the references to [RFC4244] witht [RFCXXXX]. 9.1. Registration of New SIP History-Info Header 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: Barnes, et al. Expires January 14, 2010 [Page 23] Internet-Draft History-Info July 2009 Header Name Compact Form Reference ----------- ------------ --------- History-Info none [RFCXXXX] The following has been added to the Options Tags section: Name Description Reference ---- ----------- --------- histinfo When used with the Supported header, [RFCXXXX] 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. 9.2. Registration of "history" for SIP Privacy Header This document defines a priv-value for the SIP Privacy header: 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: Name Description Registrant Reference ---- ----------- ---------- --------- history Privacy requested for Mary Barnes [RFCXXXX] History-Info header(s) mary.barnes@nortel.com Note to RFC Editor: Please replace RFC XXXX with the RFC number of this specification. 10. Contributors Cullen Jennings, Mark Watson, and Jon Peterson contributed to the development of the initial requirements for [RFC4244]. Jonathan Rosenberg, Christer Holmberg, Hans Erik van Elburg and Shida Schubert produced the document that provided the basis for the addition of the "target" parameter to the History-Info header, as well as some of the content for this document. Barnes, et al. Expires January 14, 2010 [Page 24] Internet-Draft History-Info July 2009 11. Acknowledgements 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 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. Thanks to Ian Elz for his feedback on privacy. 12. 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 isssues. o [RFC4244] is overly permissive and evasive about recording entries, causing interoperability issues. o There is an error in the ABNF. 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 o [RFC4244] gratuitly 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. Barnes, et al. Expires January 14, 2010 [Page 25] Internet-Draft History-Info July 2009 o [RFC4244] does not allow for marking History-Info entries for easy processing by User Agents. This specification is backwards compatible with [RFC4244]. The following summarizes the functional changes: 1. Added a tag to indicate an AOR that is lost during retargeted: hi-aor. 2. Added a tag to indicate the mechanism by which the target for an outgoing request is determined. 3. Rather than recommending that entries be removed in the case of certain values of the privacy header, recommend that the entries are anonymized. 4. Updated processing/handling for 3xx responses to ensure accuracy of the new tags - i.e., the redirecting entity must add the new entry since the proxy does not have access to the information as to how the Contact was determined. 5. Updated the security section to be equivalent to the security recommendations for other SIP headers inserted by intermediaries. The first 3 changes are intended to facilitate application usage of the History-Info header 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, an error in the ABNF was fixed, editorial changes were done to both condense and clarify the text and examples were simplified and updated to reflect the protocol changes. 12.1. Backwards compatibility Proxies conforming to this specification tag the hi-entry parameters with an hi-target parameter. The hi-target and hi-aor parameters did not exist in [RFC4244]; therefore, [RFC4244] implementations do not tag the hi-entry parameters. This tagging allows for distinguishing entries that were added by an [RFC4244] entity, versus one that was added by an entity conforming to this specification. 13. Changes since last Version NOTE TO THE RFC-Editor: Please remove this section prior to publication as an RFC. Barnes, et al. Expires January 14, 2010 [Page 26] Internet-Draft History-Info July 2009 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 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 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 document and RFC 4244. 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. Barnes, et al. Expires January 14, 2010 [Page 27] Internet-Draft History-Info July 2009 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 are now mandated to start at "1" instead of recommended. 6. Clarified 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 January 14, 2010 [Page 28] Internet-Draft History-Info July 2009 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. 14. References 14.1. 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. [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. 14.2. Informative References [I-D.ietf-sip-gruu] Rosenberg, J., "Obtaining and Using Globally Routable User Agent (UA) URIs (GRUU) in the Session Initiation Protocol Barnes, et al. Expires January 14, 2010 [Page 29] Internet-Draft History-Info July 2009 (SIP)", draft-ietf-sip-gruu-15 (work in progress), October 2007. [I-D.ietf-sip-sips] Audet, F., "The use of the SIPS URI Scheme in the Session Initiation Protocol (SIP)", draft-ietf-sip-sips-09 (work in progress), November 2008. [I-D.rosenberg-sip-target-uri-delivery] Rosenberg, J., Elburg, H., Holmberg, C., Audet, F., and S. Schubert, "Delivery of Request-URI Targets to User Agents", draft-rosenberg-sip-target-uri-delivery-01 (work in progress), March 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. 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 should also generate Request History information for the 'internal retargeting'. B. An entity (UA or proxy) retargeting in response to a redirect or REFER should include any Request History information from the redirect/REFER in the new request. 3. ISSUER-req: "Request History" information can be generated by a UA or proxy. It can be passed in both requests and responses. Barnes, et al. Expires January 14, 2010 [Page 30] Internet-Draft History-Info July 2009 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 wether 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 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 entry either by adding an additional entry as a result of retargeting or entering invalid information. 2. A rogue application could re-arrange the Request History information to change the nature of the end application or to mislead the receiver of the information. 3. A rogue application could delete some or all of the Request History information. Barnes, et al. Expires January 14, 2010 [Page 31] Internet-Draft History-Info July 2009 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 ougoing messages unless it is protected as described in [RFC3323]. Appendix B. Detailed call flows The scenarios in this section provide sample use cases for the History-Info header for informational purposes only. They are not intended to be normative. Barnes, et al. Expires January 14, 2010 [Page 32] Internet-Draft History-Info July 2009 B.1. Sequentially Forking (History-Info in Response) This scenario highlights an example where the History-Info in the response is useful to an application or user that originated the request. 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. In this example, note that 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. This scenario is provided to show 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 this mechanism, Alice might well attempt Office (and thus Home) and then re-attempt Home on a third manual attempt at reaching Bob. With this mechanism, either the end-user or application could know that Bob is not answering in the Office, and his busy on his home phone. If there were an alternative address for Bob known to this end-user or application, that hasn't been attempted, then either the application or the end- user could attempt that. The intent here is to highlight an example of the flexibility of this mechanism that enables applications well beyond SIP as it is certainly well beyond the scope of this document to prescribe detailed applications. Barnes, et al. Expires January 14, 2010 [Page 33] Internet-Draft History-Info July 2009 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:alice@example.com SIP/2.0 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires January 14, 2010 [Page 34] Internet-Draft History-Info July 2009 F2 INVITE example.com -> Bob INVITE sip:bob@192.0.2.4 SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Supported: histinfo Call-Id: 12345600@example.com CSeq: 1 INVITE Record-Route: History-Info: ;index=1;aor History-Info: ;index=1.1;rc Contact: Alice Content-Type: application/sdp Content-Length: F3 100 Trying example.com -> alice SIP/2.0 100 Trying Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice 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 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob ;tag=3 Call-Id: 12345600@example.com CSeq: 1 INVITE Record-Route: History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;index=1.2.1;cc Contact: Content-Length: 0 Barnes, et al. Expires January 14, 2010 [Page 35] Internet-Draft History-Info July 2009 F5 ACK 192.0.2.4 -> Bob ACK sip:home@example.com SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060 From: Alice To: Bob Call-Id: 12345600@example.com CSeq: 1 ACK Content-Length: 0 F6 INVITE example.com -> office INVITE sip:office@192.0.2.3.com SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060;branch=2 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Supported: histinfo Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;index=1.2.1;cc CSeq: 1 INVITE Contact: Alice Content-Type: application/sdp Content-Length: Barnes, et al. Expires January 14, 2010 [Page 36] Internet-Draft History-Info July 2009 F7 180 Ringing office -> example.com SIP/2.0 180 Ringing Via: SIP/2.0/TCP proxy.example.com:5060;branch=2 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob ;tag=5 Supported: histinfo Call-ID: 12345600@example.com Record-Route: History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;index=1.2.1;cc CSeq: 1 INVITE Content-Length: 0 F8 180 Ringing example.com -> alice SIP/2.0 180 Ringing Via: SIP/2.0/TCP example.com:5060 From: Alice To: Bob Supported: histinfo Call-Id: 12345600@example.com History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;index=1.2.1;cc CSeq: 1 INVITE Content-Length: 0 Barnes, et al. Expires January 14, 2010 [Page 37] Internet-Draft History-Info July 2009 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=3 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Supported: histinfo Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;\ index=1.2.1>;index=1.2.1;cc History-Info: ;index=1.3;mp;aor History-Info: ;index=1.3.1;cc 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=3 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Call-Id: 12345600@example.com CSeq: 1 INVITE Content-Length: 0 Barnes, et al. Expires January 14, 2010 [Page 38] Internet-Draft History-Info July 2009 F11 486 Busy Here home -> example.com SIP/2.0 486 Busy Here Via: SIP/2.0/TCP proxy.example.com:5060;branch=3 Via: SIP/2.0/TCP 192.0.2.3:5060 From: Alice To: Bob Call-Id: 12345600@example.com Record-Route: History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;\ index=1.2.1>;index=1.2.1;cc History-Info: ;index=1.3;mp;aor History-Info: ;index=1.3.1;cc 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 From: Alice To: Bob Call-Id: 12345600@example.com History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=1.2;mp;aor History-Info: ;\ index=1.2.1>;index=1.2.1;cc History-Info: ;index=1.3;mp;aor History-Info: ;index=1.3.1;cc CSeq: 1 INVITE Content-Length: 0 Barnes, et al. Expires January 14, 2010 [Page 39] Internet-Draft History-Info July 2009 F13 ACK example.com -> home ACK sip:home@example.com SIP/2.0 Via: SIP/2.0/TCP proxy.example.com:5060 From: Alice To: Bob 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 From: Alice To: Bob Call-Id: 12345600@example.com Route: CSeq: 1 ACK Content-Length: 0 B.2. Voicemail This scenario highlights an example where the History-Info in the request is primarily of use by an edge service (e.g., voicemail server). It should be noted that this is not intended to be a complete specification for this specific edge service as it is quite likely that additional information is needed by the edge service. History-Info is just one building block that this service can use. Alice called Bob, which had been forwarded to Carol, which forwarded to VM (voicemail server). Based upon the retargeted URIs and Reasons (and other information) in the INVITE, the VM server makes a policy decision about what mailbox to use, which greeting to play, etc. Alice example.com Bob Carol VM | INVITE sip:bob@example.com | | | |------------->| | | | | | INVITE sip:bob@192.0.2.3 | | | |------------->| | | History-Info: ;index=1;aor History-Info: ;index=1.1;rc | | | | | | 100 Trying | | | | |<-------------| 302 Moved Temporarily | | Barnes, et al. Expires January 14, 2010 [Page 40] Internet-Draft History-Info July 2009 | |<-------------| | | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc | | | | | | | INVITE sip:Carol@192.0.2.4 | | | |--------------------------->| | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc | | | | | | | 180 Ringing | | | |<---------------------------| | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc | | | | | | 180 Ringing | | | | |<-------------| | | | | | | | | | . . . | retransmit INVITE | | | |--------------------------->| | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc | . . . | | | | | | (timeout) | | | | | | | | | INVITE sip:vm@192.0.2.5 | | |-------------------------------------->| History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc History-Info: ;index=3;mp;aor History-Info: ;index=3.1;cc | | | | | | | 200 OK | | |<--------------------------------------| Barnes, et al. Expires January 14, 2010 [Page 41] Internet-Draft History-Info July 2009 History-Info: ;index=1;aor History-Info: ;\ index=1.1;rc History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rc History-Info: ;index=3;mp;aor History-Info: ;index=3.1;cc | 200 OK | | | | |<-------------| | | | | | | | | | ACK | | | | |------------->| ACK | | |-------------------------------------->| B.3. Automatic Call Distribution This scenario highlights an example of an Automatic Call Distribution service, where the agents are divided into groups based upon the type of customers they handle. In this example, the Gold customers are given higher priority than Silver customers, so a Gold call would get serviced even if all the agents servicing the Gold group were busy, by retargeting the request to the Silver Group for delivery to an agent. Upon receipt of the call at the agent assigned to handle the incoming call, based upon the History-Info header in the message, the application at the agent can provide an indication that this is a Gold call, from how many groups it might have overflowed before reaching the agent, etc. and thus can be handled appropriately by the agent. For scenarios whereby calls might overflow from the Silver to the Gold, clearly the alternate group identification, internal routing, or actual agent that handles the call should not be sent to UA1. Thus, for this scenario, one would expect that the Proxy would not support the sending of the History-Info in the response, even if requested by Alice. As with the other examples, this is not prescriptive of how one would do this type of service but an example of a subset of processing that might be associated with such a service. In addition, this example is not addressing any aspects of Agent availability, which might also be done via a SIP interface. Alice example.com Gold Silver Agent | | | | | | INVITE sip:Gold@example.com | | | |------------->| | | | Barnes, et al. Expires January 14, 2010 [Page 42] Internet-Draft History-Info July 2009 | Supported: histinfo | | | | | | | INVITE sip:Gold@example.com | | |------------->| | | History-Info: ;index=1;aor History-Info: ;index=1.1;rt | | | | | | | 302 Moved Temporarily | | | |<-------------| | | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rt Contact: | | | | | | INVITE sip:Silver@example.com | | |--------------------------->| | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rt History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rt | | | | | | | | INVITE sip:Silver@192.0.2.7 | | | |----------->| History-Info: ;index=1;aor History-Info: ;\ index=1.1;rt;aor History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rt History-Info: ;index=2.1.1;rc | | | | | | | | | 200 OK | | | | |<-----------| History-Info: ;index=1;aor History-Info: ;\ index=1.1;rt;aor History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rt History-Info: ;index=2.1.1;rc | | | | | | | 200 OK | | | |<---------------------------| | History-Info: ;index=1;aor History-Info: ;\ index=1.1;rt;aor History-Info: ;index=2;mp;aor History-Info: ;index=2.1;rt History-Info: ;index=2.1.1;rc Barnes, et al. Expires January 14, 2010 [Page 43] Internet-Draft History-Info July 2009 | | | | | 200 OK | | | | |<-------------| | | | | | | | | | ACK | | | | |------------->| ACK | | |---------------------------------------->| B.4. History-Info with Privacy Header This example provides a basic call scenario such as the one in Figure 1 but without forking, with sip:biloxi.example.com adding the Privacy header indicating that the History-Info header information is anonymized outside the biloxi.example.com domain. This scenario highlights the potential functionality lost with the use of "history" privacy in the Privacy header for the entire request and the need for careful consideration on the use of privacy for History-Info. Barnes, et al. Expires January 14, 2010 [Page 44] Internet-Draft History-Info July 2009 Alice atlanta.example.com biloxi.example.com Bob | | | | | INVITE sip:bob@biloxi.example.com;p=x | |--------------->| | | | Supported: histinfo | | | | | | | | INVITE sip:bob@biloxi.example.com;p=x | |--------------->| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt | | | | | | | INVITE sip:bob@192.0.2.3 | | |--------------->| | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | | 200 | | | |<---------------| | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | 200 | | | |<---------------| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | 200 | | | |<---------------| | | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | ACK | | | |--------------->| ACK | | | |--------------->| ACK | | | |--------------->| Figure 2: Example with Privacy Header B.5. Privacy Header for a Specific History-Info Entry This example also provides a basic call scenario such as the one in Figure 1 but without forking, 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 priv-value of "history", thus Barnes, et al. Expires January 14, 2010 [Page 45] Internet-Draft History-Info July 2009 providing Alice with some information about the history of the request, but anonymizing Bob's local URI. Alice atlanta.example.com biloxi.example.com Bob | | | | | INVITE sip:bob@biloxi.example.com;p=x | |--------------->| | | | Supported: histinfo | | | | | | | | INVITE sip:bob@biloxi.example.com;p=x | |--------------->| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt | | | | | | | INVITE sip:bob@192.0.2.3 | | |--------------->| | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | | 200 | | | |<---------------| | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | | 200 | | | |<---------------| | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | 200 | | | |<---------------| | | | History-Info: ;index=1 | History-Info: ;index=1.1;rt;aor | History-Info: ;index=1.1.1;rc | | | | | ACK | | | |--------------->| ACK | | | |--------------->| ACK | | | |--------------->| Figure 3: Example with Privacy Header for Specific URI Barnes, et al. Expires January 14, 2010 [Page 46] Internet-Draft History-Info July 2009 Authors' Addresses Mary Barnes (editor) Nortel Richardson, TX Email: mary.barnes@nortel.com Francois Audet (editor) Nortel 4655 Great America Parkway Santa Clara, CA 95054 US Email: audet@nortel.com Hans Erik van Elburg Ericsson Ericssonstraat 2 Rijen 5121 ML The Netherlands Email: ietf.hanserik@gmail.com Christer Holmberg Ericsson Hirsalantie 11, Jorvas Finland Email: christer.holmberg@ericsson.com Barnes, et al. Expires January 14, 2010 [Page 47]