SIP WG J. Elwell Internet-Draft Siemens plc Expires: October 26, 2006 April 24, 2006 Connected Identity in the Session Initiation Protocol (SIP) draft-ietf-sip-connected-identity-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 October 26, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract Because of retargeting of a Session Initiation Protocol (SIP) dialog- forming request, the UAS can have a different identity from that in the To header. This document provides a means for that UA to supply its identity to the peer UA by means of a request in the reverse direction and for that identity to be signed by an Authentication Service. The same mechanism can be used to indicate a change of identity during a dialog, e.g., because of some action in a PSTN behind a gateway. This document normatively updates RFC 3261 (SIP). Elwell Expires October 26, 2006 [Page 1] Internet-Draft SIP Connected ID April 2006 This work is being discussed on the sip@ietf.org mailing list. Table of Contents 1. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Existing mechanisms for conveying identity in the context of a call . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Existing methods for providing authenticated identity information . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Overview of solution . . . . . . . . . . . . . . . . . . . . . 5 6. Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Behaviour of a UA that issues an INVITE request outside the context of an existing dialog . . . . . . . . 6 6.2. Behaviour of a UA that receives an INVITE request outside the context of an existing dialog . . . . . . . . 6 6.3. Behaviour of a UA whose identity changes during an established INVITE-initiated dialog . . . . . . . . . . . 7 6.4. General UA behaviour . . . . . . . . . . . . . . . . . . . 7 6.5. Authentication Service Behaviour . . . . . . . . . . . . . 8 6.6. Proxy Behaviour . . . . . . . . . . . . . . . . . . . . . 8 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Sending connected identity after answering a call . . . . 9 7.2. Sending revised connected identity during a call . . . . . 12 8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17 9. Security considerations . . . . . . . . . . . . . . . . . . . 17 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 11.1. Normative References . . . . . . . . . . . . . . . . . . . 18 11.2. Informative References . . . . . . . . . . . . . . . . . . 18 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . . . 20 Elwell Expires October 26, 2006 [Page 2] Internet-Draft SIP Connected ID April 2006 1. Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [2]. 2. Introduction SIP [1] initiates sessions but it also provides information on the identities of the parties at both ends of a session. Users need this information to help determine how to deal with communications initiated by SIP. As a call proceeds, these identities may change. This can happen for many reasons: calls are forwarded, calls are parked and picked up, calls are transferred, calls are queued to be picked up by a pool of agents, and so on. This can have impact on the identity of the party that answers a call. It can also cause the identity of a party to change during an established call. This document extends the use of the From header field to allow it to convey "connected identity" information in either direction within the context of an existing INVITE-initiated dialog. The provision of the identity of the responder in a response ("response identity") for requests outside the context of an INVITE- initiated dialog is outside the scope of this document. 3. Existing mechanisms for conveying identity in the context of a call When establishing a call and its session, the SIP From header field in the INVITE request provides a means for conveying the identity of the caller from the User Agent Client (UAC) to the User Agent Server (UAS), thereby allowing the caller's identity to be presented to the callee. There is no corresponding mechanism specified for conveying the identity of the callee from the UAS to the UAC, to allow the callee's identity to be presented to the caller. The identity of the callee is normally expected to be the identity placed in the To header field of the INVITE request, but often this expectation is not met because a different party answers the call, e.g., because of call forwarding. History information [7] gathered during the routing of a request and returned in the response can provide additional information to the UAC. However, this does not necessarily clearly indicate the AoR of the UAS. Also the methods described in Section 4 for authentication do not apply to history information, which relies instead on hop-by-hop security and transitive trust. Elwell Expires October 26, 2006 [Page 3] Internet-Draft SIP Connected ID April 2006 The Reply-To header field has its own meaning and cannot be relied on in all circumstances. The Contact header field provides a contact URI, which may not reveal the identity (Address of Record) of the user on whose behalf the response is sent. Parties involved in a call can change owing to actions such as call transfer. If such actions are achieved by issuing a new INVITE request (with a Replaces header field) between the two UAs that are to be involved in the re-arranged call, the SIP From header field in the INVITE request can provide identity information in one direction, but again there is no mechanism for conveying identity information in the reverse direction. However, call re-arrangements are not always carried out using a new INVITE request. Sometimes a B2BUA performs call re-arrangements using third party call control (3PCC) techniques. With such techniques the UA involved in the original call and still involved in the re-arranged call receives only a re-INVITE or UPDATE request in the context of the original dialog between that UA and the B2BUA. This forces the UA to re-negotiate the session with the new remote party, but introduces a need to convey the identity of the new remote party to the UA. Because there is no new INVITE request (outside the context of the existing dialog), techniques applicable to new calls do not apply. Another case where call re-arrangements are not carried out using a new INVITE request is where one of the UAs is a gateway to a PSTN and a call re-arrangement such as call transfer has occurred within the PSTN. The gateway then has a need to convey the identity of the new party within the PSTN to the remote UA. This needs to be done within the context of the existing dialog between the gateway and the remote UA. In this case there is probably not even any need to re-negotiate the session - the only requirement is to update the identity information. 4. Existing methods for providing authenticated identity information Because the From header field in a request is generated by the UAC itself it can be subject to falsification. SIP has several means of providing cryptographic authentication of a request's source identity. One such means for requests is HTTP-based digest authentication, as specified in [1]. Although a UAS can require digest authentication, it is not usually feasible between an arbitrary pair of UAs because of reliance on a shared secret. To achieve scalability, methods Elwell Expires October 26, 2006 [Page 4] Internet-Draft SIP Connected ID April 2006 based on public key cryptography are essential. Another method is specified in [5], and is applicable to responses as well as requests. This requires a UA to have a private key and associated certificate in order to sign an Authenticated Identity Body (AIB) in the request or response. However, this has seen little deployment, since the public key infrastructures needed to support private keys and certificates in every UA are not generally available. A third method is specified in [3]. For signature this uses a private key and certificate associated with the domain indicated in the From header URI. An Authentication Service, typically located at the outbound proxy, authenticates the UAC by some means, using digest authentication for example, and then inserts an Identity header and an Identity-Info header in the forwarded request. The Identity header contains a signature using the domain's private key and the Identity-Info header references the corresponding certificate. 5. Overview of solution A mid-dialog request is used to provide connected identity. The UAC for that request inserts its identity in the From header field of the request and the Identity header can be used to provide authentication. A request in the opposite direction to the INVITE request prior to or at the time the call is answered can indicate the identity of the alerting or answering party. A request in the same direction as the INVITE request prior to answer can indicate a change of calling party. A request in either direction after answer can indicate a change of party. In all cases a dialog (early or confirmed) must be established before such a request can be sent. Note that it might also be possible to provide a means of indicating the identity of the alerting or answering party in the response to the INVITE request. However, at present the problem of authenticating a response is still subject to study. In the absence of a solution to this problem, the simple solution of using a request in the opposite direction to the INVITE request is sufficient. Furthermore a Globally Routable User agent URI (GRUU) [8], if used in the Contact header field in a dialog-forming response to an INVITE request, can reveal the identity of the connected user (subject to there being no need for anonymity and subject to policy for allocating GRUUs), but this does not deal with the problem of a connected identity changing mid-dialog. Elwell Expires October 26, 2006 [Page 5] Internet-Draft SIP Connected ID April 2006 This solution involves changing the URI (not the tags) in the To and From header fields of mid-dialog requests and their responses, compared with the corresponding values in the dialog forming request and response. Changing the To and From header field URIs was contemplated in Section 12.2.1.1 of RFC 3261, which says "Usage of the URI from the To and From fields in the original request within subsequent requests is done for backwards compatibility with RFC 2543, which used the URI for dialog identification. In this specification, only the tags are used for dialog identification. It is expected that mandatory reflection of the original To and From URI in mid-dialog requests will be deprecated in a subsequent revision of this specification." This document therefore deprecates mandatory reflection of the original To and From URIs in mid-dialog requests and their responses. It is assumed that deployed proxies will already be able to tolerate a change of URI, since this has been expected for a considerable time. To cater for any UAs that are not able to tolerate a change of URI, a new option tag "id-change" is introduced for providing a positive indication of support in the Supported header field. This document also requires a UA that has received a connected identity in the URI of the From header field of a mid-dialog request to use that URI in the To header field of any subsequent mid-dialog request sent by that UA. OPEN ISSUE. Should this be extended to allow a URI in the To header field of a response to change compared with the To header field in a request? This could convey a connected identity in a response to an INVITE request, but it would not be authenticated. Authentication would have to rely on transitive trust, which might be feasible in a closed environment where the sips URI scheme is used. 6. Behaviour 6.1. Behaviour of a UA that issues an INVITE request outside the context of an existing dialog When issuing an INVITE request, a UA that supports changes of URI in the From and To headers during a dialog MUST include the id-change option tag in the Supported header field. 6.2. Behaviour of a UA that receives an INVITE request outside the context of an existing dialog After receiving an INVITE request, a UA that supports changes of URI Elwell Expires October 26, 2006 [Page 6] Internet-Draft SIP Connected ID April 2006 in the From and To headers during a dialog MUST include the id-change option tag in the Supported header field of any dialog-forming response. After a dialog has been formed (after sending a reliable response to the INVITE request, i.e., a 2xx response or a reliable 1xx response), if the id-change option tag has been received in a Supported header field, the UA MUST issue a request on the same dialog containing its identity in the URI of the From header field (or an anonymous identity if anonymity is required). For this purpose the UPDATE method [4] MUST be used if supported by the peer UA. If the UPDATE method is not supported by the peer UA, the re-INVITE method MUST be used, but this will necessitate waiting until the dialog is confirmed. OPEN ISSUE: If the identity has has not changed compared with the URI in the To header field and the UAC (for the INVITE request) does not support verification of an Identity header, this UPDATE or re-INVITE transaction would fulfil no useful purpose. However, the UAS (for the INVITE transaction) does not know this. In order to save this round trip, should we have an additional option tag to indicate support for receipt of the Identity header on mid- dialog requests? Then if this option tag is not present in the INVITE request the additional transaction could be omitted. Note that the id-change option tag does not seem appropriate for this purpose, since a UA could support a change of URI without supporting Identity. 6.3. Behaviour of a UA whose identity changes during an established INVITE-initiated dialog If the id-change option tag has been received in a Supported header field during an INVITE-initiated dialog and if the identity associated with the UA changes (e.g., due to transfer) compared to that last indicated in the From header field of a request sent by that UA, the UA SHOULD issue a request on the same dialog containing the new identity in the URI of the From header field (or an anonymous identity if anonymity is required). For this purpose the UA MUST use either the UPDATE method or the re-INVITE method. However the UPDATE method cannot be used before a reliable provisional response to the dialog-forming INVITE request has been sent or received and the re- INVITE method cannot be used until the dialog is confirmed. 6.4. General UA behaviour When sending a mid-dialog request a URI MUST observe the requirements of [3] when populating the From header field URI, including provisions for achieving anonymity. Elwell Expires October 26, 2006 [Page 7] Internet-Draft SIP Connected ID April 2006 After sending a request with a revised From header field URI (i.e., revised compared to the URI sent in the From header field of the previous request on this dialog or in the To header field of the received dialog-forming INVITE request if no request has been sent), the UA MUST be prepared to receive the old URI in the To header field of a received mid-dialog request at least until a 2xx response to the request with the revised From header field URI has been received. After receiving a 2xx response to a request with a revised URI in the From header field (i.e., revised compared to the URI sent in the From header field of the previous request on this dialog or in the To header field of the received dialog-forming INVITE request if no request has been sent), the UA MUST send the same URI in the From header field of any future requests on the same dialog, unless the identity changes again. If a UA receives a mid-dialog request from the peer UA, the UA may make use of the identity in the From header field URI (e.g., by indicating to the user). The UA MAY act in accordance with [3] and verify any signature in the Identity header field and discriminate between signed and unsigned identities. If a UA receives a mid-dialog request from the peer UA in which the From header field URI differs from that received in the previous request on that dialog or that sent in the To header field of the original INVITE request and if the UA sends a 2xx response, the UA MUST use this revised URI in the To header field of any future requests it sends on the same dialog (irrespective of whether the received identity is supported by a valid signature). 6.5. Authentication Service Behaviour An Authentication Service MUST behave in accordance with [3] when dealing with mid-dialog requests. OPEN ISSUE. draft-ietf-sip-identity is silent on how to behave if the identity in the From header is not one that authenticated UA is allowed to assert. Should the request be allowed to proceed without the Identity header or should it be rejected, if so with which response code? 6.6. Proxy Behaviour A proxy that record routes during an INVITE request MUST be tolerant of changes of the From header field URI compared with that in the initial INVITE request for mid-dialog requests in the same direction as the INVITE request and MUST be tolerant of changes of the From header field URI compared with the To header field URI in the initial Elwell Expires October 26, 2006 [Page 8] Internet-Draft SIP Connected ID April 2006 INVITE request for mid-dialog requests in the opposite direction. A proxy that record routes MUST also be tolerant of changes of the To header field URI in mid dialog requests to reflect changes of the From header field URI in mid-dialog requests in the opposite direction. 7. Examples 7.1. Sending connected identity after answering a call In this example Carol's UA has been reached by retargeting at the proxy and thus her identity (AoR) is not equal to that in the To header field of the received INVITE request (Bob). Carol's UA therefore conveys its identity in the From header field of an UPDATE request. The proxy also provides an Authentication Service and therefore adds Identity and Identity-Info header field to the UPDATE request. Alice's UA PROXY + Carol's UA Authentication Service INVITE(1) INVITE(2) ----------------> ----------------> 200(4) 200(3) <---------------- <---------------- ACK(5) ACK(6) ----------------> ----------------> UPDATE(8) UPDATE(7) <---------------- <---------------- 200(9) 200(10) ----------------> ----------------> INVITE (1): INVITE sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: Elwell Expires October 26, 2006 [Page 9] Internet-Draft SIP Connected ID April 2006 etc. INVITE (2): INVITE sip:Carol@ua2.example.com SIP/2.0 From: ;tag=13adc987 To: Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: Identity: "dKJ97..." Identity-Info: ;alg=rsa-sha1 etc. 200 (3): SIP/2.0 200 OK From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: etc. 200 (4): SIP/2.0 200 OK From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: etc. ACK (5): ACK sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 ACK etc. ACK (6): Elwell Expires October 26, 2006 [Page 10] Internet-Draft SIP Connected ID April 2006 ACK sip:Carol@ua2.example.com SIP/2.0 From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 ACK etc. UPDATE (7): UPDATE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: etc. Note that the URI in the From header differs from that in the To header in the INVITE request/response. However, the tag is the same as that in the INVITE response. Elwell Expires October 26, 2006 [Page 11] Internet-Draft SIP Connected ID April 2006 UPDATE (8): UPDATE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: Identity: "cdKJH43..." Identity-Info: ;alg=rsa-sha1 etc. 200 (9): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: etc. 200 (10): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: etc. 7.2. Sending revised connected identity during a call In this example a call is established between Alice and Bob, where Bob lies behind a B2BUA or gateway to a PSTN. Bob's identity is conveyed by an UPDATE request. Then call transfer occurs in the B2BUA or PSTN, such that Alice becomes connected to Carol, and a re- INVITE request is issued allowing the session to be renegotiated. The B2BUA (or an entity behind it) or the gateway provides the Authentication Service and thus generates the Identity header in the re-INVITE request to provide authentication of Carol's identity. Alice's UA PROXY B2BUA or gateway + Authentication Service Elwell Expires October 26, 2006 [Page 12] Internet-Draft SIP Connected ID April 2006 INVITE(1) INVITE(2) ----------------> ----------------> 200(4) 200(3) <---------------- <---------------- ACK(5) ACK(6) ----------------> ----------------> UPDATE(8) UPDATE(7) <---------------- <---------------- 200(9) 200(10) ----------------> ----------------> re-INVITE(12) re-INVITE(11) <---------------- <---------------- 200(13) 200(14) ----------------> ----------------> ACK(16) ACK(15) <--------------- <---------------- INVITE (1): INVITE sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: etc. INVITE (2): INVITE sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: Identity: "dKJ97..." Identity-Info: ;alg=rsa-sha1 etc. Elwell Expires October 26, 2006 [Page 13] Internet-Draft SIP Connected ID April 2006 200 (3): SIP/2.0 200 OK From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: etc. 200 (4): SIP/2.0 200 OK From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 INVITE Supported: id-change Contact: etc. ACK (5): ACK sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 ACK etc. ACK (6): ACK sip:Bob@example.com SIP/2.0 From: ;tag=13adc987 To: ;tag=2ge46ab5 Call-ID: 12345600@example.com CSeq: 1 ACK etc. UPDATE (7): UPDATE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: Elwell Expires October 26, 2006 [Page 14] Internet-Draft SIP Connected ID April 2006 Identity: "cdKJH43..." Identity-Info: ;alg=rsa-sha1 etc. UPDATE (8): UPDATE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: Identity: "cdKJH43..." Identity-Info: ;alg=rsa-sha1 etc. 200 (9): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: etc. 200 (10): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 2 UPDATE Contact: etc. re-INVITE (11): INVITE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 INVITE Contact: Identity: "ecdFG24..." Identity-Info: ;alg=rsa-sha1 etc. Elwell Expires October 26, 2006 [Page 15] Internet-Draft SIP Connected ID April 2006 re-INVITE (12): INVITE sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 INVITE Contact: Identity: "ecdFG24..." Identity-Info: ;alg=rsa-sha1 etc. 200 (13): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 INVITE Contact: etc. 200 (14): SIP/2.0 200 OK From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 INVITE Contact: etc. ACK (15): ACK sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 ACK etc. ACK (16): ACK sip:Alice@ua1.example.com SIP/2.0 From: ;tag=2ge46ab5 To: ;tag=13adc987 Call-ID: 12345600@example.com CSeq: 3 ACK Elwell Expires October 26, 2006 [Page 16] Internet-Draft SIP Connected ID April 2006 etc. 8. IANA considerations This specification registers a new SIP option tag, as per the guidelines in Section 27.1 of RFC 3261. Name: id-change Description: This option tag is used to indicate that a UA supports changes to URIs in From and To header fields during a dialog. 9. Security considerations [3] discusses security considerations relating to the Identity header in some detail. Those same considerations apply when using the Identity header to authenticate a connected identity in the From header URI of a mid-dialog request. A received From header URI in a mid-dialog request for which no valid Identity header field (or other means of authentication) has been receivd either in this request or in an an earlier request on this dialog cannot be trusted (except in very closed environments) and should be treated in a similar way to a From header field in a dialog-initiating request that is not backed up by a valid Identity header field. A signed connected identity in a mid-dialog request (URI in the From header field accompanied by a valid Identity header field) provides information about the peer UA in a dialog. In the case of the UA that was the UAS in the dialog-forming request, this identity is not necessarily the same as that in the To header field of the dialog- forming request. This is because of retargeting during the routing of the dialog-forming request. A signed connected identity says nothing about the legitimacy of such retargeting, but merely reflects the result of that retargeting. Likewise, when a signed connected identity indicates a change of identity during a dialog, it conveys no information about the reason for such change of identity or its legitimacy. Use of the sips URI scheme can minimise the chances of attacks in which inappropriate connected identity information is sent, either at call establishment time or during a call. Anonymity may be required by the user of a connected UA. To Elwell Expires October 26, 2006 [Page 17] Internet-Draft SIP Connected ID April 2006 anonymity the UA must populate the URI in the From header field of a mid-dialog request in the way described in [3]. 10. Acknowledgments Thanks to Francois Audet, Frank Derks, Steffen Fries, Vijay Gurbani, Cullen Jennings, Hans Persson, Jon Peterson, Schida Schubert and Ya- Ching Tan for providing valuable comments. 11. References 11.1. Normative References [1] 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. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity-06 (work in progress), October 2005. [4] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE Method", RFC 3311, September 2002. 11.2. Informative References [5] Peterson, J., "Session Initiation Protocol (SIP) Authenticated Identity Body (AIB) Format", RFC 3893, September 2004. [6] Handley, M., Schulzrinne, H., Schooler, E., and J. Rosenberg, "SIP: Session Initiation Protocol", RFC 2543, March 1999. [7] Barnes, M., "An Extension to the Session Initiation Protocol (SIP) for Request History Information", RFC 4244, November 2005. [8] Rosenberg, J., "Obtaining and Using Globally Routable User Agent (UA) URIs (GRUU) in the Session Initiation Protocol (SIP)", draft-ietf-sip-gruu-07 (work in progress), March 2006. Elwell Expires October 26, 2006 [Page 18] Internet-Draft SIP Connected ID April 2006 Author's Address John Elwell Siemens plc Technology Drive Beeston, Nottingham NG9 1LA UK Phone: +44 115 943 4989 Email: john.elwell@siemens.com Elwell Expires October 26, 2006 [Page 19] Internet-Draft SIP Connected ID April 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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