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Elwell 3 Internet-Draft Siemens Enterprise Communications 4 Updates: RFC 3325 GmbH & Co KG 5 (if approved) May 16, 2008 6 Intended status: Informational 7 Expires: November 17, 2008 9 Updates to Asserted Identity in the Session Initiation Protocol (SIP) 10 draft-ietf-sipping-update-pai-02.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on November 17, 2008. 37 Abstract 39 SIP has a mechanism for conveying the asserted identity of the 40 originator of a request by means of the P-Asserted-Identity header 41 field. This header field is specified for use in requests using a 42 number of SIP methods, in particular the INVITE method. However, RFC 43 3325 does not specify the insertion of this header field by a trusted 44 UAC, does not specify the use of this header field with the SIP 45 UPDATE, REGISTER, MESSAGE or PUBLISH methods, and is unclear on the 46 use of this header field in responses. This document extends RFC 47 3325 to cover these situations. 49 This work is being discussed on the sipping@ietf.org mailing list. 51 Table of Contents 53 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3.1. Inclusion of P-Asserted-Identity by a UAC . . . . . . . . 4 57 3.2. Inclusion of P-Asserted-Identity in an UPDATE request . . 4 58 3.3. Inclusion of P-Asserted-Identity in a REGISTER request . . 5 59 3.4. Inclusion of P-Asserted-Identity or 60 P-Preferred-Identity in a MESSAGE request . . . . . . . . 5 61 3.5. Inclusion of P-Asserted-Identity or 62 P-Preferred-Identity in a PUBLISH request . . . . . . . . 6 63 3.6. Inclusion of P-Asserted-Identity in an ACK request . . . . 6 64 3.7. Inclusion of P-Asserted-Identity or 65 P-Preferred-Identity in a response . . . . . . . . . . . . 6 66 4. Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 4.1. UAC Behaviour . . . . . . . . . . . . . . . . . . . . . . 8 68 4.1.1. Request handling . . . . . . . . . . . . . . . . . . . 8 69 4.1.2. Response handling . . . . . . . . . . . . . . . . . . 9 70 4.2. Proxy Behaviour . . . . . . . . . . . . . . . . . . . . . 9 71 4.2.1. Request handling . . . . . . . . . . . . . . . . . . . 9 72 4.2.2. Response handling . . . . . . . . . . . . . . . . . . 10 73 4.3. Registrar Behaviour . . . . . . . . . . . . . . . . . . . 10 74 4.4. UAS Behaviour . . . . . . . . . . . . . . . . . . . . . . 10 75 4.4.1. Request handling . . . . . . . . . . . . . . . . . . . 10 76 4.4.2. Response handling . . . . . . . . . . . . . . . . . . 10 77 5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11 78 6. Security considerations . . . . . . . . . . . . . . . . . . . 11 79 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 80 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 81 8.1. Normative References . . . . . . . . . . . . . . . . . . . 12 82 8.2. Informative References . . . . . . . . . . . . . . . . . . 12 83 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 84 Intellectual Property and Copyright Statements . . . . . . . . . . 14 86 1. Terminology 88 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 89 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 90 document are to be interpreted as described in [RFC2119]. 92 This document uses the concepts of Trust Domain and Spec(T), as 93 specified in section 2.3 of RFC 3324 [RFC3324]. 95 2. Introduction 97 The Session Initiation Protocol (SIP) is specified in RFC 3261 98 [RFC3261]. RFC 3325 [RFC3325] specifies a mechanism for conveying 99 within a Trust Domain the asserted identity of the originator of a 100 SIP request. This is achieved by means of the P-Asserted-Identity 101 header field, which is specified for use in requests using a number 102 of SIP methods, in particular the INVITE method. 104 RFC 3325 does not specify the insertion of the P-Asserted-Identity 105 header field by a UAC in the same Trust Domain as the first proxy. 106 Also RFC 3325 does not specify the use of the P-Asserted-Identity 107 header field with the SIP UPDATE method [RFC3311], the SIP REGISTER 108 method, the SIP MESSAGE method [RFC3428], the SIP PUBLISH method 109 [RFC3903] or the SIP ACK method, and is unclear on the use of this 110 header field in responses. There are similar omissions concerning 111 the P-Preferred-Identity header field. 113 This document extends RFC 3325 by allowing inclusion of the 114 P-Asserted-Identity header field by a UAC in the same Trust Domain as 115 the first proxy, allowing use of this header field in UPDATE, 116 REGISTER, MESSAGE, PUBLISH and ACK requests and, under certain 117 conditions, allowing use of this header field in SIP responses. This 118 document also allows the use of the P-Preferred-Identity header field 119 in some of these situations. 121 This document does not alter the fact that the asserted identity 122 mechanism has limited applicability, i.e., within a Trust Domain. 123 For general applicability, including operation outside a Trust Domain 124 (e.g., over the public Internet) or between different Trust Domains, 125 a different mechanism is needed. RFC 4474 [RFC4474] specifies the 126 Identity header field, in conjunction with the From header field, for 127 providing authenticated identity in such circumstances. 129 3. Discussion 130 3.1. Inclusion of P-Asserted-Identity by a UAC 132 RFC 3325 does not include procedures for a UAC to include the 133 P-Asserted-Identity header field in a request. This can be 134 meaningful if the UAC is in the same Trust Domain as the first 135 downstream SIP entity. Examples of types of UAC that are often 136 suitable for inclusion in a Trust Domain are: 138 o PSTN gateways; 140 o media servers; 142 o application servers (or B2BUAs) that act as URI list servers 143 [I-D.ietf-sipping-uri-services]; 145 o application servers (or B2BUAs) that perform third party call 146 control. 148 In the particular case of a PSTN gateway, the PSTN gateway might be 149 able to assert an identity received from the PSTN, the proxy itself 150 having no means to authenticate such an identity. Likewise, in the 151 case of certain application server or B2BUA arrangements, the 152 application server or B2BUA may be in a position to assert an 153 identity of a user on the other side of that application server or 154 B2BUA. 156 In accordance with RFC 3325, nodes within a Trust Domain must behave 157 in accordance with a Spec(T), and this principle needs to apply 158 between a UAC and its proxy as part of the condition for considering 159 the UAC to be within the same Trust Domain. Normal proxy procedures 160 of RFC 3325 ensure that the header field is removed or replaced if 161 the first proxy considers the UAC to be outside the Trust Domain. 163 This update to RFC 3325 clarifies that a UAC may include a 164 P-Asserted-Identity header field in a request in certain 165 circumstances. 167 3.2. Inclusion of P-Asserted-Identity in an UPDATE request 169 There are several use cases that would benefit from the use of the 170 P-Asserted-Identity header field in an UPDATE request. These use 171 cases apply within a Trust Domain where the use of asserted identity 172 is appropriate (see RFC 3325). 174 In one example, an established call passes through a gateway to the 175 PSTN. The gateway becomes aware that the remote party in the PSTN 176 has changed, e.g., due to call transfer. By including the 177 P-Asserted-Identity header field in an UPDATE request, the gateway 178 can convey the identity of the new remote party to the peer SIP UA. 180 Note that the (re-)INVITE method could be used in this situation. 181 However, this forces an offer-answer exchange, which typically is 182 not required in this situation. Also it involves 3 messages 183 rather than 2. 185 In another example, a B2BUA that provides third party call control 186 (3PCC) [RFC3725] wishes to join two calls together, one of which is 187 still waiting to be answered and potentially is forked to different 188 UAs. At this point in time it is not possible to trigger the normal 189 offer-answer exchange between the two joined parties, because of the 190 mismatch between a single dialog on the one side and potentially 191 multiple early dialogs on the other side, so this action must wait 192 until one of the called UAs answers. However, it would be useful to 193 give an early indication to each user concerned of the identity of 194 the user to which they will become connected when the call is 195 answered. In other words, it would provide the new calling UA with 196 the identity of the new called user and provide the new called UA(s) 197 with the identity of the new calling user. This can be achieved by 198 the B2BUA sending an UPDATE request with a P-Asserted-Identity header 199 field on the dialogs concerned. 201 This update to RFC 3325 allows a P-Asserted-Identity header field to 202 be included in an UPDATE request. 204 3.3. Inclusion of P-Asserted-Identity in a REGISTER request 206 Within a Trust Domain, a P-Asserted-Identity header field could 207 advantageously be used in a REGISTER request between an edge proxy 208 that has authenticated the source of the request and the registrar. 210 This update to RFC 3325 allows a P-Asserted-Identity header field to 211 be included in a REGISTER request. 213 3.4. Inclusion of P-Asserted-Identity or P-Preferred-Identity in a 214 MESSAGE request 216 Within a Trust Domain, a P-Asserted-Identity header field could 217 advantageously be used in a MESSAGE request to assert the source of a 218 page mode instant message. This would complement its use in an 219 INVITE request to assert the source of an instant message session or 220 any other form of session. Similarly, between a UAC and first proxy 221 that are not within the same Trust Domain, a P-Preferred-Identity 222 header field could be used in a MESSAGE request to express a 223 preference when the user has several identities. 225 This update to RFC 3325 allows a P-Asserted-Identity or P-Preferred- 226 Identity header field to be included in a MESSAGE request. 228 3.5. Inclusion of P-Asserted-Identity or P-Preferred-Identity in a 229 PUBLISH request 231 Within a Trust Domain, a P-Asserted-Identity header field could 232 advantageously be used in a PUBLISH request to assert the source of 233 published state information. This would complement its use in 234 SUBSCRIBE and NOTIFY requests. Similarly, between a UAC and first 235 proxy that are not within the same Trust Domain, a P-Preferred- 236 Identity header field could be used in a PUBLISH request to express a 237 preference when the user has several identities. 239 This update to RFC 3325 allows a P-Asserted-Identity or P-Preferred- 240 Identity header field to be included in a PUBLISH request. 242 3.6. Inclusion of P-Asserted-Identity in an ACK request 244 Within a Trust Domain, a P-Asserted-Identity header field could 245 advantageously be used in an ACK request. Considering the 3PCC 246 scenario in Flow I of [RFC3725], the asserted identity of user B may 247 not be known when the B2BUA (controller) sends the initial INVITE 248 request to UA A, but might be known when the B2BUA sends the ACK 249 request to UA A (having received it in the 200 response from UA B). 251 This update to RFC 3325 allows a P-Asserted-Identity header field to 252 be included in an ACK request. 254 3.7. Inclusion of P-Asserted-Identity or P-Preferred-Identity in a 255 response 257 There are cases where the inclusion of the P-Asserted-Identity header 258 field in responses would be useful. Retargeting of a request can 259 result in the responding entity having a different identity from that 260 placed in the To URI of the request. Inclusion of asserted identity 261 in a response would provide the UAC with the identity of the 262 responder. Some examples of the benefits to be gained include: 264 o Asserted identity in a 2xx response to an INVITE request would 265 indicate the identity of the connected user. 267 o Asserted identity in a provisional response to an INVITE request 268 would indicate the contacted (e.g., alerted) user. 270 o Asserted identity in a 2xx response to a MESSAGE request would 271 provide confirmation of where the message was delivered to. 273 o Asserted identity in certain 4xx/5xx/6xx responses would provide 274 an indication of where the response originated. 276 In the case of a request that results in the formation of a dialog, a 277 mid-dialog request (e.g., UPDATE) in the reverse direction can 278 provide the identity of the user at the destination end of that 279 dialog, and therefore the need to include asserted identity in a 280 response to the dialog-forming request to identify the connected user 281 is debatable. There can be some benefits in terms of ease of 282 interworking with PSTN, where such information is placed in the 283 response to a call establishment request. For other responses, 284 including successful responses to requests such as MESSAGE and 285 PUBLISH and unsuccessful responses, the use of a request in the 286 reverse direction is unsuitable. 288 Note that when the authenticated identity of the connected user is 289 to be provided using the From and Identity header fields (as 290 opposed to providing asserted identity using the P-Asserted- 291 Identity header field), RFC 4916 [RFC4916] requires this to be 292 done in a mid-dialog request (e.g., UPDATE) in the reverse 293 direction. This is because the Identity header field is defined 294 only for use in requests. 296 RFC 3325 is ambiguous on inclusion of P-Asserted-Identity in a 297 response. For example, section 4 of RFC 3325 talks about inclusion 298 of the header field in messages, as opposed to requests. Moreover 299 section 5 explicitly mentions "message (request or response)". 300 However, there are other places (e.g., sections 6, 7 and 8) that only 301 mention requests. 303 Section 5 of RFC 3325 requires a proxy to authenticate the originator 304 of a message before adding a P-Asserted-Identity header field to the 305 forwarded message. In practice there is no SIP means to authenticate 306 the sender of a SIP response message. However, authentication may be 307 possible by other means. For example, if the proxy has TLS 308 connectivity with the originator of the response and has previously 309 authenticated the connected entity (e.g., using SIP digest 310 authentication at registration time), then the originator of the 311 response can be considered to be authenticated. In such 312 circumstances it is permissible for a proxy to insert a P-Asserted- 313 Identity header field in a SIP response. 315 It should also be permissible for a UAS to insert a P-Asserted- 316 Identity header field into a response if it is within the same Trust 317 Domain as the SIP entity from which the request was received. 319 Between a UAS and a SIP entity that are not within the same Trust 320 Domain, a P-Preferred-Identity header field could be used in a 321 response, in order to express a preference when the authenticated 322 user has several identities. 324 This update to RFC 3325 allows a P-Asserted-Identity or P-Preferred- 325 Identity header field to be included in a response in certain 326 circumstances. 328 4. Behaviour 330 This document updates RFC 3325 by allowing a P-Asserted-Identity 331 header field to be included by a UAC within the same Trust Domain, by 332 allowing a P-Asserted-Identity header field to appear in an UPDATE, 333 MESSAGE or PUBLISH request, and by allowing a P-Asserted-Identity 334 header field to appear in a response in certain circumstances. It 335 also allows a P-Preferred-Identity header field to appear in a 336 MESSAGE or PUBLISH request or in a response. 338 4.1. UAC Behaviour 340 4.1.1. Request handling 342 A UAC MAY include a P-Asserted-Identity header field in a request to 343 report the identity of the user on behalf of which the UAC is acting 344 and whose identity the UAC is in a position to assert. A UAC SHOULD 345 do so only in cases where it believes it is in the same Trust Domain 346 as the SIP entity to which it sends the request and is connected to 347 that SIP entity in accordance with the security requirements of RFC 348 3325. A UAC SHOULD NOT do so in other circumstances and might 349 instead use the P-Preferred-Identity header field. A UAC MUST NOT 350 include both header fields. 352 In addition to the methods specified in RFC 3325, a UAC MAY include a 353 P-Asserted-Identity header field in an UPDATE request to report a 354 changed identity mid-dialog. This can be an UPDATE request sent 355 specially for this purpose or an UPDATE request sent for some other 356 purpose. A UAC SHOULD do so only in cases where it believes it is in 357 the same Trust Domain as the SIP entity to which it sends the request 358 and is connected to that SIP entity in accordance with the security 359 requirements of RFC 3325. 361 In addition to the methods specified in RFC 3325, a UAC MAY include a 362 P-Asserted-Identity or P-Preferred-Identity header field in a 363 MESSAGE, PUBLISH or ACK request. A UAC SHOULD include a P-Asserted- 364 Identity header field only in cases where it believes it is in the 365 same Trust Domain as the SIP entity to which it sends the request and 366 is connected to that SIP entity in accordance with the security 367 requirements of RFC 3325. 369 4.1.2. Response handling 371 Typically a UA renders the value of a P-Asserted-Identity header 372 field that it receives in a response to its user. It may consider 373 the identity provided by a Trust Domain to be privileged, or 374 intrinsically more trustworthy than other information in the 375 response. However, any particular behaviour is specific to 376 implementations or services. This document also does not mandate any 377 UA handling for multiple P-Asserted-Identity header field values that 378 happen to appear in a response (such as a SIP URI alongside a tel 379 URL). 381 However, if a UAC receives a response from a previous element it does 382 not trust, it MUST NOT use the P-Asserted-Identity header field in 383 any way. 385 If a UA is part of the Trust Domain from which it received a response 386 containing a P-Asserted-Identity header field, then it can use the 387 value internally but it MUST ensure that it does not forward the 388 information to any element that is not part of the Trust Domain if 389 the responding user has requested that asserted identity information 390 be kept private. 392 4.2. Proxy Behaviour 394 4.2.1. Request handling 396 If a proxy receives a request from a UAC within the Trust Domain it 397 MUST behave as for a request from any other node within the Trust 398 Domain, in accordance with the rules of RFC 3325 for a proxy. 400 Note that this implies that the proxy must have authenticated the 401 sender of the request in accordance with the Spec(T) in force for 402 the Trust Domain and determined that the sender is indeed part of 403 the Trust Domain. 405 If a proxy receives an UPDATE, REGISTER, MESSAGE, PUBLISH or ACK 406 request containing a P-Asserted-Identity header field, it MUST behave 407 as for any other request in accordance with the rules of RFC 3325 for 408 a proxy. 410 If a proxy receives a MESSAGE or PUBLISH request containing a 411 P-Preferred-Identity header field, it MUST behave as for any other 412 request in accordance with the rules of RFC 3325 for a proxy. 414 4.2.2. Response handling 416 The proxy behaviour specified in RFC 3325 is applicable to responses 417 with the following qualifications. A proxy that receives a response 418 from a node outside the Trust Domain cannot directly authenticate the 419 UAS by SIP means. Therefore it MUST NOT include a P-Asserted- 420 Identity header field when forwarding the response unless it has 421 authenticated the UAS by other means. If a proxy receives a response 422 from a UAS within the Trust Domain it MUST behave as for a response 423 from any other node within the Trust Domain, in accordance with the 424 rules of RFC 3325 for a proxy. 426 One possible circumstance in which a proxy can include a 427 P-Asserted-Identity header field when forwarding a response from a 428 node outside the Trust Domain is when the proxy has direct TLS 429 connectivity with the UAS and has authenticated the UA by some 430 other means (e.g., SIP digest authentication) during that same TLS 431 session. 433 The proxy behaviour specified in RFC 3325 for handling a received 434 P-Preferred-Identity header field is applicable also to responses, 435 subject to the qualification above concerning authentication of the 436 UAS as a pre-requisite for inserting a P-Asserted-Identity header 437 field. 439 4.3. Registrar Behaviour 441 If a registrar receives a REGISTER request containing a P-Asserted- 442 Identity header field, it MUST disregard the asserted identity unless 443 received over a secure transport from a proxy within the Trust 444 Domain. Otherwise it MAY use this as evidence that the registering 445 UA has been authenticated as representing the identity asserted in 446 the header field. 448 4.4. UAS Behaviour 450 4.4.1. Request handling 452 If a UAS receives an UPDATE, MESSAGE, PUBLISH or ACK request 453 containing a P-Asserted-Identity header field, it MUST behave as for 454 any other request in accordance with the rules of RFC 3325 for a UAS. 456 4.4.2. Response handling 458 A UAS MAY include a P-Asserted-Identity or P-Preferred-Identity 459 header field in a response to report the identity of the user on 460 behalf of which the UAS is acting and whose identity the UAS is in a 461 position to assert. A UAS SHOULD include a P-Asserted-Identity 462 header field only in cases where it believes it is in the same Trust 463 Domain as the SIP entity from which it received the request and is 464 connected to that SIP entity in accordance with the security 465 requirements of RFC 3325. 467 5. IANA considerations 469 This document requires no IANA actions. 471 6. Security considerations 473 The use of asserted identity raises a number of security 474 considerations, which are discussed fully in [RFC3325]. This 475 document raises the following additional security considerations. 477 When receiving a request or response containing a P-Asserted-Identity 478 header field, a proxy will trust the assertion only if the source is 479 known to be within the Trust Domain and behaves in accordance with a 480 Spec(T), which defines the security requirements. This applies 481 regardless of the nature of the resource (UA or proxy). One example 482 where a trusted source might be a UA is a PSTN gateway. In this case 483 the UA can assert an identity received from the PSTN, the proxy 484 itself having no means to authenticate such an identity. A SIP 485 entity must not trust an identity asserted by a source outside the 486 Trust Domain. Typically a UA under the control of an individual user 487 (such as a desk phone or mobile phone) should not be considered part 488 of a Trust Domain. 490 When receiving a response from a node outside the Trust Domain, a 491 proxy has no direct SIP means to authenticate the node. However, if 492 authentication has taken place by other means (e.g., an earlier use 493 of SIP digest authentication) and the entity sending the response is 494 known to be the same entity (e.g., connected via the same TLS 495 session) this can be sufficient grounds for asserting an identity. 496 In other circumstances a proxy must not assert identity for a 497 responding user. 499 When receiving a REGISTER request containing a P-Asserted-Identity 500 header field, a proxy will trust the asserted identity only if 501 received over a secure connection from a proxy within the Trust 502 Domain. 504 7. Acknowledgements 506 Useful comments were received from Francois Audet, Jeroen van Bemmel, 507 Hans Erik van Elburg, Vijay Gurbani, Cullen Jennings, Hadriel Kaplan, 508 Paul Kyzivat, Jonathan Rosenberg and Thomas Stach during drafting and 509 review. 511 8. References 513 8.1. Normative References 515 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 516 Requirement Levels", BCP 14, RFC 2119, March 1997. 518 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 519 A., Peterson, J., Sparks, R., Handley, M., and E. 520 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 521 June 2002. 523 [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) 524 UPDATE Method", RFC 3311, October 2002. 526 [RFC3324] Watson, M., "Short Term Requirements for Network Asserted 527 Identity", RFC 3324, November 2002. 529 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 530 Extensions to the Session Initiation Protocol (SIP) for 531 Asserted Identity within Trusted Networks", RFC 3325, 532 November 2002. 534 [RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., 535 and D. Gurle, "Session Initiation Protocol (SIP) Extension 536 for Instant Messaging", RFC 3428, December 2002. 538 [RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension 539 for Event State Publication", RFC 3903, October 2004. 541 [I-D.ietf-sipping-uri-services] 542 Camarillo, G. and A. Roach, "Framework and Security 543 Considerations for Session Initiation Protocol (SIP) 544 Uniform Resource Identifier (URI)-List Services", 545 draft-ietf-sipping-uri-services-07 (work in progress), 546 November 2007. 548 8.2. Informative References 550 [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. 551 Camarillo, "Best Current Practices for Third Party Call 552 Control (3pcc) in the Session Initiation Protocol (SIP)", 553 BCP 85, RFC 3725, April 2004. 555 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 556 Authenticated Identity Management in the Session 557 Initiation Protocol (SIP)", RFC 4474, August 2006. 559 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 560 Protocol (SIP)", RFC 4916, June 2007. 562 Author's Address 564 John Elwell 565 Siemens Enterprise Communications GmbH & Co KG 566 Hofmannstrasse 51 567 D-81379 Munich 568 Germany 570 Phone: +44 115 943 4989 571 Email: john.elwell@siemens.com 573 Full Copyright Statement 575 Copyright (C) The IETF Trust (2008). 577 This document is subject to the rights, licenses and restrictions 578 contained in BCP 78, and except as set forth therein, the authors 579 retain all their rights. 581 This document and the information contained herein are provided on an 582 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 583 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 584 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 585 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 586 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 587 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 589 Intellectual Property 591 The IETF takes no position regarding the validity or scope of any 592 Intellectual Property Rights or other rights that might be claimed to 593 pertain to the implementation or use of the technology described in 594 this document or the extent to which any license under such rights 595 might or might not be available; nor does it represent that it has 596 made any independent effort to identify any such rights. Information 597 on the procedures with respect to rights in RFC documents can be 598 found in BCP 78 and BCP 79. 600 Copies of IPR disclosures made to the IETF Secretariat and any 601 assurances of licenses to be made available, or the result of an 602 attempt made to obtain a general license or permission for the use of 603 such proprietary rights by implementers or users of this 604 specification can be obtained from the IETF on-line IPR repository at 605 http://www.ietf.org/ipr. 607 The IETF invites any interested party to bring to its attention any 608 copyrights, patents or patent applications, or other proprietary 609 rights that may cover technology that may be required to implement 610 this standard. Please address the information to the IETF at 611 ietf-ipr@ietf.org.