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Elwell 3 Internet-Draft Siemens Enterprise Communications 4 Updates: RFC 3325 September 23, 2008 5 (if approved) 6 Intended status: Informational 7 Expires: March 27, 2009 9 Updates to Asserted Identity in the Session Initiation Protocol (SIP) 10 draft-ietf-sipping-update-pai-06.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 March 27, 2009. 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 certain SIP 45 methods such as UPDATE, REGISTER, MESSAGE, PUBLISH and ACK, and is 46 unclear on the use of this header field in responses. This document 47 extends RFC 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3.1. Inclusion of P-Asserted-Identity by a UAC . . . . . . . . 4 57 3.2. Inclusion of P-Asserted-Identity in any request . . . . . 5 58 3.3. Inclusion of P-Asserted-Identity or 59 P-Preferred-Identity in a response . . . . . . . . . . . . 6 60 3.3.1. Inclusion of P-Asserted-Identity or 61 P-Preferred-Identity by a UAS in a response . . . . . 7 62 3.3.2. Inclusion of P-Asserted-Identity by a proxy in a 63 response . . . . . . . . . . . . . . . . . . . . . . . 7 64 3.4. Dialog implications . . . . . . . . . . . . . . . . . . . 8 65 4. Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . 8 66 4.1. UAC Behaviour . . . . . . . . . . . . . . . . . . . . . . 8 67 4.1.1. Request handling . . . . . . . . . . . . . . . . . . . 8 68 4.1.2. Response handling . . . . . . . . . . . . . . . . . . 9 69 4.2. Proxy Behaviour . . . . . . . . . . . . . . . . . . . . . 9 70 4.2.1. Request handling . . . . . . . . . . . . . . . . . . . 9 71 4.2.2. Response handling . . . . . . . . . . . . . . . . . . 9 72 4.3. Registrar Behaviour . . . . . . . . . . . . . . . . . . . 10 73 4.4. UAS Behaviour . . . . . . . . . . . . . . . . . . . . . . 10 74 4.4.1. Request handling . . . . . . . . . . . . . . . . . . . 10 75 4.4.2. Response handling . . . . . . . . . . . . . . . . . . 10 76 4.5. General handling . . . . . . . . . . . . . . . . . . . . . 10 77 5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11 78 6. Security considerations . . . . . . . . . . . . . . . . . . . 11 79 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 80 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 81 8.1. Normative References . . . . . . . . . . . . . . . . . . . 12 82 8.2. Informative References . . . . . . . . . . . . . . . . . . 13 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 certain SIP methods such as UPDATE [RFC3311], 108 REGISTER, MESSAGE [RFC3428], PUBLISH [RFC3903] and ACK. Finally, RFC 109 3325 is unclear on the use of this header field in responses. There 110 are similar omissions concerning the P-Preferred-Identity header 111 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 any request 116 and, under certain conditions, allowing use of this header field in 117 SIP responses. This document also allows the use of the P-Preferred- 118 Identity header field in some of these situations. 120 RFC 3325 allows the P-Asserted-Identity and P-Preferred-Identity 121 header fields each to contain at most two URIs, where one is a SIP or 122 SIPS URI [RFC3261] and the other is a TEL URI [RFC3966]. This may be 123 unduly restrictive in future, for example if there is a need to allow 124 other URI schemes, if there is a need to allow both a SIP and a SIPS 125 URI or if there is a need to allow more than one URI with the same 126 scheme (e.g., a SIP URI based on a telephone number and a SIP URI 127 that is not based on a telephone number). This document therefore 128 provides forwards compatibility by mandating tolerance to the receipt 129 of unexpected URIs. 131 This document does not alter the fact that the asserted identity 132 mechanism has limited applicability, i.e., within a Trust Domain. 134 For general applicability, including operation outside a Trust Domain 135 (e.g., over the public Internet) or between different Trust Domains, 136 a different mechanism is needed. RFC 4474 [RFC4474] specifies the 137 Identity header field, in conjunction with the From header field, for 138 providing authenticated identity in such circumstances. 140 3. Discussion 142 3.1. Inclusion of P-Asserted-Identity by a UAC 144 RFC 3325 does not include procedures for a UAC to include the 145 P-Asserted-Identity header field in a request. This can be 146 meaningful if the UAC is in the same Trust Domain as the first 147 downstream SIP entity. Examples of types of UAC that are often 148 suitable for inclusion in a Trust Domain are: 150 o PSTN gateways; 152 o media servers; 154 o application servers (or B2BUAs) that act as URI list servers 155 [I-D.ietf-sipping-uri-services]; 157 o application servers (or B2BUAs) that perform third party call 158 control. 160 In the particular case of a PSTN gateway, the PSTN gateway might be 161 able to assert an identity received from the PSTN, the proxy itself 162 having no means to authenticate such an identity. Likewise, in the 163 case of certain application server or B2BUA arrangements, the 164 application server or B2BUA may be in a position to assert an 165 identity of a user on the other side of that application server or 166 B2BUA. 168 In accordance with RFC 3325, nodes within a Trust Domain must behave 169 in accordance with a Spec(T), and this principle needs to apply 170 between a UAC and its proxy as part of the condition for considering 171 the UAC to be within the same Trust Domain. Normal proxy procedures 172 of RFC 3325 ensure that the header field is removed or replaced if 173 the first proxy considers the UAC to be outside the Trust Domain. 175 This update to RFC 3325 clarifies that a UAC may include a 176 P-Asserted-Identity header field in a request in certain 177 circumstances. 179 3.2. Inclusion of P-Asserted-Identity in any request 181 There are several use cases that would benefit from the use of the 182 P-Asserted-Identity header field in an UPDATE request. These use 183 cases apply within a Trust Domain where the use of asserted identity 184 is appropriate (see RFC 3325). 186 In one example, an established call passes through a gateway to the 187 PSTN. The gateway becomes aware that the remote party in the PSTN 188 has changed, e.g., due to call transfer. By including the 189 P-Asserted-Identity header field in an UPDATE request, the gateway 190 can convey the identity of the new remote party to the peer SIP UA. 192 Note that the (re-)INVITE method could be used in this situation. 193 However, this forces an offer-answer exchange, which typically is 194 not required in this situation. Also it involves 3 messages 195 rather than 2. 197 In another example, a B2BUA that provides third party call control 198 (3PCC) [RFC3725] wishes to join two calls together, one of which is 199 still waiting to be answered and potentially is forked to different 200 UAs. At this point in time it is not possible to trigger the normal 201 offer-answer exchange between the two joined parties, because of the 202 mismatch between a single dialog on the one side and potentially 203 multiple early dialogs on the other side, so this action must wait 204 until one of the called UAs answers. However, it would be useful to 205 give an early indication to each user concerned of the identity of 206 the user to which they will become connected when the call is 207 answered. In other words, it would provide the new calling UA with 208 the identity of the new called user and provide the new called UA(s) 209 with the identity of the new calling user. This can be achieved by 210 the B2BUA sending an UPDATE request with a P-Asserted-Identity header 211 field on the dialogs concerned. 213 Within a Trust Domain, a P-Asserted-Identity header field could 214 advantageously be used in a REGISTER request between an edge proxy 215 that has authenticated the source of the request and the registrar. 217 Within a Trust Domain, a P-Asserted-Identity header field could 218 advantageously be used in a MESSAGE request to assert the source of a 219 page mode instant message. This would complement its use in an 220 INVITE request to assert the source of an instant message session or 221 any other form of session. Similarly, between a UAC and first proxy 222 that are not within the same Trust Domain, a P-Preferred-Identity 223 header field could be used in a MESSAGE request to express a 224 preference when the user has several identities. 226 Within a Trust Domain, a P-Asserted-Identity header field could 227 advantageously be used in a PUBLISH request to assert the source of 228 published state information. This would complement its use in 229 SUBSCRIBE and NOTIFY requests. Similarly, between a UAC and first 230 proxy that are not within the same Trust Domain, a P-Preferred- 231 Identity header field could be used in a PUBLISH request to express a 232 preference when the user has several identities. 234 Within a Trust Domain, a P-Asserted-Identity header field could 235 advantageously be used in an ACK request. Considering the 3PCC 236 scenario in Flow I of [RFC3725], the asserted identity of user B may 237 not be known when the B2BUA (controller) sends the initial INVITE 238 request to UA A, but might be known when the B2BUA sends the ACK 239 request to UA A (having received it in the 200 response from UA B). 241 Thus there are several examples where P-Asserted-Identity could be 242 used in requests with methods that are not provided for in RFC 3325 243 or any other RFC. This leaves a few methods for which use cases are 244 less obvious, but the inclusion of P-Asserted Identity would not 245 cause any harm. In any requests, the header field would simply 246 assert the source of that request, whether or not this is of any use 247 to the UAS. Similarly there are examples where P-Preferred-Identity 248 could be used in requests with methods that are not provided for in 249 RFC 3325 or any other RFC. 251 This update to RFC 3325 allows a P-Asserted-Identity or P-Preferred- 252 Identity header field to be included in any request. 254 3.3. 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 3.3.1. Inclusion of P-Asserted-Identity or P-Preferred-Identity by a 304 UAS in a response 306 It should be permissible for a UAS to insert a P-Asserted-Identity 307 header field into a response if it is within the same Trust Domain as 308 the SIP entity from which the request was received. 310 Between a UAS and a SIP entity that are not within the same Trust 311 Domain, a P-Preferred-Identity header field could be used in a 312 response, in order to express a preference when the authenticated 313 user has several identities. 315 This update to RFC 3325 allows a UAS to insert a P-Asserted-Identity 316 or P-Preferred-Identity header field in a response. 318 3.3.2. Inclusion of P-Asserted-Identity by a proxy in a response 320 Section 5 of RFC 3325 requires a proxy to authenticate the originator 321 of a message from a node outside the Trust Domain before including a 322 P-Asserted-Identity header field in the forwarded message. While 323 this is achievable for requests using SIP digest authentication, it 324 is not achievable in the same way for responses. A proxy cannot 325 challenge a response and cannot establish the authenticity of the 326 sender of a response. In practice, there is no standardised manner 327 by which a SIP proxy can authenticate the sender of the response. 328 Therefore, a proxy must not include a P-Asserted-Identity header 329 field when forwarding the response unless it has authenticated the 330 UAS by some means. The means to authenticate the UAS is outside the 331 scope of this document. However, future documents may define 332 techniques for response authentication. 334 This update to RFC 3325 allows a proxy to include a P-Asserted- 335 Identity header field in certain circumstances when forwarding a 336 response. 338 3.4. Dialog implications 340 A P-Asserted-Identity header field in a received request or response 341 asserts the identity of the source of that request or response and 342 says nothing about the source of subsequent received requests or 343 responses claiming to relate to the same dialog. The recipient can 344 make its own deductions about the source of subsequent requests or 345 responses not containing a P-Asserted-Identity header field. This 346 document does not change RFC 3325 in this respect. 348 4. Behaviour 350 This document updates RFC 3325 by allowing a P-Asserted-Identity 351 header field to be included by a UAC within the same Trust Domain, by 352 allowing a P-Asserted-Identity or P-Preferred-Identity header field 353 to appear in any request, and by allowing a P-Asserted-Identity 354 header field to appear in a response in certain circumstances. 356 4.1. UAC Behaviour 358 4.1.1. Request handling 360 A UAC MAY include a P-Asserted-Identity header field in a request to 361 report the identity of the user on behalf of which the UAC is acting 362 and whose identity the UAC is in a position to assert. A UAC SHOULD 363 do so only in cases where it believes it is in the same Trust Domain 364 as the SIP entity to which it sends the request and is connected to 365 that SIP entity in accordance with the security requirements of RFC 366 3325. A UAC SHOULD NOT do so in other circumstances and might 367 instead use the P-Preferred-Identity header field. A UAC MUST NOT 368 include both header fields. 370 A UAC MAY include a P-Asserted-Identity or P-Preferred-Identity 371 header field in any request, i.e., not limited to the methods allowed 372 in RFC 3325. 374 4.1.2. Response handling 376 Typically a UA renders the value of a P-Asserted-Identity header 377 field that it receives in a response to its user. It may consider 378 the identity provided by a Trust Domain to be privileged, or 379 intrinsically more trustworthy than other information in the 380 response. However, any particular behaviour is specific to 381 implementations or services. This document also does not mandate any 382 UA handling for multiple P-Asserted-Identity header field values that 383 happen to appear in a response (such as a SIP URI alongside a tel 384 URL). 386 However, if a UAC receives a response from a previous element it does 387 not trust, it MUST NOT use the P-Asserted-Identity header field in 388 any way. 390 If a UA is part of the Trust Domain from which it received a response 391 containing a P-Asserted-Identity header field, then it can use the 392 value internally but it MUST ensure that it does not forward the 393 information to any element that is not part of the Trust Domain if 394 the responding user has requested that asserted identity information 395 be kept private. 397 4.2. Proxy Behaviour 399 4.2.1. Request handling 401 If a proxy receives a request from a UAC within the Trust Domain it 402 MUST behave as for a request from any other node within the Trust 403 Domain, in accordance with the rules of RFC 3325 for a proxy. 405 Note that this implies that the proxy must have authenticated the 406 sender of the request in accordance with the Spec(T) in force for 407 the Trust Domain and determined that the sender is indeed part of 408 the Trust Domain. 410 If a proxy receives a request containing a P-Asserted-Identity or 411 P-Preferred-Identity header field, it MUST behave in accordance with 412 the rules of RFC 3325 for a proxy, even if the method is not one for 413 which RFC 3325 specifies use of that header field. 415 4.2.2. Response handling 417 The proxy behaviour specified in RFC 3325 is applicable to responses 418 with the following qualifications. A proxy MUST NOT include a 419 P-Asserted-Identity header field when forwarding a response from a 420 node outside the Trust Domain unless it has authenticated the UAS by 421 some means. The means to authenticate the UAS is outside the scope 422 of this document. 424 The proxy behaviour specified in RFC 3325 applies for handling a 425 P-Asserted-Identity header field in a response from a node within the 426 Trust Domain. 428 The proxy behaviour specified in RFC 3325 for handling a received 429 P-Preferred-Identity header field is applicable also to responses, 430 subject to the qualification above concerning authentication of the 431 UAS as a pre-requisite for including a P-Asserted-Identity header 432 field when forwarding a response. 434 4.3. Registrar Behaviour 436 If a registrar receives a REGISTER request containing a P-Asserted- 437 Identity header field, it MUST disregard the asserted identity unless 438 received over a secure transport from a node within the Trust Domain. 439 Otherwise it MAY use this as evidence that the registering UA has 440 been authenticated as representing the identity asserted in the 441 header field. 443 4.4. UAS Behaviour 445 4.4.1. Request handling 447 If a UAS receives any request containing a P-Asserted-Identity header 448 field, it MUST behave as for any other request in accordance with the 449 rules of RFC 3325 for a UAS, even if the method is not one for which 450 RFC 3325 specifies use of that header field. 452 4.4.2. Response handling 454 A UAS MAY include a P-Asserted-Identity or P-Preferred-Identity 455 header field in a response to report the identity of the user on 456 behalf of which the UAS is acting and whose identity the UAS is in a 457 position to assert. A UAS SHOULD include a P-Asserted-Identity 458 header field only in cases where it believes it is in the same Trust 459 Domain as the SIP entity from which it received the request and is 460 connected to that SIP entity in accordance with the security 461 requirements of RFC 3325. 463 4.5. General handling 465 If an entity receives a request or response containing a P-Asserted- 466 Identity or P-Preferred-Identity header field containing an 467 unexpected number of URIs or unexpected URI schemes it MUST act as 468 follows: 470 o ignore any URI with an unexpected URI scheme; 472 o ignore any URI for which the expected maximum number of URIs with 473 the same scheme occurred earlier in the header field; and 475 o ignore any URI whose scheme is not expected to occur in 476 combination with a scheme that occurred earlier in the header 477 field. 479 This document does not change the RFC 3325 requirement that allows 480 each of these header fields to contain at most two URIs, where one is 481 a SIP or SIPS URI and the other is a TEL URI, but future updates to 482 this document may relax that requirement. In the absence of such a 483 relaxation, the requirement above means that an entity receiving a 484 request or response containing a P-Asserted-Identity or P-Preferred- 485 Identity header field must act as follows: 487 o ignore any URI with a scheme other than SIP, SIPS or TEL; 489 o ignore a second or subsequent SIP URI, a second or subsequent SIPS 490 URI or a second or subsequent TEL URI; and 492 o ignore a SIP URI if a SIPS URI occurred earlier in the header 493 field and vice versa. 495 A proxy MUST NOT forward a URI when forwarding a message if that URI 496 is to be ignored in accordance with the requirement above. 498 5. IANA considerations 500 This document requires no IANA actions. 502 6. Security considerations 504 The use of asserted identity raises a number of security 505 considerations, which are discussed fully in [RFC3325]. This 506 document raises the following additional security considerations. 508 When receiving a request or response containing a P-Asserted-Identity 509 header field, a proxy will trust the assertion only if the source is 510 known to be within the Trust Domain and behaves in accordance with a 511 Spec(T), which defines the security requirements. This applies 512 regardless of the nature of the resource (UA or proxy). One example 513 where a trusted source might be a UA is a PSTN gateway. In this case 514 the UA can assert an identity received from the PSTN, the proxy 515 itself having no means to authenticate such an identity. A SIP 516 entity must not trust an identity asserted by a source outside the 517 Trust Domain. Typically a UA under the control of an individual user 518 (such as a desk phone or mobile phone) should not be considered part 519 of a Trust Domain. 521 When receiving a response from a node outside the Trust Domain, a 522 proxy has no standardised SIP means to authenticate the node. 523 However, if authentication has taken place by other means, outside 524 the scope of this document, this can be sufficient grounds for 525 asserting an identity. In other circumstances a proxy must not 526 assert identity for a responding user. 528 When receiving a REGISTER request containing a P-Asserted-Identity 529 header field, a proxy will trust the asserted identity only if 530 received over a secure connection from a proxy within the Trust 531 Domain. 533 7. Acknowledgements 535 Useful comments were received from Francois Audet, Jeroen van Bemmel, 536 Hans Erik van Elburg, Vijay Gurbani, Cullen Jennings, Hadriel Kaplan, 537 Paul Kyzivat, Jonathan Rosenberg, Thomas Stach and Brett Tate during 538 drafting and review. 540 8. References 542 8.1. Normative References 544 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 545 Requirement Levels", BCP 14, RFC 2119, March 1997. 547 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 548 A., Peterson, J., Sparks, R., Handley, M., and E. 549 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 550 June 2002. 552 [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) 553 UPDATE Method", RFC 3311, October 2002. 555 [RFC3324] Watson, M., "Short Term Requirements for Network Asserted 556 Identity", RFC 3324, November 2002. 558 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 559 Extensions to the Session Initiation Protocol (SIP) for 560 Asserted Identity within Trusted Networks", RFC 3325, 561 November 2002. 563 [RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., 564 and D. Gurle, "Session Initiation Protocol (SIP) Extension 565 for Instant Messaging", RFC 3428, December 2002. 567 [RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension 568 for Event State Publication", RFC 3903, October 2004. 570 [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", 571 RFC 3966, December 2004. 573 [I-D.ietf-sipping-uri-services] 574 Camarillo, G. and A. Roach, "Framework and Security 575 Considerations for Session Initiation Protocol (SIP) 576 Uniform Resource Identifier (URI)-List Services", 577 draft-ietf-sipping-uri-services-07 (work in progress), 578 November 2007. 580 8.2. Informative References 582 [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. 583 Camarillo, "Best Current Practices for Third Party Call 584 Control (3pcc) in the Session Initiation Protocol (SIP)", 585 BCP 85, RFC 3725, April 2004. 587 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 588 Authenticated Identity Management in the Session 589 Initiation Protocol (SIP)", RFC 4474, August 2006. 591 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 592 Protocol (SIP)", RFC 4916, June 2007. 594 Author's Address 596 John Elwell 597 Siemens Enterprise Communications 599 Phone: +44 115 943 4989 600 Email: john.elwell@siemens.com 602 Full Copyright Statement 604 Copyright (C) The IETF Trust (2008). 606 This document is subject to the rights, licenses and restrictions 607 contained in BCP 78, and except as set forth therein, the authors 608 retain all their rights. 610 This document and the information contained herein are provided on an 611 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 612 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 613 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 614 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 615 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 616 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 618 Intellectual Property 620 The IETF takes no position regarding the validity or scope of any 621 Intellectual Property Rights or other rights that might be claimed to 622 pertain to the implementation or use of the technology described in 623 this document or the extent to which any license under such rights 624 might or might not be available; nor does it represent that it has 625 made any independent effort to identify any such rights. Information 626 on the procedures with respect to rights in RFC documents can be 627 found in BCP 78 and BCP 79. 629 Copies of IPR disclosures made to the IETF Secretariat and any 630 assurances of licenses to be made available, or the result of an 631 attempt made to obtain a general license or permission for the use of 632 such proprietary rights by implementers or users of this 633 specification can be obtained from the IETF on-line IPR repository at 634 http://www.ietf.org/ipr. 636 The IETF invites any interested party to bring to its attention any 637 copyrights, patents or patent applications, or other proprietary 638 rights that may cover technology that may be required to implement 639 this standard. Please address the information to the IETF at 640 ietf-ipr@ietf.org.