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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- Couldn't find a document date in the document -- date freshness check skipped. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Missing reference section? '1' on line 63 looks like a reference -- Missing reference section? '4' on line 113 looks like a reference -- Missing reference section? '2' on line 966 looks like a reference -- Missing reference section? '5' on line 216 looks like a reference -- Missing reference section? '6' on line 217 looks like a reference -- Missing reference section? '7' on line 222 looks like a reference -- Missing reference section? '8' on line 1260 looks like a reference -- Missing reference section? '9' on line 273 looks like a reference -- Missing reference section? '10' on line 271 looks like a reference -- Missing reference section? '3' on line 434 looks like a reference -- Missing reference section? '12' on line 836 looks like a reference -- Missing reference section? '11' on line 1148 looks like a reference Summary: 6 errors (**), 0 flaws (~~), 9 warnings (==), 14 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIP Working Group W. Marshall 3 Internet Draft AT&T 4 Document: 5 K. Ramakrishnan 6 TeraOptic Networks 8 E. Miller 9 Terayon 11 G. Russell 12 CableLabs 14 B. Beser 15 Pacific Broadband 17 M. Mannette 18 K. Steinbrenner 19 3Com 21 D. Oran 22 F. Andreasen 23 M. Ramalho 24 Cisco 26 J. Pickens 27 Com21 29 P. Lalwaney 30 Nokia 32 J. Fellows 33 Copper Mountain Networks 35 D. Evans 36 D. R. Evans Consulting 38 K. Kelly 39 NetSpeak 41 A. Roach 42 Ericsson 44 J. Rosenberg 45 D. Willis 46 S. Donovan 47 dynamicsoft 49 H. Schulzrinne 50 Columbia University 52 February, 2001 54 Integration of Resource Management and SIP 56 SIP Working Group Expiration 2/28/02 1 57 SIP Extensions for Resource Management August 2001 59 Status of this Memo 61 This document is an Internet-Draft and is in full conformance with 62 all provisions of Section 10 of RFC2026[1]. 64 Internet-Drafts are working documents of the Internet Engineering 65 Task Force (IETF), its areas, and its working groups. Note that 66 other groups may also distribute working documents as Internet- 67 Drafts. Internet-Drafts are draft documents valid for a maximum of 68 six months and may be updated, replaced, or obsoleted by other 69 documents at any time. It is inappropriate to use Internet- Drafts 70 as reference material or to cite them other than as "work in 71 progress." 73 The list of current Internet-Drafts can be accessed at 74 http://www.ietf.org/ietf/1id-abstracts.txt 76 The list of Internet-Draft Shadow Directories can be accessed at 77 http://www.ietf.org/shadow.html. 79 The distribution of this memo is unlimited. It is filed as , and expires February 28, 2002. 81 Please send comments to the authors. 83 1. Abstract 85 This document discusses how network QoS and security establishment 86 can be made a precondition to sessions initiated by the Session 87 Initiation Protocol (SIP), and described by SDP. These preconditions 88 require that the participant reserve network resources (or establish 89 a secure media channel) before continuing with the session. We do 90 not define new QoS reservation or security mechanisms; these pre- 91 conditions simply require a participant to use existing resource 92 reservation and security mechanisms before beginning the session. 94 This results in a multi-phase call-setup mechanism, with the 95 resource management protocol interleaved between two phases of call 96 signaling. The objective of such a mechanism is to enable deployment 97 of robust IP Telephony services, by ensuring that resources are made 98 available before the phone rings and the participants of the call 99 are "invited" to participate. 101 This document also proposes an extension to the Session Initiation 102 Protocol (SIP) to add a new COMET method, which is used to confirm 103 the completion of all pre-conditions by the session originator. 105 2. Conventions used in this document 107 SIP Working Group Expiration 2/28/02 2 108 SIP Extensions for Resource Management August 2001 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 112 this document are to be interpreted as described in RFC-2119[4]. 114 3. Table of Contents 116 Status of this Memo................................................2 117 1. Abstract........................................................2 118 2. Conventions used in this document...............................2 119 3. Table of Contents...............................................3 120 4. Introduction....................................................3 121 4.1 Requirements...................................................6 122 4.2 Overview.......................................................6 123 5. SDP Extension...................................................8 124 5.1 SDP Example....................................................9 125 5.2 SDP Allowable Combinations.....................................9 126 6. SIP Extension: The COMET Method................................11 127 6.1 Header Field Support for COMET Method.........................12 128 6.2 Responses to the COMET Request Method.........................12 129 6.3 Message Body Inclusion........................................13 130 6.4 Behavior of SIP User Agents...................................13 131 6.5 Behavior of SIP Proxy and Redirect Servers....................13 132 6.5.1 Proxy Server................................................13 133 6.5.2 Forking Proxy Server........................................14 134 6.5.3 Redirection Server..........................................14 135 7. SIP Extension: The 183-Session-Progress Response...............14 136 7.1 Status Code and Reason Phrase.................................14 137 7.2 Status Code Definition........................................14 138 8. SIP Extension: The 580-Precondition-Failure Response...........14 139 8.1 Status Code and Reason Phrase.................................14 140 8.2 Status Code Definition........................................14 141 9. SIP Extension: Content-Disposition header......................15 142 10. Option tag for Requires and Supported headers.................16 143 11. SIP Usage Rules...............................................16 144 11.1 Overview.....................................................16 145 11.2 Behavior of Originator (UAC).................................17 146 11.3 Behavior of Destination (UAS)................................18 147 12. Examples......................................................19 148 12.1 Single Media Call Flow.......................................19 149 12.2 Multiple Media Call Flow.....................................22 150 13. Special considerations with Forking Proxies...................23 151 14. Advantages of the Proposed Approach...........................24 152 15. Security Considerations.......................................24 153 16. Notice Regarding Intellectual Property Rights.................24 154 17. References....................................................24 155 18. Acknowledgments...............................................25 156 19. Author's Addresses............................................25 157 Full Copyright Statement..........................................28 159 4. Introduction 161 SIP Working Group Expiration 2/28/02 3 162 SIP Extensions for Resource Management August 2001 164 For an Internet Telephony service to be successfully used by a large 165 number of subscribers, it must offer few surprises to those 166 accustomed to the behavior of existing telephony services. One 167 expectation is that of connection quality, implying resources must 168 be set aside for each call. 170 A key contribution is a recognition of the need for coordination 171 between call signaling, which controls access to telephony specific 172 services, and resource management, which controls access to network- 173 layer resources. This coordination is designed to meet the user 174 expectations and human factors associated with telephony. 176 While customers may expect, during times of heavy load, to receive a 177 "fast busy" or an announcement saying "all circuits are busy now," 178 the general expectation is that once the destination phone rings 179 that the connection can be made. Blocking a call after ringing the 180 destination is considered a "call defect" and is a very undesirable 181 exception condition. 183 This draft addresses both "QoS-Assured" and "QoS-Enabled" sessions. 184 A "QoS-Assured" session will complete only if all the required 185 resources are available and assigned to the session. A provider may 186 choose to block a call when adequate resources for the call are not 187 available. Public policy demands that the phone system provide 188 adequate quality at least in certain cases: e.g., for emergency 189 communications during times of disasters. Call blocking enables a 190 provider to meet such requirements. 192 A "QoS-Enabled" session allows the endpoints to complete the session 193 establishment either with or without the desired resources. Such 194 session will use dedicated resources if available, and use a best- 195 effort connection as an alternative if resources can not be 196 dedicated. In cases where resources are not available, the 197 originating and/or terminating User Agent might consult with the 198 customer to obtain guidance on whether the session should complete. 200 Coordination between call signaling and resource management is also 201 needed to prevent fraud and theft of service. The coordination 202 between call-signaling and QoS setup protocols ensures that users 203 are authenticated and authorized before receiving access to the 204 enhanced QoS associated with the telephony service. 206 This coordination, referred to in this draft as "preconditions," 207 require that the participant reserve network resources (or establish 208 a secure media channel) before continuing with the session. We do 209 not define new QoS reservation or security mechanisms; these pre- 210 conditions simply require a participant to use existing resource 211 reservation and security mechanisms before beginning the session. 213 In the case of SIP [2], this effectively means that the "phone won't 214 ring" until the preconditions are met. These preconditions are 215 described by new SDP parameters, defined in this document. The 216 parameters can mandate end-to-end QoS reservations based on RSVP [5] 217 or any other end-to-end reservation mechanism (such as YESSIR [6], 219 SIP Working Group Expiration 2/28/02 4 220 SIP Extensions for Resource Management August 2001 222 or PacketCable's Dynamic Quality of Service (D-QoS) [7]), and 223 security based on IPSEC [8]. The preconditions can be defined 224 independently for each media stream. 226 The QoS architecture of the Internet separates QoS signaling from 227 application level signaling. Application layer devices (such as web 228 proxies and SIP servers) are not well suited for participation in 229 network admission control or QoS management, as this is 230 fundamentally a network layer issue, independent of any particular 231 application. In addition, since application devices like SIP servers 232 are almost never on the "bearer path" (i.e., the network path the 233 RTP [9] takes), and since the RTP path and signaling paths can be 234 completely different (even traversing different autonomous systems), 235 these application servers are generally not capable of managing QoS 236 for the media. Keeping QoS out of application signaling also means 237 that there can be a single infrastructure for QoS across all 238 applications. This eliminates duplication of functionality, reducing 239 management and equipment costs. It also means that new applications, 240 with their own unique QoS requirements, can be easily supported. 242 This loose coupling works very well for a wide range of 243 applications. For example, in an interactive game, one can establish 244 the game using an application signaling protocol, and then later on 245 use RSVP to reserve network resources. The separation is also 246 effective for applications which have no explicit signaling. 247 However, certain applications may require tighter coupling. In the 248 case of Internet telephony, the following is an important 249 requirement: 251 When A calls B, B's phone should not ring unless resources 252 have been reserved from A to B, and B to A. 254 This could be achieved without coupling if A knew B's address, port, 255 and codecs before the telephony signaling took place. However, since 256 telephony signaling is used largely to obtain this information in 257 the first place, the coupling cannot be avoided. 259 A similar model exists for security. Rather than inventing new 260 security mechanisms for each new application, common security tools 261 (such as IPSEC) can be used across all applications. As with QoS, a 262 means in application level protocols is needed to indicate that a 263 security association is needed for the application to execute. 265 To solve both of these problems, we propose an extension to SDP 266 which allows indication of pre-conditions for sessions. These 267 preconditions indicate that participation in the session should not 268 proceed until the preconditions are met. The preconditions we define 269 are (1) success of end-to-end resource reservation, and (2) success 270 of end- to-end security establishment. We chose to implement these 271 extensions in SDP, rather than SIP [2] or SAP [10], since they are 272 fundamentally a media session issue. SIP is session agnostic; 273 information about codecs, ports, and RTP [9] are outside the scope 274 of SIP. Since it is the media sessions that the reservations and 275 security refer to, SDP is the appropriate venue for the extensions. 277 SIP Working Group Expiration 2/28/02 5 278 SIP Extensions for Resource Management August 2001 280 Furthermore, placement of the extensions in SDP rather than SIP or 281 SAP allows specification of preconditions for individual media 282 streams. For example, a multimedia lecture might require reservation 283 for the audio, but not the video (which is less important). 285 Our extensions are completely backward compatible. If a recipient 286 does not understand them, normal SIP or SAP processing will occur, 287 at no penalty of call setup latency. 289 4.1 Requirements 291 The basic motivation in this work is to meet and possibly exceed the 292 user expectations and human factors associated with telephony. 294 In this section, we briefly describe the application requirements 295 that led to the set of DCS signaling design principles. In its 296 basic implementation, DCS supports a residential telephone service 297 comparable to the local telephone services offered today. Some of 298 the requirements for resource management, in concert with call 299 signaling, are as follows: 301 The system must minimize call defects. These are situations where 302 either the call never completes, or an error occurs after the 303 destination is alerted. Requirements on call defects are typically 304 far more stringent than call blocking. Note that we expect the 305 provider and the endpoints to attempt to use lower bandwidth codecs 306 as the first line of defense against limited network capacity, and 307 to avoid blocking calls. 309 The system must minimize the post-dial-delay, which is the time 310 between the user dialing the last digit and receiving positive 311 confirmation from the network. This delay must be short enough that 312 users do not perceive a difference with post-dial delay in the 313 circuit switched network or conclude that the network connectivity 314 no longer exists. 316 Call signaling needs to provide enough information to the resource 317 management protocol so as to enable resources to be allocated in the 318 network. This typically requires most if not all of the components 319 of a packet classifier (source IP, destination IP, source port, 320 destination port, protocol) to be available for resource allocation. 322 4.2 Overview 324 For acceptable interactive voice communication it is important to 325 achieve end-to-end QoS. The end-to-end QoS assurance implies 326 achieving low packet delay and packet loss. End-to-end packet delay 327 must be small enough that it does not interfere with normal voice 328 conversations. The ITU recommends no greater than 300 ms roundtrip 329 delay for telephony service. Packet loss must be small enough to 330 not perceptibly impede voice quality or the performance of fax and 331 voice band modems. 333 SIP Working Group Expiration 2/28/02 6 334 SIP Extensions for Resource Management August 2001 336 If it is found that the network cannot guarantee end-to-end QoS 337 resources, there are two alternatives: either (1) allow call 338 signaling to proceed with high probability of excessive delay and 339 packet loss which could impair any interactive real-time 340 communication between the participants, or (2) block the call prior 341 to the called party being alerted. When calls are blocked because 342 of a lack of resources in a particular segment of the network, it is 343 highly desirable that such blocking occur before the called party 344 picks up. 346 We do expect the endpoints to attempt to use lower bandwidth codecs, 347 thereby avoiding blocking calls, as the first line of defense 348 against limited network capacity. 350 The call signaling and resource reservation must be achieved in such 351 a way that the post-dial-delay must be minimized without increasing 352 the probability of call defects. This means that the number of 353 round-trip messages must be kept at an absolute minimum and messages 354 must be sent directly end-system to end-system if possible. 356 The general idea behind the extension is simple. We define two new 357 SDP attributes, "qos" and "security". The "qos" attribute indicates 358 whether end-to-end resource reservation is optional or mandatory, 359 and in which direction (send, recv, or sendrecv). When the attribute 360 indicates mandatory, this means that the participant who has 361 received the SDP does not proceed with participation in the session 362 until resource reservation has completed in the direction indicated. 363 In this case, "not proceeding" means that the participant behaves as 364 if they had not received the SDP at all. If the attribute indicates 365 that QoS for the stream is optional, then the participant proceeds 366 normally with the session, but should reserve network resources in 367 the direction indicated, if they are capable. Absence of the "qos" 368 attribute means the participant reserves resources for this stream, 369 and proceeds normally with the session. This behavior is the normal 370 behavior for SDP. 372 Resource reservation takes place using whatever protocols 373 participants must use, based on support by their service provider. 374 If the ISP's of the various participants are using differing 375 resource reservation protocols, translation is necessary, but this 376 is done within the network, without knowledge of the participants. 378 The direction attribute indicates in which direction reservations 379 should be reserved. If "send", it means reservations should be made 380 in the direction of media flow from the session originator to 381 participants. If "recv", it means reservations should be made in the 382 direction of media flow from participants to the session originator. 383 In the case of "sendrecv", it means reservations should be made in 384 both directions. If the direction attribute is "sendrecv" but the 385 endpoints only support a single-direction resource reservation 386 protocol, then both the originator and participants cooperate to 387 ensure the agreed precondition is met. 389 SIP Working Group Expiration 2/28/02 7 390 SIP Extensions for Resource Management August 2001 392 In the case of security, the same attributes are defined - 393 optional/mandatory, and send/recv/sendrecv. Their meaning is 394 identical to the one above, except that a security association 395 should be established in the given direction. The details of the 396 security association are not signaled by SDP; these depend on the 397 Security Policy Database of the participant. 399 Either party can include a "confirm" attribute in the SDP. When the 400 "Confirm" attribute is present, the recipient sends a COMET message 401 to the sender, with SDP attached, telling the status of each 402 precondition as "success" or "failure." If the "confirm" attribute 403 is present in the SDP sent by the session originator to the 404 participant (e.g. in the SIP INVITE message), then the participant 405 sends the COMET message to the originator. If the "confirm" 406 attribute is present in the SDP sent by the recipient to the 407 originator (e.g. in a SIP response message), then the originator 408 sends the COMET message to the participant. 410 When the "Confirm" attribute is present in both the SDP sent by the 411 session originator to the participant (e.g. in the SIP INVITE 412 message), and in the SDP sent by the recipient back to the 413 originator (e.g. in a SIP response message), the session originator 414 would wait for the COMET message with the success/failure 415 notification before responding with a COMET message, and responds 416 instead with a CANCEL if a mandatory precondition is not met, or if 417 a sufficient combination of optional preconditions are not met. The 418 recipient does not wait for the COMET message from the originator 419 before sending its COMET message. 421 The "confirm" attribute is typically used if the direction attribute 422 is "sendrecv" and the originator or participant only supports a 423 single-direction resource reservation protocol. In such a case, the 424 originator (or participant) would reserve resources for one 425 direction of media flow, and send a confirmation with a direction 426 attribute of "send." The participant (or originator) would reserve 427 resources for the other direction. On receipt of the COMET message, 428 they would know that both directions have been reserved, and the 429 precondition is met. 431 5. SDP Extension 433 The formatting of the qos attribute in the Session Description 434 Protocol (SDP)[3] is described by the following BNF: 436 qos-attribute = "a=qos:" strength-tag SP direction-tag 437 [SP confirmation-tag] 438 strength-tag = ("mandatory" | "optional" | "success" | 439 "failure") 440 direction-tag = ("send" | "recv" | "sendrecv") 441 confirmation-tag = "confirm" 443 and the security attribute: 445 security-attribute = "a=secure:" SP strength-tag SP direction-tag 447 SIP Working Group Expiration 2/28/02 8 448 SIP Extensions for Resource Management August 2001 450 [SP confirmation-tag] 452 5.1 SDP Example 454 The following example shows an SDP description carried in a SIP 455 INVITE message from A to B: 457 v=0 458 o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4 459 s=SDP Seminar 460 i=A Seminar on the session description protocol 461 u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.03.ps 462 e=mjh@isi.edu (Mark Handley) 463 c=IN IP4 224.2.17.12/127 464 t=2873397496 2873404696 465 m=audio 49170 RTP/AVP 0 466 a=qos:mandatory recv confirm 467 m=video 51372 RTP/AVP 31 468 a=secure:mandatory sendrecv 469 m=application 32416 udp wb 470 a=orient:portrait 471 a=qos:optional sendrecv 472 a=secure:optional sendrecv 474 This SDP indicates that B should not continue its involvement in the 475 session until resources for the audio are reserved from B to A, and 476 a bi-directional security association is established for the video. 477 B can join the sessions once these preconditions are met, but should 478 reserve resources and establish a bi-directional security 479 association for the whiteboard. 481 5.2 SDP Allowable Combinations 483 If the recipient of the SDP (e.g. the UAS) is capable and willing to 484 honor the precondition(s), it returns a provisional response 485 containing SDP, along with the qos/security attributes, for each 486 such stream. This SDP MUST be a subset of the preconditions 487 indicated in the INVITE. 489 Table 1 illustrates the allowed values for the direction tag in the 490 response. Each row represents a value of the direction in the SIP 491 INVITE, and each column the value in the response. An entry of N/A 492 means that this combination is not allowed. A value of A->B (B->A) 493 implies that the precondition is for resources reserved (or security 494 established) from A to B (B to A). A value of A<->B means that the 495 precondition is for resource reservation or security establishment 496 in both directions. The value in the response is the one used by 497 both parties. 499 SIP Working Group Expiration 2/28/02 9 500 SIP Extensions for Resource Management August 2001 502 B: response 503 A: request send recv sendrecv none 504 send N/A A->B N/A -- 505 recv B->A N/A N/A -- 506 sendrecv A<-B B<-A A<->B -- 507 none -- -- -- -- 509 Table 1: Allowed values of coupling 511 Table 2 illustrates the allowed values for the strength tag in the 512 request and response. A "Y" means the combination is allowed, and a 513 "N" means it is not. The value in the response is the one used by 514 both parties. 516 B: response 517 A: request mandatory optional none 518 mandatory Y Y Y 519 optional N Y Y 520 none N N Y 522 Table 2: Allowed values of strength parameter 524 Table 3 illustrates the allowed values for the direction tag in a 525 confirmation message (COMET) sent from the originator to a 526 participant, based on the value of the direction tag negotiated in 527 the initial request and response. A "Y" means the combination is 528 allowed, and a "N" means it is not and SHOULD be ignored by the 529 participant. 531 A: confirmation 532 B: reponse send recv sendrecv 533 A->B Y N N 534 A<-B N Y N 535 A<->B Y Y Y 537 Table 3: Allowed values of direction in confirmation from A 539 Table 4 illustrates the allowed values for the direction tag in a 540 confirmation message (COMET) sent from the participant to the 541 originator, based on the value of the direction tag negotiated in 542 the initial request and response. A "Y" means the combination is 543 allowed, and a "N" means it is not and SHOULD be ignored by the 544 originator. 546 B: confirmation 547 B: reponse send recv sendrecv 548 A->B N Y N 549 A<-B Y N N 550 A<->B Y Y Y 552 Table 4: Allowed values of direction in confirmation from B 554 SIP Working Group Expiration 2/28/02 10 555 SIP Extensions for Resource Management August 2001 557 6. SIP Extension: The COMET Method 559 The COMET method is used for communicating successful completion of 560 preconditions between the user agents. 562 The signaling path for the COMET method is the signaling path 563 established as a result of the call setup. This can be either 564 direct signaling between the calling and called user agents or a 565 signaling path involving SIP proxy servers that were involved in the 566 call setup and added themselves to the Record-Route header on the 567 initial INVITE message. 569 The precondition information is communicated in the message body, 570 which MUST contain an SDP. For every agreed precondition, the 571 strength-tag MUST indicate "success" or "failure". 573 If the initial request contained Record-Route headers, the 574 provisional response MUST contain a copy of those headers, as if the 575 response were a 200 OK to the initial request. Since provisional 576 responses MAY contain Record-Route and Contact headers, the COMET 577 request MUST contain Route headers if the Record-Route headers were 578 present in the provisional response. The Route header is constructed 579 as specified in [2]. The Route header that is constructed from some 580 provisional response MUST NOT be placed in any other request except 581 for the COMET for that provisional response. 583 A UAC MUST NOT insert a Route header into a COMET request if no 584 Record-Route header was present in the response. 586 If the initial request was sent with credentials, the COMET request 587 SHOULD contain those credentials as well. 589 The Call-ID in the COMET MUST match that of the provisional 590 response. The CSeq in this request MUST be larger than the last 591 request sent by this UAC for this call leg. The To, From, and Via 592 headers MUST be present, and MUST be constructed as they would be 593 for a re-INVITE or BYE as specified in [2]. In particular, if the 594 provisional response contained a tag in the To field, this tag MUST 595 be mirrored in the To field of the COMET. 597 Once the COMET request is created, it is sent by the UAC. It is sent 598 as would any other non-INVITE request for a call. In particular, 599 when sent over UDP, the COMET request is retransmitted with an 600 exponentially increasing interval, starting at 500 milliseconds and 601 increasing to 4 seconds. Note that a UAC SHOULD NOT retransmit the 602 COMET request when it receives a retransmission of the provisional 603 response being acknowledged, although doing so does not create a 604 protocol error. As with any other non-INVITE request, the UAC 605 continues to retransmit the COMET request until it receives a final 606 response. 608 A COMET request MAY be cancelled. However, whilst allowed for 609 purposes of generality, usage of CANCEL with COMET is NOT 610 RECOMMENDED. 612 SIP Working Group Expiration 2/28/02 11 613 SIP Extensions for Resource Management August 2001 615 6.1 Header Field Support for COMET Method 617 Tables 3 and 4 are extensions of tables 4 and 5 in the SIP 618 specification[2]. Refer to Section 6 of [2] for a description of 619 the content of the tables. 621 6.2 Responses to the COMET Request Method 623 If a server receives a COMET request it MUST send a final response. 625 A 200 OK response MUST be sent by a UAS for a COMET request if the 626 COMET request was successfully received for an existing call. 627 Beyond that, no additional operations are required. 629 A 481 Call Leg/Transaction Does Not Exist message MUST be sent by a 630 UAS if the COMET request does not match any existing call leg. 632 Header Where COMET 633 ------ ----- ---- 634 Accept R o 635 Accept-Encoding R o 636 Accept-Language R o 637 Allow 200 - 638 Allow 405 o 639 Authorization R o 640 Call-ID gc m 641 Contact R o 642 Contact 1xx - 643 Contact 2xx - 644 Contact 3xx - 645 Contact 485 - 646 Content-Encoding e o 647 Content-Length e o 648 Content-Type e * 649 CSeq gc m 650 Date g o 651 Encryption g o 652 Expires g o 653 From gc m 654 Hide R o 655 Max-Forwards R o 656 Organization g o 657 Table 3 Summary of header fields, A-0 659 SIP Working Group Expiration 2/28/02 12 660 SIP Extensions for Resource Management August 2001 662 Header Where COMET 663 ------ ----- ---- 664 Priority R o 665 Proxy-Authenticate 407 o 666 Proxy-Authorization R o 667 Proxy-Require R o 668 Require R o 669 Retry-After R - 670 Retry-After 404,480,486 o 671 Retry-After 503 o 672 Retry-After 600,603 o 673 Response-Key R o 674 Record-Route R o 675 Record-Route 2xx o 676 Route R o 677 Server r o 678 Subject R o 679 Timestamp g o 680 To gc(1) m 681 Unsupported 420 o 682 User-Agent g o 683 Via gc(2) m 684 Warning r o 685 WWW-Authenticate 401 o 687 Table 4 Summary of header fields, P-Z 689 Other request failure (4xx), Server Failure (5xx) and Global Failure 690 (6xx) responses MAY be sent for the COMET Request. 692 6.3 Message Body Inclusion 694 The COMET request MUST contain a message body, with Content-type 695 "application/sdp". 697 6.4 Behavior of SIP User Agents 699 Unless stated otherwise, the protocol rules for the COMET request 700 governing the usage of tags, Route and Record-Route, retransmission 701 and reliability, CSeq incrementing and message formatting follow 702 those in [2] as defined for the BYE request. 704 A COMET request MAY be cancelled. A UAS receiving a CANCEL for a 705 COMET request SHOULD respond to the COMET with a "487 Request 706 Cancelled" response if a final response has not been sent to the 707 COMET and then behave as if the request were never received. 709 6.5 Behavior of SIP Proxy and Redirect Servers 711 6.5.1 Proxy Server 713 Unless stated otherwise, the protocol rules for the COMET request at 714 a proxy are identical to those for a BYE request as specified in 715 [2]. 717 SIP Working Group Expiration 2/28/02 13 718 SIP Extensions for Resource Management August 2001 720 6.5.2 Forking Proxy Server 722 Unless stated otherwise, the protocol rules for the COMET request at 723 a proxy are identical to those for a BYE request as specified in 724 [2]. 726 6.5.3 Redirection Server 728 Unless stated otherwise, the protocol rules for the COMET request at 729 a proxy are identical to those for a BYE request as specified in 730 [2]. 732 7. SIP Extension: The 183-Session-Progress Response 734 An additional provisional response is defined by this draft, which 735 is returned by a UAS to convey information not otherwise classified. 737 7.1 Status Code and Reason Phrase 739 The following is to be added to Figure 4 in Section 5.1.1, 740 Informational and success Status codes. 742 Informational = "183" ;Session-Progress 744 7.2 Status Code Definition 746 The following is to be added to a new section 7.1.5 748 7.1.5 183 Session Progress 750 The 183 (Session Progress) response is used to convey information 751 about the progress of the call which is not otherwise classified. 752 The Reason-Phrase MAY be used to convey more details about the call 753 progress. 755 The Session Progress response MAY contain a message body. If so, it 756 MUST contain a "Content-Disposition" header indicating the proper 757 treatment of the message body. 759 8. SIP Extension: The 580-Precondition-Failure Response 761 An additional error response is defined by this draft, which is 762 returned by a UAS if it is unable to perform the mandatory 763 preconditions for the session. 765 8.1 Status Code and Reason Phrase 767 The following is to be added to Figure 8, Server error status codes 769 Server-Error = "580" ;Precondition-Failure 771 8.2 Status Code Definition 773 SIP Working Group Expiration 2/28/02 14 774 SIP Extensions for Resource Management August 2001 776 The following is to be added to a new section 7.5.7. 778 7.5.7 580 Precondition Failure 780 The server was unable to establish the qos or security association 781 mandated by the SDP precondition. 783 The Precondition Failure response MUST contain a message body, with 784 Content-Type "application/sdp", giving the specifics of the 785 precondition that could not be met. 787 9. SIP Extension: Content-Disposition header 789 An additional entity header is defined by this draft, which is 790 returned by a UAS in a provisional response indicating preconditions 791 for the session. 793 The following is to be added to Table 3, SIP headers, in Section 3. 795 Entity-header = Content-Disposition ; Section 6.14a 797 The following entry is to be added to Table 4, Summary of header 798 fields, A-O, in Section 6. 800 where enc e-e ACK BYE CAN INV OPT REG 801 Content-Disposition e e o o - o o o 803 The following is to be added to a new section after 6.14. 805 6.14a Content-Disposition 807 Content-disposition = "Content-Disposition" ":" 808 Disposition-type *( ";" disp-param) 809 Disposition-type = "precondition" | disp-extension-token 810 Disp-extension-token = token 811 Disp-param = "handling" "=" "optional" | "required" 812 | other-handling 813 Other-handling = token 815 The Content-Disposition header field describes how the message body 816 is to be interpreted by the UAC or UAS. 818 The value "precondition" indicates the body part describes QoS 819 and/or security preconditions that SHOULD be established prior to 820 the start of the session. 822 The handling parameter, disp-param, describes how the UAC or UAS 823 should react if it receives a message body whose content type or 824 disposition type it does not understand. If the parameter has the 825 value "optional" the UAS MUST ignore the message body; if it has the 826 value "required" the UAS MUST return 415 (Unsupported Media Type). 827 If the handling parameter is missing, the value "required" is to be 828 assumed. 830 SIP Working Group Expiration 2/28/02 15 831 SIP Extensions for Resource Management August 2001 833 10. Option tag for Requires and Supported headers 835 This draft defines the option tag "precondition" for use in the 836 Require and Supported headers [12]. 838 A UAS that supports this extension MUST respond to an OPTION request 839 with a Supported header that includes the "precondition" tag. 841 A UAC MAY include a "Require: precondition" in an INVITE request if 842 it wants the session initiation to fail if the UAS does not support 843 this feature. 845 Presence of the precondition entries in the SDP message body of an 846 INVITE request or response indicates support of this feature. The 847 UAC or UAS MAY in addition include a "Supported: precondition" 848 header in the request or response. 850 11. SIP Usage Rules 852 11.1 Overview 854 The session originator (UAC) prepares an SDP message body for the 855 INVITE describing the desired QoS and security preconditions for 856 each media flow, and the desired directions. The token value "send" 857 means the direction of media from originator (whichever entity 858 created the SDP) to recipient (whichever entity received the SDP in 859 a SIP message), and "recv" is from recipient to originator. In an 860 INVITE, the UAC is the originator, and the UAS is the recipient. The 861 roles are reversed in the response. 863 The recipient of the INVITE (UAS) returns a 18x provisional response 864 containing a Content-Disposition of "precondition," and SDP with the 865 qos/security attribute for each stream having a precondition. The 866 preconditions in this SDP (i.e. strength tag and direction tag) are 867 equal to, or a subset of, the preconditions indicated in the INVITE. 868 The UAS would typically include a confirmation request in this SDP. 869 Unlike normal SIP processing, the UAS MUST NOT alert the called user 870 at this point. The UAS now attempts to reserve the qos resources 871 and establish the security associations. 873 The 18x provisional response is received by the UAC. If the 18x 874 contained SDP with mandatory qos/security parameters, the UAC does 875 not let the session proceed until the mandatory preconditions are 876 met. The UAC attempts to reserve the needed resources and establish 877 the security associations. 879 If either party requests a confirmation, a COMET message is sent to 880 that party. The COMET message contains the success/failure 881 indication for each precondition. For a precondition with a 882 direction value of "sendrecv," the COMET indicates whether the 883 sender is able to confirm both directions or only one direction. 884 Upon receipt of the COMET message, the UAC/UAS continues normal SIP 885 call handling. For a UAS this includes alerting the user and 887 SIP Working Group Expiration 2/28/02 16 888 SIP Extensions for Resource Management August 2001 890 sending a 180-Ringing or 200-OK response. The UAC SIP transaction 891 completes normally. 893 Note that this extension requires usage of reliable provisional 894 responses [11]. This is because the 18x contains SDP with 895 information required for the session originator to initiate 896 reservations towards the participant. 898 11.2 Behavior of Originator (UAC) 900 The session originator (UAC) MAY include QoS and security 901 preconditions (including the desired direction) for each media flow 902 in the SDP sent with the INVITE. The token value "send" means the 903 direction of media from originator (whichever entity created the 904 SDP) to recipient (whichever entity received the SDP in a SIP 905 message). The token value "recv" means the direction of media from 906 recipient to originator. If preconditions are included in the 907 INVITE request, the UAC MUST indicate support for reliable 908 provisional responses [11]. 910 If the UAC receives a 18x provisional response without a Content- 911 Disposition of "precondition," or without SDP, or with SDP but 912 without any qos/security preconditions in any stream, UAC treats it 913 as an indication that the UAS is unable or unwilling to perform the 914 preconditions requested. As such, the UAC SHOULD proceed with normal 915 call setup procedures. 917 If the 18x provisional response contained a Content-Disposition of 918 "precondition" and contained SDP with mandatory qos/security 919 parameters, the UAC SHOULD NOT let the session proceed until the 920 mandatory preconditions are met. 922 If the 18x provisional response with preconditions requested an 923 acknowledgement (using the methods of [11]), the UAC MUST include an 924 updated SDP in the PRACK if the UAC modified the original SDP based 925 on the response from the UAS. Such a modification MAY be due to 926 negotiation of compatible codecs, or MAY be due to negotiation of 927 mandatory preconditions. If the provisional response received from 928 the UAS is a 180-Ringing, and the direction value of a mandatory 929 precondition is "sendrecv," and the UAC uses a one-way QoS mechanism 930 (such as RSVP), the updated SDP in the PRACK SHOULD request a 931 confirmation from the UAS so that the bi-directional precondition 932 can be satisfied before performing the requested alerting function. 934 Upon receipt of the 18x provisional response with preconditions, the 935 UAC MUST initiate the qos reservations and establish the security 936 associations to the best of its capabilities. 938 If the UAC had requested confirmation in the initial SDP, it MAY 939 wait for the COMET message from the UAS containing the 940 success/failure status of each precondition. The UAC MAY set a 941 local timer to limit the time waiting for preconditions to complete. 942 The UAC SHOULD merge the success/failure status in the COMET message 943 with its local status. For example, if the COMET message indicated 945 SIP Working Group Expiration 2/28/02 17 946 SIP Extensions for Resource Management August 2001 948 success in the "send" direction, and the UAC was also able to meet 949 the precondition in the "send" direction, they combine to meet the 950 precondition in the "sendrecv" direction. 952 If any of the mandatory preconditions cannot be met, and a 953 confirmation was not requested by the UAS, the UAC MUST send a 954 CANCEL and terminate the session. If any of the optional 955 preconditions cannot be met, the UAC MAY consult with the 956 originating customer for guidance on whether to complete the 957 session. 959 When all the preconditions have either been met or have failed, and 960 the SDP received from the UAS included a confirmation request, the 961 UAC MUST send a COMET message to the UAS with SDP. Each 962 precondition is updated to indicate success/failure and the 963 appropriate direction tag is updated based on local operations 964 performed combined with the received COMET message, if any. 966 The session now completes normally, as per [2]. 968 11.3 Behavior of Destination (UAS) 970 On receipt of an INVITE request containing preconditions, the UAS 971 MUST generate a 18x provisional response containing a subset of the 972 preconditions supported by the UAS. In the response, the token 973 value "send" means the direction of the media from the UAS to the 974 UAC, and "recv" is from the UAC to the UAS. This is reversed from 975 the SDP in the initial INVITE. The 18x provisional response MUST 976 include a Content-Disposition header with parameter "precondition." 977 If the "confirm" attribute is present in the SDP received from the 978 UAC, or if the direction tag of a mandatory QoS precondition is 979 "sendrecv" and the UAS only supports a one-way QoS reservation 980 scheme (e.g. RSVP), then the UAS SHOULD include a "confirm" 981 attribute. If the UAS is able to satisfy the preconditions 982 immediately, and no confirmation is requested by the UAC, then a 983 180-Ringing response is appropriate. Otherwise a 183-Session- 984 Progress response SHOULD be used. 986 If the INVITE request did not contain any preconditions, but did 987 indicate support for reliable provisional responses[11], the UAS MAY 988 include preconditions in a 18x provisional response to the INVITE. 989 The 18x provisional response MUST include a Content-Disposition 990 header with the parameter "precondition." The 18x provisional 991 response MUST request an acknowledgement using the mechanism of 992 [11]. If the PRACK includes an SDP without any preconditions, the 993 UAS MAY complete the session without the preconditions, or MAY 994 reject the INVITE request. 996 The UAS SHOULD request an acknowledgement to the 18x provisional 997 response, using the mechanism of [11]. The UAS SHOULD wait for the 998 PRACK message before initiating resource reservation to allow the 999 resource reservation to reflect 3-way SDP negotiation, or other 1000 information available only through receipt of the PRACK. 1002 SIP Working Group Expiration 2/28/02 18 1003 SIP Extensions for Resource Management August 2001 1005 If the INVITE request or PRACK message contained mandatory 1006 preconditions, or requested a confirmation of preconditions, the UAS 1007 MUST NOT alert the called user. 1009 The UAS now attempts to reserve the qos resources and establish the 1010 security associations. The UAS MAY set a local timer to limit the 1011 time waiting for preconditions to complete. 1013 If the UAS is unable to perform any mandatory precondition, and 1014 neither the UAC nor UAS requested a confirmation, the UAS MUST send 1015 a 580-Precondition-Failure response to the UAC. If the UAS is 1016 unable to perform any optional precondition, it MAY consult with the 1017 customer to obtain guidance regarding completion of the session. 1019 When processing of all preconditions is complete, if a precondition 1020 in the initial INVITE specified a confirmation request, the UAS MUST 1021 send a COMET message to the UAC containing SDP, along with the 1022 qos/security result of success/failure for each precondition. If 1023 the direction tag of the precondition was "sendrecv" but the UAS was 1024 only able to ensure "send" or "recv," the direction tag in the COMET 1025 MUST only indicate what the UAS ensures. The Request-URI, call-leg 1026 identification, and other headers of this COMET message are to be 1027 constructed identically to a BYE. 1029 If the UAS had requested confirmation of a precondition in the 1030 response SDP, it SHOULD wait for the COMET message from the 1031 originator containing the success/failure indication of each 1032 precondition from the originator's point of view. The 1033 success/failure indications in the COMET message from the UAC SHOULD 1034 be combined with the local status to determine the overall 1035 success/failure of the precondition. For example, if the COMET 1036 message indicated success in the "send" direction, and the UAS was 1037 also able to meet the precondition in the "send" direction, they 1038 combine to meet the precondition in the "sendrecv" direction. If 1039 that combination indicates a failure for a mandatory precondition, 1040 the UAS MUST send a 580-Precondition-Failure response to the UAC. 1042 Once the preconditions are met, the UAS alerts the user, and the SIP 1043 transaction proceeds normally. 1045 The UAS MAY send additional 18x provisional responses with Content- 1046 Disposition of "precondition," and the procedures described above 1047 are repeated sequentially for each. 1049 12. Examples 1051 12.1 Single Media Call Flow 1053 Figure 1 presents a high-level overview of a basic end-point to end- 1054 point (UAC-UAS) call flow. This example is appropriate for a 1055 single-media session with a mandatory quality-of-service "sendrecv" 1056 precondition, where both the UAC and UAS can only perform a single- 1057 direction ("send") resource reservation. 1059 SIP Working Group Expiration 2/28/02 19 1060 SIP Extensions for Resource Management August 2001 1062 The session originator (UAC) prepares an SDP message body for the 1063 INVITE describing the desired QoS and security preconditions for 1064 each media flow, and the desired direction "sendrecv." This SDP is 1065 included in the INVITE message sent through the proxies, and 1066 includes an entry "a=qos:mandatory sendrecv." 1068 The recipient of the INVITE (UAS), being willing to perform the 1069 requested precondition, returns a 183-Session-Progress provisional 1070 response containing SDP, along with the qos/security attribute for 1071 each stream having a precondition. Since the "sendrecv" direction 1072 tag required a cooperative effort of the UAC and UAS, the UAS 1073 requests a confirmation when the preconditions are met, with the SDP 1074 entry "a=qos:mandatory sendrecv confirm." The UAS now attempts to 1075 reserve the qos resources and establish the security associations. 1077 The 183-Session-Progress provisional response is sent using the 1078 reliability mechanism of [11]. UAC sends the appropriate PRACK and 1079 UAS responds with a 200-OK to the PRACK. 1081 The 183-Session-Progress is received by the UAC, and the UAC 1082 requests the resources needed in its "send" direction, and 1083 establishes the security associations. Once the preconditions are 1084 met, the UAC sends a COMET message as requested by the confirmation 1085 token. This COMET message contains an entry "a=qos:success send" 1087 SIP Working Group Expiration 2/28/02 20 1088 SIP Extensions for Resource Management August 2001 1090 Originating (UAC) Terminating (UAS) 1091 | SIP-Proxy(s) | 1092 | INVITE | | 1093 |---------------------->|---------------------->| 1094 | | | 1095 | 183 w/SDP | 183 w/SDP | 1096 |<----------------------|<----------------------| 1097 | | 1098 | PRACK | 1099 |---------------------------------------------->| 1100 | 200 OK (of PRACK) | 1101 |<----------------------------------------------| 1102 | Reservation Reservation | 1103 ===========> <=========== 1104 | | 1105 | | 1106 | COMET | 1107 |---------------------------------------------->| 1108 | 200 OK (of COMET) | 1109 |<----------------------------------------------| 1110 | 1111 | 1112 | SIP-Proxy(s) User Alerted 1113 | | | 1114 | 180 Ringing | 180 Ringing | 1115 |<----------------------|<----------------------| 1116 | | 1117 | PRACK | 1118 |---------------------------------------------->| 1119 | 200 OK (of PRACK) | 1120 |<----------------------------------------------| 1121 | | 1122 | User Picks-Up 1123 | SIP-Proxy(s) the phone 1124 | | | 1125 | 200 OK | 200 OK | 1126 |<----------------------|<----------------------| 1127 | | | 1128 | | 1129 | ACK | 1130 |---------------------------------------------->| 1132 Figure 1: Basic Call Flow 1134 The UAS successfully performs its resource reservation, in its 1135 "send" direction, and waits for the COMET message from the UAC. 1137 On receipt of the COMET message, the UAS processes the "send" 1138 confirmation contained in the COMET SDP. The "send" confirmation 1139 from the UAC coupled with its own "send" success, allows the UAS to 1140 determine that all preconditions have been met. The UAS then 1141 continues with session establishment. At this point it alerts the 1142 user, and sends a 180-Ringing provisional response. This 1144 SIP Working Group Expiration 2/28/02 21 1145 SIP Extensions for Resource Management August 2001 1147 provisional response is also sent using the reliability mechanism of 1148 [11], resulting in a PRACK message and 200-OK of the PRACK. 1150 When the destination party answers, the normal SIP 200-OK final 1151 response is sent through the proxies to the originator, and the 1152 originator responds with an ACK message. 1154 Either party can terminate the call. An endpoint that detects an 1155 "on-hook" (request to terminate the call) releases the QoS resources 1156 held for the connection, and sends a SIP BYE message to the remote 1157 endpoint, which is acknowledged with a 200-OK. 1159 12.2 Multiple Media Call Flow 1161 Figure 2 presents a high-level overview of an advanced end-point to 1162 end-point (UAC-UAS) call flow. This example is appropriate for a 1163 multiple-media session with some combination of mandatory and 1164 optional quality-of-service precondition. For example, the 1165 originator may suggest five media streams, and be willing to 1166 establish the session if any three of them are satisfied. 1168 The use of reliable provisional responses is assumed, but not shown 1169 in this figure. 1171 The session originator (UAC) prepares an SDP message body for the 1172 INVITE describing the desired QoS and security preconditions for 1173 each media flow, and the desired directions. UAC also requests 1174 confirmation of the preconditions. The UAS receiving the INVITE 1175 message responds with 183-Session-Progress, as in the previous 1176 example. 1178 When the UAS has completed the resource reservations and security 1179 session establishment, it sends a confirmation to the UAC in the 1180 form of a COMET message, with each precondition marked in the SDP as 1181 either success or failure. Note that if UAS was not satisfied with 1182 the combination of successful preconditions, it could instead have 1183 responded with 580-Precondition-Failure, and ended the INVITE 1184 transaction. 1186 If the UAC has satisfied its preconditions, and is satisfied with 1187 the preconditions achieved by the UAS, it responds with the COMET 1188 message. The COMET message contains the SDP with the 1189 success/failure results of each precondition attempted by UAC. If 1190 UAC is not satisfied with the combination of successful 1191 preconditions, it could instead have sent a CANCEL message. 1193 On receipt of the COMET message, UAS examines the combination of 1194 satisfied preconditions reported by UAC, and makes a final decision 1195 whether to proceed with the session. If sufficient preconditions 1196 are not satisfied, the UAS responds with 580-Precondition-Failure. 1197 Otherwise, the session proceeds as in the previous example. 1199 SIP Working Group Expiration 2/28/02 22 1200 SIP Extensions for Resource Management August 2001 1202 Originating (UAC) Terminating (UAS) 1203 | SIP-Proxy(s) | 1204 | INVITE | | 1205 |---------------------->|---------------------->| 1206 | | | 1207 | 183 w/SDP | 183 w/SDP | 1208 |<----------------------|<----------------------| 1209 | | 1210 | Reservation Reservation | 1211 ===========> <=========== 1212 | | 1213 | COMET | 1214 |<----------------------------------------------| 1215 | 200 OK (of COMET) | 1216 |---------------------------------------------->| 1217 | | 1218 | COMET | 1219 |---------------------------------------------->| 1220 | 200 OK (of COMET) | 1221 |<----------------------------------------------| 1222 | 1223 | 1224 | SIP-Proxy(s) User Alerted 1225 | | | 1226 | 180 Ringing | 180 Ringing | 1227 |<----------------------|<----------------------| 1228 | | 1229 | | 1230 | User Picks-Up 1231 | SIP-Proxy(s) the phone 1232 | | | 1233 | 200 OK | 200 OK | 1234 |<----------------------|<----------------------| 1235 | | | 1236 | | 1237 | ACK | 1238 |---------------------------------------------->| 1240 Figure 2: Call Flow with negotiation of optional preconditions 1242 13. Special considerations with Forking Proxies 1244 If a proxy along the signaling path between the UAC and UAS forks 1245 the INVITE request, it results in two or more UASs simultaneously 1246 sending provisional responses with preconditions. The procedures 1247 above result in the UAC handling each independently, reserving 1248 resources and responding with COMET messages as required. 1250 This results in multiple resource reservations from the UAC, only 1251 one of which will be utilized for the final session. While 1252 functionally correct, this has the unfortunate side-effect of 1253 increasing the call blocking probability. 1255 SIP Working Group Expiration 2/28/02 23 1256 SIP Extensions for Resource Management August 2001 1258 Customized resource allocation protocols may be used by the UAC to 1259 reduce this duplicate allocation and prevent excess blocking of 1260 calls. For one such example, see [8]. 1262 14. Advantages of the Proposed Approach 1264 The use of two-phase call signaling makes it possible for SIP to 1265 meet user expectations that come from the telephony services. 1267 The reservation of resources before the user is alerted makes sure 1268 that the network resources are assured before the destination end- 1269 point is informed about the call. 1271 The number of messages and the total delay introduced by these 1272 messages is kept to a minimum without sacrificing compatibility with 1273 SIP servers that do not implement preconditions. 1275 15. Security Considerations 1277 If the contents of the SDP contained in the 183-Session-Progress are 1278 private then end-to-end encryption of the message body can be used 1279 to prevent unauthorized access to the content. 1281 The security considerations given in the SIP specification apply to 1282 the COMET method. No additional security considerations specific to 1283 the COMET method are necessary. 1285 16. Notice Regarding Intellectual Property Rights 1287 The IETF has been notified of intellectual property rights claimed 1288 in regard to some or all of the specification contained in this 1289 document. For more information consult the online list of claimed 1290 rights. 1292 17. References 1294 1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP 1295 9, RFC 2026, October 1996. 1297 2. M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: 1298 Session Initiation Protocol," RFC 2543, March 1999. 1300 3. M. Handley and V. Jacobson, "SDP: Session Description Protocol," 1301 RFC 2327, April 1998. 1303 4. Bradner, S., "Key words for use in RFCs to Indicate Requirement 1304 Levels", BCP 14, RFC 2119, March 1997 1306 5. R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, and S. Jamin, 1307 "Resource ReSerVation protocol (RSVP) -- version 1 functional 1308 specification," RFC 2205, September, 1997. 1310 SIP Working Group Expiration 2/28/02 24 1311 SIP Extensions for Resource Management August 2001 1313 6. P. P. Pan and H. Schulzrinne, "YESSIR: A simple reservation 1314 mechanism for the Internet," in Proc. International Workshop on 1315 Network and Operating System Support for Digital Audio and Video 1316 (NOSSDAV), (Cambridge, England), July 1998. Also IBM Research 1317 Technical Report TC20967. Available at 1318 http://www.cs.columbia.edu/~hgs/papers/Pan98_YESSIR.ps.gz. 1320 7. PacketCable, Dynamic Quality of Service Specification, pkt-sp- 1321 dqos-i01-991201, December 1, 1999. Available at 1322 http://www.packetcable.com/specs/pkt-sp-dqos-i01-991202.pdf. 1324 8. S. Kent and R. Atkinson, "Security architecture for the internet 1325 protocol," RFC 2401, November 1998. 1327 9. H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: a 1328 Transport Protocol for Real-Time Applications," RFC 1889, January 1329 1996. 1331 10. M. Handley, C. Perkins, and E. Whelan, "Session Announcement 1332 Protocol," RFC2974, October, 2000. 1334 11. "Reliability of Provisional Responses in SIP," RFC pending. 1336 12. "The SIP Supported Header," RFC pending. 1338 18. Acknowledgments 1340 The Distributed Call Signaling work in the PacketCable project is 1341 the work of a large number of people, representing many different 1342 companies. The authors would like to recognize and thank the 1343 following for their assistance: John Wheeler, Motorola; David 1344 Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jay Strater, 1345 Jeff Ollis, Clive Holborow, General Instruments; Doug Newlin, Guido 1346 Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks; Farzi 1347 Khazai, Nortel; John Chapman, Bill Guckel, Cisco; Chuck Kalmanek, 1348 Doug Nortz, John Lawser, James Cheng, Tung-Hai Hsiao, Partho Mishra, 1349 AT&T; Telcordia Technologies; and Lucent Cable Communications. 1351 19. Author's Addresses 1353 Bill Marshall 1354 AT&T 1355 Florham Park, NJ 07932 1356 Email: wtm@research.att.com 1358 K. K. Ramakrishnan 1359 TeraOptic Networks 1360 Sunnyvale, CA 1361 Email: kk@teraoptic.com 1363 SIP Working Group Expiration 2/28/02 25 1364 SIP Extensions for Resource Management August 2001 1366 Ed Miller 1367 Terayon 1368 Louisville, CO 80027 1369 Email: E.Miller@terayon.com 1371 Glenn Russell 1372 CableLabs 1373 Louisville, CO 80027 1374 Email: G.Russell@Cablelabs.com 1376 Burcak Beser 1377 Pacific Broadband Communications 1378 San Jose, CA 1379 Email: Burcak@pacband.com 1381 Mike Mannette 1382 3Com 1383 Rolling Meadows, IL 60008 1384 Email: Michael_Mannette@3com.com 1386 Kurt Steinbrenner 1387 3Com 1388 Rolling Meadows, IL 60008 1389 Email: Kurt_Steinbrenner@3com.com 1391 Dave Oran 1392 Cisco 1393 Acton, MA 01720 1394 Email: oran@cisco.com 1396 Flemming Andreasen 1397 Cisco 1398 Edison, NJ 1399 Email: fandreas@cisco.com 1401 Michael Ramalho 1402 Cisco 1403 Wall Township, NJ 1404 Email: mramalho@cisco.com 1406 John Pickens 1407 Com21 1408 San Jose, CA 1409 Email: jpickens@com21.com 1411 Poornima Lalwaney 1412 Nokia 1413 San Diego, CA 92121 1414 Email: poornima.lalwaney@nokia.com 1416 Jon Fellows 1417 Copper Mountain Networks 1418 San Diego, CA 92121 1419 Email: jfellows@coppermountain.com 1421 SIP Working Group Expiration 2/28/02 26 1422 SIP Extensions for Resource Management August 2001 1424 Doc Evans 1425 D. R. Evans Consulting 1426 Boulder, CO 80303 1427 Email: n7dr@arrl.net 1429 Keith Kelly 1430 NetSpeak 1431 Boca Raton, FL 33587 1432 Email: keith@netspeak.com 1434 Adam Roach 1435 Ericsson 1436 Richardson, TX 75081 1437 Email: adam.roach@ericsson.com 1439 Jonathan Rosenberg 1440 dynamicsoft 1441 West Orange, NJ 07052 1442 Email: jdrosen@dynamicsoft.com 1444 Dean Willis 1445 dynamicsoft 1446 West Orange, NJ 07052 1447 Email: dwillis@dynamicsoft.com 1449 Steve Donovan 1450 dynamicsoft 1451 West Orange, NJ 07052 1452 Email: sdonovan@dynamicsoft.com 1454 Henning Schulzrinne 1455 Columbia University 1456 New York, NY 1457 Email: schulzrinne@cs.columbia.edu 1459 SIP Working Group Expiration 2/28/02 27 1460 SIP Extensions for Resource Management August 2001 1462 Full Copyright Statement 1464 "Copyright (C) The Internet Society (2000). All Rights Reserved. 1465 This document and translations of it may be copied and furnished to 1466 others, and derivative works that comment on or otherwise explain it 1467 or assist in its implementation may be prepared, copied, published 1468 and distributed, in whole or in part, without restriction of any 1469 kind, provided that the above copyright notice and this paragraph 1470 are included on all such copies and derivative works. However, this 1471 document itself may not be modified in any way, such as by removing 1472 the copyright notice or references to the Internet Society or other 1473 Internet organizations, except as needed for the purpose of 1474 developing Internet standards in which case the procedures for 1475 copyrights defined in the Internet Standards process must be 1476 followed, or as required to translate it into languages other than 1477 English. The limited permissions granted above are perpetual and 1478 will not be revoked by the Internet Society or its successors or 1479 assigns. This document and the information contained herein is 1480 provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE 1481 INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 1482 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1483 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1484 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 1486 Expiration Date This memo is filed as , and expires February 28, 2002. 1489 SIP Working Group Expiration 2/28/02 28