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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Goldberg 3 Internet-Draft Cisco 4 Intended status: Standards Track M. Westerlund 5 Expires: July 24, 2010 Ericsson 6 T. Zeng 7 Nextwave Wireless, Inc. 8 January 20, 2010 10 A Network Address Translator (NAT) Traversal mechanism for media 11 controlled by Real-Time Streaming Protocol (RTSP) 12 draft-ietf-mmusic-rtsp-nat-09 14 Abstract 16 This document defines a solution for Network Address Translation 17 (NAT) traversal for datagram based media streams setup and controlled 18 with Real-time Streaming Protocol version 2 (RTSP 2.0). It uses 19 Interactive Connectivity Establishment (ICE) adapted to use RTSP as a 20 signalling channel, defining the necessary extra RTSP extensions and 21 procedures. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 27 document are to be interpreted as described in RFC 2119 [RFC2119]. 29 Status of this Memo 31 This Internet-Draft is submitted to IETF in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF), its areas, and its working groups. Note that 36 other groups may also distribute working documents as Internet- 37 Drafts. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 The list of current Internet-Drafts can be accessed at 45 http://www.ietf.org/ietf/1id-abstracts.txt. 47 The list of Internet-Draft Shadow Directories can be accessed at 48 http://www.ietf.org/shadow.html. 50 This Internet-Draft will expire on July 24, 2010. 52 Copyright Notice 54 Copyright (c) 2010 IETF Trust and the persons identified as the 55 document authors. All rights reserved. 57 This document is subject to BCP 78 and the IETF Trust's Legal 58 Provisions Relating to IETF Documents 59 (http://trustee.ietf.org/license-info) in effect on the date of 60 publication of this document. Please review these documents 61 carefully, as they describe your rights and restrictions with respect 62 to this document. Code Components extracted from this document must 63 include Simplified BSD License text as described in Section 4.e of 64 the Trust Legal Provisions and are provided without warranty as 65 described in the BSD License. 67 Table of Contents 69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4 71 3. RTSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 6 72 3.1. ICE Transport Lower Layer . . . . . . . . . . . . . . . . 6 73 3.2. ICE Candidate Transport Header Parameter . . . . . . . . . 8 74 3.3. ICE Password and Username Transport Header Parameters . . 11 75 3.4. ICE Feature Tag . . . . . . . . . . . . . . . . . . . . . 11 76 3.5. Status Codes . . . . . . . . . . . . . . . . . . . . . . . 11 77 3.5.1. 150 ICE connectivity checks in progress . . . . . . . 12 78 3.5.2. 480 ICE Processing Failed . . . . . . . . . . . . . . 12 79 3.6. New Reason for PLAY_NOTIFY . . . . . . . . . . . . . . . . 12 80 3.7. Server Side SDP Attribute for ICE Support . . . . . . . . 12 81 3.8. ICE Features Not Required in RTSP . . . . . . . . . . . . 13 82 3.8.1. ICE-Lite . . . . . . . . . . . . . . . . . . . . . . . 13 83 3.8.2. ICE-Mismatch . . . . . . . . . . . . . . . . . . . . . 13 84 3.8.3. ICE Remote Candidate Transport Header Parameter . . . 13 85 4. Detailed Solution . . . . . . . . . . . . . . . . . . . . . . 13 86 4.1. Session description and RTSP DESCRIBE (optional) . . . . . 14 87 4.2. Setting up the Media Streams . . . . . . . . . . . . . . . 15 88 4.3. RTSP SETUP Request . . . . . . . . . . . . . . . . . . . . 15 89 4.4. Gathering Candidates . . . . . . . . . . . . . . . . . . . 16 90 4.5. RTSP Server Response . . . . . . . . . . . . . . . . . . . 17 91 4.6. Server to Client ICE Connectivity Checks . . . . . . . . . 17 92 4.7. Client to Server ICE Connectivity Check . . . . . . . . . 18 93 4.8. Client Connectivity Checks Complete . . . . . . . . . . . 18 94 4.9. Server Connectivity Checks Complete . . . . . . . . . . . 18 95 4.10. Releasing Candidates . . . . . . . . . . . . . . . . . . . 19 96 4.11. Steady State . . . . . . . . . . . . . . . . . . . . . . . 19 97 4.12. re-SETUP . . . . . . . . . . . . . . . . . . . . . . . . . 19 98 4.13. Server Side Changes After Steady State . . . . . . . . . . 19 99 5. ICE and Proxies . . . . . . . . . . . . . . . . . . . . . . . 21 100 5.1. Media Handling Proxies . . . . . . . . . . . . . . . . . . 22 101 5.2. Signalling Only Proxies . . . . . . . . . . . . . . . . . 22 102 5.3. Non-supporting Proxies . . . . . . . . . . . . . . . . . . 22 103 6. RTP and RTCP Multiplexing . . . . . . . . . . . . . . . . . . 23 104 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 24 105 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 106 8.1. RTSP Feature Tags . . . . . . . . . . . . . . . . . . . . 24 107 8.2. Transport Protocol Specifications . . . . . . . . . . . . 24 108 8.3. RTSP Transport Parameters . . . . . . . . . . . . . . . . 25 109 8.4. RTSP Status Codes . . . . . . . . . . . . . . . . . . . . 25 110 8.5. Notify-Reason value . . . . . . . . . . . . . . . . . . . 25 111 8.6. SDP Attribute . . . . . . . . . . . . . . . . . . . . . . 25 112 9. Security Considerations . . . . . . . . . . . . . . . . . . . 26 113 9.1. ICE and RTSP . . . . . . . . . . . . . . . . . . . . . . . 26 114 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 115 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 116 11.1. Normative References . . . . . . . . . . . . . . . . . . . 26 117 11.2. Informative References . . . . . . . . . . . . . . . . . . 27 118 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 120 1. Introduction 122 Real-time Streaming Protocol (RTSP) 123 [RFC2326][I-D.ietf-mmusic-rfc2326bis] is a protocol used to setup and 124 control one or more media streams delivering media to receivers. It 125 is RTSP's functionality of setting up media streams that cause 126 serious issues with Network Address Translators (NAT) [RFC3022] 127 unless extra provisions are taken by the protocol. There is thus a 128 need for a NAT traversal mechanism for the media setup using RTSP. 130 RTSP 1.0 [RFC2326] has suffered from the lack of a standardized NAT 131 traversal mechanism for a long time, however due to quality of the 132 RTSP 1.0 specification, the work has had to wait on the recently 133 defined RTSP 2.0 [I-D.ietf-mmusic-rfc2326bis]. RTSP 2.0 is similar 134 to RTSP 1.0 in many respects but significantly for this work, it 135 contains a well defined extension mechanism so allowing a NAT 136 traversal extension to be defined that is backwards compatible with 137 RTSP 2.0 peers not supporting the extension. This extension 138 mechanism was not possible in RTSP 1.0 as it would break RTSP 1.0 139 syntax so causing compatibility issues. 141 There have been a number of suggested ways of resolving the NAT- 142 traversal of media for RTSP of which a large number are already used 143 in implementations. The evaluation of these NAT traversal solutions 144 in[I-D.ietf-mmusic-rtsp-nat-evaluation] has shown that there are many 145 issues to consider, so after extensive evaluation, we selected a 146 mechanism based on Interactive Connectivity Establishment (ICE). 147 This was mainly two reasons: Firstly the mechanism supports RTSP 148 servers behind NATs and secondly the mechanism solves the security 149 threat that uses RTSP servers as Distributed Denial of Service (DDoS) 150 attack tools. 152 This document specifies an ICE based solution that is optimized for 153 media delivery server to client. If in the future extensions are 154 specified for other delivery modes than PLAY, then the optimizations 155 in regards to when PLAY request are sent needs to be reconsidered. 157 The NAT problem for RTSP signalling traffic itself is beyond the 158 scope of this document and is left for future study should the need 159 arise, because it is a less prevalent problem than the NAT problem 160 for RTSP media streams. 162 2. Solution Overview 164 This overview assumes that the reader has some familiarity with how 165 ICE [I-D.ietf-mmusic-ice] works, as it primarily points out how the 166 different ICE steps are accomplished in RTSP. 168 1. RTSP server can indicate it has support for ICE via an SDP 169 [RFC4566] attribute in, for example, the SDP returned in RTSP 170 DESCRIBE message. This allows RTSP clients to only send the new 171 ICE interchanges with servers that support ICE so as to limit 172 the overhead on current non-ICE supporting RTSP servers. If 173 RTSP DESCRIBE is used the normal capability determination 174 mechanism can be used, i.e. "Supported" header and the defined 175 feature tag. 177 2. RTSP client reviews the session description returned, for 178 example by an RTSP DESCRIBE message, to determine what media 179 streams need to be setup. For each of these media streams where 180 the transport protocol supports Session Traversal Utilities for 181 (NAT) (STUN) [RFC5389] based connectivity checks, the client 182 gathers candidate addresses. See section 4.1.1 in 183 [I-D.ietf-mmusic-ice]. The client also installs the STUN 184 servers on each of the local candidates. 186 3. RTSP client sends SETUP requests with both a transport 187 specification with a lower layer indicating ICE and a new RTSP 188 Transport header parameter listing the ICE candidates for each 189 media stream. 191 4. After receiving the list of candidates from a client, the RTSP 192 server gathers its own candidates. If the server has a public 193 IP address, then a single candidate per address family (e.g. 194 IPv4 and IPv6), media stream and media component tuple can be 195 included to reduce the number of combinations and speed up the 196 completion. 198 5. The server sets up the media and if successful responds to the 199 SETUP request with a 200 OK response. In that response the 200 server selects the transport specification using ICE and 201 includes its candidates in the server candidate parameter. 203 6. The server starts the connectivity checks following the 204 procedures described in Section 5.7 and 5.8 of 205 [I-D.ietf-mmusic-ice]. If the server has a public IP address 206 with a single candidate per media stream, component and address 207 family then one may configure the server to not initiate 208 connectivity checks. 210 7. The client receives the SETUP response and learns the candidate 211 address to use for the connectivity checks, and then initiates 212 its connectivity check, following the procedures in Section 6 of 213 [I-D.ietf-mmusic-ice]. 215 8. When a connectivity check from the client reaches the server it 216 will result in a triggered check from the server. This is why 217 servers with a public IP address can wait until this triggered 218 check to send out any checks for itself so saving resources and 219 mitigating the DDoS potential from server connectivity checks. 221 9. When the client has concluded its connectivity checks and has 222 correspondingly received the server connectivity checks on the 223 promoted candidates for all mandatory components of all media 224 streams, it can issue a PLAY request. If the connectivity 225 checks have not concluded successfully then the client may send 226 a new SETUP request assuming it has any new information or 227 believes the server may be able to do more that can result in 228 successful checks. 230 10. When the RTSP servers receives a PLAY request it checks to see 231 the connectivity checks has concluded successfully and only then 232 can play the stream. If there is a problem with the checks then 233 the server sends to the client either a 150 (ICE connectivity 234 checks in progress) response to show that it is still working on 235 the connectivity checks or a 480 (ICE Processing Failed) 236 response to indicate a failure of the checks. If the checks are 237 successful then the server sends a 200 OK response and starts 238 delivering media. 240 The client and server may release unused candidates when the ICE 241 processing has concluded and a single candidate per component has 242 been promoted. 244 The client shall continue to use STUN to send keep-alive for the used 245 bindings. This is important as often RTSP media sessions only 246 contain media traffic from the server to the client so the bindings 247 in the NAT needs to be refreshed by the client to server traffic 248 provided by the STUN keep-alive. 250 3. RTSP Extensions 252 This section defines the necessary RTSP extensions for performing ICE 253 with RTSP. Note that these extensions are based on the SDP 254 attributes in the ICE specification unless expressly indicated. 256 3.1. ICE Transport Lower Layer 258 A new lower layer "D-ICE" for transport specifications is defined. 259 This lower layer is datagram clean except that the protocol used must 260 be demultiplexiable with STUN messages (see STUN [RFC5389]). With 261 datagram clean we mean that it must be capable of describing the 262 length of the datagram, transport that datagram (as a binary chunk of 263 data) and provide it at the receiving side as one single item. This 264 lower layer can be any transport type defined for ICE which does 265 provide datagram transport capabilities. Though only UDP is defined 266 at present, however DCCP or TCP with framing may be specified and 267 used in the future. 269 This lower layer uses ICE to determine which of the different 270 candidates shall be used and then when the ICE processing has 271 concluded, uses the selected candidate to transport the datagrams 272 over this transport. 274 This lower layer transport can be combined with all upper layer media 275 transport protocols that are possible to demultiplex with STUN and 276 which use datagrams. This specification defines the following 277 combinations: 279 o RTP/AVP/D-ICE 281 o RTP/AVPF/D-ICE 283 o RTP/SAVP/D-ICE 285 o RTP/SAVPF/D-ICE 287 This list can easily be extended with more transport specifications 288 after having performed the evaluation that they are compatible with 289 D-ICE as lower layer. 291 The lower-layer "D-ICE" has the following rules for the inclusion of 292 transport parameters: 294 unicast: As ICE only supports unicast operations, thus it is 295 REQUIRED that one include the unicast indicator parameter, see 296 section 16.46 in [I-D.ietf-mmusic-rfc2326bis]. 298 candidates: The "candidates" parameter SHALL be included as this 299 specify at least one candidate to try to establish a working 300 transport path with. 302 dest_addr: This parameter SHALL NOT be included as "candidates" is 303 used instead to provide the necessary address information. 305 ICE-Password: This parameter SHALL be included. 307 ICE-ufrag: This parameter SHALL be included. 309 3.2. ICE Candidate Transport Header Parameter 311 This section defines a new RTSP transport parameter for carrying ICE 312 candidates related to the transport specification they appear within, 313 which may then be validated with an end-to-end connectivity check 314 using STUN [RFC5389]. Transport parameters may only occur once in 315 each transport specification. For transport specification using 316 "D-ICE" as lower layer, this parameter needs to be present. The 317 parameter can contain one or more ICE candidates. In the SETUP 318 response there is only a single transport specification, and if that 319 uses the "D-ICE" lower layer this parameter MUST be present and 320 include the server side candidates. 322 trns-parameter = 324 trns-parameter =/ SEMI ice-trn-par 325 ice-trn-par = "candidates" EQUAL DQ SWS ice-candidate 326 *(SEMI ice-candidate) SWS DQ 327 ice-candidate = foundation SP 328 component-id SP 329 transport SP 330 priority SP 331 connection-address SP 332 port SP 333 cand-type 334 [SP rel-addr] 335 [SP rel-port] 336 *(SP extension-att-name SP extension-att-value) 338 foundation = 339 component-id = 340 transport = 341 transport-extension = 342 priority = 343 cand-type = 344 candidate-types = 345 rel-addr = 346 rel-port = 347 extension-att-name = 348 extension-att-value = 349 ice-char = 350 connection-address = 351 port = 352 EQUAL = 353 DQ = 354 SWS = 355 SEMI = 357 : is the IP address of the candidate, allowing 358 for IPv4 addresses, IPv6 addresses and Fully qualified domain names 359 (FQDN), taken from [RFC4566]. The connection address SHOULD be on 360 the same format (explicit IP or FQDN) as in the dest_addr parameter 361 used to express fallbacks. An IP address SHOULD be used, but an FQDN 362 MAY be used in place of an IP address. In that case, when receiving 363 an SETUP request or response containing an FQDN in an candidate 364 parameter, the FQDN is looked up in the DNS first using an AAAA 365 record (assuming the agent supports IPv6), and if no result is found 366 or the agent only supports IPv4, using an A record. If the DNS query 367 returns more than one IP address, one is chosen, and then used for 368 the remainder of ICE processing which in RTSP is subsequent RTSP 369 SETUPs for the same RTSP session. 371 : is the port of the candidate taken from RFC 4566 [RFC4566]. 373 : indicates the transport protocol for the candidate. The 374 ICE specification only defines UDP. However, extensibility is 375 provided to allow for future transport protocols to be used with ICE, 376 such as TCP or the Datagram Congestion Control Protocol (DCCP) 377 [RFC4340]. 379 : is an identifier that is equivalent for two candidates 380 that are of the same type, share the same base, and come from the 381 same STUN server, and is composed of one to thirty two . 382 The foundation is used to optimize ICE performance in the Frozen 383 algorithm. 385 : identifies the specific component of the media stream 386 for which this is a candidate and os a positive integer between 1 and 387 256. It MUST start at 1 and MUST increment by 1 for each component 388 of a particular candidate. For media streams based on RTP, 389 candidates for the actual RTP media MUST have a component ID of 1, 390 and candidates for RTCP MUST have a component ID of 2. Other types 391 of media streams which require multiple components MUST develop 392 specifications which define the mapping of components to component 393 IDs. See Section 14 for additional discussion on extending ICE to 394 new media streams. 396 : is a positive integer between 1 and (2**31 - 1). 398 : encodes the type of candidate. The ICE specification 399 defines the values "host", "srflx", "prflx" and "relay" for host, 400 server reflexive, peer reflexive and relayed candidates, 401 respectively. The set of candidate types is extensible for the 402 future. 404 and : convey transport addresses related to the 405 candidate, useful for diagnostics and other purposes. and 406 MUST be present for server reflexive, peer reflexive and 407 relayed candidates. If a candidate is server or peer reflexive, 408 and is equal to the base for that server or 409 peer reflexive candidate. If the candidate is relayed, 410 and is equal to the mapped address in the Allocate 411 Response that provided the client with that relayed candidate (see 412 Appendix B.3 of [I-D.ietf-mmusic-ice] for a discussion of its 413 purpose). If the candidate is a host candidate and MUST be omitted. 416 3.3. ICE Password and Username Transport Header Parameters 418 The ICE password and username for each agent needs to be transported 419 using RTSP. For that purpose new transport header parameters are 420 defined. 422 There MUST be an "ICE-Password" and "ICE-ufrag" parameter for each 423 media stream. If two SETUP requests in the same RTSP session have 424 identical ICE-ufrag's, they MUST have identical ICE-Password's. The 425 ICE-ufrag and ICE-Password attributes MUST be chosen randomly at the 426 beginning of a session. The ICE-ufrag attribute MUST contain at 427 least 24 bits of randomness, and the ICE-Password attribute MUST 428 contain at least 128 bits of randomness. This means that the ICE- 429 ufrag attribute will be at least 4 characters long, and the ICE- 430 Password at least 22 characters long, since the grammar for these 431 attributes allows for 6 bits of randomness per character. The 432 attributes MAY be longer than 4 and 22 characters respectively, of 433 course, up to 256 characters. The upper limit allows for buffer 434 sizing in implementations. Its large upper limit allows for 435 increased amounts of randomness to be added over time. 437 The ABNF [RFC5234] for these parameters are: 439 trns-parameter =/ SEMI ice-password-par 440 trns-parameter =/ SEMI ice-ufrag-par 441 ice-password-par = "ICE-Password" EQUAL password 442 ice-ufrag-par = "ICE-ufrag" EQUAL ufrag 443 password = 444 ufrag = 445 EQUAL = 446 SEMI = 448 3.4. ICE Feature Tag 450 A feature tag is defined for use in the RTSP capabilities mechanism 451 for ICE support of media transport using datagrams: "setup.ice-d-m". 452 This feature tag indicates that one supports all the mandatory 453 functions of this specification. It is applicable to all types of 454 RTSP agents; clients, servers and proxies. 456 The RTSP client SHOULD send the feature tag "setup.ice-d-m" in the 457 "Supported" header in all SETUP requests that contain the "D-ICE" 458 lower layer transport. 460 3.5. Status Codes 462 ICE needs two new RTSP response codes to indicate correctly progress 463 and errors. 465 +------+----------------------------------------------+-------------+ 466 | Code | Reason | Method | 467 +------+----------------------------------------------+-------------+ 468 | 150 | Server still working on ICE connectivity | PLAY | 469 | | checks | | 470 | 480 | ICE Connectivity check failure | PLAY, SETUP | 471 +------+----------------------------------------------+-------------+ 473 Table 1: New Status codes and their usage with RTSP methods 475 3.5.1. 150 ICE connectivity checks in progress 477 The 150 response code indicates that ICE connectivity checks are 478 still in progress and haven't concluded. This response SHALL be sent 479 within 200 milliseconds of receiving a PLAY request that currently 480 can't be fulfilled because ICE connectivity checks are still running. 481 Subsequently, every 3 seconds after the previous sent one, a 150 482 reply shall be sent until the ICE connectivity checks conclude either 483 successfully or in failure, and a final response for the request can 484 be provided. 486 3.5.2. 480 ICE Processing Failed 488 The 480 client error response code is used in cases when the request 489 can't be fulfilled due to a failure in the ICE processing, such as 490 that all the connectivity checks have timed out. This error message 491 can appear either in response to a SETUP request to indicate that no 492 candidate pair can be constructed or to a PLAY request that the 493 server's connectivity checks resulted in failure. 495 3.6. New Reason for PLAY_NOTIFY 497 A new value used in the PLAY_NOTIFY methods Notify-Reason header is 498 defined: "ice-restart". This reason indicates that a ICE restart 499 needs to happen on the identified resource and session. 501 Notify-Reas-val =/ "ice-restart" 503 3.7. Server Side SDP Attribute for ICE Support 505 If the server supports the media NAT traversal for RTSP controlled 506 sessions, as described in this RFC, then the Server SHOULD include 507 the "a=rtsp-ice-d-m" SDP attribute in any SDP (if used) describing 508 content served by the server. This is an session level attribute. 510 rtsp-ice-d-m-attr = "a=" "rtsp-ice-d-m" 512 3.8. ICE Features Not Required in RTSP 514 A number of ICE signalling features are not needed with RTSP and are 515 discussed below. 517 3.8.1. ICE-Lite 519 The ICE-Lite attribute shall not be used in the context of RTSP. The 520 ICE specification describes two implementations of ICE: Full and 521 Lite, where hosts that are not behind a NAT are allowed to implement 522 only Lite. For RTSP, the Lite implementation is insufficient because 523 it does not cause the media server to send a connectivity check, 524 which are used to protect against making the RTSP server a denial of 525 service tool. This document defines another variation implementation 526 of ICE, called ICE-RTSP. It has its own set of simplifications 527 suitable to RTSP. Conceptually, this implementation of ICE-RTSP is 528 between ICE-FULL and ICE-LITE for a server and simpler than ICE-FULL 529 for clients. 531 3.8.2. ICE-Mismatch 533 The ice-mismatch parameter indicates that the offer arrived with a 534 default destination for a media component that didn't have a 535 corresponding candidate attribute. This is not needed for RTSP as 536 the ICE based lower layer transport specification either is supported 537 or another alternative transport is used. This is always explicitly 538 indicated in the SETUP request and response. 540 3.8.3. ICE Remote Candidate Transport Header Parameter 542 The Remote candidate attribute is not needed for RTSP for the 543 following reasons. Each SETUP results in a independent ICE 544 processing chain which either fails or results in promoting a single 545 candidate pair to usage. If a new SETUP request for the same media 546 is sent this needs to use a new userfragment and password to avoid 547 any race conditions or uncertainty for which processing round the 548 STUN requests relate to. 550 4. Detailed Solution 552 This section describes in detail how the interaction and flow of ICE 553 works with RTSP messages. 555 4.1. Session description and RTSP DESCRIBE (optional) 557 The RTSP server should indicate it has support for ICE by sending the 558 "rtsp-ice-d-m" SDP attribute in the response to the RTSP DESCRIBE 559 message if SDP is used. This allows RTSP clients to only send the 560 new ICE interchanges with servers that support ICE so limiting the 561 overhead on current non-ICE supporting RTSP servers. When not using 562 RTSP DESCRIBE it is still recommended to use the SDP attribute for 563 session description. 565 A Client can also use the DESCRIBE request to determine explicitly if 566 both server and any proxies support ICE. The client includes the 567 "Supported" header with its supported feature tags, including 568 "setup.ice-d-m". Any proxy upon seeing the "Supported" header will 569 include the "Proxy-Supported" header with the feature tags it 570 supports. The server will echo back the "Proxy-Supported" header and 571 its own version of the Supported header so enabling a client to 572 determine if all involved parties support ICE or not. Note that even 573 if a proxy is present in the chain that doesn't indicate support for 574 ICE, it may still work. 576 For example: 577 C->S: DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/2.0 578 CSeq: 312 579 User-Agent: PhonyClient 1.2 580 Accept: application/sdp, application/example 581 Supported: setup.ice-d-m 583 S->C: RTSP/2.0 200 OK 584 CSeq: 312 585 Date: 23 Jan 1997 15:35:06 GMT 586 Server: PhonyServer 1.1 587 Content-Type: application/sdp 588 Content-Length: 367 589 Supported: setup.ice-d-m 591 v=0 592 o=mhandley 2890844526 2890842807 IN IP4 192.0.2.46 593 s=SDP Seminar 594 i=A Seminar on the session description protocol 595 u=http://www.example.com/lectures/sdp.ps 596 e=seminar@example.com (Seminar Management) 597 t=2873397496 2873404696 598 a=recvonly 599 a=rtsp-ice-d-m 600 a=control: * 601 m=audio 3456 RTP/AVP 0 602 a=control: /audio 603 m=video 2232 RTP/AVP 31 604 a=control: /video 606 4.2. Setting up the Media Streams 608 The RTSP client reviews the session description returned, for example 609 by an RTSP DESCRIBE message, to determine what media resources that 610 need to be setup. For each of these media streams where the 611 transport protocol supports ICE connectivity checks, the client shall 612 gather candidate addresses as described in section 4.1.1 in 613 [I-D.ietf-mmusic-ice] according to standard ICE rather than the ICE- 614 Lite implementation. 616 4.3. RTSP SETUP Request 618 The RTSP client will then send at least one SETUP request per media 619 stream to establish the media streams required for the desired 620 session. For each media stream where it desires to use ICE it will 621 include a transport specification with "D-ICE" as the lower layer, 622 and each media stream SHALL have its own unique ICE candidates. This 623 transport specification SHOULD be placed first in the list to give it 624 highest priority. It is RECOMMENDED that additional transport 625 specifications are provided as a fallback in case of non ICE 626 supporting proxies. For example (Note that some lines are broken in 627 contradiction with the defined syntax due to space restrictions in 628 the documenting format: 630 C->S: SETUP rtsp://server.example.com/fizzle/foo/audio RTSP/2.0 631 CSeq: 302 632 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=8hhY; 633 ICE-Password=asd88fgpdd777uzjYhagZg; candidates=" 634 1 1 UDP 2130706431 10.0.1.17 8998 typ host; 635 2 1 UDP 1694498815 192.0.2.3 45664 typ srflx 636 raddr 10.0.1.17 rport 9002", 637 RTP/AVP/UDP; unicast; dest_addr=":6970"/":6971", 638 RTP/AVP/TCP;unicast;interleaved=0-1 639 Accept-Ranges: NPT, UTC 640 User-Agent: PhonyClient/1.2 641 Supported: setup.ice-d-m 643 The RTSP client will be initiating and thus the controlling party in 644 the ICE processing. 646 4.4. Gathering Candidates 648 Upon receiving a SETUP request the server can determine what media 649 resource should be delivered and which transport alternatives that 650 the client supports. If one based on D-ICE is on the list of 651 supported transports and prefered among the support, the below 652 applies. 654 The transport specification will provide which media protocol is to 655 be used and based on this and the clients candidates, the server 656 determines the protocol and if it supports ICE with that protocol. 657 The server shall then gather its candidates according to section 658 4.1.1 in [I-D.ietf-mmusic-ice]. Servers that have an address that is 659 generally reachable by any clients within the address scope the 660 server intends to serve MAY be specially configured (high- 661 reachability configuration). This special configuration has the goal 662 of reducing the server side candidate to preferably a single one per 663 (address family, media stream, media component) tuple. Instead of 664 gathering all possible addresses including relayed and server 665 reflexive addresses, the server uses a single address per address 666 family that it knows it should be reachable by a client behind one or 667 more NATs. The reason for this special configuration is two fold: 668 Firstly it reduces the load on the server in address gathering and in 669 ICE processing during the connectivity checks. Secondly it will 670 reduce the number of permutations for candidate pairs significantly 671 thus potentially speeding up the conclusion of the ICE processing. 672 Note however that using this option on a server that doesn't fulfill 673 the requirement of being reachable is counter-productive and it is 674 important that this is correctly configured. 676 4.5. RTSP Server Response 678 The server determines if the SETUP request is successful from the 679 other perspectives and will return a 200 OK response, otherwise 680 returning an error code from the list in Table 4 in 681 [I-D.ietf-mmusic-rfc2326bis]. At that point the server, having 682 selected a transport specification using the "D-ICE" lower layer, 683 will need to include that transport specification in the response 684 message. The transport specification shall include the candidates 685 gathered in SectionSection 4.4 in the "candidates" transport header 686 parameter as well as the server's username and password. In the case 687 that there are no valid candidate pairs with the combination of the 688 client and servers candidates, a 480 (ICE Processing Failed) error 689 response shall be returned which must include the servers' 690 candidates. The return of a 480 error allows both the server and 691 client to release its candidates. 693 S->C: RTSP/2.0 200 OK 694 CSeq: 302 695 Session: 12345678 696 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=MkQ3; 697 ICE-Password=pos12Dgp9FcAjpq82ppaF; candidates=" 698 1 1 UDP 2130706431 192.0.2.56 50234 typ host" 699 Accept-Ranges: NPT 700 Date: 23 Jan 1997 15:35:06 GMT 701 Server: PhonyServer 1.1 702 Supported: setup.ice-d-m 704 4.6. Server to Client ICE Connectivity Checks 706 The server shall start the connectivity checks following the 707 procedures described in Section 5.7 and 5.8 of [I-D.ietf-mmusic-ice] 708 unless it is configured to use the high-reachability option. If it 709 is then it can suppress its own checks until the servers checks are 710 triggered by the client's connectivity checks. 712 Please note that section 5.8 does specify that the start of 713 initiation of the checks are paced and new ones are only started 714 every Ta seconds. The motivation for this is documented in Appendix 715 B.1 of [I-D.ietf-mmusic-ice] as for SIP/SDP all media streams within 716 an offer/answer dialog are running using the same queue. To ensure 717 the same behavior with RTSP, the server SHALL use a single pacer 718 queue for all media streams within each RTSP session. 720 The values for the pacing of STUN and TURN transactions Ta and RTO 721 can be configured but have some minimum values defined in the ICE 722 specification. 724 When a connectivity check from the client reaches the server it will 725 result in a triggered check from the server as specified in section 726 7.2.1.4 of [I-D.ietf-mmusic-ice]. This is why servers with a high 727 reachability address can wait until this triggered check to send out 728 any checks for itself so saving resources and mitigating the DDoS 729 potential. 731 4.7. Client to Server ICE Connectivity Check 733 The client receives the SETUP response and learns the candidate 734 address to use for the connectivity checks. The client shall 735 initiate its connectivity check, following the procedures in Section 736 6 of [I-D.ietf-mmusic-ice]. The STUN transaction pacer SHALL be used 737 across all media streams part of the same RTSP session. 739 Aggressive nomination SHALL be used with RTSP. This doesn't have the 740 negative impact that it has in offer/answer as media playing only 741 starts after issuing a PLAY request. 743 4.8. Client Connectivity Checks Complete 745 When the client has concluded all of its connectivity checks and has 746 nominated its desired candidate for a particular media stream, it MAY 747 issue a PLAY request for that stream. Note, that due to the 748 aggressive nomination, there is a risk that any outstanding check may 749 nominate another pair than what was already nominated. If the client 750 has locally determined that its checks have failed it may try 751 providing an extended set of candidates and update the server 752 candidate list by issuing a new SETUP request for the media stream. 754 If the client concluded its connectivity checks successfully and 755 therefore sent a PLAY request but the server cannot conclude 756 successfully, the server will respond with a 480 (ICE Processing 757 Failed). Upon receiving the 480 (ICE Processing Failed) response, 758 the client may send a new SETUP request assuming it has any new 759 information that can be included in the candidate list. If the 760 server is still performing the checks it will respond with a 150 (CE 761 connectivity checks in progress) response to indicate this. 763 4.9. Server Connectivity Checks Complete 765 When the RTSP server receives a PLAY request, it checks to see that 766 the connectivity checks have concluded successfully and only then 767 will it play the stream. If the PLAY request is for a particular 768 media stream, the server only needs to check that the connectivity 769 checks for that stream completely successfully. If the server has 770 not concluded its connectivity checks the server indicates that by 771 sending the 150 (ICE connectivity checks in progress) 772 (Section 3.5.1). If there is a problem with the checks then the 773 server sends to the client a 480 response to indicate a failure of 774 the checks. If the checks are successful then the server sends a 200 775 OK response and starts delivering media. 777 4.10. Releasing Candidates 779 Both server and client may release its non nominated candidates as 780 soon as a 200 PLAY response has been issued/received and no 781 outstanding connectivity checks exist. 783 4.11. Steady State 785 The client will continue to use STUN to send keep-alive for the used 786 bindings. This is important as normally RTSP play mode sessions only 787 contain traffic from the server to the client so the bindings in the 788 NAT need to be refreshed by the client to server traffic provided by 789 the STUN keep-alive. 791 4.12. re-SETUP 793 The server SHALL support SETUP requests in PLAYING state, as long as 794 the SETUP changes only the ICE parameters, which are: ICE-Password, 795 ICE-ufrag and the content of ICE candidates. 797 If the client decides to change any parameter related to the media 798 stream SETUP it will send a new SETUP request. In this new SETUP 799 request the client SHALL include a new different username and 800 password to use in the ICE processing. This request will also cause 801 the ICE processing to start from the beginning again. 803 If the RTSP session is in playing state at the time of sending the 804 SETUP request, the ICE connectivity checks SHALL use Regular 805 nomination. Any ongoing media delivery continues on the previously 806 nominated candidate pairs until the new pairs have been nominated for 807 the individual candidate. Once the nomination of the new candidate 808 pair has completed, all unused candidates may be released. 810 4.13. Server Side Changes After Steady State 812 A Server may require an ICE restart because of server side load 813 balancing or a failure resulting in an IP address and a port number 814 change. It shall use the PLAY_NOTIFY method to inform the client 815 (Section 13.5 [I-D.ietf-mmusic-rfc2326bis]) with a new Notify-Reason 816 header: ice-restart. The server will identify if the change is for a 817 single media or for the complete session by including the 818 corresponding URI in the PLAY_NOTIFY request. 820 Upon receiving and responding to this PLAY_NOTIFY with ice-restart 821 reason the client SHALL gather new ICE candidates, send SETUP 822 requests for each media stream part of the session. The server 823 provides its candidates in the SETUP response the same way as for the 824 first time ICE processing. Both server and client shall provide new 825 ICE usernames and passwords. The client MAY issue the SETUP request 826 while the session is in PLAYING state. 828 If the RTSP session is in PLAYING state when the client issues the 829 SETUP request the client SHALL use regular nomination. If not the 830 client will use the same procedures as for when first creating the 831 session. 833 Note that keepalives on the previous set of candidate pairs should 834 continue until all new candidate pairs have been nominated. After 835 having nominated a new set of candidate pairs, the client may 836 continue to receive media for some additional time. Even if the 837 server stops delivering media over that candidate pair at the time of 838 nomination, media may arrive for up to one maximum segment lifetime 839 as defined in TCP (2 minutes). Unfortuntately, if the RTSP server is 840 divided into a separate controller and media streame, a failure may 841 result in continued media delivery for a longer time than the maximum 842 segment liftime, thus source filtering is recommended. 844 For example: 846 S->C: PLAY_NOTIFY rtsp://example.com/fizzle/foo RTSP/2.0 847 CSeq: 854 848 Notify-Reason: ice-restart 849 Session: uZ3ci0K+Ld 850 Server: PhonyServer 1.1 852 C->S: RTSP/2.0 200 OK 853 CSeq: 854 854 User-Agent: PhonyClient/1.2 856 C->S: SETUP rtsp://server.example.com/fizzle/foo/audio RTSP/2.0 857 CSeq: 302 858 Session: uZ3ci0K+Ld 859 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=Kl1C; 860 ICE-Password=H4sICGjBsEcCA3Rlc3RzLX; candidates =" 861 1 1 UDP 2130706431 10.0.1.17 8998 typ host; 862 2 1 UDP 1694498815 192.0.2.3 51456 typ srflx 863 raddr 10.0.1.17 rport 9002", 865 RTP/AVP/UDP; unicast; dest_addr=":6970"/":6971", 866 RTP/AVP/TCP;unicast;interleaved=0-1 867 Accept-Ranges: NPT, UTC 868 User-Agent: PhonyClient/1.2 870 C->S: SETUP rtsp://server.example.com/fizzle/foo/video RTSP/2.0 871 CSeq: 303 872 Session: uZ3ci0K+Ld 873 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=hZv9; 874 ICE-Password=JAhA9myMHETTFNCrPtg+kJ; candidates=" 875 1 1 UDP 2130706431 10.0.1.17 9000 typ host; 876 2 1 UDP 1694498815 192.0.2.3 51576 typ srflx 877 raddr 10.0.1.17 rport 9004", 878 RTP/AVP/UDP; unicast; dest_addr=":6972"/":6973", 879 RTP/AVP/TCP;unicast;interleaved=0-1 880 Accept-Ranges: NPT, UTC 881 User-Agent: PhonyClient/1.2 883 S->C: RTSP/2.0 200 OK 884 CSeq: 302 885 Session: uZ3ci0K+Ld 886 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=CbDm; 887 ICE-Password=OfdXHws9XX0eBr6j2zz9Ak; candidates=" 888 1 1 UDP 2130706431 192.0.2.56 50234 typ host" 889 Accept-Ranges: NPT 890 Date: 23 Jan 1997 15:43:12 GMT 891 Server: PhonyServer 1.1 893 S->C: RTSP/2.0 200 OK 894 CSeq: 303 895 Session: uZ3ci0K+Ld 896 Transport: RTP/AVP/D-ICE; unicast; ICE-ufrag=jigs; 897 ICE-Password=Dgx6fPj2lsa2WI8b7oJ7+s; candidates=" 898 1 1 UDP 2130706431 192.0.2.56 47233 typ host" 899 Accept-Ranges: NPT 900 Date: 23 Jan 1997 15:43:13 GMT 901 Server: PhonyServer 1.1 903 5. ICE and Proxies 905 RTSP allows for proxies which can be of two fundamental types 906 depending if they relay and potentially cache the media or not. 907 Their differing impact on the RTSP NAT traversal solution, including 908 backwards compatibility, is explained below. 910 5.1. Media Handling Proxies 912 An RTSP proxy that relays or caches the media stream for a particular 913 media session can be considered to split the media transport into two 914 parts: A media transport between the server and the proxy according 915 to the proxies need, and delivery from the proxy to the client. This 916 split means that the NAT traversal solution will need to be run on 917 each individual media leg according to need. 919 It is RECOMMENDED that any media handling proxy support the media NAT 920 traversal defined within this specification. This is for two 921 reasons: Firstly to enable clients to perform NAT traversal for the 922 media between the proxy and itself and secondly to allow the proxy to 923 be topology independent so able to support performing NAT traversal 924 for non-NAT traversal capable clients present in the same address 925 domain. 927 For a proxy to support the media NAT traversal defined in this 928 specification a proxy will need to implement the solution fully and 929 be ready as both a controlling and a controlled ICE peer. The proxy 930 also SHALL include the "setup.ice-d-m" feature tag in any applicable 931 capability negotiation headers, such as "Proxy-Supported." 933 5.2. Signalling Only Proxies 935 A signalling only proxy handles only the RTSP signalling and does not 936 have the media relayed through proxy functions. This type of proxy 937 is not likely to work unless the media NAT traversal solution is in 938 place between the client and the server, because the DoS protection 939 measures usually prevent media delivery to other addresses other than 940 from where the RTSP signalling arrives at the server. 942 The solution for the Signalling Only proxy is that it must forward 943 the RTSP SETUP requests including any transport specification with 944 the "D-ICE" lower layer and the related transport parameters. A 945 proxy supporting this functionality SHOULD indicate its capability by 946 always including the "setup.ice-d-m" feature tag in the "Proxy- 947 Supported" header. 949 5.3. Non-supporting Proxies 951 A media handling proxy that doesn't support the ICE media NAT 952 traversal specified here is assumed to remove the transport 953 specification and use any of the lower prioritized transport 954 specifications if provided by the requester. The specification of 955 such a non ICE transport enables the negotiation to complete, 956 although with a less prefered method as a NAT between the proxy and 957 the client will likely result in failure of the media path. 959 A non-media handling transport proxy is expected to ignore and simply 960 forward all unknown transport specifications, however, this can only 961 be guaranteed for proxies following the published RTSP 2.0 962 specification. 964 Unfortunately the usage of the "setup.ice-d-m" feature tag in the 965 proxy-require will have contradicting results. For a non ICE 966 supporting media handling proxy, the inclusion of the feature tag 967 will result in aborting the setup and indicating that it isn't 968 supported, which is desirable if you want to provide other fallbacks 969 or other transport configurations to handle the situation. For non- 970 supporting non-media handling proxies the result will also result in 971 aborting the setup, however, setup might have worked if the proxy- 972 require tag wasn't present. This variance in results is the reason 973 we don't recommend the usage of the Proxy-Require header. Instead we 974 recommend the usage of the Supported header to force proxies to 975 include the feature tags they support in the proxy-supported which 976 will provide a positive indication when all proxies in the chain 977 between the client and server support the functionality. Even if not 978 explicitly indicating support, any SETUP response including a 979 transport specification with "D-ICE" will be implicit indication that 980 the proxy chain supports at least passthrough of this media. 982 6. RTP and RTCP Multiplexing 984 [I-D.ietf-avt-rtp-and-rtcp-mux] specifies how and when RTP and RTCP 985 can be multiplexed on the same port. This multiplexing SHALL be 986 combined with ICE as it makes RTP and RTCP need only a single 987 component per media stream instead of two, so reducing the load on 988 the connectivity checks. For details on how one negotiate RTP and 989 RTCP multiplexing, see Appendix B [I-D.ietf-mmusic-rfc2326bis]. 991 Multiplexing RTP and RTCP has the benefit that it avoids the need for 992 handling two components per media stream when RTP is used as the 993 media transport protocol. This eliminates at least one STUN check 994 per media stream and will also reduce the time needed to complete the 995 ICE processing by at least the time it takes to pace out the 996 additional STUN checks of up to one complete round trip time fpr a 997 single media stream. In addition to the protocol performance 998 improvements, the server and client side complexities are reduced as 999 multiplexing halves the total number of STUN instances and holding 1000 the associate state. Multiplexing will also reduce the combinations 1001 and length of the list of possible candidates. 1003 The implementation of RTP and RTCP multiplexing is additional work 1004 required for this solution. However, when implementing the ICE 1005 solution a server or client will need to implement a de-multiplexer 1006 between the STUN, and RTP or RTCP packets below the RTP/RTCP 1007 implementation anyway, so the additional work of one new 1008 demultiplexing point directly connected to the STUN and RTP/RTCP 1009 seems small relative to the benefits provided. 1011 Due to the above mentioned benefits, RTSP servers and clients that 1012 supports "D-ICE" lower layer transport in combination with RTP SHALL 1013 also implement RTP and RTCP multiplexing as specified in this section 1014 and [I-D.ietf-avt-rtp-and-rtcp-mux]. 1016 7. Open Issues 1018 Below is listed the known open issues and questions that needs to be 1019 resolved: 1021 1. None 1023 8. IANA Considerations 1025 This document request registration in a number of registries, both 1026 for RTSP and SDP. 1028 8.1. RTSP Feature Tags 1030 This document request that one RTSP 2.0 feature tags are registered 1031 in the "RTSP feature tag" registry: 1033 setup.ice-d-m See Section Section 3.4. 1035 8.2. Transport Protocol Specifications 1037 This document needs to register a number of transport protocol 1038 combinations are registered in RTSP's "Transport Protocol 1039 Specifications" registry. 1041 "RTP/AVP/D-ICE" 1043 "RTP/AVPF/D-ICE" 1045 "RTP/SAVP/D-ICE" 1047 "RTP/SAVPF/D-ICE" 1049 8.3. RTSP Transport Parameters 1051 This document requests that 3 transport parameters are registered in 1052 RTSP's "Transport Parameters": 1054 "candidates": See Section Section 3.2. 1056 "ICE-Password": See Section Section 3.3. 1058 "ICE-ufrag": See Section Section 3.3. 1060 8.4. RTSP Status Codes 1062 This document requests that 2 assignments are done in the "RTSP 1063 Status Codes" registry. The suggested values are: 1065 150: See Section Section 3.5.1. 1067 480: See Section Section 3.5.2. 1069 8.5. Notify-Reason value 1071 This document requests that one assignment is done in the Notify- 1072 Reason header value registry. The suggested value is: 1074 ice-restart: See section Section 3.6. 1076 8.6. SDP Attribute 1078 The registration of one SDP attribute is requested: 1079 SDP Attribute ("att-field"): 1081 Attribute name: rtsp-ice-d-m 1082 Long form: ICE for RTSP datagram media NAT traversal 1083 Type of name: att-field 1084 Type of attribute: Session level only 1085 Subject to charset: No 1086 Purpose: RFC XXXX 1087 Reference: RFC XXXX 1088 Values: No values defined. 1089 Contact: Magnus Westerlund 1090 E-mail: magnus.westerlund@ericsson.com 1091 phone: +46 10 714 82 87 1093 9. Security Considerations 1095 ICE [I-D.ietf-mmusic-ice] provides an extensive discussion on 1096 security considerations which applies here as well. 1098 9.1. ICE and RTSP 1100 A long-standing risk with transmitting a packet stream over UDP is 1101 that the host may not be interested in receiving the stream. On 1102 today's Internet many hosts are behind NATs or operate host firewalls 1103 which do not respond to unsolicited packets with an ICMP port 1104 unreachable error. Thus, an attacker can construct SDP with a 1105 victim's IP address and cause a flood of media packets to be sent to 1106 a victim. The addition of ICE, as described in this document, 1107 provides protection from the attack described above. By performing 1108 the ICE connectivity check, the media server receives confirmation 1109 that the RTSP client wants the media. While this protection could 1110 also be implemented by requiring the IP addresses in the SDP match 1111 the IP address of the RTSP signaling packet, such a mechanism does 1112 not protect other hosts with the same IP address (such as behind the 1113 same NAT), and such a mechanism would prohibit separating the RTSP 1114 controller from the media playout device (e.g., an IP-enabled remote 1115 control and an IP-enabled television). 1117 10. Acknowledgements 1119 The authors would like to thank Remi Denis-Courmont for suggesting 1120 the method of integrating ICE in RTSP signalling, Dan Wing for help 1121 with the security section and numerous other issues. 1123 11. References 1125 11.1. Normative References 1127 [I-D.ietf-avt-rtp-and-rtcp-mux] 1128 Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1129 Control Packets on a Single Port", 1130 draft-ietf-avt-rtp-and-rtcp-mux-07 (work in progress), 1131 August 2007. 1133 [I-D.ietf-mmusic-ice] 1134 Rosenberg, J., "Interactive Connectivity Establishment 1135 (ICE): A Protocol for Network Address Translator (NAT) 1136 Traversal for Offer/Answer Protocols", 1137 draft-ietf-mmusic-ice-19 (work in progress), October 2007. 1139 [I-D.ietf-mmusic-rfc2326bis] 1140 Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., 1141 and M. Stiemerling, "Real Time Streaming Protocol 2.0 1142 (RTSP)", draft-ietf-mmusic-rfc2326bis-22 (work in 1143 progress), July 2009. 1145 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1146 Requirement Levels", BCP 14, RFC 2119, March 1997. 1148 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1149 Description Protocol", RFC 4566, July 2006. 1151 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1152 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1154 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 1155 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 1156 October 2008. 1158 11.2. Informative References 1160 [I-D.ietf-mmusic-rtsp-nat-evaluation] 1161 Westerlund, M. and T. Zeng, "The evaluation of different 1162 NAT traversal Techniques for media controlled by Real- 1163 time Streaming Protocol (RTSP)", 1164 draft-ietf-mmusic-rtsp-nat-evaluation-02 (work in 1165 progress), January 2010. 1167 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 1168 Streaming Protocol (RTSP)", RFC 2326, April 1998. 1170 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 1171 Address Translator (Traditional NAT)", RFC 3022, 1172 January 2001. 1174 [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram 1175 Congestion Control Protocol (DCCP)", RFC 4340, March 2006. 1177 Authors' Addresses 1179 Jeff Goldberg 1180 Cisco 1181 11 New Square, Bedfont Lakes 1182 Feltham,, Middx TW14 8HA 1183 United Kingdom 1185 Phone: +44 20 8824 1000 1186 Fax: 1187 Email: jgoldber@cisco.com 1188 URI: 1190 Magnus Westerlund 1191 Ericsson 1192 Torshamsgatan 23 1193 Stockholm, SE-164 80 1194 Sweden 1196 Phone: +46 8 719 0000 1197 Fax: 1198 Email: magnus.westerlund@ericsson.com 1199 URI: 1201 Thomas Zeng 1202 Nextwave Wireless, Inc. 1203 12670 High Bluff Drive 1204 San Diego, CA 92130 1205 USA 1207 Phone: +1 858 480 3100 1208 Fax: 1209 Email: thomas.zeng@gmail.com 1210 URI: