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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2032 (ref. '3') (Obsoleted by RFC 4587) == Outdated reference: A later version (-19) exists of draft-ietf-avt-rtcpssm-11 ** Obsolete normative reference: RFC 4566 (ref. '8') (Obsoleted by RFC 8866) == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-ice-10 Summary: 5 errors (**), 0 flaws (~~), 3 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Perkins 3 Internet-Draft University of Glasgow 4 Updates: 3550 (if approved) M. Westerlund 5 Intended status: Standards Track Ericsson 6 Expires: June 4, 2007 December 1, 2006 8 Multiplexing RTP Data and Control Packets on a Single Port 9 draft-ietf-avt-rtp-and-rtcp-mux-03.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on June 4, 2007. 36 Copyright Notice 38 Copyright (C) The Internet Society (2006). 40 Abstract 42 This memo discusses issues that arise when multiplexing RTP data 43 packets and RTP control protocol (RTCP) packets on a single UDP port. 44 It updates RFC 3550 to describe when such multiplexing is, and is 45 not, appropriate, and explains how the Session Description Protocol 46 (SDP) can be used to signal multiplexed sessions. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 4. Distinguishable RTP and RTCP Packets . . . . . . . . . . . . . 4 54 5. Multiplexing RTP and RTCP on a Single Port . . . . . . . . . . 5 55 5.1. Unicast Sessions . . . . . . . . . . . . . . . . . . . . . 6 56 5.1.1. SDP Signalling . . . . . . . . . . . . . . . . . . . . 6 57 5.1.2. Interactions with SIP forking . . . . . . . . . . . . 7 58 5.1.3. Interactions with ICE . . . . . . . . . . . . . . . . 7 59 5.1.4. Interactions with Header Compression . . . . . . . . . 8 60 5.2. Any Source Multicast Sessions . . . . . . . . . . . . . . 8 61 5.3. Source Specific Multicast Sessions . . . . . . . . . . . . 9 62 6. Multiplexing, Bandwidth, and Quality of Service . . . . . . . 9 63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 64 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 65 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 66 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 67 10.1. Normative References . . . . . . . . . . . . . . . . . . . 11 68 10.2. Informative References . . . . . . . . . . . . . . . . . . 12 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 70 Intellectual Property and Copyright Statements . . . . . . . . . . 14 72 1. Introduction 74 The Real-time Transport Protocol (RTP) [1] comprises two components: 75 a data transfer protocol, and an associated control protocol (RTCP). 76 Historically, RTP and RTCP have been run on separate UDP ports. With 77 increased use of Network Address Translation (NAT) this has become 78 problematic, since opening multiple NAT pinholes can be costly. This 79 memo discusses how the RTP and RTCP flows for a single media type can 80 be run on a single port, to ease NAT traversal, and considers when 81 such multiplexing is appropriate. The multiplexing of several types 82 of media (e.g. audio and video) onto a single port is not considered 83 here (but see Section 5.2 of [1]). 85 This memo is structured as follows: in Section 2 we discuss the 86 design choices which led to the use of separate ports, and comment on 87 the applicability of those choices to current network environments. 88 We discuss terminology in Section 3, how to distinguish multiplexed 89 packets in Section 4, and then specify when and how RTP and RTCP 90 should be multiplexed, and how to signal multiplexed sessions, in 91 Section 5. Quality of service and bandwidth issues are discussion in 92 Section 6. We conclude with security considerations in Section 7. 94 This memo updates Section 11 of [1]. 96 2. Background 98 An RTP session comprises data packets and periodic control (RTCP) 99 packets. RTCP packets are assumed to use "the same distribution 100 mechanism as the data packets" and the "underlying protocol MUST 101 provide multiplexing of the data and control packets, for example 102 using separate port numbers with UDP" [1]. Multiplexing was deferred 103 to the underlying transport protocol, rather than being provided 104 within RTP, for the following reasons: 106 1. Simplicity: an RTP implementation is simplified by moving the RTP 107 and RTCP demultiplexing to the transport layer, since it need not 108 concern itself with the separation of data and control packets. 109 This allows the implementation to be structured in a very natural 110 fashion, with a clean separation of data and control planes. 112 2. Efficiency: following the principle of integrated layer 113 processing [14] an implementation will be more efficient when 114 demultiplexing happens in a single place (e.g. according to UDP 115 port) than when split across multiple layers of the stack (e.g. 116 according to UDP port then according to packet type). 118 3. To enable third party monitors: while unicast voice-over-IP has 119 always been considered, RTP was also designed to support loosely 120 coupled multicast conferences [15] and very large-scale multicast 121 streaming media applications (such as the so-called "triple-play" 122 IPTV service). Accordingly, the design of RTP allows the RTCP 123 packets to be multicast using a separate IP multicast group and 124 UDP port to the data packets. This not only allows participants 125 in a session to get reception quality feedback, but also enables 126 deployment of third party monitors which listen to reception 127 quality without access to the data packets. This was intended to 128 provide manageability of multicast sessions, without compromising 129 privacy. 131 While these design choices are appropriate for many use of RTP, they 132 are problematic in some cases. There are many RTP deployments which 133 don't use IP multicast, and with the increased use of Network Address 134 Translation (NAT) the simplicity of multiplexing at the transport 135 layer has become a liability, since it requires complex signalling to 136 open multiple NAT pinholes. In environments such as these, it is 137 desirable to provide an alternative to demultiplexing RTP and RTCP 138 using separate UDP ports, instead using only a single UDP port and 139 demultiplexing within the application. 141 This memo provides such an alternative by multiplexing RTP and RTCP 142 packets on a single UDP port, distinguished by the RTP payload type 143 and RTCP packet type values. This pushes some additional work onto 144 the RTP implementation, in exchange for simplified NAT traversal. 146 3. Terminology 148 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 149 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 150 document are to be interpreted as described in RFC 2119 [2]. 152 4. Distinguishable RTP and RTCP Packets 154 When RTP and RTCP packets are multiplexed onto a single port, they 155 can be distinguished provided: 1) the RTP payload type (PT) values 156 used are distinct from the RTCP packet types used; and 2) for each 157 RTP payload type, PT+128 is distinct from the RTCP packet types used. 158 The first constraint precludes a direct conflict between RTP payload 159 type and RTCP packet type, the second constraint precludes a conflict 160 between an RTP data packet with marker bit set and an RTCP packet. 161 This demultiplexing method works because the RTP payload type and 162 RTCP packet type occupy the same position within the packet. 164 The following conflicts between RTP and RTCP packet types are known: 166 o RTP payload types 64-65 conflict with the RTCP FIR and NACK 167 packets defined in the RTP Payload Format for H.261 [3]. 169 o RTP payload types 72-76 conflict with the RTCP SR, RR, SDES, BYE 170 and APP packets defined in the RTP specification [1]. 172 o RTP payload types 77-78 conflict with the RTCP RTPFB and PSFB 173 packets defined in the RTP/AVPF profile [4]. 175 o RTP payload type 79 conflicts with RTCP Extended Report (XR) [5] 176 packets. 178 o RTP payload type 80 conflicts with Receiver Summary Information 179 (RSI) packets defined in the RTCP Extensions for Single-Source 180 Multicast Sessions with Unicast Feedback [6]. 182 New RTCP packet types may be registered in future, and will further 183 reduce the RTP payload types that are available when multiplexing RTP 184 and RTCP onto a single port. To allow this multiplexing, future RTCP 185 packet type assignments SHOULD be made after the current assignments 186 in the range 209-223, then in the range 194-199, so that only the RTP 187 payload types in the range 64-95 are blocked. 189 Given these constraints, it is RECOMMENDED to follow the guidelines 190 in the RTP/AVP profile [7] for the choice of RTP payload type values, 191 with the additional restriction that payload type values in the range 192 64-95 MUST NOT be used. Specifically, dynamic RTP payload types 193 SHOULD be chosen in the range 96-127 where possible. Values below 64 194 MAY be used if that is insufficient, in which case it is RECOMMENDED 195 that payload type numbers that are not statically assigned by [7] be 196 used first. 198 Note: since all RTCP packets MUST be sent as compound packets 199 beginning with an SR or an RR packet ([1] Section 6.1), one might 200 wonder why RTP payload types other than 72 and 73 are prohibited 201 when multiplexing RTP and RTCP. This is done to ensure robustness 202 against broken nodes which send non-compliant RTCP packets, which 203 might otherwise be confused with multiplexed RTP packets. 205 5. Multiplexing RTP and RTCP on a Single Port 207 The procedures for multiplexing RTP and RTCP on a single port depend 208 on whether the session is a unicast session or a multicast session. 209 For a multicast sessions, also depends whether ASM or SSM multicast 210 is to be used. 212 5.1. Unicast Sessions 214 It is acceptable to multiplex RTP and RTCP packets on a single UDP 215 port to ease NAT traversal for unicast sessions, provided the RTP 216 payload types used in the session are chosen according to the rules 217 in Section 4. The following sections describe how such multiplexed 218 sessions can be signalled using the Session Initiation Protocol (SIP) 219 with the offer/answer model. 221 5.1.1. SDP Signalling 223 When the Session Description Protocol (SDP) [8] is used to negotiate 224 RTP sessions following the offer/answer model [9], the "a=rtcp-mux" 225 attribute (see Section 8) indicates the desire to multiplex RTP and 226 RTCP onto a single port. The initial SDP offer MUST include this 227 attribute to request multiplexing of RTP and RTCP on a single port. 228 For example: 230 v=0 231 o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e 232 s=- 233 c=IN IP6 2001:DB8::211:24ff:fea3:7a2e 234 t=1153134164 1153137764 235 m=audio 49170 RTP/AVP 97 236 a=rtpmap:97 iLBC/8000 237 a=rtcp-mux 239 This offer denotes a unicast voice-over-IP session using the RTP/AVP 240 profile with iLBC coding. The answerer is requested to send both RTP 241 and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e. 243 If the answerer wishes to multiplex RTP and RTCP onto a single port 244 it MUST include an "a=rtcp-mux" attribute in the answer. The RTP 245 payload types used in the answer MUST conform to the rules in 246 Section 4. 248 If the answer does not contain an "a=rtcp-mux" attribute, the offerer 249 SHOULD NOT multiplex RTP and RTCP packets on a single port. Instead, 250 it should send and receive RTCP on a port allocated according to the 251 usual port selection rules (either the port pair, or a signalled port 252 if the "a=rtcp:" attribute [10] is also included). This will occur 253 when talking to a peer that does not understand the "a=rtcp-mux" 254 attribute. 256 When SDP is used in a declarative manner, the presence of an "a=rtcp- 257 mux" attribute signals that the sender will multiplex RTP and RTCP on 258 the same port. The receiver MUST be prepared to receive RTCP packets 259 on the RTP port, and any resource reservation needs to be made 260 including the RTCP bandwidth. 262 5.1.2. Interactions with SIP forking 264 When using SIP with a forking proxy, it is possible that an INVITE 265 request may result in multiple 200 (OK) responses. If RTP and RTCP 266 multiplexing is offered in that INVITE, it is important to be aware 267 that some answerers may support multiplexed RTP and RTCP, some not. 268 This will require the offerer listen for RTCP on both the RTP port 269 and the usual RTCP port, and to send RTCP on both ports, unless 270 branches of the call that support multiplexing are re-negotiated to 271 use separate RTP and RTCP ports. 273 5.1.3. Interactions with ICE 275 It is common to use the Interactive Connectivity Establishment (ICE) 276 [16] methodology to establish RTP sessions in the presence of Network 277 Address Translation (NAT) devices or other middleboxes. If RTP and 278 RTCP are sent on separate ports, the RTP media stream comprises two 279 components in ICE (one for RTP and one for RTCP), with connectivity 280 checks being performed for each component. If RTP and RTCP are to be 281 multiplexed on the same port some of these connectivity checks can be 282 avoided, reducing the overhead of ICE. 284 If it is desired to use both ICE and multiplexed RTP and RTCP, the 285 initial offer MUST contain an "a=rtcp-mux" attribute to indicate that 286 RTP and RTCP multiplexing is desired, and MUST contain "a=candidate:" 287 lines for both RTP and RTCP along with an "a=rtcp:" line indicating a 288 fallback port for RTCP in the case that the answerer does not support 289 RTP and RTCP multiplexing. This MUST be done for each media where 290 RTP and RTCP multiplexing is desired. 292 If the answerer wishes to multiplex RTP and RTCP on a single port, it 293 MUST generate an answer containing an "a=rtcp-mux" attribute, and a 294 single "a=candidate:" line corresponding to the RTP port (i.e. there 295 is no candidate for RTCP), for each media where it is desired to use 296 RTP and RTCP multiplexing. The answerer then performs connectivity 297 checks for that media as if the offer had contained only a single 298 candidate for RTP. If the answerer does not want to multiplex RTP 299 and RTCP on a single port, it MUST NOT include the "a=rtcp-mux" 300 attribute in its answer, and MUST perform connectivity checks for all 301 offered candidates in the usual manner. 303 On receipt of the answer, the offerer looks for the presence of the 304 "a=rtcp-mux" line for each media where multiplexing was offered. If 305 this is present, then connectivity checks proceed as if only a single 306 candidate (for RTP) were offered, and multiplexing is used once the 307 session is established. If the "a=rtcp-mux" line is not present, the 308 session proceeds with connectivity checks using both RTP and RTCP 309 candidates, eventually leading to a session being established with 310 RTP and RTCP on separate ports (as signalled by the "a=rtcp:" 311 attribute). 313 5.1.4. Interactions with Header Compression 315 Multiplexing RTP and RTCP packets onto a single port may negatively 316 impact header compression schemes, for example Compressed RTP (CRTP) 317 [17] and RObust Header Compression (ROHC) [18]. Header compression 318 exploits patterns of change in the RTP headers of consecutive packets 319 to send an indication that the packet changed in the expected way, 320 rather than sending the complete header each time. This can lead to 321 significant bandwidth savings if flows have uniform behaviour. 323 The presence of RTCP packets multiplexed with RTP data packets can 324 disrupt the patterns of change between headers, and has the potential 325 to significantly reduce header compression efficiency. The extent of 326 this disruption depends on the header compression algorithm used, and 327 on the way flows are classified. A well designed classifier should 328 be able to separate RTP and RTCP multiplexed on the same port into 329 different compression contexts, using the payload type field, such 330 that the effect on the compression ratio is small. A classifier that 331 assigns compression contexts based only on the IP addresses and UDP 332 ports will not perform well. It is expected that implementations of 333 header compression will need to be updated to efficiently support RTP 334 and RTCP multiplexed on the same port. 336 This effect of multiplexing RTP and RTCP on header compression may be 337 especially significant in those environments, such as some wireless 338 telephony systems, which rely on the efficiency of header compression 339 to match the media to a limited capacity channel. The implications 340 of multiplexing RTP and RTCP should be carefully considered before 341 use in such environments. 343 5.2. Any Source Multicast Sessions 345 The problem of NAT traversal is less severe for any source multicast 346 (ASM) RTP sessions than for unicast RTP sessions, and the benefit of 347 using separate ports for RTP and RTCP is greater, due to the ability 348 to support third party RTCP only monitors. Accordingly, RTP and RTCP 349 packets SHOULD NOT be multiplexed onto a single port when using ASM 350 multicast RTP sessions, and SHOULD instead use separate ports and 351 multicast groups. 353 5.3. Source Specific Multicast Sessions 355 RTP sessions running over Source Specific Multicast (SSM) send RTCP 356 packets from the source to receivers via the multicast channel, but 357 use a separate unicast feedback mechanism [6] to send RTCP from the 358 receivers back to the source, with the source either reflecting the 359 RTCP packets to the group, or sending aggregate summary reports. 361 Following the terminology of [6], we identify three RTP/RTCP flows in 362 an SSM session: 364 1. RTP and RTCP flows between media sender and distribution source. 365 In many scenarios, the media sender and distribution source are 366 co-located, so multiplexing is not a concern. If the media 367 sender and distribution source are connected by a unicast 368 connection, the rules in Section 5.1 of this memo apply to that 369 connection. If the media sender and distribution source are 370 connected by an Any Source Multicast connection, the rules in 371 Section 5.2 apply to that connection. If the media sender and 372 distribution source are connected by a Source Specific Multicast 373 connection, the RTP and RTCP packets MAY be multiplexed on a 374 single port, provided this is signalled (using "a=rtcp-mux" if 375 using SDP). 377 2. RTP and RTCP sent from the distribution source to the receivers. 378 The distribution source MAY multiplex RTP and RTCP onto a single 379 port to ease NAT traversal issues on the forward SSM path, 380 although doing so may hinder third party monitoring devices if 381 the session uses the simple feedback model. When using SDP, the 382 multiplexing SHOULD be signalled using the "a=rtcp-mux" 383 attribute. 385 3. RTCP sent from receivers to distribution source. This is an RTCP 386 only path, so multiplexing is not a concern. 388 Multiplexing RTP and RTCP packets on a single port in an SSM session 389 has the potential for interactions with header compression described 390 in Section 5.1.4. 392 6. Multiplexing, Bandwidth, and Quality of Service 394 Multiplexing RTP and RTCP has implications on the use of Quality of 395 Service (QoS) mechanism that handles flow that are determined by a 396 three or five tuple (protocol, port and address for source and/or 397 destination). In these cases the RTCP flow will be merged with the 398 RTP flow when multiplexing them together. Thus the RTCP bandwidth 399 requirement needs to be considered when doing QoS reservations for 400 the combined RTP and RTCP flow. However from an RTCP perspective it 401 is beneficial to receive the same treatment of RTCP packets as for 402 RTP as it provides more accurate statistics for the measurements 403 performed by RTCP. 405 The bandwidth required for a multiplexed stream comprises the session 406 bandwidth of the RTP stream, plus the bandwidth used by RTCP. In the 407 usual case, the RTP session bandwidth is signalled in the SDP "b=AS:" 408 (or "b=TIAS:" [11]) line, and the RTCP traffic is limited to 5% of 409 this value. Any QoS reservation SHOULD therefore be made for 105% of 410 the "b=AS:" value. If a non-standard RTCP bandwidth fraction is 411 used, signalled by the SDP "b=RR:" and/or "b=RS:" lines [12], then 412 any QoS reservation SHOULD be made for bandwidth equal to (AS + RS + 413 RR), taking the RS and RR values from the SDP answer. 415 7. Security Considerations 417 The usage of multiplexing RTP and RTCP is not believed to introduce 418 any new security considerations. Known major issues are, integrity 419 and authentication of the signalling used to setup the multiplexing, 420 the integrity, authentication and confidentiality of the actual RTP 421 and RTCP traffic. The security considerations in the RTP 422 specification [1] and any applicable RTP profile (e.g. [7]) and 423 payload format(s) apply. 425 If the Secure Real-time Transport Protocol (SRTP) [13] is to be used 426 in conjunction with multiplexed RTP and RTCP, then multiplexing MUST 427 be done below the SRTP layer. The sender generates SRTP and SRTCP 428 packets in the usual manner, based on their separate cryptographic 429 contexts, and multiplexes them onto a single port immediately before 430 transmission. At the receiver, the cryptographic context is derived 431 from the SSRC, destination network address and destination transport 432 port number in the usual manner, augmented using the RTP payload type 433 and RTCP packet type to demultiplex SRTP and SRTCP according to the 434 rules in Section 4 of this memo. After the SRTP and SRTCP packets 435 have been demultiplexed, cryptographic processing happens in the 436 usual manner. 438 8. IANA Considerations 440 The IANA is requested to register one new SDP attribute, following 441 the guidelines in [8]: 443 o Contact name/email: authors of RFC XXXX 444 o Attribute name: rtcp-mux 446 o Type of attribute: media level 448 o Subject to charset: no 450 This attribute is used to signal that RTP and RTCP traffic should be 451 multiplexed on a single port (see Section 5 of this memo). It is a 452 property attribute, which does not take a value. 454 Note to RFC Editor: please replace "RFC XXXX" above with the RFC 455 number of this memo, and remove this note. 457 9. Acknowledgements 459 We wish to thank Steve Casner, Joerg Ott, Christer Holmberg, Gunnar 460 Hellstrom, Randell Jesup, Hadriel Kaplan, Harikishan Desineni, 461 Stephan Wenger, Jonathan Rosenberg, Roni Even, Ingemar Johansson and 462 Dave Singer for their comments on this memo. This work is supported 463 in part by the UK Engineering and Physical Sciences Research Council. 465 10. References 467 10.1. Normative References 469 [1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 470 "RTP: A Transport Protocol for Real-Time Applications", STD 64, 471 RFC 3550, July 2003. 473 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 474 Levels", BCP 14, RFC 2119, March 1997. 476 [3] Turletti, T., "RTP Payload Format for H.261 Video Streams", 477 RFC 2032, October 1996. 479 [4] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 480 "Extended RTP Profile for Real-time Transport Control Protocol 481 (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006. 483 [5] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol 484 Extended Reports (RTCP XR)", RFC 3611, November 2003. 486 [6] Chesterfield, J., "RTCP Extensions for Single-Source Multicast 487 Sessions with Unicast Feedback", draft-ietf-avt-rtcpssm-11 488 (work in progress), March 2006. 490 [7] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video 491 Conferences with Minimal Control", STD 65, RFC 3551, July 2003. 493 [8] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 494 Description Protocol", RFC 4566, July 2006. 496 [9] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 497 Session Description Protocol (SDP)", RFC 3264, June 2002. 499 [10] Huitema, C., "Real Time Control Protocol (RTCP) attribute in 500 Session Description Protocol (SDP)", RFC 3605, October 2003. 502 [11] Westerlund, M., "A Transport Independent Bandwidth Modifier for 503 the Session Description Protocol (SDP)", RFC 3890, 504 September 2004. 506 [12] Casner, S., "Session Description Protocol (SDP) Bandwidth 507 Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, 508 July 2003. 510 [13] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 511 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 512 RFC 3711, March 2004. 514 10.2. Informative References 516 [14] Clark, D. and D. Tennenhouse, "Architectural Considerations for 517 a New Generation of Protocols", Proceedings of ACM 518 SIGCOMM 1990, September 1990. 520 [15] Casner, S. and S. Deering, "First IETF Internet Audiocast", ACM 521 SIGCOMM Computer Communication Review, Volume 22, Number 3, 522 July 1992. 524 [16] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A 525 Methodology for Network Address Translator (NAT) Traversal for 526 Offer/Answer Protocols", draft-ietf-mmusic-ice-10 (work in 527 progress), August 2006. 529 [17] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP Headers for 530 Low-Speed Serial Links", RFC 2508, February 1999. 532 [18] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H., 533 Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le, K., 534 Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T., 535 Yoshimura, T., and H. Zheng, "RObust Header Compression (ROHC): 536 Framework and four profiles: RTP, UDP, ESP, and uncompressed", 537 RFC 3095, July 2001. 539 Authors' Addresses 541 Colin Perkins 542 University of Glasgow 543 Department of Computing Science 544 17 Lilybank Gardens 545 Glasgow G12 8QQ 546 UK 548 Email: csp@csperkins.org 550 Magnus Westerlund 551 Ericsson 552 Torshamgatan 23 553 Stockholm SE-164 80 554 Sweden 556 Email: magnus.westerlund@ericsson.com 558 Full Copyright Statement 560 Copyright (C) The Internet Society (2006). 562 This document is subject to the rights, licenses and restrictions 563 contained in BCP 78, and except as set forth therein, the authors 564 retain all their rights. 566 This document and the information contained herein are provided on an 567 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 568 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 569 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 570 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 571 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 572 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 574 Intellectual Property 576 The IETF takes no position regarding the validity or scope of any 577 Intellectual Property Rights or other rights that might be claimed to 578 pertain to the implementation or use of the technology described in 579 this document or the extent to which any license under such rights 580 might or might not be available; nor does it represent that it has 581 made any independent effort to identify any such rights. Information 582 on the procedures with respect to rights in RFC documents can be 583 found in BCP 78 and BCP 79. 585 Copies of IPR disclosures made to the IETF Secretariat and any 586 assurances of licenses to be made available, or the result of an 587 attempt made to obtain a general license or permission for the use of 588 such proprietary rights by implementers or users of this 589 specification can be obtained from the IETF on-line IPR repository at 590 http://www.ietf.org/ipr. 592 The IETF invites any interested party to bring to its attention any 593 copyrights, patents or patent applications, or other proprietary 594 rights that may cover technology that may be required to implement 595 this standard. Please address the information to the IETF at 596 ietf-ipr@ietf.org. 598 Acknowledgment 600 Funding for the RFC Editor function is provided by the IETF 601 Administrative Support Activity (IASA).