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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT F. Andreasen 3 Internet-Draft D. Oran 4 Expires: November 27, 2005 D. Wing 5 Cisco Systems, Inc. 6 May 26, 2005 8 A No-Op Payload Format for RTP 9 draft-ietf-avt-rtp-no-op-00 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 November 27, 2005. 36 Copyright Notice 38 Copyright (C) The Internet Society (2005). 40 Abstract 42 This document defines an no-op payload format for the Real-time 43 Transport Protocol (RTP), and a mechanism to request transmission of 44 an early RTCP report. This can be used to verify RTP connectivity 45 and to keep Network Address Translator (NAT) bindings and Firewall 46 pinholes open. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. RTP Payload Format for No-Op . . . . . . . . . . . . . . . . . 4 52 2.1 Registration . . . . . . . . . . . . . . . . . . . . . . . 4 53 2.2 Use of RTP Header Fields . . . . . . . . . . . . . . . . . 4 54 2.3 Payload Format . . . . . . . . . . . . . . . . . . . . . . 4 55 2.4 Sender Operation . . . . . . . . . . . . . . . . . . . . . 5 56 2.5 Mixer, Translator Operation . . . . . . . . . . . . . . . 5 57 2.6 Receiver Operation . . . . . . . . . . . . . . . . . . . . 5 58 2.7 Indication of No-OP Capability using SDP . . . . . . . . . 6 59 3. Example SDP Offer/Answer . . . . . . . . . . . . . . . . . . . 6 60 4. MIME Registration . . . . . . . . . . . . . . . . . . . . . . 7 61 4.1 audio/no-op . . . . . . . . . . . . . . . . . . . . . . . 7 62 4.2 video/no-op . . . . . . . . . . . . . . . . . . . . . . . 8 63 4.3 text/no-op . . . . . . . . . . . . . . . . . . . . . . . . 8 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 66 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 67 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 68 8.1 Normative References . . . . . . . . . . . . . . . . . . . 9 69 8.2 Informational References . . . . . . . . . . . . . . . . . 10 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10 71 Intellectual Property and Copyright Statements . . . . . . . . 12 73 1. Introduction 75 This memo defines a new RTP payload format called "no-op". This 76 payload behaves like a normal RTP payload, except the RTP packet is 77 not used to play out media. It is also explicitly designed to 78 interact constructively with the RTCP feedback profile [6]. 80 This new payload format is useful for: 82 o media session reception quality assessment, such as at the 83 beginning of a session; 84 o keepalives to keep NAT bindings and/or firewall pinholes open when 85 RTP media traffic is not otherwise being transmitted. 87 In addition it has a number of uses whose utility is speculative but 88 for which it is easy pressed into service: 90 o measurement-based admission control by probing available 91 bandwidth, and 92 o synthetic load generation for performance testing and other 93 minimally-intrusive instrumentation. 95 When an endpoint mas a media stream marked as 'recvonly' or 96 'inactive' the endpoint is not supposed to send any media (i.e. RTP 97 packets). However, to keep a NAT binding alive, the endpoint will 98 need to send packets over the RTP and RTCP ports. RTP No-Op is 99 ideally suited to this. In comparison, if one participant in an 100 audio multicast conference has a 'recvonly' or 'inactive' media 101 stream yet occasionally sends comfort noise packets in order to keep 102 its NAT binding open, these comfort noise packets are interpreted as 103 audio packets by receivers and mixers which can cause undesirable 104 behavior -- such as selection of the primary speaker or the playout 105 of comfort noise when no audio should be played. 107 Unlike Comfort noise [9], which is specific to voice RTP streams, RTP 108 No-Op is applicable to any kind of RTP stream including video, audio, 109 realtime text, or any other media type that would benefit from the 110 capabilities listed above. This gives RTP No-Op an advantage as a 111 NAT keepalive mechanism. Certain functions and RTP payload types can 112 use RTP No-Op without re-inventing their own payload-specific NAT 113 keepalive mechanism -- such as video muting, Clearmode [10], and text 114 [11]. 116 Some audio codecs have their own 'silence' packets. However, some 117 codecs only send such 'silence' packets if the noise floor changes; 118 G.729b [12] is an example of such a codec. RTP No-Op allows the RTP 119 stack itself, rather than the codec, to send periodic packets as a 120 keepalive mechanism. 122 The key words "MUST", "MUST NOT" "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 124 document are to be interpreted as described in RFC 2119 [1]. 126 2. RTP Payload Format for No-Op 128 2.1 Registration 130 The RTP payload format is designated as "no-op" and the MIME types 131 are "audio/no-op", "video/no-op", and "text/no-op". The default 132 clock rate is 8000 Hz, but other rates MAY be used. In accordance 133 with current practice, this payload format does not have a static 134 payload type number, but uses a RTP payload type number established 135 dynamically out-of-band, e.g. through SDP [4]. 137 2.2 Use of RTP Header Fields 139 Timestamp: The RTP timestamp reflects the measurement point for the 140 current packet. The receiver calculates jitter for RTCP receiver 141 reports based on all packets with a given timestamp. Note: The 142 jitter value should primarily be used as a means for comparing the 143 reception quality between two users or two time-periods, not as an 144 absolute measure. 145 Marker bit: The RTP marker bit has no special significance for this 146 payload type. 148 2.3 Payload Format 150 The payload format is shown below. 152 0 1 2 3 153 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 |R| reserved | 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 157 | padding (OPTIONAL) | 158 | .... | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 The payload contains at least 4 bytes. The first 32 bits are defined 162 as follows: 164 bit 0: "R", "Request Early RTCP", is used to request invocation 165 of RTCP feedback by timely transmission of an RTCP report 166 (see Section 2.6). 168 bits 1-31: Reserved; contents are ignored. 170 Additional padding bytes MAY be appended up to the ptime value in SDP 171 (see Section 2.7). These bytes are ignored. Padding may be useful 172 to generate RTP packets that are the same size as a normal media 173 payload. 175 2.4 Sender Operation 177 As discussed in the introduction, endpoints MUST occasionally send a 178 packet to their RTP and RTCP peer to keep NAT and firewall bindings 179 active, even if the media stream is marked 'recvonly' or 'inactive'. 180 If no other RTP packet has been sent for approximately 30 seconds, an 181 RTP No-Op packet SHOULD be sent. It is permissible to send a No-Op 182 packet even for media streams marked 'recvonly' or 'inactive'. 184 2.5 Mixer, Translator Operation 186 An RTP mixer or unicast-to-unicast RTP translator SHOULD forward RTP 187 No-Op payload packets normally. A unicast-to-multicast RTP 188 translator SHOULD replicate RTP No-Op payload packets normally. 190 A multicast-to-unicast RTP translator SHOULD NOT replicate an RTP 191 No-Op packet with the Request Early RTCP bit set unless: 193 1. all receivers are known to be operating under the bandwidth 194 limitations rules of [6], and 195 2. the restriction of applicability to "small groups" in [6] is 196 observed 197 Otherwise the sender may be flooded with RTCP reports. 199 2.6 Receiver Operation 201 Upon receipt of an RTP packet with the No-Op payload format and the 202 'Request Early RTCP Report' bit set to 0, the receiver performs 203 normal RTP receive operations on it -- incrementing the RTP receive 204 counter, calculating jitter, and so on. The receiver then discards 205 the packet -- it is not used to play out media. 207 Upon receipt of an RTP packet with the No-Op payload format and the 208 'Request Early RTCP Report' bit set to 1, the receiver adjusts 209 counters as described above and then also performs the following 210 steps (with reference to the definitions and procedures of the AVPF 211 profile [6]): 213 1. ascertains whether the associated RTP session is operating under 214 the AVPF RTP profile (or one derived from it via combination with 215 another RTP profile). If not the receiver takes no further 216 action on this packet - specifically, if the RTP/AVPF profile (or 217 one derived from it) is not used the receiver MUST NOT send an 218 early RTCP report. If so, it continues as follows. 219 2. generates a feedback "Event" which in turn may trigger the 220 generation of a "FB message". 221 3. sends the FB message as an "early RTCP packet" assuming the 222 bandwidth constraints for feedback messages are satisfied. 223 4. Otherwise, takes no further action 225 2.7 Indication of No-OP Capability using SDP 227 Senders and receivers may indicate support for the No-Op payload 228 format, for example, by using the Session Description Protocol SDP 229 [4]. If the payload format is being used for connectivity 230 verification (e.g. in conjunction with [5]) senders and receivers 231 MUST advertise the AVPF profile (or a profile used in combination 232 with it). 234 The default packetization interval for this payload type is 20ms 235 (ptime:20) but alternate values can be advertised in SDP using the 236 ptime attribute value [4]. 238 3. Example SDP Offer/Answer 240 Offer: 241 v=0 242 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com 243 s=- 244 c=IN IP4 host.atlanta.example.com 245 t=0 0 246 m=audio 49170 RTP/AVPF 0 33 247 a=rtpmap:0 PCMU/8000 248 a=rtpmap:33 no-op/8000 249 m=video 41372 RTP/AVPF 31 36 250 a=rtpmap:31 H261/90000 251 a=rtpmap:36 no-op/90000 253 Answer: 254 v=0 255 o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com 256 s=- 257 c=IN IP4 host.biloxi.example.com 258 t=0 0 259 m=audio 59174 RTP/AVPF 0 33 260 a=rtpmap:0 PCMU/8000 261 a=rtpmap:33 no-op/8000 262 m=video 59170 RTP/AVPF 32 36 263 a=rtpmap:31 H261/90000 264 a=rtpmap:36 no-op/90000 266 4. MIME Registration 268 This section registers MIME types for audio/no-op, video/no-op, and 269 text/no-op. 271 4.1 audio/no-op 273 MIME media type name: audio 275 MIME subtype name: no-op 277 Required parameters: none 279 Optional parameters: none 281 Encoding considerations: This type is only defined for transfer via 282 RTP [2] and Secure RTP [3]. 284 Security considerations: See Section 5, "Security Considerations", in 285 this document. 287 Interoperability considerations: none 289 Published specification: This document. 291 Applications which use this media: The "no-op" application subtype is 292 used to maintain network state or verify network connectivity, when a 293 more traditional RTP payload type cannot be used. 295 Additional information: 297 1. Magic number(s): N/A 298 2. File extension(s): N/A 299 3. Macintosh file type code: N/A 301 4.2 video/no-op 303 MIME media type name: video 305 MIME subtype name: no-op 307 Required parameters: none 309 Optional parameters: none 311 Encoding considerations: This type is only defined for transfer via 312 RTP [2] and Secure RTP [3]. 314 Security considerations: See Section 5, "Security Considerations", in 315 this document. 317 Interoperability considerations: none 319 Published specification: This document. 321 Applications which use this media: The "no-op" application subtype is 322 used to maintain network state or verify network connectivity, when a 323 more traditional RTP payload type cannot be used. 325 Additional information: 327 1. Magic number(s): N/A 328 2. File extension(s): N/A 329 3. Macintosh file type code: N/A 331 4.3 text/no-op 333 MIME media type name: text 335 MIME subtype name: no-op 337 Required parameters: none 339 Optional parameters: none 341 Encoding considerations: This type is only defined for transfer via 342 RTP [2] and Secure RTP [3]. 344 Security considerations: See Section 5, "Security Considerations", in 345 this document. 347 Interoperability considerations: none 349 Published specification: This document. 351 Applications which use this media: The "no-op" application subtype is 352 used to maintain network state or verify network connectivity, when a 353 more traditional RTP payload type cannot be used. 355 Additional information: 357 1. Magic number(s): N/A 358 2. File extension(s): N/A 359 3. Macintosh file type code: N/A 361 5. Security Considerations 363 Without security of the RTP stream (via SRTP [3], IPsec [8], or other 364 means), it is possible for an attacker to spoof RTP packets, 365 including this new packet type. As this new RTP payload type 366 includes a method to request early transmission of RTCP, this could 367 be used to cause endpoints to flood the network with RTCP reports. 368 Thus, the RTCP transmissions MUST NOT exceed the bandwidth 369 recommendations described in section 6.3 of RFC3550 [2]. 371 6. IANA Considerations 373 IANA is requested to make MIME type registrations as specified above 374 in Section 4 376 7. Acknowledgments 378 Thanks to Henning Schulzrinne for suggesting using RTCP as a feedback 379 mechanism. 381 8. References 383 8.1 Normative References 385 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 386 Levels", BCP 14, RFC 2119, March 1997. 388 [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 389 "RTP: A Transport Protocol for Real-Time Applications", STD 64, 390 RFC 3550, July 2003. 392 [3] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 393 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 394 RFC 3711, March 2004. 396 [4] Handley, M. and V. Jacobson, "SDP: Session Description 397 Protocol", RFC 2327, April 1998. 399 [5] Andreasen, F., "Connectivity Preconditions for Session 400 Description Protocol Media Streams", 401 draft-andreasen-mmusic-connectivityprecondition-02 (work in 402 progress), February 2005. 404 [6] Ott, J. and S. Wenger, "Extended RTP Profile for RTCP-based 405 Feedback(RTP/AVPF)", draft-ietf-avt-rtcp-feedback-11 (work in 406 progress), August 2004. 408 [7] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A 409 Methodology for Network Address Translator (NAT) Traversal for 410 Multimedia Session Establishment Protocols", 411 draft-ietf-mmusic-ice-04 (work in progress), February 2005. 413 8.2 Informational References 415 [8] Kent, S. and R. Atkinson, "Security Architecture for the 416 Internet Protocol", RFC 2401, November 1998. 418 [9] Zopf, R., "Real-time Transport Protocol (RTP) Payload for 419 Comfort Noise (CN)", RFC 3389, September 2002. 421 [10] Kreuter, R., "RTP Payload Format for a 64 kbit/s Transparent 422 Call", RFC 4040, April 2005. 424 [11] Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793, 425 May 2000. 427 [12] International Telecommunications Union, "G.729 Annex B", 428 November 1999, 429 . 431 Authors' Addresses 433 Flemming Andreasen 434 Cisco Systems, Inc. 435 499 Thornall Street, 8th Floor 436 Edison, NJ 08837 437 USA 439 Email: fandreas@cisco.com 440 David Oran 441 Cisco Systems, Inc. 442 7 Ladyslipper Lane 443 Acton, MA 01720 444 USA 446 Email: oran@cisco.com 448 Dan Wing 449 Cisco Systems, Inc. 450 170 West Tasman Drive 451 San Jose, CA 95134 452 USA 454 Email: dwing@cisco.com 456 Intellectual Property Statement 458 The IETF takes no position regarding the validity or scope of any 459 Intellectual Property Rights or other rights that might be claimed to 460 pertain to the implementation or use of the technology described in 461 this document or the extent to which any license under such rights 462 might or might not be available; nor does it represent that it has 463 made any independent effort to identify any such rights. 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