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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 AVT F. Andreasen 2 Internet-Draft D. Oran 3 Expires: April 24, 2005 D. Wing 4 Cisco Systems, Inc. 5 October 24, 2004 7 RTP No-Op Payload Format 8 draft-wing-avt-rtp-noop-01 10 Status of this Memo 12 This document is an Internet-Draft and is subject to all provisions 13 of section 3 of RFC 3667. By submitting this Internet-Draft, each 14 author represents that any applicable patent or other IPR claims of 15 which he or she is aware have been or will be disclosed, and any of 16 which he or she become aware will be disclosed, in accordance with 17 RFC 3668. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as 22 Internet-Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on April 24, 2005. 37 Copyright Notice 39 Copyright (C) The Internet Society (2004). 41 Abstract 43 This document defines an no-op payload format for the Real-time 44 Transport Protocol (RTP), and a mechanism to request an immediate 45 RTCP report. This can be used to verify RTP connectivity and to keep 46 Network Address Translator (NAT) bindings and Firewall pinholes open. 48 Requirements Language 49 The key words "MUST", "MUST NOT" "REQUIRED", "SHALL", "SHALL NOT", 50 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 51 document are to be interpreted as described in RFC 2119 [1]. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. RTP Payload Format for No-Op . . . . . . . . . . . . . . . . . 3 57 2.1 Registration . . . . . . . . . . . . . . . . . . . . . . . 3 58 2.2 Use of RTP Header Fields . . . . . . . . . . . . . . . . . 3 59 2.3 Payload Format . . . . . . . . . . . . . . . . . . . . . . 4 60 2.4 Sender Operation . . . . . . . . . . . . . . . . . . . . . 4 61 2.5 Mixer, Translator Operation . . . . . . . . . . . . . . . 4 62 2.6 Receiver Operation . . . . . . . . . . . . . . . . . . . . 4 63 2.7 Indication of No-OP Capability using SDP . . . . . . . . . 5 64 3. MIME Registration . . . . . . . . . . . . . . . . . . . . . . 5 65 3.1 audio/no-op . . . . . . . . . . . . . . . . . . . . . . . 5 66 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 67 5. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 69 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 7.1 Normative References . . . . . . . . . . . . . . . . . . . . 7 71 7.2 Informational References . . . . . . . . . . . . . . . . . . 8 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 73 Intellectual Property and Copyright Statements . . . . . . . . 9 75 1. Introduction 77 This memo defines a new RTP payload format called "no-op". This 78 payload behaves like a normal RTP payload, except that it isn't 79 played by the receiver. 81 This new payload format is useful for: 83 o bearer continuity testing, such as at the beginning of a call; 84 o keepalives to keep NAT bindings open when RTP media traffic is not 85 otherwise being transmitted; 86 o performing an RTP traceroute; 88 For testing the RTP path, an RTP sender may transmit several No-Op 89 payload packets with the Request Immediate RTCP bit set to 0, 90 followed by one No-Op payload packet with the Request Immediate RTCP 91 bit set to 1. This would cause the RTP receiver to send an RTCP 92 report indicating the quality of the RTP path. The RTP sender could 93 then decide to continue with call setup, abort the session, or 94 perform some other action. 96 2. RTP Payload Format for No-Op 98 The no-op payload format is carried as part of the RTP stream, and 99 MUST use the same sequence number space, SSRC, and timestamp base as 100 the regular media. 102 2.1 Registration 104 The RTP payload format is designated as "no-op" and the MIME type as 105 "audio/no-op". The default clock rate is 8000 Hz, but other rates 106 MAY be used. In accordance with current practice, this payload 107 format does not have a static payload type number, but uses a RTP 108 payload type number established dynamically and out-of-band. 110 2.2 Use of RTP Header Fields 112 Timestamp: The RTP timestamp reflects the measurement point for the 113 current packet. The receiver calculates jitter for RTCP receiver 114 reports based on all packets with a given timestamp. Note: The 115 jitter value should primarily be used as a means for comparing the 116 reception quality between two users or two time-periods, not as an 117 absolute measure. 118 Marker bit: The RTP marker bit has no special significance for this 119 payload type. 121 2.3 Payload Format 123 The payload format is shown below. 125 0 1 2 3 126 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 1 127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 128 |R| reserved | 129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 130 | padding (OPTIONAL) | 131 | .... | 132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 134 The payload contains at least 4 bytes. The first 32 bits are defined 135 as follows: 137 bit 0: "R", "Request immediate RTCP", is used to request 138 transmission of an immediate RTCP report (see Section 139 2.6). 140 bits 1-31: Reserved; contents are ignored. 142 Additional padding bytes MAY be appended up to the negotiated ptime 143 value in SDP (see Section 2.6). These bytes MUST contain all 0 bits. 144 Padding may be useful to generate RTP packets that are the same size 145 as a normal media payload. 147 2.4 Sender Operation 149 A source MAY send normal RTP audio and the no-op payload format for 150 the same time instants (but with different sequence numbers of 151 course). This might be done in conjunction with this payload 152 format's "Request Immediate RTCP" opcode. 154 2.5 Mixer, Translator Operation 156 An RTP mixer or unicast-to-unicast RTP translator SHOULD forward RTP 157 No-Op payload packets normally. A unicast-to-multicast RTP 158 translator SHOULD replicate RTP No-Op payload packets normally. 160 A multicast-to-unicast RTP translator SHOULD NOT replicate an RTP 161 No-Op packet with the Request Immediate RTCP bit set, because the 162 receivers won't be able to prevent flooding of the multicast RTP 163 sender. 165 2.6 Receiver Operation 167 Upon receipt of an RTP packet with the No-Op payload format and the 168 Send Immediate RTCP Report bit set to 0, the receiver performs normal 169 RTP receive operations on it -- incrementing the RTP receive counter, 170 calculating jitter, and so on. The receiver then discards the packet 171 -- it is not used to play out data. 173 Upon receipt of an RTP packet with the No-Op payload format and the 174 Send Immediate RTCP Report bit set to 1, the receiver performs the 175 steps above and: 177 o if listening on a multicast IP address, the receiver MUST not send 178 an immediate RTCP report, and the receiver MUST follow the normal 179 RTCP transmission rules RFC3550, sections 6.2 and 6.3] [2], and 180 o if listening on a unicast IP address and sending RTP traffic, the 181 receiver prepares to send an RTCP sender report, and 182 o if listening on a unicast IP address and receiving RTP traffic, 183 the receiver prepares to send an RTCP receiver report. 185 In all cases, before actually sending its RTCP report, the RTCP 186 bandwidth limits and randomization interval MUST be observed RFC3550, 187 sections 6.2 and 6.3 [2], most especially when multiple SSRCs are in 188 the same session. 190 2.7 Indication of No-OP Capability using SDP 192 Senders and receivers may indicate support for the No-Op payload 193 format, for example, by using the Session Description Protocol SDP 194 [3]. 196 If successful completion of RTP No-Op is required before completing 197 call establishment -- such as to verify the existence or quality of 198 the bearer path -- connectivity preconditions [4] can be used. 200 The default packetization interval for this payload type is 20ms 201 (ptime:20) but alternate values can be advertised in SDP using the 202 ptime attribute value [3]. 204 3. MIME Registration 206 3.1 audio/no-op 208 MIME media type name: audio 210 MIME subtype name: no-op 212 Required parameters: none 214 Optional parameters: none 216 Encoding considerations: This type is only defined for transfer via 217 RTP [2]. 219 Security considerations: See Section 4, "Security Considerations", in 220 this document. 222 Interoperability considerations: none 224 Published specification: This document. 226 Applications which use this media: The "no-op" audio subtype is used 227 to maintain network state or verify network connectivity, when a more 228 traditional RTP payload type cannot be used. 230 Additional information: 232 1. Magic number(s): N/A 233 2. File extension(s): N/A 234 3. Macintosh file type code: N/A 236 4. Security Considerations 238 Without security of the RTP stream (via SRTP [6], IPsec [5], or other 239 means), it is possible for an attacker to spoof RTP packets, 240 including this new packet type. As this new RTP payload type 241 includes a method to request immediate transmission of RTCP, this 242 could be used to cause endpoints to flood the network with RTCP 243 reports. Thus, the RTCP transmissions MUST NOT exceed the bandwidth 244 recommendations described in section 6.3 of RFC3550 [2]. 246 5. Open Issues 248 1. Issues brought up during IETF59: 249 A. Roni Even asked why only the audio/noop MIME type is listed? 250 The answer is that there is no reason for not having it for 251 all media types in use. The draft is simply missing 252 registration of all the media types that are appropriate. 253 B. Dan Romascanu noted that it is not very clear from the draft 254 how you can determine the actual media path characteristics 255 through the use of RTCP, and how to separate the reception 256 quality reports for the NOOP traffic from other media 257 traffic. Flemming noted that the RTP SSRC can be used to 258 separate traffic, and promised to work on the text, 259 clarifying this. 260 C. Magnus Westerlund and Colin Perkins noted that the draft is 261 unclear on the interactions between its immediate feedback 262 request and the usual RTCP timers (in both the standard A/V 263 profile and in the RTCP feedback profile). Clarification was 264 requested. 266 D. Jonathan Rosenberg was doubtful of the need to request 267 immediate RTCP reports. He supported the functionality of an 268 RTP payload format that is discarded, to keep NAT bindings 269 alive when media is on hold, but asked the group to consider 270 the need for requesting immediate RTCP reports and to clarify 271 the problem and requirements before jumping into the solution 272 space. 273 E. Jonathan also noted, as he did in the MMUSIC session, that 274 ICE and STUN would still be needed for NAT traversal, and so 275 can't be replaced with this mechanism. 276 F. Roni Even also commented that the use case for checking the 277 MTU might need feedback, however the QoS diagnostic does look 278 like a different issue. 279 G. Colin Perkins concluded that the draft must be updated and 280 clarified on use cases, and what problems it solves. 281 2. Discuss how this relates to AVPF. 282 3. Need to expand on the RTCP transmission interval considerations 283 and explain in more detail when you can and cannot transmit 284 (i.e., does not modify/violate normal RTCP considerations) 285 4. Should "request immediate RTCP" be a generic mechanism? 286 5. Clarify usefulness of Noop for diagnostics. 287 6. Clarify how the packet counting, etc. works. Should explain a 288 bit more in document (e.g. how everything is on a per SSRC 289 basis, packet counting works and is revealed in the RTCP reports, 290 etc.). The document isn't clear on this. 292 6. Acknowledgments 294 Thanks to Henning Schulzrinne for suggesting using RTCP as a feedback 295 mechanism. 297 7. References 299 7.1 Normative References 301 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 302 Levels", BCP 14, RFC 2119, March 1997. 304 [2] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, 305 "RTP: A Transport Protocol for Real-Time Applications", STD 64, 306 RFC 3550, July 2003. 308 [3] Handley, M. and V. Jacobson, "SDP: Session Description 309 Protocol", RFC 2327, April 1998. 311 [4] Andreasen, F., "Connectivity Preconditions for Session 312 Description Protocol Media Streams", 313 draft-andreasen-mmusic-connectivityprecondition-00 (work in 314 progress), February 2004. 316 7.2 Informational References 318 [5] Kent, S. and R. Atkinson, "Security Architecture for the 319 Internet Protocol", RFC 2401, November 1998. 321 [6] Baugher, M., McGrew, D., Naslund, M., Carrara, E. and K. 322 Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 323 3711, March 2004. 325 Authors' Addresses 327 Flemming Andreasen 328 Cisco Systems, Inc. 329 499 Thornall Street, 8th Floor 330 Edison, NJ 08837 331 USA 333 EMail: fandreas@cisco.com 335 David Oran 336 Cisco Systems, Inc. 337 7 Ladyslipper Lane 338 Acton, MA 01720 339 USA 341 EMail: oran@cisco.com 343 Dan Wing 344 Cisco Systems, Inc. 345 170 West Tasman Drive 346 San Jose, CA 95134 347 USA 349 EMail: dwing@cisco.com 351 Intellectual Property Statement 353 The IETF takes no position regarding the validity or scope of any 354 Intellectual Property Rights or other rights that might be claimed to 355 pertain to the implementation or use of the technology described in 356 this document or the extent to which any license under such rights 357 might or might not be available; nor does it represent that it has 358 made any independent effort to identify any such rights. 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