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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (March 21, 2016) is 2956 days in the past. 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) == Unused Reference: 'KEYWORDS' is defined on line 308, but no explicit reference was found in the text == Unused Reference: 'RFC3550' is defined on line 323, but no explicit reference was found in the text -- Obsolete informational reference (is this intentional?): RFC 5285 (Obsoleted by RFC 8285) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Berger 3 Internet-Draft S. Nandakumar 4 Intended status: Standards Track M. Zanaty 5 Expires: September 22, 2016 Cisco Systems 6 March 21, 2016 8 Frame Marking RTP Header Extension 9 draft-ietf-avtext-framemarking-01 11 Abstract 13 This document describes a Frame Marking RTP header extension used to 14 convey information about video frames that is critical for error 15 recovery and packet forwarding in RTP middleboxes or network nodes. 16 It is most useful when media is encrypted, and essential when the 17 middlebox or node has no access to the media encryption keys. It is 18 also useful for codec-agnostic processing of encrypted or unencrypted 19 media, while it also supports extensions for codec-specific 20 information. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 22, 2016. 39 Copyright Notice 41 Copyright (c) 2016 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2.1. Mandatory Extension . . . . . . . . . . . . . . . . . . . 4 59 2.2. Layer ID Mappings . . . . . . . . . . . . . . . . . . . . 5 60 2.2.1. H265 LID Mapping . . . . . . . . . . . . . . . . . . 5 61 2.2.2. VP9 LID Mapping . . . . . . . . . . . . . . . . . . . 5 62 2.2.3. VP8 LID Mapping . . . . . . . . . . . . . . . . . . . 5 63 2.2.4. H264-SVC LID Mapping . . . . . . . . . . . . . . . . 5 64 2.2.5. H264 (AVC) LID Mapping . . . . . . . . . . . . . . . 6 65 2.3. Signaling information . . . . . . . . . . . . . . . . . . 6 66 2.4. Considerations on use . . . . . . . . . . . . . . . . . . 6 67 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 68 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 69 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 70 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 71 6.1. Normative References . . . . . . . . . . . . . . . . . . 7 72 6.2. Informative References . . . . . . . . . . . . . . . . . 7 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 75 1. Introduction 77 Many widely deployed RTP topologies used in modern voice and video 78 conferencing systems include a centralized component that acts as an 79 RTP switch. It receives voice and video streams from each 80 participant, which may be encrypted using SRTP [RFC3711], or 81 extensions that provide participants with private media via end-to- 82 end encryption that excludes the switch. The goal is to provide a 83 set of streams back to the participants which enable them to render 84 the right media content. In a simple video configuration, for 85 example, the goal will be that each participant sees and hears just 86 the active speaker. In that case, the goal of the switch is to 87 receive the voice and video streams from each participant, determine 88 the active speaker based on energy in the voice packets, possibly 89 using the client-to-mixer audio level RTP header extension, and 90 select the corresponding video stream for transmission to 91 participants; see Figure 1. 93 In this document, an "RTP switch" is used as a common short term for 94 the terms "switching RTP mixer", "source projecting middlebox", 95 "source forwarding unit/middlebox" and "video switching MCU" as 96 discussed in [I-D.ietf-avtcore-rtp-topologies-update]. 98 +---+ +------------+ +---+ 99 | A |<---->| |<---->| B | 100 +---+ | | +---+ 101 | RTP | 102 +---+ | Switch | +---+ 103 | C |<---->| |<---->| D | 104 +---+ +------------+ +---+ 106 Figure 1: RTP switch 108 In order to properly support switching of video streams, the RTP 109 switch typically needs some critical information about video frames 110 in order to start and stop forwarding streams. 112 o Because of inter-frame dependencies, it should ideally switch 113 video streams at a point where the first frame from the new 114 speaker can be decoded by recipients without prior frames, e.g 115 switch on an intra-frame. 116 o In many cases, the switch may need to drop frames in order to 117 realize congestion control techniques, and needs to know which 118 frames can be dropped with minimal impact to video quality. 119 o Furthermore, it is highly desirable to do this in a way which is 120 not specific to the video codec. Nearly all modern video codecs 121 share common concepts around frame types. 122 o It is also desirable to be able to do this for SRTP without 123 requiring the video switch to decrypt the packets. SRTP will 124 encrypt the RTP payload format contents and consequently this data 125 is not usable for the switching function without decryption, which 126 may not even be possible in the case of end-to-end encryption of 127 private media. 129 A comprehensive discussion of SFU considerations around codec 130 agnostic selective forwarding of RTP media is described in 131 [I-D.draft-aboba-avtcore-sfu-rtp] 133 By providing meta-information about the RTP streams outside the 134 encrypted media payload an RTP switch can do selective forwarding 135 without decrypting the payload. This document provides a solution to 136 this problem. 138 2. Solution 140 The solution uses RTP header extensions as defined in [RFC5285]. A 141 subset of meta-information from the video stream is provided as an 142 RTP header extension to allow an RTP switch to do generic selective 143 forwarding of video streams encoded with potentially different video 144 codecs. 146 2.1. Mandatory Extension 148 The following information are extracted from the media payload and 149 sent in the Frame Marking RTP header extension. 151 o S: Start of Frame (1 bit) - MUST be 1 in the first packet in a 152 frame within a layer; otherwise MUST be 0. 153 o E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame 154 within a layer; otherwise MUST be 0. 155 o I: Independent Frame (1 bit) - MUST be 1 for frames that can be 156 decoded independent of prior frames, e.g. intra-frame, VPx 157 keyframe, H.264 IDR [RFC6184], H.265 CRA/BLA; otherwise MUST be 0. 158 o D: Discardable Frame (1 bit) - MUST be 1 for frames that can be 159 dropped, and still provide a decodable media stream; otherwise 160 MUST be 0. 161 o B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends 162 on the base layer; otherwise MUST be 0. 163 o TID: Temporal ID (3 bits) - The base temporal layer starts with 0, 164 and increases with 1 for each higher temporal layer/sub-layer. 165 o LID: Layer ID (8 bits) - Identifies the spatial and quality layer 166 encoded. 168 The layer information contained in TID and LID convey useful aspects 169 of the layer structure that can be utilized in selective forwarding. 170 Without further information about the layer structure, these 171 identifiers can only be used for relative priority of layers. They 172 convey a layer hierarchy with TID=0 and LID=0 identifying the base 173 layer. Higher values of TID identify higher temporal layers with 174 higher frame rates. Higher values of LID identify higher spatial or 175 quality layers with higher resolutions and bitrates. 177 With further information, for example, possible future RTCP SDES 178 items that convey full layer structure information, it may be 179 possible to map these TIDs and LIDs to specific frame rates, 180 resolutions and bitrates. Such additional layer information may be 181 useful to forwarding decisions in the RTP switch, but is beyond the 182 scope of this memo. The relative layer information is still useful 183 for many selective forwarding decisions even without such additional 184 layer information. 186 The Frame Marking RTP header extension is encoded using the one-byte 187 header as described in [RFC5285] as shown below. 189 0 1 2 190 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 | ID=2 | L=1 |S|E|I|D|B| TID | LID | 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 2.2. Layer ID Mappings 197 2.2.1. H265 LID Mapping 199 The following shows H265-LayerID (6 bits) mapped to the generic LID 200 field. 202 0 1 2 203 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 205 | ID=2 | L=1 |S|E|I|D|B| TID |0|0| LayerID | 206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 2.2.2. VP9 LID Mapping 210 The following shows VP9 Layer encoding information (4 bits for 211 spatial and quality) mapped to the generic LID field. 213 0 1 2 214 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0| RS| RQ| 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 2.2.3. VP8 LID Mapping 221 The following shows the header extension for VP8 that contains no 222 layer information. 224 0 1 2 225 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 2.2.4. H264-SVC LID Mapping 232 The following shows H264-SVC Layer encoding information (3 bits for 233 spatial and 4 bits quality) mapped to the generic LID field. 235 0 1 2 236 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 | ID=2 | L=1 |S|E|I|D|B| TID |0| DID | QID | 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 241 2.2.5. H264 (AVC) LID Mapping 243 The following shows the header extension for H264 (AVC) that contains 244 no layer information. 246 0 1 2 247 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| 250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 2.3. Signaling information 254 The URI for declaring this header extension in an extmap attribute is 255 "urn:ietf:params:rtp-hdrext:framemarking". It does not contain any 256 extension attributes. 258 An example attribute line in SDP: 260 a=extmap:3 urn:ietf:params:rtp-hdrext:framemarking 262 2.4. Considerations on use 264 The header extension values MUST represent what is already in the RTP 265 payload. 267 When a RTP switch needs to discard a received video frame due to 268 congestion control considerations, it is RECOMMENDED that it 269 preferably drop frames marked with the "discardable" bit. 271 When a RTP switch wants to forward a new video stream to a receiver, 272 it is RECOMMENDED to select the new video stream from the first 273 switching point (I bit set) and forward the same. A RTP switch can 274 request a media source to generate a switching point for H.264 by 275 sending Full Intra Request (RTCP FIR) as defined in [RFC5104], for 276 example. 278 3. Security Considerations 280 In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP 281 header extensions are authenticated but not encrypted. When header 282 extensions are used some of the payload type information are exposed 283 and is visible to middle boxes. The encrypted media data is not 284 exposed, so this is not seen as a high risk exposure. 286 4. Acknowledgements 288 Many thanks to Bernard Aboba, Jonathan Lennox for their inputs. 290 5. IANA Considerations 292 This document defines a new extension URI to the RTP Compact 293 HeaderExtensions sub-registry of the Real-Time Transport Protocol 294 (RTP) Parameters registry, according to the following data: 296 Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo 297 Description: Frame marking information for video streams 298 Contact: espeberg@cisco.com 299 Reference: RFC XXXX 301 Note to RFC Editor: please replace RFC XXXX with the number of this 302 RFC. 304 6. References 306 6.1. Normative References 308 [KEYWORDS] 309 Bradner, S., "Key words for use in RFCs to Indicate 310 Requirement Levels", BCP 14, RFC 2119, March 1997. 312 6.2. Informative References 314 [I-D.ietf-avtcore-rtp-topologies-update] 315 Westerlund, M. and S. Wenger, "RTP Topologies", draft- 316 ietf-avtcore-rtp-topologies-update (work in progress), 317 April 2013. 319 [I-D.draft-aboba-avtcore-sfu-rtp] 320 Aboba, B., "Codec-Independent Selective Forwarding", raft- 321 aboba-avtcore-sfu-rtp-00 (work in progress), July 2015. 323 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 324 Jacobson, "RTP: A Transport Protocol for Real-Time 325 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 326 July 2003, . 328 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 329 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 330 RFC 3711, DOI 10.17487/RFC3711, March 2004, 331 . 333 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 334 "Codec Control Messages in the RTP Audio-Visual Profile 335 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 336 February 2008, . 338 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 339 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 340 2008, . 342 [RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP 343 Payload Format for H.264 Video", RFC 6184, 344 DOI 10.17487/RFC6184, May 2011, 345 . 347 Authors' Addresses 349 Espen Berger 350 Cisco Systems 352 Phone: +47 98228179 353 Email: espeberg@cisco.com 355 Suhas Nandakumar 356 Cisco Systems 357 170 West Tasman Drive 358 San Jose, CA 95134 359 US 361 Email: snandaku@cisco.com 363 Mo Zanaty 364 Cisco Systems 365 170 West Tasman Drive 366 San Jose, CA 95134 367 US 369 Email: mzanaty@cisco.com