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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (October 19, 2015) is 3110 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 296, but no explicit reference was found in the text == Unused Reference: 'RFC3550' is defined on line 311, 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: April 21, 2016 Cisco Systems 6 October 19, 2015 8 Frame Marking RTP Header Extension 9 draft-ietf-avtext-framemarking-00 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 April 21, 2016. 39 Copyright Notice 41 Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . 4 60 2.2.1. H265 LID Mapping . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . . . . . . 5 65 2.3. Signaling information . . . . . . . . . . . . . . . . . . 6 66 2.4. Considerations on use . . . . . . . . . . . . . . . . . . 6 67 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 68 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 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 a RTP switch to do generic video 143 switching handling of video streams encoded with different video 144 codecs. 146 2.1. Mandatory Extension 148 The following information are extracted from the media payload: 150 o S: Start of Frame (1 bit) - MUST be 1 in the first packet in a 151 frame within a layer; otherwise MUST be 0. 152 o E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame 153 within a layer; otherwise MUST be 0. 154 o I: Independent Frame (1 bit) - MUST be 1 for frames that can be 155 decoded independent of prior frames, e.g. intra-frame, VPx 156 keyframe, H.264 IDR [RFC6184], H.265 CRA/BLA; otherwise MUST be 0. 157 o D: Discardable Frame (1 bit) - MUST be 1 for frames that can be 158 dropped, and still provide a decodable media stream; otherwise 159 MUST be 0. 160 o B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends 161 on the base layer; otherwise MUST be 0. 162 o TID: Temporal ID (3 bits) - The base temporal quality starts with 163 0, and increases with 1 for each temporal layer/sub-layer. 164 o LID: Layer ID (8 bits) - Identifies the spatial and quality layer 165 encoded. 167 NOTE:Given the opaque nature of the LID, consider having the layer 168 structure information as RTCP SDES item (either in the RTCP SDES 169 message or as the RTP SDES Header extension) to map the LIDs to 170 specific resolutions and bitrates thus enabling the RTP Switch to 171 make informed decisions 173 The values of frame information can be carried as RTP header 174 extensions encoded using the one-byte header as described in 175 [RFC5285] as shown below. 177 0 1 2 178 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 180 | ID=2 | L=1 |S|E|I|D|B| TID | LID | 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 2.2. Layer ID Mappings 185 2.2.1. H265 LID Mapping 187 The following shows H265-LayerID (6 bits) mapped to the generic LID 188 field. 190 0 1 2 191 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | ID=2 | L=1 |S|E|I|D|B| TID |0|0| LayerID | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 196 2.2.2. VP9 LID Mapping 198 The following shows VP9 Layer encoding information (4 bits for 199 spatial and quality) mapped to the generic LID field. 201 0 1 2 202 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0| RS| RQ| 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 207 2.2.3. VP8 LID Mapping 209 The following shows the header extension for VP8 that contains no 210 layer information. 212 0 1 2 213 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 2.2.4. H264-SVC LID Mapping 220 The following shows H264-SVC Layer encoding information (3 bits for 221 spatial and 4 bits quality) mapped to the generic LID field. 223 0 1 2 224 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 | ID=2 | L=1 |S|E|I|D|B| TID |0| DID | QID | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 2.2.5. H264 (AVC) LID Mapping 231 The following shows the header extension for H264 (AVC) that contains 232 no layer information. 234 0 1 2 235 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 2.3. Signaling information 242 The URI for declaring this header extension in an extmap attribute is 243 "urn:ietf:params:rtp-hdrext:framemarkinginfo". It does not contain 244 any extension attributes. 246 An example attribute line in SDP: 248 a=extmap:3 urn:ietf:params:rtp-hdrext:framemarkinginfo 250 2.4. Considerations on use 252 The header extension values MUST represent what is already in the RTP 253 payload. 255 When a RTP switch needs to discard a received video frame due to 256 congestion control considerations, it is RECOMMENDED that it 257 preferably drop frames marked with the "discardable" bit. 259 When a RTP switch wants to forward a new video stream to a receiver, 260 it is RECOMMENDED to select the new video stream from the first 261 switching point (I bit set) and forward the same. A RTP switch can 262 request a media source to generate a switching point for H.264 by 263 sending Full Intra Request (RTCP FIR) as defined in [RFC5104], for 264 example. 266 3. Security Considerations 268 In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP 269 header extensions are authenticated but not encrypted. When header 270 extensions are used some of the payload type information are exposed 271 and is visible to middle boxes. The encrypted media data is not 272 exposed, so this is not seen as a high risk exposure. 274 4. Acknowledgements 276 Many thanks to Bernard Aboba, Jonathan Lennox for their inputs. 278 5. IANA Considerations 280 This document defines a new extension URI to the RTP Compact 281 HeaderExtensions sub-registry of the Real-Time Transport Protocol 282 (RTP) Parameters registry, according to the following data: 284 Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo 285 Description: Frame marking information for video streams 286 Contact: espeberg@cisco.com 287 Reference: RFC XXXX 289 Note to RFC Editor: please replace RFC XXXX with the number of this 290 RFC. 292 6. References 294 6.1. Normative References 296 [KEYWORDS] 297 Bradner, S., "Key words for use in RFCs to Indicate 298 Requirement Levels", BCP 14, RFC 2119, March 1997. 300 6.2. Informative References 302 [I-D.ietf-avtcore-rtp-topologies-update] 303 Westerlund, M. and S. Wenger, "RTP Topologies", draft- 304 ietf-avtcore-rtp-topologies-update (work in progress), 305 April 2013. 307 [I-D.draft-aboba-avtcore-sfu-rtp] 308 Aboba, B., "Codec-Independent Selective Forwarding", raft- 309 aboba-avtcore-sfu-rtp-00 (work in progress), July 2015. 311 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 312 Jacobson, "RTP: A Transport Protocol for Real-Time 313 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 314 July 2003, . 316 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 317 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 318 RFC 3711, DOI 10.17487/RFC3711, March 2004, 319 . 321 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 322 "Codec Control Messages in the RTP Audio-Visual Profile 323 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 324 February 2008, . 326 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 327 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 328 2008, . 330 [RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP 331 Payload Format for H.264 Video", RFC 6184, DOI 10.17487/ 332 RFC6184, May 2011, 333 . 335 Authors' Addresses 337 Espen Berger 338 Cisco Systems 340 Phone: +47 98228179 341 Email: espeberg@cisco.com 343 Suhas Nandakumar 344 Cisco Systems 345 170 West Tasman Drive 346 San Jose, CA 95134 347 US 349 Email: snandaku@cisco.com 351 Mo Zanaty 352 Cisco Systems 353 170 West Tasman Drive 354 San Jose, CA 95134 355 US 357 Email: mzanaty@cisco.com