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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 informational reference (is this intentional?): RFC 5285 (Obsoleted by RFC 8285) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 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: January 19, 2017 Cisco Systems 6 July 18, 2016 8 Frame Marking RTP Header Extension 9 draft-ietf-avtext-framemarking-02 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 January 19, 2017. 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. Key Words for Normative Requirements . . . . . . . . . . . . 4 58 3. Frame Marking RTP Header Extension . . . . . . . . . . . . . 4 59 3.1. Mandatory Extension . . . . . . . . . . . . . . . . . . . 4 60 3.2. Layer ID Mappings . . . . . . . . . . . . . . . . . . . . 5 61 3.2.1. H265 LID Mapping . . . . . . . . . . . . . . . . . . 5 62 3.2.2. VP9 LID Mapping . . . . . . . . . . . . . . . . . . . 5 63 3.2.3. VP8 LID Mapping . . . . . . . . . . . . . . . . . . . 6 64 3.2.4. H264-SVC LID Mapping . . . . . . . . . . . . . . . . 6 65 3.2.5. H264 (AVC) LID Mapping . . . . . . . . . . . . . . . 6 66 3.3. Signaling information . . . . . . . . . . . . . . . . . . 6 67 3.4. Considerations on use . . . . . . . . . . . . . . . . . . 6 68 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 69 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 70 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 71 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 73 7.2. Informative References . . . . . . . . . . . . . . . . . 8 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 76 1. Introduction 78 Many widely deployed RTP [RFC3550] topologies used in modern voice 79 and video conferencing systems include a centralized component that 80 acts as an RTP switch. It receives voice and video streams from each 81 participant, which may be encrypted using SRTP [RFC3711], or 82 extensions that provide participants with private media via end-to- 83 end encryption that excludes the switch. The goal is to provide a 84 set of streams back to the participants which enable them to render 85 the right media content. In a simple video configuration, for 86 example, the goal will be that each participant sees and hears just 87 the active speaker. In that case, the goal of the switch is to 88 receive the voice and video streams from each participant, determine 89 the active speaker based on energy in the voice packets, possibly 90 using the client-to-mixer audio level RTP header extension, and 91 select the corresponding video stream for transmission to 92 participants; see Figure 1. 94 In this document, an "RTP switch" is used as a common short term for 95 the terms "switching RTP mixer", "source projecting middlebox", 96 "source forwarding unit/middlebox" and "video switching MCU" as 97 discussed in [I-D.ietf-avtcore-rtp-topologies-update]. 99 +---+ +------------+ +---+ 100 | A |<---->| |<---->| B | 101 +---+ | | +---+ 102 | RTP | 103 +---+ | Switch | +---+ 104 | C |<---->| |<---->| D | 105 +---+ +------------+ +---+ 107 Figure 1: RTP switch 109 In order to properly support switching of video streams, the RTP 110 switch typically needs some critical information about video frames 111 in order to start and stop forwarding streams. 113 o Because of inter-frame dependencies, it should ideally switch 114 video streams at a point where the first frame from the new 115 speaker can be decoded by recipients without prior frames, e.g 116 switch on an intra-frame. 117 o In many cases, the switch may need to drop frames in order to 118 realize congestion control techniques, and needs to know which 119 frames can be dropped with minimal impact to video quality. 120 o Furthermore, it is highly desirable to do this in a way which is 121 not specific to the video codec. Nearly all modern video codecs 122 share common concepts around frame types. 123 o It is also desirable to be able to do this for SRTP without 124 requiring the video switch to decrypt the packets. SRTP will 125 encrypt the RTP payload format contents and consequently this data 126 is not usable for the switching function without decryption, which 127 may not even be possible in the case of end-to-end encryption of 128 private media. 130 A comprehensive discussion of SFU considerations around codec 131 agnostic selective forwarding of RTP media is described in 132 [I-D.aboba-avtcore-sfu-rtp] 134 By providing meta-information about the RTP streams outside the 135 encrypted media payload an RTP switch can do selective forwarding 136 without decrypting the payload. This document provides a solution to 137 this problem. 139 2. Key Words for Normative Requirements 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 143 document are to be interpreted as described in [RFC2119]. 145 3. Frame Marking RTP Header Extension 147 The solution uses RTP header extensions as defined in [RFC5285]. A 148 subset of meta-information from the video stream is provided as an 149 RTP header extension to allow an RTP switch to do generic selective 150 forwarding of video streams encoded with potentially different video 151 codecs. 153 3.1. Mandatory Extension 155 The following information are extracted from the media payload and 156 sent in the Frame Marking RTP header extension. 158 o S: Start of Frame (1 bit) - MUST be 1 in the first packet in a 159 frame within a layer; otherwise MUST be 0. 160 o E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame 161 within a layer; otherwise MUST be 0. 162 o I: Independent Frame (1 bit) - MUST be 1 for frames that can be 163 decoded independent of prior frames, e.g. intra-frame, VPx 164 keyframe, H.264 IDR [RFC6184], H.265 CRA/BLA; otherwise MUST be 0. 165 o D: Discardable Frame (1 bit) - MUST be 1 for frames that can be 166 dropped, and still provide a decodable media stream; otherwise 167 MUST be 0. 168 o B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends 169 on the base layer; otherwise MUST be 0. 170 o TID: Temporal ID (3 bits) - The base temporal layer starts with 0, 171 and increases with 1 for each higher temporal layer/sub-layer. 172 o LID: Layer ID (8 bits) - Identifies the spatial and quality layer 173 encoded. 174 o TL0PICIDX: Temporal Layer 0 Picture Index (8 bits) - Running index 175 of base temporal layer 0 frames when TID is 0. When TID is not 0, 176 this indicates a dependency on the given index. 178 The layer information contained in TID and LID convey useful aspects 179 of the layer structure that can be utilized in selective forwarding. 180 Without further information about the layer structure, these 181 identifiers can only be used for relative priority of layers. They 182 convey a layer hierarchy with TID=0 and LID=0 identifying the base 183 layer. Higher values of TID identify higher temporal layers with 184 higher frame rates. Higher values of LID identify higher spatial or 185 quality layers with higher resolutions and bitrates. 187 With further information, for example, possible future RTCP SDES 188 items that convey full layer structure information, it may be 189 possible to map these TIDs and LIDs to specific frame rates, 190 resolutions and bitrates. Such additional layer information may be 191 useful to forwarding decisions in the RTP switch, but is beyond the 192 scope of this memo. The relative layer information is still useful 193 for many selective forwarding decisions even without such additional 194 layer information. 196 The Frame Marking RTP header extension is encoded using the one-byte 197 header or two-byte header as described in [RFC5285]. The one-byte 198 header format is shown below and used for examples in this memo. The 199 two-byte header format is used when other two-byte header extensions 200 are present in the same RTP packet, since mixing one-byte and two- 201 byte extensions is not possible in the same RTP packet. 203 0 1 2 3 204 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 1 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | ID=2 | L=2 |S|E|I|D|B| TID | LID | TL0PICIDX | 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 3.2. Layer ID Mappings 211 3.2.1. H265 LID Mapping 213 The following shows H265-LayerID (6 bits) mapped to the generic LID 214 field. 216 0 1 2 3 217 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 1 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | ID=2 | L=2 |S|E|I|D|B| TID |0|0| LayerID | TL0PICIDX | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 3.2.2. VP9 LID Mapping 224 The following shows VP9 Layer encoding information (4 bits for 225 spatial and quality) mapped to the generic LID field. 227 0 1 2 3 228 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 1 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | ID=2 | L=2 |S|E|I|D|B| TID |0|0|0|0| RS| RQ| TL0PICIDX | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 3.2.3. VP8 LID Mapping 235 The following shows the header extension for VP8 that contains no 236 layer information. 238 0 1 2 3 239 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 1 240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 241 | ID=2 | L=2 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| TL0PICIDX | 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 3.2.4. H264-SVC LID Mapping 246 The following shows H264-SVC Layer encoding information (3 bits for 247 spatial and 4 bits quality) mapped to the generic LID field. 249 0 1 2 3 250 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 1 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | ID=2 | L=2 |S|E|I|D|B| TID |0| DID | QID | TL0PICIDX | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 3.2.5. H264 (AVC) LID Mapping 257 The following shows the header extension for H264 (AVC) that contains 258 no layer information. 260 0 1 2 3 261 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 1 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 | ID=2 | L=2 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| TL0PICIDX | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 3.3. Signaling information 268 The URI for declaring this header extension in an extmap attribute is 269 "urn:ietf:params:rtp-hdrext:framemarking". It does not contain any 270 extension attributes. 272 An example attribute line in SDP: 274 a=extmap:3 urn:ietf:params:rtp-hdrext:framemarking 276 3.4. Considerations on use 278 The header extension values MUST represent what is already in the RTP 279 payload. 281 When a RTP switch needs to discard a received video frame due to 282 congestion control considerations, it is RECOMMENDED that it 283 preferably drop frames marked with the "discardable" bit. 285 When a RTP switch wants to forward a new video stream to a receiver, 286 it is RECOMMENDED to select the new video stream from the first 287 switching point (I bit set) and forward the same. A RTP switch can 288 request a media source to generate a switching point for H.264 by 289 sending Full Intra Request (RTCP FIR) as defined in [RFC5104], for 290 example. 292 4. Security Considerations 294 In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP 295 header extensions are authenticated but not encrypted. When header 296 extensions are used some of the payload type information are exposed 297 and is visible to middle boxes. The encrypted media data is not 298 exposed, so this is not seen as a high risk exposure. 300 5. Acknowledgements 302 Many thanks to Bernard Aboba, Jonathan Lennox, and Stephan Wenger for 303 their inputs. 305 6. IANA Considerations 307 This document defines a new extension URI to the RTP Compact 308 HeaderExtensions sub-registry of the Real-Time Transport Protocol 309 (RTP) Parameters registry, according to the following data: 311 Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo 312 Description: Frame marking information for video streams 313 Contact: espeberg@cisco.com 314 Reference: RFC XXXX 316 Note to RFC Editor: please replace RFC XXXX with the number of this 317 RFC. 319 7. References 321 7.1. Normative References 323 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 324 Requirement Levels", BCP 14, RFC 2119, 325 DOI 10.17487/RFC2119, March 1997, 326 . 328 7.2. Informative References 330 [I-D.ietf-avtcore-rtp-topologies-update] 331 Westerlund, M. and S. Wenger, "RTP Topologies", draft- 332 ietf-avtcore-rtp-topologies-update-10 (work in progress), 333 July 2015. 335 [I-D.aboba-avtcore-sfu-rtp] 336 Aboba, B., "Codec-Independent Selective Forwarding", 337 draft-aboba-avtcore-sfu-rtp-00 (work in progress), July 338 2015. 340 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 341 Jacobson, "RTP: A Transport Protocol for Real-Time 342 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 343 July 2003, . 345 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 346 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 347 RFC 3711, DOI 10.17487/RFC3711, March 2004, 348 . 350 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 351 "Codec Control Messages in the RTP Audio-Visual Profile 352 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 353 February 2008, . 355 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 356 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 357 2008, . 359 [RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP 360 Payload Format for H.264 Video", RFC 6184, 361 DOI 10.17487/RFC6184, May 2011, 362 . 364 Authors' Addresses 366 Espen Berger 367 Cisco Systems 369 Phone: +47 98228179 370 Email: espeberg@cisco.com 371 Suhas Nandakumar 372 Cisco Systems 373 170 West Tasman Drive 374 San Jose, CA 95134 375 US 377 Email: snandaku@cisco.com 379 Mo Zanaty 380 Cisco Systems 381 170 West Tasman Drive 382 San Jose, CA 95134 383 US 385 Email: mzanaty@cisco.com