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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Roach 3 Internet-Draft Mozilla 4 Intended status: Standards Track S. Nandakumar 5 Expires: February 27, 2017 Cisco Systems 6 P. Thatcher 7 Google 8 August 26, 2016 10 RTP Stream Identifier Source Description (SDES) 11 draft-ietf-avtext-rid-08 13 Abstract 15 This document defines and registers two new RTCP Stream Identifier 16 Source Description (SDES) items. One, named RtpStreamId, is used for 17 unique identification of RTP streams. The other, 18 RepairedRtpStreamId, can be used to identify which stream a 19 redundancy RTP stream is to be used to repair. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on February 27, 2017. 38 Copyright Notice 40 Copyright (c) 2016 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP 3 58 3.1. RTCP 'RtpStreamId' SDES Extension . . . . . . . . . . . . 4 59 3.2. RTCP 'RepairedRtpStreamId' SDES Extension . . . . . . . . 4 60 3.3. RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header 61 Extensions . . . . . . . . . . . . . . . . . . . . . . . 5 62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 63 4.1. New RtpStreamId SDES item . . . . . . . . . . . . . . . . 5 64 4.2. New RepairRtpStreamId SDES item . . . . . . . . . . . . . 6 65 4.3. New RtpStreamId Header Extension URI . . . . . . . . . . 6 66 4.4. New RepairRtpStreamId Header Extension URI . . . . . . . 6 67 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 68 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 69 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 71 7.2. Informative References . . . . . . . . . . . . . . . . . 8 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 74 1. Introduction 76 RTP sessions frequently consist of multiple streams, each of which is 77 identified at any given time by its SSRC; however, the SSRC 78 associated with a stream is not guaranteed to be stable over its 79 lifetime. Within a session, these streams can be tagged with a 80 number of identifiers, including CNAMEs and MSIDs 81 [I-D.ietf-mmusic-msid]. Unfortunately, none of these have the proper 82 ordinality to refer to an individual stream; all such identifiers can 83 appear in more than one stream at a time. While approaches that use 84 unique Payload Types (PTs) per stream have been used in some 85 applications, this is a semantic overloading of that field, and one 86 for which its size is inadequate: in moderately complex systems that 87 use PT to uniquely identify every potential combination of codec 88 configuration and unique stream, it is possible to simply run out of 89 values. 91 To address this situation, we define a new RTCP Stream Identifier 92 Source Description (SDES) identifier, RtpStreamId, that uniquely 93 identifies a single RTP stream. A key motivator for defining this 94 identifier is the ability to differentiate among different encodings 95 of a single Source Stream that are sent simultaneously (i.e., 96 simulcast). This need for unique identification extends to dependent 97 streams (e.g., where layers used by a layered codec are transmitted 98 on separate streams). 100 At the same time, when redundancy RTP streams are in use, we also 101 need an identifier that connects such streams to the RTP stream for 102 which they are providing redundancy. For this purpose, we define an 103 additional SDES identifier, RepairedRtpStreamId. This identifier can 104 appear only in packets associated with a redundancy RTP stream. They 105 carry the same value as the RtpStreamId of the RTP stream that the 106 redundant RTP stream is correcting. 108 2. Terminology 110 In this document, the terms "source stream", "encoded stream," "RTP 111 stream", "source RTP stream", "dependent stream", "received RTP 112 stream", and "redundancy RTP stream" are used as defined in 113 [RFC7656]. 115 3. Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP 117 The RTP fixed header includes the payload type number and the SSRC 118 values of the RTP stream. RTP defines how you de-multiplex streams 119 within an RTP session; however, in some use cases, applications need 120 further identifiers in order to effectively map the individual RTP 121 Streams to their equivalent payload configurations in the SDP. 123 This specification defines two new RTCP SDES items [RFC3550]. The 124 first item is 'RtpStreamId', which is used to carry RTP stream 125 identifiers within RTCP SDES packets. This makes it possible for a 126 receiver to associate received RTP packets (identifying the RTP 127 stream) with a media description having the format constraint 128 specified. The second is 'RepairedRtpStreamId', which can be used in 129 redundancy RTP streams to indicate the RTP stream repaired by a 130 redundancy RTP stream. 132 To be clear: the value carried in a RepairedRtpStreamId will always 133 match the RtpStreamId value from another RTP stream in the same 134 session. For example, if a source RTP stream is identified by 135 RtpStreamId "A", then any redundancy RTP stream that repairs that 136 source RTP stream will contain a RepairedRtpStreamId of "A" (if this 137 mechanism is being used to perform such correlation). These 138 redundant RTP streams may also contain their own unique RtpStreamId. 140 This specification also uses the RTP header extension for RTCP SDES 141 items [I-D.ietf-avtext-sdes-hdr-ext] to allow carrying RtpStreamId 142 and RepairedRtpStreamId values in RTP packets. This allows 143 correlation at stream startup, or after stream changes where the use 144 of RTCP may not be sufficiently responsive. This speed of response 145 is necessary since, in many cases, the stream cannot be properly 146 processed until it can be identified. 148 RtpStreamId and RepairedRtpStreamId values are scoped by source 149 identifier (e.g., CNAME) and by media session. When the media is 150 multiplexed using the BUNDLE extension 151 [I-D.ietf-mmusic-sdp-bundle-negotiation], these values are further 152 scoped by their associated MID values. For example: an RtpStreamId 153 of "1" may be present in the stream identified with a CNAME of 154 "1234@example.com", and may also be present in a stream with a CNAME 155 of "5678@example.org", and these would refer to different streams. 156 Similarly, an RtpStreamId of "1" may be present with an MID of "A", 157 and again with a MID of "B", and also refer to two different streams. 159 Note that the RepairedRtpStreamId mechanism is limited to indicating 160 one repaired stream per redundancy stream. If systems require 161 correlation for schemes in which a redundancy stream contains 162 information used to repair more than one stream, they will have to 163 use a more complex mechanism than the one defined in this 164 specification. 166 As with all SDES items, RtpStreamId and RepairedRtpStreamId are 167 limited to a total of 255 octets in length. RtpStreamId and 168 RepairedStreamId MUST contain only alphanumeric characters. For 169 avoidance of doubt, the only allowed byte values for these IDs are 170 decimal 48 through 57, 65 through 90, and 97 through 122. 172 3.1. RTCP 'RtpStreamId' SDES Extension 174 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 1 175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 176 |RtpStreamId=TBD| length | RtpStreamId ... 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 The RtpStreamId payload is ASCII encoded and is not null-terminated. 181 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 182 identifier value. 184 3.2. RTCP 'RepairedRtpStreamId' SDES Extension 186 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 1 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 |Repaired...=TBD| length | RepairRtpStreamId ... 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 The RepairedRtpStreamId payload is ASCII encoded and is not null- 192 terminated. 194 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 195 identifier value. 197 3.3. RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header Extensions 199 Because recipients of RTP packets will typically need to know which 200 streams they correspond to immediately upon receipt, this 201 specification also defines a means of carrying RtpStreamId and 202 RepairedRtpStreamId identifiers in RTP extension headers, using the 203 technique described in [I-D.ietf-avtext-sdes-hdr-ext]. 205 As described in that document, the header extension element can be 206 encoded using either the one-byte or two-byte header, and the 207 identification-tag payload is ASCII-encoded. 209 As the identifier is included in an RTP header extension, there 210 should be some consideration given to the packet expansion caused by 211 the identifier. To avoid Maximum Transmission Unit (MTU) issues for 212 the RTP packets, the header extension's size needs to be taken into 213 account when encoding media. Note that the set of header extensions 214 included in the packet needs to be padded to the next 32-bit boundary 215 [RFC5285]. 217 In many cases, a one-byte identifier will be sufficient to 218 distinguish streams in a session; implementations are strongly 219 encouraged to use the shortest identifier that fits their purposes. 220 Implementors are warned, in particular, not to include any 221 information in the identifier that is derived from potentially user- 222 identifying information, such as user ID or IP address. To avoid 223 identification of specific implementations based on their pattern of 224 tag generation, implementations are encouraged to use a simple scheme 225 that starts with the ASCII digit "1", and increments by one for each 226 subsequent identifier. 228 4. IANA Considerations 230 4.1. New RtpStreamId SDES item 232 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 233 this document. 235 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 236 identifier value. 238 This document adds the RtpStreamId SDES item to the IANA "RTP SDES 239 item types" registry as follows: 241 Value: TBD 242 Abbrev.: RtpStreamId 243 Name: RTP Stream Identifier 244 Reference: RFCXXXX 246 4.2. New RepairRtpStreamId SDES item 248 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 249 this document. 251 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 252 identifier value. 254 This document adds the RepairedRtpStreamId SDES item to the IANA "RTP 255 SDES item types" registry as follows: 257 Value: TBD 258 Abbrev.: RepairedRtpStreamId 259 Name: Repaired RTP Stream Identifier 260 Reference: RFCXXXX 262 4.3. New RtpStreamId Header Extension URI 264 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 265 this document. 267 This document defines a new extension URI in the RTP SDES Compact 268 Header Extensions sub-registry of the RTP Compact Header Extensions 269 registry sub-registry, as follows 271 Extension URI: urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id 272 Description: RTP Stream Identifier Contact: adam@nostrum.com 273 Reference: RFCXXXX 275 4.4. New RepairRtpStreamId Header Extension URI 277 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 278 this document. 280 This document defines a new extension URI in the RTP SDES Compact 281 Header Extensions sub-registry of the RTP Compact Header Extensions 282 registry sub-registry, as follows 283 Extension URI: urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-sream-id 284 Description: RTP Repaired Stream Identifier Contact: adam@nostrum.com 285 Reference: RFCXXXX 287 5. Security Considerations 289 Although the identifiers defined in this document are limited to be 290 strictly alphanumeric, SDES items have the potential to carry any 291 string. As a consequence, there exists a risk that it might carry 292 privacy-sensitive information. Implementations need to take care 293 when generating identifiers so that they do not contain information 294 that can identify the user or allow for long term tracking of the 295 device. Following the generation recommendations in Section 3.3 will 296 result in non-instance-specific labels, with only minor 297 fingerprinting possibilities in the total number of used RtpStreamIds 298 and RepairedRtpStreamIds. 300 Even if the SDES items are generated to convey as little information 301 as possible, implementors are strongly encouraged to encrypt SDES 302 items - both in RTCP and RTP header extensions - so as to preserve 303 privacy against third parties. 305 As the SDES items are used for identification of the RTP streams for 306 different application purposes, it is important that the intended 307 values are received. An attacker, either a third party or malicious 308 RTP middlebox, that removes, or changes the values for these SDES 309 items, can severely impact the application. The impact can include 310 failure to decode or display the media content of the RTP stream. It 311 can also result in incorrectly attributing media content to 312 identifiers of the media source, such as incorrectly identifying the 313 speaker. To prevent this from occurring due to third party attacks, 314 integrity and source authentication is needed. 316 Options for Securing RTP Sessions [RFC7201] discusses options for how 317 encryption, integrity and source authentication can be accomplished. 319 6. Acknowledgements 321 Many thanks for review and input from Cullen Jennings, Magnus 322 Westerlund, Colin Perkins, Jonathan Lennox, and Paul Kyzivat. Magnus 323 Westerlund provided substantially all of the Security Considerations 324 section. 326 7. References 327 7.1. Normative References 329 [I-D.ietf-avtext-sdes-hdr-ext] 330 Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 331 Header Extension for RTCP Source Description Items", 332 draft-ietf-avtext-sdes-hdr-ext-07 (work in progress), June 333 2016. 335 [I-D.ietf-mmusic-sdp-bundle-negotiation] 336 Holmberg, C., Alvestrand, H., and C. Jennings, 337 "Negotiating Media Multiplexing Using the Session 338 Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- 339 negotiation-32 (work in progress), August 2016. 341 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 342 Jacobson, "RTP: A Transport Protocol for Real-Time 343 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 344 July 2003, . 346 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 347 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 348 2008, . 350 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 351 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 352 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 353 DOI 10.17487/RFC7656, November 2015, 354 . 356 7.2. Informative References 358 [I-D.ietf-mmusic-msid] 359 Alvestrand, H., "WebRTC MediaStream Identification in the 360 Session Description Protocol", draft-ietf-mmusic-msid-15 361 (work in progress), July 2016. 363 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 364 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 365 . 367 Authors' Addresses 369 Adam Roach 370 Mozilla 372 Email: adam@nostrum.com 373 Suhas Nandakumar 374 Cisco Systems 376 Email: snandaku@cisco.com 378 Peter Thatcher 379 Google 381 Email: pthatcher@google.com