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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-07 13 Abstract 15 This document defines and registers two new RTCP SDES items. One, 16 named RtpStreamId, is used for unique identification of RTP streams. 17 The other, RepairedRtpStreamId, can be used to identify which stream 18 a redundancy RTP stream is to be used to repair. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on February 27, 2017. 37 Copyright Notice 39 Copyright (c) 2016 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3. Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP 3 57 3.1. RTCP 'RtpStreamId' SDES Extension . . . . . . . . . . . . 4 58 3.2. RTCP 'RepairedRtpStreamId' SDES Extension . . . . . . . . 4 59 3.3. RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header 60 Extensions . . . . . . . . . . . . . . . . . . . . . . . 5 61 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 62 4.1. New RtpStreamId SDES item . . . . . . . . . . . . . . . . 5 63 4.2. New RepairRtpStreamId SDES item . . . . . . . . . . . . . 6 64 4.3. New RtpStreamId Header Extension URI . . . . . . . . . . 6 65 4.4. New RepairRtpStreamId Header Extension URI . . . . . . . 6 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 67 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 70 7.2. Informative References . . . . . . . . . . . . . . . . . 8 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 73 1. Introduction 75 RTP sessions frequently consist of multiple streams, each of which is 76 identified at any given time by its SSRC; however, the SSRC 77 associated with a stream is not guaranteed to be stable over its 78 lifetime. Within a session, these streams can be tagged with a 79 number of identifiers, including CNAMEs and MSIDs 80 [I-D.ietf-mmusic-msid]. Unfortunately, none of these have the proper 81 ordinality to refer to an individual stream; all such identifiers can 82 appear in more than one stream at a time. While approaches that use 83 unique Payload Types (PTs) per stream have been used in some 84 applications, this is a semantic overloading of that field, and one 85 for which its size is inadequate: in moderately complex systems that 86 use PT to uniquely identify every potential combination of codec 87 configuration and unique stream, it is possible to simply run out of 88 values. 90 To address this situation, we define a new RTCP SDES identifier, 91 RtpStreamId, that uniquely identifies a single RTP stream. A key 92 motivator for defining this identifier is the ability to 93 differentiate among different encodings of a single Source Stream 94 that are sent simultaneously (i.e., simulcast). This need for unique 95 identification extends to dependent streams (e.g., where layers used 96 by a layered codec are transmitted on separate streams). 98 At the same time, when redundancy RTP streams are in use, we also 99 need an identifier that connects such streams to the RTP stream for 100 which they are providing redundancy. For this purpose, we define an 101 additional SDES identifier, RepairedRtpStreamId. This identifier can 102 appear only in packets associated with a redundancy RTP stream. They 103 carry the same value as the RtpStreamId of the RTP stream that the 104 redundant RTP stream is correcting. 106 2. Terminology 108 In this document, the terms "source stream", "encoded stream," "RTP 109 stream", "source RTP stream", "dependent stream", "received RTP 110 stream", and "redundancy RTP stream" are used as defined in 111 [RFC7656]. 113 3. Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP 115 The RTP fixed header includes the payload type number and the SSRC 116 values of the RTP stream. RTP defines how you de-multiplex streams 117 within an RTP session; however, in some use cases, applications need 118 further identifiers in order to effectively map the individual RTP 119 Streams to their equivalent payload configurations in the SDP. 121 This specification defines two new RTCP SDES items [RFC3550]. The 122 first item is 'RtpStreamId', which is used to carry RTP stream 123 identifiers within RTCP SDES packets. This makes it possible for a 124 receiver to associate received RTP packets (identifying the RTP 125 stream) with a media description having the format constraint 126 specified. The second is 'RepairedRtpStreamId', which can be used in 127 redundancy RTP streams to indicate the RTP stream repaired by a 128 redundancy RTP stream. 130 To be clear: the value carried in a RepairedRtpStreamId will always 131 match the RtpStreamId value from another RTP stream in the same 132 session. For example, if a source RTP stream is identified by 133 RtpStreamId "A", then any redundancy RTP stream that repairs that 134 source RTP stream will contain a RepairedRtpStreamId of "A" (if this 135 mechanism is being used to perform such correlation). These 136 redundant RTP streams may also contain their own unique RtpStreamId. 138 This specification also uses the RTP header extension for RTCP SDES 139 items [I-D.ietf-avtext-sdes-hdr-ext] to allow carrying RtpStreamId 140 and RepairedRtpStreamId values in RTP packets. This allows 141 correlation at stream startup, or after stream changes where the use 142 of RTCP may not be sufficiently responsive. This speed of response 143 is necessary since, in many cases, the stream cannot be properly 144 processed until it can be identified. 146 RtpStreamId and RepairedRtpStreamId values are scoped by source 147 identifier (e.g., CNAME) and by media session. When the media is 148 multiplexed using the BUNDLE extension 149 [I-D.ietf-mmusic-sdp-bundle-negotiation], these values are further 150 scoped by their associated MID values. For example: an RtpStreamId 151 of "1" may be present in the stream identified with a CNAME of 152 "1234@example.com", and may also be present in a stream with a CNAME 153 of "5678@example.org", and these would refer to different streams. 154 Similarly, an RtpStreamId of "1" may be present with an MID of "A", 155 and again with a MID of "B", and also refer to two different streams. 157 Note that the RepairedRtpStreamId mechanism is limited to indicating 158 one repaired stream per redundancy stream. If systems require 159 correlation for schemes in which a redundancy stream contains 160 information used to repair more than one stream, they will have to 161 use a more complex mechanism than the one defined in this 162 specification. 164 As with all SDES items, RtpStreamId and RepairedRtpStreamId are 165 limited to a total of 255 octets in length. RtpStreamId and 166 RepairedStreamId MUST contain only alphanumeric characters. For 167 avoidance of doubt, the only allowed byte values for these IDs are 168 decimal 48 through 57, 65 through 90, and 97 through 122. 170 3.1. RTCP 'RtpStreamId' SDES Extension 172 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 1 173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 174 |RtpStreamId=TBD| length | RtpStreamId ... 175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 The RtpStreamId payload is ASCII encoded and is not null-terminated. 179 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 180 identifier value. 182 3.2. RTCP 'RepairedRtpStreamId' SDES Extension 184 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 1 185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 186 |Repaired...=TBD| length | RepairRtpStreamId ... 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 The RepairedRtpStreamId payload is ASCII encoded and is not null- 190 terminated. 192 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 193 identifier value. 195 3.3. RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header Extensions 197 Because recipients of RTP packets will typically need to know which 198 streams they correspond to immediately upon receipt, this 199 specification also defines a means of carrying RtpStreamId and 200 RepairedRtpStreamId identifiers in RTP extension headers, using the 201 technique described in [I-D.ietf-avtext-sdes-hdr-ext]. 203 As described in that document, the header extension element can be 204 encoded using either the one-byte or two-byte header, and the 205 identification-tag payload is ASCII-encoded. 207 As the identifier is included in an RTP header extension, there 208 should be some consideration given to the packet expansion caused by 209 the identifier. To avoid Maximum Transmission Unit (MTU) issues for 210 the RTP packets, the header extension's size needs to be taken into 211 account when encoding media. Note that the set of header extensions 212 included in the packet needs to be padded to the next 32-bit boundary 213 [RFC5285]. 215 In many cases, a one-byte identifier will be sufficient to 216 distinguish streams in a session; implementations are strongly 217 encouraged to use the shortest identifier that fits their purposes. 218 Implementors are warned, in particular, not to include any 219 information in the identifier that is derived from potentially user- 220 identifying information, such as user ID or IP address. To avoid 221 identification of specific implementations based on their pattern of 222 tag generation, implementations are encouraged to use a simple scheme 223 that starts with the ASCII digit "1", and increments by one for each 224 subsequent identifier. 226 4. IANA Considerations 228 4.1. New RtpStreamId SDES item 230 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 231 this document. 233 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 234 identifier value. 236 This document adds the RtpStreamId SDES item to the IANA "RTP SDES 237 item types" registry as follows: 239 Value: TBD 240 Abbrev.: RtpStreamId 241 Name: RTP Stream Identifier 242 Reference: RFCXXXX 244 4.2. New RepairRtpStreamId SDES item 246 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 247 this document. 249 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 250 identifier value. 252 This document adds the RepairedRtpStreamId SDES item to the IANA "RTP 253 SDES item types" registry as follows: 255 Value: TBD 256 Abbrev.: RepairedRtpStreamId 257 Name: Repaired RTP Stream Identifier 258 Reference: RFCXXXX 260 4.3. New RtpStreamId Header Extension URI 262 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 263 this document. 265 This document defines a new extension URI in the RTP SDES Compact 266 Header Extensions sub-registry of the RTP Compact Header Extensions 267 registry sub-registry, as follows 269 Extension URI: urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id 270 Description: RTP Stream Identifier Contact: adam@nostrum.com 271 Reference: RFCXXXX 273 4.4. New RepairRtpStreamId Header Extension URI 275 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 276 this document. 278 This document defines a new extension URI in the RTP SDES Compact 279 Header Extensions sub-registry of the RTP Compact Header Extensions 280 registry sub-registry, as follows 282 Extension URI: urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-sream-id 283 Description: RTP Repaired Stream Identifier Contact: adam@nostrum.com 284 Reference: RFCXXXX 286 5. Security Considerations 288 Although the identifiers defined in this document are limited to be 289 strictly alphanumeric, SDES items have the potential to carry any 290 string. As a consequence, there exists a risk that it might carry 291 privacy-sensitive information. Implementations need to take care 292 when generating identifiers so that they do not contain information 293 that can identify the user or allow for long term tracking of the 294 device. Following the generation recommendations in Section 3.3 will 295 result in non-instance-specific labels, with only minor 296 fingerprinting possibilities in the total number of used RtpStreamIds 297 and RepairedRtpStreamIds. 299 Even if the SDES items are generated to convey as little information 300 as possible, implementors are strongly encouraged to encrypt SDES 301 items - both in RTCP and RTP header extensions - so as to preserve 302 privacy against third parties. 304 As the SDES items are used for identification of the RTP streams for 305 different application purposes, it is important that the intended 306 values are received. An attacker, either a third party or malicious 307 RTP middlebox, that removes, or exchanges the values for these SDES 308 items, can severely impact the application. The impact can include 309 failure to decode or display the media content of the RTP stream. It 310 can also result in incorrectly attributing media content to 311 identifiers of the media source, such as incorrectly identifying the 312 speaker. To prevent this from occurring due to third party attacks, 313 integrity and source authentication is needed. 315 Options for Securing RTP Sessions [RFC7201] discusses options for how 316 encryption, integrity and source authentication can be accomplished. 318 6. Acknowledgements 320 Many thanks for review and input from Cullen Jennings, Magnus 321 Westerlund, Colin Perkins, Peter Thatcher, Jonathan Lennox, and Paul 322 Kyzivat. Magnus Westerlund provided substantially all of the 323 Security Considerations section. 325 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 374 Suhas Nandakumar 375 Cisco Systems 377 Email: snandaku@cisco.com 378 Peter Thatcher 379 Google 381 Email: pthatcher@google.com