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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 normative reference: RFC 5285 (Obsoleted by RFC 8285) ** Downref: Normative reference to an Informational RFC: RFC 7656 == Outdated reference: A later version (-17) exists of draft-ietf-mmusic-msid-14 Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). 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: January 7, 2017 Cisco Systems 6 P. Thatcher 7 Google 8 July 06, 2016 10 RTP Stream Identifier Source Description (SDES) 11 draft-ietf-avtext-rid-05 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 January 7, 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 . . . . . . . . . . . . . . . . . . . . . . . 4 61 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 62 4.1. New RtpStreamId SDES item . . . . . . . . . . . . . . . . 5 63 4.2. New RepairRtpStreamId SDES item . . . . . . . . . . . . . 5 64 4.3. New RtpStreamId Header Extension URI . . . . . . . . . . 6 65 4.4. New RepairRtpStreamId Header Extension URI . . . . . . . 6 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 67 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 70 7.2. Informative References . . . . . . . . . . . . . . . . . 7 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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 3.1. RTCP 'RtpStreamId' SDES Extension 148 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 1 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 |RtpStreamId=TBD| length | RtpStreamId ... 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 The RtpStreamId payload is UTF-8 encoded and is not null-terminated. 155 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 156 identifier value. 158 3.2. RTCP 'RepairedRtpStreamId' SDES Extension 160 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 1 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 |Repaired...=TBD| length | RepairRtpStreamId ... 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 The RepairedRtpStreamId payload is UTF-8 encoded and is not null- 166 terminated. 168 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 169 identifier value. 171 3.3. RTP 'RtpStreamId' and 'RepairedRtpStreamId' Header Extensions 173 Because recipients of RTP packets will typically need to know which 174 streams they correspond to immediately upon receipt, this 175 specification also defines a means of carrying RtpStreamId and 176 RepairedRtpStreamId identifiers in RTP extension headers, using the 177 technique described in [I-D.ietf-avtext-sdes-hdr-ext]. 179 As described in that document, the header extension element can be 180 encoded using either the one-byte or two-byte header, and the 181 identification-tag payload is UTF-8 encoded, as in SDP. 183 As the identifier is included in an RTP header extension, there 184 should be some consideration given to the packet expansion caused by 185 the identifier. To avoid Maximum Transmission Unit (MTU) issues for 186 the RTP packets, the header extension's size needs to be taken into 187 account when the encoding media. Note that set of header extensions 188 included in the packet needs to be padded to the next 32-bit boundary 189 [RFC5285]. 191 In many cases, a one-byte identifier will be sufficient to 192 distinguish streams in a session; implementations are strongly 193 encouraged to use the shortest identifier that fits their purposes. 194 Implementors are warned, in particular, not to include any 195 information in the identifier that is derived from potentially user- 196 identifying information, such as user ID or IP address. To avoid 197 identification of specific implementations based on their pattern of 198 tag generation, implementations are encouraged to use a simple scheme 199 that starts with the ASCII digit "1", and increments by one for each 200 subsequent identifier. 202 4. IANA Considerations 204 4.1. New RtpStreamId SDES item 206 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 207 this document. 209 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 210 identifier value. 212 This document adds the RtpStreamId SDES item to the IANA "RTCP SDES 213 item types" registry as follows: 215 Value: TBD 216 Abbrev.: RtpStreamId 217 Name: RTP Stream Identifier 218 Reference: RFCXXXX 220 4.2. New RepairRtpStreamId SDES item 222 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 223 this document. 225 RFC EDITOR NOTE: Please replace TBD with the assigned SDES 226 identifier value. 228 This document adds the RepairedRtpStreamId SDES item to the IANA 229 "RTCP SDES item types" registry as follows: 231 Value: TBD 232 Abbrev.: RepairedRtpStreamId 233 Name: Repaired RTP Stream Identifier 234 Reference: RFCXXXX 236 4.3. New RtpStreamId Header Extension URI 238 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 239 this document. 241 This document defines a new extension URI in the RTP SDES Compact 242 Header Extensions sub-registry of the RTP Compact Header Extensions 243 registry sub-registry, as follows 245 Extension URI: urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id 246 Description: RTP Stream Identifier Contact: adam@nostrum.com 247 Reference: RFCXXXX 249 The SDES item does not reveal privacy information about the user or 250 the session contents. It serves only to bind the identity of a 251 stream to corresponding data in a session description. 253 4.4. New RepairRtpStreamId Header Extension URI 255 RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of 256 this document. 258 This document defines a new extension URI in the RTP SDES Compact 259 Header Extensions sub-registry of the RTP Compact Header Extensions 260 registry sub-registry, as follows 262 Extension URI: urn:ietf:params:rtp-hdrext:sdes:repair-rtp-sream-id 263 Description: RTP Repaired Stream Identifier Contact: adam@nostrum.com 264 Reference: RFCXXXX 266 The SDES item does not reveal privacy information about the user or 267 the session contents. It serves only to bind redundancy stream to 268 the streams they provide repair data for. 270 5. Security Considerations 272 The actual identifiers used for RtpStreamIds (and therefore 273 RepairedRtpStreamIds) are expected to be opaque. As such, they are 274 not expected to contain information that would be sensitive, were it 275 observed by third-parties. 277 6. Acknowledgements 279 Many thanks for review and input from Cullen Jennings, Magnus 280 Westerlund, Colin Perkins, Peter Thatcher, Jonathan Lennox, and Paul 281 Kyzivat. 283 7. References 285 7.1. Normative References 287 [I-D.ietf-avtext-sdes-hdr-ext] 288 Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 289 Header Extension for RTCP Source Description Items", 290 draft-ietf-avtext-sdes-hdr-ext-07 (work in progress), June 291 2016. 293 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 294 Jacobson, "RTP: A Transport Protocol for Real-Time 295 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 296 July 2003, . 298 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 299 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 300 2008, . 302 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 303 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 304 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 305 DOI 10.17487/RFC7656, November 2015, 306 . 308 7.2. Informative References 310 [I-D.ietf-mmusic-msid] 311 Alvestrand, H., "WebRTC MediaStream Identification in the 312 Session Description Protocol", draft-ietf-mmusic-msid-14 313 (work in progress), June 2016. 315 Authors' Addresses 317 Adam Roach 318 Mozilla 320 Email: adam@nostrum.com 322 Suhas Nandakumar 323 Cisco Systems 325 Email: snandaku@cisco.com 326 Peter Thatcher 327 Google 329 Email: pthatcher@google.com