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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Updates: 3264 (if approved) H. Alvestrand 5 Intended status: Standards Track Google 6 Expires: October 2, 2017 C. Jennings 7 Cisco 8 March 31, 2017 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-37.txt 14 Abstract 16 This specification defines a new Session Description Protocol (SDP) 17 Grouping Framework extension, 'BUNDLE'. The extension can be used 18 with the SDP Offer/Answer mechanism to negotiate the usage of a 19 single address:port combination (BUNDLE address) for receiving media, 20 referred to as bundled media, specified by multiple SDP media 21 descriptions ("m=" lines). 23 To assist endpoints in negotiating the use of bundle this 24 specification defines a new SDP attribute, 'bundle-only', which can 25 be used to request that specific media is only used if bundled. The 26 specification also updates RFC 3264, to allow usage of zero port 27 values without meaning that media is rejected. 29 There are multiple ways to correlate the bundled RTP packets with the 30 appropriate media descriptions. This specification defines a new 31 Real-time Transport Protocol (RTP) source description (SDES) item and 32 a new RTP header extension that provides an additional way to do this 33 correlation by using them to carry a value that associates the RTP/ 34 RTCP packets with a specific media description. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on October 2, 2017. 53 Copyright Notice 55 Copyright (c) 2017 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 This document may contain material from IETF Documents or IETF 69 Contributions published or made publicly available before November 70 10, 2008. The person(s) controlling the copyright in some of this 71 material may not have granted the IETF Trust the right to allow 72 modifications of such material outside the IETF Standards Process. 73 Without obtaining an adequate license from the person(s) controlling 74 the copyright in such materials, this document may not be modified 75 outside the IETF Standards Process, and derivative works of it may 76 not be created outside the IETF Standards Process, except to format 77 it for publication as an RFC or to translate it into languages other 78 than English. 80 Table of Contents 82 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 83 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 84 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 86 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 87 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 8 88 7. SDP Information Considerations . . . . . . . . . . . . . . . 9 89 7.1. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 90 7.2. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 91 7.3. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 92 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 93 8.1. Mux Category Considerations . . . . . . . . . . . . . . . 10 94 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 95 8.2.1. Suggesting the offerer BUNDLE address . . . . . . . . 11 96 8.2.2. Example: Initial SDP Offer . . . . . . . . . . . . . 11 97 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 12 98 8.3.1. Answerer Selection of Offerer Bundle Address . . . . 13 99 8.3.2. Answerer Selection of Answerer BUNDLE Address . . . . 14 100 8.3.3. Moving A Media Description Out Of A BUNDLE Group . . 14 101 8.3.4. Rejecting A Media Description In A BUNDLE Group . . . 15 102 8.3.5. Example: SDP Answer . . . . . . . . . . . . . . . . . 15 103 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 15 104 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 16 105 8.5.1. Suggesting a new offerer BUNDLE address . . . . . . . 16 106 8.5.2. Adding a media description to a BUNDLE group . . . . 17 107 8.5.3. Moving A Media Description Out Of A BUNDLE Group . . 17 108 8.5.4. Disabling A Media Description In A BUNDLE Group . . . 18 109 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 18 110 9.1. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 19 111 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 19 112 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 19 113 10.1.1. Payload Type (PT) Value Reuse . . . . . . . . . . . 20 114 10.2. Associating RTP/RTCP Streams With Correct SDP Media 115 Description . . . . . . . . . . . . . . . . . . . . . . 20 116 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 25 117 10.3.1. SDP Offer/Answer Procedures . . . . . . . . . . . . 26 118 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 28 119 11.1. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 28 120 11.1.1. Generating the Initial SDP Offer . . . . . . . . . . 29 121 11.1.2. Generating the SDP Answer . . . . . . . . . . . . . 29 122 11.1.3. Offerer Processing of the SDP Answer . . . . . . . . 29 123 11.1.4. Modifying the Session . . . . . . . . . . . . . . . 29 124 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 30 125 13. RTP Header Extensions Consideration . . . . . . . . . . . . . 30 126 14. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 30 127 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 31 128 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 129 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 31 130 14.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 31 131 14.4. New text replacing section 8.2 (2nd paragraph) of RFC 132 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 31 133 14.5. Original text of section 8.4 (6th paragraph) of RFC 3264 32 134 14.6. New text replacing section 8.4 (6th paragraph) of RFC 135 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 136 15. RTP/RTCP extensions for identification-tag transport . . . . 32 137 15.1. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 33 138 15.2. RTP SDES Header Extension For MID . . . . . . . . . . . 34 139 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 140 16.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 35 141 16.2. New RTP SDES Header Extension URI . . . . . . . . . . . 35 142 16.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 35 143 16.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 36 145 17. Security Considerations . . . . . . . . . . . . . . . . . . . 36 146 18. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 38 147 18.1. Example: Bundle Address Selection . . . . . . . . . . . 38 148 18.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 40 149 18.3. Example: Offerer Adds A Media Description To A BUNDLE 150 Group . . . . . . . . . . . . . . . . . . . . . . . . . 41 151 18.4. Example: Offerer Moves A Media Description Out Of A 152 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 43 153 18.5. Example: Offerer Disables A Media Description Within A 154 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 45 155 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 156 20. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 47 157 21. References . . . . . . . . . . . . . . . . . . . . . . . . . 55 158 21.1. Normative References . . . . . . . . . . . . . . . . . . 55 159 21.2. Informative References . . . . . . . . . . . . . . . . . 57 160 Appendix A. Design Considerations . . . . . . . . . . . . . . . 58 161 A.1. UA Interoperability . . . . . . . . . . . . . . . . . . . 59 162 A.2. Usage of port number value zero . . . . . . . . . . . . . 61 163 A.3. B2BUA And Proxy Interoperability . . . . . . . . . . . . 61 164 A.3.1. Traffic Policing . . . . . . . . . . . . . . . . . . 62 165 A.3.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 62 166 A.4. Candidate Gathering . . . . . . . . . . . . . . . . . . . 62 167 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 63 169 1. Introduction 171 When multimedia communications are established, each 5-tuple reserved 172 for an individual media stream consume additional resources 173 (especially when Interactive Connectivity Establishment (ICE) 174 [RFC5245] is used). For this reason, it is attractive to use a 175 5-tuple for multiple media streams. 177 This specification defines a way to use a single address:port 178 combination (BUNDLE address) for receiving media specified by 179 multiple SDP media descriptions ("m=" lines). 181 This specification defines a new SDP Grouping Framework [RFC5888] 182 extension called 'BUNDLE'. The extension can be used with the 183 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 184 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 185 BUNDLE address is used for receiving media specified by multiple "m=" 186 lines. This is referred to as bundled media. 188 The offerer and answerer [RFC3264] use the BUNDLE extension to 189 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 190 address) and one for the answerer (answerer BUNDLE address), to be 191 used for receiving the bundled media specified by a BUNDLE group. 192 Once the offerer and the answerer have negotiated a BUNDLE group, 193 they associate their respective BUNDLE address with each "m=" line in 194 the BUNDLE group. The BUNDLE addresses are used to receive all media 195 specified by the BUNDLE group. 197 The use of a BUNDLE group and a BUNDLE address also allows the usage 198 of a single set of Interactive Connectivity Establishment (ICE) 199 [RFC5245] candidates for multiple "m=" lines. 201 This specification also defines a new SDP attribute, 'bundle-only', 202 which can be used to request that specific media is only used if kept 203 within a BUNDLE group. The specification also updates RFC 3264, to 204 allow usage of zero port values without meaning that media is 205 rejected. 207 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 208 transport address (IP address and port) to multiple "m=" lines are 209 undefined, and there is no grouping defined by such means. Instead, 210 an explicit grouping mechanism needs to be used to express the 211 intended semantics. This specification provides such an extension. 213 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 214 [RFC3264]. The update allows an answerer to assign a non-zero port 215 value to an "m=" line in an SDP answer, even if the "m=" line in the 216 associated SDP offer contained a zero port value. 218 This specification also defines a new Real-time Transport Protocol 219 (RTP) [RFC3550] source description (SDES) item, 'MID', and a new RTP 220 SDES header extension that can be used to associate RTP streams with 221 media descriptions. 223 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 224 address MUST only be associated with a single BUNDLE group. The 225 procedures in this specification apply independently to a given 226 BUNDLE group. All RTP based media flows described by a single BUNDLE 227 group belong to a single RTP session [RFC3550]. 229 The BUNDLE extension is backward compatible. Endpoints that do not 230 support the extension are expected to generate offers and answers 231 without an SDP 'group:BUNDLE' attribute, and are expected to 232 associate a unique address with each "m=" line within an offer and 233 answer, according to the procedures in [RFC4566] and [RFC3264] 235 2. Terminology 237 "m=" line: SDP bodies contain one or more media descriptions. Each 238 media description is identified by an SDP "m=" line. 240 5-tuple: A collection of the following values: source address, source 241 port, destination address, destination port, and transport-layer 242 protocol. 244 Unique address: An IP address and port combination that is associated 245 with only one "m=" line in an offer or answer. 247 Shared address: An IP address and port combination that is associated 248 with multiple "m=" lines within an offer or answer. 250 Offerer BUNDLE-tag: The first identification-tag in a given SDP 251 'group:BUNDLE' attribute identification-tag list in an offer. 253 Answerer BUNDLE-tag: The first identification-tag in a given SDP 254 'group:BUNDLE' attribute identification-tag list in an answer. 256 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 257 and port combination used by an offerer to receive all media 258 specified by each "m=" line within the BUNDLE group. 260 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 261 and port combination used by an answerer to receive all media 262 specified by each "m=" line within the BUNDLE group. 264 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 265 exchange, which uses the same BUNDLE address for receiving media. 267 Bundled "m=" line: An "m=" line, whose identification-tag is placed 268 in an SDP 'group:BUNDLE' attribute identification-tag list in an 269 offer or answer. 271 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 272 'bundle-only' attribute. 274 Bundled media: All media specified by a given BUNDLE group. 276 Initial offer: The first offer, within an SDP session (e.g. a SIP 277 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 278 to carry SDP), in which the offerer indicates that it wants to create 279 a given BUNDLE group. 281 Subsequent offer: An offer which contains a BUNDLE group that has 282 been created as part of a previous offer/answer exchange. 284 Identification-tag: A unique token value that is used to identify an 285 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 286 "m=" line, carries an unique identification-tag. The session-level 287 SDP 'group' attribute [RFC5888] carries a list of identification- 288 tags, identifying the "m=" lines associated with that particular 289 'group' attribute. 291 3. Conventions 293 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 294 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 295 document are to be interpreted as described in BCP 14, RFC 2119 296 [RFC2119]. 298 4. Applicability Statement 300 The mechanism in this specification only applies to the Session 301 Description Protocol (SDP) [RFC4566], when used together with the SDP 302 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 303 scope of this document, and is thus undefined. 305 5. SDP Grouping Framework BUNDLE Extension 307 This section defines a new SDP Grouping Framework extension 308 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 309 Offer/Answer mechanism to negotiate the usage of a single 310 address:port combination (BUNDLE address) for receiving bundled 311 media. 313 A single address:port combination is also used for sending bundled 314 media. The address:port combination used for sending bundled media 315 MAY be the same as the BUNDLE address, used to receive bundled media, 316 depending on whether symmetric RTP [RFC4961] is used. 318 All media associated with a BUNDLE group MUST be transport using the 319 same transport-layer protocol (e.g., UDP or TCP). 321 The BUNDLE extension is indicated using an SDP 'group' attribute with 322 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 323 associated with each bundled "m=" line, and each identification-tag 324 is listed in the SDP 'group:BUNDLE' attribute identification-tag 325 list. Each "m=" line whose identification-tag is listed in the 326 identification-tag list is associated with a given BUNDLE group. 328 SDP bodies can contain multiple BUNDLE groups. Any given bundled 329 "m=" line MUST NOT be associated with more than one BUNDLE group. 331 NOTE: The order of the "m=" lines listed in the SDP 'group:BUNDLE' 332 attribute identification-tag list does not have to be the same as the 333 order in which the "m=" lines occur in the SDP. 335 Section 8 defines the detailed SDP Offer/Answer procedures for the 336 BUNDLE extension. 338 6. SDP 'bundle-only' Attribute 340 This section defines a new SDP media-level attribute [RFC4566], 341 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 342 hence has no value. 344 Name: bundle-only 346 Value: N/A 348 Usage Level: media 350 Charset Dependent: no 352 Example: 354 a=bundle-only 356 In order to ensure that an answerer that does not support the BUNDLE 357 extension always rejects a bundled "m=" line, the offerer can assign 358 a zero port value to the "m=" line. According to [RFC3264] an 359 answerer will reject such "m=" line. By associating an SDP 'bundle- 360 only' attribute with such "m=" line, the offerer can request that the 361 answerer accepts the "m=" line if the answerer supports the Bundle 362 extension, and if the answerer keeps the "m=" line within the 363 associated BUNDLE group. 365 NOTE: Once the offerer BUNDLE address has been selected, the offerer 366 does not need to include the 'bundle-only' attribute in subsequent 367 offers. By associating the offerer BUNDLE address with an "m=" line 368 of a subsequent offer, the offerer will ensure that the answerer will 369 either keep the "m=" line within the BUNDLE group, or the answerer 370 will have to reject the "m=" line. 372 The usage of the 'bundle-only' attribute is only defined for a 373 bundled "m=" line with a zero port value, within an offer. Other 374 usage is unspecified. 376 Section 8 defines the detailed SDP Offer/Answer procedures for the 377 'bundle-only' attribute. 379 7. SDP Information Considerations 381 This section describes restrictions associated with the usage of SDP 382 parameters within a BUNDLE group. It also describes, when parameter 383 and attribute values have been associated with each bundled "m=" 384 line, how to calculate a value for the whole BUNDLE group. 386 7.1. Connection Data (c=) 388 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 389 line MUST be 'IN'. 391 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 392 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 393 each "m=" line. 395 NOTE: Extensions to this specification can specify usage of the 396 BUNDLE mechanism for other nettype and addrtype values than the ones 397 listed above. 399 7.2. Bandwidth (b=) 401 An offerer and answerer MUST use the rules and restrictions defined 402 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP 403 bandwidth (b=) line with bundled "m=" lines. 405 7.3. Attributes (a=) 407 An offerer and answerer MUST use the rules and restrictions defined 408 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating SDP 409 attributes with bundled "m=" lines. 411 8. SDP Offer/Answer Procedures 413 This section describes the SDP Offer/Answer [RFC3264] procedures for: 415 o Negotiating and creating a BUNDLE group; and 417 o Selecting the BUNDLE addresses (offerer BUNDLE address and 418 answerer BUNDLE address); and 420 o Adding an "m=" line to a BUNDLE group; and 422 o Moving an "m=" line out of a BUNDLE group; and 424 o Disabling an "m=" line within a BUNDLE group. 426 The generic rules and procedures defined in [RFC3264] and [RFC5888] 427 also apply to the BUNDLE extension. For example, if an offer is 428 rejected by the answerer, the previously negotiated SDP parameters 429 and characteristics (including those associated with a BUNDLE group) 430 apply. Hence, if an offerer generates an offer in which the offerer 431 wants to create a BUNDLE group, and the answerer rejects the offer, 432 the BUNDLE group is not created. 434 The procedures in this section are independent of the media type or 435 "m=" line proto value represented by a bundled "m=" line. Section 10 436 defines additional considerations for RTP based media. Section 6 437 defines additional considerations for the usage of the SDP 'bundle- 438 only' attribute. Section 11 defines additional considerations for 439 the usage of Interactive Connectivity Establishment (ICE) 440 [I-D.ietf-ice-rfc5245bis] mechanism. 442 SDP offers and answers can contain multiple BUNDLE groups. The 443 procedures in this section apply independently to a given BUNDLE 444 group. 446 8.1. Mux Category Considerations 448 When an offerer associates SDP attributes with a bundled "m=" line 449 associated with a shared address, IDENTICAL and TRANSPORT mux 450 category SDP attributes [I-D.ietf-mmusic-sdp-mux-attributes] are 451 associated with the "m=" line only if the "m=" line is also 452 associated with the offerer BUNDLE-tag. Otherwise the offerer MUST 453 NOT associate such SDP attributes with the "m=" line. 455 When an answerer associates SDP attributes with a bundled "m=" line, 456 IDENTICAL and TRANSPORT mux category SDP attributes are associated 457 with the "m=" line only if the "m=" line is also associated with the 458 answerer BUNDLE-tag. Otherwise the answerer MUST NOT associated such 459 SDP attributes with the "m=" line. 461 NOTE: As bundled "m=" lines associated with a shared address will 462 share the same IDENTICAL and TRANSPORT mux category SDP attributes, 463 and attribute values, there is no need to associate such SDP 464 attributes with each "m=" line. The attributes and attribute values 465 are implicitly applied to each "m=" line associated with the shared 466 address. 468 8.2. Generating the Initial SDP Offer 470 When an offerer generates an initial offer, in order to create a 471 BUNDLE group, it MUST: 473 o Assign a unique address to each "m=" line within the offer, 474 following the procedures in [RFC3264], unless the media line is a 475 'bundle-only' "m=" line (see below); and 477 o Add an SDP 'group:BUNDLE' attribute to the offer; and 479 o Place the identification-tag of each bundled "m=" line in the SDP 480 'group:BUNDLE' attribute identification-tag list; and 482 o Indicate which unique address the offerer suggests as the offerer 483 BUNDLE address [Section 8.2.1]. 485 If the offerer wants to request that the answerer accepts a given 486 bundled "m=" line only if the answerer keeps the "m=" line within the 487 BUNDLE group, the offerer MUST: 489 o Associate an SDP 'bundle-only' attribute [Section 8.2.1] with the 490 "m=" line; and 492 o Assign a zero port value to the "m=" line. 494 NOTE: If the offerer assigns a zero port value to an "m=" line, but 495 does not also associate an SDP 'bundle-only' attribute with the "m=" 496 line, it is an indication that the offerer wants to disable the "m=" 497 line [Section 8.5.4]. 499 [Section 18.1] shows an example of an initial offer. 501 8.2.1. Suggesting the offerer BUNDLE address 503 In the offer, the address associated with the "m=" line associated 504 with the offerer BUNDLE-tag indicates the address that the offerer 505 suggests as the offerer BUNDLE address. 507 The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain 508 a zero port value or an SDP 'bundle-only' attribute. 510 8.2.2. Example: Initial SDP Offer 512 The example shows an initial SDP offer. The offer includes two "m=" 513 lines in the SDP, and suggests that both are included in a BUNDLE 514 group. The audio "m=" line is associated with the offerer BUNDLE-tag 515 (placed first in the SDP group:BUNDLE attribute identificatoin-id 516 list). 518 SDP Offer 520 v=0 521 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 522 s= 523 c=IN IP4 atlanta.example.com 524 t=0 0 525 a=group:BUNDLE foo bar 526 m=audio 10000 RTP/AVP 0 8 97 527 b=AS:200 528 a=mid:foo 529 a=rtcp-mux 530 a=rtpmap:0 PCMU/8000 531 a=rtpmap:8 PCMA/8000 532 a=rtpmap:97 iLBC/8000 533 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 534 m=video 10002 RTP/AVP 31 32 535 b=AS:1000 536 a=mid:bar 537 a=rtcp-mux 538 a=rtpmap:31 H261/90000 539 a=rtpmap:32 MPV/90000 540 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 542 8.3. Generating the SDP Answer 544 When an answerer generates an answer that contains a BUNDLE group, 545 the following general SDP grouping framework restrictions, defined in 546 [RFC5888], also apply to the BUNDLE group: 548 o The answerer MUST NOT include a BUNDLE group in the answer, unless 549 the offerer requested the BUNDLE group to be created in the 550 corresponding offer; and 552 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 553 unless the offerer requested the "m=" line to be within that 554 BUNDLE group in the corresponding offer. 556 If the answer contains a BUNDLE group, the answerer MUST: 558 o Select an Offerer BUNDLE Address [Section 8.3.1]; and 560 o Select an Answerer BUNDLE Address [Section 8.3.2]; 562 The answerer is allowed to select a new Answerer BUNDLE address each 563 time it generates an answer to an offer. 565 If the answerer does not want to keep an "m=" line within a BUNDLE 566 group, it MUST: 568 o Move the "m=" line out of the BUNDLE group [Section 8.3.3]; or 570 o Reject the "m=" line [Section 8.3.4]; 572 If the answerer keeps a bundle-only "m=" line within the BUNDLE 573 group, it follows the procedures (associates the answerer BUNDLE 574 address with the "m=" line etc) for any other "m=" line kept within 575 the BUNDLE group. 577 If the answerer does not want to keep a bundle-only "m=" line within 578 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.4]. 580 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 581 any "m=" line in an answer. 583 NOTE: If a bundled "m=" line in an offer contains a zero port value, 584 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 585 is an indication that the offerer wants to disable the "m=" line 586 [Section 8.5.4]. 588 8.3.1. Answerer Selection of Offerer Bundle Address 590 In an offer, the address (unique or shared) associated with the 591 bundled "m=" line associated with the offerer BUNDLE-tag indicates 592 the address that the offerer suggests as the offerer BUNDLE address 593 [Section 8.2.1]. The answerer MUST check whether that "m=" line 594 fulfils the following criteria: 596 o The answerer will not move the "m=" line out of the BUNDLE group 597 [Section 8.3.3]; and 599 o The answerer will not reject the "m=" line [Section 8.3.4]; and 601 o The "m=" line does not contain a zero port value. 603 If all of the criteria above are fulfilled, the answerer MUST select 604 the address associated with the "m=" line as the offerer BUNDLE 605 address. In the answer, the answerer BUNDLE-tag represents the "m=" 606 line, and the address associated with the "m=" line in the offer 607 becomes the offerer BUNDLE address. 609 If one or more of the criteria are not fulfilled, the answerer MUST 610 select the next identification-tag in the identification-tag list, 611 and perform the same criteria check for the "m=" line associated with 612 that identification-tag. If there are no more identification-tags in 613 the identification-tag list, the answerer MUST NOT create the BUNDLE 614 group. In addition, unless the answerer rejects the whole offer, the 615 answerer MUST apply the answerer procedures for moving an "m=" line 616 out of a BUNDLE group [Section 8.3.3] to each bundled "m=" line in 617 the offer when creating the answer. 619 [Section 18.1] shows an example of an offerer BUNDLE address 620 selection. 622 8.3.2. Answerer Selection of Answerer BUNDLE Address 624 When the answerer selects a BUNDLE address for itself, referred to as 625 the answerer BUNDLE address, it MUST associate that address with each 626 bundled "m=" line within the created BUNDLE group in the answer. 628 The answerer MUST NOT associate the answerer BUNDLE address with an 629 "m=" line that is not within the BUNDLE group, or to an "m=" line 630 that is within another BUNDLE group. 632 [Section 18.1] shows an example of an answerer BUNDLE address 633 selection. 635 8.3.3. Moving A Media Description Out Of A BUNDLE Group 637 When an answerer wants to move an "m=" line out of a BUNDLE group, it 638 MUST first check the following criteria: 640 o In the corresponding offer, the "m=" line is associated with a 641 shared address (e.g. a previously selected offerer BUNDLE 642 address); or 644 o In the corresponding offer, an SDP 'bundle-only' attribute is 645 associated with the "m=" line, and the "m=" line contains a zero 646 port value. 648 If either criteria above is fulfilled, the answerer MUST reject the 649 "m=" line [Section 8.3.4]. 651 Otherwise, if in the corresponding offer the "m=" line is associated 652 with a unique address, the answerer MUST associate a unique address 653 with the "m=" line in the answer (the answerer does not reject the 654 "m=" line). 656 In addition, in either case above, the answerer MUST NOT place the 657 identification-tag, associated with the moved "m=" line, in the SDP 658 'group' attribute identification-tag list associated with the BUNDLE 659 group. 661 8.3.4. Rejecting A Media Description In A BUNDLE Group 663 When an answerer rejects an "m=" line, it MUST associate an address 664 with a zero port value with the "m=" line in the answer, according to 665 the procedures in [RFC3264]. 667 In addition, the answerer MUST NOT place the identification-tag, 668 associated with the rejected "m=" line, in the SDP 'group' attribute 669 identification-tag list associated with the BUNDLE group. 671 8.3.5. Example: SDP Answer 673 The example shows an SDP answer, based on the SDP offer in 674 [Section 8.2.2]. The answers acceppts both "m=" lines in the BUNDLE 675 group. 677 SDP Answer 679 v=0 680 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 681 s= 682 c=IN IP4 biloxi.example.com 683 t=0 0 684 a=group:BUNDLE foo bar 685 m=audio 20000 RTP/AVP 0 686 b=AS:200 687 a=mid:foo 688 a=rtcp-mux 689 a=rtpmap:0 PCMU/8000 690 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 691 m=video 20000 RTP/AVP 32 692 b=AS:1000 693 a=mid:bar 694 a=rtcp-mux 695 a=rtpmap:32 MPV/90000 696 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 698 8.4. Offerer Processing of the SDP Answer 700 When an offerer receives an answer, if the answer contains a BUNDLE 701 group, the offerer MUST check that any bundled "m=" line in the 702 answer was indicated as bundled in the corresponding offer. If there 703 is no mismatch, the offerer MUST use the offerer BUNDLE address, 704 selected by the answerer [Section 8.3.1], as the address for each 705 bundled "m=" line. 707 NOTE: As the answerer might reject one or more bundled "m=" lines, or 708 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 709 line in the offer might not be indicated as bundled in the answer. 711 If the answer does not contain a BUNDLE group, the offerer MUST 712 process the answer as a normal answer. 714 8.5. Modifying the Session 716 When an offerer generates a subsequent offer, it MUST associate the 717 previously selected offerer BUNDLE address [Section 8.3.1] with each 718 bundled "m=" line (including any bundle-only "m=" line), except if: 720 o The offerer suggests a new offerer BUNDLE address [Section 8.5.1]; 721 or 723 o The offerer wants to add a bundled "m=" line to the BUNDLE group 724 [Section 8.5.2]; or 726 o The offerer wants to move a bundled "m=" line out of the BUNDLE 727 group [Section 8.5.3]; or 729 o The offerer wants to disable the bundled "m=" line 730 [Section 8.5.4]. 732 In addition, the offerer MUST select an offerer BUNDLE-tag 733 [Section 8.2.1] associated with the previously selected offerer 734 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 735 address. 737 8.5.1. Suggesting a new offerer BUNDLE address 739 When an offerer generates an offer, in which it suggests a new 740 offerer BUNDLE address [Section 8.2.1], the offerer MUST: 742 o Assign the address (shared address) to each "m=" line within the 743 BUNDLE group; or 745 o Assign the address (unique address) to one bundled "m=" line. 747 In addition, the offerer MUST indicate that the address is the new 748 suggested offerer BUNDLE address [Section 8.2.1]. 750 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 751 address with each bundled "m=" line, it can associate unique 752 addresses with any number of bundled "m=" lines (and the previously 753 selected offerer BUNDLE address to any remaining bundled "m=" line) 754 if it wants to suggest multiple alternatives for the new offerer 755 BUNDLE address. 757 8.5.2. Adding a media description to a BUNDLE group 759 When an offerer generates an offer, in which it wants to add a 760 bundled "m=" line to a BUNDLE group, the offerer MUST: 762 o Assign a unique address to the added "m=" line; or 764 o Assign the previously selected offerer BUNDLE address to the added 765 "m=" line; or 767 o If the offerer associates a new (shared address) suggested offerer 768 BUNDLE address with each bundled "m=" line [Section 8.5.1], also 769 associate that address with the added "m=" line. 771 In addition, the offerer MUST add the identification-tag associated 772 with the added "m=" line to the SDP 'group:BUNDLE' attribute 773 identification-tag list with the BUNDLE group [Section 8.2.1]. 775 NOTE: Assigning a unique address to the "m=" line allows the answerer 776 to move the "m=" line out of the BUNDLE group [Section 8.3.3], 777 without having to reject the "m=" line. 779 If the offerer associates a unique address with the added "m=" line, 780 and if the offerer suggests that address as the new offerer BUNDLE 781 address [Section 8.5.1], the offerer BUNDLE-tag MUST represent the 782 added "m=" line [Section 8.2.1]. 784 If the offerer associates a new suggested offerer BUNDLE address with 785 each bundled "m=" line [Section 8.5.1], including the added "m=" 786 line, the offerer BUNDLE-tag MAY represent the added "m=" line 787 [Section 8.2.1]. 789 [Section 18.3] shows an example where an offerer sends an offer in 790 order to add a bundled "m=" line to a BUNDLE group. 792 8.5.3. Moving A Media Description Out Of A BUNDLE Group 794 When an offerer generates an offer, in which it wants to move a 795 bundled "m=" line out of a BUNDLE group it was added to in a previous 796 offer/answer transaction, the offerer: 798 o MUST associate a unique address with the "m=" line; and 799 o MUST NOT place the identification-tag associated with the "m=" 800 line in the SDP 'group:BUNDLE' attribute identification-tag list 801 associated with the BUNDLE group. 803 NOTE: If the removed "m=" line is associated with the previously 804 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 805 [Section 8.2.1]. 807 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 808 added to another BUNDLE group, the offerer applies the procedures in 809 [Section 8.5.2] to the "m=" line. 811 [Section 18.4] shows an example of an offer for moving an "m=" line 812 out of a BUNDLE group. 814 8.5.4. Disabling A Media Description In A BUNDLE Group 816 When an offerer generates an offer, in which it wants to disable a 817 bundled "m=" line (added to the BUNDLE group in a previous offer/ 818 answer transaction), the offerer: 820 o MUST associate an address with a zero port value with the "m=" 821 line, following the procedures in [RFC4566]; and 823 o MUST NOT place the identification-tag associated with the "m=" 824 line in the SDP 'group:BUNDLE' attribute identification-tag list 825 associated with the BUNDLE group. 827 [Section 18.5] shows an example of an offer for disabling an "m=" 828 line within a BUNDLE group. 830 9. Protocol Identification 832 Each "m=" line within a BUNDLE group MUST use the same transport- 833 layer protocol. If bundled "m=" lines use different protocols on top 834 of the transport-layer protocol, there MUST exist a publicly 835 available specification which describes a mechanism, for this 836 particular protocol combination, how to associate received data with 837 the correct protocol. 839 In addition, if received data can be associated with more than one 840 bundled "m=" line, there MUST exist a publicly available 841 specification which describes a mechanism for associating the 842 received data with the correct "m=" line. 844 This document describes a mechanism to identify the protocol of 845 received data among the STUN, DTLS and SRTP protocols (in any 846 combination), when UDP is used as transport-layer protocol, but does 847 not describe how to identify different protocols transported on DTLS. 848 While the mechanism is generally applicable to other protocols and 849 transport-layer protocols, any such use requires further 850 specification around how to multiplex multiple protocols on a given 851 transport-layer protocol, and how to associate received data with the 852 correct protocols. 854 9.1. STUN, DTLS, SRTP 856 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 857 protocol of a received packet among the STUN, Datagram Transport 858 Layer Security (DTLS) and SRTP protocols (in any combination). If an 859 offer or answer includes bundled "m=" lines that represent these 860 protocols, the offerer or answerer MUST support the mechanism 861 described in [RFC5764], and no explicit negotiation is required in 862 order to indicate support and usage of the mechanism. 864 [RFC5764] does not describe how to identify different protocols 865 transported on DTLS, only how to identify the DTLS protocol itself. 866 If multiple protocols are transported on DTLS, there MUST exist a 867 specification describing a mechanism for identifying each individual 868 protocol. In addition, if a received DTLS packet can be associated 869 with more than one "m=" line, there MUST exist a specification which 870 describes a mechanism for associating the received DTLS packet with 871 the correct "m=" line. 873 [Section 10.2] describes how to associate the packets in a received 874 SRTP stream with the correct "m=" line. 876 10. RTP Considerations 878 10.1. Single RTP Session 880 All RTP-based media within a single BUNDLE group belong to a single 881 RTP session [RFC3550]. 883 Since a single RTP session is used for each bundle group, all "m=" 884 lines representing RTP-based media in a bundle group will share a 885 single SSRC numbering space [RFC3550]. 887 The following rules and restrictions apply for a single RTP session: 889 o A specific payload type value can be used in multiple bundled "m=" 890 lines only if each codec associated with the payload type number 891 shares an identical codec configuration [Section 10.1.1]. 893 o The proto value in each bundled RTP-based "m=" line MUST be 894 identical (e.g. RTP/AVPF). 896 o The RTP MID header extension MUST be enabled, by associating an 897 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 898 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 899 in every offer and answer. 901 o A given SSRC MUST NOT transmit RTP packets using payload types 902 that originate from different bundled "m=" lines. 904 NOTE: The last bullet above is to avoid sending multiple media types 905 from the same SSRC. If transmission of multiple media types are done 906 with time overlap, RTP and RTCP fail to function. Even if done in 907 proper sequence this causes RTP Timestamp rate switching issues 908 [RFC7160]. However, once an SSRC has left the RTP session (by 909 sending an RTCP BYE packet), that SSRC can be reused by another 910 source (possibly associated with a different bundled "m=" line) after 911 a delay of 5 RTCP reporting intervals (the delay is to ensure the 912 SSRC has timed out, in case the RTCP BYE packet was lost [RFC3550]). 914 10.1.1. Payload Type (PT) Value Reuse 916 Multiple bundled "m=" lines might represent RTP based media. As all 917 RTP based media specified by a BUNDLE group belong to the same RTP 918 session, in order for a given payload type value to be used inside 919 more than one bundled "m=" line, all codecs associated with the 920 payload type number MUST share an identical codec configuration. 921 This means that the codecs MUST share the same media type, encoding 922 name, clock rate and any parameter that can affect the codec 923 configuration and packetization. 924 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 925 attribute values must be identical for all codecs that use the same 926 payload type value. 928 10.2. Associating RTP/RTCP Streams With Correct SDP Media Description 930 NOTE: The text in this section is copied from Appendix B of JSEP. 931 The community has not yet agreed on the text. 933 As described in [RFC3550], RTP packets are associated with RTP 934 streams [RFC7656]. Each RTP stream is identified by an SSRC value, 935 and each RTP packet includes an SSRC field that is used to associate 936 the packet with the correct RTP stream. RTCP packets also use SSRCs 937 to identify which RTP streams the packet relates to. However, a RTCP 938 packet can contain multiple SSRC fields, in the course of providing 939 feedback or reports on different RTP streams, and therefore can be 940 associated with multiple such streams. 942 In order to be able to process received RTP/RTCP packets correctly, 943 it must be possible to associate an RTP stream with the correct "m=" 944 line, as the "m=" line and SDP attributes associated with the "m=" 945 line contain information needed to process the packets. 947 As all RTP streams associated with a BUNDLE group use the same 948 address:port combination for sending and receiving RTP/RTCP packets, 949 the local address:port combination cannot be used to associate an RTP 950 stream with the correct "m=" line. In addition, multiple RTP streams 951 might be associated with the same "m=" line. 953 An offerer and answerer can inform each other which SSRC values they 954 will use for an RTP stream by using the SDP 'ssrc' attribute 955 [RFC5576]. However, an offerer will not know which SSRC values the 956 answerer will use until the offerer has received the answer providing 957 that information. Due to this, before the offerer has received the 958 answer, the offerer will not be able to associate an RTP stream with 959 the correct "m=" line using the SSRC value associated with the RTP 960 stream. In addition, the offerer and answerer may start using new 961 SSRC values mid-session, without informing each other using the SDP 962 'ssrc' attribute. 964 In order for an offerer and answerer to always be able to associate 965 an RTP stream with the correct "m=" line, the offerer and answerer 966 using the BUNDLE extension MUST support the mechanism defined in 967 section 14, where the offerer and answerer insert the identification- 968 tag associated with an "m=" line (provided by the remote peer) into 969 RTP and RTCP packets associated with a BUNDLE group. 971 When using this mechanism, the mapping from an SSRC to an 972 identification-tag is carried in RTP header extensions or RTCP SDES 973 packets, as specified in section 14. Since a compound RTCP packet 974 can contain multiple RTCP SDES packets, and each RTCP SDES packet can 975 contain multiple chunks, a single RTCP packet can contain several 976 SSRC to identification-tag mappings. The offerer and answerer 977 maintain tables used for routing that are updated each time an RTP/ 978 RTCP packet contains new information that affects how packets should 979 be routed. 981 However, some implementations of may not include this identification- 982 tag in their RTP and RTCP traffic when using the BUNDLE mechanism, 983 and instead use a payload type based mechanism for demuxing. In this 984 situation, each "m=" line MUST use unique payload type values, in 985 order for the payload type to be a reliable indicator of the relevant 986 "m=" line for the RTP stream. Note that when using payload type 987 based demuxing, an SSRC will be mapped to an "m=" line by the first 988 packet with that SSRC, and the mapping will not be changed even if 989 the same SSRC is received with a different payload type. In other 990 words, the SSRC cannot to "move" to a different "m=" line simply by 991 changing the payload type. 993 Applications can implement RTP stacks in many different ways. The 994 algorithm below details one way that demultiplexing can be 995 accomplished, but is not meant to be prescriptive about exactly how 996 an RTP stack needs to be implemented. Applications MAY use any 997 algorithm that achieves equivalent results to those described in the 998 algorithm below. 1000 To prepare for demultiplexing RTP/RTCP packets to the correct "m=" 1001 line, the following steps MUST be followed for each BUNDLE group. 1003 Construct a table mapping MID to "m=" line for each "m=" line in 1004 this BUNDLE group. Note that an "m=" line may only have one MID. 1006 Construct a table mapping incoming SSRC to "m=" line for each "m=" 1007 line in this BUNDLE group and for each SSRC configured for 1008 receiving in that "m=" line. 1010 Construct a table mapping outgoing SSRC to "m=line" for each "m=" 1011 line in this BUNDLE group and for each SSRC configured for sending 1012 in that "m=" line. 1014 Construct a table mapping payload type to "m=" line for each "m=" 1015 line in the BUNDLE group and for each payload type configured for 1016 receiving in that "m=" line. If any payload type is configured 1017 for receiving in more than one "m=" line in the BUNDLE group, do 1018 not it include it in the table, as it cannot be used to uniquely 1019 identify a "m=" line. 1021 Note that for each of these tables, there can only be one mapping 1022 for any given key (MID, SSRC, or PT). In other words, the tables 1023 are not multimaps. 1025 As "m=" lines are added or removed from the BUNDLE groups, or their 1026 configurations are changed, the tables above MUST also be updated. 1028 For each RTP packet received, the following steps MUST be followed to 1029 route the packet to the correct "m=" section within a BUNDLE group. 1030 Note that the phrase 'deliver a packet to the "m=" line' means to 1031 further process the packet as would normally happen with RTP/RTCP, if 1032 it were received on a transport associated with that "m=" line 1033 outside of a BUNDLE group (i.e., if the "m=" line were not BUNDLEd), 1034 including dropping an RTP packet if the packet's PT does not match 1035 any PT in the "m=" line. 1037 If the packet has a MID, and that MID is not in the table mapping 1038 MID to "m=" line, drop the packet and stop. 1040 If the packet has a MID, and the packet's extended sequence number 1041 is greater than that of the last MID update, as discussed in 1042 [RFC7941], Section 4.2.6, update the incoming SSRC mapping table 1043 to include an entry that maps the packet's SSRC to the "m=" line 1044 for that MID. 1046 If the packet's SSRC is in the incoming SSRC mapping table, check 1047 that the packet's PT matches a PT included on the associated "m=" 1048 line. If so, route the packet to that associated "m=" line and 1049 stop; otherwise drop the packet and stop. 1051 If the packet's payload type is in the payload type table, update 1052 the the incoming SSRC mapping table to include an entry that maps 1053 the packet's SSRC to the "m=" line for that payload type. In 1054 addition, route the packet to the associated "m=" line and stop. 1056 Otherwise, drop the packet. 1058 For each RTCP packet received (including each RTCP packet that is 1059 part of a compound RTCP packet), the packet MUST be routed to the 1060 "m=" line for the RTP streams it contains information about. This 1061 routing is type-dependent, as each kind of RTCP packet has its own 1062 mechanism for associating it with the relevant RTP streams. 1064 Packets for which no appropriate "m=" line can be identified (i.e., 1065 for unknown RTP streams) are not relevant in the context of this 1066 algorithm and MAY be dropped. This situation may occur with certain 1067 multiparty RTP topologies. 1069 Rules for handling the various types of RTCP packets are explained 1070 below. 1072 If the packet is of type SDES, for each chunk in the packet whose 1073 SSRC is found in the incoming SSRC table, deliver a copy of the 1074 packet to the "m=" line associated with that SSRC. In addition, 1075 for any SDES MID items contained in these chunks, if the MID is 1076 found in the table mapping MID to "m=" line, update the incoming 1077 SSRC table to include an entry that maps the chunk's SSRC to the 1078 "m=" line associated with that MID, unless the packet is older 1079 than the packet that most recently updated the mapping for this 1080 SSRC, as discussed in [RFC7941], Section 4.2.6. 1082 Note that if an SDES packet is received as part of a compound RTCP 1083 packet, the SSRC to "m=" line mapping may not exist until the SDES 1084 packet is handled (e.g., in the case where RTCP for a source is 1085 received before any RTP packets). Therefore, when processing a 1086 compound packet, any contained SDES packet MUST be handled first. 1088 If the packet is of type BYE, it indicates that the RTP streams 1089 referenced in the packet are ending. Therefore, for each SSRC 1090 indicated in the packet that is found in the incoming SSRC table, 1091 first deliver a copy of the packet to the "m=" line associated 1092 with that SSRC, but then remove the entry for that SSRC from the 1093 incoming SSRC table after an appropriate delay to account for 1094 "straggler packets", as specified in [RFC3550], Section 6.2.1. 1096 If the packet is of type SR or RR, for each report block in the 1097 report whose "SSRC of source" is found in the outgoing SSRC table, 1098 deliver a copy of the RTCP packet to the "m=" line associated with 1099 that SSRC. In addition, if the packet is of type SR, and the 1100 sender SSRC for the packet is found in the incoming SSRC table, 1101 deliver a copy of the packet to the "m=" line associated with that 1102 SSRC. 1104 If the implementation supports RTCP XR and the packet is of type 1105 XR, as defined in [RFC3611], for each report block in the report 1106 whose "SSRC of source" is is found in the outgoing SSRC table, 1107 deliver a copy of the RTCP packet to the "m=" line associated with 1108 that SSRC. In addition, if the sender SSRC for the packet is 1109 found in the incoming SSRC table, deliver a copy of the packet to 1110 the "m=" line associated with that SSRC. 1112 If the packet is a feedback message of type RTPFB or PSFB, as 1113 defined in [RFC4585], it will contain a media source SSRC, and 1114 this SSRC is used for routing certain subtypes of feedback 1115 messages. However, several subtypes of PSFB messages include 1116 target SSRC(s) in a section called Feedback Control Information 1117 (FCI). For these messages, the target SSRC(s) are used for 1118 routing. 1120 If the packet is a feedback message that does not include target 1121 SSRCs in its FCI section, and the media source SSRC is found in 1122 the outgoing SSRC table, deliver the packet to the "m=" line 1123 associated with that SSRC. RTPFB and PSFB types that are handled 1124 in this way include: 1126 Generic NACK: [RFC4585] (PT=RTPFB, FMT=1). 1128 Picture Loss Indication (PLI): [RFC4585] (PT=PSFB, FMT=1). 1130 Slice Loss Indication (SLI): [RFC4585] (PT=PSFB, FMT=2). 1132 Reference Picture Selection Indication (RPSI): [RFC4585] 1133 (PT=PSFB, FMT=3). 1135 If the packet is a feedback message that does include target 1136 SSRC(s) in its FCI section, it can either be a request or a 1137 notification. Requests reference a RTP stream that is being sent 1138 by the message recipient, whereas notifications are responses to 1139 an earlier request, and therefore reference a RTP stream that is 1140 being received by the message recipient. 1142 If the packet is a feedback request that includes target SSRC(s), 1143 for each target SSRC that is found in the outgoing SSRC table, 1144 deliver a copy of the RTCP packet to the "m=" line associated with 1145 that SSRC. PSFB types that are handled in this way include: 1147 Full Intra Request (FIR): [RFC5104] (PT=PSFB, FMT=4). 1149 Temporal-Spatial Trade-off Request (TSTR): [RFC5104] (PT=PSFB, 1150 FMT=5). 1152 H.271 Video Back Channel Message (VBCM): [RFC5104] (PT=PSFB, 1153 FMT=7). 1155 Layer Refresh Request (LRR): [I-D.ietf-avtext-lrr] (PT=PSFB, 1156 FMT=TBD). 1158 If the packet is a feedback notification that include target 1159 SSRC(s), for each target SSRC that is found in the incoming SSRC 1160 table, deliver a copy of the RTCP packet to the "m=" line 1161 associated with that SSRC. PSFB types that are handled in this 1162 way include: 1164 Temporal-Spatial Trade-off Notification (TSTN): [RFC5104] 1165 (PT=PSFB, FMT=6). This message is a notification in response 1166 to a prior TSTR. 1168 If the packet is of type APP, the only routing information 1169 included is the source of the packet, and therefore the packet 1170 could be related to any existing "m=" line. Accordingly, deliver 1171 a copy of the packet to each "m=" line. 1173 10.3. RTP/RTCP Multiplexing 1175 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 1176 multiplexing [RFC5761] for the RTP-based media specified by the 1177 BUNDLE group. 1179 When RTP/RTCP multiplexing is enabled, the same address:port 1180 combination will be used for sending all RTP packets and the RTCP 1181 packets associated with the BUNDLE group. Each endpoint will send 1182 the packets towards the BUNDLE address of the other endpoint. The 1183 same address:port combination MAY be used for receiving RTP packets 1184 and RTCP packets. 1186 10.3.1. SDP Offer/Answer Procedures 1188 This section describes how an offerer and answerer use the SDP 'rtcp- 1189 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 1190 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 1191 multiplexing for RTP-based media specified by a BUNDLE group. 1193 The procedures in this section only apply to RTP-based "m=" lines. 1195 10.3.1.1. Generating the Initial SDP Offer 1197 When an offerer generates an initial offer, the offerer MUST 1198 associate an SDP 'rtcp-mux' attribute [RFC5761] with each bundled 1199 RTP-based "m=" line in the offer, including a bundle-only "m=" line. 1200 In addition, the offerer MUST associate an SDP 'rtcp-mux-only' 1201 attribute [I-D.ietf-mmusic-mux-exclusive] with each RTP-based bundle- 1202 only "m=" line, and MAY associated an SDP 'rtcp-mux-only' attribute 1203 with other bundled RTP-based "m=" lines. 1205 NOTE: Whether the offerer associates an SDP 'rtcp-mux-only' attribute 1206 with a bundled "m=" line or not depends on whether the offerer 1207 supports fallback to usage of a separate port for RTCP in case the 1208 answerer does not include the "m=" line in the BUNDLE group. 1210 NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with a 1211 bundled "m=" line, but does not associate an SDP 'rtcp-mux-only' 1212 attribute with the "m=" line, the offerer can also associate an SDP 1213 'rtcp' attribute [RFC3605] with the "m=" line in order to provide a 1214 fallback port for RTCP, as described in [RFC5761]. However, the 1215 fallback port will only be used in case the answerer does not include 1216 the "m=" line in the BUNDLE group. 1218 In the initial offer, the address:port combination for RTCP MUST be 1219 unique in each bundled RTP-based "m=" line (excluding a bundle-only 1220 "m=" line), similar to RTP. 1222 10.3.1.2. Generating the SDP Answer 1224 When an answerer generates an answer, if the answerer accepts one or 1225 more RTP-based "m=" lines within a BUNDLE group, the answerer MUST 1226 enable usage of RTP/RTCP multiplexing. The answerer MUST associate 1227 an SDP "rtcp-mux" attribute with each RTP-based "m=" line in the 1228 answer. In addition, if an "m=" line in the corresponding offer 1229 contained an SDP "rtcp-mux-only" attribute, the answerer MUST 1230 associate an SDP "rtcp-mux-only" attribute with the "m=" line in the 1231 answer. 1233 If an RTP-based "m=" line in the corresponding offer did not contain 1234 an SDP 'rtcp-mux' attribute, the answerer MUST NOT include the "m=" 1235 line within a BUNDLE group in the answer. 1237 If an RTP-based "m=" line in the corresponding offer contained an SDP 1238 "rtcp-mux-only" attribute, and if the answerer moves the "m=" line 1239 out of the BUNDLE group in the answer Section 8.3.3, the answerer 1240 MUST still either enable RTP/RTCP multiplexing for the media 1241 associated with the "m=" line, or reject the "m=" line Section 8.3.4. 1243 The answerer MUST NOT associate an SDP 'rtcp' attribute with any 1244 bundled "m=" line in the answer. The answerer will use the port 1245 value of the selected offerer BUNDLE address for sending RTP and RTCP 1246 packets associated with each RTP-based bundled "m=" line towards the 1247 offerer. 1249 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 1250 negotiated in a previous offer/answer transaction, the answerer MUST 1251 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 1252 "m=" line in the answer. 1254 10.3.1.3. Offerer Processing of the SDP Answer 1256 When an offerer receives an answer, if the answerer has accepted the 1257 usage of RTP/RTCP multiplexing (see Section 10.3.1.2), the answerer 1258 follows the procedures for RTP/RTCP multiplexing defined in 1259 [RFC5761]. The offerer will use the port value associated with the 1260 answerer BUNDLE address for sending RTP and RTCP packets associated 1261 with each RTP-based bundled "m=" line towards the answerer. 1263 NOTE: It is considered a protocol error if the answerer has not 1264 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 1265 that the answerer included in the BUNDLE group. 1267 10.3.1.4. Modifying the Session 1269 When an offerer generates a subsequent offer, for each RTP-based "m=" 1270 line that was previously added to the BUNDLE group the offerer MUST 1271 associate an SDP 'rtcp-mux' attribute and an SDP 'rtcp-mux-only' 1272 attribute with the "m=" line in the same way it was previously done, 1273 unless the offerer wants to disable or remove the "m=" line from the 1274 BUNDLE group. 1276 If the offerer wants to add a bundled RTP-based "m=" line to the 1277 BUNDLE group, it associates an SDP 'rtcp-mux' attribute and an SDP 1278 'rtcp-mux-only' attribute with the "m=" line using the procedures in 1279 [Section 10.3.1.1]. 1281 11. ICE Considerations 1283 This section describes how to use the BUNDLE grouping extension 1284 together with the Interactive Connectivity Establishment (ICE) 1285 mechanism [I-D.ietf-ice-rfc5245bis]. 1287 The generic procedures for negotiating usage of ICE using SDP, 1288 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1289 with BUNDLE, with the following exceptions: 1291 o When BUNDLE addresses for a BUNDLE group have been selected for 1292 both endpoints, ICE connectivity checks and keep-alives only need 1293 to be performed for the whole BUNDLE group, instead of per bundled 1294 "m=" line. 1296 o Among bundled "m=" lines with which the offerer has associated a 1297 shared address, the offerer only associates ICE-related media- 1298 level SDP attributes with the "m=" line associated with the 1299 offerer BUNDLE-tag. 1301 o Among bundled "m=" lines with which the answerer has associated a 1302 shared address, the answerer only associates ICE-related media- 1303 level SDP attributes with the "m=" line associated with the 1304 answerer BUNDLE-tag. 1306 Support and usage of ICE mechanism together with the BUNDLE extension 1307 is OPTIONAL. 1309 11.1. SDP Offer/Answer Procedures 1311 When an offerer associates a unique address with a bundled "m=" line 1312 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1313 'candidate' attributes (and other applicable ICE-related media-level 1314 SDP attributes), containing unique ICE properties (candidates etc), 1315 with the "m=" line, according to the procedures in 1316 [I-D.ietf-mmusic-ice-sip-sdp]. 1318 When an offerer associates a shared address with a bundled "m=" line, 1319 if the "m=" line is associated with the offerer BUNDLE-tag, the 1320 offerer MUST associate SDP 'candidate' attributes (and other 1321 applicable ICE-related media-level SDP attributes), containing shared 1322 ICE properties, with the "m=" line. If the "m=" line is not 1323 associated with the offerer BUNDLE-tag, the offerer MUST NOT 1324 associate ICE-related SDP attributes with the "m=" line. 1326 When an answerer associates a shared address with a bundled "m=" 1327 line, if the "m=" line is associated with the answerer BUNDLE-tag, 1328 the answerer MUST associate SDP 'candidate' attributes (and other 1329 applicable ICE-related media-level SDP attributes), containing shared 1330 ICE properties, with the "m=" line. If the "m=" line is not 1331 associated with the answerer BUNDLE-tag, the answerer MUST NOT 1332 associate ICE-related SDP attributes with the "m=" line. 1334 NOTE: As most ICE-related media-level SDP attributes belong to the 1335 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1336 offerer and answerer follow the rules in Section 8.1. However, in 1337 the case of ICE-related media-level attributes, the rules apply to 1338 all attributes (see note below), even if they belong to a different 1339 mux category. 1341 NOTE: The following ICE-related media-level SDP attributes are 1342 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1343 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1344 pacing'. 1346 11.1.1. Generating the Initial SDP Offer 1348 When an offerer generates an initial offer, the offerer MUST 1349 associate ICE-related media-level SDP attributes with each bundled 1350 "m=" line, according to [Section 11.1]. 1352 11.1.2. Generating the SDP Answer 1354 When an answerer generates an answer that contains a BUNDLE group, 1355 the answerer MUST associate ICE-related SDP attributes with the "m=" 1356 line associated with the answerer BUNDLE-tag, according to 1357 [Section 11.1]. 1359 11.1.3. Offerer Processing of the SDP Answer 1361 When an offerer receives an answer, if the answerer supports and uses 1362 the ICE mechanism and the BUNDLE extension, the offerer MUST 1363 associate the ICE properties associated with the offerer BUNDLE 1364 address, selected by the answerer [Section 8.3.1], with each bundled 1365 "m=" line. 1367 11.1.4. Modifying the Session 1369 When an offerer generates a subsequent offer, it MUST associate 1370 unique or shared ICE properties to one or more bundled "m=" lines, 1371 according to [Section 11.1]. 1373 12. DTLS Considerations 1375 One or more media streams within a BUNDLE group might use the 1376 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1377 to encrypt the data, or to negotiate encryption keys if another 1378 encryption mechanism is used to encrypt media. 1380 When DTLS is used within a BUNDLE group, the following rules apply: 1382 o There can only be one DTLS association [RFC6347] associated with 1383 the BUNDLE group; and 1385 o Each usage of the DTLS association within the BUNDLE group MUST 1386 use the same mechanism for determining which endpoints (the 1387 offerer or answerer) become DTLS client and DTLS server; and 1389 o Each usage of the DTLS association within the Bundle group MUST 1390 use the same mechanism for determining whether an offer or answer 1391 will trigger the establishment of a new DTLS association, or 1392 whether an existing DTLS association will be used; and 1394 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1395 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1396 [RFC5764], The client MUST include the extension even if the usage 1397 of DTLS-SRTP is not negotiated as part of the multimedia session 1398 (e.g., SIP session [RFC3261]. 1400 NOTE: The inclusion of the 'use_srtp' extension during the initial 1401 DTLS handshake ensures that a DTLS renegotiation will not be required 1402 in order to include the extension, in case DTLS-SRTP encrypted media 1403 is added to the BUNDLE group later during the multimedia session. 1405 13. RTP Header Extensions Consideration 1407 When [RFC5285] RTP header extensions are used in the context of this 1408 specification, the identifier used for a given extension MUST 1409 identify the same extension across all the bundled media 1410 descriptions. 1412 14. Update to RFC 3264 1414 This section replaces the text of the following sections of RFC 3264: 1416 o Section 5.1 (Unicast Streams). 1418 o Section 8.2 (Removing a Media Stream). 1420 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1422 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 1424 For recvonly and sendrecv streams, the port number and address in the 1425 offer indicate where the offerer would like to receive the media 1426 stream. For sendonly RTP streams, the address and port number 1427 indirectly indicate where the offerer wants to receive RTCP reports. 1428 Unless there is an explicit indication otherwise, reports are sent to 1429 the port number one higher than the number indicated. The IP address 1430 and port present in the offer indicate nothing about the source IP 1431 address and source port of RTP and RTCP packets that will be sent by 1432 the offerer. A port number of zero in the offer indicates that the 1433 stream is offered but MUST NOT be used. This has no useful semantics 1434 in an initial offer, but is allowed for reasons of completeness, 1435 since the answer can contain a zero port indicating a rejected stream 1436 (Section 6). Furthermore, existing streams can be terminated by 1437 setting the port to zero (Section 8). In general, a port number of 1438 zero indicates that the media stream is not wanted. 1440 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1442 For recvonly and sendrecv streams, the port number and address in the 1443 offer indicate where the offerer would like to receive the media 1444 stream. For sendonly RTP streams, the address and port number 1445 indirectly indicate where the offerer wants to receive RTCP reports. 1446 Unless there is an explicit indication otherwise, reports are sent to 1447 the port number one higher than the number indicated. The IP address 1448 and port present in the offer indicate nothing about the source IP 1449 address and source port of RTP and RTCP packets that will be sent by 1450 the offerer. A port number of zero in the offer by default indicates 1451 that the stream is offered but MUST NOT be used, but an extension 1452 mechanism might specify different semantics for the usage of a zero 1453 port value. Furthermore, existing streams can be terminated by 1454 setting the port to zero (Section 8). In general, a port number of 1455 zero by default indicates that the media stream is not wanted. 1457 14.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 1459 A stream that is offered with a port of zero MUST be marked with port 1460 zero in the answer. Like the offer, the answer MAY omit all 1461 attributes present previously, and MAY list just a single media 1462 format from amongst those in the offer. 1464 14.4. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1466 A stream that is offered with a port of zero MUST by default be 1467 marked with port zero in the answer, unless an extension mechanism, 1468 which specifies semantics for the usage of a non-zero port value, is 1469 used. If the stream is marked with port zero in the answer, the 1470 answer MAY omit all attributes present previously, and MAY list just 1471 a single media format from amongst those in the offer." 1473 14.5. Original text of section 8.4 (6th paragraph) of RFC 3264 1475 RFC 2543 [10] specified that placing a user on hold was accomplished 1476 by setting the connection address to 0.0.0.0. Its usage for putting 1477 a call on hold is no longer recommended, since it doesn't allow for 1478 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1479 with connection oriented media. However, it can be useful in an 1480 initial offer when the offerer knows it wants to use a particular set 1481 of media streams and formats, but doesn't know the addresses and 1482 ports at the time of the offer. Of course, when used, the port 1483 number MUST NOT be zero, which would specify that the stream has been 1484 disabled. An agent MUST be capable of receiving SDP with a 1485 connection address of 0.0.0.0, in which case it means that neither 1486 RTP nor RTCP should be sent to the peer. 1488 14.6. New text replacing section 8.4 (6th paragraph) of RFC 3264 1490 RFC 2543 [10] specified that placing a user on hold was accomplished 1491 by setting the connection address to 0.0.0.0. Its usage for putting 1492 a call on hold is no longer recommended, since it doesn't allow for 1493 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1494 with connection oriented media. However, it can be useful in an 1495 initial offer when the offerer knows it wants to use a particular set 1496 of media streams and formats, but doesn't know the addresses and 1497 ports at the time of the offer. Of course, when used, the port 1498 number MUST NOT be zero, if it would specify that the stream has been 1499 disabled. However, an extension mechanism might specify different 1500 semantics of the zero port number usage. An agent MUST be capable of 1501 receiving SDP with a connection address of 0.0.0.0, in which case it 1502 means that neither RTP nor RTCP should be sent to the peer. 1504 15. RTP/RTCP extensions for identification-tag transport 1506 SDP Offerers and Answerers [RFC3264] can associate identification- 1507 tags with "m=" lines within SDP Offers and Answers, using the 1508 procedures in [RFC5888]. Each identification-tag uniquely represents 1509 an "m=" line. 1511 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1512 used to carry identification-tags within RTCP SDES packets. This 1513 section also defines a new RTP SDES header extension [RFC7941], which 1514 is used to carry the 'MID' RTCP SDES item in RTP packets. 1516 The SDES item and RTP SDES header extension make it possible for a 1517 receiver to associate each RTP stream with with a specific "m=" line, 1518 with which the receiver has associated an identification-tag, even if 1519 those "m=" lines are part of the same RTP session. The RTP SDES 1520 header extension also ensures that the media recipient gets the 1521 identification-tag upon receipt of the first decodable media and is 1522 able to associate the media with the correct application. 1524 A media recipient informs the media sender about the identification- 1525 tag associated with an "m=" line through the use of an 'mid' 1526 attribute [RFC5888]. The media sender then inserts the 1527 identification-tag in RTCP and RTP packets sent to the media 1528 recipient. 1530 NOTE: This text above defines how identification-tags are carried in 1531 SDP Offers and Answers. The usage of other signalling protocols for 1532 carrying identification-tags is not prevented, but the usage of such 1533 protocols is outside the scope of this document. 1535 [RFC3550] defines general procedures regarding the RTCP transmission 1536 interval. The RTCP MID SDES item SHOULD be sent in the first few 1537 RTCP packets sent after joining the session, and SHOULD be sent 1538 regularly thereafter. The exact number of RTCP packets in which this 1539 SDES item is sent is intentionally not specified here, as it will 1540 depend on the expected packet loss rate, the RTCP reporting interval, 1541 and the allowable overhead. 1543 The RTP SDES header extension for carrying the 'MID' RTCP SDES SHOULD 1544 be included in some RTP packets at the start of the session and 1545 whenever the SSRC changes. It might also be useful to include the 1546 header extension in RTP packets that comprise access points in the 1547 media (e.g., with video I-frames). The exact number of RTP packets 1548 in which this header extension is sent is intentionally not specified 1549 here, as it will depend on expected packet loss rate and loss 1550 patterns, the overhead the application can tolerate, and the 1551 importance of immediate receipt of the identification-tag. 1553 For robustness purpose, endpoints need to be prepared for situations 1554 where the reception of the identification-tag is delayed, and SHOULD 1555 NOT terminate sessions in such cases, as the identification-tag is 1556 likely to arrive soon. 1558 15.1. RTCP MID SDES Item 1559 0 1 2 3 1560 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 1561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1562 | MID=TBD | length | identification-tag ... 1563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1565 The identification-tag payload is UTF-8 encoded, as in SDP. 1567 The identification-tag is not zero terminated. 1569 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1570 identifier value.] 1572 15.2. RTP SDES Header Extension For MID 1574 The payload, containing the identification-tag, of the RTP SDES 1575 header extension element can be encoded using either the one-byte or 1576 two-byte header [RFC7941]. The identification-tag payload is UTF-8 1577 encoded, as in SDP. 1579 The identification-tag is not zero terminated. Note, that the set of 1580 header extensions included in the packet needs to be padded to the 1581 next 32-bit boundary using zero bytes [RFC5285]. 1583 As the identification-tag is included in either an RTCP SDES item or 1584 an RTP SDES header extension, or both, there should be some 1585 consideration about the packet expansion caused by the 1586 identification-tag. To avoid Maximum Transmission Unit (MTU) issues 1587 for the RTP packets, the header extension's size needs to be taken 1588 into account when encoding the media. 1590 It is recommended that the identification-tag is kept short. Due to 1591 the properties of the RTP header extension mechanism, when using the 1592 one-byte header, a tag that is 1-3 bytes will result in a minimal 1593 number of 32-bit words used for the RTP SDES header extension, in 1594 case no other header extensions are included at the same time. Note, 1595 do take into account that some single characters when UTF-8 encoded 1596 will result in multiple octets. The identification-tag MUST NOT 1597 contain any user information, and applications SHALL avoid generating 1598 the identification-tag using a pattern that enables application 1599 identification. 1601 16. IANA Considerations 1602 16.1. New SDES item 1604 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1605 document.] 1607 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1608 identifier value.] 1610 This document adds the MID SDES item to the IANA "RTP SDES item 1611 types" registry as follows: 1613 Value: TBD 1614 Abbrev.: MID 1615 Name: Media Identification 1616 Reference: RFCXXXX 1618 16.2. New RTP SDES Header Extension URI 1620 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1621 document.] 1623 This document defines a new extension URI in the RTP SDES Compact 1624 Header Extensions sub-registry of the RTP Compact Header Extensions 1625 registry sub-registry, according to the following data: 1627 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1628 Description: Media identification 1629 Contact: christer.holmberg@ericsson.com 1630 Reference: RFCXXXX 1632 The SDES item does not reveal privacy information about the users. 1633 It is simply used to associate RTP-based media with the correct SDP 1634 media description (m- line) in the SDP used to negotiate the media. 1636 The purpose of the extension is for the offerer to be able to 1637 associate received multiplexed RTP-based media before the offerer 1638 receives the associated SDP answer. 1640 16.3. New SDP Attribute 1642 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1643 document.] 1644 This document defines a new SDP media-level attribute, 'bundle-only', 1645 according to the following data: 1647 Attribute name: bundle-only 1648 Type of attribute: media 1649 Subject to charset: No 1650 Purpose: Request a media description to be accepted 1651 in the answer only if kept within a BUNDLE 1652 group by the answerer. 1653 Appropriate values: N/A 1654 Contact name: Christer Holmberg 1655 Contact e-mail: christer.holmberg@ericsson.com 1656 Reference: RFCXXXX 1657 Mux category: NORMAL 1659 16.4. New SDP Group Semantics 1661 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1662 document.] 1664 This document registers the following semantics with IANA in the 1665 "Semantics for the "group" SDP Attribute" subregistry (under the 1666 "Session Description Protocol (SDP) Parameters" registry: 1668 Semantics Token Reference 1669 ------------------------------------- ------ --------- 1670 Media bundling BUNDLE [RFCXXXX] 1672 17. Security Considerations 1674 The security considerations defined in [RFC3264] and [RFC5888] apply 1675 to the BUNDLE extension. Bundle does not change which information, 1676 e.g., RTP streams, flows over the network, with the exception of the 1677 usage of the MID SDES item as discussed below. Primarily it changes 1678 which addresses and ports, and thus in which (RTP) sessions that the 1679 information is flowing in. This affects the security contexts being 1680 used and can cause previously separated information flows to share 1681 the same security context. This has very little impact on the 1682 performance of the security mechanism of the RTP sessions. In cases 1683 where one would have applied different security policies on the 1684 different RTP streams being bundled, or where the parties having 1685 access to the security contexts would have differed between the RTP 1686 stream, additional analysis of the implications are needed before 1687 selecting to apply BUNDLE. 1689 The identification-tag, independent of transport, RTCP SDES packet or 1690 RTP header extension, can expose the value to parties beyond the 1691 signaling chain. Therefore, the identification-tag values MUST be 1692 generated in a fashion that does not leak user information, e.g., 1693 randomly or using a per-bundle group counter, and SHOULD be 3 bytes 1694 or less, to allow them to efficiently fit into the MID RTP header 1695 extension. Note that if implementations use different methods for 1696 generating identification-tags this could enable fingerprinting of 1697 the implementation making it vulnerable to targeted attacks. The 1698 identification-tag is exposed on the RTP stream level when included 1699 in the RTP header extensions, however what it reveals of the RTP 1700 media stream structure of the endpoint and application was already 1701 possible to deduce from the RTP streams without the MID SDES header 1702 extensions. As the identification-tag is also used to route the 1703 media stream to the right application functionality it is also 1704 important that the value received is the one intended by the sender, 1705 thus integrity and the authenticity of the source are important to 1706 prevent denial of service on the application. Existing SRTP 1707 configurations and other security mechanisms protecting the whole 1708 RTP/RTCP packets will provide the necessary protection. 1710 When the BUNDLE extension is used, the set of configurations of the 1711 security mechanism used in all the bundled media descriptions will 1712 need to be compatible so that they can simultaneously used in 1713 parallel, at least per direction or endpoint. When using SRTP this 1714 will be the case, at least for the IETF defined key-management 1715 solutions due to their SDP attributes (a=crypto, a=fingerprint, 1716 a=mikey) and their classification in 1717 [I-D.ietf-mmusic-sdp-mux-attributes]. 1719 The security considerations of "RTP Header Extension for the RTP 1720 Control Protocol (RTCP) Source Description Items" [RFC7941] requires 1721 that when RTCP is confidentiality protected that any SDES RTP header 1722 extension carrying an SDES item, such as the MID RTP header 1723 extension, is also protected using commensurate strength algorithms. 1724 However, assuming the above requirements and recommendations are 1725 followed there are no known significant security risks with leaving 1726 the MID RTP header extension without confidentiality protection. 1727 Thus, the requirements in RFC 7941 MAY be ignored for the MID RTP 1728 header extension. Security mechanisms for RTP/RTCP are discussed in 1729 Options for Securing RTP Sessions [RFC7201], for example SRTP 1730 [RFC3711] can provide the necessary security functions of ensuring 1731 the integrity and source authenticity. 1733 18. Examples 1735 18.1. Example: Bundle Address Selection 1737 The example below shows: 1739 o An offer, in which the offerer associates a unique address with 1740 each bundled "m=" line within the BUNDLE group. 1742 o An answer, in which the answerer selects the offerer BUNDLE 1743 address, and then selects its own BUNDLE address (the answerer 1744 BUNDLE address) and associates it with each bundled "m=" line 1745 within the BUNDLE group. 1747 SDP Offer (1) 1749 v=0 1750 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1751 s= 1752 c=IN IP4 atlanta.example.com 1753 t=0 0 1754 a=group:BUNDLE foo bar 1755 m=audio 10000 RTP/AVP 0 8 97 1756 b=AS:200 1757 a=mid:foo 1758 a=rtcp-mux 1759 a=rtpmap:0 PCMU/8000 1760 a=rtpmap:8 PCMA/8000 1761 a=rtpmap:97 iLBC/8000 1762 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1763 m=video 10002 RTP/AVP 31 32 1764 b=AS:1000 1765 a=mid:bar 1766 a=rtcp-mux 1767 a=rtpmap:31 H261/90000 1768 a=rtpmap:32 MPV/90000 1769 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1771 SDP Answer (2) 1773 v=0 1774 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1775 s= 1776 c=IN IP4 biloxi.example.com 1777 t=0 0 1778 a=group:BUNDLE foo bar 1779 m=audio 20000 RTP/AVP 0 1780 b=AS:200 1781 a=mid:foo 1782 a=rtcp-mux 1783 a=rtpmap:0 PCMU/8000 1784 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1785 m=video 20000 RTP/AVP 32 1786 b=AS:1000 1787 a=mid:bar 1788 a=rtcp-mux 1789 a=rtpmap:32 MPV/90000 1790 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1792 18.2. Example: BUNDLE Extension Rejected 1794 The example below shows: 1796 o An offer, in which the offerer associates a unique address with 1797 each bundled "m=" line within the BUNDLE group. 1799 o An answer, in which the answerer rejects the offered BUNDLE group, 1800 and associates a unique address with each "m=" line (following 1801 normal RFC 3264 procedures). 1803 SDP Offer (1) 1805 v=0 1806 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1807 s= 1808 c=IN IP4 atlanta.example.com 1809 t=0 0 1810 a=group:BUNDLE foo bar 1811 m=audio 10000 RTP/AVP 0 8 97 1812 b=AS:200 1813 a=mid:foo 1814 a=rtcp-mux 1815 a=rtpmap:0 PCMU/8000 1816 a=rtpmap:8 PCMA/8000 1817 a=rtpmap:97 iLBC/8000 1818 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1819 m=video 10002 RTP/AVP 31 32 1820 b=AS:1000 1821 a=mid:bar 1822 a=rtcp-mux 1823 a=rtpmap:31 H261/90000 1824 a=rtpmap:32 MPV/90000 1825 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1827 SDP Answer (2) 1829 v=0 1830 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1831 s= 1832 c=IN IP4 biloxi.example.com 1833 t=0 0 1834 m=audio 20000 RTP/AVP 0 1835 b=AS:200 1836 a=rtcp-mux 1837 a=rtpmap:0 PCMU/8000 1838 m=video 30000 RTP/AVP 32 1839 b=AS:1000 1840 a=rtcp-mux 1841 a=rtpmap:32 MPV/90000 1843 18.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1845 The example below shows: 1847 o A subsequent offer (the BUNDLE group has been created as part of a 1848 previous offer/answer exchange), in which the offerer adds a new 1849 "m=" line, represented by the "zen" identification-tag, to a 1850 previously negotiated BUNDLE group, associates a unique address 1851 with the added "m=" line, and associates the previously selected 1852 offerer BUNDLE address with each of the other bundled "m=" lines 1853 within the BUNDLE group. 1855 o An answer, in which the answerer associates the answerer BUNDLE 1856 address with each bundled "m=" line (including the newly added 1857 "m=" line) within the BUNDLE group. 1859 SDP Offer (1) 1861 v=0 1862 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1863 s= 1864 c=IN IP4 atlanta.example.com 1865 t=0 0 1866 a=group:BUNDLE foo bar zen 1867 m=audio 10000 RTP/AVP 0 8 97 1868 b=AS:200 1869 a=mid:foo 1870 a=rtcp-mux 1871 a=rtpmap:0 PCMU/8000 1872 a=rtpmap:8 PCMA/8000 1873 a=rtpmap:97 iLBC/8000 1874 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1875 m=video 10000 RTP/AVP 31 32 1876 b=AS:1000 1877 a=mid:bar 1878 a=rtcp-mux 1879 a=rtpmap:31 H261/90000 1880 a=rtpmap:32 MPV/90000 1881 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1882 m=video 20000 RTP/AVP 66 1883 b=AS:1000 1884 a=mid:zen 1885 a=rtcp-mux 1886 a=rtpmap:66 H261/90000 1887 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1889 SDP Answer (2) 1891 v=0 1892 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1893 s= 1894 c=IN IP4 biloxi.example.com 1895 t=0 0 1896 a=group:BUNDLE foo bar zen 1897 m=audio 20000 RTP/AVP 0 1898 b=AS:200 1899 a=mid:foo 1900 a=rtcp-mux 1901 a=rtpmap:0 PCMU/8000 1902 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1903 m=video 20000 RTP/AVP 32 1904 b=AS:1000 1905 a=mid:bar 1906 a=rtcp-mux 1907 a=rtpmap:32 MPV/90000 1908 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1909 m=video 20000 RTP/AVP 66 1910 b=AS:1000 1911 a=mid:zen 1912 a=rtcp-mux 1913 a=rtpmap:66 H261/90000 1914 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1916 18.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1918 The example below shows: 1920 o A subsequent offer (the BUNDLE group has been created as part of a 1921 previous offer/answer transaction), in which the offerer moves a 1922 bundled "m=" line out of a BUNDLE group, associates a unique 1923 address with the moved "m=" line, and associates the offerer 1924 BUNDLE address with each other bundled "m=" line within the BUNDLE 1925 group. 1927 o An answer, in which the answerer moves the "m=" line out of the 1928 BUNDLE group, associates a unique address with the moved "m=" 1929 line, and associates the answerer BUNDLE address with each of the 1930 remaining bundled "m=" line within the BUNDLE group. 1932 SDP Offer (1) 1934 v=0 1935 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1936 s= 1937 c=IN IP4 atlanta.example.com 1938 t=0 0 1939 a=group:BUNDLE foo bar 1940 m=audio 10000 RTP/AVP 0 8 97 1941 b=AS:200 1942 a=mid:foo 1943 a=rtcp-mux 1944 a=rtpmap:0 PCMU/8000 1945 a=rtpmap:8 PCMA/8000 1946 a=rtpmap:97 iLBC/8000 1947 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1948 m=video 10000 RTP/AVP 31 32 1949 b=AS:1000 1950 a=mid:bar 1951 a=rtcp-mux 1952 a=rtpmap:31 H261/90000 1953 a=rtpmap:32 MPV/90000 1954 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1955 m=video 50000 RTP/AVP 66 1956 b=AS:1000 1957 a=mid:zen 1958 a=rtcp-mux 1959 a=rtpmap:66 H261/90000 1961 SDP Answer (2) 1963 v=0 1964 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1965 s= 1966 c=IN IP4 biloxi.example.com 1967 t=0 0 1968 a=group:BUNDLE foo bar 1969 m=audio 20000 RTP/AVP 0 1970 b=AS:200 1971 a=mid:foo 1972 a=rtcp-mux 1973 a=rtpmap:0 PCMU/8000 1974 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1975 m=video 20000 RTP/AVP 32 1976 b=AS:1000 1977 a=mid:bar 1978 a=rtcp-mux 1979 a=rtpmap:32 MPV/90000 1980 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1981 m=video 60000 RTP/AVP 66 1982 b=AS:1000 1983 a=mid:zen 1984 a=rtcp-mux 1985 a=rtpmap:66 H261/90000 1987 18.5. Example: Offerer Disables A Media Description Within A BUNDLE 1988 Group 1990 The example below shows: 1992 o A subsequent offer (the BUNDLE group has been created as part of a 1993 previous offer/answer transaction), in which the offerer disables 1994 a bundled "m=" line within a BUNDLE group, assigns a zero port 1995 number to the disabled "m=" line, and associates the offerer 1996 BUNDLE address with each of the other bundled "m=" lines within 1997 the BUNDLE group. 1999 o An answer, in which the answerer moves the disabled "m=" line out 2000 of the BUNDLE group, assigns a zero port value to the disabled 2001 "m=" line, and associates the answerer BUNDLE address with each of 2002 the remaining bundled "m=" line within the BUNDLE group. 2004 SDP Offer (1) 2006 v=0 2007 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2008 s= 2009 c=IN IP4 atlanta.example.com 2010 t=0 0 2011 a=group:BUNDLE foo bar 2012 m=audio 10000 RTP/AVP 0 8 97 2013 b=AS:200 2014 a=mid:foo 2015 a=rtcp-mux 2016 a=rtpmap:0 PCMU/8000 2017 a=rtpmap:8 PCMA/8000 2018 a=rtpmap:97 iLBC/8000 2019 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2020 m=video 10000 RTP/AVP 31 32 2021 b=AS:1000 2022 a=mid:bar 2023 a=rtcp-mux 2024 a=rtpmap:31 H261/90000 2025 a=rtpmap:32 MPV/90000 2026 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2027 m=video 0 RTP/AVP 66 2028 a=mid:zen 2029 a=rtpmap:66 H261/90000 2031 SDP Answer (2) 2033 v=0 2034 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2035 s= 2036 c=IN IP4 biloxi.example.com 2037 t=0 0 2038 a=group:BUNDLE foo bar 2039 m=audio 20000 RTP/AVP 0 2040 b=AS:200 2041 a=mid:foo 2042 a=rtcp-mux 2043 a=rtpmap:0 PCMU/8000 2044 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2045 m=video 20000 RTP/AVP 32 2046 b=AS:1000 2047 a=mid:bar 2048 a=rtcp-mux 2049 a=rtpmap:32 MPV/90000 2050 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2051 m=video 0 RTP/AVP 66 2052 a=mid:zen 2053 a=rtpmap:66 H261/90000 2055 19. Acknowledgements 2057 The usage of the SDP grouping extension for negotiating bundled media 2058 is based on a similar alternatives proposed by Harald Alvestrand and 2059 Cullen Jennings. The BUNDLE extension described in this document is 2060 based on the different alternative proposals, and text (e.g., SDP 2061 examples) have been borrowed (and, in some cases, modified) from 2062 those alternative proposals. 2064 The SDP examples are also modified versions from the ones in the 2065 Alvestrand proposal. 2067 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 2068 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 2069 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 2070 Justin Uberti for reading the text, and providing useful feedback. 2072 Thanks to Bernard Aboba, Cullen Jennings, Peter Thatcher, Justin 2073 Uberti, and Magnus Westerlund for providing the text for the section 2074 on RTP/RTCP stream association. 2076 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 2077 providing help and text on the RTP/RTCP procedures. 2079 Thanks to Spotify for providing music for the countless hours of 2080 document editing. 2082 20. Change Log 2084 [RFC EDITOR NOTE: Please remove this section when publishing] 2086 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-36 2088 o The following GitHub pull requests were merged: 2090 o https://github.com/cdh4u/draft-sdp-bundle/pull/32 2092 o - extmap handling in BUNDLE. 2094 o https://github.com/cdh4u/draft-sdp-bundle/pull/31 2096 o - Additional Acknowledgement text added. 2098 o https://github.com/cdh4u/draft-sdp-bundle/pull/30 2100 o - MID SDES item security procedures updated 2102 o https://github.com/cdh4u/draft-sdp-bundle/pull/29 2104 o - Appendix B of JSEP moved into BUNDLE. 2106 o - Associating RTP/RTCP packets with SDP m- lines. 2108 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-35 2110 o Editorial changes on RTP streaming mapping section based on 2111 comments from Colin Perkins. 2113 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-34 2115 o RTP streams, instead of RTP packets, are associated with m- lines. 2117 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-33 2119 o Editorial changes based on comments from Eric Rescorla and Cullen 2120 Jennings: 2122 o - Changes regarding usage of RTP/RTCP multiplexing attributes. 2124 o - Additional text regarding associating RTP/RTCP packets with SDP 2125 m- lines. 2127 o - Reference correction. 2129 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-32 2131 o Editorial changes based on comments from Eric Rescorla and Cullen 2132 Jennings: 2134 o - Justification for mechanism added to Introduction. 2136 o - Clarify that the order of m- lines in the group:BUNDLE attribute 2137 does not have to be the same as the order in which the m- lines 2138 are listed in the SDP. 2140 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31 2142 o Editorial changes based on GitHub Pull requests by Martin Thomson: 2144 o - https://github.com/cdh4u/draft-sdp-bundle/pull/2 2146 o - https://github.com/cdh4u/draft-sdp-bundle/pull/1 2148 o Editorial change based on comment from Diederick Huijbers (9th 2149 July 2016). 2151 o Changes based on comments from Flemming Andreasen (21st June 2152 2016): 2154 o - Mux category for SDP bundle-only attribute added. 2156 o - Mux category considerations editorial clarification. 2158 o - Editorial changes. 2160 o RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext. 2162 o Note whether Design Considerations appendix is to be kept removed: 2164 o - Appendix is kept within document. 2166 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30 2168 o Indicating in the Abstract and Introduction that the document 2169 updates RFC 3264. 2171 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29 2172 o Change based on WGLC comment from Colin Perkins. 2174 o - Clarify that SSRC can be reused by another source after a delay 2175 of 5 RTCP reporting intervals. 2177 o Change based on WGLC comment from Alissa Cooper. 2179 o - IANA registry name fix. 2181 o - Additional IANA registration information added. 2183 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 2185 o - Alignment with exclusive mux procedures. 2187 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 2189 o - Yet another terminology change. 2191 o - Mux category considerations added. 2193 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 2195 o - ICE considerations modified: ICE-related SDP attributes only 2196 added to the bundled m- line representing the selected BUNDLE 2197 address. 2199 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 2201 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 2202 rfc5245bis. 2204 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 2206 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 2207 considerations. 2209 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 2211 o - Reference and procedures associated with exclusive RTP/RTCP mux 2212 added 2214 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 2216 o - RTCP-MUX mandatory for bundled RTP m- lines 2218 o - Editorial fixes based on comments from Flemming Andreasen 2219 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 2221 o - Correction of Ari's family name 2223 o - Editorial fixes based on comments from Thomas Stach 2225 o - RTP/RTCP correction based on comment from Magnus Westerlund 2227 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2228 msg14861.html 2230 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 2232 o - Correct based on comment from Paul Kyzivat 2234 o -- 'received packets' replaced with 'received data' 2236 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 2238 o - Clarification based on comment from James Guballa 2240 o - Clarification based on comment from Flemming Andreasen 2242 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 2244 o - DTLS Considerations section added. 2246 o - BUNDLE semantics added to the IANA Considerations 2248 o - Changes based on WGLC comments from Adam Roach 2250 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2251 msg14673.html 2253 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 2255 o - Changes based on agreements at IETF#92 2257 o -- BAS Offer removed, based on agreement at IETF#92. 2259 o -- Procedures regarding usage of SDP "b=" line is replaced with a 2260 reference to to draft-ietf-mmusic-sdp-mux-attributes. 2262 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 2264 o - Editorial changes based on comments from Magnus Westerlund. 2266 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 2267 o - Modification of RTP/RTCP multiplexing section, based on comments 2268 from Magnus Westerlund. 2270 o - Reference updates. 2272 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 2274 o - Editorial fix. 2276 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 2278 o - Editorial changes. 2280 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 2282 o Changes to allow a new suggested offerer BUNDLE address to be 2283 assigned to each bundled m- line. 2285 o Changes based on WGLC comments from Paul Kyzivat 2287 o - Editorial fixes 2289 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 2291 o Usage of SDP 'extmap' attribute added 2293 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 2294 port value 2296 o Changes based on WGLC comments from Thomas Stach 2298 o - ICE candidates not assigned to bundle-only m- lines with a zero 2299 port value 2301 o - Editorial changes 2303 o Changes based on WGLC comments from Colin Perkins 2305 o - Editorial changes: 2307 o -- "RTP SDES item" -> "RTCP SDES item" 2309 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 2311 o - Changes in section 10.1.1: 2313 o -- "SHOULD NOT" -> "MUST NOT" 2314 o -- Additional text added to the Note 2316 o - Change to section 13.2: 2318 o -- Clarify that mid value is not zero terminated 2320 o - Change to section 13.3: 2322 o -- Clarify that mid value is not zero terminated 2324 o -- Clarify padding 2326 o Changes based on WGLC comments from Paul Kyzivat 2328 o - Editorial changes: 2330 o Changes based on WGLC comments from Jonathan Lennox 2332 o - Editorial changes: 2334 o - Defintion of SDP bundle-only attribute alligned with structure 2335 in 4566bis draft 2337 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 2339 o Editorial corrections based on comments from Harald Alvestrand. 2341 o Editorial corrections based on comments from Cullen Jennings. 2343 o Reference update (RFC 7160). 2345 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 2346 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 2347 msg13765.html). 2349 o Additional text added to the Security Considerations. 2351 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 2353 o SDP bundle-only attribute added to IANA Considerations. 2355 o SDES item and RTP header extension added to Abstract and 2356 Introduction. 2358 o Modification to text updating section 8.2 of RFC 3264. 2360 o Reference corrections. 2362 o Editorial corrections. 2364 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 2366 o Terminology change: "bundle-only attribute assigned to m= line" to 2367 "bundle-only attribute associated with m= line". 2369 o Editorial corrections. 2371 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 2373 o Editorial corrections. 2375 o - "of"->"if" (8.3.2.5). 2377 o - "optional"->"OPTIONAL" (9.1). 2379 o - Syntax/ABNF for 'bundle-only' attribute added. 2381 o - SDP Offer/Answer sections merged. 2383 o - 'Request new offerer BUNDLE address' section added 2385 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 2387 o OPEN ISSUE regarding Receiver-ID closed. 2389 o - RTP MID SDES Item. 2391 o - RTP MID Header Extension. 2393 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 2394 closed. 2396 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 2397 include an 'rtcp' attribute in the answer, based on the procedures 2398 in section 5.1.3 of RFC 5761. 2400 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 2402 o Draft title changed. 2404 o Added "SDP" to section names containing "Offer" or "Answer". 2406 o Editorial fixes based on comments from Paul Kyzivat 2407 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2408 msg13314.html). 2410 o Editorial fixed based on comments from Colin Perkins 2411 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2412 msg13318.html). 2414 o - Removed text about extending BUNDLE to allow multiple RTP 2415 sessions within a BUNDLE group. 2417 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 2419 o Major re-structure of SDP Offer/Answer sections, to align with RFC 2420 3264 structure. 2422 o Additional definitions added. 2424 o - Shared address. 2426 o - Bundled "m=" line. 2428 o - Bundle-only "m=" line. 2430 o - Offerer suggested BUNDLE mid. 2432 o - Answerer selected BUNDLE mid. 2434 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 2435 to multiple "m=" lines until it has received an SDP Answer 2436 indicating support of the BUNDLE extension. 2438 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 2439 Answerer supports the BUNDLE extension, assign a zero port value 2440 to a 'bundle-only' "m=" line. 2442 o SDP 'bundle-only' attribute section added. 2444 o Connection data nettype/addrtype restrictions added. 2446 o RFC 3264 update section added. 2448 o Indicating that a specific payload type value can be used in 2449 multiple "m=" lines, if the value represents the same codec 2450 configuration in each "m=" line. 2452 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2454 o Updated Offerer procedures (http://www.ietf.org/mail- 2455 archive/web/mmusic/current/msg12293.html). 2457 o Updated Answerer procedures (http://www.ietf.org/mail- 2458 archive/web/mmusic/current/msg12333.html). 2460 o Usage of SDP 'bundle-only' attribute added. 2462 o Reference to Trickle ICE document added. 2464 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2466 o Mechanism modified, to be based on usage of SDP Offers with both 2467 different and identical port number values, depending on whether 2468 it is known if the remote endpoint supports the extension. 2470 o Cullen Jennings added as co-author. 2472 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2474 o No changes. New version due to expiration. 2476 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2478 o No changes. New version due to expiration. 2480 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2482 o Draft name changed. 2484 o Harald Alvestrand added as co-author. 2486 o "Multiplex" terminology changed to "bundle". 2488 o Added text about single versus multiple RTP Sessions. 2490 o Added reference to RFC 3550. 2492 21. References 2494 21.1. Normative References 2496 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2497 Requirement Levels", BCP 14, RFC 2119, 2498 DOI 10.17487/RFC2119, March 1997, 2499 . 2501 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2502 with Session Description Protocol (SDP)", RFC 3264, 2503 DOI 10.17487/RFC3264, June 2002, 2504 . 2506 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2507 Jacobson, "RTP: A Transport Protocol for Real-Time 2508 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2509 July 2003, . 2511 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2512 in Session Description Protocol (SDP)", RFC 3605, 2513 DOI 10.17487/RFC3605, October 2003, 2514 . 2516 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 2517 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 2518 RFC 3711, DOI 10.17487/RFC3711, March 2004, 2519 . 2521 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2522 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2523 July 2006, . 2525 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2526 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2527 . 2529 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2530 (ICE): A Protocol for Network Address Translator (NAT) 2531 Traversal for Offer/Answer Protocols", RFC 5245, 2532 DOI 10.17487/RFC5245, April 2010, 2533 . 2535 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2536 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2537 2008, . 2539 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2540 Control Packets on a Single Port", RFC 5761, 2541 DOI 10.17487/RFC5761, April 2010, 2542 . 2544 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2545 Security (DTLS) Extension to Establish Keys for the Secure 2546 Real-time Transport Protocol (SRTP)", RFC 5764, 2547 DOI 10.17487/RFC5764, May 2010, 2548 . 2550 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2551 Protocol (SDP) Grouping Framework", RFC 5888, 2552 DOI 10.17487/RFC5888, June 2010, 2553 . 2555 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2556 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2557 January 2012, . 2559 [RFC7941] Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 2560 Header Extension for the RTP Control Protocol (RTCP) 2561 Source Description Items", RFC 7941, DOI 10.17487/RFC7941, 2562 August 2016, . 2564 [I-D.ietf-ice-rfc5245bis] 2565 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 2566 Connectivity Establishment (ICE): A Protocol for Network 2567 Address Translator (NAT) Traversal", draft-ietf-ice- 2568 rfc5245bis-08 (work in progress), December 2016. 2570 [I-D.ietf-mmusic-sdp-mux-attributes] 2571 Nandakumar, S., "A Framework for SDP Attributes when 2572 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 2573 (work in progress), December 2016. 2575 [I-D.ietf-mmusic-mux-exclusive] 2576 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2577 Multiplexing using SDP", draft-ietf-mmusic-mux- 2578 exclusive-11 (work in progress), February 2017. 2580 [I-D.ietf-mmusic-ice-sip-sdp] 2581 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, "Using 2582 Interactive Connectivity Establishment (ICE) with Session 2583 Description Protocol (SDP) offer/answer and Session 2584 Initiation Protocol (SIP)", draft-ietf-mmusic-ice-sip- 2585 sdp-12 (work in progress), March 2017. 2587 21.2. Informative References 2589 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2590 A., Peterson, J., Sparks, R., Handley, M., and E. 2591 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2592 DOI 10.17487/RFC3261, June 2002, 2593 . 2595 [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., 2596 "RTP Control Protocol Extended Reports (RTCP XR)", 2597 RFC 3611, DOI 10.17487/RFC3611, November 2003, 2598 . 2600 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 2601 "Codec Control Messages in the RTP Audio-Visual Profile 2602 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 2603 February 2008, . 2605 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 2606 "Extended RTP Profile for Real-time Transport Control 2607 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 2608 DOI 10.17487/RFC4585, July 2006, 2609 . 2611 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2612 Media Attributes in the Session Description Protocol 2613 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2614 . 2616 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2617 Clock Rates in an RTP Session", RFC 7160, 2618 DOI 10.17487/RFC7160, April 2014, 2619 . 2621 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 2622 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 2623 . 2625 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 2626 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 2627 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 2628 DOI 10.17487/RFC7656, November 2015, 2629 . 2631 [I-D.ietf-mmusic-trickle-ice] 2632 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2633 Incremental Provisioning of Candidates for the Interactive 2634 Connectivity Establishment (ICE) Protocol", draft-ietf- 2635 mmusic-trickle-ice-02 (work in progress), January 2015. 2637 [I-D.ietf-avtext-lrr] 2638 Lennox, J., Hong, D., Uberti, J., Holmer, S., and M. 2639 Flodman, "The Layer Refresh Request (LRR) RTCP Feedback 2640 Message", draft-ietf-avtext-lrr-03 (work in progress), 2641 July 2016. 2643 Appendix A. Design Considerations 2645 One of the main issues regarding the BUNDLE grouping extensions has 2646 been whether, in SDP Offers and SDP Answers, the same port value 2647 should be inserted in "m=" lines associated with a BUNDLE group, as 2648 the purpose of the extension is to negotiate the usage of a single 2649 address:port combination for media specified by the "m=" lines. 2650 Issues with both approaches, discussed in the Appendix have been 2651 raised. The outcome was to specify a mechanism which uses SDP Offers 2652 with both different and identical port values. 2654 Below are the primary issues that have been considered when defining 2655 the "BUNDLE" grouping extension: 2657 o 1) Interoperability with existing UAs. 2659 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2661 o 3) Time to gather, and the number of, ICE candidates. 2663 o 4) Different error scenarios, and when they occur. 2665 o 5) SDP Offer/Answer impacts, including usage of port number value 2666 zero. 2668 A.1. UA Interoperability 2670 Consider the following SDP Offer/Answer exchange, where Alice sends 2671 an SDP Offer to Bob: 2673 SDP Offer 2675 v=0 2676 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2677 s= 2678 c=IN IP4 atlanta.example.com 2679 t=0 0 2680 m=audio 10000 RTP/AVP 97 2681 a=rtpmap:97 iLBC/8000 2682 m=video 10002 RTP/AVP 97 2683 a=rtpmap:97 H261/90000 2685 SDP Answer 2687 v=0 2688 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2689 s= 2690 c=IN IP4 biloxi.example.com 2691 t=0 0 2692 m=audio 20000 RTP/AVP 97 2693 a=rtpmap:97 iLBC/8000 2694 m=video 20002 RTP/AVP 97 2695 a=rtpmap:97 H261/90000 2697 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2698 later invention to RTP and Bob can not assume that Alice supports RFC 2699 4961. This means that Alice may be sending RTP from a different port 2700 than 10000 or 10002 - some implementation simply send the RTP from an 2701 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2702 way that Bob knows if it should be passed to the video or audio codec 2703 is by looking at the port it was received on. This lead some SDP 2704 implementations to use the fact that each "m=" line had a different 2705 port number to use that port number as an index to find the correct m 2706 line in the SDP. As a result, some implementations that do support 2707 symmetric RTP and ICE still use a SDP data structure where SDP with 2708 "m=" lines with the same port such as: 2710 SDP Offer 2712 v=0 2713 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2714 s= 2715 c=IN IP4 atlanta.example.com 2716 t=0 0 2717 m=audio 10000 RTP/AVP 97 2718 a=rtpmap:97 iLBC/8000 2719 m=video 10000 RTP/AVP 98 2720 a=rtpmap:98 H261/90000 2722 will result in the second "m=" line being considered an SDP error 2723 because it has the same port as the first line. 2725 A.2. Usage of port number value zero 2727 In an SDP Offer or SDP Answer, the media specified by an "m=" line 2728 can be disabled/rejected by setting the port number value to zero. 2729 This is different from e.g., using the SDP direction attributes, 2730 where RTCP traffic will continue even if the SDP "inactive" attribute 2731 is indicated for the associated "m=" line. 2733 If each "m=" line associated with a BUNDLE group would contain 2734 different port values, and one of those port values would be used for 2735 a BUNDLE address associated with the BUNDLE group, problems would 2736 occur if an endpoint wants to disable/reject the "m=" line associated 2737 with that port, by setting the port value to zero. After that, no 2738 "m=" line would contain the port value which is used for the BUNDLE 2739 address. In addition, it is unclear what would happen to the ICE 2740 candidates associated with the "m=" line, as they are also used for 2741 the BUNDLE address. 2743 A.3. B2BUA And Proxy Interoperability 2745 Some back to back user agents may be configured in a mode where if 2746 the incoming call leg contains an SDP attribute the B2BUA does not 2747 understand, the B2BUA still generates that SDP attribute in the Offer 2748 for the outgoing call leg. Consider a B2BUA that did not understand 2749 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2750 Further assume that the B2BUA was configured to tear down any call 2751 where it did not see any RTCP for 5 minutes. In this case, if the 2752 B2BUA received an Offer like: 2754 SDP Offer 2756 v=0 2757 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2758 s= 2759 c=IN IP4 atlanta.example.com 2760 t=0 0 2761 m=audio 49170 RTP/AVP 0 2762 a=rtcp:53020 2764 It would be looking for RTCP on port 49172 but would not see any 2765 because the RTCP would be on port 53020 and after five minutes, it 2766 would tear down the call. Similarly, a B2BUA that did not understand 2767 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2768 wrong port and tear down the call. It is worth noting that a B2BUA 2769 that generated an Offer with capabilities it does not understand is 2770 not compliant with the specifications. 2772 A.3.1. Traffic Policing 2774 Sometimes intermediaries do not act as B2BUA, in the sense that they 2775 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2776 however, they may use SDP information (e.g., IP address and port) in 2777 order to control traffic gating functions, and to set traffic 2778 policing rules. There might be rules which will trigger a session to 2779 be terminated in case media is not sent or received on the ports 2780 retrieved from the SDP. This typically occurs once the session is 2781 already established and ongoing. 2783 A.3.2. Bandwidth Allocation 2785 Sometimes intermediaries do not act as B2BUA, in the sense that they 2786 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2787 however, they may use SDP information (e.g., codecs and media types) 2788 in order to control bandwidth allocation functions. The bandwidth 2789 allocation is done per "m=" line, which means that it might not be 2790 enough if media specified by all "m=" lines try to use that 2791 bandwidth. That may either simply lead to bad user experience, or to 2792 termination of the call. 2794 A.4. Candidate Gathering 2796 When using ICE, a candidate needs to be gathered for each port. This 2797 takes approximately 20 ms extra for each extra "m=" line due to the 2798 NAT pacing requirements. All of this gather can be overlapped with 2799 other things while for exampe a web-page is loading to minimize the 2800 impact. If the client only wants to generate TURN or STUN ICE 2801 candidates for one of the "m=" lines and then use trickle ICE 2802 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2803 the rest of the "m=" lines, it MAY do that and will not need any 2804 additional gathering time. 2806 Some people have suggested a TURN extension to get a bunch of TURN 2807 allocations at once. This would only provide a single STUN result so 2808 in cases where the other end did not support BUNDLE, may cause more 2809 use of the TURN server but would be quick in the cases where both 2810 sides supported BUNDLE and would fall back to a successful call in 2811 the other cases. 2813 Authors' Addresses 2815 Christer Holmberg 2816 Ericsson 2817 Hirsalantie 11 2818 Jorvas 02420 2819 Finland 2821 Email: christer.holmberg@ericsson.com 2823 Harald Tveit Alvestrand 2824 Google 2825 Kungsbron 2 2826 Stockholm 11122 2827 Sweden 2829 Email: harald@alvestrand.no 2831 Cullen Jennings 2832 Cisco 2833 400 3rd Avenue SW, Suite 350 2834 Calgary, AB T2P 4H2 2835 Canada 2837 Email: fluffy@iii.ca