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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: April 30, 2017 C. Jennings 7 Cisco 8 October 27, 2016 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-36.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 April 30, 2017. 53 Copyright Notice 55 Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . 22 117 10.3.1. SDP Offer/Answer Procedures . . . . . . . . . . . . 22 118 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 24 119 11.1. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 25 120 11.1.1. Generating the Initial SDP Offer . . . . . . . . . . 25 121 11.1.2. Generating the SDP Answer . . . . . . . . . . . . . 25 122 11.1.3. Offerer Processing of the SDP Answer . . . . . . . . 26 123 11.1.4. Modifying the Session . . . . . . . . . . . . . . . 26 124 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 26 125 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 27 126 13.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 27 127 13.2. New text replacing section 5.1 (2nd paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 27 129 13.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 28 130 13.4. New text replacing section 8.2 (2nd paragraph) of RFC 131 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 28 132 13.5. Original text of section 8.4 (6th paragraph) of RFC 3264 28 133 13.6. New text replacing section 8.4 (6th paragraph) of RFC 134 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 28 135 14. RTP/RTCP extensions for identification-tag transport . . . . 29 136 14.1. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 30 137 14.2. RTP SDES Header Extension For MID . . . . . . . . . . . 30 138 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 139 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 31 140 15.2. New RTP SDES Header Extension URI . . . . . . . . . . . 31 141 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 32 142 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 32 143 16. Security Considerations . . . . . . . . . . . . . . . . . . . 32 144 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 33 145 17.1. Example: Bundle Address Selection . . . . . . . . . . . 33 146 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 35 147 17.3. Example: Offerer Adds A Media Description To A BUNDLE 148 Group . . . . . . . . . . . . . . . . . . . . . . . . . 36 149 17.4. Example: Offerer Moves A Media Description Out Of A 150 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 38 151 17.5. Example: Offerer Disables A Media Description Within A 152 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 40 153 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41 154 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 42 155 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 156 20.1. Normative References . . . . . . . . . . . . . . . . . . 50 157 20.2. Informative References . . . . . . . . . . . . . . . . . 52 158 Appendix A. Design Considerations . . . . . . . . . . . . . . . 52 159 A.1. UA Interoperability . . . . . . . . . . . . . . . . . . . 53 160 A.2. Usage of port number value zero . . . . . . . . . . . . . 54 161 A.3. B2BUA And Proxy Interoperability . . . . . . . . . . . . 55 162 A.3.1. Traffic Policing . . . . . . . . . . . . . . . . . . 55 163 A.3.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 55 164 A.4. Candidate Gathering . . . . . . . . . . . . . . . . . . . 56 165 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56 167 1. Introduction 169 When multimedia communications are established, each 5-tuple reserved 170 for an individual media stream consume additional resources 171 (especially when Interactive Connectivity Establishment (ICE) 172 [RFC5245] is used). For this reason, it is attractive to use a 173 5-tuple for multiple media streams. 175 This specification defines a way to use a single address:port 176 combination (BUNDLE address) for receiving media specified by 177 multiple SDP media descriptions ("m=" lines). 179 This specification defines a new SDP Grouping Framework [RFC5888] 180 extension called 'BUNDLE'. The extension can be used with the 181 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 182 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 183 BUNDLE address is used for receiving media specified by multiple "m=" 184 lines. This is referred to as bundled media. 186 The offerer and answerer [RFC3264] use the BUNDLE extension to 187 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 188 address) and one for the answerer (answerer BUNDLE address), to be 189 used for receiving the bundled media specified by a BUNDLE group. 190 Once the offerer and the answerer have negotiated a BUNDLE group, 191 they associate their respective BUNDLE address with each "m=" line in 192 the BUNDLE group. The BUNDLE addresses are used to receive all media 193 specified by the BUNDLE group. 195 The use of a BUNDLE group and a BUNDLE address also allows the usage 196 of a single set of Interactive Connectivity Establishment (ICE) 197 [RFC5245] candidates for multiple "m=" lines. 199 This specification also defines a new SDP attribute, 'bundle-only', 200 which can be used to request that specific media is only used if kept 201 within a BUNDLE group. The specification also updates RFC 3264, to 202 allow usage of zero port values without meaning that media is 203 rejected. 205 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 206 transport address (IP address and port) to multiple "m=" lines are 207 undefined, and there is no grouping defined by such means. Instead, 208 an explicit grouping mechanism needs to be used to express the 209 intended semantics. This specification provides such an extension. 211 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 212 [RFC3264]. The update allows an answerer to assign a non-zero port 213 value to an "m=" line in an SDP answer, even if the "m=" line in the 214 associated SDP offer contained a zero port value. 216 This specification also defines a new Real-time Transport Protocol 217 (RTP) [RFC3550] source description (SDES) item, 'MID', and a new RTP 218 SDES header extension that can be used to associate RTP streams with 219 media descriptions. 221 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 222 address MUST only be associated with a single BUNDLE group. The 223 procedures in this specification apply independently to a given 224 BUNDLE group. All RTP based media flows described by a single BUNDLE 225 group belong to a single RTP session [RFC3550]. 227 The BUNDLE extension is backward compatible. Endpoints that do not 228 support the extension are expected to generate offers and answers 229 without an SDP 'group:BUNDLE' attribute, and are expected to 230 associate a unique address with each "m=" line within an offer and 231 answer, according to the procedures in [RFC4566] and [RFC3264] 233 2. Terminology 235 "m=" line: SDP bodies contain one or more media descriptions. Each 236 media description is identified by an SDP "m=" line. 238 5-tuple: A collection of the following values: source address, source 239 port, destination address, destination port, and transport-layer 240 protocol. 242 Unique address: An IP address and port combination that is associated 243 with only one "m=" line in an offer or answer. 245 Shared address: An IP address and port combination that is associated 246 with multiple "m=" lines within an offer or answer. 248 Offerer BUNDLE-tag: The first identification-tag in a given SDP 249 'group:BUNDLE' attribute identification-tag list in an offer. 251 Answerer BUNDLE-tag: The first identification-tag in a given SDP 252 'group:BUNDLE' attribute identification-tag list in an answer. 254 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 255 and port combination used by an offerer to receive all media 256 specified by each "m=" line within the BUNDLE group. 258 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 259 and port combination used by an answerer to receive all media 260 specified by each "m=" line within the BUNDLE group. 262 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 263 exchange, which uses the same BUNDLE address for receiving media. 265 Bundled "m=" line: An "m=" line, whose identification-tag is placed 266 in an SDP 'group:BUNDLE' attribute identification-tag list in an 267 offer or answer. 269 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 270 'bundle-only' attribute. 272 Bundled media: All media specified by a given BUNDLE group. 274 Initial offer: The first offer, within an SDP session (e.g. a SIP 275 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 276 to carry SDP), in which the offerer indicates that it wants to create 277 a given BUNDLE group. 279 Subsequent offer: An offer which contains a BUNDLE group that has 280 been created as part of a previous offer/answer exchange. 282 Identification-tag: A unique token value that is used to identify an 283 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 284 "m=" line, carries an unique identification-tag. The session-level 285 SDP 'group' attribute [RFC5888] carries a list of identification- 286 tags, identifying the "m=" lines associated with that particular 287 'group' attribute. 289 3. Conventions 291 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 292 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 293 document are to be interpreted as described in BCP 14, RFC 2119 294 [RFC2119]. 296 4. Applicability Statement 298 The mechanism in this specification only applies to the Session 299 Description Protocol (SDP) [RFC4566], when used together with the SDP 300 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 301 scope of this document, and is thus undefined. 303 5. SDP Grouping Framework BUNDLE Extension 305 This section defines a new SDP Grouping Framework extension 306 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 307 Offer/Answer mechanism to negotiate the usage of a single 308 address:port combination (BUNDLE address) for receiving bundled 309 media. 311 A single address:port combination is also used for sending bundled 312 media. The address:port combination used for sending bundled media 313 MAY be the same as the BUNDLE address, used to receive bundled media, 314 depending on whether symmetric RTP [RFC4961] is used. 316 All media associated with a BUNDLE group MUST be transport using the 317 same transport-layer protocol (e.g., UDP or TCP). 319 The BUNDLE extension is indicated using an SDP 'group' attribute with 320 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 321 associated with each bundled "m=" line, and each identification-tag 322 is listed in the SDP 'group:BUNDLE' attribute identification-tag 323 list. Each "m=" line whose identification-tag is listed in the 324 identification-tag list is associated with a given BUNDLE group. 326 SDP bodies can contain multiple BUNDLE groups. Any given bundled 327 "m=" line MUST NOT be associated with more than one BUNDLE group. 329 NOTE: The order of the "m=" lines listed in the SDP 'group:BUNDLE' 330 attribute identification-tag list does not have to be the same as the 331 order in which the "m=" lines occur in the SDP. 333 Section 8 defines the detailed SDP Offer/Answer procedures for the 334 BUNDLE extension. 336 6. SDP 'bundle-only' Attribute 338 This section defines a new SDP media-level attribute [RFC4566], 339 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 340 hence has no value. 342 Name: bundle-only 344 Value: N/A 346 Usage Level: media 348 Charset Dependent: no 350 Example: 352 a=bundle-only 354 In order to ensure that an answerer that does not support the BUNDLE 355 extension always rejects a bundled "m=" line, the offerer can assign 356 a zero port value to the "m=" line. According to [RFC3264] an 357 answerer will reject such "m=" line. By associating an SDP 'bundle- 358 only' attribute with such "m=" line, the offerer can request that the 359 answerer accepts the "m=" line if the answerer supports the Bundle 360 extension, and if the answerer keeps the "m=" line within the 361 associated BUNDLE group. 363 NOTE: Once the offerer BUNDLE address has been selected, the offerer 364 does not need to include the 'bundle-only' attribute in subsequent 365 offers. By associating the offerer BUNDLE address with an "m=" line 366 of a subsequent offer, the offerer will ensure that the answerer will 367 either keep the "m=" line within the BUNDLE group, or the answerer 368 will have to reject the "m=" line. 370 The usage of the 'bundle-only' attribute is only defined for a 371 bundled "m=" line with a zero port value, within an offer. Other 372 usage is unspecified. 374 Section 8 defines the detailed SDP Offer/Answer procedures for the 375 'bundle-only' attribute. 377 7. SDP Information Considerations 379 This section describes restrictions associated with the usage of SDP 380 parameters within a BUNDLE group. It also describes, when parameter 381 and attribute values have been associated with each bundled "m=" 382 line, how to calculate a value for the whole BUNDLE group. 384 7.1. Connection Data (c=) 386 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 387 line MUST be 'IN'. 389 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 390 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 391 each "m=" line. 393 NOTE: Extensions to this specification can specify usage of the 394 BUNDLE mechanism for other nettype and addrtype values than the ones 395 listed above. 397 7.2. Bandwidth (b=) 399 An offerer and answerer MUST use the rules and restrictions defined 400 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP 401 bandwidth (b=) line with bundled "m=" lines. 403 7.3. Attributes (a=) 405 An offerer and answerer MUST use the rules and restrictions defined 406 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating SDP 407 attributes with bundled "m=" lines. 409 8. SDP Offer/Answer Procedures 411 This section describes the SDP Offer/Answer [RFC3264] procedures for: 413 o Negotiating and creating a BUNDLE group; and 415 o Selecting the BUNDLE addresses (offerer BUNDLE address and 416 answerer BUNDLE address); and 418 o Adding an "m=" line to a BUNDLE group; and 420 o Moving an "m=" line out of a BUNDLE group; and 422 o Disabling an "m=" line within a BUNDLE group. 424 The generic rules and procedures defined in [RFC3264] and [RFC5888] 425 also apply to the BUNDLE extension. For example, if an offer is 426 rejected by the answerer, the previously negotiated SDP parameters 427 and characteristics (including those associated with a BUNDLE group) 428 apply. Hence, if an offerer generates an offer in which the offerer 429 wants to create a BUNDLE group, and the answerer rejects the offer, 430 the BUNDLE group is not created. 432 The procedures in this section are independent of the media type or 433 "m=" line proto value represented by a bundled "m=" line. Section 10 434 defines additional considerations for RTP based media. Section 6 435 defines additional considerations for the usage of the SDP 'bundle- 436 only' attribute. Section 11 defines additional considerations for 437 the usage of Interactive Connectivity Establishment (ICE) 438 [I-D.ietf-ice-rfc5245bis] mechanism. 440 SDP offers and answers can contain multiple BUNDLE groups. The 441 procedures in this section apply independently to a given BUNDLE 442 group. 444 8.1. Mux Category Considerations 446 When an offerer associates SDP attributes with a bundled "m=" line 447 associated with a shared address, IDENTICAL and TRANSPORT mux 448 category SDP attributes [I-D.ietf-mmusic-sdp-mux-attributes] are 449 associated with the "m=" line only if the "m=" line is also 450 associated with the offerer BUNDLE-tag. Otherwise the offerer MUST 451 NOT associate such SDP attributes with the "m=" line. 453 When an answerer associates SDP attributes with a bundled "m=" line, 454 IDENTICAL and TRANSPORT mux category SDP attributes are associated 455 with the "m=" line only if the "m=" line is also associated with the 456 answerer BUNDLE-tag. Otherwise the answerer MUST NOT associated such 457 SDP attributes with the "m=" line. 459 NOTE: As bundled "m=" lines associated with a shared address will 460 share the same IDENTICAL and TRANSPORT mux category SDP attributes, 461 and attribute values, there is no need to associate such SDP 462 attributes with each "m=" line. The attributes and attribute values 463 are implicitly applied to each "m=" line associated with the shared 464 address. 466 8.2. Generating the Initial SDP Offer 468 When an offerer generates an initial offer, in order to create a 469 BUNDLE group, it MUST: 471 o Assign a unique address to each "m=" line within the offer, 472 following the procedures in [RFC3264], unless the media line is a 473 'bundle-only' "m=" line (see below); and 475 o Add an SDP 'group:BUNDLE' attribute to the offer; and 477 o Place the identification-tag of each bundled "m=" line in the SDP 478 'group:BUNDLE' attribute identification-tag list; and 480 o Indicate which unique address the offerer suggests as the offerer 481 BUNDLE address [Section 8.2.1]. 483 If the offerer wants to request that the answerer accepts a given 484 bundled "m=" line only if the answerer keeps the "m=" line within the 485 BUNDLE group, the offerer MUST: 487 o Associate an SDP 'bundle-only' attribute [Section 8.2.1] with the 488 "m=" line; and 490 o Assign a zero port value to the "m=" line. 492 NOTE: If the offerer assigns a zero port value to an "m=" line, but 493 does not also associate an SDP 'bundle-only' attribute with the "m=" 494 line, it is an indication that the offerer wants to disable the "m=" 495 line [Section 8.5.4]. 497 [Section 17.1] shows an example of an initial offer. 499 8.2.1. Suggesting the offerer BUNDLE address 501 In the offer, the address associated with the "m=" line associated 502 with the offerer BUNDLE-tag indicates the address that the offerer 503 suggests as the offerer BUNDLE address. 505 The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain 506 a zero port value or an SDP 'bundle-only' attribute. 508 8.2.2. Example: Initial SDP Offer 510 The example shows an initial SDP offer. The offer includes two "m=" 511 lines in the SDP, and suggests that both are included in a BUNDLE 512 group. The audio "m=" line is associated with the offerer BUNDLE-tag 513 (placed first in the SDP group:BUNDLE attribute identificatoin-id 514 list). 516 SDP Offer 518 v=0 519 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 520 s= 521 c=IN IP4 atlanta.example.com 522 t=0 0 523 a=group:BUNDLE foo bar 524 m=audio 10000 RTP/AVP 0 8 97 525 b=AS:200 526 a=mid:foo 527 a=rtcp-mux 528 a=rtpmap:0 PCMU/8000 529 a=rtpmap:8 PCMA/8000 530 a=rtpmap:97 iLBC/8000 531 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 532 m=video 10002 RTP/AVP 31 32 533 b=AS:1000 534 a=mid:bar 535 a=rtcp-mux 536 a=rtpmap:31 H261/90000 537 a=rtpmap:32 MPV/90000 538 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 540 8.3. Generating the SDP Answer 542 When an answerer generates an answer that contains a BUNDLE group, 543 the following general SDP grouping framework restrictions, defined in 544 [RFC5888], also apply to the BUNDLE group: 546 o The answerer MUST NOT include a BUNDLE group in the answer, unless 547 the offerer requested the BUNDLE group to be created in the 548 corresponding offer; and 550 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 551 unless the offerer requested the "m=" line to be within that 552 BUNDLE group in the corresponding offer. 554 If the answer contains a BUNDLE group, the answerer MUST: 556 o Select an Offerer BUNDLE Address [Section 8.3.1]; and 558 o Select an Answerer BUNDLE Address [Section 8.3.2]; 560 The answerer is allowed to select a new Answerer BUNDLE address each 561 time it generates an answer to an offer. 563 If the answerer does not want to keep an "m=" line within a BUNDLE 564 group, it MUST: 566 o Move the "m=" line out of the BUNDLE group [Section 8.3.3]; or 568 o Reject the "m=" line [Section 8.3.4]; 570 If the answerer keeps a bundle-only "m=" line within the BUNDLE 571 group, it follows the procedures (associates the answerer BUNDLE 572 address with the "m=" line etc) for any other "m=" line kept within 573 the BUNDLE group. 575 If the answerer does not want to keep a bundle-only "m=" line within 576 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.4]. 578 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 579 any "m=" line in an answer. 581 NOTE: If a bundled "m=" line in an offer contains a zero port value, 582 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 583 is an indication that the offerer wants to disable the "m=" line 584 [Section 8.5.4]. 586 8.3.1. Answerer Selection of Offerer Bundle Address 588 In an offer, the address (unique or shared) associated with the 589 bundled "m=" line associated with the offerer BUNDLE-tag indicates 590 the address that the offerer suggests as the offerer BUNDLE address 591 [Section 8.2.1]. The answerer MUST check whether that "m=" line 592 fulfils the following criteria: 594 o The answerer will not move the "m=" line out of the BUNDLE group 595 [Section 8.3.3]; and 597 o The answerer will not reject the "m=" line [Section 8.3.4]; and 599 o The "m=" line does not contain a zero port value. 601 If all of the criteria above are fulfilled, the answerer MUST select 602 the address associated with the "m=" line as the offerer BUNDLE 603 address. In the answer, the answerer BUNDLE-tag represents the "m=" 604 line, and the address associated with the "m=" line in the offer 605 becomes the offerer BUNDLE address. 607 If one or more of the criteria are not fulfilled, the answerer MUST 608 select the next identification-tag in the identification-tag list, 609 and perform the same criteria check for the "m=" line associated with 610 that identification-tag. If there are no more identification-tags in 611 the identification-tag list, the answerer MUST NOT create the BUNDLE 612 group. In addition, unless the answerer rejects the whole offer, the 613 answerer MUST apply the answerer procedures for moving an "m=" line 614 out of a BUNDLE group [Section 8.3.3] to each bundled "m=" line in 615 the offer when creating the answer. 617 [Section 17.1] shows an example of an offerer BUNDLE address 618 selection. 620 8.3.2. Answerer Selection of Answerer BUNDLE Address 622 When the answerer selects a BUNDLE address for itself, referred to as 623 the answerer BUNDLE address, it MUST associate that address with each 624 bundled "m=" line within the created BUNDLE group in the answer. 626 The answerer MUST NOT associate the answerer BUNDLE address with an 627 "m=" line that is not within the BUNDLE group, or to an "m=" line 628 that is within another BUNDLE group. 630 [Section 17.1] shows an example of an answerer BUNDLE address 631 selection. 633 8.3.3. Moving A Media Description Out Of A BUNDLE Group 635 When an answerer wants to move an "m=" line out of a BUNDLE group, it 636 MUST first check the following criteria: 638 o In the corresponding offer, the "m=" line is associated with a 639 shared address (e.g. a previously selected offerer BUNDLE 640 address); or 642 o In the corresponding offer, an SDP 'bundle-only' attribute is 643 associated with the "m=" line, and the "m=" line contains a zero 644 port value. 646 If either criteria above is fulfilled, the answerer MUST reject the 647 "m=" line [Section 8.3.4]. 649 Otherwise, if in the corresponding offer the "m=" line is associated 650 with a unique address, the answerer MUST associate a unique address 651 with the "m=" line in the answer (the answerer does not reject the 652 "m=" line). 654 In addition, in either case above, the answerer MUST NOT place the 655 identification-tag, associated with the moved "m=" line, in the SDP 656 'group' attribute identification-tag list associated with the BUNDLE 657 group. 659 8.3.4. Rejecting A Media Description In A BUNDLE Group 661 When an answerer rejects an "m=" line, it MUST associate an address 662 with a zero port value with the "m=" line in the answer, according to 663 the procedures in [RFC3264]. 665 In addition, the answerer MUST NOT place the identification-tag, 666 associated with the rejected "m=" line, in the SDP 'group' attribute 667 identification-tag list associated with the BUNDLE group. 669 8.3.5. Example: SDP Answer 671 The example shows an SDP answer, based on the SDP offer in 672 [Section 8.2.2]. The answers acceppts both "m=" lines in the BUNDLE 673 group. 675 SDP Answer 677 v=0 678 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 679 s= 680 c=IN IP4 biloxi.example.com 681 t=0 0 682 a=group:BUNDLE foo bar 683 m=audio 20000 RTP/AVP 0 684 b=AS:200 685 a=mid:foo 686 a=rtcp-mux 687 a=rtpmap:0 PCMU/8000 688 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 689 m=video 20000 RTP/AVP 32 690 b=AS:1000 691 a=mid:bar 692 a=rtcp-mux 693 a=rtpmap:32 MPV/90000 694 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 696 8.4. Offerer Processing of the SDP Answer 698 When an offerer receives an answer, if the answer contains a BUNDLE 699 group, the offerer MUST check that any bundled "m=" line in the 700 answer was indicated as bundled in the corresponding offer. If there 701 is no mismatch, the offerer MUST use the offerer BUNDLE address, 702 selected by the answerer [Section 8.3.1], as the address for each 703 bundled "m=" line. 705 NOTE: As the answerer might reject one or more bundled "m=" lines, or 706 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 707 line in the offer might not be indicated as bundled in the answer. 709 If the answer does not contain a BUNDLE group, the offerer MUST 710 process the answer as a normal answer. 712 8.5. Modifying the Session 714 When an offerer generates a subsequent offer, it MUST associate the 715 previously selected offerer BUNDLE address [Section 8.3.1] with each 716 bundled "m=" line (including any bundle-only "m=" line), except if: 718 o The offerer suggests a new offerer BUNDLE address [Section 8.5.1]; 719 or 721 o The offerer wants to add a bundled "m=" line to the BUNDLE group 722 [Section 8.5.2]; or 724 o The offerer wants to move a bundled "m=" line out of the BUNDLE 725 group [Section 8.5.3]; or 727 o The offerer wants to disable the bundled "m=" line 728 [Section 8.5.4]. 730 In addition, the offerer MUST select an offerer BUNDLE-tag 731 [Section 8.2.1] associated with the previously selected offerer 732 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 733 address. 735 8.5.1. Suggesting a new offerer BUNDLE address 737 When an offerer generates an offer, in which it suggests a new 738 offerer BUNDLE address [Section 8.2.1], the offerer MUST: 740 o Assign the address (shared address) to each "m=" line within the 741 BUNDLE group; or 743 o Assign the address (unique address) to one bundled "m=" line. 745 In addition, the offerer MUST indicate that the address is the new 746 suggested offerer BUNDLE address [Section 8.2.1]. 748 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 749 address with each bundled "m=" line, it can associate unique 750 addresses with any number of bundled "m=" lines (and the previously 751 selected offerer BUNDLE address to any remaining bundled "m=" line) 752 if it wants to suggest multiple alternatives for the new offerer 753 BUNDLE address. 755 8.5.2. Adding a media description to a BUNDLE group 757 When an offerer generates an offer, in which it wants to add a 758 bundled "m=" line to a BUNDLE group, the offerer MUST: 760 o Assign a unique address to the added "m=" line; or 762 o Assign the previously selected offerer BUNDLE address to the added 763 "m=" line; or 765 o If the offerer associates a new (shared address) suggested offerer 766 BUNDLE address with each bundled "m=" line [Section 8.5.1], also 767 associate that address with the added "m=" line. 769 In addition, the offerer MUST add the identification-tag associated 770 with the added "m=" line to the SDP 'group:BUNDLE' attribute 771 identification-tag list with the BUNDLE group [Section 8.2.1]. 773 NOTE: Assigning a unique address to the "m=" line allows the answerer 774 to move the "m=" line out of the BUNDLE group [Section 8.3.3], 775 without having to reject the "m=" line. 777 If the offerer associates a unique address with the added "m=" line, 778 and if the offerer suggests that address as the new offerer BUNDLE 779 address [Section 8.5.1], the offerer BUNDLE-tag MUST represent the 780 added "m=" line [Section 8.2.1]. 782 If the offerer associates a new suggested offerer BUNDLE address with 783 each bundled "m=" line [Section 8.5.1], including the added "m=" 784 line, the offerer BUNDLE-tag MAY represent the added "m=" line 785 [Section 8.2.1]. 787 [Section 17.3] shows an example where an offerer sends an offer in 788 order to add a bundled "m=" line to a BUNDLE group. 790 8.5.3. Moving A Media Description Out Of A BUNDLE Group 792 When an offerer generates an offer, in which it wants to move a 793 bundled "m=" line out of a BUNDLE group it was added to in a previous 794 offer/answer transaction, the offerer: 796 o MUST associate a unique address with the "m=" line; and 797 o MUST NOT place the identification-tag associated with the "m=" 798 line in the SDP 'group:BUNDLE' attribute identification-tag list 799 associated with the BUNDLE group. 801 NOTE: If the removed "m=" line is associated with the previously 802 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 803 [Section 8.2.1]. 805 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 806 added to another BUNDLE group, the offerer applies the procedures in 807 [Section 8.5.2] to the "m=" line. 809 [Section 17.4] shows an example of an offer for moving an "m=" line 810 out of a BUNDLE group. 812 8.5.4. Disabling A Media Description In A BUNDLE Group 814 When an offerer generates an offer, in which it wants to disable a 815 bundled "m=" line (added to the BUNDLE group in a previous offer/ 816 answer transaction), the offerer: 818 o MUST associate an address with a zero port value with the "m=" 819 line, following the procedures in [RFC4566]; and 821 o MUST NOT place the identification-tag associated with the "m=" 822 line in the SDP 'group:BUNDLE' attribute identification-tag list 823 associated with the BUNDLE group. 825 [Section 17.5] shows an example of an offer for disabling an "m=" 826 line within a BUNDLE group. 828 9. Protocol Identification 830 Each "m=" line within a BUNDLE group MUST use the same transport- 831 layer protocol. If bundled "m=" lines use different protocols on top 832 of the transport-layer protocol, there MUST exist a publicly 833 available specification which describes a mechanism, for this 834 particular protocol combination, how to associate received data with 835 the correct protocol. 837 In addition, if received data can be associated with more than one 838 bundled "m=" line, there MUST exist a publicly available 839 specification which describes a mechanism for associating the 840 received data with the correct "m=" line. 842 This document describes a mechanism to identify the protocol of 843 received data among the STUN, DTLS and SRTP protocols (in any 844 combination), when UDP is used as transport-layer protocol, but does 845 not describe how to identify different protocols transported on DTLS. 846 While the mechanism is generally applicable to other protocols and 847 transport-layer protocols, any such use requires further 848 specification around how to multiplex multiple protocols on a given 849 transport-layer protocol, and how to associate received data with the 850 correct protocols. 852 9.1. STUN, DTLS, SRTP 854 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 855 protocol of a received packet among the STUN, Datagram Transport 856 Layer Security (DTLS) and SRTP protocols (in any combination). If an 857 offer or answer includes bundled "m=" lines that represent these 858 protocols, the offerer or answerer MUST support the mechanism 859 described in [RFC5764], and no explicit negotiation is required in 860 order to indicate support and usage of the mechanism. 862 [RFC5764] does not describe how to identify different protocols 863 transported on DTLS, only how to identify the DTLS protocol itself. 864 If multiple protocols are transported on DTLS, there MUST exist a 865 specification describing a mechanism for identifying each individual 866 protocol. In addition, if a received DTLS packet can be associated 867 with more than one "m=" line, there MUST exist a specification which 868 describes a mechanism for associating the received DTLS packet with 869 the correct "m=" line. 871 [Section 10.2] describes how to associate the packets in a received 872 SRTP stream with the correct "m=" line. 874 10. RTP Considerations 876 10.1. Single RTP Session 878 All RTP-based media within a single BUNDLE group belong to a single 879 RTP session [RFC3550]. 881 Since a single RTP session is used for each bundle group, all "m=" 882 lines representing RTP-based media in a bundle group will share a 883 single SSRC numbering space [RFC3550]. 885 The following rules and restrictions apply for a single RTP session: 887 o A specific payload type value can be used in multiple bundled "m=" 888 lines only if each codec associated with the payload type number 889 shares an identical codec configuration [Section 10.1.1]. 891 o The proto value in each bundled RTP-based "m=" line MUST be 892 identical (e.g. RTP/AVPF). 894 o The RTP MID header extension MUST be enabled, by associating an 895 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 896 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 897 in every offer and answer. 899 o A given SSRC MUST NOT transmit RTP packets using payload types 900 that originate from different bundled "m=" lines. 902 NOTE: The last bullet above is to avoid sending multiple media types 903 from the same SSRC. If transmission of multiple media types are done 904 with time overlap, RTP and RTCP fail to function. Even if done in 905 proper sequence this causes RTP Timestamp rate switching issues 906 [RFC7160]. However, once an SSRC has left the RTP session (by 907 sending an RTCP BYE packet), that SSRC can be reused by another 908 source (possibly associated with a different bundled "m=" line) after 909 a delay of 5 RTCP reporting intervals (the delay is to ensure the 910 SSRC has timed out, in case the RTCP BYE packet was lost [RFC3550]). 912 10.1.1. Payload Type (PT) Value Reuse 914 Multiple bundled "m=" lines might represent RTP based media. As all 915 RTP based media specified by a BUNDLE group belong to the same RTP 916 session, in order for a given payload type value to be used inside 917 more than one bundled "m=" line, all codecs associated with the 918 payload type number MUST share an identical codec configuration. 919 This means that the codecs MUST share the same media type, encoding 920 name, clock rate and any parameter that can affect the codec 921 configuration and packetization. 922 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 923 attribute values must be identical for all codecs that use the same 924 payload type value. 926 10.2. Associating RTP/RTCP Streams With Correct SDP Media Description 928 As described in [RFC3550], RTP/RTCP packets are associated with RTP 929 streams [RFC7656]. Each RTP stream is identified by an SSRC value, 930 and each RTP/RTCP packet carries an SSRC value that is used to 931 associate the packet with the correct RTP stream (an RTCP packet can 932 carry multiple SSRC values, and might therefore be associated with 933 multiple RTP streams). 935 In order to be able to process received RTP/RTCP packets correctly it 936 must be possible to associate an RTP stream with the correct "m=" 937 line, as the "m=" line and SDP attributes associated with the "m=" 938 line contain information needed to process the packets. 940 As all RTP streams associated with a BUNDLE group are using the same 941 address:port combination for sending and receiving RTP/RTCP packets, 942 the local address:port combination cannot be used to associate an RTP 943 stream with the correct "m=" line. In addition, multiple RTP streams 944 might be associated with the same "m=" line. 946 Also, as described in [Section 10.1.1], the same payload type value 947 might be used by multiple RTP streams, in which case the payload type 948 value cannot be used to associate an RTP stream with the correct "m=" 949 line. 951 An offerer and answerer can inform each other which SSRC values they 952 will use for an RTP stream by using the SDP 'ssrc' attribute 953 [RFC5576]. However, an offerer will not know which SSRC values the 954 answerer will use until the offerer has received the answer providing 955 that information. Due to this, before the offerer has received the 956 answer, the offerer will not be able to associate an RTP stream with 957 the correct "m=" line using the SSRC value associated with the RTP 958 stream. In addition, the offerer and answerer may start using new 959 SSRC values mid-session, without informing each other using the SDP 960 'ssrc' attribute. 962 In order for an offerer and answerer to always be able to associate 963 an RTP stream with the correct "m=" line, the offerer and answerer 964 using the BUNDLE extension MUST support the mechanism defined in 965 Section 14, where the offerer and answerer insert the identification- 966 tag (provided by the remote peer) associated with an "m=" line in RTP 967 and RTCP packets associated with a BUNDLE group. 969 The mapping from an SSRC to an identification-tag is carried in RTCP 970 SDES packets or in RTP header extensions (Section 14). Since a 971 compound RTCP packet can contain multiple RTCP SDES packets, and each 972 RTCP SDES packet can contain multiple chunks, an RTCP packet can 973 contain several SSRC to identification-tag mappings. The offerer and 974 answerer maintain tables mapping RTP streams identified by SSRC, to 975 a€œm=a€œ lines identified by the identification- 976 tag. These tables are updated each time an RTP/RTCP packet 977 containing one or more mappings from SSRC to identification-tag is 978 received. Note that the mapping from SSRC to identification-tag can 979 change at any time during an RTP session. Once an offerer or 980 answerer recieve an RTP/RTCP packet carrying an identification-tag 981 and an SSRC value (an RTCP packet might carry multiple 982 identification-tags and SSRC values), it creates a mapping between 983 the SSRC value and the identification-tag, in order to associate the 984 RTP stream with the "m=" line associated with the identification-tag. 985 Note that the mapping might change mid-session if, for a given SSRC 986 value, a different identification-tag is provided in an RTP/RTCP 987 packet. 989 If an offerer and answerer is not able to associate an RTP stream 990 with an "m=" line (using the mechanisms described in this section, or 991 using other appropriate mechanism, e.g, based on the payload type 992 value if it is unique to a single "m=" line), it MUST either drop the 993 RTP/RTCP packets associated with the RTP stream, or process them in 994 an application specific manner, once non-stream specific processing 995 (e.g., related to congestion control) of the packets have occurred. 996 Note that RTCP packets can report on multiple RTP streams. 998 10.3. RTP/RTCP Multiplexing 1000 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 1001 multiplexing [RFC5761] for the RTP-based media specified by the 1002 BUNDLE group. 1004 When RTP/RTCP multiplexing is enabled, the same address:port 1005 combination will be used for sending all RTP packets and the RTCP 1006 packets associated with the BUNDLE group. Each endpoint will send 1007 the packets towards the BUNDLE address of the other endpoint. The 1008 same address:port combination MAY be used for receiving RTP packets 1009 and RTCP packets. 1011 10.3.1. SDP Offer/Answer Procedures 1013 This section describes how an offerer and answerer use the SDP 'rtcp- 1014 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 1015 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 1016 multiplexing for RTP-based media specified by a BUNDLE group. 1018 The procedures in this section only apply to RTP-based "m=" lines. 1020 10.3.1.1. Generating the Initial SDP Offer 1022 When an offerer generates an initial offer, the offerer MUST 1023 associate an SDP 'rtcp-mux' attribute [RFC5761] with each bundled 1024 RTP-based "m=" line in the offer, including a bundle-only "m=" line. 1025 In addition, the offerer MUST associate an SDP 'rtcp-mux-only' 1026 attribute [I-D.ietf-mmusic-mux-exclusive] with each RTP-based bundle- 1027 only "m=" line, and MAY associated an SDP 'rtcp-mux-only' attribute 1028 with other bundled RTP-based "m=" lines. 1030 NOTE: Whether the offerer associates an SDP 'rtcp-mux-only' attribute 1031 with a bundled "m=" line or not depends on whether the offerer 1032 supports fallback to usage of a separate port for RTCP in case the 1033 answerer does not include the "m=" line in the BUNDLE group. 1035 NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with a 1036 bundled "m=" line, but does not associate an SDP 'rtcp-mux-only' 1037 attribute with the "m=" line, the offerer can also associate an SDP 1038 'rtcp' attribute [RFC3605] with the "m=" line in order to provide a 1039 fallback port for RTCP, as described in [RFC5761]. However, the 1040 fallback port will only be used in case the answerer does not include 1041 the "m=" line in the BUNDLE group. 1043 In the initial offer, the address:port combination for RTCP MUST be 1044 unique in each bundled RTP-based "m=" line (excluding a bundle-only 1045 "m=" line), similar to RTP. 1047 10.3.1.2. Generating the SDP Answer 1049 When an answerer generates an answer, if the answerer accepts one or 1050 more RTP-based "m=" lines within a BUNDLE group, the answerer MUST 1051 enable usage of RTP/RTCP multiplexing. The answerer MUST associate 1052 an SDP "rtcp-mux" attribute with each RTP-based "m=" line in the 1053 answer. In addition, if an "m=" line in the corresponding offer 1054 contained an SDP "rtcp-mux-only" attribute, the answerer MUST 1055 associate an SDP "rtcp-mux-only" attribute with the "m=" line in the 1056 answer. 1058 If an RTP-based "m=" line in the corresponding offer did not contain 1059 an SDP 'rtcp-mux' attribute, the answerer MUST NOT include the "m=" 1060 line within a BUNDLE group in the answer. 1062 If an RTP-based "m=" line in the corresponding offer contained an SDP 1063 "rtcp-mux-only" attribute, and if the answerer moves the "m=" line 1064 out of the BUNDLE group in the answer Section 8.3.3, the answerer 1065 MUST still either enable RTP/RTCP multiplexing for the media 1066 associated with the "m=" line, or reject the "m=" line Section 8.3.4. 1068 The answerer MUST NOT associate an SDP 'rtcp' attribute with any 1069 bundled "m=" line in the answer. The answerer will use the port 1070 value of the selected offerer BUNDLE address for sending RTP and RTCP 1071 packets associated with each RTP-based bundled "m=" line towards the 1072 offerer. 1074 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 1075 negotiated in a previous offer/answer transaction, the answerer MUST 1076 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 1077 "m=" line in the answer. 1079 10.3.1.3. Offerer Processing of the SDP Answer 1081 When an offerer receives an answer, if the answerer has accepted the 1082 usage of RTP/RTCP multiplexing (see Section 10.3.1.2), the answerer 1083 follows the procedures for RTP/RTCP multiplexing defined in 1084 [RFC5761]. The offerer will use the port value associated with the 1085 answerer BUNDLE address for sending RTP and RTCP packets associated 1086 with each RTP-based bundled "m=" line towards the answerer. 1088 NOTE: It is considered a protocol error if the answerer has not 1089 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 1090 that the answerer included in the BUNDLE group. 1092 10.3.1.4. Modifying the Session 1094 When an offerer generates a subsequent offer, for each RTP-based "m=" 1095 line that was previously added to the BUNDLE group the offerer MUST 1096 associate an SDP 'rtcp-mux' attribute and an SDP 'rtcp-mux-only' 1097 attribute with the "m=" line in the same way it was previously done, 1098 unless the offerer wants to disable or remove the "m=" line from the 1099 BUNDLE group. 1101 If the offerer wants to add a bundled RTP-based "m=" line to the 1102 BUNDLE group, it associates an SDP 'rtcp-mux' attribute and an SDP 1103 'rtcp-mux-only' attribute with the "m=" line using the procedures in 1104 [Section 10.3.1.1]. 1106 11. ICE Considerations 1108 This section describes how to use the BUNDLE grouping extension 1109 together with the Interactive Connectivity Establishment (ICE) 1110 mechanism [I-D.ietf-ice-rfc5245bis]. 1112 The generic procedures for negotiating usage of ICE using SDP, 1113 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1114 with BUNDLE, with the following exceptions: 1116 o When BUNDLE addresses for a BUNDLE group have been selected for 1117 both endpoints, ICE connectivity checks and keep-alives only need 1118 to be performed for the whole BUNDLE group, instead of per bundled 1119 "m=" line. 1121 o Among bundled "m=" lines with which the offerer has associated a 1122 shared address, the offerer only associates ICE-related media- 1123 level SDP attributes with the "m=" line associated with the 1124 offerer BUNDLE-tag. 1126 o Among bundled "m=" lines with which the answerer has associated a 1127 shared address, the answerer only associates ICE-related media- 1128 level SDP attributes with the "m=" line associated with the 1129 answerer BUNDLE-tag. 1131 Support and usage of ICE mechanism together with the BUNDLE extension 1132 is OPTIONAL. 1134 11.1. SDP Offer/Answer Procedures 1136 When an offerer associates a unique address with a bundled "m=" line 1137 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1138 'candidate' attributes (and other applicable ICE-related media-level 1139 SDP attributes), containing unique ICE properties (candidates etc), 1140 with the "m=" line, according to the procedures in 1141 [I-D.ietf-mmusic-ice-sip-sdp]. 1143 When an offerer associates a shared address with a bundled "m=" line, 1144 if the "m=" line is associated with the offerer BUNDLE-tag, the 1145 offerer MUST associate SDP 'candidate' attributes (and other 1146 applicable ICE-related media-level SDP attributes), containing shared 1147 ICE properties, with the "m=" line. If the "m=" line is not 1148 associated with the offerer BUNDLE-tag, the offerer MUST NOT 1149 associate ICE-related SDP attributes with the "m=" line. 1151 When an answerer associates a shared address with a bundled "m=" 1152 line, if the "m=" line is associated with the answerer BUNDLE-tag, 1153 the answerer MUST associate SDP 'candidate' attributes (and other 1154 applicable ICE-related media-level SDP attributes), containing shared 1155 ICE properties, with the "m=" line. If the "m=" line is not 1156 associated with the answerer BUNDLE-tag, the answerer MUST NOT 1157 associate ICE-related SDP attributes with the "m=" line. 1159 NOTE: As most ICE-related media-level SDP attributes belong to the 1160 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1161 offerer and answerer follow the rules in Section 8.1. However, in 1162 the case of ICE-related media-level attributes, the rules apply to 1163 all attributes (see note below), even if they belong to a different 1164 mux category. 1166 NOTE: The following ICE-related media-level SDP attributes are 1167 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1168 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1169 pacing'. 1171 11.1.1. Generating the Initial SDP Offer 1173 When an offerer generates an initial offer, the offerer MUST 1174 associate ICE-related media-level SDP attributes with each bundled 1175 "m=" line, according to [Section 11.1]. 1177 11.1.2. Generating the SDP Answer 1179 When an answerer generates an answer that contains a BUNDLE group, 1180 the answerer MUST associate ICE-related SDP attributes with the "m=" 1181 line associated with the answerer BUNDLE-tag, according to 1182 [Section 11.1]. 1184 11.1.3. Offerer Processing of the SDP Answer 1186 When an offerer receives an answer, if the answerer supports and uses 1187 the ICE mechanism and the BUNDLE extension, the offerer MUST 1188 associate the ICE properties associated with the offerer BUNDLE 1189 address, selected by the answerer [Section 8.3.1], with each bundled 1190 "m=" line. 1192 11.1.4. Modifying the Session 1194 When an offerer generates a subsequent offer, it MUST associate 1195 unique or shared ICE properties to one or more bundled "m=" lines, 1196 according to [Section 11.1]. 1198 12. DTLS Considerations 1200 One or more media streams within a BUNDLE group might use the 1201 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1202 to encrypt the data, or to negotiate encryption keys if another 1203 encryption mechanism is used to encrypt media. 1205 When DTLS is used within a BUNDLE group, the following rules apply: 1207 o There can only be one DTLS association [RFC6347] associated with 1208 the BUNDLE group; and 1210 o Each usage of the DTLS association within the BUNDLE group MUST 1211 use the same mechanism for determining which endpoints (the 1212 offerer or answerer) become DTLS client and DTLS server; and 1214 o Each usage of the DTLS association within the Bundle group MUST 1215 use the same mechanism for determining whether an offer or answer 1216 will trigger the establishment of a new DTLS association, or 1217 whether an existing DTLS association will be used; and 1219 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1220 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1221 [RFC5764], The client MUST include the extension even if the usage 1222 of DTLS-SRTP is not negotiated as part of the multimedia session 1223 (e.g., SIP session [RFC3261]. 1225 NOTE: The inclusion of the 'use_srtp' extension during the initial 1226 DTLS handshake ensures that a DTLS renegotiation will not be required 1227 in order to include the extension, in case DTLS-SRTP encrypted media 1228 is added to the BUNDLE group later during the multimedia session. 1230 13. Update to RFC 3264 1232 This section replaces the text of the following sections of RFC 3264: 1234 o Section 5.1 (Unicast Streams). 1236 o Section 8.2 (Removing a Media Stream). 1238 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1240 13.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 1242 For recvonly and sendrecv streams, the port number and address in the 1243 offer indicate where the offerer would like to receive the media 1244 stream. For sendonly RTP streams, the address and port number 1245 indirectly indicate where the offerer wants to receive RTCP reports. 1246 Unless there is an explicit indication otherwise, reports are sent to 1247 the port number one higher than the number indicated. The IP address 1248 and port present in the offer indicate nothing about the source IP 1249 address and source port of RTP and RTCP packets that will be sent by 1250 the offerer. A port number of zero in the offer indicates that the 1251 stream is offered but MUST NOT be used. This has no useful semantics 1252 in an initial offer, but is allowed for reasons of completeness, 1253 since the answer can contain a zero port indicating a rejected stream 1254 (Section 6). Furthermore, existing streams can be terminated by 1255 setting the port to zero (Section 8). In general, a port number of 1256 zero indicates that the media stream is not wanted. 1258 13.2. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1260 For recvonly and sendrecv streams, the port number and address in the 1261 offer indicate where the offerer would like to receive the media 1262 stream. For sendonly RTP streams, the address and port number 1263 indirectly indicate where the offerer wants to receive RTCP reports. 1264 Unless there is an explicit indication otherwise, reports are sent to 1265 the port number one higher than the number indicated. The IP address 1266 and port present in the offer indicate nothing about the source IP 1267 address and source port of RTP and RTCP packets that will be sent by 1268 the offerer. A port number of zero in the offer by default indicates 1269 that the stream is offered but MUST NOT be used, but an extension 1270 mechanism might specify different semantics for the usage of a zero 1271 port value. Furthermore, existing streams can be terminated by 1272 setting the port to zero (Section 8). In general, a port number of 1273 zero by default indicates that the media stream is not wanted. 1275 13.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 1277 A stream that is offered with a port of zero MUST be marked with port 1278 zero in the answer. Like the offer, the answer MAY omit all 1279 attributes present previously, and MAY list just a single media 1280 format from amongst those in the offer. 1282 13.4. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1284 A stream that is offered with a port of zero MUST by default be 1285 marked with port zero in the answer, unless an extension mechanism, 1286 which specifies semantics for the usage of a non-zero port value, is 1287 used. If the stream is marked with port zero in the answer, the 1288 answer MAY omit all attributes present previously, and MAY list just 1289 a single media format from amongst those in the offer." 1291 13.5. Original text of section 8.4 (6th paragraph) of RFC 3264 1293 RFC 2543 [10] specified that placing a user on hold was accomplished 1294 by setting the connection address to 0.0.0.0. Its usage for putting 1295 a call on hold is no longer recommended, since it doesn't allow for 1296 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1297 with connection oriented media. However, it can be useful in an 1298 initial offer when the offerer knows it wants to use a particular set 1299 of media streams and formats, but doesn't know the addresses and 1300 ports at the time of the offer. Of course, when used, the port 1301 number MUST NOT be zero, which would specify that the stream has been 1302 disabled. An agent MUST be capable of receiving SDP with a 1303 connection address of 0.0.0.0, in which case it means that neither 1304 RTP nor RTCP should be sent to the peer. 1306 13.6. New text replacing section 8.4 (6th paragraph) of RFC 3264 1308 RFC 2543 [10] specified that placing a user on hold was accomplished 1309 by setting the connection address to 0.0.0.0. Its usage for putting 1310 a call on hold is no longer recommended, since it doesn't allow for 1311 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1312 with connection oriented media. However, it can be useful in an 1313 initial offer when the offerer knows it wants to use a particular set 1314 of media streams and formats, but doesn't know the addresses and 1315 ports at the time of the offer. Of course, when used, the port 1316 number MUST NOT be zero, if it would specify that the stream has been 1317 disabled. However, an extension mechanism might specify different 1318 semantics of the zero port number usage. An agent MUST be capable of 1319 receiving SDP with a connection address of 0.0.0.0, in which case it 1320 means that neither RTP nor RTCP should be sent to the peer. 1322 14. RTP/RTCP extensions for identification-tag transport 1324 SDP Offerers and Answerers [RFC3264] can associate identification- 1325 tags with "m=" lines within SDP Offers and Answers, using the 1326 procedures in [RFC5888]. Each identification-tag uniquely represents 1327 an "m=" line. 1329 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1330 used to carry identification-tags within RTCP SDES packets. This 1331 section also defines a new RTP SDES header extension [RFC7941], which 1332 is used to carry the 'MID' RTCP SDES item in RTP packets. 1334 The SDES item and RTP SDES header extension make it possible for a 1335 receiver to associate each RTP stream with with a specific "m=" line, 1336 with which the receiver has associated an identification-tag, even if 1337 those "m=" lines are part of the same RTP session. The RTP SDES 1338 header extension also ensures that the media recipient gets the 1339 identification-tag upon receipt of the first decodable media and is 1340 able to associate the media with the correct application. 1342 A media recipient informs the media sender about the identification- 1343 tag associated with an "m=" line through the use of an 'mid' 1344 attribute [RFC5888]. The media sender then inserts the 1345 identification-tag in RTCP and RTP packets sent to the media 1346 recipient. 1348 NOTE: This text above defines how identification-tags are carried in 1349 SDP Offers and Answers. The usage of other signalling protocols for 1350 carrying identification-tags is not prevented, but the usage of such 1351 protocols is outside the scope of this document. 1353 [RFC3550] defines general procedures regarding the RTCP transmission 1354 interval. The RTCP MID SDES item SHOULD be sent in the first few 1355 RTCP packets sent after joining the session, and SHOULD be sent 1356 regularly thereafter. The exact number of RTCP packets in which this 1357 SDES item is sent is intentionally not specified here, as it will 1358 depend on the expected packet loss rate, the RTCP reporting interval, 1359 and the allowable overhead. 1361 The RTP SDES header extension for carrying the 'MID' RTCP SDES SHOULD 1362 be included in some RTP packets at the start of the session and 1363 whenever the SSRC changes. It might also be useful to include the 1364 header extension in RTP packets that comprise access points in the 1365 media (e.g., with video I-frames). The exact number of RTP packets 1366 in which this header extension is sent is intentionally not specified 1367 here, as it will depend on expected packet loss rate and loss 1368 patterns, the overhead the application can tolerate, and the 1369 importance of immediate receipt of the identification-tag. 1371 For robustness purpose, endpoints need to be prepared for situations 1372 where the reception of the identification-tag is delayed, and SHOULD 1373 NOT terminate sessions in such cases, as the identification-tag is 1374 likely to arrive soon. 1376 14.1. RTCP MID SDES Item 1378 0 1 2 3 1379 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 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1381 | MID=TBD | length | identification-tag ... 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1384 The identification-tag payload is UTF-8 encoded, as in SDP. 1386 The identification-tag is not zero terminated. 1388 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1389 identifier value.] 1391 14.2. RTP SDES Header Extension For MID 1393 The payload, containing the identification-tag, of the RTP SDES 1394 header extension element can be encoded using either the one-byte or 1395 two-byte header [RFC7941]. The identification-tag payload is UTF-8 1396 encoded, as in SDP. 1398 The identification-tag is not zero terminated. Note, that the set of 1399 header extensions included in the packet needs to be padded to the 1400 next 32-bit boundary using zero bytes [RFC5285]. 1402 As the identification-tag is included in either an RTCP SDES item or 1403 an RTP SDES header extension, or both, there should be some 1404 consideration about the packet expansion caused by the 1405 identification-tag. To avoid Maximum Transmission Unit (MTU) issues 1406 for the RTP packets, the header extension's size needs to be taken 1407 into account when encoding the media. 1409 It is recommended that the identification-tag is kept short. Due to 1410 the properties of the RTP header extension mechanism, when using the 1411 one-byte header, a tag that is 1-3 bytes will result in a minimal 1412 number of 32-bit words used for the RTP SDES header extension, in 1413 case no other header extensions are included at the same time. Note, 1414 do take into account that some single characters when UTF-8 encoded 1415 will result in multiple octets. The identification-tag MUST NOT 1416 contain any user information, and applications SHALL avoid generating 1417 the identification-tag using a pattern that enables application 1418 identification. 1420 15. IANA Considerations 1422 15.1. New SDES item 1424 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1425 document.] 1427 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1428 identifier value.] 1430 This document adds the MID SDES item to the IANA "RTP SDES item 1431 types" registry as follows: 1433 Value: TBD 1434 Abbrev.: MID 1435 Name: Media Identification 1436 Reference: RFCXXXX 1438 15.2. New RTP SDES Header Extension URI 1440 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1441 document.] 1443 This document defines a new extension URI in the RTP SDES Compact 1444 Header Extensions sub-registry of the RTP Compact Header Extensions 1445 registry sub-registry, according to the following data: 1447 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1448 Description: Media identification 1449 Contact: christer.holmberg@ericsson.com 1450 Reference: RFCXXXX 1452 The SDES item does not reveal privacy information about the users. 1453 It is simply used to associate RTP-based media with the correct SDP 1454 media description (m- line) in the SDP used to negotiate the media. 1456 The purpose of the extension is for the offerer to be able to 1457 associate received multiplexed RTP-based media before the offerer 1458 receives the associated SDP answer. 1460 15.3. New SDP Attribute 1462 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1463 document.] 1465 This document defines a new SDP media-level attribute, 'bundle-only', 1466 according to the following data: 1468 Attribute name: bundle-only 1469 Type of attribute: media 1470 Subject to charset: No 1471 Purpose: Request a media description to be accepted 1472 in the answer only if kept within a BUNDLE 1473 group by the answerer. 1474 Appropriate values: N/A 1475 Contact name: Christer Holmberg 1476 Contact e-mail: christer.holmberg@ericsson.com 1477 Reference: RFCXXXX 1478 Mux category: NORMAL 1480 15.4. New SDP Group Semantics 1482 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1483 document.] 1485 This document registers the following semantics with IANA in the 1486 "Semantics for the "group" SDP Attribute" subregistry (under the 1487 "Session Description Protocol (SDP) Parameters" registry: 1489 Semantics Token Reference 1490 ------------------------------------- ------ --------- 1491 Media bundling BUNDLE [RFCXXXX] 1493 16. Security Considerations 1495 The security considerations defined in [RFC3264] and [RFC5888] apply 1496 to the BUNDLE extension. Bundle does not change which information 1497 flows over the network but only changes which addresses and ports 1498 that information is flowing on and thus has very little impact on the 1499 security of the RTP sessions. 1501 When the BUNDLE extension is used, a single set of security 1502 credentials might be used for all media streams specified by a BUNDLE 1503 group. 1505 When the BUNDLE extension is used, the number of SSRC values within a 1506 single RTP session increases, which increases the risk of SSRC 1507 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1508 and SRTCP encryption in certain situations. 1510 17. Examples 1512 17.1. Example: Bundle Address Selection 1514 The example below shows: 1516 o An offer, in which the offerer associates a unique address with 1517 each bundled "m=" line within the BUNDLE group. 1519 o An answer, in which the answerer selects the offerer BUNDLE 1520 address, and then selects its own BUNDLE address (the answerer 1521 BUNDLE address) and associates it with each bundled "m=" line 1522 within the BUNDLE group. 1524 SDP Offer (1) 1526 v=0 1527 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1528 s= 1529 c=IN IP4 atlanta.example.com 1530 t=0 0 1531 a=group:BUNDLE foo bar 1532 m=audio 10000 RTP/AVP 0 8 97 1533 b=AS:200 1534 a=mid:foo 1535 a=rtcp-mux 1536 a=rtpmap:0 PCMU/8000 1537 a=rtpmap:8 PCMA/8000 1538 a=rtpmap:97 iLBC/8000 1539 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1540 m=video 10002 RTP/AVP 31 32 1541 b=AS:1000 1542 a=mid:bar 1543 a=rtcp-mux 1544 a=rtpmap:31 H261/90000 1545 a=rtpmap:32 MPV/90000 1546 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1548 SDP Answer (2) 1550 v=0 1551 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1552 s= 1553 c=IN IP4 biloxi.example.com 1554 t=0 0 1555 a=group:BUNDLE foo bar 1556 m=audio 20000 RTP/AVP 0 1557 b=AS:200 1558 a=mid:foo 1559 a=rtcp-mux 1560 a=rtpmap:0 PCMU/8000 1561 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1562 m=video 20000 RTP/AVP 32 1563 b=AS:1000 1564 a=mid:bar 1565 a=rtcp-mux 1566 a=rtpmap:32 MPV/90000 1567 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1569 17.2. Example: BUNDLE Extension Rejected 1571 The example below shows: 1573 o An offer, in which the offerer associates a unique address with 1574 each bundled "m=" line within the BUNDLE group. 1576 o An answer, in which the answerer rejects the offered BUNDLE group, 1577 and associates a unique address with each "m=" line (following 1578 normal RFC 3264 procedures). 1580 SDP Offer (1) 1582 v=0 1583 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1584 s= 1585 c=IN IP4 atlanta.example.com 1586 t=0 0 1587 a=group:BUNDLE foo bar 1588 m=audio 10000 RTP/AVP 0 8 97 1589 b=AS:200 1590 a=mid:foo 1591 a=rtcp-mux 1592 a=rtpmap:0 PCMU/8000 1593 a=rtpmap:8 PCMA/8000 1594 a=rtpmap:97 iLBC/8000 1595 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1596 m=video 10002 RTP/AVP 31 32 1597 b=AS:1000 1598 a=mid:bar 1599 a=rtcp-mux 1600 a=rtpmap:31 H261/90000 1601 a=rtpmap:32 MPV/90000 1602 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1604 SDP Answer (2) 1606 v=0 1607 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1608 s= 1609 c=IN IP4 biloxi.example.com 1610 t=0 0 1611 m=audio 20000 RTP/AVP 0 1612 b=AS:200 1613 a=rtcp-mux 1614 a=rtpmap:0 PCMU/8000 1615 m=video 30000 RTP/AVP 32 1616 b=AS:1000 1617 a=rtcp-mux 1618 a=rtpmap:32 MPV/90000 1620 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1622 The example below shows: 1624 o A subsequent offer (the BUNDLE group has been created as part of a 1625 previous offer/answer exchange), in which the offerer adds a new 1626 "m=" line, represented by the "zen" identification-tag, to a 1627 previously negotiated BUNDLE group, associates a unique address 1628 with the added "m=" line, and associates the previously selected 1629 offerer BUNDLE address with each of the other bundled "m=" lines 1630 within the BUNDLE group. 1632 o An answer, in which the answerer associates the answerer BUNDLE 1633 address with each bundled "m=" line (including the newly added 1634 "m=" line) within the BUNDLE group. 1636 SDP Offer (1) 1638 v=0 1639 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1640 s= 1641 c=IN IP4 atlanta.example.com 1642 t=0 0 1643 a=group:BUNDLE foo bar zen 1644 m=audio 10000 RTP/AVP 0 8 97 1645 b=AS:200 1646 a=mid:foo 1647 a=rtcp-mux 1648 a=rtpmap:0 PCMU/8000 1649 a=rtpmap:8 PCMA/8000 1650 a=rtpmap:97 iLBC/8000 1651 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1652 m=video 10000 RTP/AVP 31 32 1653 b=AS:1000 1654 a=mid:bar 1655 a=rtcp-mux 1656 a=rtpmap:31 H261/90000 1657 a=rtpmap:32 MPV/90000 1658 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1659 m=video 20000 RTP/AVP 66 1660 b=AS:1000 1661 a=mid:zen 1662 a=rtcp-mux 1663 a=rtpmap:66 H261/90000 1664 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1666 SDP Answer (2) 1668 v=0 1669 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1670 s= 1671 c=IN IP4 biloxi.example.com 1672 t=0 0 1673 a=group:BUNDLE foo bar zen 1674 m=audio 20000 RTP/AVP 0 1675 b=AS:200 1676 a=mid:foo 1677 a=rtcp-mux 1678 a=rtpmap:0 PCMU/8000 1679 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1680 m=video 20000 RTP/AVP 32 1681 b=AS:1000 1682 a=mid:bar 1683 a=rtcp-mux 1684 a=rtpmap:32 MPV/90000 1685 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1686 m=video 20000 RTP/AVP 66 1687 b=AS:1000 1688 a=mid:zen 1689 a=rtcp-mux 1690 a=rtpmap:66 H261/90000 1691 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1693 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1695 The example below shows: 1697 o A subsequent offer (the BUNDLE group has been created as part of a 1698 previous offer/answer transaction), in which the offerer moves a 1699 bundled "m=" line out of a BUNDLE group, associates a unique 1700 address with the moved "m=" line, and associates the offerer 1701 BUNDLE address with each other bundled "m=" line within the BUNDLE 1702 group. 1704 o An answer, in which the answerer moves the "m=" line out of the 1705 BUNDLE group, associates a unique address with the moved "m=" 1706 line, and associates the answerer BUNDLE address with each of the 1707 remaining bundled "m=" line within the BUNDLE group. 1709 SDP Offer (1) 1711 v=0 1712 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1713 s= 1714 c=IN IP4 atlanta.example.com 1715 t=0 0 1716 a=group:BUNDLE foo bar 1717 m=audio 10000 RTP/AVP 0 8 97 1718 b=AS:200 1719 a=mid:foo 1720 a=rtcp-mux 1721 a=rtpmap:0 PCMU/8000 1722 a=rtpmap:8 PCMA/8000 1723 a=rtpmap:97 iLBC/8000 1724 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1725 m=video 10000 RTP/AVP 31 32 1726 b=AS:1000 1727 a=mid:bar 1728 a=rtcp-mux 1729 a=rtpmap:31 H261/90000 1730 a=rtpmap:32 MPV/90000 1731 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1732 m=video 50000 RTP/AVP 66 1733 b=AS:1000 1734 a=mid:zen 1735 a=rtcp-mux 1736 a=rtpmap:66 H261/90000 1738 SDP Answer (2) 1740 v=0 1741 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1742 s= 1743 c=IN IP4 biloxi.example.com 1744 t=0 0 1745 a=group:BUNDLE foo bar 1746 m=audio 20000 RTP/AVP 0 1747 b=AS:200 1748 a=mid:foo 1749 a=rtcp-mux 1750 a=rtpmap:0 PCMU/8000 1751 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1752 m=video 20000 RTP/AVP 32 1753 b=AS:1000 1754 a=mid:bar 1755 a=rtcp-mux 1756 a=rtpmap:32 MPV/90000 1757 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1758 m=video 60000 RTP/AVP 66 1759 b=AS:1000 1760 a=mid:zen 1761 a=rtcp-mux 1762 a=rtpmap:66 H261/90000 1764 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1765 Group 1767 The example below shows: 1769 o A subsequent offer (the BUNDLE group has been created as part of a 1770 previous offer/answer transaction), in which the offerer disables 1771 a bundled "m=" line within a BUNDLE group, assigns a zero port 1772 number to the disabled "m=" line, and associates the offerer 1773 BUNDLE address with each of the other bundled "m=" lines within 1774 the BUNDLE group. 1776 o An answer, in which the answerer moves the disabled "m=" line out 1777 of the BUNDLE group, assigns a zero port value to the disabled 1778 "m=" line, and associates the answerer BUNDLE address with each of 1779 the remaining bundled "m=" line within the BUNDLE group. 1781 SDP Offer (1) 1783 v=0 1784 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1785 s= 1786 c=IN IP4 atlanta.example.com 1787 t=0 0 1788 a=group:BUNDLE foo bar 1789 m=audio 10000 RTP/AVP 0 8 97 1790 b=AS:200 1791 a=mid:foo 1792 a=rtcp-mux 1793 a=rtpmap:0 PCMU/8000 1794 a=rtpmap:8 PCMA/8000 1795 a=rtpmap:97 iLBC/8000 1796 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1797 m=video 10000 RTP/AVP 31 32 1798 b=AS:1000 1799 a=mid:bar 1800 a=rtcp-mux 1801 a=rtpmap:31 H261/90000 1802 a=rtpmap:32 MPV/90000 1803 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1804 m=video 0 RTP/AVP 66 1805 a=mid:zen 1806 a=rtpmap:66 H261/90000 1808 SDP Answer (2) 1810 v=0 1811 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1812 s= 1813 c=IN IP4 biloxi.example.com 1814 t=0 0 1815 a=group:BUNDLE foo bar 1816 m=audio 20000 RTP/AVP 0 1817 b=AS:200 1818 a=mid:foo 1819 a=rtcp-mux 1820 a=rtpmap:0 PCMU/8000 1821 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1822 m=video 20000 RTP/AVP 32 1823 b=AS:1000 1824 a=mid:bar 1825 a=rtcp-mux 1826 a=rtpmap:32 MPV/90000 1827 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1828 m=video 0 RTP/AVP 66 1829 a=mid:zen 1830 a=rtpmap:66 H261/90000 1832 18. Acknowledgements 1834 The usage of the SDP grouping extension for negotiating bundled media 1835 is based on a similar alternatives proposed by Harald Alvestrand and 1836 Cullen Jennings. The BUNDLE extension described in this document is 1837 based on the different alternative proposals, and text (e.g., SDP 1838 examples) have been borrowed (and, in some cases, modified) from 1839 those alternative proposals. 1841 The SDP examples are also modified versions from the ones in the 1842 Alvestrand proposal. 1844 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1845 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 1846 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1847 Justin Uberti for reading the text, and providing useful feedback. 1849 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1850 providing help and text on the RTP/RTCP procedures. 1852 Thanks to Spotify for providing music for the countless hours of 1853 document editing. 1855 19. Change Log 1857 [RFC EDITOR NOTE: Please remove this section when publishing] 1859 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-35 1861 o Editorial changes on RTP streaming mapping section based on 1862 comments from Colin Perkins. 1864 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-34 1866 o RTP streams, instead of RTP packets, are associated with m- lines. 1868 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-33 1870 o Editorial changes based on comments from Eric Rescorla and Cullen 1871 Jennings: 1873 o - Changes regarding usage of RTP/RTCP multiplexing attributes. 1875 o - Additional text regarding associating RTP/RTCP packets with SDP 1876 m- lines. 1878 o - Reference correction. 1880 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-32 1882 o Editorial changes based on comments from Eric Rescorla and Cullen 1883 Jennings: 1885 o - Justification for mechanism added to Introduction. 1887 o - Clarify that the order of m- lines in the group:BUNDLE attribute 1888 does not have to be the same as the order in which the m- lines 1889 are listed in the SDP. 1891 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31 1893 o Editorial changes based on GitHub Pull requests by Martin Thomson: 1895 o - https://github.com/cdh4u/draft-sdp-bundle/pull/2 1897 o - https://github.com/cdh4u/draft-sdp-bundle/pull/1 1899 o Editorial change based on comment from Diederick Huijbers (9th 1900 July 2016). 1902 o Changes based on comments from Flemming Andreasen (21st June 1903 2016): 1905 o - Mux category for SDP bundle-only attribute added. 1907 o - Mux category considerations editorial clarification. 1909 o - Editorial changes. 1911 o RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext. 1913 o Note whether Design Considerations appendix is to be kept removed: 1915 o - Appendix is kept within document. 1917 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30 1919 o Indicating in the Abstract and Introduction that the document 1920 updates RFC 3264. 1922 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29 1924 o Change based on WGLC comment from Colin Perkins. 1926 o - Clarify that SSRC can be reused by another source after a delay 1927 of 5 RTCP reporting intervals. 1929 o Change based on WGLC comment from Alissa Cooper. 1931 o - IANA registry name fix. 1933 o - Additional IANA registration information added. 1935 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 1937 o - Alignment with exclusive mux procedures. 1939 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 1941 o - Yet another terminology change. 1943 o - Mux category considerations added. 1945 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 1947 o - ICE considerations modified: ICE-related SDP attributes only 1948 added to the bundled m- line representing the selected BUNDLE 1949 address. 1951 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 1953 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 1954 rfc5245bis. 1956 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 1958 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 1959 considerations. 1961 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 1963 o - Reference and procedures associated with exclusive RTP/RTCP mux 1964 added 1966 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 1968 o - RTCP-MUX mandatory for bundled RTP m- lines 1970 o - Editorial fixes based on comments from Flemming Andreasen 1972 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 1974 o - Correction of Ari's family name 1976 o - Editorial fixes based on comments from Thomas Stach 1978 o - RTP/RTCP correction based on comment from Magnus Westerlund 1980 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1981 msg14861.html 1983 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 1985 o - Correct based on comment from Paul Kyzivat 1987 o -- 'received packets' replaced with 'received data' 1989 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1991 o - Clarification based on comment from James Guballa 1993 o - Clarification based on comment from Flemming Andreasen 1995 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1997 o - DTLS Considerations section added. 1999 o - BUNDLE semantics added to the IANA Considerations 2001 o - Changes based on WGLC comments from Adam Roach 2003 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2004 msg14673.html 2006 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 2008 o - Changes based on agreements at IETF#92 2010 o -- BAS Offer removed, based on agreement at IETF#92. 2012 o -- Procedures regarding usage of SDP "b=" line is replaced with a 2013 reference to to draft-ietf-mmusic-sdp-mux-attributes. 2015 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 2017 o - Editorial changes based on comments from Magnus Westerlund. 2019 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 2021 o - Modification of RTP/RTCP multiplexing section, based on comments 2022 from Magnus Westerlund. 2024 o - Reference updates. 2026 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 2028 o - Editorial fix. 2030 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 2032 o - Editorial changes. 2034 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 2036 o Changes to allow a new suggested offerer BUNDLE address to be 2037 assigned to each bundled m- line. 2039 o Changes based on WGLC comments from Paul Kyzivat 2041 o - Editorial fixes 2043 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 2045 o Usage of SDP 'extmap' attribute added 2046 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 2047 port value 2049 o Changes based on WGLC comments from Thomas Stach 2051 o - ICE candidates not assigned to bundle-only m- lines with a zero 2052 port value 2054 o - Editorial changes 2056 o Changes based on WGLC comments from Colin Perkins 2058 o - Editorial changes: 2060 o -- "RTP SDES item" -> "RTCP SDES item" 2062 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 2064 o - Changes in section 10.1.1: 2066 o -- "SHOULD NOT" -> "MUST NOT" 2068 o -- Additional text added to the Note 2070 o - Change to section 13.2: 2072 o -- Clarify that mid value is not zero terminated 2074 o - Change to section 13.3: 2076 o -- Clarify that mid value is not zero terminated 2078 o -- Clarify padding 2080 o Changes based on WGLC comments from Paul Kyzivat 2082 o - Editorial changes: 2084 o Changes based on WGLC comments from Jonathan Lennox 2086 o - Editorial changes: 2088 o - Defintion of SDP bundle-only attribute alligned with structure 2089 in 4566bis draft 2091 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 2093 o Editorial corrections based on comments from Harald Alvestrand. 2095 o Editorial corrections based on comments from Cullen Jennings. 2097 o Reference update (RFC 7160). 2099 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 2100 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 2101 msg13765.html). 2103 o Additional text added to the Security Considerations. 2105 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 2107 o SDP bundle-only attribute added to IANA Considerations. 2109 o SDES item and RTP header extension added to Abstract and 2110 Introduction. 2112 o Modification to text updating section 8.2 of RFC 3264. 2114 o Reference corrections. 2116 o Editorial corrections. 2118 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 2120 o Terminology change: "bundle-only attribute assigned to m= line" to 2121 "bundle-only attribute associated with m= line". 2123 o Editorial corrections. 2125 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 2127 o Editorial corrections. 2129 o - "of"->"if" (8.3.2.5). 2131 o - "optional"->"OPTIONAL" (9.1). 2133 o - Syntax/ABNF for 'bundle-only' attribute added. 2135 o - SDP Offer/Answer sections merged. 2137 o - 'Request new offerer BUNDLE address' section added 2139 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 2141 o OPEN ISSUE regarding Receiver-ID closed. 2143 o - RTP MID SDES Item. 2145 o - RTP MID Header Extension. 2147 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 2148 closed. 2150 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 2151 include an 'rtcp' attribute in the answer, based on the procedures 2152 in section 5.1.3 of RFC 5761. 2154 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 2156 o Draft title changed. 2158 o Added "SDP" to section names containing "Offer" or "Answer". 2160 o Editorial fixes based on comments from Paul Kyzivat 2161 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2162 msg13314.html). 2164 o Editorial fixed based on comments from Colin Perkins 2165 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2166 msg13318.html). 2168 o - Removed text about extending BUNDLE to allow multiple RTP 2169 sessions within a BUNDLE group. 2171 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 2173 o Major re-structure of SDP Offer/Answer sections, to align with RFC 2174 3264 structure. 2176 o Additional definitions added. 2178 o - Shared address. 2180 o - Bundled "m=" line. 2182 o - Bundle-only "m=" line. 2184 o - Offerer suggested BUNDLE mid. 2186 o - Answerer selected BUNDLE mid. 2188 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 2189 to multiple "m=" lines until it has received an SDP Answer 2190 indicating support of the BUNDLE extension. 2192 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 2193 Answerer supports the BUNDLE extension, assign a zero port value 2194 to a 'bundle-only' "m=" line. 2196 o SDP 'bundle-only' attribute section added. 2198 o Connection data nettype/addrtype restrictions added. 2200 o RFC 3264 update section added. 2202 o Indicating that a specific payload type value can be used in 2203 multiple "m=" lines, if the value represents the same codec 2204 configuration in each "m=" line. 2206 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2208 o Updated Offerer procedures (http://www.ietf.org/mail- 2209 archive/web/mmusic/current/msg12293.html). 2211 o Updated Answerer procedures (http://www.ietf.org/mail- 2212 archive/web/mmusic/current/msg12333.html). 2214 o Usage of SDP 'bundle-only' attribute added. 2216 o Reference to Trickle ICE document added. 2218 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2220 o Mechanism modified, to be based on usage of SDP Offers with both 2221 different and identical port number values, depending on whether 2222 it is known if the remote endpoint supports the extension. 2224 o Cullen Jennings added as co-author. 2226 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2228 o No changes. New version due to expiration. 2230 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2232 o No changes. New version due to expiration. 2234 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2236 o Draft name changed. 2238 o Harald Alvestrand added as co-author. 2240 o "Multiplex" terminology changed to "bundle". 2242 o Added text about single versus multiple RTP Sessions. 2244 o Added reference to RFC 3550. 2246 20. References 2248 20.1. Normative References 2250 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2251 Requirement Levels", BCP 14, RFC 2119, 2252 DOI 10.17487/RFC2119, March 1997, 2253 . 2255 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2256 with Session Description Protocol (SDP)", RFC 3264, 2257 DOI 10.17487/RFC3264, June 2002, 2258 . 2260 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2261 Jacobson, "RTP: A Transport Protocol for Real-Time 2262 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2263 July 2003, . 2265 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2266 in Session Description Protocol (SDP)", RFC 3605, 2267 DOI 10.17487/RFC3605, October 2003, 2268 . 2270 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2271 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2272 July 2006, . 2274 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2275 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2276 . 2278 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2279 (ICE): A Protocol for Network Address Translator (NAT) 2280 Traversal for Offer/Answer Protocols", RFC 5245, 2281 DOI 10.17487/RFC5245, April 2010, 2282 . 2284 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2285 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2286 2008, . 2288 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2289 Control Packets on a Single Port", RFC 5761, 2290 DOI 10.17487/RFC5761, April 2010, 2291 . 2293 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2294 Security (DTLS) Extension to Establish Keys for the Secure 2295 Real-time Transport Protocol (SRTP)", RFC 5764, 2296 DOI 10.17487/RFC5764, May 2010, 2297 . 2299 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2300 Protocol (SDP) Grouping Framework", RFC 5888, 2301 DOI 10.17487/RFC5888, June 2010, 2302 . 2304 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2305 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2306 January 2012, . 2308 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 2309 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 2310 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 2311 DOI 10.17487/RFC7656, November 2015, 2312 . 2314 [RFC7941] Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 2315 Header Extension for the RTP Control Protocol (RTCP) 2316 Source Description Items", RFC 7941, DOI 10.17487/RFC7941, 2317 August 2016, . 2319 [I-D.ietf-ice-rfc5245bis] 2320 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 2321 Connectivity Establishment (ICE): A Protocol for Network 2322 Address Translator (NAT) Traversal", draft-ietf-ice- 2323 rfc5245bis-04 (work in progress), June 2016. 2325 [I-D.ietf-mmusic-sdp-mux-attributes] 2326 Nandakumar, S., "A Framework for SDP Attributes when 2327 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-14 2328 (work in progress), September 2016. 2330 [I-D.ietf-mmusic-mux-exclusive] 2331 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2332 Multiplexing using SDP", draft-ietf-mmusic-mux- 2333 exclusive-10 (work in progress), August 2016. 2335 [I-D.ietf-mmusic-ice-sip-sdp] 2336 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, "Using 2337 Interactive Connectivity Establishment (ICE) with Session 2338 Description Protocol (SDP) offer/answer and Session 2339 Initiation Protocol (SIP)", draft-ietf-mmusic-ice-sip- 2340 sdp-10 (work in progress), July 2016. 2342 20.2. Informative References 2344 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2345 A., Peterson, J., Sparks, R., Handley, M., and E. 2346 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2347 DOI 10.17487/RFC3261, June 2002, 2348 . 2350 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2351 Description Protocol (SDP) Security Descriptions for Media 2352 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2353 . 2355 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2356 Media Attributes in the Session Description Protocol 2357 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2358 . 2360 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2361 Clock Rates in an RTP Session", RFC 7160, 2362 DOI 10.17487/RFC7160, April 2014, 2363 . 2365 [I-D.ietf-mmusic-trickle-ice] 2366 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2367 Incremental Provisioning of Candidates for the Interactive 2368 Connectivity Establishment (ICE) Protocol", draft-ietf- 2369 mmusic-trickle-ice-02 (work in progress), January 2015. 2371 Appendix A. Design Considerations 2373 One of the main issues regarding the BUNDLE grouping extensions has 2374 been whether, in SDP Offers and SDP Answers, the same port value 2375 should be inserted in "m=" lines associated with a BUNDLE group, as 2376 the purpose of the extension is to negotiate the usage of a single 2377 address:port combination for media specified by the "m=" lines. 2378 Issues with both approaches, discussed in the Appendix have been 2379 raised. The outcome was to specify a mechanism which uses SDP Offers 2380 with both different and identical port values. 2382 Below are the primary issues that have been considered when defining 2383 the "BUNDLE" grouping extension: 2385 o 1) Interoperability with existing UAs. 2387 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2389 o 3) Time to gather, and the number of, ICE candidates. 2391 o 4) Different error scenarios, and when they occur. 2393 o 5) SDP Offer/Answer impacts, including usage of port number value 2394 zero. 2396 A.1. UA Interoperability 2398 Consider the following SDP Offer/Answer exchange, where Alice sends 2399 an SDP Offer to Bob: 2401 SDP Offer 2403 v=0 2404 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2405 s= 2406 c=IN IP4 atlanta.example.com 2407 t=0 0 2408 m=audio 10000 RTP/AVP 97 2409 a=rtpmap:97 iLBC/8000 2410 m=video 10002 RTP/AVP 97 2411 a=rtpmap:97 H261/90000 2413 SDP Answer 2415 v=0 2416 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2417 s= 2418 c=IN IP4 biloxi.example.com 2419 t=0 0 2420 m=audio 20000 RTP/AVP 97 2421 a=rtpmap:97 iLBC/8000 2422 m=video 20002 RTP/AVP 97 2423 a=rtpmap:97 H261/90000 2425 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2426 later invention to RTP and Bob can not assume that Alice supports RFC 2427 4961. This means that Alice may be sending RTP from a different port 2428 than 10000 or 10002 - some implementation simply send the RTP from an 2429 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2430 way that Bob knows if it should be passed to the video or audio codec 2431 is by looking at the port it was received on. This lead some SDP 2432 implementations to use the fact that each "m=" line had a different 2433 port number to use that port number as an index to find the correct m 2434 line in the SDP. As a result, some implementations that do support 2435 symmetric RTP and ICE still use a SDP data structure where SDP with 2436 "m=" lines with the same port such as: 2438 SDP Offer 2440 v=0 2441 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2442 s= 2443 c=IN IP4 atlanta.example.com 2444 t=0 0 2445 m=audio 10000 RTP/AVP 97 2446 a=rtpmap:97 iLBC/8000 2447 m=video 10000 RTP/AVP 98 2448 a=rtpmap:98 H261/90000 2450 will result in the second "m=" line being considered an SDP error 2451 because it has the same port as the first line. 2453 A.2. Usage of port number value zero 2455 In an SDP Offer or SDP Answer, the media specified by an "m=" line 2456 can be disabled/rejected by setting the port number value to zero. 2457 This is different from e.g., using the SDP direction attributes, 2458 where RTCP traffic will continue even if the SDP "inactive" attribute 2459 is indicated for the associated "m=" line. 2461 If each "m=" line associated with a BUNDLE group would contain 2462 different port values, and one of those port values would be used for 2463 a BUNDLE address associated with the BUNDLE group, problems would 2464 occur if an endpoint wants to disable/reject the "m=" line associated 2465 with that port, by setting the port value to zero. After that, no 2466 "m=" line would contain the port value which is used for the BUNDLE 2467 address. In addition, it is unclear what would happen to the ICE 2468 candidates associated with the "m=" line, as they are also used for 2469 the BUNDLE address. 2471 A.3. B2BUA And Proxy Interoperability 2473 Some back to back user agents may be configured in a mode where if 2474 the incoming call leg contains an SDP attribute the B2BUA does not 2475 understand, the B2BUA still generates that SDP attribute in the Offer 2476 for the outgoing call leg. Consider a B2BUA that did not understand 2477 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2478 Further assume that the B2BUA was configured to tear down any call 2479 where it did not see any RTCP for 5 minutes. In this case, if the 2480 B2BUA received an Offer like: 2482 SDP Offer 2484 v=0 2485 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2486 s= 2487 c=IN IP4 atlanta.example.com 2488 t=0 0 2489 m=audio 49170 RTP/AVP 0 2490 a=rtcp:53020 2492 It would be looking for RTCP on port 49172 but would not see any 2493 because the RTCP would be on port 53020 and after five minutes, it 2494 would tear down the call. Similarly, a B2BUA that did not understand 2495 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2496 wrong port and tear down the call. It is worth noting that a B2BUA 2497 that generated an Offer with capabilities it does not understand is 2498 not compliant with the specifications. 2500 A.3.1. Traffic Policing 2502 Sometimes intermediaries do not act as B2BUA, in the sense that they 2503 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2504 however, they may use SDP information (e.g., IP address and port) in 2505 order to control traffic gating functions, and to set traffic 2506 policing rules. There might be rules which will trigger a session to 2507 be terminated in case media is not sent or received on the ports 2508 retrieved from the SDP. This typically occurs once the session is 2509 already established and ongoing. 2511 A.3.2. Bandwidth Allocation 2513 Sometimes intermediaries do not act as B2BUA, in the sense that they 2514 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2515 however, they may use SDP information (e.g., codecs and media types) 2516 in order to control bandwidth allocation functions. The bandwidth 2517 allocation is done per "m=" line, which means that it might not be 2518 enough if media specified by all "m=" lines try to use that 2519 bandwidth. That may either simply lead to bad user experience, or to 2520 termination of the call. 2522 A.4. Candidate Gathering 2524 When using ICE, a candidate needs to be gathered for each port. This 2525 takes approximately 20 ms extra for each extra "m=" line due to the 2526 NAT pacing requirements. All of this gather can be overlapped with 2527 other things while for exampe a web-page is loading to minimize the 2528 impact. If the client only wants to generate TURN or STUN ICE 2529 candidates for one of the "m=" lines and then use trickle ICE 2530 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2531 the rest of the "m=" lines, it MAY do that and will not need any 2532 additional gathering time. 2534 Some people have suggested a TURN extension to get a bunch of TURN 2535 allocations at once. This would only provide a single STUN result so 2536 in cases where the other end did not support BUNDLE, may cause more 2537 use of the TURN server but would be quick in the cases where both 2538 sides supported BUNDLE and would fall back to a successful call in 2539 the other cases. 2541 Authors' Addresses 2543 Christer Holmberg 2544 Ericsson 2545 Hirsalantie 11 2546 Jorvas 02420 2547 Finland 2549 Email: christer.holmberg@ericsson.com 2551 Harald Tveit Alvestrand 2552 Google 2553 Kungsbron 2 2554 Stockholm 11122 2555 Sweden 2557 Email: harald@alvestrand.no 2558 Cullen Jennings 2559 Cisco 2560 400 3rd Avenue SW, Suite 350 2561 Calgary, AB T2P 4H2 2562 Canada 2564 Email: fluffy@iii.ca