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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: August 27, 2016 C. Jennings 7 Cisco 8 February 24, 2016 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-27.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, associated with 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. 27 There are multiple ways to correlate the bundled RTP packets with the 28 appropriate media descriptions. This specification defines a new 29 Real-time Transport Protocol (RTP) source description (SDES) item and 30 a new RTP header extension that provides an additional way to do this 31 correlation by using them to carry a value that associates the RTP/ 32 RTCP packets with a specific media description. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on August 27, 2016. 50 Copyright Notice 52 Copyright (c) 2016 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 71 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 72 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 7 73 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 74 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 7.2. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 76 7.3. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 77 7.4. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 78 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 79 8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 80 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 81 8.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 82 8.2.2. Suggesting the offerer BUNDLE address . . . . . . . . 11 83 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 11 84 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 11 85 8.3.2. Answerer Selection of Offerer Bundle Address . . . . 12 86 8.3.3. Answerer Selection of Answerer BUNDLE Address . . . . 13 87 8.3.4. Moving A Media Description Out Of A BUNDLE Group . . 13 88 8.3.5. Rejecting A Media Description In A BUNDLE Group . . . 13 89 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14 90 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 14 91 8.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 92 8.5.2. Suggesting a new offerer BUNDLE address . . . . . . . 14 93 8.5.3. Adding a media description to a BUNDLE group . . . . 15 94 8.5.4. Moving A Media Description Out Of A BUNDLE Group . . 16 95 8.5.5. Disabling A Media Description In A BUNDLE Group . . . 16 97 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 16 98 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 16 99 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 100 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 17 101 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 17 102 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 18 103 10.1.2. Payload Type (PT) Value Reuse . . . . . . . . . . . 18 104 10.2. Associating RTP/RTCP Packets With Correct SDP Media 105 Description . . . . . . . . . . . . . . . . . . . . . . 19 106 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 19 107 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 20 108 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 109 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 22 110 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 111 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 22 112 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 23 113 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 23 114 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 23 115 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 24 116 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 24 117 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 24 118 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 25 119 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 25 120 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 25 121 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 122 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 123 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 26 124 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 126 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 26 127 13.7. New text replacing section 8.4 (6th paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 129 14. RTP/RTCP extensions for identification-tag transport . . . . 27 130 14.1. General . . . . . . . . . . . . . . . . . . . . . . . . 27 131 14.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 28 132 14.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 28 133 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 134 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 29 135 15.2. New RTP Header Extension URI . . . . . . . . . . . . . . 29 136 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 29 137 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 30 138 16. Security Considerations . . . . . . . . . . . . . . . . . . . 30 139 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 31 140 17.1. Example: Bundle Address Selection . . . . . . . . . . . 31 141 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 33 142 17.3. Example: Offerer Adds A Media Description To A BUNDLE 143 Group . . . . . . . . . . . . . . . . . . . . . . . . . 34 144 17.4. Example: Offerer Moves A Media Description Out Of A 145 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 36 146 17.5. Example: Offerer Disables A Media Description Within A 147 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 37 148 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39 149 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 39 150 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 151 20.1. Normative References . . . . . . . . . . . . . . . . . . 46 152 20.2. Informative References . . . . . . . . . . . . . . . . . 47 153 Appendix A. Design Considerations . . . . . . . . . . . . . . . 48 154 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 48 155 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 49 156 A.3. Usage of port number value zero . . . . . . . . . . . . . 50 157 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 50 158 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 51 159 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 51 160 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 52 161 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52 163 1. Introduction 165 This specification defines a way to use a single address:port 166 combination (BUNDLE address) for receiving media associated with 167 multiple SDP media descriptions ("m=" lines). 169 This specification defines a new SDP Grouping Framework [RFC5888] 170 extension called 'BUNDLE'. The extension can be used with the 171 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 172 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 173 BUNDLE address is used for receiving media associated with multiple 174 "m=" lines. This is referred to as bundled media. 176 The offerer and answerer [RFC3264] use the BUNDLE extension to 177 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 178 address) and one for the answerer (answerer BUNDLE address), to be 179 used for receiving the bundled media associated with a BUNDLE group. 180 Once the offerer and the answerer have negotiated a BUNDLE group, 181 they associate their respective BUNDLE address with each "m=" line in 182 the BUNDLE group. The BUNDLE addresses are used to receive all media 183 associated with the BUNDLE group. 185 The use of a BUNDLE group and a BUNDLE address also allows the usage 186 of a single set of Interactive Connectivity Establishment (ICE) 187 [I-D.ietf-ice-rfc5245bis] candidates for multiple "m=" lines. 189 This specification also defines a new SDP attribute, 'bundle-only', 190 which can be used to request that specific media is only used if kept 191 within a BUNDLE group. 193 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 194 port value to multiple "m=" lines are undefined, and there is no 195 grouping defined by such means. Instead, an explicit grouping 196 mechanism needs to be used to express the intended semantics. This 197 specification provides such an extension. 199 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 200 [RFC3264]. The update allows an answerer to assign a non-zero port 201 value to an "m=" line in an SDP answer, even if the "m=" line in the 202 associated SDP offer contained a zero port value. 204 This specification also defines a new Real-time Transport Protocol 205 (RTP) [RFC3550] source description (SDES) item and a new RTP header 206 extension that can be used to carry a value that associates RTP/RTCP 207 packets with a specific media description. This can be used to 208 correlate a RTP packet with the correct media. 210 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 211 address MUST only be associated with a single BUNDLE group. The 212 procedures in this specification apply independently to a given 213 BUNDLE group. All RTP based media flows associated with a single 214 BUNDLE group belong to a single RTP session [RFC3550]. 216 The BUNDLE extension is backward compatible. Endpoints that do not 217 support the extension are expected to generate offers and answers 218 without an SDP 'group:BUNDLE' attribute, and are expected to 219 associate a unique address with each "m=" line within an offer and 220 answer, according to the procedures in [RFC4566] and [RFC3264] 222 2. Terminology 224 "m=" line: SDP bodies contain one or more media descriptions. Each 225 media description is identified by an SDP "m=" line. 227 5-tuple: A collection of the following values: source address, source 228 port, destination address, destination port, and transport-layer 229 protocol. 231 Unique address: An IP address and port combination that is associated 232 with only one "m=" line in an offer or answer. 234 Shared address: An IP address and port combination that is associated 235 with multiple "m=" lines within an offer or answer. 237 Offerer BUNDLE-tag: The first identification-tag in a given SDP 238 'group:BUNDLE' attribute identification-tag list in an offer. 240 Answerer BUNDLE-tag: The first identification-tag in a given SDP 241 'group:BUNDLE' attribute identification-tag list in an answer. 243 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 244 and port combination used by an offerer to receive all media 245 associated with each "m=" line within the BUNDLE group. 247 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 248 and port combination used by an answerer to receive all media 249 associated with each "m=" line within the BUNDLE group. 251 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 252 exchange, which uses the same BUNDLE address for receiving media. 254 Bundled "m=" line: An "m=" line, whose identification-tag is placed 255 in an SDP 'group:BUNDLE' attribute identification-tag list in an 256 offer or answer. 258 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 259 'bundle-only' attribute. 261 Bundled media: All media associated with a given BUNDLE group. 263 Initial offer: The first offer, within an SDP session (e.g. a SIP 264 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 265 to carry SDP), in which the offerer indicates that it wants to create 266 a given BUNDLE group. 268 Subsequent offer: An offer which contains a BUNDLE group that has 269 been created as part of a previous offer/answer exchange. 271 Identification-tag: A unique token value that is used to identify an 272 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 273 "m=" line, carries an unique identification-tag. The session-level 274 SDP 'group' attribute [RFC5888] carries a list of identification- 275 tags, identifying the "m=" lines associated with that particular 276 'group' attribute. 278 3. Conventions 280 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 281 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 282 document are to be interpreted as described in BCP 14, RFC 2119 283 [RFC2119]. 285 4. Applicability Statement 287 The mechanism in this specification only applies to the Session 288 Description Protocol (SDP) [RFC4566], when used together with the SDP 289 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 290 scope of this document, and is thus undefined. 292 5. SDP Grouping Framework BUNDLE Extension 294 This section defines a new SDP Grouping Framework extension 295 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 296 Offer/Answer mechanism to negotiate the usage of a single 297 address:port combination (BUNDLE address) for receiving bundled 298 media. 300 A single address:port combination is also used for sending bundled 301 media. The address:port combination used for sending bundled media 302 MAY be the same as the BUNDLE address, used to receive bundled media, 303 depending on whether symmetric RTP [RFC4961] is used. 305 All media associated with a BUNDLE group share a single 5-tuple, i.e. 306 in addition to using a single address:port combination all bundled 307 media MUST be transported using the same transport-layer protocol 308 (e.g. UDP or TCP). 310 The BUNDLE extension is indicated using an SDP 'group' attribute with 311 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 312 associated with each bundled "m=" line, and each identification-tag 313 is listed in the SDP 'group:BUNDLE' attribute identification-tag 314 list. Each "m=" line whose identification-tag is listed in the 315 identification-tag list is associated with a given BUNDLE group. 317 SDP bodies can contain multiple BUNDLE groups. Any given bundled 318 "m=" line MUST NOT be associated with more than one BUNDLE group. 320 Section 8 defines the detailed SDP Offer/Answer procedures for the 321 BUNDLE extension. 323 6. SDP 'bundle-only' Attribute 325 This section defines a new SDP media-level attribute [RFC4566], 326 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 327 hence has no value. 329 Name: bundle-only 331 Value: N/A 333 Usage Level: media 335 Charset Dependent: no 337 Example: 339 a=bundle-only 341 In order to ensure that an answerer that does not support the BUNDLE 342 extension always rejects a bundled "m=" line, the offerer can assign 343 a zero port value to the "m=" line. According to [RFC4566] an 344 answerer will reject such "m=" line. By associating an SDP 'bundle- 345 only' attribute with such "m=" line, the offerer can request that the 346 answerer accepts the "m=" line if the answerer supports the Bundle 347 extension, and if the answerer keeps the "m=" line within the 348 associated BUNDLE group. 350 NOTE: Once the offerer BUNDLE address has been selected, the offerer 351 does not need to include the 'bundle-only' attribute in subsequent 352 offers. By associating the offerer BUNDLE address with an "m=" line 353 of a subsequent offer, the offerer will ensure that the answerer will 354 either keep the "m=" line within the BUNDLE group, or the answerer 355 will have to reject the "m=" line. 357 The usage of the 'bundle-only' attribute is only defined for a 358 bundled "m=" line with a zero port value, within an offer. Other 359 usage is unspecified. 361 Section 8 defines the detailed SDP Offer/Answer procedures for the 362 'bundle-only' attribute. 364 7. SDP Information Considerations 366 7.1. General 368 This section describes restrictions associated with the usage of SDP 369 parameters within a BUNDLE group. It also describes, when parameter 370 and attribute values have been associated with each bundled "m=" 371 line, how to calculate a value for the whole BUNDLE group. 373 7.2. Connection Data (c=) 375 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 376 line MUST be 'IN'. 378 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 379 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 380 each "m=" line. 382 NOTE: Extensions to this specification can specify usage of the 383 BUNDLE mechanism for other nettype and addrtype values than the ones 384 listed above. 386 7.3. Bandwidth (b=) 388 An offerer and answerer MUST use the rules and restrictions defined 389 in [I-D.ietf-mmusic-sdp-mux-attributes] for when associating the SDP 390 bandwidth (b=) line with bundled "m=" lines. 392 7.4. Attributes (a=) 394 An offerer and answerer MUST use the rules and restrictions defined 395 in [I-D.ietf-mmusic-sdp-mux-attributes] for when associating SDP 396 attributes with bundled "m=" lines. 398 8. SDP Offer/Answer Procedures 400 8.1. General 402 This section describes the SDP Offer/Answer [RFC3264] procedures for: 404 o Negotiating and creating of a BUNDLE group; and 406 o Selecting the BUNDLE addresses (offerer BUNDLE address and 407 answerer BUNDLE address); and 409 o Adding an "m=" line to a BUNDLE group; and 411 o Moving an "m=" line out of a BUNDLE group; and 413 o Disabling an "m=" line within a BUNDLE group. 415 The generic rules and procedures defined in [RFC3264] and [RFC5888] 416 also apply to the BUNDLE extension. For example, if an offer is 417 rejected by the answerer, the previously negotiated SDP parameters 418 and characteristics (including those associated with a BUNDLE group) 419 apply. Hence, if an offerer generates an offer in which the offerer 420 wants to create a BUNDLE group, and the answerer rejects the offer, 421 the BUNDLE group is not created. 423 The procedures in this section are independent of the media type or 424 "m=" line proto value represented by a bundled "m=" line. Section 10 425 defines additional considerations for RTP based media. Section 6 426 defines additional considerations for the usage of the SDP 'bundle- 427 only' attribute. Section 11 defines additional considerations for 428 the usage of Interactive Connectivity Establishment (ICE) 429 [I-D.ietf-ice-rfc5245bis] mechanism . 431 SDP offers and answers can contain multiple BUNDLE groups. The 432 procedures in this section apply independently to a given BUNDLE 433 group. 435 8.2. Generating the Initial SDP Offer 437 8.2.1. General 439 When an offerer generates an initial offer, in order to create a 440 BUNDLE group, it MUST: 442 o Assign a unique address to each "m=" line within the offer, 443 following the procedures in [RFC3264], unless the media line is a 444 'bundle-only' "m=" line (see below); and 446 o Add an SDP 'group:BUNDLE' attribute to the offer; and 448 o Place the identification-tag of each bundled "m=" line in the SDP 449 'group:BUNDLE' attribute identification-tag list; and 451 o Indicate which unique address the offerer suggests as the offerer 452 BUNDLE address [Section 8.2.2]. 454 If the offerer wants to request that the answerer accepts a given 455 bundled "m=" line only if the answerer keeps the "m=" line within the 456 BUNDLE group, the offerer MUST: 458 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 459 "m=" line; and 461 o Assign a zero port value to the "m=" line. 463 NOTE: If the offerer assigns a zero port value to an "m=" line, but 464 does not also associate an SDP 'bundle-only' attribute with the "m=" 465 line, it is an indication that the offerer wants to disable the "m=" 466 line [Section 8.5.5]. 468 [Section 17.1] shows an example of an initial offer. 470 8.2.2. Suggesting the offerer BUNDLE address 472 In the offer, the address associated with the "m=" line associated 473 with the offerer BUNDLE-tag indicates the address that the offerer 474 suggests as the offerer BUNDLE address. 476 The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain 477 a zero port value or an SDP 'bundle-only' attribute. 479 8.3. Generating the SDP Answer 481 8.3.1. General 483 When an answerer generates an answer that contains a BUNDLE group, 484 the following general SDP grouping framework restrictions, defined in 485 [RFC5888], also apply to the BUNDLE group: 487 o The answerer MUST NOT include a BUNDLE group in the answer, unless 488 the offerer requested the BUNDLE group to be created in the 489 associated offer; and 491 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 492 unless the offerer requested the "m=" line to be within that 493 BUNDLE group in the associated offer. 495 If the answer contains a BUNDLE group, the answerer MUST: 497 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 499 o Select an Answerer BUNDLE Address [Section 8.3.3]; 501 The answerer is allowed to select a new Answerer BUNDLE address each 502 time it generates an answer to an offer. 504 If the answerer does not want to keep an "m=" line within a BUNDLE 505 group, it MUST: 507 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 509 o Reject the "m=" line [Section 8.3.5]; 511 If the answerer keeps a bundle-only "m=" line within the BUNDLE 512 group, it follows the procedures (associates the answerer BUNDLE 513 address with the "m=" line etc) for any other "m=" line kept within 514 the BUNDLE group. 516 If the answerer does not want to keep a bundle-only "m=" line within 517 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 519 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 520 any "m=" line in an answer. 522 NOTE: If a bundled "m=" line in an offer contains a zero port value, 523 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 524 is an indication that the offerer wants to disable the "m=" line 525 [Section 8.5.5]. 527 8.3.2. Answerer Selection of Offerer Bundle Address 529 In an offer, the address (unique or shared) associated with the 530 bundled "m=" line associated with the offerer BUNDLE-tag indicates 531 the address that the offerer suggests as the offerer BUNDLE address 532 [Section 8.2.2]. The answerer MUST check whether that "m=" line 533 fulfils the following criteria: 535 o The answerer will not move the "m=" line out of the BUNDLE group 536 [Section 8.3.4]; and 538 o The answerer will not reject the "m=" line [Section 8.3.5]; and 540 o The "m=" line does not contain a zero port value. 542 If all of the criteria above are fulfilled, the answerer MUST select 543 the address associated with the "m=" line as the offerer BUNDLE 544 address. In the answer, the answerer BUNDLE-tag represents the "m=" 545 line, and the address associated with the "m=" line in the offer 546 becomes the offerer BUNDLE address. 548 If one or more of the criteria are not fulfilled, the answerer MUST 549 select the next identification-tag in the identification-tag list, 550 and perform the same criteria check for the "m=" line associated with 551 that identification-tag. If there are no more identification-tags in 552 the identification-tag list, the answerer MUST NOT create the BUNDLE 553 group. In addition, unless the answerer rejects the whole offer, the 554 answerer MUST apply the answerer procedures for moving an "m=" line 555 out of a BUNDLE group [Section 8.3.4] to each bundled "m=" line in 556 the offer when creating the answer. 558 [Section 17.1] shows an example of an offerer BUNDLE address 559 selection. 561 8.3.3. Answerer Selection of Answerer BUNDLE Address 563 When the answerer selects a BUNDLE address for itself, referred to as 564 the answerer BUNDLE address, it MUST associate that address with each 565 bundled "m=" line within the created BUNDLE group in the answer. 567 The answerer MUST NOT associate the answerer BUNDLE address with an 568 "m=" line that is not within the BUNDLE group, or to an "m=" line 569 that is within another BUNDLE group. 571 [Section 17.1] shows an example of an answerer BUNDLE address 572 selection. 574 8.3.4. Moving A Media Description Out Of A BUNDLE Group 576 When an answerer wants to move an "m=" line out of a BUNDLE group, it 577 MUST first check the following criteria: 579 o In the associated offer, the "m=" line is associated with a shared 580 address (e.g. a previously selected offerer BUNDLE address); or 582 o In the associated offer, if an SDP 'bundle-only' attribute is 583 associated with the "m=" line, and if the "m=" line contains a 584 zero port value. 586 If either criteria above is fulfilled, the answerer MUST reject the 587 "m=" line [Section 8.3.5]. 589 Otherwise, if in the associated offer the "m=" line is associated 590 with a unique address, the answerer MUST associate a unique address 591 with the "m=" line in the answer (the answerer does not reject the 592 "m=" line). 594 In addition, in either case above, the answerer MUST NOT place the 595 identification-tag, associated with the moved "m=" line, in the SDP 596 'group' attribute identification-tag list associated with the BUNDLE 597 group. 599 8.3.5. Rejecting A Media Description In A BUNDLE Group 601 When an answerer rejects an "m=" line, it MUST associate an address 602 with a zero port value with the "m=" line in the answer, according to 603 the procedures in [RFC4566]. 605 In addition, the answerer MUST NOT place the identification-tag, 606 associated with the rejected "m=" line, in the SDP 'group' attribute 607 identification-tag list associated with the BUNDLE group. 609 8.4. Offerer Processing of the SDP Answer 611 When an offerer receives an answer, if the answer contains a BUNDLE 612 group, the offerer MUST check that any bundled "m=" line in the 613 answer was indicated as bundled in the associated offer. If there is 614 no mismatch, the offerer MUST use the offerer BUNDLE address, 615 selected by the answerer [Section 8.3.2], as the address for each 616 bundled "m=" line. 618 NOTE: As the answerer might reject one or more bundled "m=" lines, or 619 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 620 line in the offer might not be indicated as bundled in the answer. 622 If the answer does not contain a BUNDLE group, the offerer MUST 623 process the answer as a normal answer. 625 8.5. Modifying the Session 627 8.5.1. General 629 When an offerer generates a subsequent offer, it MUST associate the 630 previously selected offerer BUNDLE address [Section 8.3.2] with each 631 bundled "m=" line (including any bundle-only "m=" line), except if: 633 o The offerer suggests a new offerer BUNDLE address [Section 8.5.2]; 634 or 636 o The offerer wants to add a bundled "m=" line to the BUNDLE group 637 [Section 8.5.3]; or 639 o The offerer wants to move a bundled "m=" line out of the BUNDLE 640 group [Section 8.5.4]; or 642 o The offerer wants to disable the bundled "m=" line 643 [Section 8.5.5]. 645 In addition, the offerer MUST select an offerer BUNDLE-tag 646 [Section 8.2.2] associated with the previously selected offerer 647 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 648 address. 650 8.5.2. Suggesting a new offerer BUNDLE address 652 When an offerer generates an offer, in which it suggests a new 653 offerer BUNDLE address [Section 8.2.2], the offerer MUST: 655 o Assign the address (shared address) to each "m=" line within the 656 BUNDLE group; or 658 o Assign the address (unique address) to one bundled "m=" line. 660 In addition, the offerer MUST indicate that the address is the new 661 suggested offerer BUNDLE address [Section 8.2.2]. 663 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 664 address with each bundled "m=" line, it can associate unique 665 addresses with any number of bundled "m=" lines (and the previously 666 selected offerer BUNDLE address to any remaining bundled "m=" line) 667 if it wants to suggest multiple alternatives for the new offerer 668 BUNDLE address. 670 8.5.3. Adding a media description to a BUNDLE group 672 When an offerer generates an offer, in which it wants to add a 673 bundled "m=" line to a BUNDLE group, the offerer MUST: 675 o Assign a unique address to the added "m=" line; or 677 o Assign the previously selected offerer BUNDLE address to the added 678 "m=" line; or 680 o If the offerer associates a new (shared address) suggested offerer 681 BUNDLE address with each bundled "m=" line [Section 8.5.2], also 682 associate that address with the added "m=" line. 684 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 685 identification-tag list with the BUNDLE group [Section 8.2.2] by 686 adding the identification-tag associated with the added "m=" line to 687 the list. 689 NOTE: Assigning a unique address to the "m=" line allows the answerer 690 to move the "m=" line out of the BUNDLE group [Section 8.3.4], 691 without having to reject the "m=" line. 693 If the offerer associates a unique address with the added "m=" line, 694 and if the offerer suggests that address as the new offerer BUNDLE 695 address [Section 8.5.2], the offerer BUNDLE-tag MUST represent the 696 added "m=" line [Section 8.2.2]. 698 If the offerer associates a new suggested offerer BUNDLE address with 699 each bundled "m=" line [Section 8.5.2], including the added "m=" 700 line, the offerer BUNDLE-tag MAY represent the added "m=" line 701 [Section 8.2.2]. 703 [Section 17.3] shows an example where an offerer sends an offer in 704 order to add a bundled "m=" line to a BUNDLE group. 706 8.5.4. Moving A Media Description Out Of A BUNDLE Group 708 When an offerer generates an offer, in which it wants to move a 709 bundled "m=" line out of a BUNDLE group it was added to in a previous 710 offer/answer transaction, the offerer: 712 o MUST associate a unique address with the "m=" line; and 714 o MUST NOT place the identification-tag associated with the "m=" 715 line in the SDP 'group:BUNDLE' attribute identification-tag list 716 associated with the BUNDLE group. 718 NOTE: If the removed "m=" line is associated with the previously 719 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 720 [Section 8.2.2]. 722 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 723 added to another BUNDLE group, the offerer applies the procedures in 724 [Section 8.5.3] to the "m=" line. 726 [Section 17.4] shows an example of an offer for moving an "m=" line 727 out of a BUNDLE group. 729 8.5.5. Disabling A Media Description In A BUNDLE Group 731 When an offerer generates an offer, in which it wants to disable a 732 bundled "m=" line (added to the BUNDLE group in a previous offer/ 733 answer transaction), the offerer: 735 o MUST associate an address with a zero port value with the "m=" 736 line, following the procedures in [RFC4566]; and 738 o MUST NOT place the identification-tag associated with the "m=" 739 line in the SDP 'group:BUNDLE' attribute identification-tag list 740 associated with the BUNDLE group. 742 [Section 17.5] shows an example of an offer for disabling an "m=" 743 line within a BUNDLE group. 745 9. Protocol Identification 747 9.1. General 749 Each "m=" line within a BUNDLE group MUST use the same transport- 750 layer protocol. If bundled "m=" lines use different protocols on top 751 of the transport-layer protocol, there MUST exist a publicly 752 available specification which describes a mechanism, for this 753 particular protocol combination, how to associate received data with 754 the correct protocol. 756 In addition, if received data can be associated with more than one 757 bundled "m=" line, there MUST exist a publicly available 758 specification which describes a mechanism for associating the 759 received data with the correct "m=" line. 761 This document describes a mechanism to identify the protocol of 762 received data among the STUN, DTLS and SRTP protocols (in any 763 combination), when UDP is used as transport-layer protocol, but does 764 not describe how to identify different protocols transported on DTLS. 765 While the mechanism is generally applicable to other protocols and 766 transport-layers protocols, any such use requires further 767 specification around how to multiplex multiple protocols on a given 768 transport-layer protocols, and how to associate received data with 769 the correct protocols. 771 9.2. STUN, DTLS, SRTP 773 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 774 protocol of a received packet among the STUN, Datagram Transport 775 Layer Security (DTLS) and SRTP protocols (in any combination). If an 776 offer or answer includes bundled "m=" lines that represent these 777 protocols, the offerer or answerer MUST support the mechanism 778 described in [RFC5764], and no explicit negotiation is required in 779 order to indicate support and usage of the mechanism. 781 [RFC5764] does not describe how to identify different protocols 782 transported on DTLS, only how to identify the DTLS protocol itself. 783 If multiple protocols are transported on DTLS, there MUST exist a 784 specification describing a mechanism for identifying each individual 785 protocol. In addition, if a received DTLS packet can be associated 786 with more than one "m=" line, there MUST exist a specification which 787 describes a mechanism for associating the received DTLS packet with 788 the correct "m=" line. 790 [Section 10.2] describes how to associate a received (S)RTP packet 791 with the correct "m=" line. 793 10. RTP Considerations 795 10.1. Single RTP Session 796 10.1.1. General 798 All RTP-based media within a single BUNDLE group belong to a single 799 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 800 sessions, one per BUNDLE group. 802 Since a single RTP session is used for each bundle group, all "m=" 803 lines representing RTP-based media in a bundle group will share a 804 single SSRC numbering space [RFC3550]. 806 The following rules and restrictions apply for a single RTP session: 808 o A specific payload type value can be used in multiple bundled "m=" 809 lines if each codec associated with the payload type number shares 810 an identical codec configuration [Section 10.1.2]. 812 o The proto value in each bundled RTP-based "m=" line MUST be 813 identical (e.g. RTP/AVPF). 815 o The RTP MID header extension MUST be enabled, by associating an 816 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 817 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 818 in every offer and answer. 820 o A given SSRC MUST NOT transmit RTP packets using payload types 821 that originate from different bundled "m=" lines. 823 NOTE: The last bullet above is to avoid sending multiple media types 824 from the same SSRC. If transmission of multiple media types are done 825 with time overlap, RTP and RTCP fail to function. Even if done in 826 proper sequence this causes RTP Timestamp rate switching issues 827 [RFC7160]. However, once an SSRC has left the RTP session (by 828 sending an RTCP BYE packet), that SSRC value can later be reused by 829 another source(possibly associated with a different bundled "m=" 830 line. 832 10.1.2. Payload Type (PT) Value Reuse 834 Multiple bundled "m=" lines might represent RTP based media. As all 835 RTP based media associated with a BUNDLE group belong to the same RTP 836 session, in order for a given payload type value to be used inside 837 more than one bundled "m=" line, all codecs associated with the 838 payload type number MUST share an identical codec configuration. 839 This means that the codecs MUST share the same media type, encoding 840 name, clock rate and any parameter that can affect the codec 841 configuration and packetization. 842 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 843 attribute values must be identical for all codecs that use the same 844 payload type value. 846 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 848 There are multiple mechanisms that can be used by an endpoint in 849 order to associate received RTP/RTCP packets with a bundled "m=" 850 line. Such mechanisms include using the payload type value carried 851 inside the RTP packets, the SSRC values carried inside the RTP 852 packets, and other "m=" line specific information carried inside the 853 RTP packets. 855 As all RTP/RTCP packets associated with a BUNDLE group are received 856 (and sent) using single address:port combinations, the local 857 address:port combination cannot be used to associate received RTP 858 packets with the correct "m=" line. 860 As described in [Section 10.1.2], the same payload type value might 861 be used inside RTP packets described by multiple "m=" lines. In such 862 cases, the payload type value cannot be used to associate received 863 RTP packets with the correct "m=" line. 865 An offerer and answerer can inform each other which SSRC values they 866 will use for RTP and RTCP by using the SDP 'ssrc' attribute 867 [RFC5576]. To allow for proper association with this mechanism, the 868 'ssrc' attribute needs to be associated with each "m=" line that 869 shares a payload type with any other "m=" line in the same bundle. 870 As the SSRC values will be carried inside the RTP/RTCP packets, the 871 offerer and answerer can then use that information to associate 872 received RTP packets with the correct "m=" line. However, an offerer 873 will not know which SSRC values the answerer will use until it has 874 received the answer providing that information. Due to this, before 875 the offerer has received the answer, the offerer will not be able to 876 associate received RTP/RTCP packets with the correct "m=" line using 877 the SSRC values. 879 In order for an offerer and answerer to always be able to associate 880 received RTP and RTCP packets with the correct "m=" line, an offerer 881 and answerer using the BUNDLE extension MUST support the mechanism 882 defined in Section 14, where the remote endpoint inserts the 883 identification-tag associated with an "m=" line in RTP and RTCP 884 packets associated with that "m=" line. 886 10.3. RTP/RTCP Multiplexing 887 10.3.1. General 889 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 890 multiplexing [RFC5761] for the RTP-based media associated with the 891 BUNDLE group. 893 When RTP/RTCP multiplexing is enabled, the same address:port 894 combination will be used for sending all RTP packets and the RTCP 895 packets associated with the BUNDLE group. Each endpoint will send 896 the packets towards the BUNDLE address of the other endpoint. The 897 same address:port combination MAY be used for receiving RTP packets 898 and RTCP packets. 900 10.3.2. SDP Offer/Answer Procedures 902 10.3.2.1. General 904 This section describes how an offerer and answerer use the SDP 'rtcp- 905 mux' attribute [RFC5761] to negotiate usage of RTP/RTCP multiplexing 906 for RTP-based media associated with a BUNDLE group. 908 The procedures in this section only apply to RTP-based "m=" lines. 910 10.3.2.2. Generating the Initial SDP Offer 912 When an offerer generates an initial offer, the offerer MUST 913 associate an SDP 'rtcp-mux' attribute [RFC5761] with each bundled 914 RTP-based "m=" line (including any bundle-only "m=" line) in the 915 offer. 917 If an offerer wants to indicate exclusive support of RTP/RTCP 918 multiplexing [I-D.ietf-mmusic-mux-exclusive] for one or more "m=" 919 lines within the BUNDLE group, the offerer MUST associate an SDP 920 'rtcp-mux-exclusive' attribute with those "m=" lines. 922 NOTE: The offerer might also associate an SDP 'rtcp' attribute 923 [RFC3605] with a bundled "m=" line, excluding a bundle-only "m=" 924 line, in order to provide a fallback port for RTCP. However, the 925 fallback port will only be used in case the answerer does not include 926 the "m=" line in the BUNDLE group in the associated answer. 928 In the initial offer, the address:port combination for RTCP MUST be 929 unique in each bundled RTP-based "m=" line (excluding a 'bundle-only' 930 "m=" line), similar to RTP. 932 10.3.2.3. Generating the SDP Answer 934 When an answerer generates an answer, if the answerer accepts an RTP- 935 based "m=" line within a BUNDLE group, the answerer MUST enable usage 936 of RTP/RTCP multiplexing. The answerer MUST associate an SDP "rtcp- 937 mux" attribute with the "m=" line in the answer. In addition, if the 938 "m=" line in the associated offer contained an SDP "rtcp-mux- 939 exclusive" attribute, the answerer MUST associate an SDP "rtcp-mux- 940 exclusive" attribute with the "m=" line in the answer. 942 If an RTP-based "m=" line in the associated offer did not contain an 943 SDP "rtcp-mux" attribute, the answerer MUST NOT accept the "m=" line 944 within a BUNDLE group in the answer. 946 If an RTP-based "m=" line in the associated offer contained an SDP 947 "rtcp-mux-exclusive" attribute, and if the answerer moves the "m=" 948 line out of the BUNDLE group in the answer Section 8.3.4, the 949 answerer MUST still either enable RTP/RTCP multiplexing, or reject 950 the "m=" line Section 8.3.5. 952 When the answerer accepts the usage of RTP/RTCP multiplexing within 953 the BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with 954 each bundled RTP-based "m=" line in the answer. In addition, if the 955 "m=" line in the associated offer contained an SDP 'rtcp-mux- 956 exclusive' attribute, the answerer MUST associated an SDP 'rtcp-mux- 957 exclusive' attribute with the corresponding "m=" line in the answer, 958 as described in. 960 The answerer MUST NOT associate an SDP 'rtcp' attribute with any 961 bundled "m=" line in the answer. The answerer will use the port 962 value of the selected offerer BUNDLE address for sending RTP and RTCP 963 packets associated with each RTP-based bundled "m=" line towards the 964 offerer. 966 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 967 negotiated in a previous offer/answer transaction, the answerer MUST 968 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 969 "m=" line in the answer. 971 10.3.2.4. Offerer Processing of the SDP Answer 973 When an offerer receives an answer, if the answerer has accepted the 974 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 975 follows the procedures for RTP/RTCP multiplexing defined in 976 [RFC5761]. The offerer will use the port value associated with the 977 answerer BUNDLE address for sending RTP and RTCP packets associated 978 with each RTP-based bundled "m=" line towards the answerer. 980 NOTE: It is considered a protocol error if the answerer has not 981 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 982 that the answerer included in the BUNDLE group. 984 10.3.2.5. Modifying the Session 986 When an offerer generates a subsequent offer, it MUST associate an 987 SDP 'rtcp-mux' attribute with each RTP-based bundled "m=" line 988 (including any bundled "m=" line that the offerer wants to add to the 989 BUNDLE group), unless the offerer wants to disable or remove the "m=" 990 line from the BUNDLE group. 992 11. ICE Considerations 994 11.1. General 996 This section describes how to use the BUNDLE grouping extension 997 together with the Interactive Connectivity Establishment (ICE) 998 mechanism [I-D.ietf-ice-rfc5245bis]. 1000 The generic procedures for negotiating usage of ICE using SDP, 1001 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1002 with BUNDLE, with the following exceptions: 1004 o When BUNDLE addresses for a BUNDLE group have been selected for 1005 both endpoints, ICE connectivity checks and keep-alives only need 1006 to be performed for the whole BUNDLE group, instead of per bundled 1007 "m=" line. 1009 o Among bundled "m=" lines with which the offerer has associated a 1010 shared address, the offerer only associates ICE-related media- 1011 level SDP attributes with the "m=" line associated with the 1012 offerer BUNDLE-tag. 1014 o Among bundled "m=" lines with which the answerer has associated a 1015 shared address, the answerer only associates ICE-related media- 1016 level SDP attributes with the "m=" line associated with the 1017 answerer BUNDLE-tag. 1019 Support and usage of ICE mechanism together with the BUNDLE extension 1020 is OPTIONAL. 1022 11.2. SDP Offer/Answer Procedures 1023 11.2.1. General 1025 When an offerer associates a unique address with a bundled "m=" line 1026 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1027 'candidate' attributes (and other applicable ICE-related media-level 1028 SDP attributes), containing unique ICE properties (candidates etc), 1029 with the "m=" line, according to the procedures in 1030 [I-D.ietf-mmusic-ice-sip-sdp]. 1032 When an offerer associates a shared address with a bundled "m=" line, 1033 if the "m=" line is associated with the offerer BUNDLE-tag, the 1034 offerer MUST associate SDP 'candidate' attributes (and other 1035 applicable ICE-related media-level SDP attributes), containing shared 1036 ICE properties, with the "m=" line. If the "m=" line is not 1037 associated with the offerer BUNDLE-tag, the offerer MUST NOT 1038 associate ICE-related SDP attributes with the "m=" line. 1040 When an answerer associates a shared address with a bundled "m=" 1041 line, if the "m=" line is associated with the answerer BUNDLE-tag, 1042 the answerer MUST associate SDP 'candidate' attributes (and other 1043 applicable ICE-related media-level SDP attributes), containing shared 1044 ICE properties, with the "m=" line. If the "m=" line is not 1045 associated with the answerer BUNDLE-tag, the answerer MUST NOT 1046 associate ICE-related SDP attributes with the "m=" line. 1048 NOTE: As bundled "m=" lines associated with a shared address will 1049 share the same ICE properties, there is no need to associated ICE- 1050 related media-level SDP attributes with each "m=" line. 1052 NOTE: The following ICE-related media-level SDP attributes are 1053 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1054 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1055 pacing'. 1057 11.2.2. Generating the Initial SDP Offer 1059 When an offerer generates an initial offer, the offerer MUST 1060 associate ICE-related media-level SDP attributes with each bundled 1061 "m=" line, according to [Section 11.2.1]. 1063 11.2.3. Generating the SDP Answer 1065 When an answerer generates an answer that contains a BUNDLE group, 1066 the answerer MUST associated ICE-related SDP attributes with the "m=" 1067 line associated with the answerer BUNDLE-tag, according to 1068 [Section 11.2.1]. 1070 11.2.4. Offerer Processing of the SDP Answer 1072 When an offerer receives an answer, if the answerer supports and uses 1073 the ICE mechanism and the BUNDLE extension, the offerer MUST 1074 associate the ICE properties associated with the offerer BUNDLE 1075 address, selected by the answerer [Section 8.3.2], with each bundled 1076 "m=" line. 1078 11.2.5. Modifying the Session 1080 When an offerer generates a subsequent offer, it MUST associated 1081 unique or shared ICE properties to one or more bundled "m=" lines, 1082 according to [Section 11.2.1]. 1084 12. DTLS Considerations 1086 One or more media streams within a BUNDLE group might use the 1087 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1088 to encrypt the data, or to negotiate encryption keys if another 1089 encryption mechanism is used to encrypt media. 1091 When DTLS is used within a BUNDLE group, the following rules apply: 1093 o There can only be one DTLS association [RFC6347] associated with 1094 the BUNDLE group; and 1096 o Each usage of the DTLS association within the BUNDLE group MUST 1097 use the same mechanism for determining which endpoints (the 1098 offerer or answerer) becomes DTLS client and DTLS server; and 1100 o Each usage of the DTLS association within the Bundle group MUST 1101 use the same mechanism for determining whether an offer or answer 1102 will trigger the establishment of a new DTLS association, or 1103 whether an existing DTLS association will be used; and 1105 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1106 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1107 [RFC5764], The client MUST include the extension even if the usage 1108 of DTLS-SRTP is not negotiated as part of the multimedia session 1109 (e.g. SIP session [RFC3261]. 1111 NOTE: The inclusion of the 'use_srtp' extension during the initial 1112 DTLS handshake ensures that a DTLS renegotiation will not be required 1113 in order to include the extension, in case DTLS-SRTP encrypted media 1114 is added to the BUNDLE group later during the multimedia session. 1116 13. Update to RFC 3264 1118 13.1. General 1120 This section replaces the text of the following sections of RFC 3264: 1122 o Section 5.1 (Unicast Streams). 1124 o Section 8.2 (Removing a Media Stream). 1126 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1128 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1130 For recvonly and sendrecv streams, the port number and address in the 1131 offer indicate where the offerer would like to receive the media 1132 stream. For sendonly RTP streams, the address and port number 1133 indirectly indicate where the offerer wants to receive RTCP reports. 1134 Unless there is an explicit indication otherwise, reports are sent to 1135 the port number one higher than the number indicated. The IP address 1136 and port present in the offer indicate nothing about the source IP 1137 address and source port of RTP and RTCP packets that will be sent by 1138 the offerer. A port number of zero in the offer indicates that the 1139 stream is offered but MUST NOT be used. This has no useful semantics 1140 in an initial offer, but is allowed for reasons of completeness, 1141 since the answer can contain a zero port indicating a rejected stream 1142 (Section 6). Furthermore, existing streams can be terminated by 1143 setting the port to zero (Section 8). In general, a port number of 1144 zero indicates that the media stream is not wanted. 1146 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1148 For recvonly and sendrecv streams, the port number and address in the 1149 offer indicate where the offerer would like to receive the media 1150 stream. For sendonly RTP streams, the address and port number 1151 indirectly indicate where the offerer wants to receive RTCP reports. 1152 Unless there is an explicit indication otherwise, reports are sent to 1153 the port number one higher than the number indicated. The IP address 1154 and port present in the offer indicate nothing about the source IP 1155 address and source port of RTP and RTCP packets that will be sent by 1156 the offerer. A port number of zero in the offer by default indicates 1157 that the stream is offered but MUST NOT be used, but an extension 1158 mechanism might specify different semantics for the usage of a zero 1159 port value. Furthermore, existing streams can be terminated by 1160 setting the port to zero (Section 8). In general, a port number of 1161 zero by default indicates that the media stream is not wanted. 1163 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1165 A stream that is offered with a port of zero MUST be marked with port 1166 zero in the answer. Like the offer, the answer MAY omit all 1167 attributes present previously, and MAY list just a single media 1168 format from amongst those in the offer. 1170 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1172 A stream that is offered with a port of zero MUST by default be 1173 marked with port zero in the answer, unless an extension mechanism, 1174 which specifies semantics for the usage of a non-zero port value, is 1175 used. If the stream is marked with port zero in the answer, the 1176 answer MAY omit all attributes present previously, and MAY list just 1177 a single media format from amongst those in the offer." 1179 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1181 RFC 2543 [10] specified that placing a user on hold was accomplished 1182 by setting the connection address to 0.0.0.0. Its usage for putting 1183 a call on hold is no longer recommended, since it doesn't allow for 1184 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1185 with connection oriented media. However, it can be useful in an 1186 initial offer when the offerer knows it wants to use a particular set 1187 of media streams and formats, but doesn't know the addresses and 1188 ports at the time of the offer. Of course, when used, the port 1189 number MUST NOT be zero, which would specify that the stream has been 1190 disabled. An agent MUST be capable of receiving SDP with a 1191 connection address of 0.0.0.0, in which case it means that neither 1192 RTP nor RTCP should be sent to the peer. 1194 13.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1196 RFC 2543 [10] specified that placing a user on hold was accomplished 1197 by setting the connection address to 0.0.0.0. Its usage for putting 1198 a call on hold is no longer recommended, since it doesn't allow for 1199 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1200 with connection oriented media. However, it can be useful in an 1201 initial offer when the offerer knows it wants to use a particular set 1202 of media streams and formats, but doesn't know the addresses and 1203 ports at the time of the offer. Of course, when used, the port 1204 number MUST NOT be zero, if it would specify that the stream has been 1205 disabled. However, an extension mechanism might specify different 1206 semantics of the zero port number usage. An agent MUST be capable of 1207 receiving SDP with a connection address of 0.0.0.0, in which case it 1208 means that neither RTP nor RTCP should be sent to the peer. 1210 14. RTP/RTCP extensions for identification-tag transport 1212 14.1. General 1214 SDP Offerers and Answerers [RFC3264] can associate identification- 1215 tags with "m=" lines within SDP Offers and Answers, using the 1216 procedures in [RFC5888]. Each identification-tag uniquely represents 1217 an "m=" line. 1219 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1220 used to carry identification-tags within RTCP SDES packets. This 1221 section also defines a new RTP header extension [RFC5285], which is 1222 used to carry identification-tags in RTP packets. 1224 The SDES item and RTP header extension make it possible for a 1225 receiver to associate received RTCP- and RTP packets with a specific 1226 "m=" line, with which the receiver has associated an identification- 1227 tag, even if those "m=" lines are part of the same RTP session. A 1228 media recipient informs the media sender about the identification-tag 1229 associated with an "m=" line through the use of an 'mid' attribute 1230 [RFC5888]. The media sender then inserts the identification-tag in 1231 RTCP and RTP packets sent to the media recipient. 1233 NOTE: This text above defines how identification-tags are carried in 1234 SDP Offers and Answers. The usage of other signalling protocols for 1235 carrying identification-tags is not prevented, but the usage of such 1236 protocols is outside the scope of this document. 1238 [RFC3550] defines general procedures regarding the RTCP transmission 1239 interval. The RTCP MID SDES item SHOULD be sent in the first few 1240 RTCP packets sent on joining the session, and SHOULD be sent 1241 regularly thereafter. The exact number of RTCP packets in which this 1242 SDES item is sent is intentionally not specified here, as it will 1243 depend on the expected packet loss rate, the RTCP reporting interval, 1244 and the allowable overhead. 1246 The RTP MID header extension SHOULD be included in some RTP packets 1247 at the start of the session and whenever the SSRC changes. It might 1248 also be useful to include the header extension in RTP packets that 1249 comprise random access points in the media (e.g., with video 1250 I-frames). The exact number of RTP packets in which this header 1251 extension is sent is intentionally not specified here, as it will 1252 depend on expected packet loss rate and loss patterns, the overhead 1253 the application can tolerate, and the importance of immediate receipt 1254 of the identification-tag. 1256 For robustness purpose, endpoints need to be prepared for situations 1257 where the reception of the identification-tag is delayed, and SHOULD 1258 NOT terminate sessions in such cases, as the identification-tag is 1259 likely to arrive soon. 1261 14.2. RTCP MID SDES Item 1263 0 1 2 3 1264 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 1265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1266 | MID=TBD | length | identification-tag ... 1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1269 The identification-tag payload is UTF-8 encoded, as in SDP. 1271 The identification-tag is not zero terminated. 1273 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1274 identifier value.] 1276 14.3. RTP MID Header Extension 1278 The payload, containing the identification-tag, of the RTP MID header 1279 extension element can be encoded using either the one-byte or two- 1280 byte header [RFC5285]. The identification-tag payload is UTF-8 1281 encoded, as in SDP. 1283 The identification-tag is not zero terminated. Note, that set of 1284 header extensions included in the packet needs to be padded to the 1285 next 32-bit boundary using zero bytes [RFC5285]. 1287 As the identification-tag is included in either an RTCP SDES item or 1288 an RTP header extension, or both, there should be some consideration 1289 about the packet expansion caused by the identification-tag. To 1290 avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the 1291 header extension's size needs to be taken into account when encoding 1292 the media. 1294 It is recommended that the identification-tag is kept short. Due to 1295 the properties of the RTP header extension mechanism, when using the 1296 one-byte header, a tag that is 1-3 bytes will result in that a 1297 minimal number of 32-bit words are used for the RTP header extension, 1298 in case no other header extensions are included at the same time. 1299 Note, do take into account that some single characters when UTF-8 1300 encoded will result in multiple octets. 1302 15. IANA Considerations 1304 15.1. New SDES item 1306 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1307 document.] 1309 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1310 identifier value.] 1312 This document adds the MID SDES item to the IANA "RTCP SDES item 1313 types" registry as follows: 1315 Value: TBD 1316 Abbrev.: MID 1317 Name: Media Identification 1318 Reference: RFCXXXX 1320 15.2. New RTP Header Extension URI 1322 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1323 document.] 1325 This document defines a new extension URI in the RTP Compact Header 1326 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1327 Parameters registry, according to the following data: 1329 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1330 Description: Media identification 1331 Contact: christer.holmberg@ericsson.com 1332 Reference: RFCXXXX 1334 15.3. New SDP Attribute 1336 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1337 document.] 1339 This document defines a new SDP media-level attribute, 'bundle-only', 1340 according to the following data: 1342 Attribute name: bundle-only 1343 Type of attribute: media 1344 Subject to charset: No 1345 Purpose: Request a media description to be accepted 1346 in the answer only if kept within a BUNDLE 1347 group by the answerer. 1348 Appropriate values: N/A 1349 Contact name: Christer Holmberg 1350 Contact e-mail: christer.holmberg@ericsson.com 1351 Reference: RFCXXXX 1353 15.4. New SDP Group Semantics 1355 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1356 document.] 1358 This document registers the following semantics with IANA in the 1359 "Semantics for the "group" SDP Attribute" subregistry (under the 1360 "Session Description Protocol (SDP) Parameters" registry: 1362 Semantics Token Reference 1363 ------------------------------------- ------ --------- 1364 Media bundling BUNDLE [RFCXXXX] 1366 16. Security Considerations 1368 The security considerations defined in [RFC3264] and [RFC5888] apply 1369 to the BUNDLE extension. Bundle does not change which information 1370 flows over the network but only changes which addresses and ports 1371 that information is flowing on and thus has very little impact on the 1372 security of the RTP sessions. 1374 When the BUNDLE extension is used, a single set of security 1375 credentials might be used for all media streams associated with a 1376 BUNDLE group. 1378 When the BUNDLE extension is used, the number of SSRC values within a 1379 single RTP session increases, which increases the risk of SSRC 1380 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1381 and SRTCP encryption in certain situations. 1383 17. Examples 1385 17.1. Example: Bundle Address Selection 1387 The example below shows: 1389 o An offer, in which the offerer associates a unique address with 1390 each bundled "m=" line within the BUNDLE group. 1392 o An answer, in which the answerer selects the offerer BUNDLE 1393 address, and in which selects its own BUNDLE address (the answerer 1394 BUNDLE address) and associates it with each bundled "m=" line 1395 within the BUNDLE group. 1397 SDP Offer (1) 1399 v=0 1400 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1401 s= 1402 c=IN IP4 atlanta.example.com 1403 t=0 0 1404 a=group:BUNDLE foo bar 1405 m=audio 10000 RTP/AVP 0 8 97 1406 b=AS:200 1407 a=mid:foo 1408 a=rtpmap:0 PCMU/8000 1409 a=rtpmap:8 PCMA/8000 1410 a=rtpmap:97 iLBC/8000 1411 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1412 m=video 10002 RTP/AVP 31 32 1413 b=AS:1000 1414 a=mid:bar 1415 a=rtpmap:31 H261/90000 1416 a=rtpmap:32 MPV/90000 1417 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1419 SDP Answer (2) 1421 v=0 1422 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1423 s= 1424 c=IN IP4 biloxi.example.com 1425 t=0 0 1426 a=group:BUNDLE foo bar 1427 m=audio 20000 RTP/AVP 0 1428 b=AS:200 1429 a=mid:foo 1430 a=rtpmap:0 PCMU/8000 1431 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1432 m=video 20000 RTP/AVP 32 1433 b=AS:1000 1434 a=mid:bar 1435 a=rtpmap:32 MPV/90000 1436 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1438 17.2. Example: BUNDLE Extension Rejected 1440 The example below shows: 1442 o An offer, in which the offerer associates a unique address with 1443 each bundled "m=" line within the BUNDLE group. 1445 o An answer, in which the answerer rejects the offered BUNDLE group, 1446 and associates a unique address with each "m=" line (following 1447 normal RFC 3264 procedures). 1449 SDP Offer (1) 1451 v=0 1452 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1453 s= 1454 c=IN IP4 atlanta.example.com 1455 t=0 0 1456 a=group:BUNDLE foo bar 1457 m=audio 10000 RTP/AVP 0 8 97 1458 b=AS:200 1459 a=mid:foo 1460 a=rtpmap:0 PCMU/8000 1461 a=rtpmap:8 PCMA/8000 1462 a=rtpmap:97 iLBC/8000 1463 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1464 m=video 10002 RTP/AVP 31 32 1465 b=AS:1000 1466 a=mid:bar 1467 a=rtpmap:31 H261/90000 1468 a=rtpmap:32 MPV/90000 1469 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1471 SDP Answer (2) 1473 v=0 1474 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1475 s= 1476 c=IN IP4 biloxi.example.com 1477 t=0 0 1478 m=audio 20000 RTP/AVP 0 1479 b=AS:200 1480 a=rtpmap:0 PCMU/8000 1481 m=video 30000 RTP/AVP 32 1482 b=AS:1000 1483 a=rtpmap:32 MPV/90000 1485 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1487 The example below shows: 1489 o A subsequent offer (the BUNDLE group has been created as part of a 1490 previous offer/answer transaction), in which the offerer adds a 1491 new "m=" line, represented by the "zen" identification-tag, to a 1492 previously negotiated BUNDLE group, associates a unique address 1493 with the added "m=" line, and associates the previously selected 1494 offerer BUNDLE address with each of the other bundled "m=" lines 1495 within the BUNDLE group. 1497 o An answer, in which the answerer associates the answerer BUNDLE 1498 address with each bundled "m=" line (including the newly added 1499 "m=" line) within the BUNDLE group. 1501 SDP Offer (1) 1503 v=0 1504 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1505 s= 1506 c=IN IP4 atlanta.example.com 1507 t=0 0 1508 a=group:BUNDLE foo bar zen 1509 m=audio 10000 RTP/AVP 0 8 97 1510 b=AS:200 1511 a=mid:foo 1512 a=rtpmap:0 PCMU/8000 1513 a=rtpmap:8 PCMA/8000 1514 a=rtpmap:97 iLBC/8000 1515 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1516 m=video 10000 RTP/AVP 31 32 1517 b=AS:1000 1518 a=mid:bar 1519 a=rtpmap:31 H261/90000 1520 a=rtpmap:32 MPV/90000 1521 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1522 m=video 20000 RTP/AVP 66 1523 b=AS:1000 1524 a=mid:zen 1525 a=rtpmap:66 H261/90000 1526 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1528 SDP Answer (2) 1530 v=0 1531 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1532 s= 1533 c=IN IP4 biloxi.example.com 1534 t=0 0 1535 a=group:BUNDLE foo bar zen 1536 m=audio 20000 RTP/AVP 0 1537 b=AS:200 1538 a=mid:foo 1539 a=rtpmap:0 PCMU/8000 1540 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1541 m=video 20000 RTP/AVP 32 1542 b=AS:1000 1543 a=mid:bar 1544 a=rtpmap:32 MPV/90000 1545 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1546 m=video 20000 RTP/AVP 66 1547 b=AS:1000 1548 a=mid:zen 1549 a=rtpmap:66 H261/90000 1550 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1552 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1554 The example below shows: 1556 o A subsequent offer (the BUNDLE group has been created as part of a 1557 previous offer/answer transaction), in which the offerer moves a 1558 bundled "m=" line out of a BUNDLE group, associates a unique 1559 address with the moved "m=" line, and associates the offerer 1560 BUNDLE address with each other bundled "m=" line within the BUNDLE 1561 group. 1563 o An answer, in which the answerer moves the "m=" line out of the 1564 BUNDLE group, associates unique address with the moved "m=" line, 1565 and associates the answerer BUNDLE address with each of the 1566 remaining bundled "m=" line within the BUNDLE group. 1568 SDP Offer (1) 1570 v=0 1571 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1572 s= 1573 c=IN IP4 atlanta.example.com 1574 t=0 0 1575 a=group:BUNDLE foo bar 1576 m=audio 10000 RTP/AVP 0 8 97 1577 b=AS:200 1578 a=mid:foo 1579 a=rtpmap:0 PCMU/8000 1580 a=rtpmap:8 PCMA/8000 1581 a=rtpmap:97 iLBC/8000 1582 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1583 m=video 10000 RTP/AVP 31 32 1584 b=AS:1000 1585 a=mid:bar 1586 a=rtpmap:31 H261/90000 1587 a=rtpmap:32 MPV/90000 1588 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1589 m=video 50000 RTP/AVP 66 1590 b=AS:1000 1591 a=mid:zen 1592 a=rtpmap:66 H261/90000 1594 SDP Answer (2) 1596 v=0 1597 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1598 s= 1599 c=IN IP4 biloxi.example.com 1600 t=0 0 1601 a=group:BUNDLE foo bar 1602 m=audio 20000 RTP/AVP 0 1603 b=AS:200 1604 a=mid:foo 1605 a=rtpmap:0 PCMU/8000 1606 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1607 m=video 20000 RTP/AVP 32 1608 b=AS:1000 1609 a=mid:bar 1610 a=rtpmap:32 MPV/90000 1611 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1612 m=video 60000 RTP/AVP 66 1613 b=AS:1000 1614 a=mid:zen 1615 a=rtpmap:66 H261/90000 1617 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1618 Group 1620 The example below shows: 1622 o A subsequent offer (the BUNDLE group has been created as part of a 1623 previous offer/answer transaction), in which the offerer disables 1624 a bundled "m=" line within BUNDLE group, assigns a zero port 1625 number to the disabled "m=" line, and associates the offerer 1626 BUNDLE address with each of the other bundled "m=" lines within 1627 the BUNDLE group. 1629 o An answer, in which the answerer moves the disabled "m=" line out 1630 of the BUNDLE group, assigns a zero port value to the disabled 1631 "m=" line, and associates the answerer BUNDLE address with each of 1632 the remaining bundled "m=" line within the BUNDLE group. 1634 SDP Offer (1) 1636 v=0 1637 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1638 s= 1639 c=IN IP4 atlanta.example.com 1640 t=0 0 1641 a=group:BUNDLE foo bar 1642 m=audio 10000 RTP/AVP 0 8 97 1643 b=AS:200 1644 a=mid:foo 1645 a=rtpmap:0 PCMU/8000 1646 a=rtpmap:8 PCMA/8000 1647 a=rtpmap:97 iLBC/8000 1648 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1649 m=video 10000 RTP/AVP 31 32 1650 b=AS:1000 1651 a=mid:bar 1652 a=rtpmap:31 H261/90000 1653 a=rtpmap:32 MPV/90000 1654 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1655 m=video 0 RTP/AVP 66 1656 a=mid:zen 1657 a=rtpmap:66 H261/90000 1659 SDP Answer (2) 1661 v=0 1662 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1663 s= 1664 c=IN IP4 biloxi.example.com 1665 t=0 0 1666 a=group:BUNDLE foo bar 1667 m=audio 20000 RTP/AVP 0 1668 b=AS:200 1669 a=mid:foo 1670 a=rtpmap:0 PCMU/8000 1671 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1672 m=video 20000 RTP/AVP 32 1673 b=AS:1000 1674 a=mid:bar 1675 a=rtpmap:32 MPV/90000 1676 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1677 m=video 0 RTP/AVP 66 1678 a=mid:zen 1679 a=rtpmap:66 H261/90000 1681 18. Acknowledgements 1683 The usage of the SDP grouping extension for negotiating bundled media 1684 is based on a similar alternatives proposed by Harald Alvestrand and 1685 Cullen Jennings. The BUNDLE extension described in this document is 1686 based on the different alternative proposals, and text (e.g. SDP 1687 examples) have been borrowed (and, in some cases, modified) from 1688 those alternative proposals. 1690 The SDP examples are also modified versions from the ones in the 1691 Alvestrand proposal. 1693 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1694 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 1695 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1696 Justin Uberti for reading the text, and providing useful feedback. 1698 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1699 providing help and text on the RTP/RTCP procedures. 1701 Thanks to Spotify for providing music for the countless hours of 1702 document editing. 1704 19. Change Log 1706 [RFC EDITOR NOTE: Please remove this section when publishing] 1708 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 1710 o - ICE considerations modified: ICE-related SDP attributes only 1711 added to the bundled m- line representing the selected BUNDLE 1712 address. 1714 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 1716 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 1717 rfc5245bis. 1719 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 1720 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 1721 considerations. 1723 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 1725 o - Reference and procedures associated with exclusive RTP/RTCP mux 1726 added 1728 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 1730 o - RTCP-MUX mandatory for bundled RTP m- lines 1732 o - Editorial fixes based on comments from Flemming Andreasen 1734 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 1736 o - Correction of Ari's family name 1738 o - Editorial fixes based on comments from Thomas Stach 1740 o - RTP/RTCP correction based on comment from Magnus Westerlund 1742 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1743 msg14861.html 1745 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 1747 o - Correct based on comment from Paul Kyzivat 1749 o -- 'received packets' replaced with 'received data' 1751 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1753 o - Clarification based on comment from James Guballa 1755 o - Clarification based on comment from Flemming Andreasen 1757 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1759 o - DTLS Considerations section added. 1761 o - BUNDLE semantics added to the IANA Considerations 1763 o - Changes based on WGLC comments from Adam Roach 1765 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1766 msg14673.html 1768 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1770 o - Changes based on agreements at IETF#92 1772 o -- BAS Offer removed, based on agreement at IETF#92. 1774 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1775 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1777 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1779 o - Editorial changes based on comments from Magnus Westerlund. 1781 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1783 o - Modification of RTP/RTCP multiplexing section, based on comments 1784 from Magnus Westerlund. 1786 o - Reference updates. 1788 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1790 o - Editorial fix. 1792 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1794 o - Editorial changes. 1796 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1798 o Changes to allow a new suggested offerer BUNDLE address to be 1799 assigned to each bundled m- line. 1801 o Changes based on WGLC comments from Paul Kyzivat 1803 o - Editorial fixes 1805 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1807 o Usage of SDP 'extmap' attribute added 1809 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1810 port value 1812 o Changes based on WGLC comments from Thomas Stach 1814 o - ICE candidates not assigned to bundle-only m- lines with a zero 1815 port value 1817 o - Editorial changes 1819 o Changes based on WGLC comments from Colin Perkins 1821 o - Editorial changes: 1823 o -- "RTP SDES item" -> "RTCP SDES item" 1825 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1827 o - Changes in section 10.1.1: 1829 o -- "SHOULD NOT" -> "MUST NOT" 1831 o -- Additional text added to the Note 1833 o - Change to section 13.2: 1835 o -- Clarify that mid value is not zero terminated 1837 o - Change to section 13.3: 1839 o -- Clarify that mid value is not zero terminated 1841 o -- Clarify padding 1843 o Changes based on WGLC comments from Paul Kyzivat 1845 o - Editorial changes: 1847 o Changes based on WGLC comments from Jonathan Lennox 1849 o - Editorial changes: 1851 o - Defintion of SDP bundle-only attribute alligned with structure 1852 in 4566bis draft 1854 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1856 o Editorial corrections based on comments from Harald Alvestrand. 1858 o Editorial corrections based on comments from Cullen Jennings. 1860 o Reference update (RFC 7160). 1862 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1863 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1864 msg13765.html). 1866 o Additional text added to the Security Considerations. 1868 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1870 o SDP bundle-only attribute added to IANA Considerations. 1872 o SDES item and RTP header extension added to Abstract and 1873 Introduction. 1875 o Modification to text updating section 8.2 of RFC 3264. 1877 o Reference corrections. 1879 o Editorial corrections. 1881 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1883 o Terminology change: "bundle-only attribute assigned to m= line" to 1884 "bundle-only attribute associated with m= line". 1886 o Editorial corrections. 1888 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1890 o Editorial corrections. 1892 o - "of"->"if" (8.3.2.5). 1894 o - "optional"->"OPTIONAL" (9.1). 1896 o - Syntax/ABNF for 'bundle-only' attribute added. 1898 o - SDP Offer/Answer sections merged. 1900 o - 'Request new offerer BUNDLE address' section added 1902 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1904 o OPEN ISSUE regarding Receiver-ID closed. 1906 o - RTP MID SDES Item. 1908 o - RTP MID Header Extension. 1910 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1911 closed. 1913 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1914 include an 'rtcp' attribute in the answer, based on the procedures 1915 in section 5.1.3 of RFC 5761. 1917 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1919 o Draft title changed. 1921 o Added "SDP" to section names containing "Offer" or "Answer". 1923 o Editorial fixes based on comments from Paul Kyzivat 1924 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1925 msg13314.html). 1927 o Editorial fixed based on comments from Colin Perkins 1928 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1929 msg13318.html). 1931 o - Removed text about extending BUNDLE to allow multiple RTP 1932 sessions within a BUNDLE group. 1934 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1936 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1937 3264 structure. 1939 o Additional definitions added. 1941 o - Shared address. 1943 o - Bundled "m=" line. 1945 o - Bundle-only "m=" line. 1947 o - Offerer suggested BUNDLE mid. 1949 o - Answerer selected BUNDLE mid. 1951 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1952 to multiple "m=" lines until it has received an SDP Answer 1953 indicating support of the BUNDLE extension. 1955 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1956 Answerer supports the BUNDLE extension, assign a zero port value 1957 to a 'bundle-only' "m=" line. 1959 o SDP 'bundle-only' attribute section added. 1961 o Connection data nettype/addrtype restrictions added. 1963 o RFC 3264 update section added. 1965 o Indicating that a specific payload type value can be used in 1966 multiple "m=" lines, if the value represents the same codec 1967 configuration in each "m=" line. 1969 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1971 o Updated Offerer procedures (http://www.ietf.org/mail- 1972 archive/web/mmusic/current/msg12293.html). 1974 o Updated Answerer procedures (http://www.ietf.org/mail- 1975 archive/web/mmusic/current/msg12333.html). 1977 o Usage of SDP 'bundle-only' attribute added. 1979 o Reference to Trickle ICE document added. 1981 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1983 o Mechanism modified, to be based on usage of SDP Offers with both 1984 different and identical port number values, depending on whether 1985 it is known if the remote endpoint supports the extension. 1987 o Cullen Jennings added as co-author. 1989 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1991 o No changes. New version due to expiration. 1993 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1995 o No changes. New version due to expiration. 1997 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1999 o Draft name changed. 2001 o Harald Alvestrand added as co-author. 2003 o "Multiplex" terminology changed to "bundle". 2005 o Added text about single versus multiple RTP Sessions. 2007 o Added reference to RFC 3550. 2009 20. References 2011 20.1. Normative References 2013 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2014 Requirement Levels", BCP 14, RFC 2119, 2015 DOI 10.17487/RFC2119, March 1997, 2016 . 2018 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2019 with Session Description Protocol (SDP)", RFC 3264, 2020 DOI 10.17487/RFC3264, June 2002, 2021 . 2023 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2024 Jacobson, "RTP: A Transport Protocol for Real-Time 2025 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2026 July 2003, . 2028 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2029 in Session Description Protocol (SDP)", RFC 3605, 2030 DOI 10.17487/RFC3605, October 2003, 2031 . 2033 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2034 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2035 July 2006, . 2037 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2038 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2039 . 2041 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2042 (ICE): A Protocol for Network Address Translator (NAT) 2043 Traversal for Offer/Answer Protocols", RFC 5245, 2044 DOI 10.17487/RFC5245, April 2010, 2045 . 2047 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2048 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2049 2008, . 2051 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2052 Control Packets on a Single Port", RFC 5761, 2053 DOI 10.17487/RFC5761, April 2010, 2054 . 2056 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2057 Security (DTLS) Extension to Establish Keys for the Secure 2058 Real-time Transport Protocol (SRTP)", RFC 5764, 2059 DOI 10.17487/RFC5764, May 2010, 2060 . 2062 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2063 Protocol (SDP) Grouping Framework", RFC 5888, 2064 DOI 10.17487/RFC5888, June 2010, 2065 . 2067 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2068 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2069 January 2012, . 2071 [I-D.ietf-ice-rfc5245bis] 2072 Keranen, A. and J. Rosenberg, "Interactive Connectivity 2073 Establishment (ICE): A Protocol for Network Address 2074 Translator (NAT) Traversal", draft-ietf-ice-rfc5245bis-01 2075 (work in progress), December 2015. 2077 [I-D.ietf-mmusic-sdp-mux-attributes] 2078 Nandakumar, S., "A Framework for SDP Attributes when 2079 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-12 2080 (work in progress), January 2016. 2082 [I-D.ietf-mmusic-mux-exclusive] 2083 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2084 Multiplexing using SDP", draft-ietf-mmusic-mux- 2085 exclusive-03 (work in progress), February 2016. 2087 [I-D.ietf-mmusic-ice-sip-sdp] 2088 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, "Using 2089 Interactive Connectivity Establishment (ICE) with Session 2090 Description Protocol (SDP) offer/answer and Session 2091 Initiation Protocol (SIP)", draft-ietf-mmusic-ice-sip- 2092 sdp-07 (work in progress), October 2015. 2094 20.2. Informative References 2096 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2097 A., Peterson, J., Sparks, R., Handley, M., and E. 2098 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2099 DOI 10.17487/RFC3261, June 2002, 2100 . 2102 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2103 Description Protocol (SDP) Security Descriptions for Media 2104 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2105 . 2107 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2108 Media Attributes in the Session Description Protocol 2109 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2110 . 2112 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2113 Clock Rates in an RTP Session", RFC 7160, 2114 DOI 10.17487/RFC7160, April 2014, 2115 . 2117 [I-D.ietf-mmusic-trickle-ice] 2118 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2119 Incremental Provisioning of Candidates for the Interactive 2120 Connectivity Establishment (ICE) Protocol", draft-ietf- 2121 mmusic-trickle-ice-02 (work in progress), January 2015. 2123 Appendix A. Design Considerations 2125 A.1. General 2127 One of the main issues regarding the BUNDLE grouping extensions has 2128 been whether, in SDP Offers and SDP Answers, the same port value 2129 should be inserted in "m=" lines associated with a BUNDLE group, as 2130 the purpose of the extension is to negotiate the usage of a single 2131 address:port combination for media associated with the "m=" lines. 2132 Issues with both approaches, discussed in the Appendix have been 2133 raised. The outcome was to specify a mechanism which uses SDP Offers 2134 with both different and identical port values. 2136 Below are the primary issues that have been considered when defining 2137 the "BUNDLE" grouping extension: 2139 o 1) Interoperability with existing UAs. 2141 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2143 o 3) Time to gather, and the number of, ICE candidates. 2145 o 4) Different error scenarios, and when they occur. 2147 o 5) SDP Offer/Answer impacts, including usage of port number value 2148 zero. 2150 NOTE: Before this document is published as an RFC, this 2151 Appendix might be removed. 2153 A.2. UA Interoperability 2155 Consider the following SDP Offer/Answer exchange, where Alice sends 2156 an SDP Offer to Bob: 2158 SDP Offer 2160 v=0 2161 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2162 s= 2163 c=IN IP4 atlanta.example.com 2164 t=0 0 2165 m=audio 10000 RTP/AVP 97 2166 a=rtpmap:97 iLBC/8000 2167 m=video 10002 RTP/AVP 97 2168 a=rtpmap:97 H261/90000 2170 SDP Answer 2172 v=0 2173 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2174 s= 2175 c=IN IP4 biloxi.example.com 2176 t=0 0 2177 m=audio 20000 RTP/AVP 97 2178 a=rtpmap:97 iLBC/8000 2179 m=video 20002 RTP/AVP 97 2180 a=rtpmap:97 H261/90000 2182 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2183 later invention to RTP and Bob can not assume that Alice supports RFC 2184 4961. This means that Alice may be sending RTP from a different port 2185 than 10000 or 10002 - some implementation simply send the RTP from an 2186 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2187 way that Bob know if it should be passed to the video or audio codec 2188 is by looking at the port it was received on. This lead some SDP 2189 implementations to use the fact that each "m=" line had a different 2190 port number to use that port number as an index to find the correct m 2191 line in the SDP. As a result, some implementations that do support 2192 symmetric RTP and ICE still use a SDP data structure where SDP with 2193 "m=" lines with the same port such as: 2195 SDP Offer 2197 v=0 2198 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2199 s= 2200 c=IN IP4 atlanta.example.com 2201 t=0 0 2202 m=audio 10000 RTP/AVP 97 2203 a=rtpmap:97 iLBC/8000 2204 m=video 10000 RTP/AVP 98 2205 a=rtpmap:98 H261/90000 2207 will result in the second "m=" line being considered an SDP error 2208 because it has the same port as the first line. 2210 A.3. Usage of port number value zero 2212 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2213 can be disabled/rejected by setting the port number value to zero. 2214 This is different from e.g. using the SDP direction attributes, where 2215 RTCP traffic will continue even if the SDP "inactive" attribute is 2216 indicated for the associated "m=" line. 2218 If each "m=" line associated with a BUNDLE group would contain 2219 different port values, and one of those port values would be used for 2220 a BUNDLE address associated with the BUNDLE group, problems would 2221 occur if an endpoint wants to disable/reject the "m=" line associated 2222 with that port, by setting the port value to zero. After that, no 2223 "m=" line would contain the port value which is used for the BUNDLE 2224 address. In addition, it is unclear what would happen to the ICE 2225 candidates associated with the "m=" line, as they are also used for 2226 the BUNDLE address. 2228 A.4. B2BUA And Proxy Interoperability 2230 Some back to back user agents may be configured in a mode where if 2231 the incoming call leg contains an SDP attribute the B2BUA does not 2232 understand, the B2BUS still generates that SDP attribute in the Offer 2233 for the outgoing call leg. Consider an B2BUA that did not understand 2234 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2235 Further assume that the B2BUA was configured to tear down any call 2236 where it did not see any RTCP for 5 minutes. In this cases, if the 2237 B2BUA received an Offer like: 2239 SDP Offer 2241 v=0 2242 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2243 s= 2244 c=IN IP4 atlanta.example.com 2245 t=0 0 2246 m=audio 49170 RTP/AVP 0 2247 a=rtcp:53020 2249 It would be looking for RTCP on port 49172 but would not see any 2250 because the RTCP would be on port 53020 and after five minutes, it 2251 would tear down the call. Similarly, an SBC that did not understand 2252 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2253 wrong port and tear down the call. It is worth noting that a B2BUA 2254 that generated an Offer with capabilities it does not understand is 2255 not compliant with the specifications. 2257 A.4.1. Traffic Policing 2259 Sometimes intermediaries do not act as B2BUA, in the sense that they 2260 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2261 however, they may use SDP information (e.g. IP address and port) in 2262 order to control traffic gating functions, and to set traffic 2263 policing rules. There might be rules which will trigger a session to 2264 be terminated in case media is not sent or received on the ports 2265 retrieved from the SDP. This typically occurs once the session is 2266 already established and ongoing. 2268 A.4.2. Bandwidth Allocation 2270 Sometimes intermediaries do not act as B2BUA, in the sense that they 2271 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2272 however, they may use SDP information (e.g. codecs and media types) 2273 in order to control bandwidth allocation functions. The bandwidth 2274 allocation is done per "m=" line, which means that it might not be 2275 enough if media associated with all "m=" lines try to use that 2276 bandwidth. That may either simply lead to bad user experience, or to 2277 termination of the call. 2279 A.5. Candidate Gathering 2281 When using ICE, an candidate needs to be gathered for each port. 2282 This takes approximately 20 ms extra for each extra "m=" line due to 2283 the NAT pacing requirements. All of this gather can be overlapped 2284 with other things while the page is loading to minimize the impact. 2285 If the client only wants to generate TURN or STUN ICE candidates for 2286 one of the "m=" lines and then use trickle ICE 2287 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2288 the rest of the "m=" lines, it MAY do that and will not need any 2289 additional gathering time. 2291 Some people have suggested a TURN extension to get a bunch of TURN 2292 allocation at once. This would only provide a single STUN result so 2293 in cases where the other end did not support BUNDLE, may cause more 2294 use of the TURN server but would be quick in the cases where both 2295 sides supported BUNDLE and would fall back to a successful call in 2296 the other cases. 2298 Authors' Addresses 2300 Christer Holmberg 2301 Ericsson 2302 Hirsalantie 11 2303 Jorvas 02420 2304 Finland 2306 Email: christer.holmberg@ericsson.com 2308 Harald Tveit Alvestrand 2309 Google 2310 Kungsbron 2 2311 Stockholm 11122 2312 Sweden 2314 Email: harald@alvestrand.no 2316 Cullen Jennings 2317 Cisco 2318 400 3rd Avenue SW, Suite 350 2319 Calgary, AB T2P 4H2 2320 Canada 2322 Email: fluffy@iii.ca