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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: July 14, 2016 C. Jennings 7 Cisco 8 January 11, 2016 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-24.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 July 14, 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 . . . . . . . . . . . . . . . . . . . . . . 19 108 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 109 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 21 110 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 21 111 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 22 112 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 22 113 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 22 114 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 22 115 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 22 116 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 22 117 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 23 118 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 23 119 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 23 120 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 24 121 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 122 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 123 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 24 124 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 126 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 25 127 13.7. New text replacing section 8.4 (6th paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 129 14. RTP/RTCP extensions for identification-tag transport . . . . 25 130 14.1. General . . . . . . . . . . . . . . . . . . . . . . . . 25 131 14.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 26 132 14.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 27 133 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 134 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 27 135 15.2. New RTP Header Extension URI . . . . . . . . . . . . . . 28 136 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 28 137 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 28 138 16. Security Considerations . . . . . . . . . . . . . . . . . . . 29 139 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 29 140 17.1. Example: Bundle Address Selection . . . . . . . . . . . 29 141 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 31 142 17.3. Example: Offerer Adds A Media Description To A BUNDLE 143 Group . . . . . . . . . . . . . . . . . . . . . . . . . 32 144 17.4. Example: Offerer Moves A Media Description Out Of A 145 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 34 146 17.5. Example: Offerer Disables A Media Description Within A 147 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 35 148 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 149 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 37 150 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 151 20.1. Normative References . . . . . . . . . . . . . . . . . . 43 152 20.2. Informative References . . . . . . . . . . . . . . . . . 45 153 Appendix A. Design Considerations . . . . . . . . . . . . . . . 45 154 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 45 155 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 46 156 A.3. Usage of port number value zero . . . . . . . . . . . . . 47 157 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 48 158 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 48 159 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 48 160 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 49 161 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49 163 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 [RFC5245] 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.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.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) [RFC5245] 429 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. [I-D.mmusic-sdp-mux-attributes] 842 lists SDP attributes, whose attribute values must be identical for 843 all codecs that use the same payload type value. 845 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 847 There are multiple mechanisms that can be used by an endpoint in 848 order to associate received RTP/RTCP packets with a bundled "m=" 849 line. Such mechanisms include using the payload type value carried 850 inside the RTP packets, the SSRC values carried inside the RTP 851 packets, and other "m=" line specific information carried inside the 852 RTP packets. 854 As all RTP/RTCP packets associated with a BUNDLE group are received 855 (and sent) using single address:port combinations, the local 856 address:port combination cannot be used to associate received RTP 857 packets with the correct "m=" line. 859 As described in [Section 10.1.2], the same payload type value might 860 be used inside RTP packets described by multiple "m=" lines. In such 861 cases, the payload type value cannot be used to associate received 862 RTP packets with the correct "m=" line. 864 An offerer and answerer can inform each other which SSRC values they 865 will use for RTP and RTCP by using the SDP 'ssrc' attribute 866 [RFC5576]. To allow for proper association with this mechanism, the 867 'ssrc' attribute needs to be associated with each "m=" line that 868 shares a payload type with any other "m=" line in the same bundle. 869 As the SSRC values will be carried inside the RTP/RTCP packets, the 870 offerer and answerer can then use that information to associate 871 received RTP packets with the correct "m=" line. However, an offerer 872 will not know which SSRC values the answerer will use until it has 873 received the answer providing that information. Due to this, before 874 the offerer has received the answer, the offerer will not be able to 875 associate received RTP/RTCP packets with the correct "m=" line using 876 the SSRC values. 878 In order for an offerer and answerer to always be able to associate 879 received RTP and RTCP packets with the correct "m=" line, an offerer 880 and answerer using the BUNDLE extension MUST support the mechanism 881 defined in Section 14, where the remote endpoint inserts the 882 identification-tag associated with an "m=" line in RTP and RTCP 883 packets associated with that "m=" line. 885 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 NOTE: The offerer might also associate an SDP 'rtcp' attribute 918 [RFC3605] with a bundled "m=" line, excluding a bundle-only "m=" 919 line, in order to provide a fallback port for RTCP. However, the 920 fallback port will only be used in case the answerer does not include 921 the "m=" line in the BUNDLE group in the associated answer. 923 In the initial offer, the IP address and port combination for RTCP 924 MUST be unique in each bundled RTP-based "m=" line (excluding a 925 'bundle-only' "m=" line), similar to RTP. 927 10.3.2.3. Generating the SDP Answer 929 When an answerer generates an answer, if the offerer indicated 930 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 931 the associated offer, the answerer MUST accept usage of RTP/RTCP 932 multiplexing within the BUNDLE group. If an SDP "rtcp-mux" attribute 933 was not associated with a bundled "m=" line in the associated offer, 934 the answerer MUST NOT included that "m=" line in the BUNDLE group. 936 When the answerer accepts the usage of RTP/RTCP multiplexing within 937 the BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with 938 each bundled RTP-based "m=" line in the answer. The answerer MUST 939 NOT associate an SDP 'rtcp' attribute with any bundled "m=" line in 940 the answer. The answerer will use the port value of the selected 941 offerer BUNDLE address for sending RTP and RTCP packets associated 942 with each RTP-based bundled "m=" line towards the offerer. 944 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 945 negotiated in a previous offer/answer transaction, the answerer MUST 946 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 947 "m=" line in the answer. 949 10.3.2.4. Offerer Processing of the SDP Answer 951 When an offerer receives an answer, if the answerer has accepted the 952 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 953 follows the procedures for RTP/RTCP multiplexing defined in 954 [RFC5761]. The offerer will use the port value associated with the 955 answerer BUNDLE address for sending RTP and RTCP packets associated 956 with each RTP-based bundled "m=" line towards the answerer. 958 NOTE: If is considered a protocol error if the answerer has not 959 accpeted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 960 that the answerer included in the BUNDLE group. 962 10.3.2.5. Modifying the Session 964 When an offerer generatees a subsequent offer, it MUST associate an 965 SDP 'rtcp-mux' attribute with each RTP-based bundled "m=" line 966 (including any bundled "m=" line that the offerer wants to add to the 967 BUNDLE group), unless the offerer wants to disable or remove the "m=" 968 line from the BUNDLE group. 970 11. ICE Considerations 972 11.1. General 974 This section describes how to use the BUNDLE grouping extension 975 together with the Interactive Connectivity Establishment (ICE) 976 mechanism [RFC5245]. 978 The procedures defined in [RFC5245] also apply to usage of ICE with 979 BUNDLE, with the following exception: 981 o When BUNDLE addresses for a BUNDLE group have been selected for 982 both endpoints, ICE connectivity checks and keep-alives only need 983 to be performed for the whole BUNDLE group, instead of per bundled 984 "m=" line. 986 Support and usage of ICE mechanism together with the BUNDLE extension 987 is OPTIONAL. 989 11.2. SDP Offer/Answer Procedures 991 11.2.1. General 993 When an offerer associates a unique address with a bundled "m=" line 994 (excluding any bundle-only "m=" line), it MUST also associate unique 995 ICE candidates [RFC5245] to the "m=" line. 997 An offerer MUST NOT associate ICE candidates with a bundle-only "m=" 998 line with a zero port value. 1000 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1001 inherit the candidates associated with the selected offerer BUNDLE 1002 address. An answerer that does not support BUNDLE would not accept a 1003 bundle-only "m=" line. 1005 When an offerer or answerer associates a shared address (i.e. a 1006 previously selected BUNDLE address) with one or more bundled "m=" 1007 lines, it MUST associate identical ICE candidates (referred to as 1008 shared ICE candidates) with each of those "m=" lines. 1010 11.2.2. Generating the Initial SDP Offer 1012 When an offerer generates an initial offer, it associates unique ICE 1013 candidates with the bundled "m=" lines, according to Section 11.2.1. 1015 11.2.3. Generating the SDP Answer 1017 When an answerer generates an answer that contains a BUNDLE group, 1018 the answerer MUST associate shared ICE candidates with each bundled 1019 "m=" line (including "m=" lines that were indicated as bundle-only in 1020 the associated offer) in the answer. 1022 11.2.4. Offerer Processing of the SDP Answer 1024 When an offerer receives an answer, if the answerer supports and uses 1025 the ICE mechanism and the BUNDLE extension, the offerer MUST 1026 associate the same ICE candidates, associated with the "m=" line 1027 representing the offerer BUNDLE address (selected by the answerer), 1028 with each bundled "m=" line. 1030 11.2.5. Modifying the Session 1032 When an offerer generates a subsequent offer, it associates unique or 1033 shared ICE candidates with the bundled "m=" lines, according to 1034 (Section 11.2.1). 1036 12. DTLS Considerations 1038 One or more media streams within a BUNDLE group might use the 1039 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1040 to encrypt the data, or to negotiate encryption keys if another 1041 encryption mechanism is used to encrypt media. 1043 When DTLS is used within a BUNDLE group, the following rules apply: 1045 o There can only be one DTLS association [RFC6347] associated with 1046 the BUNDLE group; and 1048 o Each usage of the DTLS association within the BUNDLE group MUST 1049 use the same mechanism for determining which endpoints (the 1050 offerer or answerer) becomes DTLS client and DTLS server; and 1052 o Each usage of the DTLS association within the Bundle group MUST 1053 use the same mechanism for determining whether an offer or answer 1054 will trigger the establishment of a new DTLS association, or 1055 whether an existing DTLS association will be used; and 1057 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1058 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1059 [RFC5764], The client MUST include the extension even if the usage 1060 of DTLS-SRTP is not negotiated as part of the multimedia session 1061 (e.g. SIP session [RFC3261]. 1063 NOTE: The inclusion of the 'use_srtp' extension during the initial 1064 DTLS handshake ensures that a DTLS renegotiation will not be required 1065 in order to include the extension, in case DTLS-SRTP encrypted media 1066 is added to the BUNDLE group later during the multimedia session. 1068 13. Update to RFC 3264 1070 13.1. General 1072 This section replaces the text of the following sections of RFC 3264: 1074 o Section 5.1 (Unicast Streams). 1076 o Section 8.2 (Removing a Media Stream). 1078 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1080 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1082 For recvonly and sendrecv streams, the port number and address in the 1083 offer indicate where the offerer would like to receive the media 1084 stream. For sendonly RTP streams, the address and port number 1085 indirectly indicate where the offerer wants to receive RTCP reports. 1086 Unless there is an explicit indication otherwise, reports are sent to 1087 the port number one higher than the number indicated. The IP address 1088 and port present in the offer indicate nothing about the source IP 1089 address and source port of RTP and RTCP packets that will be sent by 1090 the offerer. A port number of zero in the offer indicates that the 1091 stream is offered but MUST NOT be used. This has no useful semantics 1092 in an initial offer, but is allowed for reasons of completeness, 1093 since the answer can contain a zero port indicating a rejected stream 1094 (Section 6). Furthermore, existing streams can be terminated by 1095 setting the port to zero (Section 8). In general, a port number of 1096 zero indicates that the media stream is not wanted. 1098 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1100 For recvonly and sendrecv streams, the port number and address in the 1101 offer indicate where the offerer would like to receive the media 1102 stream. For sendonly RTP streams, the address and port number 1103 indirectly indicate where the offerer wants to receive RTCP reports. 1104 Unless there is an explicit indication otherwise, reports are sent to 1105 the port number one higher than the number indicated. The IP address 1106 and port present in the offer indicate nothing about the source IP 1107 address and source port of RTP and RTCP packets that will be sent by 1108 the offerer. A port number of zero in the offer by default indicates 1109 that the stream is offered but MUST NOT be used, but an extension 1110 mechanism might specify different semantics for the usage of a zero 1111 port value. Furthermore, existing streams can be terminated by 1112 setting the port to zero (Section 8). In general, a port number of 1113 zero by default indicates that the media stream is not wanted. 1115 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1117 A stream that is offered with a port of zero MUST be marked with port 1118 zero in the answer. Like the offer, the answer MAY omit all 1119 attributes present previously, and MAY list just a single media 1120 format from amongst those in the offer. 1122 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1124 A stream that is offered with a port of zero MUST by default be 1125 marked with port zero in the answer, unless an extension mechanism, 1126 which specifies semantics for the usage of a non-zero port value, is 1127 used. If the stream is marked with port zero in the answer, the 1128 answer MAY omit all attributes present previously, and MAY list just 1129 a single media format from amongst those in the offer." 1131 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1133 RFC 2543 [10] specified that placing a user on hold was accomplished 1134 by setting the connection address to 0.0.0.0. Its usage for putting 1135 a call on hold is no longer recommended, since it doesn't allow for 1136 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1137 with connection oriented media. However, it can be useful in an 1138 initial offer when the offerer knows it wants to use a particular set 1139 of media streams and formats, but doesn't know the addresses and 1140 ports at the time of the offer. Of course, when used, the port 1141 number MUST NOT be zero, which would specify that the stream has been 1142 disabled. An agent MUST be capable of receiving SDP with a 1143 connection address of 0.0.0.0, in which case it means that neither 1144 RTP nor RTCP should be sent to the peer. 1146 13.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1148 RFC 2543 [10] specified that placing a user on hold was accomplished 1149 by setting the connection address to 0.0.0.0. Its usage for putting 1150 a call on hold is no longer recommended, since it doesn't allow for 1151 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1152 with connection oriented media. However, it can be useful in an 1153 initial offer when the offerer knows it wants to use a particular set 1154 of media streams and formats, but doesn't know the addresses and 1155 ports at the time of the offer. Of course, when used, the port 1156 number MUST NOT be zero, if it would specify that the stream has been 1157 disabled. However, an extension mechanism might specify different 1158 semantics of the zero port number usage. An agent MUST be capable of 1159 receiving SDP with a connection address of 0.0.0.0, in which case it 1160 means that neither RTP nor RTCP should be sent to the peer. 1162 14. RTP/RTCP extensions for identification-tag transport 1164 14.1. General 1166 SDP Offerers and Answerers [RFC3264] can associate identification- 1167 tags with "m=" lines within SDP Offers and Answers, using the 1168 procedures in [RFC5888]. Each identification-tag uniquely represents 1169 an "m=" line. 1171 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1172 used to carry identification-tags within RTCP SDES packets. This 1173 section also defines a new RTP header extension [RFC5285], which is 1174 used to carry identification-tags in RTP packets. 1176 The SDES item and RTP header extension make it possible for a 1177 receiver to associate received RTCP- and RTP packets with a specific 1178 "m=" line, with which the receiver has associated an identification- 1179 tag, even if those "m=" lines are part of the same RTP session. A 1180 media recipient informs the media sender about the identification-tag 1181 associated with an "m=" line through the use of an 'mid' attribute 1182 [RFC5888]. The media sender then inserts the identification-tag in 1183 RTCP and RTP packets sent to the media recipient. 1185 NOTE: This text above defines how identification-tags are carried in 1186 SDP Offers and Answers. The usage of other signalling protocols for 1187 carrying identification-tags is not prevented, but the usage of such 1188 protocols is outside the scope of this document. 1190 [RFC3550] defines general procedures regarding the RTCP transmission 1191 interval. The RTCP MID SDES item SHOULD be sent in the first few 1192 RTCP packets sent on joining the session, and SHOULD be sent 1193 regularly thereafter. The exact number of RTCP packets in which this 1194 SDES item is sent is intentionally not specified here, as it will 1195 depend on the expected packet loss rate, the RTCP reporting interval, 1196 and the allowable overhead. 1198 The RTP MID header extension SHOULD be included in some RTP packets 1199 at the start of the session and whenever the SSRC changes. It might 1200 also be useful to include the header extension in RTP packets that 1201 comprise random access points in the media (e.g., with video 1202 I-frames). The exact number of RTP packets in which this header 1203 extension is sent is intentionally not specified here, as it will 1204 depend on expected packet loss rate and loss patterns, the overhead 1205 the application can tolerate, and the importance of immediate receipt 1206 of the identification-tag. 1208 For robustness purpose, endpoints need to be prepared for situations 1209 where the reception of the identification-tag is delayed, and SHOULD 1210 NOT terminate sessions in such cases, as the identification-tag is 1211 likely to arrive soon. 1213 14.2. RTCP MID SDES Item 1215 0 1 2 3 1216 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 1217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1218 | MID=TBD | length | identification-tag ... 1219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 The identification-tag payload is UTF-8 encoded, as in SDP. 1223 The identification-tag is not zero terminated. 1225 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1226 identifier value.] 1228 14.3. RTP MID Header Extension 1230 The payload, containing the identification-tag, of the RTP MID header 1231 extension element can be encoded using either the one-byte or two- 1232 byte header [RFC5285]. The identification-tag payload is UTF-8 1233 encoded, as in SDP. 1235 The identification-tag is not zero terminated. Note, that set of 1236 header extensions included in the packet needs to be padded to the 1237 next 32-bit boundary using zero bytes [RFC5285]. 1239 As the identification-tag is included in either an RTCP SDES item or 1240 an RTP header extension, or both, there should be some consideration 1241 about the packet expansion caused by the identification-tag. To 1242 avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the 1243 header extension's size needs to be taken into account when encoding 1244 the media. 1246 It is recommended that the identification-tag is kept short. Due to 1247 the properties of the RTP header extension mechanism, when using the 1248 one-byte header, a tag that is 1-3 bytes will result in that a 1249 minimal number of 32-bit words are used for the RTP header extension, 1250 in case no other header extensions are included at the same time. 1251 Note, do take into account that some single characters when UTF-8 1252 encoded will result in multiple octets. 1254 15. IANA Considerations 1256 15.1. New SDES item 1258 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1259 document.] 1261 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1262 identifier value.] 1264 This document adds the MID SDES item to the IANA "RTCP SDES item 1265 types" registry as follows: 1267 Value: TBD 1268 Abbrev.: MID 1269 Name: Media Identification 1270 Reference: RFCXXXX 1272 15.2. New RTP Header Extension URI 1274 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1275 document.] 1277 This document defines a new extension URI in the RTP Compact Header 1278 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1279 Parameters registry, according to the following data: 1281 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1282 Description: Media identification 1283 Contact: christer.holmberg@ericsson.com 1284 Reference: RFCXXXX 1286 15.3. New SDP Attribute 1288 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1289 document.] 1291 This document defines a new SDP media-level attribute, 'bundle-only', 1292 according to the following data: 1294 Attribute name: bundle-only 1295 Type of attribute: media 1296 Subject to charset: No 1297 Purpose: Request a media description to be accepted 1298 in the answer only if kept within a BUNDLE 1299 group by the answerer. 1300 Appropriate values: N/A 1301 Contact name: Christer Holmberg 1302 Contact e-mail: christer.holmberg@ericsson.com 1303 Reference: RFCXXXX 1305 15.4. New SDP Group Semantics 1307 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1308 document.] 1309 This document registers the following semantics with IANA in the 1310 "Semantics for the "group" SDP Attribute" subregistry (under the 1311 "Session Description Protocol (SDP) Parameters" registry: 1313 Semantics Token Reference 1314 ------------------------------------- ------ --------- 1315 Media bundling BUNDLE [RFCXXXX] 1317 16. Security Considerations 1319 The security considerations defined in [RFC3264] and [RFC5888] apply 1320 to the BUNDLE extension. Bundle does not change which information 1321 flows over the network but only changes which addresses and ports 1322 that information is flowing on and thus has very little impact on the 1323 security of the RTP sessions. 1325 When the BUNDLE extension is used, a single set of security 1326 credentials might be used for all media streams associated with a 1327 BUNDLE group. 1329 When the BUNDLE extension is used, the number of SSRC values within a 1330 single RTP session increases, which increases the risk of SSRC 1331 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1332 and SRTCP encryption in certain situations. 1334 17. Examples 1336 17.1. Example: Bundle Address Selection 1338 The example below shows: 1340 o An offer, in which the offerer associates a unique address with 1341 each bundled "m=" line within the BUNDLE group. 1343 o An answer, in which the answerer selects the offerer BUNDLE 1344 address, and in which selects its own BUNDLE address (the answerer 1345 BUNDLE address) and associates it with each bundled "m=" line 1346 within the BUNDLE group. 1348 SDP Offer (1) 1350 v=0 1351 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1352 s= 1353 c=IN IP4 atlanta.example.com 1354 t=0 0 1355 a=group:BUNDLE foo bar 1356 m=audio 10000 RTP/AVP 0 8 97 1357 b=AS:200 1358 a=mid:foo 1359 a=rtpmap:0 PCMU/8000 1360 a=rtpmap:8 PCMA/8000 1361 a=rtpmap:97 iLBC/8000 1362 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1363 m=video 10002 RTP/AVP 31 32 1364 b=AS:1000 1365 a=mid:bar 1366 a=rtpmap:31 H261/90000 1367 a=rtpmap:32 MPV/90000 1368 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1370 SDP Answer (2) 1372 v=0 1373 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1374 s= 1375 c=IN IP4 biloxi.example.com 1376 t=0 0 1377 a=group:BUNDLE foo bar 1378 m=audio 20000 RTP/AVP 0 1379 b=AS:200 1380 a=mid:foo 1381 a=rtpmap:0 PCMU/8000 1382 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1383 m=video 20000 RTP/AVP 32 1384 b=AS:1000 1385 a=mid:bar 1386 a=rtpmap:32 MPV/90000 1387 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1389 17.2. Example: BUNDLE Extension Rejected 1391 The example below shows: 1393 o An offer, in which the offerer associates a unique address with 1394 each bundled "m=" line within the BUNDLE group. 1396 o An answer, in which the answerer rejects the offered BUNDLE group, 1397 and associates a unique address with each "m=" line (following 1398 normal RFC 3264 procedures). 1400 SDP Offer (1) 1402 v=0 1403 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1404 s= 1405 c=IN IP4 atlanta.example.com 1406 t=0 0 1407 a=group:BUNDLE foo bar 1408 m=audio 10000 RTP/AVP 0 8 97 1409 b=AS:200 1410 a=mid:foo 1411 a=rtpmap:0 PCMU/8000 1412 a=rtpmap:8 PCMA/8000 1413 a=rtpmap:97 iLBC/8000 1414 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1415 m=video 10002 RTP/AVP 31 32 1416 b=AS:1000 1417 a=mid:bar 1418 a=rtpmap:31 H261/90000 1419 a=rtpmap:32 MPV/90000 1420 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1422 SDP Answer (2) 1424 v=0 1425 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1426 s= 1427 c=IN IP4 biloxi.example.com 1428 t=0 0 1429 m=audio 20000 RTP/AVP 0 1430 b=AS:200 1431 a=rtpmap:0 PCMU/8000 1432 m=video 30000 RTP/AVP 32 1433 b=AS:1000 1434 a=rtpmap:32 MPV/90000 1436 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1438 The example below shows: 1440 o A subsequent offer (the BUNDLE group has been created as part of a 1441 previous offer/answer transaction), in which the offerer adds a 1442 new "m=" line, represented by the "zen" identification-tag, to a 1443 previously negotiated BUNDLE group, associates a unique address 1444 with the added "m=" line, and associates the previously selected 1445 offerer BUNDLE address with each of the other bundled "m=" lines 1446 within the BUNDLE group. 1448 o An answer, in which the answerer associates the answerer BUNDLE 1449 address with each bundled "m=" line (including the newly added 1450 "m=" line) within the BUNDLE group. 1452 SDP Offer (1) 1454 v=0 1455 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1456 s= 1457 c=IN IP4 atlanta.example.com 1458 t=0 0 1459 a=group:BUNDLE foo bar zen 1460 m=audio 10000 RTP/AVP 0 8 97 1461 b=AS:200 1462 a=mid:foo 1463 a=rtpmap:0 PCMU/8000 1464 a=rtpmap:8 PCMA/8000 1465 a=rtpmap:97 iLBC/8000 1466 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1467 m=video 10000 RTP/AVP 31 32 1468 b=AS:1000 1469 a=mid:bar 1470 a=rtpmap:31 H261/90000 1471 a=rtpmap:32 MPV/90000 1472 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1473 m=video 20000 RTP/AVP 66 1474 b=AS:1000 1475 a=mid:zen 1476 a=rtpmap:66 H261/90000 1477 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1479 SDP Answer (2) 1481 v=0 1482 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1483 s= 1484 c=IN IP4 biloxi.example.com 1485 t=0 0 1486 a=group:BUNDLE foo bar zen 1487 m=audio 20000 RTP/AVP 0 1488 b=AS:200 1489 a=mid:foo 1490 a=rtpmap:0 PCMU/8000 1491 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1492 m=video 20000 RTP/AVP 32 1493 b=AS:1000 1494 a=mid:bar 1495 a=rtpmap:32 MPV/90000 1496 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1497 m=video 20000 RTP/AVP 66 1498 b=AS:1000 1499 a=mid:zen 1500 a=rtpmap:66 H261/90000 1501 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1503 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1505 The example below shows: 1507 o A subsequent offer (the BUNDLE group has been created as part of a 1508 previous offer/answer transaction), in which the offerer moves a 1509 bundled "m=" line out of a BUNDLE group, associates a unique 1510 address with the moved "m=" line, and associates the offerer 1511 BUNDLE address with each other bundled "m=" line within the BUNDLE 1512 group. 1514 o An answer, in which the answerer moves the "m=" line out of the 1515 BUNDLE group, associates unique address with the moved "m=" line, 1516 and associates the answerer BUNDLE address with each of the 1517 remaining bundled "m=" line within the BUNDLE group. 1519 SDP Offer (1) 1521 v=0 1522 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1523 s= 1524 c=IN IP4 atlanta.example.com 1525 t=0 0 1526 a=group:BUNDLE foo bar 1527 m=audio 10000 RTP/AVP 0 8 97 1528 b=AS:200 1529 a=mid:foo 1530 a=rtpmap:0 PCMU/8000 1531 a=rtpmap:8 PCMA/8000 1532 a=rtpmap:97 iLBC/8000 1533 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1534 m=video 10000 RTP/AVP 31 32 1535 b=AS:1000 1536 a=mid:bar 1537 a=rtpmap:31 H261/90000 1538 a=rtpmap:32 MPV/90000 1539 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1540 m=video 50000 RTP/AVP 66 1541 b=AS:1000 1542 a=mid:zen 1543 a=rtpmap:66 H261/90000 1545 SDP Answer (2) 1547 v=0 1548 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1549 s= 1550 c=IN IP4 biloxi.example.com 1551 t=0 0 1552 a=group:BUNDLE foo bar 1553 m=audio 20000 RTP/AVP 0 1554 b=AS:200 1555 a=mid:foo 1556 a=rtpmap:0 PCMU/8000 1557 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1558 m=video 20000 RTP/AVP 32 1559 b=AS:1000 1560 a=mid:bar 1561 a=rtpmap:32 MPV/90000 1562 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1563 m=video 60000 RTP/AVP 66 1564 b=AS:1000 1565 a=mid:zen 1566 a=rtpmap:66 H261/90000 1568 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1569 Group 1571 The example below shows: 1573 o A subsequent offer (the BUNDLE group has been created as part of a 1574 previous offer/answer transaction), in which the offerer disables 1575 a bundled "m=" line within BUNDLE group, assigns a zero port 1576 number to the disabled "m=" line, and associates the offerer 1577 BUNDLE address with each of the other bundled "m=" lines within 1578 the BUNDLE group. 1580 o An answer, in which the answerer moves the disabled "m=" line out 1581 of the BUNDLE group, assigns a zero port value to the disabled 1582 "m=" line, and associates the answerer BUNDLE address with each of 1583 the remaining bundled "m=" line within the BUNDLE group. 1585 SDP Offer (1) 1587 v=0 1588 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1589 s= 1590 c=IN IP4 atlanta.example.com 1591 t=0 0 1592 a=group:BUNDLE foo bar 1593 m=audio 10000 RTP/AVP 0 8 97 1594 b=AS:200 1595 a=mid:foo 1596 a=rtpmap:0 PCMU/8000 1597 a=rtpmap:8 PCMA/8000 1598 a=rtpmap:97 iLBC/8000 1599 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1600 m=video 10000 RTP/AVP 31 32 1601 b=AS:1000 1602 a=mid:bar 1603 a=rtpmap:31 H261/90000 1604 a=rtpmap:32 MPV/90000 1605 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1606 m=video 0 RTP/AVP 66 1607 a=mid:zen 1608 a=rtpmap:66 H261/90000 1610 SDP Answer (2) 1612 v=0 1613 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1614 s= 1615 c=IN IP4 biloxi.example.com 1616 t=0 0 1617 a=group:BUNDLE foo bar 1618 m=audio 20000 RTP/AVP 0 1619 b=AS:200 1620 a=mid:foo 1621 a=rtpmap:0 PCMU/8000 1622 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1623 m=video 20000 RTP/AVP 32 1624 b=AS:1000 1625 a=mid:bar 1626 a=rtpmap:32 MPV/90000 1627 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1628 m=video 0 RTP/AVP 66 1629 a=mid:zen 1630 a=rtpmap:66 H261/90000 1632 18. Acknowledgements 1634 The usage of the SDP grouping extension for negotiating bundled media 1635 is based on a similar alternatives proposed by Harald Alvestrand and 1636 Cullen Jennings. The BUNDLE extension described in this document is 1637 based on the different alternative proposals, and text (e.g. SDP 1638 examples) have been borrowed (and, in some cases, modified) from 1639 those alternative proposals. 1641 The SDP examples are also modified versions from the ones in the 1642 Alvestrand proposal. 1644 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1645 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 1646 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1647 Justin Uberti for reading the text, and providing useful feedback. 1649 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1650 providing help and text on the RTP/RTCP procedures. 1652 Thanks to Spotify for providing music for the countless hours of 1653 document editing. 1655 19. Change Log 1657 [RFC EDITOR NOTE: Please remove this section when publishing] 1659 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 1661 o - RTCP-MUX mandatory for bundled RTP m- lines 1663 o - Editorial fixes based on comments from Flemming Andreasen 1665 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 1667 o - Correction of Ari's family name 1669 o - Editorial fixes based on comments from Thomas Stach 1671 o - RTP/RTCP correction based on comment from Magnus Westerlund 1672 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1673 msg14861.html 1675 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 1677 o - Correct based on comment from Paul Kyzivat 1679 o -- 'received packets' replaced with 'received data' 1681 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1683 o - Clarification based on comment from James Guballa 1685 o - Clarification based on comment from Flemming Andreasen 1687 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1689 o - DTLS Considerations section added. 1691 o - BUNDLE semantics added to the IANA Considerations 1693 o - Changes based on WGLC comments from Adam Roach 1695 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1696 msg14673.html 1698 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1700 o - Changes based on agreements at IETF#92 1702 o -- BAS Offer removed, based on agreement at IETF#92. 1704 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1705 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1707 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1709 o - Editorial changes based on comments from Magnus Westerlund. 1711 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1713 o - Modification of RTP/RTCP multiplexing section, based on comments 1714 from Magnus Westerlund. 1716 o - Reference updates. 1718 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1719 o - Editorial fix. 1721 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1723 o - Editorial changes. 1725 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1727 o Changes to allow a new suggested offerer BUNDLE address to be 1728 assigned to each bundled m- line. 1730 o Changes based on WGLC comments from Paul Kyzivat 1732 o - Editorial fixes 1734 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1736 o Usage of SDP 'extmap' attribute added 1738 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1739 port value 1741 o Changes based on WGLC comments from Thomas Stach 1743 o - ICE candidates not assigned to bundle-only m- lines with a zero 1744 port value 1746 o - Editorial changes 1748 o Changes based on WGLC comments from Colin Perkins 1750 o - Editorial changes: 1752 o -- "RTP SDES item" -> "RTCP SDES item" 1754 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1756 o - Changes in section 10.1.1: 1758 o -- "SHOULD NOT" -> "MUST NOT" 1760 o -- Additional text added to the Note 1762 o - Change to section 13.2: 1764 o -- Clarify that mid value is not zero terminated 1766 o - Change to section 13.3: 1768 o -- Clarify that mid value is not zero terminated 1770 o -- Clarify padding 1772 o Changes based on WGLC comments from Paul Kyzivat 1774 o - Editorial changes: 1776 o Changes based on WGLC comments from Jonathan Lennox 1778 o - Editorial changes: 1780 o - Defintion of SDP bundle-only attribute alligned with structure 1781 in 4566bis draft 1783 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1785 o Editorial corrections based on comments from Harald Alvestrand. 1787 o Editorial corrections based on comments from Cullen Jennings. 1789 o Reference update (RFC 7160). 1791 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1792 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1793 msg13765.html). 1795 o Additional text added to the Security Considerations. 1797 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1799 o SDP bundle-only attribute added to IANA Considerations. 1801 o SDES item and RTP header extension added to Abstract and 1802 Introduction. 1804 o Modification to text updating section 8.2 of RFC 3264. 1806 o Reference corrections. 1808 o Editorial corrections. 1810 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1812 o Terminology change: "bundle-only attribute assigned to m= line" to 1813 "bundle-only attribute associated with m= line". 1815 o Editorial corrections. 1817 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1819 o Editorial corrections. 1821 o - "of"->"if" (8.3.2.5). 1823 o - "optional"->"OPTIONAL" (9.1). 1825 o - Syntax/ABNF for 'bundle-only' attribute added. 1827 o - SDP Offer/Answer sections merged. 1829 o - 'Request new offerer BUNDLE address' section added 1831 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1833 o OPEN ISSUE regarding Receiver-ID closed. 1835 o - RTP MID SDES Item. 1837 o - RTP MID Header Extension. 1839 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1840 closed. 1842 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1843 include an 'rtcp' attribute in the answer, based on the procedures 1844 in section 5.1.3 of RFC 5761. 1846 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1848 o Draft title changed. 1850 o Added "SDP" to section names containing "Offer" or "Answer". 1852 o Editorial fixes based on comments from Paul Kyzivat 1853 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1854 msg13314.html). 1856 o Editorial fixed based on comments from Colin Perkins 1857 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1858 msg13318.html). 1860 o - Removed text about extending BUNDLE to allow multiple RTP 1861 sessions within a BUNDLE group. 1863 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1864 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1865 3264 structure. 1867 o Additional definitions added. 1869 o - Shared address. 1871 o - Bundled "m=" line. 1873 o - Bundle-only "m=" line. 1875 o - Offerer suggested BUNDLE mid. 1877 o - Answerer selected BUNDLE mid. 1879 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1880 to multiple "m=" lines until it has received an SDP Answer 1881 indicating support of the BUNDLE extension. 1883 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1884 Answerer supports the BUNDLE extension, assign a zero port value 1885 to a 'bundle-only' "m=" line. 1887 o SDP 'bundle-only' attribute section added. 1889 o Connection data nettype/addrtype restrictions added. 1891 o RFC 3264 update section added. 1893 o Indicating that a specific payload type value can be used in 1894 multiple "m=" lines, if the value represents the same codec 1895 configuration in each "m=" line. 1897 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1899 o Updated Offerer procedures (http://www.ietf.org/mail- 1900 archive/web/mmusic/current/msg12293.html). 1902 o Updated Answerer procedures (http://www.ietf.org/mail- 1903 archive/web/mmusic/current/msg12333.html). 1905 o Usage of SDP 'bundle-only' attribute added. 1907 o Reference to Trickle ICE document added. 1909 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1910 o Mechanism modified, to be based on usage of SDP Offers with both 1911 different and identical port number values, depending on whether 1912 it is known if the remote endpoint supports the extension. 1914 o Cullen Jennings added as co-author. 1916 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1918 o No changes. New version due to expiration. 1920 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1922 o No changes. New version due to expiration. 1924 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1926 o Draft name changed. 1928 o Harald Alvestrand added as co-author. 1930 o "Multiplex" terminology changed to "bundle". 1932 o Added text about single versus multiple RTP Sessions. 1934 o Added reference to RFC 3550. 1936 20. References 1938 20.1. Normative References 1940 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1941 Requirement Levels", BCP 14, RFC 2119, 1942 DOI 10.17487/RFC2119, March 1997, 1943 . 1945 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1946 with Session Description Protocol (SDP)", RFC 3264, 1947 DOI 10.17487/RFC3264, June 2002, 1948 . 1950 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1951 Jacobson, "RTP: A Transport Protocol for Real-Time 1952 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 1953 July 2003, . 1955 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1956 in Session Description Protocol (SDP)", RFC 3605, 1957 DOI 10.17487/RFC3605, October 2003, 1958 . 1960 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1961 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1962 July 2006, . 1964 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 1965 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 1966 . 1968 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1969 (ICE): A Protocol for Network Address Translator (NAT) 1970 Traversal for Offer/Answer Protocols", RFC 5245, 1971 DOI 10.17487/RFC5245, April 2010, 1972 . 1974 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1975 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 1976 2008, . 1978 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1979 Control Packets on a Single Port", RFC 5761, 1980 DOI 10.17487/RFC5761, April 2010, 1981 . 1983 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1984 Security (DTLS) Extension to Establish Keys for the Secure 1985 Real-time Transport Protocol (SRTP)", RFC 5764, 1986 DOI 10.17487/RFC5764, May 2010, 1987 . 1989 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1990 Protocol (SDP) Grouping Framework", RFC 5888, 1991 DOI 10.17487/RFC5888, June 2010, 1992 . 1994 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1995 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1996 January 2012, . 1998 [I-D.mmusic-sdp-mux-attributes] 1999 Nandakumar, S., "A Framework for SDP Attributes when 2000 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08 2001 (work in progress), January 2015. 2003 20.2. Informative References 2005 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2006 A., Peterson, J., Sparks, R., Handley, M., and E. 2007 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2008 DOI 10.17487/RFC3261, June 2002, 2009 . 2011 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2012 Description Protocol (SDP) Security Descriptions for Media 2013 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2014 . 2016 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2017 Media Attributes in the Session Description Protocol 2018 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2019 . 2021 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2022 Clock Rates in an RTP Session", RFC 7160, 2023 DOI 10.17487/RFC7160, April 2014, 2024 . 2026 [I-D.ietf-mmusic-trickle-ice] 2027 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2028 Incremental Provisioning of Candidates for the Interactive 2029 Connectivity Establishment (ICE) Protocol", draft-ietf- 2030 mmusic-trickle-ice-02 (work in progress), January 2015. 2032 Appendix A. Design Considerations 2034 A.1. General 2036 One of the main issues regarding the BUNDLE grouping extensions has 2037 been whether, in SDP Offers and SDP Answers, the same port value 2038 should be inserted in "m=" lines associated with a BUNDLE group, as 2039 the purpose of the extension is to negotiate the usage of a single 2040 address:port combination for media associated with the "m=" lines. 2041 Issues with both approaches, discussed in the Appendix have been 2042 raised. The outcome was to specify a mechanism which uses SDP Offers 2043 with both different and identical port values. 2045 Below are the primary issues that have been considered when defining 2046 the "BUNDLE" grouping extension: 2048 o 1) Interoperability with existing UAs. 2050 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2052 o 3) Time to gather, and the number of, ICE candidates. 2054 o 4) Different error scenarios, and when they occur. 2056 o 5) SDP Offer/Answer impacts, including usage of port number value 2057 zero. 2059 NOTE: Before this document is published as an RFC, this 2060 Appendix might be removed. 2062 A.2. UA Interoperability 2064 Consider the following SDP Offer/Answer exchange, where Alice sends 2065 an SDP Offer to Bob: 2067 SDP Offer 2069 v=0 2070 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2071 s= 2072 c=IN IP4 atlanta.example.com 2073 t=0 0 2074 m=audio 10000 RTP/AVP 97 2075 a=rtpmap:97 iLBC/8000 2076 m=video 10002 RTP/AVP 97 2077 a=rtpmap:97 H261/90000 2079 SDP Answer 2081 v=0 2082 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2083 s= 2084 c=IN IP4 biloxi.example.com 2085 t=0 0 2086 m=audio 20000 RTP/AVP 97 2087 a=rtpmap:97 iLBC/8000 2088 m=video 20002 RTP/AVP 97 2089 a=rtpmap:97 H261/90000 2091 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2092 later invention to RTP and Bob can not assume that Alice supports RFC 2093 4961. This means that Alice may be sending RTP from a different port 2094 than 10000 or 10002 - some implementation simply send the RTP from an 2095 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2096 way that Bob know if it should be passed to the video or audio codec 2097 is by looking at the port it was received on. This lead some SDP 2098 implementations to use the fact that each "m=" line had a different 2099 port number to use that port number as an index to find the correct m 2100 line in the SDP. As a result, some implementations that do support 2101 symmetric RTP and ICE still use a SDP data structure where SDP with 2102 "m=" lines with the same port such as: 2104 SDP Offer 2106 v=0 2107 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2108 s= 2109 c=IN IP4 atlanta.example.com 2110 t=0 0 2111 m=audio 10000 RTP/AVP 97 2112 a=rtpmap:97 iLBC/8000 2113 m=video 10000 RTP/AVP 98 2114 a=rtpmap:98 H261/90000 2116 will result in the second "m=" line being considered an SDP error 2117 because it has the same port as the first line. 2119 A.3. Usage of port number value zero 2121 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2122 can be disabled/rejected by setting the port number value to zero. 2123 This is different from e.g. using the SDP direction attributes, where 2124 RTCP traffic will continue even if the SDP "inactive" attribute is 2125 indicated for the associated "m=" line. 2127 If each "m=" line associated with a BUNDLE group would contain 2128 different port values, and one of those port values would be used for 2129 a BUNDLE address associated with the BUNDLE group, problems would 2130 occur if an endpoint wants to disable/reject the "m=" line associated 2131 with that port, by setting the port value to zero. After that, no 2132 "m=" line would contain the port value which is used for the BUNDLE 2133 address. In addition, it is unclear what would happen to the ICE 2134 candidates associated with the "m=" line, as they are also used for 2135 the BUNDLE address. 2137 A.4. B2BUA And Proxy Interoperability 2139 Some back to back user agents may be configured in a mode where if 2140 the incoming call leg contains an SDP attribute the B2BUA does not 2141 understand, the B2BUS still generates that SDP attribute in the Offer 2142 for the outgoing call leg. Consider an B2BUA that did not understand 2143 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2144 Further assume that the B2BUA was configured to tear down any call 2145 where it did not see any RTCP for 5 minutes. In this cases, if the 2146 B2BUA received an Offer like: 2148 SDP Offer 2150 v=0 2151 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2152 s= 2153 c=IN IP4 atlanta.example.com 2154 t=0 0 2155 m=audio 49170 RTP/AVP 0 2156 a=rtcp:53020 2158 It would be looking for RTCP on port 49172 but would not see any 2159 because the RTCP would be on port 53020 and after five minutes, it 2160 would tear down the call. Similarly, an SBC that did not understand 2161 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2162 wrong port and tear down the call. It is worth noting that a B2BUA 2163 that generated an Offer with capabilities it does not understand is 2164 not compliant with the specifications. 2166 A.4.1. Traffic Policing 2168 Sometimes intermediaries do not act as B2BUA, in the sense that they 2169 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2170 however, they may use SDP information (e.g. IP address and port) in 2171 order to control traffic gating functions, and to set traffic 2172 policing rules. There might be rules which will trigger a session to 2173 be terminated in case media is not sent or received on the ports 2174 retrieved from the SDP. This typically occurs once the session is 2175 already established and ongoing. 2177 A.4.2. Bandwidth Allocation 2179 Sometimes intermediaries do not act as B2BUA, in the sense that they 2180 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2181 however, they may use SDP information (e.g. codecs and media types) 2182 in order to control bandwidth allocation functions. The bandwidth 2183 allocation is done per "m=" line, which means that it might not be 2184 enough if media associated with all "m=" lines try to use that 2185 bandwidth. That may either simply lead to bad user experience, or to 2186 termination of the call. 2188 A.5. Candidate Gathering 2190 When using ICE, an candidate needs to be gathered for each port. 2191 This takes approximately 20 ms extra for each extra "m=" line due to 2192 the NAT pacing requirements. All of this gather can be overlapped 2193 with other things while the page is loading to minimize the impact. 2194 If the client only wants to generate TURN or STUN ICE candidates for 2195 one of the "m=" lines and then use trickle ICE 2196 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2197 the rest of the "m=" lines, it MAY do that and will not need any 2198 additional gathering time. 2200 Some people have suggested a TURN extension to get a bunch of TURN 2201 allocation at once. This would only provide a single STUN result so 2202 in cases where the other end did not support BUNDLE, may cause more 2203 use of the TURN server but would be quick in the cases where both 2204 sides supported BUNDLE and would fall back to a successful call in 2205 the other cases. 2207 Authors' Addresses 2209 Christer Holmberg 2210 Ericsson 2211 Hirsalantie 11 2212 Jorvas 02420 2213 Finland 2215 Email: christer.holmberg@ericsson.com 2217 Harald Tveit Alvestrand 2218 Google 2219 Kungsbron 2 2220 Stockholm 11122 2221 Sweden 2223 Email: harald@alvestrand.no 2224 Cullen Jennings 2225 Cisco 2226 400 3rd Avenue SW, Suite 350 2227 Calgary, AB T2P 4H2 2228 Canada 2230 Email: fluffy@iii.ca