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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: December 17, 2015 C. Jennings 7 Cisco 8 June 15, 2015 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-21.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 December 17, 2015. 50 Copyright Notice 52 Copyright (c) 2015 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 . . . . 12 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 . . . . . . . . . . 13 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 . . 15 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 . . . . . . . . . . . . . . . . . . . . . . 17 103 10.1.2. Payload Type (PT) Value Reuse . . . . . . . . . . . 18 104 10.2. Associating RTP/RTCP Packets With Correct SDP Media 105 Description . . . . . . . . . . . . . . . . . . . . . . 18 106 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 . . . . . . . . . . . . . . . . . . . . . 22 110 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 111 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 23 112 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 . . . . . . . . 23 116 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 24 117 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 24 118 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 24 119 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 24 120 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 25 124 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 126 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 . . . . 26 130 14.1. General . . . . . . . . . . . . . . . . . . . . . . . . 26 131 14.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 27 132 14.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 28 133 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 134 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 28 135 15.2. New RTP Header Extension URI . . . . . . . . . . . . . . 29 136 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 29 137 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 29 138 16. Security Considerations . . . . . . . . . . . . . . . . . . . 30 139 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 30 140 17.1. Example: Bundle Address Selection . . . . . . . . . . . 30 141 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 32 142 17.3. Example: Offerer Adds A Media Description To A BUNDLE 143 Group . . . . . . . . . . . . . . . . . . . . . . . . . 33 144 17.4. Example: Offerer Moves A Media Description Out Of A 145 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 35 146 17.5. Example: Offerer Disables A Media Description Within A 147 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 36 148 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38 149 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 38 150 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 151 20.1. Normative References . . . . . . . . . . . . . . . . . . 44 152 20.2. Informative References . . . . . . . . . . . . . . . . . 44 153 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 assign their respective BUNDLE address to each "m=" line in the 182 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 assign a 219 unique address to each "m=" line within an offer and answer, 220 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 assigned 232 to only one "m=" line in an offer or answer. 234 Shared address: An IP address and port combination that is assigned 235 to 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 assigned to each bundled "m=" line, and each identification-tag is 313 listed in the SDP 'group:BUNDLE' attribute identification-tag list. 314 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'. 328 Name: bundle-only 330 Value: 332 Usage Level: media 334 Charset Dependent: no 336 Example: 338 a=bundle-only 340 In order to ensure that an answerer that does not support the BUNDLE 341 extension always rejects a bundled "m=" line, the offerer can assign 342 a zero port value to the "m=" line. According to [RFC4566] an 343 answerer will reject such "m=" line. By associating an SDP 'bundle- 344 only' attribute with such "m=" line, the offerer can request that the 345 answerer accepts the "m=" line if the answerer supports the Bundle 346 extension, and if the answerer keeps the "m=" line within the 347 associated BUNDLE group. 349 NOTE: Once the offerer BUNDLE address has been selected, the offerer 350 does not need to include the 'bundle-only' attribute in subsequent 351 offers. By assigning the offerer BUNDLE address to an "m=" line of a 352 subsequent offer, the offerer will ensure that the answerer will 353 either keep the "m=" line within the BUNDLE group, or the answerer 354 will have to reject the "m=" line. 356 The usage of the 'bundle-only' attribute is only defined for a 357 bundled "m=" line with a zero port value, within an offer. Other 358 usage is unspecified. 360 Section 8 defines the detailed SDP Offer/Answer procedures for the 361 'bundle-only' attribute. 363 7. SDP Information Considerations 365 7.1. General 367 This section describes restrictions associated with the usage of SDP 368 parameters within a BUNDLE group. It also describes, when parameter 369 and attribute values have been associated with each bundled "m=" 370 line, how to calculate a value for the whole BUNDLE group. 372 7.2. Connection Data (c=) 374 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 375 line MUST be 'IN'. 377 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 378 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 379 each "m=" line. 381 NOTE: Extensions to this specification can specify usage of the 382 BUNDLE mechanism for other nettype and addrtype values than the ones 383 listed above. 385 7.3. Bandwidth (b=) 387 An offerer and answerer MUST use the rules and restrictions defined 388 in [I-D.mmusic-sdp-mux-attributes] for when associating the SDP 389 bandwidth (b=) line with bundled "m=" lines. 391 7.4. Attributes (a=) 393 An offerer and answerer MUST use the rules and restrictions defined 394 in [I-D.mmusic-sdp-mux-attributes] for when associating SDP 395 attributes with bundled "m=" lines. 397 8. SDP Offer/Answer Procedures 399 8.1. General 401 This section describes the SDP Offer/Answer [RFC3264] procedures for: 403 o Negotiating and creating of a BUNDLE group; 405 o Selecting the BUNDLE addresses (offerer BUNDLE address and 406 answerer BUNDLE address); 408 o Adding an "m=" line to a BUNDLE group; 410 o Moving an "m=" line out of a BUNDLE group; and 412 o Disabling an "m=" line within a BUNDLE group. 414 The generic rules and procedures defined in [RFC3264] and [RFC5888] 415 also apply to the BUNDLE extension. For example, if an offer is 416 rejected by the answerer, the previously negotiated SDP parameters 417 and characteristics (including those associated with a BUNDLE group) 418 apply. Hence, if an offerer generates an offer in which the offerer 419 wants to create a BUNDLE group, and the answerer rejects the offer, 420 the BUNDLE group is not created. 422 The procedures in this section are independent of the media type or 423 "m=" line proto value represented by a bundled "m=" line. Section 10 424 defines additional considerations for RTP based media. Section 6 425 defines additional considerations for the usage of the SDP 'bundle- 426 only' attribute. Section 11 defines additional considerations for 427 the usage of Interactive Connectivity Establishment (ICE) [RFC5245] 428 mechanism . 430 SDP offers and answers can contain multiple BUNDLE groups. The 431 procedures in this section apply independently to a given BUNDLE 432 group. 434 8.2. Generating the Initial SDP Offer 436 8.2.1. General 438 When an offerer generates an initial offer, in order to create a 439 BUNDLE group, it MUST: 441 o Assign a unique address to each "m=" line within the offer, 442 following the procedures in [RFC3264], unless the media line is a 443 'bundle-only' "m=" line (see below); 445 o Add an SDP 'group:BUNDLE' attribute to the offer; 447 o Place the identification-tag of each bundled "m=" line in the SDP 448 'group:BUNDLE' attribute identification-tag list; and 450 o Indicate which unique address the offerer suggests as the offerer 451 BUNDLE address [Section 8.2.2]. 453 If the offerer wants to request that the answerer accepts a given 454 bundled "m=" line only if the answerer keeps the "m=" line within the 455 BUNDLE group, the offerer MUST: 457 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 458 "m=" line; and 460 o Assign a zero port value to the "m=" line. 462 NOTE: If the offerer assigns a zero port value to an "m=" line, but 463 does not also associate an SDP 'bundle-only' attribute with the "m=" 464 line, it is an indication that the offerer wants to disable the "m=" 465 line [Section 8.5.5]. 467 [Section 17.1] shows an example of an initial offer. 469 8.2.2. Suggesting the offerer BUNDLE address 471 In the offer, the address assigned to the "m=" line associated with 472 the offerer BUNDLE-tag indicates the address that the offerer 473 suggests as the offerer BUNDLE address. 475 8.3. Generating the SDP Answer 477 8.3.1. General 479 When an answerer generates an answer that contains a BUNDLE group, 480 the following general SDP grouping framework restrictions, defined in 481 [RFC5888], also apply to the BUNDLE group: 483 o The answerer MUST NOT include a BUNDLE group in the answer, unless 484 the offerer requested the BUNDLE group to be created in the 485 associated offer; and 487 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 488 unless the offerer requested the "m=" line to be within that 489 BUNDLE group in the associated offer. 491 If the answer contains a BUNDLE group, the answerer MUST: 493 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 495 o Select an Answerer BUNDLE Address [Section 8.3.3]; 497 The answerer is allowed to select a new Answerer BUNDLE address each 498 time it generates an answer to an offer. 500 If the answerer does not want to keep an "m=" line within a BUNDLE 501 group, it MUST: 503 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 505 o Reject the "m=" line [Section 8.3.5]; 507 If the answerer keeps a bundle-only "m=" line within the BUNDLE 508 group, it follows the procedures (assigns the answerer BUNDLE address 509 to the "m=" line etc) for any other "m=" line kept within the BUNDLE 510 group. 512 If the answerer does not want to keep a bundle-only "m=" line within 513 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 515 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 516 any "m=" line in an answer. 518 NOTE: If a bundled "m=" line in an offer contains a zero port value, 519 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 520 is an indication that the offerer wants to disable the "m=" line 521 [Section 8.5.5]. 523 8.3.2. Answerer Selection of Offerer Bundle Address 525 In an offer, the address (unique or shared) assigned to the bundled 526 "m=" line associated with the offerer BUNDLE-tag indicates the 527 address that the offerer suggests as the offerer BUNDLE address 528 [Section 8.2.2]. The answerer MUST check whether that "m=" line 529 fulfills the following criteria: 531 o The answerer will not move the "m=" line out of the BUNDLE group 532 [Section 8.3.4]; 534 o The answerer will not reject the "m=" line [Section 8.3.5]; and 536 o The "m=" line does not contain a zero port value. 538 If all of the criteria above are fulfilled, the answerer MUST select 539 the address associated with the "m=" line as the offerer BUNDLE 540 address. In the answer, the answerer BUNDLE-tag represents the "m=" 541 line, and the address associated with the "m=" line in the offer 542 becomes the offerer BUNDLE address. 544 If one or more of the criteria are not fulfilled, the answerer MUST 545 select the next identification-tag in the identification-tag list, 546 and perform the same criteria check for the "m=" line associated with 547 that identification-tag. If there are no more identification-tags in 548 the identification-tag list, the answerer MUST NOT create the BUNDLE 549 group. In addition, unless the answerer rejects the whole offer, the 550 answerer MUST apply the answerer procedures for moving an "m=" line 551 out of a BUNDLE group [Section 8.3.4] to each bundled "m=" line in 552 the offer when creating the answer. 554 [Section 17.1] shows an example of an offerer BUNDLE address 555 selection. 557 8.3.3. Answerer Selection of Answerer BUNDLE Address 559 When the answerer selects a BUNDLE address for itself, referred to as 560 the answerer BUNDLE address, it MUST assign that address to each 561 bundled "m=" line within the created BUNDLE group in the answer. 563 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 564 line that is not within the BUNDLE group, or to an "m=" line that is 565 within another BUNDLE group. 567 [Section 17.1] shows an example of an answerer BUNDLE address 568 selection. 570 8.3.4. Moving A Media Description Out Of A BUNDLE Group 572 When an answerer wants to move an "m=" line out of a BUNDLE group, it 573 MUST first check the following criteria: 575 o In the associated offer, the "m=" line contains a shared address 576 (e.g. a previously selected offerer BUNDLE address); or 578 o In the associated offer, if an SDP 'bundle-only' attribute is 579 associated with the "m=" line, and if the "m=" line contains a 580 zero port value. 582 If either criteria above is fulfilled, the answerer MUST reject the 583 "m=" line [Section 8.3.5]. 585 Otherwise, if in the associated offer the "m=" line contains a unique 586 address, the answerer MUST assign a unique address to the "m=" line 587 in the answer (the answerer does not reject the "m=" line). 589 In addition, in either case above, the answerer MUST NOT place the 590 identification-tag, associated with the moved "m=" line, in the SDP 591 'group' attribute identification-tag list associated with the BUNDLE 592 group. 594 8.3.5. Rejecting A Media Description In A BUNDLE Group 596 When an answerer rejects an "m=" line, it MUST assign an address with 597 a zero port value to the "m=" line in the answer, according to the 598 procedures in [RFC4566]. 600 In addition, the answerer MUST NOT place the identification-tag, 601 associated with the rejected "m=" line, in the SDP 'group' attribute 602 identification-tag list associated with the BUNDLE group. 604 8.4. Offerer Processing of the SDP Answer 606 When an offerer receives an answer, if the answer contains a BUNDLE 607 group, the offerer MUST check that any bundled "m=" line in the 608 answer was indicated as bundled in the associated offer. If there is 609 no mismatch, the offerer MUST use the offerer BUNDLE address, 610 selected by the answerer [Section 8.3.2], as the address for each 611 bundled "m=" line. 613 NOTE: As the answerer might reject one or more bundled "m=" lines, or 614 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 615 line in the offer might not be indicated as bundled in the answer. 617 If the answer does not contain a BUNDLE group, the offerer MUST 618 process the answer as a normal answer. 620 8.5. Modifying the Session 622 8.5.1. General 624 When an offerer generates a subsequent offer, it MUST assign the 625 previously selected offerer BUNDLE address [Section 8.3.2], to each 626 bundled "m=" line (including any bundle-only "m=" line), except if: 628 o The offerer suggests a new offerer BUNDLE address [Section 8.5.2]; 630 o The offerer wants to add a bundled "m=" line to the BUNDLE group 631 [Section 8.5.3]; 633 o The offerer wants to move a bundled "m=" line out of the BUNDLE 634 group [Section 8.5.4]; or 636 o The offerer wants to disable the bundled "m=" line 637 [Section 8.5.5]. 639 In addition, the offerer MUST select an offerer BUNDLE-tag 640 [Section 8.2.2] associated with the previously selected offerer 641 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 642 address. 644 8.5.2. Suggesting a new offerer BUNDLE address 646 When an offerer generates an offer, in which it suggests a new 647 offerer BUNDLE address [Section 8.2.2], the offerer MUST: 649 o Assign the address (shared address) to each "m=" line within the 650 BUNDLE group; or 652 o Assign the address (unique address) to one bundled "m=" line. 654 In addition, the offerer MUST indicate that the address is the new 655 suggested offerer BUNDLE address [Section 8.2.2]. 657 NOTE: Unless the offerer assigns the new suggested offerer BUNDLE 658 address to each bundled "m=" line, it can assign unique addresses to 659 any number of bundled "m=" lines (and the previously selected offerer 660 BUNDLE address to any remaining bundled "m=" line) if it wants to 661 suggest multiple alternatives for the new offerer BUNDLE address. 663 8.5.3. Adding a media description to a BUNDLE group 665 When an offerer generates an offer, in which it wants to add a 666 bundled "m=" line to a BUNDLE group, the offerer MUST: 668 o Assign a unique address to the "m=" line; 670 o Assign the previously selected offerer BUNDLE address to the "m=" 671 line; or 673 o If the offerer assigns a new (shared address) suggested offerer 674 BUNDLE address to each bundled "m=" line [Section 8.5.2], also 675 assign that address to the added "m=" line. 677 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 678 identification-tag list with the BUNDLE group [Section 8.2.2] by 679 adding the identification-tag associated with the added "m=" line to 680 the list. 682 NOTE: Assigning a unique address to the "m=" line allows the answerer 683 to move the "m=" line out of the BUNDLE group [Section 8.3.4], 684 without having to reject the "m=" line. 686 If the offerer assigns a unique address to the added "m=" line, and 687 if the offerer suggests that address as the new offerer BUNDLE 688 address [Section 8.5.2], the offerer BUNDLE-tag MUST represent the 689 added "m=" line [Section 8.2.2]. 691 If the offerer assigns a new suggested offerer BUNDLE address to each 692 bundled "m=" line [Section 8.5.2], including the added "m=" line, the 693 offerer BUNDLE-tag MAY represent the added "m=" line [Section 8.2.2]. 695 [Section 17.3] shows an example where an offerer sends an offer in 696 order to add a bundled "m=" line to a BUNDLE group. 698 8.5.4. Moving A Media Description Out Of A BUNDLE Group 700 When an offerer generates an offer, in which it wants to move a 701 bundled "m=" line out of a BUNDLE group it was added to in a previous 702 offer/answer transaction, the offerer: 704 o MUST assign a unique address to the "m=" line; and 705 o MUST NOT place the identification-tag associated with the "m=" 706 line in the SDP 'group:BUNDLE' attribute identification-tag list 707 associated with the BUNDLE group. 709 NOTE: If the removed "m=" line is associated with the previously 710 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 711 [Section 8.2.2]. 713 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 714 added to another BUNDLE group, the offerer applies the procedures in 715 [Section 8.5.3] to the "m=" line. 717 [Section 17.4] shows an example of an offer for moving an "m=" line 718 out of a BUNDLE group. 720 8.5.5. Disabling A Media Description In A BUNDLE Group 722 When an offerer generates an offer, in which it wants to disable a 723 bundled "m=" line (added to the BUNDLE group in a previous offer/ 724 answer transaction), the offerer: 726 o MUST assign an address with a zero port value to the "m=" line, 727 following the procedures in [RFC4566]; and 729 o MUST NOT place the identification-tag associated with the "m=" 730 line in the SDP 'group:BUNDLE' attribute identification-tag list 731 associated with the BUNDLE group. 733 [Section 17.5] shows an example of an offer for disabling an "m=" 734 line within a BUNDLE group. 736 9. Protocol Identification 738 9.1. General 740 Each "m=" line within a BUNDLE group MUST use the same transport- 741 layer protocol. If bundled "m=" lines use different protocols on top 742 of the transport-layer protocol, there MUST exist a publicly 743 available specification which describes a mechanism, for this 744 particular protocol combination, how to associate a received packet 745 with the correct protocol. 747 In addition, if a received packet can be associated with more than 748 one bundled "m=" line, there MUST exist a publicly available 749 specification which describes a mechanism for associating the 750 received packet with the correct "m=" line. 752 This document describes a mechanism to identify the protocol of a 753 received packet among the STUN, DTLS and SRTP protocols (in any 754 combination), when UDP is used as transport-layer protocol, but does 755 not describe how to identify different protocols transported on DTLS. 756 While the mechanism is generally applicable to other protocols and 757 transport-layers protocols, any such use requires further 758 specification around how to multiplex multiple protocols on a given 759 transport-layer protocols, and how to associate received packets with 760 the correct protocols. 762 9.2. STUN, DTLS, SRTP 764 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 765 protocol of a received packet among the STUN, Datagram Transport 766 Layer Security (DTLS) and SRTP protocols (in any combination). If an 767 offer or answer includes bundled "m=" lines that represent these 768 protocols, the offerer or answerer MUST support the mechanism 769 described in [RFC5764], and no explicit negotiation is required in 770 order to indicate support and usage of the mechanism. 772 [RFC5764] does not describe how to identify different protocols 773 transported on DTLS, only how to identify the DTLS protocol itself. 774 If multiple protocols are transported on DTLS, there MUST exist a 775 specification describing a mechanism for identifying each individual 776 protocol. In addition, if a received DTLS packet can be associated 777 with more than one "m=" line, there MUST exist a specification which 778 describes a mechanism for associating the received DTLS packet with 779 the correct "m=" line. 781 [Section 10.2] describes how to associate a received (S)RTP packet 782 with the correct "m=" line. 784 10. RTP Considerations 786 10.1. Single RTP Session 788 10.1.1. General 790 All RTP-based media within a single BUNDLE group belong to a single 791 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 792 sessions, one per BUNDLE group. 794 Since a single RTP session is used for each bundle group, all "m=" 795 lines representing RTP-based media in a bundle group will share a 796 single SSRC numbering space [RFC3550]. 798 The following rules and restrictions apply for a single RTP session: 800 o A specific payload type value can be used in multiple bundled "m=" 801 lines if each codec associated with the payload type number shares 802 an identical codec configuration [Section 10.1.2]. 804 o The proto value in each bundled RTP-based "m=" line MUST be 805 identical (e.g. RTP/AVPF). 807 o The RTP MID header extension MUST be enabled, by associating an 808 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 809 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 810 in every offer and answer. 812 o A given SSRC MUST NOT transmit RTP packets using payload types 813 that originate from different bundled "m=" lines. 815 NOTE: The last bullet above is to avoid sending multiple media types 816 from the same SSRC. If transmission of multiple media types are done 817 with time overlap, RTP and RTCP fail to function. Even if done in 818 proper sequence this causes RTP Timestamp rate switching issues 819 [RFC7160]. However, once an SSRC has left the RTP session (by 820 sending an RTCP BYE packet), that SSRC value can later be reused by 821 another source(possible associated with a different bundled "m=" 822 line. 824 10.1.2. Payload Type (PT) Value Reuse 826 Multiple bundled "m=" lines might represent RTP based media. As all 827 RTP based media associated with a BUNDLE group belong to the same RTP 828 session, in order for a given payload type value to be used inside 829 more than one bundled "m=" line, all codecs associated with the 830 payload type number MUST share an identical codec configuration. 831 This means that the codecs MUST share the same media type, encoding 832 name, clock rate and any parameter that can affect the codec 833 configuration and packetization. [I-D.mmusic-sdp-mux-attributes] 834 lists SDP attributes, whose attribute values must be identical for 835 all codecs that use the same payload type value. 837 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 839 There are multiple mechanisms that can be used by an endpoint in 840 order to associate received RTP/RTCP packets with a bundled "m=" 841 line. Such mechanisms include using the payload type value carried 842 inside the RTP packets, the SSRC values carried inside the RTP 843 packets, and other "m=" line specific information carried inside the 844 RTP packets. 846 As all RTP/RTCP packets associated with a BUNDLE group are received 847 (and sent) using single address:port combinations, the local 848 address:port combination cannot be used to associate received RTP 849 packets with the correct "m=" line. 851 As described in [Section 10.1.2], the same payload type value might 852 be used inside RTP packets described by multiple "m=" lines. In such 853 cases, the payload type value cannot be used to associate received 854 RTP packets with the correct "m=" line. 856 An offerer and answerer can inform each other which SSRC values they 857 will use or RTP and RTCP by using the SDP 'ssrc' attribute [RFC5576]. 858 To allow for proper association with this mechanism, the 'ssrc' 859 attribute needs to be associated with each "m=" line that shares a 860 payload type with any other "m=" line in the same bundle. As the 861 SSRC values will be carried inside the RTP/RTCP packets, the offerer 862 and answerer can then use that information to associate received RTP 863 packets with the correct "m=" line. However, an offerer will not 864 know which SSRC values the answerer will use until it has received 865 the answer providing that information. Due to this, before the 866 offerer has received the answer, the offerer will not be able to 867 associate received RTP/RTCP packets with the correct "m=" line using 868 the SSRC values. 870 In order for an offerer and answerer to always be able to associate 871 received RTP and RTCP packets with the correct "m=" line, an offerer 872 and answerer using the BUNDLE extension MUST support the mechanism 873 defined in Section 14, where the remote endpoint inserts the 874 identification-tag associated with an "m=" line in RTP and RTCP 875 packets associated with that "m=" line. 877 10.3. RTP/RTCP Multiplexing 879 10.3.1. General 881 When a BUNDLE group, which contains RTP based media, is created, the 882 offerer and answerer MUST negotiate whether to enable RTP/RTCP 883 multiplexing for the RTP based media associated with the BUNDLE group 884 [RFC5761]. 886 If RTP/RTCP multiplexing is enabled, the same address:port 887 combination will be used for receiving (and sending) all RTP packets 888 and the RTCP packets associated with the BUNDLE group. Each endpoint 889 will send the packets towards the BUNDLE address of the other 890 endpoint. 892 If RTP/RTCP multiplexing is not enabled, separate address:port 893 combinations will be used for receiving (and sending) the RTP packets 894 and the RTCP packets. If the remote endpoint has associated an SDP 895 'rtcp' attribute with the "m=" line associated with the BUNDLE-tag, 896 the attribute value will be used for sending all RTCP packets 897 associated with the BUNDLE group towards that endpoint. 899 10.3.2. SDP Offer/Answer Procedures 901 10.3.2.1. General 903 This section describes how an offerer and answerer can use the SDP 904 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 905 to negotiate usage of RTP/RTCP multiplexing for RTP based media 906 associated with a BUNDLE group. 908 10.3.2.2. Generating the Initial SDP Offer 910 When an offerer generates an initial offer, if the offerer wants to 911 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 912 offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with 913 each bundled RTP-based "m=" line (including any bundle-only "m=" 914 line) in the offer. 916 If the offerer does not want to negotiate usage of RTP/RTCP 917 multiplexing, it MUST NOT associate an SDP 'rtcp-mux' attribute with 918 any bundled "m=" line in the offer. 920 In addition, the offerer can associate an SDP 'rtcp' attribute 921 [RFC3605] with one or more bundled RTP-based "m=" lines (including 922 any bundle-only "m=" line) in the offer, in order to provide a port 923 for receiving RTCP packets (if the answerer does not accept usage of 924 RTP/RTCP multiplexing, or if the offerer does not want to negotiate 925 usage of RTP/RTCP multiplexing). 927 In the initial offer, the IP address and port combination for RTCP 928 MUST be unique in each bundled RTP-based "m=" line, similar to RTP. 930 NOTE: In case the offer wants to receive RTCP packets on the next 931 higher port value, the SDP 'rtcp' attribute is not needed. 933 10.3.2.3. Generating the SDP Answer 935 When an answerer generates an answer, if the offerer indicated 936 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 937 the associated offer, the answerer MUST either accept or reject the 938 usage of RTP/RTCP multiplexing for the whole BUNDLE group in the 939 answer. 941 If the answerer accepts the usage of RTP/RTCP multiplexing within the 942 BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each 943 bundled RTP-based "m=" line in the answer. The answerer MUST NOT 944 associate an SDP 'rtcp' attribute with any bundled "m=" line in the 945 answer. The answerer will use the port value of the selected offerer 946 BUNDLE address for sending RTP and RTCP packets associated with each 947 RTP-based bundled "m=" line towards the offerer. 949 If the answerer does not accept the usage of RTP/RTCP multiplexing 950 within the BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux' 951 attribute with any bundled "m=" line in the answer. The answerer 952 will use the RTP and RTCP port values associated with the selected 953 offerer BUNDLE address for sending RTP and RTCP packets associated 954 with each RTP-based bundled "m=" line towards the offerer. 956 In addition, if the answerer rejects the usage of RTP/RTCP 957 multiplexing within the BUNDLE group, it MAY associate an SDP 'rtcp' 958 attribute, with identical attribute values, with each RTP-based 959 bundled "m=" line in the answer, in order to provide a port value for 960 receiving RTCP packets from the offerer. 962 NOTE: In case the answerer wants to receive RTCP packets on the next 963 higher port value, the SDP 'rtcp' attribute is not needed. 965 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 966 negotiated in a previous offer/answer transaction, and if the offerer 967 indicates that it wants to continue using RTP/RTCP multiplexing in a 968 subsequent offer, the answerer MUST associate an SDP 'rtcp-mux' 969 attribute with each bundled "m=" line in the answer. I.e. the 970 answerer MUST NOT disable the usage of RTP/RTCP multiplexing. 972 If the usage of RTP/RTCP multiplexing within a BUNDLE group has not 973 been negotiated in a previous offer/answer transaction, and if the 974 offerer indicates that it wants to use RTP/RTCP multiplexing in a 975 subsequent offer, the answerer either accepts or rejects the usage, 976 using the procedures above. 978 10.3.2.4. Offerer Processing of the SDP Answer 980 When an offerer receives an answer, if the answerer has accepted the 981 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 982 follows the procedures for RTP/RTCP multiplexing defined in 983 [RFC5761]. The offerer will use the port value associated with the 984 answerer BUNDLE address for sending RTP and RTCP packets associated 985 with each RTP-based bundled "m=" line towards the answerer. 987 If the answerer did not accept the usage of RTP/RTCP multiplexing 988 (see Section 10.3.2.3), the offerer will use separate address:port 989 combinations for sending RTP and RTCP packets towards the answerer. 990 If the answerer associated an SDP 'rtcp' attribute with the "m=" line 991 representing the answerer BUNDLE address, the offerer will use the 992 attribute port value for sending RTCP packets associated with each 993 bundled RTP-based "m=" line towards the answerer. Otherwise the 994 offerer will use the next higher port value associated with the 995 answerer BUNDLE address for sending RTCP packets towards the 996 answerer. 998 10.3.2.5. Modifying the Session 1000 When an offerer generates a subsequent offer, if it wants to 1001 negotiate the usage of RTP/RTCP multiplexing within a BUNDLE group, 1002 or if it wants to continue the use of previously negotiated RTP/RTCP 1003 multiplexing, it MUST associate an SDP 'rtcp-mux' attribute with each 1004 RTP-based bundled "m=" line (including any bundled "m=" line that the 1005 offerer wants to add to the BUNDLE group), unless the offerer wants 1006 to disable or remove the "m=" line from the BUNDLE group. 1008 If the offerer does not want to negotiate the usage of RTP/RTCP 1009 multiplexing within the BUNDLE group, or if it wants to disable 1010 previously negotiated usage of RTP/RTCP multiplexing, it MUST NOT 1011 associate an SDP 'rtcp-mux' and attribute with any bundled "m=" line 1012 in the subsequent offer. 1014 In addition, if the offerer does not indicate support of RTP/RTCP 1015 multiplexing within the subsequent offer, it MAY associate an SDP 1016 'rtcp' attribute, with identical attribute values, with each RTP- 1017 based bundled "m=" line (including any bundled "m=" line that the 1018 offerer wants to add to the BUNDLE group), in order to provide a port 1019 for receiving RTCP packets. 1021 NOTE: It is RECOMMENDED that, once the usage of RTP/RTCP multiplexing 1022 has been negotiated within a BUNDLE group, that the usage is not 1023 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 1024 answerer need to reserve new ports, to be used for sending and 1025 receiving RTCP packets. Similar, if the usage of a specific RTCP 1026 port has been negotiated within a BUNDLE group, it is RECOMMENDED 1027 that the port value is not modified. 1029 11. ICE Considerations 1031 11.1. General 1033 This section describes how to use the BUNDLE grouping extension 1034 together with the Interactive Connectivity Establishment (ICE) 1035 mechanism [RFC5245]. 1037 The procedures defined in [RFC5245] also apply to usage of ICE with 1038 BUNDLE, with the following exception: 1040 o When BUNDLE addresses for a BUNDLE group have been selected for 1041 both endpoints, ICE connectivity checks and keep-alives only need 1042 to be performed for the whole BUNDLE group, instead of per bundled 1043 "m=" line. 1045 Support and usage of ICE mechanism together with the BUNDLE extension 1046 is OPTIONAL. 1048 11.2. SDP Offer/Answer Procedures 1050 11.2.1. General 1052 When an offerer assigns a unique address to a bundled "m=" line 1053 (excluding any bundle-only "m=" line), it MUST also associate unique 1054 ICE candidates [RFC5245] to the "m=" line. 1056 An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line 1057 with a zero port value. 1059 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1060 inherit the candidates associated with the selected offerer BUNDLE 1061 address. An answerer that does not support BUNDLE would not accept a 1062 bundle-only "m=" line. 1064 When an offerer or answerer assigns a shared address (i.e. a 1065 previously selected BUNDLE address) to one or more bundled "m=" 1066 lines, it MUST associate identical ICE candidates (referred to as 1067 shared ICE candidates) to each of those "m=" lines. 1069 11.2.2. Generating the Initial SDP Offer 1071 When an offerer generates an initial offer, it assigns unique or 1072 shared ICE candidates to the bundled "m=" lines, according to 1073 Section 11.1. 1075 11.2.3. Generating the SDP Answer 1077 When an answerer generates an answer that contains a BUNDLE group, 1078 the answerer MUST assign shared ICE candidates to each bundled "m=" 1079 line (including "m=" lines that were indicated as bundle-only in the 1080 associated offer) in the answer. 1082 11.2.4. Offerer Processing of the SDP Answer 1084 When an offerer receives an answer, if the answerer supports and uses 1085 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1086 the same ICE candidates, associated with the "m=" line representing 1087 the offerer BUNDLE address (selected by the answerer), to each 1088 bundled "m=" line. 1090 11.2.5. Modifying the Session 1092 When an offerer generates a subsequent offer, it assigns unique or 1093 shared ICE candidates to the bundled "m=" lines, according to 1094 (Section 11.1). 1096 12. DTLS Considerations 1098 One or more media streams within a BUNDLE group might use the 1099 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1100 to encrypt the data, or to negotiate encryption keys if another 1101 encryption mechanism is used to encrypt media. 1103 When DTLS is used within a BUNDLE group, the following rules apply: 1105 o There can only be one DTLS association [RFC6347] associated with 1106 the BUNDLE group; 1108 o Each usage of the DTLS association within the BUNDLE group MUST 1109 use the same mechanism for determining which endpoints (the 1110 offerer or answerer) becomes DTLS client and DTLS server; and 1112 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1113 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1114 [RFC5764], The client MUST include the extension even if the usage 1115 of DTLS-SRTP is not negotiated as part of the multimedia session 1116 (e.g. SIP session [RFC3261]. 1118 NOTE: The inclusion of the 'use_srtp' extension during the initial 1119 DTLS handshake ensures that a DTLS renegotiation will not be required 1120 in order to include the extension, in case DTLS-SRTP encrypted media 1121 is added to the BUNDLE group later during the multimedia session. 1123 13. Update to RFC 3264 1125 13.1. General 1127 This section replaces the text of the following sections of RFC 3264: 1129 o Section 5.1 (Unicast Streams). 1131 o Section 8.2 (Removing a Media Stream). 1133 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1135 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1137 For recvonly and sendrecv streams, the port number and address in the 1138 offer indicate where the offerer would like to receive the media 1139 stream. For sendonly RTP streams, the address and port number 1140 indirectly indicate where the offerer wants to receive RTCP reports. 1141 Unless there is an explicit indication otherwise, reports are sent to 1142 the port number one higher than the number indicated. The IP address 1143 and port present in the offer indicate nothing about the source IP 1144 address and source port of RTP and RTCP packets that will be sent by 1145 the offerer. A port number of zero in the offer indicates that the 1146 stream is offered but MUST NOT be used. This has no useful semantics 1147 in an initial offer, but is allowed for reasons of completeness, 1148 since the answer can contain a zero port indicating a rejected stream 1149 (Section 6). Furthermore, existing streams can be terminated by 1150 setting the port to zero (Section 8). In general, a port number of 1151 zero indicates that the media stream is not wanted. 1153 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1155 For recvonly and sendrecv streams, the port number and address in the 1156 offer indicate where the offerer would like to receive the media 1157 stream. For sendonly RTP streams, the address and port number 1158 indirectly indicate where the offerer wants to receive RTCP reports. 1159 Unless there is an explicit indication otherwise, reports are sent to 1160 the port number one higher than the number indicated. The IP address 1161 and port present in the offer indicate nothing about the source IP 1162 address and source port of RTP and RTCP packets that will be sent by 1163 the offerer. A port number of zero in the offer by default indicates 1164 that the stream is offered but MUST NOT be used, but an extension 1165 mechanism might specify different semantics for the usage of a zero 1166 port value. Furthermore, existing streams can be terminated by 1167 setting the port to zero (Section 8). In general, a port number of 1168 zero by default indicates that the media stream is not wanted. 1170 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1172 A stream that is offered with a port of zero MUST be marked with port 1173 zero in the answer. Like the offer, the answer MAY omit all 1174 attributes present previously, and MAY list just a single media 1175 format from amongst those in the offer. 1177 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1179 A stream that is offered with a port of zero MUST by default be 1180 marked with port zero in the answer, unless an extension mechanism, 1181 which specifies semantics for the usage of a non-zero port value, is 1182 used. If the stream is marked with port zero in the answer, the 1183 answer MAY omit all attributes present previously, and MAY list just 1184 a single media format from amongst those in the offer." 1186 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1188 RFC 2543 [10] specified that placing a user on hold was accomplished 1189 by setting the connection address to 0.0.0.0. Its usage for putting 1190 a call on hold is no longer recommended, since it doesn't allow for 1191 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1192 with connection oriented media. However, it can be useful in an 1193 initial offer when the offerer knows it wants to use a particular set 1194 of media streams and formats, but doesn't know the addresses and 1195 ports at the time of the offer. Of course, when used, the port 1196 number MUST NOT be zero, which would specify that the stream has been 1197 disabled. An agent MUST be capable of receiving SDP with a 1198 connection address of 0.0.0.0, in which case it means that neither 1199 RTP nor RTCP should be sent to the peer. 1201 13.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1203 RFC 2543 [10] specified that placing a user on hold was accomplished 1204 by setting the connection address to 0.0.0.0. Its usage for putting 1205 a call on hold is no longer recommended, since it doesn't allow for 1206 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1207 with connection oriented media. However, it can be useful in an 1208 initial offer when the offerer knows it wants to use a particular set 1209 of media streams and formats, but doesn't know the addresses and 1210 ports at the time of the offer. Of course, when used, the port 1211 number MUST NOT be zero, if it would specify that the stream has been 1212 disabled. However, an extension mechanism might specify different 1213 semantics of the zero port number usage. An agent MUST be capable of 1214 receiving SDP with a connection address of 0.0.0.0, in which case it 1215 means that neither RTP nor RTCP should be sent to the peer. 1217 14. RTP/RTCP extensions for identification-tag transport 1219 14.1. General 1221 SDP Offerers and Answerers [RFC3264] can associate identification- 1222 tags with "m=" lines within SDP Offers and Answers, using the 1223 procedures in [RFC5888]. Each identification-tag uniquely represents 1224 an "m=" line. 1226 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1227 used to carry identification-tags within RTCP SDES packets. This 1228 section also defines a new RTP header extension [RFC5285], which is 1229 used to carry identification-tags in RTP packets. 1231 The SDES item and RTP header extension make it possible for a 1232 receiver to associate received RTCP- and RTP packets with a specific 1233 "m=" line, to which the receiver has assigned an identification-tag, 1234 even if those "m=" lines are part of the same RTP session. A media 1235 recipient informs the media sender about the identification-tag 1236 associated with an "m=" line through the use of an 'mid' attribute 1237 [RFC5888]. The media sender then inserts the identification-tag in 1238 RTCP and RTP packets sent to the media recipient. 1240 NOTE: This text above defines how identification-tags are carried in 1241 SDP Offers and Answers. The usage of other signalling protocols for 1242 carrying identification-tags is not prevented, but the usage of such 1243 protocols is outside the scope of this document. 1245 [RFC3550] defines general procedures regarding the RTCP transmission 1246 interval. The RTCP MID SDES item SHOULD be sent in the first few 1247 RTCP packets sent on joining the session, and SHOULD be sent 1248 regularly thereafter. The exact number of RTCP packets in which this 1249 SDES item is sent is intentionally not specified here, as it will 1250 depend on the expected packet loss rate, the RTCP reporting interval, 1251 and the allowable overhead. 1253 The RTP MID header extension SHOULD be included in some RTP packets 1254 at the start of the session and whenever the SSRC changes. It might 1255 also be useful to include the header extension in RTP packets that 1256 comprise random access points in the media (e.g., with video 1257 I-frames). The exact number of RTP packets in which this header 1258 extension is sent is intentionally not specified here, as it will 1259 depend on expected packet loss rate and loss patterns, the overhead 1260 the application can tolerate, and the importance of immediate receipt 1261 of the identification-tag. 1263 For robustness purpose, endpoints need to be prepared for situations 1264 where the reception of the identification-tag is delayed, and SHOULD 1265 NOT terminate sessions in such cases, as the identification-tag is 1266 likely to arrive soon. 1268 14.2. RTCP MID SDES Item 1270 0 1 2 3 1271 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 1272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1273 | MID=TBD | length | identification-tag ... 1274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1276 The identification-tag payload is UTF-8 encoded, as in SDP. 1278 The identification-tag is not zero terminated. 1280 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1281 identifier value.] 1283 14.3. RTP MID Header Extension 1285 The payload, containing the identification-tag, of the RTP MID header 1286 extension element can be encoded using either the one-byte or two- 1287 byte header [RFC5285]. The identification-tag payload is UTF-8 1288 encoded, as in SDP. 1290 The identification-tag is not zero terminated. Note, that set of 1291 header extensions included in the packet needs to be padded to the 1292 next 32-bit boundary using zero bytes [RFC5285]. 1294 As the identification-tag is included in either an RTCP SDES item or 1295 an RTP header extension, or both, there should be some consideration 1296 about the packet expansion caused by the identification-tag. To 1297 avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the 1298 header extension's size needs to be taken into account when the 1299 encoding media. 1301 It is recommended that the identification-tag is kept short. Due to 1302 the properties of the RTP header extension mechanism, when using the 1303 one-byte header, a tag that is 1-3 bytes will result in that a 1304 minimal number of 32-bit words are used for the RTP header extension, 1305 in case no other header extensions are included at the same time. 1306 Note, do take into account that some single characters when UTF-8 1307 encoded will result in multiple octets. 1309 15. IANA Considerations 1311 15.1. New SDES item 1313 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1314 document.] 1316 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1317 identifier value.] 1319 This document adds the MID SDES item to the IANA "RTCP SDES item 1320 types" registry as follows: 1322 Value: TBD 1323 Abbrev.: MID 1324 Name: Media Identification 1325 Reference: RFCXXXX 1327 15.2. New RTP Header Extension URI 1329 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1330 document.] 1332 This document defines a new extension URI in the RTP Compact Header 1333 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1334 Parameters registry, according to the following data: 1336 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1337 Description: Media identification 1338 Contact: christer.holmberg@ericsson.com 1339 Reference: RFCXXXX 1341 15.3. New SDP Attribute 1343 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1344 document.] 1346 This document defines a new SDP media-level attribute, 'bundle-only', 1347 according to the following data: 1349 Attribute name: bundle-only 1350 Type of attribute: media 1351 Subject to charset: No 1352 Purpose: Request a media description to be accepted 1353 in the answer only if kept within a BUNDLE 1354 group by the answerer. 1355 Appropriate values: N/A 1356 Contact name: Christer Holmberg 1357 Contact e-mail: christer.holmberg@ericsson.com 1358 Reference: RFCXXXX 1360 15.4. New SDP Group Semantics 1362 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1363 document.] 1364 This document registers the following semantics with IANA in the 1365 "Semantics for the "group" SDP Attribute" subregistry (under the 1366 "Session Description Protocol (SDP) Parameters" registry: 1368 Semantics Token Reference 1369 ------------------------------------- ------ --------- 1370 Media bundling BUNDLE [RFCXXXX] 1372 16. Security Considerations 1374 The security considerations defined in [RFC3264] and [RFC5888] apply 1375 to the BUNDLE extension. Bundle does not change which information 1376 flows over the network but only changes which ports that information 1377 is flowing on and thus has very little impact on the security of the 1378 RTP sessions. 1380 When the BUNDLE extension is used, a single set of security 1381 credentials might be used for all media streams associated with a 1382 BUNDLE group. 1384 When the BUNDLE extension is used, the number of SSRC values within a 1385 single RTP session increases, which increases the risk of SSRC 1386 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1387 and SRTCP encryption in certain situations. 1389 17. Examples 1391 17.1. Example: Bundle Address Selection 1393 The example below shows: 1395 o 1. An offer, in which the offerer assigns a unique address to 1396 each bundled "m=" line within the BUNDLE group. 1398 o 2. An answer, in which the answerer selects the offerer BUNDLE 1399 address, and in which selects its own BUNDLE address (the answerer 1400 BUNDLE address) and assigns it each bundled "m=" line within the 1401 BUNDLE group. 1403 SDP Offer (1) 1405 v=0 1406 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1407 s= 1408 c=IN IP4 atlanta.example.com 1409 t=0 0 1410 a=group:BUNDLE foo bar 1411 m=audio 10000 RTP/AVP 0 8 97 1412 b=AS:200 1413 a=mid:foo 1414 a=rtpmap:0 PCMU/8000 1415 a=rtpmap:8 PCMA/8000 1416 a=rtpmap:97 iLBC/8000 1417 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1418 m=video 10002 RTP/AVP 31 32 1419 b=AS:1000 1420 a=mid:bar 1421 a=rtpmap:31 H261/90000 1422 a=rtpmap:32 MPV/90000 1423 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1425 SDP Answer (2) 1427 v=0 1428 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1429 s= 1430 c=IN IP4 biloxi.example.com 1431 t=0 0 1432 a=group:BUNDLE foo bar 1433 m=audio 20000 RTP/AVP 0 1434 b=AS:200 1435 a=mid:foo 1436 a=rtpmap:0 PCMU/8000 1437 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1438 m=video 20000 RTP/AVP 32 1439 b=AS:1000 1440 a=mid:bar 1441 a=rtpmap:32 MPV/90000 1442 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1444 17.2. Example: BUNDLE Extension Rejected 1446 The example below shows: 1448 o 1. An offer, in which the offerer assigns a unique address to 1449 each bundled "m=" line within the BUNDLE group. 1451 o 2. An answer, in which the answerer rejects the offered BUNDLE 1452 group, and assigns a unique addresses to each "m=" line (following 1453 normal RFC 3264 procedures). 1455 SDP Offer (1) 1457 v=0 1458 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1459 s= 1460 c=IN IP4 atlanta.example.com 1461 t=0 0 1462 a=group:BUNDLE foo bar 1463 m=audio 10000 RTP/AVP 0 8 97 1464 b=AS:200 1465 a=mid:foo 1466 a=rtpmap:0 PCMU/8000 1467 a=rtpmap:8 PCMA/8000 1468 a=rtpmap:97 iLBC/8000 1469 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1470 m=video 10002 RTP/AVP 31 32 1471 b=AS:1000 1472 a=mid:bar 1473 a=rtpmap:31 H261/90000 1474 a=rtpmap:32 MPV/90000 1475 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1477 SDP Answer (2) 1479 v=0 1480 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1481 s= 1482 c=IN IP4 biloxi.example.com 1483 t=0 0 1484 m=audio 20000 RTP/AVP 0 1485 b=AS:200 1486 a=rtpmap:0 PCMU/8000 1487 m=video 30000 RTP/AVP 32 1488 b=AS:1000 1489 a=rtpmap:32 MPV/90000 1491 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1493 The example below shows: 1495 o 1. A subsequent offer (the BUNDLE group has been created as part 1496 of a previous offer/answer transaction), in which the offerer adds 1497 a new "m=" line, represented by the "zen" identification-tag, to a 1498 previously negotiated BUNDLE group, assigns a unique address to 1499 the added "m=" line, and assigns the previously selected offerer 1500 BUNDLE address to each of the other bundled "m=" lines within the 1501 BUNDLE group. 1503 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1504 address to each bundled "m=" line (including the newly added "m=" 1505 line) within the BUNDLE group. 1507 SDP Offer (1) 1509 v=0 1510 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1511 s= 1512 c=IN IP4 atlanta.example.com 1513 t=0 0 1514 a=group:BUNDLE foo bar zen 1515 m=audio 10000 RTP/AVP 0 8 97 1516 b=AS:200 1517 a=mid:foo 1518 a=rtpmap:0 PCMU/8000 1519 a=rtpmap:8 PCMA/8000 1520 a=rtpmap:97 iLBC/8000 1521 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1522 m=video 10000 RTP/AVP 31 32 1523 b=AS:1000 1524 a=mid:bar 1525 a=rtpmap:31 H261/90000 1526 a=rtpmap:32 MPV/90000 1527 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1528 m=video 20000 RTP/AVP 66 1529 b=AS:1000 1530 a=mid:zen 1531 a=rtpmap:66 H261/90000 1532 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1534 SDP Answer (2) 1536 v=0 1537 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1538 s= 1539 c=IN IP4 biloxi.example.com 1540 t=0 0 1541 a=group:BUNDLE foo bar zen 1542 m=audio 20000 RTP/AVP 0 1543 b=AS:200 1544 a=mid:foo 1545 a=rtpmap:0 PCMU/8000 1546 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1547 m=video 20000 RTP/AVP 32 1548 b=AS:1000 1549 a=mid:bar 1550 a=rtpmap:32 MPV/90000 1551 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1552 m=video 20000 RTP/AVP 66 1553 b=AS:1000 1554 a=mid:zen 1555 a=rtpmap:66 H261/90000 1556 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1558 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1560 The example below shows: 1562 o 1. A subsequent offer (the BUNDLE group has been created as part 1563 of a previous offer/answer transaction), in which the offerer 1564 moves a bundled "m=" line out of a BUNDLE group, assigns a unique 1565 address to the moved "m=" line, and assigns the offerer BUNDLE 1566 address to each other bundled "m=" line within the BUNDLE group. 1568 o 2. An answer, in which the answerer moves the "m=" line out of 1569 the BUNDLE group, assigns unique address to the moved "m=" line, 1570 and assigns the answerer BUNDLE address to each of the remaining 1571 bundled "m=" line within the BUNDLE group. 1573 SDP Offer (1) 1575 v=0 1576 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1577 s= 1578 c=IN IP4 atlanta.example.com 1579 t=0 0 1580 a=group:BUNDLE foo bar 1581 m=audio 10000 RTP/AVP 0 8 97 1582 b=AS:200 1583 a=mid:foo 1584 a=rtpmap:0 PCMU/8000 1585 a=rtpmap:8 PCMA/8000 1586 a=rtpmap:97 iLBC/8000 1587 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1588 m=video 10000 RTP/AVP 31 32 1589 b=AS:1000 1590 a=mid:bar 1591 a=rtpmap:31 H261/90000 1592 a=rtpmap:32 MPV/90000 1593 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1594 m=video 50000 RTP/AVP 66 1595 b=AS:1000 1596 a=mid:zen 1597 a=rtpmap:66 H261/90000 1599 SDP Answer (2) 1601 v=0 1602 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1603 s= 1604 c=IN IP4 biloxi.example.com 1605 t=0 0 1606 a=group:BUNDLE foo bar 1607 m=audio 20000 RTP/AVP 0 1608 b=AS:200 1609 a=mid:foo 1610 a=rtpmap:0 PCMU/8000 1611 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1612 m=video 20000 RTP/AVP 32 1613 b=AS:1000 1614 a=mid:bar 1615 a=rtpmap:32 MPV/90000 1616 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1617 m=video 60000 RTP/AVP 66 1618 b=AS:1000 1619 a=mid:zen 1620 a=rtpmap:66 H261/90000 1622 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1623 Group 1625 The example below shows: 1627 o 1. A subsequent offer (the BUNDLE group has been created as part 1628 of a previous offer/answer transaction), in which the offerer 1629 disables a bundled "m=" line within BUNDLE group, assigns a zero 1630 port number to the disabled "m=" line, and assigns the offerer 1631 BUNDLE address to each of the other bundled "m=" lines within the 1632 BUNDLE group. 1634 o 2. An answer, in which the answerer moves the disabled "m=" line 1635 out of the BUNDLE group, assigns a zero port value to the disabled 1636 "m=" line, and assigns the answerer BUNDLE address to each of the 1637 remaining bundled "m=" line within the BUNDLE group. 1639 SDP Offer (1) 1641 v=0 1642 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1643 s= 1644 c=IN IP4 atlanta.example.com 1645 t=0 0 1646 a=group:BUNDLE foo bar 1647 m=audio 10000 RTP/AVP 0 8 97 1648 b=AS:200 1649 a=mid:foo 1650 a=rtpmap:0 PCMU/8000 1651 a=rtpmap:8 PCMA/8000 1652 a=rtpmap:97 iLBC/8000 1653 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1654 m=video 10000 RTP/AVP 31 32 1655 b=AS:1000 1656 a=mid:bar 1657 a=rtpmap:31 H261/90000 1658 a=rtpmap:32 MPV/90000 1659 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1660 m=video 0 RTP/AVP 66 1661 a=mid:zen 1662 a=rtpmap:66 H261/90000 1664 SDP Answer (2) 1666 v=0 1667 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1668 s= 1669 c=IN IP4 biloxi.example.com 1670 t=0 0 1671 a=group:BUNDLE foo bar 1672 m=audio 20000 RTP/AVP 0 1673 b=AS:200 1674 a=mid:foo 1675 a=rtpmap:0 PCMU/8000 1676 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1677 m=video 20000 RTP/AVP 32 1678 b=AS:1000 1679 a=mid:bar 1680 a=rtpmap:32 MPV/90000 1681 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1682 m=video 0 RTP/AVP 66 1683 a=mid:zen 1684 a=rtpmap:66 H261/90000 1686 18. Acknowledgements 1688 The usage of the SDP grouping extension for negotiating bundled media 1689 is based on a similar alternatives proposed by Harald Alvestrand and 1690 Cullen Jennings. The BUNDLE extension described in this document is 1691 based on the different alternative proposals, and text (e.g. SDP 1692 examples) have been borrowed (and, in some cases, modified) from 1693 those alternative proposals. 1695 The SDP examples are also modified versions from the ones in the 1696 Alvestrand proposal. 1698 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1699 Stach, Ari Keraenen, Adam Roach, Christian Groves, Roman Shpount, 1700 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1701 Justin Uberti for reading the text, and providing useful feedback. 1703 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1704 providing help and text on the RTP/RTCP procedures. 1706 Thanks to Spotify for providing music for the countless hours of 1707 document editing. 1709 19. Change Log 1711 [RFC EDITOR NOTE: Please remove this section when publishing] 1713 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1715 o - Clarification based on comment from James Guballa. 1717 o - Clarification based on comment from Flemming Andreasen 1719 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1721 o - DTLS Considerations section added. 1723 o - BUNDLE semantics added to the IANA Considerations 1725 o - Changes based on WGLC comments from Adam Roach 1726 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1727 msg14673.html 1729 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1731 o - Changes based on agreements at IETF#92 1733 o -- BAS Offer removed, based on agreement at IETF#92. 1735 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1736 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1738 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1740 o - Editorial changes based on comments from Magnus Westerlund. 1742 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1744 o - Modification of RTP/RTCP multiplexing section, based on comments 1745 from Magnus Westerlund. 1747 o - Reference updates. 1749 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1751 o - Editorial fix. 1753 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1755 o - Editorial changes. 1757 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1759 o Changes to allow a new suggested offerer BUNDLE address to be 1760 assigned to each bundled m- line. 1762 o Changes based on WGLC comments from Paul Kyzivat 1764 o - Editorial fixes 1766 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1768 o Usage of SDP 'extmap' attribute added 1770 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1771 port value 1773 o Changes based on WGLC comments from Thomas Stach 1774 o - ICE candidates not assigned to bundle-only m- lines with a zero 1775 port value 1777 o - Editorial changes 1779 o Changes based on WGLC comments from Colin Perkins 1781 o - Editorial changes: 1783 o -- "RTP SDES item" -> "RTCP SDES item" 1785 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1787 o - Changes in section 10.1.1: 1789 o -- "SHOULD NOT" -> "MUST NOT" 1791 o -- Additional text added to the Note 1793 o - Change to section 13.2: 1795 o -- Clarify that mid value is not zero terminated 1797 o - Change to section 13.3: 1799 o -- Clarify that mid value is not zero terminated 1801 o -- Clarify padding 1803 o Changes based on WGLC comments from Paul Kyzivat 1805 o - Editorial changes: 1807 o Changes based on WGLC comments from Jonathan Lennox 1809 o - Editorial changes: 1811 o - Defintion of SDP bundle-only attribute alligned with structure 1812 in 4566bis draft 1814 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1816 o Editorial corrections based on comments from Harald Alvestrand. 1818 o Editorial corrections based on comments from Cullen Jennings. 1820 o Reference update (RFC 7160). 1822 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1823 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1824 msg13765.html). 1826 o Additional text added to the Security Considerations. 1828 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1830 o SDP bundle-only attribute added to IANA Considerations. 1832 o SDES item and RTP header extension added to Abstract and 1833 Introduction. 1835 o Modification to text updating section 8.2 of RFC 3264. 1837 o Reference corrections. 1839 o Editorial corrections. 1841 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1843 o Terminology change: "bundle-only attribute assigned to m= line" to 1844 "bundle-only attribute associated with m= line". 1846 o Editorial corrections. 1848 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1850 o Editorial corrections. 1852 o - "of"->"if" (8.3.2.5). 1854 o - "optional"->"OPTIONAL" (9.1). 1856 o - Syntax/ABNF for 'bundle-only' attribute added. 1858 o - SDP Offer/Answer sections merged. 1860 o - 'Request new offerer BUNDLE address' section added 1862 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1864 o OPEN ISSUE regarding Receiver-ID closed. 1866 o - RTP MID SDES Item. 1868 o - RTP MID Header Extension. 1870 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1871 closed. 1873 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1874 include an 'rtcp' attribute in the answer, based on the procedures 1875 in section 5.1.3 of RFC 5761. 1877 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1879 o Draft title changed. 1881 o Added "SDP" to section names containing "Offer" or "Answer". 1883 o Editorial fixes based on comments from Paul Kyzivat 1884 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1885 msg13314.html). 1887 o Editorial fixed based on comments from Colin Perkins 1888 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1889 msg13318.html). 1891 o - Removed text about extending BUNDLE to allow multiple RTP 1892 sessions within a BUNDLE group. 1894 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1896 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1897 3264 structure. 1899 o Additional definitions added. 1901 o - Shared address. 1903 o - Bundled "m=" line. 1905 o - Bundle-only "m=" line. 1907 o - Offerer suggested BUNDLE mid. 1909 o - Answerer selected BUNDLE mid. 1911 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1912 to multiple "m=" lines until it has received an SDP Answer 1913 indicating support of the BUNDLE extension. 1915 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1916 Answerer supports the BUNDLE extension, assign a zero port value 1917 to a 'bundle-only' "m=" line. 1919 o SDP 'bundle-only' attribute section added. 1921 o Connection data nettype/addrtype restrictions added. 1923 o RFC 3264 update section added. 1925 o Indicating that a specific payload type value can be used in 1926 multiple "m=" lines, if the value represents the same codec 1927 configuration in each "m=" line. 1929 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1931 o Updated Offerer procedures (http://www.ietf.org/mail- 1932 archive/web/mmusic/current/msg12293.html). 1934 o Updated Answerer procedures (http://www.ietf.org/mail- 1935 archive/web/mmusic/current/msg12333.html). 1937 o Usage of SDP 'bundle-only' attribute added. 1939 o Reference to Trickle ICE document added. 1941 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1943 o Mechanism modified, to be based on usage of SDP Offers with both 1944 different and identical port number values, depending on whether 1945 it is known if the remote endpoint supports the extension. 1947 o Cullen Jennings added as co-author. 1949 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1951 o No changes. New version due to expiration. 1953 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1955 o No changes. New version due to expiration. 1957 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1959 o Draft name changed. 1961 o Harald Alvestrand added as co-author. 1963 o "Multiplex" terminology changed to "bundle". 1965 o Added text about single versus multiple RTP Sessions. 1967 o Added reference to RFC 3550. 1969 20. References 1971 20.1. Normative References 1973 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1974 Requirement Levels", BCP 14, RFC 2119, March 1997. 1976 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1977 with Session Description Protocol (SDP)", RFC 3264, June 1978 2002. 1980 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1981 Description Protocol", RFC 4566, July 2006. 1983 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1984 Header Extensions", RFC 5285, July 2008. 1986 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1987 Control Packets on a Single Port", RFC 5761, April 2010. 1989 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1990 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1992 [I-D.mmusic-sdp-mux-attributes] 1993 Nandakumar, S., "A Framework for SDP Attributes when 1994 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08 1995 (work in progress), January 2015. 1997 20.2. Informative References 1999 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2000 A., Peterson, J., Sparks, R., Handley, M., and E. 2001 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2002 June 2002. 2004 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2005 Jacobson, "RTP: A Transport Protocol for Real-Time 2006 Applications", STD 64, RFC 3550, July 2003. 2008 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2009 in Session Description Protocol (SDP)", RFC 3605, October 2010 2003. 2012 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2013 Description Protocol (SDP) Security Descriptions for Media 2014 Streams", RFC 4568, July 2006. 2016 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2017 BCP 131, RFC 4961, July 2007. 2019 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2020 (ICE): A Protocol for Network Address Translator (NAT) 2021 Traversal for Offer/Answer Protocols", RFC 5245, April 2022 2010. 2024 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2025 Media Attributes in the Session Description Protocol 2026 (SDP)", RFC 5576, June 2009. 2028 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2029 Security (DTLS) Extension to Establish Keys for the Secure 2030 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 2032 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2033 Security Version 1.2", RFC 6347, January 2012. 2035 [RFC7160] Petit-Huguenin, M. and G. Zorn, "Support for Multiple 2036 Clock Rates in an RTP Session", RFC 7160, April 2014. 2038 [I-D.ietf-mmusic-trickle-ice] 2039 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2040 Incremental Provisioning of Candidates for the Interactive 2041 Connectivity Establishment (ICE) Protocol", draft-ietf- 2042 mmusic-trickle-ice-02 (work in progress), January 2015. 2044 Appendix A. Design Considerations 2046 A.1. General 2048 One of the main issues regarding the BUNDLE grouping extensions has 2049 been whether, in SDP Offers and SDP Answers, the same port value 2050 should be inserted in "m=" lines associated with a BUNDLE group, as 2051 the purpose of the extension is to negotiate the usage of a single 2052 address:port combination for media associated with the "m=" lines. 2053 Issues with both approaches, discussed in the Appendix have been 2054 raised. The outcome was to specify a mechanism which uses SDP Offers 2055 with both different and identical port values. 2057 Below are the primary issues that have been considered when defining 2058 the "BUNDLE" grouping extension: 2060 o 1) Interoperability with existing UAs. 2062 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2064 o 3) Time to gather, and the number of, ICE candidates. 2066 o 4) Different error scenarios, and when they occur. 2068 o 5) SDP Offer/Answer impacts, including usage of port number value 2069 zero. 2071 NOTE: Before this document is published as an RFC, this 2072 Appendix might be removed. 2074 A.2. UA Interoperability 2076 Consider the following SDP Offer/Answer exchange, where Alice sends 2077 an SDP Offer to Bob: 2079 SDP Offer 2081 v=0 2082 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2083 s= 2084 c=IN IP4 atlanta.example.com 2085 t=0 0 2086 m=audio 10000 RTP/AVP 97 2087 a=rtpmap:97 iLBC/8000 2088 m=video 10002 RTP/AVP 97 2089 a=rtpmap:97 H261/90000 2091 SDP Answer 2093 v=0 2094 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2095 s= 2096 c=IN IP4 biloxi.example.com 2097 t=0 0 2098 m=audio 20000 RTP/AVP 97 2099 a=rtpmap:97 iLBC/8000 2100 m=video 20002 RTP/AVP 97 2101 a=rtpmap:97 H261/90000 2103 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2104 later invention to RTP and Bob can not assume that Alice supports RFC 2105 4961. This means that Alice may be sending RTP from a different port 2106 than 10000 or 10002 - some implementation simply send the RTP from an 2107 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2108 way that Bob know if it should be passed to the video or audio codec 2109 is by looking at the port it was received on. This lead some SDP 2110 implementations to use the fact that each "m=" line had a different 2111 port number to use that port number as an index to find the correct m 2112 line in the SDP. As a result, some implementations that do support 2113 symmetric RTP and ICE still use a SDP data structure where SDP with 2114 "m=" lines with the same port such as: 2116 SDP Offer 2118 v=0 2119 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2120 s= 2121 c=IN IP4 atlanta.example.com 2122 t=0 0 2123 m=audio 10000 RTP/AVP 97 2124 a=rtpmap:97 iLBC/8000 2125 m=video 10000 RTP/AVP 98 2126 a=rtpmap:98 H261/90000 2128 will result in the second "m=" line being considered an SDP error 2129 because it has the same port as the first line. 2131 A.3. Usage of port number value zero 2133 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2134 can be disabled/rejected by setting the port number value to zero. 2135 This is different from e.g. using the SDP direction attributes, where 2136 RTCP traffic will continue even if the SDP "inactive" attribute is 2137 indicated for the associated "m=" line. 2139 If each "m=" line associated with a BUNDLE group would contain 2140 different port values, and one of those port values would be used for 2141 a BUNDLE address associated with the BUNDLE group, problems would 2142 occur if an endpoint wants to disable/reject the "m=" line associated 2143 with that port, by setting the port value to zero. After that, no 2144 "m=" line would contain the port value which is used for the BUNDLE 2145 address. In addition, it is unclear what would happen to the ICE 2146 candidates associated with the "m=" line, as they are also used for 2147 the BUNDLE address. 2149 A.4. B2BUA And Proxy Interoperability 2151 Some back to back user agents may be configured in a mode where if 2152 the incoming call leg contains an SDP attribute the B2BUA does not 2153 understand, the B2BUS still generates that SDP attribute in the Offer 2154 for the outgoing call leg. Consider an B2BUA that did not understand 2155 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2156 Further assume that the B2BUA was configured to tear down any call 2157 where it did not see any RTCP for 5 minutes. In this cases, if the 2158 B2BUA received an Offer like: 2160 SDP Offer 2162 v=0 2163 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2164 s= 2165 c=IN IP4 atlanta.example.com 2166 t=0 0 2167 m=audio 49170 RTP/AVP 0 2168 a=rtcp:53020 2170 It would be looking for RTCP on port 49172 but would not see any 2171 because the RTCP would be on port 53020 and after five minutes, it 2172 would tear down the call. Similarly, an SBC that did not understand 2173 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2174 wrong port and tear down the call. It is worth noting that a B2BUA 2175 that generated an Offer with capabilities it does not understand is 2176 not compliant with the specifications. 2178 A.4.1. Traffic Policing 2180 Sometimes intermediaries do not act as B2BUA, in the sense that they 2181 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2182 however, they may use SDP information (e.g. IP address and port) in 2183 order to control traffic gating functions, and to set traffic 2184 policing rules. There might be rules which will trigger a session to 2185 be terminated in case media is not sent or received on the ports 2186 retrieved from the SDP. This typically occurs once the session is 2187 already established and ongoing. 2189 A.4.2. Bandwidth Allocation 2191 Sometimes intermediaries do not act as B2BUA, in the sense that they 2192 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2193 however, they may use SDP information (e.g. codecs and media types) 2194 in order to control bandwidth allocation functions. The bandwidth 2195 allocation is done per "m=" line, which means that it might not be 2196 enough if media associated with all "m=" lines try to use that 2197 bandwidth. That may either simply lead to bad user experience, or to 2198 termination of the call. 2200 A.5. Candidate Gathering 2202 When using ICE, an candidate needs to be gathered for each port. 2203 This takes approximately 20 ms extra for each extra "m=" line due to 2204 the NAT pacing requirements. All of this gather can be overlapped 2205 with other things while the page is loading to minimize the impact. 2206 If the client only wants to generate TURN or STUN ICE candidates for 2207 one of the "m=" lines and then use trickle ICE 2208 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2209 the rest of the "m=" lines, it MAY do that and will not need any 2210 additional gathering time. 2212 Some people have suggested a TURN extension to get a bunch of TURN 2213 allocation at once. This would only provide a single STUN result so 2214 in cases where the other end did not support BUNDLE, may cause more 2215 use of the TURN server but would be quick in the cases where both 2216 sides supported BUNDLE and would fall back to a successful call in 2217 the other cases. 2219 Authors' Addresses 2221 Christer Holmberg 2222 Ericsson 2223 Hirsalantie 11 2224 Jorvas 02420 2225 Finland 2227 Email: christer.holmberg@ericsson.com 2229 Harald Tveit Alvestrand 2230 Google 2231 Kungsbron 2 2232 Stockholm 11122 2233 Sweden 2235 Email: harald@alvestrand.no 2236 Cullen Jennings 2237 Cisco 2238 400 3rd Avenue SW, Suite 350 2239 Calgary, AB T2P 4H2 2240 Canada 2242 Email: fluffy@iii.ca