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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Updates: 3264 (if approved) H. Alvestrand 5 Intended status: Standards Track Google 6 Expires: October 17, 2016 C. Jennings 7 Cisco 8 April 15, 2016 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-29.txt 14 Abstract 16 This specification defines a new Session Description Protocol (SDP) 17 Grouping Framework extension, 'BUNDLE'. The extension can be used 18 with the SDP Offer/Answer mechanism to negotiate the usage of a 19 single address:port combination (BUNDLE address) for receiving media, 20 referred to as bundled media, specified by multiple SDP media 21 descriptions ("m=" lines). 23 To assist endpoints in negotiating the use of bundle this 24 specification defines a new SDP attribute, 'bundle-only', which can 25 be used to request that specific media is only used if bundled. 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 October 17, 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. Mux Category Considerations . . . . . . . . . . . . . . . 10 81 8.3. Generating the Initial SDP Offer . . . . . . . . . . . . 10 82 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 83 8.3.2. Suggesting the offerer BUNDLE address . . . . . . . . 11 84 8.4. Generating the SDP Answer . . . . . . . . . . . . . . . . 11 85 8.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 11 86 8.4.2. Answerer Selection of Offerer Bundle Address . . . . 12 87 8.4.3. Answerer Selection of Answerer BUNDLE Address . . . . 13 88 8.4.4. Moving A Media Description Out Of A BUNDLE Group . . 13 89 8.4.5. Rejecting A Media Description In A BUNDLE Group . . . 14 90 8.5. Offerer Processing of the SDP Answer . . . . . . . . . . 14 91 8.6. Modifying the Session . . . . . . . . . . . . . . . . . . 14 92 8.6.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 93 8.6.2. Suggesting a new offerer BUNDLE address . . . . . . . 15 94 8.6.3. Adding a media description to a BUNDLE group . . . . 15 95 8.6.4. Moving A Media Description Out Of A BUNDLE Group . . 16 96 8.6.5. Disabling A Media Description In A BUNDLE Group . . . 16 97 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 17 98 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 17 99 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 100 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 18 101 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 18 102 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 18 103 10.1.2. Payload Type (PT) Value Reuse . . . . . . . . . . . 19 104 10.2. Associating RTP/RTCP Packets With Correct SDP Media 105 Description . . . . . . . . . . . . . . . . . . . . . . 19 106 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 20 107 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 20 108 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 109 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 22 110 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 111 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 23 112 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 23 113 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 24 114 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 24 115 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 24 116 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 24 117 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 24 118 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 25 119 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 25 120 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 25 121 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 122 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 123 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 26 124 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 126 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 26 127 13.7. New text replacing section 8.4 (6th paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 129 14. RTP/RTCP extensions for identification-tag transport . . . . 27 130 14.1. General . . . . . . . . . . . . . . . . . . . . . . . . 27 131 14.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 28 132 14.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 28 133 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 134 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 29 135 15.2. New RTP Header Extension URI . . . . . . . . . . . . . . 29 136 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 30 137 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 30 138 16. Security Considerations . . . . . . . . . . . . . . . . . . . 30 139 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 31 140 17.1. Example: Bundle Address Selection . . . . . . . . . . . 31 141 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 33 142 17.3. Example: Offerer Adds A Media Description To A BUNDLE 143 Group . . . . . . . . . . . . . . . . . . . . . . . . . 34 145 17.4. Example: Offerer Moves A Media Description Out Of A 146 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 36 147 17.5. Example: Offerer Disables A Media Description Within A 148 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 37 149 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39 150 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 39 151 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 152 20.1. Normative References . . . . . . . . . . . . . . . . . . 46 153 20.2. Informative References . . . . . . . . . . . . . . . . . 48 154 Appendix A. Design Considerations . . . . . . . . . . . . . . . 48 155 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 48 156 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 49 157 A.3. Usage of port number value zero . . . . . . . . . . . . . 50 158 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 51 159 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 51 160 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 51 161 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 52 162 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52 164 1. Introduction 166 This specification defines a way to use a single address:port 167 combination (BUNDLE address) for receiving media specified by 168 multiple SDP media descriptions ("m=" lines). 170 This specification defines a new SDP Grouping Framework [RFC5888] 171 extension called 'BUNDLE'. The extension can be used with the 172 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 173 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 174 BUNDLE address is used for receiving media specified by multiple "m=" 175 lines. This is referred to as bundled media. 177 The offerer and answerer [RFC3264] use the BUNDLE extension to 178 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 179 address) and one for the answerer (answerer BUNDLE address), to be 180 used for receiving the bundled media specified by a BUNDLE group. 181 Once the offerer and the answerer have negotiated a BUNDLE group, 182 they associate their respective BUNDLE address with each "m=" line in 183 the BUNDLE group. The BUNDLE addresses are used to receive all media 184 specified by the BUNDLE group. 186 The use of a BUNDLE group and a BUNDLE address also allows the usage 187 of a single set of Interactive Connectivity Establishment (ICE) 188 [I-D.ietf-ice-rfc5245bis] candidates for multiple "m=" lines. 190 This specification also defines a new SDP attribute, 'bundle-only', 191 which can be used to request that specific media is only used if kept 192 within a BUNDLE group. 194 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 195 port value to multiple "m=" lines are undefined, and there is no 196 grouping defined by such means. Instead, an explicit grouping 197 mechanism needs to be used to express the intended semantics. This 198 specification provides such an extension. 200 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 201 [RFC3264]. The update allows an answerer to assign a non-zero port 202 value to an "m=" line in an SDP answer, even if the "m=" line in the 203 associated SDP offer contained a zero port value. 205 This specification also defines a new Real-time Transport Protocol 206 (RTP) [RFC3550] source description (SDES) item and a new RTP header 207 extension that can be used to carry a value that associates RTP/RTCP 208 packets with a specific media description. This can be used to 209 correlate a RTP packet with the correct media. 211 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 212 address MUST only be associated with a single BUNDLE group. The 213 procedures in this specification apply independently to a given 214 BUNDLE group. All RTP based media flows described by a single BUNDLE 215 group belong to a single RTP session [RFC3550]. 217 The BUNDLE extension is backward compatible. Endpoints that do not 218 support the extension are expected to generate offers and answers 219 without an SDP 'group:BUNDLE' attribute, and are expected to 220 associate a unique address with each "m=" line within an offer and 221 answer, according to the procedures in [RFC4566] and [RFC3264] 223 2. Terminology 225 "m=" line: SDP bodies contain one or more media descriptions. Each 226 media description is identified by an SDP "m=" line. 228 5-tuple: A collection of the following values: source address, source 229 port, destination address, destination port, and transport-layer 230 protocol. 232 Unique address: An IP address and port combination that is associated 233 with only one "m=" line in an offer or answer. 235 Shared address: An IP address and port combination that is associated 236 with multiple "m=" lines within an offer or answer. 238 Offerer BUNDLE-tag: The first identification-tag in a given SDP 239 'group:BUNDLE' attribute identification-tag list in an offer. 241 Answerer BUNDLE-tag: The first identification-tag in a given SDP 242 'group:BUNDLE' attribute identification-tag list in an answer. 244 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 245 and port combination used by an offerer to receive all media 246 specified by each "m=" line within the BUNDLE group. 248 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 249 and port combination used by an answerer to receive all media 250 specified by each "m=" line within the BUNDLE group. 252 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 253 exchange, which uses the same BUNDLE address for receiving media. 255 Bundled "m=" line: An "m=" line, whose identification-tag is placed 256 in an SDP 'group:BUNDLE' attribute identification-tag list in an 257 offer or answer. 259 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 260 'bundle-only' attribute. 262 Bundled media: All media specified by a given BUNDLE group. 264 Initial offer: The first offer, within an SDP session (e.g. a SIP 265 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 266 to carry SDP), in which the offerer indicates that it wants to create 267 a given BUNDLE group. 269 Subsequent offer: An offer which contains a BUNDLE group that has 270 been created as part of a previous offer/answer exchange. 272 Identification-tag: A unique token value that is used to identify an 273 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 274 "m=" line, carries an unique identification-tag. The session-level 275 SDP 'group' attribute [RFC5888] carries a list of identification- 276 tags, identifying the "m=" lines associated with that particular 277 'group' attribute. 279 3. Conventions 281 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 282 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 283 document are to be interpreted as described in BCP 14, RFC 2119 284 [RFC2119]. 286 4. Applicability Statement 288 The mechanism in this specification only applies to the Session 289 Description Protocol (SDP) [RFC4566], when used together with the SDP 290 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 291 scope of this document, and is thus undefined. 293 5. SDP Grouping Framework BUNDLE Extension 295 This section defines a new SDP Grouping Framework extension 296 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 297 Offer/Answer mechanism to negotiate the usage of a single 298 address:port combination (BUNDLE address) for receiving bundled 299 media. 301 A single address:port combination is also used for sending bundled 302 media. The address:port combination used for sending bundled media 303 MAY be the same as the BUNDLE address, used to receive bundled media, 304 depending on whether symmetric RTP [RFC4961] is used. 306 All media specified by a BUNDLE group share a single 5-tuple, i.e. in 307 addition to using a single address:port combination all bundled media 308 MUST be transported using the same transport-layer protocol (e.g. 309 UDP or TCP). 311 The BUNDLE extension is indicated using an SDP 'group' attribute with 312 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 313 associated with each bundled "m=" line, and each identification-tag 314 is listed in the SDP 'group:BUNDLE' attribute identification-tag 315 list. Each "m=" line whose identification-tag is listed in the 316 identification-tag list is associated with a given BUNDLE group. 318 SDP bodies can contain multiple BUNDLE groups. Any given bundled 319 "m=" line MUST NOT be associated with more than one BUNDLE group. 321 Section 8 defines the detailed SDP Offer/Answer procedures for the 322 BUNDLE extension. 324 6. SDP 'bundle-only' Attribute 326 This section defines a new SDP media-level attribute [RFC4566], 327 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 328 hence has no value. 330 Name: bundle-only 332 Value: N/A 334 Usage Level: media 336 Charset Dependent: no 338 Example: 340 a=bundle-only 342 In order to ensure that an answerer that does not support the BUNDLE 343 extension always rejects a bundled "m=" line, the offerer can assign 344 a zero port value to the "m=" line. According to [RFC4566] an 345 answerer will reject such "m=" line. By associating an SDP 'bundle- 346 only' attribute with such "m=" line, the offerer can request that the 347 answerer accepts the "m=" line if the answerer supports the Bundle 348 extension, and if the answerer keeps the "m=" line within the 349 associated BUNDLE group. 351 NOTE: Once the offerer BUNDLE address has been selected, the offerer 352 does not need to include the 'bundle-only' attribute in subsequent 353 offers. By associating the offerer BUNDLE address with an "m=" line 354 of a subsequent offer, the offerer will ensure that the answerer will 355 either keep the "m=" line within the BUNDLE group, or the answerer 356 will have to reject the "m=" line. 358 The usage of the 'bundle-only' attribute is only defined for a 359 bundled "m=" line with a zero port value, within an offer. Other 360 usage is unspecified. 362 Section 8 defines the detailed SDP Offer/Answer procedures for the 363 'bundle-only' attribute. 365 7. SDP Information Considerations 367 7.1. General 369 This section describes restrictions associated with the usage of SDP 370 parameters within a BUNDLE group. It also describes, when parameter 371 and attribute values have been associated with each bundled "m=" 372 line, how to calculate a value for the whole BUNDLE group. 374 7.2. Connection Data (c=) 376 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 377 line MUST be 'IN'. 379 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 380 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 381 each "m=" line. 383 NOTE: Extensions to this specification can specify usage of the 384 BUNDLE mechanism for other nettype and addrtype values than the ones 385 listed above. 387 7.3. Bandwidth (b=) 389 An offerer and answerer MUST use the rules and restrictions defined 390 in [I-D.ietf-mmusic-sdp-mux-attributes] for when associating the SDP 391 bandwidth (b=) line with bundled "m=" lines. 393 7.4. Attributes (a=) 395 An offerer and answerer MUST use the rules and restrictions defined 396 in [I-D.ietf-mmusic-sdp-mux-attributes] for when associating SDP 397 attributes with bundled "m=" lines. 399 8. SDP Offer/Answer Procedures 401 8.1. General 403 This section describes the SDP Offer/Answer [RFC3264] procedures for: 405 o Negotiating and creating of a BUNDLE group; and 407 o Selecting the BUNDLE addresses (offerer BUNDLE address and 408 answerer BUNDLE address); and 410 o Adding an "m=" line to a BUNDLE group; and 412 o Moving an "m=" line out of a BUNDLE group; and 414 o Disabling an "m=" line within a BUNDLE group. 416 The generic rules and procedures defined in [RFC3264] and [RFC5888] 417 also apply to the BUNDLE extension. For example, if an offer is 418 rejected by the answerer, the previously negotiated SDP parameters 419 and characteristics (including those associated with a BUNDLE group) 420 apply. Hence, if an offerer generates an offer in which the offerer 421 wants to create a BUNDLE group, and the answerer rejects the offer, 422 the BUNDLE group is not created. 424 The procedures in this section are independent of the media type or 425 "m=" line proto value represented by a bundled "m=" line. Section 10 426 defines additional considerations for RTP based media. Section 6 427 defines additional considerations for the usage of the SDP 'bundle- 428 only' attribute. Section 11 defines additional considerations for 429 the usage of Interactive Connectivity Establishment (ICE) 430 [I-D.ietf-ice-rfc5245bis] mechanism. 432 SDP offers and answers can contain multiple BUNDLE groups. The 433 procedures in this section apply independently to a given BUNDLE 434 group. 436 8.2. Mux Category Considerations 438 When an offerer associates a shared address with a bundled "m=" line, 439 the offerer shall associate IDENTICAL and TRANSPORT mux category SDP 440 attributes [I-D.ietf-mmusic-sdp-mux-attributes] with the "m=" line 441 only if the "m=" line is associated with the offerer BUNDLE-tag. 442 Otherwise the offerer MUST NOT associate such SDP attributes with the 443 "m=" line. 445 When an answerer associates a shared address with a bundled "m=" 446 line, the answerer shall associate IDENTICAL and TRANSPORT category 447 SDP attributes with the "m=" line only if the "m=" line is associated 448 with the answerer BUNDLE-tag. Otherwise the answerer MUST NOT 449 associate such SDP attributes with the "m=" line. 451 NOTE: As bundled "m=" lines associated with a shared address will 452 share the same IDENTICAL and TRANSPORT mux category SDP attributes, 453 and attribute values, there is no need to associate such SDP 454 attributes with each "m=" line. 456 8.3. Generating the Initial SDP Offer 458 8.3.1. General 460 When an offerer generates an initial offer, in order to create a 461 BUNDLE group, it MUST: 463 o Assign a unique address to each "m=" line within the offer, 464 following the procedures in [RFC3264], unless the media line is a 465 'bundle-only' "m=" line (see below); and 467 o Add an SDP 'group:BUNDLE' attribute to the offer; and 468 o Place the identification-tag of each bundled "m=" line in the SDP 469 'group:BUNDLE' attribute identification-tag list; and 471 o Indicate which unique address the offerer suggests as the offerer 472 BUNDLE address [Section 8.3.2]. 474 If the offerer wants to request that the answerer accepts a given 475 bundled "m=" line only if the answerer keeps the "m=" line within the 476 BUNDLE group, the offerer MUST: 478 o Associate an SDP 'bundle-only' attribute [Section 8.3.2] with the 479 "m=" line; and 481 o Assign a zero port value to the "m=" line. 483 NOTE: If the offerer assigns a zero port value to an "m=" line, but 484 does not also associate an SDP 'bundle-only' attribute with the "m=" 485 line, it is an indication that the offerer wants to disable the "m=" 486 line [Section 8.6.5]. 488 [Section 17.1] shows an example of an initial offer. 490 8.3.2. Suggesting the offerer BUNDLE address 492 In the offer, the address associated with the "m=" line associated 493 with the offerer BUNDLE-tag indicates the address that the offerer 494 suggests as the offerer BUNDLE address. 496 The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain 497 a zero port value or an SDP 'bundle-only' attribute. 499 8.4. Generating the SDP Answer 501 8.4.1. General 503 When an answerer generates an answer that contains a BUNDLE group, 504 the following general SDP grouping framework restrictions, defined in 505 [RFC5888], also apply to the BUNDLE group: 507 o The answerer MUST NOT include a BUNDLE group in the answer, unless 508 the offerer requested the BUNDLE group to be created in the 509 corresponding offer; and 511 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 512 unless the offerer requested the "m=" line to be within that 513 BUNDLE group in the corresponding offer. 515 If the answer contains a BUNDLE group, the answerer MUST: 517 o Select an Offerer BUNDLE Address [Section 8.4.2]; and 519 o Select an Answerer BUNDLE Address [Section 8.4.3]; 521 The answerer is allowed to select a new Answerer BUNDLE address each 522 time it generates an answer to an offer. 524 If the answerer does not want to keep an "m=" line within a BUNDLE 525 group, it MUST: 527 o Move the "m=" line out of the BUNDLE group [Section 8.4.4]; or 529 o Reject the "m=" line [Section 8.4.5]; 531 If the answerer keeps a bundle-only "m=" line within the BUNDLE 532 group, it follows the procedures (associates the answerer BUNDLE 533 address with the "m=" line etc) for any other "m=" line kept within 534 the BUNDLE group. 536 If the answerer does not want to keep a bundle-only "m=" line within 537 the BUNDLE group, it MUST reject the "m=" line [Section 8.4.5]. 539 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 540 any "m=" line in an answer. 542 NOTE: If a bundled "m=" line in an offer contains a zero port value, 543 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 544 is an indication that the offerer wants to disable the "m=" line 545 [Section 8.6.5]. 547 8.4.2. Answerer Selection of Offerer Bundle Address 549 In an offer, the address (unique or shared) associated with the 550 bundled "m=" line associated with the offerer BUNDLE-tag indicates 551 the address that the offerer suggests as the offerer BUNDLE address 552 [Section 8.3.2]. The answerer MUST check whether that "m=" line 553 fulfils the following criteria: 555 o The answerer will not move the "m=" line out of the BUNDLE group 556 [Section 8.4.4]; and 558 o The answerer will not reject the "m=" line [Section 8.4.5]; and 560 o The "m=" line does not contain a zero port value. 562 If all of the criteria above are fulfilled, the answerer MUST select 563 the address associated with the "m=" line as the offerer BUNDLE 564 address. In the answer, the answerer BUNDLE-tag represents the "m=" 565 line, and the address associated with the "m=" line in the offer 566 becomes the offerer BUNDLE address. 568 If one or more of the criteria are not fulfilled, the answerer MUST 569 select the next identification-tag in the identification-tag list, 570 and perform the same criteria check for the "m=" line associated with 571 that identification-tag. If there are no more identification-tags in 572 the identification-tag list, the answerer MUST NOT create the BUNDLE 573 group. In addition, unless the answerer rejects the whole offer, the 574 answerer MUST apply the answerer procedures for moving an "m=" line 575 out of a BUNDLE group [Section 8.4.4] to each bundled "m=" line in 576 the offer when creating the answer. 578 [Section 17.1] shows an example of an offerer BUNDLE address 579 selection. 581 8.4.3. Answerer Selection of Answerer BUNDLE Address 583 When the answerer selects a BUNDLE address for itself, referred to as 584 the answerer BUNDLE address, it MUST associate that address with each 585 bundled "m=" line within the created BUNDLE group in the answer. 587 The answerer MUST NOT associate the answerer BUNDLE address with an 588 "m=" line that is not within the BUNDLE group, or to an "m=" line 589 that is within another BUNDLE group. 591 [Section 17.1] shows an example of an answerer BUNDLE address 592 selection. 594 8.4.4. Moving A Media Description Out Of A BUNDLE Group 596 When an answerer wants to move an "m=" line out of a BUNDLE group, it 597 MUST first check the following criteria: 599 o In the corresponding offer, the "m=" line is associated with a 600 shared address (e.g. a previously selected offerer BUNDLE 601 address); or 603 o In the corresponding offer, if an SDP 'bundle-only' attribute is 604 associated with the "m=" line, and if the "m=" line contains a 605 zero port value. 607 If either criteria above is fulfilled, the answerer MUST reject the 608 "m=" line [Section 8.4.5]. 610 Otherwise, if in the corresponding offer the "m=" line is associated 611 with a unique address, the answerer MUST associate a unique address 612 with the "m=" line in the answer (the answerer does not reject the 613 "m=" line). 615 In addition, in either case above, the answerer MUST NOT place the 616 identification-tag, associated with the moved "m=" line, in the SDP 617 'group' attribute identification-tag list associated with the BUNDLE 618 group. 620 8.4.5. Rejecting A Media Description In A BUNDLE Group 622 When an answerer rejects an "m=" line, it MUST associate an address 623 with a zero port value with the "m=" line in the answer, according to 624 the procedures in [RFC4566]. 626 In addition, the answerer MUST NOT place the identification-tag, 627 associated with the rejected "m=" line, in the SDP 'group' attribute 628 identification-tag list associated with the BUNDLE group. 630 8.5. Offerer Processing of the SDP Answer 632 When an offerer receives an answer, if the answer contains a BUNDLE 633 group, the offerer MUST check that any bundled "m=" line in the 634 answer was indicated as bundled in the corresponding offer. If there 635 is no mismatch, the offerer MUST use the offerer BUNDLE address, 636 selected by the answerer [Section 8.4.2], as the address for each 637 bundled "m=" line. 639 NOTE: As the answerer might reject one or more bundled "m=" lines, or 640 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 641 line in the offer might not be indicated as bundled in the answer. 643 If the answer does not contain a BUNDLE group, the offerer MUST 644 process the answer as a normal answer. 646 8.6. Modifying the Session 648 8.6.1. General 650 When an offerer generates a subsequent offer, it MUST associate the 651 previously selected offerer BUNDLE address [Section 8.4.2] with each 652 bundled "m=" line (including any bundle-only "m=" line), except if: 654 o The offerer suggests a new offerer BUNDLE address [Section 8.6.2]; 655 or 657 o The offerer wants to add a bundled "m=" line to the BUNDLE group 658 [Section 8.6.3]; or 660 o The offerer wants to move a bundled "m=" line out of the BUNDLE 661 group [Section 8.6.4]; or 663 o The offerer wants to disable the bundled "m=" line 664 [Section 8.6.5]. 666 In addition, the offerer MUST select an offerer BUNDLE-tag 667 [Section 8.3.2] associated with the previously selected offerer 668 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 669 address. 671 8.6.2. Suggesting a new offerer BUNDLE address 673 When an offerer generates an offer, in which it suggests a new 674 offerer BUNDLE address [Section 8.3.2], the offerer MUST: 676 o Assign the address (shared address) to each "m=" line within the 677 BUNDLE group; or 679 o Assign the address (unique address) to one bundled "m=" line. 681 In addition, the offerer MUST indicate that the address is the new 682 suggested offerer BUNDLE address [Section 8.3.2]. 684 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 685 address with each bundled "m=" line, it can associate unique 686 addresses with any number of bundled "m=" lines (and the previously 687 selected offerer BUNDLE address to any remaining bundled "m=" line) 688 if it wants to suggest multiple alternatives for the new offerer 689 BUNDLE address. 691 8.6.3. Adding a media description to a BUNDLE group 693 When an offerer generates an offer, in which it wants to add a 694 bundled "m=" line to a BUNDLE group, the offerer MUST: 696 o Assign a unique address to the added "m=" line; or 698 o Assign the previously selected offerer BUNDLE address to the added 699 "m=" line; or 701 o If the offerer associates a new (shared address) suggested offerer 702 BUNDLE address with each bundled "m=" line [Section 8.6.2], also 703 associate that address with the added "m=" line. 705 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 706 identification-tag list with the BUNDLE group [Section 8.3.2] by 707 adding the identification-tag associated with the added "m=" line to 708 the list. 710 NOTE: Assigning a unique address to the "m=" line allows the answerer 711 to move the "m=" line out of the BUNDLE group [Section 8.4.4], 712 without having to reject the "m=" line. 714 If the offerer associates a unique address with the added "m=" line, 715 and if the offerer suggests that address as the new offerer BUNDLE 716 address [Section 8.6.2], the offerer BUNDLE-tag MUST represent the 717 added "m=" line [Section 8.3.2]. 719 If the offerer associates a new suggested offerer BUNDLE address with 720 each bundled "m=" line [Section 8.6.2], including the added "m=" 721 line, the offerer BUNDLE-tag MAY represent the added "m=" line 722 [Section 8.3.2]. 724 [Section 17.3] shows an example where an offerer sends an offer in 725 order to add a bundled "m=" line to a BUNDLE group. 727 8.6.4. Moving A Media Description Out Of A BUNDLE Group 729 When an offerer generates an offer, in which it wants to move a 730 bundled "m=" line out of a BUNDLE group it was added to in a previous 731 offer/answer transaction, the offerer: 733 o MUST associate a unique address with the "m=" line; and 735 o MUST NOT place the identification-tag associated with the "m=" 736 line in the SDP 'group:BUNDLE' attribute identification-tag list 737 associated with the BUNDLE group. 739 NOTE: If the removed "m=" line is associated with the previously 740 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 741 [Section 8.3.2]. 743 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 744 added to another BUNDLE group, the offerer applies the procedures in 745 [Section 8.6.3] to the "m=" line. 747 [Section 17.4] shows an example of an offer for moving an "m=" line 748 out of a BUNDLE group. 750 8.6.5. Disabling A Media Description In A BUNDLE Group 752 When an offerer generates an offer, in which it wants to disable a 753 bundled "m=" line (added to the BUNDLE group in a previous offer/ 754 answer transaction), the offerer: 756 o MUST associate an address with a zero port value with the "m=" 757 line, following the procedures in [RFC4566]; and 759 o MUST NOT place the identification-tag associated with the "m=" 760 line in the SDP 'group:BUNDLE' attribute identification-tag list 761 associated with the BUNDLE group. 763 [Section 17.5] shows an example of an offer for disabling an "m=" 764 line within a BUNDLE group. 766 9. Protocol Identification 768 9.1. General 770 Each "m=" line within a BUNDLE group MUST use the same transport- 771 layer protocol. If bundled "m=" lines use different protocols on top 772 of the transport-layer protocol, there MUST exist a publicly 773 available specification which describes a mechanism, for this 774 particular protocol combination, how to associate received data with 775 the correct protocol. 777 In addition, if received data can be associated with more than one 778 bundled "m=" line, there MUST exist a publicly available 779 specification which describes a mechanism for associating the 780 received data with the correct "m=" line. 782 This document describes a mechanism to identify the protocol of 783 received data among the STUN, DTLS and SRTP protocols (in any 784 combination), when UDP is used as transport-layer protocol, but does 785 not describe how to identify different protocols transported on DTLS. 786 While the mechanism is generally applicable to other protocols and 787 transport-layers protocols, any such use requires further 788 specification around how to multiplex multiple protocols on a given 789 transport-layer protocols, and how to associate received data with 790 the correct protocols. 792 9.2. STUN, DTLS, SRTP 794 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 795 protocol of a received packet among the STUN, Datagram Transport 796 Layer Security (DTLS) and SRTP protocols (in any combination). If an 797 offer or answer includes bundled "m=" lines that represent these 798 protocols, the offerer or answerer MUST support the mechanism 799 described in [RFC5764], and no explicit negotiation is required in 800 order to indicate support and usage of the mechanism. 802 [RFC5764] does not describe how to identify different protocols 803 transported on DTLS, only how to identify the DTLS protocol itself. 805 If multiple protocols are transported on DTLS, there MUST exist a 806 specification describing a mechanism for identifying each individual 807 protocol. In addition, if a received DTLS packet can be associated 808 with more than one "m=" line, there MUST exist a specification which 809 describes a mechanism for associating the received DTLS packet with 810 the correct "m=" line. 812 [Section 10.2] describes how to associate a received (S)RTP packet 813 with the correct "m=" line. 815 10. RTP Considerations 817 10.1. Single RTP Session 819 10.1.1. General 821 All RTP-based media within a single BUNDLE group belong to a single 822 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 823 sessions, one per BUNDLE group. 825 Since a single RTP session is used for each bundle group, all "m=" 826 lines representing RTP-based media in a bundle group will share a 827 single SSRC numbering space [RFC3550]. 829 The following rules and restrictions apply for a single RTP session: 831 o A specific payload type value can be used in multiple bundled "m=" 832 lines if each codec associated with the payload type number shares 833 an identical codec configuration [Section 10.1.2]. 835 o The proto value in each bundled RTP-based "m=" line MUST be 836 identical (e.g. RTP/AVPF). 838 o The RTP MID header extension MUST be enabled, by associating an 839 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 840 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 841 in every offer and answer. 843 o A given SSRC MUST NOT transmit RTP packets using payload types 844 that originate from different bundled "m=" lines. 846 NOTE: The last bullet above is to avoid sending multiple media types 847 from the same SSRC. If transmission of multiple media types are done 848 with time overlap, RTP and RTCP fail to function. Even if done in 849 proper sequence this causes RTP Timestamp rate switching issues 850 [RFC7160]. However, once an SSRC has left the RTP session (by 851 sending an RTCP BYE packet), that SSRC value can later be reused by 852 another source(possibly associated with a different bundled "m=" 853 line. 855 10.1.2. Payload Type (PT) Value Reuse 857 Multiple bundled "m=" lines might represent RTP based media. As all 858 RTP based media specified by a BUNDLE group belong to the same RTP 859 session, in order for a given payload type value to be used inside 860 more than one bundled "m=" line, all codecs associated with the 861 payload type number MUST share an identical codec configuration. 862 This means that the codecs MUST share the same media type, encoding 863 name, clock rate and any parameter that can affect the codec 864 configuration and packetization. 865 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 866 attribute values must be identical for all codecs that use the same 867 payload type value. 869 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 871 There are multiple mechanisms that can be used by an endpoint in 872 order to associate received RTP/RTCP packets with a bundled "m=" 873 line. Such mechanisms include using the payload type value carried 874 inside the RTP packets, the SSRC values carried inside the RTP 875 packets, and other "m=" line specific information carried inside the 876 RTP packets. 878 As all RTP/RTCP packets associated with a BUNDLE group are received 879 (and sent) using single address:port combinations, the local 880 address:port combination cannot be used to associate received RTP 881 packets with the correct "m=" line. 883 As described in [Section 10.1.2], the same payload type value might 884 be used inside RTP packets described by multiple "m=" lines. In such 885 cases, the payload type value cannot be used to associate received 886 RTP packets with the correct "m=" line. 888 An offerer and answerer can inform each other which SSRC values they 889 will use for RTP and RTCP by using the SDP 'ssrc' attribute 890 [RFC5576]. To allow for proper association with this mechanism, the 891 'ssrc' attribute needs to be associated with each "m=" line that 892 shares a payload type with any other "m=" line in the same bundle. 893 As the SSRC values will be carried inside the RTP/RTCP packets, the 894 offerer and answerer can then use that information to associate 895 received RTP packets with the correct "m=" line. However, an offerer 896 will not know which SSRC values the answerer will use until it has 897 received the answer providing that information. Due to this, before 898 the offerer has received the answer, the offerer will not be able to 899 associate received RTP/RTCP packets with the correct "m=" line using 900 the SSRC values. 902 In order for an offerer and answerer to always be able to associate 903 received RTP and RTCP packets with the correct "m=" line, an offerer 904 and answerer using the BUNDLE extension MUST support the mechanism 905 defined in Section 14, where the remote endpoint inserts the 906 identification-tag associated with an "m=" line in RTP and RTCP 907 packets associated with that "m=" line. 909 10.3. RTP/RTCP Multiplexing 911 10.3.1. General 913 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 914 multiplexing [RFC5761] for the RTP-based media specified by the 915 BUNDLE group. 917 When RTP/RTCP multiplexing is enabled, the same address:port 918 combination will be used for sending all RTP packets and the RTCP 919 packets associated with the BUNDLE group. Each endpoint will send 920 the packets towards the BUNDLE address of the other endpoint. The 921 same address:port combination MAY be used for receiving RTP packets 922 and RTCP packets. 924 10.3.2. SDP Offer/Answer Procedures 926 10.3.2.1. General 928 This section describes how an offerer and answerer use the SDP 'rtcp- 929 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 930 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 931 multiplexing for RTP-based media specified by a BUNDLE group. 933 The procedures in this section only apply to RTP-based "m=" lines. 935 10.3.2.2. Generating the Initial SDP Offer 937 When an offerer generates an initial offer, the offerer MUST 938 associate either an SDP 'rtcp-mux' attribute [RFC5761] or an SDP 939 'rtcp-mux-only' attribute [I-D.ietf-mmusic-mux-exclusive] with each 940 bundled RTP-based "m=" line in the offer. The offerer MUST associate 941 an SDP 'rtcp-mux-only' attribute with each bundle-only "m=" line. If 942 the offerer associates a 'rtcp-mux-only' attribute with an "m=" line, 943 the offerer may also associate a 'rtcp-mux' attribute with the same 944 "m=" line, as described in [I-D.ietf-mmusic-mux-exclusive]. 946 NOTE: Within a BUNDLE group, the offerer can associate the SDP 'rtcp- 947 mux' attribute with some of the RTP-based "m=" lines, while it 948 associates the SDP 'rtcp-mux-only' attribute to other RTP-based "m=" 949 lines, depending on whether the offerer supports fallback to usage of 950 a separate port for RTCP in case the answerer does not include the 951 "m=" line in the BUNDLE group. 953 NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with an 954 "m=" line, the offerer can also associate an SDP 'rtcp' attribute 955 [RFC3605] with a bundled "m=" line, excluding a bundle-only "m=" 956 line, in order to provide a fallback port for RTCP, as described in 957 [RFC5761]. However, the fallback port will only be used in case the 958 answerer does not include the "m=" line in the BUNDLE group in the 959 associated answer. 961 In the initial offer, the address:port combination for RTCP MUST be 962 unique in each bundled RTP-based "m=" line (excluding a 'bundle-only' 963 "m=" line), similar to RTP. 965 10.3.2.3. Generating the SDP Answer 967 When an answerer generates an answer, if the answerer accepts one or 968 more RTP-based "m=" lines within a BUNDLE group, the answerer MUST 969 enable usage of RTP/RTCP multiplexing. The answerer MUST associate 970 an SDP "rtcp-mux" attribute with each RTP-based "m=" line in the 971 answer. In addition, if an "m=" line in the corresponding offer 972 contained an SDP "rtcp-mux-only" attribute, the answerer MUST also 973 associate an SDP "rtcp-mux-only" attribute with the "m=" line in the 974 answer. 976 If an RTP-based "m=" line in the corresponding offer did not contain 977 an SDP "rtcp-mux" attribute or an SDP "rtcp-mux-only" attribute, the 978 answerer MUST NOT include the "m=" line within a BUNDLE group in the 979 answer. 981 If an RTP-based "m=" line in the corresponding offer contained an SDP 982 "rtcp-mux-only" attribute, and if the answerer moves the "m=" line 983 out of the BUNDLE group in the answer Section 8.4.4, the answerer 984 MUST still either enable RTP/RTCP multiplexing for the media 985 associated with the "m=" line, or reject the "m=" line Section 8.4.5. 987 The answerer MUST NOT associate an SDP 'rtcp' attribute with any 988 bundled "m=" line in the answer. The answerer will use the port 989 value of the selected offerer BUNDLE address for sending RTP and RTCP 990 packets associated with each RTP-based bundled "m=" line towards the 991 offerer. 993 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 994 negotiated in a previous offer/answer transaction, the answerer MUST 995 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 996 "m=" line in the answer. 998 10.3.2.4. Offerer Processing of the SDP Answer 1000 When an offerer receives an answer, if the answerer has accepted the 1001 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 1002 follows the procedures for RTP/RTCP multiplexing defined in 1003 [RFC5761]. The offerer will use the port value associated with the 1004 answerer BUNDLE address for sending RTP and RTCP packets associated 1005 with each RTP-based bundled "m=" line towards the answerer. 1007 NOTE: It is considered a protocol error if the answerer has not 1008 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 1009 that the answerer included in the BUNDLE group. 1011 10.3.2.5. Modifying the Session 1013 When an offerer generates a subsequent offer, it MUST associate an 1014 SDP 'rtcp-mux' attribute or an SDP 'rtcp-mux-only' attribute with 1015 each RTP-based bundled "m=" line within the BUNDLE group (including 1016 any bundled RTP-based "m=" line that the offerer wants to add to the 1017 BUNDLE group), unless the offerer wants to disable or remove the "m=" 1018 line from the BUNDLE group. 1020 11. ICE Considerations 1022 11.1. General 1024 This section describes how to use the BUNDLE grouping extension 1025 together with the Interactive Connectivity Establishment (ICE) 1026 mechanism [I-D.ietf-ice-rfc5245bis]. 1028 The generic procedures for negotiating usage of ICE using SDP, 1029 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1030 with BUNDLE, with the following exceptions: 1032 o When BUNDLE addresses for a BUNDLE group have been selected for 1033 both endpoints, ICE connectivity checks and keep-alives only need 1034 to be performed for the whole BUNDLE group, instead of per bundled 1035 "m=" line. 1037 o Among bundled "m=" lines with which the offerer has associated a 1038 shared address, the offerer only associates ICE-related media- 1039 level SDP attributes with the "m=" line associated with the 1040 offerer BUNDLE-tag. 1042 o Among bundled "m=" lines with which the answerer has associated a 1043 shared address, the answerer only associates ICE-related media- 1044 level SDP attributes with the "m=" line associated with the 1045 answerer BUNDLE-tag. 1047 Support and usage of ICE mechanism together with the BUNDLE extension 1048 is OPTIONAL. 1050 11.2. SDP Offer/Answer Procedures 1052 11.2.1. General 1054 When an offerer associates a unique address with a bundled "m=" line 1055 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1056 'candidate' attributes (and other applicable ICE-related media-level 1057 SDP attributes), containing unique ICE properties (candidates etc), 1058 with the "m=" line, according to the procedures in 1059 [I-D.ietf-mmusic-ice-sip-sdp]. 1061 When an offerer associates a shared address with a bundled "m=" line, 1062 if the "m=" line is associated with the offerer BUNDLE-tag, the 1063 offerer MUST associate SDP 'candidate' attributes (and other 1064 applicable ICE-related media-level SDP attributes), containing shared 1065 ICE properties, with the "m=" line. If the "m=" line is not 1066 associated with the offerer BUNDLE-tag, the offerer MUST NOT 1067 associate ICE-related SDP attributes with the "m=" line. 1069 When an answerer associates a shared address with a bundled "m=" 1070 line, if the "m=" line is associated with the answerer BUNDLE-tag, 1071 the answerer MUST associate SDP 'candidate' attributes (and other 1072 applicable ICE-related media-level SDP attributes), containing shared 1073 ICE properties, with the "m=" line. If the "m=" line is not 1074 associated with the answerer BUNDLE-tag, the answerer MUST NOT 1075 associate ICE-related SDP attributes with the "m=" line. 1077 NOTE: As most ICE-related media-level SDP attributes belong to the 1078 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1079 offerer and answerer follow the rules in Section 8.2. However, in 1080 the case of ICE-related media-level attributes, the rules apply to 1081 all attributes (see note below), even if they belong to a different 1082 mux category. 1084 NOTE: The following ICE-related media-level SDP attributes are 1085 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1086 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1087 pacing'. 1089 11.2.2. Generating the Initial SDP Offer 1091 When an offerer generates an initial offer, the offerer MUST 1092 associate ICE-related media-level SDP attributes with each bundled 1093 "m=" line, according to [Section 11.2.1]. 1095 11.2.3. Generating the SDP Answer 1097 When an answerer generates an answer that contains a BUNDLE group, 1098 the answerer MUST associated ICE-related SDP attributes with the "m=" 1099 line associated with the answerer BUNDLE-tag, according to 1100 [Section 11.2.1]. 1102 11.2.4. Offerer Processing of the SDP Answer 1104 When an offerer receives an answer, if the answerer supports and uses 1105 the ICE mechanism and the BUNDLE extension, the offerer MUST 1106 associate the ICE properties associated with the offerer BUNDLE 1107 address, selected by the answerer [Section 8.4.2], with each bundled 1108 "m=" line. 1110 11.2.5. Modifying the Session 1112 When an offerer generates a subsequent offer, it MUST associated 1113 unique or shared ICE properties to one or more bundled "m=" lines, 1114 according to [Section 11.2.1]. 1116 12. DTLS Considerations 1118 One or more media streams within a BUNDLE group might use the 1119 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1120 to encrypt the data, or to negotiate encryption keys if another 1121 encryption mechanism is used to encrypt media. 1123 When DTLS is used within a BUNDLE group, the following rules apply: 1125 o There can only be one DTLS association [RFC6347] associated with 1126 the BUNDLE group; and 1128 o Each usage of the DTLS association within the BUNDLE group MUST 1129 use the same mechanism for determining which endpoints (the 1130 offerer or answerer) becomes DTLS client and DTLS server; and 1132 o Each usage of the DTLS association within the Bundle group MUST 1133 use the same mechanism for determining whether an offer or answer 1134 will trigger the establishment of a new DTLS association, or 1135 whether an existing DTLS association will be used; and 1137 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1138 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1139 [RFC5764], The client MUST include the extension even if the usage 1140 of DTLS-SRTP is not negotiated as part of the multimedia session 1141 (e.g. SIP session [RFC3261]. 1143 NOTE: The inclusion of the 'use_srtp' extension during the initial 1144 DTLS handshake ensures that a DTLS renegotiation will not be required 1145 in order to include the extension, in case DTLS-SRTP encrypted media 1146 is added to the BUNDLE group later during the multimedia session. 1148 13. Update to RFC 3264 1150 13.1. General 1152 This section replaces the text of the following sections of RFC 3264: 1154 o Section 5.1 (Unicast Streams). 1156 o Section 8.2 (Removing a Media Stream). 1158 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1160 13.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1162 For recvonly and sendrecv streams, the port number and address in the 1163 offer indicate where the offerer would like to receive the media 1164 stream. For sendonly RTP streams, the address and port number 1165 indirectly indicate where the offerer wants to receive RTCP reports. 1166 Unless there is an explicit indication otherwise, reports are sent to 1167 the port number one higher than the number indicated. The IP address 1168 and port present in the offer indicate nothing about the source IP 1169 address and source port of RTP and RTCP packets that will be sent by 1170 the offerer. A port number of zero in the offer indicates that the 1171 stream is offered but MUST NOT be used. This has no useful semantics 1172 in an initial offer, but is allowed for reasons of completeness, 1173 since the answer can contain a zero port indicating a rejected stream 1174 (Section 6). Furthermore, existing streams can be terminated by 1175 setting the port to zero (Section 8). In general, a port number of 1176 zero indicates that the media stream is not wanted. 1178 13.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1180 For recvonly and sendrecv streams, the port number and address in the 1181 offer indicate where the offerer would like to receive the media 1182 stream. For sendonly RTP streams, the address and port number 1183 indirectly indicate where the offerer wants to receive RTCP reports. 1184 Unless there is an explicit indication otherwise, reports are sent to 1185 the port number one higher than the number indicated. The IP address 1186 and port present in the offer indicate nothing about the source IP 1187 address and source port of RTP and RTCP packets that will be sent by 1188 the offerer. A port number of zero in the offer by default indicates 1189 that the stream is offered but MUST NOT be used, but an extension 1190 mechanism might specify different semantics for the usage of a zero 1191 port value. Furthermore, existing streams can be terminated by 1192 setting the port to zero (Section 8). In general, a port number of 1193 zero by default indicates that the media stream is not wanted. 1195 13.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1197 A stream that is offered with a port of zero MUST be marked with port 1198 zero in the answer. Like the offer, the answer MAY omit all 1199 attributes present previously, and MAY list just a single media 1200 format from amongst those in the offer. 1202 13.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1204 A stream that is offered with a port of zero MUST by default be 1205 marked with port zero in the answer, unless an extension mechanism, 1206 which specifies semantics for the usage of a non-zero port value, is 1207 used. If the stream is marked with port zero in the answer, the 1208 answer MAY omit all attributes present previously, and MAY list just 1209 a single media format from amongst those in the offer." 1211 13.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1213 RFC 2543 [10] specified that placing a user on hold was accomplished 1214 by setting the connection address to 0.0.0.0. Its usage for putting 1215 a call on hold is no longer recommended, since it doesn't allow for 1216 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1217 with connection oriented media. However, it can be useful in an 1218 initial offer when the offerer knows it wants to use a particular set 1219 of media streams and formats, but doesn't know the addresses and 1220 ports at the time of the offer. Of course, when used, the port 1221 number MUST NOT be zero, which would specify that the stream has been 1222 disabled. An agent MUST be capable of receiving SDP with a 1223 connection address of 0.0.0.0, in which case it means that neither 1224 RTP nor RTCP should be sent to the peer. 1226 13.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1228 RFC 2543 [10] specified that placing a user on hold was accomplished 1229 by setting the connection address to 0.0.0.0. Its usage for putting 1230 a call on hold is no longer recommended, since it doesn't allow for 1231 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1232 with connection oriented media. However, it can be useful in an 1233 initial offer when the offerer knows it wants to use a particular set 1234 of media streams and formats, but doesn't know the addresses and 1235 ports at the time of the offer. Of course, when used, the port 1236 number MUST NOT be zero, if it would specify that the stream has been 1237 disabled. However, an extension mechanism might specify different 1238 semantics of the zero port number usage. An agent MUST be capable of 1239 receiving SDP with a connection address of 0.0.0.0, in which case it 1240 means that neither RTP nor RTCP should be sent to the peer. 1242 14. RTP/RTCP extensions for identification-tag transport 1244 14.1. General 1246 SDP Offerers and Answerers [RFC3264] can associate identification- 1247 tags with "m=" lines within SDP Offers and Answers, using the 1248 procedures in [RFC5888]. Each identification-tag uniquely represents 1249 an "m=" line. 1251 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1252 used to carry identification-tags within RTCP SDES packets. This 1253 section also defines a new RTP header extension [RFC5285], which is 1254 used to carry identification-tags in RTP packets. 1256 The SDES item and RTP header extension make it possible for a 1257 receiver to associate received RTCP- and RTP packets with a specific 1258 "m=" line, with which the receiver has associated an identification- 1259 tag, even if those "m=" lines are part of the same RTP session. A 1260 media recipient informs the media sender about the identification-tag 1261 associated with an "m=" line through the use of an 'mid' attribute 1262 [RFC5888]. The media sender then inserts the identification-tag in 1263 RTCP and RTP packets sent to the media recipient. 1265 NOTE: This text above defines how identification-tags are carried in 1266 SDP Offers and Answers. The usage of other signalling protocols for 1267 carrying identification-tags is not prevented, but the usage of such 1268 protocols is outside the scope of this document. 1270 [RFC3550] defines general procedures regarding the RTCP transmission 1271 interval. The RTCP MID SDES item SHOULD be sent in the first few 1272 RTCP packets sent on joining the session, and SHOULD be sent 1273 regularly thereafter. The exact number of RTCP packets in which this 1274 SDES item is sent is intentionally not specified here, as it will 1275 depend on the expected packet loss rate, the RTCP reporting interval, 1276 and the allowable overhead. 1278 The RTP MID header extension SHOULD be included in some RTP packets 1279 at the start of the session and whenever the SSRC changes. It might 1280 also be useful to include the header extension in RTP packets that 1281 comprise random access points in the media (e.g., with video 1282 I-frames). The exact number of RTP packets in which this header 1283 extension is sent is intentionally not specified here, as it will 1284 depend on expected packet loss rate and loss patterns, the overhead 1285 the application can tolerate, and the importance of immediate receipt 1286 of the identification-tag. 1288 For robustness purpose, endpoints need to be prepared for situations 1289 where the reception of the identification-tag is delayed, and SHOULD 1290 NOT terminate sessions in such cases, as the identification-tag is 1291 likely to arrive soon. 1293 14.2. RTCP MID SDES Item 1295 0 1 2 3 1296 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 1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1298 | MID=TBD | length | identification-tag ... 1299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1301 The identification-tag payload is UTF-8 encoded, as in SDP. 1303 The identification-tag is not zero terminated. 1305 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1306 identifier value.] 1308 14.3. RTP MID Header Extension 1310 The payload, containing the identification-tag, of the RTP MID header 1311 extension element can be encoded using either the one-byte or two- 1312 byte header [RFC5285]. The identification-tag payload is UTF-8 1313 encoded, as in SDP. 1315 The identification-tag is not zero terminated. Note, that set of 1316 header extensions included in the packet needs to be padded to the 1317 next 32-bit boundary using zero bytes [RFC5285]. 1319 As the identification-tag is included in either an RTCP SDES item or 1320 an RTP header extension, or both, there should be some consideration 1321 about the packet expansion caused by the identification-tag. To 1322 avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the 1323 header extension's size needs to be taken into account when encoding 1324 the media. 1326 It is recommended that the identification-tag is kept short. Due to 1327 the properties of the RTP header extension mechanism, when using the 1328 one-byte header, a tag that is 1-3 bytes will result in that a 1329 minimal number of 32-bit words are used for the RTP header extension, 1330 in case no other header extensions are included at the same time. 1331 Note, do take into account that some single characters when UTF-8 1332 encoded will result in multiple octets. 1334 15. IANA Considerations 1336 15.1. New SDES item 1338 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1339 document.] 1341 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1342 identifier value.] 1344 This document adds the MID SDES item to the IANA "RTCP SDES item 1345 types" registry as follows: 1347 Value: TBD 1348 Abbrev.: MID 1349 Name: Media Identification 1350 Reference: RFCXXXX 1352 15.2. New RTP Header Extension URI 1354 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1355 document.] 1357 This document defines a new extension URI in the RTP Compact Header 1358 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1359 Parameters registry, according to the following data: 1361 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1362 Description: Media identification 1363 Contact: christer.holmberg@ericsson.com 1364 Reference: RFCXXXX 1366 15.3. New SDP Attribute 1368 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1369 document.] 1371 This document defines a new SDP media-level attribute, 'bundle-only', 1372 according to the following data: 1374 Attribute name: bundle-only 1375 Type of attribute: media 1376 Subject to charset: No 1377 Purpose: Request a media description to be accepted 1378 in the answer only if kept within a BUNDLE 1379 group by the answerer. 1380 Appropriate values: N/A 1381 Contact name: Christer Holmberg 1382 Contact e-mail: christer.holmberg@ericsson.com 1383 Reference: RFCXXXX 1385 15.4. New SDP Group Semantics 1387 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1388 document.] 1390 This document registers the following semantics with IANA in the 1391 "Semantics for the "group" SDP Attribute" subregistry (under the 1392 "Session Description Protocol (SDP) Parameters" registry: 1394 Semantics Token Reference 1395 ------------------------------------- ------ --------- 1396 Media bundling BUNDLE [RFCXXXX] 1398 16. Security Considerations 1400 The security considerations defined in [RFC3264] and [RFC5888] apply 1401 to the BUNDLE extension. Bundle does not change which information 1402 flows over the network but only changes which addresses and ports 1403 that information is flowing on and thus has very little impact on the 1404 security of the RTP sessions. 1406 When the BUNDLE extension is used, a single set of security 1407 credentials might be used for all media streams specified by a BUNDLE 1408 group. 1410 When the BUNDLE extension is used, the number of SSRC values within a 1411 single RTP session increases, which increases the risk of SSRC 1412 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1413 and SRTCP encryption in certain situations. 1415 17. Examples 1417 17.1. Example: Bundle Address Selection 1419 The example below shows: 1421 o An offer, in which the offerer associates a unique address with 1422 each bundled "m=" line within the BUNDLE group. 1424 o An answer, in which the answerer selects the offerer BUNDLE 1425 address, and in which selects its own BUNDLE address (the answerer 1426 BUNDLE address) and associates it with each bundled "m=" line 1427 within the BUNDLE group. 1429 SDP Offer (1) 1431 v=0 1432 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1433 s= 1434 c=IN IP4 atlanta.example.com 1435 t=0 0 1436 a=group:BUNDLE foo bar 1437 m=audio 10000 RTP/AVP 0 8 97 1438 b=AS:200 1439 a=mid:foo 1440 a=rtpmap:0 PCMU/8000 1441 a=rtpmap:8 PCMA/8000 1442 a=rtpmap:97 iLBC/8000 1443 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1444 m=video 10002 RTP/AVP 31 32 1445 b=AS:1000 1446 a=mid:bar 1447 a=rtpmap:31 H261/90000 1448 a=rtpmap:32 MPV/90000 1449 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1451 SDP Answer (2) 1453 v=0 1454 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1455 s= 1456 c=IN IP4 biloxi.example.com 1457 t=0 0 1458 a=group:BUNDLE foo bar 1459 m=audio 20000 RTP/AVP 0 1460 b=AS:200 1461 a=mid:foo 1462 a=rtpmap:0 PCMU/8000 1463 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1464 m=video 20000 RTP/AVP 32 1465 b=AS:1000 1466 a=mid:bar 1467 a=rtpmap:32 MPV/90000 1468 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1470 17.2. Example: BUNDLE Extension Rejected 1472 The example below shows: 1474 o An offer, in which the offerer associates a unique address with 1475 each bundled "m=" line within the BUNDLE group. 1477 o An answer, in which the answerer rejects the offered BUNDLE group, 1478 and associates a unique address with each "m=" line (following 1479 normal RFC 3264 procedures). 1481 SDP Offer (1) 1483 v=0 1484 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1485 s= 1486 c=IN IP4 atlanta.example.com 1487 t=0 0 1488 a=group:BUNDLE foo bar 1489 m=audio 10000 RTP/AVP 0 8 97 1490 b=AS:200 1491 a=mid:foo 1492 a=rtpmap:0 PCMU/8000 1493 a=rtpmap:8 PCMA/8000 1494 a=rtpmap:97 iLBC/8000 1495 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1496 m=video 10002 RTP/AVP 31 32 1497 b=AS:1000 1498 a=mid:bar 1499 a=rtpmap:31 H261/90000 1500 a=rtpmap:32 MPV/90000 1501 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1503 SDP Answer (2) 1505 v=0 1506 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1507 s= 1508 c=IN IP4 biloxi.example.com 1509 t=0 0 1510 m=audio 20000 RTP/AVP 0 1511 b=AS:200 1512 a=rtpmap:0 PCMU/8000 1513 m=video 30000 RTP/AVP 32 1514 b=AS:1000 1515 a=rtpmap:32 MPV/90000 1517 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1519 The example below shows: 1521 o A subsequent offer (the BUNDLE group has been created as part of a 1522 previous offer/answer transaction), in which the offerer adds a 1523 new "m=" line, represented by the "zen" identification-tag, to a 1524 previously negotiated BUNDLE group, associates a unique address 1525 with the added "m=" line, and associates the previously selected 1526 offerer BUNDLE address with each of the other bundled "m=" lines 1527 within the BUNDLE group. 1529 o An answer, in which the answerer associates the answerer BUNDLE 1530 address with each bundled "m=" line (including the newly added 1531 "m=" line) within the BUNDLE group. 1533 SDP Offer (1) 1535 v=0 1536 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1537 s= 1538 c=IN IP4 atlanta.example.com 1539 t=0 0 1540 a=group:BUNDLE foo bar zen 1541 m=audio 10000 RTP/AVP 0 8 97 1542 b=AS:200 1543 a=mid:foo 1544 a=rtpmap:0 PCMU/8000 1545 a=rtpmap:8 PCMA/8000 1546 a=rtpmap:97 iLBC/8000 1547 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1548 m=video 10000 RTP/AVP 31 32 1549 b=AS:1000 1550 a=mid:bar 1551 a=rtpmap:31 H261/90000 1552 a=rtpmap:32 MPV/90000 1553 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1554 m=video 20000 RTP/AVP 66 1555 b=AS:1000 1556 a=mid:zen 1557 a=rtpmap:66 H261/90000 1558 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1560 SDP Answer (2) 1562 v=0 1563 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1564 s= 1565 c=IN IP4 biloxi.example.com 1566 t=0 0 1567 a=group:BUNDLE foo bar zen 1568 m=audio 20000 RTP/AVP 0 1569 b=AS:200 1570 a=mid:foo 1571 a=rtpmap:0 PCMU/8000 1572 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1573 m=video 20000 RTP/AVP 32 1574 b=AS:1000 1575 a=mid:bar 1576 a=rtpmap:32 MPV/90000 1577 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1578 m=video 20000 RTP/AVP 66 1579 b=AS:1000 1580 a=mid:zen 1581 a=rtpmap:66 H261/90000 1582 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1584 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1586 The example below shows: 1588 o A subsequent offer (the BUNDLE group has been created as part of a 1589 previous offer/answer transaction), in which the offerer moves a 1590 bundled "m=" line out of a BUNDLE group, associates a unique 1591 address with the moved "m=" line, and associates the offerer 1592 BUNDLE address with each other bundled "m=" line within the BUNDLE 1593 group. 1595 o An answer, in which the answerer moves the "m=" line out of the 1596 BUNDLE group, associates unique address with the moved "m=" line, 1597 and associates the answerer BUNDLE address with each of the 1598 remaining bundled "m=" line within the BUNDLE group. 1600 SDP Offer (1) 1602 v=0 1603 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1604 s= 1605 c=IN IP4 atlanta.example.com 1606 t=0 0 1607 a=group:BUNDLE foo bar 1608 m=audio 10000 RTP/AVP 0 8 97 1609 b=AS:200 1610 a=mid:foo 1611 a=rtpmap:0 PCMU/8000 1612 a=rtpmap:8 PCMA/8000 1613 a=rtpmap:97 iLBC/8000 1614 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1615 m=video 10000 RTP/AVP 31 32 1616 b=AS:1000 1617 a=mid:bar 1618 a=rtpmap:31 H261/90000 1619 a=rtpmap:32 MPV/90000 1620 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1621 m=video 50000 RTP/AVP 66 1622 b=AS:1000 1623 a=mid:zen 1624 a=rtpmap:66 H261/90000 1626 SDP Answer (2) 1628 v=0 1629 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1630 s= 1631 c=IN IP4 biloxi.example.com 1632 t=0 0 1633 a=group:BUNDLE foo bar 1634 m=audio 20000 RTP/AVP 0 1635 b=AS:200 1636 a=mid:foo 1637 a=rtpmap:0 PCMU/8000 1638 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1639 m=video 20000 RTP/AVP 32 1640 b=AS:1000 1641 a=mid:bar 1642 a=rtpmap:32 MPV/90000 1643 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1644 m=video 60000 RTP/AVP 66 1645 b=AS:1000 1646 a=mid:zen 1647 a=rtpmap:66 H261/90000 1649 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1650 Group 1652 The example below shows: 1654 o A subsequent offer (the BUNDLE group has been created as part of a 1655 previous offer/answer transaction), in which the offerer disables 1656 a bundled "m=" line within BUNDLE group, assigns a zero port 1657 number to the disabled "m=" line, and associates the offerer 1658 BUNDLE address with each of the other bundled "m=" lines within 1659 the BUNDLE group. 1661 o An answer, in which the answerer moves the disabled "m=" line out 1662 of the BUNDLE group, assigns a zero port value to the disabled 1663 "m=" line, and associates the answerer BUNDLE address with each of 1664 the remaining bundled "m=" line within the BUNDLE group. 1666 SDP Offer (1) 1668 v=0 1669 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1670 s= 1671 c=IN IP4 atlanta.example.com 1672 t=0 0 1673 a=group:BUNDLE foo bar 1674 m=audio 10000 RTP/AVP 0 8 97 1675 b=AS:200 1676 a=mid:foo 1677 a=rtpmap:0 PCMU/8000 1678 a=rtpmap:8 PCMA/8000 1679 a=rtpmap:97 iLBC/8000 1680 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1681 m=video 10000 RTP/AVP 31 32 1682 b=AS:1000 1683 a=mid:bar 1684 a=rtpmap:31 H261/90000 1685 a=rtpmap:32 MPV/90000 1686 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1687 m=video 0 RTP/AVP 66 1688 a=mid:zen 1689 a=rtpmap:66 H261/90000 1691 SDP Answer (2) 1693 v=0 1694 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1695 s= 1696 c=IN IP4 biloxi.example.com 1697 t=0 0 1698 a=group:BUNDLE foo bar 1699 m=audio 20000 RTP/AVP 0 1700 b=AS:200 1701 a=mid:foo 1702 a=rtpmap:0 PCMU/8000 1703 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1704 m=video 20000 RTP/AVP 32 1705 b=AS:1000 1706 a=mid:bar 1707 a=rtpmap:32 MPV/90000 1708 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1709 m=video 0 RTP/AVP 66 1710 a=mid:zen 1711 a=rtpmap:66 H261/90000 1713 18. Acknowledgements 1715 The usage of the SDP grouping extension for negotiating bundled media 1716 is based on a similar alternatives proposed by Harald Alvestrand and 1717 Cullen Jennings. The BUNDLE extension described in this document is 1718 based on the different alternative proposals, and text (e.g. SDP 1719 examples) have been borrowed (and, in some cases, modified) from 1720 those alternative proposals. 1722 The SDP examples are also modified versions from the ones in the 1723 Alvestrand proposal. 1725 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1726 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 1727 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1728 Justin Uberti for reading the text, and providing useful feedback. 1730 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1731 providing help and text on the RTP/RTCP procedures. 1733 Thanks to Spotify for providing music for the countless hours of 1734 document editing. 1736 19. Change Log 1738 [RFC EDITOR NOTE: Please remove this section when publishing] 1740 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 1742 o - Alignment with exclusive mux procedures. 1744 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 1746 o - Yet another terminology change. 1748 o - Mux category considerations added. 1750 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 1751 o - ICE considerations modified: ICE-related SDP attributes only 1752 added to the bundled m- line representing the selected BUNDLE 1753 address. 1755 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 1757 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 1758 rfc5245bis. 1760 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 1762 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 1763 considerations. 1765 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 1767 o - Reference and procedures associated with exclusive RTP/RTCP mux 1768 added 1770 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 1772 o - RTCP-MUX mandatory for bundled RTP m- lines 1774 o - Editorial fixes based on comments from Flemming Andreasen 1776 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 1778 o - Correction of Ari's family name 1780 o - Editorial fixes based on comments from Thomas Stach 1782 o - RTP/RTCP correction based on comment from Magnus Westerlund 1784 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1785 msg14861.html 1787 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 1789 o - Correct based on comment from Paul Kyzivat 1791 o -- 'received packets' replaced with 'received data' 1793 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1795 o - Clarification based on comment from James Guballa 1797 o - Clarification based on comment from Flemming Andreasen 1798 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1800 o - DTLS Considerations section added. 1802 o - BUNDLE semantics added to the IANA Considerations 1804 o - Changes based on WGLC comments from Adam Roach 1806 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1807 msg14673.html 1809 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1811 o - Changes based on agreements at IETF#92 1813 o -- BAS Offer removed, based on agreement at IETF#92. 1815 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1816 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1818 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1820 o - Editorial changes based on comments from Magnus Westerlund. 1822 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1824 o - Modification of RTP/RTCP multiplexing section, based on comments 1825 from Magnus Westerlund. 1827 o - Reference updates. 1829 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1831 o - Editorial fix. 1833 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1835 o - Editorial changes. 1837 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1839 o Changes to allow a new suggested offerer BUNDLE address to be 1840 assigned to each bundled m- line. 1842 o Changes based on WGLC comments from Paul Kyzivat 1844 o - Editorial fixes 1845 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1847 o Usage of SDP 'extmap' attribute added 1849 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1850 port value 1852 o Changes based on WGLC comments from Thomas Stach 1854 o - ICE candidates not assigned to bundle-only m- lines with a zero 1855 port value 1857 o - Editorial changes 1859 o Changes based on WGLC comments from Colin Perkins 1861 o - Editorial changes: 1863 o -- "RTP SDES item" -> "RTCP SDES item" 1865 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1867 o - Changes in section 10.1.1: 1869 o -- "SHOULD NOT" -> "MUST NOT" 1871 o -- Additional text added to the Note 1873 o - Change to section 13.2: 1875 o -- Clarify that mid value is not zero terminated 1877 o - Change to section 13.3: 1879 o -- Clarify that mid value is not zero terminated 1881 o -- Clarify padding 1883 o Changes based on WGLC comments from Paul Kyzivat 1885 o - Editorial changes: 1887 o Changes based on WGLC comments from Jonathan Lennox 1889 o - Editorial changes: 1891 o - Defintion of SDP bundle-only attribute alligned with structure 1892 in 4566bis draft 1894 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1896 o Editorial corrections based on comments from Harald Alvestrand. 1898 o Editorial corrections based on comments from Cullen Jennings. 1900 o Reference update (RFC 7160). 1902 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1903 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1904 msg13765.html). 1906 o Additional text added to the Security Considerations. 1908 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1910 o SDP bundle-only attribute added to IANA Considerations. 1912 o SDES item and RTP header extension added to Abstract and 1913 Introduction. 1915 o Modification to text updating section 8.2 of RFC 3264. 1917 o Reference corrections. 1919 o Editorial corrections. 1921 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1923 o Terminology change: "bundle-only attribute assigned to m= line" to 1924 "bundle-only attribute associated with m= line". 1926 o Editorial corrections. 1928 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1930 o Editorial corrections. 1932 o - "of"->"if" (8.3.2.5). 1934 o - "optional"->"OPTIONAL" (9.1). 1936 o - Syntax/ABNF for 'bundle-only' attribute added. 1938 o - SDP Offer/Answer sections merged. 1940 o - 'Request new offerer BUNDLE address' section added 1941 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1943 o OPEN ISSUE regarding Receiver-ID closed. 1945 o - RTP MID SDES Item. 1947 o - RTP MID Header Extension. 1949 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1950 closed. 1952 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1953 include an 'rtcp' attribute in the answer, based on the procedures 1954 in section 5.1.3 of RFC 5761. 1956 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1958 o Draft title changed. 1960 o Added "SDP" to section names containing "Offer" or "Answer". 1962 o Editorial fixes based on comments from Paul Kyzivat 1963 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1964 msg13314.html). 1966 o Editorial fixed based on comments from Colin Perkins 1967 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1968 msg13318.html). 1970 o - Removed text about extending BUNDLE to allow multiple RTP 1971 sessions within a BUNDLE group. 1973 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1975 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1976 3264 structure. 1978 o Additional definitions added. 1980 o - Shared address. 1982 o - Bundled "m=" line. 1984 o - Bundle-only "m=" line. 1986 o - Offerer suggested BUNDLE mid. 1988 o - Answerer selected BUNDLE mid. 1990 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1991 to multiple "m=" lines until it has received an SDP Answer 1992 indicating support of the BUNDLE extension. 1994 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1995 Answerer supports the BUNDLE extension, assign a zero port value 1996 to a 'bundle-only' "m=" line. 1998 o SDP 'bundle-only' attribute section added. 2000 o Connection data nettype/addrtype restrictions added. 2002 o RFC 3264 update section added. 2004 o Indicating that a specific payload type value can be used in 2005 multiple "m=" lines, if the value represents the same codec 2006 configuration in each "m=" line. 2008 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2010 o Updated Offerer procedures (http://www.ietf.org/mail- 2011 archive/web/mmusic/current/msg12293.html). 2013 o Updated Answerer procedures (http://www.ietf.org/mail- 2014 archive/web/mmusic/current/msg12333.html). 2016 o Usage of SDP 'bundle-only' attribute added. 2018 o Reference to Trickle ICE document added. 2020 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2022 o Mechanism modified, to be based on usage of SDP Offers with both 2023 different and identical port number values, depending on whether 2024 it is known if the remote endpoint supports the extension. 2026 o Cullen Jennings added as co-author. 2028 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2030 o No changes. New version due to expiration. 2032 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2034 o No changes. New version due to expiration. 2036 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2037 o Draft name changed. 2039 o Harald Alvestrand added as co-author. 2041 o "Multiplex" terminology changed to "bundle". 2043 o Added text about single versus multiple RTP Sessions. 2045 o Added reference to RFC 3550. 2047 20. References 2049 20.1. Normative References 2051 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2052 Requirement Levels", BCP 14, RFC 2119, 2053 DOI 10.17487/RFC2119, March 1997, 2054 . 2056 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2057 with Session Description Protocol (SDP)", RFC 3264, 2058 DOI 10.17487/RFC3264, June 2002, 2059 . 2061 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2062 Jacobson, "RTP: A Transport Protocol for Real-Time 2063 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2064 July 2003, . 2066 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2067 in Session Description Protocol (SDP)", RFC 3605, 2068 DOI 10.17487/RFC3605, October 2003, 2069 . 2071 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2072 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2073 July 2006, . 2075 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2076 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2077 . 2079 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2080 (ICE): A Protocol for Network Address Translator (NAT) 2081 Traversal for Offer/Answer Protocols", RFC 5245, 2082 DOI 10.17487/RFC5245, April 2010, 2083 . 2085 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2086 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2087 2008, . 2089 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2090 Control Packets on a Single Port", RFC 5761, 2091 DOI 10.17487/RFC5761, April 2010, 2092 . 2094 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2095 Security (DTLS) Extension to Establish Keys for the Secure 2096 Real-time Transport Protocol (SRTP)", RFC 5764, 2097 DOI 10.17487/RFC5764, May 2010, 2098 . 2100 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2101 Protocol (SDP) Grouping Framework", RFC 5888, 2102 DOI 10.17487/RFC5888, June 2010, 2103 . 2105 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2106 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2107 January 2012, . 2109 [I-D.ietf-ice-rfc5245bis] 2110 Keranen, A. and J. Rosenberg, "Interactive Connectivity 2111 Establishment (ICE): A Protocol for Network Address 2112 Translator (NAT) Traversal", draft-ietf-ice-rfc5245bis-01 2113 (work in progress), December 2015. 2115 [I-D.ietf-mmusic-sdp-mux-attributes] 2116 Nandakumar, S., "A Framework for SDP Attributes when 2117 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-12 2118 (work in progress), January 2016. 2120 [I-D.ietf-mmusic-mux-exclusive] 2121 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2122 Multiplexing using SDP", draft-ietf-mmusic-mux- 2123 exclusive-03 (work in progress), February 2016. 2125 [I-D.ietf-mmusic-ice-sip-sdp] 2126 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, "Using 2127 Interactive Connectivity Establishment (ICE) with Session 2128 Description Protocol (SDP) offer/answer and Session 2129 Initiation Protocol (SIP)", draft-ietf-mmusic-ice-sip- 2130 sdp-07 (work in progress), October 2015. 2132 20.2. Informative References 2134 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2135 A., Peterson, J., Sparks, R., Handley, M., and E. 2136 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2137 DOI 10.17487/RFC3261, June 2002, 2138 . 2140 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2141 Description Protocol (SDP) Security Descriptions for Media 2142 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2143 . 2145 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2146 Media Attributes in the Session Description Protocol 2147 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2148 . 2150 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2151 Clock Rates in an RTP Session", RFC 7160, 2152 DOI 10.17487/RFC7160, April 2014, 2153 . 2155 [I-D.ietf-mmusic-trickle-ice] 2156 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2157 Incremental Provisioning of Candidates for the Interactive 2158 Connectivity Establishment (ICE) Protocol", draft-ietf- 2159 mmusic-trickle-ice-02 (work in progress), January 2015. 2161 Appendix A. Design Considerations 2163 A.1. General 2165 One of the main issues regarding the BUNDLE grouping extensions has 2166 been whether, in SDP Offers and SDP Answers, the same port value 2167 should be inserted in "m=" lines associated with a BUNDLE group, as 2168 the purpose of the extension is to negotiate the usage of a single 2169 address:port combination for media specified by the "m=" lines. 2170 Issues with both approaches, discussed in the Appendix have been 2171 raised. The outcome was to specify a mechanism which uses SDP Offers 2172 with both different and identical port values. 2174 Below are the primary issues that have been considered when defining 2175 the "BUNDLE" grouping extension: 2177 o 1) Interoperability with existing UAs. 2179 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2181 o 3) Time to gather, and the number of, ICE candidates. 2183 o 4) Different error scenarios, and when they occur. 2185 o 5) SDP Offer/Answer impacts, including usage of port number value 2186 zero. 2188 NOTE: Before this document is published as an RFC, this 2189 Appendix might be removed. 2191 A.2. UA Interoperability 2193 Consider the following SDP Offer/Answer exchange, where Alice sends 2194 an SDP Offer to Bob: 2196 SDP Offer 2198 v=0 2199 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2200 s= 2201 c=IN IP4 atlanta.example.com 2202 t=0 0 2203 m=audio 10000 RTP/AVP 97 2204 a=rtpmap:97 iLBC/8000 2205 m=video 10002 RTP/AVP 97 2206 a=rtpmap:97 H261/90000 2208 SDP Answer 2210 v=0 2211 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2212 s= 2213 c=IN IP4 biloxi.example.com 2214 t=0 0 2215 m=audio 20000 RTP/AVP 97 2216 a=rtpmap:97 iLBC/8000 2217 m=video 20002 RTP/AVP 97 2218 a=rtpmap:97 H261/90000 2220 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2221 later invention to RTP and Bob can not assume that Alice supports RFC 2222 4961. This means that Alice may be sending RTP from a different port 2223 than 10000 or 10002 - some implementation simply send the RTP from an 2224 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2225 way that Bob know if it should be passed to the video or audio codec 2226 is by looking at the port it was received on. This lead some SDP 2227 implementations to use the fact that each "m=" line had a different 2228 port number to use that port number as an index to find the correct m 2229 line in the SDP. As a result, some implementations that do support 2230 symmetric RTP and ICE still use a SDP data structure where SDP with 2231 "m=" lines with the same port such as: 2233 SDP Offer 2235 v=0 2236 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2237 s= 2238 c=IN IP4 atlanta.example.com 2239 t=0 0 2240 m=audio 10000 RTP/AVP 97 2241 a=rtpmap:97 iLBC/8000 2242 m=video 10000 RTP/AVP 98 2243 a=rtpmap:98 H261/90000 2245 will result in the second "m=" line being considered an SDP error 2246 because it has the same port as the first line. 2248 A.3. Usage of port number value zero 2250 In an SDP Offer or SDP Answer, the media specified by an "m=" line 2251 can be disabled/rejected by setting the port number value to zero. 2252 This is different from e.g. using the SDP direction attributes, where 2253 RTCP traffic will continue even if the SDP "inactive" attribute is 2254 indicated for the associated "m=" line. 2256 If each "m=" line associated with a BUNDLE group would contain 2257 different port values, and one of those port values would be used for 2258 a BUNDLE address associated with the BUNDLE group, problems would 2259 occur if an endpoint wants to disable/reject the "m=" line associated 2260 with that port, by setting the port value to zero. After that, no 2261 "m=" line would contain the port value which is used for the BUNDLE 2262 address. In addition, it is unclear what would happen to the ICE 2263 candidates associated with the "m=" line, as they are also used for 2264 the BUNDLE address. 2266 A.4. B2BUA And Proxy Interoperability 2268 Some back to back user agents may be configured in a mode where if 2269 the incoming call leg contains an SDP attribute the B2BUA does not 2270 understand, the B2BUS still generates that SDP attribute in the Offer 2271 for the outgoing call leg. Consider an B2BUA that did not understand 2272 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2273 Further assume that the B2BUA was configured to tear down any call 2274 where it did not see any RTCP for 5 minutes. In this cases, if the 2275 B2BUA received an Offer like: 2277 SDP Offer 2279 v=0 2280 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2281 s= 2282 c=IN IP4 atlanta.example.com 2283 t=0 0 2284 m=audio 49170 RTP/AVP 0 2285 a=rtcp:53020 2287 It would be looking for RTCP on port 49172 but would not see any 2288 because the RTCP would be on port 53020 and after five minutes, it 2289 would tear down the call. Similarly, an SBC that did not understand 2290 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2291 wrong port and tear down the call. It is worth noting that a B2BUA 2292 that generated an Offer with capabilities it does not understand is 2293 not compliant with the specifications. 2295 A.4.1. Traffic Policing 2297 Sometimes intermediaries do not act as B2BUA, in the sense that they 2298 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2299 however, they may use SDP information (e.g. IP address and port) in 2300 order to control traffic gating functions, and to set traffic 2301 policing rules. There might be rules which will trigger a session to 2302 be terminated in case media is not sent or received on the ports 2303 retrieved from the SDP. This typically occurs once the session is 2304 already established and ongoing. 2306 A.4.2. Bandwidth Allocation 2308 Sometimes intermediaries do not act as B2BUA, in the sense that they 2309 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2310 however, they may use SDP information (e.g. codecs and media types) 2311 in order to control bandwidth allocation functions. The bandwidth 2312 allocation is done per "m=" line, which means that it might not be 2313 enough if media specified by all "m=" lines try to use that 2314 bandwidth. That may either simply lead to bad user experience, or to 2315 termination of the call. 2317 A.5. Candidate Gathering 2319 When using ICE, an candidate needs to be gathered for each port. 2320 This takes approximately 20 ms extra for each extra "m=" line due to 2321 the NAT pacing requirements. All of this gather can be overlapped 2322 with other things while the page is loading to minimize the impact. 2323 If the client only wants to generate TURN or STUN ICE candidates for 2324 one of the "m=" lines and then use trickle ICE 2325 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2326 the rest of the "m=" lines, it MAY do that and will not need any 2327 additional gathering time. 2329 Some people have suggested a TURN extension to get a bunch of TURN 2330 allocation at once. This would only provide a single STUN result so 2331 in cases where the other end did not support BUNDLE, may cause more 2332 use of the TURN server but would be quick in the cases where both 2333 sides supported BUNDLE and would fall back to a successful call in 2334 the other cases. 2336 Authors' Addresses 2338 Christer Holmberg 2339 Ericsson 2340 Hirsalantie 11 2341 Jorvas 02420 2342 Finland 2344 Email: christer.holmberg@ericsson.com 2346 Harald Tveit Alvestrand 2347 Google 2348 Kungsbron 2 2349 Stockholm 11122 2350 Sweden 2352 Email: harald@alvestrand.no 2353 Cullen Jennings 2354 Cisco 2355 400 3rd Avenue SW, Suite 350 2356 Calgary, AB T2P 4H2 2357 Canada 2359 Email: fluffy@iii.ca