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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: February 18, 2017 C. Jennings 7 Cisco 8 August 17, 2016 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-32.txt 14 Abstract 16 This specification defines a new Session Description Protocol (SDP) 17 Grouping Framework extension, 'BUNDLE'. The extension can be used 18 with the SDP Offer/Answer mechanism to negotiate the usage of a 19 single address:port combination (BUNDLE address) for receiving media, 20 referred to as bundled media, specified by multiple SDP media 21 descriptions ("m=" lines). 23 To assist endpoints in negotiating the use of bundle this 24 specification defines a new SDP attribute, 'bundle-only', which can 25 be used to request that specific media is only used if bundled. The 26 specification also updates RFC 3264, to allow usage of zero port 27 values without meaning that media is rejected. 29 There are multiple ways to correlate the bundled RTP packets with the 30 appropriate media descriptions. This specification defines a new 31 Real-time Transport Protocol (RTP) source description (SDES) item and 32 a new RTP header extension that provides an additional way to do this 33 correlation by using them to carry a value that associates the RTP/ 34 RTCP packets with a specific media description. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on February 18, 2017. 53 Copyright Notice 55 Copyright (c) 2016 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 This document may contain material from IETF Documents or IETF 69 Contributions published or made publicly available before November 70 10, 2008. The person(s) controlling the copyright in some of this 71 material may not have granted the IETF Trust the right to allow 72 modifications of such material outside the IETF Standards Process. 73 Without obtaining an adequate license from the person(s) controlling 74 the copyright in such materials, this document may not be modified 75 outside the IETF Standards Process, and derivative works of it may 76 not be created outside the IETF Standards Process, except to format 77 it for publication as an RFC or to translate it into languages other 78 than English. 80 Table of Contents 82 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 83 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 84 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 86 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 87 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 8 88 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 89 7.1. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 90 7.2. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 91 7.3. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 92 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 93 8.1. Mux Category Considerations . . . . . . . . . . . . . . . 10 94 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 95 8.2.1. Suggesting the offerer BUNDLE address . . . . . . . . 11 97 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 11 98 8.3.1. Answerer Selection of Offerer Bundle Address . . . . 12 99 8.3.2. Answerer Selection of Answerer BUNDLE Address . . . . 13 100 8.3.3. Moving A Media Description Out Of A BUNDLE Group . . 13 101 8.3.4. Rejecting A Media Description In A BUNDLE Group . . . 14 102 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14 103 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 14 104 8.5.1. Suggesting a new offerer BUNDLE address . . . . . . . 15 105 8.5.2. Adding a media description to a BUNDLE group . . . . 15 106 8.5.3. Moving A Media Description Out Of A BUNDLE Group . . 16 107 8.5.4. Disabling A Media Description In A BUNDLE Group . . . 16 108 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 17 109 9.1. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 110 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 18 111 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 18 112 10.1.1. Payload Type (PT) Value Reuse . . . . . . . . . . . 18 113 10.2. Associating RTP/RTCP Packets With Correct SDP Media 114 Description . . . . . . . . . . . . . . . . . . . . . . 19 115 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 20 116 10.3.1. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 117 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 22 118 11.1. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 22 119 11.1.1. Generating the Initial SDP Offer . . . . . . . . . . 23 120 11.1.2. Generating the SDP Answer . . . . . . . . . . . . . 23 121 11.1.3. Offerer Processing of the SDP Answer . . . . . . . . 24 122 11.1.4. Modifying the Session . . . . . . . . . . . . . . . 24 123 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 24 124 13. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 25 125 13.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 25 126 13.2. New text replacing section 5.1 (2nd paragraph) of RFC 127 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 128 13.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 26 129 13.4. New text replacing section 8.2 (2nd paragraph) of RFC 130 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 131 13.5. Original text of section 8.4 (6th paragraph) of RFC 3264 26 132 13.6. New text replacing section 8.4 (6th paragraph) of RFC 133 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 134 14. RTP/RTCP extensions for identification-tag transport . . . . 27 135 14.1. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 28 136 14.2. RTP SDES Header Extension For MID . . . . . . . . . . . 28 137 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 138 15.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 29 139 15.2. New RTP SDES Header Extension URI . . . . . . . . . . . 29 140 15.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 30 141 15.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 30 142 16. Security Considerations . . . . . . . . . . . . . . . . . . . 31 143 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 31 144 17.1. Example: Bundle Address Selection . . . . . . . . . . . 31 145 17.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 33 146 17.3. Example: Offerer Adds A Media Description To A BUNDLE 147 Group . . . . . . . . . . . . . . . . . . . . . . . . . 34 148 17.4. Example: Offerer Moves A Media Description Out Of A 149 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 36 150 17.5. Example: Offerer Disables A Media Description Within A 151 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 38 152 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39 153 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 40 154 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 47 155 20.1. Normative References . . . . . . . . . . . . . . . . . . 47 156 20.2. Informative References . . . . . . . . . . . . . . . . . 49 157 Appendix A. Design Considerations . . . . . . . . . . . . . . . 50 158 A.1. UA Interoperability . . . . . . . . . . . . . . . . . . . 50 159 A.2. Usage of port number value zero . . . . . . . . . . . . . 52 160 A.3. B2BUA And Proxy Interoperability . . . . . . . . . . . . 52 161 A.3.1. Traffic Policing . . . . . . . . . . . . . . . . . . 53 162 A.3.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 53 163 A.4. Candidate Gathering . . . . . . . . . . . . . . . . . . . 53 164 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54 166 1. Introduction 168 This specification defines a way to use a single address:port 169 combination (BUNDLE address) for receiving media specified by 170 multiple SDP media descriptions ("m=" lines). 172 This specification defines a new SDP Grouping Framework [RFC5888] 173 extension called 'BUNDLE'. The extension can be used with the 174 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 175 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 176 BUNDLE address is used for receiving media specified by multiple "m=" 177 lines. This is referred to as bundled media. 179 The offerer and answerer [RFC3264] use the BUNDLE extension to 180 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 181 address) and one for the answerer (answerer BUNDLE address), to be 182 used for receiving the bundled media specified by a BUNDLE group. 183 Once the offerer and the answerer have negotiated a BUNDLE group, 184 they associate their respective BUNDLE address with each "m=" line in 185 the BUNDLE group. The BUNDLE addresses are used to receive all media 186 specified by the BUNDLE group. 188 The use of a BUNDLE group and a BUNDLE address also allows the usage 189 of a single set of Interactive Connectivity Establishment (ICE) 190 [RFC5245] candidates for multiple "m=" lines. 192 This specification also defines a new SDP attribute, 'bundle-only', 193 which can be used to request that specific media is only used if kept 194 within a BUNDLE group. The specification also updates RFC 3264, to 195 allow usage of zero port values without meaning that media is 196 rejected. 198 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 199 transport address (IP address and port) to multiple "m=" lines are 200 undefined, and there is no grouping defined by such means. Instead, 201 an explicit grouping mechanism needs to be used to express the 202 intended semantics. This specification provides such an extension. 204 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 205 [RFC3264]. The update allows an answerer to assign a non-zero port 206 value to an "m=" line in an SDP answer, even if the "m=" line in the 207 associated SDP offer contained a zero port value. 209 This specification also defines a new Real-time Transport Protocol 210 (RTP) [RFC3550] source description (SDES) item and a new RTP header 211 extension that can be used to carry a value that associates RTP/RTCP 212 packets with a specific media description. This can be used to 213 correlate a RTP packet with the correct media. 215 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 216 address MUST only be associated with a single BUNDLE group. The 217 procedures in this specification apply independently to a given 218 BUNDLE group. All RTP based media flows described by a single BUNDLE 219 group belong to a single RTP session [RFC3550]. 221 The BUNDLE extension is backward compatible. Endpoints that do not 222 support the extension are expected to generate offers and answers 223 without an SDP 'group:BUNDLE' attribute, and are expected to 224 associate a unique address with each "m=" line within an offer and 225 answer, according to the procedures in [RFC4566] and [RFC3264] 227 2. Terminology 229 "m=" line: SDP bodies contain one or more media descriptions. Each 230 media description is identified by an SDP "m=" line. 232 5-tuple: A collection of the following values: source address, source 233 port, destination address, destination port, and transport-layer 234 protocol. 236 Unique address: An IP address and port combination that is associated 237 with only one "m=" line in an offer or answer. 239 Shared address: An IP address and port combination that is associated 240 with multiple "m=" lines within an offer or answer. 242 Offerer BUNDLE-tag: The first identification-tag in a given SDP 243 'group:BUNDLE' attribute identification-tag list in an offer. 245 Answerer BUNDLE-tag: The first identification-tag in a given SDP 246 'group:BUNDLE' attribute identification-tag list in an answer. 248 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 249 and port combination used by an offerer to receive all media 250 specified by each "m=" line within the BUNDLE group. 252 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 253 and port combination used by an answerer to receive all media 254 specified by each "m=" line within the BUNDLE group. 256 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 257 exchange, which uses the same BUNDLE address for receiving media. 259 Bundled "m=" line: An "m=" line, whose identification-tag is placed 260 in an SDP 'group:BUNDLE' attribute identification-tag list in an 261 offer or answer. 263 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 264 'bundle-only' attribute. 266 Bundled media: All media specified by a given BUNDLE group. 268 Initial offer: The first offer, within an SDP session (e.g. a SIP 269 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 270 to carry SDP), in which the offerer indicates that it wants to create 271 a given BUNDLE group. 273 Subsequent offer: An offer which contains a BUNDLE group that has 274 been created as part of a previous offer/answer exchange. 276 Identification-tag: A unique token value that is used to identify an 277 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 278 "m=" line, carries an unique identification-tag. The session-level 279 SDP 'group' attribute [RFC5888] carries a list of identification- 280 tags, identifying the "m=" lines associated with that particular 281 'group' attribute. 283 3. Conventions 285 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 286 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 287 document are to be interpreted as described in BCP 14, RFC 2119 288 [RFC2119]. 290 4. Applicability Statement 292 The mechanism in this specification only applies to the Session 293 Description Protocol (SDP) [RFC4566], when used together with the SDP 294 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 295 scope of this document, and is thus undefined. 297 5. SDP Grouping Framework BUNDLE Extension 299 This section defines a new SDP Grouping Framework extension 300 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 301 Offer/Answer mechanism to negotiate the usage of a single 302 address:port combination (BUNDLE address) for receiving bundled 303 media. 305 A single address:port combination is also used for sending bundled 306 media. The address:port combination used for sending bundled media 307 MAY be the same as the BUNDLE address, used to receive bundled media, 308 depending on whether symmetric RTP [RFC4961] is used. 310 All media specified by a BUNDLE group share a single 5-tuple, i.e. in 311 addition to using a single address:port combination all bundled media 312 MUST be transported using the same transport-layer protocol (e.g. 313 UDP or TCP). 315 The BUNDLE extension is indicated using an SDP 'group' attribute with 316 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 317 associated with each bundled "m=" line, and each identification-tag 318 is listed in the SDP 'group:BUNDLE' attribute identification-tag 319 list. Each "m=" line whose identification-tag is listed in the 320 identification-tag list is associated with a given BUNDLE group. 322 SDP bodies can contain multiple BUNDLE groups. Any given bundled 323 "m=" line MUST NOT be associated with more than one BUNDLE group. 325 Section 8 defines the detailed SDP Offer/Answer procedures for the 326 BUNDLE extension. 328 6. SDP 'bundle-only' Attribute 330 This section defines a new SDP media-level attribute [RFC4566], 331 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 332 hence has no value. 334 Name: bundle-only 336 Value: N/A 338 Usage Level: media 340 Charset Dependent: no 342 Example: 344 a=bundle-only 346 In order to ensure that an answerer that does not support the BUNDLE 347 extension always rejects a bundled "m=" line, the offerer can assign 348 a zero port value to the "m=" line. According to [RFC3264] an 349 answerer will reject such "m=" line. By associating an SDP 'bundle- 350 only' attribute with such "m=" line, the offerer can request that the 351 answerer accepts the "m=" line if the answerer supports the Bundle 352 extension, and if the answerer keeps the "m=" line within the 353 associated BUNDLE group. 355 NOTE: Once the offerer BUNDLE address has been selected, the offerer 356 does not need to include the 'bundle-only' attribute in subsequent 357 offers. By associating the offerer BUNDLE address with an "m=" line 358 of a subsequent offer, the offerer will ensure that the answerer will 359 either keep the "m=" line within the BUNDLE group, or the answerer 360 will have to reject the "m=" line. 362 The usage of the 'bundle-only' attribute is only defined for a 363 bundled "m=" line with a zero port value, within an offer. Other 364 usage is unspecified. 366 Section 8 defines the detailed SDP Offer/Answer procedures for the 367 'bundle-only' attribute. 369 7. SDP Information Considerations 371 This section describes restrictions associated with the usage of SDP 372 parameters within a BUNDLE group. It also describes, when parameter 373 and attribute values have been associated with each bundled "m=" 374 line, how to calculate a value for the whole BUNDLE group. 376 7.1. Connection Data (c=) 378 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 379 line MUST be 'IN'. 381 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 382 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 383 each "m=" line. 385 NOTE: Extensions to this specification can specify usage of the 386 BUNDLE mechanism for other nettype and addrtype values than the ones 387 listed above. 389 7.2. Bandwidth (b=) 391 An offerer and answerer MUST use the rules and restrictions defined 392 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP 393 bandwidth (b=) line with bundled "m=" lines. 395 7.3. Attributes (a=) 397 An offerer and answerer MUST use the rules and restrictions defined 398 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating SDP 399 attributes with bundled "m=" lines. 401 8. SDP Offer/Answer Procedures 403 This section describes the SDP Offer/Answer [RFC3264] procedures for: 405 o Negotiating and creating 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 8.1. Mux Category Considerations 438 When an offerer associates SDP attributes with a bundled "m=" line 439 associated with a shared address, IDENTICAL and TRANSPORT mux 440 category SDP attributes [I-D.ietf-mmusic-sdp-mux-attributes] are 441 associated with the "m=" line only if the "m=" line is also 442 associated with the offerer BUNDLE-tag. Otherwise the offerer MUST 443 NOT associate such SDP attributes with the "m=" line. 445 When an answerer associates SDP attributes with a bundled "m=" line, 446 IDENTICAL and TRANSPORT mux category SDP attributes are associated 447 with the "m=" line only if the "m=" line is also associated with the 448 answerer BUNDLE-tag. Otherwise the answerer MUST NOT associated such 449 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. The attributes and attribute values 455 are implicitly applied to each "m=" line associated with the shared 456 address. 458 8.2. Generating the Initial SDP Offer 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 8.2.1]. 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 8.2.1] 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 8.5.4]. 488 [Section 17.1] shows an example of an initial offer. 490 8.2.1. 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 8.3. Generating the SDP Answer 501 When an answerer generates an answer that contains a BUNDLE group, 502 the following general SDP grouping framework restrictions, defined in 503 [RFC5888], also apply to the BUNDLE group: 505 o The answerer MUST NOT include a BUNDLE group in the answer, unless 506 the offerer requested the BUNDLE group to be created in the 507 corresponding offer; and 509 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 510 unless the offerer requested the "m=" line to be within that 511 BUNDLE group in the corresponding offer. 513 If the answer contains a BUNDLE group, the answerer MUST: 515 o Select an Offerer BUNDLE Address [Section 8.3.1]; and 516 o Select an Answerer BUNDLE Address [Section 8.3.2]; 518 The answerer is allowed to select a new Answerer BUNDLE address each 519 time it generates an answer to an offer. 521 If the answerer does not want to keep an "m=" line within a BUNDLE 522 group, it MUST: 524 o Move the "m=" line out of the BUNDLE group [Section 8.3.3]; or 526 o Reject the "m=" line [Section 8.3.4]; 528 If the answerer keeps a bundle-only "m=" line within the BUNDLE 529 group, it follows the procedures (associates the answerer BUNDLE 530 address with the "m=" line etc) for any other "m=" line kept within 531 the BUNDLE group. 533 If the answerer does not want to keep a bundle-only "m=" line within 534 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.4]. 536 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 537 any "m=" line in an answer. 539 NOTE: If a bundled "m=" line in an offer contains a zero port value, 540 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 541 is an indication that the offerer wants to disable the "m=" line 542 [Section 8.5.4]. 544 8.3.1. Answerer Selection of Offerer Bundle Address 546 In an offer, the address (unique or shared) associated with the 547 bundled "m=" line associated with the offerer BUNDLE-tag indicates 548 the address that the offerer suggests as the offerer BUNDLE address 549 [Section 8.2.1]. The answerer MUST check whether that "m=" line 550 fulfils the following criteria: 552 o The answerer will not move the "m=" line out of the BUNDLE group 553 [Section 8.3.3]; and 555 o The answerer will not reject the "m=" line [Section 8.3.4]; and 557 o The "m=" line does not contain a zero port value. 559 If all of the criteria above are fulfilled, the answerer MUST select 560 the address associated with the "m=" line as the offerer BUNDLE 561 address. In the answer, the answerer BUNDLE-tag represents the "m=" 562 line, and the address associated with the "m=" line in the offer 563 becomes the offerer BUNDLE address. 565 If one or more of the criteria are not fulfilled, the answerer MUST 566 select the next identification-tag in the identification-tag list, 567 and perform the same criteria check for the "m=" line associated with 568 that identification-tag. If there are no more identification-tags in 569 the identification-tag list, the answerer MUST NOT create the BUNDLE 570 group. In addition, unless the answerer rejects the whole offer, the 571 answerer MUST apply the answerer procedures for moving an "m=" line 572 out of a BUNDLE group [Section 8.3.3] to each bundled "m=" line in 573 the offer when creating the answer. 575 [Section 17.1] shows an example of an offerer BUNDLE address 576 selection. 578 8.3.2. Answerer Selection of Answerer BUNDLE Address 580 When the answerer selects a BUNDLE address for itself, referred to as 581 the answerer BUNDLE address, it MUST associate that address with each 582 bundled "m=" line within the created BUNDLE group in the answer. 584 The answerer MUST NOT associate the answerer BUNDLE address with an 585 "m=" line that is not within the BUNDLE group, or to an "m=" line 586 that is within another BUNDLE group. 588 [Section 17.1] shows an example of an answerer BUNDLE address 589 selection. 591 8.3.3. Moving A Media Description Out Of A BUNDLE Group 593 When an answerer wants to move an "m=" line out of a BUNDLE group, it 594 MUST first check the following criteria: 596 o In the corresponding offer, the "m=" line is associated with a 597 shared address (e.g. a previously selected offerer BUNDLE 598 address); or 600 o In the corresponding offer, an SDP 'bundle-only' attribute is 601 associated with the "m=" line, and the "m=" line contains a zero 602 port value. 604 If either criteria above is fulfilled, the answerer MUST reject the 605 "m=" line [Section 8.3.4]. 607 Otherwise, if in the corresponding offer the "m=" line is associated 608 with a unique address, the answerer MUST associate a unique address 609 with the "m=" line in the answer (the answerer does not reject the 610 "m=" line). 612 In addition, in either case above, the answerer MUST NOT place the 613 identification-tag, associated with the moved "m=" line, in the SDP 614 'group' attribute identification-tag list associated with the BUNDLE 615 group. 617 8.3.4. Rejecting A Media Description In A BUNDLE Group 619 When an answerer rejects an "m=" line, it MUST associate an address 620 with a zero port value with the "m=" line in the answer, according to 621 the procedures in [RFC3264]. 623 In addition, the answerer MUST NOT place the identification-tag, 624 associated with the rejected "m=" line, in the SDP 'group' attribute 625 identification-tag list associated with the BUNDLE group. 627 8.4. Offerer Processing of the SDP Answer 629 When an offerer receives an answer, if the answer contains a BUNDLE 630 group, the offerer MUST check that any bundled "m=" line in the 631 answer was indicated as bundled in the corresponding offer. If there 632 is no mismatch, the offerer MUST use the offerer BUNDLE address, 633 selected by the answerer [Section 8.3.1], as the address for each 634 bundled "m=" line. 636 NOTE: As the answerer might reject one or more bundled "m=" lines, or 637 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 638 line in the offer might not be indicated as bundled in the answer. 640 If the answer does not contain a BUNDLE group, the offerer MUST 641 process the answer as a normal answer. 643 8.5. Modifying the Session 645 When an offerer generates a subsequent offer, it MUST associate the 646 previously selected offerer BUNDLE address [Section 8.3.1] with each 647 bundled "m=" line (including any bundle-only "m=" line), except if: 649 o The offerer suggests a new offerer BUNDLE address [Section 8.5.1]; 650 or 652 o The offerer wants to add a bundled "m=" line to the BUNDLE group 653 [Section 8.5.2]; or 655 o The offerer wants to move a bundled "m=" line out of the BUNDLE 656 group [Section 8.5.3]; or 658 o The offerer wants to disable the bundled "m=" line 659 [Section 8.5.4]. 661 In addition, the offerer MUST select an offerer BUNDLE-tag 662 [Section 8.2.1] associated with the previously selected offerer 663 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 664 address. 666 8.5.1. Suggesting a new offerer BUNDLE address 668 When an offerer generates an offer, in which it suggests a new 669 offerer BUNDLE address [Section 8.2.1], the offerer MUST: 671 o Assign the address (shared address) to each "m=" line within the 672 BUNDLE group; or 674 o Assign the address (unique address) to one bundled "m=" line. 676 In addition, the offerer MUST indicate that the address is the new 677 suggested offerer BUNDLE address [Section 8.2.1]. 679 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 680 address with each bundled "m=" line, it can associate unique 681 addresses with any number of bundled "m=" lines (and the previously 682 selected offerer BUNDLE address to any remaining bundled "m=" line) 683 if it wants to suggest multiple alternatives for the new offerer 684 BUNDLE address. 686 8.5.2. Adding a media description to a BUNDLE group 688 When an offerer generates an offer, in which it wants to add a 689 bundled "m=" line to a BUNDLE group, the offerer MUST: 691 o Assign a unique address to the added "m=" line; or 693 o Assign the previously selected offerer BUNDLE address to the added 694 "m=" line; or 696 o If the offerer associates a new (shared address) suggested offerer 697 BUNDLE address with each bundled "m=" line [Section 8.5.1], also 698 associate that address with the added "m=" line. 700 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 701 identification-tag list with the BUNDLE group [Section 8.2.1] by 702 adding the identification-tag associated with the added "m=" line to 703 the list. 705 NOTE: Assigning a unique address to the "m=" line allows the answerer 706 to move the "m=" line out of the BUNDLE group [Section 8.3.3], 707 without having to reject the "m=" line. 709 If the offerer associates a unique address with the added "m=" line, 710 and if the offerer suggests that address as the new offerer BUNDLE 711 address [Section 8.5.1], the offerer BUNDLE-tag MUST represent the 712 added "m=" line [Section 8.2.1]. 714 If the offerer associates a new suggested offerer BUNDLE address with 715 each bundled "m=" line [Section 8.5.1], including the added "m=" 716 line, the offerer BUNDLE-tag MAY represent the added "m=" line 717 [Section 8.2.1]. 719 [Section 17.3] shows an example where an offerer sends an offer in 720 order to add a bundled "m=" line to a BUNDLE group. 722 8.5.3. Moving A Media Description Out Of A BUNDLE Group 724 When an offerer generates an offer, in which it wants to move a 725 bundled "m=" line out of a BUNDLE group it was added to in a previous 726 offer/answer transaction, the offerer: 728 o MUST associate a unique address with the "m=" line; and 730 o MUST NOT place the identification-tag associated with the "m=" 731 line in the SDP 'group:BUNDLE' attribute identification-tag list 732 associated with the BUNDLE group. 734 NOTE: If the removed "m=" line is associated with the previously 735 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 736 [Section 8.2.1]. 738 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 739 added to another BUNDLE group, the offerer applies the procedures in 740 [Section 8.5.2] to the "m=" line. 742 [Section 17.4] shows an example of an offer for moving an "m=" line 743 out of a BUNDLE group. 745 8.5.4. Disabling A Media Description In A BUNDLE Group 747 When an offerer generates an offer, in which it wants to disable a 748 bundled "m=" line (added to the BUNDLE group in a previous offer/ 749 answer transaction), the offerer: 751 o MUST associate an address with a zero port value with the "m=" 752 line, following the procedures in [RFC4566]; and 754 o MUST NOT place the identification-tag associated with the "m=" 755 line in the SDP 'group:BUNDLE' attribute identification-tag list 756 associated with the BUNDLE group. 758 [Section 17.5] shows an example of an offer for disabling an "m=" 759 line within a BUNDLE group. 761 9. Protocol Identification 763 Each "m=" line within a BUNDLE group MUST use the same transport- 764 layer protocol. If bundled "m=" lines use different protocols on top 765 of the transport-layer protocol, there MUST exist a publicly 766 available specification which describes a mechanism, for this 767 particular protocol combination, how to associate received data with 768 the correct protocol. 770 In addition, if received data can be associated with more than one 771 bundled "m=" line, there MUST exist a publicly available 772 specification which describes a mechanism for associating the 773 received data with the correct "m=" line. 775 This document describes a mechanism to identify the protocol of 776 received data among the STUN, DTLS and SRTP protocols (in any 777 combination), when UDP is used as transport-layer protocol, but does 778 not describe how to identify different protocols transported on DTLS. 779 While the mechanism is generally applicable to other protocols and 780 transport-layer protocols, any such use requires further 781 specification around how to multiplex multiple protocols on a given 782 transport-layer protocol, and how to associate received data with the 783 correct protocols. 785 9.1. STUN, DTLS, SRTP 787 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 788 protocol of a received packet among the STUN, Datagram Transport 789 Layer Security (DTLS) and SRTP protocols (in any combination). If an 790 offer or answer includes bundled "m=" lines that represent these 791 protocols, the offerer or answerer MUST support the mechanism 792 described in [RFC5764], and no explicit negotiation is required in 793 order to indicate support and usage of the mechanism. 795 [RFC5764] does not describe how to identify different protocols 796 transported on DTLS, only how to identify the DTLS protocol itself. 797 If multiple protocols are transported on DTLS, there MUST exist a 798 specification describing a mechanism for identifying each individual 799 protocol. In addition, if a received DTLS packet can be associated 800 with more than one "m=" line, there MUST exist a specification which 801 describes a mechanism for associating the received DTLS packet with 802 the correct "m=" line. 804 [Section 10.2] describes how to associate a received (S)RTP packet 805 with the correct "m=" line. 807 10. RTP Considerations 809 10.1. Single RTP Session 811 All RTP-based media within a single BUNDLE group belong to a single 812 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 813 sessions, one per BUNDLE group. 815 Since a single RTP session is used for each bundle group, all "m=" 816 lines representing RTP-based media in a bundle group will share a 817 single SSRC numbering space [RFC3550]. 819 The following rules and restrictions apply for a single RTP session: 821 o A specific payload type value can be used in multiple bundled "m=" 822 lines if each codec associated with the payload type number shares 823 an identical codec configuration [Section 10.1.1]. 825 o The proto value in each bundled RTP-based "m=" line MUST be 826 identical (e.g. RTP/AVPF). 828 o The RTP MID header extension MUST be enabled, by associating an 829 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 830 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 831 in every offer and answer. 833 o A given SSRC MUST NOT transmit RTP packets using payload types 834 that originate from different bundled "m=" lines. 836 NOTE: The last bullet above is to avoid sending multiple media types 837 from the same SSRC. If transmission of multiple media types are done 838 with time overlap, RTP and RTCP fail to function. Even if done in 839 proper sequence this causes RTP Timestamp rate switching issues 840 [RFC7160]. However, once an SSRC has left the RTP session (by 841 sending an RTCP BYE packet), that SSRC can be reused by another 842 source (possibly associated with a different bundled "m=" line) after 843 a delay of 5 RTCP reporting intervals (the delay is to ensure the 844 SSRC has timed out, in case the RTCP BYE packet was lost [RFC3550]). 846 10.1.1. Payload Type (PT) Value Reuse 848 Multiple bundled "m=" lines might represent RTP based media. As all 849 RTP based media specified by a BUNDLE group belong to the same RTP 850 session, in order for a given payload type value to be used inside 851 more than one bundled "m=" line, all codecs associated with the 852 payload type number MUST share an identical codec configuration. 853 This means that the codecs MUST share the same media type, encoding 854 name, clock rate and any parameter that can affect the codec 855 configuration and packetization. 856 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 857 attribute values must be identical for all codecs that use the same 858 payload type value. 860 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 862 There are multiple mechanisms that can be used by an endpoint in 863 order to associate received RTP/RTCP packets with a bundled "m=" 864 line. Such mechanisms include using the payload type value carried 865 inside the RTP packets, the SSRC values carried inside the RTP 866 packets, and other "m=" line specific information carried inside the 867 RTP packets. 869 As all RTP/RTCP packets associated with a BUNDLE group are received 870 (and sent) using single address:port combinations, the local 871 address:port combination cannot be used to associate received RTP 872 packets with the correct "m=" line. 874 As described in [Section 10.1.1], the same payload type value might 875 be used inside RTP packets described by multiple "m=" lines. In such 876 cases, the payload type value cannot be used to associate received 877 RTP packets with the correct "m=" line. 879 An offerer and answerer can inform each other which SSRC values they 880 will use for RTP and RTCP by using the SDP 'ssrc' attribute 881 [RFC5576]. To allow for proper association with this mechanism, the 882 'ssrc' attribute needs to be associated with each "m=" line that 883 shares a payload type with any other "m=" line in the same bundle. 884 As the SSRC values will be carried inside the RTP/RTCP packets, the 885 offerer and answerer can then use that information to associate 886 received RTP packets with the correct "m=" line. However, an offerer 887 will not know which SSRC values the answerer will use until it has 888 received the answer providing that information. Due to this, before 889 the offerer has received the answer, the offerer will not be able to 890 associate received RTP/RTCP packets with the correct "m=" line using 891 the SSRC values. 893 In order for an offerer and answerer to always be able to associate 894 received RTP and RTCP packets with the correct "m=" line, an offerer 895 and answerer using the BUNDLE extension MUST support the mechanism 896 defined in Section 14, where the remote endpoint inserts the 897 identification-tag associated with an "m=" line in RTP and RTCP 898 packets associated with that "m=" line. 900 10.3. RTP/RTCP Multiplexing 902 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 903 multiplexing [RFC5761] for the RTP-based media specified by the 904 BUNDLE group. 906 When RTP/RTCP multiplexing is enabled, the same address:port 907 combination will be used for sending all RTP packets and the RTCP 908 packets associated with the BUNDLE group. Each endpoint will send 909 the packets towards the BUNDLE address of the other endpoint. The 910 same address:port combination MAY be used for receiving RTP packets 911 and RTCP packets. 913 10.3.1. SDP Offer/Answer Procedures 915 This section describes how an offerer and answerer use the SDP 'rtcp- 916 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 917 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 918 multiplexing for RTP-based media specified by a BUNDLE group. 920 The procedures in this section only apply to RTP-based "m=" lines. 922 10.3.1.1. Generating the Initial SDP Offer 924 When an offerer generates an initial offer, the offerer MUST 925 associate either an SDP 'rtcp-mux' attribute [RFC5761] or an SDP 926 'rtcp-mux-only' attribute [I-D.ietf-mmusic-mux-exclusive] with each 927 bundled RTP-based "m=" line in the offer. The offerer MUST associate 928 an SDP 'rtcp-mux-only' attribute with each bundle-only "m=" line. If 929 the offerer associates a 'rtcp-mux-only' attribute with an "m=" line, 930 the offerer may also associate a 'rtcp-mux' attribute with the same 931 "m=" line, as described in [I-D.ietf-mmusic-mux-exclusive]. 933 NOTE: Within a BUNDLE group, the offerer can associate the SDP 'rtcp- 934 mux' attribute with some of the RTP-based "m=" lines, while it 935 associates the SDP 'rtcp-mux-only' attribute to other RTP-based "m=" 936 lines, depending on whether the offerer supports fallback to usage of 937 a separate port for RTCP in case the answerer does not include the 938 "m=" line in the BUNDLE group. 940 NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with an 941 "m=" line, the offerer can also associate an SDP 'rtcp' attribute 942 [RFC3605] with a bundled "m=" line, excluding a bundle-only "m=" 943 line, in order to provide a fallback port for RTCP, as described in 944 [RFC5761]. However, the fallback port will only be used in case the 945 answerer does not include the "m=" line in the BUNDLE group in the 946 associated answer. 948 In the initial offer, the address:port combination for RTCP MUST be 949 unique in each bundled RTP-based "m=" line (excluding a 'bundle-only' 950 "m=" line), similar to RTP. 952 10.3.1.2. Generating the SDP Answer 954 When an answerer generates an answer, if the answerer accepts one or 955 more RTP-based "m=" lines within a BUNDLE group, the answerer MUST 956 enable usage of RTP/RTCP multiplexing. The answerer MUST associate 957 an SDP "rtcp-mux" attribute with each RTP-based "m=" line in the 958 answer. In addition, if an "m=" line in the corresponding offer 959 contained an SDP "rtcp-mux-only" attribute, the answerer MUST also 960 associate an SDP "rtcp-mux-only" attribute with the "m=" line in the 961 answer. 963 If an RTP-based "m=" line in the corresponding offer did not contain 964 an SDP "rtcp-mux" attribute or an SDP "rtcp-mux-only" attribute, the 965 answerer MUST NOT include the "m=" line within a BUNDLE group in the 966 answer. 968 If an RTP-based "m=" line in the corresponding offer contained an SDP 969 "rtcp-mux-only" attribute, and if the answerer moves the "m=" line 970 out of the BUNDLE group in the answer Section 8.3.3, the answerer 971 MUST still either enable RTP/RTCP multiplexing for the media 972 associated with the "m=" line, or reject the "m=" line Section 8.3.4. 974 The answerer MUST NOT associate an SDP 'rtcp' attribute with any 975 bundled "m=" line in the answer. The answerer will use the port 976 value of the selected offerer BUNDLE address for sending RTP and RTCP 977 packets associated with each RTP-based bundled "m=" line towards the 978 offerer. 980 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 981 negotiated in a previous offer/answer transaction, the answerer MUST 982 associate an SDP 'rtcp-mux' attribute with each bundled RTP-based 983 "m=" line in the answer. 985 10.3.1.3. Offerer Processing of the SDP Answer 987 When an offerer receives an answer, if the answerer has accepted the 988 usage of RTP/RTCP multiplexing (see Section 10.3.1.2), the answerer 989 follows the procedures for RTP/RTCP multiplexing defined in 990 [RFC5761]. The offerer will use the port value associated with the 991 answerer BUNDLE address for sending RTP and RTCP packets associated 992 with each RTP-based bundled "m=" line towards the answerer. 994 NOTE: It is considered a protocol error if the answerer has not 995 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 996 that the answerer included in the BUNDLE group. 998 10.3.1.4. Modifying the Session 1000 When an offerer generates a subsequent offer, it MUST associate an 1001 SDP 'rtcp-mux' attribute or an SDP 'rtcp-mux-only' attribute with 1002 each RTP-based bundled "m=" line within the BUNDLE group (including 1003 any bundled RTP-based "m=" line that the offerer wants to add to the 1004 BUNDLE group), unless the offerer wants to disable or remove the "m=" 1005 line from the BUNDLE group. 1007 11. ICE Considerations 1009 This section describes how to use the BUNDLE grouping extension 1010 together with the Interactive Connectivity Establishment (ICE) 1011 mechanism [I-D.ietf-ice-rfc5245bis]. 1013 The generic procedures for negotiating usage of ICE using SDP, 1014 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1015 with BUNDLE, with the following exceptions: 1017 o When BUNDLE addresses for a BUNDLE group have been selected for 1018 both endpoints, ICE connectivity checks and keep-alives only need 1019 to be performed for the whole BUNDLE group, instead of per bundled 1020 "m=" line. 1022 o Among bundled "m=" lines with which the offerer has associated a 1023 shared address, the offerer only associates ICE-related media- 1024 level SDP attributes with the "m=" line associated with the 1025 offerer BUNDLE-tag. 1027 o Among bundled "m=" lines with which the answerer has associated a 1028 shared address, the answerer only associates ICE-related media- 1029 level SDP attributes with the "m=" line associated with the 1030 answerer BUNDLE-tag. 1032 Support and usage of ICE mechanism together with the BUNDLE extension 1033 is OPTIONAL. 1035 11.1. SDP Offer/Answer Procedures 1037 When an offerer associates a unique address with a bundled "m=" line 1038 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1039 'candidate' attributes (and other applicable ICE-related media-level 1040 SDP attributes), containing unique ICE properties (candidates etc), 1041 with the "m=" line, according to the procedures in 1042 [I-D.ietf-mmusic-ice-sip-sdp]. 1044 When an offerer associates a shared address with a bundled "m=" line, 1045 if the "m=" line is associated with the offerer BUNDLE-tag, the 1046 offerer MUST associate SDP 'candidate' attributes (and other 1047 applicable ICE-related media-level SDP attributes), containing shared 1048 ICE properties, with the "m=" line. If the "m=" line is not 1049 associated with the offerer BUNDLE-tag, the offerer MUST NOT 1050 associate ICE-related SDP attributes with the "m=" line. 1052 When an answerer associates a shared address with a bundled "m=" 1053 line, if the "m=" line is associated with the answerer BUNDLE-tag, 1054 the answerer MUST associate SDP 'candidate' attributes (and other 1055 applicable ICE-related media-level SDP attributes), containing shared 1056 ICE properties, with the "m=" line. If the "m=" line is not 1057 associated with the answerer BUNDLE-tag, the answerer MUST NOT 1058 associate ICE-related SDP attributes with the "m=" line. 1060 NOTE: As most ICE-related media-level SDP attributes belong to the 1061 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1062 offerer and answerer follow the rules in Section 8.1. However, in 1063 the case of ICE-related media-level attributes, the rules apply to 1064 all attributes (see note below), even if they belong to a different 1065 mux category. 1067 NOTE: The following ICE-related media-level SDP attributes are 1068 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1069 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1070 pacing'. 1072 11.1.1. Generating the Initial SDP Offer 1074 When an offerer generates an initial offer, the offerer MUST 1075 associate ICE-related media-level SDP attributes with each bundled 1076 "m=" line, according to [Section 11.1]. 1078 11.1.2. Generating the SDP Answer 1080 When an answerer generates an answer that contains a BUNDLE group, 1081 the answerer MUST associate ICE-related SDP attributes with the "m=" 1082 line associated with the answerer BUNDLE-tag, according to 1083 [Section 11.1]. 1085 11.1.3. Offerer Processing of the SDP Answer 1087 When an offerer receives an answer, if the answerer supports and uses 1088 the ICE mechanism and the BUNDLE extension, the offerer MUST 1089 associate the ICE properties associated with the offerer BUNDLE 1090 address, selected by the answerer [Section 8.3.1], with each bundled 1091 "m=" line. 1093 11.1.4. Modifying the Session 1095 When an offerer generates a subsequent offer, it MUST associate 1096 unique or shared ICE properties to one or more bundled "m=" lines, 1097 according to [Section 11.1]. 1099 12. DTLS Considerations 1101 One or more media streams within a BUNDLE group might use the 1102 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1103 to encrypt the data, or to negotiate encryption keys if another 1104 encryption mechanism is used to encrypt media. 1106 When DTLS is used within a BUNDLE group, the following rules apply: 1108 o There can only be one DTLS association [RFC6347] associated with 1109 the BUNDLE group; and 1111 o Each usage of the DTLS association within the BUNDLE group MUST 1112 use the same mechanism for determining which endpoints (the 1113 offerer or answerer) become DTLS client and DTLS server; and 1115 o Each usage of the DTLS association within the Bundle group MUST 1116 use the same mechanism for determining whether an offer or answer 1117 will trigger the establishment of a new DTLS association, or 1118 whether an existing DTLS association will be used; and 1120 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1121 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1122 [RFC5764], The client MUST include the extension even if the usage 1123 of DTLS-SRTP is not negotiated as part of the multimedia session 1124 (e.g., SIP session [RFC3261]. 1126 NOTE: The inclusion of the 'use_srtp' extension during the initial 1127 DTLS handshake ensures that a DTLS renegotiation will not be required 1128 in order to include the extension, in case DTLS-SRTP encrypted media 1129 is added to the BUNDLE group later during the multimedia session. 1131 13. Update to RFC 3264 1133 This section replaces the text of the following sections of RFC 3264: 1135 o Section 5.1 (Unicast Streams). 1137 o Section 8.2 (Removing a Media Stream). 1139 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1141 13.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 1143 For recvonly and sendrecv streams, the port number and address in the 1144 offer indicate where the offerer would like to receive the media 1145 stream. For sendonly RTP streams, the address and port number 1146 indirectly indicate where the offerer wants to receive RTCP reports. 1147 Unless there is an explicit indication otherwise, reports are sent to 1148 the port number one higher than the number indicated. The IP address 1149 and port present in the offer indicate nothing about the source IP 1150 address and source port of RTP and RTCP packets that will be sent by 1151 the offerer. A port number of zero in the offer indicates that the 1152 stream is offered but MUST NOT be used. This has no useful semantics 1153 in an initial offer, but is allowed for reasons of completeness, 1154 since the answer can contain a zero port indicating a rejected stream 1155 (Section 6). Furthermore, existing streams can be terminated by 1156 setting the port to zero (Section 8). In general, a port number of 1157 zero indicates that the media stream is not wanted. 1159 13.2. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1161 For recvonly and sendrecv streams, the port number and address in the 1162 offer indicate where the offerer would like to receive the media 1163 stream. For sendonly RTP streams, the address and port number 1164 indirectly indicate where the offerer wants to receive RTCP reports. 1165 Unless there is an explicit indication otherwise, reports are sent to 1166 the port number one higher than the number indicated. The IP address 1167 and port present in the offer indicate nothing about the source IP 1168 address and source port of RTP and RTCP packets that will be sent by 1169 the offerer. A port number of zero in the offer by default indicates 1170 that the stream is offered but MUST NOT be used, but an extension 1171 mechanism might specify different semantics for the usage of a zero 1172 port value. Furthermore, existing streams can be terminated by 1173 setting the port to zero (Section 8). In general, a port number of 1174 zero by default indicates that the media stream is not wanted. 1176 13.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 1178 A stream that is offered with a port of zero MUST be marked with port 1179 zero in the answer. Like the offer, the answer MAY omit all 1180 attributes present previously, and MAY list just a single media 1181 format from amongst those in the offer. 1183 13.4. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1185 A stream that is offered with a port of zero MUST by default be 1186 marked with port zero in the answer, unless an extension mechanism, 1187 which specifies semantics for the usage of a non-zero port value, is 1188 used. If the stream is marked with port zero in the answer, the 1189 answer MAY omit all attributes present previously, and MAY list just 1190 a single media format from amongst those in the offer." 1192 13.5. Original text of section 8.4 (6th paragraph) of RFC 3264 1194 RFC 2543 [10] specified that placing a user on hold was accomplished 1195 by setting the connection address to 0.0.0.0. Its usage for putting 1196 a call on hold is no longer recommended, since it doesn't allow for 1197 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1198 with connection oriented media. However, it can be useful in an 1199 initial offer when the offerer knows it wants to use a particular set 1200 of media streams and formats, but doesn't know the addresses and 1201 ports at the time of the offer. Of course, when used, the port 1202 number MUST NOT be zero, which would specify that the stream has been 1203 disabled. An agent MUST be capable of receiving SDP with a 1204 connection address of 0.0.0.0, in which case it means that neither 1205 RTP nor RTCP should be sent to the peer. 1207 13.6. New text replacing section 8.4 (6th paragraph) of RFC 3264 1209 RFC 2543 [10] specified that placing a user on hold was accomplished 1210 by setting the connection address to 0.0.0.0. Its usage for putting 1211 a call on hold is no longer recommended, since it doesn't allow for 1212 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1213 with connection oriented media. However, it can be useful in an 1214 initial offer when the offerer knows it wants to use a particular set 1215 of media streams and formats, but doesn't know the addresses and 1216 ports at the time of the offer. Of course, when used, the port 1217 number MUST NOT be zero, if it would specify that the stream has been 1218 disabled. However, an extension mechanism might specify different 1219 semantics of the zero port number usage. An agent MUST be capable of 1220 receiving SDP with a connection address of 0.0.0.0, in which case it 1221 means that neither RTP nor RTCP should be sent to the peer. 1223 14. RTP/RTCP extensions for identification-tag transport 1225 SDP Offerers and Answerers [RFC3264] can associate identification- 1226 tags with "m=" lines within SDP Offers and Answers, using the 1227 procedures in [RFC5888]. Each identification-tag uniquely represents 1228 an "m=" line. 1230 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1231 used to carry identification-tags within RTCP SDES packets. This 1232 section also defines a new RTP SDES header extension 1233 [I-D.ietf-avtext-sdes-hdr-ext], which is used to carry the 'MID' RTCP 1234 SDES item in RTP packets. 1236 The SDES item and RTP SDES header extension make it possible for a 1237 receiver to associate received RTCP- and RTP packets with a specific 1238 "m=" line, with which the receiver has associated an identification- 1239 tag, even if those "m=" lines are part of the same RTP session. The 1240 RTP SDES header extension also ensures that the media recipient gets 1241 the identification-tag upon receipt of the first decodable media and 1242 is able to associate the media with the correct application. 1244 A media recipient informs the media sender about the identification- 1245 tag associated with an "m=" line through the use of an 'mid' 1246 attribute [RFC5888]. The media sender then inserts the 1247 identification-tag in RTCP and RTP packets sent to the media 1248 recipient. 1250 NOTE: This text above defines how identification-tags are carried in 1251 SDP Offers and Answers. The usage of other signalling protocols for 1252 carrying identification-tags is not prevented, but the usage of such 1253 protocols is outside the scope of this document. 1255 [RFC3550] defines general procedures regarding the RTCP transmission 1256 interval. The RTCP MID SDES item SHOULD be sent in the first few 1257 RTCP packets sent after joining the session, and SHOULD be sent 1258 regularly thereafter. The exact number of RTCP packets in which this 1259 SDES item is sent is intentionally not specified here, as it will 1260 depend on the expected packet loss rate, the RTCP reporting interval, 1261 and the allowable overhead. 1263 The RTP SDES header extension for carrying the 'MID' RTCP SDES SHOULD 1264 be included in some RTP packets at the start of the session and 1265 whenever the SSRC changes. It might also be useful to include the 1266 header extension in RTP packets that comprise access points in the 1267 media (e.g., with video I-frames). The exact number of RTP packets 1268 in which this header extension is sent is intentionally not specified 1269 here, as it will depend on expected packet loss rate and loss 1270 patterns, the overhead the application can tolerate, and the 1271 importance of immediate receipt of the identification-tag. 1273 For robustness purpose, endpoints need to be prepared for situations 1274 where the reception of the identification-tag is delayed, and SHOULD 1275 NOT terminate sessions in such cases, as the identification-tag is 1276 likely to arrive soon. 1278 14.1. RTCP MID SDES Item 1280 0 1 2 3 1281 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 1282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1283 | MID=TBD | length | identification-tag ... 1284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1286 The identification-tag payload is UTF-8 encoded, as in SDP. 1288 The identification-tag is not zero terminated. 1290 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1291 identifier value.] 1293 14.2. RTP SDES Header Extension For MID 1295 The payload, containing the identification-tag, of the RTP SDES 1296 header extension element can be encoded using either the one-byte or 1297 two-byte header [I-D.ietf-avtext-sdes-hdr-ext]. The identification- 1298 tag payload is UTF-8 encoded, as in SDP. 1300 The identification-tag is not zero terminated. Note, that the set of 1301 header extensions included in the packet needs to be padded to the 1302 next 32-bit boundary using zero bytes [RFC5285]. 1304 As the identification-tag is included in either an RTCP SDES item or 1305 an RTP SDES header extension, or both, there should be some 1306 consideration about the packet expansion caused by the 1307 identification-tag. To avoid Maximum Transmission Unit (MTU) issues 1308 for the RTP packets, the header extension's size needs to be taken 1309 into account when encoding the media. 1311 It is recommended that the identification-tag is kept short. Due to 1312 the properties of the RTP header extension mechanism, when using the 1313 one-byte header, a tag that is 1-3 bytes will result in a minimal 1314 number of 32-bit words used for the RTP SDES header extension, in 1315 case no other header extensions are included at the same time. Note, 1316 do take into account that some single characters when UTF-8 encoded 1317 will result in multiple octets. The identification-tag MUST NOT 1318 contain any user information, and applications SHALL avoid generating 1319 the identification-tag using a pattern that enables application 1320 identification. 1322 15. IANA Considerations 1324 15.1. New SDES item 1326 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1327 document.] 1329 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1330 identifier value.] 1332 This document adds the MID SDES item to the IANA "RTP SDES item 1333 types" registry as follows: 1335 Value: TBD 1336 Abbrev.: MID 1337 Name: Media Identification 1338 Reference: RFCXXXX 1340 15.2. New RTP SDES Header Extension URI 1342 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1343 document.] 1345 This document defines a new extension URI in the RTP SDES Compact 1346 Header Extensions sub-registry of the RTP Compact Header Extensions 1347 registry sub-registry, according to the following data: 1349 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1350 Description: Media identification 1351 Contact: christer.holmberg@ericsson.com 1352 Reference: RFCXXXX 1354 The SDES item does not reveal privacy information about the users. 1355 It is simply used to associate RTP-based media with the correct SDP 1356 media description (m- line) in the SDP used to negotiate the media. 1358 The purpose of the extension is for the offerer to be able to 1359 associate received multiplexed RTP-based media before the offerer 1360 receives the associated SDP answer. 1362 15.3. New SDP Attribute 1364 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1365 document.] 1367 This document defines a new SDP media-level attribute, 'bundle-only', 1368 according to the following data: 1370 Attribute name: bundle-only 1371 Type of attribute: media 1372 Subject to charset: No 1373 Purpose: Request a media description to be accepted 1374 in the answer only if kept within a BUNDLE 1375 group by the answerer. 1376 Appropriate values: N/A 1377 Contact name: Christer Holmberg 1378 Contact e-mail: christer.holmberg@ericsson.com 1379 Reference: RFCXXXX 1380 Mux category: NORMAL 1382 15.4. New SDP Group Semantics 1384 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1385 document.] 1387 This document registers the following semantics with IANA in the 1388 "Semantics for the "group" SDP Attribute" subregistry (under the 1389 "Session Description Protocol (SDP) Parameters" registry: 1391 Semantics Token Reference 1392 ------------------------------------- ------ --------- 1393 Media bundling BUNDLE [RFCXXXX] 1395 16. Security Considerations 1397 The security considerations defined in [RFC3264] and [RFC5888] apply 1398 to the BUNDLE extension. Bundle does not change which information 1399 flows over the network but only changes which addresses and ports 1400 that information is flowing on and thus has very little impact on the 1401 security of the RTP sessions. 1403 When the BUNDLE extension is used, a single set of security 1404 credentials might be used for all media streams specified by a BUNDLE 1405 group. 1407 When the BUNDLE extension is used, the number of SSRC values within a 1408 single RTP session increases, which increases the risk of SSRC 1409 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1410 and SRTCP encryption in certain situations. 1412 17. Examples 1414 17.1. Example: Bundle Address Selection 1416 The example below shows: 1418 o An offer, in which the offerer associates a unique address with 1419 each bundled "m=" line within the BUNDLE group. 1421 o An answer, in which the answerer selects the offerer BUNDLE 1422 address, and then selects its own BUNDLE address (the answerer 1423 BUNDLE address) and associates it with each bundled "m=" line 1424 within the BUNDLE group. 1426 SDP Offer (1) 1428 v=0 1429 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1430 s= 1431 c=IN IP4 atlanta.example.com 1432 t=0 0 1433 a=group:BUNDLE foo bar 1434 m=audio 10000 RTP/AVP 0 8 97 1435 b=AS:200 1436 a=mid:foo 1437 a=rtcp-mux 1438 a=rtpmap:0 PCMU/8000 1439 a=rtpmap:8 PCMA/8000 1440 a=rtpmap:97 iLBC/8000 1441 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1442 m=video 10002 RTP/AVP 31 32 1443 b=AS:1000 1444 a=mid:bar 1445 a=rtcp-mux 1446 a=rtpmap:31 H261/90000 1447 a=rtpmap:32 MPV/90000 1448 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1450 SDP Answer (2) 1452 v=0 1453 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1454 s= 1455 c=IN IP4 biloxi.example.com 1456 t=0 0 1457 a=group:BUNDLE foo bar 1458 m=audio 20000 RTP/AVP 0 1459 b=AS:200 1460 a=mid:foo 1461 a=rtcp-mux 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=rtcp-mux 1468 a=rtpmap:32 MPV/90000 1469 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1471 17.2. Example: BUNDLE Extension Rejected 1473 The example below shows: 1475 o An offer, in which the offerer associates a unique address with 1476 each bundled "m=" line within the BUNDLE group. 1478 o An answer, in which the answerer rejects the offered BUNDLE group, 1479 and associates a unique address with each "m=" line (following 1480 normal RFC 3264 procedures). 1482 SDP Offer (1) 1484 v=0 1485 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1486 s= 1487 c=IN IP4 atlanta.example.com 1488 t=0 0 1489 a=group:BUNDLE foo bar 1490 m=audio 10000 RTP/AVP 0 8 97 1491 b=AS:200 1492 a=mid:foo 1493 a=rtcp-mux 1494 a=rtpmap:0 PCMU/8000 1495 a=rtpmap:8 PCMA/8000 1496 a=rtpmap:97 iLBC/8000 1497 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1498 m=video 10002 RTP/AVP 31 32 1499 b=AS:1000 1500 a=mid:bar 1501 a=rtcp-mux 1502 a=rtpmap:31 H261/90000 1503 a=rtpmap:32 MPV/90000 1504 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1506 SDP Answer (2) 1508 v=0 1509 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1510 s= 1511 c=IN IP4 biloxi.example.com 1512 t=0 0 1513 m=audio 20000 RTP/AVP 0 1514 b=AS:200 1515 a=rtcp-mux 1516 a=rtpmap:0 PCMU/8000 1517 m=video 30000 RTP/AVP 32 1518 b=AS:1000 1519 a=rtcp-mux 1520 a=rtpmap:32 MPV/90000 1522 17.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1524 The example below shows: 1526 o A subsequent offer (the BUNDLE group has been created as part of a 1527 previous offer/answer exchange), in which the offerer adds a new 1528 "m=" line, represented by the "zen" identification-tag, to a 1529 previously negotiated BUNDLE group, associates a unique address 1530 with the added "m=" line, and associates the previously selected 1531 offerer BUNDLE address with each of the other bundled "m=" lines 1532 within the BUNDLE group. 1534 o An answer, in which the answerer associates the answerer BUNDLE 1535 address with each bundled "m=" line (including the newly added 1536 "m=" line) within the BUNDLE group. 1538 SDP Offer (1) 1540 v=0 1541 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1542 s= 1543 c=IN IP4 atlanta.example.com 1544 t=0 0 1545 a=group:BUNDLE foo bar zen 1546 m=audio 10000 RTP/AVP 0 8 97 1547 b=AS:200 1548 a=mid:foo 1549 a=rtcp-mux 1550 a=rtpmap:0 PCMU/8000 1551 a=rtpmap:8 PCMA/8000 1552 a=rtpmap:97 iLBC/8000 1553 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1554 m=video 10000 RTP/AVP 31 32 1555 b=AS:1000 1556 a=mid:bar 1557 a=rtcp-mux 1558 a=rtpmap:31 H261/90000 1559 a=rtpmap:32 MPV/90000 1560 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1561 m=video 20000 RTP/AVP 66 1562 b=AS:1000 1563 a=mid:zen 1564 a=rtcp-mux 1565 a=rtpmap:66 H261/90000 1566 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1568 SDP Answer (2) 1570 v=0 1571 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1572 s= 1573 c=IN IP4 biloxi.example.com 1574 t=0 0 1575 a=group:BUNDLE foo bar zen 1576 m=audio 20000 RTP/AVP 0 1577 b=AS:200 1578 a=mid:foo 1579 a=rtcp-mux 1580 a=rtpmap:0 PCMU/8000 1581 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1582 m=video 20000 RTP/AVP 32 1583 b=AS:1000 1584 a=mid:bar 1585 a=rtcp-mux 1586 a=rtpmap:32 MPV/90000 1587 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1588 m=video 20000 RTP/AVP 66 1589 b=AS:1000 1590 a=mid:zen 1591 a=rtcp-mux 1592 a=rtpmap:66 H261/90000 1593 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1595 17.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1597 The example below shows: 1599 o A subsequent offer (the BUNDLE group has been created as part of a 1600 previous offer/answer transaction), in which the offerer moves a 1601 bundled "m=" line out of a BUNDLE group, associates a unique 1602 address with the moved "m=" line, and associates the offerer 1603 BUNDLE address with each other bundled "m=" line within the BUNDLE 1604 group. 1606 o An answer, in which the answerer moves the "m=" line out of the 1607 BUNDLE group, associates a unique address with the moved "m=" 1608 line, and associates the answerer BUNDLE address with each of the 1609 remaining bundled "m=" line within the BUNDLE group. 1611 SDP Offer (1) 1613 v=0 1614 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1615 s= 1616 c=IN IP4 atlanta.example.com 1617 t=0 0 1618 a=group:BUNDLE foo bar 1619 m=audio 10000 RTP/AVP 0 8 97 1620 b=AS:200 1621 a=mid:foo 1622 a=rtcp-mux 1623 a=rtpmap:0 PCMU/8000 1624 a=rtpmap:8 PCMA/8000 1625 a=rtpmap:97 iLBC/8000 1626 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1627 m=video 10000 RTP/AVP 31 32 1628 b=AS:1000 1629 a=mid:bar 1630 a=rtcp-mux 1631 a=rtpmap:31 H261/90000 1632 a=rtpmap:32 MPV/90000 1633 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1634 m=video 50000 RTP/AVP 66 1635 b=AS:1000 1636 a=mid:zen 1637 a=rtcp-mux 1638 a=rtpmap:66 H261/90000 1640 SDP Answer (2) 1642 v=0 1643 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1644 s= 1645 c=IN IP4 biloxi.example.com 1646 t=0 0 1647 a=group:BUNDLE foo bar 1648 m=audio 20000 RTP/AVP 0 1649 b=AS:200 1650 a=mid:foo 1651 a=rtcp-mux 1652 a=rtpmap:0 PCMU/8000 1653 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1654 m=video 20000 RTP/AVP 32 1655 b=AS:1000 1656 a=mid:bar 1657 a=rtcp-mux 1658 a=rtpmap:32 MPV/90000 1659 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1660 m=video 60000 RTP/AVP 66 1661 b=AS:1000 1662 a=mid:zen 1663 a=rtcp-mux 1664 a=rtpmap:66 H261/90000 1666 17.5. Example: Offerer Disables A Media Description Within A BUNDLE 1667 Group 1669 The example below shows: 1671 o A subsequent offer (the BUNDLE group has been created as part of a 1672 previous offer/answer transaction), in which the offerer disables 1673 a bundled "m=" line within a BUNDLE group, assigns a zero port 1674 number to the disabled "m=" line, and associates the offerer 1675 BUNDLE address with each of the other bundled "m=" lines within 1676 the BUNDLE group. 1678 o An answer, in which the answerer moves the disabled "m=" line out 1679 of the BUNDLE group, assigns a zero port value to the disabled 1680 "m=" line, and associates the answerer BUNDLE address with each of 1681 the remaining bundled "m=" line within the BUNDLE group. 1683 SDP Offer (1) 1685 v=0 1686 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1687 s= 1688 c=IN IP4 atlanta.example.com 1689 t=0 0 1690 a=group:BUNDLE foo bar 1691 m=audio 10000 RTP/AVP 0 8 97 1692 b=AS:200 1693 a=mid:foo 1694 a=rtcp-mux 1695 a=rtpmap:0 PCMU/8000 1696 a=rtpmap:8 PCMA/8000 1697 a=rtpmap:97 iLBC/8000 1698 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1699 m=video 10000 RTP/AVP 31 32 1700 b=AS:1000 1701 a=mid:bar 1702 a=rtcp-mux 1703 a=rtpmap:31 H261/90000 1704 a=rtpmap:32 MPV/90000 1705 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1706 m=video 0 RTP/AVP 66 1707 a=mid:zen 1708 a=rtpmap:66 H261/90000 1710 SDP Answer (2) 1712 v=0 1713 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1714 s= 1715 c=IN IP4 biloxi.example.com 1716 t=0 0 1717 a=group:BUNDLE foo bar 1718 m=audio 20000 RTP/AVP 0 1719 b=AS:200 1720 a=mid:foo 1721 a=rtcp-mux 1722 a=rtpmap:0 PCMU/8000 1723 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1724 m=video 20000 RTP/AVP 32 1725 b=AS:1000 1726 a=mid:bar 1727 a=rtcp-mux 1728 a=rtpmap:32 MPV/90000 1729 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1730 m=video 0 RTP/AVP 66 1731 a=mid:zen 1732 a=rtpmap:66 H261/90000 1734 18. Acknowledgements 1736 The usage of the SDP grouping extension for negotiating bundled media 1737 is based on a similar alternatives proposed by Harald Alvestrand and 1738 Cullen Jennings. The BUNDLE extension described in this document is 1739 based on the different alternative proposals, and text (e.g., SDP 1740 examples) have been borrowed (and, in some cases, modified) from 1741 those alternative proposals. 1743 The SDP examples are also modified versions from the ones in the 1744 Alvestrand proposal. 1746 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1747 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 1748 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 1749 Justin Uberti for reading the text, and providing useful feedback. 1751 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 1752 providing help and text on the RTP/RTCP procedures. 1754 Thanks to Spotify for providing music for the countless hours of 1755 document editing. 1757 19. Change Log 1759 [RFC EDITOR NOTE: Please remove this section when publishing] 1761 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31 1763 o Editorial changes based on GitHub Pull requests by Martin Thomson: 1765 o - https://github.com/cdh4u/draft-sdp-bundle/pull/2 1767 o - https://github.com/cdh4u/draft-sdp-bundle/pull/1 1769 o Editorial change based on comment from Diederick Huijbers (9th 1770 July 2016). 1772 o Changes based on comments from Flemming Andreasen (21st June 1773 2016): 1775 o - Mux category for SDP bundle-only attribute added. 1777 o - Mux category considerations editorial clarification. 1779 o - Editorial changes. 1781 o RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext. 1783 o Note whether Design Considerations appendix is to be kept removed: 1785 o - Appendix is kept within document. 1787 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30 1789 o Indicating in the Abstract and Introduction that the document 1790 updates RFC 3264. 1792 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29 1794 o Change based on WGLC comment from Colin Perkins. 1796 o - Clarify that SSRC can be reused by another source after a delay 1797 of 5 RTCP reporting intervals. 1799 o Change based on WGLC comment from Alissa Cooper. 1801 o - IANA registry name fix. 1803 o - Additional IANA registration information added. 1805 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 1807 o - Alignment with exclusive mux procedures. 1809 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 1811 o - Yet another terminology change. 1813 o - Mux category considerations added. 1815 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 1817 o - ICE considerations modified: ICE-related SDP attributes only 1818 added to the bundled m- line representing the selected BUNDLE 1819 address. 1821 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 1823 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 1824 rfc5245bis. 1826 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 1828 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 1829 considerations. 1831 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 1833 o - Reference and procedures associated with exclusive RTP/RTCP mux 1834 added 1836 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 1838 o - RTCP-MUX mandatory for bundled RTP m- lines 1840 o - Editorial fixes based on comments from Flemming Andreasen 1842 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 1844 o - Correction of Ari's family name 1846 o - Editorial fixes based on comments from Thomas Stach 1848 o - RTP/RTCP correction based on comment from Magnus Westerlund 1850 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1851 msg14861.html 1853 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 1855 o - Correct based on comment from Paul Kyzivat 1857 o -- 'received packets' replaced with 'received data' 1859 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 1861 o - Clarification based on comment from James Guballa 1863 o - Clarification based on comment from Flemming Andreasen 1865 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 1867 o - DTLS Considerations section added. 1869 o - BUNDLE semantics added to the IANA Considerations 1871 o - Changes based on WGLC comments from Adam Roach 1873 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 1874 msg14673.html 1876 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1878 o - Changes based on agreements at IETF#92 1880 o -- BAS Offer removed, based on agreement at IETF#92. 1882 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1883 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1885 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1887 o - Editorial changes based on comments from Magnus Westerlund. 1889 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1891 o - Modification of RTP/RTCP multiplexing section, based on comments 1892 from Magnus Westerlund. 1894 o - Reference updates. 1896 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1898 o - Editorial fix. 1900 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1901 o - Editorial changes. 1903 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1905 o Changes to allow a new suggested offerer BUNDLE address to be 1906 assigned to each bundled m- line. 1908 o Changes based on WGLC comments from Paul Kyzivat 1910 o - Editorial fixes 1912 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1914 o Usage of SDP 'extmap' attribute added 1916 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1917 port value 1919 o Changes based on WGLC comments from Thomas Stach 1921 o - ICE candidates not assigned to bundle-only m- lines with a zero 1922 port value 1924 o - Editorial changes 1926 o Changes based on WGLC comments from Colin Perkins 1928 o - Editorial changes: 1930 o -- "RTP SDES item" -> "RTCP SDES item" 1932 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1934 o - Changes in section 10.1.1: 1936 o -- "SHOULD NOT" -> "MUST NOT" 1938 o -- Additional text added to the Note 1940 o - Change to section 13.2: 1942 o -- Clarify that mid value is not zero terminated 1944 o - Change to section 13.3: 1946 o -- Clarify that mid value is not zero terminated 1948 o -- Clarify padding 1949 o Changes based on WGLC comments from Paul Kyzivat 1951 o - Editorial changes: 1953 o Changes based on WGLC comments from Jonathan Lennox 1955 o - Editorial changes: 1957 o - Defintion of SDP bundle-only attribute alligned with structure 1958 in 4566bis draft 1960 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1962 o Editorial corrections based on comments from Harald Alvestrand. 1964 o Editorial corrections based on comments from Cullen Jennings. 1966 o Reference update (RFC 7160). 1968 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1969 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1970 msg13765.html). 1972 o Additional text added to the Security Considerations. 1974 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1976 o SDP bundle-only attribute added to IANA Considerations. 1978 o SDES item and RTP header extension added to Abstract and 1979 Introduction. 1981 o Modification to text updating section 8.2 of RFC 3264. 1983 o Reference corrections. 1985 o Editorial corrections. 1987 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1989 o Terminology change: "bundle-only attribute assigned to m= line" to 1990 "bundle-only attribute associated with m= line". 1992 o Editorial corrections. 1994 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1996 o Editorial corrections. 1998 o - "of"->"if" (8.3.2.5). 2000 o - "optional"->"OPTIONAL" (9.1). 2002 o - Syntax/ABNF for 'bundle-only' attribute added. 2004 o - SDP Offer/Answer sections merged. 2006 o - 'Request new offerer BUNDLE address' section added 2008 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 2010 o OPEN ISSUE regarding Receiver-ID closed. 2012 o - RTP MID SDES Item. 2014 o - RTP MID Header Extension. 2016 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 2017 closed. 2019 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 2020 include an 'rtcp' attribute in the answer, based on the procedures 2021 in section 5.1.3 of RFC 5761. 2023 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 2025 o Draft title changed. 2027 o Added "SDP" to section names containing "Offer" or "Answer". 2029 o Editorial fixes based on comments from Paul Kyzivat 2030 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2031 msg13314.html). 2033 o Editorial fixed based on comments from Colin Perkins 2034 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2035 msg13318.html). 2037 o - Removed text about extending BUNDLE to allow multiple RTP 2038 sessions within a BUNDLE group. 2040 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 2042 o Major re-structure of SDP Offer/Answer sections, to align with RFC 2043 3264 structure. 2045 o Additional definitions added. 2047 o - Shared address. 2049 o - Bundled "m=" line. 2051 o - Bundle-only "m=" line. 2053 o - Offerer suggested BUNDLE mid. 2055 o - Answerer selected BUNDLE mid. 2057 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 2058 to multiple "m=" lines until it has received an SDP Answer 2059 indicating support of the BUNDLE extension. 2061 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 2062 Answerer supports the BUNDLE extension, assign a zero port value 2063 to a 'bundle-only' "m=" line. 2065 o SDP 'bundle-only' attribute section added. 2067 o Connection data nettype/addrtype restrictions added. 2069 o RFC 3264 update section added. 2071 o Indicating that a specific payload type value can be used in 2072 multiple "m=" lines, if the value represents the same codec 2073 configuration in each "m=" line. 2075 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2077 o Updated Offerer procedures (http://www.ietf.org/mail- 2078 archive/web/mmusic/current/msg12293.html). 2080 o Updated Answerer procedures (http://www.ietf.org/mail- 2081 archive/web/mmusic/current/msg12333.html). 2083 o Usage of SDP 'bundle-only' attribute added. 2085 o Reference to Trickle ICE document added. 2087 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2089 o Mechanism modified, to be based on usage of SDP Offers with both 2090 different and identical port number values, depending on whether 2091 it is known if the remote endpoint supports the extension. 2093 o Cullen Jennings added as co-author. 2095 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2097 o No changes. New version due to expiration. 2099 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2101 o No changes. New version due to expiration. 2103 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2105 o Draft name changed. 2107 o Harald Alvestrand added as co-author. 2109 o "Multiplex" terminology changed to "bundle". 2111 o Added text about single versus multiple RTP Sessions. 2113 o Added reference to RFC 3550. 2115 20. References 2117 20.1. Normative References 2119 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2120 Requirement Levels", BCP 14, RFC 2119, 2121 DOI 10.17487/RFC2119, March 1997, 2122 . 2124 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2125 with Session Description Protocol (SDP)", RFC 3264, 2126 DOI 10.17487/RFC3264, June 2002, 2127 . 2129 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2130 Jacobson, "RTP: A Transport Protocol for Real-Time 2131 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2132 July 2003, . 2134 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2135 in Session Description Protocol (SDP)", RFC 3605, 2136 DOI 10.17487/RFC3605, October 2003, 2137 . 2139 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2140 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2141 July 2006, . 2143 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2144 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2145 . 2147 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2148 (ICE): A Protocol for Network Address Translator (NAT) 2149 Traversal for Offer/Answer Protocols", RFC 5245, 2150 DOI 10.17487/RFC5245, April 2010, 2151 . 2153 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2154 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2155 2008, . 2157 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2158 Control Packets on a Single Port", RFC 5761, 2159 DOI 10.17487/RFC5761, April 2010, 2160 . 2162 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2163 Security (DTLS) Extension to Establish Keys for the Secure 2164 Real-time Transport Protocol (SRTP)", RFC 5764, 2165 DOI 10.17487/RFC5764, May 2010, 2166 . 2168 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2169 Protocol (SDP) Grouping Framework", RFC 5888, 2170 DOI 10.17487/RFC5888, June 2010, 2171 . 2173 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2174 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2175 January 2012, . 2177 [I-D.ietf-ice-rfc5245bis] 2178 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 2179 Connectivity Establishment (ICE): A Protocol for Network 2180 Address Translator (NAT) Traversal", draft-ietf-ice- 2181 rfc5245bis-04 (work in progress), June 2016. 2183 [I-D.ietf-mmusic-sdp-mux-attributes] 2184 Nandakumar, S., "A Framework for SDP Attributes when 2185 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-13 2186 (work in progress), June 2016. 2188 [I-D.ietf-mmusic-mux-exclusive] 2189 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2190 Multiplexing using SDP", draft-ietf-mmusic-mux- 2191 exclusive-10 (work in progress), August 2016. 2193 [I-D.ietf-mmusic-ice-sip-sdp] 2194 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, "Using 2195 Interactive Connectivity Establishment (ICE) with Session 2196 Description Protocol (SDP) offer/answer and Session 2197 Initiation Protocol (SIP)", draft-ietf-mmusic-ice-sip- 2198 sdp-10 (work in progress), July 2016. 2200 [I-D.ietf-avtext-sdes-hdr-ext] 2201 Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 2202 Header Extension for RTCP Source Description Items", 2203 draft-ietf-avtext-sdes-hdr-ext-07 (work in progress), June 2204 2016. 2206 20.2. Informative References 2208 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2209 A., Peterson, J., Sparks, R., Handley, M., and E. 2210 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2211 DOI 10.17487/RFC3261, June 2002, 2212 . 2214 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2215 Description Protocol (SDP) Security Descriptions for Media 2216 Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, 2217 . 2219 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2220 Media Attributes in the Session Description Protocol 2221 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2222 . 2224 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2225 Clock Rates in an RTP Session", RFC 7160, 2226 DOI 10.17487/RFC7160, April 2014, 2227 . 2229 [I-D.ietf-mmusic-trickle-ice] 2230 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2231 Incremental Provisioning of Candidates for the Interactive 2232 Connectivity Establishment (ICE) Protocol", draft-ietf- 2233 mmusic-trickle-ice-02 (work in progress), January 2015. 2235 Appendix A. Design Considerations 2237 One of the main issues regarding the BUNDLE grouping extensions has 2238 been whether, in SDP Offers and SDP Answers, the same port value 2239 should be inserted in "m=" lines associated with a BUNDLE group, as 2240 the purpose of the extension is to negotiate the usage of a single 2241 address:port combination for media specified by the "m=" lines. 2242 Issues with both approaches, discussed in the Appendix have been 2243 raised. The outcome was to specify a mechanism which uses SDP Offers 2244 with both different and identical port values. 2246 Below are the primary issues that have been considered when defining 2247 the "BUNDLE" grouping extension: 2249 o 1) Interoperability with existing UAs. 2251 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2253 o 3) Time to gather, and the number of, ICE candidates. 2255 o 4) Different error scenarios, and when they occur. 2257 o 5) SDP Offer/Answer impacts, including usage of port number value 2258 zero. 2260 A.1. UA Interoperability 2262 Consider the following SDP Offer/Answer exchange, where Alice sends 2263 an SDP Offer to Bob: 2265 SDP Offer 2267 v=0 2268 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2269 s= 2270 c=IN IP4 atlanta.example.com 2271 t=0 0 2272 m=audio 10000 RTP/AVP 97 2273 a=rtpmap:97 iLBC/8000 2274 m=video 10002 RTP/AVP 97 2275 a=rtpmap:97 H261/90000 2277 SDP Answer 2279 v=0 2280 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2281 s= 2282 c=IN IP4 biloxi.example.com 2283 t=0 0 2284 m=audio 20000 RTP/AVP 97 2285 a=rtpmap:97 iLBC/8000 2286 m=video 20002 RTP/AVP 97 2287 a=rtpmap:97 H261/90000 2289 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2290 later invention to RTP and Bob can not assume that Alice supports RFC 2291 4961. This means that Alice may be sending RTP from a different port 2292 than 10000 or 10002 - some implementation simply send the RTP from an 2293 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2294 way that Bob knows if it should be passed to the video or audio codec 2295 is by looking at the port it was received on. This lead some SDP 2296 implementations to use the fact that each "m=" line had a different 2297 port number to use that port number as an index to find the correct m 2298 line in the SDP. As a result, some implementations that do support 2299 symmetric RTP and ICE still use a SDP data structure where SDP with 2300 "m=" lines with the same port such as: 2302 SDP Offer 2304 v=0 2305 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2306 s= 2307 c=IN IP4 atlanta.example.com 2308 t=0 0 2309 m=audio 10000 RTP/AVP 97 2310 a=rtpmap:97 iLBC/8000 2311 m=video 10000 RTP/AVP 98 2312 a=rtpmap:98 H261/90000 2314 will result in the second "m=" line being considered an SDP error 2315 because it has the same port as the first line. 2317 A.2. Usage of port number value zero 2319 In an SDP Offer or SDP Answer, the media specified by an "m=" line 2320 can be disabled/rejected by setting the port number value to zero. 2321 This is different from e.g., using the SDP direction attributes, 2322 where RTCP traffic will continue even if the SDP "inactive" attribute 2323 is indicated for the associated "m=" line. 2325 If each "m=" line associated with a BUNDLE group would contain 2326 different port values, and one of those port values would be used for 2327 a BUNDLE address associated with the BUNDLE group, problems would 2328 occur if an endpoint wants to disable/reject the "m=" line associated 2329 with that port, by setting the port value to zero. After that, no 2330 "m=" line would contain the port value which is used for the BUNDLE 2331 address. In addition, it is unclear what would happen to the ICE 2332 candidates associated with the "m=" line, as they are also used for 2333 the BUNDLE address. 2335 A.3. B2BUA And Proxy Interoperability 2337 Some back to back user agents may be configured in a mode where if 2338 the incoming call leg contains an SDP attribute the B2BUA does not 2339 understand, the B2BUA still generates that SDP attribute in the Offer 2340 for the outgoing call leg. Consider a B2BUA that did not understand 2341 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2342 Further assume that the B2BUA was configured to tear down any call 2343 where it did not see any RTCP for 5 minutes. In this case, if the 2344 B2BUA received an Offer like: 2346 SDP Offer 2348 v=0 2349 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2350 s= 2351 c=IN IP4 atlanta.example.com 2352 t=0 0 2353 m=audio 49170 RTP/AVP 0 2354 a=rtcp:53020 2356 It would be looking for RTCP on port 49172 but would not see any 2357 because the RTCP would be on port 53020 and after five minutes, it 2358 would tear down the call. Similarly, a B2BUA that did not understand 2359 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2360 wrong port and tear down the call. It is worth noting that a B2BUA 2361 that generated an Offer with capabilities it does not understand is 2362 not compliant with the specifications. 2364 A.3.1. Traffic Policing 2366 Sometimes intermediaries do not act as B2BUA, in the sense that they 2367 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2368 however, they may use SDP information (e.g., IP address and port) in 2369 order to control traffic gating functions, and to set traffic 2370 policing rules. There might be rules which will trigger a session to 2371 be terminated in case media is not sent or received on the ports 2372 retrieved from the SDP. This typically occurs once the session is 2373 already established and ongoing. 2375 A.3.2. Bandwidth Allocation 2377 Sometimes intermediaries do not act as B2BUA, in the sense that they 2378 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2379 however, they may use SDP information (e.g., codecs and media types) 2380 in order to control bandwidth allocation functions. The bandwidth 2381 allocation is done per "m=" line, which means that it might not be 2382 enough if media specified by all "m=" lines try to use that 2383 bandwidth. That may either simply lead to bad user experience, or to 2384 termination of the call. 2386 A.4. Candidate Gathering 2388 When using ICE, a candidate needs to be gathered for each port. This 2389 takes approximately 20 ms extra for each extra "m=" line due to the 2390 NAT pacing requirements. All of this gather can be overlapped with 2391 other things while for exampe a web-page is loading to minimize the 2392 impact. If the client only wants to generate TURN or STUN ICE 2393 candidates for one of the "m=" lines and then use trickle ICE 2394 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2395 the rest of the "m=" lines, it MAY do that and will not need any 2396 additional gathering time. 2398 Some people have suggested a TURN extension to get a bunch of TURN 2399 allocations at once. This would only provide a single STUN result so 2400 in cases where the other end did not support BUNDLE, may cause more 2401 use of the TURN server but would be quick in the cases where both 2402 sides supported BUNDLE and would fall back to a successful call in 2403 the other cases. 2405 Authors' Addresses 2407 Christer Holmberg 2408 Ericsson 2409 Hirsalantie 11 2410 Jorvas 02420 2411 Finland 2413 Email: christer.holmberg@ericsson.com 2415 Harald Tveit Alvestrand 2416 Google 2417 Kungsbron 2 2418 Stockholm 11122 2419 Sweden 2421 Email: harald@alvestrand.no 2423 Cullen Jennings 2424 Cisco 2425 400 3rd Avenue SW, Suite 350 2426 Calgary, AB T2P 4H2 2427 Canada 2429 Email: fluffy@iii.ca