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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: June 21, 2018 C. Jennings 7 Cisco 8 December 18, 2017 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-47.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 transport (5-tuple) for sending and receiving media described 20 by multiple SDP media descriptions ("m=" sections). Such transport 21 is referred to as a BUNDLE transport, and the media is referred to as 22 bundled media. The "m=" sections that use the BUNDLE transport form 23 a BUNDLE group. 25 To assist endpoints in negotiating the use of bundle this 26 specification defines a new SDP attribute, 'bundle-only', which can 27 be used to request that specific media is only used if bundled. The 28 specification also updates RFC 3264, to allow assigning a zero port 29 value to a "m=" section without meaning that the media described by 30 the "m=" section is disabled or rejected. 32 When Real-time Transport Protocol (RTP)-based media is used, there 33 are multiple ways to correlate bundled RTP packets with the 34 appropriate "m=" section. This specification defines a new RTP 35 Control Protocol (RTCP) source description (SDES) item and a new RTP 36 header extension that provides an additional way to do this 37 correlation by using them to carry a value that associates the RTP/ 38 RTCP packets with a specific "m=" section. 40 Status of This Memo 42 This Internet-Draft is submitted in full conformance with the 43 provisions of BCP 78 and BCP 79. 45 Internet-Drafts are working documents of the Internet Engineering 46 Task Force (IETF). Note that other groups may also distribute 47 working documents as Internet-Drafts. The list of current Internet- 48 Drafts is at https://datatracker.ietf.org/drafts/current/. 50 Internet-Drafts are draft documents valid for a maximum of six months 51 and may be updated, replaced, or obsoleted by other documents at any 52 time. It is inappropriate to use Internet-Drafts as reference 53 material or to cite them other than as "work in progress." 55 This Internet-Draft will expire on June 21, 2018. 57 Copyright Notice 59 Copyright (c) 2017 IETF Trust and the persons identified as the 60 document authors. All rights reserved. 62 This document is subject to BCP 78 and the IETF Trust's Legal 63 Provisions Relating to IETF Documents 64 (https://trustee.ietf.org/license-info) in effect on the date of 65 publication of this document. Please review these documents 66 carefully, as they describe your rights and restrictions with respect 67 to this document. Code Components extracted from this document must 68 include Simplified BSD License text as described in Section 4.e of 69 the Trust Legal Provisions and are provided without warranty as 70 described in the Simplified BSD License. 72 This document may contain material from IETF Documents or IETF 73 Contributions published or made publicly available before November 74 10, 2008. The person(s) controlling the copyright in some of this 75 material may not have granted the IETF Trust the right to allow 76 modifications of such material outside the IETF Standards Process. 77 Without obtaining an adequate license from the person(s) controlling 78 the copyright in such materials, this document may not be modified 79 outside the IETF Standards Process, and derivative works of it may 80 not be created outside the IETF Standards Process, except to format 81 it for publication as an RFC or to translate it into languages other 82 than English. 84 Table of Contents 86 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 87 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 88 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7 89 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 90 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 91 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 8 92 7. SDP Information Considerations . . . . . . . . . . . . . . . 9 93 7.1. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 94 7.2. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 95 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 96 8.1. Mux Category Considerations . . . . . . . . . . . . . . . 10 97 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 11 98 8.2.1. Suggesting the Offerer BUNDLE Address . . . . . . . . 12 99 8.2.2. Example: Initial SDP Offer . . . . . . . . . . . . . 12 100 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 13 101 8.3.1. Answerer Selection of Offerer BUNDLE Address . . . . 14 102 8.3.2. Answerer Selection of Answerer BUNDLE Address . . . . 15 103 8.3.3. Moving A Media Description Out Of A BUNDLE Group . . 15 104 8.3.4. Rejecting a Media Description in a BUNDLE Group . . . 16 105 8.3.5. Example: SDP Answer . . . . . . . . . . . . . . . . . 17 106 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 17 107 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 18 108 8.5.1. Suggesting a New Offerer BUNDLE Address . . . . . . . 18 109 8.5.2. Adding a Media Description to a BUNDLE group . . . . 18 110 8.5.3. Moving a Media Description Out of a BUNDLE Group . . 19 111 8.5.4. Disabling a Media Description in a BUNDLE Group . . . 19 112 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 20 113 9.1. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 20 114 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 21 115 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 21 116 10.1.1. Payload Type (PT) Value Reuse . . . . . . . . . . . 22 117 10.2. Associating RTP/RTCP Streams with Correct SDP Media 118 Description . . . . . . . . . . . . . . . . . . . . . . 22 119 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 28 120 10.3.1. SDP Offer/Answer Procedures . . . . . . . . . . . . 28 121 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 30 122 11.1. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 31 123 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 31 124 13. RTP Header Extensions Consideration . . . . . . . . . . . . . 32 125 14. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 32 126 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 33 127 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 33 129 14.3. Original text of section 6 (4th paragraph) of RFC 3264 . 33 130 14.4. New text replacing section 6 (4th paragraph) of RFC 3264 34 131 14.5. Original text of section 8.2 (2nd paragraph) of RFC 3264 34 132 14.6. New text replacing section 8.2 (2nd paragraph) of RFC 133 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 34 134 14.7. Original text of section 8.4 (6th paragraph) of RFC 3264 34 135 14.8. New text replacing section 8.4 (6th paragraph) of RFC 136 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 34 137 15. RTP/RTCP extensions for identification-tag transport . . . . 35 138 15.1. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 36 139 15.2. RTP SDES Header Extension For MID . . . . . . . . . . . 36 140 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 141 16.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 37 142 16.2. New RTP SDES Header Extension URI . . . . . . . . . . . 37 143 16.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 38 144 16.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 38 145 17. Security Considerations . . . . . . . . . . . . . . . . . . . 39 146 18. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 40 147 18.1. Example: Bundle Address Selection . . . . . . . . . . . 40 148 18.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 42 149 18.3. Example: Offerer Adds a Media Description to a BUNDLE 150 Group . . . . . . . . . . . . . . . . . . . . . . . . . 43 151 18.4. Example: Offerer Moves a Media Description Out of a 152 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 45 153 18.5. Example: Offerer Disables a Media Description Within a 154 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 47 155 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 156 20. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 49 157 21. References . . . . . . . . . . . . . . . . . . . . . . . . . 59 158 21.1. Normative References . . . . . . . . . . . . . . . . . . 59 159 21.2. Informative References . . . . . . . . . . . . . . . . . 61 160 Appendix A. Design Considerations . . . . . . . . . . . . . . . 63 161 A.1. UA Interoperability . . . . . . . . . . . . . . . . . . . 63 162 A.2. Usage of Port Number Value Zero . . . . . . . . . . . . . 65 163 A.3. B2BUA And Proxy Interoperability . . . . . . . . . . . . 65 164 A.3.1. Traffic Policing . . . . . . . . . . . . . . . . . . 66 165 A.3.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 66 166 A.4. Candidate Gathering . . . . . . . . . . . . . . . . . . . 66 167 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 67 169 1. Introduction 171 When multimedia communications are established, each transport 172 (5-tuple) reserved for an individual media stream consume additional 173 resources (especially when Interactive Connectivity Establishment 174 (ICE) [I-D.ietf-ice-rfc5245bis] is used). For this reason, it is 175 attractive to use a single transport for multiple media streams. 177 This specification defines a way to use a single transport (BUNDLE 178 transport) for sending and receiving media (bundled media) described 179 by multiple SDP media descriptions ("m=" sections). The same BUNDLE 180 transport is used for sending and receiving bundled media, which 181 means that the symmetric Real-time Transport Protocol (RTP) mechanism 182 [RFC4961] is always used for RTP-based bundled media. 184 This specification defines a new SDP Grouping Framework [RFC5888] 185 extension called 'BUNDLE'. The extension can be used with the 186 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 187 to negotiate which "m=" sections will become part of a BUNDLE group. 188 Within a BUNDLE group, each "m=" section will use a BUNDLE transport 189 for sending and receiving bundled media. 191 Within a BUNDLE group, each endpoint uses a single address:port 192 combination for sending and receiving bundled media. The 193 address:port combination is referred to as the BUNDLE address. In 194 addition to negotiating the BUNDLE group, the offerer and answerer 195 [RFC3264] use the BUNDLE extension to negotiate the BUNDLE addresses, 196 one for the offerer (offerer BUNDLE address) and one for the answerer 197 (answerer BUNDLE address). Once the offerer and the answerer have 198 negotiated the BUNDLE addresses, and a BUNDLE group has been formed, 199 they assign their respective BUNDLE address to each "m=" section 200 within the BUNDLE group. The endpoints then use the BUNDLE addresses 201 for sending and receiving the bundled media associated with the 202 BUNDLE group. 204 The use of a BUNDLE transport also allows the usage of a single set 205 of Interactive Connectivity Establishment (ICE) 206 [I-D.ietf-ice-rfc5245bis] candidates for the whole BUNDLE group. 208 This specification also defines a new SDP attribute, 'bundle-only', 209 which can be used to request that specific media is only used if the 210 "m=" section describing the media is kept within a BUNDLE group. The 211 specification also updates RFC 3264, to allow usage of zero port 212 values without meaning that media is rejected. 214 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 215 transport address (IP address and port) to multiple "m=" sections are 216 undefined, and there is no grouping defined by such means. Instead, 217 an explicit grouping mechanism needs to be used to express the 218 intended semantics. This specification provides such an extension. 220 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 221 [RFC3264]. The update allows an answerer to assign a non-zero port 222 value to an "m=" section in an SDP answer, even if the "m=" section 223 in the associated SDP offer contained a zero port value. 225 This specification also defines a new RTP Control Protocol (RTCP) 226 [RFC3550] source description (SDES) item, 'MID', and a new RTP SDES 227 header extension that can be used to associate RTP streams with "m=" 228 sections. 230 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 231 address MUST only be associated with a single BUNDLE group. The 232 procedures in this specification apply independently to a given 233 BUNDLE group. All RTP based media flows described by a single BUNDLE 234 group belong to a single RTP session [RFC3550]. 236 The BUNDLE extension is backward compatible. Endpoints that do not 237 support the extension are expected to generate offers and answers 238 without an SDP 'group:BUNDLE' attribute, and are expected to assign a 239 unique address to each "m=" section within an offer and answer, 240 according to the procedures in [RFC4566] and [RFC3264]. 242 2. Terminology 244 "m=" section: SDP bodies contain one or more media descriptions, 245 referred to as "m=" sections. Each "m=" section is represented by an 246 SDP "m=" line, and zero or more SDP attributes associated with the 247 "m=" line. A local address:port combination is assigned to each "m=" 248 section. 250 5-tuple: A collection of the following values: source address, source 251 port, destination address, destination port, and transport-layer 252 protocol. 254 Unique address: An address:port combination that is assigned to only 255 one "m=" section in an offer or answer. 257 Offerer BUNDLE-tag: The first identification-tag in a given SDP 258 'group:BUNDLE' attribute identification-tag list in an offer. 260 Answerer BUNDLE-tag: The first identification-tag in a given SDP 261 'group:BUNDLE' attribute identification-tag list in an answer. 263 BUNDLE address: An address:port combination that an endpoint uses for 264 sending and receiving bundled media. 266 Offerer BUNDLE address: the address:port combination used by the 267 offerer for sending and receiving media. 269 Suggested Offerer BUNDLE address: before an offerer BUNDLE address 270 has been selected by the answerer, or when the offerer wants to 271 change a previously selected offerer BUNDLE address, the address:port 272 combination that the offerer wants to use for sending and receiving 273 media. While suggested by the offerer, the selection of the offerer 274 BUNDLE address is done by the answerer. 276 Answerer BUNDLE address: the address:port combination used by the 277 answerer for sending and receiving media. 279 BUNDLE transport: The transport (5-tuple) used by all media described 280 by the "m=" sections within a BUNDLE group. 282 BUNDLE group: A set of "m=" sections, created using an SDP Offer/ 283 Answer exchange, which uses a single BUNDLE transport for sending and 284 receiving all media (bundled media) described by the set of "m=" 285 sections. The same BUNDLE transport is used for sending and 286 receiving bundled media. 288 Bundled "m=" section: An "m=" section, whose identification-tag is 289 placed in an SDP 'group:BUNDLE' attribute identification-tag list in 290 an offer or answer. 292 Bundle-only "m=" section: A bundled "m=" section that contains an SDP 293 'bundle-only' attribute. 295 Bundled media: All media associated with a given BUNDLE group. 297 Initial offer: The first offer, within an SDP session (e.g. a SIP 298 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 299 to carry SDP), in which the offerer indicates that it wants to create 300 a given BUNDLE group. 302 Subsequent offer: An offer which contains a BUNDLE group that has 303 been created as part of a previous offer/answer exchange. 305 Identification-tag: A unique token value that is used to identify an 306 "m=" section. The SDP 'mid' attribute [RFC5888] in an "m=" section 307 carries the unique identification-tag assigned to that "m=" section. 308 The session-level SDP 'group' attribute [RFC5888] carries a list of 309 identification-tags, identifying the "m=" sections associated with 310 that particular 'group' attribute. 312 3. Conventions 314 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 315 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 316 document are to be interpreted as described in BCP 14, RFC 2119 317 [RFC2119]. 319 4. Applicability Statement 321 The mechanism in this specification only applies to the Session 322 Description Protocol (SDP) [RFC4566], when used together with the SDP 323 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 324 scope of this document, and is thus undefined. 326 5. SDP Grouping Framework BUNDLE Extension 328 This section defines a new SDP Grouping Framework [RFC5888] 329 extension, 'BUNDLE'. The BUNDLE extension can be used with the SDP 330 Offer/Answer mechanism to negotiate a set of "m=" sections that will 331 become part of a BUNDLE group. Within a BUNDLE group, each "m=" 332 section will use a BUNDLE transport for sending and receiving bundled 333 media. Each endpoint uses a single address:port combination for 334 sending and receiving the bundled media. 336 The BUNDLE extension is indicated using an SDP 'group' attribute with 337 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 338 assigned to each bundled "m=" section, and each identification-tag is 339 listed in the SDP 'group:BUNDLE' attribute identification-tag list. 340 Each "m=" section whose identification-tag is listed in the 341 identification-tag list is associated with a given BUNDLE group. 343 SDP bodies can contain multiple BUNDLE groups. Any given bundled 344 "m=" section MUST NOT be associated with more than one BUNDLE group 345 at any given time. 347 NOTE: The order of the "m=" sections listed in the SDP 'group:BUNDLE' 348 attribute identification-tag list does not have to be the same as the 349 order in which the "m=" sections occur in the SDP. 351 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 352 'group:BUNDLE' attribute is 'NORMAL'. 354 Section 8 defines the detailed SDP Offer/Answer procedures for the 355 BUNDLE extension. 357 6. SDP 'bundle-only' Attribute 359 This section defines a new SDP media-level attribute [RFC4566], 360 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 361 hence has no value. 363 Name: bundle-only 365 Value: N/A 367 Usage Level: media 369 Charset Dependent: no 371 Example: 373 a=bundle-only 375 In order to ensure that an answerer that does not support the BUNDLE 376 extension always rejects a bundled "m=" section, the offerer can 377 assign a zero port value to the "m=" section. According to [RFC3264] 378 an answerer will reject such an "m=" section. By including an SDP 379 'bundle-only' attribute in such an "m=" section, the offerer can 380 request that the answerer accepts the "m=" section if the answerer 381 supports the BUNDLE extension, and if the answerer keeps the "m=" 382 section within the associated BUNDLE group. 384 Once the offerer and answerer BUNDLE addresses have been selected, an 385 offerer and answerer only assign the BUNDLE address to one bundled 386 "m=" section. The offerer and answerer assign a zero port value and 387 includes an SDP 'bundle-only' attribute to every other bundled "m=" 388 section. 390 The usage of the 'bundle-only' attribute is only defined for a 391 bundled "m=" section with a zero port value. Other usage is 392 unspecified. 394 Section 8 defines the detailed SDP Offer/Answer procedures for the 395 'bundle-only' attribute. 397 7. SDP Information Considerations 399 This section describes restrictions associated with the usage of SDP 400 parameters within a BUNDLE group. It also describes how to calculate 401 a value for the whole BUNDLE group, when parameter and attribute 402 values have been assigned to each bundled "m=" section. 404 7.1. Connection Data (c=) 406 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 407 section MUST be 'IN'. 409 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 410 section MUST be 'IP4' or 'IP6'. The same value MUST be associated 411 with each "m=" section. 413 NOTE: Extensions to this specification can specify usage of the 414 BUNDLE mechanism for other nettype and addrtype values than the ones 415 listed above. 417 7.2. Bandwidth (b=) 419 An offerer and answerer MUST use the rules and restrictions defined 420 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP 421 bandwidth (b=) line with bundled "m=" sections. 423 8. SDP Offer/Answer Procedures 425 This section describes the SDP Offer/Answer [RFC3264] procedures for: 427 o Negotiating a BUNDLE group; and 428 o Selecting the BUNDLE addresses (offerer BUNDLE address and 429 answerer BUNDLE address); and 431 o Adding an "m=" section to a BUNDLE group; and 433 o Moving an "m=" section out of a BUNDLE group; and 435 o Disabling an "m=" section within a BUNDLE group. 437 The generic rules and procedures defined in [RFC3264] and [RFC5888] 438 also apply to the BUNDLE extension. For example, if an offer is 439 rejected by the answerer, the previously negotiated SDP parameters 440 and characteristics (including those associated with a BUNDLE group) 441 apply. Hence, if an offerer generates an offer in which the offerer 442 wants to create a BUNDLE group, and the answerer rejects the offer, 443 the BUNDLE group is not created. 445 The procedures in this section are independent of the media type or 446 "m=" line proto value assigned to a bundled "m=" section. Section 10 447 defines additional considerations for RTP based media. Section 6 448 defines additional considerations for the usage of the SDP 'bundle- 449 only' attribute. Section 11 defines additional considerations for 450 the usage of Interactive Connectivity Establishment (ICE) 451 [I-D.ietf-ice-rfc5245bis] mechanism. 453 SDP offers and answers can contain multiple BUNDLE groups. The 454 procedures in this section apply independently to a given BUNDLE 455 group. 457 8.1. Mux Category Considerations 459 When a BUNDLE group is initially negotiated, and a unique address is 460 assigned to each bundled "m=" section (excluding any bundle-only "m=" 461 section) in the initial offer [Section 8.2], IDENTICAL and TRANSPORT 462 mux category SDP attributes MUST explicitly be included in each 463 bundled "m=" section (excluding any bundle-only "m=" sections). 465 When an offerer or answerer includes SDP attributes in bundled "m=" 466 sections within a BUNDLE group for which the offerer and answerer 467 BUNDLE addresses have been selected, IDENTICAL and TRANSPORT mux 468 category SDP attributes [I-D.ietf-mmusic-sdp-mux-attributes] are only 469 included in the "m=" section represented by the BUNDLE-tag in the 470 offer or answer. The SDP attribute values are implicitly applied to 471 each bundled "m=" section (including any bundle-only "m=" section). 472 The offerer and answerer MUST NOT include such SDP attributes in any 473 other bundled "m=" section. 475 The semantics of some SDP attributes only apply to specific types of 476 media. For example, the semantics of the SDP 'rtcp-mux' and SDP 477 'rtcp-mux-only' attributes only apply to "m=" sections describing 478 RTP-based media. However, as described in Section 8.1, there are 479 cases where IDENTICAL and TRANSPORT mux category SDP attributes are 480 only included in the "m=" sections represented by the BUNDLE-tag. 481 That means that media-specific IDENTICAL and TRANSPORT mux category 482 attributes can be included in an "m=" section associated with another 483 type of media. 485 8.2. Generating the Initial SDP Offer 487 When an offerer generates an initial offer, to negotiate a BUNDLE 488 group, it MUST: 490 o Assign a unique address to each "m=" section within the offer, 491 following the procedures in [RFC3264], excluding any bundle-only 492 "m=" sections (see below); and 494 o Include an SDP 'group:BUNDLE' attribute in the offer; and 496 o Place the identification-tag of each bundled "m=" section in the 497 SDP 'group:BUNDLE' attribute identification-tag list; and 499 o Indicate which unique address the offerer suggests as the offerer 500 BUNDLE address [Section 8.2.1]. 502 If the offerer wants to request that the answerer accepts a given 503 bundled "m=" section only if the answerer keeps the "m=" section 504 within the BUNDLE group, the offerer MUST: 506 o Include an SDP 'bundle-only' attribute [Section 8.2.1] in the "m=" 507 secction; and 509 o Assign a zero port value to the "m=" section. 511 NOTE: If the offerer assigns a zero port value to an "m=" section, 512 but does not include an SDP 'bundle-only' attribute in the "m=" 513 section, it is an indication that the offerer wants to disable the 514 "m=" section [Section 8.5.4]. 516 NOTE: If the offerer assigns unique addresses to multiple bundled 517 "m=" sections, the offerer needs to be prepared to receive bundled 518 media on each unique address, until it receives the associated answer 519 and finds out which address:port combination has been selected as the 520 offerer BUNDLE-address. 522 [Section 8.2.2] and [Section 18.1] show an example of an initial 523 offer. 525 8.2.1. Suggesting the Offerer BUNDLE Address 527 In the offer, the address:port combination assigned to the "m=" 528 section represented by the offerer BUNDLE-tag indicates the offerer 529 BUNDLE address, i.e., the address:port combination that the offerer 530 suggests for sending and receiving bundled media. 532 The offerer BUNDLE-tag MUST NOT represent a bundle-only "m=" section. 533 Hence, the offer MUST contain at least one bundled "m=" section with 534 a unique address (and a non-zero port value). 536 It is RECOMMENDED that the offerer assigns the suggested offerer 537 BUNDLE address to a bundled "m=" section that the offerer assumes it 538 is unlikely that the answerer will reject, or move out of the BUNDLE 539 group. How such assumption is made is outside the scope of this 540 document. 542 8.2.2. Example: Initial SDP Offer 544 The example shows an initial SDP offer. The offer includes two "m=" 545 sections in the SDP, and suggests that both are included in a BUNDLE 546 group. The audio "m=" section is represented by the offerer BUNDLE- 547 tag (placed first in the SDP group:BUNDLE attribute identification-id 548 list). 550 SDP Offer 552 v=0 553 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 554 s= 555 c=IN IP4 atlanta.example.com 556 t=0 0 557 a=group:BUNDLE foo bar 558 m=audio 10000 RTP/AVP 0 8 97 559 b=AS:200 560 a=mid:foo 561 a=rtcp-mux 562 a=rtpmap:0 PCMU/8000 563 a=rtpmap:8 PCMA/8000 564 a=rtpmap:97 iLBC/8000 565 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 566 m=video 10002 RTP/AVP 31 32 567 b=AS:1000 568 a=mid:bar 569 a=rtcp-mux 570 a=rtpmap:31 H261/90000 571 a=rtpmap:32 MPV/90000 572 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 574 8.3. Generating the SDP Answer 576 When an answerer generates an answer that contains a BUNDLE group, 577 the following general SDP grouping framework restrictions, defined in 578 [RFC5888], also apply to the BUNDLE group: 580 o The answerer MUST NOT include a BUNDLE group in the answer, unless 581 the offerer requested the BUNDLE group to be negotiated in the 582 corresponding offer; and 584 o The answerer MUST NOT include an "m=" section within a BUNDLE 585 group, unless the offerer requested the "m=" section to be within 586 that BUNDLE group in the corresponding offer. 588 o If the answer contains multiple BUNDLE groups, the answerer MUST 589 NOT move an "m=" section from one BUNDLE group to another. 591 If the answer contains a BUNDLE group, the answerer MUST: 593 o Select an offerer BUNDLE Address [Section 8.3.1]; and 595 o Select an answerer BUNDLE Address [Section 8.3.2]. 597 The answerer is allowed to select a new answerer BUNDLE address each 598 time it generates an answer to an offer. 600 If the answerer does not want to keep an "m=" section within a BUNDLE 601 group, it MUST: 603 o Move the "m=" section out of the BUNDLE group [Section 8.3.3]; or 605 o Reject the "m=" section [Section 8.3.4]. 607 When the answerer creates the answer, it selects the offerer BUNDLE 608 address [Section 8.3.1] and the answerer BUNDLE address 609 [Section 8.3.2]. The answerer then assigns the answerer BUNDLE 610 address to the bundled "m=" section represented by the answerer 611 BUNDLE-tag. In every other bundled "m=" section the answerer 612 includes an SDP 'bundle-only' attribute and assigns a zero port value 613 to the "m=" section. 615 If the answerer does not want to keep a bundle-only "m=" section 616 within the BUNDLE group, it MUST reject the "m=" section 617 [Section 8.3.4]. 619 NOTE: If a bundled "m=" section in an offer contains a zero port 620 value, but the "m=" section does not contain an SDP 'bundle-only' 621 attribute, it is an indication that the offerer wants to disable the 622 "m=" section [Section 8.5.4]. 624 8.3.1. Answerer Selection of Offerer BUNDLE Address 626 In an offer, the bundled "m=" section represented by the offerer 627 BUNDLE-tag contains the suggested offerer BUNDLE address, i.e, the 628 address:port combination that the offerer wants to use for sending 629 and receiving bundled media [Section 8.2.1]. The answerer MUST check 630 whether that "m=" section fulfils the following criteria: 632 o The answerer will not move the "m=" section out of the BUNDLE 633 group [Section 8.3.3]; and 635 o The answerer will not reject the "m=" section [Section 8.3.4]; and 637 o The "m=" section does not contain a zero port value. 639 If all of the criteria above are fulfilled, the answerer MUST select 640 the suggested offerer BUNDLE address. 642 If one or more of the criteria are not fulfilled, the answerer MUST 643 pick the next identification-tag in the identification-tag list in 644 the offer, and perform the same criteria check for the "m=" section 645 represented by that identification-tag. If there are no more 646 identification-tags in the identification-tag list, the answerer MUST 647 NOT create the BUNDLE group. Unless the answerer rejects the whole 648 offer, the answerer MUST apply the answerer procedures for moving an 649 "m=" section out of a BUNDLE group [Section 8.3.3] or rejecting an 650 "m=" section within a BUNDLE group [Section 8.3.4] to every bundled 651 "m=" section in the offer when creating the answer. 653 [Section 18.1] shows an example of an offerer BUNDLE address 654 selection. 656 8.3.2. Answerer Selection of Answerer BUNDLE Address 658 When the answerer selects a BUNDLE address for itself (answerer 659 BUNDLE address), the answerer MUST assign the answerer BUNDLE address 660 to the "m=" section that contains the selected offerer BUNDLE address 661 in the corresponding offer. The answerer BUNDLE-tag represents that 662 "m=" section in the answer. To every other bundled "m=" section the 663 answerer MUST assign a zero port value and include an SDP 'bundle- 664 only' attribute. 666 The answerer MUST NOT assign an answerer BUNDLE address to an "m=" 667 section that is not within the BUNDLE group, or to an "m=" section 668 that is within another BUNDLE group. 670 [Section 8.3.5] and [Section 18.1] show an example of an answerer 671 BUNDLE address selection. 673 8.3.3. Moving A Media Description Out Of A BUNDLE Group 675 When an answerer wants to move a bundled "m=" section out of a BUNDLE 676 group in an answer, it MUST first check the following criteria: 678 o In the corresponding offer, an offerer BUNDLE address (previously 679 selected [Section 8.3.1] or new suggested [Section 8.5.1]) has 680 been assigned to the "m=" section by the offerer; or 682 o In the corresponding offer, the "m=" section contains an SDP 683 'bundle-only' attribute and a zero port value. 685 If either criteria above is fulfilled, the answerer can not move the 686 "m=" section out of the BUNDLE group in the answer. The answerer can 687 either reject the whole offer, reject each bundled "m=" section 688 within the BUNDLE group [Section 8.3.4], or keep the "m=" section 689 within the BUNDLE group in the answer and later create an offer where 690 the "m=" section is moved out of the BUNDLE group [Section 8.5.3]. 692 When the answerer generates an answer, in which it moves a bundled 693 "m=" section out of a BUNDLE group, the answerer: 695 o MUST assign a unique address to the "m=" section; and 697 o MUST NOT place the identification-tag associated with the "m=" 698 section in the SDP 'group:BUNDLE' attribute identification-tag 699 list associated with the BUNDLE group; and 701 o MUST NOT assign an SDP 'bundle-only' attribute to the "m=" 702 section. 704 An answerer MUST NOT move an "m=" section from one BUNDLE group to 705 another within an answer. If the answerer wants to move an "m=" 706 section from one BUNDLE group to another it MUST first move the "m=" 707 section out of the current BUNDLE group, and then generate an offer 708 where the "m=" section is added to another BUNDLE group 709 [Section 8.5.2]. 711 8.3.4. Rejecting a Media Description in a BUNDLE Group 713 When an answerer wants to reject a bundled "m=" section in an answer, 714 it MUST first check the following criteria: 716 o In the corresponding offer, an offerer BUNDLE address (previously 717 selected [Section 8.3.1] or new suggested [Section 8.5.1]) has 718 been assigned to the "m=" section by the offerer. 720 If the criteria above is fulfilled, the answerer can not reject the 721 "m=" section in the answer (unless the answerer rejects each bundled 722 "m=" section within the BUNDLE group). The answerer can either 723 reject the whole offer, reject each bundled "m=" section within the 724 BUNDLE group, or keep the "m=" section within the BUNDLE group in the 725 answer and later create an offer where the "m=" section is disabled 726 within the BUNDLE group [Section 8.5.4]. 728 When an answerer generates an answer, in which it rejects a bundled 729 "m=" section, the answerer: 731 o MUST assign a zero port value to the "m=" section, according to 732 the procedures in [RFC3264]; and 734 o MUST NOT place the identification-tag associated with the "m=" 735 section in the SDP 'group:BUNDLE' attribute identification-tag 736 list associated with the BUNDLE group; and 738 o MUST NOT assign an SDP 'bundle-only' attribute to the "m=" 739 section. 741 8.3.5. Example: SDP Answer 743 The example below shows an SDP answer, based on the SDP offer in 744 [Section 8.2.2]. The answerer accepts both "m=" sections within the 745 BUNDLE group. The answerer assigns the answerer BUNDLE address to 746 the "m=" section represented by the answerer BUNDLE-tag. The 747 answerer assigns a zero port value and an SDP 'bundle-only' attribute 748 to the other bundled "m=" section. 750 SDP Answer 752 v=0 753 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 754 s= 755 c=IN IP4 biloxi.example.com 756 t=0 0 757 a=group:BUNDLE foo bar 758 m=audio 20000 RTP/AVP 0 759 b=AS:200 760 a=mid:foo 761 a=rtcp-mux 762 a=rtpmap:0 PCMU/8000 763 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 764 m=video 0 RTP/AVP 32 765 b=AS:1000 766 a=mid:bar 767 a=bundle-only 768 a=rtpmap:32 MPV/90000 769 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 771 8.4. Offerer Processing of the SDP Answer 773 When an offerer receives an answer, if the answer contains a BUNDLE 774 group, the offerer MUST check that any bundled "m=" section in the 775 answer was indicated as bundled in the corresponding offer. If there 776 is no mismatch, the offerer MUST use the offerer BUNDLE address, 777 selected by the answerer [Section 8.3.1], as the address for each 778 bundled "m=" section. 780 NOTE: As the answerer might reject one or more bundled "m=" sections, 781 or move a bundled "m=" section out of a BUNDLE group, each bundled 782 "m=" section in the offer might not be indicated as bundled in the 783 answer. 785 If the answer does not contain a BUNDLE group, the offerer MUST 786 process the answer as a normal answer. 788 8.5. Modifying the Session 790 When an offerer generates a subsequent offer (i.e., a BUNDLE group 791 has previously been negotiated), it MUST assign the previously 792 selected offer BUNDLE address [Section 8.3.1], or a new suggested 793 offerer BUNDLE address [Section 8.5.1], to exactly one "m=" section 794 within the BUNDLE group. 796 The offerer MUST NOT assign an offerer BUNDLE address (previously 797 selected [Section 8.3.1] or new suggested [Section 8.5.1]) to a 798 bundled "m=" section if: 800 o The offerer wants to move the bundled "m=" section out of the 801 BUNDLE group [Section 8.5.3]; or 803 o The offerer wants to disable the bundled "m=" section 804 [Section 8.5.4]. 806 To every other "m=" section within the BUNDLE group, the offerer MUST 807 assign a zero port value and an SDP 'bundle-only' attribute. 809 When the offerer generates a subsequent offer, the offerer BUNDLE-tag 810 MUST represent the bundled "m=" section to which the offerer BUNDLE 811 address (previously negotiated or new suggested) has been assigned. 813 8.5.1. Suggesting a New Offerer BUNDLE Address 815 When an offerer generates an offer, in which it suggests a new 816 offerer BUNDLE address [Section 8.2.1], the offerer MUST: 818 o Assign the new suggested offerer BUNDLE address to exactly one 819 "m=" section within the BUNDLE group; and 821 o Assign a zero port value and an SDP 'bundle-only' attribute to 822 every other "m=" section within the BUNDLE group. 824 8.5.2. Adding a Media Description to a BUNDLE group 826 When an offerer generates an offer, in which it wants to add a 827 bundled "m=" section, the offerer MUST: 829 o Assign the offerer BUNDLE address (previously selected 830 [Section 8.3.1] or new suggested [Section 8.5.1]) to the added 831 "m=" section; or 833 o Assign a zero port value and an SDP 'bundle-only' attribute to the 834 added "m=" section (in this case the offerer BUNDLE address is 835 assigned to another "m=" section within the BUNDLE group). 837 In addition, the offerer MUST place the identification-tag associated 838 with the added "m=" section in the SDP 'group:BUNDLE' attribute 839 identification-tag list associated with the BUNDLE group 840 [Section 8.2.1]. 842 NOTE: If the offerer also wants to suggest a new offerer BUNDLE 843 address to the BUNDLE group, the offerer can assign the new suggested 844 offerer BUNDLE address either to the added "m=" section, or to some 845 other "m=" section within the BUNDLE group [Section 8.5.1]. 847 [Section 18.3] shows an example where an offerer sends an offer in 848 order to add a bundled "m=" section to a BUNDLE group. 850 8.5.3. Moving a Media Description Out of a BUNDLE Group 852 When an offerer generates an offer, in which it wants to move a 853 bundled "m=" section out of a BUNDLE group, the offerer: 855 o MUST assign a unique address to the "m=" section; and 857 o MUST NOT place the identification-tag associated with the "m=" 858 section in the SDP 'group:BUNDLE' attribute identification-tag 859 list associated with the BUNDLE group; and 861 o MUST NOT assign an SDP 'bundle-only' attribute to the "m=" 862 section. 864 An offerer MUST NOT move an "m=" section from one BUNDLE group to 865 another within a single offer. If the offerer wants to move an "m=" 866 section from one BUNDLE group to another it MUST first move the 867 BUNDLE group out of the current BUNDLE group, and then generate a 868 second offer where the "m=" section is added to another BUNDLE group 869 [Section 8.5.2]. 871 [Section 18.4] shows an example of an offer for moving an "m=" 872 section out of a BUNDLE group. 874 8.5.4. Disabling a Media Description in a BUNDLE Group 876 When an offerer generates an offer, in which it wants to disable a 877 bundled "m=" section, the offerer: 879 o MUST assign a zero port value to the "m=" section, following the 880 procedures in [RFC4566]; and 882 o MUST NOT place the identification-tag associated with the "m=" 883 section in the SDP 'group:BUNDLE' attribute identification-tag 884 list associated with the BUNDLE group; and 886 o MUST NOT assign an SDP 'bundle-only' attribute to the "m=" 887 section. 889 [Section 18.5] shows an example of an offer and answer for disabling 890 an "m=" section within a BUNDLE group. 892 9. Protocol Identification 894 Each "m=" section within a BUNDLE group MUST use the same transport- 895 layer protocol. If bundled "m=" sections use different protocols on 896 top of the transport-layer protocol, there MUST exist a publicly 897 available specification which describes a mechanism how to associate 898 received data with the correct protocol for this particular protocol 899 combination. 901 In addition, if received data can be associated with more than one 902 bundled "m=" section, there MUST exist a publicly available 903 specification which describes a mechanism for associating the 904 received data with the correct "m=" section. 906 This document describes a mechanism to identify the protocol of 907 received data among the STUN, DTLS and SRTP protocols (in any 908 combination), when UDP is used as transport-layer protocol, but it 909 does not describe how to identify different protocols transported on 910 DTLS. While the mechanism is generally applicable to other protocols 911 and transport-layer protocols, any such use requires further 912 specification around how to multiplex multiple protocols on a given 913 transport-layer protocol, and how to associate received data with the 914 correct protocols. 916 9.1. STUN, DTLS, SRTP 918 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 919 protocol of a received packet among the STUN, DTLS and SRTP protocols 920 (in any combination). If an offer or answer includes a bundled "m=" 921 section that represents these protocols, the offerer or answerer MUST 922 support the mechanism described in [RFC5764], and no explicit 923 negotiation is required in order to indicate support and usage of the 924 mechanism. 926 [RFC5764] does not describe how to identify different protocols 927 transported on DTLS, only how to identify the DTLS protocol itself. 928 If multiple protocols are transported on DTLS, there MUST exist a 929 specification describing a mechanism for identifying each individual 930 protocol. In addition, if a received DTLS packet can be associated 931 with more than one "m=" section, there MUST exist a specification 932 which describes a mechanism for associating the received DTLS packets 933 with the correct "m=" section. 935 [Section 10.2] describes how to associate the packets in a received 936 SRTP stream with the correct "m=" section. 938 10. RTP Considerations 940 10.1. Single RTP Session 942 All RTP-based media within a single BUNDLE group belong to a single 943 RTP session [RFC3550]. 945 Since a single BUNDLE transport is used for sending and receiving 946 bundled media, the symmetric RTP mechanism [RFC4961] MUST be used for 947 RTP-based bundled media. 949 Since a single RTP session is used for each BUNDLE group, all "m=" 950 sections representing RTP-based media within a BUNDLE group will 951 share a single SSRC numbering space [RFC3550]. 953 The following rules and restrictions apply for a single RTP session: 955 o A specific payload type value can be used in multiple bundled "m=" 956 sections only if each codec associated with the payload type 957 number shares an identical codec configuration [Section 10.1.1]. 959 o The proto value in each bundled RTP-based "m=" section MUST be 960 identical (e.g., RTP/AVPF). 962 o The RTP MID header extension MUST be enabled, by including an SDP 963 'extmap' attribute [RFC8285], with a 'urn:ietf:params:rtp- 964 hdrext:sdes:mid' URI value, in each bundled RTP-based "m=" section 965 in every offer and answer. 967 o A given SSRC MUST NOT transmit RTP packets using payload types 968 that originate from different bundled "m=" sections. 970 NOTE: The last bullet above is to avoid sending multiple media types 971 from the same SSRC. If transmission of multiple media types are done 972 with time overlap, RTP and RTCP fail to function. Even if done in 973 proper sequence this causes RTP Timestamp rate switching issues 974 [RFC7160]. However, once an SSRC has left the RTP session (by 975 sending an RTCP BYE packet), that SSRC can be reused by another 976 source (possibly associated with a different bundled "m=" section) 977 after a delay of 5 RTCP reporting intervals (the delay is to ensure 978 the SSRC has timed out, in case the RTCP BYE packet was lost 979 [RFC3550]). 981 10.1.1. Payload Type (PT) Value Reuse 983 Multiple bundled "m=" sections might describe RTP based media. As 984 all RTP based media associated with a BUNDLE group belong to the same 985 RTP session, in order for a given payload type value to be used 986 inside more than one bundled "m=" section, all codecs associated with 987 the payload type number MUST share an identical codec configuration. 988 This means that the codecs MUST share the same media type, encoding 989 name, clock rate and any parameter that can affect the codec 990 configuration and packetization. 991 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 992 attribute values must be identical for all codecs that use the same 993 payload type value. 995 10.2. Associating RTP/RTCP Streams with Correct SDP Media Description 997 As described in [RFC3550], RTP packets are associated with RTP 998 streams [RFC7656]. Each RTP stream is identified by an SSRC value, 999 and each RTP packet includes an SSRC field that is used to associate 1000 the packet with the correct RTP stream. RTCP packets also use SSRCs 1001 to identify which RTP streams the packet relates to. However, a RTCP 1002 packet can contain multiple SSRC fields, in the course of providing 1003 feedback or reports on different RTP streams, and therefore can be 1004 associated with multiple such streams. 1006 In order to be able to process received RTP/RTCP packets correctly, 1007 it must be possible to associate an RTP stream with the correct "m=" 1008 section, as the "m=" section and SDP attributes associated with the 1009 "m=" section contains information needed to process the packets. 1011 As all RTP streams associated with a BUNDLE group use the same 1012 transport for sending and receiving RTP/RTCP packets, the local 1013 address:port combination part of the transport cannot be used to 1014 associate an RTP stream with the correct "m=" section. In addition, 1015 multiple RTP streams might be associated with the same "m=" section. 1017 An offerer and answerer can inform each other which SSRC values they 1018 will use for an RTP stream by using the SDP 'ssrc' attribute 1019 [RFC5576]. However, an offerer will not know which SSRC values the 1020 answerer will use until the offerer has received the answer providing 1021 that information. Due to this, before the offerer has received the 1022 answer, the offerer will not be able to associate an RTP stream with 1023 the correct "m=" section using the SSRC value associated with the RTP 1024 stream. In addition, the offerer and answerer may start using new 1025 SSRC values mid-session, without informing each other using the SDP 1026 'ssrc' attribute. 1028 In order for an offerer and answerer to always be able to associate 1029 an RTP stream with the correct "m=" section, the offerer and answerer 1030 using the BUNDLE extension MUST support the mechanism defined in 1031 Section 15, where the offerer and answerer insert the identification- 1032 tag associated with an "m=" section (provided by the remote peer) 1033 into RTP and RTCP packets associated with a BUNDLE group. 1035 When using this mechanism, the mapping from an SSRC to an 1036 identification-tag is carried in RTP header extensions or RTCP SDES 1037 packets, as specified in Section 15. Since a compound RTCP packet 1038 can contain multiple RTCP SDES packets, and each RTCP SDES packet can 1039 contain multiple chunks, a single RTCP packet can contain several 1040 SSRC to identification-tag mappings. The offerer and answerer 1041 maintain tables used for routing that are updated each time an RTP/ 1042 RTCP packet contains new information that affects how packets should 1043 be routed. 1045 However, some implementations may not include this identification-tag 1046 in their RTP and RTCP traffic when using the BUNDLE mechanism, and 1047 instead use a payload type based mechanism to associate RTP streams 1048 with SDP "m=" sections. In this situation, each "m=" section MUST 1049 use unique payload type values, in order for the payload type to be a 1050 reliable indicator of the relevant "m=" section for the RTP stream. 1051 Note that when using the payload type to associate RTP streams with 1052 "m=" sections an RTP stream, identified by its SSRC, will be mapped 1053 to an "m=" section when the first packet of that RTP stream is 1054 received, and the mapping will not be changed even if the payload 1055 type used by that RTP stream changes. In other words, the SSRC 1056 cannot "move" to a different "m=" section simply by changing the 1057 payload type. 1059 Applications can implement RTP stacks in many different ways. The 1060 algorithm below details one way that RTP streams can be associated 1061 with "m=" sections, but is not meant to be prescriptive about exactly 1062 how an RTP stack needs to be implemented. Applications MAY use any 1063 algorithm that achieves equivalent results to those described in the 1064 algorithm below. 1066 To prepare to associate RTP streams with the correct "m=" section, 1067 the following steps MUST be followed for each BUNDLE group: 1069 Construct a table mapping MID to "m=" section for each "m=" 1070 section in this BUNDLE group. Note that an "m=" section may only 1071 have one MID. 1073 Construct a table mapping SSRCs of incoming RTP streams to "m=" 1074 section for each "m=" section in this BUNDLE group and for each 1075 SSRC configured for receiving in that "m=" section. 1077 Construct a table mapping the SSRC of each outgoing RTP stream to 1078 "m=" section for each "m=" section in this BUNDLE group and for 1079 each SSRC configured for sending in that "m=" section. 1081 Construct a table mapping payload type to "m=" section for each 1082 "m=" section in the BUNDLE group and for each payload type 1083 configured for receiving in that "m=" section. If any payload 1084 type is configured for receiving in more than one "m=" section in 1085 the BUNDLE group, do not include it in the table, as it cannot be 1086 used to uniquely identify an "m=" section. 1088 Note that for each of these tables, there can only be one mapping 1089 for any given key (MID, SSRC, or PT). In other words, the tables 1090 are not multimaps. 1092 As "m=" sections are added or removed from the BUNDLE groups, or 1093 their configurations are changed, the tables above MUST also be 1094 updated. 1096 When an RTP packet is received, it MUST be delivered to the RTP 1097 stream corresponding to its SSRC. That RTP stream MUST then be 1098 associated with the correct "m=" section within a BUNDLE group, for 1099 additional processing, according to the following steps: 1101 If the MID associated with the RTP stream is not in the table 1102 mapping MID to "m=" section, then the RTP stream is not decoded 1103 and the payload data is discarded. 1105 If the packet has a MID, and the packet's extended sequence number 1106 is greater than that of the last MID update, as discussed in 1107 [RFC7941], Section 4.2.6, update the MID associated with the RTP 1108 stream to match the MID carried in the RTP packet, then update the 1109 mapping tables to include an entry that maps the SSRC of that RTP 1110 stream to the "m=" section for that MID. 1112 If the SSRC of the RTP stream is in the incoming SSRC mapping 1113 table, check that the payload type used by the RTP stream matches 1114 a payload type included on the matching "m=" section. If so, 1115 associate the RTP stream with that "m=" section. Otherwise, the 1116 RTP stream is not decoded and the payload data is discarded. 1118 If the payload type used by the RTP stream is in the payload type 1119 table, update the incoming SSRC mapping table to include an entry 1120 that maps the RTP stream's SSRC to the "m=" section for that 1121 payload type. Associate the RTP stream with the corresponding 1122 "m=" section. 1124 Otherwise, mark the RTP stream as not for decoding and discard the 1125 payload. 1127 If the RTP packet contains one or more contributing source (CSRC) 1128 identifiers, then each CSRC is looked up in the incoming SSRC table 1129 and a copy of the RTP packet is associated with the corresponding 1130 "m=" section for additional processing. 1132 For each RTCP packet received (including each RTCP packet that is 1133 part of a compound RTCP packet), the packet is processed as usual by 1134 the RTP layer, then passed to the "m=" sections corresponding to the 1135 RTP streams it contains information about for additional processing. 1136 This routing is type-dependent, as each kind of RTCP packet has its 1137 own mechanism for associating it with the relevant RTP streams. 1139 RTCP packets for which no appropriate "m=" section can be identified 1140 MUST be processed as usual by the RTP layer, updating the metadata 1141 associated with the corresponding RTP streams, but are not passed to 1142 any "m=" section. This situation can occur with certain multiparty 1143 RTP topologies, or when RTCP packets are sent containing a subset of 1144 the SDES information. 1146 Rules for additional processing of the various types of RTCP packets 1147 are explained below. 1149 If the RTCP packet is of type SDES, for each chunk in the packet 1150 whose SSRC is found in the incoming SSRC table, deliver a copy of 1151 the SDES packet to the "m=" section associated with that SSRC. In 1152 addition, for any SDES MID items contained in these chunks, if the 1153 MID is found in the table mapping MID to "m=" section, update the 1154 incoming SSRC table to include an entry that maps the RTP stream 1155 associated with the chunk's SSRC to the "m=" section associated 1156 with that MID, unless the packet is older than the packet that 1157 most recently updated the mapping for this SSRC, as discussed in 1158 [RFC7941], Section 4.2.6. 1160 Note that if an SDES packet is received as part of a compound RTCP 1161 packet, the SSRC to "m=" section mapping may not exist until the 1162 SDES packet is handled (e.g., in the case where RTCP for a source 1163 is received before any RTP packets). Therefore, when processing a 1164 compound packet, any contained SDES packet MUST be handled first. 1165 Note that this is a change from [RFC3550] Section 6.1, which 1166 states that "Each individual RTCP packet in the compound packet 1167 may be processed independently with no requirements upon the order 1168 or combination of packets". 1170 If the RTCP packet is of type BYE, it indicates that the RTP 1171 streams referenced in the packet are ending. Therefore, for each 1172 SSRC indicated in the packet that is found in the incoming SSRC 1173 table, first deliver a copy of the BYE packet to the "m=" section 1174 associated with that SSRC, then remove the entry for that SSRC 1175 from the incoming SSRC table after an appropriate delay to account 1176 for "straggler packets", as specified in [RFC3550], Section 6.2.1. 1178 If the RTCP packet is of type SR or RR, for each report block in 1179 the report whose "SSRC of source" is found in the outgoing SSRC 1180 table, deliver a copy of the SR or RR packet to the "m=" section 1181 associated with that SSRC. In addition, if the packet is of type 1182 SR, and the sender SSRC for the packet is found in the incoming 1183 SSRC table, deliver a copy of the SR packet to the "m=" section 1184 associated with that SSRC. 1186 If the implementation supports RTCP XR and the packet is of type 1187 XR, as defined in [RFC3611], for each report block in the report 1188 whose "SSRC of source" is found in the outgoing SSRC table, 1189 deliver a copy of the XR packet to the "m=" section associated 1190 with that SSRC. In addition, if the sender SSRC for the packet is 1191 found in the incoming SSRC table, deliver a copy of the XR packet 1192 to the "m=" section associated with that SSRC. 1194 If the RTCP packet is a feedback message of type RTPFB or PSFB, as 1195 defined in [RFC4585], it will contain a media source SSRC, and 1196 this SSRC is used for routing certain subtypes of feedback 1197 messages. However, several subtypes of PSFB and RTPFB messages 1198 include target SSRC(s) in a section called Feedback Control 1199 Information (FCI). For these messages, the target SSRC(s) are 1200 used for routing. 1202 If the RTCP packet is a feedback packet that does not include 1203 target SSRCs in its FCI section, and the media source SSRC is 1204 found in the outgoing SSRC table, deliver the feedback packet to 1205 the "m=" section associated with that SSRC. RTPFB and PSFB types 1206 that are handled in this way include: 1208 Generic NACK: [RFC4585] (PT=RTPFB, FMT=1). 1210 Picture Loss Indication (PLI): [RFC4585] (PT=PSFB, FMT=1). 1212 Slice Loss Indication (SLI): [RFC4585] (PT=PSFB, FMT=2). 1214 Reference Picture Selection Indication (RPSI): [RFC4585] 1215 (PT=PSFB, FMT=3). 1217 If the RTCP packet is a feedback message that does include target 1218 SSRC(s) in its FCI section, it can either be a request or a 1219 notification. Requests reference a RTP stream that is being sent 1220 by the message recipient, whereas notifications are responses to 1221 an earlier request, and therefore reference a RTP stream that is 1222 being received by the message recipient. 1224 If the RTCP packet is a feedback request that includes target 1225 SSRC(s), for each target SSRC that is found in the outgoing SSRC 1226 table, deliver a copy of the RTCP packet to the "m=" section 1227 associated with that SSRC. PSFB and RTPFB types that are handled 1228 in this way include: 1230 Full Intra Request (FIR): [RFC5104] (PT=PSFB, FMT=4). 1232 Temporal-Spatial Trade-off Request (TSTR): [RFC5104] (PT=PSFB, 1233 FMT=5). 1235 H.271 Video Back Channel Message (VBCM): [RFC5104] (PT=PSFB, 1236 FMT=7). 1238 Temporary Maximum Media Bit Rate Request (TMMBR): [RFC5104] 1239 (PT=RTPFB, FMT=3). 1241 Layer Refresh Request (LRR): [I-D.ietf-avtext-lrr] (PT=PSFB, 1242 FMT=TBD). 1244 If the RTCP packet is a feedback notification that includes target 1245 SSRC(s), for each target SSRC that is found in the incoming SSRC 1246 table, deliver a copy of the RTCP packet to the "m=" section 1247 associated with the RTP stream with matching SSRC. PSFB and RTPFB 1248 types that are handled in this way include: 1250 Temporal-Spatial Trade-off Notification (TSTN): [RFC5104] 1251 (PT=PSFB, FMT=6). This message is a notification in response 1252 to a prior TSTR. 1254 Temporary Maximum Media Bit Rate Notification (TMMBN): [RFC5104] 1255 (PT=RTPFB, FMT=4). This message is a notification in response 1256 to a prior TMMBR, but can also be sent unsolicited. 1258 If the RTCP packet is of type APP, then it is handled in an 1259 application specific manner. If the application does not 1260 recognise the APP packet, then it MUST be discarded. 1262 10.3. RTP/RTCP Multiplexing 1264 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 1265 multiplexing [RFC5761] for the RTP-based media specified by the 1266 BUNDLE group. 1268 When RTP/RTCP multiplexing is enabled, the same transport will be 1269 used for both RTP packets and RTCP packets associated with the BUNDLE 1270 group. 1272 10.3.1. SDP Offer/Answer Procedures 1274 This section describes how an offerer and answerer use the SDP 'rtcp- 1275 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 1276 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 1277 multiplexing for RTP-based media associated with a BUNDLE group. 1279 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] of the SDP 1280 'rtcp-mux' and 'rtcp-mux-only' attributes is IDENTICAL. Section 8.1 1281 describes the details regarding which bundled "m=" sections an 1282 offerer and answerer associates the attributes with. 1284 RTP/RTCP multiplexing only applies to RTP-based media. However, as 1285 described in Section 8.1, within a BUNDLE group the SDP 'rtcp-mux' 1286 and SDP 'rtcp-mux-only' attributes might be included in a non-RTP- 1287 based bundled "m=" section (if such "m=" line is represented by a 1288 BUNDLE-tag). 1290 10.3.1.1. Generating the Initial SDP Offer 1292 When an offerer generates an initial offer, if the offer contains one 1293 or more RTP-based bundled "m=" sections (or, if there is a chance 1294 that RTP-based "m=" sections will later be added to the BUNDLE 1295 group), the offerer MUST include an SDP 'rtcp-mux' attribute 1296 [RFC5761] in each bundled "m=" section (excluding any bundle-only 1297 "m=" sections), following the procedures for IDENTICAL mux category 1298 attributes in Section 8.1. In addition, the offerer MAY include an 1299 SDP 'rtcp-mux-only' attribute [I-D.ietf-mmusic-mux-exclusive] in a 1300 RTP-based bundled "m=" section. 1302 NOTE: Whether the offerer associates the SDP 'rtcp-mux-only' 1303 attribute depends on whether the offerer supports fallback to usage 1304 of a separate port for RTCP in case the answerer moves one or more 1305 RTP-based "m=" section out of the BUNDLE group in the answer. 1307 NOTE: If the offerer includes an SDP 'rtcp-mux' attribute in the 1308 bundled "m=" sections, but does not include an SDP 'rtcp-mux-only' 1309 attribute, the offerer can also include an SDP 'rtcp' attribute 1311 [RFC3605] in one or more RTP-based bundled "m=" sections in order to 1312 provide a fallback port for RTCP, as described in [RFC5761]. 1313 However, the fallback port will only be used for RTP-based "m=" 1314 sections moved out of the BUNDLE group by the answerer. 1316 In the initial offer, the address:port combination for RTCP MUST be 1317 unique in each bundled RTP-based "m=" section (excluding a bundle- 1318 only "m=" section), similar to RTP. 1320 10.3.1.2. Generating the SDP Answer 1322 When an answerer generates an answer, if the answerer supports RTP- 1323 based media, and if a bundled "m=" section in the offer contained an 1324 SDP 'rtcp-mux' attribute, the answerer MUST enable usage of RTP/RTCP 1325 multiplexing, even if there currently are no RTP-based "m=" sections 1326 within the BUNDLE group. The answerer MUST include an SDP 'rtcp-mux' 1327 attribute in the bundled "m=" section represented by the answerer 1328 BUNDLE-tag, following the procedures for IDENTICAL mux category 1329 attributes in Section 8.1. In addition, if the "m=" section in the 1330 offer contained an SDP "rtcp-mux-only" attribute, the answerer MUST 1331 include an SDP "rtcp-mux-only" attribute in the bundled "m=" section 1332 represented by the answerer BUNDLE-tag in the answer. 1334 If the "m=" section represented by the offerer BUNDLE-tag in the 1335 offer contained an SDP 'rtcp-mux-only' attribute, and if the answerer 1336 moves an RTP-based "m=" section out of the BUNDLE group in the answer 1337 [Section 8.3.3], the answerer MUST either include the attribute in 1338 the moved "m=" section (and enable RTP/RTCP multiplexing for the 1339 media associated with the "m=" section), or reject the "m=" section 1340 [Section 8.3.4]. 1342 The answerer MUST NOT include an SDP 'rtcp' attribute in any "m=" 1343 section within the BUNDLE group in the answer. The answerer will use 1344 the port value of the selected offerer BUNDLE address for sending RTP 1345 and RTCP packets associated with each RTP-based bundled "m=" section 1346 towards the offerer. 1348 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 1349 negotiated in a previous offer/answer exchange, the answerer MUST 1350 include an SDP 'rtcp-mux' attribute in the "m=" section associated 1351 with the answerer BUNDLE-tag in the answer. It is not possible to 1352 disable RTP/RTCP multiplexing within a BUNDLE group. 1354 10.3.1.3. Offerer Processing of the SDP Answer 1356 When an offerer receives an answer, if the answerer has accepted the 1357 usage of RTP/RTCP multiplexing (see Section 10.3.1.2), the answerer 1358 follows the procedures for RTP/RTCP multiplexing defined in 1360 [RFC5761]. The offerer will use the port value associated with the 1361 answerer BUNDLE address for sending RTP and RTCP packets associated 1362 with each RTP-based bundled "m=" section towards the answerer. 1364 NOTE: It is considered a protocol error if the answerer has not 1365 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" 1366 sections that the answerer included in the BUNDLE group. 1368 10.3.1.4. Modifying the Session 1370 When an offerer generates a subsequent offer, the offerer MUST 1371 include an SDP 'rtcp-mux' attribute in the bundled "m=" section 1372 represented by the offerer BUNDLE-tag, following the procedures for 1373 IDENTICAL mux category attributes in Section 8.1. 1375 11. ICE Considerations 1377 This section describes how to use the BUNDLE grouping extension 1378 together with the Interactive Connectivity Establishment (ICE) 1379 mechanism [I-D.ietf-ice-rfc5245bis]. 1381 The generic procedures for negotiating usage of ICE using SDP, 1382 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1383 with BUNDLE, with the following exceptions: 1385 o When the BUNDLE transport has been established, ICE connectivity 1386 checks and keep-alives only need to be performed for the BUNDLE 1387 transport, instead of per individual "m=" section within the 1388 BUNDLE group. 1390 o In an offer, if the offer assigns a unique address to one or more 1391 bundled "m=" sections (excluding any bundle-only "m=" sections), 1392 the offerer MUST include ICE-related media-level attributes in 1393 each of those "m=" sections. If the offerer assigns an offerer 1394 BUNDLE address (previously selected [Section 8.3.1] or new 1395 suggested [Section 8.5.1]) to a bundled "m=" section (the "m=" 1396 section represented by the offerer BUNDLE-tag), the offerer only 1397 includes ICE-related media-level SDP attributes in that "m=" 1398 section, following the procedures in Section 8.1. 1400 o In an answer, the answerer only includes ICE-related media-level 1401 SDP attributes in the bundled "m=" section to which the answerer 1402 has assigned the answerer BUNDLE address (the "m=" section 1403 represented by the answerer BUNDLE-tag), following the procedures 1404 in Section 8.1. 1406 Initially, before ICE has produced a candidate pair that will be used 1407 for media, there might be multiple transports established (if 1408 multiple candidate pairs are tested). Once ICE has produced a 1409 transport that will be used for media, that becomes the BUNDLE 1410 transport. 1412 Support and usage of ICE mechanism together with the BUNDLE extension 1413 is OPTIONAL, and the procedures in this section only apply when the 1414 ICE mechanism is used. 1416 11.1. SDP Offer/Answer Procedures 1418 When an offerer assigns a unique address to one or more bundled "m=" 1419 sections (excluding any bundle-only "m=" section), the offerer MUST 1420 include SDP 'candidate' attributes (and other applicable ICE-related 1421 media-level SDP attributes), containing unique ICE properties 1422 (candidates etc), in each of those "m=" sections, following the 1423 procedures in [I-D.ietf-mmusic-ice-sip-sdp]. 1425 When an offerer assigns a BUNDLE address (previously selected or new 1426 suggested) to a bundled "m=" section, (the "m=" section represented 1427 by the offerer BUNDLE-tag) the offerer MUST only include SDP 1428 'candidate' attributes (and other applicable ICE-related media-level 1429 SDP attributes) in that "m=" section, following the procedures in 1430 Section 8.1. 1432 When an answerer assigns a BUNDLE address to an "m=" section within a 1433 BUNDLE group (the "m=" section represented by the answerer BUNDLE- 1434 tag), the answerer MUST only include SDP 'candidate' attributes (and 1435 other applicable ICE-related media-level SDP attributes) in that "m=" 1436 section, following the procedures in Section 8.1. 1438 NOTE: As most ICE-related media-level SDP attributes belong to the 1439 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1440 offerer and answerer follow the procedures in Section 8.1 when 1441 deciding whether to include an attribute in a bundled "m=" section. 1442 However, in the case of ICE-related media-level attributes, the rules 1443 apply to all attributes (see note below), even if they belong to a 1444 different mux category. 1446 NOTE: The following ICE-related media-level SDP attributes are 1447 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidate', 'remote- 1448 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1449 pacing'. 1451 12. DTLS Considerations 1453 One or more media streams within a BUNDLE group might use the 1454 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1455 to encrypt the data, or to negotiate encryption keys if another 1456 encryption mechanism is used to encrypt media. 1458 When DTLS is used within a BUNDLE group, the following rules apply: 1460 o There can only be one DTLS association [RFC6347] associated with 1461 the BUNDLE group; and 1463 o Each usage of the DTLS association within the BUNDLE group MUST 1464 use the same mechanism for determining which endpoints (the 1465 offerer or answerer) become DTLS client and DTLS server; and 1467 o Each usage of the DTLS association within the BUNDLE group MUST 1468 use the same mechanism for determining whether an offer or answer 1469 will trigger the establishment of a new DTLS association, or 1470 whether an existing DTLS association will be used; and 1472 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1473 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1474 [RFC5764]. The client MUST include the extension even if the 1475 usage of DTLS-SRTP is not negotiated as part of the multimedia 1476 session (e.g., SIP session [RFC3261]. 1478 NOTE: The inclusion of the 'use_srtp' extension during the initial 1479 DTLS handshake ensures that a DTLS renegotiation will not be required 1480 in order to include the extension, in case DTLS-SRTP encrypted media 1481 is added to the BUNDLE group later during the multimedia session. 1483 13. RTP Header Extensions Consideration 1485 When [RFC8285] RTP header extensions are used in the context of this 1486 specification, the identifier used for a given extension MUST 1487 identify the same extension across all the bundled media 1488 descriptions. 1490 14. Update to RFC 3264 1492 This section replaces the text of the following sections of RFC 3264: 1494 o Section 5.1 (Unicast Streams). 1496 o Section 6 (Generating the Answer). 1498 o Section 8.2 (Removing a Media Stream). 1500 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1502 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 1504 For recvonly and sendrecv streams, the port number and address in the 1505 offer indicate where the offerer would like to receive the media 1506 stream. For sendonly RTP streams, the address and port number 1507 indirectly indicate where the offerer wants to receive RTCP reports. 1508 Unless there is an explicit indication otherwise, reports are sent to 1509 the port number one higher than the number indicated. The IP address 1510 and port present in the offer indicate nothing about the source IP 1511 address and source port of RTP and RTCP packets that will be sent by 1512 the offerer. A port number of zero in the offer indicates that the 1513 stream is offered but MUST NOT be used. This has no useful semantics 1514 in an initial offer, but is allowed for reasons of completeness, 1515 since the answer can contain a zero port indicating a rejected stream 1516 (Section 6). Furthermore, existing streams can be terminated by 1517 setting the port to zero (Section 8). In general, a port number of 1518 zero indicates that the media stream is not wanted. 1520 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1522 For recvonly and sendrecv streams, the port number and address in the 1523 offer indicate where the offerer would like to receive the media 1524 stream. For sendonly RTP streams, the address and port number 1525 indirectly indicate where the offerer wants to receive RTCP reports. 1526 Unless there is an explicit indication otherwise, reports are sent to 1527 the port number one higher than the number indicated. The IP address 1528 and port present in the offer indicate nothing about the source IP 1529 address and source port of RTP and RTCP packets that will be sent by 1530 the offerer. A port number of zero in the offer by default indicates 1531 that the stream is offered but MUST NOT be used, but an extension 1532 mechanism might specify different semantics for the usage of a zero 1533 port value. Furthermore, existing streams can be terminated by 1534 setting the port to zero (Section 8). In general, a port number of 1535 zero by default indicates that the media stream is not wanted. 1537 14.3. Original text of section 6 (4th paragraph) of RFC 3264 1539 An offered stream MAY be rejected in the answer, for any reason. If 1540 a stream is rejected, the offerer and answerer MUST NOT generate 1541 media (or RTCP packets) for that stream. To reject an offered 1542 stream, the port number in the corresponding stream in the answer 1543 MUST be set to zero. Any media formats listed are ignored. At least 1544 one MUST be present, as specified by SDP. 1546 14.4. New text replacing section 6 (4th paragraph) of RFC 3264 1548 An offered stream MAY be rejected in the answer, for any reason. If 1549 a stream is rejected, the offerer and answerer MUST NOT generate 1550 media (or RTCP packets) for that stream. A port number of zero in 1551 the answer by default indicates that the offered stream is rejected, 1552 but an extension mechanism might specify different semantics for the 1553 usage of a zero port value. If a stream is rejected, any media 1554 formats listed are ignored. At least one MUST be present, as 1555 specified by SDP. 1557 14.5. Original text of section 8.2 (2nd paragraph) of RFC 3264 1559 A stream that is offered with a port of zero MUST be marked with port 1560 zero in the answer. Like the offer, the answer MAY omit all 1561 attributes present previously, and MAY list just a single media 1562 format from amongst those in the offer. 1564 14.6. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1566 A stream that is offered with a port of zero MUST by default be 1567 marked with port zero in the answer, unless an extension mechanism, 1568 which specifies semantics for the usage of a non-zero port value, is 1569 used. If the stream is marked with port zero in the answer, the 1570 answer MAY omit all attributes present previously, and MAY list just 1571 a single media format from amongst those in the offer. 1573 14.7. Original text of section 8.4 (6th paragraph) of RFC 3264 1575 RFC 2543 [10] specified that placing a user on hold was accomplished 1576 by setting the connection address to 0.0.0.0. Its usage for putting 1577 a call on hold is no longer recommended, since it doesn't allow for 1578 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1579 with connection oriented media. However, it can be useful in an 1580 initial offer when the offerer knows it wants to use a particular set 1581 of media streams and formats, but doesn't know the addresses and 1582 ports at the time of the offer. Of course, when used, the port 1583 number MUST NOT be zero, which would specify that the stream has been 1584 disabled. An agent MUST be capable of receiving SDP with a 1585 connection address of 0.0.0.0, in which case it means that neither 1586 RTP nor RTCP should be sent to the peer. 1588 14.8. New text replacing section 8.4 (6th paragraph) of RFC 3264 1590 RFC 2543 [10] specified that placing a user on hold was accomplished 1591 by setting the connection address to 0.0.0.0. Its usage for putting 1592 a call on hold is no longer recommended, since it doesn't allow for 1593 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1594 with connection oriented media. However, it can be useful in an 1595 initial offer when the offerer knows it wants to use a particular set 1596 of media streams and formats, but doesn't know the addresses and 1597 ports at the time of the offer. Of course, when used, the port 1598 number MUST NOT be zero, if it would specify that the stream has been 1599 disabled. However, an extension mechanism might specify different 1600 semantics of the zero port number usage. An agent MUST be capable of 1601 receiving SDP with a connection address of 0.0.0.0, in which case it 1602 means that neither RTP nor RTCP should be sent to the peer. 1604 15. RTP/RTCP extensions for identification-tag transport 1606 SDP Offerers and Answerers [RFC3264] can associate identification- 1607 tags with "m=" sections within SDP Offers and Answers, using the 1608 procedures in [RFC5888]. Each identification-tag uniquely represents 1609 an "m=" section. 1611 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1612 used to carry identification-tags within RTCP SDES packets. This 1613 section also defines a new RTP SDES header extension [RFC7941], which 1614 is used to carry the 'MID' RTCP SDES item in RTP packets. 1616 The SDES item and RTP SDES header extension make it possible for a 1617 receiver to associate each RTP stream with a specific "m=" section, 1618 with which the receiver has associated an identification-tag, even if 1619 those "m=" sections are part of the same RTP session. The RTP SDES 1620 header extension also ensures that the media recipient gets the 1621 identification-tag upon receipt of the first decodable media and is 1622 able to associate the media with the correct application. 1624 A media recipient informs the media sender about the identification- 1625 tag associated with an "m=" section through the use of an 'mid' 1626 attribute [RFC5888]. The media sender then inserts the 1627 identification-tag in RTCP and RTP packets sent to the media 1628 recipient. 1630 NOTE: This text above defines how identification-tags are carried in 1631 SDP Offers and Answers. The usage of other signaling protocols for 1632 carrying identification-tags is not prevented, but the usage of such 1633 protocols is outside the scope of this document. 1635 [RFC3550] defines general procedures regarding the RTCP transmission 1636 interval. The RTCP MID SDES item SHOULD be sent in the first few 1637 RTCP packets sent after joining the session, and SHOULD be sent 1638 regularly thereafter. The exact number of RTCP packets in which this 1639 SDES item is sent is intentionally not specified here, as it will 1640 depend on the expected packet loss rate, the RTCP reporting interval, 1641 and the allowable overhead. 1643 The RTP SDES header extension for carrying the 'MID' RTCP SDES SHOULD 1644 be included in some RTP packets at the start of the session and 1645 whenever the SSRC changes. It might also be useful to include the 1646 header extension in RTP packets that comprise access points in the 1647 media (e.g., with video I-frames). The exact number of RTP packets 1648 in which this header extension is sent is intentionally not specified 1649 here, as it will depend on expected packet loss rate and loss 1650 patterns, the overhead the application can tolerate, and the 1651 importance of immediate receipt of the identification-tag. 1653 For robustness, endpoints need to be prepared for situations where 1654 the reception of the identification-tag is delayed, and SHOULD NOT 1655 terminate sessions in such cases, as the identification-tag is likely 1656 to arrive soon. 1658 15.1. RTCP MID SDES Item 1660 0 1 2 3 1661 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 1662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1663 | MID=TBD | length | identification-tag ... 1664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1666 The identification-tag payload is UTF-8 encoded, as in SDP. 1668 The identification-tag is not zero terminated. 1670 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1671 identifier value.] 1673 15.2. RTP SDES Header Extension For MID 1675 The payload, containing the identification-tag, of the RTP SDES 1676 header extension element can be encoded using either the one-byte or 1677 two-byte header [RFC7941]. The identification-tag payload is UTF-8 1678 encoded, as in SDP. 1680 The identification-tag is not zero terminated. Note, that the set of 1681 header extensions included in the packet needs to be padded to the 1682 next 32-bit boundary using zero bytes [RFC8285]. 1684 As the identification-tag is included in either an RTCP SDES item or 1685 an RTP SDES header extension, or both, there should be some 1686 consideration about the packet expansion caused by the 1687 identification-tag. To avoid Maximum Transmission Unit (MTU) issues 1688 for the RTP packets, the header extension's size needs to be taken 1689 into account when encoding the media. 1691 It is recommended that the identification-tag is kept short. Due to 1692 the properties of the RTP header extension mechanism, when using the 1693 one-byte header, a tag that is 1-3 bytes will result in a minimal 1694 number of 32-bit words used for the RTP SDES header extension, in 1695 case no other header extensions are included at the same time. Note, 1696 do take into account that some single characters when UTF-8 encoded 1697 will result in multiple octets. The identification-tag MUST NOT 1698 contain any user information, and applications SHALL avoid generating 1699 the identification-tag using a pattern that enables application 1700 identification. 1702 16. IANA Considerations 1704 16.1. New SDES item 1706 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1707 document.] 1709 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1710 identifier value.] 1712 This document adds the MID SDES item to the IANA "RTP SDES item 1713 types" registry as follows: 1715 Value: TBD 1716 Abbrev.: MID 1717 Name: Media Identification 1718 Reference: RFCXXXX 1720 16.2. New RTP SDES Header Extension URI 1722 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1723 document.] 1725 This document defines a new extension URI in the RTP SDES Compact 1726 Header Extensions sub-registry of the RTP Compact Header Extensions 1727 registry sub-registry, according to the following data: 1729 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1730 Description: Media identification 1731 Contact: christer.holmberg@ericsson.com 1732 Reference: RFCXXXX 1734 The SDES item does not reveal privacy information about the users. 1735 It is simply used to associate RTP-based media with the correct SDP 1736 media description ("m=" section) in the SDP used to negotiate the 1737 media. 1739 The purpose of the extension is for the offerer to be able to 1740 associate received multiplexed RTP-based media before the offerer 1741 receives the associated SDP answer. 1743 16.3. New SDP Attribute 1745 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1746 document.] 1748 This document defines a new SDP media-level attribute, 'bundle-only', 1749 according to the following data: 1751 Attribute name: bundle-only 1752 Type of attribute: media 1753 Subject to charset: No 1754 Purpose: Request a media description to be accepted 1755 in the answer only if kept within a BUNDLE 1756 group by the answerer. 1757 Appropriate values: N/A 1758 Contact name: Christer Holmberg 1759 Contact e-mail: christer.holmberg@ericsson.com 1760 Reference: RFCXXXX 1761 Mux category: NORMAL 1763 16.4. New SDP Group Semantics 1765 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1766 document.] 1768 This document registers the following semantics with IANA in the 1769 "Semantics for the "group" SDP Attribute" subregistry (under the 1770 "Session Description Protocol (SDP) Parameters" registry: 1772 Semantics Token Reference 1773 ------------------------------------- ------ --------- 1774 Media bundling BUNDLE [RFCXXXX] 1776 17. Security Considerations 1778 The security considerations defined in [RFC3264] and [RFC5888] apply 1779 to the BUNDLE extension. Bundle does not change which information, 1780 e.g., RTP streams, flows over the network, with the exception of the 1781 usage of the MID SDES item as discussed below. Primarily it changes 1782 which addresses and ports, and thus in which (RTP) sessions the 1783 information is flowing. This affects the security contexts being 1784 used and can cause previously separated information flows to share 1785 the same security context. This has very little impact on the 1786 performance of the security mechanism of the RTP sessions. In cases 1787 where one would have applied different security policies on the 1788 different RTP streams being bundled, or where the parties having 1789 access to the security contexts would have differed between the RTP 1790 streams, additional analysis of the implications are needed before 1791 selecting to apply BUNDLE. 1793 The identification-tag, independent of transport, RTCP SDES packet or 1794 RTP header extension, can expose the value to parties beyond the 1795 signaling chain. Therefore, the identification-tag values MUST be 1796 generated in a fashion that does not leak user information, e.g., 1797 randomly or using a per-bundle group counter, and SHOULD be 3 bytes 1798 or less, to allow them to efficiently fit into the MID RTP header 1799 extension. Note that if implementations use different methods for 1800 generating identification-tags this could enable fingerprinting of 1801 the implementation making it vulnerable to targeted attacks. The 1802 identification-tag is exposed on the RTP stream level when included 1803 in the RTP header extensions, however what it reveals of the RTP 1804 media stream structure of the endpoint and application was already 1805 possible to deduce from the RTP streams without the MID SDES header 1806 extensions. As the identification-tag is also used to route the 1807 media stream to the right application functionality it is important 1808 that the value received is the one intended by the sender, thus 1809 integrity and the authenticity of the source are important to prevent 1810 denial of service on the application. Existing SRTP configurations 1811 and other security mechanisms protecting the whole RTP/RTCP packets 1812 will provide the necessary protection. 1814 When the BUNDLE extension is used, the set of configurations of the 1815 security mechanism used in all the bundled media descriptions will 1816 need to be compatible so that they can be used simultaneously, at 1817 least per direction or endpoint. When using SRTP this will be the 1818 case, at least for the IETF defined key-management solutions due to 1819 their SDP attributes (a=crypto, a=fingerprint, a=mikey) and their 1820 classification in [I-D.ietf-mmusic-sdp-mux-attributes]. 1822 The security considerations of "RTP Header Extension for the RTP 1823 Control Protocol (RTCP) Source Description Items" [RFC7941] requires 1824 that when RTCP is confidentiality protected, and that any SDES RTP 1825 header extension carrying an SDES item, such as the MID RTP header 1826 extension, is also protected using commensurate strength algorithms. 1827 However, assuming the above requirements and recommendations are 1828 followed, there are no known significant security risks with leaving 1829 the MID RTP header extension without confidentiality protection. 1830 Thus, the requirements in RFC 7941 MAY be ignored for the MID RTP 1831 header extension. Security mechanisms for RTP/RTCP are discussed in 1832 Options for Securing RTP Sessions [RFC7201], for example SRTP 1833 [RFC3711] can provide the necessary security functions of ensuring 1834 the integrity and source authenticity. 1836 18. Examples 1838 18.1. Example: Bundle Address Selection 1840 The example below shows: 1842 o An offer, in which the offerer assigns a unique address to each 1843 bundled "m=" section within the BUNDLE group. 1845 o An answer, in which the answerer selects the offerer BUNDLE 1846 address, and then selects its own BUNDLE address (the answerer 1847 BUNDLE address) and assigns it to the bundled "m=" section 1848 represented by the answerer BUNDLE-tag. 1850 SDP Offer (1) 1852 v=0 1853 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1854 s= 1855 c=IN IP4 atlanta.example.com 1856 t=0 0 1857 a=group:BUNDLE foo bar 1858 m=audio 10000 RTP/AVP 0 8 97 1859 b=AS:200 1860 a=mid:foo 1861 a=rtcp-mux 1862 a=rtpmap:0 PCMU/8000 1863 a=rtpmap:8 PCMA/8000 1864 a=rtpmap:97 iLBC/8000 1865 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1866 m=video 10002 RTP/AVP 31 32 1867 b=AS:1000 1868 a=mid:bar 1869 a=rtcp-mux 1870 a=rtpmap:31 H261/90000 1871 a=rtpmap:32 MPV/90000 1872 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1874 SDP Answer (2) 1876 v=0 1877 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1878 s= 1879 c=IN IP4 biloxi.example.com 1880 t=0 0 1881 a=group:BUNDLE foo bar 1882 m=audio 20000 RTP/AVP 0 1883 b=AS:200 1884 a=mid:foo 1885 a=rtcp-mux 1886 a=rtpmap:0 PCMU/8000 1887 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1888 m=video 0 RTP/AVP 32 1889 b=AS:1000 1890 a=mid:bar 1891 a=bundle-only 1892 a=rtpmap:32 MPV/90000 1893 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1895 18.2. Example: BUNDLE Extension Rejected 1897 The example below shows: 1899 o An offer, in which the offerer assigns a unique address to each 1900 bundled "m=" section within the BUNDLE group. 1902 o An answer, in which the answerer rejects the offered BUNDLE group, 1903 and assigns a unique address to each "m=" section (following 1904 normal RFC 3264 procedures). 1906 SDP Offer (1) 1908 v=0 1909 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1910 s= 1911 c=IN IP4 atlanta.example.com 1912 t=0 0 1913 a=group:BUNDLE foo bar 1914 m=audio 10000 RTP/AVP 0 8 97 1915 b=AS:200 1916 a=mid:foo 1917 a=rtcp-mux 1918 a=rtpmap:0 PCMU/8000 1919 a=rtpmap:8 PCMA/8000 1920 a=rtpmap:97 iLBC/8000 1921 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1922 m=video 10002 RTP/AVP 31 32 1923 b=AS:1000 1924 a=mid:bar 1925 a=rtcp-mux 1926 a=rtpmap:31 H261/90000 1927 a=rtpmap:32 MPV/90000 1928 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1930 SDP Answer (2) 1932 v=0 1933 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1934 s= 1935 c=IN IP4 biloxi.example.com 1936 t=0 0 1937 m=audio 20000 RTP/AVP 0 1938 b=AS:200 1939 a=rtcp-mux 1940 a=rtpmap:0 PCMU/8000 1941 m=video 30000 RTP/AVP 32 1942 b=AS:1000 1943 a=rtcp-mux 1944 a=rtpmap:32 MPV/90000 1946 18.3. Example: Offerer Adds a Media Description to a BUNDLE Group 1948 The example below shows: 1950 o A subsequent offer (the BUNDLE group has been created as part of a 1951 previous offer/answer exchange), in which the offerer adds a new 1952 "m=" section, represented by the "zen" identification-tag, to a 1953 previously negotiated BUNDLE group, assigns the previously 1954 selected offerer BUNDLE address to the added "m=" section, 1955 represented by the offerer BUNDLE-tag. To every other bundled 1956 "m=" section the offerer assigns a zero port value and includes an 1957 SDP 'bundle-only' attribute. 1959 o An answer, in which the answerer assigns the answerer BUNDLE 1960 address to the bundled "m=" section represented by the answerer 1961 BUNDLE-tag. To every other bundled "m=" section the answerer 1962 assigns a zero port value and includes an SDP 'bundle-only' 1963 attribute. 1965 SDP Offer (1) 1967 v=0 1968 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1969 s= 1970 c=IN IP4 atlanta.example.com 1971 t=0 0 1972 a=group:BUNDLE zen foo bar 1973 m=audio 0 RTP/AVP 0 8 97 1974 b=AS:200 1975 a=mid:foo 1976 a=bundle-only 1977 a=rtpmap:0 PCMU/8000 1978 a=rtpmap:8 PCMA/8000 1979 a=rtpmap:97 iLBC/8000 1980 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1981 m=video 0 RTP/AVP 31 32 1982 b=AS:1000 1983 a=mid:bar 1984 a=bundle-only 1985 a=rtpmap:31 H261/90000 1986 a=rtpmap:32 MPV/90000 1987 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1988 m=video 10000 RTP/AVP 66 1989 b=AS:1000 1990 a=mid:zen 1991 a=rtcp-mux 1992 a=rtpmap:66 H261/90000 1993 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1995 SDP Answer (2) 1996 v=0 1997 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1998 s= 1999 c=IN IP4 biloxi.example.com 2000 t=0 0 2001 a=group:BUNDLE zen foo bar 2002 m=audio 0 RTP/AVP 0 2003 b=AS:200 2004 a=mid:foo 2005 a=bundle-only 2006 a=rtpmap:0 PCMU/8000 2007 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2008 m=video 0 RTP/AVP 32 2009 b=AS:1000 2010 a=mid:bar 2011 a=bundle-only 2012 a=rtpmap:32 MPV/90000 2013 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2014 m=video 20000 RTP/AVP 66 2015 b=AS:1000 2016 a=mid:zen 2017 a=rtcp-mux 2018 a=rtpmap:66 H261/90000 2019 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2021 18.4. Example: Offerer Moves a Media Description Out of a BUNDLE Group 2023 The example below shows: 2025 o A subsequent offer (the BUNDLE group has been created as part of a 2026 previous offer/answer transaction), in which the offerer moves a 2027 bundled "m=" section, represented by the "zen" identification-tag, 2028 out of a BUNDLE group, assigns a unique address to the moved "m=" 2029 section, and assigns the previously selected offerer BUNDLE 2030 address to another bundled "m=" section, represented by the 2031 offerer BUNDLE-tag. To every other bundled "m=" section the 2032 offerer assigns a zero port value and includes an SDP 'bundle- 2033 only' attribute. 2035 o An answer, in which the answerer moves the "m=" section out of the 2036 BUNDLE group, assigns a unique address to the moved "m=" section, 2037 and assigns the answerer BUNDLE address to the bundled "m=" 2038 section represented by the answerer BUNDLE-tag. To every other 2039 bundled "m=" section the answerer assigns a zero port value and 2040 includes an SDP 'bundle-only' attribute. 2042 SDP Offer (1) 2044 v=0 2045 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2046 s= 2047 c=IN IP4 atlanta.example.com 2048 t=0 0 2049 a=group:BUNDLE foo bar 2050 m=audio 10000 RTP/AVP 0 8 97 2051 b=AS:200 2052 a=mid:foo 2053 a=rtcp-mux 2054 a=rtpmap:0 PCMU/8000 2055 a=rtpmap:8 PCMA/8000 2056 a=rtpmap:97 iLBC/8000 2057 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2058 m=video 0 RTP/AVP 31 32 2059 b=AS:1000 2060 a=mid:bar 2061 a=bundle-only 2062 a=rtpmap:31 H261/90000 2063 a=rtpmap:32 MPV/90000 2064 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2065 m=video 50000 RTP/AVP 66 2066 b=AS:1000 2067 a=mid:zen 2068 a=rtcp-mux 2069 a=rtpmap:66 H261/90000 2071 SDP Answer (2) 2073 v=0 2074 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2075 s= 2076 c=IN IP4 biloxi.example.com 2077 t=0 0 2078 a=group:BUNDLE foo bar 2079 m=audio 20000 RTP/AVP 0 2080 b=AS:200 2081 a=mid:foo 2082 a=rtcp-mux 2083 a=rtpmap:0 PCMU/8000 2084 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2085 m=video 0 RTP/AVP 32 2086 b=AS:1000 2087 a=mid:bar 2088 a=bundle-only 2089 a=rtpmap:32 MPV/90000 2090 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2091 m=video 60000 RTP/AVP 66 2092 b=AS:1000 2093 a=mid:zen 2094 a=rtcp-mux 2095 a=rtpmap:66 H261/90000 2097 18.5. Example: Offerer Disables a Media Description Within a BUNDLE 2098 Group 2100 The example below shows: 2102 o A subsequent offer (the BUNDLE group has been created as part of a 2103 previous offer/answer transaction), in which the offerer disables 2104 a bundled "m=" section represented by the "zen" identification- 2105 tag, within a BUNDLE group, assigns a zero port number to the 2106 disabled "m=" section, and assigns the offerer BUNDLE address to 2107 another bundled "m=" section, represented by the offerer BUNDLE- 2108 tag. To every other bundled "m=" section the offerer assigns a 2109 zero port value and includes an SDP 'bundle-only' attribute. 2111 o An answer, in which the answerer moves the disabled "m=" sections 2112 out of the BUNDLE group, assigns a zero port value to the disabled 2113 "m=" section, and assigns the answerer BUNDLE address to the 2114 bundled "m=" section represented by the answerer BUNDLE-tag. To 2115 every other bundled "m=" section the answerer assigns a zero port 2116 value and includes an SDP 'bundle-only' attribute. 2118 SDP Offer (1) 2120 v=0 2121 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2122 s= 2123 c=IN IP4 atlanta.example.com 2124 t=0 0 2125 a=group:BUNDLE foo bar 2126 m=audio 10000 RTP/AVP 0 8 97 2127 b=AS:200 2128 a=mid:foo 2129 a=rtcp-mux 2130 a=rtpmap:0 PCMU/8000 2131 a=rtpmap:8 PCMA/8000 2132 a=rtpmap:97 iLBC/8000 2133 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2134 m=video 0 RTP/AVP 31 32 2135 b=AS:1000 2136 a=mid:bar 2137 a=bundle-only 2138 a=rtpmap:31 H261/90000 2139 a=rtpmap:32 MPV/90000 2140 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2141 m=video 0 RTP/AVP 66 2142 a=mid:zen 2143 a=rtpmap:66 H261/90000 2145 SDP Answer (2) 2147 v=0 2148 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2149 s= 2150 c=IN IP4 biloxi.example.com 2151 t=0 0 2152 a=group:BUNDLE foo bar 2153 m=audio 20000 RTP/AVP 0 2154 b=AS:200 2155 a=mid:foo 2156 a=rtcp-mux 2157 a=rtpmap:0 PCMU/8000 2158 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2159 m=video 0 RTP/AVP 32 2160 b=AS:1000 2161 a=mid:bar 2162 a=bundle-only 2163 a=rtpmap:32 MPV/90000 2164 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2165 m=video 0 RTP/AVP 66 2166 a=mid:zen 2167 a=rtpmap:66 H261/90000 2169 19. Acknowledgements 2171 The usage of the SDP grouping extension for negotiating bundled media 2172 is based on similar alternatives proposed by Harald Alvestrand and 2173 Cullen Jennings. The BUNDLE extension described in this document is 2174 based on the different alternative proposals, and text (e.g., SDP 2175 examples) have been borrowed (and, in some cases, modified) from 2176 those alternative proposals. 2178 The SDP examples are also modified versions from the ones in the 2179 Alvestrand proposal. 2181 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 2182 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 2183 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju, Justin 2184 Uberti, Taylor Brandstetter, Byron Campen and Eric Rescorla for 2185 reading the text, and providing useful feedback. 2187 Thanks to Bernard Aboba, Cullen Jennings, Peter Thatcher, Justin 2188 Uberti, and Magnus Westerlund for providing the text for the section 2189 on RTP/RTCP stream association. 2191 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 2192 providing help and text on the RTP/RTCP procedures. 2194 Thanks to Spotify for providing music for the countless hours of 2195 document editing. 2197 20. Change Log 2199 [RFC EDITOR NOTE: Please remove this section when publishing] 2201 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-46 2203 o Pre-RFC5378 disclaimer removed put back. 2205 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-45 2207 o Mux category for SDP 'group:BUNDLE' attribute added. 2209 o https://github.com/cdh4u/draft-sdp-bundle/pull/54 2211 o Pre-RFC5378 disclaimer removed. 2213 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-44 2215 o Minor editorial nits based on pull request by Colin P. 2217 o https://github.com/cdh4u/draft-sdp-bundle/pull/53 2219 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-43 2221 o Changes based on WG chairs review. 2223 o Text added in order to close GitHub issues by Taylor B. 2225 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-42 2226 o Changes based on final WG review. 2228 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-41 2230 o Update to section 6 o RFC 3264: 2232 o https://github.com/cdh4u/draft-sdp-bundle/pull/47 2234 o Editorial clarification on BUNDLE address selection: 2236 o https://github.com/cdh4u/draft-sdp-bundle/pull/46 2238 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-40 2240 o Editorial changes and technical restrictions in order to make the 2241 specification more understandable: 2243 o https://github.com/cdh4u/draft-sdp-bundle/pull/45 2245 o - BUNDLE address is only assigned to m- section represented by 2246 BUNDLE-tag. 2248 o - bundle-only attribute also used in answers and subsequent 2249 offers. 2251 o - Answerer cannot reject, or remove, the bundled m- section that 2252 contains the BUNDLE address. 2254 o - ICE Offer/Answer sections removed, due to duplicated 2255 information. 2257 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-39 2259 o Editorial terminology changes. 2261 o RFC 5285 reference replaced by reference to RFC 8285. 2263 o https://github.com/cdh4u/draft-sdp-bundle/pull/44 2265 o - Clarify that an m- section can not be moved between BUNDLE 2266 groups without first moving the m- section out of a BUNDLE group. 2268 o https://github.com/cdh4u/draft-sdp-bundle/pull/41 2270 o - Addition of BUNDLE transport concept. 2272 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-38 2273 o Changes to RTP streaming mapping section based on text from Colin 2274 Perkins. 2276 o The following GitHub pull requests were merged: 2278 o https://github.com/cdh4u/draft-sdp-bundle/pull/34 2280 o - Proposed updates to RTP processing 2282 o https://github.com/cdh4u/draft-sdp-bundle/pull/35 2284 o - fixed reference to receiver-id section 2286 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-37 2288 o The following GitHub pull request was merged: 2290 o https://github.com/cdh4u/draft-sdp-bundle/pull/33 2292 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-36 2294 o The following GitHub pull requests were merged: 2296 o https://github.com/cdh4u/draft-sdp-bundle/pull/32 2298 o - extmap handling in BUNDLE. 2300 o https://github.com/cdh4u/draft-sdp-bundle/pull/31 2302 o - Additional Acknowledgement text added. 2304 o https://github.com/cdh4u/draft-sdp-bundle/pull/30 2306 o - MID SDES item security procedures updated 2308 o https://github.com/cdh4u/draft-sdp-bundle/pull/29 2310 o - Appendix B of JSEP moved into BUNDLE. 2312 o - Associating RTP/RTCP packets with SDP m- lines. 2314 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-35 2316 o Editorial changes on RTP streaming mapping section based on 2317 comments from Colin Perkins. 2319 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-34 2320 o RTP streams, instead of RTP packets, are associated with m- lines. 2322 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-33 2324 o Editorial changes based on comments from Eric Rescorla and Cullen 2325 Jennings: 2327 o - Changes regarding usage of RTP/RTCP multiplexing attributes. 2329 o - Additional text regarding associating RTP/RTCP packets with SDP 2330 m- lines. 2332 o - Reference correction. 2334 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-32 2336 o Editorial changes based on comments from Eric Rescorla and Cullen 2337 Jennings: 2339 o - Justification for mechanism added to Introduction. 2341 o - Clarify that the order of m- lines in the group:BUNDLE attribute 2342 does not have to be the same as the order in which the m- lines 2343 are listed in the SDP. 2345 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31 2347 o Editorial changes based on GitHub Pull requests by Martin Thomson: 2349 o - https://github.com/cdh4u/draft-sdp-bundle/pull/2 2351 o - https://github.com/cdh4u/draft-sdp-bundle/pull/1 2353 o Editorial change based on comment from Diederick Huijbers (9th 2354 July 2016). 2356 o Changes based on comments from Flemming Andreasen (21st June 2357 2016): 2359 o - Mux category for SDP bundle-only attribute added. 2361 o - Mux category considerations editorial clarification. 2363 o - Editorial changes. 2365 o RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext. 2367 o Note whether Design Considerations appendix is to be kept removed: 2369 o - Appendix is kept within document. 2371 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30 2373 o Indicating in the Abstract and Introduction that the document 2374 updates RFC 3264. 2376 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29 2378 o Change based on WGLC comment from Colin Perkins. 2380 o - Clarify that SSRC can be reused by another source after a delay 2381 of 5 RTCP reporting intervals. 2383 o Change based on WGLC comment from Alissa Cooper. 2385 o - IANA registry name fix. 2387 o - Additional IANA registration information added. 2389 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 2391 o - Alignment with exclusive mux procedures. 2393 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 2395 o - Yet another terminology change. 2397 o - Mux category considerations added. 2399 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 2401 o - ICE considerations modified: ICE-related SDP attributes only 2402 added to the bundled m- line representing the selected BUNDLE 2403 address. 2405 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 2407 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 2408 rfc5245bis. 2410 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 2412 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 2413 considerations. 2415 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 2416 o - Reference and procedures associated with exclusive RTP/RTCP mux 2417 added 2419 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 2421 o - RTCP-MUX mandatory for bundled RTP m- lines 2423 o - Editorial fixes based on comments from Flemming Andreasen 2425 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 2427 o - Correction of Ari's family name 2429 o - Editorial fixes based on comments from Thomas Stach 2431 o - RTP/RTCP correction based on comment from Magnus Westerlund 2433 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2434 msg14861.html 2436 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 2438 o - Correct based on comment from Paul Kyzivat 2440 o -- 'received packets' replaced with 'received data' 2442 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 2444 o - Clarification based on comment from James Guballa 2446 o - Clarification based on comment from Flemming Andreasen 2448 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 2450 o - DTLS Considerations section added. 2452 o - BUNDLE semantics added to the IANA Considerations 2454 o - Changes based on WGLC comments from Adam Roach 2456 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2457 msg14673.html 2459 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 2461 o - Changes based on agreements at IETF#92 2463 o -- BAS Offer removed, based on agreement at IETF#92. 2465 o -- Procedures regarding usage of SDP "b=" line is replaced with a 2466 reference to to draft-ietf-mmusic-sdp-mux-attributes. 2468 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 2470 o - Editorial changes based on comments from Magnus Westerlund. 2472 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 2474 o - Modification of RTP/RTCP multiplexing section, based on comments 2475 from Magnus Westerlund. 2477 o - Reference updates. 2479 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 2481 o - Editorial fix. 2483 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 2485 o - Editorial changes. 2487 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 2489 o Changes to allow a new suggested offerer BUNDLE address to be 2490 assigned to each bundled m- line. 2492 o Changes based on WGLC comments from Paul Kyzivat 2494 o - Editorial fixes 2496 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 2498 o Usage of SDP 'extmap' attribute added 2500 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 2501 port value 2503 o Changes based on WGLC comments from Thomas Stach 2505 o - ICE candidates not assigned to bundle-only m- lines with a zero 2506 port value 2508 o - Editorial changes 2510 o Changes based on WGLC comments from Colin Perkins 2512 o - Editorial changes: 2514 o -- "RTP SDES item" -> "RTCP SDES item" 2516 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 2518 o - Changes in section 10.1.1: 2520 o -- "SHOULD NOT" -> "MUST NOT" 2522 o -- Additional text added to the Note 2524 o - Change to section 13.2: 2526 o -- Clarify that mid value is not zero terminated 2528 o - Change to section 13.3: 2530 o -- Clarify that mid value is not zero terminated 2532 o -- Clarify padding 2534 o Changes based on WGLC comments from Paul Kyzivat 2536 o - Editorial changes: 2538 o Changes based on WGLC comments from Jonathan Lennox 2540 o - Editorial changes: 2542 o - Defintion of SDP bundle-only attribute alligned with structure 2543 in 4566bis draft 2545 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 2547 o Editorial corrections based on comments from Harald Alvestrand. 2549 o Editorial corrections based on comments from Cullen Jennings. 2551 o Reference update (RFC 7160). 2553 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 2554 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 2555 msg13765.html). 2557 o Additional text added to the Security Considerations. 2559 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 2561 o SDP bundle-only attribute added to IANA Considerations. 2563 o SDES item and RTP header extension added to Abstract and 2564 Introduction. 2566 o Modification to text updating section 8.2 of RFC 3264. 2568 o Reference corrections. 2570 o Editorial corrections. 2572 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 2574 o Terminology change: "bundle-only attribute assigned to m= line" to 2575 "bundle-only attribute associated with m= line". 2577 o Editorial corrections. 2579 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 2581 o Editorial corrections. 2583 o - "of"->"if" (8.3.2.5). 2585 o - "optional"->"OPTIONAL" (9.1). 2587 o - Syntax/ABNF for 'bundle-only' attribute added. 2589 o - SDP Offer/Answer sections merged. 2591 o - 'Request new offerer BUNDLE address' section added 2593 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 2595 o OPEN ISSUE regarding Receiver-ID closed. 2597 o - RTP MID SDES Item. 2599 o - RTP MID Header Extension. 2601 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 2602 closed. 2604 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 2605 include an 'rtcp' attribute in the answer, based on the procedures 2606 in section 5.1.3 of RFC 5761. 2608 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 2610 o Draft title changed. 2612 o Added "SDP" to section names containing "Offer" or "Answer". 2614 o Editorial fixes based on comments from Paul Kyzivat 2615 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2616 msg13314.html). 2618 o Editorial fixed based on comments from Colin Perkins 2619 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2620 msg13318.html). 2622 o - Removed text about extending BUNDLE to allow multiple RTP 2623 sessions within a BUNDLE group. 2625 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 2627 o Major re-structure of SDP Offer/Answer sections, to align with RFC 2628 3264 structure. 2630 o Additional definitions added. 2632 o - Shared address. 2634 o - Bundled "m=" line. 2636 o - Bundle-only "m=" line. 2638 o - Offerer suggested BUNDLE mid. 2640 o - Answerer selected BUNDLE mid. 2642 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 2643 to multiple "m=" lines until it has received an SDP Answer 2644 indicating support of the BUNDLE extension. 2646 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 2647 Answerer supports the BUNDLE extension, assign a zero port value 2648 to a 'bundle-only' "m=" line. 2650 o SDP 'bundle-only' attribute section added. 2652 o Connection data nettype/addrtype restrictions added. 2654 o RFC 3264 update section added. 2656 o Indicating that a specific payload type value can be used in 2657 multiple "m=" lines, if the value represents the same codec 2658 configuration in each "m=" line. 2660 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2662 o Updated Offerer procedures (http://www.ietf.org/mail- 2663 archive/web/mmusic/current/msg12293.html). 2665 o Updated Answerer procedures (http://www.ietf.org/mail- 2666 archive/web/mmusic/current/msg12333.html). 2668 o Usage of SDP 'bundle-only' attribute added. 2670 o Reference to Trickle ICE document added. 2672 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2674 o Mechanism modified, to be based on usage of SDP Offers with both 2675 different and identical port number values, depending on whether 2676 it is known if the remote endpoint supports the extension. 2678 o Cullen Jennings added as co-author. 2680 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2682 o No changes. New version due to expiration. 2684 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2686 o No changes. New version due to expiration. 2688 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2690 o Draft name changed. 2692 o Harald Alvestrand added as co-author. 2694 o "Multiplex" terminology changed to "bundle". 2696 o Added text about single versus multiple RTP Sessions. 2698 o Added reference to RFC 3550. 2700 21. References 2702 21.1. Normative References 2704 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2705 Requirement Levels", BCP 14, RFC 2119, 2706 DOI 10.17487/RFC2119, March 1997, 2707 . 2709 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2710 with Session Description Protocol (SDP)", RFC 3264, 2711 DOI 10.17487/RFC3264, June 2002, 2712 . 2714 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2715 Jacobson, "RTP: A Transport Protocol for Real-Time 2716 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2717 July 2003, . 2719 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2720 in Session Description Protocol (SDP)", RFC 3605, 2721 DOI 10.17487/RFC3605, October 2003, 2722 . 2724 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 2725 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 2726 RFC 3711, DOI 10.17487/RFC3711, March 2004, 2727 . 2729 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2730 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2731 July 2006, . 2733 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2734 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2735 . 2737 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2738 Control Packets on a Single Port", RFC 5761, 2739 DOI 10.17487/RFC5761, April 2010, 2740 . 2742 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2743 Security (DTLS) Extension to Establish Keys for the Secure 2744 Real-time Transport Protocol (SRTP)", RFC 5764, 2745 DOI 10.17487/RFC5764, May 2010, 2746 . 2748 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2749 Protocol (SDP) Grouping Framework", RFC 5888, 2750 DOI 10.17487/RFC5888, June 2010, 2751 . 2753 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2754 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2755 January 2012, . 2757 [RFC7941] Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 2758 Header Extension for the RTP Control Protocol (RTCP) 2759 Source Description Items", RFC 7941, DOI 10.17487/RFC7941, 2760 August 2016, . 2762 [RFC8285] Singer, D., Desineni, H., and R. Even, Ed., "A General 2763 Mechanism for RTP Header Extensions", RFC 8285, 2764 DOI 10.17487/RFC8285, October 2017, 2765 . 2767 [I-D.ietf-ice-rfc5245bis] 2768 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 2769 Connectivity Establishment (ICE): A Protocol for Network 2770 Address Translator (NAT) Traversal", draft-ietf-ice- 2771 rfc5245bis-15 (work in progress), November 2017. 2773 [I-D.ietf-mmusic-sdp-mux-attributes] 2774 Nandakumar, S., "A Framework for SDP Attributes when 2775 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 2776 (work in progress), December 2016. 2778 [I-D.ietf-mmusic-mux-exclusive] 2779 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2780 Multiplexing using SDP", draft-ietf-mmusic-mux- 2781 exclusive-12 (work in progress), May 2017. 2783 [I-D.ietf-mmusic-ice-sip-sdp] 2784 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, 2785 "Session Description Protocol (SDP) Offer/Answer 2786 procedures for Interactive Connectivity Establishment 2787 (ICE)", draft-ietf-mmusic-ice-sip-sdp-16 (work in 2788 progress), November 2017. 2790 21.2. Informative References 2792 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2793 A., Peterson, J., Sparks, R., Handley, M., and E. 2794 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2795 DOI 10.17487/RFC3261, June 2002, 2796 . 2798 [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., 2799 "RTP Control Protocol Extended Reports (RTCP XR)", 2800 RFC 3611, DOI 10.17487/RFC3611, November 2003, 2801 . 2803 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 2804 "Codec Control Messages in the RTP Audio-Visual Profile 2805 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 2806 February 2008, . 2808 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 2809 "Extended RTP Profile for Real-time Transport Control 2810 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 2811 DOI 10.17487/RFC4585, July 2006, 2812 . 2814 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2815 Media Attributes in the Session Description Protocol 2816 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2817 . 2819 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2820 Clock Rates in an RTP Session", RFC 7160, 2821 DOI 10.17487/RFC7160, April 2014, 2822 . 2824 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 2825 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 2826 . 2828 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 2829 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 2830 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 2831 DOI 10.17487/RFC7656, November 2015, 2832 . 2834 [I-D.ietf-ice-trickle] 2835 Ivov, E., Rescorla, E., Uberti, J., and P. Saint-Andre, 2836 "Trickle ICE: Incremental Provisioning of Candidates for 2837 the Interactive Connectivity Establishment (ICE) 2838 Protocol", draft-ietf-ice-trickle-15 (work in progress), 2839 November 2017. 2841 [I-D.ietf-avtext-lrr] 2842 Lennox, J., Hong, D., Uberti, J., Holmer, S., and M. 2843 Flodman, "The Layer Refresh Request (LRR) RTCP Feedback 2844 Message", draft-ietf-avtext-lrr-07 (work in progress), 2845 July 2017. 2847 Appendix A. Design Considerations 2849 One of the main issues regarding the BUNDLE grouping extensions has 2850 been whether, in SDP Offers and SDP Answers, the same port value 2851 should be inserted in "m=" lines associated with a BUNDLE group, as 2852 the purpose of the extension is to negotiate the usage of a single 2853 transport for media specified by the "m=" sections. Issues with both 2854 approaches, discussed in the Appendix have been raised. The outcome 2855 was to specify a mechanism which uses SDP Offers with both different 2856 and identical port values. 2858 Below are the primary issues that have been considered when defining 2859 the "BUNDLE" grouping extension: 2861 o 1) Interoperability with existing UAs. 2863 o 2) Interoperability with intermediary Back to Back User Agent 2864 (B2BUA) and proxy entities. 2866 o 3) Time to gather, and the number of, ICE candidates. 2868 o 4) Different error scenarios, and when they occur. 2870 o 5) SDP Offer/Answer impacts, including usage of port number value 2871 zero. 2873 A.1. UA Interoperability 2875 Consider the following SDP Offer/Answer exchange, where Alice sends 2876 an SDP Offer to Bob: 2878 SDP Offer 2880 v=0 2881 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2882 s= 2883 c=IN IP4 atlanta.example.com 2884 t=0 0 2885 m=audio 10000 RTP/AVP 97 2886 a=rtpmap:97 iLBC/8000 2887 m=video 10002 RTP/AVP 97 2888 a=rtpmap:97 H261/90000 2890 SDP Answer 2892 v=0 2893 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2894 s= 2895 c=IN IP4 biloxi.example.com 2896 t=0 0 2897 m=audio 20000 RTP/AVP 97 2898 a=rtpmap:97 iLBC/8000 2899 m=video 20002 RTP/AVP 97 2900 a=rtpmap:97 H261/90000 2902 RFC 4961 specifies a way of doing symmetric RTP but that is a later 2903 extension to RTP and Bob can not assume that Alice supports RFC 4961. 2904 This means that Alice may be sending RTP from a different port than 2905 10000 or 10002 - some implementations simply send the RTP from an 2906 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2907 way that Bob knows if it should be passed to the video or audio codec 2908 is by looking at the port it was received on. This led some SDP 2909 implementations to use the fact that each "m=" section had a 2910 different port number to use that port number as an index to find the 2911 correct m line in the SDP. As a result, some implementations that do 2912 support symmetric RTP and ICE still use an SDP data structure where 2913 SDP with "m=" sections with the same port such as: 2915 SDP Offer 2917 v=0 2918 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2919 s= 2920 c=IN IP4 atlanta.example.com 2921 t=0 0 2922 m=audio 10000 RTP/AVP 97 2923 a=rtpmap:97 iLBC/8000 2924 m=video 10000 RTP/AVP 98 2925 a=rtpmap:98 H261/90000 2927 will result in the second "m=" section being considered an SDP error 2928 because it has the same port as the first line. 2930 A.2. Usage of Port Number Value Zero 2932 In an SDP Offer or SDP Answer, the media specified by an "m=" section 2933 can be disabled/rejected by setting the port number value to zero. 2934 This is different from e.g., using the SDP direction attributes, 2935 where RTCP traffic will continue even if the SDP "inactive" attribute 2936 is indicated for the associated "m=" section. 2938 If each "m=" section associated with a BUNDLE group would contain 2939 different port values, and one of those port values would be used for 2940 a BUNDLE address associated with the BUNDLE group, problems would 2941 occur if an endpoint wants to disable/reject the "m=" section 2942 associated with that port, by setting the port value to zero. After 2943 that, no "m=" section would contain the port value which is used for 2944 the BUNDLE address. In addition, it is unclear what would happen to 2945 the ICE candidates associated with the "m=" section, as they are also 2946 used for the BUNDLE address. 2948 A.3. B2BUA And Proxy Interoperability 2950 Some back to back user agents may be configured in a mode where if 2951 the incoming call leg contains an SDP attribute the B2BUA does not 2952 understand, the B2BUA still generates that SDP attribute in the Offer 2953 for the outgoing call leg. Consider a B2BUA that did not understand 2954 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2955 Further assume that the B2BUA was configured to tear down any call 2956 where it did not see any RTCP for 5 minutes. In this case, if the 2957 B2BUA received an Offer like: 2959 SDP Offer 2961 v=0 2962 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2963 s= 2964 c=IN IP4 atlanta.example.com 2965 t=0 0 2966 m=audio 49170 RTP/AVP 0 2967 a=rtcp:53020 2969 It would be looking for RTCP on port 49171 but would not see any 2970 because the RTCP would be on port 53020 and after five minutes, it 2971 would tear down the call. Similarly, a B2BUA that did not understand 2972 BUNDLE yet put BUNDLE in its offer may be looking for media on the 2973 wrong port and tear down the call. It is worth noting that a B2BUA 2974 that generated an Offer with capabilities it does not understand is 2975 not compliant with the specifications. 2977 A.3.1. Traffic Policing 2979 Sometimes intermediaries do not act as B2BUAs, in the sense that they 2980 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2981 however, they may use SDP information (e.g., IP address and port) in 2982 order to control traffic gating functions, and to set traffic 2983 policing rules. There might be rules which will trigger a session to 2984 be terminated in case media is not sent or received on the ports 2985 retrieved from the SDP. This typically occurs once the session is 2986 already established and ongoing. 2988 A.3.2. Bandwidth Allocation 2990 Sometimes intermediaries do not act as B2BUAs, in the sense that they 2991 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2992 however, they may use SDP information (e.g., codecs and media types) 2993 in order to control bandwidth allocation functions. The bandwidth 2994 allocation is done per "m=" section, which means that it might not be 2995 enough if media specified by all "m=" sections try to use that 2996 bandwidth. That may either simply lead to bad user experience, or to 2997 termination of the call. 2999 A.4. Candidate Gathering 3001 When using ICE, a candidate needs to be gathered for each port. This 3002 takes approximately 20 ms extra for each extra "m=" section due to 3003 the NAT pacing requirements. All of this gathering can be overlapped 3004 with other things while e.g., a web-page is loading to minimize the 3005 impact. If the client only wants to generate TURN or STUN ICE 3006 candidates for one of the "m=" lines and then use trickle ICE 3007 [I-D.ietf-ice-trickle] to get the non host ICE candidates for the 3008 rest of the "m=" sections, it MAY do that and will not need any 3009 additional gathering time. 3011 Some people have suggested a TURN extension to get a bunch of TURN 3012 allocations at once. This would only provide a single STUN result so 3013 in cases where the other end did not support BUNDLE, it may cause 3014 more use of the TURN server but would be quick in the cases where 3015 both sides supported BUNDLE and would fall back to a successful call 3016 in the other cases. 3018 Authors' Addresses 3020 Christer Holmberg 3021 Ericsson 3022 Hirsalantie 11 3023 Jorvas 02420 3024 Finland 3026 Email: christer.holmberg@ericsson.com 3028 Harald Tveit Alvestrand 3029 Google 3030 Kungsbron 2 3031 Stockholm 11122 3032 Sweden 3034 Email: harald@alvestrand.no 3036 Cullen Jennings 3037 Cisco 3038 400 3rd Avenue SW, Suite 350 3039 Calgary, AB T2P 4H2 3040 Canada 3042 Email: fluffy@iii.ca