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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: March 26, 2015 C. Jennings 7 Cisco 8 September 22, 2014 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-11.txt 14 Abstract 16 This specification defines a new SDP Grouping Framework extension, 17 'BUNDLE'. The extension can be used with the Session Description 18 Protocol (SDP) Offer/Answer mechanism to negotiate the usage of a 19 single 5-tuple for sending and receiving media associated with 20 multiple SDP media descriptions ("m="). This is referred to as 21 bundled media. This specification also defines a new SDP attribute, 22 'bundle-only', which can be used to request that specific media is 23 only used if bundled. 25 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 26 3264. The update allows an answerer to assign a non-zero port value 27 to an "m=" line in an SDP answer, even if the "m=" line in the 28 associated SDP offer contained a zero port value. 30 This specification also defines a new RTP SDES item, and a new RTP 31 header extension, that can be used to carry a value that associates 32 RTP/RTCP packets with a specific media description. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on March 26, 2015. 50 Copyright Notice 52 Copyright (c) 2014 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6 71 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 72 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 7 74 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 75 6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 77 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 78 7.2. Connection Data (c=) . . . . . . . . . . . . . . . . . . 8 79 7.3. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 8 80 7.4. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 81 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 82 8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 83 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 84 8.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 85 8.2.2. Request offerer BUNDLE address selection . . . . . . 10 86 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 10 87 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 88 8.3.2. Answerer Selection of Offerer Bundle Address . . . . 11 89 8.3.3. Answerer Selection of Answerer BUNDLE Address . . . . 12 90 8.3.4. Moving A Media Description Out Of A BUNDLE Group . . 12 91 8.3.5. Rejecting A Media Description In A BUNDLE Group . . . 13 92 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 13 93 8.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 13 94 8.4.2. Bundle Address Synchronization (BAS) . . . . . . . . 13 95 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 14 96 8.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 97 8.5.2. Request a new offerer BUNDLE address . . . . . . . . 15 98 8.5.3. Adding a media description to a BUNDLE group . . . . 15 99 8.5.4. Moving A Media Description Out Of A BUNDLE Group . . 16 100 8.5.5. Disabling A Media Description In A BUNDLE Group . . . 16 101 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 17 102 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 17 103 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 104 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 18 105 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 18 106 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 18 107 10.1.2. Payload Type (PT) Value Re-usage . . . . . . . . . . 18 108 10.2. Associating RTP/RTCP Packets With Correct SDP Media 109 Description . . . . . . . . . . . . . . . . . . . . . . 19 110 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 19 111 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 19 112 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 113 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 21 114 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 21 115 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 22 116 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 22 117 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 22 118 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 22 119 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 22 120 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 23 121 12. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 23 122 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 23 123 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 23 124 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 23 126 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 24 127 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 129 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 24 130 12.7. New text replacing section 8.4 (6th paragraph) of RFC 131 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 132 13. RTP/RTCP extensions for mid value transport . . . . . . . . . 25 133 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 25 134 13.2. RTP MID SDES Item . . . . . . . . . . . . . . . . . . . 26 135 13.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 26 136 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 137 14.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 26 138 14.2. New RTP Header Extension URI . . . . . . . . . . . . . . 27 139 14.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 27 140 15. Security Considerations . . . . . . . . . . . . . . . . . . . 27 141 16. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 27 142 16.1. Example: Bundle Address Selection . . . . . . . . . . . 27 143 16.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 29 144 16.3. Example: Offerer Adds A Media Description To A BUNDLE 145 Group . . . . . . . . . . . . . . . . . . . . . . . . . 30 146 16.4. Example: Offerer Moves A Media Description Out Of A 147 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 32 148 16.5. Example: Offerer Disables A Media Description Within A 149 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 34 150 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 151 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36 152 19. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 36 153 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 154 20.1. Normative References . . . . . . . . . . . . . . . . . . 39 155 20.2. Informative References . . . . . . . . . . . . . . . . . 40 156 Appendix A. Design Considerations . . . . . . . . . . . . . . . 40 157 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 40 158 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 41 159 A.3. Usage of port number value zero . . . . . . . . . . . . . 43 160 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 43 161 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 44 162 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 44 163 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 44 164 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 166 1. Introduction 168 In the IETF RTCWEB WG, a need to use a single 5-tuple for sending and 169 receiving media associated with multiple SDP media descriptions ("m=" 170 lines) has been identified. This would e.g. allow the usage of a 171 single set of Interactive Connectivity Establishment (ICE) [RFC5245] 172 candidates for multiple media descriptions. 174 This specification defines a new SDP Grouping Framework [RFC5888] 175 extension , 'BUNDLE'. The extension can be used with the Session 176 Description Protocol (SDP) Offer/Answer mechanism [RFC3264] to 177 negotiate the usage of a single 5-tuple for sending and receiving 178 media associated with multiple SDP media descriptions ("m="). This 179 is referred to as bundled media. This specification also defines a 180 new SDP attribute, 'bundle-only', which can be used to request that 181 specific media is only used if bundled. 183 The offerer and answerer [RFC3264] use the BUNDLE extension to 184 negotiate the 5-tuples (BUNDLE addresses), one for the offerer 185 (offerer BUNDLE address) and one for the answerer (answerer BUNDLE 186 address) to be used for the bundled media associated with a BUNDLE 187 group. 189 Once the offerer and the answerer have negotiated a BUNDLE group, 190 they assign their respective BUNDLE address to each "m=" line in the 191 BUNDLE group. The BUNDLE address is used to send and receive all 192 media associated with the BUNDLE group. 194 NOTE: As defined in RFC 4566 [RFC4566], the semantics of assigning 195 the same port value to multiple "m=" lines are undefined, and there 196 is no grouping defined by such means. Instead, an explicit grouping 197 mechanism needs to be used to express the intended semantics. This 198 specification provides such an extension. 200 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 201 [RFC3264]. The update allows an answerer to assign a non-zero port 202 value to an "m=" line in an SDP answer, even if the "m=" line in the 203 associated SDP offer contained a zero port value. 205 This specification also defines a new RTP SDES item, and a new RTP 206 header extension, that can be used to carry a value that associates 207 RTP/RTCP packets with a specific media description. 209 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 210 address MUST only be associated with a single BUNDLE group. 212 The procedures in this specification apply independently to a given 213 BUNDLE group. 215 All Real-time Transport Protocol (RTP) [RFC3550] based media flows 216 associated with a single BUNDLE group belong to a single RTP session 217 [RFC3550]. 219 The BUNDLE extension is backward compatible. Endpoints that do not 220 support the extension are expected to generate offers and answers 221 without an SDP 'group:BUNDLE' attribute, and are expected to assign a 222 unique address to each "m=" line within an offer and answer, 223 according to the procedures in [RFC4566] and [RFC3264] 225 2. Terminology 227 5-tuple: A collection of the following values: source address, source 228 port, destination address, destination port and protocol. 230 Unique address: An IP address and IP port combination that is 231 assigned to only one "m=" line in an offer or answer. 233 Shared address: An IP address and IP port combination that is 234 assigned to multiple "m=" lines within an offer or answer. 236 Offerer suggested BUNDLE mid: The first mid value in a given SDP 237 'group:BUNDLE' attribute mid list in an offer. 239 Answerer selected BUNDLE mid: The first mid value in a given SDP 240 'group:BUNDLE' attribute mid list in an answer. 242 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 243 and IP port combination used by an offerer to receive all media 244 associated with each "m=" line within the BUNDLE group. 246 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 247 and IP port combination used by an answerer to receive all media 248 associated with each "m=" line within the BUNDLE group. 250 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 251 exchange, for which each endpoint uses a single 5-tuple to send and 252 receive media. Each endpoint uses its BUNDLE address, associated 253 with the BUNDLE group, to send and receive the media. 255 Bundled "m=" line: An "m=" line, whose SDP 'mid' attribute value is 256 placed in a SDP 'group:BUNDLE' attribute mid value list in an offer 257 or answer. 259 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 260 'bundle-only' attribute. 262 Bundled media: All media associated with a given BUNDLE group. 264 Initial offer: The first offer, within an SDP session, in which the 265 offerer indicates that it wants to create a given BUNDLE group. 267 Subsequent offer: An offer which contains a BUNDLE group that has 268 been created as part of a previous SDP Offer/Answer exchange. 270 3. Conventions 272 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 273 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 274 document are to be interpreted as described in BCP 14, RFC 2119 275 [RFC2119]. 277 4. Applicability Statement 279 The mechanism in this specification only applies to the Session 280 Description Protocol (SDP) [RFC4566], when used together with the SDP 281 Offer/Answer mechanism [RFC3264]. 283 5. SDP Grouping Framework BUNDLE Extension 285 5.1. General 287 This section defines a new SDP Grouping Framework extension 288 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the 289 Session Description Protocol (SDP) Offer/Answer mechanism to 290 negotiate the usage of a single 5-tuple for sending and receiving 291 media, referred to as bundled media, associated with multiple SDP 292 media descriptions ("m=" lines). Within a successfully created 293 BUNDLE group, media described with "m=" lines associated with the 294 BUNDLE group will be sent and received using a single 5-tuple. 296 The BUNDLE extension is indicated using an SDP 'group' attribute with 297 a "BUNDLE" semantics value [RFC5888]. An SDP "mid" attribute is 298 assigned to each bundled "m=" line, and the "mid" attribute value is 299 listed in the 'group:BUNDLE' attribute mid value list. Each "m=" 300 line, whose mid value is listed in the mid value list, is associated 301 with a given BUNDLE group. 303 SDP bodies can contain multiple BUNDLE groups. Any given bundled 304 "m=" line MUST NOT be associated with more than one BUNDLE group. 306 [Section 8] defines the detailed SDP Offer/Answer procedures for the 307 BUNDLE extension. 309 6. SDP 'bundle-only' Attribute 311 6.1. General 313 This section defines a new SDP media-level attribute [RFC4566], 314 'bundle-only'. 316 The 'bundle-only' attribute can be associated with a bundled "m=" 317 line in an offer, to request that the answerer only accepts the "m=" 318 line if the answerer keeps the "m=" line within the associated BUNDLE 319 group. 321 In order to ensure that an answerer that does not supports the BUNDLE 322 extension always rejects a 'bundle-only' "m=" line, the offerer can 323 assign a zero port value to the "m=" line. According to [RFC4566] an 324 answerer will reject such "m=" line. 326 The usage of the 'bundle-only' attribute is only defined for a 327 bundled "m=" line within an offer. Other usage is unspecified. 329 [Section 8] defines the detailed SDP Offer/Answer procedures for the 330 'bundle-only' attribute. 332 6.2. Syntax 334 This section defines the Augmented Backus-Naur Form (ABNF) [RFC5234] 335 for the SDP 'bundle-only' attribute, based on the SDP [RFC4566] 336 grammar. 338 attribute =/ bundle-only-attribute 340 bundle-only-attribute = "bundle-only" 342 7. SDP Information Considerations 344 7.1. General 346 This section describes restrictions associated with the usage of SDP 347 parameters within a BUNDLE group. It also describes, when parameter 348 and attribute values have been assigned to each bundled "m=" line, 349 how to calculate a value for the whole BUNDLE group. 351 7.2. Connection Data (c=) 353 The "c=" line nettype value [RFC4566] assigned to a bundled "m=" line 354 MUST be 'IN'. 356 The "c=" line addrtype value [RFC4566] assigned to a bundled "m=" 357 line MUST be 'IP4' or 'IP6'. The same value MUST be assigned to each 358 "m=" line. 360 NOTE: Extensions to this specification can specify usage of the 361 BUNDLE mechanism for other nettype and addrtype values than the ones 362 listed above. 364 7.3. Bandwidth (b=) 366 The proposed bandwidth for a bundled "m=" line SHOULD be calculated 367 in the same way as for a non-bundled "m=" line. 369 The total proposed bandwidth for a BUNDLE group is the sum of the 370 proposed bandwidth for each bundled "m=" line. 372 The total proposed bandwidth for an offer or answer is the sum of the 373 proposed bandwidth for each "m=" line (bundled and non-bundled) 374 within the offer or answer. 376 7.4. Attributes (a=) 378 An offerer and answerer MUST use the rules and restrictions defined 379 in [I-D.mmusic-sdp-mux-attributes] for when associating SDP 380 attributes with bundled "m=" lines. 382 8. SDP Offer/Answer Procedures 384 8.1. General 386 This section describes the SDP Offer/Answer [RFC3264] procedures for: 388 o Negotiating and creating of a BUNDLE group; 390 o Selecting the BUNDLE addresses (offerer BUNDLE address and 391 answerer BUNDLE address); 393 o Adding an "m=" line to a BUNDLE group; 395 o Moving an "m=" line out of a BUNDLE group; and 397 o Disabling an "m=" line within a BUNDLE group. 399 The generic rules and procedures defined in [RFC3264] and [RFC5888] 400 also apply to the BUNDLE extension. For example, if an offer is 401 rejected by the answerer, the previously negotiated SDP parameters 402 and characteristics (including those associated with a BUNDLE group) 403 apply. Hence, if an offerer generates an offer in which the offerer 404 wants to create a BUNDLE group, and the answerer rejects the offer, 405 the BUNDLE group is not created. 407 The procedures in this section are independent of the media type or 408 transport protocol represented by a bundled "m=" line. [Section 10] 409 defines additional considerations for RTP based media. [Section 6] 410 defines additional considerations for the usage of the SDP 'bundle- 411 only' attribute. [Section 11] defines additional considerations for 412 the usage of Interactive Connectivity Establishment (ICE) mechanism 413 [RFC5245]. 415 The offerer and answerer MUST follow the rules and restrictions 416 defined in [Section 7] when creating offers and answers. 418 SDP bodies can contain multiple BUNDLE groups. The procedures in 419 this section apply independently to a given BUNDLE group. 421 8.2. Generating the Initial SDP Offer 423 8.2.1. General 425 When an offerer generates an initial offer, in order to create a 426 BUNDLE group, it MUST: 428 o Assign a unique address to each "m=" line within the offer, 429 following the procedures in [RFC3264]; 431 o Assign an SDP 'group:BUNDLE' attribute to the offer; 433 o Place the SDP 'mid' attribute value [RFC5888] of each bundled "m=" 434 line to the SDP 'group:BUNDLE' attribute mid value list; and 436 o Indicate which unique address the offerer wants the answerer to 437 select as the offerer BUNDLE address [Section 8.2.2]. 439 If the offerer wants to request that the answerer accepts a given 440 "m=" line only if the answerer keeps the "m=" line within the BUNDLE 441 group, the offerer MUST: 443 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 444 "m=" line; and 446 o Assign a zero port value to the "m=" line. 448 NOTE: If the offerer assigns a zero port value to an "m=" line, but 449 does not also associate an SDP 'bundle-only' attribute with the "m=" 450 line, it is an indication that the offerer wants to disable the "m=" 451 line [Section 8.5.5]. 453 [Section 16.1] shows an example of an initial offer. 455 8.2.2. Request offerer BUNDLE address selection 457 In the offer, the address assigned to the "m=" line associated with 458 the offerer suggested BUNDLE mid indicates the address that the 459 offerer wants the answer to select as the offerer BUNDLE address 460 [Section 8.3.2]. 462 8.3. Generating the SDP Answer 464 8.3.1. General 466 When an answerer generates an answer, which contains a BUNDLE group, 467 the following general SDP grouping framework restrictions, defined in 468 [RFC5888], also apply to the BUNDLE group: 470 o The answerer MUST NOT include a BUNDLE group in the answer, unless 471 the offerer requested the BUNDLE group to be created in the 472 associated offer; and 474 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 475 unless the offerer requested the "m=" line to be within that 476 BUNDLE group in the associated offer. 478 If the answer contains a BUNDLE group, the answerer MUST: 480 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 482 o Select an Answerer BUNDLE Address [Section 8.3.3]; 484 The answerer is allowed to select a new Answerer BUNDLE address each 485 time it generates an answer to an offer. 487 If the answerer does not want to keep an "m=" line within a BUNDLE 488 group, it MUST: 490 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 492 o Reject the "m=" line [Section 8.3.5]; 494 If the answerer keeps a bundle-only "m=" line within the BUNDLE 495 group, it follows the procedures (assigns the answerer BUNDLE address 496 to the "m=" line etc) for any other "m=" line kept within the BUNDLE 497 group. 499 If the answerer does not want to keep a bundle-only "m=" line within 500 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 502 The answerer MUST NOT include a 'bundle-only' attribute in an 503 answer." 505 NOTE: If a bundled "m=" line in an offer contains a port zero value, 506 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 507 is an indication that the offerer wants to disable the "m=" line 508 [Section 8.5.5]. 510 8.3.2. Answerer Selection of Offerer Bundle Address 512 In an offer, the address (unique or shared) assigned to the bundled 513 "m=" line associated with the offerer suggested BUNDLE mid indicates 514 the address that the offerer wants the answer to select as the 515 offerer BUNDLE address [Section 8.2.2]. The answerer MUST check 516 whether the "m=" line fulfils the following criteria: 518 o The answerer will not move the "m=" line out of the BUNDLE group 519 [Section 8.3.4]; 521 o The answerer will not reject the "m=" line [Section 8.3.5]; and 523 o The "m=" line does not contain a zero port value. 525 If all of the criteria above is fulfilled, the answerer MUST select 526 the address associated with the "m=" line as the offerer BUNDLE 527 address. In the answer, the answerer selected BUNDLE mid represents 528 the "m=" line, and the address associated with the "m=" line in the 529 offer becomes the offerer BUNDLE address. 531 If all of the criteria is not fulfilled, the answerer MUST select the 532 next mid value in the mid list, and perform the same criteria check 533 for the "m=" line associated with that mid value. If there are no 534 more mid values in the mid list, the answerer MUST NOT create the 535 BUNDLE group. 537 [Section 16.1] shows an example of an offerer BUNDLE address 538 selection. 540 8.3.3. Answerer Selection of Answerer BUNDLE Address 542 When the answerer selects a BUNDLE address for itself, referred to as 543 the answerer BUNDLE address, it MUST assign the address to each 544 bundled "m=" line within the created BUNDLE group in the answer. 546 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 547 line that is not within the BUNDLE group, or to an "m=" line that is 548 within another BUNDLE group. 550 [Section 16.1] shows an example of an answerer BUNDLE address 551 selection. 553 8.3.4. Moving A Media Description Out Of A BUNDLE Group 555 When an answerer moves a "m=" line out of a BUNDLE group, it assigns 556 an address to the "m=" line in the answer based on the following 557 rules: 559 o In the associated offer, if the "m=" line contains a shared 560 address (e.g. a previously selected offerer BUNDLE address), the 561 answerer MUST reject the moved "m=" line [Section 8.3.5]; 563 o In the associated offer, if the "m=" line contains a unique 564 address, the answerer MUST assign a unique address to the "m=" 565 line in the answer; or 567 o In the associated offer, if the "m=" line contains an SDP 'bundle- 568 only' attribute the answerer MUST reject the "m=" line 569 [Section 8.3.5]. 571 In addition, in either case above, the answerer MUST NOT include a 572 mid value, associated with the moved "m=" line, in the SDP 573 'group:BUNDLE' attribute mid list associated with the BUNDLE group. 575 8.3.5. Rejecting A Media Description In A BUNDLE Group 577 When an answerer rejects an "m=" line, it MUST assign an address with 578 a zero port value to the "m=" line in the answer, according to the 579 procedures in [RFC4566]. 581 In addition, the answerer MUST NOT include a mid value, associated 582 with the rejected "m=" line, in the SDP 'group:BUNDLE' attribute mid 583 list associated with the BUNDLE group. 585 8.4. Offerer Processing of the SDP Answer 587 8.4.1. General 589 When an offerer receives an answer, if the answer contains a BUNDLE 590 group, the offerer MUST check that any bundled "m=" line in the 591 answer was indicated as bundled in the associated offer. If there is 592 no mismatch, the offerer MUST apply the offerer BUNDLE address, 593 selected by the answerer [Section 8.3.2], to each bundled "m=" line. 595 NOTE: As the answerer might reject one or more bundled "m=" lines, or 596 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 597 line in the offer might not be indicated as bundled in the answer. 599 If the answer does not contain a BUNDLE group, the offerer MUST 600 process the answer as a normal answer. 602 8.4.2. Bundle Address Synchronization (BAS) 604 When an offerer receives an answer, if the answer contains a BUNDLE 605 group, the offerer MUST check whether the offerer BUNDLE address, 606 selected by the answerer [Section 8.3.2], matches what was assigned 607 to each bundled "m=" line (excluding any bundled "m=" line that was 608 rejected, or moved out of the BUNDLE group, by the answer) in the 609 associated offer. If there is a mismatch, the offerer SHOULD as soon 610 as possible generate a subsequent offer, in which it assigns the 611 offerer BUNDLE address to each bundled "m=" line. Such offer is 612 referred to as a Bundle Address Synchronization (BAS) offer. 614 A BAS offer is typically sent in the following scenarios: 616 o The offerer receives an answer to an initial offer, as the bundled 617 "m=" lines in the initial offer always contain unique addresses 618 [Section 8.2]; or 620 o The offerer receives an answer to an offer, in which a new bundled 621 "m=" line has been added to the BUNDLE group [Section 8.5.3], and 622 the offerer assigned a unique address to the bundled "m=" line in 623 the offer. 625 The offerer is allowed to modify any SDP parameter in the BAS offer. 627 NOTE: It is important that the BAS offer gets accepted by the 628 answerer. For that reason the offerer needs to consider the 629 necessity to modify SDP parameters in the BAS offer, in such a way 630 that could trigger the answerer to reject the BAS offer. Disabling 631 "m=" lines, or reducing the number of codecs, in a BAS offer is 632 considered to have a low risk of being rejected. 634 NOTE: The main purpose of the BAS offer is to ensure that 635 intermediaries, that might not support the BUNDLE extension, have 636 correct information regarding the address is going to be used to 637 transport the bundled media. 639 [Section 16.1] shows an example of a BAS offer. 641 8.5. Modifying the Session 643 8.5.1. General 645 When an offerer generates a subsequent offer, it MUST assign the 646 previously selected offerer BUNDLE address [Section 8.3.2], to each 647 bundled "m=" line (including any bundle-only "m=" line), with the 648 following exceptions: 650 o The offerer wants to request the answerer to select a new offerer 651 BUNDLE address [Section 8.5.2]; 653 o The offerer wants to add a bundled "m=" line to the BUNDLE group 654 [Section 8.5.3]; 656 o The offerer wants to move a bundled "m=" line out of the BUNDLE 657 group [Section 8.5.4]; or 659 o The offerer wants to disable the bundled "m=" line 660 [Section 8.5.5]. 662 In addition, the offerer MUST select an offerer suggested BUNDLE mid 663 [Section 8.2.2], even if the offerer does not want the answerer to 664 select a new offerer BUNDLE address. 666 If the offerer associates an SDP 'bundle-only' attribute with a 667 bundled "m=" line in the subsequent offer, if MUST assign the offerer 668 BUNDLE address to the "m=" line. The offerer MUST NOT assign a 669 unique address, or a zero port value, to a bundle-only "m=" line in a 670 subsequent offer. 672 NOTE: The offerer can associate an SDP 'bundle-only' attribute with a 673 bundled "m=" line in a subsequent offer, even if the offerer did not 674 associate a 'bundle-only' attribute with the same "m=" line in a 675 previous offer. 677 8.5.2. Request a new offerer BUNDLE address 679 When an offerer generates an offer, in which it wants the answerer to 680 select a new offerer BUNDLE address [Section 8.2.2], the offerer 681 MUST: 683 o Assign a unique address, which the offerer wants the answerer to 684 select as the offerer BUNDLE address, to a bundled "m=" line; and 686 o Indicate that the offerer wants the answerer to select the unique 687 address as the offerer BUNDLE address [Section 8.2.2] 689 NOTE: The offerer can assign a unique address to each bundled "m=" 690 line in the offer, or it can assign the previously negotiated offerer 691 BUNDLE address to each "m=" line (except the "m=" line to which it 692 assigns the unique address that it wants the answerer to select as 693 the new offerer BUNDLE address). 695 8.5.3. Adding a media description to a BUNDLE group 697 When an offerer generates an offer, in which it wants to add a 698 bundled "m=" line to BUNDLE group, the offerer MUST: 700 o Assign a unique address (excluding bundle-only "m=" lines), or the 701 offerer BUNDLE address (selected by the answerer in a previous 702 offer/answer transaction), to the "m=" line; 704 o Place the SDP 'mid' attribute value associated with the "m=" line 705 in the SDP 'group:BUNDLE' attribute mid list associated with the 706 BUNDLE group [Section 8.2.2]. 708 NOTE: Adding a unique address to the "m=" line allows the answerer to 709 move the "m=" line out of the BUNDLE group [Section 8.3.4], without 710 having to reject the "m=" line. 712 If the offerer wants the answerer to select the address associated 713 with the added "m=" line as the new offerer BUNDLE address, the 714 offerer suggested BUNDLE mid MUST represent the added "m=" line 715 [Section 8.2.2]. 717 If the offerer associates an SDP 'bundle-only' attribute with the 718 added "m=" line, the offerer MUST assign the offerer BUNDLE address 719 (selected by the answerer in a previous offer/answer transaction) to 720 the "m=" line. 722 [Section 16.3] shows an example where an offerer sends an offer in 723 order to add a bundled "m=" line to a BUNDLE group. 725 8.5.4. Moving A Media Description Out Of A BUNDLE Group 727 When an offerer generates an offer, in which it wants to move a 728 bundled "m=" line out of a BUNDLE group it was added to in a previous 729 offer/answer transaction, the offerer: 731 o MUST assign a unique address to the "m=" line; 733 o MUST NOT place a mid value associated with the "m=" line in the 734 SDP 'group:BUNDLE' attribute mid list associated with that BUNDLE 735 group; and 737 o MUST NOT associate an SDP 'bundle-only' attribute with the "m=" 738 line. 740 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 741 added to another BUNDLE group, the offerer applies the procedures in 742 [Section 8.5.3] to the "m=" line. 744 [Section 16.4] shows an example of an offer for moving an "m=" line 745 out of a BUNDLE group. 747 8.5.5. Disabling A Media Description In A BUNDLE Group 749 When an offerer generates an offer, in which it wants to disable a 750 bundled "m=" line (added to the BUNDLE group in a previous offer/ 751 answer transaction), the offerer: 753 o MUST assign an address with a zero port value to the "m=" line, 754 following the procedures in [RFC4566]; 756 o MUST NOT place a mid value associated with the "m=" line in the 757 SDP 'group:BUNDLE' attribute mid list associated with the BUNDLE 758 group; and 760 o MUST NOT associate an SDP 'bundle-only' attribute with the "m=" 761 line. 763 [Section 16.5] shows an example of an offer for disabling an "m=" 764 line within a BUNDLE group. 766 9. Protocol Identification 768 9.1. General 770 If bundled "m=" lines represent different transport protocols, there 771 MUST exist a publically available specification which describes a 772 mechanism, for this specific transport protocol combination, how to 773 associate a received packet with the correct transport protocol. 775 In addition, if a received packet can be associated with more than 776 one bundled "m=" line, there MUST exist a publically available 777 specification which describes a mechanism how to associate the 778 received packet with the correct "m=" line. 780 9.2. STUN, DTLS, SRTP 782 Section 5.1.2 of [RFC5764] describes a mechanism how to identify the 783 protocol among the STUN, DTLS and SRTP protocols (in any 784 combination). If an offer or answerer in offers or answers include 785 bundled "m=" lines that represent these protocols, the offerer or 786 answerer MUST support the mechanism described in [RFC5764], and no 787 explicit negotiation is required in order to indicate support and 788 usage of the mechanism. 790 [RFC5764] does not describe how to identify different protocols 791 transported on DTLS, only how to identify the DTLS protocol itself. 792 If multiple protocols are transported on DTLS, there MUST exist a 793 specification describing a mechanism how to identify each individual 794 protocol. In addition, if a received DTLS packet can be associated 795 with more than one "m=" line, there MUST exist a specification which 796 describes a mechanism how to associate the received DTLS packet with 797 the correct "m=" line. 799 [Section 10.2] describes how to associate a received (S)RTP packet 800 with the correct "m=" line. 802 10. RTP Considerations 804 10.1. Single RTP Session 806 10.1.1. General 808 All RTP-based media within a single BUNDLE group belong to a single 809 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 810 sessions, one per BUNDLE group. 812 Since a single RTP session is used for each bundle group, all "m=" 813 lines representing RTP-based media in a bundle group will share a 814 single SSRC numbering space [RFC3550]. 816 The following rules and restrictions apply for a single RTP session: 818 o A specific payload type value can be used in multiple bundled "m=" 819 lines if each codec associated with the payload type number shares 820 an identical codec configuration [Section 10.1.2]. 822 o The "proto" value in each bundled "m=" line MUST be identical 823 (e.g. RTP/AVPF). 825 o A given SSRC SHOULD NOT transmit RTP packets using payload types 826 that originate from different bundled "m=" lines. 828 NOTE: The last bullet above is to avoid sending multiple media types 829 from the same SSRC. If transmission of multiple media types are done 830 with time overlap, RTP and RTCP fail to function. Even if done in 831 proper sequence this causes RTP Timestamp rate switching issues [ref 832 to draft-ietf-avtext-multiple-clock-rates]. 834 10.1.2. Payload Type (PT) Value Re-usage 836 Multiple bundled "m=" lines might represent RTP based media. As all 837 RTP based media associated with a BUNDLE group belong to the same RTP 838 session, in order for a given payload type value to used inside more 839 than one bundled "m=" line, all codecs associated with the payload 840 type numbers MUST share an identical codec configuration. This means 841 that the codecs MUST share the same media type, encoding name, clock 842 rate and any parameter that can affect the codec configuration and 843 packetization. [I-D.mmusic-sdp-mux-attributes] lists SDP attributes, 844 whose attribute values must be identical for all codecs that use the 845 same payload type value. 847 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 849 In general, there are multiple mechanisms that can be used by an 850 endpoint in order to associate received RTP/RTCP packets with the 851 bundled "m=" line representing the RTP packets. Such mechanisms 852 include using the local address:port combination on which the RTP 853 packets are received, the payload type value carried inside the RTP 854 packets, the SSRC values carried inside the RTP packets, and other 855 "m=" line specific information carried inside the RTP packets. 857 As all RTP/RTCP packets associated with a BUNDLE group are sent and 858 received using the same 5-tuple, the local address:port combination 859 cannot be used to associate received RTP packets with the correct 860 "m=" line. 862 As described in [Section 10.1.2], the same payload type value might 863 be used inside RTP packets described by multiple "m=" lines. In such 864 cases, the payload type value cannot be used to associate received 865 RTP packets with the correct "m=" line. 867 An offerer and answerer can in an offer and answer inform each other 868 which SSRC values they will use inside sent RTP/RTCP packets, by 869 assigning an SDP 'ssrc' attribute [RFC5576] to each bundled "m=" line 870 which contains a payload type value that is also used inside another 871 bundled "m=" line. As the SSRC values will be carried inside the 872 RTP/RTCP packets, the offerer and answerer can then use that 873 information to associate received RTP packets with the correct "m=" 874 line. However, an offerer will not know which SSRC values the 875 answerer will use until it has received the answer providing that 876 information. Due to this, before the offerer has received the 877 answer, the offerer will not be able to associate received RTP/RTCP 878 packets with the correct "m=" line using the SSRC values. 880 In order for an offerer and answerer to always be able to associate 881 received RTP and RTCP packets with the correct "m=" line, an offerer 882 and answerer using the BUNDLE extension MUST use the mechanism 883 defined in [Section 13], where the remote endpoint inserts the SDP 884 'mid' attribute value of an "m=" line in RTP and RTCP packets 885 associated with that "m=" line. 887 10.3. RTP/RTCP Multiplexing 889 10.3.1. General 891 When a BUNDLE group, which contains RTP based media, is created, the 892 offerer and answerer MUST negotiate whether to enable RTP/RTCP 893 multiplexing for the RTP based media associated with the BUNDLE group 894 [RFC5761]. 896 If RTP/RTCP multiplexing is not enabled, separate 5-tuples will be 897 used for sending and receiving the RTP packets and the RTCP packets. 899 10.3.2. SDP Offer/Answer Procedures 901 10.3.2.1. General 903 This section describes how an offerer and answerer can use the SDP 904 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 905 to negotiate usage of RTP/RTCP multiplexing for RTP based media 906 associated with a BUNDLE group. 908 10.3.2.2. Generating the Initial SDP Offer 910 When an offerer generates an initial offer, if the offerer wants to 911 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 912 offerer MUST assign an SDP 'rtcp-mux' attribute [RFC5761] to each 913 bundled "m=" line (including any bundle-only "m=" line) in the offer. 914 In addition, the offerer MUST assign an SDP 'rtcp' attribute 915 [RFC3605] to each bundled "m=" line (including any bundle-only "m=" 916 line), with an attribute value that is identical to the port value 917 assigned to the "m=" line itself, in the offer. 919 If the offerer does not want to negotiate usage of RTP/RTCP 920 multiplexing, it MUST NOT assign the SDP attributes above to any 921 bundled "m=" line. 923 10.3.2.3. Generating the SDP Answer 925 When an answerer generates an answer, if the offerer indicated 926 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 927 the associated offer, the answerer MUST either accept or reject the 928 usage of RTP/RTCP multiplexing in the answer. 930 If the answerer accepts usage of RTP/RTCP multiplexing within the 931 BUNDLE group, it MUST assign an SDP 'rtcp-mux' attribute to each 932 bundled "m=" line in the answer. The answerer MUST NOT assign an SDP 933 'rtcp' attribute to any bundled "m=" line in the answer. 935 If the answerer rejects usage of RTP/RTCP multiplexing within the 936 BUNDLE group, it MUST NOT assign an SDP 'rtcp-mux' or SDP 'rtcp' 937 attribute to any bundled "m=" line in the answer. 939 If the usage of RTP/RTCP multiplexing has been negotiated in a 940 previous offer/answer transaction, and the offerer indicates that it 941 wants to continue using RTP/RTCP multiplexing in a subsequent offer, 942 the answerer MUST assign an SDP 'rtcp-mux' attribute to each bundled 943 "m=" line in the answer. I.e. the answerer MUST NOT disable the 944 usage of RTP/RTCP multiplexing. 946 10.3.2.4. Offerer Processing of the SDP Answer 948 When the offerer receives an answer, if the answerer accepts the 949 usage of RTP/RTCP multiplexing, by including an SDP 'rtcp-mux' 950 attribute to each bundled "m=" line in the answer [Section 10.3.2.3], 951 the answerer follows the procedures for RTP/RTCP multiplexing defined 952 in [RFC5761]. 954 If the answerer does not accept the usage of RTP/RTCP multiplexing 955 [Section 10.3.2.3], the offerer MUST use separate 5-tuples for RTP 956 and RTCP. 958 10.3.2.5. Modifying the Session 960 When an offerer generates a subsequent offer, if it wants to 961 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or if 962 it wants to continue usage of RTP/RTCP multiplexing (negotiated in a 963 previous offer/answer transaction), it MUST assign SDP 'rtcp-mux' and 964 'rtcp' attributes to each bundled "m=" line (including bundle-only 965 "m=" lines, and a bundled "m=" line that the offerer wants to add to 966 the BUNDLE group), unless the offerer wants to disable or remove the 967 "m=" line from the BUNDLE group. 969 If the offerer does not want to negotiate usage of RTP/RTCP 970 multiplexing within the BUNDLE group, or if it wants to disable usage 971 of RTP/RTCP multiplexing (negotiated in a previous offer/answer 972 transaction), the offerer MUST NOT assign SDP 'rtcp-mux' and 'rtcp' 973 attributes to any bundled "m=" line in the subsequent offer. 975 NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has 976 been negotiated within a BUNDLE group, that the usage is not 977 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 978 answerer need to reserve new IP ports, to be used for sending and 979 receiving RTCP packets. 981 11. ICE Considerations 983 11.1. General 985 This section describes how to use the BUNDLE grouping extension 986 together with the Interactive Connectivity Establishment (ICE) 987 mechanism [RFC5245]. 989 The procedures defined in [RFC5245] also apply to usage of ICE with 990 BUNDLE, with the following exception: 992 o When BUNDLE addresses for a BUNDLE group have been selected for 993 both endpoints, ICE connectivity checks and keep-alives only need 994 to be performed for the whole BUNDLE group, instead of per bundled 995 "m=" line. 997 Support and usage of ICE mechanism together with the BUNDLE extension 998 is OPTIONAL. 1000 11.2. SDP Offer/Answer Procedures 1002 11.2.1. General 1004 When an offerer or answerer assigns a unique address to a bundled 1005 "m=" line (excluding bundle-only "m=" lines), it MUST also assign 1006 unique ICE candidates [RFC5245] to the "m=" line. 1008 When an offerer or answerer assigns a shared address (i.e. a 1009 previously selected BUNDLE address) to one or more bundled "m=" line 1010 (including bundle-only "m=" lines), and when it assigns an address 1011 with a zero port value to one or more bundle-only "m=" lines, it MUST 1012 assign identical ICE candidates (referred to as shared ICE 1013 candidates) to each of those "m=" lines. 1015 11.2.2. Generating the Initial SDP Offer 1017 When an offerer generates an initial offer, it assigns unique or 1018 shared ICE candidates to the bundled "m=" lines, according to 1019 [Section 11.1]. 1021 11.2.3. Generating the SDP Answer 1023 When an answerer generates an answer, which contains a BUNDLE group, 1024 the answerer MUST assign shared ICE candidates to each bundled "m=" 1025 line (including "m=" lines that were indicated as bundle-only in the 1026 associated offer) in the answer. 1028 11.2.4. Offerer Processing of the SDP Answer 1030 When an offerer receives an answer, if the answerer supports and uses 1031 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1032 the ICE candidates, associated with the "m=" line representing the 1033 offerer BUNDLE address (selected by the answerer) to each bundled 1034 "m=" line. 1036 11.2.5. Modifying the Session 1038 When an offerer generates a subsequent offer, it assigns unique or 1039 shared ICE candidates to the bundled "m=" lines, according to 1040 [Section 11.1]. 1042 12. Update to RFC 3264 1044 12.1. General 1046 This section replaces the text of the following sections of RFC 3264: 1048 o Section 5.1 (Unicast Streams). 1050 o Section 8.2 (Removing a Media Stream). 1052 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1054 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1056 For recvonly and sendrecv streams, the port number and address in the 1057 offer indicate where the offerer would like to receive the media 1058 stream. For sendonly RTP streams, the address and port number 1059 indirectly indicate where the offerer wants to receive RTCP reports. 1060 Unless there is an explicit indication otherwise, reports are sent to 1061 the port number one higher than the number indicated. The IP address 1062 and port present in the offer indicate nothing about the source IP 1063 address and source port of RTP and RTCP packets that will be sent by 1064 the offerer. A port number of zero in the offer indicates that the 1065 stream is offered but MUST NOT be used. This has no useful semantics 1066 in an initial offer, but is allowed for reasons of completeness, 1067 since the answer can contain a zero port indicating a rejected stream 1068 (Section 6). Furthermore, existing streams can be terminated by 1069 setting the port to zero (Section 8). In general, a port number of 1070 zero indicates that the media stream is not wanted. 1072 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1074 For recvonly and sendrecv streams, the port number and address in the 1075 offer indicate where the offerer would like to receive the media 1076 stream. For sendonly RTP streams, the address and port number 1077 indirectly indicate where the offerer wants to receive RTCP reports. 1078 Unless there is an explicit indication otherwise, reports are sent to 1079 the port number one higher than the number indicated. The IP address 1080 and port present in the offer indicate nothing about the source IP 1081 address and source port of RTP and RTCP packets that will be sent by 1082 the offerer. A port number of zero in the offer by default indicates 1083 that the stream is offered but MUST NOT be used, but an extension 1084 mechanism might specify different semantics for the usage of a zero 1085 port value. Furthermore, existing streams can be terminated by 1086 setting the port to zero (Section 8). In general, a port number of 1087 zero by default indicates that the media stream is not wanted. 1089 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1091 A stream that is offered with a port of zero MUST be marked with port 1092 zero in the answer. Like the offer, the answer MAY omit all 1093 attributes present previously, and MAY list just a single media 1094 format from amongst those in the offer. 1096 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1098 A stream that is offered with a port of zero MUST by default be 1099 marked with port zero in the answer, unless an extension mechanism, 1100 which specifies semantics for the usage of a non-zero port value, is 1101 used. If the stream is marked with port zero in the answer, the 1102 answer MAY omit (like the offer) all attributes present previously, 1103 and MAY list just a single media format from amongst those in the 1104 offer." 1106 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1108 RFC 2543 [10] specified that placing a user on hold was accomplished 1109 by setting the connection address to 0.0.0.0. Its usage for putting 1110 a call on hold is no longer recommended, since it doesn't allow for 1111 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1112 with connection oriented media. However, it can be useful in an 1113 initial offer when the offerer knows it wants to use a particular set 1114 of media streams and formats, but doesn't know the addresses and 1115 ports at the time of the offer. Of course, when used, the port 1116 number MUST NOT be zero, which would specify that the stream has been 1117 disabled. An agent MUST be capable of receiving SDP with a 1118 connection address of 0.0.0.0, in which case it means that neither 1119 RTP nor RTCP should be sent to the peer. 1121 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1123 RFC 2543 [10] specified that placing a user on hold was accomplished 1124 by setting the connection address to 0.0.0.0. Its usage for putting 1125 a call on hold is no longer recommended, since it doesn't allow for 1126 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1127 with connection oriented media. However, it can be useful in an 1128 initial offer when the offerer knows it wants to use a particular set 1129 of media streams and formats, but doesn't know the addresses and 1130 ports at the time of the offer. Of course, when used, the port 1131 number MUST NOT be zero, if it would specify that the stream has been 1132 disabled. However, an extension mechanism might specify different 1133 semantics of the zero port number usage. An agent MUST be capable of 1134 receiving SDP with a connection address of 0.0.0.0, in which case it 1135 means that neither RTP nor RTCP should be sent to the peer. 1137 13. RTP/RTCP extensions for mid value transport 1139 13.1. General 1141 SDP Offerers and Answerers [RFC3264] can assign mid values to SDP 1142 Media Descriptions (m= lines) within SDP Offers and Answers, using 1143 the procedures in [RFC5888]. Each mid value uniquely identifies an 1144 m= line. 1146 This section defines a new RTP SDES item [RFC3550], 'MID', which is 1147 used to carry mid values within RTCP SDES packets. This section also 1148 defines a new RTP header extension [RFC5285], which can be used to 1149 carry the mid value in RTP packets. 1151 The SDES item and RTP header extension makes is possible for a 1152 receiver to associate received RTCP- and RTP packets with a specific 1153 m= line, to which the receiver has assigned a mid value, even if 1154 those m= lines are part of the same RTP session. The endpoint 1155 informs the remote endpoint about the mid values using the procedures 1156 in [RFC5888], and the remote endpoint then inserts the mid values in 1157 RTCP- and RTP packets sent towards the other endpoint. 1159 NOTE: This text above defines how the mid value is carried in SDP 1160 Offers and Answers. The usage of other signalling protocols for 1161 carrying the mid value is not prevented, but the usage of such 1162 protocols is outside the scope of this document. 1164 [RFC3550] defines general procedures regarding the RTCP transmission 1165 interval. The RTP MID SDES item SHOULD be sent in the first few RTCP 1166 packets sent on joining the session, and SHOULD be sent regularly 1167 thereafter. The exact number of RTCP packets in which this SDES item 1168 is sent is intentionally not specified here, as it will depend on the 1169 expected packet loss rate, the RTCP reporting interval, and the 1170 allowable overhead. 1172 The RTP MID header extension SHOULD be included in some RTP packets 1173 at the start of the session and whenever the SSRC changes. It might 1174 also be useful to include the header extension in RTP packets that 1175 comprise random access points in the media (e.g., with video 1176 I-frames). The exact number of RTP packets in which this header 1177 extension is sent is intentionally not specified here, as it will 1178 depend on expected packet loss rate and loss patterns, the overhead 1179 the application can tolerate, and the importance of immediate receipt 1180 of the mid value. 1182 For robustness purpose, endpoints need to be prepared for situations 1183 where the mid value is delayed, and SHOULD NOT terminate sessions in 1184 such cases, as the mid value is likely to arrive soon. 1186 13.2. RTP MID SDES Item 1188 0 1 2 3 1189 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 1190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1191 | MID=TBD | length | mid value ... 1192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1194 The mid value payload is UTF-8 encoded, as in SDP. 1196 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1197 identifier value.] 1199 13.3. RTP MID Header Extension 1201 The payload, containing the mid value, of the RTP MID header 1202 extension element can be encoded using either the one-byte or two- 1203 byte header [RFC5285]. The mid value payload is UTF-8 encoded, as in 1204 SDP. 1206 14. IANA Considerations 1208 14.1. New SDES item 1210 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1211 document.] 1213 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1214 identifier value.] 1216 This document adds the MID SDES item to the IANA "RTP SDES item 1217 types" registry as follows: 1219 Value: TBD 1220 Abbrev.: MID 1221 Name: Media Identification 1222 Reference: RFCXXXX 1224 14.2. New RTP Header Extension URI 1226 This document defines a new extension URI in the RTP Compact Header 1227 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1228 Parameters registry, according to the following data: 1230 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1231 Description: Media identification 1232 Contact: christer.holmberg@ericsson.com 1233 Reference: RFCXXXX 1235 14.3. New SDP Attribute 1237 This document defines a new SDP media-level attribute, according to 1238 the following data: 1240 Attribute name: bundle-only 1241 Type of attribute: Media-level 1242 Subject to charset: No 1243 Purpose: Request a media description to be accepted 1244 in the answer only if kept within a BUNDLE group 1245 by the answerer 1246 Appropriate values: N/A 1247 Contact name: Christer Holmberg 1248 Contact e-mail: christer.holmberg@ericsson.com 1250 15. Security Considerations 1252 The security considerations defined in [RFC3264] and [RFC5888] apply 1253 to the BUNDLE extension. 1255 When the BUNDLE extension is used a single set of security 1256 credentials might be used for all media streams associated with a 1257 BUNDLE group. If the security credentials are compromised, an 1258 attacker will have access to all media content. 1260 16. Examples 1262 16.1. Example: Bundle Address Selection 1264 The example below shows: 1266 o 1. An offer, in which the offerer assigns a unique address to 1267 each bundled "m=" line within the BUNDLE group. 1269 o 2. An answer, in which the answerer selects the offerer BUNDLE 1270 address, and in which selects its own BUNDLE address (the answerer 1271 BUNDLE address) and assigns it each bundled "m=" line within the 1272 BUNDLE group. 1274 o 3. A subsequent offer (BAS offer), which is used to perform a 1275 Bundle Address Synchronization (BAS). 1277 SDP Offer (1) 1279 v=0 1280 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1281 s= 1282 c=IN IP4 atlanta.example.com 1283 t=0 0 1284 a=group:BUNDLE foo bar 1285 m=audio 10000 RTP/AVP 0 8 97 1286 a=mid:foo 1287 b=AS:200 1288 a=rtpmap:0 PCMU/8000 1289 a=rtpmap:8 PCMA/8000 1290 a=rtpmap:97 iLBC/8000 1291 m=video 10002 RTP/AVP 31 32 1292 a=mid:bar 1293 b=AS:1000 1294 a=rtpmap:31 H261/90000 1295 a=rtpmap:32 MPV/90000 1297 SDP Answer (2) 1299 v=0 1300 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1301 s= 1302 c=IN IP4 biloxi.example.com 1303 t=0 0 1304 a=group:BUNDLE foo bar 1305 m=audio 20000 RTP/AVP 0 1306 a=mid:foo 1307 b=AS:200 1308 a=rtpmap:0 PCMU/8000 1309 m=video 20000 RTP/AVP 32 1310 a=mid:bar 1311 b=AS:1000 1312 a=rtpmap:32 MPV/90000 1314 SDP Offer (3) 1316 v=0 1317 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1318 s= 1319 c=IN IP4 atlanta.example.com 1320 t=0 0 1321 a=group:BUNDLE foo bar 1322 m=audio 10000 RTP/AVP 0 8 97 1323 a=mid:foo 1324 b=AS:200 1325 a=rtpmap:0 PCMU/8000 1326 a=rtpmap:8 PCMA/8000 1327 a=rtpmap:97 iLBC/8000 1328 m=video 10000 RTP/AVP 31 32 1329 a=mid:bar 1330 b=AS:1000 1331 a=rtpmap:31 H261/90000 1332 a=rtpmap:32 MPV/90000 1334 16.2. Example: BUNDLE Extension Rejected 1336 The example below shows: 1338 o 1. An offer, in which the offerer assigns a unique address to 1339 each bundled "m=" line within the BUNDLE group. 1341 o 2. An answer, in which the answerer rejects the offered BUNDLE 1342 group, and assigns a unique addresses to each "m=" line (following 1343 normal RFC 3264 procedures). 1345 SDP Offer (1) 1347 v=0 1348 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1349 s= 1350 c=IN IP4 atlanta.example.com 1351 t=0 0 1352 a=group:BUNDLE foo bar 1353 m=audio 10000 RTP/AVP 0 8 97 1354 a=mid:foo 1355 b=AS:200 1356 a=rtpmap:0 PCMU/8000 1357 a=rtpmap:8 PCMA/8000 1358 a=rtpmap:97 iLBC/8000 1359 m=video 10002 RTP/AVP 31 32 1360 a=mid:bar 1361 b=AS:1000 1362 a=rtpmap:31 H261/90000 1363 a=rtpmap:32 MPV/90000 1365 SDP Answer (2) 1367 v=0 1368 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1369 s= 1370 c=IN IP4 biloxi.example.com 1371 t=0 0 1372 m=audio 20000 RTP/AVP 0 1373 b=AS:200 1374 a=rtpmap:0 PCMU/8000 1375 m=video 30000 RTP/AVP 32 1376 b=AS:1000 1377 a=rtpmap:32 MPV/90000 1379 16.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1381 The example below shows: 1383 o 1. An offer, in which the offerer adds a new "m=" line, 1384 represented by the "zen" mid value, to a previously negotiated 1385 BUNDLE group, assigns a unique address to the added "m=" line, and 1386 assigns the previously selected offerer BUNDLE address to each of 1387 the other bundled "m=" lines within the BUNDLE group. 1389 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1390 address to each bundled "m=" line (including the newly added "m=" 1391 line) within the BUNDLE group. 1393 o 3. A subsequent offer (BAS offer), which is used to perform a 1394 Bundle Address Synchronization (BAS). 1396 SDP Offer (1) 1398 v=0 1399 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1400 s= 1401 c=IN IP4 atlanta.example.com 1402 t=0 0 1403 a=group:BUNDLE foo bar zen 1404 m=audio 10000 RTP/AVP 0 8 97 1405 a=mid:foo 1406 b=AS:200 1407 a=rtpmap:0 PCMU/8000 1408 a=rtpmap:8 PCMA/8000 1409 a=rtpmap:97 iLBC/8000 1410 m=video 10000 RTP/AVP 31 32 1411 a=mid:bar 1412 b=AS:1000 1413 a=rtpmap:31 H261/90000 1414 a=rtpmap:32 MPV/90000 1415 m=video 20000 RTP/AVP 66 1416 a=mid:zen 1417 b=AS:1000 1418 a=rtpmap:66 H261/90000 1420 SDP Answer (2) 1422 v=0 1423 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1424 s= 1425 c=IN IP4 biloxi.example.com 1426 t=0 0 1427 a=group:BUNDLE foo bar zen 1428 m=audio 20000 RTP/AVP 0 1429 a=mid:foo 1430 b=AS:200 1431 a=rtpmap:0 PCMU/8000 1432 m=video 20000 RTP/AVP 32 1433 a=mid:bar 1434 b=AS:1000 1435 a=rtpmap:32 MPV/90000 1436 m=video 20000 RTP/AVP 66 1437 a=mid:zen 1438 b=AS:1000 1439 a=rtpmap:66 H261/90000 1441 SDP Offer (3) 1443 v=0 1444 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1445 s= 1446 c=IN IP4 atlanta.example.com 1447 t=0 0 1448 a=group:BUNDLE foo bar zen 1449 m=audio 10000 RTP/AVP 0 8 97 1450 a=mid:foo 1451 b=AS:200 1452 a=rtpmap:0 PCMU/8000 1453 a=rtpmap:8 PCMA/8000 1454 a=rtpmap:97 iLBC/8000 1455 m=video 10000 RTP/AVP 31 32 1456 a=mid:bar 1457 b=AS:1000 1458 a=rtpmap:31 H261/90000 1459 a=rtpmap:32 MPV/90000 1460 m=video 10000 RTP/AVP 66 1461 a=mid:zen 1462 b=AS:1000 1463 a=rtpmap:66 H261/90000 1465 16.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1467 The example below shows: 1469 o 1. An offer, in which the offerer moves a bundled "m=" line out 1470 of a BUNDLE group, assigns a unique address to the moved "m=" 1471 line, and assigns the offerer BUNDLE address to each other bundled 1472 "m=" line within the BUNDLE group. 1474 o 2. An answer, in which the answerer moves the "m=" line out of 1475 the BUNDLE group, assigns unique address to the moved "m=" line, 1476 and assigns the answerer BUNDLE address to each other bundled "m=" 1477 line within the BUNDLE group. 1479 SDP Offer (1) 1481 v=0 1482 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1483 s= 1484 c=IN IP4 atlanta.example.com 1485 t=0 0 1486 a=group:BUNDLE foo bar 1487 m=audio 10000 RTP/AVP 0 8 97 1488 a=mid:foo 1489 b=AS:200 1490 a=rtpmap:0 PCMU/8000 1491 a=rtpmap:8 PCMA/8000 1492 a=rtpmap:97 iLBC/8000 1493 m=video 10000 RTP/AVP 31 32 1494 a=mid:bar 1495 b=AS:1000 1496 a=rtpmap:31 H261/90000 1497 a=rtpmap:32 MPV/90000 1498 m=video 50000 RTP/AVP 66 1499 b=AS:1000 1500 a=rtpmap:66 H261/90000 1502 SDP Answer (2) 1504 v=0 1505 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1506 s= 1507 c=IN IP4 biloxi.example.com 1508 t=0 0 1509 a=group:BUNDLE foo bar 1510 m=audio 20000 RTP/AVP 0 1511 a=mid:foo 1512 b=AS:200 1513 a=rtpmap:0 PCMU/8000 1514 m=video 20000 RTP/AVP 32 1515 a=mid:bar 1516 b=AS:1000 1517 a=rtpmap:32 MPV/90000 1518 m=video 60000 RTP/AVP 66 1519 b=AS:1000 1520 a=rtpmap:66 H261/90000 1522 16.5. Example: Offerer Disables A Media Description Within A BUNDLE 1523 Group 1525 The example below shows: 1527 o 1. An offer, in which the offerer disables a bundled "m=" line 1528 within BUNDLE group, assigns a zero port number the disabled "m=" 1529 line, and assigns the offerer BUNDLE address to each of the other 1530 bundled "m=" lines within the BUNDLE group. 1532 o 2. An answer, in which the answerer moves the disabled "m=" line 1533 out of the BUNDLE group, assigns a zero port value to the disabled 1534 "m=" line, and assigns the answerer BUNDLE address to each of the 1535 other bundled "m=" lines within the BUNDLE group. 1537 SDP Offer (1) 1539 v=0 1540 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1541 s= 1542 c=IN IP4 atlanta.example.com 1543 t=0 0 1544 a=group:BUNDLE foo bar 1545 m=audio 10000 RTP/AVP 0 8 97 1546 a=mid:foo 1547 b=AS:200 1548 a=rtpmap:0 PCMU/8000 1549 a=rtpmap:8 PCMA/8000 1550 a=rtpmap:97 iLBC/8000 1551 m=video 10000 RTP/AVP 31 32 1552 a=mid:bar 1553 b=AS:1000 1554 a=rtpmap:31 H261/90000 1555 a=rtpmap:32 MPV/90000 1556 m=video 0 RTP/AVP 66 1557 a=rtpmap:66 H261/90000 1559 SDP Answer (2) 1561 v=0 1562 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1563 s= 1564 c=IN IP4 biloxi.example.com 1565 t=0 0 1566 a=group:BUNDLE foo bar 1567 m=audio 20000 RTP/AVP 0 1568 a=mid:foo 1569 b=AS:200 1570 a=rtpmap:0 PCMU/8000 1571 m=video 20000 RTP/AVP 32 1572 a=mid:bar 1573 b=AS:1000 1574 a=rtpmap:32 MPV/90000 1575 m=video 0 RTP/AVP 66 1576 a=rtpmap:66 H261/90000 1578 17. IANA Considerations 1580 This document requests IANA to register the new SDP Grouping semantic 1581 extension called BUNDLE. 1583 18. Acknowledgements 1585 The usage of the SDP grouping extension for negotiating bundled media 1586 is based on a similar alternatives proposed by Harald Alvestrand and 1587 Cullen Jennings. The BUNDLE extension described in this document is 1588 based on the different alternative proposals, and text (e.g. SDP 1589 examples) have been borrowed (and, in some cases, modified) from 1590 those alternative proposals. 1592 The SDP examples are also modified versions from the ones in the 1593 Alvestrand proposal. 1595 Thanks to Paul Kyzivat, Martin Thomson and Flemming Andreasen for 1596 taking the time to read the text along the way, and providing useful 1597 feedback. 1599 19. Change Log 1601 [RFC EDITOR NOTE: Please remove this section when publishing] 1603 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1605 o SDP bundle-only attribute added to IANA Considerations. 1607 o SDES item and RTP header extension added to Abstract and 1608 Introduction. 1610 o Modification to text updating section 8.2 of RFC 3264. 1612 o Reference corrections. 1614 o Editorial corrections. 1616 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1618 o Terminology change: "bundle-only attribute assigned to m= line" to 1619 "bundle-only attribute associated with m= line". 1621 o Editorial corrections. 1623 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1625 o Editorial corrections. 1627 o - "of"->"if" (8.3.2.5). 1629 o - "optional"->"OPTIONAL" (9.1). 1631 o - Syntax/ABNF for 'bundle-only' attribute added. 1633 o - SDP Offer/Answer sections merged. 1635 o - 'Request new offerer BUNDLE address' section added 1637 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1639 o OPEN ISSUE regarding Receiver-ID closed. 1641 o - RTP MID SDES Item. 1643 o - RTP MID Header Extension. 1645 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1646 closed. 1648 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1649 include an 'rtcp' attribute in the answer, based on the procedures 1650 in section 5.1.3 of RFC 5761. 1652 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1654 o Draft title changed. 1656 o Added "SDP" to section names containing "Offer" or "Answer". 1658 o Editorial fixes based on comments from Paul Kyzivat 1659 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1660 msg13314.html). 1662 o Editorial fixed based on comments from Colin Perkins 1663 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1664 msg13318.html). 1666 o - Removed text about extending BUNDLE to allow multiple RTP 1667 sessions within a BUNDLE group. 1669 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1671 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1672 3264 structure. 1674 o Additional definitions added. 1676 o - Shared address. 1678 o - Bundled "m=" line. 1680 o - Bundle-only "m=" line. 1682 o - Offerer suggested BUNDLE mid. 1684 o - Answerer selected BUNDLE mid. 1686 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1687 to multiple "m=" lines until it has received an SDP Answer 1688 indicating support of the BUNDLE extension. 1690 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1691 Answerer supports the BUNDLE extension, assign a zero port value 1692 to a 'bundle-only' "m=" line. 1694 o SDP 'bundle-only' attribute section added. 1696 o Connection data nettype/addrtype restrictions added. 1698 o RFC 3264 update section added. 1700 o Indicating that a specific payload type value can be used in 1701 multiple "m=" lines, if the value represents the same codec 1702 configuration in each "m=" line. 1704 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1706 o Updated Offerer procedures (http://www.ietf.org/mail- 1707 archive/web/mmusic/current/msg12293.html). 1709 o Updated Answerer procedures (http://www.ietf.org/mail- 1710 archive/web/mmusic/current/msg12333.html). 1712 o Usage of SDP 'bundle-only' attribute added. 1714 o Reference to Trickle ICE document added. 1716 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1718 o Mechanism modified, to be based on usage of SDP Offers with both 1719 different and identical port number values, depending on whether 1720 it is known if the remote endpoint supports the extension. 1722 o Cullen Jennings added as co-author. 1724 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1726 o No changes. New version due to expiration. 1728 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1730 o No changes. New version due to expiration. 1732 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1734 o Draft name changed. 1736 o Harald Alvestrand added as co-author. 1738 o "Multiplex" terminology changed to "bundle". 1740 o Added text about single versus multiple RTP Sessions. 1742 o Added reference to RFC 3550. 1744 20. References 1746 20.1. Normative References 1748 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1749 Requirement Levels", BCP 14, RFC 2119, March 1997. 1751 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1752 with Session Description Protocol (SDP)", RFC 3264, June 1753 2002. 1755 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1756 Description Protocol", RFC 4566, July 2006. 1758 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1759 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1761 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1762 Header Extensions", RFC 5285, July 2008. 1764 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1765 Control Packets on a Single Port", RFC 5761, April 2010. 1767 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1768 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1770 [I-D.mmusic-sdp-mux-attributes] 1771 Nandakumar, S., "A Framework for SDP Attributes when 1772 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-02 1773 (work in progress), July 2014. 1775 20.2. Informative References 1777 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1778 Jacobson, "RTP: A Transport Protocol for Real-Time 1779 Applications", STD 64, RFC 3550, July 2003. 1781 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1782 in Session Description Protocol (SDP)", RFC 3605, October 1783 2003. 1785 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1786 (ICE): A Protocol for Network Address Translator (NAT) 1787 Traversal for Offer/Answer Protocols", RFC 5245, April 1788 2010. 1790 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1791 Media Attributes in the Session Description Protocol 1792 (SDP)", RFC 5576, June 2009. 1794 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1795 Security (DTLS) Extension to Establish Keys for the Secure 1796 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 1798 [I-D.ietf-mmusic-trickle-ice] 1799 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 1800 Incremental Provisioning of Candidates for the Interactive 1801 Connectivity Establishment (ICE) Protocol", draft-ietf- 1802 mmusic-trickle-ice-01 (work in progress), February 2014. 1804 Appendix A. Design Considerations 1806 A.1. General 1808 One of the main issues regarding the BUNDLE grouping extensions has 1809 been whether, in SDP Offers and SDP Answers, the same port number 1810 value should be inserted in "m=" lines associated with a BUNDLE 1811 group, as the purpose of the extension is to negotiate the usage of a 1812 single 5-tuple for media associated with the "m=" lines. Issues with 1813 both approaches, discussed in the Appendix have been raised. The 1814 outcome was to specify a mechanism which uses SDP Offers with both 1815 different and identical port number values. 1817 Below are the primary issues that have been considered when defining 1818 the "BUNDLE" grouping extension: 1820 o 1) Interoperability with existing UAs. 1822 o 2) Interoperability with intermediary B2BUA- and proxy entities. 1824 o 3) Time to gather, and the number of, ICE candidates. 1826 o 4) Different error scenarios, and when they occur. 1828 o 5) SDP Offer/Answer impacts, including usage of port number value 1829 zero. 1831 NOTE: Before this document is published as an RFC, this 1832 Appendix might be removed. 1834 A.2. UA Interoperability 1836 Consider the following SDP Offer/Answer exchange, where Alice sends 1837 an SDP Offer to Bob: 1839 SDP Offer 1841 v=0 1842 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1843 s= 1844 c=IN IP4 atlanta.example.com 1845 t=0 0 1846 m=audio 10000 RTP/AVP 97 1847 a=rtpmap:97 iLBC/8000 1848 m=video 10002 RTP/AVP 97 1849 a=rtpmap:97 H261/90000 1851 SDP Answer 1853 v=0 1854 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1855 s= 1856 c=IN IP4 biloxi.example.com 1857 t=0 0 1858 m=audio 20000 RTP/AVP 97 1859 a=rtpmap:97 iLBC/8000 1860 m=video 20002 RTP/AVP 97 1861 a=rtpmap:97 H261/90000 1863 RFC 4961 specifies a way of doing symmetric RTP but that is an a 1864 later invention to RTP and Bob can not assume that Alice supports RFC 1865 4961. This means that Alice may be sending RTP from a different port 1866 than 10000 or 10002 - some implementation simply send the RTP from an 1867 ephemeral port. When Bob's endpoint receives an RTP packet, the only 1868 way that Bob know if it should be passed to the video or audio codec 1869 is by looking at the port it was received on. This lead some SDP 1870 implementations to use the fact that each "m=" line had a different 1871 port number to use that port number as an index to find the correct m 1872 line in the SDP. As a result, some implementations that do support 1873 symmetric RTP and ICE still use a SDP data structure where SDP with 1874 "m=" lines with the same port such as: 1876 SDP Offer 1878 v=0 1879 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1880 s= 1881 c=IN IP4 atlanta.example.com 1882 t=0 0 1883 m=audio 10000 RTP/AVP 97 1884 a=rtpmap:97 iLBC/8000 1885 m=video 10000 RTP/AVP 98 1886 a=rtpmap:98 H261/90000 1888 will result in the second "m=" line being considered an SDP error 1889 because it has the same port as the first line. 1891 A.3. Usage of port number value zero 1893 In an SDP Offer or SDP Answer, the media associated with an "m=" line 1894 can be disabled/rejected by setting the port number value to zero. 1895 This is different from e.g. using the SDP direction attributes, where 1896 RTCP traffic will continue even if the SDP "inactive" attribute is 1897 indicated for the associated "m=" line. 1899 If each "m=" line associated with a BUNDLE group would contain 1900 different port number values, and one of those port would be used for 1901 the 5-tuple, problems would occur if an endpoint wants to disable/ 1902 reject the "m=" line associated with that port, by setting the port 1903 number value to zero. After that, no "m=" line would contain the 1904 port number value which is used for the 5-tuple. In addition, it is 1905 unclear what would happen to the ICE candidates associated with the 1906 "m=" line, as they are also used for the 5-tuple. 1908 A.4. B2BUA And Proxy Interoperability 1910 Some back to back user agents may be configured in a mode where if 1911 the incoming call leg contains an SDP attribute the B2BUA does not 1912 understand, the B2BUS still generates that SDP attribute in the Offer 1913 for the outgoing call leg. Consider an B2BUA that did not understand 1914 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 1915 Further assume that the B2BUA was configured to tear down any call 1916 where it did not see any RTCP for 5 minutes. In this cases, if the 1917 B2BUA received an Offer like: 1919 SDP Offer 1921 v=0 1922 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1923 s= 1924 c=IN IP4 atlanta.example.com 1925 t=0 0 1926 m=audio 49170 RTP/AVP 0 1927 a=rtcp:53020 1929 It would be looking for RTCP on port 49172 but would not see any 1930 because the RTCP would be on port 53020 and after five minutes, it 1931 would tear down the call. Similarly, an SBC that did not understand 1932 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 1933 wrong port and tear down the call. It is worth noting that a B2BUA 1934 that generated an Offer with capabilities it does not understand is 1935 not compliant with the specifications. 1937 A.4.1. Traffic Policing 1939 Sometimes intermediaries do not act as B2BUA, in the sense that they 1940 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 1941 however, they may use SDP information (e.g. IP address and port) in 1942 order to control traffic gating functions, and to set traffic 1943 policing rules. There might be rules which will trigger a session to 1944 be terminated in case media is not sent or received on the ports 1945 retrieved from the SDP. This typically occurs once the session is 1946 already established and ongoing. 1948 A.4.2. Bandwidth Allocation 1950 Sometimes intermediaries do not act as B2BUA, in the sense that they 1951 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 1952 however, they may use SDP information (e.g. codecs and media types) 1953 in order to control bandwidth allocation functions. The bandwidth 1954 allocation is done per "m=" line, which means that it might not be 1955 enough if media associated with all "m=" lines try to use that 1956 bandwidth. That may either simply lead to bad user experience, or to 1957 termination of the call. 1959 A.5. Candidate Gathering 1961 When using ICE, an candidate needs to be gathered for each port. 1962 This takes approximately 20 ms extra for each extra "m=" line due to 1963 the NAT pacing requirements. All of this gather can be overlapped 1964 with other things while the page is loading to minimize the impact. 1965 If the client only wants to generate TURN or STUN ICE candidates for 1966 one of the "m=" lines and then use trickle ICE 1967 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 1968 the rest of the "m=" lines, it MAY do that and will not need any 1969 additional gathering time. 1971 Some people have suggested a TURN extension to get a bunch of TURN 1972 allocation at once. This would only provide a single STUN result so 1973 in cases where the other end did not support BUNDLE, may cause more 1974 use of the TURN server but would be quick in the cases where both 1975 sides supported BUNDLE and would fall back to a successful call in 1976 the other cases. 1978 Authors' Addresses 1979 Christer Holmberg 1980 Ericsson 1981 Hirsalantie 11 1982 Jorvas 02420 1983 Finland 1985 Email: christer.holmberg@ericsson.com 1987 Harald Tveit Alvestrand 1988 Google 1989 Kungsbron 2 1990 Stockholm 11122 1991 Sweden 1993 Email: harald@alvestrand.no 1995 Cullen Jennings 1996 Cisco 1997 400 3rd Avenue SW, Suite 350 1998 Calgary, AB T2P 4H2 1999 Canada 2001 Email: fluffy@iii.ca