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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 14, 2015 C. Jennings 7 Cisco 8 September 10, 2014 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-10.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 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on March 14, 2015. 47 Copyright Notice 49 Copyright (c) 2014 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6 68 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 6 69 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 7 71 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 74 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 7.2. Connection Data (c=) . . . . . . . . . . . . . . . . . . 8 76 7.3. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 8 77 7.4. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 8 78 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 8 79 8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 80 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 9 81 8.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 9 82 8.2.2. Request offerer BUNDLE address selection . . . . . . 10 83 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 10 84 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 85 8.3.2. Answerer Selection of Offerer Bundle Address . . . . 11 86 8.3.3. Answerer Selection of Answerer BUNDLE Address . . . . 12 87 8.3.4. Moving A Media Description Out Of A BUNDLE Group . . 12 88 8.3.5. Rejecting A Media Description In A BUNDLE Group . . . 12 89 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 13 90 8.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 13 91 8.4.2. Bundle Address Synchronization (BAS) . . . . . . . . 13 92 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 14 93 8.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 94 8.5.2. Request a new offerer BUNDLE address . . . . . . . . 15 95 8.5.3. Adding a media description to a BUNDLE group . . . . 15 96 8.5.4. Moving A Media Description Out Of A BUNDLE Group . . 16 97 8.5.5. Disabling A Media Description In A BUNDLE Group . . . 16 98 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 16 99 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 16 100 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 101 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 17 102 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 17 103 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 17 104 10.1.2. Payload Type (PT) Value Re-usage . . . . . . . . . . 18 105 10.2. Associating RTP/RTCP Packets With Correct SDP Media 106 Description . . . . . . . . . . . . . . . . . . . . . . 18 107 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 19 108 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 19 109 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 19 110 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 21 111 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 21 112 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 21 113 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 21 114 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 22 115 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 22 116 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 22 117 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 22 118 12. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 22 119 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 120 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 22 121 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 122 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 23 123 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 23 124 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 125 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 23 126 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 23 127 12.7. New text replacing section 8.4 (6th paragraph) of RFC 128 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 129 13. RTP/RTCP extensions for mid value transport . . . . . . . . . 24 130 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 24 131 13.2. RTP MID SDES Item . . . . . . . . . . . . . . . . . . . 25 132 13.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 25 133 13.4. IANA Considerations . . . . . . . . . . . . . . . . . . 25 134 14. Security Considerations . . . . . . . . . . . . . . . . . . . 26 135 15. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 26 136 15.1. Example: Bundle Address Selection . . . . . . . . . . . 26 137 15.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 28 138 15.3. Example: Offerer Adds A Media Description To A BUNDLE 139 Group . . . . . . . . . . . . . . . . . . . . . . . . . 29 140 15.4. Example: Offerer Moves A Media Description Out Of A 141 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 31 142 15.5. Example: Offerer Disables A Media Description Within A 143 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 33 144 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 145 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35 146 18. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 35 147 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 38 148 19.1. Normative References . . . . . . . . . . . . . . . . . . 38 149 19.2. Informative References . . . . . . . . . . . . . . . . . 38 150 Appendix A. Design Considerations . . . . . . . . . . . . . . . 39 151 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 39 152 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 40 153 A.3. Usage of port number value zero . . . . . . . . . . . . . 41 154 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 41 155 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 42 156 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 42 157 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 43 158 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 160 1. Introduction 162 In the IETF RTCWEB WG, a need to use a single 5-tuple for sending and 163 receiving media associated with multiple SDP media descriptions ("m=" 164 lines) has been identified. This would e.g. allow the usage of a 165 single set of Interactive Connectivity Establishment (ICE) [RFC5245] 166 candidates for multiple media descriptions. 168 This specification defines a new SDP Grouping Framework [RFC5888] 169 extension , 'BUNDLE'. The extension can be used with the Session 170 Description Protocol (SDP) Offer/Answer mechanism [RFC3264] to 171 negotiate the usage of a single 5-tuple for sending and receiving 172 media associated with multiple SDP media descriptions ("m="). This 173 is referred to as bundled media. This specification also defines a 174 new SDP attribute, 'bundle-only', which can be used to request that 175 specific media is only used if bundled. 177 The offerer and answerer [RFC3264] use the BUNDLE extension to 178 negotiate the 5-tuples (BUNDLE addresses), one for the offerer 179 (offerer BUNDLE address) and one for the answerer (answerer BUNDLE 180 address) to be used for the bundled media associated with a BUNDLE 181 group. 183 Once the offerer and the answerer have negotiated a BUNDLE group, and 184 the associated BUNDLE addresses, each endpoint can assign its BUNDLE 185 address to each "m=" line within, and use the address to send and 186 receive all media associated with, the BUNDLE group. 188 NOTE: As defined in RFC 4566 [RFC4566], the semantics of assigning 189 the same port value to multiple "m=" lines are undefined, and there 190 is no grouping defined by such means. Instead, an explicit grouping 191 mechanism needs to be used to express the intended semantics. This 192 specification provides such an extension. 194 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 195 [RFC3264]. The update allows an answerer to assign a non-zero port 196 value to an "m=" line in an SDP answer, even if the "m=" line in the 197 associated SDP offer contained a zero port value. 199 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 200 address MUST only be associated with a single BUNDLE group. 202 The procedures in this specification apply independently to a given 203 BUNDLE group. 205 All Real-time Transport Protocol (RTP) [RFC3550] based media flows 206 associated with a single BUNDLE group belong to a single RTP session 207 [RFC3550]. 209 The BUNDLE extension is backward compatible. Endpoints that do not 210 support the extension are expected to generate offers and answers 211 without an SDP 'group:BUNDLE' attribute, and are expected to assign a 212 unique address to each "m=" line within an offer and answer, 213 according to the procedures in [RFC4566] and [RFC3264] 215 2. Terminology 217 5-tuple: A collection of the following values: source address, source 218 port, destination address, destination port and protocol. 220 Unique address: An IP address and IP port combination that is 221 assigned to only one "m=" line in an offer or answer. 223 Shared address: An IP address and IP port combination that is 224 assigned to multiple "m=" lines within an offer or answer. 226 Offerer suggested BUNDLE mid: The first mid value in a given SDP 227 'group:BUNDLE' attribute mid list in an offer. 229 Answerer selected BUNDLE mid: The first mid value in a given SDP 230 'group:BUNDLE' attribute mid list in an answer. 232 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 233 and IP port combination used by an offerer to receive all media 234 associated with each "m=" line within the BUNDLE group. 236 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 237 and IP port combination used by an answerer to receive all media 238 associated with each "m=" line within the BUNDLE group. 240 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 241 exchange, for which each endpoint use a single 5-tuple is to send and 242 receive media. Each endpoint uses its BUNDLE address, associated 243 with the BUNDLE group, to send and receive the media. 245 Bundled "m=" line: An "m=" line, which SDP 'mid' attribute value is 246 placed in a SDP 'group:BUNDLE' attribute mid value list in an offer 247 or answer. 249 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 250 'bundle-only' attribute. 252 Bundled media: All media associated with a given BUNDLE group. 254 Initial offer: The first offer, within an SDP session, in which the 255 offerer indicates that it wants to create a given BUNDLE group. 257 Subsequent offer: An offer which contains a BUNDLE group that has 258 been created as part of a previous SDP Offer/Answer exchange. 260 3. Conventions 262 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 263 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 264 document are to be interpreted as described in BCP 14, RFC 2119 265 [RFC2119]. 267 4. Applicability Statement 269 The mechanism in this specification only applies to the Session 270 Description Protocol (SDP) [RFC4566], when used together with the SDP 271 Offer/Answer mechanism [RFC3264]. 273 5. SDP Grouping Framework BUNDLE Extension 275 5.1. General 277 This section defines a new SDP Grouping Framework extension 278 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the 279 Session Description Protocol (SDP) Offer/Answer mechanism to 280 negotiate the usage of a single 5-tuple for sending and receiving 281 media, referred to as bundled media, associated with multiple SDP 282 media descriptions ("m=" lines). Within a successfully created 283 BUNDLE group, media described with "m=" lines associated with the 284 BUNDLE group will be sent and received using a single 5-tuple. 286 The BUNDLE extension is indicated using an SDP 'group' attribute with 287 a "BUNDLE" semantics value [RFC5888]. An SDP "mid" attribute is 288 assigned to each bundled "m=" line, and the "mid" attribute value is 289 listed in the 'group:BUNDLE' attribute mid value list. Each "m=" 290 line, which mid value is listed in the mid value list, is associated 291 with a given BUNDLE group. 293 SDP bodies can contain multiple BUNDLE groups. Any given bundled 294 "m=" line MUST NOT be associated with more than one BUNDLE group. 296 [Section 8] defines the detailed SDP Offer/Answer procedures for the 297 BUNDLE extension. 299 6. SDP 'bundle-only' Attribute 301 6.1. General 303 This section defines a new SDP media-level attribute [RFC4566], 304 'bundle-only'. 306 The 'bundle-only' attribute can be associated with a bundled "m=" 307 line in an offer, to request that the answerer only accepts the "m=" 308 line if the answerer keeps the "m=" line within the associated BUNDLE 309 group. 311 In order to ensure that an answerer that does not supports the BUNDLE 312 extension always rejects a 'bundle-only' "m=" line, the offerer can 313 assign a zero port value to the "m=" line. According to [RFC4566] an 314 answerer will reject such "m=" line. 316 The usage of the 'bundle-only' attribute is only defined for a 317 bundled "m=" line within an offer. Other usage is unspecified. 319 [Section 8] defines the detailed SDP Offer/Answer procedures for the 320 'bundle-only' attribute. 322 6.2. Syntax 324 This section defines the Augmented Backus-Naur Form (ABNF) [RFC5234] 325 for the SDP 'bundle-only' attribute, based on the SDP [RFC4566] 326 grammar. 328 attribute =/ bundle-only-attribute 330 bundle-only-attribute = "bundle-only" 332 7. SDP Information Considerations 334 7.1. General 336 This section describes restrictions associated with the usage of SDP 337 parameters within a BUNDLE group. It also describes, when parameter 338 and attribute values have been assigned to each bundled "m=" line, 339 how to calculate a value for the whole BUNDLE group. 341 7.2. Connection Data (c=) 343 The "c=" line nettype value [RFC4566] assigned to a bundled "m=" line 344 MUST be 'IN'. 346 The "c=" line addrtype value [RFC4566] assigned to a bundled "m=" 347 line MUST be 'IP4' or 'IP6'. The same value MUST be assigned to each 348 "m=" line. 350 NOTE: Extensions to this specification can specify usage of the 351 BUNDLE mechanism for other nettype and addrtype values than the ones 352 listed above. 354 7.3. Bandwidth (b=) 356 The proposed bandwidth for a bundled "m=" line SHOULD be calculated 357 in the same way as for a non-bundled "m=" line. 359 The total proposed bandwidth for a BUNDLE group is the sum of the 360 proposed bandwidth for each bundled "m=" line. 362 The total proposed bandwidth for an offer or answer is the sum of the 363 proposed bandwidth for each "m=" line (bundled and non-bundled) 364 within the offer or answer. 366 7.4. Attributes (a=) 368 An offerer and answerer MUST use the rules and restrictions defined 369 in [I-D.mmusic-sdp-mux-attributes] for when associating SDP 370 attributes with bundled "m=" lines. 372 8. SDP Offer/Answer Procedures 374 8.1. General 376 This section describes the SDP Offer/Answer [RFC3264] procedures for: 378 o Negotiating and creating of a BUNDLE group; 379 o Selecting the BUNDLE addresses (offerer BUNDLE address and 380 answerer BUNDLE address); 382 o Adding an "m=" line to a BUNDLE group; 384 o Moving an "m=" line out of a BUNDLE group; and 386 o Disabling an "m=" line within a BUNDLE group. 388 The generic rules and procedures defined in [RFC3264] and [RFC5888] 389 also apply to the BUNDLE extension. For example, if an offer is 390 rejected by the answerer, the previously negotiated SDP parameters 391 and characteristics (including those associated with a BUNDLE group) 392 apply. Hence, if an offerer generates an offer in which the offerer 393 wants to create a BUNDLE group, and the answerer rejects the offer, 394 the BUNDLE group is not created. 396 The procedures in this section are independent of the media type or 397 transport protocol represented by a bundled "m=" line. [Section 10] 398 defines additional considerations for RTP based media. [Section 6] 399 defines additional considerations for the usage of the SDP 'bundle- 400 only' attribute. [Section 11] defines additional considerations for 401 the usage of Interactive Connectivity Establishment (ICE) mechanism 402 [RFC5245]. 404 The offerer and answerer MUST follow the rules and restrictions 405 defined in [Section 7] when creating offers and answers. 407 8.2. Generating the Initial SDP Offer 409 8.2.1. General 411 When an offerer generates an initial offer, in order to create a 412 BUNDLE group, it MUST: 414 o Assign a unique address to each "m=" line within the offer, 415 following the procedures in [RFC3264]; 417 o Assign an SDP 'group:BUNDLE' attribute to the offer; 419 o Place the SDP 'mid' attribute value [RFC5888] of each bundled "m=" 420 line to the SDP 'group:BUNDLE' attribute mid value list; and 422 o Indicate which unique address the offerer wants the answerer to 423 select as the offerer BUNDLE address [Section 8.2.2]. 425 If the offerer wants to request that the answerer accepts a given 426 "m=" line only if the the answerer keeps the "m=" line within the 427 BUNDLE group, the offerer MUST: 429 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 430 "m=" line; and 432 o Assign a zero port value to the "m=" line. 434 NOTE: If the offerer assigns a zero port value to an "m=" line, but 435 does not also associate an SDP 'bundle-only' attribute with the "m=" 436 line, it is an indication that the offerer wants to disable the "m=" 437 line [Section 8.5.5]. 439 [Section 15.1] shows an example of an initial offer. 441 8.2.2. Request offerer BUNDLE address selection 443 In the offer, the address assigned to the "m=" line associated with 444 the offerer suggested BUNDLE mid indicates the address that the 445 offerer wants the answer to select as the offerer BUNDLE address 446 [Section 8.3.2]. 448 8.3. Generating the SDP Answer 450 8.3.1. General 452 When an answerer generates an answer, which contains a BUNDLE group, 453 the following general SDP grouping framework restrictions, defined in 454 [RFC5888], also apply to the BUNDLE group: 456 o The answerer MUST NOT include a BUNDLE group in the answer, unless 457 the offerer requested the BUNDLE group to be created in the 458 associated offer; and 460 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 461 unless the offerer requested to "m=" line to be within a BUNDLE 462 group in the associated offer. 464 If the answer contains a BUNDLE group, the answerer MUST: 466 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 468 o Select an Answerer BUNDLE Address [Section 8.3.3]; 470 The answerer is allowed to select a new Answerer BUNDLE address each 471 time it generates an answer to an offer. 473 If the answerer does not want to keep an "m=" line within a BUNDLE 474 group, it MUST: 476 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 478 o Reject the "m=" line [Section 8.3.5]; 480 If a bundled "m=" line in an offer has an associated SDP 'bundle- 481 only' attribute, and if the answerer keeps the "m=" line within the 482 BUNDLE group, the answerer MUST process the "m=" line as any other 483 bundled "m=" line in the offer. The answerer MUST NOT include a 484 'bundle-only' attribute in an answer. 486 NOTE: If a bundled "m=" line in an offer contains a port zero value, 487 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 488 is an indication that the offerer wants to disable the "m=" line 489 [Section 8.5.5]. 491 8.3.2. Answerer Selection of Offerer Bundle Address 493 In an offer, the address (unique or shared) assigned to the bundled 494 "m=" line associated with the offerer suggested BUNDLE mid indicates 495 the address that the offerer wants the answer to select as the 496 offerer BUNDLE address [Section 8.2.2]. The answerer MUST check 497 whether the "m=" line fulfills the following criteria: 499 o The answerer will not move the "m=" line out of the BUNDLE group 500 [Section 8.3.4]; 502 o The answerer will not reject the "m=" line [Section 8.3.5]; and 504 o The "m=" line does not contain a zero port value. 506 If all of the criteria above is fulfilled, the answerer MUST select 507 the address associated with the "m=" line as the offerer BUNDLE 508 address. In the answer, the answerer selected BUNDLE mid represents 509 the "m=" line, and the address associated with the "m=" line in the 510 offer becomes the offerer BUNDLE address. 512 If all of the criteria is not fulfilled, the answerer MUST select the 513 next mid value in the mid list, and perform the same criteria check 514 for the "m=" line associated with that mid value. If there are no 515 more mid values in the mid list, the answerer MUST NOT create the 516 BUNDLE group. 518 [Section 15.1] shows an example of an offerer BUNDLE address 519 selection. 521 8.3.3. Answerer Selection of Answerer BUNDLE Address 523 When the answerer selects a BUNDLE address for itself, referred to as 524 the answerer BUNDLE address, it MUST assign the address to each 525 bundled "m=" line within the created BUNDLE group in the answer. 527 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 528 line that is not within the BUNDLE group, or to an "m=" line that is 529 within another BUNDLE group. 531 [Section 15.1] shows an example of an answerer BUNDLE address 532 selection. 534 8.3.4. Moving A Media Description Out Of A BUNDLE Group 536 When an answerer moves a "m=" line out of a BUNDLE group, it assigns 537 an address to the "m=" line in the answer based on the following 538 rules: 540 o In the associated offer, if the "m=" line contains a shared 541 address (e.g. a previously selected offerer BUNDLE address), the 542 answerer MUST reject the moved "m=" line [Section 8.3.5]; 544 o In the associated offer, if the "m=" line contains a unique 545 address, the answerer MUST assign a unique address to the "m=" 546 line in the answer; or 548 o In the associated offer, if the "m=" line contains an SDP 'bundle- 549 only' attribute the answerer MUST reject the "m=" line 550 [Section 8.3.5]. 552 In addition, in either case above, the answerer MUST NOT include a 553 mid value, associated with the moved "m=" line, in the SDP 554 'group:BUNDLE' attribute mid list associated with the BUNDLE group. 556 8.3.5. Rejecting A Media Description In A BUNDLE Group 558 When an answerer rejects an "m=" line, it MUST assign an address with 559 a zero port value to the "m=" line in the answer, according to the 560 procedures in [RFC4566]. 562 In addition, the answerer MUST NOT include a mid value, associated 563 with the rejected "m=" line, in the SDP 'group:BUNDLE' attribute mid 564 list associated with the BUNDLE group. 566 8.4. Offerer Processing of the SDP Answer 568 8.4.1. General 570 When an offerer receives an answer, if the answer contains a BUNDLE 571 group, the offerer MUST check that any bundled "m=" line in the 572 answer was indicated as bundled in the associated offer. If there is 573 no mismatch, the offerer MUST apply the offerer BUNDLE address, 574 selected by the answerer [Section 8.3.2], to each bundled "m=" line. 575 The offerer MUST assign the address to each bundled "m=" line 576 (excluding a bundled "m=" line added to a BUNDLE group, to which the 577 offerer MAY assign a unique address [Section 8.5.3]) in any 578 subsequent offer. 580 NOTE: As the answerer might reject one or more bundled "m=" lines, or 581 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 582 line in the offer might not be indicated as bundled in the answer. 584 If the answer does not contain a BUNDLE group, the offerer MUST 585 process the answer as a normal answer. 587 8.4.2. Bundle Address Synchronization (BAS) 589 When an offerer receives an answer, if the answer contains a BUNDLE 590 group, the offerer MUST check whether the offerer BUNDLE address, 591 selected by the answerer [Section 8.3.2], matches was assigned to 592 each bundled "m=" line (excluding any bundled "m=" line that was 593 rejected, or moved out of the BUNDLE group, by the answer) in the 594 associated offer. If there is a mismatch, the offerer SHOULD as soon 595 as possible generate a subsequent offer, in which it assigns the 596 offerer BUNDLE address to each bundled "m=" line. Such offer is 597 referred to as a Bundle Address Synchronization (BAS) offer. 599 A BAS offer is typically sent in the following scenarios: 601 o The offerer receives an answer to an initial offer, as the bundled 602 "m=" lines in the initial offer always contain unique addresses 603 [Section 8.2]; or 605 o The offerer receives an answer to an offer, in which a new bundled 606 "m=" line has been added to the BUNDLE group [Section 8.5.3], and 607 the offerer assigned a unique address to the bundled "m=" line in 608 the offer. 610 The offerer is allowed to modify any SDP parameter in the BAS offer. 612 NOTE: It is important that the BAS offer gets accepted by the 613 answerer. For that reason the offerer needs to consider the 614 necessity to modify SDP parameters in the BAS offer, in such a way 615 that could trigger the answerer to reject the BAS offer. Disabling 616 "m=" lines, or reducing the number of codecs, in a BAS offer is 617 considered to have a low risk of being rejected. 619 NOTE: The main purpose of the BAS offer is to ensure that 620 intermediaries, that might not support the BUNDLE extension, have 621 correct information regarding the address is going to be used to 622 transport the bundled media. 624 [Section 15.1] shows an example of a BAS offer. 626 8.5. Modifying the Session 628 8.5.1. General 630 When an offerer generates a subsequent offer, it MUST assign the 631 previously selected offerer BUNDLE address [Section 8.3.2], to each 632 bundled "m=" line (including any bundle-only "m=" line), with the 633 following exceptions: 635 o The offerer wants to request the answerer to select a new offerer 636 BUNDLE address [Section 8.5.2]; 638 o The offerer wants to add a bundled "m=" line to the BUNDLE group 639 [Section 8.5.3]; 641 o The offerer wants to move a bundled "m=" line out of the BUNDLE 642 group [Section 8.5.4]; or 644 o The offerer wants to disable the bundled "m=" line 645 [Section 8.5.5]. 647 In addition, the offerer MUST select an offerer suggested BUNDLE mid 648 [Section 8.2.2], even if the offerer does not want the answerer to 649 select a new offerer BUNDLE address. 651 If the offerer associates an SDP 'bundle-only' attribute with a 652 bundled "m=" line in the subsequent offer, if MUST assign the offerer 653 BUNDLE address to the "m=" line. The offerer MUST NOT assign a 654 unique address, or a zero port value, to a bundle-only "m=" line in a 655 subsequent offer. 657 NOTE: The offerer can associate an SDP 'bundle-only' attribute with a 658 bundled "m=" line in a subsequent offer, even if the offerer did not 659 associate a 'bundle-only' attribute with the same "m=" line in a 660 previous offer. 662 8.5.2. Request a new offerer BUNDLE address 664 When an offerer generates an offer, in which it wants the answerer to 665 select a new offerer BUNDLE address [Section 8.2.2], the offerer 666 MUST: 668 o Assign a unique address, which the offerer wants the answerer to 669 select as the offerer BUNDLE address, to a bundled "m=" line 670 (added to the BUNDLE group in a previous offer/answer transaction, 671 or requested to be added to the BUNDLE group in the current 672 offer); and 674 o Indicate that the offerer wants the answerer to select the unique 675 address as the offerer BUNDLE address [Section 8.2.2] 677 NOTE: The offerer can assign a unique address to each bundled "m=" 678 line in the offer, or it can assign the previously negotiated offerer 679 BUNDLE address to each "m=" line (except the "m=" line to which it 680 assigns the unique address that it wants the answerer to select as 681 the new offerer BUNDLE address). 683 8.5.3. Adding a media description to a BUNDLE group 685 When an offerer generates an offer, in which it wants to add a 686 bundled "m=" line to BUNDLE group, the offerer MUST: 688 o Assign a unique address (excluding bundle-only "m=" lines), or the 689 offerer BUNDLE address (selected by the answerer in a previous 690 offer/answer transaction), to the "m=" line; 692 o Place the SDP 'mid' attribute value associated with the "m=" line 693 in the SDP 'group:BUNDLE' attribute mid list associated with the 694 BUNDLE group [Section 8.2.2]. 696 NOTE: Adding a unique address to the "m=" line allows the answerer to 697 move the "m=" line out of the BUNDLE group [Section 8.3.4], without 698 having to reject the "m=" line. 700 If the offerer wants the answerer to select the address associated 701 with the added "m=" line as the new offerer BUNDLE address, the 702 offerer suggested BUNDLE mid MUST represent the added "m=" line 703 [Section 8.2.2]. 705 If the offerer associates an SDP 'bundle-only' attribute with the 706 added "m=" line, the offerer MUST assign the offerer BUNDLE address 707 (selected by the answerer in a previous offer/answer transaction) to 708 the "m=" line. 710 [Section 15.3] shows an example where an offerer sends an offer in 711 order to add a bundled "m=" line to a BUNDLE group. 713 8.5.4. Moving A Media Description Out Of A BUNDLE Group 715 When an offerer generates an offer, in which it wants to move a 716 bundled "m=" line (added to the BUNDLE group in a previous offer/ 717 answer transaction), the offerer: 719 o MUST assign a unique address to the "m=" line; 721 o MUST NOT place a mid value associated with the "m=" line in the 722 SDP 'group:BUNDLE' attribute mid list associated with the BUNDLE 723 group; and 725 o MUST NOT associate an SDP 'bundle-only' attribute with the "m=" 726 line. 728 [Section 15.4] shows an example of an offer for moving an "m=" line 729 out of a BUNDLE group. 731 8.5.5. Disabling A Media Description In A BUNDLE Group 733 When an offerer generates an offer, in which it wants to disable a 734 bundled "m=" line (added to the BUNDLE group in a previous offer/ 735 answer transaction), the offerer: 737 o MUST assign an address with a zero port value to the "m=" line, 738 following the procedures in [RFC4566]; 740 o MUST NOT place a mid value associated with the "m=" line in the 741 SDP 'group:BUNDLE' attribute mid list associated with the BUNDLE 742 group; and 744 o MUST NOT associate an SDP 'bundle-only' attribute with the "m=" 745 line. 747 [Section 15.5] shows an example of an offer for disabling an "m=" 748 line within a BUNDLE group. 750 9. Protocol Identification 752 9.1. General 754 If bundled "m=" lines represent different transport protocols, there 755 MUST exist a publically available specification which describes a 756 mechanism, for this specific transport protocol combination, how to 757 associate a received packet with the correct transport protocol. 759 In addition, if a received packet can be associated with more than 760 one bundled "m=" line, there MUST exist a publically available 761 specification which describes a mechanism how to associated the 762 received packet with the correct "m=" line. 764 9.2. STUN, DTLS, SRTP 766 Section 5.1.2 of [RFC5764] describes a mechanism how to identify the 767 protocol among the STUN, DTLS and SRTP protocols (in any 768 combination). If an offer or answerer in offers or answers include 769 bundled "m=" lines that represent these protocols, the offerer or 770 answerer MUST support the mechanism described in [RFC5764], and no 771 explicit negotiation is required in order to indicate support and 772 usage of the mechanism. 774 [RFC5764] does not describe how to identify different protocols 775 transported on DTLS, only how to identify the DTLS protocol itself. 776 If multiple protocols are transported on DTLS, there MUST exist a 777 specification describing a mechanism how to identify each individual 778 protocol. In addition, if a received DTLS packet can be associated 779 with more than one "m=" line, there MUST exist a specification which 780 describes a mechanism how to associate the received DTLS packet with 781 the correct "m=" line. 783 [Section 10.2] describes how to associate a received (S)RTP packet 784 with the correct "m=" line. 786 10. RTP Considerations 788 10.1. Single RTP Session 790 10.1.1. General 792 All RTP-based media within a single BUNDLE group belong to a single 793 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 794 sessions, one per BUNDLE group. 796 Since a single RTP session is used for each bundle group, all "m=" 797 lines representing RTP-based media in a bundle group will share a 798 single SSRC numbering space [RFC3550]. 800 The following rules and restrictions apply for a single RTP session: 802 o A specific payload type value can be used in multiple bundled "m=" 803 lines if each codec associated with the payload type number shares 804 an identical codec configuration [Section 10.1.2]. 806 o The "proto" value in each bundled "m=" line MUST be identical 807 (e.g. RTP/AVPF). 809 o A given SSRC SHOULD NOT transmit RTP packets using payload types 810 that originates from different bundled "m=" lines. 812 NOTE: The last bullet above is to avoid sending multiple media types 813 from the same SSRC. If transmission of multiple media types are done 814 with time overlap RTP and RTCP fails to function. Even if done in 815 proper sequence this causes RTP Timestamp rate switching issues [ref 816 to draft-ietf-avtext-multiple-clock-rates]. 818 10.1.2. Payload Type (PT) Value Re-usage 820 Multiple bundled "m=" lines might represent RTP based media. As all 821 RTP based media associated with a BUNDLE group belong to the same RTP 822 session, in order for a given payload type value to used inside more 823 than one bundled "m=" line, all codecs associated with the payload 824 type numbers MUST share an identical codec configuration. This means 825 that the codecs MUST share the same media type, encoding name, clock 826 rate and any parameter that can affect the codec configuration and 827 packetization. [I-D.mmusic-sdp-mux-attributes] lists SDP attributes, 828 which attribute values must be identical for all codecs that use the 829 same payload type value. 831 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 833 In general, there are multiple mechanisms that can be used by an 834 endpoint in order to associate received RTP/RTCP packets with the 835 bundled "m=" line representing the RTP packets. Such mechanisms 836 include using the local address:port combination on which the RTP 837 packets are received, the payload type value carried inside the RTP 838 packets, the SSRC values carried inside the RTP packets, and other 839 "m=" line specific information carried inside the RTP packets. 841 As all RTP/RTCP packets associated with a BUNDLE group are sent and 842 received using the same 5-tuple, the local address:port combination 843 cannot be used to associate received RTP packets with the correct 844 "m=" line. 846 As described in [Section 10.1.2], the same payload type value might 847 be used inside RTP packets described by multiple "m=" lines. In such 848 cases, the payload type value cannot be used to associate received 849 RTP packets with the correct "m=" line. 851 An offerer and answerer can in an offer and answer inform each other 852 which SSRC values they will use inside sent RTP/RTCP packets by, by 853 assigning an SDP 'ssrc' attribute [RFC5576] to each bundled "m=" line 854 which contains a payload type value that is also used inside another 855 bundled "m=" line. As the SSRC values will be carried inside the 856 RTP/RTCP packets, the offerer and answerer can then use that 857 information to associate received RTP packets with the correct "m=" 858 line. However, an offerer will not know which SSRC values the 859 answerer will use until it has received the answer providing that 860 information. Due to this, before the offerer has received the 861 answer, the offerer will not be able to associate received RTP/RTCP 862 packets with the correct "m=" line using the SSRC values. 864 In order for an offerer and answerer to always be able to associate 865 received RTP and RTCP packets with the correct "m=" line, an offerer 866 and answerer using the BUNDLE extension MUST use the mechanism 867 defined in [Section 13], where the remote endpoint inserts the SDP 868 'mid' attribute value of an "m=" line in RTP and RTCP packets 869 associated with that "m=" line. 871 10.3. RTP/RTCP Multiplexing 873 10.3.1. General 875 When a BUNDLE group, which contains RTP based media, is created, the 876 offerer and answerer MUST negotiate whether to enable RTP/RTCP 877 multiplexing for the RTP based media associated with the BUNDLE group 878 [RFC5761]. 880 If RTP/RTCP multiplexing is not enabled, separate 5-tuples will be 881 used for sending and receiving the RTP packets and the RTCP packets. 883 10.3.2. SDP Offer/Answer Procedures 885 10.3.2.1. General 887 This section describes how an offerer and answerer can use the SDP 888 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 889 to negotiate usage of RTP/RTCP multiplexing for RTP based associated 890 with a BUNDLE group. 892 10.3.2.2. Generating the Initial SDP Offer 894 When an offerer generates an initial offer, if the offerer wants to 895 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 896 offerer MUST assign an SDP 'rtcp-mux' attribute [RFC5761] to each 897 bundled "m=" line (including any bundle-only "m=" line) in the offer. 898 In addition, the offerer MUST assign an SDP 'rtcp' attribute 899 [RFC3605] to each bundled "m=" line (including any bundle-only "m=" 900 line), with an attribute value that is identical to the port value 901 assigned to the "m=" line itself, in the offer. 903 If the offerer does not want to negotiate usage of RTP/RTCP 904 multiplexing, it MUST NOT assign the SDP attributes above to any 905 bundled "m=" line. 907 10.3.2.3. Generating the SDP Answer 909 When an answerer generates an answer, if the offerer indicated 910 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 911 the associated offer, the answerer MUST either accept or reject the 912 usage of RTP/RTCP multiplexing in the answer. 914 If the answerer accepts usage of RTP/RTCP multiplexing within the 915 BUNDLE group, it MUST assign an SDP 'rtcp-mux' attribute to each 916 bundled "m=" line in the answer. The answerer MUST NOT assign an SDP 917 'rtcp' attribute to any bundled "m=" line in the answer. 919 If the answerer rejects usage of RTP/RTCP multiplexing within the 920 BUNDLE group, it MUST NOT assign an SDP 'rtcp-mux' or SDP 'rtcp' 921 attribute to any bundled "m=" line in the answer. 923 If the usage of RTP/RTCP multiplexing has been negotiated in a 924 previous offer/answer transaction, and the offerer indicates that it 925 wants to continue using RTP/RTCP multiplexing in a subsequent offer, 926 the answerer MUST assign an SDP 'rtcp-mux' attribute to each bundled 927 "m=" line in the answer. I.e. the answerer MUST NOT disable the 928 usage of RTP/RTCP multiplexing. 930 10.3.2.4. Offerer Processing of the SDP Answer 932 When the offerer receives an answer, if the answerer accepts the 933 usage of RTP/RTCP multiplexing, by including an SDP 'rtcp-mux' 934 attribute to each bundled "m=" line in the answer [Section 10.3.2.3], 935 the answerer follows the procedures for RTP/RTCP multiplexing defined 936 in [RFC5245]. 938 If the answerer does not accept the usage of RTP/RTCP multiplexing 939 [Section 10.3.2.3], the offerer MUST use separate 5-tuples for RTP 940 and RTCP. 942 10.3.2.5. Modifying the Session 944 When an offerer generates a subsequent offer, if it wants to 945 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or if 946 it wants to continue usage of RTP/RTCP multiplexing (negotiated in a 947 previous offer/answer transaction), it MUST assign SDP 'rtcp-mux' and 948 'rtcp' attributes to each bundled "m=" line (including bundle-only 949 "m=" lines, and a bundled "m=" line that the offerer wants to add to 950 the BUNDLE group), unless the offerer wants to disable or remove the 951 "m=" line from the BUNDLE group. 953 If the offerer does not want to negotiate usage of RTP/RTCP 954 multiplexing within the BUNDLE group, or if it wants to disable usage 955 of RTP/RTCP multiplexing (negotiated in a previous offer/answer 956 transaction), the offerer MUST NOT assign SDP 'rtcp-mux' and 'rtcp' 957 attributes to any bundled "m=" line in the subsequent offer. 959 NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has 960 been negotiated within a BUNDLE group, that the usage is not 961 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 962 answerer need to reserve new IP ports, to be used for sending and 963 receiving RTCP packets. 965 11. ICE Considerations 967 11.1. General 969 This section describes how to use the BUNDLE grouping extension 970 together with the Interactive Connectivity Establishment (ICE) 971 mechanism [RFC5245]. 973 The procedures defined in [RFC5245] also apply to usage of ICE with 974 BUNDLE, with the following exception: 976 o When BUNDLE addresses for a BUNDLE group have been selected for 977 both endpoints, ICE connectivity checks and keep-alives only need 978 to be performed for the whole BUNDLE group, instead of per bundled 979 "m=" line. 981 Support and usage of ICE mechanism together with the BUNDLE extension 982 is OPTIONAL. 984 11.2. SDP Offer/Answer Procedures 986 11.2.1. General 988 When an offerer or answerer assigns a unique address to a bundled 989 "m=" line (excluding bundle-only "m=" lines), it MUST also assign 990 unique ICE candidates [RFC5245] to the "m=" line. 992 When an offerer or answerer assigns a shared address (i.e. a 993 previously selected BUNDLE address) to one or more bundled "m=" line 994 (including bundle-only "m=" lines), and when it assigns an address 995 with a zero port value to one or more bundle-only "m=" lines, it MUST 996 assign identical ICE candidates (referred to as shared ICE 997 candidates) to each of those "m=" lines. 999 11.2.2. Generating the Initial SDP Offer 1001 When an offerer generates an initial offer, it assigns unique or 1002 shared ICE candidates to the bundled "m=" lines, according to 1003 [Section 11.1]. 1005 11.2.3. Generating the SDP Answer 1007 When an answerer generates an answer, which contains a BUNDLE group, 1008 the answerer MUST assign shared ICE candidates to each bundled "m=" 1009 line (including "m=" lines that were indicated as bundle-only in the 1010 associated offer) in the answer. 1012 11.2.4. Offerer Processing of the SDP Answer 1014 When an offerer receives an answer, if the answerer supports and uses 1015 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1016 the ICE candidates, associated with the "m=" line representing the 1017 offerer BUNDLE address (selected by the answerer) to each bundled 1018 "m=" line. 1020 11.2.5. Modifying the Session 1022 When an offerer generates a subsequent offer, it assigns unique or 1023 shared ICE candidates to the bundled "m=" lines, according to 1024 [Section 11.1]. 1026 12. Update to RFC 3264 1028 12.1. General 1030 This section replaces the text of the following sections of RFC 3264: 1032 o Section 5.1 (Unicast Streams). 1034 o Section 8.2 (Removing a Media Stream). 1036 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1038 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1040 For recvonly and sendrecv streams, the port number and address in the 1041 offer indicate where the offerer would like to receive the media 1042 stream. For sendonly RTP streams, the address and port number 1043 indirectly indicate where the offerer wants to receive RTCP reports. 1044 Unless there is an explicit indication otherwise, reports are sent to 1045 the port number one higher than the number indicated. The IP address 1046 and port present in the offer indicate nothing about the source IP 1047 address and source port of RTP and RTCP packets that will be sent by 1048 the offerer. A port number of zero in the offer indicates that the 1049 stream is offered but MUST NOT be used. This has no useful semantics 1050 in an initial offer, but is allowed for reasons of completeness, 1051 since the answer can contain a zero port indicating a rejected stream 1052 (Section 6). Furthermore, existing streams can be terminated by 1053 setting the port to zero (Section 8). In general, a port number of 1054 zero indicates that the media stream is not wanted. 1056 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1058 For recvonly and sendrecv streams, the port number and address in the 1059 offer indicate where the offerer would like to receive the media 1060 stream. For sendonly RTP streams, the address and port number 1061 indirectly indicate where the offerer wants to receive RTCP reports. 1062 Unless there is an explicit indication otherwise, reports are sent to 1063 the port number one higher than the number indicated. The IP address 1064 and port present in the offer indicate nothing about the source IP 1065 address and source port of RTP and RTCP packets that will be sent by 1066 the offerer. A port number of zero in the offer by default indicates 1067 that the stream is offered but MUST NOT be used, but an extension 1068 mechanism might specify different semantics for the usage of a zero 1069 port value. Furthermore, existing streams can be terminated by 1070 setting the port to zero (Section 8). In general, a port number of 1071 zero by default indicates that the media stream is not wanted. 1073 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1075 A stream that is offered with a port of zero MUST be marked with port 1076 zero in the answer. Like the offer, the answer MAY omit all 1077 attributes present previously, and MAY list just a single media 1078 format from amongst those in the offer. 1080 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1082 A stream that is offered with a port of zero MUST by default be 1083 marked with port zero in the answer, unless an extension mechanism, 1084 which specifies semantics for the usage of a non-zero port value, is 1085 used. 1087 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1089 RFC 2543 [10] specified that placing a user on hold was accomplished 1090 by setting the connection address to 0.0.0.0. Its usage for putting 1091 a call on hold is no longer recommended, since it doesn't allow for 1092 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1093 with connection oriented media. However, it can be useful in an 1094 initial offer when the offerer knows it wants to use a particular set 1095 of media streams and formats, but doesn't know the addresses and 1096 ports at the time of the offer. Of course, when used, the port 1097 number MUST NOT be zero, which would specify that the stream has been 1098 disabled. An agent MUST be capable of receiving SDP with a 1099 connection address of 0.0.0.0, in which case it means that neither 1100 RTP nor RTCP should be sent to the peer. 1102 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1104 RFC 2543 [10] specified that placing a user on hold was accomplished 1105 by setting the connection address to 0.0.0.0. Its usage for putting 1106 a call on hold is no longer recommended, since it doesn't allow for 1107 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1108 with connection oriented media. However, it can be useful in an 1109 initial offer when the offerer knows it wants to use a particular set 1110 of media streams and formats, but doesn't know the addresses and 1111 ports at the time of the offer. Of course, when used, the port 1112 number MUST NOT be zero, if it would specify that the stream has been 1113 disabled. However, an extension mechanism might specify different 1114 semantics of the zero port number usage. An agent MUST be capable of 1115 receiving SDP with a connection address of 0.0.0.0, in which case it 1116 means that neither RTP nor RTCP should be sent to the peer. 1118 13. RTP/RTCP extensions for mid value transport 1120 13.1. General 1122 SDP Offerers and Answerers [RFC3264] can assign values, mid values, 1123 to SDP Media Descriptions (m= lines) within SDP Offers and Answers, 1124 using the procedures in [RFC5888]. Each mid value uniquely 1125 references an m= line. 1127 This section defines a new RTP SDES item [RFC3550], 'MID', which is 1128 used to carry mid values within RTCP SDES packets. This section also 1129 defines a new RTP header extension [RFC5285], which can be used to 1130 carry the mid value in RTP packets. 1132 The SDES item and RTP header extension makes is possible for a 1133 receiver to associate received RTCP- and RTP packets with a specific 1134 m= line, to which the receiver has assigned a mid value, even if 1135 those m= lines are part of the same RTP session. The endpoint 1136 informs the remote endpoint about the mid values using the procedures 1137 in [RFC5888], and the remote endpoint then inserts the mid values in 1138 RTCP- and RTP packets sent towards the other endpoint. 1140 NOTE: This text above defines how the mid value is carried in SDP 1141 Offers and Answers. The usage of other signalling protocols for 1142 carrying the mid value is not prevented, but the usage of such 1143 protocols is outside the scope of this document. 1145 The RTP MID SDES item SHOULD be sent in the first few RTCP packets 1146 sent on joining the session, and SHOULD be sent regularly thereafter. 1147 The exact number of RTCP packets in which this SDES item is sent is 1148 intentionally not specified here, as it will depend on the expected 1149 packet loss rate, the RTCP reporting interval, and the allowable 1150 overhead. 1152 The RTP MID header extension SHOULD be included in some RTP packets 1153 at the start of the session and whenever the SSRC changes. It might 1154 also be useful to include the header extension in RTP packets that 1155 comprise random access points in the media (e.g., with video 1156 I-frames). The exact number of RTP packets in which this header 1157 extension is sent is intentionally not specified here, as it will 1158 depend on expected packet loss rate and loss patterns, the overhead 1159 the application can tolerate, and the importance of immediate receipt 1160 of the mid value. 1162 For robustness purpose, endpoints need to be prepared for situations 1163 where the mid value is delayed, and SHOULD NOT terminate sessions in 1164 such cases, as the mid value is likely to arrive soon. 1166 13.2. RTP MID SDES Item 1168 0 1 2 3 1169 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 1170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1171 | MID=TBD | length | mid value ... 1172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1174 The mid value payload is UTF-8 encoded, as in SDP. 1176 13.3. RTP MID Header Extension 1178 The payload, containing the mid value, of the RTP MID header 1179 extension element can be encoded using either the one-byte or two- 1180 byte header [RFC5285]. The mid value payload is UTF-8 encoded, as in 1181 SDP. 1183 13.4. IANA Considerations 1185 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1186 document.] 1188 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1189 identifier value.] 1191 This document adds the MID SDES item to the IANA "RTP SDES item 1192 types" registry as follows: 1194 Value: TBD 1195 Abbrev.: MID 1196 Name: Media Identification 1197 Reference: RFCXXXX 1199 This document defines a new extension URI in the RTP Compact Header 1200 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1201 Parameters registry, according to the following data: 1203 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1204 Description: Media identification 1205 Contact: christer.holmberg@ericsson.com 1206 Reference: RFCXXXX 1208 14. Security Considerations 1210 The security considerations defined in [RFC3264] and [RFC5888] apply 1211 to the BUNDLE extension. 1213 When the BUNDLE extension is used the a single set of security 1214 credentials might be used for all media streams associated with a 1215 BUNDLE group. If the security credentials are compromised, an 1216 attacker will have access to all media content. 1218 15. Examples 1220 15.1. Example: Bundle Address Selection 1222 The example below shows: 1224 o 1. An offer, in which the offerer assigns a unique address to 1225 each bundled "m=" line within the BUNDLE group. 1227 o 2. An answer, in which the answerer selects the offerer BUNDLE 1228 address, and in which selects its own BUNDLE address (the answerer 1229 BUNDLE address) and assigns it each bundled "m=" line within the 1230 BUNDLE group. 1232 o 3. A subsequent offer (BAS offer), which is used to perform a 1233 Bundle Address Synchronization (BAS). 1235 SDP Offer (1) 1237 v=0 1238 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1239 s= 1240 c=IN IP4 atlanta.example.com 1241 t=0 0 1242 a=group:BUNDLE foo bar 1243 m=audio 10000 RTP/AVP 0 8 97 1244 a=mid:foo 1245 b=AS:200 1246 a=rtpmap:0 PCMU/8000 1247 a=rtpmap:8 PCMA/8000 1248 a=rtpmap:97 iLBC/8000 1249 m=video 10002 RTP/AVP 31 32 1250 a=mid:bar 1251 b=AS:1000 1252 a=rtpmap:31 H261/90000 1253 a=rtpmap:32 MPV/90000 1255 SDP Answer (2) 1257 v=0 1258 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1259 s= 1260 c=IN IP4 biloxi.example.com 1261 t=0 0 1262 a=group:BUNDLE foo bar 1263 m=audio 20000 RTP/AVP 0 1264 a=mid:foo 1265 b=AS:200 1266 a=rtpmap:0 PCMU/8000 1267 m=video 20000 RTP/AVP 32 1268 a=mid:bar 1269 b=AS:1000 1270 a=rtpmap:32 MPV/90000 1272 SDP Offer (3) 1274 v=0 1275 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1276 s= 1277 c=IN IP4 atlanta.example.com 1278 t=0 0 1279 a=group:BUNDLE foo bar 1280 m=audio 10000 RTP/AVP 0 8 97 1281 a=mid:foo 1282 b=AS:200 1283 a=rtpmap:0 PCMU/8000 1284 a=rtpmap:8 PCMA/8000 1285 a=rtpmap:97 iLBC/8000 1286 m=video 10000 RTP/AVP 31 32 1287 a=mid:bar 1288 b=AS:1000 1289 a=rtpmap:31 H261/90000 1290 a=rtpmap:32 MPV/90000 1292 15.2. Example: BUNDLE Extension Rejected 1294 The example below shows: 1296 o 1. An offer, in which the offerer assigns a unique address to 1297 each bundled "m=" line within the BUNDLE group. 1299 o 2. An answer, in which the answerer rejects the offered BUNDLE 1300 group, and assigns a unique addresses to each "m=" line (following 1301 normal RFC 3264 procedures). 1303 SDP Offer (1) 1305 v=0 1306 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1307 s= 1308 c=IN IP4 atlanta.example.com 1309 t=0 0 1310 a=group:BUNDLE foo bar 1311 m=audio 10000 RTP/AVP 0 8 97 1312 a=mid:foo 1313 b=AS:200 1314 a=rtpmap:0 PCMU/8000 1315 a=rtpmap:8 PCMA/8000 1316 a=rtpmap:97 iLBC/8000 1317 m=video 10002 RTP/AVP 31 32 1318 a=mid:bar 1319 b=AS:1000 1320 a=rtpmap:31 H261/90000 1321 a=rtpmap:32 MPV/90000 1323 SDP Answer (2) 1325 v=0 1326 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1327 s= 1328 c=IN IP4 biloxi.example.com 1329 t=0 0 1330 m=audio 20000 RTP/AVP 0 1331 b=AS:200 1332 a=rtpmap:0 PCMU/8000 1333 m=video 30000 RTP/AVP 32 1334 b=AS:1000 1335 a=rtpmap:32 MPV/90000 1337 15.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1339 The example below shows: 1341 o 1. An offer, in which the offerer adds a new "m=" line, 1342 represented by the "zen" mid value, to a previously negotiated 1343 BUNDLE group, assigns a unique address to the added "m=" line, and 1344 assigns the previously selected offerer BUNDLE address to each of 1345 the other bundled "m=" lines within the BUNDLE group. 1347 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1348 address to each bundled "m=" line (including the newly added "m=" 1349 line) within the BUNDLE group. 1351 o 3. A subsequent offer (BAS offer), which is used to perform a 1352 Bundle Address Synchronization (BAS). 1354 SDP Offer (1) 1356 v=0 1357 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1358 s= 1359 c=IN IP4 atlanta.example.com 1360 t=0 0 1361 a=group:BUNDLE foo bar zen 1362 m=audio 10000 RTP/AVP 0 8 97 1363 a=mid:foo 1364 b=AS:200 1365 a=rtpmap:0 PCMU/8000 1366 a=rtpmap:8 PCMA/8000 1367 a=rtpmap:97 iLBC/8000 1368 m=video 10000 RTP/AVP 31 32 1369 a=mid:bar 1370 b=AS:1000 1371 a=rtpmap:31 H261/90000 1372 a=rtpmap:32 MPV/90000 1373 m=video 20000 RTP/AVP 66 1374 a=mid:zen 1375 b=AS:1000 1376 a=rtpmap:66 H261/90000 1378 SDP Answer (2) 1380 v=0 1381 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1382 s= 1383 c=IN IP4 biloxi.example.com 1384 t=0 0 1385 a=group:BUNDLE foo bar zen 1386 m=audio 20000 RTP/AVP 0 1387 a=mid:foo 1388 b=AS:200 1389 a=rtpmap:0 PCMU/8000 1390 m=video 20000 RTP/AVP 32 1391 a=mid:bar 1392 b=AS:1000 1393 a=rtpmap:32 MPV/90000 1394 m=video 20000 RTP/AVP 66 1395 a=mid:zen 1396 b=AS:1000 1397 a=rtpmap:66 H261/90000 1399 SDP Offer (3) 1401 v=0 1402 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1403 s= 1404 c=IN IP4 atlanta.example.com 1405 t=0 0 1406 a=group:BUNDLE foo bar zen 1407 m=audio 10000 RTP/AVP 0 8 97 1408 a=mid:foo 1409 b=AS:200 1410 a=rtpmap:0 PCMU/8000 1411 a=rtpmap:8 PCMA/8000 1412 a=rtpmap:97 iLBC/8000 1413 m=video 10000 RTP/AVP 31 32 1414 a=mid:bar 1415 b=AS:1000 1416 a=rtpmap:31 H261/90000 1417 a=rtpmap:32 MPV/90000 1418 m=video 10000 RTP/AVP 66 1419 a=mid:zen 1420 b=AS:1000 1421 a=rtpmap:66 H261/90000 1423 15.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1425 The example below shows: 1427 o 1. An offer, in which the offerer moves a bundled "m=" line out 1428 of a BUNDLE group, assigns a unique address to the moved "m=" 1429 line, and assigns the offerer BUNDLE address to each other bundled 1430 "m=" line within the BUNDLE group. 1432 o 2. An answer, in which the answerer moves the "m=" line out of 1433 the BUNDLE group, assigns unique address to the moved "m=" line, 1434 and assigns the answerer BUNDLE address to each other bundled "m=" 1435 line within the BUNDLE group. 1437 SDP Offer (1) 1439 v=0 1440 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1441 s= 1442 c=IN IP4 atlanta.example.com 1443 t=0 0 1444 a=group:BUNDLE foo bar 1445 m=audio 10000 RTP/AVP 0 8 97 1446 a=mid:foo 1447 b=AS:200 1448 a=rtpmap:0 PCMU/8000 1449 a=rtpmap:8 PCMA/8000 1450 a=rtpmap:97 iLBC/8000 1451 m=video 10000 RTP/AVP 31 32 1452 a=mid:bar 1453 b=AS:1000 1454 a=rtpmap:31 H261/90000 1455 a=rtpmap:32 MPV/90000 1456 m=video 50000 RTP/AVP 66 1457 b=AS:1000 1458 a=rtpmap:66 H261/90000 1460 SDP Answer (2) 1462 v=0 1463 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1464 s= 1465 c=IN IP4 biloxi.example.com 1466 t=0 0 1467 a=group:BUNDLE foo bar 1468 m=audio 20000 RTP/AVP 0 1469 a=mid:foo 1470 b=AS:200 1471 a=rtpmap:0 PCMU/8000 1472 m=video 20000 RTP/AVP 32 1473 a=mid:bar 1474 b=AS:1000 1475 a=rtpmap:32 MPV/90000 1476 m=video 60000 RTP/AVP 66 1477 b=AS:1000 1478 a=rtpmap:66 H261/90000 1480 15.5. Example: Offerer Disables A Media Description Within A BUNDLE 1481 Group 1483 The example below shows: 1485 o 1. An offer, in which the offerer disables a bundled "m=" line 1486 within BUNDLE group, assigns a zero port number the disabled "m=" 1487 line, and assigns the offerer BUNDLE address to each of the other 1488 bundled "m=" lines within the BUNDLE group. 1490 o 2. An answer, in which the answerer moves the disabled "m=" line 1491 out of the BUNDLE group, assigns a zero port value to the disabled 1492 "m=" line, and assigns the answerer BUNDLE address to each of the 1493 other bundled "m=" lines within the BUNDLE group. 1495 SDP Offer (1) 1497 v=0 1498 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1499 s= 1500 c=IN IP4 atlanta.example.com 1501 t=0 0 1502 a=group:BUNDLE foo bar 1503 m=audio 10000 RTP/AVP 0 8 97 1504 a=mid:foo 1505 b=AS:200 1506 a=rtpmap:0 PCMU/8000 1507 a=rtpmap:8 PCMA/8000 1508 a=rtpmap:97 iLBC/8000 1509 m=video 10000 RTP/AVP 31 32 1510 a=mid:bar 1511 b=AS:1000 1512 a=rtpmap:31 H261/90000 1513 a=rtpmap:32 MPV/90000 1514 m=video 0 RTP/AVP 66 1515 a=rtpmap:66 H261/90000 1517 SDP Answer (2) 1519 v=0 1520 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1521 s= 1522 c=IN IP4 biloxi.example.com 1523 t=0 0 1524 a=group:BUNDLE foo bar 1525 m=audio 20000 RTP/AVP 0 1526 a=mid:foo 1527 b=AS:200 1528 a=rtpmap:0 PCMU/8000 1529 m=video 20000 RTP/AVP 32 1530 a=mid:bar 1531 b=AS:1000 1532 a=rtpmap:32 MPV/90000 1533 m=video 0 RTP/AVP 66 1534 a=rtpmap:66 H261/90000 1536 16. IANA Considerations 1538 This document requests IANA to register the new SDP Grouping semantic 1539 extension called BUNDLE. 1541 17. Acknowledgements 1543 The usage of the SDP grouping extension for negotiating bundled media 1544 is based on a similar alternatives proposed by Harald Alvestrand and 1545 Cullen Jennings. The BUNDLE extension described in this document is 1546 based on the different alternative proposals, and text (e.g. SDP 1547 examples) have been borrowed (and, in some cases, modified) from 1548 those alternative proposals. 1550 The SDP examples are also modified versions from the ones in the 1551 Alvestrand proposal. 1553 Thanks to Paul Kyzivat, Martin Thompson and Flemming Andreasen for 1554 taking the time to read the text along the way, and providing useful 1555 feedback. 1557 18. Change Log 1559 [RFC EDITOR NOTE: Please remove this section when publishing] 1561 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1563 o Terminology change: "bundle-only attribute assigned to m= line" to 1564 "bundle-only attribute associated with m= line". 1566 o Editorial corrections. 1568 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1570 o Editorial corrections. 1572 o - "of"->"if" (8.3.2.5). 1574 o - "optional"->"OPTIONAL" (9.1). 1576 o - Syntax/ABNF for 'bundle-only' attribute added. 1578 o - SDP Offer/Answer sections merged. 1580 o - 'Request new offerer BUNDLE address' section added 1582 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1583 o OPEN ISSUE regarding Receiver-ID closed. 1585 o - RTP MID SDES Item. 1587 o - RTP MID Header Extension. 1589 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1590 closed. 1592 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1593 include an 'rtcp' attribute in the answer, based on the procedures 1594 in section 5.1.3 of RFC 5761. 1596 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1598 o Draft title changed. 1600 o Added "SDP" to section names containing "Offer" or "Answer". 1602 o Editorial fixes based on comments from Paul Kyzivat 1603 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1604 msg13314.html). 1606 o Editorial fixed based on comments from Colin Perkins 1607 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1608 msg13318.html). 1610 o - Removed text about extending BUNDLE to allow multiple RTP 1611 sessions within a BUNDLE group. 1613 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1615 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1616 3264 structure. 1618 o Additional definitions added. 1620 o - Shared address. 1622 o - Bundled "m=" line. 1624 o - Bundle-only "m=" line. 1626 o - Offerer suggested BUNDLE mid. 1628 o - Answerer selected BUNDLE mid. 1630 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1631 to multiple "m=" lines until it has received an SDP Answer 1632 indicating support of the BUNDLE extension. 1634 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1635 Answerer supports the BUNDLE extension, assign a zero port value 1636 to a 'bundle-only' "m=" line. 1638 o SDP 'bundle-only' attribute section added. 1640 o Connection data nettype/addrtype restrictions added. 1642 o RFC 3264 update section added. 1644 o Indicating that a specific payload type value can be used in 1645 multiple "m=" lines, if the value represents the same codec 1646 configuration in each "m=" line. 1648 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1650 o Updated Offerer procedures (http://www.ietf.org/mail- 1651 archive/web/mmusic/current/msg12293.html). 1653 o Updated Answerer procedures (http://www.ietf.org/mail- 1654 archive/web/mmusic/current/msg12333.html). 1656 o Usage of SDP 'bundle-only' attribute added. 1658 o Reference to Trickle ICE document added. 1660 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1662 o Mechanism modified, to be based on usage of SDP Offers with both 1663 different and identical port number values, depending on whether 1664 it is known if the remote endpoint supports the extension. 1666 o Cullen Jennings added as co-author. 1668 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1670 o No changes. New version due to expiration. 1672 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1674 o No changes. New version due to expiration. 1676 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1677 o Draft name changed. 1679 o Harald Alvestrand added as co-author. 1681 o "Multiplex" terminology changed to "bundle". 1683 o Added text about single versus multiple RTP Sessions. 1685 o Added reference to RFC 3550. 1687 19. References 1689 19.1. Normative References 1691 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1692 Requirement Levels", BCP 14, RFC 2119, March 1997. 1694 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1695 with Session Description Protocol (SDP)", RFC 3264, June 1696 2002. 1698 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1699 Description Protocol", RFC 4566, July 2006. 1701 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1702 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1704 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1705 Header Extensions", RFC 5285, July 2008. 1707 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1708 Control Packets on a Single Port", RFC 5761, April 2010. 1710 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1711 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1713 [I-D.mmusic-sdp-mux-attributes] 1714 Nandakumar, S., "A Framework for SDP Attributes when 1715 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-02 1716 (work in progress), July 2014. 1718 19.2. Informative References 1720 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1721 Jacobson, "RTP: A Transport Protocol for Real-Time 1722 Applications", STD 64, RFC 3550, July 2003. 1724 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1725 in Session Description Protocol (SDP)", RFC 3605, October 1726 2003. 1728 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1729 (ICE): A Protocol for Network Address Translator (NAT) 1730 Traversal for Offer/Answer Protocols", RFC 5245, April 1731 2010. 1733 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1734 Media Attributes in the Session Description Protocol 1735 (SDP)", RFC 5576, June 2009. 1737 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1738 Security (DTLS) Extension to Establish Keys for the Secure 1739 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 1741 [I-D.ietf-mmusic-trickle-ice] 1742 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 1743 Incremental Provisioning of Candidates for the Interactive 1744 Connectivity Establishment (ICE) Protocol", draft-ietf- 1745 mmusic-trickle-ice-01 (work in progress), February 2014. 1747 Appendix A. Design Considerations 1749 A.1. General 1751 One of the main issues regarding the BUNDLE grouping extensions has 1752 been whether, in SDP Offers and SDP Answers, the same port number 1753 value should be inserted in "m=" lines associated with a BUNDLE 1754 group, as the purpose of the extension is to negotiate the usage of a 1755 single 5-tuple for media associated with the "m=" lines. Issues with 1756 both approaches, discussed in the Appendix have been raised. The 1757 outcome was to specify a mechanism which uses SDP Offers with both 1758 different and identical port number values. 1760 Below are the primary issues that have been considered when defining 1761 the "BUNDLE" grouping extension: 1763 o 1) Interoperability with existing UAs. 1765 o 2) Interoperability with intermediary B2BUA- and proxy entities. 1767 o 3) Time to gather, and the number of, ICE candidates. 1769 o 4) Different error scenarios, and when they occur. 1771 o 5) SDP Offer/Answer impacts, including usage of port number value 1772 zero. 1774 NOTE: Before this document is published as an RFC, this 1775 Appendix might be removed. 1777 A.2. UA Interoperability 1779 Consider the following SDP Offer/Answer exchange, where Alice sends 1780 an SDP Offer to Bob: 1782 SDP Offer 1784 v=0 1785 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1786 s= 1787 c=IN IP4 atlanta.example.com 1788 t=0 0 1789 m=audio 10000 RTP/AVP 97 1790 a=rtpmap:97 iLBC/8000 1791 m=video 10002 RTP/AVP 97 1792 a=rtpmap:97 H261/90000 1794 SDP Answer 1796 v=0 1797 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1798 s= 1799 c=IN IP4 biloxi.example.com 1800 t=0 0 1801 m=audio 20000 RTP/AVP 97 1802 a=rtpmap:97 iLBC/8000 1803 m=video 20002 RTP/AVP 97 1804 a=rtpmap:97 H261/90000 1806 RFC 4961 specifies a way of doing symmetric RTP but that is an a 1807 later invention to RTP and Bob can not assume that Alice supports RFC 1808 4961. This means that Alice may be sending RTP from a different port 1809 than 10000 or 10002 - some implementation simply send the RTP from an 1810 ephemeral port. When Bob's endpoint receives an RTP packet, the only 1811 way that Bob know if it should be passed to the video or audio codec 1812 is by looking at the port it was received on. This lead some SDP 1813 implementations to use the fact that each "m=" line had a different 1814 port number to use that port number as an index to find the correct m 1815 line in the SDP. As a result, some implementations that do support 1816 symmetric RTP and ICE still use a SDP data structure where SDP with 1817 "m=" lines with the same port such as: 1819 SDP Offer 1821 v=0 1822 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1823 s= 1824 c=IN IP4 atlanta.example.com 1825 t=0 0 1826 m=audio 10000 RTP/AVP 97 1827 a=rtpmap:97 iLBC/8000 1828 m=video 10000 RTP/AVP 98 1829 a=rtpmap:98 H261/90000 1831 will result in the second "m=" line being considered an SDP error 1832 because it has the same port as the first line. 1834 A.3. Usage of port number value zero 1836 In an SDP Offer or SDP Answer, the media associated with an "m=" line 1837 can be disabled/rejected by setting the port number value to zero. 1838 This is different from e.g. using the SDP direction attributes, where 1839 RTCP traffic will continue even if the SDP "inactive" attribute is 1840 indicated for the associated "m=" line. 1842 If each "m=" line associated with a BUNDLE group would contain 1843 different port number values, and one of those port would be used for 1844 the 5-tuple, problems would occur if an endpoint wants to disable/ 1845 reject the "m=" line associated with that port, by setting the port 1846 number value to zero. After that, no "m=" line would contain the 1847 port number value which is used for the 5-tuple. In addition, it is 1848 unclear what would happen to the ICE candidates associated with the 1849 "m=" line, as they are also used for the 5-tuple. 1851 A.4. B2BUA And Proxy Interoperability 1853 Some back to back user agents may be configured in a mode where if 1854 the incoming call leg contains an SDP attribute the B2BUA does not 1855 understand, the B2BUS still generates that SDP attribute in the Offer 1856 for the outgoing call leg. Consider an B2BUA that did not understand 1857 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 1858 Further assume that the B2BUA was configured to tear down any call 1859 where it did not see any RTCP for 5 minutes. In this cases, if the 1860 B2BUA received an Offer like: 1862 SDP Offer 1864 v=0 1865 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1866 s= 1867 c=IN IP4 atlanta.example.com 1868 t=0 0 1869 m=audio 49170 RTP/AVP 0 1870 a=rtcp:53020 1872 It would be looking for RTCP on port 49172 but would not see any 1873 because the RTCP would be on port 53020 and after five minutes, it 1874 would tear down the call. Similarly, an SBC that did not understand 1875 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 1876 wrong port and tear down the call. It is worth noting that a B2BUA 1877 that generated an Offer with capabilities it does not understand is 1878 not compliant with the specifications. 1880 A.4.1. Traffic Policing 1882 Sometimes intermediaries do not act as B2BUA, in the sense that they 1883 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 1884 however, they may use SDP information (e.g. IP address and port) in 1885 order to control traffic gating functions, and to set traffic 1886 policing rules. There might be rules which will trigger a session to 1887 be terminated in case media is not sent or received on the ports 1888 retrieved from the SDP. This typically occurs once the session is 1889 already established and ongoing. 1891 A.4.2. Bandwidth Allocation 1893 Sometimes intermediaries do not act as B2BUA, in the sense that they 1894 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 1895 however, they may use SDP information (e.g. codecs and media types) 1896 in order to control bandwidth allocation functions. The bandwidth 1897 allocation is done per "m=" line, which means that it might not be 1898 enough if media associated with all "m=" lines try to use that 1899 bandwidth. That may either simply lead to bad user experience, or to 1900 termination of the call. 1902 A.5. Candidate Gathering 1904 When using ICE, an candidate needs to be gathered for each port. 1905 This takes approximately 20 ms extra for each extra "m=" line due to 1906 the NAT pacing requirements. All of this gather can be overlapped 1907 with other things while the page is loading to minimize the impact. 1908 If the client only wants to generate TURN or STUN ICE candidates for 1909 one of the "m=" lines and then use trickle ICE 1910 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 1911 the rest of the "m=" lines, it MAY do that and will not need any 1912 additional gathering time. 1914 Some people have suggested a TURN extension to get a bunch of TURN 1915 allocation at once. This would only provide a single STUN result so 1916 in cases where the other end did not support BUNDLE, may cause more 1917 use of the TURN server but would be quick in the cases where both 1918 sides supported BUNDLE and would fall back to a successful call in 1919 the other cases. 1921 Authors' Addresses 1923 Christer Holmberg 1924 Ericsson 1925 Hirsalantie 11 1926 Jorvas 02420 1927 Finland 1929 Email: christer.holmberg@ericsson.com 1931 Harald Tveit Alvestrand 1932 Google 1933 Kungsbron 2 1934 Stockholm 11122 1935 Sweden 1937 Email: harald@alvestrand.no 1939 Cullen Jennings 1940 Cisco 1941 400 3rd Avenue SW, Suite 350 1942 Calgary, AB T2P 4H2 1943 Canada 1945 Email: fluffy@iii.ca