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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '10' on line 1163 ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 5285 (Obsoleted by RFC 8285) == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-08 -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 5 comments (--). 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: September 27, 2015 C. Jennings 7 Cisco 8 March 26, 2015 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-19.txt 14 Abstract 16 This specification defines a new Session Description Protocol (SDP) 17 Grouping Framework extension, 'BUNDLE'. The extension can be used 18 with the SDP Offer/Answer mechanism to negotiate the usage of a 19 single address:port combination (BUNDLE address) for receiving media, 20 referred to as bundled media, associated with multiple SDP media 21 descriptions ("m=" lines). 23 To assist endpoints in negotiating the use of bundle this 24 specification defines a new SDP attribute, 'bundle-only', which can 25 be used to request that specific media is only used if bundled. This 26 specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 to 27 allow an answerer to assign a non-zero port value to an "m=" line in 28 an SDP answer, even if the "m=" line in the associated SDP offer 29 contained a zero port value. 31 There are multiple ways to correlate the bundled RTP packets with the 32 appropriate media descriptions. This specification defines a new 33 RTCP source description (SDES) item and a new RTP header extension 34 that provides an additional way to do this correlation by using them 35 to carry a value that associates the RTP/RTCP packets with a specific 36 media description. 38 Status of This Memo 40 This Internet-Draft is submitted in full conformance with the 41 provisions of BCP 78 and BCP 79. 43 Internet-Drafts are working documents of the Internet Engineering 44 Task Force (IETF). Note that other groups may also distribute 45 working documents as Internet-Drafts. The list of current Internet- 46 Drafts is at http://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on September 27, 2015. 55 Copyright Notice 57 Copyright (c) 2015 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (http://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 73 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 74 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 76 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 77 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 7 78 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 79 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 80 7.2. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 81 7.3. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 82 7.4. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 83 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 84 8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 85 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 86 8.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 87 8.2.2. Suggesting the offerer BUNDLE address . . . . . . . . 11 88 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 11 89 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 11 90 8.3.2. Answerer Selection of Offerer Bundle Address . . . . 12 91 8.3.3. Answerer Selection of Answerer BUNDLE Address . . . . 13 92 8.3.4. Moving A Media Description Out Of A BUNDLE Group . . 13 93 8.3.5. Rejecting A Media Description In A BUNDLE Group . . . 13 94 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14 95 8.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 97 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 14 98 8.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 99 8.5.2. Suggesting a new offerer BUNDLE address . . . . . . . 14 100 8.5.3. Adding a media description to a BUNDLE group . . . . 15 101 8.5.4. Moving A Media Description Out Of A BUNDLE Group . . 16 102 8.5.5. Disabling A Media Description In A BUNDLE Group . . . 16 103 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 16 104 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 16 105 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 17 106 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 17 107 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 17 108 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 17 109 10.1.2. Payload Type (PT) Value Reuse . . . . . . . . . . . 18 110 10.2. Associating RTP/RTCP Packets With Correct SDP Media 111 Description . . . . . . . . . . . . . . . . . . . . . . 18 112 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 19 113 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 19 114 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 19 115 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 22 116 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 117 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 22 118 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 22 119 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 23 120 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 23 121 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 23 122 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 23 123 12. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 23 124 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 23 125 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 24 126 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 127 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 128 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 24 129 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 130 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 131 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 25 132 12.7. New text replacing section 8.4 (6th paragraph) of RFC 133 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 134 13. RTP/RTCP extensions for identification-tag transport . . . . 25 135 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 25 136 13.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 26 137 13.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 27 138 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 139 14.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 27 140 14.2. New RTP Header Extension URI . . . . . . . . . . . . . . 28 141 14.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 28 142 15. Security Considerations . . . . . . . . . . . . . . . . . . . 28 143 16. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 29 144 16.1. Example: Bundle Address Selection . . . . . . . . . . . 29 145 16.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 31 146 16.3. Example: Offerer Adds A Media Description To A BUNDLE 147 Group . . . . . . . . . . . . . . . . . . . . . . . . . 32 148 16.4. Example: Offerer Moves A Media Description Out Of A 149 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 34 150 16.5. Example: Offerer Disables A Media Description Within A 151 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 35 152 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 153 18. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 37 154 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 42 155 19.1. Normative References . . . . . . . . . . . . . . . . . . 42 156 19.2. Informative References . . . . . . . . . . . . . . . . . 43 157 Appendix A. Design Considerations . . . . . . . . . . . . . . . 44 158 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 44 159 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 44 160 A.3. Usage of port number value zero . . . . . . . . . . . . . 46 161 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 46 162 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 47 163 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 47 164 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 47 165 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 167 1. Introduction 169 This specification defines a way to use a single address:port 170 combination (BUNDLE address) for receiving media associated with 171 multiple SDP media descriptions ("m=" lines). 173 This specification defines a new SDP Grouping Framework [RFC5888] 174 extension called 'BUNDLE'. The extension can be used with the 175 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 176 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 177 BUNDLE address is used for receiving media associated with multiple 178 "m=" lines. This is referred to as bundled media. 180 The offerer and answerer [RFC3264] use the BUNDLE extension to 181 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 182 address) and one for the answerer (answerer BUNDLE address), to be 183 used for receiving the bundled media associated with a BUNDLE group. 184 Once the offerer and the answerer have negotiated a BUNDLE group, 185 they assign their respective BUNDLE address to each "m=" line in the 186 BUNDLE group. The BUNDLE addresses are used to receive all media 187 associated with the BUNDLE group. 189 The use of a BUNDLE group and a BUNDLE address also allows the usage 190 of a single set of Interactive Connectivity Establishment (ICE) 191 [RFC5245] candidates for multiple "m=" lines. 193 This specification also defines a new SDP attribute, 'bundle-only', 194 which can be used to request that specific media is only used if kept 195 within a BUNDLE group. 197 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 198 port value to multiple "m=" lines are undefined, and there is no 199 grouping defined by such means. Instead, an explicit grouping 200 mechanism needs to be used to express the intended semantics. This 201 specification provides such an extension. 203 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 204 [RFC3264]. The update allows an answerer to assign a non-zero port 205 value to an "m=" line in an SDP answer, even if the "m=" line in the 206 associated SDP offer contained a zero port value. 208 This specification also defines a new Real-time Transport Protocol 209 (RTP) [RFC3550] SDES item and a new RTP header extension that can be 210 used to carry a value that associates RTP/RTCP packets with a 211 specific media description. This can be used to correlate a RTP 212 packet with the correct media. 214 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 215 address MUST only be associated with a single BUNDLE group. The 216 procedures in this specification apply independently to a given 217 BUNDLE group. All RTP based media flows associated with a single 218 BUNDLE group belong to a single RTP session [RFC3550]. 220 The BUNDLE extension is backward compatible. Endpoints that do not 221 support the extension are expected to generate offers and answers 222 without an SDP 'group:BUNDLE' attribute, and are expected to assign a 223 unique address to each "m=" line within an offer and answer, 224 according to the procedures in [RFC4566] and [RFC3264] 226 2. Terminology 228 5-tuple: A collection of the following values: source address, source 229 port, destination address, destination port, and transport-layer 230 protocol. 232 Unique address: An IP address and port combination that is assigned 233 to only one "m=" line in an offer or answer. 235 Shared address: An IP address and port combination that is assigned 236 to multiple "m=" lines within an offer or answer. 238 Offerer BUNDLE-tag: The first identification-tag in a given SDP 239 'group:BUNDLE' attribute identification-tag list in an offer. 241 Answerer BUNDLE-tag: The first identification-tag in a given SDP 242 'group:BUNDLE' attribute identification-tag list in an answer. 244 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 245 and port combination used by an offerer to receive all media 246 associated with each "m=" line within the BUNDLE group. 248 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 249 and port combination used by an answerer to receive all media 250 associated with each "m=" line within the BUNDLE group. 252 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 253 exchange, which uses the same BUNDLE address for receiving media. 255 Bundled "m=" line: An "m=" line, whose identification-tag is placed 256 in an SDP 'group:BUNDLE' attribute identification-tag list in an 257 offer or answer. 259 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 260 'bundle-only' attribute. 262 Bundled media: All media associated with a given BUNDLE group. 264 Initial offer: The first offer, within an SDP session (e.g. a SIP 265 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 266 to carry SDP), in which the offerer indicates that it wants to create 267 a given BUNDLE group. 269 Subsequent offer: An offer which contains a BUNDLE group that has 270 been created as part of a previous offer/answer exchange. 272 Identification-tag: A unique token value that is used to identify an 273 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 274 "m=" line, carries an unique identification-tag. The session-level 275 SDP 'group' attribute [RFC5888] carries a list of identification- 276 tags, identifying the "m=" lines associated with that particular 277 'group' attribute. 279 3. Conventions 281 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 282 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 283 document are to be interpreted as described in BCP 14, RFC 2119 284 [RFC2119]. 286 4. Applicability Statement 288 The mechanism in this specification only applies to the Session 289 Description Protocol (SDP) [RFC4566], when used together with the SDP 290 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 291 scope of this document, and is thus undefined. 293 5. SDP Grouping Framework BUNDLE Extension 295 This section defines a new SDP Grouping Framework extension 296 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 297 Offer/Answer mechanism to negotiate the usage of a single 298 address:port combination (BUNDLE address) for receiving bundled 299 media. 301 A single address:port combination is also used for sending bundled 302 media. The address:port combination used for sending bundled media 303 MAY be the same as the BUNDLE address, used to receive bundled media, 304 depending on whether symmetric RTP is used. A given address:port 305 combination MUST NOT be used for sending media associated with 306 multiple BUNDLE groups. 308 All media associated with a BUNDLE group share a single 5-tuple, i.e. 309 in addition to using a single address:port combination all bundled 310 media MUST be transported using the same transport-layer protocol 311 (e.g. UDP or TCP). 313 The BUNDLE extension is indicated using an SDP 'group' attribute with 314 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 315 assigned to each bundled "m=" line, and each identification-tag is 316 listed in the SDP 'group:BUNDLE' attribute identification-tag list. 317 Each "m=" line, whose identification-tag is listed in the 318 identification-tag list, is associated with a given BUNDLE group. 320 SDP bodies can contain multiple BUNDLE groups. Any given bundled 321 "m=" line MUST NOT be associated with more than one BUNDLE group. 323 Section 8 defines the detailed SDP Offer/Answer procedures for the 324 BUNDLE extension. 326 6. SDP 'bundle-only' Attribute 328 This section defines a new SDP media-level attribute [RFC4566], 329 'bundle-only'. 331 Name: bundle-only 333 Value: 335 Usage Level: media 337 Charset Dependent: no 339 Example: 341 a=bundle-only 343 In order to ensure that an answerer that does not supports the BUNDLE 344 extension always rejects a bundled "m=" line, the offerer can assign 345 a zero port value to the "m=" line. According to [RFC4566] an 346 answerer will reject such "m=" line. By associating an SDP 'bundle- 347 only' attribute with such "m=" line, the offerer can request that the 348 answerer accepts the "m=" line if the answerer supports the Bundle 349 extension, and if the answerer keeps the "m=" line within the 350 associated BUNDLE group. 352 NOTE: Once an offerer BUNDLE address has been selected, the offerer 353 can ensure that an bundled "m=" line is accepted by the answerer only 354 if the answerer keeps the "m=" line within the associated BUNDLE 355 group by assigning the offerer BUNDLE address to the "m=" line. If 356 the answerer does not keep that "m=" line within the BUNDLE group, 357 the answerer will reject it. Therefore, the SDP 'bundle-only' 358 attribute is not needed in such cases 360 The usage of the 'bundle-only' attribute is only defined for a 361 bundled "m=" line with a zero port value, within an offer. Other 362 usage is unspecified. 364 Section 8 defines the detailed SDP Offer/Answer procedures for the 365 'bundle-only' attribute. 367 7. SDP Information Considerations 369 7.1. General 371 This section describes restrictions associated with the usage of SDP 372 parameters within a BUNDLE group. It also describes, when parameter 373 and attribute values have been associated with each bundled "m=" 374 line, how to calculate a value for the whole BUNDLE group. 376 7.2. Connection Data (c=) 378 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 379 line MUST be 'IN'. 381 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 382 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 383 each "m=" line. 385 NOTE: Extensions to this specification can specify usage of the 386 BUNDLE mechanism for other nettype and addrtype values than the ones 387 listed above. 389 7.3. Bandwidth (b=) 391 An offerer and answerer MUST use the rules and restrictions defined 392 in [I-D.mmusic-sdp-mux-attributes] for when associating the SDP 393 bandwidth (b=) line with bundled "m=" lines. 395 7.4. Attributes (a=) 397 An offerer and answerer MUST use the rules and restrictions defined 398 in [I-D.mmusic-sdp-mux-attributes] for when associating SDP 399 attributes with bundled "m=" lines. 401 8. SDP Offer/Answer Procedures 403 8.1. General 405 This section describes the SDP Offer/Answer [RFC3264] procedures for: 407 o Negotiating and creating of a BUNDLE group; 409 o Selecting the BUNDLE addresses (offerer BUNDLE address and 410 answerer BUNDLE address); 412 o Adding an "m=" line to a BUNDLE group; 414 o Moving an "m=" line out of a BUNDLE group; and 416 o Disabling an "m=" line within a BUNDLE group. 418 The generic rules and procedures defined in [RFC3264] and [RFC5888] 419 also apply to the BUNDLE extension. For example, if an offer is 420 rejected by the answerer, the previously negotiated SDP parameters 421 and characteristics (including those associated with a BUNDLE group) 422 apply. Hence, if an offerer generates an offer in which the offerer 423 wants to create a BUNDLE group, and the answerer rejects the offer, 424 the BUNDLE group is not created. 426 The procedures in this section are independent of the media type or 427 "m=" line proto value represented by a bundled "m=" line. Section 10 428 defines additional considerations for RTP based media. Section 6 429 defines additional considerations for the usage of the SDP 'bundle- 430 only' attribute. Section 11 defines additional considerations for 431 the usage of Interactive Connectivity Establishment (ICE) [RFC5245] 432 mechanism . 434 The offerer and answerer MUST follow the rules and restrictions 435 defined in Section 7 when creating offers and answers. 437 SDP offers and answers can contain multiple BUNDLE groups. The 438 procedures in this section apply independently to a given BUNDLE 439 group. 441 8.2. Generating the Initial SDP Offer 443 8.2.1. General 445 When an offerer generates an initial offer, in order to create a 446 BUNDLE group, it MUST: 448 o Assign a unique address to each "m=" line within the offer, 449 following the procedures in [RFC3264], unless the media line is a 450 'bundle-only' "m=" line (see below); 452 o Add an SDP 'group:BUNDLE' attribute to the offer; 454 o Place the identification-tag of each bundled "m=" line in the SDP 455 'group:BUNDLE' attribute identification-tag list; and 457 o Indicate which unique address the offerer suggests as the offerer 458 BUNDLE address [Section 8.2.2]. 460 If the offerer wants to request that the answerer accepts a given 461 bundled "m=" line only if the answerer keeps the "m=" line within the 462 BUNDLE group, the offerer MUST: 464 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 465 "m=" line; and 467 o Assign a zero port value to the "m=" line. 469 NOTE: If the offerer assigns a zero port value to an "m=" line, but 470 does not also associate an SDP 'bundle-only' attribute with the "m=" 471 line, it is an indication that the offerer wants to disable the "m=" 472 line [Section 8.5.5]. 474 [Section 16.1] shows an example of an initial offer. 476 8.2.2. Suggesting the offerer BUNDLE address 478 In the offer, the address assigned to the "m=" line associated with 479 the offerer BUNDLE-tag indicates the address that the offerer 480 suggests as the offerer BUNDLE address. 482 8.3. Generating the SDP Answer 484 8.3.1. General 486 When an answerer generates an answer, which contains a BUNDLE group, 487 the following general SDP grouping framework restrictions, defined in 488 [RFC5888], also apply to the BUNDLE group: 490 o The answerer MUST NOT include a BUNDLE group in the answer, unless 491 the offerer requested the BUNDLE group to be created in the 492 associated offer; and 494 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 495 unless the offerer requested the "m=" line to be within that 496 BUNDLE group in the associated offer. 498 If the answer contains a BUNDLE group, the answerer MUST: 500 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 502 o Select an Answerer BUNDLE Address [Section 8.3.3]; 504 The answerer is allowed to select a new Answerer BUNDLE address each 505 time it generates an answer to an offer. 507 If the answerer does not want to keep an "m=" line within a BUNDLE 508 group, it MUST: 510 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 512 o Reject the "m=" line [Section 8.3.5]; 514 If the answerer keeps a bundle-only "m=" line within the BUNDLE 515 group, it follows the procedures (assigns the answerer BUNDLE address 516 to the "m=" line etc) for any other "m=" line kept within the BUNDLE 517 group. 519 If the answerer does not want to keep a bundle-only "m=" line within 520 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 522 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 523 any "m=" line in an answer. 525 NOTE: If a bundled "m=" line in an offer contains a zero port value, 526 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 527 is an indication that the offerer wants to disable the "m=" line 528 [Section 8.5.5]. 530 8.3.2. Answerer Selection of Offerer Bundle Address 532 In an offer, the address (unique or shared) assigned to the bundled 533 "m=" line associated with the offerer BUNDLE-tag indicates the 534 address that the offerer suggests as the offerer BUNDLE address 535 [Section 8.2.2]. The answerer MUST check whether that "m=" line 536 fulfills the following criteria: 538 o The answerer will not move the "m=" line out of the BUNDLE group 539 [Section 8.3.4]; 541 o The answerer will not reject the "m=" line [Section 8.3.5]; and 543 o The "m=" line does not contain a zero port value. 545 If all of the criteria above are fulfilled, the answerer MUST select 546 the address associated with the "m=" line as the offerer BUNDLE 547 address. In the answer, the answerer BUNDLE-tag represents the "m=" 548 line, and the address associated with the "m=" line in the offer 549 becomes the offerer BUNDLE address. 551 If one or more of the criteria are not fulfilled, the answerer MUST 552 select the next identification-tag in the identification-tag list, 553 and perform the same criteria check for the "m=" line associated with 554 that identification-tag. If there are no more identification-tags in 555 the identification-tag list, the answerer MUST NOT create the BUNDLE 556 group. In addition, unless the answerer rejects the whole offer, the 557 answerer MUST apply the answerer procedures for moving an "m=" line 558 out of a BUNDLE group [Section 8.3.4] to each bundled "m=" line in 559 the offer when creating the answer. 561 [Section 16.1] shows an example of an offerer BUNDLE address 562 selection. 564 8.3.3. Answerer Selection of Answerer BUNDLE Address 566 When the answerer selects a BUNDLE address for itself, referred to as 567 the answerer BUNDLE address, it MUST assign that address to each 568 bundled "m=" line within the created BUNDLE group in the answer. 570 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 571 line that is not within the BUNDLE group, or to an "m=" line that is 572 within another BUNDLE group. 574 [Section 16.1] shows an example of an answerer BUNDLE address 575 selection. 577 8.3.4. Moving A Media Description Out Of A BUNDLE Group 579 When an answerer moves a "m=" line out of a BUNDLE group, it assigns 580 an address to the "m=" line in the answer based on the following 581 rules: 583 o In the associated offer, if the "m=" line contains a shared 584 address (e.g. a previously selected offerer BUNDLE address), the 585 answerer MUST reject the moved "m=" line [Section 8.3.5]; 587 o In the associated offer, if the "m=" line contains a unique 588 address, the answerer MUST assign a unique address also to the 589 "m=" line in the answer; or 591 o In the associated offer, if an SDP 'bundle-only' attribute is 592 associated with the "m=" line, and if the "m=" line contains a 593 zero port value, the answerer MUST reject the "m=" line 594 [Section 8.3.5]. 596 In addition, in either case above, the answerer MUST NOT place the 597 identification-tag, associated with the moved "m=" line, in the SDP 598 'group' attribute identification-tag list associated with the BUNDLE 599 group. 601 8.3.5. Rejecting A Media Description In A BUNDLE Group 603 When an answerer rejects an "m=" line, it MUST assign an address with 604 a zero port value to the "m=" line in the answer, according to the 605 procedures in [RFC4566]. 607 In addition, the answerer MUST NOT place the identification-tag, 608 associated with the rejected "m=" line, in the SDP 'group' attribute 609 identification-tag list associated with the BUNDLE group. 611 8.4. Offerer Processing of the SDP Answer 613 8.4.1. General 615 When an offerer receives an answer, if the answer contains a BUNDLE 616 group, the offerer MUST check that any bundled "m=" line in the 617 answer was indicated as bundled in the associated offer. If there is 618 no mismatch, the offerer MUST use the offerer BUNDLE address, 619 selected by the answerer [Section 8.3.2], as the address for each 620 bundled "m=" line. 622 NOTE: As the answerer might reject one or more bundled "m=" lines, or 623 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 624 line in the offer might not be indicated as bundled in the answer. 626 If the answer does not contain a BUNDLE group, the offerer MUST 627 process the answer as a normal answer. 629 8.5. Modifying the Session 631 8.5.1. General 633 When an offerer generates a subsequent offer, it MUST assign the 634 previously selected offerer BUNDLE address [Section 8.3.2], to each 635 bundled "m=" line (including any bundle-only "m=" line), except if: 637 o The offerer suggests a new offerer BUNDLE address [Section 8.5.2]; 639 o The offerer wants to add a bundled "m=" line to the BUNDLE group 640 [Section 8.5.3]; 642 o The offerer wants to move a bundled "m=" line out of the BUNDLE 643 group [Section 8.5.4]; or 645 o The offerer wants to disable the bundled "m=" line 646 [Section 8.5.5]. 648 In addition, the offerer MUST select an offerer BUNDLE-tag 649 [Section 8.2.2] associated with the previously selected offerer 650 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 651 address. 653 8.5.2. Suggesting a new offerer BUNDLE address 655 When an offerer generates an offer, in which it suggests a new 656 offerer BUNDLE address [Section 8.2.2], the offerer MUST: 658 o Assign the address (shared address) to each "m=" line within the 659 BUNDLE group; or 661 o Assign the address (unique address) to one bundled "m=" line. 663 In addition, the offerer MUST indicate that the address is the new 664 suggested offerer BUNDLE address [Section 8.2.2]. 666 NOTE: Unless the offerer assigns the new suggested offerer BUNDLE 667 address to each bundled "m=" line, it can assign unique addresses to 668 any number of bundled "m=" lines (and the previously selected offerer 669 BUNDLE address to any remaining bundled "m=" line) if it wants to 670 suggest multiple alternatives for the new offerer BUNDLE address. 672 8.5.3. Adding a media description to a BUNDLE group 674 When an offerer generates an offer, in which it wants to add a 675 bundled "m=" line to a BUNDLE group, the offerer MUST: 677 o Assign a unique address to the "m=" line; 679 o Assign the previously selected offerer BUNDLE address to the "m=" 680 line; or 682 o If the offerer assigns a new (shared address) suggested offerer 683 BUNDLE address to each bundled "m=" line [Section 8.5.2], also 684 assign that address to the added "m=" line. 686 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 687 identification-tag list with the BUNDLE group [Section 8.2.2] by 688 adding the identification-tag associated with the added "m=" line to 689 the list. 691 NOTE: Assigning a unique address to the "m=" line allows the answerer 692 to move the "m=" line out of the BUNDLE group [Section 8.3.4], 693 without having to reject the "m=" line. 695 If the offerer assigns a unique address to the added "m=" line, and 696 if the offerer suggests that address as the new offerer BUNDLE 697 address [Section 8.5.2], the offerer BUNDLE-tag MUST represent the 698 added "m=" line [Section 8.2.2]. 700 If the offerer assigns a new suggested offerer BUNDLE address to each 701 bundled "m=" line [Section 8.5.2], including the added "m=" line, the 702 offerer BUNDLE-tag MAY represent the added "m=" line [Section 8.2.2]. 704 [Section 16.3] shows an example where an offerer sends an offer in 705 order to add a bundled "m=" line to a BUNDLE group. 707 8.5.4. Moving A Media Description Out Of A BUNDLE Group 709 When an offerer generates an offer, in which it wants to move a 710 bundled "m=" line out of a BUNDLE group it was added to in a previous 711 offer/answer transaction, the offerer: 713 o MUST assign a unique address to the "m=" line; and 715 o MUST NOT place the identification-tag associated with the "m=" 716 line in the SDP 'group:BUNDLE' attribute identification-tag list 717 associated with the BUNDLE group. 719 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 720 added to another BUNDLE group, the offerer applies the procedures in 721 [Section 8.5.3] to the "m=" line. 723 [Section 16.4] shows an example of an offer for moving an "m=" line 724 out of a BUNDLE group. 726 8.5.5. Disabling A Media Description In A BUNDLE Group 728 When an offerer generates an offer, in which it wants to disable a 729 bundled "m=" line (added to the BUNDLE group in a previous offer/ 730 answer transaction), the offerer: 732 o MUST assign an address with a zero port value to the "m=" line, 733 following the procedures in [RFC4566]; and 735 o MUST NOT place the identification-tag associated with the "m=" 736 line in the SDP 'group:BUNDLE' attribute identification-tag list 737 associated with the BUNDLE group. 739 [Section 16.5] shows an example of an offer for disabling an "m=" 740 line within a BUNDLE group. 742 9. Protocol Identification 744 9.1. General 746 Each "m=" line within a BUNDLE group MUST use the same transport- 747 layer protocol. If bundled "m=" lines use different protocols on top 748 of the transport-layer protocol, there MUST exist a publicly 749 available specification which describes a mechanism, for this 750 particular protocol combination, how to associate a received packet 751 with the correct protocol. 753 In addition, if a received packet can be associated with more than 754 one bundled "m=" line, there MUST exist a publically available 755 specification which describes a mechanism for associating the 756 received packet with the correct "m=" line. 758 9.2. STUN, DTLS, SRTP 760 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 761 protocol of a received packet among the STUN, DTLS and SRTP protocols 762 (in any combination). If an offer or answer includes bundled "m=" 763 lines that represent these protocols, the offerer or answerer MUST 764 support the mechanism described in [RFC5764], and no explicit 765 negotiation is required in order to indicate support and usage of the 766 mechanism. 768 [RFC5764] does not describe how to identify different protocols 769 transported on DTLS, only how to identify the DTLS protocol itself. 770 If multiple protocols are transported on DTLS, there MUST exist a 771 specification describing a mechanism for identifying each individual 772 protocol. In addition, if a received DTLS packet can be associated 773 with more than one "m=" line, there MUST exist a specification which 774 describes a mechanism for associating the received DTLS packet with 775 the correct "m=" line. 777 [Section 10.2] describes how to associate a received (S)RTP packet 778 with the correct "m=" line. 780 10. RTP Considerations 782 10.1. Single RTP Session 784 10.1.1. General 786 All RTP-based media within a single BUNDLE group belong to a single 787 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 788 sessions, one per BUNDLE group. 790 Since a single RTP session is used for each bundle group, all "m=" 791 lines representing RTP-based media in a bundle group will share a 792 single SSRC numbering space [RFC3550]. 794 The following rules and restrictions apply for a single RTP session: 796 o A specific payload type value can be used in multiple bundled "m=" 797 lines if each codec associated with the payload type number shares 798 an identical codec configuration [Section 10.1.2]. 800 o The proto value in each bundled RTP-based "m=" line MUST be 801 identical (e.g. RTP/AVPF). 803 o The RTP MID header extension MUST be enabled, by associating an 804 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 805 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 806 in every offer and answer. 808 o A given SSRC MUST NOT transmit RTP packets using payload types 809 that originate from different bundled "m=" lines. 811 NOTE: The last bullet above is to avoid sending multiple media types 812 from the same SSRC. If transmission of multiple media types are done 813 with time overlap, RTP and RTCP fail to function. Even if done in 814 proper sequence this causes RTP Timestamp rate switching issues 815 [RFC7160]. However, once an SSRC has left the RTP session (by 816 sending an RTCP BYE packet), that SSRC value can later be reused by 817 another source(possible associated with a different bundled "m=" 818 line. 820 10.1.2. Payload Type (PT) Value Reuse 822 Multiple bundled "m=" lines might represent RTP based media. As all 823 RTP based media associated with a BUNDLE group belong to the same RTP 824 session, in order for a given payload type value to be used inside 825 more than one bundled "m=" line, all codecs associated with the 826 payload type number MUST share an identical codec configuration. 827 This means that the codecs MUST share the same media type, encoding 828 name, clock rate and any parameter that can affect the codec 829 configuration and packetization. [I-D.mmusic-sdp-mux-attributes] 830 lists SDP attributes, whose attribute values must be identical for 831 all codecs that use the same payload type value. 833 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 835 There are multiple mechanisms that can be used by an endpoint in 836 order to associate received RTP/RTCP packets with a bundled "m=" 837 line. Such mechanisms include using the payload type value carried 838 inside the RTP packets, the SSRC values carried inside the RTP 839 packets, and other "m=" line specific information carried inside the 840 RTP packets. 842 As all RTP/RTCP packets associated with a BUNDLE group are received 843 (and sent) using single address:port combinations, the local 844 address:port combination cannot be used to associate received RTP 845 packets with the correct "m=" line. 847 As described in [Section 10.1.2], the same payload type value might 848 be used inside RTP packets described by multiple "m=" lines. In such 849 cases, the payload type value cannot be used to associate received 850 RTP packets with the correct "m=" line. 852 An offerer and answerer can in an offer and answer inform each other 853 which SSRC values they will use inside sent RTP/RTCP packets, by 854 associating one or more SDP 'ssrc' attributes [RFC5576] with each 855 bundled "m=" line which contains a payload type value that is also 856 used inside another bundled "m=" line. As the SSRC values will be 857 carried inside the RTP/RTCP packets, the offerer and answerer can 858 then use that information to associate received RTP packets with the 859 correct "m=" line. However, an offerer will not know which SSRC 860 values the answerer will use until it has received the answer 861 providing that information. Due to this, before the offerer has 862 received the answer, the offerer will not be able to associate 863 received RTP/RTCP packets with the correct "m=" line using the SSRC 864 values. 866 In order for an offerer and answerer to always be able to associate 867 received RTP and RTCP packets with the correct "m=" line, an offerer 868 and answerer using the BUNDLE extension MUST support the mechanism 869 defined in Section 13, where the remote endpoint inserts the 870 identification-tag associated with an "m=" line in RTP and RTCP 871 packets associated with that "m=" line. 873 10.3. RTP/RTCP Multiplexing 875 10.3.1. General 877 When a BUNDLE group, which contains RTP based media, is created, the 878 offerer and answerer MUST negotiate whether to enable RTP/RTCP 879 multiplexing for the RTP based media associated with the BUNDLE group 880 [RFC5761]. 882 If RTP/RTCP multiplexing is not enabled, separate address:port 883 combinations will be used for receiving (and sending) the RTP packets 884 and the RTCP packets. 886 10.3.2. SDP Offer/Answer Procedures 888 10.3.2.1. General 890 This section describes how an offerer and answerer can use the SDP 891 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 892 to negotiate usage of RTP/RTCP multiplexing for RTP based media 893 associated with a BUNDLE group. 895 10.3.2.2. Generating the Initial SDP Offer 897 When an offerer generates an initial offer, if the offerer wants to 898 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 899 offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with 900 each bundled RTP-based "m=" line (including any bundle-only "m=" 901 line) in the offer. 903 If the offerer does not want to negotiate usage of RTP/RTCP 904 multiplexing, it MUST NOT associate an SDP 'rtcp-mux' attribute with 905 any bundled "m=" line in the offer. 907 In addition, the offerer can associate an SDP 'rtcp' attribute 908 [RFC3605] with one or more bundled RTP-based "m=" lines (including 909 any bundle-only "m=" line) in the offer, in order to provide a port 910 for receiving RTCP packets (if the answerer does not accept usage of 911 RTP/RTCP multiplexing, or if the offerer does not want to negotiate 912 usage of RTP/RTCP multiplexing). 914 In the initial offer, the IP address and port combination for RTCP 915 MUST be unique in each bundled RTP-based "m=" line, similar to RTP. 917 NOTE: In case the offer wants to receive RTCP packets on the next 918 higher port value, the SDP 'rtcp' attribute is not needed. 920 10.3.2.3. Generating the SDP Answer 922 When an answerer generates an answer, if the offerer indicated 923 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 924 the associated offer, the answerer MUST either accept or reject the 925 usage of RTP/RTCP multiplexing for the whole BUNDLE group in the 926 answer. 928 If the answerer accepts the usage of RTP/RTCP multiplexing within the 929 BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each 930 bundled RTP-based "m=" line in the answer. The answerer MUST NOT 931 associate an SDP 'rtcp' attribute with any bundled "m=" line in the 932 answer. The answerer will use the port value of the selected offerer 933 BUNDLE address for sending RTP and RTCP packets associated with each 934 RTP-based bundled "m=" line towards the offerer. 936 If the answerer does not accept the usage of RTP/RTCP multiplexing 937 within the BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux' 938 attribute with any bundled "m=" line in the answer. The answerer 939 will use the RTP and RTCP port values associated with the selected 940 offerer BUNDLE address for sending RTP and RTCP packets associated 941 with each RTP-based bundled "m=" line towards the offerer. 943 In addition, if the answerer rejects the usage of RTP/RTCP 944 multiplexing within the BUNDLE group, it MAY associate an SDP 'rtcp' 945 attribute, with identical attribute values, with each RTP-based 946 bundled "m=" line in the answer, in order to provide a port value for 947 receiving RTCP packets from the offerer. 949 NOTE: In case the answerer wants to receive RTCP packets on the next 950 higher port value, the SDP 'rtcp' attribute is not needed. 952 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 953 negotiated in a previous offer/answer transaction, and if the offerer 954 indicates that it wants to continue using RTP/RTCP multiplexing in a 955 subsequent offer, the answerer MUST associate an SDP 'rtcp-mux' 956 attribute with each bundled "m=" line in the answer. I.e. the 957 answerer MUST NOT disable the usage of RTP/RTCP multiplexing. 959 If the usage of RTP/RTCP multiplexing within a BUNDLE group has not 960 been negotiated in a previous offer/answer transaction, and if the 961 offerer indicates that it wants to use RTP/RTCP multiplexing in a 962 subsequent offer, the answerer either accepts or rejects the usage, 963 using the procedures above. 965 10.3.2.4. Offerer Processing of the SDP Answer 967 When an offerer receives an answer, if the answerer has accepted the 968 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 969 follows the procedures for RTP/RTCP multiplexing defined in 970 [RFC5761]. The offerer will use the port value associated with the 971 answerer BUNDLE address for sending RTP and RTCP packets associated 972 with each RTP-based bundled "m=" line towards the answerer. 974 If the answerer did not accept the usage of RTP/RTCP multiplexing 975 (see Section 10.3.2.3), the offerer will use separate address:port 976 combinations for sending RTP and RTCP packets towards the answerer. 977 If the answerer associated an SDP 'rtcp' attribute with the "m=" line 978 representing the answerer BUNDLE address, the offerer will use the 979 attribute port value for sending RTCP packets associated with each 980 bundled RTP-based "m=" line towards the answerer. Otherwise the 981 offerer will use the next higher port value associated with the 982 answerer BUNDLE address for sending RTCP packets towards the 983 answerer. 985 10.3.2.5. Modifying the Session 987 When an offerer generates a subsequent offer, if it wants to 988 negotiate the usage of RTP/RTCP multiplexing within a BUNDLE group, 989 or if it wants to continue the use of previously negotiated RTP/RTCP 990 multiplexing, it MUST associate an SDP 'rtcp-mux' attribute with each 991 RTP-based bundled "m=" line (including any bundled "m=" line that the 992 offerer wants to add to the BUNDLE group), unless the offerer wants 993 to disable or remove the "m=" line from the BUNDLE group. 995 If the offerer does not want to negotiate the usage of RTP/RTCP 996 multiplexing within the BUNDLE group, or if it wants to disable 997 previously negotiated usage of RTP/RTCP multiplexing, it MUST NOT 998 associate an SDP 'rtcp-mux' and attribute with any bundled "m=" line 999 in the subsequent offer. 1001 In addition, if the offerer does not indicate support of RTP/RTCP 1002 multiplexing within the subsequent offer, it MAY associate an SDP 1003 'rtcp' attribute, with identical attribute values, with each RTP- 1004 based bundled "m=" line (including any bundled "m=" line that the 1005 offerer wants to add to the BUNDLE group), in order to provide a port 1006 for receiving RTCP packets. 1008 NOTE: It is RECOMMENDED that, once the usage of RTP/RTCP multiplexing 1009 has been negotiated within a BUNDLE group, that the usage is not 1010 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 1011 answerer need to reserve new ports, to be used for sending and 1012 receiving RTCP packets. Similar, if the usage of a specific RTCP 1013 port has been negotiated within a BUNDLE group, it is RECOMMENDED 1014 that the port value is not modified. 1016 11. ICE Considerations 1018 11.1. General 1020 This section describes how to use the BUNDLE grouping extension 1021 together with the Interactive Connectivity Establishment (ICE) 1022 mechanism [RFC5245]. 1024 The procedures defined in [RFC5245] also apply to usage of ICE with 1025 BUNDLE, with the following exception: 1027 o When BUNDLE addresses for a BUNDLE group have been selected for 1028 both endpoints, ICE connectivity checks and keep-alives only need 1029 to be performed for the whole BUNDLE group, instead of per bundled 1030 "m=" line. 1032 Support and usage of ICE mechanism together with the BUNDLE extension 1033 is OPTIONAL. 1035 11.2. SDP Offer/Answer Procedures 1037 11.2.1. General 1039 When an offerer assigns a unique address to a bundled "m=" line 1040 (excluding any bundle-only "m=" line), it MUST also associate unique 1041 ICE candidates [RFC5245] to the "m=" line. 1043 An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line 1044 with a zero port value. 1046 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1047 inherit the candidates associated with the selected offerer BUNDLE 1048 address. An answerer that does not support BUNDLE would not accept a 1049 bundle-only "m=" line. 1051 When an offerer or answerer assigns a shared address (i.e. a 1052 previously selected BUNDLE address) to one or more bundled "m=" 1053 lines, it MUST associate identical ICE candidates (referred to as 1054 shared ICE candidates) to each of those "m=" lines. 1056 11.2.2. Generating the Initial SDP Offer 1058 When an offerer generates an initial offer, it assigns unique or 1059 shared ICE candidates to the bundled "m=" lines, according to 1060 Section 11.1. 1062 11.2.3. Generating the SDP Answer 1064 When an answerer generates an answer, which contains a BUNDLE group, 1065 the answerer MUST assign shared ICE candidates to each bundled "m=" 1066 line (including "m=" lines that were indicated as bundle-only in the 1067 associated offer) in the answer. 1069 11.2.4. Offerer Processing of the SDP Answer 1071 When an offerer receives an answer, if the answerer supports and uses 1072 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1073 the same ICE candidates, associated with the "m=" line representing 1074 the offerer BUNDLE address (selected by the answerer), to each 1075 bundled "m=" line. 1077 11.2.5. Modifying the Session 1079 When an offerer generates a subsequent offer, it assigns unique or 1080 shared ICE candidates to the bundled "m=" lines, according to 1081 (Section 11.1). 1083 12. Update to RFC 3264 1085 12.1. General 1087 This section replaces the text of the following sections of RFC 3264: 1089 o Section 5.1 (Unicast Streams). 1091 o Section 8.2 (Removing a Media Stream). 1093 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1095 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1097 For recvonly and sendrecv streams, the port number and address in the 1098 offer indicate where the offerer would like to receive the media 1099 stream. For sendonly RTP streams, the address and port number 1100 indirectly indicate where the offerer wants to receive RTCP reports. 1101 Unless there is an explicit indication otherwise, reports are sent to 1102 the port number one higher than the number indicated. The IP address 1103 and port present in the offer indicate nothing about the source IP 1104 address and source port of RTP and RTCP packets that will be sent by 1105 the offerer. A port number of zero in the offer indicates that the 1106 stream is offered but MUST NOT be used. This has no useful semantics 1107 in an initial offer, but is allowed for reasons of completeness, 1108 since the answer can contain a zero port indicating a rejected stream 1109 (Section 6). Furthermore, existing streams can be terminated by 1110 setting the port to zero (Section 8). In general, a port number of 1111 zero indicates that the media stream is not wanted. 1113 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1115 For recvonly and sendrecv streams, the port number and address in the 1116 offer indicate where the offerer would like to receive the media 1117 stream. For sendonly RTP streams, the address and port number 1118 indirectly indicate where the offerer wants to receive RTCP reports. 1119 Unless there is an explicit indication otherwise, reports are sent to 1120 the port number one higher than the number indicated. The IP address 1121 and port present in the offer indicate nothing about the source IP 1122 address and source port of RTP and RTCP packets that will be sent by 1123 the offerer. A port number of zero in the offer by default indicates 1124 that the stream is offered but MUST NOT be used, but an extension 1125 mechanism might specify different semantics for the usage of a zero 1126 port value. Furthermore, existing streams can be terminated by 1127 setting the port to zero (Section 8). In general, a port number of 1128 zero by default indicates that the media stream is not wanted. 1130 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1132 A stream that is offered with a port of zero MUST be marked with port 1133 zero in the answer. Like the offer, the answer MAY omit all 1134 attributes present previously, and MAY list just a single media 1135 format from amongst those in the offer. 1137 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1139 A stream that is offered with a port of zero MUST by default be 1140 marked with port zero in the answer, unless an extension mechanism, 1141 which specifies semantics for the usage of a non-zero port value, is 1142 used. If the stream is marked with port zero in the answer, the 1143 answer MAY omit all attributes present previously, and MAY list just 1144 a single media format from amongst those in the offer." 1146 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1148 RFC 2543 [10] specified that placing a user on hold was accomplished 1149 by setting the connection address to 0.0.0.0. Its usage for putting 1150 a call on hold is no longer recommended, since it doesn't allow for 1151 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1152 with connection oriented media. However, it can be useful in an 1153 initial offer when the offerer knows it wants to use a particular set 1154 of media streams and formats, but doesn't know the addresses and 1155 ports at the time of the offer. Of course, when used, the port 1156 number MUST NOT be zero, which would specify that the stream has been 1157 disabled. An agent MUST be capable of receiving SDP with a 1158 connection address of 0.0.0.0, in which case it means that neither 1159 RTP nor RTCP should be sent to the peer. 1161 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1163 RFC 2543 [10] specified that placing a user on hold was accomplished 1164 by setting the connection address to 0.0.0.0. Its usage for putting 1165 a call on hold is no longer recommended, since it doesn't allow for 1166 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1167 with connection oriented media. However, it can be useful in an 1168 initial offer when the offerer knows it wants to use a particular set 1169 of media streams and formats, but doesn't know the addresses and 1170 ports at the time of the offer. Of course, when used, the port 1171 number MUST NOT be zero, if it would specify that the stream has been 1172 disabled. However, an extension mechanism might specify different 1173 semantics of the zero port number usage. An agent MUST be capable of 1174 receiving SDP with a connection address of 0.0.0.0, in which case it 1175 means that neither RTP nor RTCP should be sent to the peer. 1177 13. RTP/RTCP extensions for identification-tag transport 1179 13.1. General 1181 SDP Offerers and Answerers [RFC3264] can associate identification- 1182 tags with "m=" lines within SDP Offers and Answers, using the 1183 procedures in [RFC5888]. Each identification-tag uniquely represents 1184 an "m=" line. 1186 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1187 used to carry identification-tags within RTCP SDES packets. This 1188 section also defines a new RTP header extension [RFC5285], which is 1189 used to carry identification-tags in RTP packets. 1191 The SDES item and RTP header extension make it possible for a 1192 receiver to associate received RTCP- and RTP packets with a specific 1193 "m=" line, to which the receiver has assigned an identification-tag, 1194 even if those "m=" lines are part of the same RTP session. The 1195 endpoint informs the remote endpoint about the identification-tag 1196 using the procedures in [RFC5888], and the remote endpoint then 1197 inserts the identification-tag in RTCP- and RTP packets sent towards 1198 the other endpoint. 1200 NOTE: This text above defines how identification-tags are carried in 1201 SDP Offers and Answers. The usage of other signalling protocols for 1202 carrying identification-tags is not prevented, but the usage of such 1203 protocols is outside the scope of this document. 1205 [RFC3550] defines general procedures regarding the RTCP transmission 1206 interval. The RTCP MID SDES item SHOULD be sent in the first few 1207 RTCP packets sent on joining the session, and SHOULD be sent 1208 regularly thereafter. The exact number of RTCP packets in which this 1209 SDES item is sent is intentionally not specified here, as it will 1210 depend on the expected packet loss rate, the RTCP reporting interval, 1211 and the allowable overhead. 1213 The RTP MID header extension SHOULD be included in some RTP packets 1214 at the start of the session and whenever the SSRC changes. It might 1215 also be useful to include the header extension in RTP packets that 1216 comprise random access points in the media (e.g., with video 1217 I-frames). The exact number of RTP packets in which this header 1218 extension is sent is intentionally not specified here, as it will 1219 depend on expected packet loss rate and loss patterns, the overhead 1220 the application can tolerate, and the importance of immediate receipt 1221 of the identification-tag. 1223 For robustness purpose, endpoints need to be prepared for situations 1224 where the reception of the identification-tag is delayed, and SHOULD 1225 NOT terminate sessions in such cases, as the identification-tag is 1226 likely to arrive soon. 1228 13.2. RTCP MID SDES Item 1230 0 1 2 3 1231 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 1232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1233 | MID=TBD | length | identification-tag ... 1234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1236 The identification-tag payload is UTF-8 encoded, as in SDP. 1238 The identification-tag is not zero terminated. 1240 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1241 identifier value.] 1243 13.3. RTP MID Header Extension 1245 The payload, containing the identification-tag, of the RTP MID header 1246 extension element can be encoded using either the one-byte or two- 1247 byte header [RFC5285]. The identification-tag payload is UTF-8 1248 encoded, as in SDP. 1250 The identification-tag is not zero terminated. Note, that set of 1251 header extensions included in the packet needs to be padded to the 1252 next 32-bit boundary using zero bytes [RFC5285]. 1254 As the identification-tag is included in either an RTCP SDES item or 1255 an RTP header extension, or both, there should be some consideration 1256 about the packet expansion caused by the identification-tag. To 1257 avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the 1258 header extension's size needs to be taken into account when the 1259 encoding media. 1261 It is recommended that the identification-tag is kept short. Due to 1262 the properties of the RTP header extension mechanism, when using the 1263 one-byte header, a tag that is 1-3 bytes will result in that a 1264 minimal number of 32-bit words are used for the RTP header extension, 1265 in case no other header extensions are included at the same time. 1266 Note, do take into account that some single characters when UTF-8 1267 encoded will result in multiple octets. 1269 14. IANA Considerations 1271 14.1. New SDES item 1273 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1274 document.] 1276 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1277 identifier value.] 1279 This document adds the MID SDES item to the IANA "RTCP SDES item 1280 types" registry as follows: 1282 Value: TBD 1283 Abbrev.: MID 1284 Name: Media Identification 1285 Reference: RFCXXXX 1287 14.2. New RTP Header Extension URI 1289 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1290 document.] 1292 This document defines a new extension URI in the RTP Compact Header 1293 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1294 Parameters registry, according to the following data: 1296 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1297 Description: Media identification 1298 Contact: christer.holmberg@ericsson.com 1299 Reference: RFCXXXX 1301 14.3. New SDP Attribute 1303 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1304 document.] 1306 This document defines a new SDP media-level attribute, 'bundle-only', 1307 according to the following data: 1309 Attribute name: bundle-only 1310 Type of attribute: media 1311 Subject to charset: No 1312 Purpose: Request a media description to be accepted 1313 in the answer only if kept within a BUNDLE 1314 group by the answerer. 1315 Appropriate values: N/A 1316 Contact name: Christer Holmberg 1317 Contact e-mail: christer.holmberg@ericsson.com 1318 Reference: RFCXXXX 1320 15. Security Considerations 1322 The security considerations defined in [RFC3264] and [RFC5888] apply 1323 to the BUNDLE extension. Bundle does not change which information 1324 flows over the network but only changes which ports that information 1325 is flowing on and thus has very little impact on the security of the 1326 RTP sessions. 1328 When the BUNDLE extension is used, a single set of security 1329 credentials might be used for all media streams associated with a 1330 BUNDLE group. 1332 When the BUNDLE extension is used, the number of SSRC values within a 1333 single RTP session increases, which increases the risk of SSRC 1334 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1335 and SRTCP encryption in certain situations. 1337 16. Examples 1339 16.1. Example: Bundle Address Selection 1341 The example below shows: 1343 o 1. An offer, in which the offerer assigns a unique address to 1344 each bundled "m=" line within the BUNDLE group. 1346 o 2. An answer, in which the answerer selects the offerer BUNDLE 1347 address, and in which selects its own BUNDLE address (the answerer 1348 BUNDLE address) and assigns it each bundled "m=" line within the 1349 BUNDLE group. 1351 SDP Offer (1) 1353 v=0 1354 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1355 s= 1356 c=IN IP4 atlanta.example.com 1357 t=0 0 1358 a=group:BUNDLE foo bar 1359 m=audio 10000 RTP/AVP 0 8 97 1360 b=AS:200 1361 a=mid:foo 1362 a=rtpmap:0 PCMU/8000 1363 a=rtpmap:8 PCMA/8000 1364 a=rtpmap:97 iLBC/8000 1365 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1366 m=video 10002 RTP/AVP 31 32 1367 b=AS:1000 1368 a=mid:bar 1369 a=rtpmap:31 H261/90000 1370 a=rtpmap:32 MPV/90000 1371 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1373 SDP Answer (2) 1375 v=0 1376 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1377 s= 1378 c=IN IP4 biloxi.example.com 1379 t=0 0 1380 a=group:BUNDLE foo bar 1381 m=audio 20000 RTP/AVP 0 1382 b=AS:200 1383 a=mid:foo 1384 a=rtpmap:0 PCMU/8000 1385 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1386 m=video 20000 RTP/AVP 32 1387 b=AS:1000 1388 a=mid:bar 1389 a=rtpmap:32 MPV/90000 1390 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1392 16.2. Example: BUNDLE Extension Rejected 1394 The example below shows: 1396 o 1. An offer, in which the offerer assigns a unique address to 1397 each bundled "m=" line within the BUNDLE group. 1399 o 2. An answer, in which the answerer rejects the offered BUNDLE 1400 group, and assigns a unique addresses to each "m=" line (following 1401 normal RFC 3264 procedures). 1403 SDP Offer (1) 1405 v=0 1406 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1407 s= 1408 c=IN IP4 atlanta.example.com 1409 t=0 0 1410 a=group:BUNDLE foo bar 1411 m=audio 10000 RTP/AVP 0 8 97 1412 b=AS:200 1413 a=mid:foo 1414 a=rtpmap:0 PCMU/8000 1415 a=rtpmap:8 PCMA/8000 1416 a=rtpmap:97 iLBC/8000 1417 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1418 m=video 10002 RTP/AVP 31 32 1419 b=AS:1000 1420 a=mid:bar 1421 a=rtpmap:31 H261/90000 1422 a=rtpmap:32 MPV/90000 1423 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1425 SDP Answer (2) 1427 v=0 1428 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1429 s= 1430 c=IN IP4 biloxi.example.com 1431 t=0 0 1432 m=audio 20000 RTP/AVP 0 1433 b=AS:200 1434 a=rtpmap:0 PCMU/8000 1435 m=video 30000 RTP/AVP 32 1436 b=AS:1000 1437 a=rtpmap:32 MPV/90000 1439 16.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1441 The example below shows: 1443 o 1. A subsequent offer (the BUNDLE group has been created as part 1444 of a previous offer/answer transaction), in which the offerer adds 1445 a new "m=" line, represented by the "zen" identification-tag, to a 1446 previously negotiated BUNDLE group, assigns a unique address to 1447 the added "m=" line, and assigns the previously selected offerer 1448 BUNDLE address to each of the other bundled "m=" lines within the 1449 BUNDLE group. 1451 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1452 address to each bundled "m=" line (including the newly added "m=" 1453 line) within the BUNDLE group. 1455 SDP Offer (1) 1457 v=0 1458 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1459 s= 1460 c=IN IP4 atlanta.example.com 1461 t=0 0 1462 a=group:BUNDLE foo bar zen 1463 m=audio 10000 RTP/AVP 0 8 97 1464 b=AS:200 1465 a=mid:foo 1466 a=rtpmap:0 PCMU/8000 1467 a=rtpmap:8 PCMA/8000 1468 a=rtpmap:97 iLBC/8000 1469 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1470 m=video 10000 RTP/AVP 31 32 1471 b=AS:1000 1472 a=mid:bar 1473 a=rtpmap:31 H261/90000 1474 a=rtpmap:32 MPV/90000 1475 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1476 m=video 20000 RTP/AVP 66 1477 b=AS:1000 1478 a=mid:zen 1479 a=rtpmap:66 H261/90000 1480 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1482 SDP Answer (2) 1484 v=0 1485 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1486 s= 1487 c=IN IP4 biloxi.example.com 1488 t=0 0 1489 a=group:BUNDLE foo bar zen 1490 m=audio 20000 RTP/AVP 0 1491 b=AS:200 1492 a=mid:foo 1493 a=rtpmap:0 PCMU/8000 1494 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1495 m=video 20000 RTP/AVP 32 1496 b=AS:1000 1497 a=mid:bar 1498 a=rtpmap:32 MPV/90000 1499 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1500 m=video 20000 RTP/AVP 66 1501 b=AS:1000 1502 a=mid:zen 1503 a=rtpmap:66 H261/90000 1504 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1506 16.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1508 The example below shows: 1510 o 1. A subsequent offer (the BUNDLE group has been created as part 1511 of a previous offer/answer transaction), in which the offerer 1512 moves a bundled "m=" line out of a BUNDLE group, assigns a unique 1513 address to the moved "m=" line, and assigns the offerer BUNDLE 1514 address to each other bundled "m=" line within the BUNDLE group. 1516 o 2. An answer, in which the answerer moves the "m=" line out of 1517 the BUNDLE group, assigns unique address to the moved "m=" line, 1518 and assigns the answerer BUNDLE address to each of the remaining 1519 bundled "m=" line within the BUNDLE group. 1521 SDP Offer (1) 1523 v=0 1524 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1525 s= 1526 c=IN IP4 atlanta.example.com 1527 t=0 0 1528 a=group:BUNDLE foo bar 1529 m=audio 10000 RTP/AVP 0 8 97 1530 b=AS:200 1531 a=mid:foo 1532 a=rtpmap:0 PCMU/8000 1533 a=rtpmap:8 PCMA/8000 1534 a=rtpmap:97 iLBC/8000 1535 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1536 m=video 10000 RTP/AVP 31 32 1537 b=AS:1000 1538 a=mid:bar 1539 a=rtpmap:31 H261/90000 1540 a=rtpmap:32 MPV/90000 1541 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1542 m=video 50000 RTP/AVP 66 1543 b=AS:1000 1544 a=mid:zen 1545 a=rtpmap:66 H261/90000 1547 SDP Answer (2) 1549 v=0 1550 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1551 s= 1552 c=IN IP4 biloxi.example.com 1553 t=0 0 1554 a=group:BUNDLE foo bar 1555 m=audio 20000 RTP/AVP 0 1556 b=AS:200 1557 a=mid:foo 1558 a=rtpmap:0 PCMU/8000 1559 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1560 m=video 20000 RTP/AVP 32 1561 b=AS:1000 1562 a=mid:bar 1563 a=rtpmap:32 MPV/90000 1564 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1565 m=video 60000 RTP/AVP 66 1566 b=AS:1000 1567 a=mid:zen 1568 a=rtpmap:66 H261/90000 1570 16.5. Example: Offerer Disables A Media Description Within A BUNDLE 1571 Group 1573 The example below shows: 1575 o 1. A subsequent offer (the BUNDLE group has been created as part 1576 of a previous offer/answer transaction), in which the offerer 1577 disables a bundled "m=" line within BUNDLE group, assigns a zero 1578 port number to the disabled "m=" line, and assigns the offerer 1579 BUNDLE address to each of the other bundled "m=" lines within the 1580 BUNDLE group. 1582 o 2. An answer, in which the answerer moves the disabled "m=" line 1583 out of the BUNDLE group, assigns a zero port value to the disabled 1584 "m=" line, and assigns the answerer BUNDLE address to each of the 1585 remaining bundled "m=" line within the BUNDLE group. 1587 SDP Offer (1) 1589 v=0 1590 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1591 s= 1592 c=IN IP4 atlanta.example.com 1593 t=0 0 1594 a=group:BUNDLE foo bar 1595 m=audio 10000 RTP/AVP 0 8 97 1596 b=AS:200 1597 a=mid:foo 1598 a=rtpmap:0 PCMU/8000 1599 a=rtpmap:8 PCMA/8000 1600 a=rtpmap:97 iLBC/8000 1601 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1602 m=video 10000 RTP/AVP 31 32 1603 b=AS:1000 1604 a=mid:bar 1605 a=rtpmap:31 H261/90000 1606 a=rtpmap:32 MPV/90000 1607 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1608 m=video 0 RTP/AVP 66 1609 a=mid:zen 1610 a=rtpmap:66 H261/90000 1612 SDP Answer (2) 1614 v=0 1615 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1616 s= 1617 c=IN IP4 biloxi.example.com 1618 t=0 0 1619 a=group:BUNDLE foo bar 1620 m=audio 20000 RTP/AVP 0 1621 b=AS:200 1622 a=mid:foo 1623 a=rtpmap:0 PCMU/8000 1624 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1625 m=video 20000 RTP/AVP 32 1626 b=AS:1000 1627 a=mid:bar 1628 a=rtpmap:32 MPV/90000 1629 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1630 m=video 0 RTP/AVP 66 1631 a=mid:zen 1632 a=rtpmap:66 H261/90000 1634 17. Acknowledgements 1636 The usage of the SDP grouping extension for negotiating bundled media 1637 is based on a similar alternatives proposed by Harald Alvestrand and 1638 Cullen Jennings. The BUNDLE extension described in this document is 1639 based on the different alternative proposals, and text (e.g. SDP 1640 examples) have been borrowed (and, in some cases, modified) from 1641 those alternative proposals. 1643 The SDP examples are also modified versions from the ones in the 1644 Alvestrand proposal. 1646 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1647 Stach and Ari Keraenen for taking the time to read the text along the 1648 way, and providing useful feedback. 1650 18. Change Log 1652 [RFC EDITOR NOTE: Please remove this section when publishing] 1654 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 1656 o - Changes based on agreements at IETF#92 1658 o -- BAS Offer removed, based on agreement at IETF#92. 1660 o -- Procedures regarding usage of SDP "b=" line is replaced with a 1661 reference to to draft-ietf-mmusic-sdp-mux-attributes. 1663 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 1665 o - Editorial changes based on comments from Magnus Westerlund. 1667 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1669 o - Modification of RTP/RTCP multiplexing section, based on comments 1670 from Magnus Westerlund. 1672 o - Reference updates. 1674 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1675 o - Editorial fix. 1677 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1679 o - Editorial changes. 1681 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1683 o Changes to allow a new suggested offerer BUNDLE address to be 1684 assigned to each bundled m- line. 1686 o Changes based on WGLC comments from Paul Kyzivat 1688 o - Editorial fixes 1690 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1692 o Usage of SDP 'extmap' attribute added 1694 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1695 port value 1697 o Changes based on WGLC comments from Thomas Stach 1699 o - ICE candidates not assigned to bundle-only m- lines with a zero 1700 port value 1702 o - Editorial changes 1704 o Changes based on WGLC comments from Colin Perkins 1706 o - Editorial changes: 1708 o -- "RTP SDES item" -> "RTCP SDES item" 1710 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1712 o - Changes in section 10.1.1: 1714 o -- "SHOULD NOT" -> "MUST NOT" 1716 o -- Additional text added to the Note 1718 o - Change to section 13.2: 1720 o -- Clarify that mid value is not zero terminated 1722 o - Change to section 13.3: 1724 o -- Clarify that mid value is not zero terminated 1726 o -- Clarify padding 1728 o Changes based on WGLC comments from Paul Kyzivat 1730 o - Editorial changes: 1732 o Changes based on WGLC comments from Jonathan Lennox 1734 o - Editorial changes: 1736 o - Defintion of SDP bundle-only attribute alligned with structure 1737 in 4566bis draft 1739 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1741 o Editorial corrections based on comments from Harald Alvestrand. 1743 o Editorial corrections based on comments from Cullen Jennings. 1745 o Reference update (RFC 7160). 1747 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1748 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1749 msg13765.html). 1751 o Additional text added to the Security Considerations. 1753 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1755 o SDP bundle-only attribute added to IANA Considerations. 1757 o SDES item and RTP header extension added to Abstract and 1758 Introduction. 1760 o Modification to text updating section 8.2 of RFC 3264. 1762 o Reference corrections. 1764 o Editorial corrections. 1766 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1768 o Terminology change: "bundle-only attribute assigned to m= line" to 1769 "bundle-only attribute associated with m= line". 1771 o Editorial corrections. 1773 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1775 o Editorial corrections. 1777 o - "of"->"if" (8.3.2.5). 1779 o - "optional"->"OPTIONAL" (9.1). 1781 o - Syntax/ABNF for 'bundle-only' attribute added. 1783 o - SDP Offer/Answer sections merged. 1785 o - 'Request new offerer BUNDLE address' section added 1787 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1789 o OPEN ISSUE regarding Receiver-ID closed. 1791 o - RTP MID SDES Item. 1793 o - RTP MID Header Extension. 1795 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1796 closed. 1798 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1799 include an 'rtcp' attribute in the answer, based on the procedures 1800 in section 5.1.3 of RFC 5761. 1802 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1804 o Draft title changed. 1806 o Added "SDP" to section names containing "Offer" or "Answer". 1808 o Editorial fixes based on comments from Paul Kyzivat 1809 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1810 msg13314.html). 1812 o Editorial fixed based on comments from Colin Perkins 1813 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1814 msg13318.html). 1816 o - Removed text about extending BUNDLE to allow multiple RTP 1817 sessions within a BUNDLE group. 1819 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1820 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1821 3264 structure. 1823 o Additional definitions added. 1825 o - Shared address. 1827 o - Bundled "m=" line. 1829 o - Bundle-only "m=" line. 1831 o - Offerer suggested BUNDLE mid. 1833 o - Answerer selected BUNDLE mid. 1835 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1836 to multiple "m=" lines until it has received an SDP Answer 1837 indicating support of the BUNDLE extension. 1839 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1840 Answerer supports the BUNDLE extension, assign a zero port value 1841 to a 'bundle-only' "m=" line. 1843 o SDP 'bundle-only' attribute section added. 1845 o Connection data nettype/addrtype restrictions added. 1847 o RFC 3264 update section added. 1849 o Indicating that a specific payload type value can be used in 1850 multiple "m=" lines, if the value represents the same codec 1851 configuration in each "m=" line. 1853 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1855 o Updated Offerer procedures (http://www.ietf.org/mail- 1856 archive/web/mmusic/current/msg12293.html). 1858 o Updated Answerer procedures (http://www.ietf.org/mail- 1859 archive/web/mmusic/current/msg12333.html). 1861 o Usage of SDP 'bundle-only' attribute added. 1863 o Reference to Trickle ICE document added. 1865 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1866 o Mechanism modified, to be based on usage of SDP Offers with both 1867 different and identical port number values, depending on whether 1868 it is known if the remote endpoint supports the extension. 1870 o Cullen Jennings added as co-author. 1872 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1874 o No changes. New version due to expiration. 1876 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1878 o No changes. New version due to expiration. 1880 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1882 o Draft name changed. 1884 o Harald Alvestrand added as co-author. 1886 o "Multiplex" terminology changed to "bundle". 1888 o Added text about single versus multiple RTP Sessions. 1890 o Added reference to RFC 3550. 1892 19. References 1894 19.1. Normative References 1896 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1897 Requirement Levels", BCP 14, RFC 2119, March 1997. 1899 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1900 with Session Description Protocol (SDP)", RFC 3264, June 1901 2002. 1903 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1904 Description Protocol", RFC 4566, July 2006. 1906 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1907 Header Extensions", RFC 5285, July 2008. 1909 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1910 Control Packets on a Single Port", RFC 5761, April 2010. 1912 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1913 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1915 [I-D.mmusic-sdp-mux-attributes] 1916 Nandakumar, S., "A Framework for SDP Attributes when 1917 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08 1918 (work in progress), January 2015. 1920 19.2. Informative References 1922 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1923 A., Peterson, J., Sparks, R., Handley, M., and E. 1924 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1925 June 2002. 1927 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1928 Jacobson, "RTP: A Transport Protocol for Real-Time 1929 Applications", STD 64, RFC 3550, July 2003. 1931 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1932 in Session Description Protocol (SDP)", RFC 3605, October 1933 2003. 1935 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1936 Description Protocol (SDP) Security Descriptions for Media 1937 Streams", RFC 4568, July 2006. 1939 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1940 (ICE): A Protocol for Network Address Translator (NAT) 1941 Traversal for Offer/Answer Protocols", RFC 5245, April 1942 2010. 1944 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1945 Media Attributes in the Session Description Protocol 1946 (SDP)", RFC 5576, June 2009. 1948 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1949 Security (DTLS) Extension to Establish Keys for the Secure 1950 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 1952 [RFC7160] Petit-Huguenin, M. and G. Zorn, "Support for Multiple 1953 Clock Rates in an RTP Session", RFC 7160, April 2014. 1955 [I-D.ietf-mmusic-trickle-ice] 1956 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 1957 Incremental Provisioning of Candidates for the Interactive 1958 Connectivity Establishment (ICE) Protocol", draft-ietf- 1959 mmusic-trickle-ice-02 (work in progress), January 2015. 1961 Appendix A. Design Considerations 1963 A.1. General 1965 One of the main issues regarding the BUNDLE grouping extensions has 1966 been whether, in SDP Offers and SDP Answers, the same port value 1967 should be inserted in "m=" lines associated with a BUNDLE group, as 1968 the purpose of the extension is to negotiate the usage of a single 1969 address:port combination for media associated with the "m=" lines. 1970 Issues with both approaches, discussed in the Appendix have been 1971 raised. The outcome was to specify a mechanism which uses SDP Offers 1972 with both different and identical port values. 1974 Below are the primary issues that have been considered when defining 1975 the "BUNDLE" grouping extension: 1977 o 1) Interoperability with existing UAs. 1979 o 2) Interoperability with intermediary B2BUA- and proxy entities. 1981 o 3) Time to gather, and the number of, ICE candidates. 1983 o 4) Different error scenarios, and when they occur. 1985 o 5) SDP Offer/Answer impacts, including usage of port number value 1986 zero. 1988 NOTE: Before this document is published as an RFC, this 1989 Appendix might be removed. 1991 A.2. UA Interoperability 1993 Consider the following SDP Offer/Answer exchange, where Alice sends 1994 an SDP Offer to Bob: 1996 SDP Offer 1998 v=0 1999 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2000 s= 2001 c=IN IP4 atlanta.example.com 2002 t=0 0 2003 m=audio 10000 RTP/AVP 97 2004 a=rtpmap:97 iLBC/8000 2005 m=video 10002 RTP/AVP 97 2006 a=rtpmap:97 H261/90000 2008 SDP Answer 2010 v=0 2011 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2012 s= 2013 c=IN IP4 biloxi.example.com 2014 t=0 0 2015 m=audio 20000 RTP/AVP 97 2016 a=rtpmap:97 iLBC/8000 2017 m=video 20002 RTP/AVP 97 2018 a=rtpmap:97 H261/90000 2020 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2021 later invention to RTP and Bob can not assume that Alice supports RFC 2022 4961. This means that Alice may be sending RTP from a different port 2023 than 10000 or 10002 - some implementation simply send the RTP from an 2024 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2025 way that Bob know if it should be passed to the video or audio codec 2026 is by looking at the port it was received on. This lead some SDP 2027 implementations to use the fact that each "m=" line had a different 2028 port number to use that port number as an index to find the correct m 2029 line in the SDP. As a result, some implementations that do support 2030 symmetric RTP and ICE still use a SDP data structure where SDP with 2031 "m=" lines with the same port such as: 2033 SDP Offer 2035 v=0 2036 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2037 s= 2038 c=IN IP4 atlanta.example.com 2039 t=0 0 2040 m=audio 10000 RTP/AVP 97 2041 a=rtpmap:97 iLBC/8000 2042 m=video 10000 RTP/AVP 98 2043 a=rtpmap:98 H261/90000 2045 will result in the second "m=" line being considered an SDP error 2046 because it has the same port as the first line. 2048 A.3. Usage of port number value zero 2050 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2051 can be disabled/rejected by setting the port number value to zero. 2052 This is different from e.g. using the SDP direction attributes, where 2053 RTCP traffic will continue even if the SDP "inactive" attribute is 2054 indicated for the associated "m=" line. 2056 If each "m=" line associated with a BUNDLE group would contain 2057 different port values, and one of those port values would be used for 2058 a BUNDLE address associated with the BUNDLE group, problems would 2059 occur if an endpoint wants to disable/reject the "m=" line associated 2060 with that port, by setting the port value to zero. After that, no 2061 "m=" line would contain the port value which is used for the BUNDLE 2062 address. In addition, it is unclear what would happen to the ICE 2063 candidates associated with the "m=" line, as they are also used for 2064 the BUNDLE address. 2066 A.4. B2BUA And Proxy Interoperability 2068 Some back to back user agents may be configured in a mode where if 2069 the incoming call leg contains an SDP attribute the B2BUA does not 2070 understand, the B2BUS still generates that SDP attribute in the Offer 2071 for the outgoing call leg. Consider an B2BUA that did not understand 2072 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2073 Further assume that the B2BUA was configured to tear down any call 2074 where it did not see any RTCP for 5 minutes. In this cases, if the 2075 B2BUA received an Offer like: 2077 SDP Offer 2079 v=0 2080 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2081 s= 2082 c=IN IP4 atlanta.example.com 2083 t=0 0 2084 m=audio 49170 RTP/AVP 0 2085 a=rtcp:53020 2087 It would be looking for RTCP on port 49172 but would not see any 2088 because the RTCP would be on port 53020 and after five minutes, it 2089 would tear down the call. Similarly, an SBC that did not understand 2090 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2091 wrong port and tear down the call. It is worth noting that a B2BUA 2092 that generated an Offer with capabilities it does not understand is 2093 not compliant with the specifications. 2095 A.4.1. Traffic Policing 2097 Sometimes intermediaries do not act as B2BUA, in the sense that they 2098 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2099 however, they may use SDP information (e.g. IP address and port) in 2100 order to control traffic gating functions, and to set traffic 2101 policing rules. There might be rules which will trigger a session to 2102 be terminated in case media is not sent or received on the ports 2103 retrieved from the SDP. This typically occurs once the session is 2104 already established and ongoing. 2106 A.4.2. Bandwidth Allocation 2108 Sometimes intermediaries do not act as B2BUA, in the sense that they 2109 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2110 however, they may use SDP information (e.g. codecs and media types) 2111 in order to control bandwidth allocation functions. The bandwidth 2112 allocation is done per "m=" line, which means that it might not be 2113 enough if media associated with all "m=" lines try to use that 2114 bandwidth. That may either simply lead to bad user experience, or to 2115 termination of the call. 2117 A.5. Candidate Gathering 2119 When using ICE, an candidate needs to be gathered for each port. 2120 This takes approximately 20 ms extra for each extra "m=" line due to 2121 the NAT pacing requirements. All of this gather can be overlapped 2122 with other things while the page is loading to minimize the impact. 2124 If the client only wants to generate TURN or STUN ICE candidates for 2125 one of the "m=" lines and then use trickle ICE 2126 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2127 the rest of the "m=" lines, it MAY do that and will not need any 2128 additional gathering time. 2130 Some people have suggested a TURN extension to get a bunch of TURN 2131 allocation at once. This would only provide a single STUN result so 2132 in cases where the other end did not support BUNDLE, may cause more 2133 use of the TURN server but would be quick in the cases where both 2134 sides supported BUNDLE and would fall back to a successful call in 2135 the other cases. 2137 Authors' Addresses 2139 Christer Holmberg 2140 Ericsson 2141 Hirsalantie 11 2142 Jorvas 02420 2143 Finland 2145 Email: christer.holmberg@ericsson.com 2147 Harald Tveit Alvestrand 2148 Google 2149 Kungsbron 2 2150 Stockholm 11122 2151 Sweden 2153 Email: harald@alvestrand.no 2155 Cullen Jennings 2156 Cisco 2157 400 3rd Avenue SW, Suite 350 2158 Calgary, AB T2P 4H2 2159 Canada 2161 Email: fluffy@iii.ca