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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 1212 ** 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reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 5285 (Obsoleted by RFC 8285) == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-08 -- Obsolete informational reference (is this intentional?): RFC 5245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 4, 2015 C. Jennings 7 Cisco 8 March 3, 2015 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-17.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 4, 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 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 78 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 7 79 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 80 6.2. bundle-only . . . . . . . . . . . . . . . . . . . . . . . 8 81 7. SDP Information Considerations . . . . . . . . . . . . . . . 8 82 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 83 7.2. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 84 7.3. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 85 7.4. Attributes (a=) . . . . . . . . . . . . . . . . . . . . . 9 86 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 87 8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 88 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 89 8.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 90 8.2.2. Suggesting the offerer BUNDLE address . . . . . . . . 11 91 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 11 92 8.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 11 93 8.3.2. Answerer Selection of Offerer Bundle Address . . . . 12 94 8.3.3. Answerer Selection of Answerer BUNDLE Address . . . . 13 95 8.3.4. Moving A Media Description Out Of A BUNDLE Group . . 13 96 8.3.5. Rejecting A Media Description In A BUNDLE Group . . . 13 97 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14 98 8.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 14 99 8.4.2. Bundle Address Synchronization (BAS) . . . . . . . . 14 100 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 15 101 8.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 15 102 8.5.2. Suggesting a new offerer BUNDLE address . . . . . . . 15 103 8.5.3. Adding a media description to a BUNDLE group . . . . 16 104 8.5.4. Moving A Media Description Out Of A BUNDLE Group . . 17 105 8.5.5. Disabling A Media Description In A BUNDLE Group . . . 17 106 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 17 107 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 17 108 9.2. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 18 109 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 18 110 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 18 111 10.1.1. General . . . . . . . . . . . . . . . . . . . . . . 18 112 10.1.2. Payload Type (PT) Value Reuse . . . . . . . . . . . 19 113 10.2. Associating RTP/RTCP Packets With Correct SDP Media 114 Description . . . . . . . . . . . . . . . . . . . . . . 19 115 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 20 116 10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 20 117 10.3.2. SDP Offer/Answer Procedures . . . . . . . . . . . . 20 118 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 23 119 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 23 120 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 23 121 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 23 122 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 24 123 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 24 124 11.2.4. Offerer Processing of the SDP Answer . . . . . . . . 24 125 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 24 126 12. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 24 127 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 24 128 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 25 129 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 130 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 131 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 25 132 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 133 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 134 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 26 135 12.7. New text replacing section 8.4 (6th paragraph) of RFC 136 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 137 13. RTP/RTCP extensions for identification-tag transport . . . . 26 138 13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 26 139 13.2. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 27 140 13.3. RTP MID Header Extension . . . . . . . . . . . . . . . . 28 141 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 142 14.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 28 143 14.2. New RTP Header Extension URI . . . . . . . . . . . . . . 28 144 14.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 29 145 15. Security Considerations . . . . . . . . . . . . . . . . . . . 29 146 16. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 30 147 16.1. Example: Bundle Address Selection . . . . . . . . . . . 30 148 16.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 31 149 16.3. Example: Offerer Adds A Media Description To A BUNDLE 150 Group . . . . . . . . . . . . . . . . . . . . . . . . . 32 151 16.4. Example: Offerer Moves A Media Description Out Of A 152 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 35 153 16.5. Example: Offerer Disables A Media Description Within A 154 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 36 155 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 156 18. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 38 157 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 158 19.1. Normative References . . . . . . . . . . . . . . . . . . 43 159 19.2. Informative References . . . . . . . . . . . . . . . . . 43 160 Appendix A. Design Considerations . . . . . . . . . . . . . . . 44 161 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 44 162 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 45 163 A.3. Usage of port number value zero . . . . . . . . . . . . . 46 164 A.4. B2BUA And Proxy Interoperability . . . . . . . . . . . . 46 165 A.4.1. Traffic Policing . . . . . . . . . . . . . . . . . . 47 166 A.4.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 47 167 A.5. Candidate Gathering . . . . . . . . . . . . . . . . . . . 47 168 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 170 1. Introduction 172 This specification defines a way to use a single address:port 173 combination (BUNDLE address) for receiving media associated with 174 multiple SDP media descriptions ("m=" lines). 176 This specification defines a new SDP Grouping Framework [RFC5888] 177 extension called 'BUNDLE'. The extension can be used with the 178 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 179 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 180 BUNDLE address is used for receiving media associated with multiple 181 "m=" lines. This is referred to as bundled media. 183 The offerer and answerer [RFC3264] use the BUNDLE extension to 184 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 185 address) and one for the answerer (answerer BUNDLE address), to be 186 used for receiving the bundled media associated with a BUNDLE group. 187 Once the offerer and the answerer have negotiated a BUNDLE group, 188 they assign their respective BUNDLE address to each "m=" line in the 189 BUNDLE group. The BUNDLE addresses are used to receive all media 190 associated with the BUNDLE group. 192 The use of a BUNDLE group and a BUNDLE address also allows the usage 193 of a single set of Interactive Connectivity Establishment (ICE) 194 [RFC5245] candidates for multiple "m=" lines. 196 This specification also defines a new SDP attribute, 'bundle-only', 197 which can be used to request that specific media is only used if kept 198 within a BUNDLE group. 200 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 201 port value to multiple "m=" lines are undefined, and there is no 202 grouping defined by such means. Instead, an explicit grouping 203 mechanism needs to be used to express the intended semantics. This 204 specification provides such an extension. 206 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 207 [RFC3264]. The update allows an answerer to assign a non-zero port 208 value to an "m=" line in an SDP answer, even if the "m=" line in the 209 associated SDP offer contained a zero port value. 211 This specification also defines a new Real-time Transport Protocol 212 (RTP) [RFC3550] SDES item and a new RTP header extension that can be 213 used to carry a value that associates RTP/RTCP packets with a 214 specific media description. This can be used to correlate a RTP 215 packet with the correct media. 217 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 218 address MUST only be associated with a single BUNDLE group. The 219 procedures in this specification apply independently to a given 220 BUNDLE group. All RTP based media flows associated with a single 221 BUNDLE group belong to a single RTP session [RFC3550]. 223 The BUNDLE extension is backward compatible. Endpoints that do not 224 support the extension are expected to generate offers and answers 225 without an SDP 'group:BUNDLE' attribute, and are expected to assign a 226 unique address to each "m=" line within an offer and answer, 227 according to the procedures in [RFC4566] and [RFC3264] 229 2. Terminology 231 5-tuple: A collection of the following values: source address, source 232 port, destination address, destination port, and transport-layer 233 protocol. 235 Unique address: An IP address and port combination that is assigned 236 to only one "m=" line in an offer or answer. 238 Shared address: An IP address and port combination that is assigned 239 to multiple "m=" lines within an offer or answer. 241 Offerer BUNDLE-tag: The first identification-tag in a given SDP 242 'group:BUNDLE' attribute identification-tag list in an offer. 244 Answerer BUNDLE-tag: The first identification-tag in a given SDP 245 'group:BUNDLE' attribute identification-tag list in an answer. 247 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 248 and port combination used by an offerer to receive all media 249 associated with each "m=" line within the BUNDLE group. 251 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 252 and port combination used by an answerer to receive all media 253 associated with each "m=" line within the BUNDLE group. 255 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 256 exchange, which uses the same BUNDLE address for receiving media. 258 Bundled "m=" line: An "m=" line, whose identification-tag is placed 259 in an SDP 'group:BUNDLE' attribute identification-tag list in an 260 offer or answer. 262 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 263 'bundle-only' attribute. 265 Bundled media: All media associated with a given BUNDLE group. 267 Initial offer: The first offer, within an SDP session, in which the 268 offerer indicates that it wants to create a given BUNDLE group. 270 Subsequent offer: An offer which contains a BUNDLE group that has 271 been created as part of a previous offer/answer exchange. 273 Identification-tag: A unique token value that is used to identify an 274 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 275 "m=" line, carries an unique identification-tag. The session-level 276 SDP 'group' attribute [RFC5888] carries a list of identification- 277 tags, identifying the "m=" lines associated with that particular 278 'group' attribute. 280 3. Conventions 282 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 283 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 284 document are to be interpreted as described in BCP 14, RFC 2119 285 [RFC2119]. 287 4. Applicability Statement 289 The mechanism in this specification only applies to the Session 290 Description Protocol (SDP) [RFC4566], when used together with the SDP 291 offer/answer mechanism [RFC3264]. 293 5. SDP Grouping Framework BUNDLE Extension 295 5.1. General 297 This section defines a new SDP Grouping Framework extension 298 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 299 Offer/Answer mechanism to negotiate the usage of a single 300 address:port combination (BUNDLE address) for receiving bundled 301 media. 303 A single address:port combination is also used for sending bundled 304 media. The address:port combination used for sending bundled media 305 MAY be the same as the BUNDLE address, used to receive bundled media, 306 depending on whether symmetric RTP is used. A given address:port 307 combination MUST NOT be used for sending media associated with 308 multiple BUNDLE groups. 310 All media associated with a BUNDLE group share a single 5-tuple, i.e. 311 in addition to using a single address:port combination all bundled 312 media MUST be transported using the same transport-layer protocol. 314 The BUNDLE extension is indicated using an SDP 'group' attribute with 315 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 316 assigned to each bundled "m=" line, and each identification-tag is 317 listed in the SDP 'group:BUNDLE' attribute identification-tag list. 318 Each "m=" line, whose identification-tag is listed in the 319 identification-tag list, is associated with a given BUNDLE group. 321 SDP bodies can contain multiple BUNDLE groups. Any given bundled 322 "m=" line MUST NOT be associated with more than one BUNDLE group. 324 Section 8 defines the detailed SDP Offer/Answer procedures for the 325 BUNDLE extension. 327 6. SDP 'bundle-only' Attribute 329 6.1. General 331 This section defines a new SDP media-level attribute [RFC4566], 332 'bundle-only'. 334 6.2. bundle-only 336 Name: bundle-only 338 Value: 340 Usage Level: media 342 Charset Dependent: no 344 Example: 346 a=bundle-only 348 In order to ensure that an answerer that does not supports the BUNDLE 349 extension always rejects a bundled "m=" line, the offerer can assign 350 a zero port value to the "m=" line. According to [RFC4566] an 351 answerer will reject such "m=" line. By associating an SDP 'bundle- 352 only' attribute with such "m=" line, the offerer can request that the 353 answerer accepts the "m=" line if the answerer supports the Bundle 354 extension, and if the answerer keeps the "m=" line within the 355 associated BUNDLE group. 357 NOTE: Once an offerer BUNDLE address has been selected, the offerer 358 can ensure that an bundled "m=" line is accepted by the answerer only 359 if the answerer keeps the "m=" line within the associated BUNDLE 360 group by assigning the offerer BUNDLE address to the "m=" line. If 361 the answerer does not keep that "m=" line within the BUNDLE group, 362 the answerer will reject it. Therefore, the SDP 'bundle-only' 363 attribute is not needed in such cases 365 The usage of the 'bundle-only' attribute is only defined for a 366 bundled "m=" line with a zero port value, within an offer. Other 367 usage is unspecified. 369 Section 8 defines the detailed SDP Offer/Answer procedures for the 370 'bundle-only' attribute. 372 7. SDP Information Considerations 374 7.1. General 376 This section describes restrictions associated with the usage of SDP 377 parameters within a BUNDLE group. It also describes, when parameter 378 and attribute values have been associated with each bundled "m=" 379 line, how to calculate a value for the whole BUNDLE group. 381 7.2. Connection Data (c=) 383 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 384 line MUST be 'IN'. 386 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 387 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 388 each "m=" line. 390 NOTE: Extensions to this specification can specify usage of the 391 BUNDLE mechanism for other nettype and addrtype values than the ones 392 listed above. 394 7.3. Bandwidth (b=) 396 The proposed bandwidth for a bundled "m=" line SHOULD be calculated 397 in the same way as for a non-bundled "m=" line. 399 The total proposed bandwidth for a BUNDLE group is the sum of the 400 proposed bandwidth for each bundled "m=" line. 402 The total proposed bandwidth for an offer or answer is the sum of the 403 proposed bandwidth for each "m=" line (bundled and non-bundled) 404 within the offer or answer. 406 7.4. Attributes (a=) 408 An offerer and answerer MUST use the rules and restrictions defined 409 in [I-D.mmusic-sdp-mux-attributes] for when associating SDP 410 attributes with bundled "m=" lines. 412 8. SDP Offer/Answer Procedures 414 8.1. General 416 This section describes the SDP Offer/Answer [RFC3264] procedures for: 418 o Negotiating and creating of a BUNDLE group; 420 o Selecting the BUNDLE addresses (offerer BUNDLE address and 421 answerer BUNDLE address); 423 o Adding an "m=" line to a BUNDLE group; 425 o Moving an "m=" line out of a BUNDLE group; and 427 o Disabling an "m=" line within a BUNDLE group. 429 The generic rules and procedures defined in [RFC3264] and [RFC5888] 430 also apply to the BUNDLE extension. For example, if an offer is 431 rejected by the answerer, the previously negotiated SDP parameters 432 and characteristics (including those associated with a BUNDLE group) 433 apply. Hence, if an offerer generates an offer in which the offerer 434 wants to create a BUNDLE group, and the answerer rejects the offer, 435 the BUNDLE group is not created. 437 The procedures in this section are independent of the media type or 438 transport protocol represented by a bundled "m=" line. Section 10 439 defines additional considerations for RTP based media. Section 6 440 defines additional considerations for the usage of the SDP 'bundle- 441 only' attribute. Section 11 defines additional considerations for 442 the usage of Interactive Connectivity Establishment (ICE) [RFC5245] 443 mechanism . 445 The offerer and answerer MUST follow the rules and restrictions 446 defined in Section 7 when creating offers and answers. 448 SDP offers and answers can contain multiple BUNDLE groups. The 449 procedures in this section apply independently to a given BUNDLE 450 group. 452 8.2. Generating the Initial SDP Offer 454 8.2.1. General 456 When an offerer generates an initial offer, in order to create a 457 BUNDLE group, it MUST: 459 o Assign a unique address to each "m=" line within the offer, 460 following the procedures in [RFC3264]; 462 o Assign a unique address to each "m=" line within the offer, 463 following the procedures in [RFC3264]; 465 o Add an SDP 'group:BUNDLE' attribute to the offer; 467 o Place the identification-tag of each bundled "m=" line in the SDP 468 'group:BUNDLE' attribute identification-tag list; and 470 o Indicate which unique address the offerer suggests as the offerer 471 BUNDLE address [Section 8.2.2]. 473 If the offerer wants to request that the answerer accepts a given 474 bundled "m=" line only if the answerer keeps the "m=" line within the 475 BUNDLE group, the offerer MUST: 477 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 478 "m=" line; and 480 o Assign a zero port value to the "m=" line. 482 NOTE: If the offerer assigns a zero port value to an "m=" line, but 483 does not also associate an SDP 'bundle-only' attribute with the "m=" 484 line, it is an indication that the offerer wants to disable the "m=" 485 line [Section 8.5.5]. 487 [Section 16.1] shows an example of an initial offer. 489 8.2.2. Suggesting the offerer BUNDLE address 491 In the offer, the address assigned to the "m=" line associated with 492 the offerer BUNDLE-tag indicates the address that the offerer 493 suggests as the offerer BUNDLE address. 495 8.3. Generating the SDP Answer 497 8.3.1. General 499 When an answerer generates an answer, which contains a BUNDLE group, 500 the following general SDP grouping framework restrictions, defined in 501 [RFC5888], also apply to the BUNDLE group: 503 o The answerer MUST NOT include a BUNDLE group in the answer, unless 504 the offerer requested the BUNDLE group to be created in the 505 associated offer; and 507 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 508 unless the offerer requested the "m=" line to be within that 509 BUNDLE group in the associated offer. 511 If the answer contains a BUNDLE group, the answerer MUST: 513 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 515 o Select an Answerer BUNDLE Address [Section 8.3.3]; 517 The answerer is allowed to select a new Answerer BUNDLE address each 518 time it generates an answer to an offer. 520 If the answerer does not want to keep an "m=" line within a BUNDLE 521 group, it MUST: 523 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 524 o Reject the "m=" line [Section 8.3.5]; 526 If the answerer keeps a bundle-only "m=" line within the BUNDLE 527 group, it follows the procedures (assigns the answerer BUNDLE address 528 to the "m=" line etc) for any other "m=" line kept within the BUNDLE 529 group. 531 If the answerer does not want to keep a bundle-only "m=" line within 532 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 534 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 535 any "m=" line in an answer. 537 NOTE: If a bundled "m=" line in an offer contains a zero port value, 538 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 539 is an indication that the offerer wants to disable the "m=" line 540 [Section 8.5.5]. 542 8.3.2. Answerer Selection of Offerer Bundle Address 544 In an offer, the address (unique or shared) assigned to the bundled 545 "m=" line associated with the offerer BUNDLE-tag indicates the 546 address that the offerer suggests as the offerer BUNDLE address 547 [Section 8.2.2]. The answerer MUST check whether that "m=" line 548 fulfills the following criteria: 550 o The answerer will not move the "m=" line out of the BUNDLE group 551 [Section 8.3.4]; 553 o The answerer will not reject the "m=" line [Section 8.3.5]; and 555 o The "m=" line does not contain a zero port value. 557 If all of the criteria above are fulfilled, the answerer MUST select 558 the address associated with the "m=" line as the offerer BUNDLE 559 address. In the answer, the answerer BUNDLE-tag represents the "m=" 560 line, and the address associated with the "m=" line in the offer 561 becomes the offerer BUNDLE address. 563 If one or more of the criteria are not fulfilled, the answerer MUST 564 select the next identification-tag in the identification-tag list, 565 and perform the same criteria check for the "m=" line associated with 566 that identification-tag. If there are no more identification-tags in 567 the identification-tag list, the answerer MUST NOT create the BUNDLE 568 group. In addition, unless the answerer rejects the whole offer, the 569 answerer MUST apply the answerer procedures for moving an "m=" line 570 out of a BUNDLE group [Section 8.3.4] to each bundled "m=" line in 571 the offer when creating the answer. 573 [Section 16.1] shows an example of an offerer BUNDLE address 574 selection. 576 8.3.3. Answerer Selection of Answerer BUNDLE Address 578 When the answerer selects a BUNDLE address for itself, referred to as 579 the answerer BUNDLE address, it MUST assign that address to each 580 bundled "m=" line within the created BUNDLE group in the answer. 582 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 583 line that is not within the BUNDLE group, or to an "m=" line that is 584 within another BUNDLE group. 586 [Section 16.1] shows an example of an answerer BUNDLE address 587 selection. 589 8.3.4. Moving A Media Description Out Of A BUNDLE Group 591 When an answerer moves a "m=" line out of a BUNDLE group, it assigns 592 an address to the "m=" line in the answer based on the following 593 rules: 595 o In the associated offer, if the "m=" line contains a shared 596 address (e.g. a previously selected offerer BUNDLE address), the 597 answerer MUST reject the moved "m=" line [Section 8.3.5]; 599 o In the associated offer, if the "m=" line contains a unique 600 address, the answerer MUST assign a unique address also to the 601 "m=" line in the answer; or 603 o In the associated offer, if an SDP 'bundle-only' attribute is 604 associated with the "m=" line, and if the "m=" line contains a 605 zero port value, the answerer MUST reject the "m=" line 606 [Section 8.3.5]. 608 In addition, in either case above, the answerer MUST NOT place the 609 identification-tag, associated with the moved "m=" line, in the SDP 610 'group' attribute identification-tag list associated with the BUNDLE 611 group. 613 8.3.5. Rejecting A Media Description In A BUNDLE Group 615 When an answerer rejects an "m=" line, it MUST assign an address with 616 a zero port value to the "m=" line in the answer, according to the 617 procedures in [RFC4566]. 619 In addition, the answerer MUST NOT place the identification-tag, 620 associated with the rejected "m=" line, in the SDP 'group' attribute 621 identification-tag list associated with the BUNDLE group. 623 8.4. Offerer Processing of the SDP Answer 625 8.4.1. General 627 When an offerer receives an answer, if the answer contains a BUNDLE 628 group, the offerer MUST check that any bundled "m=" line in the 629 answer was indicated as bundled in the associated offer. If there is 630 no mismatch, the offerer MUST use the offerer BUNDLE address, 631 selected by the answerer [Section 8.3.2], as the address for each 632 bundled "m=" line. 634 NOTE: As the answerer might reject one or more bundled "m=" lines, or 635 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 636 line in the offer might not be indicated as bundled in the answer. 638 If the answer does not contain a BUNDLE group, the offerer MUST 639 process the answer as a normal answer. 641 8.4.2. Bundle Address Synchronization (BAS) 643 When an offerer receives an answer, if the answer contains a BUNDLE 644 group, the offerer MUST check whether the offerer BUNDLE address, 645 selected by the answerer [Section 8.3.2], matches what was assigned 646 to each bundled "m=" line (excluding any bundled "m=" line that was 647 rejected, or moved out of the BUNDLE group, by the answerer) in the 648 associated offer. If there is a mismatch, the offerer SHOULD as soon 649 as possible generate a subsequent offer, in which it assigns the 650 offerer BUNDLE address to each bundled "m=" line. Such offer is 651 referred to as a Bundle Address Synchronization (BAS) offer. 653 A BAS offer is typically sent in the following scenarios: 655 o The offerer receives an answer to an initial offer, as the bundled 656 "m=" lines in the initial offer always contain unique addresses 657 [Section 8.2]; or 659 o The offerer receives an answer to an offer, in which a new bundled 660 "m=" line has been added to the BUNDLE group [Section 8.5.3], and 661 the offerer assigned a unique address to the bundled "m=" line in 662 the offer. 664 The offerer is allowed to modify any SDP parameter in the BAS offer. 666 NOTE: It is important that the BAS offer gets accepted by the 667 answerer. For that reason the offerer needs to consider the 668 necessity to modify SDP parameters in the BAS offer, in such a way 669 that could trigger the answerer to reject the BAS offer. Disabling 670 "m=" lines, or reducing the number of codecs, in a BAS offer is 671 considered to have a low risk of being rejected. 673 NOTE: The main purpose of the BAS offer is to ensure that 674 intermediaries, that might not support the BUNDLE extension, have 675 correct information regarding the address that is going to be used to 676 transport the bundled media. 678 [Section 16.1] shows an example of a BAS offer. 680 8.5. Modifying the Session 682 8.5.1. General 684 When an offerer generates a subsequent offer, it MUST assign the 685 previously selected offerer BUNDLE address [Section 8.3.2], to each 686 bundled "m=" line (including any bundle-only "m=" line), except if: 688 o The offerer suggests a new offerer BUNDLE address [Section 8.5.2]; 690 o The offerer wants to add a bundled "m=" line to the BUNDLE group 691 [Section 8.5.3]; 693 o The offerer wants to move a bundled "m=" line out of the BUNDLE 694 group [Section 8.5.4]; or 696 o The offerer wants to disable the bundled "m=" line 697 [Section 8.5.5]. 699 In addition, the offerer MUST select an offerer BUNDLE-tag 700 [Section 8.2.2], even if the offerer does not suggest a new offerer 701 BUNDLE address. 703 8.5.2. Suggesting a new offerer BUNDLE address 705 When an offerer generates an offer, in which it suggests a new 706 offerer BUNDLE address [Section 8.2.2], the offerer MUST: 708 o Assign the address (shared address) to each "m=" line within the 709 BUNDLE group; or 711 o Assign the address (unique address) to one bundled "m=" line. 713 In addition, the offerer MUST indicate that the address is the new 714 suggested offerer BUNDLE address [Section 8.2.2]. 716 NOTE: Unless the offerer assigns the new suggested offerer BUNDLE 717 address to each bundled "m=" line, it can assign unique addresses to 718 any number of bundled "m=" lines (and the previously selected offerer 719 BUNDLE address to any remaining bundled "m=" line) if it wants to 720 suggest multiple alternatives for the new offerer BUNDLE address. 722 8.5.3. Adding a media description to a BUNDLE group 724 When an offerer generates an offer, in which it wants to add a 725 bundled "m=" line to a BUNDLE group, the offerer MUST: 727 o Assign a unique address to the "m=" line; 729 o Assign the previously selected offerer BUNDLE address to the "m=" 730 line; or 732 o If the offerer assigns a new suggested offerer BUNDLE address to 733 each bundled "m=" line [Section 8.5.2], also assign that address 734 to the added "m=" line. 736 In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute 737 identification-tag list with the BUNDLE group [Section 8.2.2] by 738 adding the identification-tag associated with the added "m=" line to 739 the list. 741 NOTE: Assigning a unique address to the "m=" line allows the answerer 742 to move the "m=" line out of the BUNDLE group [Section 8.3.4], 743 without having to reject the "m=" line. 745 If the offerer assigns a unique address to the added "m=" line, and 746 if the offerer suggests that address as the new offerer BUNDLE 747 address [Section 8.5.2], the offerer BUNDLE-tag MUST represent the 748 added "m=" line [Section 8.2.2]. 750 If the offerer assigns a new suggested offerer BUNDLE address to each 751 bundled "m=" line [Section 8.5.2], including the added "m=" line, the 752 offerer BUNDLE-tag MAY represent the added "m=" line [Section 8.2.2]. 754 [Section 16.3] shows an example where an offerer sends an offer in 755 order to add a bundled "m=" line to a BUNDLE group. 757 8.5.4. Moving A Media Description Out Of A BUNDLE Group 759 When an offerer generates an offer, in which it wants to move a 760 bundled "m=" line out of a BUNDLE group it was added to in a previous 761 offer/answer transaction, the offerer: 763 o MUST assign a unique address to the "m=" line; and 765 o MUST NOT place the identification-tag associated with the "m=" 766 line in the SDP 'group:BUNDLE' attribute identification-tag list 767 associated with the BUNDLE group. 769 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 770 added to another BUNDLE group, the offerer applies the procedures in 771 [Section 8.5.3] to the "m=" line. 773 [Section 16.4] shows an example of an offer for moving an "m=" line 774 out of a BUNDLE group. 776 8.5.5. Disabling A Media Description In A BUNDLE Group 778 When an offerer generates an offer, in which it wants to disable a 779 bundled "m=" line (added to the BUNDLE group in a previous offer/ 780 answer transaction), the offerer: 782 o MUST assign an address with a zero port value to the "m=" line, 783 following the procedures in [RFC4566]; and 785 o MUST NOT place the identification-tag associated with the "m=" 786 line in the SDP 'group:BUNDLE' attribute identification-tag list 787 associated with the BUNDLE group. 789 [Section 16.5] shows an example of an offer for disabling an "m=" 790 line within a BUNDLE group. 792 9. Protocol Identification 794 9.1. General 796 Each "m=" line within a BUNDLE group MUST use the same transport- 797 layer protocol. If bundled "m=" lines use different protocols on top 798 of the transport-layer protocol, there MUST exist a publicly 799 available specification which describes a mechanism, for this 800 particular protocol combination, how to associate a received packet 801 with the correct protocol. 803 In addition, if a received packet can be associated with more than 804 one bundled "m=" line, there MUST exist a publically available 805 specification which describes a mechanism for associating the 806 received packet with the correct "m=" line. 808 9.2. STUN, DTLS, SRTP 810 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 811 protocol of a received packet among the STUN, DTLS and SRTP protocols 812 (in any combination). If an offer or answer includes bundled "m=" 813 lines that represent these protocols, the offerer or answerer MUST 814 support the mechanism described in [RFC5764], and no explicit 815 negotiation is required in order to indicate support and usage of the 816 mechanism. 818 [RFC5764] does not describe how to identify different protocols 819 transported on DTLS, only how to identify the DTLS protocol itself. 820 If multiple protocols are transported on DTLS, there MUST exist a 821 specification describing a mechanism for identifying each individual 822 protocol. In addition, if a received DTLS packet can be associated 823 with more than one "m=" line, there MUST exist a specification which 824 describes a mechanism for associating the received DTLS packet with 825 the correct "m=" line. 827 [Section 10.2] describes how to associate a received (S)RTP packet 828 with the correct "m=" line. 830 10. RTP Considerations 832 10.1. Single RTP Session 834 10.1.1. General 836 All RTP-based media within a single BUNDLE group belong to a single 837 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 838 sessions, one per BUNDLE group. 840 Since a single RTP session is used for each bundle group, all "m=" 841 lines representing RTP-based media in a bundle group will share a 842 single SSRC numbering space [RFC3550]. 844 The following rules and restrictions apply for a single RTP session: 846 o A specific payload type value can be used in multiple bundled "m=" 847 lines if each codec associated with the payload type number shares 848 an identical codec configuration [Section 10.1.2]. 850 o The "proto" value in each bundled RTP-based "m=" line MUST be 851 identical (e.g. RTP/AVPF). 853 o An SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 854 hdrext:sdes:mid' URI value, MUST, in every offer and answer, be 855 associated with each bundled "m=" line representing RTP-based 856 media. 858 o A given SSRC MUST NOT transmit RTP packets using payload types 859 that originate from different bundled "m=" lines. 861 NOTE: The last bullet above is to avoid sending multiple media types 862 from the same SSRC. If transmission of multiple media types are done 863 with time overlap, RTP and RTCP fail to function. Even if done in 864 proper sequence this causes RTP Timestamp rate switching issues 865 [RFC7160]. However, once an SSRC has left the RTP session (by 866 sending an RTCP BYE packet), that SSRC value can later be reused by 867 another source(possible associated with a different bundled "m=" 868 line. 870 10.1.2. Payload Type (PT) Value Reuse 872 Multiple bundled "m=" lines might represent RTP based media. As all 873 RTP based media associated with a BUNDLE group belong to the same RTP 874 session, in order for a given payload type value to be used inside 875 more than one bundled "m=" line, all codecs associated with the 876 payload type number MUST share an identical codec configuration. 877 This means that the codecs MUST share the same media type, encoding 878 name, clock rate and any parameter that can affect the codec 879 configuration and packetization. [I-D.mmusic-sdp-mux-attributes] 880 lists SDP attributes, whose attribute values must be identical for 881 all codecs that use the same payload type value. 883 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 885 There are multiple mechanisms that can be used by an endpoint in 886 order to associate received RTP/RTCP packets with a bundled "m=" 887 line. Such mechanisms include using the payload type value carried 888 inside the RTP packets, the SSRC values carried inside the RTP 889 packets, and other "m=" line specific information carried inside the 890 RTP packets. 892 As all RTP/RTCP packets associated with a BUNDLE group are received 893 (and sent) using single address:port combinations, the local 894 address:port combination cannot be used to associate received RTP 895 packets with the correct "m=" line. 897 As described in [Section 10.1.2], the same payload type value might 898 be used inside RTP packets described by multiple "m=" lines. In such 899 cases, the payload type value cannot be used to associate received 900 RTP packets with the correct "m=" line. 902 An offerer and answerer can in an offer and answer inform each other 903 which SSRC values they will use inside sent RTP/RTCP packets, by 904 associating an SDP 'ssrc' attribute [RFC5576] with each bundled "m=" 905 line which contains a payload type value that is also used inside 906 another bundled "m=" line. As the SSRC values will be carried inside 907 the RTP/RTCP packets, the offerer and answerer can then use that 908 information to associate received RTP packets with the correct "m=" 909 line. However, an offerer will not know which SSRC values the 910 answerer will use until it has received the answer providing that 911 information. Due to this, before the offerer has received the 912 answer, the offerer will not be able to associate received RTP/RTCP 913 packets with the correct "m=" line using the SSRC values. 915 In order for an offerer and answerer to always be able to associate 916 received RTP and RTCP packets with the correct "m=" line, an offerer 917 and answerer using the BUNDLE extension MUST support the mechanism 918 defined in Section 13, where the remote endpoint inserts the 919 identification-tag associated with an "m=" line in RTP and RTCP 920 packets associated with that "m=" line. 922 10.3. RTP/RTCP Multiplexing 924 10.3.1. General 926 When a BUNDLE group, which contains RTP based media, is created, the 927 offerer and answerer MUST negotiate whether to enable RTP/RTCP 928 multiplexing for the RTP based media associated with the BUNDLE group 929 [RFC5761]. 931 If RTP/RTCP multiplexing is not enabled, separate address:port 932 combinations will be used for receiving (and sending) the RTP packets 933 and the RTCP packets. 935 10.3.2. SDP Offer/Answer Procedures 937 10.3.2.1. General 939 This section describes how an offerer and answerer can use the SDP 940 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 941 to negotiate usage of RTP/RTCP multiplexing for RTP based media 942 associated with a BUNDLE group. 944 10.3.2.2. Generating the Initial SDP Offer 946 When an offerer generates an initial offer, if the offerer wants to 947 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 948 offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with 949 each bundled RTP-based "m=" line (including any bundle-only "m=" 950 line) in the offer. 952 If the offerer does not want to negotiate usage of RTP/RTCP 953 multiplexing, it MUST NOT associate an SDP 'rtcp-mux' attribute with 954 any bundled "m=" line in the offer. 956 In addition, the offerer can associate an SDP 'rtcp' attribute 957 [RFC3605] with one or more bundled RTP-based "m=" lines (including 958 any bundle-only "m=" line) in the offer, in order to provide a port 959 for receiving RTCP packets (if the answerer does not accept usage of 960 RTP/RTCP multiplexing, or if the offerer does not want to negotiate 961 usage of RTP/RTCP multiplexing). 963 In the initial offer, the IP address and port combination for RTCP 964 MUST be unique in each bundled RTP-based "m=" line, similar to RTP. 966 NOTE: In case the offer wants to receive RTCP packets on the next 967 higher port value, the SDP 'rtcp' attribute is not needed. 969 10.3.2.3. Generating the SDP Answer 971 When an answerer generates an answer, if the offerer indicated 972 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 973 the associated offer, the answerer MUST either accept or reject the 974 usage of RTP/RTCP multiplexing for the whole BUNDLE group in the 975 answer. 977 If the answerer accepts the usage of RTP/RTCP multiplexing within the 978 BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each 979 bundled RTP-based "m=" line in the answer. The answerer MUST NOT 980 associate an SDP 'rtcp' attribute with any bundled "m=" line in the 981 answer. The answerer will use the port value of the selected offerer 982 BUNDLE address for sending RTP and RTCP packets associated with each 983 RTP-based bundled "m=" line towards the offerer. 985 If the answerer does not accept the usage of RTP/RTCP multiplexing 986 within the BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux' 987 attribute with any bundled "m=" line in the answer. The answerer 988 will use the RTP and RTCP port values associated with the selected 989 offerer BUNDLE address for sending RTP and RTCP packets associated 990 with each RTP-based bundled "m=" line towards the offerer. 992 In addition, if the answerer rejects the usage of RTP/RTCP 993 multiplexing within the BUNDLE group, it MAY associate an SDP 'rtcp' 994 attribute, with identical attribute values, with each RTP-based 995 bundled "m=" line in the answer, in order to provide a port value for 996 receiving RTCP packets from the offerer. 998 NOTE: In case the answerer wants to receive RTCP packets on the next 999 higher port value, the SDP 'rtcp' attribute is not needed. 1001 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 1002 negotiated in a previous offer/answer transaction, and if the offerer 1003 indicates that it wants to continue using RTP/RTCP multiplexing in a 1004 subsequent offer, the answerer MUST associate an SDP 'rtcp-mux' 1005 attribute with each bundled "m=" line in the answer. I.e. the 1006 answerer MUST NOT disable the usage of RTP/RTCP multiplexing. 1008 If the usage of RTP/RTCP multiplexing within a BUNDLE group has not 1009 been negotiated in a previous offer/answer transaction, and if the 1010 offerer indicates that it wants to use RTP/RTCP multiplexing in a 1011 subsequent offer, the answerer either accepts or rejects the usage, 1012 using the procedures above. 1014 10.3.2.4. Offerer Processing of the SDP Answer 1016 When an offerer receives an answer, if the answerer has accepted the 1017 usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer 1018 follows the procedures for RTP/RTCP multiplexing defined in 1019 [RFC5761]. The offerer will use the port value associated with the 1020 answerer BUNDLE address for sending RTP and RTCP packets associated 1021 with each RTP-based bundled "m=" line towards the answerer. 1023 If the answerer did not accept the usage of RTP/RTCP multiplexing 1024 (see Section 10.3.2.3), the offerer will use separate address + port 1025 combinations for sending RTP and RTCP packets towards the answerer. 1026 If the answerer associated an SDP 'rtcp' attribute with the "m=" line 1027 representing the answerer BUNDLE address, the offerer will use the 1028 attribute port value for sending RTCP packets associated with each 1029 bundled RTP-based "m=" line towards the answerer. Otherwise the 1030 offerer will use the next higher port value associated with the 1031 answerer BUNDLE address for sending RTCP packets towards the 1032 answerer. 1034 10.3.2.5. Modifying the Session 1036 When an offerer generates a subsequent offer, if it wants to 1037 negotiate the usage of RTP/RTCP multiplexing within a BUNDLE group, 1038 or if it wants to continue the use of previously negotiated RTP/RTCP 1039 multiplexing, it MUST associate an SDP 'rtcp-mux' attribute with each 1040 RTP-based bundled "m=" line (including any bundled "m=" line that the 1041 offerer wants to add to the BUNDLE group), unless the offerer wants 1042 to disable or remove the "m=" line from the BUNDLE group. 1044 If the offerer does not want to negotiate the usage of RTP/RTCP 1045 multiplexing within the BUNDLE group, or if it wants to disable 1046 previously negotiated usage of RTP/RTCP multiplexing, it MUST NOT 1047 associate an SDP 'rtcp-mux' and attribute with any bundled "m=" line 1048 in the subsequent offer. 1050 In addition, if the offerer does not indicate support of RTP/RTCP 1051 multiplexing within the subsequent offer, it MAY associate an SDP 1052 'rtcp' attribute, with identical attribute values, with each RTP- 1053 based bundled "m=" line (including any bundled "m=" line that the 1054 offerer wants to add to the BUNDLE group), in order to provide a port 1055 for receiving RTCP packets. 1057 NOTE: It is RECOMMENDED that, once the usage of RTP/RTCP multiplexing 1058 has been negotiated within a BUNDLE group, that the usage is not 1059 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 1060 answerer need to reserve new ports, to be used for sending and 1061 receiving RTCP packets. Similar, if the usage of a specific RTCP 1062 port has been negotiated within a BUNDLE group, it is RECOMMENDED 1063 that the port value is not modified. 1065 11. ICE Considerations 1067 11.1. General 1069 This section describes how to use the BUNDLE grouping extension 1070 together with the Interactive Connectivity Establishment (ICE) 1071 mechanism [RFC5245]. 1073 The procedures defined in [RFC5245] also apply to usage of ICE with 1074 BUNDLE, with the following exception: 1076 o When BUNDLE addresses for a BUNDLE group have been selected for 1077 both endpoints, ICE connectivity checks and keep-alives only need 1078 to be performed for the whole BUNDLE group, instead of per bundled 1079 "m=" line. 1081 Support and usage of ICE mechanism together with the BUNDLE extension 1082 is OPTIONAL. 1084 11.2. SDP Offer/Answer Procedures 1086 11.2.1. General 1088 When an offerer assigns a unique address to a bundled "m=" line 1089 (excluding any bundle-only "m=" line), it MUST also associate unique 1090 ICE candidates [RFC5245] to the "m=" line. 1092 An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line 1093 with a zero port value. 1095 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1096 inherit the candidates associated with the selected offerer BUNDLE 1097 address. An answerer that does not support BUNDLE would not accept a 1098 bundle-only "m=" line. 1100 When an offerer or answerer assigns a shared address (i.e. a 1101 previously selected BUNDLE address) to one or more bundled "m=" 1102 lines, it MUST associate identical ICE candidates (referred to as 1103 shared ICE candidates) to each of those "m=" lines. 1105 11.2.2. Generating the Initial SDP Offer 1107 When an offerer generates an initial offer, it assigns unique or 1108 shared ICE candidates to the bundled "m=" lines, according to 1109 Section 11.1. 1111 11.2.3. Generating the SDP Answer 1113 When an answerer generates an answer, which contains a BUNDLE group, 1114 the answerer MUST assign shared ICE candidates to each bundled "m=" 1115 line (including "m=" lines that were indicated as bundle-only in the 1116 associated offer) in the answer. 1118 11.2.4. Offerer Processing of the SDP Answer 1120 When an offerer receives an answer, if the answerer supports and uses 1121 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1122 the same ICE candidates, associated with the "m=" line representing 1123 the offerer BUNDLE address (selected by the answerer), to each 1124 bundled "m=" line. 1126 11.2.5. Modifying the Session 1128 When an offerer generates a subsequent offer, it assigns unique or 1129 shared ICE candidates to the bundled "m=" lines, according to 1130 (Section 11.1). 1132 12. Update to RFC 3264 1134 12.1. General 1136 This section replaces the text of the following sections of RFC 3264: 1138 o Section 5.1 (Unicast Streams). 1140 o Section 8.2 (Removing a Media Stream). 1142 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1144 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1146 For recvonly and sendrecv streams, the port number and address in the 1147 offer indicate where the offerer would like to receive the media 1148 stream. For sendonly RTP streams, the address and port number 1149 indirectly indicate where the offerer wants to receive RTCP reports. 1150 Unless there is an explicit indication otherwise, reports are sent to 1151 the port number one higher than the number indicated. The IP address 1152 and port present in the offer indicate nothing about the source IP 1153 address and source port of RTP and RTCP packets that will be sent by 1154 the offerer. A port number of zero in the offer indicates that the 1155 stream is offered but MUST NOT be used. This has no useful semantics 1156 in an initial offer, but is allowed for reasons of completeness, 1157 since the answer can contain a zero port indicating a rejected stream 1158 (Section 6). Furthermore, existing streams can be terminated by 1159 setting the port to zero (Section 8). In general, a port number of 1160 zero indicates that the media stream is not wanted. 1162 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1164 For recvonly and sendrecv streams, the port number and address in the 1165 offer indicate where the offerer would like to receive the media 1166 stream. For sendonly RTP streams, the address and port number 1167 indirectly indicate where the offerer wants to receive RTCP reports. 1168 Unless there is an explicit indication otherwise, reports are sent to 1169 the port number one higher than the number indicated. The IP address 1170 and port present in the offer indicate nothing about the source IP 1171 address and source port of RTP and RTCP packets that will be sent by 1172 the offerer. A port number of zero in the offer by default indicates 1173 that the stream is offered but MUST NOT be used, but an extension 1174 mechanism might specify different semantics for the usage of a zero 1175 port value. Furthermore, existing streams can be terminated by 1176 setting the port to zero (Section 8). In general, a port number of 1177 zero by default indicates that the media stream is not wanted. 1179 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1181 A stream that is offered with a port of zero MUST be marked with port 1182 zero in the answer. Like the offer, the answer MAY omit all 1183 attributes present previously, and MAY list just a single media 1184 format from amongst those in the offer. 1186 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1188 A stream that is offered with a port of zero MUST by default be 1189 marked with port zero in the answer, unless an extension mechanism, 1190 which specifies semantics for the usage of a non-zero port value, is 1191 used. If the stream is marked with port zero in the answer, the 1192 answer MAY omit all attributes present previously, and MAY list just 1193 a single media format from amongst those in the offer." 1195 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1197 RFC 2543 [10] specified that placing a user on hold was accomplished 1198 by setting the connection address to 0.0.0.0. Its usage for putting 1199 a call on hold is no longer recommended, since it doesn't allow for 1200 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1201 with connection oriented media. However, it can be useful in an 1202 initial offer when the offerer knows it wants to use a particular set 1203 of media streams and formats, but doesn't know the addresses and 1204 ports at the time of the offer. Of course, when used, the port 1205 number MUST NOT be zero, which would specify that the stream has been 1206 disabled. An agent MUST be capable of receiving SDP with a 1207 connection address of 0.0.0.0, in which case it means that neither 1208 RTP nor RTCP should be sent to the peer. 1210 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1212 RFC 2543 [10] specified that placing a user on hold was accomplished 1213 by setting the connection address to 0.0.0.0. Its usage for putting 1214 a call on hold is no longer recommended, since it doesn't allow for 1215 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1216 with connection oriented media. However, it can be useful in an 1217 initial offer when the offerer knows it wants to use a particular set 1218 of media streams and formats, but doesn't know the addresses and 1219 ports at the time of the offer. Of course, when used, the port 1220 number MUST NOT be zero, if it would specify that the stream has been 1221 disabled. However, an extension mechanism might specify different 1222 semantics of the zero port number usage. An agent MUST be capable of 1223 receiving SDP with a connection address of 0.0.0.0, in which case it 1224 means that neither RTP nor RTCP should be sent to the peer. 1226 13. RTP/RTCP extensions for identification-tag transport 1228 13.1. General 1230 SDP Offerers and Answerers [RFC3264] can associate identification- 1231 tags with "m=" lines within SDP Offers and Answers, using the 1232 procedures in [RFC5888]. Each identification-tag uniquely represents 1233 an "m=" line. 1235 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1236 used to carry identification-tags within RTCP SDES packets. This 1237 section also defines a new RTP header extension [RFC5285], which is 1238 used to carry identification-tags in RTP packets. 1240 The SDES item and RTP header extension make it possible for a 1241 receiver to associate received RTCP- and RTP packets with a specific 1242 "m=" line, to which the receiver has assigned an identification-tag, 1243 even if those "m=" lines are part of the same RTP session. The 1244 endpoint informs the remote endpoint about the identification-tag 1245 using the procedures in [RFC5888], and the remote endpoint then 1246 inserts the identification-tag in RTCP- and RTP packets sent towards 1247 the other endpoint. 1249 NOTE: This text above defines how identification-tags are carried in 1250 SDP Offers and Answers. The usage of other signalling protocols for 1251 carrying identification-tags is not prevented, but the usage of such 1252 protocols is outside the scope of this document. 1254 [RFC3550] defines general procedures regarding the RTCP transmission 1255 interval. The RTCP MID SDES item SHOULD be sent in the first few 1256 RTCP packets sent on joining the session, and SHOULD be sent 1257 regularly thereafter. The exact number of RTCP packets in which this 1258 SDES item is sent is intentionally not specified here, as it will 1259 depend on the expected packet loss rate, the RTCP reporting interval, 1260 and the allowable overhead. 1262 The RTP MID header extension SHOULD be included in some RTP packets 1263 at the start of the session and whenever the SSRC changes. It might 1264 also be useful to include the header extension in RTP packets that 1265 comprise random access points in the media (e.g., with video 1266 I-frames). The exact number of RTP packets in which this header 1267 extension is sent is intentionally not specified here, as it will 1268 depend on expected packet loss rate and loss patterns, the overhead 1269 the application can tolerate, and the importance of immediate receipt 1270 of the identification-tag. 1272 For robustness purpose, endpoints need to be prepared for situations 1273 where the reception of the identification-tag is delayed, and SHOULD 1274 NOT terminate sessions in such cases, as the identification-tag is 1275 likely to arrive soon. 1277 13.2. RTCP MID SDES Item 1279 0 1 2 3 1280 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 1281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1282 | MID=TBD | length | identification-tag ... 1283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1285 The identification-tag payload is UTF-8 encoded, as in SDP. 1287 The identification-tag is not zero terminated. 1289 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1290 identifier value.] 1292 13.3. RTP MID Header Extension 1294 The payload, containing the identification-tag, of the RTP MID header 1295 extension element can be encoded using either the one-byte or two- 1296 byte header [RFC5285]. The identification-tag payload is UTF-8 1297 encoded, as in SDP. 1299 The identification-tag is not zero terminated. Note, however, that 1300 RTP header extensions that are not a multiple of 32 bits in length 1301 MUST be padded to the next 32-bit boundary using zero bytes; these 1302 padding bytes are not included in the header length field [RFC3550]. 1304 14. IANA Considerations 1306 14.1. New SDES item 1308 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1309 document.] 1311 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1312 identifier value.] 1314 This document adds the MID SDES item to the IANA "RTCP SDES item 1315 types" registry as follows: 1317 Value: TBD 1318 Abbrev.: MID 1319 Name: Media Identification 1320 Reference: RFCXXXX 1322 14.2. New RTP Header Extension URI 1324 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1325 document.] 1327 This document defines a new extension URI in the RTP Compact Header 1328 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1329 Parameters registry, according to the following data: 1331 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1332 Description: Media identification 1333 Contact: christer.holmberg@ericsson.com 1334 Reference: RFCXXXX 1336 14.3. New SDP Attribute 1338 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1339 document.] 1341 This document defines a new SDP media-level attribute, 'bundle-only', 1342 according to the following data: 1344 Attribute name: bundle-only 1345 Type of attribute: media 1346 Subject to charset: No 1347 Purpose: Request a media description to be accepted 1348 in the answer only if kept within a BUNDLE 1349 group by the answerer. 1350 Appropriate values: N/A 1351 Contact name: Christer Holmberg 1352 Contact e-mail: christer.holmberg@ericsson.com 1353 Reference: RFCXXXX 1355 15. Security Considerations 1357 The security considerations defined in [RFC3264] and [RFC5888] apply 1358 to the BUNDLE extension. Bundle does not change which information 1359 flows over the network but only changes which ports that information 1360 is flowing on and thus has very little impact on the security of the 1361 RTP sessions. 1363 When the BUNDLE extension is used, a single set of security 1364 credentials might be used for all media streams associated with a 1365 BUNDLE group. 1367 When the BUNDLE extension is used, the number of SSRC values within a 1368 single RTP session increases, which increases the risk of SSRC 1369 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1370 and SRTCP encryption in certain situations. 1372 16. Examples 1374 16.1. Example: Bundle Address Selection 1376 The example below shows: 1378 o 1. An offer, in which the offerer assigns a unique address to 1379 each bundled "m=" line within the BUNDLE group. 1381 o 2. An answer, in which the answerer selects the offerer BUNDLE 1382 address, and in which selects its own BUNDLE address (the answerer 1383 BUNDLE address) and assigns it each bundled "m=" line within the 1384 BUNDLE group. 1386 o 3. A subsequent offer (BAS offer), which is used to perform a 1387 Bundle Address Synchronization (BAS). 1389 SDP Offer (1) 1391 v=0 1392 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1393 s= 1394 c=IN IP4 atlanta.example.com 1395 t=0 0 1396 a=group:BUNDLE foo bar 1397 m=audio 10000 RTP/AVP 0 8 97 1398 b=AS:200 1399 a=mid:foo 1400 a=rtpmap:0 PCMU/8000 1401 a=rtpmap:8 PCMA/8000 1402 a=rtpmap:97 iLBC/8000 1403 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1404 m=video 10002 RTP/AVP 31 32 1405 b=AS:1000 1406 a=mid:bar 1407 a=rtpmap:31 H261/90000 1408 a=rtpmap:32 MPV/90000 1409 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1411 SDP Answer (2) 1413 v=0 1414 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1415 s= 1416 c=IN IP4 biloxi.example.com 1417 t=0 0 1418 a=group:BUNDLE foo bar 1419 m=audio 20000 RTP/AVP 0 1420 b=AS:200 1421 a=mid:foo 1422 a=rtpmap:0 PCMU/8000 1423 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1424 m=video 20000 RTP/AVP 32 1425 b=AS:1000 1426 a=mid:bar 1427 a=rtpmap:32 MPV/90000 1428 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1430 SDP Offer (3) 1432 v=0 1433 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1434 s= 1435 c=IN IP4 atlanta.example.com 1436 t=0 0 1437 a=group:BUNDLE foo bar 1438 m=audio 10000 RTP/AVP 0 8 97 1439 b=AS:200 1440 a=mid:foo 1441 a=rtpmap:0 PCMU/8000 1442 a=rtpmap:8 PCMA/8000 1443 a=rtpmap:97 iLBC/8000 1444 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1445 m=video 10000 RTP/AVP 31 32 1446 b=AS:1000 1447 a=mid:bar 1448 a=rtpmap:31 H261/90000 1449 a=rtpmap:32 MPV/90000 1450 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1452 16.2. Example: BUNDLE Extension Rejected 1454 The example below shows: 1456 o 1. An offer, in which the offerer assigns a unique address to 1457 each bundled "m=" line within the BUNDLE group. 1459 o 2. An answer, in which the answerer rejects the offered BUNDLE 1460 group, and assigns a unique addresses to each "m=" line (following 1461 normal RFC 3264 procedures). 1463 SDP Offer (1) 1465 v=0 1466 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1467 s= 1468 c=IN IP4 atlanta.example.com 1469 t=0 0 1470 a=group:BUNDLE foo bar 1471 m=audio 10000 RTP/AVP 0 8 97 1472 b=AS:200 1473 a=mid:foo 1474 a=rtpmap:0 PCMU/8000 1475 a=rtpmap:8 PCMA/8000 1476 a=rtpmap:97 iLBC/8000 1477 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1478 m=video 10002 RTP/AVP 31 32 1479 b=AS:1000 1480 a=mid:bar 1481 a=rtpmap:31 H261/90000 1482 a=rtpmap:32 MPV/90000 1483 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1485 SDP Answer (2) 1487 v=0 1488 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1489 s= 1490 c=IN IP4 biloxi.example.com 1491 t=0 0 1492 m=audio 20000 RTP/AVP 0 1493 b=AS:200 1494 a=rtpmap:0 PCMU/8000 1495 m=video 30000 RTP/AVP 32 1496 b=AS:1000 1497 a=rtpmap:32 MPV/90000 1499 16.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1501 The example below shows: 1503 o 1. A subsequent offer (the BUNDLE group has been created as part 1504 of a previous offer/answer transaction), in which the offerer adds 1505 a new "m=" line, represented by the "zen" identification-tag, to a 1506 previously negotiated BUNDLE group, assigns a unique address to 1507 the added "m=" line, and assigns the previously selected offerer 1508 BUNDLE address to each of the other bundled "m=" lines within the 1509 BUNDLE group. 1511 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1512 address to each bundled "m=" line (including the newly added "m=" 1513 line) within the BUNDLE group. 1515 o 3. A subsequent offer (BAS offer), which is used to perform a 1516 Bundle Address Synchronization (BAS). 1518 SDP Offer (1) 1520 v=0 1521 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1522 s= 1523 c=IN IP4 atlanta.example.com 1524 t=0 0 1525 a=group:BUNDLE foo bar zen 1526 m=audio 10000 RTP/AVP 0 8 97 1527 b=AS:200 1528 a=mid:foo 1529 a=rtpmap:0 PCMU/8000 1530 a=rtpmap:8 PCMA/8000 1531 a=rtpmap:97 iLBC/8000 1532 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1533 m=video 10000 RTP/AVP 31 32 1534 b=AS:1000 1535 a=mid:bar 1536 a=rtpmap:31 H261/90000 1537 a=rtpmap:32 MPV/90000 1538 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1539 m=video 20000 RTP/AVP 66 1540 b=AS:1000 1541 a=mid:zen 1542 a=rtpmap:66 H261/90000 1543 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1545 SDP Answer (2) 1547 v=0 1548 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1549 s= 1550 c=IN IP4 biloxi.example.com 1551 t=0 0 1552 a=group:BUNDLE foo bar zen 1553 m=audio 20000 RTP/AVP 0 1554 b=AS:200 1555 a=mid:foo 1556 a=rtpmap:0 PCMU/8000 1557 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1558 m=video 20000 RTP/AVP 32 1559 b=AS:1000 1560 a=mid:bar 1561 a=rtpmap:32 MPV/90000 1562 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1563 m=video 20000 RTP/AVP 66 1564 b=AS:1000 1565 a=mid:zen 1566 a=rtpmap:66 H261/90000 1567 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1569 SDP Offer (3) 1571 v=0 1572 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1573 s= 1574 c=IN IP4 atlanta.example.com 1575 t=0 0 1576 a=group:BUNDLE foo bar zen 1577 m=audio 10000 RTP/AVP 0 8 97 1578 b=AS:200 1579 a=mid:foo 1580 a=rtpmap:0 PCMU/8000 1581 a=rtpmap:8 PCMA/8000 1582 a=rtpmap:97 iLBC/8000 1583 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1584 m=video 10000 RTP/AVP 31 32 1585 b=AS:1000 1586 a=mid:bar 1587 a=rtpmap:31 H261/90000 1588 a=rtpmap:32 MPV/90000 1589 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1590 m=video 10000 RTP/AVP 66 1591 b=AS:1000 1592 a=mid:zen 1593 a=rtpmap:66 H261/90000 1594 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1596 16.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1598 The example below shows: 1600 o 1. A subsequent offer (the BUNDLE group has been created as part 1601 of a previous offer/answer transaction), in which the offerer 1602 moves a bundled "m=" line out of a BUNDLE group, assigns a unique 1603 address to the moved "m=" line, and assigns the offerer BUNDLE 1604 address to each other bundled "m=" line within the BUNDLE group. 1606 o 2. An answer, in which the answerer moves the "m=" line out of 1607 the BUNDLE group, assigns unique address to the moved "m=" line, 1608 and assigns the answerer BUNDLE address to each of the remaining 1609 bundled "m=" line within the BUNDLE group. 1611 SDP Offer (1) 1613 v=0 1614 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1615 s= 1616 c=IN IP4 atlanta.example.com 1617 t=0 0 1618 a=group:BUNDLE foo bar 1619 m=audio 10000 RTP/AVP 0 8 97 1620 b=AS:200 1621 a=mid:foo 1622 a=rtpmap:0 PCMU/8000 1623 a=rtpmap:8 PCMA/8000 1624 a=rtpmap:97 iLBC/8000 1625 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1626 m=video 10000 RTP/AVP 31 32 1627 b=AS:1000 1628 a=mid:bar 1629 a=rtpmap:31 H261/90000 1630 a=rtpmap:32 MPV/90000 1631 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1632 m=video 50000 RTP/AVP 66 1633 b=AS:1000 1634 a=mid:zen 1635 a=rtpmap:66 H261/90000 1637 SDP Answer (2) 1639 v=0 1640 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1641 s= 1642 c=IN IP4 biloxi.example.com 1643 t=0 0 1644 a=group:BUNDLE foo bar 1645 m=audio 20000 RTP/AVP 0 1646 b=AS:200 1647 a=mid:foo 1648 a=rtpmap:0 PCMU/8000 1649 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1650 m=video 20000 RTP/AVP 32 1651 b=AS:1000 1652 a=mid:bar 1653 a=rtpmap:32 MPV/90000 1654 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1655 m=video 60000 RTP/AVP 66 1656 b=AS:1000 1657 a=mid:zen 1658 a=rtpmap:66 H261/90000 1660 16.5. Example: Offerer Disables A Media Description Within A BUNDLE 1661 Group 1663 The example below shows: 1665 o 1. A subsequent offer (the BUNDLE group has been created as part 1666 of a previous offer/answer transaction), in which the offerer 1667 disables a bundled "m=" line within BUNDLE group, assigns a zero 1668 port number to the disabled "m=" line, and assigns the offerer 1669 BUNDLE address to each of the other bundled "m=" lines within the 1670 BUNDLE group. 1672 o 2. An answer, in which the answerer moves the disabled "m=" line 1673 out of the BUNDLE group, assigns a zero port value to the disabled 1674 "m=" line, and assigns the answerer BUNDLE address to each of the 1675 remaining bundled "m=" line within the BUNDLE group. 1677 SDP Offer (1) 1679 v=0 1680 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1681 s= 1682 c=IN IP4 atlanta.example.com 1683 t=0 0 1684 a=group:BUNDLE foo bar 1685 m=audio 10000 RTP/AVP 0 8 97 1686 b=AS:200 1687 a=mid:foo 1688 a=rtpmap:0 PCMU/8000 1689 a=rtpmap:8 PCMA/8000 1690 a=rtpmap:97 iLBC/8000 1691 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1692 m=video 10000 RTP/AVP 31 32 1693 b=AS:1000 1694 a=mid:bar 1695 a=rtpmap:31 H261/90000 1696 a=rtpmap:32 MPV/90000 1697 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1698 m=video 0 RTP/AVP 66 1699 a=mid:zen 1700 a=rtpmap:66 H261/90000 1702 SDP Answer (2) 1704 v=0 1705 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1706 s= 1707 c=IN IP4 biloxi.example.com 1708 t=0 0 1709 a=group:BUNDLE foo bar 1710 m=audio 20000 RTP/AVP 0 1711 b=AS:200 1712 a=mid:foo 1713 a=rtpmap:0 PCMU/8000 1714 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1715 m=video 20000 RTP/AVP 32 1716 b=AS:1000 1717 a=mid:bar 1718 a=rtpmap:32 MPV/90000 1719 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1720 m=video 0 RTP/AVP 66 1721 a=mid:zen 1722 a=rtpmap:66 H261/90000 1724 17. Acknowledgements 1726 The usage of the SDP grouping extension for negotiating bundled media 1727 is based on a similar alternatives proposed by Harald Alvestrand and 1728 Cullen Jennings. The BUNDLE extension described in this document is 1729 based on the different alternative proposals, and text (e.g. SDP 1730 examples) have been borrowed (and, in some cases, modified) from 1731 those alternative proposals. 1733 The SDP examples are also modified versions from the ones in the 1734 Alvestrand proposal. 1736 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1737 Stach and Ari Keraenen for taking the time to read the text along the 1738 way, and providing useful feedback. 1740 18. Change Log 1742 [RFC EDITOR NOTE: Please remove this section when publishing] 1744 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 1746 o - Modification of RTP/RTCP multiplexing section, based on comments 1747 from Magnus Westerlund. 1749 o - Reference updates. 1751 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 1753 o - Editorial fix. 1755 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 1757 o - Editorial changes. 1759 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1761 o Changes to allow a new suggested offerer BUNDLE address to be 1762 assigned to each bundled m- line. 1764 o Changes based on WGLC comments from Paul Kyzivat 1766 o - Editorial fixes 1768 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1770 o Usage of SDP 'extmap' attribute added 1772 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1773 port value 1775 o Changes based on WGLC comments from Thomas Stach 1777 o - ICE candidates not assigned to bundle-only m- lines with a zero 1778 port value 1780 o - Editorial changes 1781 o Changes based on WGLC comments from Colin Perkins 1783 o - Editorial changes: 1785 o -- "RTP SDES item" -> "RTCP SDES item" 1787 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1789 o - Changes in section 10.1.1: 1791 o -- "SHOULD NOT" -> "MUST NOT" 1793 o -- Additional text added to the Note 1795 o - Change to section 13.2: 1797 o -- Clarify that mid value is not zero terminated 1799 o - Change to section 13.3: 1801 o -- Clarify that mid value is not zero terminated 1803 o -- Clarify padding 1805 o Changes based on WGLC comments from Paul Kyzivat 1807 o - Editorial changes: 1809 o Changes based on WGLC comments from Jonathan Lennox 1811 o - Editorial changes: 1813 o - Defintion of SDP bundle-only attribute alligned with structure 1814 in 4566bis draft 1816 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1818 o Editorial corrections based on comments from Harald Alvestrand. 1820 o Editorial corrections based on comments from Cullen Jennings. 1822 o Reference update (RFC 7160). 1824 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1825 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1826 msg13765.html). 1828 o Additional text added to the Security Considerations. 1830 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1832 o SDP bundle-only attribute added to IANA Considerations. 1834 o SDES item and RTP header extension added to Abstract and 1835 Introduction. 1837 o Modification to text updating section 8.2 of RFC 3264. 1839 o Reference corrections. 1841 o Editorial corrections. 1843 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1845 o Terminology change: "bundle-only attribute assigned to m= line" to 1846 "bundle-only attribute associated with m= line". 1848 o Editorial corrections. 1850 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1852 o Editorial corrections. 1854 o - "of"->"if" (8.3.2.5). 1856 o - "optional"->"OPTIONAL" (9.1). 1858 o - Syntax/ABNF for 'bundle-only' attribute added. 1860 o - SDP Offer/Answer sections merged. 1862 o - 'Request new offerer BUNDLE address' section added 1864 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1866 o OPEN ISSUE regarding Receiver-ID closed. 1868 o - RTP MID SDES Item. 1870 o - RTP MID Header Extension. 1872 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1873 closed. 1875 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1876 include an 'rtcp' attribute in the answer, based on the procedures 1877 in section 5.1.3 of RFC 5761. 1879 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1881 o Draft title changed. 1883 o Added "SDP" to section names containing "Offer" or "Answer". 1885 o Editorial fixes based on comments from Paul Kyzivat 1886 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1887 msg13314.html). 1889 o Editorial fixed based on comments from Colin Perkins 1890 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1891 msg13318.html). 1893 o - Removed text about extending BUNDLE to allow multiple RTP 1894 sessions within a BUNDLE group. 1896 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1898 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1899 3264 structure. 1901 o Additional definitions added. 1903 o - Shared address. 1905 o - Bundled "m=" line. 1907 o - Bundle-only "m=" line. 1909 o - Offerer suggested BUNDLE mid. 1911 o - Answerer selected BUNDLE mid. 1913 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1914 to multiple "m=" lines until it has received an SDP Answer 1915 indicating support of the BUNDLE extension. 1917 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1918 Answerer supports the BUNDLE extension, assign a zero port value 1919 to a 'bundle-only' "m=" line. 1921 o SDP 'bundle-only' attribute section added. 1923 o Connection data nettype/addrtype restrictions added. 1925 o RFC 3264 update section added. 1927 o Indicating that a specific payload type value can be used in 1928 multiple "m=" lines, if the value represents the same codec 1929 configuration in each "m=" line. 1931 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1933 o Updated Offerer procedures (http://www.ietf.org/mail- 1934 archive/web/mmusic/current/msg12293.html). 1936 o Updated Answerer procedures (http://www.ietf.org/mail- 1937 archive/web/mmusic/current/msg12333.html). 1939 o Usage of SDP 'bundle-only' attribute added. 1941 o Reference to Trickle ICE document added. 1943 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1945 o Mechanism modified, to be based on usage of SDP Offers with both 1946 different and identical port number values, depending on whether 1947 it is known if the remote endpoint supports the extension. 1949 o Cullen Jennings added as co-author. 1951 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1953 o No changes. New version due to expiration. 1955 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1957 o No changes. New version due to expiration. 1959 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1961 o Draft name changed. 1963 o Harald Alvestrand added as co-author. 1965 o "Multiplex" terminology changed to "bundle". 1967 o Added text about single versus multiple RTP Sessions. 1969 o Added reference to RFC 3550. 1971 19. References 1973 19.1. Normative References 1975 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1976 Requirement Levels", BCP 14, RFC 2119, March 1997. 1978 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1979 with Session Description Protocol (SDP)", RFC 3264, June 1980 2002. 1982 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1983 Description Protocol", RFC 4566, July 2006. 1985 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1986 Header Extensions", RFC 5285, July 2008. 1988 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1989 Control Packets on a Single Port", RFC 5761, April 2010. 1991 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1992 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1994 [I-D.mmusic-sdp-mux-attributes] 1995 Nandakumar, S., "A Framework for SDP Attributes when 1996 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08 1997 (work in progress), January 2015. 1999 19.2. Informative References 2001 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2002 Jacobson, "RTP: A Transport Protocol for Real-Time 2003 Applications", STD 64, RFC 3550, July 2003. 2005 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2006 in Session Description Protocol (SDP)", RFC 3605, October 2007 2003. 2009 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 2010 Description Protocol (SDP) Security Descriptions for Media 2011 Streams", RFC 4568, July 2006. 2013 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2014 (ICE): A Protocol for Network Address Translator (NAT) 2015 Traversal for Offer/Answer Protocols", RFC 5245, April 2016 2010. 2018 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2019 Media Attributes in the Session Description Protocol 2020 (SDP)", RFC 5576, June 2009. 2022 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2023 Security (DTLS) Extension to Establish Keys for the Secure 2024 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 2026 [RFC7160] Petit-Huguenin, M. and G. Zorn, "Support for Multiple 2027 Clock Rates in an RTP Session", RFC 7160, April 2014. 2029 [I-D.ietf-mmusic-trickle-ice] 2030 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 2031 Incremental Provisioning of Candidates for the Interactive 2032 Connectivity Establishment (ICE) Protocol", draft-ietf- 2033 mmusic-trickle-ice-02 (work in progress), January 2015. 2035 Appendix A. Design Considerations 2037 A.1. General 2039 One of the main issues regarding the BUNDLE grouping extensions has 2040 been whether, in SDP Offers and SDP Answers, the same port value 2041 should be inserted in "m=" lines associated with a BUNDLE group, as 2042 the purpose of the extension is to negotiate the usage of a single 2043 address:port combination for media associated with the "m=" lines. 2044 Issues with both approaches, discussed in the Appendix have been 2045 raised. The outcome was to specify a mechanism which uses SDP Offers 2046 with both different and identical port values. 2048 Below are the primary issues that have been considered when defining 2049 the "BUNDLE" grouping extension: 2051 o 1) Interoperability with existing UAs. 2053 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2055 o 3) Time to gather, and the number of, ICE candidates. 2057 o 4) Different error scenarios, and when they occur. 2059 o 5) SDP Offer/Answer impacts, including usage of port number value 2060 zero. 2062 NOTE: Before this document is published as an RFC, this 2063 Appendix might be removed. 2065 A.2. UA Interoperability 2067 Consider the following SDP Offer/Answer exchange, where Alice sends 2068 an SDP Offer to Bob: 2070 SDP Offer 2072 v=0 2073 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2074 s= 2075 c=IN IP4 atlanta.example.com 2076 t=0 0 2077 m=audio 10000 RTP/AVP 97 2078 a=rtpmap:97 iLBC/8000 2079 m=video 10002 RTP/AVP 97 2080 a=rtpmap:97 H261/90000 2082 SDP Answer 2084 v=0 2085 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2086 s= 2087 c=IN IP4 biloxi.example.com 2088 t=0 0 2089 m=audio 20000 RTP/AVP 97 2090 a=rtpmap:97 iLBC/8000 2091 m=video 20002 RTP/AVP 97 2092 a=rtpmap:97 H261/90000 2094 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2095 later invention to RTP and Bob can not assume that Alice supports RFC 2096 4961. This means that Alice may be sending RTP from a different port 2097 than 10000 or 10002 - some implementation simply send the RTP from an 2098 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2099 way that Bob know if it should be passed to the video or audio codec 2100 is by looking at the port it was received on. This lead some SDP 2101 implementations to use the fact that each "m=" line had a different 2102 port number to use that port number as an index to find the correct m 2103 line in the SDP. As a result, some implementations that do support 2104 symmetric RTP and ICE still use a SDP data structure where SDP with 2105 "m=" lines with the same port such as: 2107 SDP Offer 2109 v=0 2110 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2111 s= 2112 c=IN IP4 atlanta.example.com 2113 t=0 0 2114 m=audio 10000 RTP/AVP 97 2115 a=rtpmap:97 iLBC/8000 2116 m=video 10000 RTP/AVP 98 2117 a=rtpmap:98 H261/90000 2119 will result in the second "m=" line being considered an SDP error 2120 because it has the same port as the first line. 2122 A.3. Usage of port number value zero 2124 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2125 can be disabled/rejected by setting the port number value to zero. 2126 This is different from e.g. using the SDP direction attributes, where 2127 RTCP traffic will continue even if the SDP "inactive" attribute is 2128 indicated for the associated "m=" line. 2130 If each "m=" line associated with a BUNDLE group would contain 2131 different port values, and one of those port values would be used for 2132 a BUNDLE address associated with the BUNDLE group, problems would 2133 occur if an endpoint wants to disable/reject the "m=" line associated 2134 with that port, by setting the port value to zero. After that, no 2135 "m=" line would contain the port value which is used for the BUNDLE 2136 address. In addition, it is unclear what would happen to the ICE 2137 candidates associated with the "m=" line, as they are also used for 2138 the BUNDLE address. 2140 A.4. B2BUA And Proxy Interoperability 2142 Some back to back user agents may be configured in a mode where if 2143 the incoming call leg contains an SDP attribute the B2BUA does not 2144 understand, the B2BUS still generates that SDP attribute in the Offer 2145 for the outgoing call leg. Consider an B2BUA that did not understand 2146 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2147 Further assume that the B2BUA was configured to tear down any call 2148 where it did not see any RTCP for 5 minutes. In this cases, if the 2149 B2BUA received an Offer like: 2151 SDP Offer 2153 v=0 2154 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2155 s= 2156 c=IN IP4 atlanta.example.com 2157 t=0 0 2158 m=audio 49170 RTP/AVP 0 2159 a=rtcp:53020 2161 It would be looking for RTCP on port 49172 but would not see any 2162 because the RTCP would be on port 53020 and after five minutes, it 2163 would tear down the call. Similarly, an SBC that did not understand 2164 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2165 wrong port and tear down the call. It is worth noting that a B2BUA 2166 that generated an Offer with capabilities it does not understand is 2167 not compliant with the specifications. 2169 A.4.1. Traffic Policing 2171 Sometimes intermediaries do not act as B2BUA, in the sense that they 2172 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2173 however, they may use SDP information (e.g. IP address and port) in 2174 order to control traffic gating functions, and to set traffic 2175 policing rules. There might be rules which will trigger a session to 2176 be terminated in case media is not sent or received on the ports 2177 retrieved from the SDP. This typically occurs once the session is 2178 already established and ongoing. 2180 A.4.2. Bandwidth Allocation 2182 Sometimes intermediaries do not act as B2BUA, in the sense that they 2183 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2184 however, they may use SDP information (e.g. codecs and media types) 2185 in order to control bandwidth allocation functions. The bandwidth 2186 allocation is done per "m=" line, which means that it might not be 2187 enough if media associated with all "m=" lines try to use that 2188 bandwidth. That may either simply lead to bad user experience, or to 2189 termination of the call. 2191 A.5. Candidate Gathering 2193 When using ICE, an candidate needs to be gathered for each port. 2194 This takes approximately 20 ms extra for each extra "m=" line due to 2195 the NAT pacing requirements. All of this gather can be overlapped 2196 with other things while the page is loading to minimize the impact. 2198 If the client only wants to generate TURN or STUN ICE candidates for 2199 one of the "m=" lines and then use trickle ICE 2200 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2201 the rest of the "m=" lines, it MAY do that and will not need any 2202 additional gathering time. 2204 Some people have suggested a TURN extension to get a bunch of TURN 2205 allocation at once. This would only provide a single STUN result so 2206 in cases where the other end did not support BUNDLE, may cause more 2207 use of the TURN server but would be quick in the cases where both 2208 sides supported BUNDLE and would fall back to a successful call in 2209 the other cases. 2211 Authors' Addresses 2213 Christer Holmberg 2214 Ericsson 2215 Hirsalantie 11 2216 Jorvas 02420 2217 Finland 2219 Email: christer.holmberg@ericsson.com 2221 Harald Tveit Alvestrand 2222 Google 2223 Kungsbron 2 2224 Stockholm 11122 2225 Sweden 2227 Email: harald@alvestrand.no 2229 Cullen Jennings 2230 Cisco 2231 400 3rd Avenue SW, Suite 350 2232 Calgary, AB T2P 4H2 2233 Canada 2235 Email: fluffy@iii.ca