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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 1182 ** 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reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 5285 (Obsoleted by RFC 8285) == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-05 -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) == Outdated reference: A later version (-02) exists of draft-ietf-mmusic-trickle-ice-01 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--).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: June 22, 2015 C. Jennings 7 Cisco 8 December 19, 2014 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-14.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 June 22, 2015. 55 Copyright Notice 57 Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . 22 119 11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 22 120 11.2. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 23 121 11.2.1. General . . . . . . . . . . . . . . . . . . . . . . 23 122 11.2.2. Generating the Initial SDP Offer . . . . . . . . . . 23 123 11.2.3. Generating the SDP Answer . . . . . . . . . . . . . 23 124 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 24 129 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 25 135 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 . . . . . . . . . . . . . . . . 27 141 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 . . . . . . . . . . . . . . . . . . . 28 145 15. Security Considerations . . . . . . . . . . . . . . . . . . . 29 146 16. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 29 147 16.1. Example: Bundle Address Selection . . . . . . . . . . . 29 148 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 . . . . . . . . . . . . . . . . . . . . . . . . . 42 158 19.1. Normative References . . . . . . . . . . . . . . . . . . 42 159 19.2. Informative References . . . . . . . . . . . . . . . . . 43 160 Appendix A. Design Considerations . . . . . . . . . . . . . . . 44 161 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 44 162 A.2. UA Interoperability . . . . . . . . . . . . . . . . . . . 44 163 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 offerer suggests 714 address as the new 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. In addition, the offerer MUST associate an SDP 951 'rtcp' attribute [RFC3605] with each bundled RTP-based "m=" line 952 (including any bundle-only "m=" line), with an attribute value that 953 is identical to the port value assigned to the "m=" line itself, in 954 the offer. 956 If the offerer does not want to negotiate usage of RTP/RTCP 957 multiplexing, it MUST NOT associate the SDP attributes above with any 958 bundled "m=" line. 960 10.3.2.3. Generating the SDP Answer 962 When an answerer generates an answer, if the offerer indicated 963 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 964 the associated offer, the answerer MUST either accept or reject the 965 usage of RTP/RTCP multiplexing in the answer. 967 If the answerer accepts usage of RTP/RTCP multiplexing within the 968 BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each 969 bundled RTP-based "m=" line in the answer. The answerer MUST NOT 970 associate an SDP 'rtcp' attribute with any bundled "m=" line in the 971 answer. The answerer will use the port number of the selected 972 offerer BUNDLE address for sending RTP and RTCP packets associated 973 with each bundled RTP-based "m=" line towards the offerer. 975 If the answerer rejects usage of RTP/RTCP multiplexing within the 976 BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux' or SDP 'rtcp' 977 attribute with any bundled "m=" line in the answer. The answerer 978 MUST, based on the port number of the selected offerer BUNDLE 979 address, use the next higher (odd) destination port number [RFC3550] 980 for sending RTCP packets associated with each bundled RTP-based "m=" 981 line towards the offerer. 983 NOTE: When the answerer rejects usage of RTP/RTCP multiplexing, the 984 reason for mandating usage of the next higher (odd) destination port 985 number for RTCP is to allign the procedures for the corresponding 986 offer. 988 If the usage of RTP/RTCP multiplexing has been negotiated in a 989 previous offer/answer transaction, and the offerer indicates that it 990 wants to continue using RTP/RTCP multiplexing in a subsequent offer, 991 the answerer MUST associate an SDP 'rtcp-mux' attribute with each 992 bundled "m=" line in the answer. I.e. the answerer MUST NOT disable 993 the usage of RTP/RTCP multiplexing. 995 10.3.2.4. Offerer Processing of the SDP Answer 997 When the offerer receives an answer, if the answerer accepts the 998 usage of RTP/RTCP multiplexing, by including an SDP 'rtcp-mux' 999 attribute to each bundled "m=" line in the answer [Section 10.3.2.3], 1000 the answerer follows the procedures for RTP/RTCP multiplexing defined 1001 in [RFC5761]. The offerer will use the port number of the answerer 1002 BUNDLE address for sending RTP and RTCP packets associated with each 1003 bundled "m=" line towards the answerer. 1005 If the answerer does not accept the usage of RTP/RTCP multiplexing 1006 [Section 10.3.2.3], the offerer MUST use separate address:port 1007 combinations for RTP and RTCP. The offerer will, based on the port 1008 number of the answerer BUNDLE address, use the next higher (odd) 1009 destination port number [RFC3550] for sending RTCP packets associated 1010 with a bundled "m=" line towards the answerer. 1012 10.3.2.5. Modifying the Session 1014 When an offerer generates a subsequent offer, if it wants to 1015 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or if 1016 it wants to continue usage of RTP/RTCP multiplexing (negotiated in a 1017 previous offer/answer transaction), it MUST associate SDP 'rtcp-mux' 1018 and 'rtcp' attributes with each bundled "m=" line (including any 1019 bundled "m=" line that the offerer wants to add to the BUNDLE group), 1020 unless the offerer wants to disable or remove the "m=" line from the 1021 BUNDLE group. 1023 If the offerer does not want to negotiate usage of RTP/RTCP 1024 multiplexing within the BUNDLE group, or if it wants to disable usage 1025 of RTP/RTCP multiplexing (negotiated in a previous offer/answer 1026 transaction), the offerer MUST NOT associate SDP 'rtcp-mux' and 1027 'rtcp' attributes with any bundled "m=" line in the subsequent offer. 1029 NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has 1030 been negotiated within a BUNDLE group, that the usage is not 1031 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 1032 answerer need to reserve new ports, to be used for sending and 1033 receiving RTCP packets. 1035 11. ICE Considerations 1037 11.1. General 1039 This section describes how to use the BUNDLE grouping extension 1040 together with the Interactive Connectivity Establishment (ICE) 1041 mechanism [RFC5245]. 1043 The procedures defined in [RFC5245] also apply to usage of ICE with 1044 BUNDLE, with the following exception: 1046 o When BUNDLE addresses for a BUNDLE group have been selected for 1047 both endpoints, ICE connectivity checks and keep-alives only need 1048 to be performed for the whole BUNDLE group, instead of per bundled 1049 "m=" line. 1051 Support and usage of ICE mechanism together with the BUNDLE extension 1052 is OPTIONAL. 1054 11.2. SDP Offer/Answer Procedures 1056 11.2.1. General 1058 When an offerer assigns a unique address to a bundled "m=" line 1059 (excluding any bundle-only "m=" line), it MUST also associate unique 1060 ICE candidates [RFC5245] to the "m=" line. 1062 An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line 1063 with a zero port value. 1065 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1066 inherit the candidates associated with the selected offerer BUNDLE 1067 address. An answerer that does not support BUNDLE would not accept a 1068 bundle-only "m=" line. 1070 When an offerer or answerer assigns a shared address (i.e. a 1071 previously selected BUNDLE address) to one or more bundled "m=" 1072 lines, it MUST associate identical ICE candidates (referred to as 1073 shared ICE candidates) to each of those "m=" lines. 1075 11.2.2. Generating the Initial SDP Offer 1077 When an offerer generates an initial offer, it assigns unique or 1078 shared ICE candidates to the bundled "m=" lines, according to 1079 Section 11.1. 1081 11.2.3. Generating the SDP Answer 1083 When an answerer generates an answer, which contains a BUNDLE group, 1084 the answerer MUST assign shared ICE candidates to each bundled "m=" 1085 line (including "m=" lines that were indicated as bundle-only in the 1086 associated offer) in the answer. 1088 11.2.4. Offerer Processing of the SDP Answer 1090 When an offerer receives an answer, if the answerer supports and uses 1091 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1092 the same ICE candidates, associated with the "m=" line representing 1093 the offerer BUNDLE address (selected by the answerer), to each 1094 bundled "m=" line. 1096 11.2.5. Modifying the Session 1098 When an offerer generates a subsequent offer, it assigns unique or 1099 shared ICE candidates to the bundled "m=" lines, according to 1100 (Section 11.1). 1102 12. Update to RFC 3264 1104 12.1. General 1106 This section replaces the text of the following sections of RFC 3264: 1108 o Section 5.1 (Unicast Streams). 1110 o Section 8.2 (Removing a Media Stream). 1112 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1114 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1116 For recvonly and sendrecv streams, the port number and address in the 1117 offer indicate where the offerer would like to receive the media 1118 stream. For sendonly RTP streams, the address and port number 1119 indirectly indicate where the offerer wants to receive RTCP reports. 1120 Unless there is an explicit indication otherwise, reports are sent to 1121 the port number one higher than the number indicated. The IP address 1122 and port present in the offer indicate nothing about the source IP 1123 address and source port of RTP and RTCP packets that will be sent by 1124 the offerer. A port number of zero in the offer indicates that the 1125 stream is offered but MUST NOT be used. This has no useful semantics 1126 in an initial offer, but is allowed for reasons of completeness, 1127 since the answer can contain a zero port indicating a rejected stream 1128 (Section 6). Furthermore, existing streams can be terminated by 1129 setting the port to zero (Section 8). In general, a port number of 1130 zero indicates that the media stream is not wanted. 1132 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1134 For recvonly and sendrecv streams, the port number and address in the 1135 offer indicate where the offerer would like to receive the media 1136 stream. For sendonly RTP streams, the address and port number 1137 indirectly indicate where the offerer wants to receive RTCP reports. 1138 Unless there is an explicit indication otherwise, reports are sent to 1139 the port number one higher than the number indicated. The IP address 1140 and port present in the offer indicate nothing about the source IP 1141 address and source port of RTP and RTCP packets that will be sent by 1142 the offerer. A port number of zero in the offer by default indicates 1143 that the stream is offered but MUST NOT be used, but an extension 1144 mechanism might specify different semantics for the usage of a zero 1145 port value. Furthermore, existing streams can be terminated by 1146 setting the port to zero (Section 8). In general, a port number of 1147 zero by default indicates that the media stream is not wanted. 1149 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1151 A stream that is offered with a port of zero MUST be marked with port 1152 zero in the answer. Like the offer, the answer MAY omit all 1153 attributes present previously, and MAY list just a single media 1154 format from amongst those in the offer. 1156 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1158 A stream that is offered with a port of zero MUST by default be 1159 marked with port zero in the answer, unless an extension mechanism, 1160 which specifies semantics for the usage of a non-zero port value, is 1161 used. If the stream is marked with port zero in the answer, the 1162 answer MAY omit all attributes present previously, and MAY list just 1163 a single media format from amongst those in the offer." 1165 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1167 RFC 2543 [10] specified that placing a user on hold was accomplished 1168 by setting the connection address to 0.0.0.0. Its usage for putting 1169 a call on hold is no longer recommended, since it doesn't allow for 1170 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1171 with connection oriented media. However, it can be useful in an 1172 initial offer when the offerer knows it wants to use a particular set 1173 of media streams and formats, but doesn't know the addresses and 1174 ports at the time of the offer. Of course, when used, the port 1175 number MUST NOT be zero, which would specify that the stream has been 1176 disabled. An agent MUST be capable of receiving SDP with a 1177 connection address of 0.0.0.0, in which case it means that neither 1178 RTP nor RTCP should be sent to the peer. 1180 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1182 RFC 2543 [10] specified that placing a user on hold was accomplished 1183 by setting the connection address to 0.0.0.0. Its usage for putting 1184 a call on hold is no longer recommended, since it doesn't allow for 1185 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1186 with connection oriented media. However, it can be useful in an 1187 initial offer when the offerer knows it wants to use a particular set 1188 of media streams and formats, but doesn't know the addresses and 1189 ports at the time of the offer. Of course, when used, the port 1190 number MUST NOT be zero, if it would specify that the stream has been 1191 disabled. However, an extension mechanism might specify different 1192 semantics of the zero port number usage. An agent MUST be capable of 1193 receiving SDP with a connection address of 0.0.0.0, in which case it 1194 means that neither RTP nor RTCP should be sent to the peer. 1196 13. RTP/RTCP extensions for identification-tag transport 1198 13.1. General 1200 SDP Offerers and Answerers [RFC3264] can associate identification- 1201 tags with "m=" lines within SDP Offers and Answers, using the 1202 procedures in [RFC5888]. Each identification-tag uniquely represents 1203 an "m=" line. 1205 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1206 used to carry identification-tags within RTCP SDES packets. This 1207 section also defines a new RTP header extension [RFC5285], which is 1208 used to carry identification-tags in RTP packets. 1210 The SDES item and RTP header extension make it possible for a 1211 receiver to associate received RTCP- and RTP packets with a specific 1212 "m=" line, to which the receiver has assigned an identification-tag, 1213 even if those "m=" lines are part of the same RTP session. The 1214 endpoint informs the remote endpoint about the identification-tag 1215 using the procedures in [RFC5888], and the remote endpoint then 1216 inserts the identification-tag in RTCP- and RTP packets sent towards 1217 the other endpoint. 1219 NOTE: This text above defines how identification-tags are carried in 1220 SDP Offers and Answers. The usage of other signalling protocols for 1221 carrying identification-tags is not prevented, but the usage of such 1222 protocols is outside the scope of this document. 1224 [RFC3550] defines general procedures regarding the RTCP transmission 1225 interval. The RTCP MID SDES item SHOULD be sent in the first few 1226 RTCP packets sent on joining the session, and SHOULD be sent 1227 regularly thereafter. The exact number of RTCP packets in which this 1228 SDES item is sent is intentionally not specified here, as it will 1229 depend on the expected packet loss rate, the RTCP reporting interval, 1230 and the allowable overhead. 1232 The RTP MID header extension SHOULD be included in some RTP packets 1233 at the start of the session and whenever the SSRC changes. It might 1234 also be useful to include the header extension in RTP packets that 1235 comprise random access points in the media (e.g., with video 1236 I-frames). The exact number of RTP packets in which this header 1237 extension is sent is intentionally not specified here, as it will 1238 depend on expected packet loss rate and loss patterns, the overhead 1239 the application can tolerate, and the importance of immediate receipt 1240 of the identification-tag. 1242 For robustness purpose, endpoints need to be prepared for situations 1243 where the reception of the identification-tag is delayed, and SHOULD 1244 NOT terminate sessions in such cases, as the identification-tag is 1245 likely to arrive soon. 1247 13.2. RTCP MID SDES Item 1249 0 1 2 3 1250 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 1251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1252 | MID=TBD | length | identification-tag ... 1253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1255 The identification-tag payload is UTF-8 encoded, as in SDP. 1257 The identification-tag is not zero terminated. 1259 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1260 identifier value.] 1262 13.3. RTP MID Header Extension 1264 The payload, containing the mid value, of the RTP MID header 1265 extension element can be encoded using either the one-byte or two- 1266 byte header [RFC5285]. The identification-tag payload is UTF-8 1267 encoded, as in SDP. 1269 The identification-tag is not zero terminated. Note, however, that 1270 RTP header extensions that are not a multiple of 32 bits in length 1271 MUST be padded to the next 32-bit boundary using zero bytes; these 1272 padding bytes are not included in the header length field [RFC3550]. 1274 14. IANA Considerations 1276 14.1. New SDES item 1278 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1279 document.] 1281 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1282 identifier value.] 1284 This document adds the MID SDES item to the IANA "RTCP SDES item 1285 types" registry as follows: 1287 Value: TBD 1288 Abbrev.: MID 1289 Name: Media Identification 1290 Reference: RFCXXXX 1292 14.2. New RTP Header Extension URI 1294 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1295 document.] 1297 This document defines a new extension URI in the RTP Compact Header 1298 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1299 Parameters registry, according to the following data: 1301 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1302 Description: Media identification 1303 Contact: christer.holmberg@ericsson.com 1304 Reference: RFCXXXX 1306 14.3. New SDP Attribute 1308 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1309 document.] 1311 This document defines a new SDP media-level attribute, 'bundle-only', 1312 according to the following data: 1314 Attribute name: bundle-only 1315 Type of attribute: media 1316 Subject to charset: No 1317 Purpose: Request a media description to be accepted 1318 in the answer only if kept within a BUNDLE 1319 group by the answerer. 1320 Appropriate values: N/A 1321 Contact name: Christer Holmberg 1322 Contact e-mail: christer.holmberg@ericsson.com 1323 Reference: RFCXXXX 1325 15. Security Considerations 1327 The security considerations defined in [RFC3264] and [RFC5888] apply 1328 to the BUNDLE extension. Bundle does not change which information 1329 flows over the network but only changes which ports that information 1330 is flowing on and thus has very little impact on the security of the 1331 RTP sessions. 1333 When the BUNDLE extension is used, a single set of security 1334 credentials might be used for all media streams associated with a 1335 BUNDLE group. 1337 When the BUNDLE extension is used, the number of SSRC values within a 1338 single RTP session increases, which increases the risk of SSRC 1339 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1340 and SRTCP encryption in certain situations. 1342 16. Examples 1344 16.1. Example: Bundle Address Selection 1346 The example below shows: 1348 o 1. An offer, in which the offerer assigns a unique address to 1349 each bundled "m=" line within the BUNDLE group. 1351 o 2. An answer, in which the answerer selects the offerer BUNDLE 1352 address, and in which selects its own BUNDLE address (the answerer 1353 BUNDLE address) and assigns it each bundled "m=" line within the 1354 BUNDLE group. 1356 o 3. A subsequent offer (BAS offer), which is used to perform a 1357 Bundle Address Synchronization (BAS). 1359 SDP Offer (1) 1360 v=0 1361 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1362 s= 1363 c=IN IP4 atlanta.example.com 1364 t=0 0 1365 a=group:BUNDLE foo bar 1366 m=audio 10000 RTP/AVP 0 8 97 1367 b=AS:200 1368 a=mid:foo 1369 a=rtpmap:0 PCMU/8000 1370 a=rtpmap:8 PCMA/8000 1371 a=rtpmap:97 iLBC/8000 1372 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1373 m=video 10002 RTP/AVP 31 32 1374 b=AS:1000 1375 a=mid:bar 1376 a=rtpmap:31 H261/90000 1377 a=rtpmap:32 MPV/90000 1378 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1380 SDP Answer (2) 1382 v=0 1383 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1384 s= 1385 c=IN IP4 biloxi.example.com 1386 t=0 0 1387 a=group:BUNDLE foo bar 1388 m=audio 20000 RTP/AVP 0 1389 b=AS:200 1390 a=mid:foo 1391 a=rtpmap:0 PCMU/8000 1392 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1393 m=video 20000 RTP/AVP 32 1394 b=AS:1000 1395 a=mid:bar 1396 a=rtpmap:32 MPV/90000 1397 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1399 SDP Offer (3) 1401 v=0 1402 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1403 s= 1404 c=IN IP4 atlanta.example.com 1405 t=0 0 1406 a=group:BUNDLE foo bar 1407 m=audio 10000 RTP/AVP 0 8 97 1408 b=AS:200 1409 a=mid:foo 1410 a=rtpmap:0 PCMU/8000 1411 a=rtpmap:8 PCMA/8000 1412 a=rtpmap:97 iLBC/8000 1413 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1414 m=video 10000 RTP/AVP 31 32 1415 b=AS:1000 1416 a=mid:bar 1417 a=rtpmap:31 H261/90000 1418 a=rtpmap:32 MPV/90000 1419 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1421 16.2. Example: BUNDLE Extension Rejected 1423 The example below shows: 1425 o 1. An offer, in which the offerer assigns a unique address to 1426 each bundled "m=" line within the BUNDLE group. 1428 o 2. An answer, in which the answerer rejects the offered BUNDLE 1429 group, and assigns a unique addresses to each "m=" line (following 1430 normal RFC 3264 procedures). 1432 SDP Offer (1) 1434 v=0 1435 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1436 s= 1437 c=IN IP4 atlanta.example.com 1438 t=0 0 1439 a=group:BUNDLE foo bar 1440 m=audio 10000 RTP/AVP 0 8 97 1441 b=AS:200 1442 a=mid:foo 1443 a=rtpmap:0 PCMU/8000 1444 a=rtpmap:8 PCMA/8000 1445 a=rtpmap:97 iLBC/8000 1446 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1447 m=video 10002 RTP/AVP 31 32 1448 b=AS:1000 1449 a=mid:bar 1450 a=rtpmap:31 H261/90000 1451 a=rtpmap:32 MPV/90000 1452 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1454 SDP Answer (2) 1456 v=0 1457 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1458 s= 1459 c=IN IP4 biloxi.example.com 1460 t=0 0 1461 m=audio 20000 RTP/AVP 0 1462 b=AS:200 1463 a=rtpmap:0 PCMU/8000 1464 m=video 30000 RTP/AVP 32 1465 b=AS:1000 1466 a=rtpmap:32 MPV/90000 1468 16.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1470 The example below shows: 1472 o 1. A subsequent offer (the BUNDLE group has been created as part 1473 of a previous offer/answer transaction), in which the offerer adds 1474 a new "m=" line, represented by the "zen" identification-tag, to a 1475 previously negotiated BUNDLE group, assigns a unique address to 1476 the added "m=" line, and assigns the previously selected offerer 1477 BUNDLE address to each of the other bundled "m=" lines within the 1478 BUNDLE group. 1480 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1481 address to each bundled "m=" line (including the newly added "m=" 1482 line) within the BUNDLE group. 1484 o 3. A subsequent offer (BAS offer), which is used to perform a 1485 Bundle Address Synchronization (BAS). 1487 SDP Offer (1) 1489 v=0 1490 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1491 s= 1492 c=IN IP4 atlanta.example.com 1493 t=0 0 1494 a=group:BUNDLE foo bar zen 1495 m=audio 10000 RTP/AVP 0 8 97 1496 b=AS:200 1497 a=mid:foo 1498 a=rtpmap:0 PCMU/8000 1499 a=rtpmap:8 PCMA/8000 1500 a=rtpmap:97 iLBC/8000 1501 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1502 m=video 10000 RTP/AVP 31 32 1503 b=AS:1000 1504 a=mid:bar 1505 a=rtpmap:31 H261/90000 1506 a=rtpmap:32 MPV/90000 1507 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1508 m=video 20000 RTP/AVP 66 1509 b=AS:1000 1510 a=mid:zen 1511 a=rtpmap:66 H261/90000 1512 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1514 SDP Answer (2) 1516 v=0 1517 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1518 s= 1519 c=IN IP4 biloxi.example.com 1520 t=0 0 1521 a=group:BUNDLE foo bar zen 1522 m=audio 20000 RTP/AVP 0 1523 b=AS:200 1524 a=mid:foo 1525 a=rtpmap:0 PCMU/8000 1526 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1527 m=video 20000 RTP/AVP 32 1528 b=AS:1000 1529 a=mid:bar 1530 a=rtpmap:32 MPV/90000 1531 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1532 m=video 20000 RTP/AVP 66 1533 b=AS:1000 1534 a=mid:zen 1535 a=rtpmap:66 H261/90000 1536 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1538 SDP Offer (3) 1540 v=0 1541 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1542 s= 1543 c=IN IP4 atlanta.example.com 1544 t=0 0 1545 a=group:BUNDLE foo bar zen 1546 m=audio 10000 RTP/AVP 0 8 97 1547 b=AS:200 1548 a=mid:foo 1549 a=rtpmap:0 PCMU/8000 1550 a=rtpmap:8 PCMA/8000 1551 a=rtpmap:97 iLBC/8000 1552 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1553 m=video 10000 RTP/AVP 31 32 1554 b=AS:1000 1555 a=mid:bar 1556 a=rtpmap:31 H261/90000 1557 a=rtpmap:32 MPV/90000 1558 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1559 m=video 10000 RTP/AVP 66 1560 b=AS:1000 1561 a=mid:zen 1562 a=rtpmap:66 H261/90000 1563 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1565 16.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1567 The example below shows: 1569 o 1. A subsequent offer (the BUNDLE group has been created as part 1570 of a previous offer/answer transaction), in which the offerer 1571 moves a bundled "m=" line out of a BUNDLE group, assigns a unique 1572 address to the moved "m=" line, and assigns the offerer BUNDLE 1573 address to each other bundled "m=" line within the BUNDLE group. 1575 o 2. An answer, in which the answerer moves the "m=" line out of 1576 the BUNDLE group, assigns unique address to the moved "m=" line, 1577 and assigns the answerer BUNDLE address to each of the remaining 1578 bundled "m=" line within the BUNDLE group. 1580 SDP Offer (1) 1582 v=0 1583 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1584 s= 1585 c=IN IP4 atlanta.example.com 1586 t=0 0 1587 a=group:BUNDLE foo bar 1588 m=audio 10000 RTP/AVP 0 8 97 1589 b=AS:200 1590 a=mid:foo 1591 a=rtpmap:0 PCMU/8000 1592 a=rtpmap:8 PCMA/8000 1593 a=rtpmap:97 iLBC/8000 1594 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1595 m=video 10000 RTP/AVP 31 32 1596 b=AS:1000 1597 a=mid:bar 1598 a=rtpmap:31 H261/90000 1599 a=rtpmap:32 MPV/90000 1600 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1601 m=video 50000 RTP/AVP 66 1602 b=AS:1000 1603 a=mid:zen 1604 a=rtpmap:66 H261/90000 1606 SDP Answer (2) 1608 v=0 1609 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1610 s= 1611 c=IN IP4 biloxi.example.com 1612 t=0 0 1613 a=group:BUNDLE foo bar 1614 m=audio 20000 RTP/AVP 0 1615 b=AS:200 1616 a=mid:foo 1617 a=rtpmap:0 PCMU/8000 1618 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1619 m=video 20000 RTP/AVP 32 1620 b=AS:1000 1621 a=mid:bar 1622 a=rtpmap:32 MPV/90000 1623 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1624 m=video 60000 RTP/AVP 66 1625 b=AS:1000 1626 a=mid:zen 1627 a=rtpmap:66 H261/90000 1629 16.5. Example: Offerer Disables A Media Description Within A BUNDLE 1630 Group 1632 The example below shows: 1634 o 1. A subsequent offer (the BUNDLE group has been created as part 1635 of a previous offer/answer transaction), in which the offerer 1636 disables a bundled "m=" line within BUNDLE group, assigns a zero 1637 port number to the disabled "m=" line, and assigns the offerer 1638 BUNDLE address to each of the other bundled "m=" lines within the 1639 BUNDLE group. 1641 o 2. An answer, in which the answerer moves the disabled "m=" line 1642 out of the BUNDLE group, assigns a zero port value to the disabled 1643 "m=" line, and assigns the answerer BUNDLE address to each of the 1644 remaining bundled "m=" line within the BUNDLE group. 1646 SDP Offer (1) 1648 v=0 1649 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1650 s= 1651 c=IN IP4 atlanta.example.com 1652 t=0 0 1653 a=group:BUNDLE foo bar 1654 m=audio 10000 RTP/AVP 0 8 97 1655 b=AS:200 1656 a=mid:foo 1657 a=rtpmap:0 PCMU/8000 1658 a=rtpmap:8 PCMA/8000 1659 a=rtpmap:97 iLBC/8000 1660 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1661 m=video 10000 RTP/AVP 31 32 1662 b=AS:1000 1663 a=mid:bar 1664 a=rtpmap:31 H261/90000 1665 a=rtpmap:32 MPV/90000 1666 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1667 m=video 0 RTP/AVP 66 1668 a=mid:zen 1669 a=rtpmap:66 H261/90000 1671 SDP Answer (2) 1673 v=0 1674 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1675 s= 1676 c=IN IP4 biloxi.example.com 1677 t=0 0 1678 a=group:BUNDLE foo bar 1679 m=audio 20000 RTP/AVP 0 1680 b=AS:200 1681 a=mid:foo 1682 a=rtpmap:0 PCMU/8000 1683 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1684 m=video 20000 RTP/AVP 32 1685 b=AS:1000 1686 a=mid:bar 1687 a=rtpmap:32 MPV/90000 1688 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1689 m=video 0 RTP/AVP 66 1690 a=mid:zen 1691 a=rtpmap:66 H261/90000 1693 17. Acknowledgements 1695 The usage of the SDP grouping extension for negotiating bundled media 1696 is based on a similar alternatives proposed by Harald Alvestrand and 1697 Cullen Jennings. The BUNDLE extension described in this document is 1698 based on the different alternative proposals, and text (e.g. SDP 1699 examples) have been borrowed (and, in some cases, modified) from 1700 those alternative proposals. 1702 The SDP examples are also modified versions from the ones in the 1703 Alvestrand proposal. 1705 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1706 Stach and Ari Keraenen for taking the time to read the text along the 1707 way, and providing useful feedback. 1709 18. Change Log 1711 [RFC EDITOR NOTE: Please remove this section when publishing] 1713 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 1715 o Changes to allow a new suggested offerer BUNDLE address to be 1716 assigned to each bundled m- line. 1718 o Changes based on WGLC comments from Paul Kyzivat 1720 o - Editorial fixes 1722 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1724 o Usage of SDP 'extmap' attribute added 1726 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1727 port value 1729 o Changes based on WGLC comments from Thomas Stach 1731 o - ICE candidates not assigned to bundle-only m- lines with a zero 1732 port value 1734 o - Editorial changes 1736 o Changes based on WGLC comments from Colin Perkins 1738 o - Editorial changes: 1740 o -- "RTP SDES item" -> "RTCP SDES item" 1742 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1744 o - Changes in section 10.1.1: 1746 o -- "SHOULD NOT" -> "MUST NOT" 1748 o -- Additional text added to the Note 1749 o - Change to section 13.2: 1751 o -- Clarify that mid value is not zero terminated 1753 o - Change to section 13.3: 1755 o -- Clarify that mid value is not zero terminated 1757 o -- Clarify padding 1759 o Changes based on WGLC comments from Paul Kyzivat 1761 o - Editorial changes: 1763 o Changes based on WGLC comments from Jonathan Lennox 1765 o - Editorial changes: 1767 o - Defintion of SDP bundle-only attribute alligned with structure 1768 in 4566bis draft 1770 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1772 o Editorial corrections based on comments from Harald Alvestrand. 1774 o Editorial corrections based on comments from Cullen Jennings. 1776 o Reference update (RFC 7160). 1778 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1779 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1780 msg13765.html). 1782 o Additional text added to the Security Considerations. 1784 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1786 o SDP bundle-only attribute added to IANA Considerations. 1788 o SDES item and RTP header extension added to Abstract and 1789 Introduction. 1791 o Modification to text updating section 8.2 of RFC 3264. 1793 o Reference corrections. 1795 o Editorial corrections. 1797 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1799 o Terminology change: "bundle-only attribute assigned to m= line" to 1800 "bundle-only attribute associated with m= line". 1802 o Editorial corrections. 1804 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1806 o Editorial corrections. 1808 o - "of"->"if" (8.3.2.5). 1810 o - "optional"->"OPTIONAL" (9.1). 1812 o - Syntax/ABNF for 'bundle-only' attribute added. 1814 o - SDP Offer/Answer sections merged. 1816 o - 'Request new offerer BUNDLE address' section added 1818 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1820 o OPEN ISSUE regarding Receiver-ID closed. 1822 o - RTP MID SDES Item. 1824 o - RTP MID Header Extension. 1826 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1827 closed. 1829 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1830 include an 'rtcp' attribute in the answer, based on the procedures 1831 in section 5.1.3 of RFC 5761. 1833 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1835 o Draft title changed. 1837 o Added "SDP" to section names containing "Offer" or "Answer". 1839 o Editorial fixes based on comments from Paul Kyzivat 1840 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1841 msg13314.html). 1843 o Editorial fixed based on comments from Colin Perkins 1844 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1845 msg13318.html). 1847 o - Removed text about extending BUNDLE to allow multiple RTP 1848 sessions within a BUNDLE group. 1850 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1852 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1853 3264 structure. 1855 o Additional definitions added. 1857 o - Shared address. 1859 o - Bundled "m=" line. 1861 o - Bundle-only "m=" line. 1863 o - Offerer suggested BUNDLE mid. 1865 o - Answerer selected BUNDLE mid. 1867 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1868 to multiple "m=" lines until it has received an SDP Answer 1869 indicating support of the BUNDLE extension. 1871 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1872 Answerer supports the BUNDLE extension, assign a zero port value 1873 to a 'bundle-only' "m=" line. 1875 o SDP 'bundle-only' attribute section added. 1877 o Connection data nettype/addrtype restrictions added. 1879 o RFC 3264 update section added. 1881 o Indicating that a specific payload type value can be used in 1882 multiple "m=" lines, if the value represents the same codec 1883 configuration in each "m=" line. 1885 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1887 o Updated Offerer procedures (http://www.ietf.org/mail- 1888 archive/web/mmusic/current/msg12293.html). 1890 o Updated Answerer procedures (http://www.ietf.org/mail- 1891 archive/web/mmusic/current/msg12333.html). 1893 o Usage of SDP 'bundle-only' attribute added. 1895 o Reference to Trickle ICE document added. 1897 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1899 o Mechanism modified, to be based on usage of SDP Offers with both 1900 different and identical port number values, depending on whether 1901 it is known if the remote endpoint supports the extension. 1903 o Cullen Jennings added as co-author. 1905 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1907 o No changes. New version due to expiration. 1909 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1911 o No changes. New version due to expiration. 1913 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1915 o Draft name changed. 1917 o Harald Alvestrand added as co-author. 1919 o "Multiplex" terminology changed to "bundle". 1921 o Added text about single versus multiple RTP Sessions. 1923 o Added reference to RFC 3550. 1925 19. References 1927 19.1. Normative References 1929 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1930 Requirement Levels", BCP 14, RFC 2119, March 1997. 1932 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1933 with Session Description Protocol (SDP)", RFC 3264, June 1934 2002. 1936 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1937 Description Protocol", RFC 4566, July 2006. 1939 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1940 Header Extensions", RFC 5285, July 2008. 1942 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1943 Control Packets on a Single Port", RFC 5761, April 2010. 1945 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1946 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1948 [I-D.mmusic-sdp-mux-attributes] 1949 Nandakumar, S., "A Framework for SDP Attributes when 1950 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-05 1951 (work in progress), November 2014. 1953 19.2. Informative References 1955 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1956 Jacobson, "RTP: A Transport Protocol for Real-Time 1957 Applications", STD 64, RFC 3550, July 2003. 1959 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1960 in Session Description Protocol (SDP)", RFC 3605, October 1961 2003. 1963 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1964 Description Protocol (SDP) Security Descriptions for Media 1965 Streams", RFC 4568, July 2006. 1967 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1968 (ICE): A Protocol for Network Address Translator (NAT) 1969 Traversal for Offer/Answer Protocols", RFC 5245, April 1970 2010. 1972 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1973 Media Attributes in the Session Description Protocol 1974 (SDP)", RFC 5576, June 2009. 1976 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1977 Security (DTLS) Extension to Establish Keys for the Secure 1978 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 1980 [RFC7160] Petit-Huguenin, M. and G. Zorn, "Support for Multiple 1981 Clock Rates in an RTP Session", RFC 7160, April 2014. 1983 [I-D.ietf-mmusic-trickle-ice] 1984 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 1985 Incremental Provisioning of Candidates for the Interactive 1986 Connectivity Establishment (ICE) Protocol", draft-ietf- 1987 mmusic-trickle-ice-01 (work in progress), February 2014. 1989 Appendix A. Design Considerations 1991 A.1. General 1993 One of the main issues regarding the BUNDLE grouping extensions has 1994 been whether, in SDP Offers and SDP Answers, the same port value 1995 should be inserted in "m=" lines associated with a BUNDLE group, as 1996 the purpose of the extension is to negotiate the usage of a single 1997 address:port combination for media associated with the "m=" lines. 1998 Issues with both approaches, discussed in the Appendix have been 1999 raised. The outcome was to specify a mechanism which uses SDP Offers 2000 with both different and identical port values. 2002 Below are the primary issues that have been considered when defining 2003 the "BUNDLE" grouping extension: 2005 o 1) Interoperability with existing UAs. 2007 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2009 o 3) Time to gather, and the number of, ICE candidates. 2011 o 4) Different error scenarios, and when they occur. 2013 o 5) SDP Offer/Answer impacts, including usage of port number value 2014 zero. 2016 NOTE: Before this document is published as an RFC, this 2017 Appendix might be removed. 2019 A.2. UA Interoperability 2021 Consider the following SDP Offer/Answer exchange, where Alice sends 2022 an SDP Offer to Bob: 2024 SDP Offer 2026 v=0 2027 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2028 s= 2029 c=IN IP4 atlanta.example.com 2030 t=0 0 2031 m=audio 10000 RTP/AVP 97 2032 a=rtpmap:97 iLBC/8000 2033 m=video 10002 RTP/AVP 97 2034 a=rtpmap:97 H261/90000 2036 SDP Answer 2038 v=0 2039 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2040 s= 2041 c=IN IP4 biloxi.example.com 2042 t=0 0 2043 m=audio 20000 RTP/AVP 97 2044 a=rtpmap:97 iLBC/8000 2045 m=video 20002 RTP/AVP 97 2046 a=rtpmap:97 H261/90000 2048 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2049 later invention to RTP and Bob can not assume that Alice supports RFC 2050 4961. This means that Alice may be sending RTP from a different port 2051 than 10000 or 10002 - some implementation simply send the RTP from an 2052 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2053 way that Bob know if it should be passed to the video or audio codec 2054 is by looking at the port it was received on. This lead some SDP 2055 implementations to use the fact that each "m=" line had a different 2056 port number to use that port number as an index to find the correct m 2057 line in the SDP. As a result, some implementations that do support 2058 symmetric RTP and ICE still use a SDP data structure where SDP with 2059 "m=" lines with the same port such as: 2061 SDP Offer 2063 v=0 2064 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2065 s= 2066 c=IN IP4 atlanta.example.com 2067 t=0 0 2068 m=audio 10000 RTP/AVP 97 2069 a=rtpmap:97 iLBC/8000 2070 m=video 10000 RTP/AVP 98 2071 a=rtpmap:98 H261/90000 2073 will result in the second "m=" line being considered an SDP error 2074 because it has the same port as the first line. 2076 A.3. Usage of port number value zero 2078 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2079 can be disabled/rejected by setting the port number value to zero. 2080 This is different from e.g. using the SDP direction attributes, where 2081 RTCP traffic will continue even if the SDP "inactive" attribute is 2082 indicated for the associated "m=" line. 2084 If each "m=" line associated with a BUNDLE group would contain 2085 different port values, and one of those port values would be used for 2086 a BUNDLE address associated with the BUNDLE group, problems would 2087 occur if an endpoint wants to disable/reject the "m=" line associated 2088 with that port, by setting the port value to zero. After that, no 2089 "m=" line would contain the port value which is used for the BUNDLE 2090 address. In addition, it is unclear what would happen to the ICE 2091 candidates associated with the "m=" line, as they are also used for 2092 the BUNDLE address. 2094 A.4. B2BUA And Proxy Interoperability 2096 Some back to back user agents may be configured in a mode where if 2097 the incoming call leg contains an SDP attribute the B2BUA does not 2098 understand, the B2BUS still generates that SDP attribute in the Offer 2099 for the outgoing call leg. Consider an B2BUA that did not understand 2100 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2101 Further assume that the B2BUA was configured to tear down any call 2102 where it did not see any RTCP for 5 minutes. In this cases, if the 2103 B2BUA received an Offer like: 2105 SDP Offer 2107 v=0 2108 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2109 s= 2110 c=IN IP4 atlanta.example.com 2111 t=0 0 2112 m=audio 49170 RTP/AVP 0 2113 a=rtcp:53020 2115 It would be looking for RTCP on port 49172 but would not see any 2116 because the RTCP would be on port 53020 and after five minutes, it 2117 would tear down the call. Similarly, an SBC that did not understand 2118 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2119 wrong port and tear down the call. It is worth noting that a B2BUA 2120 that generated an Offer with capabilities it does not understand is 2121 not compliant with the specifications. 2123 A.4.1. Traffic Policing 2125 Sometimes intermediaries do not act as B2BUA, in the sense that they 2126 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2127 however, they may use SDP information (e.g. IP address and port) in 2128 order to control traffic gating functions, and to set traffic 2129 policing rules. There might be rules which will trigger a session to 2130 be terminated in case media is not sent or received on the ports 2131 retrieved from the SDP. This typically occurs once the session is 2132 already established and ongoing. 2134 A.4.2. Bandwidth Allocation 2136 Sometimes intermediaries do not act as B2BUA, in the sense that they 2137 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2138 however, they may use SDP information (e.g. codecs and media types) 2139 in order to control bandwidth allocation functions. The bandwidth 2140 allocation is done per "m=" line, which means that it might not be 2141 enough if media associated with all "m=" lines try to use that 2142 bandwidth. That may either simply lead to bad user experience, or to 2143 termination of the call. 2145 A.5. Candidate Gathering 2147 When using ICE, an candidate needs to be gathered for each port. 2148 This takes approximately 20 ms extra for each extra "m=" line due to 2149 the NAT pacing requirements. All of this gather can be overlapped 2150 with other things while the page is loading to minimize the impact. 2152 If the client only wants to generate TURN or STUN ICE candidates for 2153 one of the "m=" lines and then use trickle ICE 2154 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2155 the rest of the "m=" lines, it MAY do that and will not need any 2156 additional gathering time. 2158 Some people have suggested a TURN extension to get a bunch of TURN 2159 allocation at once. This would only provide a single STUN result so 2160 in cases where the other end did not support BUNDLE, may cause more 2161 use of the TURN server but would be quick in the cases where both 2162 sides supported BUNDLE and would fall back to a successful call in 2163 the other cases. 2165 Authors' Addresses 2167 Christer Holmberg 2168 Ericsson 2169 Hirsalantie 11 2170 Jorvas 02420 2171 Finland 2173 Email: christer.holmberg@ericsson.com 2175 Harald Tveit Alvestrand 2176 Google 2177 Kungsbron 2 2178 Stockholm 11122 2179 Sweden 2181 Email: harald@alvestrand.no 2183 Cullen Jennings 2184 Cisco 2185 400 3rd Avenue SW, Suite 350 2186 Calgary, AB T2P 4H2 2187 Canada 2189 Email: fluffy@iii.ca