idnits 2.17.1 draft-ietf-mmusic-sdp-bundle-negotiation-13.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document updates RFC3264, but the abstract doesn't seem to directly say this. It does mention RFC3264 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC3264, updated by this document, for RFC5378 checks: 2002-01-31) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (December 8, 2014) is 3426 days in the past. Is this intentional? 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 1168 ** 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reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 5285 (Obsoleted by RFC 8285) == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-05 -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) == Outdated reference: A later version (-02) exists of draft-ietf-mmusic-trickle-ice-01 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--).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 11, 2015 C. Jennings 7 Cisco 8 December 8, 2014 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-13.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 11, 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. Request 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 . . 16 105 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 . . . . . . . . . . . . . . . . . . . . 17 109 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 . . . . . . . . . . . . . . 22 121 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 . . . . . . . . 23 125 11.2.5. Modifying the Session . . . . . . . . . . . . . . . 23 126 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 131 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 25 137 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 . . . . . . . . . . . . . . . . . . . . . 27 142 14.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 27 143 14.2. New RTP Header Extension URI . . . . . . . . . . . . . . 28 144 14.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 28 145 15. Security Considerations . . . . . . . . . . . . . . . . . . . 28 146 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 . . . . . . . . . . . . . . . 43 161 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 43 162 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 SDP 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 bodies can contain multiple BUNDLE groups. The procedures in 449 this section apply independently to a given BUNDLE group. 451 8.2. Generating the Initial SDP Offer 453 8.2.1. General 455 When an offerer generates an initial offer, in order to create a 456 BUNDLE group, it MUST: 458 o Assign a unique address to each "m=" line within the offer, 459 following the procedures in [RFC3264]; 461 o Assign a unique address to each "m=" line within the offer, 462 following the procedures in [RFC3264]; 464 o Add an SDP 'group:BUNDLE' attribute to the offer; 466 o Place the identification-tag of each bundled "m=" line in the SDP 467 'group:BUNDLE' attribute identification-tag list; and 469 o Indicate which unique address the offerer suggests as the offerer 470 BUNDLE address [Section 8.2.2]. 472 If the offerer wants to request that the answerer accepts a given 473 "m=" line only if the answerer keeps the "m=" line within the BUNDLE 474 group, the offerer MUST: 476 o Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the 477 "m=" line; and 479 o Assign a zero port value to the "m=" line. 481 NOTE: If the offerer assigns a zero port value to an "m=" line, but 482 does not also associate an SDP 'bundle-only' attribute with the "m=" 483 line, it is an indication that the offerer wants to disable the "m=" 484 line [Section 8.5.5]. 486 [Section 16.1] shows an example of an initial offer. 488 8.2.2. Suggesting the offerer BUNDLE address 490 In the offer, the address assigned to the "m=" line associated with 491 the offerer BUNDLE-tag indicates the address that the offerer 492 suggests as the offerer BUNDLE address. 494 8.3. Generating the SDP Answer 496 8.3.1. General 498 When an answerer generates an answer, which contains a BUNDLE group, 499 the following general SDP grouping framework restrictions, defined in 500 [RFC5888], also apply to the BUNDLE group: 502 o The answerer MUST NOT include a BUNDLE group in the answer, unless 503 the offerer requested the BUNDLE group to be created in the 504 associated offer; and 506 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 507 unless the offerer requested the "m=" line to be within that 508 BUNDLE group in the associated offer. 510 If the answer contains a BUNDLE group, the answerer MUST: 512 o Select an Offerer BUNDLE Address [Section 8.3.2]; and 514 o Select an Answerer BUNDLE Address [Section 8.3.3]; 516 The answerer is allowed to select a new Answerer BUNDLE address each 517 time it generates an answer to an offer. 519 If the answerer does not want to keep an "m=" line within a BUNDLE 520 group, it MUST: 522 o Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or 523 o Reject the "m=" line [Section 8.3.5]; 525 If the answerer keeps a bundle-only "m=" line within the BUNDLE 526 group, it follows the procedures (assigns the answerer BUNDLE address 527 to the "m=" line etc) for any other "m=" line kept within the BUNDLE 528 group. 530 If the answerer does not want to keep a bundle-only "m=" line within 531 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5]. 533 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 534 any "m=" line in an answer. 536 NOTE: If a bundled "m=" line in an offer contains a zero port value, 537 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 538 is an indication that the offerer wants to disable the "m=" line 539 [Section 8.5.5]. 541 8.3.2. Answerer Selection of Offerer Bundle Address 543 In an offer, the address (unique or shared) assigned to the bundled 544 "m=" line associated with the offerer BUNDLE-tag indicates the 545 address that the offerer suggests as the offerer BUNDLE address 546 [Section 8.2.2]. The answerer MUST check whether that "m=" line 547 fulfills the following criteria: 549 o The answerer will not move the "m=" line out of the BUNDLE group 550 [Section 8.3.4]; 552 o The answerer will not reject the "m=" line [Section 8.3.5]; and 554 o The "m=" line does not contain a zero port value. 556 If all of the criteria above are fulfilled, the answerer MUST select 557 the address associated with the "m=" line as the offerer BUNDLE 558 address. In the answer, the answerer BUNDLE-tag represents the "m=" 559 line, and the address associated with the "m=" line in the offer 560 becomes the offerer BUNDLE address. 562 If one or more of the criteria are not fulfilled, the answerer MUST 563 select the next identification-tag in the identification-tag list, 564 and perform the same criteria check for the "m=" line associated with 565 that identification-tag. If there are no more identification-tags in 566 the identification-tag list, the answerer MUST NOT create the BUNDLE 567 group. 569 [Section 16.1] shows an example of an offerer BUNDLE address 570 selection. 572 8.3.3. Answerer Selection of Answerer BUNDLE Address 574 When the answerer selects a BUNDLE address for itself, referred to as 575 the answerer BUNDLE address, it MUST assign that address to each 576 bundled "m=" line within the created BUNDLE group in the answer. 578 The answerer MUST NOT assign the answerer BUNDLE address to an "m=" 579 line that is not within the BUNDLE group, or to an "m=" line that is 580 within another BUNDLE group. 582 [Section 16.1] shows an example of an answerer BUNDLE address 583 selection. 585 8.3.4. Moving A Media Description Out Of A BUNDLE Group 587 When an answerer moves a "m=" line out of a BUNDLE group, it assigns 588 an address to the "m=" line in the answer based on the following 589 rules: 591 o In the associated offer, if the "m=" line contains a shared 592 address (e.g. a previously selected offerer BUNDLE address), the 593 answerer MUST reject the moved "m=" line [Section 8.3.5]; 595 o In the associated offer, if the "m=" line contains a unique 596 address, the answerer MUST assign a unique address also to the 597 "m=" line in the answer; or 599 o In the associated offer, if an SDP 'bundle-only' attribute is 600 associated with the "m=" line, and if the "m=" line contains a 601 zero port value, the answerer MUST reject the "m=" line 602 [Section 8.3.5]. 604 In addition, in either case above, the answerer MUST NOT place the 605 identification-tag, associated with the moved "m=" line, in the SDP 606 'group' attribute identification-tag list associated with the BUNDLE 607 group. 609 8.3.5. Rejecting A Media Description In A BUNDLE Group 611 When an answerer rejects an "m=" line, it MUST assign an address with 612 a zero port value to the "m=" line in the answer, according to the 613 procedures in [RFC4566]. 615 In addition, the answerer MUST NOT place the identification-tag, 616 associated with the rejected "m=" line, in the SDP 'group' attribute 617 identification-tag list associated with the BUNDLE group. 619 8.4. Offerer Processing of the SDP Answer 621 8.4.1. General 623 When an offerer receives an answer, if the answer contains a BUNDLE 624 group, the offerer MUST check that any bundled "m=" line in the 625 answer was indicated as bundled in the associated offer. If there is 626 no mismatch, the offerer MUST use the offerer BUNDLE address, 627 selected by the answerer [Section 8.3.2], as the address for each 628 bundled "m=" line. 630 NOTE: As the answerer might reject one or more bundled "m=" lines, or 631 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 632 line in the offer might not be indicated as bundled in the answer. 634 If the answer does not contain a BUNDLE group, the offerer MUST 635 process the answer as a normal answer. 637 8.4.2. Bundle Address Synchronization (BAS) 639 When an offerer receives an answer, if the answer contains a BUNDLE 640 group, the offerer MUST check whether the offerer BUNDLE address, 641 selected by the answerer [Section 8.3.2], matches what was assigned 642 to each bundled "m=" line (excluding any bundled "m=" line that was 643 rejected, or moved out of the BUNDLE group, by the answer) in the 644 associated offer. If there is a mismatch, the offerer SHOULD as soon 645 as possible generate a subsequent offer, in which it assigns the 646 offerer BUNDLE address to each bundled "m=" line. Such offer is 647 referred to as a Bundle Address Synchronization (BAS) offer. 649 A BAS offer is typically sent in the following scenarios: 651 o The offerer receives an answer to an initial offer, as the bundled 652 "m=" lines in the initial offer always contain unique addresses 653 [Section 8.2]; or 655 o The offerer receives an answer to an offer, in which a new bundled 656 "m=" line has been added to the BUNDLE group [Section 8.5.3], and 657 the offerer assigned a unique address to the bundled "m=" line in 658 the offer. 660 The offerer is allowed to modify any SDP parameter in the BAS offer. 662 NOTE: It is important that the BAS offer gets accepted by the 663 answerer. For that reason the offerer needs to consider the 664 necessity to modify SDP parameters in the BAS offer, in such a way 665 that could trigger the answerer to reject the BAS offer. Disabling 666 "m=" lines, or reducing the number of codecs, in a BAS offer is 667 considered to have a low risk of being rejected. 669 NOTE: The main purpose of the BAS offer is to ensure that 670 intermediaries, that might not support the BUNDLE extension, have 671 correct information regarding the address that is going to be used to 672 transport the bundled media. 674 [Section 16.1] shows an example of a BAS offer. 676 8.5. Modifying the Session 678 8.5.1. General 680 When an offerer generates a subsequent offer, it MUST assign the 681 previously selected offerer BUNDLE address [Section 8.3.2], to each 682 bundled "m=" line (including any bundle-only "m=" line), except if: 684 o The offerer suggests a new offerer BUNDLE address [Section 8.5.2]; 686 o The offerer wants to add a bundled "m=" line to the BUNDLE group 687 [Section 8.5.3]; 689 o The offerer wants to move a bundled "m=" line out of the BUNDLE 690 group [Section 8.5.4]; or 692 o The offerer wants to disable the bundled "m=" line 693 [Section 8.5.5]. 695 In addition, the offerer MUST select an offerer BUNDLE-tag 696 [Section 8.2.2], even if the offerer does not suggest a new offerer 697 BUNDLE address. 699 The offerer MUST NOT associate an SDP 'bundle-only' attribute with a 700 bundled "m=" line in a subsequent offer, unless the offerer also 701 assigns a zero port value to the "m=" line. 703 8.5.2. Request 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 a unique address, which the offerer suggests as the new 709 offerer BUNDLE address, to a bundled "m=" line; and 711 o Indicate that the offerer suggests the unique address as the new 712 offerer BUNDLE address [Section 8.2.2] 714 NOTE: The offerer can assign a unique address to each bundled "m=" 715 line in the offer, or it can assign the previously selected offerer 716 BUNDLE address to each "m=" line (except to the "m=" line to which it 717 assigns the unique address that it suggests as the new offerer BUNDLE 718 address). 720 8.5.3. Adding a media description to a BUNDLE group 722 When an offerer generates an offer, in which it wants to add a 723 bundled "m=" line to a BUNDLE group, the offerer MUST: 725 o Assign a unique address, or the previously selected offerer BUNDLE 726 address, to the "m=" line; and 728 o Extend the SDP 'group:BUNDLE' attribute identification-tag list 729 with the BUNDLE group [Section 8.2.2] by adding the 730 identification-tag associated with the added "m=" line to the 731 list. 733 NOTE: Assigning a unique address to the "m=" line allows the answerer 734 to move the "m=" line out of the BUNDLE group [Section 8.3.4], 735 without having to reject the "m=" line. 737 If the offerer suggests the address associated with the added "m=" 738 line as the new offerer BUNDLE address, the offerer BUNDLE-tag MUST 739 represent the added "m=" line [Section 8.2.2]. 741 [Section 16.3] shows an example where an offerer sends an offer in 742 order to add a bundled "m=" line to a BUNDLE group. 744 8.5.4. Moving A Media Description Out Of A BUNDLE Group 746 When an offerer generates an offer, in which it wants to move a 747 bundled "m=" line out of a BUNDLE group it was added to in a previous 748 offer/answer transaction, the offerer: 750 o MUST assign a unique address to the "m=" line; and 752 o MUST NOT place the identification-tag associated with the "m=" 753 line in the SDP 'group:BUNDLE' attribute identification-tag list 754 associated with the BUNDLE group. 756 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 757 added to another BUNDLE group, the offerer applies the procedures in 758 [Section 8.5.3] to the "m=" line. 760 [Section 16.4] shows an example of an offer for moving an "m=" line 761 out of a BUNDLE group. 763 8.5.5. Disabling A Media Description In A BUNDLE Group 765 When an offerer generates an offer, in which it wants to disable a 766 bundled "m=" line (added to the BUNDLE group in a previous offer/ 767 answer transaction), the offerer: 769 o MUST assign an address with a zero port value to the "m=" line, 770 following the procedures in [RFC4566]; and 772 o MUST NOT place the identification-tag associated with the "m=" 773 line in the SDP 'group:BUNDLE' attribute identification-tag list 774 associated with the BUNDLE group. 776 [Section 16.5] shows an example of an offer for disabling an "m=" 777 line within a BUNDLE group. 779 9. Protocol Identification 781 9.1. General 783 Each "m=" line within a BUNDLE group MUST use the same transport- 784 layer protocol. If bundled "m=" lines use different protocols on top 785 of the transport-layer protocol, there MUST exist a publicly 786 available specification which describes a mechanism, for this 787 particular protocol combination, how to associate a received packet 788 with the correct protocol. 790 In addition, if a received packet can be associated with more than 791 one bundled "m=" line, there MUST exist a publically available 792 specification which describes a mechanism for associating the 793 received packet with the correct "m=" line. 795 9.2. STUN, DTLS, SRTP 797 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 798 protocol of a received packet among the STUN, DTLS and SRTP protocols 799 (in any combination). If an offer or answer includes bundled "m=" 800 lines that represent these protocols, the offerer or answerer MUST 801 support the mechanism described in [RFC5764], and no explicit 802 negotiation is required in order to indicate support and usage of the 803 mechanism. 805 [RFC5764] does not describe how to identify different protocols 806 transported on DTLS, only how to identify the DTLS protocol itself. 807 If multiple protocols are transported on DTLS, there MUST exist a 808 specification describing a mechanism for identifying each individual 809 protocol. In addition, if a received DTLS packet can be associated 810 with more than one "m=" line, there MUST exist a specification which 811 describes a mechanism for associating the received DTLS packet with 812 the correct "m=" line. 814 [Section 10.2] describes how to associate a received (S)RTP packet 815 with the correct "m=" line. 817 10. RTP Considerations 819 10.1. Single RTP Session 821 10.1.1. General 823 All RTP-based media within a single BUNDLE group belong to a single 824 RTP session [RFC3550]. Disjoint BUNDLE groups will form multiple RTP 825 sessions, one per BUNDLE group. 827 Since a single RTP session is used for each bundle group, all "m=" 828 lines representing RTP-based media in a bundle group will share a 829 single SSRC numbering space [RFC3550]. 831 The following rules and restrictions apply for a single RTP session: 833 o A specific payload type value can be used in multiple bundled "m=" 834 lines if each codec associated with the payload type number shares 835 an identical codec configuration [Section 10.1.2]. 837 o The "proto" value in each bundled RTP-based "m=" line MUST be 838 identical (e.g. RTP/AVPF). 840 o An SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 841 hdrext:sdes:mid' URI value, MUST, in every offer and answer, be 842 associated with each bundled "m=" line representing RTP-based 843 media. 845 o A given SSRC MUST NOT transmit RTP packets using payload types 846 that originate from different bundled "m=" lines. 848 NOTE: The last bullet above is to avoid sending multiple media types 849 from the same SSRC. If transmission of multiple media types are done 850 with time overlap, RTP and RTCP fail to function. Even if done in 851 proper sequence this causes RTP Timestamp rate switching issues 852 [RFC7160]. However, once an SSRC has left the RTP session (by 853 sending an RTCP BYE packet), that SSRC value can later be reused by 854 another source(possible associated with a different bundled "m=" 855 line. 857 10.1.2. Payload Type (PT) Value Reuse 859 Multiple bundled "m=" lines might represent RTP based media. As all 860 RTP based media associated with a BUNDLE group belong to the same RTP 861 session, in order for a given payload type value to be used inside 862 more than one bundled "m=" line, all codecs associated with the 863 payload type number MUST share an identical codec configuration. 864 This means that the codecs MUST share the same media type, encoding 865 name, clock rate and any parameter that can affect the codec 866 configuration and packetization. [I-D.mmusic-sdp-mux-attributes] 867 lists SDP attributes, whose attribute values must be identical for 868 all codecs that use the same payload type value. 870 10.2. Associating RTP/RTCP Packets With Correct SDP Media Description 872 There are multiple mechanisms that can be used by an endpoint in 873 order to associate received RTP/RTCP packets with a bundled "m=" 874 line. Such mechanisms include using the payload type value carried 875 inside the RTP packets, the SSRC values carried inside the RTP 876 packets, and other "m=" line specific information carried inside the 877 RTP packets. 879 As all RTP/RTCP packets associated with a BUNDLE group are received 880 (and sent) using single address:port combinations, the local 881 address:port combination cannot be used to associate received RTP 882 packets with the correct "m=" line. 884 As described in [Section 10.1.2], the same payload type value might 885 be used inside RTP packets described by multiple "m=" lines. In such 886 cases, the payload type value cannot be used to associate received 887 RTP packets with the correct "m=" line. 889 An offerer and answerer can in an offer and answer inform each other 890 which SSRC values they will use inside sent RTP/RTCP packets, by 891 associating an SDP 'ssrc' attribute [RFC5576] with each bundled "m=" 892 line which contains a payload type value that is also used inside 893 another bundled "m=" line. As the SSRC values will be carried inside 894 the RTP/RTCP packets, the offerer and answerer can then use that 895 information to associate received RTP packets with the correct "m=" 896 line. However, an offerer will not know which SSRC values the 897 answerer will use until it has received the answer providing that 898 information. Due to this, before the offerer has received the 899 answer, the offerer will not be able to associate received RTP/RTCP 900 packets with the correct "m=" line using the SSRC values. 902 In order for an offerer and answerer to always be able to associate 903 received RTP and RTCP packets with the correct "m=" line, an offerer 904 and answerer using the BUNDLE extension MUST support the mechanism 905 defined in Section 13, where the remote endpoint inserts the 906 identification-tag associated with an "m=" line in RTP and RTCP 907 packets associated with that "m=" line. 909 10.3. RTP/RTCP Multiplexing 911 10.3.1. General 913 When a BUNDLE group, which contains RTP based media, is created, the 914 offerer and answerer MUST negotiate whether to enable RTP/RTCP 915 multiplexing for the RTP based media associated with the BUNDLE group 916 [RFC5761]. 918 If RTP/RTCP multiplexing is not enabled, separate address:port 919 combinations will be used for receiving (and sending) the RTP packets 920 and the RTCP packets. 922 10.3.2. SDP Offer/Answer Procedures 924 10.3.2.1. General 926 This section describes how an offerer and answerer can use the SDP 927 'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605] 928 to negotiate usage of RTP/RTCP multiplexing for RTP based media 929 associated with a BUNDLE group. 931 10.3.2.2. Generating the Initial SDP Offer 933 When an offerer generates an initial offer, if the offerer wants to 934 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the 935 offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with 936 each bundled RTP-based "m=" line (including any bundle-only "m=" 937 line) in the offer. In addition, the offerer MUST associate an SDP 938 'rtcp' attribute [RFC3605] with each bundled RTP-based "m=" line 939 (including any bundle-only "m=" line), with an attribute value that 940 is identical to the port value assigned to the "m=" line itself, in 941 the offer. 943 If the offerer does not want to negotiate usage of RTP/RTCP 944 multiplexing, it MUST NOT associate the SDP attributes above with any 945 bundled "m=" line. 947 10.3.2.3. Generating the SDP Answer 949 When an answerer generates an answer, if the offerer indicated 950 support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in 951 the associated offer, the answerer MUST either accept or reject the 952 usage of RTP/RTCP multiplexing in the answer. 954 If the answerer accepts usage of RTP/RTCP multiplexing within the 955 BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each 956 bundled RTP-based "m=" line in the answer. The answerer MUST NOT 957 associate an SDP 'rtcp' attribute with any bundled "m=" line in the 958 answer. The answerer will use the port number of the selected 959 offerer BUNDLE address for sending RTP and RTCP packets associated 960 with each bundled RTP-based "m=" line towards the offerer. 962 If the answerer rejects usage of RTP/RTCP multiplexing within the 963 BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux' or SDP 'rtcp' 964 attribute with any bundled "m=" line in the answer. The answerer 965 MUST, based on the port number of the selected offerer BUNDLE 966 address, use the next higher (odd) destination port number [RFC3550] 967 for sending RTCP packets associated with each bundled RTP-based "m=" 968 line towards the offerer. 970 NOTE: When the answerer rejects usage of RTP/RTCP multiplexing, the 971 reason for mandating usage of the next higher (odd) destination port 972 number for RTCP is to allign the procedures for the corresponding 973 offer. 975 If the usage of RTP/RTCP multiplexing has been negotiated in a 976 previous offer/answer transaction, and the offerer indicates that it 977 wants to continue using RTP/RTCP multiplexing in a subsequent offer, 978 the answerer MUST associate an SDP 'rtcp-mux' attribute with each 979 bundled "m=" line in the answer. I.e. the answerer MUST NOT disable 980 the usage of RTP/RTCP multiplexing. 982 10.3.2.4. Offerer Processing of the SDP Answer 984 When the offerer receives an answer, if the answerer accepts the 985 usage of RTP/RTCP multiplexing, by including an SDP 'rtcp-mux' 986 attribute to each bundled "m=" line in the answer [Section 10.3.2.3], 987 the answerer follows the procedures for RTP/RTCP multiplexing defined 988 in [RFC5761]. The offerer will use the port number of the answerer 989 BUNDLE address for sending RTP and RTCP packets associated with each 990 bundled "m=" line towards the answerer. 992 If the answerer does not accept the usage of RTP/RTCP multiplexing 993 [Section 10.3.2.3], the offerer MUST use separate address:port 994 combinations for RTP and RTCP. The offerer will, based on the port 995 number of the answerer BUNDLE address, use the next higher (odd) 996 destination port number [RFC3550] for sending RTCP packets associated 997 with a bundled "m=" line towards the answerer. 999 10.3.2.5. Modifying the Session 1001 When an offerer generates a subsequent offer, if it wants to 1002 negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or if 1003 it wants to continue usage of RTP/RTCP multiplexing (negotiated in a 1004 previous offer/answer transaction), it MUST associate SDP 'rtcp-mux' 1005 and 'rtcp' attributes with each bundled "m=" line (including any 1006 bundled "m=" line that the offerer wants to add to the BUNDLE group), 1007 unless the offerer wants to disable or remove the "m=" line from the 1008 BUNDLE group. 1010 If the offerer does not want to negotiate usage of RTP/RTCP 1011 multiplexing within the BUNDLE group, or if it wants to disable usage 1012 of RTP/RTCP multiplexing (negotiated in a previous offer/answer 1013 transaction), the offerer MUST NOT associate SDP 'rtcp-mux' and 1014 'rtcp' attributes with any bundled "m=" line in the subsequent offer. 1016 NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has 1017 been negotiated within a BUNDLE group, that the usage is not 1018 disabled. Disabling RTP/RTCP multiplexing means that the offerer and 1019 answerer need to reserve new ports, to be used for sending and 1020 receiving RTCP packets. 1022 11. ICE Considerations 1024 11.1. General 1026 This section describes how to use the BUNDLE grouping extension 1027 together with the Interactive Connectivity Establishment (ICE) 1028 mechanism [RFC5245]. 1030 The procedures defined in [RFC5245] also apply to usage of ICE with 1031 BUNDLE, with the following exception: 1033 o When BUNDLE addresses for a BUNDLE group have been selected for 1034 both endpoints, ICE connectivity checks and keep-alives only need 1035 to be performed for the whole BUNDLE group, instead of per bundled 1036 "m=" line. 1038 Support and usage of ICE mechanism together with the BUNDLE extension 1039 is OPTIONAL. 1041 11.2. SDP Offer/Answer Procedures 1042 11.2.1. General 1044 When an offerer assigns a unique address to a bundled "m=" line 1045 (excluding and bundle-only "m=" line), it MUST also associate unique 1046 ICE candidates [RFC5245] to the "m=" line. 1048 An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line 1049 with a zero port value. 1051 NOTE: The bundle-only "m=" line, if accepted by the answerer, will 1052 inherit the candidates associated with the selected offerer BUNDLE 1053 address. An answerer that does not support BUNDLE would not accept a 1054 bundle-only "m=" line. 1056 When an offerer or answerer assigns a shared address (i.e. a 1057 previously selected BUNDLE address) to one or more bundled "m=" 1058 lines, it MUST associate identical ICE candidates (referred to as 1059 shared ICE candidates) to each of those "m=" lines. 1061 11.2.2. Generating the Initial SDP Offer 1063 When an offerer generates an initial offer, it assigns unique or 1064 shared ICE candidates to the bundled "m=" lines, according to 1065 Section 11.1. 1067 11.2.3. Generating the SDP Answer 1069 When an answerer generates an answer, which contains a BUNDLE group, 1070 the answerer MUST assign shared ICE candidates to each bundled "m=" 1071 line (including "m=" lines that were indicated as bundle-only in the 1072 associated offer) in the answer. 1074 11.2.4. Offerer Processing of the SDP Answer 1076 When an offerer receives an answer, if the answerer supports and uses 1077 the ICE mechanism and the BUNDLE extension, the offerer MUST assign 1078 the same ICE candidates, associated with the "m=" line representing 1079 the offerer BUNDLE address (selected by the answerer), to each 1080 bundled "m=" line. 1082 11.2.5. Modifying the Session 1084 When an offerer generates a subsequent offer, it assigns unique or 1085 shared ICE candidates to the bundled "m=" lines, according to 1086 (Section 11.1). 1088 12. Update to RFC 3264 1090 12.1. General 1092 This section replaces the text of the following sections of RFC 3264: 1094 o Section 5.1 (Unicast Streams). 1096 o Section 8.2 (Removing a Media Stream). 1098 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1100 12.2. Original text of section 5.1 (2nd paragraph) of RFC 3264 1102 For recvonly and sendrecv streams, the port number and address in the 1103 offer indicate where the offerer would like to receive the media 1104 stream. For sendonly RTP streams, the address and port number 1105 indirectly indicate where the offerer wants to receive RTCP reports. 1106 Unless there is an explicit indication otherwise, reports are sent to 1107 the port number one higher than the number indicated. The IP address 1108 and port present in the offer indicate nothing about the source IP 1109 address and source port of RTP and RTCP packets that will be sent by 1110 the offerer. A port number of zero in the offer indicates that the 1111 stream is offered but MUST NOT be used. This has no useful semantics 1112 in an initial offer, but is allowed for reasons of completeness, 1113 since the answer can contain a zero port indicating a rejected stream 1114 (Section 6). Furthermore, existing streams can be terminated by 1115 setting the port to zero (Section 8). In general, a port number of 1116 zero indicates that the media stream is not wanted. 1118 12.3. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1120 For recvonly and sendrecv streams, the port number and address in the 1121 offer indicate where the offerer would like to receive the media 1122 stream. For sendonly RTP streams, the address and port number 1123 indirectly indicate where the offerer wants to receive RTCP reports. 1124 Unless there is an explicit indication otherwise, reports are sent to 1125 the port number one higher than the number indicated. The IP address 1126 and port present in the offer indicate nothing about the source IP 1127 address and source port of RTP and RTCP packets that will be sent by 1128 the offerer. A port number of zero in the offer by default indicates 1129 that the stream is offered but MUST NOT be used, but an extension 1130 mechanism might specify different semantics for the usage of a zero 1131 port value. Furthermore, existing streams can be terminated by 1132 setting the port to zero (Section 8). In general, a port number of 1133 zero by default indicates that the media stream is not wanted. 1135 12.4. Original text of section 8.2 (2nd paragraph) of RFC 3264 1137 A stream that is offered with a port of zero MUST be marked with port 1138 zero in the answer. Like the offer, the answer MAY omit all 1139 attributes present previously, and MAY list just a single media 1140 format from amongst those in the offer. 1142 12.5. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1144 A stream that is offered with a port of zero MUST by default be 1145 marked with port zero in the answer, unless an extension mechanism, 1146 which specifies semantics for the usage of a non-zero port value, is 1147 used. If the stream is marked with port zero in the answer, the 1148 answer MAY omit all attributes present previously, and MAY list just 1149 a single media format from amongst those in the offer." 1151 12.6. Original text of section 8.4 (6th paragraph) of RFC 3264 1153 RFC 2543 [10] specified that placing a user on hold was accomplished 1154 by setting the connection address to 0.0.0.0. Its usage for putting 1155 a call on hold is no longer recommended, since it doesn't allow for 1156 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1157 with connection oriented media. However, it can be useful in an 1158 initial offer when the offerer knows it wants to use a particular set 1159 of media streams and formats, but doesn't know the addresses and 1160 ports at the time of the offer. Of course, when used, the port 1161 number MUST NOT be zero, which would specify that the stream has been 1162 disabled. An agent MUST be capable of receiving SDP with a 1163 connection address of 0.0.0.0, in which case it means that neither 1164 RTP nor RTCP should be sent to the peer. 1166 12.7. New text replacing section 8.4 (6th paragraph) of RFC 3264 1168 RFC 2543 [10] specified that placing a user on hold was accomplished 1169 by setting the connection address to 0.0.0.0. Its usage for putting 1170 a call on hold is no longer recommended, since it doesn't allow for 1171 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1172 with connection oriented media. However, it can be useful in an 1173 initial offer when the offerer knows it wants to use a particular set 1174 of media streams and formats, but doesn't know the addresses and 1175 ports at the time of the offer. Of course, when used, the port 1176 number MUST NOT be zero, if it would specify that the stream has been 1177 disabled. However, an extension mechanism might specify different 1178 semantics of the zero port number usage. An agent MUST be capable of 1179 receiving SDP with a connection address of 0.0.0.0, in which case it 1180 means that neither RTP nor RTCP should be sent to the peer. 1182 13. RTP/RTCP extensions for identification-tag transport 1184 13.1. General 1186 SDP Offerers and Answerers [RFC3264] can associate identification- 1187 tags with "m=" lines within SDP Offers and Answers, using the 1188 procedures in [RFC5888]. Each identification-tag uniquely represents 1189 an "m=" line. 1191 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1192 used to carry identification-tags within RTCP SDES packets. This 1193 section also defines a new RTP header extension [RFC5285], which is 1194 used to carry identification-tags in RTP packets. 1196 The SDES item and RTP header extension make it possible for a 1197 receiver to associate received RTCP- and RTP packets with a specific 1198 "m=" line, to which the receiver has assigned an identification-tag, 1199 even if those "m=" lines are part of the same RTP session. The 1200 endpoint informs the remote endpoint about the identification-tag 1201 using the procedures in [RFC5888], and the remote endpoint then 1202 inserts the identification-tag in RTCP- and RTP packets sent towards 1203 the other endpoint. 1205 NOTE: This text above defines how identification-tags are carried in 1206 SDP Offers and Answers. The usage of other signalling protocols for 1207 carrying identification-tags is not prevented, but the usage of such 1208 protocols is outside the scope of this document. 1210 [RFC3550] defines general procedures regarding the RTCP transmission 1211 interval. The RTCP MID SDES item SHOULD be sent in the first few 1212 RTCP packets sent on joining the session, and SHOULD be sent 1213 regularly thereafter. The exact number of RTCP packets in which this 1214 SDES item is sent is intentionally not specified here, as it will 1215 depend on the expected packet loss rate, the RTCP reporting interval, 1216 and the allowable overhead. 1218 The RTP MID header extension SHOULD be included in some RTP packets 1219 at the start of the session and whenever the SSRC changes. It might 1220 also be useful to include the header extension in RTP packets that 1221 comprise random access points in the media (e.g., with video 1222 I-frames). The exact number of RTP packets in which this header 1223 extension is sent is intentionally not specified here, as it will 1224 depend on expected packet loss rate and loss patterns, the overhead 1225 the application can tolerate, and the importance of immediate receipt 1226 of the identification-tag. 1228 For robustness purpose, endpoints need to be prepared for situations 1229 where the reception of the identification-tag is delayed, and SHOULD 1230 NOT terminate sessions in such cases, as the identification-tag is 1231 likely to arrive soon. 1233 13.2. RTCP MID SDES Item 1235 0 1 2 3 1236 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 1237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1238 | MID=TBD | length | identification-tag ... 1239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1241 The identification-tag payload is UTF-8 encoded, as in SDP. 1243 The identification-tag is not zero terminated. 1245 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1246 identifier value.] 1248 13.3. RTP MID Header Extension 1250 The payload, containing the mid value, of the RTP MID header 1251 extension element can be encoded using either the one-byte or two- 1252 byte header [RFC5285]. The identification-tag payload is UTF-8 1253 encoded, as in SDP. 1255 The identification-tag is not zero terminated. Note, however, that 1256 RTP header extensions that are not a multiple of 32 bits in length 1257 MUST be padded to the next 32-bit boundary using zero bytes; these 1258 padding bytes are not included in the header length field [RFC3550]. 1260 14. IANA Considerations 1262 14.1. New SDES item 1264 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1265 document.] 1267 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1268 identifier value.] 1270 This document adds the MID SDES item to the IANA "RTCP SDES item 1271 types" registry as follows: 1273 Value: TBD 1274 Abbrev.: MID 1275 Name: Media Identification 1276 Reference: RFCXXXX 1278 14.2. New RTP Header Extension URI 1280 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1281 document.] 1283 This document defines a new extension URI in the RTP Compact Header 1284 Extensions subregistry of the Real-Time Transport Protocol (RTP) 1285 Parameters registry, according to the following data: 1287 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1288 Description: Media identification 1289 Contact: christer.holmberg@ericsson.com 1290 Reference: RFCXXXX 1292 14.3. New SDP Attribute 1294 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1295 document.] 1297 This document defines a new SDP media-level attribute, 'bundle-only', 1298 according to the following data: 1300 Attribute name: bundle-only 1301 Type of attribute: media 1302 Subject to charset: No 1303 Purpose: Request a media description to be accepted 1304 in the answer only if kept within a BUNDLE 1305 group by the answerer. 1306 Appropriate values: N/A 1307 Contact name: Christer Holmberg 1308 Contact e-mail: christer.holmberg@ericsson.com 1309 Reference: RFCXXXX 1311 15. Security Considerations 1313 The security considerations defined in [RFC3264] and [RFC5888] apply 1314 to the BUNDLE extension. Bundle does not change which information 1315 flows over the network but only changes which ports that information 1316 is flowing on and thus has very little impact on the security of the 1317 RTP sessions. 1319 When the BUNDLE extension is used, a single set of security 1320 credentials might be used for all media streams associated with a 1321 BUNDLE group. 1323 When the BUNDLE extension is used, the number of SSRC values within a 1324 single RTP session increases, which increases the risk of SSRC 1325 collision. [RFC4568] describes how SSRC collision may weaken SRTP 1326 and SRTCP encryption in certain situations. 1328 16. Examples 1330 16.1. Example: Bundle Address Selection 1332 The example below shows: 1334 o 1. An offer, in which the offerer assigns a unique address to 1335 each bundled "m=" line within the BUNDLE group. 1337 o 2. An answer, in which the answerer selects the offerer BUNDLE 1338 address, and in which selects its own BUNDLE address (the answerer 1339 BUNDLE address) and assigns it each bundled "m=" line within the 1340 BUNDLE group. 1342 o 3. A subsequent offer (BAS offer), which is used to perform a 1343 Bundle Address Synchronization (BAS). 1345 SDP Offer (1) 1347 v=0 1348 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1349 s= 1350 c=IN IP4 atlanta.example.com 1351 t=0 0 1352 a=group:BUNDLE foo bar 1353 m=audio 10000 RTP/AVP 0 8 97 1354 b=AS:200 1355 a=mid:foo 1356 a=rtpmap:0 PCMU/8000 1357 a=rtpmap:8 PCMA/8000 1358 a=rtpmap:97 iLBC/8000 1359 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1360 m=video 10002 RTP/AVP 31 32 1361 b=AS:1000 1362 a=mid:bar 1363 a=rtpmap:31 H261/90000 1364 a=rtpmap:32 MPV/90000 1365 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1367 SDP Answer (2) 1369 v=0 1370 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1371 s= 1372 c=IN IP4 biloxi.example.com 1373 t=0 0 1374 a=group:BUNDLE foo bar 1375 m=audio 20000 RTP/AVP 0 1376 b=AS:200 1377 a=mid:foo 1378 a=rtpmap:0 PCMU/8000 1379 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1380 m=video 20000 RTP/AVP 32 1381 b=AS:1000 1382 a=mid:bar 1383 a=rtpmap:32 MPV/90000 1384 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1386 SDP Offer (3) 1388 v=0 1389 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1390 s= 1391 c=IN IP4 atlanta.example.com 1392 t=0 0 1393 a=group:BUNDLE foo bar 1394 m=audio 10000 RTP/AVP 0 8 97 1395 b=AS:200 1396 a=mid:foo 1397 a=rtpmap:0 PCMU/8000 1398 a=rtpmap:8 PCMA/8000 1399 a=rtpmap:97 iLBC/8000 1400 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1401 m=video 10000 RTP/AVP 31 32 1402 b=AS:1000 1403 a=mid:bar 1404 a=rtpmap:31 H261/90000 1405 a=rtpmap:32 MPV/90000 1406 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1408 16.2. Example: BUNDLE Extension Rejected 1410 The example below shows: 1412 o 1. An offer, in which the offerer assigns a unique address to 1413 each bundled "m=" line within the BUNDLE group. 1415 o 2. An answer, in which the answerer rejects the offered BUNDLE 1416 group, and assigns a unique addresses to each "m=" line (following 1417 normal RFC 3264 procedures). 1419 SDP Offer (1) 1421 v=0 1422 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1423 s= 1424 c=IN IP4 atlanta.example.com 1425 t=0 0 1426 a=group:BUNDLE foo bar 1427 m=audio 10000 RTP/AVP 0 8 97 1428 b=AS:200 1429 a=mid:foo 1430 a=rtpmap:0 PCMU/8000 1431 a=rtpmap:8 PCMA/8000 1432 a=rtpmap:97 iLBC/8000 1433 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1434 m=video 10002 RTP/AVP 31 32 1435 b=AS:1000 1436 a=mid:bar 1437 a=rtpmap:31 H261/90000 1438 a=rtpmap:32 MPV/90000 1439 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1441 SDP Answer (2) 1443 v=0 1444 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1445 s= 1446 c=IN IP4 biloxi.example.com 1447 t=0 0 1448 m=audio 20000 RTP/AVP 0 1449 b=AS:200 1450 a=rtpmap:0 PCMU/8000 1451 m=video 30000 RTP/AVP 32 1452 b=AS:1000 1453 a=rtpmap:32 MPV/90000 1455 16.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1457 The example below shows: 1459 o 1. A subsequent offer (the BUNDLE group has been created as part 1460 of a previous offer/answer transaction), in which the offerer adds 1461 a new "m=" line, represented by the "zen" identification-tag, to a 1462 previously negotiated BUNDLE group, assigns a unique address to 1463 the added "m=" line, and assigns the previously selected offerer 1464 BUNDLE address to each of the other bundled "m=" lines within the 1465 BUNDLE group. 1467 o 2. An answer, in which the answerer assigns the answerer BUNDLE 1468 address to each bundled "m=" line (including the newly added "m=" 1469 line) within the BUNDLE group. 1471 o 3. A subsequent offer (BAS offer), which is used to perform a 1472 Bundle Address Synchronization (BAS). 1474 SDP Offer (1) 1476 v=0 1477 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1478 s= 1479 c=IN IP4 atlanta.example.com 1480 t=0 0 1481 a=group:BUNDLE foo bar zen 1482 m=audio 10000 RTP/AVP 0 8 97 1483 b=AS:200 1484 a=mid:foo 1485 a=rtpmap:0 PCMU/8000 1486 a=rtpmap:8 PCMA/8000 1487 a=rtpmap:97 iLBC/8000 1488 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1489 m=video 10000 RTP/AVP 31 32 1490 b=AS:1000 1491 a=mid:bar 1492 a=rtpmap:31 H261/90000 1493 a=rtpmap:32 MPV/90000 1494 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1495 m=video 20000 RTP/AVP 66 1496 b=AS:1000 1497 a=mid:zen 1498 a=rtpmap:66 H261/90000 1499 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1501 SDP Answer (2) 1503 v=0 1504 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1505 s= 1506 c=IN IP4 biloxi.example.com 1507 t=0 0 1508 a=group:BUNDLE foo bar zen 1509 m=audio 20000 RTP/AVP 0 1510 b=AS:200 1511 a=mid:foo 1512 a=rtpmap:0 PCMU/8000 1513 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1514 m=video 20000 RTP/AVP 32 1515 b=AS:1000 1516 a=mid:bar 1517 a=rtpmap:32 MPV/90000 1518 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1519 m=video 20000 RTP/AVP 66 1520 b=AS:1000 1521 a=mid:zen 1522 a=rtpmap:66 H261/90000 1523 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1525 SDP Offer (3) 1527 v=0 1528 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1529 s= 1530 c=IN IP4 atlanta.example.com 1531 t=0 0 1532 a=group:BUNDLE foo bar zen 1533 m=audio 10000 RTP/AVP 0 8 97 1534 b=AS:200 1535 a=mid:foo 1536 a=rtpmap:0 PCMU/8000 1537 a=rtpmap:8 PCMA/8000 1538 a=rtpmap:97 iLBC/8000 1539 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1540 m=video 10000 RTP/AVP 31 32 1541 b=AS:1000 1542 a=mid:bar 1543 a=rtpmap:31 H261/90000 1544 a=rtpmap:32 MPV/90000 1545 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1546 m=video 10000 RTP/AVP 66 1547 b=AS:1000 1548 a=mid:zen 1549 a=rtpmap:66 H261/90000 1550 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1552 16.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1554 The example below shows: 1556 o 1. A subsequent offer (the BUNDLE group has been created as part 1557 of a previous offer/answer transaction), in which the offerer 1558 moves a bundled "m=" line out of a BUNDLE group, assigns a unique 1559 address to the moved "m=" line, and assigns the offerer BUNDLE 1560 address to each other bundled "m=" line within the BUNDLE group. 1562 o 2. An answer, in which the answerer moves the "m=" line out of 1563 the BUNDLE group, assigns unique address to the moved "m=" line, 1564 and assigns the answerer BUNDLE address to each of the remaining 1565 bundled "m=" line within the BUNDLE group. 1567 SDP Offer (1) 1569 v=0 1570 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1571 s= 1572 c=IN IP4 atlanta.example.com 1573 t=0 0 1574 a=group:BUNDLE foo bar 1575 m=audio 10000 RTP/AVP 0 8 97 1576 b=AS:200 1577 a=mid:foo 1578 a=rtpmap:0 PCMU/8000 1579 a=rtpmap:8 PCMA/8000 1580 a=rtpmap:97 iLBC/8000 1581 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1582 m=video 10000 RTP/AVP 31 32 1583 b=AS:1000 1584 a=mid:bar 1585 a=rtpmap:31 H261/90000 1586 a=rtpmap:32 MPV/90000 1587 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1588 m=video 50000 RTP/AVP 66 1589 b=AS:1000 1590 a=mid:zen 1591 a=rtpmap:66 H261/90000 1593 SDP Answer (2) 1595 v=0 1596 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1597 s= 1598 c=IN IP4 biloxi.example.com 1599 t=0 0 1600 a=group:BUNDLE foo bar 1601 m=audio 20000 RTP/AVP 0 1602 b=AS:200 1603 a=mid:foo 1604 a=rtpmap:0 PCMU/8000 1605 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1606 m=video 20000 RTP/AVP 32 1607 b=AS:1000 1608 a=mid:bar 1609 a=rtpmap:32 MPV/90000 1610 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1611 m=video 60000 RTP/AVP 66 1612 b=AS:1000 1613 a=mid:zen 1614 a=rtpmap:66 H261/90000 1616 16.5. Example: Offerer Disables A Media Description Within A BUNDLE 1617 Group 1619 The example below shows: 1621 o 1. A subsequent offer (the BUNDLE group has been created as part 1622 of a previous offer/answer transaction), in which the offerer 1623 disables a bundled "m=" line within BUNDLE group, assigns a zero 1624 port number to the disabled "m=" line, and assigns the offerer 1625 BUNDLE address to each of the other bundled "m=" lines within the 1626 BUNDLE group. 1628 o 2. An answer, in which the answerer moves the disabled "m=" line 1629 out of the BUNDLE group, assigns a zero port value to the disabled 1630 "m=" line, and assigns the answerer BUNDLE address to each of the 1631 remaining bundled "m=" line within the BUNDLE group. 1633 SDP Offer (1) 1635 v=0 1636 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1637 s= 1638 c=IN IP4 atlanta.example.com 1639 t=0 0 1640 a=group:BUNDLE foo bar 1641 m=audio 10000 RTP/AVP 0 8 97 1642 b=AS:200 1643 a=mid:foo 1644 a=rtpmap:0 PCMU/8000 1645 a=rtpmap:8 PCMA/8000 1646 a=rtpmap:97 iLBC/8000 1647 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1648 m=video 10000 RTP/AVP 31 32 1649 b=AS:1000 1650 a=mid:bar 1651 a=rtpmap:31 H261/90000 1652 a=rtpmap:32 MPV/90000 1653 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1654 m=video 0 RTP/AVP 66 1655 a=mid:zen 1656 a=rtpmap:66 H261/90000 1658 SDP Answer (2) 1660 v=0 1661 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1662 s= 1663 c=IN IP4 biloxi.example.com 1664 t=0 0 1665 a=group:BUNDLE foo bar 1666 m=audio 20000 RTP/AVP 0 1667 b=AS:200 1668 a=mid:foo 1669 a=rtpmap:0 PCMU/8000 1670 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1671 m=video 20000 RTP/AVP 32 1672 b=AS:1000 1673 a=mid:bar 1674 a=rtpmap:32 MPV/90000 1675 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1676 m=video 0 RTP/AVP 66 1677 a=mid:zen 1678 a=rtpmap:66 H261/90000 1680 17. Acknowledgements 1682 The usage of the SDP grouping extension for negotiating bundled media 1683 is based on a similar alternatives proposed by Harald Alvestrand and 1684 Cullen Jennings. The BUNDLE extension described in this document is 1685 based on the different alternative proposals, and text (e.g. SDP 1686 examples) have been borrowed (and, in some cases, modified) from 1687 those alternative proposals. 1689 The SDP examples are also modified versions from the ones in the 1690 Alvestrand proposal. 1692 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 1693 Stach and Ari Keraenen for taking the time to read the text along the 1694 way, and providing useful feedback. 1696 18. Change Log 1698 [RFC EDITOR NOTE: Please remove this section when publishing] 1700 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 1702 o Usage of SDP 'extmap' attribute added 1704 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 1705 port value 1707 o Changes based on WGLC comments from Thomas Stach 1709 o - ICE candidates not assigned to bundle-only m- lines with a zero 1710 port value 1712 o - Editorial changes 1714 o Changes based on WGLC comments from Colin Perkins 1716 o - Editorial changes: 1718 o -- "RTP SDES item" -> "RTCP SDES item" 1720 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 1722 o - Changes in section 10.1.1: 1724 o -- "SHOULD NOT" -> "MUST NOT" 1726 o -- Additional text added to the Note 1728 o - Change to section 13.2: 1730 o -- Clarify that mid value is not zero terminated 1732 o - Change to section 13.3: 1734 o -- Clarify that mid value is not zero terminated 1736 o -- Clarify padding 1737 o Changes based on WGLC comments from Paul Kyzivat 1739 o - Editorial changes: 1741 o Changes based on WGLC comments from Jonathan Lennox 1743 o - Editorial changes: 1745 o - Defintion of SDP bundle-only attribute alligned with structure 1746 in 4566bis draft 1748 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 1750 o Editorial corrections based on comments from Harald Alvestrand. 1752 o Editorial corrections based on comments from Cullen Jennings. 1754 o Reference update (RFC 7160). 1756 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 1757 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 1758 msg13765.html). 1760 o Additional text added to the Security Considerations. 1762 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 1764 o SDP bundle-only attribute added to IANA Considerations. 1766 o SDES item and RTP header extension added to Abstract and 1767 Introduction. 1769 o Modification to text updating section 8.2 of RFC 3264. 1771 o Reference corrections. 1773 o Editorial corrections. 1775 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 1777 o Terminology change: "bundle-only attribute assigned to m= line" to 1778 "bundle-only attribute associated with m= line". 1780 o Editorial corrections. 1782 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 1784 o Editorial corrections. 1786 o - "of"->"if" (8.3.2.5). 1788 o - "optional"->"OPTIONAL" (9.1). 1790 o - Syntax/ABNF for 'bundle-only' attribute added. 1792 o - SDP Offer/Answer sections merged. 1794 o - 'Request new offerer BUNDLE address' section added 1796 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 1798 o OPEN ISSUE regarding Receiver-ID closed. 1800 o - RTP MID SDES Item. 1802 o - RTP MID Header Extension. 1804 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 1805 closed. 1807 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 1808 include an 'rtcp' attribute in the answer, based on the procedures 1809 in section 5.1.3 of RFC 5761. 1811 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 1813 o Draft title changed. 1815 o Added "SDP" to section names containing "Offer" or "Answer". 1817 o Editorial fixes based on comments from Paul Kyzivat 1818 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1819 msg13314.html). 1821 o Editorial fixed based on comments from Colin Perkins 1822 (http://www.ietf.org/mail-archive/web/mmusic/current/ 1823 msg13318.html). 1825 o - Removed text about extending BUNDLE to allow multiple RTP 1826 sessions within a BUNDLE group. 1828 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 1830 o Major re-structure of SDP Offer/Answer sections, to align with RFC 1831 3264 structure. 1833 o Additional definitions added. 1835 o - Shared address. 1837 o - Bundled "m=" line. 1839 o - Bundle-only "m=" line. 1841 o - Offerer suggested BUNDLE mid. 1843 o - Answerer selected BUNDLE mid. 1845 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 1846 to multiple "m=" lines until it has received an SDP Answer 1847 indicating support of the BUNDLE extension. 1849 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 1850 Answerer supports the BUNDLE extension, assign a zero port value 1851 to a 'bundle-only' "m=" line. 1853 o SDP 'bundle-only' attribute section added. 1855 o Connection data nettype/addrtype restrictions added. 1857 o RFC 3264 update section added. 1859 o Indicating that a specific payload type value can be used in 1860 multiple "m=" lines, if the value represents the same codec 1861 configuration in each "m=" line. 1863 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 1865 o Updated Offerer procedures (http://www.ietf.org/mail- 1866 archive/web/mmusic/current/msg12293.html). 1868 o Updated Answerer procedures (http://www.ietf.org/mail- 1869 archive/web/mmusic/current/msg12333.html). 1871 o Usage of SDP 'bundle-only' attribute added. 1873 o Reference to Trickle ICE document added. 1875 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 1877 o Mechanism modified, to be based on usage of SDP Offers with both 1878 different and identical port number values, depending on whether 1879 it is known if the remote endpoint supports the extension. 1881 o Cullen Jennings added as co-author. 1883 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 1885 o No changes. New version due to expiration. 1887 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 1889 o No changes. New version due to expiration. 1891 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 1893 o Draft name changed. 1895 o Harald Alvestrand added as co-author. 1897 o "Multiplex" terminology changed to "bundle". 1899 o Added text about single versus multiple RTP Sessions. 1901 o Added reference to RFC 3550. 1903 19. References 1905 19.1. Normative References 1907 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1908 Requirement Levels", BCP 14, RFC 2119, March 1997. 1910 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1911 with Session Description Protocol (SDP)", RFC 3264, June 1912 2002. 1914 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1915 Description Protocol", RFC 4566, July 2006. 1917 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 1918 Header Extensions", RFC 5285, July 2008. 1920 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1921 Control Packets on a Single Port", RFC 5761, April 2010. 1923 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 1924 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 1926 [I-D.mmusic-sdp-mux-attributes] 1927 Nandakumar, S., "A Framework for SDP Attributes when 1928 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-05 1929 (work in progress), November 2014. 1931 19.2. Informative References 1933 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1934 Jacobson, "RTP: A Transport Protocol for Real-Time 1935 Applications", STD 64, RFC 3550, July 2003. 1937 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 1938 in Session Description Protocol (SDP)", RFC 3605, October 1939 2003. 1941 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1942 Description Protocol (SDP) Security Descriptions for Media 1943 Streams", RFC 4568, July 2006. 1945 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1946 (ICE): A Protocol for Network Address Translator (NAT) 1947 Traversal for Offer/Answer Protocols", RFC 5245, April 1948 2010. 1950 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 1951 Media Attributes in the Session Description Protocol 1952 (SDP)", RFC 5576, June 2009. 1954 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 1955 Security (DTLS) Extension to Establish Keys for the Secure 1956 Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. 1958 [RFC7160] Petit-Huguenin, M. and G. Zorn, "Support for Multiple 1959 Clock Rates in an RTP Session", RFC 7160, April 2014. 1961 [I-D.ietf-mmusic-trickle-ice] 1962 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 1963 Incremental Provisioning of Candidates for the Interactive 1964 Connectivity Establishment (ICE) Protocol", draft-ietf- 1965 mmusic-trickle-ice-01 (work in progress), February 2014. 1967 Appendix A. Design Considerations 1969 A.1. General 1971 One of the main issues regarding the BUNDLE grouping extensions has 1972 been whether, in SDP Offers and SDP Answers, the same port value 1973 should be inserted in "m=" lines associated with a BUNDLE group, as 1974 the purpose of the extension is to negotiate the usage of a single 1975 address:port combination for media associated with the "m=" lines. 1976 Issues with both approaches, discussed in the Appendix have been 1977 raised. The outcome was to specify a mechanism which uses SDP Offers 1978 with both different and identical port values. 1980 Below are the primary issues that have been considered when defining 1981 the "BUNDLE" grouping extension: 1983 o 1) Interoperability with existing UAs. 1985 o 2) Interoperability with intermediary B2BUA- and proxy entities. 1987 o 3) Time to gather, and the number of, ICE candidates. 1989 o 4) Different error scenarios, and when they occur. 1991 o 5) SDP Offer/Answer impacts, including usage of port number value 1992 zero. 1994 NOTE: Before this document is published as an RFC, this 1995 Appendix might be removed. 1997 A.2. UA Interoperability 1999 Consider the following SDP Offer/Answer exchange, where Alice sends 2000 an SDP Offer to Bob: 2002 SDP Offer 2004 v=0 2005 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2006 s= 2007 c=IN IP4 atlanta.example.com 2008 t=0 0 2009 m=audio 10000 RTP/AVP 97 2010 a=rtpmap:97 iLBC/8000 2011 m=video 10002 RTP/AVP 97 2012 a=rtpmap:97 H261/90000 2014 SDP Answer 2016 v=0 2017 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2018 s= 2019 c=IN IP4 biloxi.example.com 2020 t=0 0 2021 m=audio 20000 RTP/AVP 97 2022 a=rtpmap:97 iLBC/8000 2023 m=video 20002 RTP/AVP 97 2024 a=rtpmap:97 H261/90000 2026 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2027 later invention to RTP and Bob can not assume that Alice supports RFC 2028 4961. This means that Alice may be sending RTP from a different port 2029 than 10000 or 10002 - some implementation simply send the RTP from an 2030 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2031 way that Bob know if it should be passed to the video or audio codec 2032 is by looking at the port it was received on. This lead some SDP 2033 implementations to use the fact that each "m=" line had a different 2034 port number to use that port number as an index to find the correct m 2035 line in the SDP. As a result, some implementations that do support 2036 symmetric RTP and ICE still use a SDP data structure where SDP with 2037 "m=" lines with the same port such as: 2039 SDP Offer 2041 v=0 2042 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2043 s= 2044 c=IN IP4 atlanta.example.com 2045 t=0 0 2046 m=audio 10000 RTP/AVP 97 2047 a=rtpmap:97 iLBC/8000 2048 m=video 10000 RTP/AVP 98 2049 a=rtpmap:98 H261/90000 2051 will result in the second "m=" line being considered an SDP error 2052 because it has the same port as the first line. 2054 A.3. Usage of port number value zero 2056 In an SDP Offer or SDP Answer, the media associated with an "m=" line 2057 can be disabled/rejected by setting the port number value to zero. 2058 This is different from e.g. using the SDP direction attributes, where 2059 RTCP traffic will continue even if the SDP "inactive" attribute is 2060 indicated for the associated "m=" line. 2062 If each "m=" line associated with a BUNDLE group would contain 2063 different port values, and one of those port values would be used for 2064 a BUNDLE address associated with the BUNDLE group, problems would 2065 occur if an endpoint wants to disable/reject the "m=" line associated 2066 with that port, by setting the port value to zero. After that, no 2067 "m=" line would contain the port value which is used for the BUNDLE 2068 address. In addition, it is unclear what would happen to the ICE 2069 candidates associated with the "m=" line, as they are also used for 2070 the BUNDLE address. 2072 A.4. B2BUA And Proxy Interoperability 2074 Some back to back user agents may be configured in a mode where if 2075 the incoming call leg contains an SDP attribute the B2BUA does not 2076 understand, the B2BUS still generates that SDP attribute in the Offer 2077 for the outgoing call leg. Consider an B2BUA that did not understand 2078 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2079 Further assume that the B2BUA was configured to tear down any call 2080 where it did not see any RTCP for 5 minutes. In this cases, if the 2081 B2BUA received an Offer like: 2083 SDP Offer 2085 v=0 2086 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2087 s= 2088 c=IN IP4 atlanta.example.com 2089 t=0 0 2090 m=audio 49170 RTP/AVP 0 2091 a=rtcp:53020 2093 It would be looking for RTCP on port 49172 but would not see any 2094 because the RTCP would be on port 53020 and after five minutes, it 2095 would tear down the call. Similarly, an SBC that did not understand 2096 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2097 wrong port and tear down the call. It is worth noting that a B2BUA 2098 that generated an Offer with capabilities it does not understand is 2099 not compliant with the specifications. 2101 A.4.1. Traffic Policing 2103 Sometimes intermediaries do not act as B2BUA, in the sense that they 2104 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2105 however, they may use SDP information (e.g. IP address and port) in 2106 order to control traffic gating functions, and to set traffic 2107 policing rules. There might be rules which will trigger a session to 2108 be terminated in case media is not sent or received on the ports 2109 retrieved from the SDP. This typically occurs once the session is 2110 already established and ongoing. 2112 A.4.2. Bandwidth Allocation 2114 Sometimes intermediaries do not act as B2BUA, in the sense that they 2115 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2116 however, they may use SDP information (e.g. codecs and media types) 2117 in order to control bandwidth allocation functions. The bandwidth 2118 allocation is done per "m=" line, which means that it might not be 2119 enough if media associated with all "m=" lines try to use that 2120 bandwidth. That may either simply lead to bad user experience, or to 2121 termination of the call. 2123 A.5. Candidate Gathering 2125 When using ICE, an candidate needs to be gathered for each port. 2126 This takes approximately 20 ms extra for each extra "m=" line due to 2127 the NAT pacing requirements. All of this gather can be overlapped 2128 with other things while the page is loading to minimize the impact. 2129 If the client only wants to generate TURN or STUN ICE candidates for 2130 one of the "m=" lines and then use trickle ICE 2131 [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for 2132 the rest of the "m=" lines, it MAY do that and will not need any 2133 additional gathering time. 2135 Some people have suggested a TURN extension to get a bunch of TURN 2136 allocation at once. This would only provide a single STUN result so 2137 in cases where the other end did not support BUNDLE, may cause more 2138 use of the TURN server but would be quick in the cases where both 2139 sides supported BUNDLE and would fall back to a successful call in 2140 the other cases. 2142 Authors' Addresses 2144 Christer Holmberg 2145 Ericsson 2146 Hirsalantie 11 2147 Jorvas 02420 2148 Finland 2150 Email: christer.holmberg@ericsson.com 2152 Harald Tveit Alvestrand 2153 Google 2154 Kungsbron 2 2155 Stockholm 11122 2156 Sweden 2158 Email: harald@alvestrand.no 2160 Cullen Jennings 2161 Cisco 2162 400 3rd Avenue SW, Suite 350 2163 Calgary, AB T2P 4H2 2164 Canada 2166 Email: fluffy@iii.ca