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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC K. Drage 3 Internet-Draft Unaffiliated 4 Intended status: Standards Track M. Makaraju 5 Expires: December 2, 2018 Nokia 6 J. Stoetzer-Bradler 7 R. Ejzak 8 J. Marcon 9 Unaffiliated 10 R. Even, Ed. 11 Huawei 12 May 31, 2018 14 SDP-based Data Channel Negotiation 15 draft-ietf-mmusic-data-channel-sdpneg-19 17 Abstract 19 The Real-Time Communication in WEB-browsers (RTCWeb) working group is 20 charged to provide protocols to support direct interactive rich 21 communications using audio, video, and data between two peers' web- 22 browsers. For the support of data communication, the RTCWeb working 23 group has in particular defined the concept of bi-directional data 24 channels over SCTP (Stream Control Transmission Protocol), where each 25 data channel might be used to transport other protocols, called 26 subprotocols. Data channel setup can be done using either the in- 27 band Data Channel Establishment Protocol (DCEP) or using some out-of- 28 band non-DCEP protocol. This document specifies how the SDP (Session 29 Description Protocol) offer/answer exchange can be used to achieve 30 such an out-of-band non-DCEP negotiation. Even though data channels 31 are designed for RTCWeb use initially, they may be used by other 32 protocols like, but not limited to, the CLUE protocol (which is 33 defined by the IETF "ControLling mUltiple streams for tElepresence" 34 working group). This document is intended to be used wherever data 35 channels are used. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at https://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on December 2, 2018. 54 Copyright Notice 56 Copyright (c) 2018 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (https://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 72 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 73 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 74 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6 75 5. SDP Data Channel Attributes . . . . . . . . . . . . . . . . . 6 76 5.1. SDP DCMAP Attribute . . . . . . . . . . . . . . . . . . . 6 77 5.1.1. DCMAP Attribute Syntax . . . . . . . . . . . . . . . 6 78 5.1.2. Dcmap-stream-id Parameter . . . . . . . . . . . . . . 8 79 5.1.3. Label Parameter . . . . . . . . . . . . . . . . . . . 8 80 5.1.4. Subprotocol Parameter . . . . . . . . . . . . . . . . 8 81 5.1.5. Max-retr Parameter . . . . . . . . . . . . . . . . . 9 82 5.1.6. Max-time Parameter . . . . . . . . . . . . . . . . . 9 83 5.1.7. Ordered Parameter . . . . . . . . . . . . . . . . . . 9 84 5.1.8. Priority Parameter . . . . . . . . . . . . . . . . . 9 85 5.1.9. DCMAP Multiplexing Category . . . . . . . . . . . . . 10 86 5.2. SDP DCSA Attribute . . . . . . . . . . . . . . . . . . . 10 87 5.2.1. DCSA Syntax . . . . . . . . . . . . . . . . . . . . . 10 88 5.2.2. DCSA Multiplexing Category . . . . . . . . . . . . . 12 89 6. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 12 90 6.1. Managing Stream Identifiers . . . . . . . . . . . . . . . 12 91 6.2. Negotiating Data Channel Parameters . . . . . . . . . . . 13 92 6.3. Generating the Initial Offer for A Data Channel . . . . . 13 93 6.4. Generating SDP Answer . . . . . . . . . . . . . . . . . . 14 94 6.5. Offerer Processing of the SDP Answer . . . . . . . . . . 14 95 6.6. Modifying the Session . . . . . . . . . . . . . . . . . . 15 96 6.6.1. Closing a Data Channel . . . . . . . . . . . . . . . 15 98 6.7. Various SDP Offer/Answer Considerations . . . . . . . . . 15 99 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16 100 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 101 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 102 9.1. Subprotocol Identifiers . . . . . . . . . . . . . . . . . 19 103 9.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 19 104 9.2.1. dcmap . . . . . . . . . . . . . . . . . . . . . . . . 19 105 9.2.2. dcsa . . . . . . . . . . . . . . . . . . . . . . . . 20 106 9.3. New Usage Level . . . . . . . . . . . . . . . . . . . . . 20 107 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 108 11. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 21 109 11.1. Changes against 'draft-ietf-mmusic-data-channel- 110 sdpneg-15' . . . . . . . . . . . . . . . . . . . . . . . 21 111 11.2. Changes against 'draft-ietf-mmusic-data-channel- 112 sdpneg-14' . . . . . . . . . . . . . . . . . . . . . . . 21 113 11.3. Changes against 'draft-ietf-mmusic-data-channel- 114 sdpneg-12' . . . . . . . . . . . . . . . . . . . . . . . 21 115 11.4. Changes against 'draft-ietf-mmusic-data-channel- 116 sdpneg-11' . . . . . . . . . . . . . . . . . . . . . . . 21 117 11.5. Changes against 'draft-ietf-mmusic-data-channel- 118 sdpneg-10' . . . . . . . . . . . . . . . . . . . . . . . 22 119 11.6. Changes against 'draft-ietf-mmusic-data-channel- 120 sdpneg-09' . . . . . . . . . . . . . . . . . . . . . . . 22 121 11.7. Changes against 'draft-ietf-mmusic-data-channel- 122 sdpneg-08' . . . . . . . . . . . . . . . . . . . . . . . 23 123 11.8. Changes against 'draft-ietf-mmusic-data-channel- 124 sdpneg-07' . . . . . . . . . . . . . . . . . . . . . . . 23 125 11.9. Changes against 'draft-ietf-mmusic-data-channel- 126 sdpneg-06' . . . . . . . . . . . . . . . . . . . . . . . 23 127 11.10. Changes against 'draft-ietf-mmusic-data-channel- 128 sdpneg-05' . . . . . . . . . . . . . . . . . . . . . . . 23 129 11.11. Changes against 'draft-ietf-mmusic-data-channel- 130 sdpneg-04' . . . . . . . . . . . . . . . . . . . . . . . 24 131 11.12. Changes against 'draft-ietf-mmusic-data-channel- 132 sdpneg-03' . . . . . . . . . . . . . . . . . . . . . . . 25 133 11.13. Changes against 'draft-ietf-mmusic-data-channel- 134 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 26 135 11.14. Changes against 'draft-ietf-mmusic-data-channel- 136 sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 27 137 11.15. Changes against 'draft-ietf-mmusic-data-channel- 138 sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 29 139 11.16. Changes against 'draft-ejzak-mmusic-data-channel- 140 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 32 141 11.17. Changes against '-01' . . . . . . . . . . . . . . . . . 33 142 11.18. Changes against '-00' . . . . . . . . . . . . . . . . . 33 143 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 144 12.1. Normative References . . . . . . . . . . . . . . . . . . 34 145 12.2. Informative References . . . . . . . . . . . . . . . . . 35 147 Appendix A. Generic Data Channel Negotiation Aspects When Not 148 Using DCEP . . . . . . . . . . . . . . . . . . . . . 36 149 A.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 37 150 A.2. Generic Data Channel Negotiation Not Using DCEP . . . . . 37 151 A.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 37 152 A.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 37 153 A.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 38 154 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39 156 1. Introduction 158 The RTCWeb working group has defined the concept of bi-directional 159 data channels running on top of the Stream Control Transmission 160 Protocol (SCTP) [I-D.ietf-rtcweb-data-channel]. RTCWeb allows 161 applications to use data channels. RTCWeb defines an in-band Data 162 Channel Establishment Protocol (DCEP) 163 [I-D.ietf-rtcweb-data-protocol], however other in-band or out-of-band 164 protocols may be used for establishing data channels. Each data 165 channel consists of paired SCTP streams sharing the same SCTP Stream 166 Identifier. Data channels are created by endpoint applications 167 through the WebRTC API (Application Programming Interface), or other 168 users of a data channel like CLUE [I-D.ietf-clue-datachannel] They 169 can be used to transport proprietary or well-defined protocols, which 170 in the latter case can be signaled by the data channel "subprotocol" 171 parameter, conceptually similar to the WebSocket "subprotocol". 172 However, apart from the "subprotocol" value transmitted to the peer, 173 RTCWeb leaves it open how endpoint applications can agree on how to 174 instantiate a given subprotocol on a data channel, and whether it is 175 signaled in-band using DCEP or out-of-band using a non-DCEP protocol 176 (or both). In particular, the SDP offer generated by the RTCweb data 177 channel stack includes no channel-specific information. 179 This document defines SDP offer/answer [RFC3264] procedures that 180 enable out-of-band negotiation for establishing data channels for 181 transport of well-defined subprotocols. These procedures are based 182 on generic SDP offer/answer negotiation rules for SCTP based media 183 transport as specified in [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" 184 line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP. 186 This document makes use of MSRP (Message Session Relay Protocol) 187 [RFC4975] and BFCP (Binary Floor Control Protocol) [RFC4582] in many 188 of the examples. It does not provide a complete specification of how 189 to negotiate the use of a data channel to transport MSRP. Procedures 190 specific to each subprotocol would have to be documented elsewhere. 191 For MSRP they are documented in 192 [I-D.ietf-mmusic-msrp-usage-data-channel] . The use of MSRP in some 193 examples is only to show how the generic procedures described herein 194 might apply to a specific subprotocol. 196 2. Conventions 198 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 199 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 200 document are to be interpreted as described in [RFC2119]. 202 3. Terminology 204 This document uses the following terms: 206 Data channel: A WebRTC data channel as specified in 207 [I-D.ietf-rtcweb-data-channel]. 209 Data channel stack: An entity which, upon application request, 210 runs the data channel protocol to keep track of states, sending 211 and receiving data. If the application is a browser based 212 JavaScript application then this stack resides in the browser. If 213 the application is a native application then this stack resides in 214 the application and is accessible via some sort of APIs. 216 Data channel properties: Fixed properties assigned to a data 217 channel at the time of its creation. Some of these properties 218 determine the way the data channel stack transmits data on this 219 channel (e.g., stream identifier, reliability, order of 220 delivery...). 222 Data channel subprotocol: The application protocol which is 223 transported over a single data channel. Data channel subprotocol 224 messages are sent as data channel payload over an established data 225 channel. If an SDP offer/answer exchange is used as specified in 226 this document to negotiate the establishment of data channels, 227 corresponding data channel properties, associated data channel 228 subprotocols and data channel subprotocol properties, then the 229 data channel subprotocols may be identified by the values of the 230 "subprotocol" parameters of the SDP "a=dcmap" attribute as 231 described in Section 5.1.4. Within this document the term "data 232 channel subprotocol" is often abbreviated as just "subprotocol". 234 DCEP: Data Channel Establishment Protocol defined in 235 [I-D.ietf-rtcweb-data-protocol]. 237 In-band: Transmission through the peer-to-peer SCTP association. 239 Out-of-band: Transmission through the application signaling path. 241 Peer: From the perspective of one of the agents in a session, its 242 peer is the other agent. Specifically, from the perspective of 243 the SDP offerer, the peer is the SDP answerer. From the 244 perspective of the SDP answerer, the peer is the SDP offerer. 246 SCTP Stream Sequence Number (SSN): the SCTP stream sequence number 247 as specified in [RFC4960]. 249 Stream identifier: The identifier of the outbound and inbound SCTP 250 streams composing a data channel. 252 4. Applicability Statement 254 The mechanism in this document only applies to the Session 255 Description Protocol (SDP) [RFC4566], when used together with the SDP 256 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 257 scope of this document, and is thus undefined. 259 5. SDP Data Channel Attributes 261 This sections defines two new SDP media-level attributes, that can be 262 used together with the SDP Offer/Answer mechanism to negotiate data 263 channel-specific and subprotocol-specific parameters, without the 264 usage of DCEP [I-D.ietf-rtcweb-data-protocol]. The first attribute 265 provides for negotiation of channel-specific parameters. The second 266 attribute provides for negotiation of subprotocol-specific 267 parameters. 269 Note: Appendix A provides information how data channels work in 270 general and especially summarizes some key aspects, which should be 271 considered for the negotiation of data channels if DCEP is not used. 273 5.1. SDP DCMAP Attribute 275 This section defines a new media level attribute "a=dcmap:" that 276 defines the data channel parameters for each data channel to be 277 negotiated. 279 The attribute is used to create, on two peers matched data channels 280 as pairs of oppositely directed SCTP streams having the same set of 281 attributes. It is assumed that the data channel properties 282 (reliable/partially reliable, ordered/unordered) are suitable per the 283 subprotocol transport requirements. 285 5.1.1. DCMAP Attribute Syntax 287 "a=dcmap:" is a media level attribute having the following ABNF 288 (Augmented Backus-Naur Form, [RFC5234]) syntax. 290 Formal Syntax: 292 Name: dcmap 294 Value: dcmap-value 296 Usage Level: media 298 Charset Dependent: no 300 Syntax: 302 dcmap-value = dcmap-stream-id 303 [ SP dcmap-opt *(";" dcmap-opt) ] 304 dcmap-opt = ordering-opt / subprotocol-opt / label-opt 305 / maxretr-opt / maxtime-opt / priority-opt 306 ; Either only maxretr-opt or maxtime-opt 307 ; is present. 309 dcmap-stream-id = 1*5DIGIT 310 ordering-opt = "ordered=" ordering-value 311 ordering-value = "true" / "false" 312 subprotocol-opt = "subprotocol=" quoted-string 313 label-opt = "label=" quoted-string 314 maxretr-opt = "max-retr=" maxretr-value 315 maxretr-value = "0" / integer 316 ; number of retransmissions, 317 ; less than 2^32, 318 ; derived from 'Reliability Parameter' of 319 ; [I-D.ietf-rtcweb-data-protocol] 320 maxtime-opt = "max-time=" maxtime-value 321 maxtime-value = "0" / integer 322 ; milliseconds, 323 ; less than 2^32, 324 ; derived from 'Reliability Parameter' of 325 ; [I-D.ietf-rtcweb-data-protocol] 326 priority-opt = "priority=" priority-value 327 priority-value = "0" / integer 328 ; unsigned integer value indicating the priority of 329 ; the data channel, 330 ; less than 2^16, 331 ; derived from 'Priority' of 332 ; [I-D.ietf-rtcweb-data-protocol] 334 quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE 335 quoted-char = SP / quoted-visible 336 quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or % 337 escaped-char = "%" HEXDIG HEXDIG 338 DQUOTE = 339 integer = 340 Examples: 342 a=dcmap:0 343 a=dcmap:1 subprotocol="BFCP";max-time=60000;priority=512 344 a=dcmap:2 subprotocol="MSRP";ordered=true;label="MSRP" 345 a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128 346 a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000 348 Note: The last example (a=dcmap:4) shows a 'label' parameter value 349 which contains one non-printable 'escaped-char' character (the 350 tabulator character). 352 Within an 'a=dcmap:' attribute line's 'dcmap-opt' value either only 353 one 'maxretr-opt' parameter or one 'maxtime-opt' parameter MAY be 354 present. Both MUST NOT be present. 356 5.1.2. Dcmap-stream-id Parameter 358 The 'dcmap-stream-id' parameter indicates the SCTP stream identifier 359 within the SCTP association used to form the data channel. 361 5.1.3. Label Parameter 363 The 'label' parameter indicates the name of the channel. It 364 represents a label that can be used to distinguish, in the context of 365 the WebRTC API [WebRtcAPI], an RTCDataChannel object from other 366 RTCDataChannel objects. This parameter maps to the 'Label' parameter 367 defined in [I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is 368 optional. If it is not present, then its value defaults to the empty 369 string. 371 Note: The empty string MAY also be explicitly used as a 'label' 372 value, such that 'label=""' is equivalent to the 'label' parameter 373 not being present at all. [I-D.ietf-rtcweb-data-protocol] allows the 374 DATA_CHANNEL_OPEN message's 'Label' value to be an empty string. 376 5.1.4. Subprotocol Parameter 378 The 'subprotocol' parameter indicates which protocol the client 379 expects to exchange via the channel. This parameter maps to the 380 'Protocol' parameter defined in [I-D.ietf-rtcweb-data-protocol]. 381 Section 9.1 specifies how new subprotocol parameter values are 382 registered. 'Subprotocol' is an optional parameter. If the 383 'subprotocol' parameter is not present, then its value defaults to an 384 empty string. 386 Note: The empty string MAY also be explicitly used as 'subprotocol' 387 value, such that 'subprotocol=""' is equivalent to the 'subprotocol' 388 parameter not being present at all. [I-D.ietf-rtcweb-data-protocol] 389 allows the DATA_CHANNEL_OPEN message's 'Subprotocol' value to be an 390 empty string. 392 5.1.5. Max-retr Parameter 394 This parameter indicates that the data channel is partially reliable. 395 The 'max-retr' parameter indicates the maximal number of times a user 396 message will be retransmitted. The max-retr parameter is optional. 397 If the max-retr parameter is not present, then the maximal number of 398 retransmissions is determined as per the generic SCTP retransmission 399 rules as specified in [RFC4960]. This parameter maps to the 'Number 400 of RTX' parameter defined in [I-D.ietf-rtcweb-data-protocol]. 402 5.1.6. Max-time Parameter 404 This parameter indicates that the data channel is partially reliable. 405 A user message will no longer be transmitted or retransmitted after a 406 specified life-time given in milliseconds in the 'max-time' 407 parameter. The max-time parameter is optional. If the max-time 408 parameter is not present, then the generic SCTP retransmission timing 409 rules apply as specified in [RFC4960]. This parameter maps to the 410 'Lifetime in ms' parameter defined in 411 [I-D.ietf-rtcweb-data-protocol]. 413 5.1.7. Ordered Parameter 415 The 'ordered' parameter with value "true" indicates that the receiver 416 MUST dispatch DATA chunks in the data channel to the upper layer 417 while preserving the order. The ordered parameter is optional and 418 takes two values: "true" for ordered and "false" for unordered 419 delivery with "true" as the default value. Any other value is 420 ignored and default "ordered=true" is assumed. In the absence of 421 this parameter "ordered=true" is assumed. This parameter maps to the 422 ordered or unordered data channel types as defined in 423 [I-D.ietf-rtcweb-data-protocol]. 425 5.1.8. Priority Parameter 427 The 'priority' parameter indicates the data channel's priority 428 relative to the priorities of other data channels, which may 429 additionally exist over the same SCTP association. The 'priority' 430 parameter maps to the 'Priority' parameter defined in 431 [I-D.ietf-rtcweb-data-protocol]. The 'priority' parameter is 432 optional. In the absence of this parameter "priority=256" is 433 assumed. 435 5.1.9. DCMAP Multiplexing Category 437 The multiplexing category [I-D.ietf-mmusic-sdp-mux-attributes] of the 438 "a=dcmap:" attribute is SPECIAL. 440 As the usage of multiple SCTP associations on top of a single DTLS 441 association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no 442 "a=dcmap:" attribute multiplexing rules are specified for the 443 UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions 444 of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of 445 multiple SCTP associations on top of a single DTLS association, or 446 how to add multiple SCTP associations to one BUNDLE group, then 447 multiplexing rules for the "a=dcmap:" attribute need to be defined as 448 well, for instance in an extension of this SDP offer/answer based 449 data channel negotiation specification. 451 5.2. SDP DCSA Attribute 453 In the SDP media description, each data channel declaration MAY also 454 be followed by other media level SDP attributes, which are either 455 specifically defined for or applied to the subprotocol in use. Each 456 of these attributes is represented by one new attribute line, and it 457 includes the contents of a media-level SDP attribute already defined 458 for use with this (sub)protocol in another IETF (Internet Engineering 459 Task Force) document. Subprotocol specific attributes MAY also be 460 defined for exclusive use with data channel transport, but MUST use 461 the same syntax described here for other subprotocol related 462 attributes. 464 Each SDP attribute, related to the subprotocol, that would normally 465 be used to negotiate the subprotocol using SDP offer/answer is 466 replaced with an attribute of the form "a=dcsa:stream-id original- 467 attribute", where dcsa stands for "data channel subprotocol 468 attribute", stream-id is the SCTP stream identifier assigned to this 469 subprotocol instance, and original-attribute represents the contents 470 of the subprotocol related attribute to be included. 472 The same syntax applies to any other SDP attribute required for 473 negotiation of this instance of the subprotocol. 475 5.2.1. DCSA Syntax 476 Formal Syntax: 478 Name: dcsa 480 Value: dcsa-value 482 Usage Level: media 484 Charset Dependent: no 486 Syntax: 488 dcsa-value = stream-id SP attribute 489 attribute = 491 Example: 493 a=dcmap:2 subprotocol="MSRP";ordered=true;label="MSRP" 495 a=dcsa:2 accept-types:text/plain 497 Note that the above reference to [RFC4566] defines where the 498 attribute definition can be found; it does not provide any limitation 499 on support of attributes defined in other documents in accordance 500 with this attribute definition. Note however that not all SDP 501 attributes are suitable as a "a=dcsa:" parameter. 502 [IANA-SDP-Parameters] contains the lists of IANA (Internet Assigned 503 Numbers Authority) registered session and media level or media level 504 only SDP attributes. 506 Thus in the example above, the original attribute line "a=accept- 507 types:text/plain" is represented by the attribute line "a=dcsa:2 508 accept-types:text/plain", which specifies that this instance of the 509 MSRP subprotocol being transported on the SCTP association using the 510 data channel with stream id 2 accepts plain text files. 512 As opposed to the data channel "a=dcmap:" attribute parameters, these 513 parameters are subject to offer/answer negotiation following the 514 procedures defined in the subprotocol specific documents. 516 It is assumed that in general the usages of subprotocol related media 517 level attributes are independent from the subprotocol's transport 518 protocol. Such transport protocol independent subprotocol related 519 attributes are used in the same way as defined in the original 520 subprotocol specification, also if the subprotocol is transported 521 over a data channel and if the attribute is correspondingly embedded 522 in a "a=dcsa" attribute. 524 There may be cases, where the usage of a subprotocol related media 525 level attribute depends on the subprotocol's transport protocol. In 526 such cases the subprotocol related usage of the attribute is expected 527 to be described for the data channel transport. A data channel 528 specific usage of a subprotocol attribute is expected to be specified 529 in the same document that registers the subprotocol's identifier for 530 data channel usage as described in Section 9.1. 532 5.2.2. DCSA Multiplexing Category 534 The multiplexing category of the "a=dcsa:" attribute is SPECIAL. 536 As the usage of multiple SCTP associations on top of a single DTLS 537 association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no 538 "a=dcsa:" attribute multiplexing rules are specified for the 539 UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions 540 of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of 541 multiple SCTP associations on top of a single DTLS association, or 542 how to add multiple SCTP associations to one BUNDLE group, then 543 multiplexing rules for the "a=dcsa:" attribute need to be defined as 544 well, for instance in an extension of this SDP based data channel 545 negotiation specification. 547 6. SDP Offer/Answer Procedures 549 This section defines how data channels can be negotiated using the 550 SDP offer/answer mechanism. The procedures apply for a given data 551 channel. 553 The generic offer/answer procedures for negotiating the SCTP 554 association used to realize are defined in 555 [I-D.ietf-mmusic-sctp-sdp]. This section only defines the data 556 channel specific procedures. 558 "Initial offer" refers to the offer in which a data channel is 559 opened. It can be the initial offer, or a subsequent offer, of the 560 associated SDP session. 562 6.1. Managing Stream Identifiers 564 As described in [I-D.ietf-rtcweb-data-protocol], in order to avoid 565 SCTP Stream identifier collisions, the endpoint acting as DTLS client 566 (for the SCTP association used to realize data channels) will use 567 even identifier values, and the endpoint acting as DTLS server will 568 use odd identifier values. Those rules also apply when SCTP streams 569 for data channels are negotiated using the offer/answer mechanism. 571 SCTP stream identifiers associated with data channels that have been 572 negotiated using DCEP MUST NOT be included in SDP offers and answers. 574 6.2. Negotiating Data Channel Parameters 576 The data channel types defined in [I-D.ietf-rtcweb-data-protocol] are 577 mapped to the dcmap SDP media description in the following manner 578 where "ordered=true" is the default and may be omitted: 580 DATA_CHANNEL_RELIABLE 581 ordered=true 583 DATA_CHANNEL_RELIABLE_UNORDERED 584 ordered=false 586 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT 587 ordered=true;max-retr= 589 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED 590 ordered=false;max-retr= 592 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED 593 ordered=true;max-time= 595 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED 596 ordered=false;max-time= 598 By definition max-retr and max-time are mutually exclusive, so at 599 most one of them MAY be present in the "a=dcmap:" attribute line. If 600 a SDP offer contains both of these parameters then the receiver of 601 such an SDP offer MUST reject the SDP offer. If a SDP answer 602 contains both of these parameters then the offerer MUST treat the 603 associated SDP offer/answer failed. 605 The SDP answer SHALL echo the same subprotocol, max-retr, max-time, 606 and ordered parameters, form the offer, and MAY include a label 607 parameter. They MAY appear in any order, which could be different 608 from the SDP offer, in the SDP answer. 610 When sending a subsequent offer or an answer, and for as long as the 611 data channel is still open, the sender MUST replicate the same 612 information. 614 6.3. Generating the Initial Offer for A Data Channel 616 When an offerer sends an initial offer, in order to negotiate an SCTP 617 stream for a data channel, the offerer: 619 o SHALL include an SDP dcmap attribute (Section 5 and Section 6.2) 620 associated with the data channel in the "m=" section representing 621 the SCTP association used to realize the data channel; and 623 o MAY include one or more SDP dcsa attributes (Section 6.2) 624 associated with the data channel. The value of the stream-id part 625 of each attribute SHALL match the dcmap-stream-id value of the 626 dcmap attribute. 628 6.4. Generating SDP Answer 630 When an answerer receives an offer that includes an "m=" section for 631 an SCTP association, that describes an SCTP stream for a data 632 channel, if the answerer accepts the data channel it: 634 o SHALL include an SDP dcmap attribute (Section 5 and Section 6.2) 635 associated with the data channel in the "m=" section representing 636 the SCTP association used to realize the data channel. The value 637 of the dcmap-stream-id value of the dcmap attribute SHALL be 638 identical to the value used for the data channel in the offer; and 640 o MAY include one or more SDP dcsa attributes (Section 6.2) 641 associated with the data channel. 643 6.5. Offerer Processing of the SDP Answer 645 An offerer receiving a SDP answer performs the following: 647 o SHALL closes any created data channels as described in 648 Section 6.6.1 for which the expected "a=dcmap:" attributes are not 649 present in the SDP answer. If the SDP answer has no "a=dcmap" 650 attribute either the peer does not support "a=dcmap:" attributes 651 or it rejected all the data channels. In either case the offerer 652 closes all the SDP offered data channels that were open at the 653 time of offer. The DTLS association and SCTP association will 654 still be setup. 656 Each agent application MUST wait to send data until it has 657 confirmation that the data channel at the peer is instantiated. For 658 WebRTC, this is when both data channel stacks have channel parameters 659 instantiated. This occurs: 661 o At both peers when a data channel is created without a previously 662 established SCTP association, as soon as the SCTP association is 663 successfully established. 665 o At the agent receiving an SDP offer for which there is an 666 established SCTP association, as soon as it creates the negotiated 667 data channel based on information signaled in the SDP offer. 669 o At the agent sending an SDP offer to create a new data channel for 670 which there is an established SCTP association, when it receives 671 the SDP answer confirming acceptance of the data channel or when 672 it begins to receive data on the data channel from the peer, 673 whichever occurs first. 675 Note: DCEP is not used, that is neither the SDP offerer nor the SDP 676 answerer send an in-band DCEP DATA_CHANNEL_OPEN message. 678 6.6. Modifying the Session 680 When an offer sends a subsequent offer, that includes information for 681 a previously negotiated SCTP stream for a data channel, unless the 682 offerer intends to close the data channel (Section 6.6.1), the 683 offerer SHALL include the previously negotiated SDP attributes and 684 attribute values associated with the data channel. 686 6.6.1. Closing a Data Channel 688 In order to close a data channel the endpoint that wants to close 689 SHALL send the SCTP SSN reset message [RFC6525], following the 690 procedures in section 6.7 of [I-D.ietf-rtcweb-data-channel]. In 691 addition, if the closed data channel was negotiated using the offer/ 692 answer mechanism Section 6.3, the endpoint that closed the data 693 channel SHALL send a subsequent offer, in which it either: 695 o removes the SDP dcmap attribute and SDP dcsa attributes associated 696 with the closed data channel. Once the endpoint receives a 697 successful answer, the SCTP stream identifier value can later be 698 used for a new data channel (negotiated using DCTP or using the 699 offer/answer mechanism); or 701 o immediately re-uses the SCTP stream used for the closed data 702 channel for a new data channel, using the procedures in 703 Section 6.3. The offerer SHALL use a different SDP dcmap 704 attribute value for the data channel using the same SCTP stream. 706 6.7. Various SDP Offer/Answer Considerations 708 An SDP offer or answer has no "a=dcmap:" attributes but has 709 "a=dcsa:" attributes. 711 * This is considered an error case. In this case the receiver of 712 such an SDP offer or answer SHOULD ignore the "a=dcsa:" 713 attributes and SHOULD process the SDP offer or answer as per 714 above case 'SDP offer has no "a=dcmap:" attributes' or case 715 'SDP answer has no "a=dcmap:" attributes'. 717 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 718 attribute is unknown. 720 * The receiver of such an SDP offer or answer SHOULD ignore this 721 entire "a=dcsa" attribute line. 723 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 724 attribute is known, but whose subprotocol attribute semantic is 725 not known for the data channel transport case. 727 * The receiver of such an SDP offer or answer SHOULD ignore this 728 entire "a=dcsa" attribute line. 730 7. Examples 732 SDP offer: 734 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 735 c=IN IP6 IP6 2001:db8::3 736 a=max-message-size:100000 737 a=sctp-port:5000 738 a=setup:actpass 739 a=fingerprint:SHA-1 \ 740 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 741 a=tls-id:abc3de65cddef001be82 742 a=dcmap:0 subprotocol="BFCP";label="BFCP" 744 SDP answer: 746 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 747 c=IN IP6 IP6 2001:db8::1 748 a=max-message-size:100000 749 a=sctp-port:5002 750 a=setup:passive 751 a=fingerprint:SHA-1 \ 752 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 753 a=tls-id:dcb3ae65cddef0532d42 755 Figure 1: Example 1 757 In the above example the SDP answerer rejected the data channel with 758 stream id 0 either for explicit reasons or because it does not 759 understand the "a=dcmap:" attribute. As a result the offerer will 760 close the data channel created with the SDP offer/answer negotiation 761 option. The SCTP association will still be setup over DTLS. At this 762 point the offerer or the answerer may use DCEP negotiation to open 763 data channels. 765 SDP offer: 767 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 768 c=IN IP4 192.0.2.1 769 a=max-message-size:100000 770 a=sctp-port:5000 771 a=setup:actpass 772 a=fingerprint:SHA-1 \ 773 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 774 a=tls-id:abc3de65cddef001be82 775 a=dcmap:0 subprotocol="BFCP";label="BFCP" 776 a=dcmap:2 subprotocol="MSRP";label="MSRP" 777 a=dcsa:2 accept-types:message/cpim text/plain 778 a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc 780 SDP answer: 782 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 783 c=IN IP4 192.0.2.2 784 a=max-message-size:100000 785 a=sctp-port:5002 786 a=setup:passive 787 a=fingerprint:SHA-1 \ 788 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 789 a=tls-id:dcb3ae65cddef0532d42 790 a=dcmap:2 subprotocol="MSRP";label="MSRP" 791 a=dcsa:2 accept-types:message/cpim text/plain 792 a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc 794 Figure 2: Example 2 796 In the above example the SDP offer contains data channels for BFCP 797 (Binary Floor Control Protocol) and MSRP subprotocols. The SDP 798 answer rejected BFCP and accepted MSRP. So, the offerer closes the 799 data channel for BFCP and both offerer and answerer may start using 800 the MSRP data channel (after the SCTP association is set up). The 801 data channel with stream id 0 is free and can be used for future DCEP 802 or SDP offer/answer negotiation. 804 Continuing the example in Figure 2. 806 Subsequent SDP offer: 808 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 809 c=IN IP4 192.0.2.1 810 a=max-message-size:100000 811 a=sctp-port:5000 812 a=setup:actpass 813 a=fingerprint:SHA-1 \ 814 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 815 a=tls-id:abc3de65cddef001be82 816 a=dcmap:4 subprotocol="MSRP";label="MSRP" 817 a=dcsa:4 accept-types:message/cpim text/plain 818 a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc 820 Subsequent SDP answer: 822 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 823 c=IN IP4 192.0.2.2 824 a=max-message-size:100000 825 a=sctp-port:5002 826 a=setup:passive 827 a=fingerprint:SHA-1 \ 828 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 829 a=tls-id:dcb3ae65cddef0532d42 830 a=dcmap:4 subprotocol="MSRP";label="MSRP" 831 a=dcsa:4 accept-types:message/cpim text/plain 832 a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc 834 Figure 3: Example 3 836 The above example is a continuation of the example in Figure 2. The 837 SDP offerer now removes the MSRP data channel with stream id 2, but 838 opens a new MSRP data channel with stream id 4. The answerer accepts 839 the entire offer. As a result the offerer closes the earlier 840 negotiated MSRP related data channel and both offerer and answerer 841 may start using new the MSRP related data channel. 843 8. Security Considerations 845 This document specifies new SDP attributes used in the negotiation of 846 the DATA channel parameters. 848 These parameter are negotiated as part of opening a SCTP channel over 849 DTLS as specified in [I-D.ietf-mmusic-sctp-sdp]. This document do 850 not add any security considerations to the ones specified in the 851 above document 852 Error cases like the use of unknown parameter values or violation the 853 odd/even rule must be handled by closing the corresponding Data 854 Channel. 856 9. IANA Considerations 858 9.1. Subprotocol Identifiers 860 Registration of new subprotocol identifiers is performed using the 861 existing IANA "WebSocket Subprotocol Name Registry" table. 863 The following text should be added following the title of the table. 865 "This table also includes subprotocol identifiers specified for usage 866 within a WebRTC data channel." 868 The following reference should be added to under the heading 869 reference: "RFC XXXX". 871 This document assigns no new values to this table. 873 A subprotocol may simultaneously be defined for data channel 874 transport and for Websocket transport. In such a case the 875 "Subprotocol Definition" and "Reference" cells in the subprotocol's 876 row of the IANA "WebSocket Subprotocol Name Registry" table should 877 contain two entries. One entry in each of these cells should refer 878 to the Websocket related subprotocol specification, and the other 879 entry should refer to the data channel related subprotocol 880 specification. 882 NOTE to RFC Editor: Please replace "XXXX" with the number of this 883 RFC. 885 9.2. New SDP Attributes 887 9.2.1. dcmap 889 NOTE to RFC Editor: Please replace "XXXX" with the number of this 890 RFC. 892 This document defines a new SDP media-level attribute "a=dcmap:" as 893 follows: 895 +-----------------------+-------------------------------------------+ 896 | Contact name: | IESG Chairs | 897 | Contact email: | iesg@ietf.org | 898 | Attribute name: | dcmap | 899 | Attribute syntax: | As per Section 5.1.1 | 900 | Attribute semantics: | As per Section 5.1.1 | 901 | Usage level: | media | 902 | Charset dependent: | No | 903 | Purpose: | Define data channel specific parameters | 904 | Appropriate values: | As per Section 5.1.1 | 905 | O/A procedures: | As per Section 6 | 906 | Mux category: | SPECIAL. See Section 5.1.9 | 907 | Reference: | RFCXXXX | 908 +-----------------------+-------------------------------------------+ 910 9.2.2. dcsa 912 NOTE to RFC Editor: Please replace "XXXX" with the number of this 913 RFC. 915 This document defines a new SDP media-level attribute "a=dcsa:" as 916 follows: 918 +-----------------------+-------------------------------------------+ 919 | Contact name: | IESG Chairs | 920 | Contact email: | iesg@ietf.org | 921 | Attribute name: | dcsa | 922 | Attribute syntax: | As per Section 5.2.1 | 923 | Attribute semantics: | As per Section 5.2.1 | 924 | Usage level: | media | 925 | Charset dependent: | No | 926 | Purpose: | Define data channel subprotocol specific | 927 | | attributes | 928 | Appropriate values: | As per Section 5.2.1 | 929 | O/A procedures: | As per Section 6 | 930 | Mux category: | SPECIAL. See Section 5.2.2 | 931 | Reference: | RFCXXXX | 932 +-----------------------+-------------------------------------------+ 934 9.3. New Usage Level 936 This document introduces a new "Data Channel Subprotocol Attribute" 937 (dcsa) usage level of the SDP media description to the IANA SDP att- 938 field registry. SDP attributes that are defined for use at the dcsa 939 usage level only SHALL use the dcsa usage level when registering the 940 attribute. If existing media attributes are used in a datachannel 941 subprotocol specific way (Section 5.2.1), then a new dcsa usage level 942 MUST be defined for the existing media attribute. Where the SDP 943 attribute is applicable to a particular subprotocol/s this SHALL also 944 be registered by indicating the applicable subprotocol identifiers 945 (see Section 9.1) along with the dcsa usage level. E.g. 947 +-----------------------+-------------------------------------------+ 948 | ... | ... | 949 | Usage level: | dcsa(MSRP) | 950 | ... | ... | 951 +-----------------------+-------------------------------------------+ 953 10. Acknowledgments 955 The authors wish to acknowledge the borrowing of ideas from other 956 internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley 957 and Gavin Llewellyn, and to thank Flemming Andreasen, Christian 958 Groves, Gunnar Hellstrom, Paul Kyzivat, Jonathan Lennox, Uwe 959 Rauschenbach and Roman Shpount for their invaluable comments. 961 Special thanks to Christer Holmberg for helping finish the document 962 and cleaning the SDP offer/answer section. 964 11. CHANGE LOG 966 11.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-15' 968 o Editorial changes separate sections for offer/answer procedures. 970 o Update security section. 972 11.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-14' 974 o Change "dtls-id" to "tls-id" and assign 20 octet long values 976 o Remove of RFC4566bis draft from list of normative references. 978 11.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-12' 980 o Modification of Keith's address information. 982 11.4. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-11' 984 o dcmap-stream-id syntax change to limit size to 5 digits. 986 o Add missing 'x' prefix to quoted-visible syntax. 988 o Align SDP offerer and answerer handling when both max-retr and 989 max-time are present. 991 o Use of TEST-NET-1 ip addresses in examples. 993 o Add missing a=dtls-id in one example. 995 11.5. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-10' 997 o Removal of the "a=connection" attribute lines from all SDP 998 examples. 1000 11.6. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-09' 1002 o In the introduction: 1004 * Replacement of the sentence "The RTCWeb working group has 1005 defined the concept of bi-directional data channels running on 1006 top of SCTP/DTLS (SCTP over the Datagram Transport Layer 1007 Security protocol)" with "The RTCWeb working group has defined 1008 the concept of bi-directional data channels running on top of 1009 the Stream Control Transmission Protocol (SCTP)". 1011 * Addition of following sentences to the second paragraph: "These 1012 procedures are based on generic SDP offer/answer negotiation 1013 rules for SCTP based media transport as specified in 1014 [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" line proto values 1015 UDP/DTLS/SCTP and TCP/DTLS/SCTP. In the future, data channels 1016 could be defined over other SCTP based protocols, such as SCTP 1017 over IP. However, corresponding potential other "m" line proto 1018 values are not considered in this document." 1020 o Replacement of "DTLS connection" with "DTLS association" 1021 throughout the document. 1023 o In sections Section 5.1.9 and Section 5.2.2 removal of the 1024 sentences "This document also does not specify multiplexing rules 1025 for this attribute for SCTP or SCTP/DTLS proto values". 1027 o In the text related to "Subsequent SDP answer" in section 1028 Section 6.7 replacement of "The DTLS/SCTP association remains open 1029 ..." with "The SCTP association remains open ...". 1031 o In the text after the second SDP answer in section Section 7 1032 replacement of "... (after SCTP/DTLS association is setup)" with 1033 "... (after the SCTP association is set up)". 1035 o Addition of [I-D.ietf-mmusic-dtls-sdp] to the list of informative 1036 references. 1038 o Addition of "a=dtls-id" attribute lines to the SDP offer/answer 1039 examples in Section 7. 1041 11.7. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-08' 1043 o Addition of definition of "data channel subprotocol" to Section 3 1044 as proposed on the MMUSIC list, https://www.ietf.org/mail- 1045 archive/web/mmusic/current/msg15827.html. 1047 o Addition of RFC4566bis draft to list of normative references. 1049 o Updates of tables in Section 9.2.1 and Section 9.2.2 as per 1050 section 8.2.4 of RFC4566bis draft. 1052 o Addition of new Section 9.3. 1054 11.8. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-07' 1056 o Addition of two new paragraphs to Section 5.2.1 regarding 1057 subprotocol attribute relationship with transport protocol. 1059 o Addition of a note to Section 9.1 regarding subprotocols 1060 simultaneously defined for data channel and Websocket usage. 1062 o Addition of two further SDP offer/answer considerations to 1063 Section 6.7 regarding unknown subprotocol attributes and known 1064 subprotocol attributes with unknown data channel transport related 1065 semantic. 1067 11.9. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-06' 1069 o Changes addressing Christian Groves's WGLC review comments raised 1070 in http://www.ietf.org/mail-archive/web/mmusic/current/ 1071 msg15357.html and http://www.ietf.org/mail- 1072 archive/web/mmusic/current/msg15359.html. 1074 11.10. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-05' 1076 o In IANA registration Section 9.2.1 and Section 9.2.2 replacement 1077 of contact name and e-mail address with "MMUSIC Chairs" and 1078 "mmusic-chairs@ietf.org". 1080 o In Section 5.2.1 replacement of "Thus in the example above, the 1081 original attribute line "a=accept- types:text/plain" is 1082 represented by the attribute line "a=dcsa:2 accept-types:text/ 1083 plain", which specifies that this instance of MSRP being 1084 transported on the SCTP association using the data channel with 1085 stream id 2 accepts plain text files." with "... which specifies 1086 that this instance of the MSRP subprotocol being transported ...". 1088 o The last paragraph of Section 5.2.1 started with "Note: This 1089 document does not provide a complete specification ...". Removal 1090 of "Note:" and move of this paragraph to the introduction in 1091 Section 1 as last paragraph. 1093 o Section 5.2's headline was "Subprotocol Specific Attributes". 1094 Change of this headline to "Other Media Level Attributes" and 1095 adaptations of the first paragraph of this section and the first 1096 paragraph of Section 5.2.1 in order to clarify that not only those 1097 attributes may be encapsulated in a "dcsa" attribute, which are 1098 specifically defined for the subprotocol, but that also other 1099 attributes may be encapsulated if they are related to the specific 1100 subprotocol instance. 1102 o Move of the last but one paragraph of Section 5.2.1 starting with 1103 "The same syntax applies to ..." right in front of the formal 1104 syntax definition of the "dcsa" attribute. 1106 o Modifications of the text in Section 5.1.9 and Section 5.2.2 in 1107 order not to explicitly restrict usage of the "a=dcmap:" and 1108 "a=dcsa:" attributes to "m" lines with proto values "UDP/DTLS/ 1109 SCTP" or "TCP/DTLS/SCTP". 1111 11.11. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-04' 1113 o In Section 5.1.4 the first (and only) paragraph was "The 1114 'subprotocol' parameter indicates which protocol the client 1115 expects to exchange via the channel. 'Subprotocol' is an optional 1116 parameter. If the 'subprotocol' parameter is not present, then 1117 its value defaults to the empty string." Replacement of this 1118 paragraph with following two paragraphs: 1120 * The 'subprotocol' parameter indicates which protocol the client 1121 expects to exchange via the channel. This parameter maps to 1122 the 'Protocol' parameter defined in 1123 [I-D.ietf-rtcweb-data-protocol]. Section 9.1 specifies how new 1124 subprotocol parameter values are registered. 'Subprotocol' is 1125 an optional parameter. If the 'subprotocol' parameter is not 1126 present, then its value defaults to the empty string. 1128 * Note: The empty string MAY also be explicitly used as 1129 'subprotocol' value, such that 'subprotocol=""' is equivalent 1130 to the 'subprotocol' parameter not being present at all. 1131 [I-D.ietf-rtcweb-data-protocol] allows the DATA_CHANNEL_OPEN 1132 message's 'Subprotocol' value to be an empty string. 1134 o Addition of [I-D.ietf-mmusic-sdp-mux-attributes] to list the of 1135 normative references. 1137 o Addition of dcmap attribute specific IANA registration 1138 Section 9.2.1. 1140 o Addition of dcsa attribute specific IANA registration 1141 Section 9.2.2. 1143 o Addition of new Section 5.1.9 describing the mux category of the 1144 dcmap SDP attribute. This section and the new "a=dcsa:" attribute 1145 related mux category section are similar to the "Mux Category" 1146 sections of the "a=sctp-port:" and "a=max-message-size:" 1147 attributes in [I-D.ietf-mmusic-sctp-sdp]. 1149 o Addition of new Section 5.2.2 describing the mux category of the 1150 dcsa SDP attribute. 1152 11.12. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-03' 1154 o In Section 1 replacement of "RTCWeb leaves it open for other 1155 applications to use data channels and its in-band DCEP or out-of- 1156 band non-DCEP protocols for creating them" with "... to use data 1157 channels and its in-band DCEP or other in-band or out-of-band 1158 protocols for creating them". Additionally replacement of "In 1159 particular, the SDP offer generated by the application includes no 1160 channel-specific information" with "... generated by the RTCweb 1161 data channel stack includes no channel-specific information". 1163 o Move of former section 5 ("Data Channels") to new Appendix A and 1164 removal of JavaScript API specific discussions from this moved 1165 text (like mentioning of data channel stack specific states). 1166 Therefore former section 6 ("SDP Offer/Answer Negotiation") is now 1167 Section 5. 1169 o In Section 5: 1171 * Relacement of Section 5's first paragraph "This section defines 1172 a method of non-DCEP negotiation by which two clients can 1173 negotiate data channel-specific and subprotocol-specific 1174 parameters, using the out-of-band SDP offer/answer exchange. 1175 This SDP extension can only be used with the SDP offer/answer 1176 model." with "This section defines an SDP extension by which 1177 two clients can negotiate data channel-specific and 1178 subprotocol-specific parameters without using DCEP 1179 [I-D.ietf-rtcweb-data-protocol]. This SDP extension only 1180 defines usage in the context of SDP offer/answer." 1182 * Addition of new paragraph: "Appendix A provides information how 1183 data channels work in general and especially summarizes some 1184 key aspects, which should be considered for the negotiation of 1185 data channels if DCEP is not used." 1187 o In Section 5.1 replacement of "The intention of exchanging these 1188 attributes is to create data channels on both the peers with the 1189 same set of attributes without actually using the DCEP 1190 [I-D.ietf-rtcweb-data-protocol]" with "The intention in exchanging 1191 these attributes is to create, on two peers, without use of DCEP 1192 [I-D.ietf-rtcweb-data-protocol], matched pairs of oppositely 1193 directed data channels having the same set of attributes". 1195 o In Section 5.1.5 replacement of "The 'max-retr' parameter 1196 indicates the maximal number a user message will be retransmitted" 1197 with "The 'max-retr' parameter indicates the maximal number of 1198 times a user message will be retransmitted". 1200 o In Section 6.1 replacement of "However, an SDP offer/answer 1201 exchange MUST NOT be initiated if the associated SCTP stream is 1202 already negotiated via DCEP" with "However, an SCTP stream MUST 1203 NOT be referenced in a dcmap or dcsa attribute of an SDP offer/ 1204 answer exchange if the associated SCTP stream has already been 1205 negotiated via DCEP". 1207 o In the examples in Section 7 addition of the previously missing 1208 colons to the "a=sctp-port" attribute lines. 1210 11.13. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02' 1212 o Move of reference draft-ietf-rtcweb-jsep from the list of 1213 normative references to the list of informative references. 1214 Remover in -07 since not referenced 1216 o Addition of [IANA-SDP-Parameters] to the list of informative 1217 references and addition of following two sentences to the first 1218 paragraph after the ABNF definition: "Note however that not all 1219 SDP attributes are suitable as "a=dcsa:" parameter. 1220 [IANA-SDP-Parameters] contains the lists of IANA registered 1221 session and media level or media level only SDP attributes." 1223 o In the introduction replacement of last sentence "This document 1224 defines SDP-based out-of-band negotiation procedures to establish 1225 data channels for transport of well-defined subprotocols" with 1226 "This document defines SDP offer/answer negotiation procedures to 1227 establish data channels for transport of well-defined 1228 subprotocols, to enable out-of-band negotiation". 1230 o Throughout the document replacement of "external negotiation" with 1231 "SDP offer/answer negotiation" and removal of term "external 1232 negotiation" from the terminology list in Section 3. 1234 o Throughout the document replacement of "internal negotiation" with 1235 "DCEP" and removal of terms "internal negotiation" and "in-band 1236 negotiation" from the terminology list in Section 3. 1238 o Addition of "SCTP Stream Sequence Number (SSN)" to the list of 1239 terms. 1241 o In Section 6.1 replacement of sentence "However, a single stream 1242 is managed using one method at a time." with "However, an SDP 1243 offer/answer exchange MUST NOT be initiated if the associated SCTP 1244 stream is already negotiated via DCEP". 1246 o In Section 6.2 replacement of sentence "By definition max-retr and 1247 max-time are mutually exclusive, so only one of them can be 1248 present in a=dcmap" with "By definition max-retr and max-time are 1249 mutually exclusive, so at most one of them MAY be present in 1250 a=dcmap". 1252 o Move of reference [WebRtcAPI] from list of normative references to 1253 list of informative references. 1255 o Removal of almost all text parts, which discussed JavaScript or 1256 other API specific aspects. Such API specific aspects were mainly 1257 discussed in sub-sections of Section 5 and Section 5 of draft- 1258 ietf-mmusic-data-channel-sdpneg-02. 1260 11.14. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01' 1262 o New Section 4 regarding applicability to SDP offer/answer only. 1264 o Addition of new Section 9.1 "Subprotocol identifiers" as 1265 subsection of the "IANA Considerations" related Section 9. Also 1266 removal of the temporary note "To be completed. As [I-D.ietf- 1267 rtcweb-data-protocol] this document should refer to IANA's 1268 WebSocket Subprotocol Name Registry defined in [RFC6455]" 1270 o In Section 6.2: 1272 * In the first paragraph replacement of the sentence "If an SDP 1273 offer contains both of these parameters then such an SDP offer 1274 will be rejected." with "If an SDP offer contains both of these 1275 parameters then the receiver of such an SDP offer MUST reject 1276 the SDP offer." 1278 * In the second paragraph capitalization of "shall" and "may" 1279 such that both sentences now read: "The SDP answer SHALL echo 1280 the same subprotocol, max-retr, max-time, ordered parameters, 1281 if those were present in the offer, and MAY include a label 1282 parameter. They MAY appear in any order, which could be 1283 different from the SDP offer, in the SDP answer." 1285 * In the third paragraph replacement of the sentence "The same 1286 information MUST be replicated without changes in any 1287 subsequent offer or answer, as long as the data channel is 1288 still opened at the time of offer or answer generation." with 1289 "When sending a subsequent offer or an answer, and for as long 1290 as the data channel is still open, the sender MUST replicate 1291 the same information.". 1293 o In Section 6.2 the mapping of data channel types defined in 1294 [I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute 1295 parameters were illustrated using example "a=dcmap" attribute 1296 lines. Replacement of these example "a=dcmap" attribute lines 1297 with just the "a=dcmap" attribute parameters being relevant for 1298 the channel type. 1300 o In Section 6.7 the description of bullet point "SDP offer has no 1301 a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer: 1302 No data channel negotiated yet." Replacement of this description 1303 with "Initial SDP offer: No data channel is negotiated yet. The 1304 DTLS connection and SCTP association is negotiated and, if agreed, 1305 established as per [I-D.ietf-mmusic-sctp-sdp]." 1307 o In Section 6.7 in both bullet points related to "Subsequent SDP 1308 offer" and "Subsequent SDP answer" replacement of "All the 1309 externally negotiated data channels must be closed now." with "All 1310 the externally negotiated data channels are expected to be closed 1311 now.". 1313 o In Appendix A.2.2's sixth paragraph replacement of the two 1314 occurrences of "must" with "MUST". 1316 o In Section 5.1.1 in the definition of the ABNF rule "dcmap-opt" 1317 there was a comment saying that "Either only maxretr-opt or 1318 maxtime-opt is present. Both MUST NOT be present." Removal of 1319 the second normative sentence and instead addition of following 1320 new paragraph to the end of this section: "Within an 'a=dcmap' 1321 attribute line's 'dcmap-opt' value either only one 'maxretr-opt' 1322 parameter or one 'maxtime-opt' parameter is present. Both MUST 1323 NOT be present." 1325 o In Section 5.1.7 replacement of the first sentence "The 'ordered' 1326 parameter with value "true" indicates that DATA chunks in the 1327 channel MUST be dispatched to the upper layer by the receiver 1328 while preserving the order." with "The 'ordered' parameter with 1329 value "true" indicates that the receiver MUST dispatch DATA chunks 1330 in the data channel to the upper layer while preserving the 1331 order.". 1333 o In Section 6.3's first paragraph replacement of the one occurrence 1334 of "must" with "..., it MUST wait until ...". 1336 o In Section 6.6.1: 1338 * In the second paragraph replacement of "must" with "... whether 1339 this closing MUST in addition ..." 1341 * In the third paragraph replacement of the sentence "The port 1342 value for the "m" line SHOULD NOT be changed (e.g., to zero) 1343 when closing a data channel ..." with "The offerer SHOULD NOT 1344 change the port value for the "m" line (e.g., to zero) when 1345 closing a data channel ...". 1347 * In the last but two paragraph replacement of the sentence "... 1348 then an SDP offer which excludes this closed data channel 1349 SHOULD be generated." with "... then the client SHOULD generate 1350 an SDP offer which excludes this closed data channel.". 1352 * In the last but one paragraph replacement of "must" with "The 1353 application MUST also close...". 1355 o In Section 5.2 addition of following note after the formal 1356 definition of the 'a=dcsa' attribute: "Note that the above 1357 reference to RFC 4566 defines were the attribute definition can be 1358 found; it does not provide any limitation on support of attributes 1359 defined in other documents in accordance with this attribute 1360 definition." 1362 11.15. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00' 1364 o In Section 3 "WebRTC data channel" was defined as "A bidirectional 1365 channel consisting of paired SCTP outbound and inbound streams." 1366 Replacement of this definition with "Data channel: A WebRTC data 1367 channel as specified in [I-D.ietf-rtcweb-data-channel]", and 1368 consistent usage of "data channel" in the remainder of the 1369 document including the document's headline." 1371 o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in 1372 [I-D.ietf-mmusic-sctp-sdp] may change as that document progresses. 1374 In particular we expect "webrtc-datachannel" to become a more 1375 general term.' 1377 o Consistent usage of '"m" line' in whole document as per [RFC4566]. 1379 o In Section 5.1 removal of the example dcmap attribute line 1380 'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are 1381 already four examples right after the ABNF rules in Section 5.1.1. 1382 Corresponding removal of following related note: "Note: This 1383 document does not provide a complete specification of how to 1384 negotiate the use of a WebRTC data channel to transport BFCP. 1385 Procedures specific to each subprotocol such as BFCP will be 1386 documented elsewhere. The use of BFCP is only an example of how 1387 the generic procedures described herein might apply to a specific 1388 subprotocol." 1390 o In Section 5.1 removal of following note: "Note: This attribute is 1391 derived from attribute "webrtc-DataChannel", which was defined in 1392 old version 03 of the following draft, but which was removed along 1393 with any support for SDP external negotiation in subsequent 1394 versions: [I-D.ietf-mmusic-sctp-sdp]." 1396 o Insertion of following new sentence to the beginning of 1397 Section 5.1.1: "dcmap is a media level attribute having following 1398 ABNF syntax:" 1400 o Insertion of new Section 5.1.2 containing the dcmap-stream-id 1401 specifying sentence, which previously was placed right before the 1402 formal ABNF rules. Removal of the sentence 'Stream is a mandatory 1403 parameter and is noted directly after the "a=dcmap:" attribute's 1404 colon' as this information is part of the ABNF specification. 1406 o In Section 5.1.1 modification of the 'ordering-value' values from 1407 "0" or "1" to "true" or "false". Corresponding text modifications 1408 in Section 5.1.7. 1410 o In Section 5.1.1 the ABNF definition of "quoted-string" referred 1411 to rule name "escaped-char", which was not defined. Instead a 1412 rule with name "escaped" was defined. Renamed that rule's name to 1413 "escaped-char". 1415 o Insertion of a dedicated note right after the "a=dcmap:4" 1416 attribute example in Section 5.1.1 regarding the non-printable 1417 "escaped-char" character within the "label" value. 1419 o In Section 5.2's second paragraph replacement of "sctp stream 1420 identifier" with "SCTP stream identifier". 1422 o In first paragraph of Section 6.1 replacement of first two 1423 sentences 'For the SDP-based external negotiation described in 1424 this document, the initial offerer based "SCTP over DTLS" owns by 1425 convention the even stream identifiers whereas the initial 1426 answerer owns the odd stream identifiers. This ownership is 1427 invariant for the whole lifetime of the signaling session, e.g. it 1428 does not change if the initial answerer sends a new offer to the 1429 initial offerer.' with 'If an SDP offer/answer exchange (could be 1430 the initial or a subsequent one) results in a UDP/DTLS/SCTP or 1431 TCP/DTLS/SCTP based media description being accepted, and if this 1432 SDP offer/answer exchange results in the establishment of a new 1433 SCTP association, then the SDP offerer owns the even SCTP stream 1434 ids of this new SCTP association and the answerer owns the odd 1435 SCTP stream identifiers. If this "m" line is removed from the 1436 signaling session (its port number set to zero), and if usage of 1437 this or of a new UDP/DTLS/SCTP or TCP/DTLS/SCTP based "m" line is 1438 renegotiated later on, then the even and odd SCTP stream 1439 identifier ownership is redetermined as well as described above.' 1441 o In Section 6.3 the first action of an SDP answerer, when receiving 1442 an SDP offer, was described as "Applies the SDP offer. Note that 1443 the browser ignores data channel specific attributes in the SDP." 1444 Replacement of these two sentences with "Parses and applies the 1445 SDP offer. Note that the typical parser normally ignores unknown 1446 SDP attributes, which includes data channel related attributes." 1448 o In Section 6.3 the second sentence of the third SDP answerer 1449 action was "Note that the browser is asked to create data channels 1450 with stream identifiers not "owned" by the agent.". Replacement 1451 of this sentence with "Note that the agent is asked to create data 1452 channels with SCTP stream identifiers contained in the SDP offer 1453 if the SDP offer is accepted." 1455 o In Section 6.6.1 the third paragraph began with "A data channel 1456 can be closed by sending a new SDP offer which excludes the dcmap 1457 and dcsa attribute lines for the data channel. The port value for 1458 the m line SHOULD NOT be changed (e.g., to zero) when closing a 1459 data channel (unless all data channels are being closed and the 1460 SCTP association is no longer needed), since this would close the 1461 SCTP association and impact all of the data channels. If the 1462 answerer accepts the SDP offer then it MUST also exclude the 1463 corresponding attribute lines in the answer. ..." Replacement of 1464 this part with "The intention to close a data channel can be 1465 signaled by sending a new SDP offer which excludes the "a=dcmap:" 1466 and "a=dcsa:" attribute lines for the data channel. The port 1467 value for the "m" line SHOULD NOT be changed (e.g., to zero) when 1468 closing a data channel (unless all data channels are being closed 1469 and the SCTP association is no longer needed), since this would 1470 close the SCTP association and impact all of the data channels. 1471 If the answerer accepts the SDP offer then it MUST close those 1472 data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were 1473 excluded from the received SDP offer, unless those data channels 1474 were already closed, and it MUST also exclude the corresponding 1475 attribute lines in the answer." 1477 o In Section 6.6.1 the hanging text after the third paragraph was 1478 "This delayed close is to handle cases where a successful SDP 1479 answer is not received, in which case the state of session should 1480 be kept per the last successful SDP offer/answer." Replacement of 1481 this sentence with "This delayed closure is RECOMMENDED in order 1482 to handle cases where a successful SDP answer is not received, in 1483 which case the state of the session SHOULD be kept per the last 1484 successful SDP offer/answer." 1486 o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects 1487 Section 5.1 contained already procedural descriptions related to 1488 data channel reliability negotiation. Creation of new Section 6.2 1489 and moval of reliability negotiation related text to this new 1490 section. 1492 11.16. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02' 1494 o Removal of note "ACTION ITEM" from section "subprotocol 1495 parameter". As [I-D.ietf-rtcweb-data-protocol] this document 1496 should refer to IANA's WebSocket Subprotocol Name Registry defined 1497 in [RFC6455] 1499 o In whole document, replacement of "unreliable" with "partially 1500 reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in 1501 [I-D.ietf-rtcweb-data-protocol] in most places. 1503 o Clarification of the semantic if the "max-retr" parameter is not 1504 present in an "a=dcmap" attribute line. In section "max-retr 1505 parameter" the sentence "The max-retr parameter is optional with 1506 default value unbounded" was replaced with "The max-retr parameter 1507 is optional. If the max-retr parameter is not present, then the 1508 maximal number of retransmissions is determined as per the generic 1509 SCTP retransmission rules as specified in [RFC4960]". 1511 o Clarification of the semantic if the "max-time" parameter is not 1512 present in an "a=dcmap" attribute line. In section "max-time 1513 parameter" the sentence "The max-time parameter is optional with 1514 default value unbounded" was replaced with "The max-time parameter 1515 is optional. If the max-time parameter is not present, then the 1516 generic SCTP retransmission timing rules apply as specified in 1517 [RFC4960]". 1519 o In section "label parameter" the sentence "Label is a mandatory 1520 parameter." was removed and following new sentences (including the 1521 note) were added: "The 'label' parameter is optional. If it is 1522 not present, then its value defaults to the empty string. Note: 1523 The empty string may also be explicitly used as 'label' value, 1524 such that 'label=""' is equivalent to the 'label' parameter not 1525 being present at all. [I-D.ietf-rtcweb-data-protocol] allows the 1526 DATA_CHANNEL_OPEN message's 'Label' value to be an empty string." 1528 o In section "subprotocol parameter" the sentence "Subprotocol is a 1529 mandatory parameter." was replaced with "'Subprotocol' is an 1530 optional parameter. If the 'subprotocol' parameter is not 1531 present, then its value defaults to the empty string." 1533 o In the "Examples" section, in the first two SDP offer examples in 1534 the "a=dcmap" attribute lines 'label="BGCP"' was replaced with 1535 'label="BFCP"'. 1537 o In all examples, the "m" line proto value "DTLS/SCTP" was replaced 1538 with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were 1539 replaced with "a=max-message-size" attribute lines, as per draft- 1540 ietf-mmusic-sctp-sdp-12. 1542 11.17. Changes against '-01' 1544 o Formal syntax for dcmap and dcsa attribute lines. 1546 o Making subprotocol as an optional parameter in dcmap. 1548 o Specifying disallowed parameter combinations for max-time and max- 1549 retr. 1551 o Clarifications on WebRTC data channel close procedures. 1553 11.18. Changes against '-00' 1555 o Revisions to identify difference between internal and external 1556 negotiation and their usage. 1558 o Introduction of more generic terminology, e.g. "application" 1559 instead of "browser". 1561 o Clarification of how "max-retr and max-time affect the usage of 1562 unreliable and reliable WebRTC data channels. 1564 o Updates of examples to take into account the SDP syntax changes 1565 introduced with draft-ietf-mmusic-sctp-sdp-07. 1567 o Removal of the SCTP port number from the "a=dcmap" and "a=dcsa" 1568 attributes as this is now contained in the a=sctp-port attribute, 1569 and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP 1570 association on top of the DTLS connection. 1572 12. References 1574 12.1. Normative References 1576 [I-D.ietf-mmusic-sctp-sdp] 1577 Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo, 1578 "Session Description Protocol (SDP) Offer/Answer 1579 Procedures For Stream Control Transmission Protocol (SCTP) 1580 over Datagram Transport Layer Security (DTLS) Transport.", 1581 draft-ietf-mmusic-sctp-sdp-26 (work in progress), April 1582 2017. 1584 [I-D.ietf-mmusic-sdp-mux-attributes] 1585 Nandakumar, S., "A Framework for SDP Attributes when 1586 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17 1587 (work in progress), February 2018. 1589 [I-D.ietf-rtcweb-data-channel] 1590 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 1591 Channels", draft-ietf-rtcweb-data-channel-13 (work in 1592 progress), January 2015. 1594 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1595 Requirement Levels", BCP 14, RFC 2119, 1596 DOI 10.17487/RFC2119, March 1997, 1597 . 1599 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1600 with Session Description Protocol (SDP)", RFC 3264, 1601 DOI 10.17487/RFC3264, June 2002, 1602 . 1604 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1605 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1606 July 2006, . 1608 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1609 Specifications: ABNF", STD 68, RFC 5234, 1610 DOI 10.17487/RFC5234, January 2008, 1611 . 1613 [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control 1614 Transmission Protocol (SCTP) Stream Reconfiguration", 1615 RFC 6525, DOI 10.17487/RFC6525, February 2012, 1616 . 1618 12.2. Informative References 1620 [I-D.ietf-clue-datachannel] 1621 Holmberg, C., "CLUE Protocol data channel", draft-ietf- 1622 clue-datachannel-14 (work in progress), August 2016. 1624 [I-D.ietf-mmusic-dtls-sdp] 1625 Holmberg, C. and R. Shpount, "Session Description Protocol 1626 (SDP) Offer/Answer Considerations for Datagram Transport 1627 Layer Security (DTLS) and Transport Layer Security (TLS)", 1628 draft-ietf-mmusic-dtls-sdp-32 (work in progress), October 1629 2017. 1631 [I-D.ietf-mmusic-msrp-usage-data-channel] 1632 Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., 1633 Marcon, J., and J. Recio, "MSRP over Data Channels", 1634 draft-ietf-mmusic-msrp-usage-data-channel-09 (work in 1635 progress), May 2018. 1637 [I-D.ietf-rtcweb-data-protocol] 1638 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 1639 Establishment Protocol", draft-ietf-rtcweb-data- 1640 protocol-09 (work in progress), January 2015. 1642 [IANA-SDP-Parameters] 1643 "Session Description Protocol (SDP) Parameters", Internet 1644 Assigned Numbers Authority Protocol Assignments Session 1645 Description Protocol (SDP) Parameters, 1646 . 1649 [RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor 1650 Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582, 1651 November 2006, . 1653 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1654 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1655 . 1657 [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., 1658 "The Message Session Relay Protocol (MSRP)", RFC 4975, 1659 DOI 10.17487/RFC4975, September 2007, 1660 . 1662 [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", 1663 RFC 6455, DOI 10.17487/RFC6455, December 2011, 1664 . 1666 [WebRtcAPI] 1667 Bergkvist, A., Burnett, D., Jennings, C., and A. 1668 Narayanan, "WebRTC 1.0: Real-time Communication Between 1669 Browsers", World Wide Web Consortium WD-webrtc-20150210, 1670 February 2015, 1671 . 1673 Appendix A. Generic Data Channel Negotiation Aspects When Not Using 1674 DCEP 1676 This appendix summarizes how data channels work in general and 1677 discusses some key aspects, which should be considered for the out- 1678 of-band negotiation of data channels if DCEP is not used. 1680 A WebRTC application creates a data channel by providing a number of 1681 setup parameters (subprotocol, label, maximal number of 1682 retransmissions, maximal retransmission time, order of delivery, 1683 priority). The application also specifies if it wants to make use of 1684 the negotiation using the DCEP [I-D.ietf-rtcweb-data-protocol], or if 1685 the application intends to negotiate data channels using the SDP 1686 offer/answer protocol. 1688 In any case, the SDP offer generated by the application is per 1689 [I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one "m" line for 1690 the SCTP association on top of which data channels will run: 1692 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 1693 c=IN IP4 192.0.2.1 1694 a=max-message-size:100000 1695 a=sctp-port:5000 1696 a=tls-id:abc3de65cddef001be82 1697 a=setup:actpass 1698 a=fingerprint:SHA-1 \ 1699 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 1701 Note: A WebRTC application will only use "m" line format "webrtc- 1702 datachannel", and will not use other formats in the "m" line for 1703 other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports 1704 only one SCTP association to be established on top of a DTLS 1705 association. 1707 Note: The above SDP media description does not contain any channel- 1708 specific information. 1710 A.1. Stream Identifier Numbering 1712 Independently from the requested type of negotiation, the application 1713 creating a data channel can either pass the stream identifier to the 1714 data channel stack to assign to the data channel or else let the data 1715 channel stack pick one identifier from the unused ones. 1717 To avoid glare situations, each endpoint can moreover own an 1718 exclusive set of stream identifiers, in which case an endpoint can 1719 only create a data channel with a stream identifier it owns. 1721 Which set of stream identifiers is owned by which endpoint is 1722 determined by convention or other means. 1724 Note:For data channels negotiated with the DCEP, one endpoint owns 1725 by convention the even stream identifiers, whereas the other owns 1726 the odd stream identifiers, as defined in 1727 [I-D.ietf-rtcweb-data-protocol]. 1729 Note:For data channels negotiated via different protocol from 1730 DCEP, no convention is defined by default. 1732 A.2. Generic Data Channel Negotiation Not Using DCEP 1734 A.2.1. Overview 1736 DCEP negotiation only provides for negotiation of data channel 1737 transport parameters and does not provide for negotiation of 1738 subprotocol specific parameters. DCEP-less data channel negotiation 1739 can be defined to allow negotiation of parameters beyond those 1740 handled by DCEP, e.g., parameters specific to the subprotocol 1741 instantiated on a particular data channel. 1743 The following procedures are common to all methods of data channel 1744 negotiation not using DCEP, whether in-band (communicated using 1745 proprietary means on an already established data channel) or out-of- 1746 band (using SDP offer/answer or some other protocol associated with 1747 the signaling channel). 1749 A.2.2. Opening a Data Channel 1751 In the case of DCEP-less negotiation, the endpoint application has 1752 the option to fully control the stream identifier assignments. 1753 However these assignments have to coexist with the assignments 1754 controlled by the data channel stack for the DCEP negotiated data 1755 channels (if any). It is the responsibility of the application to 1756 ensure consistent assignment of stream identifiers. 1758 When the application requests the creation of a new data channel to 1759 be set up via DCEP-less negotiation, the data channel stack creates 1760 the data channel locally without sending any DATA_CHANNEL_OPEN 1761 message in-band. However, even if the ICE (Interactive Connectivity 1762 Establishment), DTLS and SCTP procedures were already successfully 1763 completed, the application can't send data on this data channel until 1764 the negotiation is complete with the peer. This is because the peer 1765 needs to be aware of and accept the usage of this data channel. The 1766 peer, after accepting the data channel offer, can start sending data 1767 immediately. This implies that the offerer may receive data channel 1768 subprotocol messages before the negotiation is complete and the 1769 application should be ready to handle it. 1771 If the peer rejects the data channel part of the offer then it 1772 doesn't have to do anything as the data channel was not created using 1773 the stack. The offerer on the other hand needs to close the data 1774 channel that was opened by invoking relevant data channel stack API 1775 procedures. 1777 It is also worth noting that a data channel stack implementation may 1778 not provide any API to create and close data channels; instead the 1779 data channels may be used on the fly as needed just by communicating 1780 via non-DCEP means or by even having some local configuration/ 1781 assumptions on both the peers. 1783 The application then negotiates the data channel properties and 1784 subprotocol properties with the peer's application using a mechanism 1785 different from DCEP. 1787 The peer then symmetrically creates a data channel with these 1788 negotiated data channel properties. This is the only way for the 1789 peer's data channel stack to know which properties to apply when 1790 transmitting data on this channel. The data channel stack must allow 1791 data channel creation with any non-conflicting stream identifier so 1792 that both peers can create the data channel with the same stream 1793 identifier. 1795 A.2.3. Closing a Data Channel 1797 When the application requests the closing of a data channel 1798 negotiated without DCEP, the data channel stack always performs an 1799 SCTP SSN reset for this channel. 1801 Depending upon the method used for DCEP-less negotiation and the 1802 subprotocol associated with the data channel, the closing might in 1803 addition be signaled to the peer via SDP offer/answer negotiation. 1805 Authors' Addresses 1807 Keith Drage 1808 Unaffiliated 1810 Email: drageke@ntlworld.com 1812 Maridi R. Makaraju (Raju) 1813 Nokia 1814 2000 Lucent Lane 1815 Naperville, Illinois 1816 US 1818 Email: Raju.Makaraju@nokia.com 1820 Juergen Stoetzer-Bradler 1821 Unaffiliated 1823 Email: Juergen.S-B.ietf@email.de 1825 Richard Ejzak 1826 Unaffiliated 1828 Email: richard.ejzak@gmail.com 1830 Jerome Marcon 1831 Unaffiliated 1833 Email: jeromee.marcon@free.fr 1835 Roni Even (editor) 1836 Huawei 1838 Email: roni.even@huawei.com