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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 25, 2018 Nokia 6 J. Stoetzer-Bradler 7 R. Ejzak 8 J. Marcon 9 Unaffiliated 10 R. Even, Ed. 11 Huawei 12 June 23, 2018 14 SDP-based Data Channel Negotiation 15 draft-ietf-mmusic-data-channel-sdpneg-20 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 25, 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 . . . . . . . . . . . . . . . 13 91 6.2. Negotiating Data Channel Parameters . . . . . . . . . . . 13 92 6.3. Generating the Initial Offer for A Data Channel . . . . . 14 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 . . . . . . . . . 16 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. A given media description can describe 551 multiple data channels (each represented by a separate SDP dcmap 552 attribute) that can be created, modified and closed using different 553 offer/answer exchanges. The procedures in this section apply for a 554 given data channel. 556 The generic offer/answer procedures for negotiating the SCTP 557 association used to realize data channels are defined in 558 [I-D.ietf-mmusic-sctp-sdp]. This section only defines the data 559 channel specific procedures. 561 "Initial offer" refers to the offer in which a data channel is 562 opened. It can be the initial offer, or a subsequent offer, of the 563 associated SDP session. 565 The detailed offer/answer procedures for the dcsa attribute are 566 dependent on the associated sub-protocol. A sub-protocol 567 specification MUST define the offer/answer procedures for the dsca 568 attribute (if applicable) associated with the sub-protocol. 570 6.1. Managing Stream Identifiers 572 In order to avoid SCTP Stream identifier collisions, in alignment 573 with [I-D.ietf-rtcweb-data-protocol], the endpoint acting as DTLS 574 client (for the SCTP association used to realize data channels) MUST 575 use even identifier values, and the endpoint acting as DTLS server 576 MUST use odd identifier values. SCTP stream identifiers associated 577 with data channels that have been negotiated using DCEP MUST NOT be 578 included in SDP offers and answers. 580 SCTP stream identifiers associated with data channels that have been 581 negotiated using DCEP MUST NOT be included in SDP offers and answers. 583 6.2. Negotiating Data Channel Parameters 585 The data channel types defined in [I-D.ietf-rtcweb-data-protocol] are 586 mapped to the dcmap SDP attribute parameters in the following manner 587 where "ordered=true" is the default and may be omitted: 589 DATA_CHANNEL_RELIABLE 590 ordered=true 592 DATA_CHANNEL_RELIABLE_UNORDERED 593 ordered=false 595 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT 596 ordered=true;max-retr= 598 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED 599 ordered=false;max-retr= 601 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED 602 ordered=true;max-time= 604 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED 605 ordered=false;max-time= 607 By definition max-retr and max-time are mutually exclusive, so at 608 most one of them MAY be present in the "a=dcmap:" attribute line. If 609 a SDP offer contains both of these parameters then the receiver of 610 such an SDP offer MUST reject the SDP offer. If a SDP answer 611 contains both of these parameters then the offerer MUST treat the 612 associated SDP offer/answer failed. 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 5.2) 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, max-retr and max-time values of the dcmap 638 attribute SHALL be identical to the value used for the data 639 channel in the offer; and 641 o MAY include one or more SDP dcsa attributes (Section 5.2) 642 associated with the data channel. 644 6.5. Offerer Processing of the SDP Answer 646 An offerer receiving a SDP answer performs the following: 648 o SHALL closes any created data channels as described in 649 Section 6.6.1 for which the expected "a=dcmap:" attributes are not 650 present in the SDP answer. If the SDP answer has no "a=dcmap" 651 attribute either the peer does not support "a=dcmap:" attributes 652 or it rejected all the data channels. In either case the offerer 653 closes all the SDP offered data channels that were open at the 654 time of offer. The DTLS association and SCTP association will 655 still be setup. 657 Each agent application MUST wait to send data until it has 658 confirmation that the data channel at the peer is instantiated. For 659 WebRTC, this is when both data channel stacks have channel parameters 660 instantiated. This occurs: 662 o At both peers when a data channel is created without a previously 663 established SCTP association, as soon as the SCTP association is 664 successfully established. 666 o At the agent receiving an SDP offer for which there is an 667 established SCTP association, as soon as it creates the negotiated 668 data channel based on information signaled in the SDP offer. 670 o At the agent sending an SDP offer to create a new data channel for 671 which there is an established SCTP association, when it receives 672 the SDP answer confirming acceptance of the data channel or when 673 it begins to receive data on the data channel from the peer, 674 whichever occurs first. 676 Note: DCEP is not used, that is neither the SDP offerer nor the SDP 677 answerer send an in-band DCEP DATA_CHANNEL_OPEN message. 679 6.6. Modifying the Session 681 When an offer sends a subsequent offer, that includes information for 682 a previously negotiated data channel, unless the offerer intends to 683 close the data channel (Section 6.6.1), the offerer SHALL include the 684 previously negotiated SDP attributes and attribute values associated 685 with the data channel. 687 6.6.1. Closing a Data Channel 689 In order to close a data channel the endpoint that wants to close 690 SHALL send the SCTP SSN reset message [RFC6525], following the 691 procedures in section 6.7 of [I-D.ietf-rtcweb-data-channel]. In 692 addition, if the closed data channel was negotiated using the offer/ 693 answer mechanism Section 6.3, the endpoint that closed the data 694 channel SHALL send a subsequent offer, in which it either: 696 o removes the SDP dcmap attribute and SDP dcsa attributes associated 697 with the closed data channel. Once the endpoint receives a 698 successful answer, the SCTP stream identifier value can later be 699 used for a new data channel (negotiated using DCTP or using the 700 offer/answer mechanism); or 702 o immediately re-uses the SCTP stream used for the closed data 703 channel for a new data channel, using the procedures in 704 Section 6.3. The offerer SHALL use a different SDP dcmap 705 attribute value for the data channel using the same SCTP stream. 707 6.7. Various SDP Offer/Answer Considerations 709 An SDP offer or answer has no "a=dcmap:" attributes but has 710 "a=dcsa:" attributes. 712 * This is considered an error case. In this case the receiver of 713 such an SDP offer or answer MUST discard this "a=dcsa:" 714 attributes. 716 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 717 attribute is unknown. 719 * The receiver of such an SDP offer or answer SHOULD ignore this 720 entire "a=dcsa" attribute line. 722 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 723 attribute is known, but whose subprotocol attribute semantic is 724 not known for the data channel transport case. 726 * The receiver of such an SDP offer or answer SHOULD ignore this 727 entire "a=dcsa" attribute line. 729 7. Examples 731 SDP offer: 733 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 734 c=IN IP6 IP6 2001:db8::3 735 a=max-message-size:100000 736 a=sctp-port:5000 737 a=setup:actpass 738 a=fingerprint:SHA-1 \ 739 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 740 a=tls-id:abc3de65cddef001be82 741 a=dcmap:0 subprotocol="BFCP";label="BFCP" 743 SDP answer: 745 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 746 c=IN IP6 IP6 2001:db8::1 747 a=max-message-size:100000 748 a=sctp-port:5002 749 a=setup:passive 750 a=fingerprint:SHA-1 \ 751 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 752 a=tls-id:dcb3ae65cddef0532d42 754 Figure 1: Example 1 756 In the above example the SDP answerer rejected the data channel with 757 stream id 0 either for explicit reasons or because it does not 758 understand the "a=dcmap:" attribute. As a result the offerer will 759 close the data channel created with the SDP offer/answer negotiation 760 option. The SCTP association will still be setup over DTLS. At this 761 point the offerer or the answerer may use DCEP negotiation to open 762 data channels. 764 SDP offer: 766 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 767 c=IN IP4 192.0.2.1 768 a=max-message-size:100000 769 a=sctp-port:5000 770 a=setup:actpass 771 a=fingerprint:SHA-1 \ 772 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 773 a=tls-id:abc3de65cddef001be82 774 a=dcmap:0 subprotocol="BFCP";label="BFCP" 775 a=dcmap:2 subprotocol="MSRP";label="MSRP" 776 a=dcsa:2 accept-types:message/cpim text/plain 777 a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc 779 SDP answer: 781 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 782 c=IN IP4 192.0.2.2 783 a=max-message-size:100000 784 a=sctp-port:5002 785 a=setup:passive 786 a=fingerprint:SHA-1 \ 787 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 788 a=tls-id:dcb3ae65cddef0532d42 789 a=dcmap:2 subprotocol="MSRP";label="MSRP" 790 a=dcsa:2 accept-types:message/cpim text/plain 791 a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc 793 Figure 2: Example 2 795 In the above example the SDP offer contains data channels for BFCP 796 (Binary Floor Control Protocol) and MSRP subprotocols. The SDP 797 answer rejected BFCP and accepted MSRP. So, the offerer closes the 798 data channel for BFCP and both offerer and answerer may start using 799 the MSRP data channel (after the SCTP association is set up). The 800 data channel with stream id 0 is free and can be used for future DCEP 801 or SDP offer/answer negotiation. 803 Continuing the example in Figure 2. 805 Subsequent SDP offer: 807 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 808 c=IN IP4 192.0.2.1 809 a=max-message-size:100000 810 a=sctp-port:5000 811 a=setup:actpass 812 a=fingerprint:SHA-1 \ 813 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 814 a=tls-id:abc3de65cddef001be82 815 a=dcmap:4 subprotocol="MSRP";label="MSRP" 816 a=dcsa:4 accept-types:message/cpim text/plain 817 a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc 819 Subsequent SDP answer: 821 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 822 c=IN IP4 192.0.2.2 823 a=max-message-size:100000 824 a=sctp-port:5002 825 a=setup:passive 826 a=fingerprint:SHA-1 \ 827 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 828 a=tls-id:dcb3ae65cddef0532d42 829 a=dcmap:4 subprotocol="MSRP";label="MSRP" 830 a=dcsa:4 accept-types:message/cpim text/plain 831 a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc 833 Figure 3: Example 3 835 The above example is a continuation of the example in Figure 2. The 836 SDP offerer now removes the MSRP data channel with stream id 2, but 837 opens a new MSRP data channel with stream id 4. The answerer accepts 838 the entire offer. As a result the offerer closes the earlier 839 negotiated MSRP related data channel and both offerer and answerer 840 may start using new the MSRP related data channel. 842 8. Security Considerations 844 This document specifies new SDP attributes used in the negotiation of 845 the DATA channel parameters. 847 These parameter are negotiated as part of opening a SCTP channel over 848 DTLS as specified in [I-D.ietf-mmusic-sctp-sdp]. This document do 849 not add any security considerations to the ones specified in the 850 above document 851 Error cases like the use of unknown parameter values or violation the 852 odd/even rule must be handled by closing the corresponding Data 853 Channel. 855 9. IANA Considerations 857 9.1. Subprotocol Identifiers 859 Registration of new subprotocol identifiers is performed using the 860 existing IANA "WebSocket Subprotocol Name Registry" table. 862 The following text should be added following the title of the table. 864 "This table also includes subprotocol identifiers specified for usage 865 within a WebRTC data channel." 867 The following reference should be added to under the heading 868 reference: "RFC XXXX". 870 This document assigns no new values to this table. 872 A subprotocol may simultaneously be defined for data channel 873 transport and for Websocket transport. In such a case the 874 "Subprotocol Definition" and "Reference" cells in the subprotocol's 875 row of the IANA "WebSocket Subprotocol Name Registry" table should 876 contain two entries. One entry in each of these cells should refer 877 to the Websocket related subprotocol specification, and the other 878 entry should refer to the data channel related subprotocol 879 specification. 881 NOTE to RFC Editor: Please replace "XXXX" with the number of this 882 RFC. 884 9.2. New SDP Attributes 886 9.2.1. dcmap 888 NOTE to RFC Editor: Please replace "XXXX" with the number of this 889 RFC. 891 This document defines a new SDP media-level attribute "a=dcmap:" as 892 follows: 894 +-----------------------+-------------------------------------------+ 895 | Contact name: | IESG Chairs | 896 | Contact email: | iesg@ietf.org | 897 | Attribute name: | dcmap | 898 | Attribute syntax: | As per Section 5.1.1 | 899 | Attribute semantics: | As per Section 5.1.1 | 900 | Usage level: | media | 901 | Charset dependent: | No | 902 | Purpose: | Define data channel specific parameters | 903 | Appropriate values: | As per Section 5.1.1 | 904 | O/A procedures: | As per Section 6 | 905 | Mux category: | SPECIAL. See Section 5.1.9 | 906 | Reference: | RFCXXXX | 907 +-----------------------+-------------------------------------------+ 909 9.2.2. dcsa 911 NOTE to RFC Editor: Please replace "XXXX" with the number of this 912 RFC. 914 This document defines a new SDP media-level attribute "a=dcsa:" as 915 follows: 917 +-----------------------+-------------------------------------------+ 918 | Contact name: | IESG Chairs | 919 | Contact email: | iesg@ietf.org | 920 | Attribute name: | dcsa | 921 | Attribute syntax: | As per Section 5.2.1 | 922 | Attribute semantics: | As per Section 5.2.1 | 923 | Usage level: | media | 924 | Charset dependent: | No | 925 | Purpose: | Define data channel subprotocol specific | 926 | | attributes | 927 | Appropriate values: | As per Section 5.2.1 | 928 | O/A procedures: | As per Section 6 | 929 | Mux category: | SPECIAL. See Section 5.2.2 | 930 | Reference: | RFCXXXX | 931 +-----------------------+-------------------------------------------+ 933 9.3. New Usage Level 935 This document introduces a new "Data Channel Subprotocol Attribute" 936 (dcsa) usage level of the SDP media description to the IANA SDP att- 937 field registry. SDP attributes that are defined for use at the dcsa 938 usage level only SHALL use the dcsa usage level when registering the 939 attribute. If existing media attributes are used in a datachannel 940 subprotocol specific way (Section 5.2.1), then a new dcsa usage level 941 MUST be defined for the existing media attribute. Where the SDP 942 attribute is applicable to a particular subprotocol/s this SHALL also 943 be registered by indicating the applicable subprotocol identifiers 944 (see Section 9.1) along with the dcsa usage level. E.g. 946 +-----------------------+-------------------------------------------+ 947 | ... | ... | 948 | Usage level: | dcsa(MSRP) | 949 | ... | ... | 950 +-----------------------+-------------------------------------------+ 952 10. Acknowledgments 954 The authors wish to acknowledge the borrowing of ideas from other 955 internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley 956 and Gavin Llewellyn, and to thank Flemming Andreasen, Christian 957 Groves, Gunnar Hellstrom, Paul Kyzivat, Jonathan Lennox, Uwe 958 Rauschenbach and Roman Shpount for their invaluable comments. 960 Special thanks to Christer Holmberg for helping finish the document 961 and cleaning the SDP offer/answer section. 963 11. CHANGE LOG 965 11.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-15' 967 o Editorial changes separate sections for offer/answer procedures. 969 o Update security section. 971 11.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-14' 973 o Change "dtls-id" to "tls-id" and assign 20 octet long values 975 o Remove of RFC4566bis draft from list of normative references. 977 11.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-12' 979 o Modification of Keith's address information. 981 11.4. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-11' 983 o dcmap-stream-id syntax change to limit size to 5 digits. 985 o Add missing 'x' prefix to quoted-visible syntax. 987 o Align SDP offerer and answerer handling when both max-retr and 988 max-time are present. 990 o Use of TEST-NET-1 ip addresses in examples. 992 o Add missing a=dtls-id in one example. 994 11.5. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-10' 996 o Removal of the "a=connection" attribute lines from all SDP 997 examples. 999 11.6. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-09' 1001 o In the introduction: 1003 * Replacement of the sentence "The RTCWeb working group has 1004 defined the concept of bi-directional data channels running on 1005 top of SCTP/DTLS (SCTP over the Datagram Transport Layer 1006 Security protocol)" with "The RTCWeb working group has defined 1007 the concept of bi-directional data channels running on top of 1008 the Stream Control Transmission Protocol (SCTP)". 1010 * Addition of following sentences to the second paragraph: "These 1011 procedures are based on generic SDP offer/answer negotiation 1012 rules for SCTP based media transport as specified in 1013 [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" line proto values 1014 UDP/DTLS/SCTP and TCP/DTLS/SCTP. In the future, data channels 1015 could be defined over other SCTP based protocols, such as SCTP 1016 over IP. However, corresponding potential other "m" line proto 1017 values are not considered in this document." 1019 o Replacement of "DTLS connection" with "DTLS association" 1020 throughout the document. 1022 o In sections Section 5.1.9 and Section 5.2.2 removal of the 1023 sentences "This document also does not specify multiplexing rules 1024 for this attribute for SCTP or SCTP/DTLS proto values". 1026 o In the text related to "Subsequent SDP answer" in section 1027 Section 6.7 replacement of "The DTLS/SCTP association remains open 1028 ..." with "The SCTP association remains open ...". 1030 o In the text after the second SDP answer in section Section 7 1031 replacement of "... (after SCTP/DTLS association is setup)" with 1032 "... (after the SCTP association is set up)". 1034 o Addition of [I-D.ietf-mmusic-dtls-sdp] to the list of informative 1035 references. 1037 o Addition of "a=dtls-id" attribute lines to the SDP offer/answer 1038 examples in Section 7. 1040 11.7. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-08' 1042 o Addition of definition of "data channel subprotocol" to Section 3 1043 as proposed on the MMUSIC list, https://www.ietf.org/mail- 1044 archive/web/mmusic/current/msg15827.html. 1046 o Addition of RFC4566bis draft to list of normative references. 1048 o Updates of tables in Section 9.2.1 and Section 9.2.2 as per 1049 section 8.2.4 of RFC4566bis draft. 1051 o Addition of new Section 9.3. 1053 11.8. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-07' 1055 o Addition of two new paragraphs to Section 5.2.1 regarding 1056 subprotocol attribute relationship with transport protocol. 1058 o Addition of a note to Section 9.1 regarding subprotocols 1059 simultaneously defined for data channel and Websocket usage. 1061 o Addition of two further SDP offer/answer considerations to 1062 Section 6.7 regarding unknown subprotocol attributes and known 1063 subprotocol attributes with unknown data channel transport related 1064 semantic. 1066 11.9. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-06' 1068 o Changes addressing Christian Groves's WGLC review comments raised 1069 in http://www.ietf.org/mail-archive/web/mmusic/current/ 1070 msg15357.html and http://www.ietf.org/mail- 1071 archive/web/mmusic/current/msg15359.html. 1073 11.10. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-05' 1075 o In IANA registration Section 9.2.1 and Section 9.2.2 replacement 1076 of contact name and e-mail address with "MMUSIC Chairs" and 1077 "mmusic-chairs@ietf.org". 1079 o In Section 5.2.1 replacement of "Thus in the example above, the 1080 original attribute line "a=accept- types:text/plain" is 1081 represented by the attribute line "a=dcsa:2 accept-types:text/ 1082 plain", which specifies that this instance of MSRP being 1083 transported on the SCTP association using the data channel with 1084 stream id 2 accepts plain text files." with "... which specifies 1085 that this instance of the MSRP subprotocol being transported ...". 1087 o The last paragraph of Section 5.2.1 started with "Note: This 1088 document does not provide a complete specification ...". Removal 1089 of "Note:" and move of this paragraph to the introduction in 1090 Section 1 as last paragraph. 1092 o Section 5.2's headline was "Subprotocol Specific Attributes". 1093 Change of this headline to "Other Media Level Attributes" and 1094 adaptations of the first paragraph of this section and the first 1095 paragraph of Section 5.2.1 in order to clarify that not only those 1096 attributes may be encapsulated in a "dcsa" attribute, which are 1097 specifically defined for the subprotocol, but that also other 1098 attributes may be encapsulated if they are related to the specific 1099 subprotocol instance. 1101 o Move of the last but one paragraph of Section 5.2.1 starting with 1102 "The same syntax applies to ..." right in front of the formal 1103 syntax definition of the "dcsa" attribute. 1105 o Modifications of the text in Section 5.1.9 and Section 5.2.2 in 1106 order not to explicitly restrict usage of the "a=dcmap:" and 1107 "a=dcsa:" attributes to "m" lines with proto values "UDP/DTLS/ 1108 SCTP" or "TCP/DTLS/SCTP". 1110 11.11. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-04' 1112 o In Section 5.1.4 the first (and only) paragraph was "The 1113 'subprotocol' parameter indicates which protocol the client 1114 expects to exchange via the channel. 'Subprotocol' is an optional 1115 parameter. If the 'subprotocol' parameter is not present, then 1116 its value defaults to the empty string." Replacement of this 1117 paragraph with following two paragraphs: 1119 * The 'subprotocol' parameter indicates which protocol the client 1120 expects to exchange via the channel. This parameter maps to 1121 the 'Protocol' parameter defined in 1122 [I-D.ietf-rtcweb-data-protocol]. Section 9.1 specifies how new 1123 subprotocol parameter values are registered. 'Subprotocol' is 1124 an optional parameter. If the 'subprotocol' parameter is not 1125 present, then its value defaults to the empty string. 1127 * Note: The empty string MAY also be explicitly used as 1128 'subprotocol' value, such that 'subprotocol=""' is equivalent 1129 to the 'subprotocol' parameter not being present at all. 1130 [I-D.ietf-rtcweb-data-protocol] allows the DATA_CHANNEL_OPEN 1131 message's 'Subprotocol' value to be an empty string. 1133 o Addition of [I-D.ietf-mmusic-sdp-mux-attributes] to list the of 1134 normative references. 1136 o Addition of dcmap attribute specific IANA registration 1137 Section 9.2.1. 1139 o Addition of dcsa attribute specific IANA registration 1140 Section 9.2.2. 1142 o Addition of new Section 5.1.9 describing the mux category of the 1143 dcmap SDP attribute. This section and the new "a=dcsa:" attribute 1144 related mux category section are similar to the "Mux Category" 1145 sections of the "a=sctp-port:" and "a=max-message-size:" 1146 attributes in [I-D.ietf-mmusic-sctp-sdp]. 1148 o Addition of new Section 5.2.2 describing the mux category of the 1149 dcsa SDP attribute. 1151 11.12. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-03' 1153 o In Section 1 replacement of "RTCWeb leaves it open for other 1154 applications to use data channels and its in-band DCEP or out-of- 1155 band non-DCEP protocols for creating them" with "... to use data 1156 channels and its in-band DCEP or other in-band or out-of-band 1157 protocols for creating them". Additionally replacement of "In 1158 particular, the SDP offer generated by the application includes no 1159 channel-specific information" with "... generated by the RTCweb 1160 data channel stack includes no channel-specific information". 1162 o Move of former section 5 ("Data Channels") to new Appendix A and 1163 removal of JavaScript API specific discussions from this moved 1164 text (like mentioning of data channel stack specific states). 1165 Therefore former section 6 ("SDP Offer/Answer Negotiation") is now 1166 Section 5. 1168 o In Section 5: 1170 * Relacement of Section 5's first paragraph "This section defines 1171 a method of non-DCEP negotiation by which two clients can 1172 negotiate data channel-specific and subprotocol-specific 1173 parameters, using the out-of-band SDP offer/answer exchange. 1174 This SDP extension can only be used with the SDP offer/answer 1175 model." with "This section defines an SDP extension by which 1176 two clients can negotiate data channel-specific and 1177 subprotocol-specific parameters without using DCEP 1178 [I-D.ietf-rtcweb-data-protocol]. This SDP extension only 1179 defines usage in the context of SDP offer/answer." 1181 * Addition of new paragraph: "Appendix A provides information how 1182 data channels work in general and especially summarizes some 1183 key aspects, which should be considered for the negotiation of 1184 data channels if DCEP is not used." 1186 o In Section 5.1 replacement of "The intention of exchanging these 1187 attributes is to create data channels on both the peers with the 1188 same set of attributes without actually using the DCEP 1189 [I-D.ietf-rtcweb-data-protocol]" with "The intention in exchanging 1190 these attributes is to create, on two peers, without use of DCEP 1191 [I-D.ietf-rtcweb-data-protocol], matched pairs of oppositely 1192 directed data channels having the same set of attributes". 1194 o In Section 5.1.5 replacement of "The 'max-retr' parameter 1195 indicates the maximal number a user message will be retransmitted" 1196 with "The 'max-retr' parameter indicates the maximal number of 1197 times a user message will be retransmitted". 1199 o In Section 6.1 replacement of "However, an SDP offer/answer 1200 exchange MUST NOT be initiated if the associated SCTP stream is 1201 already negotiated via DCEP" with "However, an SCTP stream MUST 1202 NOT be referenced in a dcmap or dcsa attribute of an SDP offer/ 1203 answer exchange if the associated SCTP stream has already been 1204 negotiated via DCEP". 1206 o In the examples in Section 7 addition of the previously missing 1207 colons to the "a=sctp-port" attribute lines. 1209 11.13. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02' 1211 o Move of reference draft-ietf-rtcweb-jsep from the list of 1212 normative references to the list of informative references. 1213 Remover in -07 since not referenced 1215 o Addition of [IANA-SDP-Parameters] to the list of informative 1216 references and addition of following two sentences to the first 1217 paragraph after the ABNF definition: "Note however that not all 1218 SDP attributes are suitable as "a=dcsa:" parameter. 1219 [IANA-SDP-Parameters] contains the lists of IANA registered 1220 session and media level or media level only SDP attributes." 1222 o In the introduction replacement of last sentence "This document 1223 defines SDP-based out-of-band negotiation procedures to establish 1224 data channels for transport of well-defined subprotocols" with 1225 "This document defines SDP offer/answer negotiation procedures to 1226 establish data channels for transport of well-defined 1227 subprotocols, to enable out-of-band negotiation". 1229 o Throughout the document replacement of "external negotiation" with 1230 "SDP offer/answer negotiation" and removal of term "external 1231 negotiation" from the terminology list in Section 3. 1233 o Throughout the document replacement of "internal negotiation" with 1234 "DCEP" and removal of terms "internal negotiation" and "in-band 1235 negotiation" from the terminology list in Section 3. 1237 o Addition of "SCTP Stream Sequence Number (SSN)" to the list of 1238 terms. 1240 o In Section 6.1 replacement of sentence "However, a single stream 1241 is managed using one method at a time." with "However, an SDP 1242 offer/answer exchange MUST NOT be initiated if the associated SCTP 1243 stream is already negotiated via DCEP". 1245 o In Section 6.2 replacement of sentence "By definition max-retr and 1246 max-time are mutually exclusive, so only one of them can be 1247 present in a=dcmap" with "By definition max-retr and max-time are 1248 mutually exclusive, so at most one of them MAY be present in 1249 a=dcmap". 1251 o Move of reference [WebRtcAPI] from list of normative references to 1252 list of informative references. 1254 o Removal of almost all text parts, which discussed JavaScript or 1255 other API specific aspects. Such API specific aspects were mainly 1256 discussed in sub-sections of Section 5 and Section 5 of draft- 1257 ietf-mmusic-data-channel-sdpneg-02. 1259 11.14. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01' 1261 o New Section 4 regarding applicability to SDP offer/answer only. 1263 o Addition of new Section 9.1 "Subprotocol identifiers" as 1264 subsection of the "IANA Considerations" related Section 9. Also 1265 removal of the temporary note "To be completed. As [I-D.ietf- 1266 rtcweb-data-protocol] this document should refer to IANA's 1267 WebSocket Subprotocol Name Registry defined in [RFC6455]" 1269 o In Section 6.2: 1271 * In the first paragraph replacement of the sentence "If an SDP 1272 offer contains both of these parameters then such an SDP offer 1273 will be rejected." with "If an SDP offer contains both of these 1274 parameters then the receiver of such an SDP offer MUST reject 1275 the SDP offer." 1277 * In the second paragraph capitalization of "shall" and "may" 1278 such that both sentences now read: "The SDP answer SHALL echo 1279 the same subprotocol, max-retr, max-time, ordered parameters, 1280 if those were present in the offer, and MAY include a label 1281 parameter. They MAY appear in any order, which could be 1282 different from the SDP offer, in the SDP answer." 1284 * In the third paragraph replacement of the sentence "The same 1285 information MUST be replicated without changes in any 1286 subsequent offer or answer, as long as the data channel is 1287 still opened at the time of offer or answer generation." with 1288 "When sending a subsequent offer or an answer, and for as long 1289 as the data channel is still open, the sender MUST replicate 1290 the same information.". 1292 o In Section 6.2 the mapping of data channel types defined in 1293 [I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute 1294 parameters were illustrated using example "a=dcmap" attribute 1295 lines. Replacement of these example "a=dcmap" attribute lines 1296 with just the "a=dcmap" attribute parameters being relevant for 1297 the channel type. 1299 o In Section 6.7 the description of bullet point "SDP offer has no 1300 a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer: 1301 No data channel negotiated yet." Replacement of this description 1302 with "Initial SDP offer: No data channel is negotiated yet. The 1303 DTLS connection and SCTP association is negotiated and, if agreed, 1304 established as per [I-D.ietf-mmusic-sctp-sdp]." 1306 o In Section 6.7 in both bullet points related to "Subsequent SDP 1307 offer" and "Subsequent SDP answer" replacement of "All the 1308 externally negotiated data channels must be closed now." with "All 1309 the externally negotiated data channels are expected to be closed 1310 now.". 1312 o In Appendix A.2.2's sixth paragraph replacement of the two 1313 occurrences of "must" with "MUST". 1315 o In Section 5.1.1 in the definition of the ABNF rule "dcmap-opt" 1316 there was a comment saying that "Either only maxretr-opt or 1317 maxtime-opt is present. Both MUST NOT be present." Removal of 1318 the second normative sentence and instead addition of following 1319 new paragraph to the end of this section: "Within an 'a=dcmap' 1320 attribute line's 'dcmap-opt' value either only one 'maxretr-opt' 1321 parameter or one 'maxtime-opt' parameter is present. Both MUST 1322 NOT be present." 1324 o In Section 5.1.7 replacement of the first sentence "The 'ordered' 1325 parameter with value "true" indicates that DATA chunks in the 1326 channel MUST be dispatched to the upper layer by the receiver 1327 while preserving the order." with "The 'ordered' parameter with 1328 value "true" indicates that the receiver MUST dispatch DATA chunks 1329 in the data channel to the upper layer while preserving the 1330 order.". 1332 o In Section 6.3's first paragraph replacement of the one occurrence 1333 of "must" with "..., it MUST wait until ...". 1335 o In Section 6.6.1: 1337 * In the second paragraph replacement of "must" with "... whether 1338 this closing MUST in addition ..." 1340 * In the third paragraph replacement of the sentence "The port 1341 value for the "m" line SHOULD NOT be changed (e.g., to zero) 1342 when closing a data channel ..." with "The offerer SHOULD NOT 1343 change the port value for the "m" line (e.g., to zero) when 1344 closing a data channel ...". 1346 * In the last but two paragraph replacement of the sentence "... 1347 then an SDP offer which excludes this closed data channel 1348 SHOULD be generated." with "... then the client SHOULD generate 1349 an SDP offer which excludes this closed data channel.". 1351 * In the last but one paragraph replacement of "must" with "The 1352 application MUST also close...". 1354 o In Section 5.2 addition of following note after the formal 1355 definition of the 'a=dcsa' attribute: "Note that the above 1356 reference to RFC 4566 defines were the attribute definition can be 1357 found; it does not provide any limitation on support of attributes 1358 defined in other documents in accordance with this attribute 1359 definition." 1361 11.15. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00' 1363 o In Section 3 "WebRTC data channel" was defined as "A bidirectional 1364 channel consisting of paired SCTP outbound and inbound streams." 1365 Replacement of this definition with "Data channel: A WebRTC data 1366 channel as specified in [I-D.ietf-rtcweb-data-channel]", and 1367 consistent usage of "data channel" in the remainder of the 1368 document including the document's headline." 1370 o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in 1371 [I-D.ietf-mmusic-sctp-sdp] may change as that document progresses. 1373 In particular we expect "webrtc-datachannel" to become a more 1374 general term.' 1376 o Consistent usage of '"m" line' in whole document as per [RFC4566]. 1378 o In Section 5.1 removal of the example dcmap attribute line 1379 'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are 1380 already four examples right after the ABNF rules in Section 5.1.1. 1381 Corresponding removal of following related note: "Note: This 1382 document does not provide a complete specification of how to 1383 negotiate the use of a WebRTC data channel to transport BFCP. 1384 Procedures specific to each subprotocol such as BFCP will be 1385 documented elsewhere. The use of BFCP is only an example of how 1386 the generic procedures described herein might apply to a specific 1387 subprotocol." 1389 o In Section 5.1 removal of following note: "Note: This attribute is 1390 derived from attribute "webrtc-DataChannel", which was defined in 1391 old version 03 of the following draft, but which was removed along 1392 with any support for SDP external negotiation in subsequent 1393 versions: [I-D.ietf-mmusic-sctp-sdp]." 1395 o Insertion of following new sentence to the beginning of 1396 Section 5.1.1: "dcmap is a media level attribute having following 1397 ABNF syntax:" 1399 o Insertion of new Section 5.1.2 containing the dcmap-stream-id 1400 specifying sentence, which previously was placed right before the 1401 formal ABNF rules. Removal of the sentence 'Stream is a mandatory 1402 parameter and is noted directly after the "a=dcmap:" attribute's 1403 colon' as this information is part of the ABNF specification. 1405 o In Section 5.1.1 modification of the 'ordering-value' values from 1406 "0" or "1" to "true" or "false". Corresponding text modifications 1407 in Section 5.1.7. 1409 o In Section 5.1.1 the ABNF definition of "quoted-string" referred 1410 to rule name "escaped-char", which was not defined. Instead a 1411 rule with name "escaped" was defined. Renamed that rule's name to 1412 "escaped-char". 1414 o Insertion of a dedicated note right after the "a=dcmap:4" 1415 attribute example in Section 5.1.1 regarding the non-printable 1416 "escaped-char" character within the "label" value. 1418 o In Section 5.2's second paragraph replacement of "sctp stream 1419 identifier" with "SCTP stream identifier". 1421 o In first paragraph of Section 6.1 replacement of first two 1422 sentences 'For the SDP-based external negotiation described in 1423 this document, the initial offerer based "SCTP over DTLS" owns by 1424 convention the even stream identifiers whereas the initial 1425 answerer owns the odd stream identifiers. This ownership is 1426 invariant for the whole lifetime of the signaling session, e.g. it 1427 does not change if the initial answerer sends a new offer to the 1428 initial offerer.' with 'If an SDP offer/answer exchange (could be 1429 the initial or a subsequent one) results in a UDP/DTLS/SCTP or 1430 TCP/DTLS/SCTP based media description being accepted, and if this 1431 SDP offer/answer exchange results in the establishment of a new 1432 SCTP association, then the SDP offerer owns the even SCTP stream 1433 ids of this new SCTP association and the answerer owns the odd 1434 SCTP stream identifiers. If this "m" line is removed from the 1435 signaling session (its port number set to zero), and if usage of 1436 this or of a new UDP/DTLS/SCTP or TCP/DTLS/SCTP based "m" line is 1437 renegotiated later on, then the even and odd SCTP stream 1438 identifier ownership is redetermined as well as described above.' 1440 o In Section 6.3 the first action of an SDP answerer, when receiving 1441 an SDP offer, was described as "Applies the SDP offer. Note that 1442 the browser ignores data channel specific attributes in the SDP." 1443 Replacement of these two sentences with "Parses and applies the 1444 SDP offer. Note that the typical parser normally ignores unknown 1445 SDP attributes, which includes data channel related attributes." 1447 o In Section 6.3 the second sentence of the third SDP answerer 1448 action was "Note that the browser is asked to create data channels 1449 with stream identifiers not "owned" by the agent.". Replacement 1450 of this sentence with "Note that the agent is asked to create data 1451 channels with SCTP stream identifiers contained in the SDP offer 1452 if the SDP offer is accepted." 1454 o In Section 6.6.1 the third paragraph began with "A data channel 1455 can be closed by sending a new SDP offer which excludes the dcmap 1456 and dcsa attribute lines for the data channel. The port value for 1457 the m line SHOULD NOT be changed (e.g., to zero) when closing a 1458 data channel (unless all data channels are being closed and the 1459 SCTP association is no longer needed), since this would close the 1460 SCTP association and impact all of the data channels. If the 1461 answerer accepts the SDP offer then it MUST also exclude the 1462 corresponding attribute lines in the answer. ..." Replacement of 1463 this part with "The intention to close a data channel can be 1464 signaled by sending a new SDP offer which excludes the "a=dcmap:" 1465 and "a=dcsa:" attribute lines for the data channel. The port 1466 value for the "m" line SHOULD NOT be changed (e.g., to zero) when 1467 closing a data channel (unless all data channels are being closed 1468 and the SCTP association is no longer needed), since this would 1469 close the SCTP association and impact all of the data channels. 1470 If the answerer accepts the SDP offer then it MUST close those 1471 data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were 1472 excluded from the received SDP offer, unless those data channels 1473 were already closed, and it MUST also exclude the corresponding 1474 attribute lines in the answer." 1476 o In Section 6.6.1 the hanging text after the third paragraph was 1477 "This delayed close is to handle cases where a successful SDP 1478 answer is not received, in which case the state of session should 1479 be kept per the last successful SDP offer/answer." Replacement of 1480 this sentence with "This delayed closure is RECOMMENDED in order 1481 to handle cases where a successful SDP answer is not received, in 1482 which case the state of the session SHOULD be kept per the last 1483 successful SDP offer/answer." 1485 o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects 1486 Section 5.1 contained already procedural descriptions related to 1487 data channel reliability negotiation. Creation of new Section 6.2 1488 and moval of reliability negotiation related text to this new 1489 section. 1491 11.16. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02' 1493 o Removal of note "ACTION ITEM" from section "subprotocol 1494 parameter". As [I-D.ietf-rtcweb-data-protocol] this document 1495 should refer to IANA's WebSocket Subprotocol Name Registry defined 1496 in [RFC6455] 1498 o In whole document, replacement of "unreliable" with "partially 1499 reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in 1500 [I-D.ietf-rtcweb-data-protocol] in most places. 1502 o Clarification of the semantic if the "max-retr" parameter is not 1503 present in an "a=dcmap" attribute line. In section "max-retr 1504 parameter" the sentence "The max-retr parameter is optional with 1505 default value unbounded" was replaced with "The max-retr parameter 1506 is optional. If the max-retr parameter is not present, then the 1507 maximal number of retransmissions is determined as per the generic 1508 SCTP retransmission rules as specified in [RFC4960]". 1510 o Clarification of the semantic if the "max-time" parameter is not 1511 present in an "a=dcmap" attribute line. In section "max-time 1512 parameter" the sentence "The max-time parameter is optional with 1513 default value unbounded" was replaced with "The max-time parameter 1514 is optional. If the max-time parameter is not present, then the 1515 generic SCTP retransmission timing rules apply as specified in 1516 [RFC4960]". 1518 o In section "label parameter" the sentence "Label is a mandatory 1519 parameter." was removed and following new sentences (including the 1520 note) were added: "The 'label' parameter is optional. If it is 1521 not present, then its value defaults to the empty string. Note: 1522 The empty string may also be explicitly used as 'label' value, 1523 such that 'label=""' is equivalent to the 'label' parameter not 1524 being present at all. [I-D.ietf-rtcweb-data-protocol] allows the 1525 DATA_CHANNEL_OPEN message's 'Label' value to be an empty string." 1527 o In section "subprotocol parameter" the sentence "Subprotocol is a 1528 mandatory parameter." was replaced with "'Subprotocol' is an 1529 optional parameter. If the 'subprotocol' parameter is not 1530 present, then its value defaults to the empty string." 1532 o In the "Examples" section, in the first two SDP offer examples in 1533 the "a=dcmap" attribute lines 'label="BGCP"' was replaced with 1534 'label="BFCP"'. 1536 o In all examples, the "m" line proto value "DTLS/SCTP" was replaced 1537 with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were 1538 replaced with "a=max-message-size" attribute lines, as per draft- 1539 ietf-mmusic-sctp-sdp-12. 1541 11.17. Changes against '-01' 1543 o Formal syntax for dcmap and dcsa attribute lines. 1545 o Making subprotocol as an optional parameter in dcmap. 1547 o Specifying disallowed parameter combinations for max-time and max- 1548 retr. 1550 o Clarifications on WebRTC data channel close procedures. 1552 11.18. Changes against '-00' 1554 o Revisions to identify difference between internal and external 1555 negotiation and their usage. 1557 o Introduction of more generic terminology, e.g. "application" 1558 instead of "browser". 1560 o Clarification of how "max-retr and max-time affect the usage of 1561 unreliable and reliable WebRTC data channels. 1563 o Updates of examples to take into account the SDP syntax changes 1564 introduced with draft-ietf-mmusic-sctp-sdp-07. 1566 o Removal of the SCTP port number from the "a=dcmap" and "a=dcsa" 1567 attributes as this is now contained in the a=sctp-port attribute, 1568 and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP 1569 association on top of the DTLS connection. 1571 12. References 1573 12.1. Normative References 1575 [I-D.ietf-mmusic-sctp-sdp] 1576 Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo, 1577 "Session Description Protocol (SDP) Offer/Answer 1578 Procedures For Stream Control Transmission Protocol (SCTP) 1579 over Datagram Transport Layer Security (DTLS) Transport.", 1580 draft-ietf-mmusic-sctp-sdp-26 (work in progress), April 1581 2017. 1583 [I-D.ietf-mmusic-sdp-mux-attributes] 1584 Nandakumar, S., "A Framework for SDP Attributes when 1585 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17 1586 (work in progress), February 2018. 1588 [I-D.ietf-rtcweb-data-channel] 1589 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 1590 Channels", draft-ietf-rtcweb-data-channel-13 (work in 1591 progress), January 2015. 1593 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1594 Requirement Levels", BCP 14, RFC 2119, 1595 DOI 10.17487/RFC2119, March 1997, 1596 . 1598 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1599 with Session Description Protocol (SDP)", RFC 3264, 1600 DOI 10.17487/RFC3264, June 2002, 1601 . 1603 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1604 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1605 July 2006, . 1607 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1608 Specifications: ABNF", STD 68, RFC 5234, 1609 DOI 10.17487/RFC5234, January 2008, 1610 . 1612 [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control 1613 Transmission Protocol (SCTP) Stream Reconfiguration", 1614 RFC 6525, DOI 10.17487/RFC6525, February 2012, 1615 . 1617 12.2. Informative References 1619 [I-D.ietf-clue-datachannel] 1620 Holmberg, C., "CLUE Protocol data channel", draft-ietf- 1621 clue-datachannel-14 (work in progress), August 2016. 1623 [I-D.ietf-mmusic-dtls-sdp] 1624 Holmberg, C. and R. Shpount, "Session Description Protocol 1625 (SDP) Offer/Answer Considerations for Datagram Transport 1626 Layer Security (DTLS) and Transport Layer Security (TLS)", 1627 draft-ietf-mmusic-dtls-sdp-32 (work in progress), October 1628 2017. 1630 [I-D.ietf-mmusic-msrp-usage-data-channel] 1631 Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., 1632 Marcon, J., and J. Recio, "MSRP over Data Channels", 1633 draft-ietf-mmusic-msrp-usage-data-channel-09 (work in 1634 progress), May 2018. 1636 [I-D.ietf-rtcweb-data-protocol] 1637 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 1638 Establishment Protocol", draft-ietf-rtcweb-data- 1639 protocol-09 (work in progress), January 2015. 1641 [IANA-SDP-Parameters] 1642 "Session Description Protocol (SDP) Parameters", Internet 1643 Assigned Numbers Authority Protocol Assignments Session 1644 Description Protocol (SDP) Parameters, 1645 . 1648 [RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor 1649 Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582, 1650 November 2006, . 1652 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1653 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1654 . 1656 [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., 1657 "The Message Session Relay Protocol (MSRP)", RFC 4975, 1658 DOI 10.17487/RFC4975, September 2007, 1659 . 1661 [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", 1662 RFC 6455, DOI 10.17487/RFC6455, December 2011, 1663 . 1665 [WebRtcAPI] 1666 Bergkvist, A., Burnett, D., Jennings, C., and A. 1667 Narayanan, "WebRTC 1.0: Real-time Communication Between 1668 Browsers", World Wide Web Consortium WD-webrtc-20150210, 1669 February 2015, 1670 . 1672 Appendix A. Generic Data Channel Negotiation Aspects When Not Using 1673 DCEP 1675 This appendix summarizes how data channels work in general and 1676 discusses some key aspects, which should be considered for the out- 1677 of-band negotiation of data channels if DCEP is not used. 1679 A WebRTC application creates a data channel by providing a number of 1680 setup parameters (subprotocol, label, maximal number of 1681 retransmissions, maximal retransmission time, order of delivery, 1682 priority). The application also specifies if it wants to make use of 1683 the negotiation using the DCEP [I-D.ietf-rtcweb-data-protocol], or if 1684 the application intends to negotiate data channels using the SDP 1685 offer/answer protocol. 1687 In any case, the SDP offer generated by the application is per 1688 [I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one "m" line for 1689 the SCTP association on top of which data channels will run: 1691 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 1692 c=IN IP4 192.0.2.1 1693 a=max-message-size:100000 1694 a=sctp-port:5000 1695 a=tls-id:abc3de65cddef001be82 1696 a=setup:actpass 1697 a=fingerprint:SHA-1 \ 1698 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 1700 Note: A WebRTC application will only use "m" line format "webrtc- 1701 datachannel", and will not use other formats in the "m" line for 1702 other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports 1703 only one SCTP association to be established on top of a DTLS 1704 association. 1706 Note: The above SDP media description does not contain any channel- 1707 specific information. 1709 A.1. Stream Identifier Numbering 1711 Independently from the requested type of negotiation, the application 1712 creating a data channel can either pass the stream identifier to the 1713 data channel stack to assign to the data channel or else let the data 1714 channel stack pick one identifier from the unused ones. 1716 To avoid glare situations, each endpoint can moreover own an 1717 exclusive set of stream identifiers, in which case an endpoint can 1718 only create a data channel with a stream identifier it owns. 1720 Which set of stream identifiers is owned by which endpoint is 1721 determined by convention or other means. 1723 Note:For data channels negotiated with the DCEP, one endpoint owns 1724 by convention the even stream identifiers, whereas the other owns 1725 the odd stream identifiers, as defined in 1726 [I-D.ietf-rtcweb-data-protocol]. 1728 Note:For data channels negotiated via different protocol from 1729 DCEP, no convention is defined by default. 1731 A.2. Generic Data Channel Negotiation Not Using DCEP 1733 A.2.1. Overview 1735 DCEP negotiation only provides for negotiation of data channel 1736 transport parameters and does not provide for negotiation of 1737 subprotocol specific parameters. DCEP-less data channel negotiation 1738 can be defined to allow negotiation of parameters beyond those 1739 handled by DCEP, e.g., parameters specific to the subprotocol 1740 instantiated on a particular data channel. 1742 The following procedures are common to all methods of data channel 1743 negotiation not using DCEP, whether in-band (communicated using 1744 proprietary means on an already established data channel) or out-of- 1745 band (using SDP offer/answer or some other protocol associated with 1746 the signaling channel). 1748 A.2.2. Opening a Data Channel 1750 In the case of DCEP-less negotiation, the endpoint application has 1751 the option to fully control the stream identifier assignments. 1752 However these assignments have to coexist with the assignments 1753 controlled by the data channel stack for the DCEP negotiated data 1754 channels (if any). It is the responsibility of the application to 1755 ensure consistent assignment of stream identifiers. 1757 When the application requests the creation of a new data channel to 1758 be set up via DCEP-less negotiation, the data channel stack creates 1759 the data channel locally without sending any DATA_CHANNEL_OPEN 1760 message in-band. However, even if the ICE (Interactive Connectivity 1761 Establishment), DTLS and SCTP procedures were already successfully 1762 completed, the application can't send data on this data channel until 1763 the negotiation is complete with the peer. This is because the peer 1764 needs to be aware of and accept the usage of this data channel. The 1765 peer, after accepting the data channel offer, can start sending data 1766 immediately. This implies that the offerer may receive data channel 1767 subprotocol messages before the negotiation is complete and the 1768 application should be ready to handle it. 1770 If the peer rejects the data channel part of the offer then it 1771 doesn't have to do anything as the data channel was not created using 1772 the stack. The offerer on the other hand needs to close the data 1773 channel that was opened by invoking relevant data channel stack API 1774 procedures. 1776 It is also worth noting that a data channel stack implementation may 1777 not provide any API to create and close data channels; instead the 1778 data channels may be used on the fly as needed just by communicating 1779 via non-DCEP means or by even having some local configuration/ 1780 assumptions on both the peers. 1782 The application then negotiates the data channel properties and 1783 subprotocol properties with the peer's application using a mechanism 1784 different from DCEP. 1786 The peer then symmetrically creates a data channel with these 1787 negotiated data channel properties. This is the only way for the 1788 peer's data channel stack to know which properties to apply when 1789 transmitting data on this channel. The data channel stack must allow 1790 data channel creation with any non-conflicting stream identifier so 1791 that both peers can create the data channel with the same stream 1792 identifier. 1794 A.2.3. Closing a Data Channel 1796 When the application requests the closing of a data channel 1797 negotiated without DCEP, the data channel stack always performs an 1798 SCTP SSN reset for this channel. 1800 Depending upon the method used for DCEP-less negotiation and the 1801 subprotocol associated with the data channel, the closing might in 1802 addition be signaled to the peer via SDP offer/answer negotiation. 1804 Authors' Addresses 1806 Keith Drage 1807 Unaffiliated 1809 Email: drageke@ntlworld.com 1811 Maridi R. Makaraju (Raju) 1812 Nokia 1813 2000 Lucent Lane 1814 Naperville, Illinois 1815 US 1817 Email: Raju.Makaraju@nokia.com 1819 Juergen Stoetzer-Bradler 1820 Unaffiliated 1822 Email: Juergen.S-B.ietf@email.de 1824 Richard Ejzak 1825 Unaffiliated 1827 Email: richard.ejzak@gmail.com 1829 Jerome Marcon 1830 Unaffiliated 1832 Email: jeromee.marcon@free.fr 1834 Roni Even (editor) 1835 Huawei 1837 Email: roni.even@huawei.com