idnits 2.17.1 draft-ietf-mmusic-data-channel-sdpneg-12.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 1 instance of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. -- The document has examples using IPv4 documentation addresses according to RFC6890, but does not use any IPv6 documentation addresses. Maybe there should be IPv6 examples, too? Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: o In Section 5.1.1.1 in the definition of the ABNF rule "dcmap-opt" there was a comment saying that "Either only maxretr-opt or maxtime-opt is present. Both MUST not be present." Removal of the second normative sentence and instead addition of following new paragraph to the end of this section: "Within an 'a=dcmap' attribute line's 'dcmap-opt' value either only one 'maxretr-opt' parameter or one 'maxtime-opt' parameter is present. Both MUST NOT be present." == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: * In the third paragraph replacement of the sentence "The port value for the "m" line SHOULD not be changed (e.g., to zero) when closing a data channel ..." with "The offerer SHOULD NOT change the port value for the "m" line (e.g., to zero) when closing a data channel ...". == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: o In Section 5.2.4 the third paragraph began with "A data channel can be closed by sending a new SDP offer which excludes the dcmap and dcsa attribute lines for the data channel. The port value for the m line should not be changed (e.g., to zero) when closing a data channel (unless all data channels are being closed and the SCTP association is no longer needed), since this would close the SCTP association and impact all of the data channels. If the answerer accepts the SDP offer then it MUST also exclude the corresponding attribute lines in the answer. ..." Replacement of this part with "The intention to close a data channel can be signaled by sending a new SDP offer which excludes the "a=dcmap:" and "a=dcsa:" attribute lines for the data channel. The port value for the "m" line SHOULD not be changed (e.g., to zero) when closing a data channel (unless all data channels are being closed and the SCTP association is no longer needed), since this would close the SCTP association and impact all of the data channels. If the answerer accepts the SDP offer then it MUST close those data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were excluded from the received SDP offer, unless those data channels were already closed, and it MUST also exclude the corresponding attribute lines in the answer." -- The document date (March 27, 2017) is 2586 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'I-D.ietf-rtcweb-jsep' is mentioned on line 1275, but not defined == Missing Reference: 'RFC6455' is mentioned on line 1559, but not defined ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-37) exists of draft-ietf-mmusic-rfc4566bis-17 == Outdated reference: A later version (-26) exists of draft-ietf-mmusic-sctp-sdp-25 == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-sdp-mux-attributes-16 == Outdated reference: A later version (-32) exists of draft-ietf-mmusic-dtls-sdp-22 -- Obsolete informational reference (is this intentional?): RFC 4960 (Obsoleted by RFC 9260) Summary: 1 error (**), 0 flaws (~~), 11 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC K. Drage, Ed. 3 Internet-Draft M. Makaraju 4 Intended status: Standards Track Nokia 5 Expires: September 19, 2017 J. Stoetzer-Bradler 7 R. Ejzak 8 J. Marcon 9 Unaffiliated 10 March 27, 2017 12 SDP-based Data Channel Negotiation 13 draft-ietf-mmusic-data-channel-sdpneg-12 15 Abstract 17 The Real-Time Communication in WEB-browsers (RTCWeb) working group is 18 charged to provide protocols to support direct interactive rich 19 communications using audio, video, and data between two peers' web- 20 browsers. For the support of data communication, the RTCWeb working 21 group has in particular defined the concept of bi-directional data 22 channels over SCTP (Stream Control Transmission Protocol), where each 23 data channel might be used to transport other protocols, called 24 subprotocols. Data channel setup can be done using either the in- 25 band Data Channel Establishment Protocol (DCEP) or using some out-of- 26 band non-DCEP protocol. This document specifies how the SDP (Session 27 Description Protocol) offer/answer exchange can be used to achieve 28 such an out-of-band non-DCEP negotiation. Even though data channels 29 are designed for RTCWeb use initially, they may be used by other 30 protocols like, but not limited to, the CLUE protocol (which is 31 defined by the IETF "ControLling mUltiple streams for tElepresence" 32 working group). This document is intended to be used wherever data 33 channels are used. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on September 19, 2017. 51 Copyright Notice 53 Copyright (c) 2017 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 69 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6 72 5. SDP Offer/Answer Negotiation . . . . . . . . . . . . . . . . 6 73 5.1. SDP Syntax . . . . . . . . . . . . . . . . . . . . . . . 6 74 5.1.1. SDP Attribute for Data Channel Parameter Negotiation 6 75 5.1.1.1. dcmap Attribute . . . . . . . . . . . . . . . . . 7 76 5.1.1.2. dcmap Multiplexing Category . . . . . . . . . . . 8 77 5.1.1.3. dcmap-stream-id Parameter . . . . . . . . . . . . 8 78 5.1.1.4. label Parameter . . . . . . . . . . . . . . . . . 9 79 5.1.1.5. subprotocol Parameter . . . . . . . . . . . . . . 9 80 5.1.1.6. max-retr Parameter . . . . . . . . . . . . . . . 9 81 5.1.1.7. max-time Parameter . . . . . . . . . . . . . . . 9 82 5.1.1.8. ordered Parameter . . . . . . . . . . . . . . . . 10 83 5.1.1.9. priority Parameter . . . . . . . . . . . . . . . 10 84 5.1.2. Other Media Level Attributes . . . . . . . . . . . . 10 85 5.1.2.1. dcsa Attribute . . . . . . . . . . . . . . . . . 10 86 5.1.2.2. dcsa Multiplexing Category . . . . . . . . . . . 12 87 5.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 12 88 5.2.1. Managing Stream Identifiers . . . . . . . . . . . . . 12 89 5.2.2. Negotiating Data Channel Parameters . . . . . . . . . 13 90 5.2.3. Opening a Data Channel . . . . . . . . . . . . . . . 14 91 5.2.4. Closing a Data Channel . . . . . . . . . . . . . . . 16 92 5.2.5. Various SDP Offer/Answer Scenarios and Considerations 17 93 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18 94 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 95 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 96 8.1. Subprotocol Identifiers . . . . . . . . . . . . . . . . . 21 97 8.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 21 98 8.2.1. dcmap . . . . . . . . . . . . . . . . . . . . . . . . 21 99 8.2.2. dcsa . . . . . . . . . . . . . . . . . . . . . . . . 22 100 8.3. New Usage Level . . . . . . . . . . . . . . . . . . . . . 22 101 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 102 10. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 23 103 10.1. Changes against 'draft-ietf-mmusic-data-channel- 104 sdpneg-11' . . . . . . . . . . . . . . . . . . . . . . . 23 105 10.2. Changes against 'draft-ietf-mmusic-data-channel- 106 sdpneg-10' . . . . . . . . . . . . . . . . . . . . . . . 23 107 10.3. Changes against 'draft-ietf-mmusic-data-channel- 108 sdpneg-09' . . . . . . . . . . . . . . . . . . . . . . . 23 109 10.4. Changes against 'draft-ietf-mmusic-data-channel- 110 sdpneg-08' . . . . . . . . . . . . . . . . . . . . . . . 24 111 10.5. Changes against 'draft-ietf-mmusic-data-channel- 112 sdpneg-07' . . . . . . . . . . . . . . . . . . . . . . . 25 113 10.6. Changes against 'draft-ietf-mmusic-data-channel- 114 sdpneg-06' . . . . . . . . . . . . . . . . . . . . . . . 25 115 10.7. Changes against 'draft-ietf-mmusic-data-channel- 116 sdpneg-05' . . . . . . . . . . . . . . . . . . . . . . . 25 117 10.8. Changes against 'draft-ietf-mmusic-data-channel- 118 sdpneg-04' . . . . . . . . . . . . . . . . . . . . . . . 26 119 10.9. Changes against 'draft-ietf-mmusic-data-channel- 120 sdpneg-03' . . . . . . . . . . . . . . . . . . . . . . . 27 121 10.10. Changes against 'draft-ietf-mmusic-data-channel- 122 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 28 123 10.11. Changes against 'draft-ietf-mmusic-data-channel- 124 sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 29 125 10.12. Changes against 'draft-ietf-mmusic-data-channel- 126 sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 31 127 10.13. Changes against 'draft-ejzak-mmusic-data-channel- 128 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 34 129 10.14. Changes against '-01' . . . . . . . . . . . . . . . . . 35 130 10.15. Changes against '-00' . . . . . . . . . . . . . . . . . 35 131 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 132 11.1. Normative References . . . . . . . . . . . . . . . . . . 35 133 11.2. Informative References . . . . . . . . . . . . . . . . . 36 134 Appendix A. Generic Data Channel Negotiation Aspects When Not 135 Using DCEP . . . . . . . . . . . . . . . . . . . . . 37 136 A.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 38 137 A.2. Generic Data Channel Negotiation Not Using DCEP . . . . . 38 138 A.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 38 139 A.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 39 140 A.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 40 141 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40 143 1. Introduction 145 The RTCWeb working group has defined the concept of bi-directional 146 data channels running on top of the Stream Control Transmission 147 Protocol (SCTP). RTCWeb allows applications to use data channels. 148 RTCWeb defines an in-band Data Channel Establishment Protocol (DCEP), 149 however other in-band or out-of-band protocols may be used for 150 establishing data channels. Each data channel consists of paired 151 SCTP streams sharing the same SCTP Stream Identifier. Data channels 152 are created by endpoint applications through the WebRTC API 153 (Application Programming Interface), or other users of a data channel 154 like CLUE. They can be used to transport proprietary or well-defined 155 protocols, which in the latter case can be signaled by the data 156 channel "subprotocol" parameter, conceptually similar to the 157 WebSocket "subprotocol". However, apart from the "subprotocol" value 158 transmitted to the peer, RTCWeb leaves it open how endpoint 159 applications can agree on how to instantiate a given subprotocol on a 160 data channel, and whether it is signaled in-band using DCEP or out- 161 of-band using a non-DCEP protocol (or both). In particular, the SDP 162 offer generated by the RTCweb data channel stack includes no channel- 163 specific information. 165 This document defines SDP offer/answer negotiation procedures to 166 establish data channels for transport of well-defined subprotocols, 167 to enable out-of-band negotiation. These procedures are based on 168 generic SDP offer/answer negotiation rules for SCTP based media 169 transport as specified in [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" 170 line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP. In the future, 171 data channels could be defined over other SCTP based protocols, such 172 as SCTP over IP. However, corresponding potential other "m" line 173 proto values are not considered in this document. 175 This document makes use of MSRP (Message Session Relay Protocol) and 176 BFCP (Binary Floor Control Protocol) in many of the examples. It 177 does not provide a complete specification of how to negotiate the use 178 of a data channel to transport MSRP. Procedures specific to each 179 subprotocol such as MSRP are documented elsewhere. The use of MSRP 180 in some examples is only to show how the generic procedures described 181 herein might apply to a specific subprotocol. 183 2. Conventions 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 187 document are to be interpreted as described in [RFC2119]. 189 3. Terminology 191 This document uses the following terms: 193 Data channel: A WebRTC data channel as specified in 194 [I-D.ietf-rtcweb-data-channel]. 196 Data channel stack: An entity which, upon application request, 197 runs the data channel protocol to keep track of states, sending 198 and receiving data. If the application is a browser based 199 JavaScript application then this stack resides in the browser. If 200 the application is a native application then this stack resides in 201 the application and is accessible via some sort of APIs. 203 Data channel properties: Fixed properties assigned to a data 204 channel at the time of its creation. Some of these properties 205 determine the way the data channel stack transmits data on this 206 channel (e.g., stream identifier, reliability, order of 207 delivery...). 209 Data channel subprotocol: The application protocol which is 210 transported over a single data channel. Data channel subprotocol 211 messages are sent as data channel payload over an established data 212 channel. If an SDP offer/answer exchange is used as specified in 213 this document to negotiate the establishment of data channels, 214 corresponding data channel properties, associated data channel 215 subprotocols and data channel subprotocol properties, then the 216 data channel subprotocols may be identified by the values of the 217 "subprotocol" parameters of the SDP "a=dcmap" attribute as 218 described in Section 5.1.1.5. Within this document the term "data 219 channel subprotocol" is often abbreviated as just "subprotocol". 221 DCEP: Data Channel Establishment Protocol defined in 222 [I-D.ietf-rtcweb-data-protocol]. 224 In-band: Transmission through the peer-to-peer SCTP association. 226 Out-of-band: Transmission through the application signaling path. 228 Peer: From the perspective of one of the agents in a session, its 229 peer is the other agent. Specifically, from the perspective of 230 the SDP offerer, the peer is the SDP answerer. From the 231 perspective of the SDP answerer, the peer is the SDP offerer. 233 SCTP Stream Sequence Number (SSN): the SCTP stream sequence number 234 as specified in [RFC4960]. 236 Stream identifier: The identifier of the outbound and inbound SCTP 237 streams composing a data channel. 239 4. Applicability Statement 241 The mechanism in this document only applies to the Session 242 Description Protocol (SDP) [RFC4566], when used together with the SDP 243 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 244 scope of this document, and is thus undefined. 246 5. SDP Offer/Answer Negotiation 248 This section defines an SDP extension by which two clients can 249 negotiate data channel-specific and subprotocol-specific parameters 250 without using DCEP [I-D.ietf-rtcweb-data-protocol]. This SDP 251 extension only defines usage in the context of SDP offer/answer. 253 Appendix A provides information how data channels work in general and 254 especially summarizes some key aspects, which should be considered 255 for the negotiation of data channels if DCEP is not used. 257 5.1. SDP Syntax 259 Two new SDP attributes are defined to support SDP offer/answer 260 negotiation of data channels. The first attribute provides for 261 negotiation of channel-specific parameters. The second attribute 262 provides for negotiation of subprotocol-specific parameters. 264 5.1.1. SDP Attribute for Data Channel Parameter Negotiation 266 Associated with the SDP "m" line that defines the SCTP association 267 for data channels (defined in Section 3), each SDP offer and answer 268 includes one "a=dcmap:" attribute that defines the data channel 269 parameters for each data channel to be negotiated. Each such 270 attribute line specifies the following parameters for a data channel: 271 SCTP stream identifier, subprotocol, label, maximal number of 272 retransmissions, maximal retransmission time, order of delivery, and 273 priority. 275 The intention in exchanging these attributes is to create, on two 276 peers, without use of DCEP [I-D.ietf-rtcweb-data-protocol], matched 277 pairs of oppositely directed data channels having the same set of 278 attributes. It is assumed that the data channel properties 279 (reliable/partially reliable, ordered/unordered) are suitable per the 280 subprotocol transport requirements. 282 5.1.1.1. dcmap Attribute 284 "a=dcmap:" is a media level attribute having following ABNF 285 (Augmented Backus-Naur Form, [RFC5234]) syntax. 287 Formal Syntax: 289 Name: dcmap 291 Value: dcmap-value 293 Usage Level: media 295 Charset Dependent: no 297 Syntax: 299 dcmap-value = dcmap-stream-id 300 [ SP dcmap-opt *(";" dcmap-opt) ] 301 dcmap-opt = ordering-opt / subprotocol-opt / label-opt 302 / maxretr-opt / maxtime-opt / priority-opt 303 ; Either only maxretr-opt or maxtime-opt 304 ; is present. 306 dcmap-stream-id = 1*5DIGIT 307 ordering-opt = "ordered=" ordering-value 308 ordering-value = "true" / "false" 309 subprotocol-opt = "subprotocol=" quoted-string 310 label-opt = "label=" quoted-string 311 maxretr-opt = "max-retr=" maxretr-value 312 maxretr-value = "0" / integer 313 ; number of retransmissions, 314 ; less than 2^32, 315 ; derived from 'Reliability Parameter' of 316 ; [I-D.ietf-rtcweb-data-protocol] 317 maxtime-opt = "max-time=" maxtime-value 318 maxtime-value = "0" / integer 319 ; milliseconds, 320 ; less than 2^32, 321 ; derived from 'Reliability Parameter' of 322 ; [I-D.ietf-rtcweb-data-protocol] 323 priority-opt = "priority=" priority-value 324 priority-value = "0" / integer 325 ; unsigned integer value indicating the priority of 326 ; the data channel, 327 ; less than 2^16, 328 ; derived from 'Priority' of 329 ; [I-D.ietf-rtcweb-data-protocol] 331 quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE 332 quoted-char = SP / quoted-visible 333 quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or % 334 escaped-char = "%" HEXDIG HEXDIG 335 DQUOTE = 336 integer = 338 Examples: 340 a=dcmap:0 341 a=dcmap:1 subprotocol="BFCP";max-time=60000;priority=512 342 a=dcmap:2 subprotocol="MSRP";ordered=true;label="MSRP" 343 a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128 344 a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000 346 Note: The last example (a=dcmap:4) shows a 'label' parameter value 347 which contains one non-printable 'escaped-char' character (the 348 tabulator character). 350 Within an 'a=dcmap:' attribute line's 'dcmap-opt' value either only 351 one 'maxretr-opt' parameter or one 'maxtime-opt' parameter MAY be 352 present. Both MUST NOT be present. 354 5.1.1.2. dcmap Multiplexing Category 356 Multiplexing characteristics of SDP attributes are described in 357 [I-D.ietf-mmusic-sdp-mux-attributes]. Various SDP attribute 358 multiplexing categories are introduced there. 360 The multiplexing category of the "a=dcmap:" attribute is SPECIAL. 362 As the usage of multiple SCTP associations on top of a single DTLS 363 association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no 364 "a=dcmap:" attribute multiplexing rules are specified for the 365 UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions 366 of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of 367 multiple SCTP associations on top of a single DTLS association, or 368 how to add multiple SCTP associations to one BUNDLE group, then 369 multiplexing rules for the "a=dcmap:" attribute need to be defined as 370 well, for instance in an extension of this SDP based data channel 371 negotiation specification. 373 5.1.1.3. dcmap-stream-id Parameter 375 The 'dcmap-stream-id' parameter indicates the SCTP stream identifier 376 within the SCTP association used to form the data channel. 378 5.1.1.4. label Parameter 380 The 'label' parameter indicates the name of the channel. It 381 represents a label that can be used to distinguish, in the context of 382 the WebRTC API [WebRtcAPI], an RTCDataChannel object from other 383 RTCDataChannel objects. This parameter maps to the 'Label' parameter 384 defined in [I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is 385 optional. If it is not present, then its value defaults to the empty 386 string. 388 Note: The empty string MAY also be explicitly used as a 'label' 389 value, such that 'label=""' is equivalent to the 'label' parameter 390 not being present at all. [I-D.ietf-rtcweb-data-protocol] allows the 391 DATA_CHANNEL_OPEN message's 'Label' value to be an empty string. 393 5.1.1.5. subprotocol Parameter 395 The 'subprotocol' parameter indicates which protocol the client 396 expects to exchange via the channel. This parameter maps to the 397 'Protocol' parameter defined in [I-D.ietf-rtcweb-data-protocol]. 398 Section 8.1 specifies how new subprotocol parameter values are 399 registered. 'Subprotocol' is an optional parameter. If the 400 'subprotocol' parameter is not present, then its value defaults to an 401 empty string. 403 Note: The empty string MAY also be explicitly used as 'subprotocol' 404 value, such that 'subprotocol=""' is equivalent to the 'subprotocol' 405 parameter not being present at all. [I-D.ietf-rtcweb-data-protocol] 406 allows the DATA_CHANNEL_OPEN message's 'Subprotocol' value to be an 407 empty string. 409 5.1.1.6. max-retr Parameter 411 This parameter indicates that the data channel is partially reliable. 412 The 'max-retr' parameter indicates the maximal number of times a user 413 message will be retransmitted. The max-retr parameter is optional. 414 If the max-retr parameter is not present, then the maximal number of 415 retransmissions is determined as per the generic SCTP retransmission 416 rules as specified in [RFC4960]. This parameter maps to the 'Number 417 of RTX' parameter defined in [I-D.ietf-rtcweb-data-protocol]. 419 5.1.1.7. max-time Parameter 421 This parameter indicates that the data channel is partially reliable. 422 A user message will no longer be transmitted or retransmitted after a 423 specified life-time given in milliseconds in the 'max-time' 424 parameter. The max-time parameter is optional. If the max-time 425 parameter is not present, then the generic SCTP retransmission timing 426 rules apply as specified in [RFC4960]. This parameter maps to the 427 'Lifetime in ms' parameter defined in 428 [I-D.ietf-rtcweb-data-protocol]. 430 5.1.1.8. ordered Parameter 432 The 'ordered' parameter with value "true" indicates that the receiver 433 MUST dispatch DATA chunks in the data channel to the upper layer 434 while preserving the order. The ordered parameter is optional and 435 takes two values: "true" for ordered and "false" for unordered 436 delivery with "true" as the default value. Any other value is 437 ignored and default "ordered=true" is assumed. In the absence of 438 this parameter "ordered=true" is assumed. This parameter maps to the 439 ordered or unordered data channel types as defined in 440 [I-D.ietf-rtcweb-data-protocol]. 442 5.1.1.9. priority Parameter 444 The 'priority' parameter indicates the data channel's priority 445 relative to the priorities of other data channels, which may 446 additionally exist over the same SCTP association. The 'priority' 447 parameter maps to the 'Priority' parameter defined in 448 [I-D.ietf-rtcweb-data-protocol]. The 'priority' parameter is 449 optional. In the absence of this parameter "priority=256" is 450 assumed. 452 5.1.2. Other Media Level Attributes 454 In the SDP, each data channel declaration MAY also be followed by 455 other media level SDP attributes, which are either specifically 456 defined for or applied to the subprotocol in use. Each of these 457 attributes is represented by one new attribute line, and it includes 458 the contents of a media-level SDP attribute already defined for use 459 with this (sub)protocol in another IETF (Internet Engineering Task 460 Force) document. Subprotocol specific attributes MAY also be defined 461 for exclusive use with data channel transport, but MUST use the same 462 syntax described here for other subprotocol related attributes. 464 5.1.2.1. dcsa Attribute 466 Each SDP attribute, related to the subprotocol, that would normally 467 be used to negotiate the subprotocol using SDP is replaced with an 468 attribute of the form "a=dcsa:stream-id original-attribute", where 469 dcsa stands for "data channel subprotocol attribute", stream-id is 470 the SCTP stream identifier assigned to this subprotocol instance, and 471 original-attribute represents the contents of the subprotocol related 472 attribute to be included. 474 The same syntax applies to any other SDP attribute required for 475 negotiation of this instance of the subprotocol. 477 Formal Syntax: 479 Name: dcsa 481 Value: dcsa-value 483 Usage Level: media 485 Charset Dependent: no 487 Syntax: 489 dcsa-value = stream-id SP attribute 490 attribute = 492 Example (other MSRP related SDP attributes are omitted for brevity): 494 a=dcsa:2 accept-types:text/plain 496 Note that the above reference to [RFC4566] defines where the 497 attribute definition can be found; it does not provide any limitation 498 on support of attributes defined in other documents in accordance 499 with this attribute definition. Note however that not all SDP 500 attributes are suitable as a "a=dcsa:" parameter. 501 [IANA-SDP-Parameters] contains the lists of IANA (Internet Assigned 502 Numbers Authority) registered session and media level or media level 503 only SDP attributes. 505 Thus in the example above, the original attribute line "a=accept- 506 types:text/plain" is represented by the attribute line "a=dcsa:2 507 accept-types:text/plain", which specifies that this instance of the 508 MSRP subprotocol being transported on the SCTP association using the 509 data channel with stream id 2 accepts plain text files. 511 As opposed to the data channel "a=dcmap:" attribute parameters, these 512 parameters are subject to offer/answer negotiation following the 513 procedures defined in the subprotocol specific documents. 515 It is assumed that in general the usages of subprotocol related media 516 level attributes are independent from the subprotocol's transport 517 protocol. Such transport protocol independent subprotocol related 518 attributes are used in the same way as defined in the original 519 subprotocol specification, also if the subprotocol is transported 520 over a data channel and if the attribute is correspondingly embedded 521 in a "a=dcsa" attribute. 523 There may be cases, where the usage of a subprotocol related media 524 level attribute depends on the subprotocol's transport protocol. In 525 such cases the subprotocol related usage of the attribute is expected 526 to be described for the data channel transport. A data channel 527 specific usage of a subprotocol attribute is expected to be specified 528 in the same document, that registers the subprotocol's identifier for 529 data channel usage as described in Section 8.1. 531 5.1.2.2. dcsa Multiplexing Category 533 The multiplexing category of the "a=dcsa:" attribute is SPECIAL. 535 As the usage of multiple SCTP associations on top of a single DTLS 536 association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no 537 "a=dcsa:" attribute multiplexing rules are specified for the 538 UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions 539 of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of 540 multiple SCTP associations on top of a single DTLS association, or 541 how to add multiple SCTP associations to one BUNDLE group, then 542 multiplexing rules for the "a=dcsa:" attribute need to be defined as 543 well, for instance in an extension of this SDP based data channel 544 negotiation specification. 546 5.2. Procedures 548 5.2.1. Managing Stream Identifiers 550 If a SDP offer/answer exchange (could be the initial or a subsequent 551 one) results in a UDP/DTLS/SCTP or TCP/DTLS/SCTP based media 552 description being accepted, and if this SDP offer/answer exchange 553 results in the establishment of a new SCTP association, then the SDP 554 offerer owns the even SCTP stream ids of this new SCTP association 555 and the answerer owns the odd SCTP stream identifiers. If this "m" 556 line is removed from the signaling session (its port number set to 557 zero), and if usage of this or of a new UDP/DTLS/SCTP or TCP/DTLS/ 558 SCTP based "m" line is renegotiated later on, then the even and odd 559 SCTP stream identifier ownership is re-determined as described above. 561 This document allows simultaneous use of SDP offer/answer and DCEP 562 negotiation. However, an SCTP stream MUST NOT be referenced in a 563 "a=dcmap:" or "a=dcsa:" attribute of an SDP offer/answer exchange if 564 the associated SCTP stream has already been negotiated via DCEP. 565 Stream ids that are not currently used in SDP can be used for DCEP 566 negotiation. Stream id allocation per SDP offer/answer negotiation 567 may not align with DTLS role based allocation. This could cause 568 glare conditions when one side tries to do SDP offer/answer 569 negotiation on a stream id while the other end tries to open a data 570 channel on the same stream id using DCEP negotiation. To avoid these 571 glare conditions this document recommends that the data channel stack 572 user always selects stream ids per the above described SDP offer/ 573 answer rule even when DCEP negotiation is used. To avoid glare 574 conditions, it is possible to come up with a different stream id 575 allocation scheme, but such schemes are outside the scope of this 576 document. 578 5.2.2. Negotiating Data Channel Parameters 580 Conveying a reliable data channel is achieved by including neither 581 'max-retr' nor 'max-time' in corresponding SDP offer's or answer's 582 "a=dcmap:" attribute line. Conveying a partially reliable data 583 channel is achieved by including only one of 'max-retr' or 'max- 584 time'. By definition max-retr and max-time are mutually exclusive, 585 so at most one of them MAY be present in the "a=dcmap:" attribute 586 line. If a SDP offer contains both of these parameters then the 587 receiver of such an SDP offer MUST reject the SDP offer. If a SDP 588 answer contains both of these parameters then the offerer MUST treat 589 the associated SDP offer/answer failed and take appropriate recovery 590 actions. These recovery options are outside the scope of this 591 document. 593 The SDP answer SHALL echo the same subprotocol, max-retr, max-time, 594 ordered parameters, if those were present in the offer, and MAY 595 include a label parameter. They MAY appear in any order, which could 596 be different from the SDP offer, in the SDP answer. 598 When sending a subsequent offer or an answer, and for as long as the 599 data channel is still open, the sender MUST replicate the same 600 information. 602 Data channel types defined in [I-D.ietf-rtcweb-data-protocol] are 603 mapped to SDP in the following manner, where "ordered=true" is the 604 default and may be omitted: 606 DATA_CHANNEL_RELIABLE 607 ordered=true 609 DATA_CHANNEL_RELIABLE_UNORDERED 610 ordered=false 612 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT 613 ordered=true;max-retr= 615 DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED 616 ordered=false;max-retr= 618 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED 619 ordered=true;max-time= 621 DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED 622 ordered=false;max-time= 624 5.2.3. Opening a Data Channel 626 The procedure for opening a data channel using SDP offer/answer 627 negotiation starts with the agent preparing to send an SDP offer. If 628 a peer receives an SDP offer before starting to send a new SDP offer 629 with data channels that are to be SDP offer/answer negotiated, or 630 loses an SDP offer glare resolution procedure in this case, it MUST 631 wait until the ongoing SDP offer/answer completes before resuming the 632 SDP offer/answer negotiation procedure. 634 The agent that intends to send an SDP offer to create data channels 635 through SDP offer/answer negotiation performs the following: 637 o Creates data channels using stream identifiers from the owned set 638 (see Section 5.2.1). 640 o Generates a new SDP offer. 642 o Determines the list of stream identifiers assigned to data 643 channels opened through SDP offer/answer negotiation. 645 o Completes the SDP offer with the "a=dcmap:" and "a=dcsa:" 646 attributes needed, if any, for each SDP offer/answer negotiated 647 data channel, as described in Section 5.1 and in Section 5.2.2. 649 o If it adds "a=dcsa" attributes to the SDP offer, then it SHOULD 650 add the subprotocol parameter to the "a=dcmap" attribute with a 651 non-empty subprotocol identifier. 653 o Sends the SDP offer. 655 The peer receiving such an SDP offer performs the following: 657 o Parses and applies the SDP offer, taking into account the 658 considerations discussed in Section 5.2.5. 660 o Analyzes the channel parameters and subprotocol attributes to 661 determine whether to accept each offered data channel. 663 o For accepted data channels, the agent MUST create peer instances 664 for the data channels using the SCTP stream identifiers and 665 channel parameters contained in the SDP offer. 667 o Generates an SDP answer. 669 o Completes the SDP answer with the "a=dcmap:" and optional 670 "a=dcsa:" attributes needed for each SDP offer/answer negotiated 671 data channel, as described in Section 5.1 and in Section 5.2.2. 673 o Sends the SDP answer. 675 The agent receiving such an SDP answer performs the following: 677 o Closes any created data channels as described in Section 5.2.4 for 678 which the expected "a=dcmap:" and "a=dcsa:" attributes are not 679 present in the SDP answer. 681 o Applies the SDP answer. 683 Each agent application MUST wait to send data until it has 684 confirmation that the data channel at the peer is instantiated. For 685 WebRTC, this is when both data channel stacks have channel parameters 686 instantiated. This occurs: 688 o At both peers when a data channel is created without an 689 established SCTP association, as soon as the SCTP association is 690 successfully established. 692 o At the agent receiving an SDP offer for which there is an 693 established SCTP association, as soon as it creates an SDP offer/ 694 answer negotiated data channel based on information signaled in 695 the SDP offer. 697 o At the agent sending an SDP offer to create a new SDP offer/answer 698 negotiated data channel for which there is an established SCTP 699 association, when it receives the SDP answer confirming acceptance 700 of the data channel or when it begins to receive data on the data 701 channel from the peer, whichever occurs first. 703 Note: DCEP is not used, that is neither the SDP offerer nor the SDP 704 answerer send an in-band DCEP DATA_CHANNEL_OPEN message. 706 5.2.4. Closing a Data Channel 708 When the application requests the closing of a data channel that was 709 negotiated via SDP offer/answer, the data channel stack always 710 performs an SCTP SSN reset for this channel. 712 It is specific to the subprotocol whether this closing MUST in 713 addition be signaled to the peer via a new SDP offer/answer exchange. 715 The intention to close a data channel can be signaled by sending a 716 new SDP offer which excludes the "a=dcmap:" and "a=dcsa:" attribute 717 lines for the data channel. The offerer SHOULD NOT change the port 718 value for the "m" line (e.g. to zero) when closing a data channel 719 (unless all data channels are being closed and the SCTP association 720 is no longer needed), since this would close the SCTP association and 721 impact all of the data channels. If the answerer accepts the SDP 722 offer then the answerer MUST close those data channels whose 723 "a=dcmap:" and "a=dcsa:" attribute lines were excluded from the 724 received SDP offer, unless those data channels were already closed, 725 and the answerer MUST also exclude the corresponding attribute lines 726 in the answer. In addition to that, the SDP answerer MAY exclude 727 other data channels which were closed but not yet communicated to the 728 peer. So, the offerer MUST inspect the answer to see if it has to 729 close other data channels that are now not included in the answer. 731 If a new SDP offer/answer is used to close data channels then the 732 data channel(s) SHOULD only be closed by the answerer/offerer after a 733 successful SDP answer is sent/received. 735 This delayed closure is RECOMMENDED in order to handle cases where 736 a successful SDP answer is not received, in which case the state 737 of the session SHOULD be kept per the last successful SDP offer/ 738 answer. 740 If a client receives a data channel close indication (due to inband 741 SCTP SSN reset or some other reason) without associated SDP offer 742 then the client SHOULD generate an SDP offer which excludes this 743 closed data channel. 745 The application MUST also close any data channel that was negotiated 746 via SDP offer/answer, for which the stream identifiers are not listed 747 in an incoming SDP offer. 749 A closed data channel using local close (SCTP SSN reset), without an 750 additional SDP offer/answer to close it, may be reused for a new data 751 channel. This can only be done via new SDP offer/answer, describing 752 the new subprotocol and its attributes, only after the corresponding 753 data channel close acknowledgement is received from the peer (i.e. 754 SCTP SSN reset of both incoming and outgoing streams is completed). 755 This restriction is to avoid the race conditions between arrival of 756 "SDP offer which reuses stream" with "SCTP SSN reset which closes 757 outgoing stream" at the peer. 759 5.2.5. Various SDP Offer/Answer Scenarios and Considerations 761 SDP offer has no "a=dcmap:" attributes. 763 * Initial SDP offer: No data channel is negotiated yet. The DTLS 764 association and SCTP association is negotiated and, if agreed, 765 established as per [I-D.ietf-mmusic-sctp-sdp]. 767 * Subsequent SDP offer: All the SDP offer/answer negotiated data 768 channels are expected to be closed now. The DTLS/SCTP 769 association remains open for SDP offer/answer or DCEP 770 negotiation of data channels. 772 SDP answer has no "a=dcmap:" attributes. 774 * Initial SDP answer: Either the peer does not support "a=dcmap:" 775 attributes or it rejected all the data channels. In either 776 case the offerer closes all the SDP offer/answer negotiated 777 data channels that were open at the time of initial offer. The 778 DTLS association and SCTP association will still be setup. 780 * Subsequent SDP answer: All the SDP offer/answer negotiated data 781 channels are expected to be closed now. The SCTP association 782 remains open for future SDP offer/answer or DCEP negotiation of 783 data channels. 785 SDP offer or answer has no "a=dcmap:" attributes but has "a=dcsa:" 786 attributes. 788 * This is considered an error case. In this case the receiver of 789 such an SDP offer or answer SHOULD ignore the "a=dcsa:" 790 attributes and SHOULD process the SDP offer or answer as per 791 above case 'SDP offer has no "a=dcmap:" attributes' or case 792 'SDP answer has no "a=dcmap:" attributes'. 794 SDP offer has no "a=dcsa:" attributes for a data channel. 796 * This is allowed and indicates there are no subprotocol 797 parameters to convey. 799 SDP answer has no "a=dcsa:" attributes for a data channel. 801 * This is allowed and indicates there are no subprotocol 802 parameters to convey in the SDP answer. The number of 803 "a=dcsa:" attributes in the SDP answer does not have to match 804 the number of "a=dcsa:" attributes in the SDP offer. 806 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 807 attribute is unknown. 809 * The receiver of such an SDP offer or answer SHOULD ignore this 810 entire "a=dcsa" attribute line. 812 SDP offer or answer has an "a=dcsa" attribute, whose subprotocol 813 attribute is known, but whose subprotocol attribute semantic is 814 not known for the data channel transport case. 816 * The receiver of such an SDP offer or answer SHOULD ignore this 817 entire "a=dcsa" attribute line. 819 6. Examples 821 SDP offer: 823 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 824 c=IN IP4 192.0.2.1 825 a=max-message-size:100000 826 a=sctp-port:5000 827 a=setup:actpass 828 a=fingerprint:SHA-1 \ 829 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 830 a=dtls-id:4a7565 831 a=dcmap:0 subprotocol="BFCP";label="BFCP" 833 SDP answer: 835 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 836 c=IN IP4 192.0.2.2 837 a=max-message-size:100000 838 a=sctp-port:5002 839 a=setup:passive 840 a=fingerprint:SHA-1 \ 841 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 842 a=dtls-id:532d42 844 Figure 1: Example 1 846 In the above example the SDP answerer rejected the data channel with 847 stream id 0 either for explicit reasons or because it does not 848 understand the "a=dcmap:" attribute. As a result the offerer will 849 close the data channel created with the SDP offer/answer negotiation 850 option. The SCTP association will still be setup over DTLS. At this 851 point the offerer or the answerer may use DCEP negotiation to open 852 data channels. 854 SDP offer: 856 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 857 c=IN IP4 192.0.2.1 858 a=max-message-size:100000 859 a=sctp-port:5000 860 a=setup:actpass 861 a=fingerprint:SHA-1 \ 862 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 863 a=dtls-id:4a7565 864 a=dcmap:0 subprotocol="BFCP";label="BFCP" 865 a=dcmap:2 subprotocol="MSRP";label="MSRP" 866 a=dcsa:2 accept-types:message/cpim text/plain 867 a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc 869 SDP answer: 871 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 872 c=IN IP4 192.0.2.2 873 a=max-message-size:100000 874 a=sctp-port:5002 875 a=setup:passive 876 a=fingerprint:SHA-1 \ 877 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 878 a=dtls-id:532d42 879 a=dcmap:2 subprotocol="MSRP";label="MSRP" 880 a=dcsa:2 accept-types:message/cpim text/plain 881 a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc 883 Figure 2: Example 2 885 In the above example the SDP offer contains data channels for BFCP 886 (Binary Floor Control Protocol) and MSRP subprotocols. The SDP 887 answer rejected BFCP and accepted MSRP. So, the offerer closes the 888 data channel for BFCP and both offerer and answerer may start using 889 the MSRP data channel (after the SCTP association is set up). The 890 data channel with stream id 0 is free and can be used for future DCEP 891 or SDP offer/answer negotiation. 893 Continuing the example in Figure 2. 895 Subsequent SDP offer: 897 m=application 10001 UDP/DTLS/SCTP webrtc-datachannel 898 c=IN IP4 192.0.2.1 899 a=max-message-size:100000 900 a=sctp-port:5000 901 a=setup:actpass 902 a=fingerprint:SHA-1 \ 903 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 904 a=dtls-id:4a7565 905 a=dcmap:4 subprotocol="MSRP";label="MSRP" 906 a=dcsa:4 accept-types:message/cpim text/plain 907 a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc 909 Subsequent SDP answer: 911 m=application 10002 UDP/DTLS/SCTP webrtc-datachannel 912 c=IN IP4 192.0.2.2 913 a=max-message-size:100000 914 a=sctp-port:5002 915 a=setup:passive 916 a=fingerprint:SHA-1 \ 917 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 918 a=dtls-id:532d42 919 a=dcmap:4 subprotocol="MSRP";label="MSRP" 920 a=dcsa:4 accept-types:message/cpim text/plain 921 a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc 923 Figure 3: Example 3 925 The above example is a continuation of the example in Figure 2. The 926 SDP offerer now removes the MSRP data channel with stream id 2, but 927 opens a new MSRP data channel with stream id 4. The answerer accepts 928 the entire offer. As a result the offerer closes the earlier 929 negotiated MSRP related data channel and both offerer and answerer 930 may start using new the MSRP related data channel. 932 7. Security Considerations 934 No security considerations are envisaged beyond those already 935 documented in [RFC4566]. 937 8. IANA Considerations 938 8.1. Subprotocol Identifiers 940 Registration of new subprotocol identifiers is performed using the 941 existing IANA "WebSocket Subprotocol Name Registry" table. 943 The following text should be added following the title of the table. 945 "This table also includes subprotocol identifiers specified for usage 946 within a WebRTC data channel." 948 The following reference should be added to under the heading 949 reference: "RFC XXXX". 951 This document assigns no new values to this table. 953 A subprotocol may simultaneously be defined for data channel 954 transport and for Websocket transport. In such a case the 955 "Subprotocol Definition" and "Reference" cells in the subprotocol's 956 row of the IANA "WebSocket Subprotocol Name Registry" table should 957 contain two entries. One entry in each of these cells should refer 958 to the Websocket related subprotocol specification, and the other 959 entry should refer to the data channel related subprotocol 960 specification. 962 NOTE to RFC Editor: Please replace "XXXX" with the number of this 963 RFC. 965 8.2. New SDP Attributes 967 8.2.1. dcmap 969 NOTE to RFC Editor: Please replace "XXXX" with the number of this 970 RFC. 972 This document defines a new SDP media-level attribute "a=dcmap:" as 973 follows: 975 +-----------------------+-------------------------------------------+ 976 | Contact name: | MMUSIC Chairs | 977 | Contact email: | mmusic-chairs@ietf.org | 978 | Attribute name: | dcmap | 979 | Attribute syntax: | As per Section 5.1.1.1 | 980 | Attribute semantics: | As per Section 5.1.1.1 | 981 | Usage level: | media | 982 | Charset dependent: | No | 983 | Purpose: | Define data channel specific parameters | 984 | Appropriate values: | As per Section 5.1.1.1 | 985 | O/A procedures: | As per Section 5.2 | 986 | Mux category: | SPECIAL. See Section 5.1.1.2 | 987 | Reference: | RFCXXXX | 988 +-----------------------+-------------------------------------------+ 990 8.2.2. dcsa 992 NOTE to RFC Editor: Please replace "XXXX" with the number of this 993 RFC. 995 This document defines a new SDP media-level attribute "a=dcsa:" as 996 follows: 998 +-----------------------+-------------------------------------------+ 999 | Contact name: | MMUSIC Chairs | 1000 | Contact email: | mmusic-chairs@ietf.org | 1001 | Attribute name: | dcsa | 1002 | Attribute syntax: | As per Section 5.1.2.1 | 1003 | Attribute semantics: | As per Section 5.1.2.1 | 1004 | Usage level: | media | 1005 | Charset dependent: | No | 1006 | Purpose: | Define data channel subprotocol specific | 1007 | | attributes | 1008 | Appropriate values: | As per Section 5.1.2.1 | 1009 | O/A procedures: | As per Section 5.2 | 1010 | Mux category: | SPECIAL. See Section 5.1.2.2 | 1011 | Reference: | RFCXXXX | 1012 +-----------------------+-------------------------------------------+ 1014 8.3. New Usage Level 1016 This document introduces a new "Data Channel Subprotocol Attribute" 1017 (dcsa) usage level to the SDP to the IANA SDP att-field registry. 1018 SDP attributes that are defined for use at the dcsa usage level only 1019 SHALL use the dcsa usage level when registering the attribute. If 1020 existing media attributes are used in a datachannel subprotocol 1021 specific way (Section 5.1.2.1), then a new dcsa usage level MUST be 1022 defined for the existing media attribute. Where the SDP attribute is 1023 applicable to a particular subprotocol/s this SHALL also be 1024 registered by indicating the applicable subprotocol identifiers (see 1025 Section 8.1) along with the dcsa usage level. E.g. 1027 +-----------------------+-------------------------------------------+ 1028 | ... | ... | 1029 | Usage level: | dcsa(MSRP) | 1030 | ... | ... | 1031 +-----------------------+-------------------------------------------+ 1033 9. Acknowledgments 1035 The authors wish to acknowledge the borrowing of ideas from other 1036 internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley 1037 and Gavin Llewellyn, and to thank Flemming Andreasen, Roni Even, 1038 Christian Groves, Gunnar Hellstrom, Christer Holmberg, Paul Kyzivat, 1039 Jonathan Lennox, Uwe Rauschenbach and Roman Shpount for their 1040 invaluable comments. 1042 10. CHANGE LOG 1044 10.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-11' 1046 o dcmap-stream-id syntax change to limit size to 5 digits. 1048 o Add missing 'x' prefix to quoted-visible syntax. 1050 o Align SDP offerer and answerer handling when both max-retr and 1051 max-time are present. 1053 o Use of TEST-NET-1 ip addresses in examples. 1055 o Add missing a=dtls-id in one example. 1057 10.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-10' 1059 o Removal of the "a=connection" attribute lines from all SDP 1060 examples. 1062 10.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-09' 1064 o In the introduction: 1066 * Replacement of the sentence "The RTCWeb working group has 1067 defined the concept of bi-directional data channels running on 1068 top of SCTP/DTLS (SCTP over the Datagram Transport Layer 1069 Security protocol)" with "The RTCWeb working group has defined 1070 the concept of bi-directional data channels running on top of 1071 the Stream Control Transmission Protocol (SCTP)". 1073 * Addition of following sentences to the second paragraph: "These 1074 procedures are based on generic SDP offer/answer negotiation 1075 rules for SCTP based media transport as specified in 1076 [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" line proto values 1077 UDP/DTLS/SCTP and TCP/DTLS/SCTP. In the future, data channels 1078 could be defined over other SCTP based protocols, such as SCTP 1079 over IP. However, corresponding potential other "m" line proto 1080 values are not considered in this document." 1082 o Replacement of "DTLS connection" with "DTLS association" 1083 throughout the document. 1085 o In sections Section 5.1.1.2 and Section 5.1.2.2 removal of the 1086 sentences "This document also does not specify multiplexing rules 1087 for this attribute for SCTP or SCTP/DTLS proto values". 1089 o In the text related to "Subsequent SDP answer" in section 1090 Section 5.2.5 replacement of "The DTLS/SCTP association remains 1091 open ..." with "The SCTP association remains open ...". 1093 o In the text after the second SDP answer in section Section 6 1094 replacement of "... (after SCTP/DTLS association is setup)" with 1095 "... (after the SCTP association is set up)". 1097 o Addition of [I-D.ietf-mmusic-dtls-sdp] to the list of informative 1098 references. 1100 o Addition of "a=dtls-id" attribute lines to the SDP offer/answer 1101 examples in Section 6. 1103 10.4. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-08' 1105 o Addition of definition of "data channel subprotocol" to Section 3 1106 as proposed on the MMUSIC list, https://www.ietf.org/mail- 1107 archive/web/mmusic/current/msg15827.html. 1109 o Addition of [I-D.ietf-mmusic-rfc4566bis] to list of normative 1110 references. 1112 o Updates of tables in Section 8.2.1 and Section 8.2.2 as per 1113 section 8.2.4 of [I-D.ietf-mmusic-rfc4566bis]. 1115 o Addition of new Section 8.3. 1117 10.5. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-07' 1119 o Addition of two new paragraphs to Section 5.1.2.1 regarding 1120 subprotocol attribute relationship with transport protocol. 1122 o Addition of a note to Section 8.1 regarding subprotocols 1123 simultaneously defined for data channel and Websocket usage. 1125 o Addition of two further SDP offer/answer considerations to 1126 Section 5.2.5 regarding unknown subprotocol attributes and known 1127 subprotocol attributes with unknown data channel transport related 1128 semantic. 1130 10.6. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-06' 1132 o Changes addressing Christian Groves's WGLC review comments raised 1133 in http://www.ietf.org/mail-archive/web/mmusic/current/ 1134 msg15357.html and http://www.ietf.org/mail- 1135 archive/web/mmusic/current/msg15359.html. 1137 10.7. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-05' 1139 o In IANA registration Section 8.2.1 and Section 8.2.2 replacement 1140 of contact name and e-mail address with "MMUSIC Chairs" and 1141 "mmusic-chairs@ietf.org". 1143 o In Section 5.1.2.1 replacement of "Thus in the example above, the 1144 original attribute line "a=accept- types:text/plain" is 1145 represented by the attribute line "a=dcsa:2 accept-types:text/ 1146 plain", which specifies that this instance of MSRP being 1147 transported on the SCTP association using the data channel with 1148 stream id 2 accepts plain text files." with "... which specifies 1149 that this instance of the MSRP subprotocol being transported ...". 1151 o The last paragraph of Section 5.1.2.1 started with "Note: This 1152 document does not provide a complete specification ...". Removal 1153 of "Note:" and move of this paragraph to the introduction in 1154 Section 1 as last paragraph. 1156 o Section 5.1.2's headline was "Subprotocol Specific Attributes". 1157 Change of this headline to "Other Media Level Attributes" and 1158 adaptations of the first paragraph of this section and the first 1159 paragraph of Section 5.1.2.1 in order to clarify that not only 1160 those attributes may be encapsulated in a "dcsa" attribute, which 1161 are specifically defined for the subprotocol, but that also other 1162 attributes may be encapsulated if they are related to the specific 1163 subprotocol instance. 1165 o Move of the last but one paragraph of Section 5.1.2.1 starting 1166 with "The same syntax applies to ..." right in front of the formal 1167 syntax definition of the "dcsa" attribute. 1169 o Modifications of the text in Section 5.1.1.2 and Section 5.1.2.2 1170 in order not to explicitly restrict usage of the "a=dcmap:" and 1171 "a=dcsa:" attributes to "m" lines with proto values "UDP/DTLS/ 1172 SCTP" or "TCP/DTLS/SCTP". 1174 10.8. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-04' 1176 o In Section 5.1.1.5 the first (and only) paragraph was "The 1177 'subprotocol' parameter indicates which protocol the client 1178 expects to exchange via the channel. 'Subprotocol' is an optional 1179 parameter. If the 'subprotocol' parameter is not present, then 1180 its value defaults to the empty string." Replacement of this 1181 paragraph with following two paragraphs: 1183 * The 'subprotocol' parameter indicates which protocol the client 1184 expects to exchange via the channel. This parameter maps to 1185 the 'Protocol' parameter defined in 1186 [I-D.ietf-rtcweb-data-protocol]. Section 8.1 specifies how new 1187 subprotocol parameter values are registered. 'Subprotocol' is 1188 an optional parameter. If the 'subprotocol' parameter is not 1189 present, then its value defaults to the empty string. 1191 * Note: The empty string MAY also be explicitly used as 1192 'subprotocol' value, such that 'subprotocol=""' is equivalent 1193 to the 'subprotocol' parameter not being present at all. 1194 [I-D.ietf-rtcweb-data-protocol] allows the DATA_CHANNEL_OPEN 1195 message's 'Subprotocol' value to be an empty string. 1197 o Addition of [I-D.ietf-mmusic-sdp-mux-attributes] to list the of 1198 normative references. 1200 o Addition of dcmap attribute specific IANA registration 1201 Section 8.2.1. 1203 o Addition of dcsa attribute specific IANA registration 1204 Section 8.2.2. 1206 o Addition of new Section 5.1.1.2 describing the mux category of the 1207 dcmap SDP attribute. This section and the new "a=dcsa:" attribute 1208 related mux category section are similar to the "Mux Category" 1209 sections of the "a=sctp-port:" and "a=max-message-size:" 1210 attributes in [I-D.ietf-mmusic-sctp-sdp]. 1212 o Addition of new Section 5.1.2.2 describing the mux category of the 1213 dcsa SDP attribute. 1215 10.9. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-03' 1217 o In Section 1 replacement of "RTCWeb leaves it open for other 1218 applications to use data channels and its in-band DCEP or out-of- 1219 band non-DCEP protocols for creating them" with "... to use data 1220 channels and its in-band DCEP or other in-band or out-of-band 1221 protocols for creating them". Additionally replacement of "In 1222 particular, the SDP offer generated by the application includes no 1223 channel-specific information" with "... generated by the RTCweb 1224 data channel stack includes no channel-specific information". 1226 o Move of former section 5 ("Data Channels") to new Appendix A and 1227 removal of JavaScript API specific discussions from this moved 1228 text (like mentioning of data channel stack specific states). 1229 Therefore former section 6 ("SDP Offer/Answer Negotiation") is now 1230 Section 5. 1232 o In Section 5: 1234 * Relacement of Section 5's first paragraph "This section defines 1235 a method of non-DCEP negotiation by which two clients can 1236 negotiate data channel-specific and subprotocol-specific 1237 parameters, using the out-of-band SDP offer/answer exchange. 1238 This SDP extension can only be used with the SDP offer/answer 1239 model." with "This section defines an SDP extension by which 1240 two clients can negotiate data channel-specific and 1241 subprotocol-specific parameters without using DCEP 1242 [I-D.ietf-rtcweb-data-protocol]. This SDP extension only 1243 defines usage in the context of SDP offer/answer." 1245 * Addition of new paragraph: "Appendix A provides information how 1246 data channels work in general and especially summarizes some 1247 key aspects, which should be considered for the negotiation of 1248 data channels if DCEP is not used." 1250 o In Section 5.1.1 replacement of "The intention of exchanging these 1251 attributes is to create data channels on both the peers with the 1252 same set of attributes without actually using the DCEP 1253 [I-D.ietf-rtcweb-data-protocol]" with "The intention in exchanging 1254 these attributes is to create, on two peers, without use of DCEP 1255 [I-D.ietf-rtcweb-data-protocol], matched pairs of oppositely 1256 directed data channels having the same set of attributes". 1258 o In Section 5.1.1.6 replacement of "The 'max-retr' parameter 1259 indicates the maximal number a user message will be retransmitted" 1260 with "The 'max-retr' parameter indicates the maximal number of 1261 times a user message will be retransmitted". 1263 o In Section 5.2.1 replacement of "However, an SDP offer/answer 1264 exchange MUST NOT be initiated if the associated SCTP stream is 1265 already negotiated via DCEP" with "However, an SCTP stream MUST 1266 NOT be referenced in a dcmap or dcsa attribute of an SDP offer/ 1267 answer exchange if the associated SCTP stream has already been 1268 negotiated via DCEP". 1270 o In the examples in Section 6 addition of the previously missing 1271 colons to the "a=sctp-port" attribute lines. 1273 10.10. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02' 1275 o Move of reference [I-D.ietf-rtcweb-jsep] from the list of 1276 normative references to the list of informative references. 1278 o Addition of [IANA-SDP-Parameters] to the list of informative 1279 references and addition of following two sentences to the first 1280 paragraph after the ABNF definition: "Note however that not all 1281 SDP attributes are suitable as "a=dcsa:" parameter. 1282 [IANA-SDP-Parameters] contains the lists of IANA registered 1283 session and media level or media level only SDP attributes." 1285 o In the introduction replacement of last sentence "This document 1286 defines SDP-based out-of-band negotiation procedures to establish 1287 data channels for transport of well-defined subprotocols" with 1288 "This document defines SDP offer/answer negotiation procedures to 1289 establish data channels for transport of well-defined 1290 subprotocols, to enable out-of-band negotiation". 1292 o Throughout the document replacement of "external negotiation" with 1293 "SDP offer/answer negotiation" and removal of term "external 1294 negotiation" from the terminology list in Section 3. 1296 o Throughout the document replacement of "internal negotiation" with 1297 "DCEP" and removal of terms "internal negotiation" and "in-band 1298 negotiation" from the terminology list in Section 3. 1300 o Addition of "SCTP Stream Sequence Number (SSN)" to the list of 1301 terms. 1303 o In Section 5.2.1 replacement of sentence "However, a single stream 1304 is managed using one method at a time." with "However, an SDP 1305 offer/answer exchange MUST NOT be initiated if the associated SCTP 1306 stream is already negotiated via DCEP". 1308 o In Section 5.2.2 replacement of sentence "By definition max-retr 1309 and max-time are mutually exclusive, so only one of them can be 1310 present in a=dcmap" with "By definition max-retr and max-time are 1311 mutually exclusive, so at most one of them MAY be present in 1312 a=dcmap". 1314 o Move of reference [WebRtcAPI] from list of normative references to 1315 list of informative references. 1317 o Removal of almost all text parts, which discussed JavaScript or 1318 other API specific aspects. Such API specific aspects were mainly 1319 discussed in sub-sections of Section 5 and Section 5 of draft- 1320 ietf-mmusic-data-channel-sdpneg-02. 1322 10.11. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01' 1324 o New Section 4 regarding applicability to SDP offer/answer only. 1326 o Addition of new Section 8.1 "Subprotocol identifiers" as 1327 subsection of the "IANA Considerations" related Section 8. Also 1328 removal of the temporary note "To be completed. As [I-D.ietf- 1329 rtcweb-data-protocol] this document should refer to IANA's 1330 WebSocket Subprotocol Name Registry defined in [RFC6455]." 1332 o In Section 5.2.2: 1334 * In the first paragraph replacement of the sentence "If an SDP 1335 offer contains both of these parameters then such an SDP offer 1336 will be rejected." with "If an SDP offer contains both of these 1337 parameters then the receiver of such an SDP offer MUST reject 1338 the SDP offer." 1340 * In the second paragraph capitalization of "shall" and "may" 1341 such that both sentences now read: "The SDP answer SHALL echo 1342 the same subprotocol, max-retr, max-time, ordered parameters, 1343 if those were present in the offer, and MAY include a label 1344 parameter. They MAY appear in any order, which could be 1345 different from the SDP offer, in the SDP answer." 1347 * In the third paragraph replacement of the sentence "The same 1348 information MUST be replicated without changes in any 1349 subsequent offer or answer, as long as the data channel is 1350 still opened at the time of offer or answer generation." with 1351 "When sending a subsequent offer or an answer, and for as long 1352 as the data channel is still open, the sender MUST replicate 1353 the same information.". 1355 o In Section 5.2.2 the mapping of data channel types defined in 1356 [I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute 1357 parameters were illustrated using example "a=dcmap" attribute 1358 lines. Replacement of these example "a=dcmap" attribute lines 1359 with just the "a=dcmap" attribute parameters being relevant for 1360 the channel type. 1362 o In Section 5.2.5 the description of bullet point "SDP offer has no 1363 a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer: 1364 No data channel negotiated yet." Replacement of this description 1365 with "Initial SDP offer: No data channel is negotiated yet. The 1366 DTLS connection and SCTP association is negotiated and, if agreed, 1367 established as per [I-D.ietf-mmusic-sctp-sdp]." 1369 o In Section 5.2.5 in both bullet points related to "Subsequent SDP 1370 offer" and "Subsequent SDP answer" replacement of "All the 1371 externally negotiated data channels must be closed now." with "All 1372 the externally negotiated data channels are expected to be closed 1373 now.". 1375 o In Appendix A.2.2's sixth paragraph beginning with "[ASSUMPTION]" 1376 replacement of the two occurrences of "must" with "MUST". 1378 o In Section 5.1.1.1 in the definition of the ABNF rule "dcmap-opt" 1379 there was a comment saying that "Either only maxretr-opt or 1380 maxtime-opt is present. Both MUST not be present." Removal of 1381 the second normative sentence and instead addition of following 1382 new paragraph to the end of this section: "Within an 'a=dcmap' 1383 attribute line's 'dcmap-opt' value either only one 'maxretr-opt' 1384 parameter or one 'maxtime-opt' parameter is present. Both MUST 1385 NOT be present." 1387 o In Section 5.1.1.8 replacement of the first sentence "The 1388 'ordered' parameter with value "true" indicates that DATA chunks 1389 in the channel MUST be dispatched to the upper layer by the 1390 receiver while preserving the order." with "The 'ordered' 1391 parameter with value "true" indicates that the receiver MUST 1392 dispatch DATA chunks in the data channel to the upper layer while 1393 preserving the order.". 1395 o In Section 5.2.3's first paragraph replacement of the one 1396 occurrence of "must" with "..., it MUST wait until ...". 1398 o In Section 5.2.4: 1400 * In the second paragraph replacement of "must" with "... whether 1401 this closing MUST in addition ..." 1403 * In the third paragraph replacement of the sentence "The port 1404 value for the "m" line SHOULD not be changed (e.g., to zero) 1405 when closing a data channel ..." with "The offerer SHOULD NOT 1406 change the port value for the "m" line (e.g., to zero) when 1407 closing a data channel ...". 1409 * In the last but two paragraph replacement of the sentence "... 1410 then an SDP offer which excludes this closed data channel 1411 SHOULD be generated." with "... then the client SHOULD generate 1412 an SDP offer which excludes this closed data channel.". 1414 * In the last but one paragraph replacement of "must" with "The 1415 application MUST also close...". 1417 o In Section 5.1.2 addition of following note after the formal 1418 definition of the 'a=dcsa' attribute: "Note that the above 1419 reference to RFC 4566 defines were the attribute definition can be 1420 found; it does not provide any limitation on support of attributes 1421 defined in other documents in accordance with this attribute 1422 definition." 1424 10.12. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00' 1426 o In Section 3 "WebRTC data channel" was defined as "A bidirectional 1427 channel consisting of paired SCTP outbound and inbound streams." 1428 Replacement of this definition with "Data channel: A WebRTC data 1429 channel as specified in [I-D.ietf-rtcweb-data-channel]", and 1430 consistent usage of "data channel" in the remainder of the 1431 document including the document's headline." 1433 o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in 1434 [I-D.ietf-mmusic-sctp-sdp] may change as that document progresses. 1435 In particular we expect "webrtc-datachannel" to become a more 1436 general term.' 1438 o Consistent usage of '"m" line' in whole document as per [RFC4566]. 1440 o In Section 5.1.1 removal of the example dcmap attribute line 1441 'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are 1442 already four examples right after the ABNF rules in 1443 Section 5.1.1.1. Corresponding removal of following related note: 1444 "Note: This document does not provide a complete specification of 1445 how to negotiate the use of a WebRTC data channel to transport 1446 BFCP. Procedures specific to each subprotocol such as BFCP will 1447 be documented elsewhere. The use of BFCP is only an example of 1448 how the generic procedures described herein might apply to a 1449 specific subprotocol." 1451 o In Section 5.1.1 removal of following note: "Note: This attribute 1452 is derived from attribute "webrtc-DataChannel", which was defined 1453 in old version 03 of the following draft, but which was removed 1454 along with any support for SDP external negotiation in subsequent 1455 versions: [I-D.ietf-mmusic-sctp-sdp]." 1457 o Insertion of following new sentence to the beginning of 1458 Section 5.1.1.1: "dcmap is a media level attribute having 1459 following ABNF syntax:" 1461 o Insertion of new Section 5.1.1.3 containing the dcmap-stream-id 1462 specifying sentence, which previously was placed right before the 1463 formal ABNF rules. Removal of the sentence 'Stream is a mandatory 1464 parameter and is noted directly after the "a=dcmap:" attribute's 1465 colon' as this information is part of the ABNF specification. 1467 o In Section 5.1.1.1 modification of the 'ordering-value' values 1468 from "0" or "1" to "true" or "false". Corresponding text 1469 modifications in Section 5.1.1.8. 1471 o In Section 5.1.1.1 the ABNF definition of "quoted-string" referred 1472 to rule name "escaped-char", which was not defined. Instead a 1473 rule with name "escaped" was defined. Renamed that rule's name to 1474 "escaped-char". 1476 o Insertion of a dedicated note right after the "a=dcmap:4" 1477 attribute example in Section 5.1.1.1 regarding the non-printable 1478 "escaped-char" character within the "label" value. 1480 o In Section 5.1.2's second paragraph replacement of "sctp stream 1481 identifier" with "SCTP stream identifier". 1483 o In first paragraph of Section 5.2.1 replacement of first two 1484 sentences 'For the SDP-based external negotiation described in 1485 this document, the initial offerer based "SCTP over DTLS" owns by 1486 convention the even stream identifiers whereas the initial 1487 answerer owns the odd stream identifiers. This ownership is 1488 invariant for the whole lifetime of the signaling session, e.g. it 1489 does not change if the initial answerer sends a new offer to the 1490 initial offerer.' with 'If an SDP offer/answer exchange (could be 1491 the initial or a subsequent one) results in a UDP/DTLS/SCTP or 1492 TCP/DTLS/SCTP based media description being accepted, and if this 1493 SDP offer/answer exchange results in the establishment of a new 1494 SCTP association, then the SDP offerer owns the even SCTP stream 1495 ids of this new SCTP association and the answerer owns the odd 1496 SCTP stream identifiers. If this "m" line is removed from the 1497 signaling session (its port number set to zero), and if usage of 1498 this or of a new UDP/DTLS/SCTP or TCP/DTLS/SCTP based "m" line is 1499 renegotiated later on, then the even and odd SCTP stream 1500 identifier ownership is redetermined as well as described above.' 1502 o In Section 5.2.3 the first action of an SDP answerer, when 1503 receiving an SDP offer, was described as "Applies the SDP offer. 1504 Note that the browser ignores data channel specific attributes in 1505 the SDP." Replacement of these two sentences with "Parses and 1506 applies the SDP offer. Note that the typical parser normally 1507 ignores unknown SDP attributes, which includes data channel 1508 related attributes." 1510 o In Section 5.2.3 the second sentence of the third SDP answerer 1511 action was "Note that the browser is asked to create data channels 1512 with stream identifiers not "owned" by the agent.". Replacement 1513 of this sentence with "Note that the agent is asked to create data 1514 channels with SCTP stream identifiers contained in the SDP offer 1515 if the SDP offer is accepted." 1517 o In Section 5.2.4 the third paragraph began with "A data channel 1518 can be closed by sending a new SDP offer which excludes the dcmap 1519 and dcsa attribute lines for the data channel. The port value for 1520 the m line should not be changed (e.g., to zero) when closing a 1521 data channel (unless all data channels are being closed and the 1522 SCTP association is no longer needed), since this would close the 1523 SCTP association and impact all of the data channels. If the 1524 answerer accepts the SDP offer then it MUST also exclude the 1525 corresponding attribute lines in the answer. ..." Replacement of 1526 this part with "The intention to close a data channel can be 1527 signaled by sending a new SDP offer which excludes the "a=dcmap:" 1528 and "a=dcsa:" attribute lines for the data channel. The port 1529 value for the "m" line SHOULD not be changed (e.g., to zero) when 1530 closing a data channel (unless all data channels are being closed 1531 and the SCTP association is no longer needed), since this would 1532 close the SCTP association and impact all of the data channels. 1533 If the answerer accepts the SDP offer then it MUST close those 1534 data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were 1535 excluded from the received SDP offer, unless those data channels 1536 were already closed, and it MUST also exclude the corresponding 1537 attribute lines in the answer." 1539 o In Section 5.2.4 the hanging text after the third paragraph was 1540 "This delayed close is to handle cases where a successful SDP 1541 answer is not received, in which case the state of session should 1542 be kept per the last successful SDP offer/answer." Replacement of 1543 this sentence with "This delayed closure is RECOMMENDED in order 1544 to handle cases where a successful SDP answer is not received, in 1545 which case the state of the session SHOULD be kept per the last 1546 successful SDP offer/answer." 1548 o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects 1549 Section 5.1.1 contained already procedural descriptions related to 1550 data channel reliability negotiation. Creation of new 1551 Section 5.2.2 and moval of reliability negotiation related text to 1552 this new section. 1554 10.13. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02' 1556 o Removal of note "[ACTION ITEM]" from section "subprotocol 1557 parameter". As [I-D.ietf-rtcweb-data-protocol] this document 1558 should refer to IANA's WebSocket Subprotocol Name Registry defined 1559 in [RFC6455]. 1561 o In whole document, replacement of "unreliable" with "partially 1562 reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in 1563 [I-D.ietf-rtcweb-data-protocol] in most places. 1565 o Clarification of the semantic if the "max-retr" parameter is not 1566 present in an a=dcmap attribute line. In section "max-retr 1567 parameter" the sentence "The max-retr parameter is optional with 1568 default value unbounded" was replaced with "The max-retr parameter 1569 is optional. If the max-retr parameter is not present, then the 1570 maximal number of retransmissions is determined as per the generic 1571 SCTP retransmission rules as specified in [RFC4960]". 1573 o Clarification of the semantic if the "max-time" parameter is not 1574 present in an a=dcmap attribute line. In section "max-time 1575 parameter" the sentence "The max-time parameter is optional with 1576 default value unbounded" was replaced with "The max-time parameter 1577 is optional. If the max-time parameter is not present, then the 1578 generic SCTP retransmission timing rules apply as specified in 1579 [RFC4960]". 1581 o In section "label parameter" the sentence "Label is a mandatory 1582 parameter." was removed and following new sentences (including the 1583 note) were added: "The 'label' parameter is optional. If it is 1584 not present, then its value defaults to the empty string. Note: 1585 The empty string may also be explicitly used as 'label' value, 1586 such that 'label=""' is equivalent to the 'label' parameter not 1587 being present at all. [I-D.ietf-rtcweb-data-protocol] allows the 1588 DATA_CHANNEL_OPEN message's 'Label' value to be an empty string." 1590 o In section "subprotocol parameter" the sentence "Subprotocol is a 1591 mandatory parameter." was replaced with "'Subprotocol' is an 1592 optional parameter. If the 'subprotocol' parameter is not 1593 present, then its value defaults to the empty string." 1595 o In the "Examples" section, in the first two SDP offer examples in 1596 the a=dcmap attribute lines 'label="BGCP"' was replaced with 1597 'label="BFCP"'. 1599 o In all examples, the "m" line proto value "DTLS/SCTP" was replaced 1600 with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were 1601 replaced with "a=max-message-size" attribute lines, as per draft- 1602 ietf-mmusic-sctp-sdp-12. 1604 10.14. Changes against '-01' 1606 o Formal syntax for dcmap and dcsa attribute lines. 1608 o Making subprotocol as an optional parameter in dcmap. 1610 o Specifying disallowed parameter combinations for max-time and max- 1611 retr. 1613 o Clarifications on WebRTC data channel close procedures. 1615 10.15. Changes against '-00' 1617 o Revisions to identify difference between internal and external 1618 negotiation and their usage. 1620 o Introduction of more generic terminology, e.g. "application" 1621 instead of "browser". 1623 o Clarification of how "max-retr and max-time affect the usage of 1624 unreliable and reliable WebRTC data channels. 1626 o Updates of examples to take into account the SDP syntax changes 1627 introduced with draft-ietf-mmusic-sctp-sdp-07. 1629 o Removal of the SCTP port number from the a=dcmap and a=dcsa 1630 attributes as this is now contained in the a=sctp-port attribute, 1631 and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP 1632 association on top of the DTLS connection. 1634 11. References 1636 11.1. Normative References 1638 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1639 Requirement Levels", BCP 14, RFC 2119, 1640 DOI 10.17487/RFC2119, March 1997, 1641 . 1643 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1644 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1645 July 2006, . 1647 [I-D.ietf-mmusic-rfc4566bis] 1648 Handley, M., Jacobson, V., Perkins, C., and A. Begen, 1649 "SDP: Session Description Protocol", draft-ietf-mmusic- 1650 rfc4566bis-17 (work in progress), June 2016. 1652 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1653 with Session Description Protocol (SDP)", RFC 3264, 1654 DOI 10.17487/RFC3264, June 2002, 1655 . 1657 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1658 Specifications: ABNF", STD 68, RFC 5234, 1659 DOI 10.17487/RFC5234, January 2008, 1660 . 1662 [I-D.ietf-rtcweb-data-channel] 1663 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 1664 Channels", draft-ietf-rtcweb-data-channel-13 (work in 1665 progress), January 2015. 1667 [I-D.ietf-mmusic-sctp-sdp] 1668 Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo, 1669 "Session Description Protocol (SDP) Offer/Answer 1670 Procedures For Stream Control Transmission Protocol (SCTP) 1671 over Datagram Transport Layer Security (DTLS) Transport.", 1672 draft-ietf-mmusic-sctp-sdp-25 (work in progress), March 1673 2017. 1675 [I-D.ietf-mmusic-sdp-mux-attributes] 1676 Nandakumar, S., "A Framework for SDP Attributes when 1677 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 1678 (work in progress), December 2016. 1680 11.2. Informative References 1682 [I-D.ietf-rtcweb-data-protocol] 1683 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 1684 Establishment Protocol", draft-ietf-rtcweb-data- 1685 protocol-09 (work in progress), January 2015. 1687 [I-D.ietf-mmusic-dtls-sdp] 1688 Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer 1689 Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-22 (work 1690 in progress), March 2017. 1692 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1693 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1694 . 1696 [IANA-SDP-Parameters] 1697 "Session Description Protocol (SDP) Parameters", Internet 1698 Assigned Numbers Authority Protocol Assignments Session 1699 Description Protocol (SDP) Parameters, 1700 . 1703 [WebRtcAPI] 1704 Bergkvist, A., Burnett, D., Jennings, C., and A. 1705 Narayanan, "WebRTC 1.0: Real-time Communication Between 1706 Browsers", World Wide Web Consortium WD-webrtc-20150210, 1707 February 2015, 1708 . 1710 Appendix A. Generic Data Channel Negotiation Aspects When Not Using 1711 DCEP 1713 This appendix summarizes how data channels work in general and 1714 discusses some key aspects, which should be considered for the out- 1715 of-band negotiation of data channels if DCEP is not used. 1717 A WebRTC application creates a data channel by providing a number of 1718 setup parameters (subprotocol, label, maximal number of 1719 retransmissions, maximal retransmission time, order of delivery, 1720 priority). The application also specifies if it wants to make use of 1721 the negotiation using the DCEP [I-D.ietf-rtcweb-data-protocol], or if 1722 the application intends to negotiate data channels using the SDP 1723 offer/answer protocol. 1725 In any case, the SDP offer generated by the application is per 1726 [I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one "m" line for 1727 the SCTP association on top of which data channels will run: 1729 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 1730 c=IN IP4 10.10.10.1 1731 a=max-message-size:100000 1732 a=sctp-port:5000 1733 a=dtls-id:abcdef1234567 1734 a=setup:actpass 1735 a=fingerprint:SHA-1 \ 1736 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 1738 Note: A WebRTC application will only use "m" line format "webrtc- 1739 datachannel", and will not use other formats in the "m" line for 1740 other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports 1741 only one SCTP association to be established on top of a DTLS 1742 association. 1744 Note: The above SDP media description does not contain any channel- 1745 specific information. 1747 A.1. Stream Identifier Numbering 1749 Independently from the requested type of negotiation, the application 1750 creating a data channel can either pass the stream identifier to the 1751 data channel stack to assign to the data channel or else let the data 1752 channel stack pick one identifier from the unused ones. 1754 To avoid glare situations, each endpoint can moreover own an 1755 exclusive set of stream identifiers, in which case an endpoint can 1756 only create a data channel with a stream identifier it owns. 1758 Which set of stream identifiers is owned by which endpoint is 1759 determined by convention or other means. 1761 Note:For data channels negotiated with the DCEP, one endpoint owns 1762 by convention the even stream identifiers, whereas the other owns 1763 the odd stream identifiers, as defined in 1764 [I-D.ietf-rtcweb-data-protocol]. 1766 Note:For data channels negotiated via some protocol different from 1767 DCEP, no convention is defined by default. 1769 A.2. Generic Data Channel Negotiation Not Using DCEP 1771 A.2.1. Overview 1773 DCEP negotiation only provides for negotiation of data channel 1774 transport parameters and does not provide for negotiation of 1775 subprotocol specific parameters. DCEP-less data channel negotiation 1776 can be defined to allow negotiation of parameters beyond those 1777 handled by DCEP, e.g., parameters specific to the subprotocol 1778 instantiated on a particular data channel. 1780 The following procedures are common to all methods of data channel 1781 negotiation not using DCEP, whether in-band (communicated using 1782 proprietary means on an already established data channel) or out-of- 1783 band (using SDP offer/answer or some other protocol associated with 1784 the signaling channel). 1786 A.2.2. Opening a Data Channel 1788 In the case of DCEP-less negotiation, the endpoint application has 1789 the option to fully control the stream identifier assignments. 1790 However these assignments have to coexist with the assignments 1791 controlled by the data channel stack for the DCEP negotiated data 1792 channels (if any). It is the responsibility of the application to 1793 ensure consistent assignment of stream identifiers. 1795 When the application requests the creation of a new data channel to 1796 be set up via DCEP-less negotiation, the data channel stack creates 1797 the data channel locally without sending any DATA_CHANNEL_OPEN 1798 message in-band. However, even if the ICE (Interactive Connectivity 1799 Establishment), DTLS and SCTP procedures were already successfully 1800 completed, the application can't send data on this data channel until 1801 the negotiation is complete with the peer. This is because the peer 1802 needs to be aware of and accept the usage of this data channel. The 1803 peer, after accepting the data channel offer, can start sending data 1804 immediately. This implies that the offerer may receive data channel 1805 subprotocol messages before the negotiation is complete and the 1806 application should be ready to handle it. 1808 If the peer rejects the data channel part of the offer then it 1809 doesn't have to do anything as the data channel was not created using 1810 the stack. The offerer on the other hand needs to close the data 1811 channel that was opened by invoking relevant data channel stack API 1812 procedures. 1814 It is also worth noting that a data channel stack implementation may 1815 not provide any API to create and close data channels; instead the 1816 data channels may be used on the fly as needed just by communicating 1817 via non-DCEP means or by even having some local configuration/ 1818 assumptions on both the peers. 1820 The application then negotiates the data channel properties and 1821 subprotocol properties with the peer's application using a mechanism 1822 different from DCEP. 1824 The peer then symmetrically creates a data channel with these 1825 negotiated data channel properties. This is the only way for the 1826 peer's data channel stack to know which properties to apply when 1827 transmitting data on this channel. The data channel stack must allow 1828 data channel creation with any non-conflicting stream identifier so 1829 that both peers can create the data channel with the same stream 1830 identifier. 1832 A.2.3. Closing a Data Channel 1834 When the application requests the closing of a data channel 1835 negotiated without DCEP, the data channel stack always performs an 1836 SCTP SSN reset for this channel. 1838 Depending upon the method used for DCEP-less negotiation and the 1839 subprotocol associated with the data channel, the closing might in 1840 addition be signaled to the peer via SDP offer/answer negotiation. 1842 Authors' Addresses 1844 Keith Drage (editor) 1845 Nokia 1846 Quadrant, Stonehill Green, Westlea 1847 Swindon 1848 UK 1850 Email: Keith.Drage@nokia.com 1852 Maridi R. Makaraju (Raju) 1853 Nokia 1854 2000 Lucent Lane 1855 Naperville, Illinois 1856 US 1858 Email: Raju.Makaraju@nokia.com 1860 Juergen Stoetzer-Bradler 1862 Email: Juergen.S-B.ietf@email.de 1864 Richard Ejzak 1865 Unaffiliated 1867 Email: richard.ejzak@gmail.com 1869 Jerome Marcon 1870 Unaffiliated