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Holmberg 3 Internet-Draft Ericsson 4 Updates: RFC8373 (if approved) September 17, 2019 5 Intended status: Standards Track 6 Expires: March 20, 2020 8 T.140 Real-time Text Conversation over WebRTC Data Channels 9 draft-ietf-mmusic-t140-usage-data-channel-03 11 Abstract 13 This document specifies how a WebRTC data channel can be used as a 14 transport mechanism for Real-time text using the ITU-T Protocol for 15 multimedia application text conversation (Recommendation ITU-T 16 T.140), and how the SDP offer/answer mechanism can be used to 17 negotiate such data channel, referred to as T.140 data channel. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on March 20, 2020. 36 Copyright Notice 38 Copyright (c) 2019 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. WebRTC Data Channel Considerations . . . . . . . . . . . . . 3 56 4. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 4 57 4.1. Use of dcmap Attribute . . . . . . . . . . . . . . . . . 4 58 4.2. Use of dcsa Attribute . . . . . . . . . . . . . . . . . . 5 59 4.2.1. Maximum Character Transmission . . . . . . . . . . . 5 60 4.2.2. Real-time Text Conversation Languages . . . . . . . . 5 61 4.2.3. Real-time Text Direction . . . . . . . . . . . . . . 5 62 4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7 63 5. T.140 Considerations . . . . . . . . . . . . . . . . . . . . 9 64 5.1. Session Layer Functions . . . . . . . . . . . . . . . . . 9 65 5.2. Data Encoding and Sending . . . . . . . . . . . . . . . . 10 66 5.3. Data Buffering . . . . . . . . . . . . . . . . . . . . . 10 67 5.4. Loss of T140blocks . . . . . . . . . . . . . . . . . . . 10 68 5.5. Multi-party Considerations . . . . . . . . . . . . . . . 11 69 6. Gateway Considerations . . . . . . . . . . . . . . . . . . . 11 70 7. Update to RFC 8373 . . . . . . . . . . . . . . . . . . . . . 12 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 72 9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 13 73 9.1. Subprotocol Identifier t140 . . . . . . . . . . . . . . . 13 74 9.2. SDP fmtp Attribute . . . . . . . . . . . . . . . . . . . 13 75 9.3. SDP Language Attributes . . . . . . . . . . . . . . . . . 13 76 9.4. SDP Media Direction Attributes . . . . . . . . . . . . . 14 77 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 78 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 79 11.1. Normative References . . . . . . . . . . . . . . . . . . 16 80 11.2. Informative References . . . . . . . . . . . . . . . . . 17 81 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 83 1. Introduction 85 The ITU-T Protocol for multimedia application text conversation 86 (Recommendation ITU-T T.140) [T140] defines a protocol for text 87 conversation, also known as real-time text. The native transport for 88 IP networks is the "RTP Payload for Text Conversation" [RFC4103] 89 mechanism, based on the Real-time Transport Protocol (RTP) [RFC4103]. 91 This document specifies how a WebRTC data channel 92 [I-D.ietf-rtcweb-data-channel] can be used as a transport mechanism 93 for T.140, and how the SDP offer/answer mechanism 94 [I-D.ietf-mmusic-data-channel-sdpneg] can be used to negotiate such 95 data channel. 97 In this document, a T.140 data channel refers to a WebRTC data 98 channel for which the instantiated sub-protocol is "t140", and where 99 the channel is negotiated using the SDP-based external negotiation 100 method [I-D.ietf-mmusic-data-channel-sdpneg]. 102 NOTE 1: This WebRTC term of a "T.140 data channel" is actually 103 synonym to the originally introduced concept of a "T.140 data 104 channel" for the T.140 protocol, see Section 4.3 of [T140]. 106 NOTE 2: The decision to transport realtime text over a data channel, 107 instead of using RTP based transport [RFC4103], in WebRTC is 108 constituted by use-case "U-C 5: Realtime text chat during an audio 109 and/or video call with an individual or with multiple people in a 110 conference", see Section 3.2 of [I-D.ietf-rtcweb-data-channel]. 112 The brief notation "T.140" is used as a synonym for the text 113 conversation protocol according to [T140]. 115 Section 3 defines the generic data channel properties for a T.140 116 data channel, and Section 4 defines how they are conveyed in an SDP 117 dcmap attribute. While this document defines how to establish a 118 T.140 data channel using the SDP-based external negotiation method 119 [I-D.ietf-mmusic-data-channel-sdpneg], the generic T.140 and gateway 120 considerations defined in Section 3, Section 5 and Section 6 of this 121 document can also be applied when a T.140 data channel is established 122 using another mechanism (e.g., the mechanism defined in 123 [I-D.ietf-rtcweb-data-protocol]). Section 5 of 124 [I-D.ietf-mmusic-data-channel-sdpneg] defines the mapping between the 125 SDP dcmap attribute parameters and the protocol parameters used in 126 [I-D.ietf-rtcweb-data-protocol]. 128 This document is based on an earlier Internet draft edited by Keith 129 Drage, Juergen Stoetzer-Bradler and Albrecht Schwarz. 131 2. Conventions 133 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 134 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 135 "OPTIONAL" in this document are to be interpreted as described in BCP 136 14 [RFC2119] [RFC8174] when, and only when, they appear in all 137 capitals, as shown here. 139 3. WebRTC Data Channel Considerations 141 The following WebRTC data channel property values 142 [I-D.ietf-rtcweb-data-channel] apply to a T.140 data channel: 144 +--------------------------+-------------------------------+ 145 | Subprotocol Identifier | t140 | 146 | Transmission reliability | reliable | 147 | Transmission order | in-order | 148 | Label | See Section 4.1 and Section 6 | 149 +--------------------------+-------------------------------+ 151 4. SDP Considerations 153 The generic SDP considerations, including the SDP Offer/Answer 154 proceudres, for negotiating a WebRTC data channel are defined in 155 [I-D.ietf-mmusic-data-channel-sdpneg]. This section defines the SDP 156 considerations that are specific to a T.140 data channel. 158 4.1. Use of dcmap Attribute 160 An offerer and answerer MUST, in each offer and answer, include an 161 SDP 'dcmap' attribute [I-D.ietf-mmusic-data-channel-sdpneg] in the 162 SDP media descripton (m= section) [RFC4566] describing the SCTP 163 association [RFC4960] used to realize the T.140 data channel. 165 The offerer and answerer MUST include the subprotocol attribute 166 parameter, with a "t140" parameter value, in the 'dcmap' attribute 167 value. 169 The offerer and answerer MAY include the priority attribute parameter 170 and the label attribute parameter in the 'dcmap' attribute value. If 171 the offerer includes a label attribute parameter, the answerer MUST 172 NOT change the value in the answer. 174 NOTE: As specified in [I-D.ietf-rtcweb-data-channel], when a data 175 channel is negotied using the mechanism defined in 176 [I-D.ietf-rtcweb-data-protocol], the label attribute parameter value 177 has to be the same in both directions. That rule also applies to 178 data channels negotiated using the mechanism defined in this 179 document. 181 The offerer and answerer MUST NOT include the max-retr and max-time 182 attribute parameters in the 'dcmap' attribute. 184 If the ordered attribute parameter is included in the 'dcmap' 185 attribute, it MUST be assigned the value 'true'. 187 Below is an example of the 'dcmap' attribute for a T.140 data channel 188 with stream id=3 and without any label: 190 a=dcmap:3 subprotocol="t140" 192 4.2. Use of dcsa Attribute 194 An offerer and answerer MAY, in each offer and answer, include an SDP 195 'dcsa' attribute [I-D.ietf-mmusic-data-channel-sdpneg] in the m= 196 section describing the SCTP association used to realize the T.140 197 data channel. 199 NOTE: At the time of writing this specification, the latest verion of 200 the API defined in [W3C.webrtc] does not support the use of the SDP 201 attributes defined in this section. 203 4.2.1. Maximum Character Transmission 205 A 'dcsa' attribute can contain the SDP 'fmtp' attribute used to 206 indicate a maximum character transmission rate [RFC4103]. The 'cps' 207 attribute parameter is used indicate the maximum character 208 transmission rate that the endpoint that includes the attribute is 209 able to receive. 211 If the 'fmtp' attribute is included, the 'format' attribute parameter 212 MUST be set to "-". 214 If the 'fmtp' attribute is not included, it indicates that no maximum 215 character transmission rate is indicated. It does not mean that the 216 default value of 30 applies [RFC4103]. 218 The offerer and answerer MAY modify the 'cps' attribute parameter 219 value in subsequent offers and answers. 221 NOTE: The 'cps' attribute parameter is especially useful when a T.140 222 data channel endpoint is acting as a gateway [Section 6] and is 223 interworking with a T.140 transport mechanism that have restrictions 224 on how many characters can be sent per second. 226 4.2.2. Real-time Text Conversation Languages 228 'dcsa' attributes can contain the SDP 'hlang-send' and 'hlang-recv' 229 attributes [RFC8373] to negotiate the language to be used for the 230 real-time text conversation. 232 For a T.140 data channel, the modality is "written" [RFC8373]. 234 4.2.3. Real-time Text Direction 236 'dcsa' attributes can contain the SDP 'sendonly', 'recvonly', 237 'sendrecv' and 'inactive' attributes [RFC4566] to negotite the 238 direction in which text can be transmitted in a real-time text 239 conversation. 241 NOTE: A WebRTC data channel is always bi-directional. The usage of 242 the 'dcsa' attribute only affects the direction in which 243 implementations are allowed to transmit text on a T.140 data channel. 245 The offer/answer rules for the direction attributes are based on the 246 rules for unicast streams defined in [RFC3264], as described below. 247 Note that the rules only apply to the direction attributes. 249 Session level direction attributes [RFC4566] have no impact on a 250 T.140 data channel. An offerer and answerer MUST mark the direction 251 of the text by sending a direction attribute inside 'dcsa' attribute. 253 4.2.3.1. Negotiate Text Direction 255 4.2.3.1.1. Generating an Offer 257 If the offerer wishes to both send or receive text on a T.140 data 258 channel, it SHOULD mark the data channel as sendrecv with a 259 'sendrecv' attribute inside a 'dcsa' attribute. If the offerer does 260 not explicitly mark the data channel, a 'sendrecv' attribute inside a 261 'dcsa' attribute is implicitly applied. 263 If the offerer wishes to only send text on a T.140 data channel, it 264 MUST mark the data channel as sendonly with a 'sendonly' attribute 265 inside a 'dcsa' attribute. 267 If the offerer wishes to only receive text on a T.140 data channel, 268 it MUST mark the data channel as recvonly with a 'recvonly' attribute 269 inside a 'dcsa' attribute. 271 If the offerer wishes to neither send or receive text on a T.140 data 272 channel, it MUST mark the data channel as inactive with a 'inactive' 273 attribute inside a 'dcsa' attribute. 275 If the offerer has marked a data channel as sendrecv (implicit or 276 explicit) or recvonly, it MUST be prepared to receive T.140 data as 277 soon as the state of the T.140 data channel allows it. 279 When the offerer receives an answer to the offer, if the answerer has 280 marked a data channel as sendrecv (implicit or explicit) or recvonly 281 in the answer, the offerer can start to send T.140 data as soon as 282 the state of the T.140 data channel allows it. If the answerer has 283 marked the data channel as inactive or sendonly, the offerer MUST NOT 284 send any T.140 data. 286 As the answerer implementation might not support the procedures in 287 this section, if the answerer has not marked the direction of a T.140 288 data channel in accordance with the procedures above, it is 289 RECOMMENDED that the offerer does not process that as an error 290 situation, but rather assume that the answerer might both send and 291 receive T.140 data on the data channel. 293 4.2.3.1.2. Generating an Answer 295 When the answerer accepts an offer, and marks the direction of the 296 text in the corresponding answer, the marking is based on the marking 297 (explicit or implicit) in the offer. 299 If the offerer marked the data channel as sendrecv (implicitly or 300 explicitly), the answerer MUST mark the data channel as sendrecv, 301 sendonly, recvonly or inactive with a 'sendrecv', 'sendonly', 302 'recvonly' respective 'inactive' attribute inside a 'dcsa' attribute. 303 If the answerer does not explicitly mark the data channel, a 304 'sendrecv' attribute inside a 'dcsa' attribute is implicitly applied. 306 If the offerer marked the data channel as sendonly, the answerer MUST 307 mark the data channel as recvonly or inactive with a 'recvonly' 308 respective 'inactive' attribute inside a 'dcsa' attribute. 310 If the offerer marked the data channel as recvonly, the answerer MUST 311 mark the data channel as sendonly or inactive with a 'sendonly' 312 respective 'inactive' attribute inside a 'dcsa' attribute. 314 If the offerer marked the data channel as inactive, the answerer MUST 315 mark the data channel as inactive with a 'inactive' attribute inside 316 a 'dcsa' attribute. 318 If the answerer has marked a data channel as sendrecv or recvonly, it 319 MUST be prepared to receive data as soon as the state of the T.140 320 data channel allows transmission of data. 322 4.2.3.2. Modify Text Direction 324 If an endpoint wishes to modify a previously negotiated text 325 direction in an ongoing session, it MUST initiate an offer that 326 indicates the new direction, following the rules in 327 Section 4.2.3.1.1. If the answerer accepts the offer it follows the 328 procedures in Section 4.2.3.1.2. 330 4.3. Examples 332 Below is an example of an m= section describing a T.140 data channel, 333 without any dcsa attributes. The default text transmission direction 334 "sendrecv", applies. 336 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 337 c=IN IP6 2001:db8::3 338 a=max-message-size:1000 339 a=sctp-port 5000 340 a=dcmap:1 label="text conversation";subprotocol="t140" 342 Below is an example of an m= section describing a T.140 data channel, 343 where the maximum character transmission rate is set to 20, and the 344 text transmission direction is set to "sendrecv". 346 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 347 c=IN IP6 2001:db8::3 348 a=max-message-size:1000 349 a=sctp-port 5000 350 a=dcmap:1 label="text conversation";subprotocol="t140" 351 a=dcsa:1 fmtp:- cps=20 352 a=dcsa:1 sendrecv 354 Below is an example of an m= section of an offer for a T.140 data 355 channel offering real-time text conversation in Spanish and 356 Esperanto, and an m= section in the associated answer accepting 357 Esperanto. 359 Offer: 361 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 362 c=IN IP6 2001:db8::3 363 a=max-message-size:1000 364 a=sctp-port 5000 365 a=dcmap:1 label="ACME customer service";subprotocol="t140" 366 a=dcsa:1 fmtp:- cps=30 367 a=dcsa:1 hlang-send:es eo 368 a=dcsa:1 hlang-recv:es eo 370 Answer: 372 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 373 c=IN IP6 2001:db8::1 374 a=max-message-size:1000 375 a=sctp-port 5000 376 a=dcmap:1 label="ACME customer service";subprotocol="t140" 377 a=dcsa:1 fmtp:- cps=30 378 a=dcsa:1 hlang-send:eo 379 a=dcsa:1 hlang-recv:eo 381 Below is an example of an m= section of an offer for a T.140 data 382 channel where the offerer wishes to only receive real-time text, and 383 an m= section in the associated answer indicating that the answerer 384 will only send real-time text. 386 Offer: 388 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 389 c=IN IP6 2001:db8::3 390 a=max-message-size:1000 391 a=sctp-port 5000 392 a=dcmap:1 label="ACME customer service";subprotocol="t140" 393 a=dcsa:1 recvonly 395 Answer: 397 m=application 911 UDP/DTLS/SCTP webrtc-datachannel 398 c=IN IP6 2001:db8::1 399 a=max-message-size:1000 400 a=sctp-port 5000 401 a=dcmap:1 label="ACME customer service";subprotocol="t140" 402 a=dcsa:1 sendonly 404 5. T.140 Considerations 406 5.1. Session Layer Functions 408 Section 6.1 of [T140] describes the generic T.140 session control 409 functions at high-level and a signalling protocol independent manner. 410 The list below describes how the functions are realized when using a 411 T.140 data channel. 413 o Prepare session: An endpoint can indicate its support of T.140 414 data channels using signalling specific means (e.g., using SIP 415 OPTIONS [RFC3261]), or by indicating the support in an offer or 416 answer (Section 4) 417 o Initiate session: An offer used to request the establishment of a 418 T.140 data channel (Section 4) 419 o Accept session: An answer used to accept a request to establish a 420 T.140 data channel (Section 4) 421 o Deny session: An answer used to reject a request to establish a 422 T.140 data channel, using the generic procedures for rejecting a 423 data channel [I-D.ietf-mmusic-data-channel-sdpneg] 424 o Disconnect session: An offer or answer used to disable a 425 previously established T.140 data channel, using the generic 426 procedures for closing a data channel 427 [I-D.ietf-mmusic-data-channel-sdpneg] 428 o Data: Data sent on an established T.140 data channel (Section 5.2) 430 5.2. Data Encoding and Sending 432 T.140 text is encoded and framed as T140blocks [RFC4103]. 434 Each T140block is sent on the SCTP stream [RFC4960] used to realize 435 the T.140 data channel using standard T.140 transmission procedures 436 [T140]. One or more T140blocks can be sent in a single SCTP user 437 message [RFC4960]. Unlike RTP based transport for realtime text 438 [RFC4103], T.140 data channels do not use redundant transmission of 439 text. The reason for this is that the T.140 data channel achieves 440 robust transmission by using the "reliable" mode of the data channel. 442 Data sending and reporting procedures conform to [T140]. 444 See Section 8 of [T140] for coding details. 446 5.3. Data Buffering 448 As described in [T140], buffering can be used to reduce overhead, 449 with the maximum buffering time being 500 ms. It can also be used 450 for staying within the maximum character transmission rate 451 (Section 4.2), if such has been provided by the peer. 453 An implementation needs to take the user requirements for smooth flow 454 and low latency in real-time text conversation into consideration 455 when assigning a buffer time. It is RECOMMENDED to use the default 456 transmission interval of 300 milliseconds [RFC4103], or lower, for 457 T.140 data channels. 459 5.4. Loss of T140blocks 461 In case of network failure or congestion, T.140 data channels might 462 fail and get torn down. If this happens but the session sustains, it 463 is RECOMMENDED that a low number of retries are made to reestablish 464 the T.140 data channels. If reestablishment of the T.140 data 465 channel is successful, an implementation MUST evaluate if any 466 T140blocks were lost. Retransmission of already successfully 467 transmitted T140blocks MUST be avoided, and missing text markers 468 [T140ad1] SHOULD be inserted in the received data stream where loss 469 is detected or suspected. 471 5.5. Multi-party Considerations 473 If an implementation needs to support multi-party scenarios, the 474 implementation needs to support multiple simultaneous T.140 data 475 channels, one for each remote party. At the time of writing this 476 document, this is true even in scenarios where each participant 477 communicate via a centralized conference server. The reason is that, 478 unlike RTP media, WebRTC data channels and the T.140 protocol do not 479 support the indication of the source of T.140 data. The SDP 'dcmap' 480 attribute label attribute parameter (Section 4.1) can be used by the 481 offerer to provide additional information about each T.140 data 482 channel, and help implementations to distinguish between them. 484 NOTE: Future extensions to T.140, or to the T140block, might allow 485 indicating the source of T.140 data, in which case it might be 486 possible to use a single T.140 data channel to transport data from 487 multiple remote sources. That is useful for multi-party aware 488 clients that are able present the conference in a way that is adapted 489 to user expectations regarding presentation style and real-time 490 performance. Conference mixers that use a single T.140 data channel 491 to transmit real-time text towards clients might, without any 492 protocol extensions, produce a multi-party presentation completely 493 within the text stream, and with limitations in real-time performance 494 and presentation style. 496 6. Gateway Considerations 498 A number of real-time text transports and protocols have been defined 499 for both packet switched and circuit switched networks. Many are 500 based on the ITU-T T.140 protocol on application and presentation 501 level [T140]. At the time of writing this document, some mechanisms 502 are no longer used, as the technologies they use have been obsoleted 503 etc, while others are still in use. 505 When performing interworking between T.140 data channels and real- 506 time text in other transports and protocols, a number of factors need 507 to be considered. At the time of writing this document, the most 508 common IP-based real-time text transport is the RTP based mechanism 509 defined in [RFC4103]. While this document does not define a complete 510 interworking solution, this list below provides some guidance and 511 considerations to take into account when designing a gateway for 512 interworking between T.140 data channels and RTP-based T.140 513 transport: 515 o For each T.140 data channel there is an RTP stream for real-time 516 text [RFC4103] . Redundancy is by default declared and used on 517 RTP stream. On the T.140 data channel there is no redundancy, but 518 the reliable property [I-D.ietf-mmusic-data-channel-sdpneg] of 519 T.140 the data channel is set. 520 o During a normal text flow, T140blocks received from one network 521 are forwarded towards the other network. Keep-alive traffic is 522 implicit on the T.140 data channel. A gateway might have to 523 extract keep-alives from incoming RTP streams, and MAY generate 524 keep-alives on outgoing RTP streams. 525 o If the gateway detects or suspects loss of data on the RTP stream, 526 the gateway gateway SHOULD insert the T.140 missing text marker 527 [T140ad1] in the data sent on the outgoing T.140 data channel. 528 o If the gateway detects that the T.140 data channel has failed and 529 got torn down, once the data channel has been reestablished the 530 gateway SHOULD insert the T.140 missing text marker [T140ad1] in 531 the data sent on the outgoing RTP stream if it detects or suspects 532 that data on the T.140 data channel was lost. 533 o The gateway MUST indicate the same text transmission direction 534 (Section 4.2.3) on the T.140 data channel and the RTP stream. 536 NOTE: In order for the gateway to insert a missing text marker, or to 537 perform other actions that require that the gateway has access to the 538 T.140 data, the T.140 data cannot be encrypted end-to-end between the 539 T.140 data channel endpoint and the RTP endpoint. At the time of 540 writing this document, a mechanism to provide such end-to-end 541 encryption has not been defined. 543 7. Update to RFC 8373 545 This document updates RFC 8373, by defining how the SDP hlang-send 546 and hlang-recv attributes are used for the "application/webrtc- 547 datachannel" media type. 549 SDP offerers and answerers MUST NOT include the attributes directly 550 in the m= section associated with the 'application/webrtc- 551 datachannel' media type. Instead, the attributes MUST be associated 552 with individual data channels, using the SDP 'dcsa' attribute. A 553 specification that defines a subprotocol that uses the attributes 554 MUST specify the modality for that subprotocol, or how to retreive 555 the modality if the subprotocol supports multiple modalities. 557 8. Security Considerations 559 The generic security considerations for WebRTC data channels are 560 defined in [I-D.ietf-rtcweb-data-channel]. As data channels are 561 always encrypted by design, the T.140 data channels will also be 562 encrypted. 564 The generic security considerations for the SDP-based external 565 negotiation method are defined in 566 [I-D.ietf-mmusic-data-channel-sdpneg]. 568 9. IANA considerations 570 [RFC EDITOR NOTE: Please replace all instances of RFCXXXX with the 571 RFC number of this document.] 573 9.1. Subprotocol Identifier t140 575 This document adds the subprotocol identifier "t140" to the 576 "WebSocket Subprotocol Name Registry" as follows: 578 +--------------------------+-------------+ 579 | Subprotocol Identifier: | t140 | 580 | Subprotocol Common Name: | ITU-T T.140 | 581 | Subprotocol Definition: | RFCXXXX | 582 | Reference: | RFCXXXX | 583 +--------------------------+-------------+ 585 9.2. SDP fmtp Attribute 587 This document modifies the usage of the SDP 'fmtp' attribute, if this 588 attribute is included in an SDP 'dcsa' attribute and associated with 589 an T.140 real-time text session over a WebRTC data channel. The 590 modified usage is described in Section 4.2.1. 592 The usage level "dcsa(t140)" is added to the IANA registration of the 593 SDP 'fmtp' attribute as follows: 595 +-----------------------+-------------------------------------------+ 596 | Contact name: | MMUSIC Chairs | 597 | Contact email: | mmusic-chairs@ietf.org | 598 | Attribute name: | fmtp | 599 | Usage level: | dcsa(t140) | 600 | Purpose: | Indicate the maximum transmission rate | 601 | | that an endpoint is willing to recive on | 602 | | a T.140 data channel. | 603 | Reference: | RFCXXXX | 604 +-----------------------+-------------------------------------------+ 606 9.3. SDP Language Attributes 608 This document modifies the usage of the SDP 'hlang-send' and 'hlang- 609 recv' attributes, if these attributes are included in SDP 'dcsa' 610 attributes associated with an T.140 data channel. The modified usage 611 is described in Section 4.2.2. 613 The usage level "dcsa(t140)" is added to the IANA registration of the 614 SDP 'hlang-send' attribute as follows: 616 +-----------------------+-------------------------------------------+ 617 | Contact name: | MMUSIC Chairs | 618 | Contact email: | mmusic-chairs@ietf.org | 619 | Attribute name: | hlang-send | 620 | Usage level: | dcsa(t140) | 621 | Purpose: | Negotiate the language to be used on a | 622 | | T.140 data channel. | 623 | Reference: | RFCXXXX | 624 +-----------------------+-------------------------------------------+ 626 The usage level "dcsa(t140)" is added to the IANA registration of the 627 SDP 'hlang-recv' attribute as follows: 629 +-----------------------+-------------------------------------------+ 630 | Contact name: | MMUSIC Chairs | 631 | Contact email: | mmusic-chairs@ietf.org | 632 | Attribute name: | hlang-recv | 633 | Usage level: | dcsa(t140) | 634 | Purpose: | Negotiate the language to be used on a | 635 | | T.140 data channel. | 636 | Reference: | RFCXXXX | 637 +-----------------------+-------------------------------------------+ 639 9.4. SDP Media Direction Attributes 641 This document modifies the usage of the SDP 'sendonly', 'recvonly', 642 'sendrecv' and 'inactive' attributes, if these attributes are 643 included in SDP 'dcsa' attributes associated T.140 data channel. The 644 modified usage is described in Section 4.2.3. 646 The usage level "dcsa(t140)" is added to the IANA registration of the 647 SDP 'sendonly' attribute as follows: 649 +-----------------------+-------------------------------------------+ 650 | Contact name: | MMUSIC Chairs | 651 | Contact email: | mmusic-chairs@ietf.org | 652 | Attribute name: | sendonly | 653 | Usage level: | dcsa(t140) | 654 | Purpose: | Negotiate the direction in which real- | 655 | | time text can be sent on a T.140 data | 656 | | channel. | 657 | Reference: | RFCXXXX | 658 +-----------------------+-------------------------------------------+ 659 The usage level "dcsa(t140)" is added to the IANA registration of the 660 SDP 'recvonly' attribute as follows: 662 +-----------------------+-------------------------------------------+ 663 | Contact name: | MMUSIC Chairs | 664 | Contact email: | mmusic-chairs@ietf.org | 665 | Attribute name: | recvonly | 666 | Usage level: | dcsa(t140) | 667 | Purpose: | Negotiate the direction in which real- | 668 | | time text can be sent on a T.140 data | 669 | | channel. | 670 | Reference: | RFCXXXX | 671 +-----------------------+-------------------------------------------+ 673 The usage level "dcsa(t140)" is added to the IANA registration of the 674 SDP 'sendrecv' attribute as follows: 676 +-----------------------+-------------------------------------------+ 677 | Contact name: | MMUSIC Chairs | 678 | Contact email: | mmusic-chairs@ietf.org | 679 | Attribute name: | sendrecv | 680 | Usage level: | dcsa(t140) | 681 | Purpose: | Negotiate the direction in which real- | 682 | | time text can be sent on a T.140 data | 683 | | channel. | 684 | Reference: | RFCXXXX | 685 +-----------------------+-------------------------------------------+ 687 The usage level "dcsa(t140)" is added to the IANA registration of the 688 SDP 'inactive' attribute as follows: 690 +-----------------------+-------------------------------------------+ 691 | Contact name: | MMUSIC Chairs | 692 | Contact email: | mmusic-chairs@ietf.org | 693 | Attribute name: | inactive | 694 | Usage level: | dcsa(t140) | 695 | Purpose: | Negotiate the direction in which real- | 696 | | time text can be sent on a T.140 data | 697 | | channel. | 698 | Reference: | RFCXXXX | 699 +-----------------------+-------------------------------------------+ 701 10. Acknowledgements 703 This document is based on an earlier Internet draft edited by Keith 704 Drage, Juergen Stoetzer-Bradler and Albrecht Schwarz. 706 Thomas Belling provided useful comments on the initial (pre- 707 submission) version of the draft. Gunnar Hellstrom provided comments 708 and text on the draft. 710 11. References 712 11.1. Normative References 714 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 715 Requirement Levels", BCP 14, RFC 2119, 716 DOI 10.17487/RFC2119, March 1997, . 719 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 720 with Session Description Protocol (SDP)", RFC 3264, 721 DOI 10.17487/RFC3264, June 2002, . 724 [RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text 725 Conversation", RFC 4103, DOI 10.17487/RFC4103, June 2005, 726 . 728 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 729 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 730 July 2006, . 732 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 733 RFC 4960, DOI 10.17487/RFC4960, September 2007, 734 . 736 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 737 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 738 May 2017, . 740 [RFC8373] Gellens, R., "Negotiating Human Language in Real-Time 741 Communications", RFC 8373, DOI 10.17487/RFC8373, May 2018, 742 . 744 [I-D.ietf-rtcweb-data-channel] 745 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 746 Channels", draft-ietf-rtcweb-data-channel-13 (work in 747 progress), January 2015. 749 [I-D.ietf-mmusic-data-channel-sdpneg] 750 Drage, K., Makaraju, M., Ejzak, R., Marcon, J., and R. 751 Even, "SDP-based Data Channel Negotiation", draft-ietf- 752 mmusic-data-channel-sdpneg-28 (work in progress), May 753 2019. 755 [T140] ITU-T, "Recommendation ITU-T T.140 (02/1998), "Protocol 756 for multimedia application text conversation"", February 757 1998. 759 [T140ad1] ITU-T, "Recommendation ITU-T.140 aEUR" Addendum 1 760 (02/2000), "Protocol for multimedia application text 761 conversation"", February 2000. 763 11.2. Informative References 765 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 766 A., Peterson, J., Sparks, R., Handley, M., and E. 767 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 768 DOI 10.17487/RFC3261, June 2002, . 771 [I-D.ietf-rtcweb-data-protocol] 772 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 773 Establishment Protocol", draft-ietf-rtcweb-data- 774 protocol-09 (work in progress), January 2015. 776 [W3C.webrtc] 777 Bergkvist, A., Burnett, D., Jennings, C., Narayanan, A., 778 Aboba, B., and T. Brandstetter, "WebRTC 1.0: Real-time 779 Communication Between Browsers", World Wide Web Consortium 780 WD CR-webrtc-20180927, September 2018, 781 . 783 Author's Address 785 Christer Holmberg 786 Ericsson 787 Hirsalantie 11 788 Jorvas 02420 789 Finland 791 Email: christer.holmberg@ericsson.com