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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Gellens 3 Internet-Draft Core Technology Consulting 4 Intended status: Standards Track July 21, 2016 5 Expires: January 22, 2017 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-04 10 Abstract 12 Users have various human (natural) language needs, abilities, and 13 preferences regarding spoken, written, and signed languages. When 14 establishing interactive communication ("calls") there needs to be a 15 way to negotiate (communicate and match) the caller's language and 16 media needs with the capabilities of the called party. This is 17 especially important with emergency calls, where a call can be 18 handled by a call taker capable of communicating with the user, or a 19 translator or relay operator can be bridged into the call during 20 setup, but this applies to non-emergency calls as well (as an 21 example, when calling a company call center). 23 This document describes the need and a solution using new SDP stream 24 attributes. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on January 22, 2017. 43 Copyright Notice 45 Copyright (c) 2016 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 62 3. Expected Use . . . . . . . . . . . . . . . . . . . . . . . . 5 63 4. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5 64 5. The existing 'lang' attribute . . . . . . . . . . . . . . . . 6 65 6. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 6 66 6.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 6 67 6.2. New 'humintlang-send' and 'humintlang-recv' attributes . 6 68 6.3. Advisory vs Required . . . . . . . . . . . . . . . . . . 8 69 6.4. Silly States . . . . . . . . . . . . . . . . . . . . . . 9 70 6.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 71 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 73 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10 74 10. Changes from Previous Versions . . . . . . . . . . . . . . . 10 75 10.1. Changes from draft-ietf-slim-...-02 to draft-ietf- 76 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . 10 77 10.2. Changes from draft-ietf-slim-...-01 to draft-ietf- 78 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . 10 79 10.3. Changes from draft-ietf-slim-...-00 to draft-ietf- 80 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . 10 81 10.4. Changes from draft-gellens-slim-...-03 to draft-ietf- 82 slim-...-00 . . . . . . . . . . . . . . . . . . . . . . 11 83 10.5. Changes from draft-gellens-slim-...-02 to draft-gellens- 84 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . 11 85 10.6. Changes from draft-gellens-slim-...-01 to draft-gellens- 86 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . 11 87 10.7. Changes from draft-gellens-slim-...-00 to draft-gellens- 88 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . 11 89 10.8. Changes from draft-gellens-mmusic-...-02 to draft- 90 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . 11 91 10.9. Changes from draft-gellens-mmusic-...-01 to -02 . . . . 11 92 10.10. Changes from draft-gellens-mmusic-...-00 to -01 . . . . 12 93 10.11. Changes from draft-gellens-...-02 to draft-gellens- 94 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . 12 95 10.12. Changes from draft-gellens-...-01 to -02 . . . . . . . . 12 96 10.13. Changes from draft-gellens-...-00 to -01 . . . . . . . . 13 97 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 98 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 99 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 100 13.1. Normative References . . . . . . . . . . . . . . . . . . 13 101 13.2. Informational References . . . . . . . . . . . . . . . . 14 102 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 14 103 A.1. Use of Caller Preferences Without Additions . . . . . . . 15 104 A.2. Additional Caller Preferences for Asymmetric Needs . . . 17 105 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 17 106 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 18 107 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18 109 1. Introduction 111 A mutually comprehensible language is helpful for human 112 communication. This document addresses the real-time, interactive 113 side of the issue. A companion document on language selection in 114 email [I-D.ietf-slim-multilangcontent] addresses the non-real-time 115 side. 117 When setting up interactive communication sessions (using SIP or 118 other protocols), human (natural) language and media modality (voice, 119 video, text) negotiation may be needed. Unless the caller and callee 120 know each other or there is contextual or out of band information 121 from which the language(s) and media modalities can be determined, 122 there is a need for spoken, signed, or written languages to be 123 negotiated based on the caller's needs and the callee's capabilities. 124 This need applies to both emergency and non-emergency calls. For 125 various reasons, including the ability to establish multiple streams 126 using different media (e.g., voice, text, video), it makes sense to 127 use a per-stream negotiation mechanism, in this case, SDP. 129 This approach has a number of benefits, including that it is generic 130 (applies to all interactive communications negotiated using SDP) and 131 not limited to emergency calls. In some cases such a facility isn't 132 needed, because the language is known from the context (such as when 133 a caller places a call to a sign language relay center, to a friend, 134 or colleague). But it is clearly useful in many other cases. For 135 example, someone calling a company call center or a Public Safety 136 Answering Point (PSAP) should be able to indicate if one or more 137 specific signed, written, and/or spoken languages are preferred, the 138 callee should be able to indicate its capabilities in this area, and 139 the call proceed using in-common language(s) and media forms. 141 Since this is a protocol mechanism, the user equipment (UE client) 142 needs to know the user's preferred languages; a reasonable technique 143 could include a configuration mechanism with a default of the 144 language of the user interface. In some cases, a UE could tie 145 language and media preferences, such as a preference for a video 146 stream using a signed language and/or a text or audio stream using a 147 written/spoken language. 149 Including the user's human (natural) language preferences in the 150 session establishment negotiation is independent of the use of a 151 relay service and is transparent to a voice service provider. For 152 example, assume a user within the United States who speaks Spanish 153 but not English places a voice call. The call could be an emergency 154 call or perhaps to an airline reservation desk. The language 155 information is transparent to the voice service provider, but is part 156 of the session negotiation between the UE and the terminating entity. 157 In the case of a call to e.g., an airline, the call could be 158 automatically handled by a Spanish-speaking agent. In the case of an 159 emergency call, the Emergency Services IP network (ESInet) and the 160 PSAP may choose to take the language and media preferences into 161 account when determining how to process the call. 163 By treating language as another attribute that is negotiated along 164 with other aspects of a media stream, it becomes possible to 165 accommodate a range of users' needs and called party facilities. For 166 example, some users may be able to speak several languages, but have 167 a preference. Some called parties may support some of those 168 languages internally but require the use of a translation service for 169 others, or may have a limited number of call takers able to use 170 certain languages. Another example would be a user who is able to 171 speak but is deaf or hard-of-hearing and requires a voice stream plus 172 a text stream (known as voice carry over). Making language a media 173 attribute allows the standard session negotiation mechanism to handle 174 this by providing the information and mechanism for the endpoints to 175 make appropriate decisions. 177 Regarding relay services, in the case of an emergency call requiring 178 sign language such as ASL, there are two common approaches: the 179 caller initiates the call to a relay center, or the caller places the 180 call to emergency services (e.g., 911 in the U.S. or 112 in Europe). 181 (In a variant of the second case, the voice service provider invokes 182 a relay service as well as emergency services.) In the former case, 183 the language need is ancillary and supplemental. In the non-variant 184 second case, the ESInet and/or PSAP may take the need for sign 185 language into account and bridge in a relay center. In this case, 186 the ESInet and PSAP have all the standard information available (such 187 as location) but are able to bridge the relay sooner in the call 188 processing. 190 By making this facility part of the end-to-end negotiation, the 191 question of which entity provides or engages the relay service 192 becomes separate from the call processing mechanics; if the caller 193 directs the call to a relay service then the human language 194 negotiation facility provides extra information to the relay service 195 but calls will still function without it; if the caller directs the 196 call to emergency services, then the ESInet/PSAP are able to take the 197 user's human language needs into account, e.g., by assigning to a 198 specific queue or call taker or bridging in a relay service or 199 translator. 201 The term "negotiation" is used here rather than "indication" because 202 human language (spoken/written/signed) is something that can be 203 negotiated in the same way as which forms of media (audio/text/video) 204 or which codecs. For example, if we think of non-emergency calls, 205 such as a user calling an airline reservation center, the user may 206 have a set of languages he or she speaks, with perhaps preferences 207 for one or a few, while the airline reservation center will support a 208 fixed set of languages. Negotiation should select the user's most 209 preferred language that is supported by the call center. Both sides 210 should be aware of which language was negotiated. This is 211 conceptually similar to the way other aspects of each media stream 212 are negotiated using SDP (e.g., media type and codecs). 214 2. Terminology 216 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 217 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 218 document are to be interpreted as described in RFC 2119 [RFC2119]. 220 3. Expected Use 222 This facility may be used by NENA and 3GPP. NENA has already 223 referenced it in NENA 08-01 (i3 Stage 3 version 2) in describing 224 attributes of calls presented to an ESInet, and may add further 225 details in that or other documents. 3GPP may reference this 226 mechanism in general call handling and emergency call handling. Some 227 CRs introduced in SA1 have anticipated this functionality being 228 provided within SDP. 230 4. Desired Semantics 232 The desired solution is a media attribute (preferably per direction) 233 that may be used within an offer to indicate the preferred language 234 of each (direction of a) media stream, and within an answer to 235 indicate the accepted language. The semantics of including multiple 236 values for a media stream within an offer is that the languages are 237 listed in order of preference. 239 (Negotiating multiple simultaneous languages within a media stream is 240 out of scope, as the complexity of doing so outweighs the 241 usefulness.) 243 5. The existing 'lang' attribute 245 RFC 4566 [RFC4566] specifies an attribute 'lang' which appears 246 similar to what is needed here, but is not sufficiently detailed for 247 use here. In addition, it does not seem to be in common use, which 248 means there is low risk of conflict or confusion in defining new 249 attributes. Further, there is value in being able to specify 250 language per direction (sending and receiving). This document 251 therefore defines two new attributes. 253 6. Proposed Solution 255 An SDP attribute (per direction) seems the natural choice to 256 negotiate human (natural) language of an interactive media stream. 257 The attribute value should be a language tag per RFC 5646 [RFC5646] 259 6.1. Rationale 261 The decision to base the proposal at the media negotiation level, and 262 specifically to use SDP, came after significant debate and 263 discussion. From an engineering standpoint, it is possible to meet 264 the objectives using a variety of mechanisms, but none are perfect. 265 None of the proposed alternatives was clearly better technically in 266 enough ways to win over proponents of the others, and none were 267 clearly so bad technically as to be easily rejected. As is often the 268 case in engineering, choosing the solution is a matter of balancing 269 trade-offs, and ultimately more a matter of taste than technical 270 merit. The two main proposals were to use SDP and SIP. SDP has the 271 advantage that the language is negotiated with the media to which it 272 applies, while SIP has the issue that the languages expressed may not 273 match the SDP media negotiated (for example, a session could 274 negotiate video at the SIP level but fail to negotiate any video 275 media stream at the SDP layer). 277 The mechanism described here for SDP can be adapted to media 278 negotiation protocols other than SDP. 280 6.2. New 'humintlang-send' and 'humintlang-recv' attributes 282 Rather than re-use 'lang' we define two new media-level attributes 283 starting with 'humintlang' (short for "human interactive language") 284 to negotiate which human language is used in each (interactive) media 285 stream. There are two attributes, one ending in "-send" and the 286 other in "-recv": 288 a=humintlang-send: 289 a=humintlang-recv: 291 Each can appear multiple times in an offer for a media stream. 293 In an offer, 'humintlang-send' indicates the language(s) the offerer 294 is willing to use when sending using the media, and 'humintlang-recv' 295 indicates the language(s) the offerer is willing to use when 296 receiving using the media. The values constitute a list of languages 297 in preference order (first is most preferred). When a media is 298 intended for use in one direction only (such as a speech-impaired 299 user sending using text and receiving using audio), either 300 humintlang-send or humintlang-recv MAY be omitted. When a media is 301 not primarily intended for language (for example, a video or audio 302 stream intended for background only) both SHOULD be omitted. 303 Otherwise, both SHOULD have the same values in the same order. The 304 two SHOULD NOT be set to languages which are difficult to match 305 together (e.g., specifying a desire to send audio in Hungarian and 306 receive audio in Portuguese will make it difficult to successfully 307 complete the call). 309 In an answer, 'humintlang-send' is the accepted language the answerer 310 will send (which in most cases is one of the languages in the offer's 311 'humintlang-recv'), and 'humintlang-recv' is the accepted language 312 the answerer expects to receive (which in most cases is one of the 313 languages in the offer's 'humintlang-send'). 315 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 316 describes mechanisms for matching language tags. While RFC 5646 317 provides a mechanism accommodating increasingly fine-grained 318 distinctions, in the interest of maximum interoperability for real- 319 time interactive communications, each 'humintlang-send' and 320 'humintlang-recv' value SHOULD be restricted to the largest 321 granularity of language tags; in other words, it is RECOMMENDED to 322 specify only a Primary-subtag and NOT to include subtags (e.g., for 323 region or dialect) unless the languages might be mutually 324 incomprehensible without them. 326 In an offer, each language tag value MAY have an asterisk appended as 327 the last character (after the registry value). The asterisk 328 indicates a request by the caller to not fail the call if there is no 329 language in common. See Section 6.3 for more information and 330 discussion. 332 When placing an emergency call, and in any other case where the 333 language cannot be assumed from context, each media stream in an 334 offer primarily intended for human language communication SHOULD 335 specify both (or in some cases, one of) the 'humintlang-send' and 336 'humintlang-recv' attributes. 338 Note that while signed language tags are used with a video stream to 339 indicate sign language, a spoken language tag for a video stream in 340 parallel with an audio stream with the same spoken language tag 341 indicates a request for a supplemental video stream to see the 342 speaker. 344 Clients acting on behalf of end users are expected to set one or both 345 'humintlang-send' and 'humintlang-recv' attributes on each media 346 stream primarily intended for human communication in an offer when 347 placing an outgoing session, and either ignore or take into 348 consideration the attributes when receiving incoming calls, based on 349 local configuration and capabilities. Systems acting on behalf of 350 call centers and PSAPs are expected to take into account the values 351 when processing inbound calls. 353 Note that media and language negotiation might result in more media 354 streams being accepted than are needed by the users (e.g., if more 355 preferred and less preferred combinations of media and language are 356 all accepted). 358 6.3. Advisory vs Required 360 One important consideration with this mechanism is if the call fails 361 if the callee does not support any of the languages requested by the 362 caller. 364 In order to provide for maximum likelihood of a successful 365 communication session, especially in the case of emergency calling, 366 the mechanism defined here provides a way for the caller to indicate 367 a preference for the call failing or succeeding when there is no 368 language in common. However, the callee is NOT REQUIRED to honor 369 this preference. For example, a PSAP MAY choose to attempt the call 370 even with no language in common, while a corporate call center MAY 371 choose to fail the call. 373 The mechanism for indicating this preference is that, in an offer, if 374 the last character of any of the 'humintlang-recv' or 'humintlang- 375 send' values is an asterisk, this indicates a request to not fail the 376 call (similar to SIP Accept-Language syntax). Either way, the called 377 party MAY ignore this, e.g., for the emergency services use case, a 378 PSAP will likely not fail the call. 380 6.4. Silly States 382 It is possible to specify a "silly state" where the language 383 specified does not make sense for the media type, such as specifying 384 a signed language for an audio media stream. 386 An offer MUST NOT be created where the language does not make sense 387 for the media type. If such an offer is received, the receiver MAY 388 reject the media, ignore the language specified, or attempt to 389 interpret the intent (e.g., if American Sign Language is specified 390 for an audio media stream, this might be interpreted as a desire to 391 use spoken English). 393 A spoken language tag for a video stream in conjunction with an audio 394 stream with the same language might indicate a request for 395 supplemental video to see the speaker. 397 6.5. Examples 399 Some examples are shown below. Only the most directly relevant 400 portions of the SDP block are shown, for clarity. 402 m=audio 49170 RTP/AVP 0 403 a=humintlang-send:en 404 a=humintlang-recv:en 406 m=video 51372 RTP/AVP 31 32 407 a=humintlang-send:ase* 408 a=humintlang-recv:ase* 410 m=audio 49250 RTP/AVP 20 411 a=humintlang-send:es* 412 a=humintlang-recv:es* 413 a=humintlang-send:eu* 414 a=humintlang-recv:eu* 415 a=humintlang-send:en* 416 a=humintlang-recv:en* 418 m=text 45020 RTP/AVP 103 104 419 a=humintlang-send:gr 420 a=humintlang-recv:gr 422 7. IANA Considerations 424 IANA is kindly requested to add two entries to the 'att-field (media 425 level only)' table of the SDP parameters registry: 427 +------------------------------+-----------------+-----------------+ 428 | Type | Name | Reference | 429 +------------------------------+-----------------+-----------------+ 430 | att-field (media level only) | humintlang-send | (this document) | 431 | att-field (media level only) | humintlang-recv | (this document) | 432 +------------------------------+-----------------+-----------------+ 434 Table 1: att-field (media level only)' entries 436 8. Security Considerations 438 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 439 use of that RFC). In addition, if the 'humintlang-send' or 440 'humintlang-recv' values are altered or deleted en route, the session 441 could fail or languages incomprehensible to the caller could be 442 selected; however, this is also a risk if any SDP parameters are 443 modified en route. 445 9. Privacy Considerations 447 Language and media information can suggest a user's nationality, 448 background, abilities, disabilities, etc. 450 10. Changes from Previous Versions 452 10.1. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 454 o Added Examples 455 o Added Privacy Considerations section 456 o Other editorial changes for clarity 458 10.2. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 460 o Deleted most of Section 5 and replaced with a very short summary 461 o Replaced "wishes to" with "is willing to" in Section 6.2 462 o Reworded description of attribute usage to clarify when to set 463 both, only one, or neither 464 o Deleted all uses of "IMS" 465 o Other editorial changes for clarity 467 10.3. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 469 o Editorial changes to wording in Section 5. 471 10.4. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 473 o Updated title to reflect WG adoption 475 10.5. Changes from draft-gellens-slim-...-02 to draft-gellens- 476 slim-...-03 478 o Removed Use Cases section, per face-to-face discussion at IETF 93 479 o Removed discussion of routing, per face-to-face discussion at IETF 480 93 482 10.6. Changes from draft-gellens-slim-...-01 to draft-gellens- 483 slim-...-02 485 o Updated NENA usage mention 486 o Removed background text reference to draft-saintandre-sip-xmpp- 487 chat-04 since that draft expired 489 10.7. Changes from draft-gellens-slim-...-00 to draft-gellens- 490 slim-...-01 492 o Revision to keep draft from expiring 494 10.8. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 495 slim-...-00 497 o Changed name from -mmusic- to -slim- to reflect proposed WG name 498 o As a result of the face-to-face discussion in Toronto, the SDP vs 499 SIP issue was resolved by going back to SDP, taking out the SIP 500 hint, and converting what had been a set of alternate proposals 501 for various ways of doing it within SIP into an informative annex 502 section which includes background on why SDP is the proposal 503 o Added mention that enabling a mutually comprehensible language is 504 a general problem of which this document addresses the real-time 505 side, with reference to [I-D.ietf-slim-multilangcontent] which 506 addresses the non-real-time side. 508 10.9. Changes from draft-gellens-mmusic-...-01 to -02 510 o Added clarifying text on leaving attributes unset for media not 511 primarily intended for human language communication (e.g., 512 background audio or video). 513 o Added new section Appendix A ("Alternative Proposal: Caller- 514 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 515 level. 517 10.10. Changes from draft-gellens-mmusic-...-00 to -01 519 o Relaxed language on setting -send and -receive to same values; 520 added text on leaving on empty to indicate asymmetric usage. 521 o Added text that clients on behalf of end users are expected to set 522 the attributes on outgoing calls and ignore on incoming calls 523 while systems on behalf of call centers and PSAPs are expected to 524 take the attributes into account when processing incoming calls. 526 10.11. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 528 o Updated text to refer to RFC 5646 rather than the IANA language 529 subtags registry directly. 530 o Moved discussion of existing 'lang' attribute out of "Proposed 531 Solution" section and into own section now that it is not part of 532 proposal. 533 o Updated text about existing 'lang' attribute. 534 o Added example use cases. 535 o Replaced proposed single 'humintlang' attribute with 'humintlang- 536 send' and 'humintlang-recv' per Harald's request/information that 537 it was a misuse of SDP to use the same attribute for sending and 538 receiving. 539 o Added section describing usage being advisory vs required and text 540 in attribute section. 541 o Added section on SIP "hint" header (not yet nailed down between 542 new and existing header). 543 o Added text discussing usage in policy-based routing function or 544 use of SIP header "hint" if unable to do so. 545 o Added SHOULD that the value of the parameters stick to the largest 546 granularity of language tags. 547 o Added text to Introduction to be try and be more clear about 548 purpose of document and problem being solved. 549 o Many wording improvements and clarifications throughout the 550 document. 551 o Filled in Security Considerations. 552 o Filled in IANA Considerations. 553 o Added to Acknowledgments those who participated in the Orlando ad- 554 hoc discussion as well as those who participated in email 555 discussion and side one-on-one discussions. 557 10.12. Changes from draft-gellens-...-01 to -02 559 o Updated text for (possible) new attribute "humintlang" to 560 reference RFC 5646 561 o Added clarifying text for (possible) re-use of existing 'lang' 562 attribute saying that the registration would be updated to reflect 563 different semantics for multiple values for interactive versus 564 non-interactive media. 566 o Added clarifying text for (possible) new attribute "humintlang" to 567 attempt to better describe the role of language tags in media in 568 an offer and an answer. 570 10.13. Changes from draft-gellens-...-00 to -01 572 o Changed name of (possible) new attribute from 'humlang" to 573 "humintlang" 574 o Added discussion of silly state (language not appropriate for 575 media type) 576 o Added Voice Carry Over example 577 o Added mention of multilingual people and multiple languages 578 o Minor text clarifications 580 11. Contributors 582 Gunnar Hellstrom deserves special mention for his reviews, 583 assistance, and especially for contributing the core text in 584 Appendix A. 586 12. Acknowledgments 588 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 589 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 590 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 591 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 592 Peter Saint-Andre, and Dale Worley for reviews, corrections, 593 suggestions, and participating in in-person and email discussions. 595 13. References 597 13.1. Normative References 599 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 600 Requirement Levels", BCP 14, RFC 2119, 601 DOI 10.17487/RFC2119, March 1997, 602 . 604 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 605 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 606 July 2006, . 608 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 609 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 610 September 2009, . 612 13.2. Informational References 614 [I-D.iab-privacy-considerations] 615 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 616 Morris, J., Hansen, M., and R. Smith, "Privacy 617 Considerations for Internet Protocols", draft-iab-privacy- 618 considerations-09 (work in progress), May 2013. 620 [I-D.ietf-slim-multilangcontent] 621 Tomkinson, N. and N. Borenstein, "Multiple Language 622 Content Type", draft-ietf-slim-multilangcontent-02 (work 623 in progress), July 2016. 625 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 626 "Indicating User Agent Capabilities in the Session 627 Initiation Protocol (SIP)", RFC 3840, 628 DOI 10.17487/RFC3840, August 2004, 629 . 631 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 632 Preferences for the Session Initiation Protocol (SIP)", 633 RFC 3841, DOI 10.17487/RFC3841, August 2004, 634 . 636 Appendix A. Historic Alternative Proposal: Caller-prefs 638 The decision to base the proposal at the media negotiation level, and 639 specifically to use SDP, came after significant debate and 640 discussion. It is possible to meet the objectives using a variety of 641 mechanisms, but none are perfect. Using SDP means dealing with the 642 complexity of SDP, and leaves out real-time session protocols that do 643 not use SDP. The major alternative proposal was to use SIP. Using 644 SIP leaves out non-SIP session protocols, but more fundamentally, 645 would occur at a different layer than the media negotiation. This 646 results in a more fragile solution since the media modality and 647 language would be negotiated using SIP, and then the specific media 648 formats (which inherently include the modality) would be negotiated 649 at a different level (typically SDP, especially in the emergency 650 calling cases), making it easier to have mismatches (such as where 651 the media modality negotiated in SIP don't match what was negotiated 652 using SDP). 654 An alternative proposal was to use the SIP-level Caller Preferences 655 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 657 The Caller-prefs mechanism includes a priority system; this would 658 allow different combinations of media and languages to be assigned 659 different priorities. The evaluation and decisions on what to do 660 with the call can be done either by proxies along the call path, or 661 by the addressed UA. Evaluation of alternatives for routing is 662 described in RFC 3841 [RFC3841]. 664 A.1. Use of Caller Preferences Without Additions 666 The following would be possible without adding any new registered 667 tags: 669 Potential callers and recipients MAY include in the Contact field in 670 their SIP registrations media and language tags according to the 671 joint capabilities of the UA and the human user according to RFC 3840 672 [RFC3840]. 674 The most relevant media capability tags are "video", "text" and 675 "audio". Each tag represents a capability to use the media in two- 676 way communication. 678 Language capabilities are declared with a comma-separated list of 679 languages that can be used in the call as parameters to the tag 680 "language=". 682 This is an example of how it is used in a SIP REGISTER: 684 REGISTER user@example.net 685 Contact: audio; video; text; 686 language="en,es,ase" 688 Including this information in SIP REGISTER allows proxies to act on 689 the information. For the problem set addressed by this document, it 690 is not anticipated that proxies will do so using registration data. 691 Further, there are classes of devices (such as cellular mobile 692 phones) that are not anticipated to include this information in their 693 registrations. Hence, use in registration is OPTIONAL. 695 In a call, a list of acceptable media and language combinations is 696 declared, and a priority assigned to each combination. 698 This is done by the Accept-Contact header field, which defines 699 different combinations of media and languages and assigns priorities 700 for completing the call with the SIP URI represented by that Contact. 701 A priority is assigned to each set as a so-called "q-value" which 702 ranges from 1 (most preferred) to 0 (least preferred). 704 Using the Accept-Contact header field in INVITE requests and 705 responses allows these capabilities to be expressed and used during 706 call set-up. Clients SHOULD include this information in INVITE 707 requests and responses. 709 Example: 711 Accept-Contact: *; text; language="en"; q=0.2 712 Accept-Contact: *; video; language="ase"; q=0.8 714 This example shows the highest preference expressed by the caller is 715 to use video with American Sign Language (language code "ase"). As a 716 fallback, it is acceptable to get the call connected with only 717 English text used for human communication. Other media may of course 718 be connected as well, without expectation that it will be usable by 719 the caller for interactive communications (but may still be helpful 720 to the caller). 722 This system satisfies all the needs described in the previous 723 chapters, except that language specifications do not make any 724 distinction between spoken and written language, and that the need 725 for directionality in the specification cannot be fulfilled. 727 To some degree the lack of media specification between speech and 728 text in language tags can be compensated by only specifying the 729 important medium in the Accept-Contact field. 731 Thus, a user who wants to use English mainly for text would specify: 733 Accept-Contact: *;text;language="en";q=1.0 735 While a user who wants to use English mainly for speech but accept it 736 for text would specify: 738 Accept-Contact: *;audio;language="en";q=0.8 739 Accept-Contact: *;text;language="en";q=0.2 741 However, a user who would like to talk, but receive text back has no 742 way to do it with the existing specification. 744 A.2. Additional Caller Preferences for Asymmetric Needs 746 In order to be able to specify asymmetric preferences, there are two 747 possibilities. Either new language tags in the style of the 748 humintlang parameters described above for SDP could be registered, or 749 additional media tags describing the asymmetry could be registered. 751 A.2.1. Caller Preferences for Asymmetric Modality Needs 753 The following new media tags should be defined: 755 speech-receive 756 speech-send 757 text-receive 758 text-send 759 sign-send 760 sign-receive 762 A user who prefers to talk and get text in return in English would 763 register the following (if including this information in registration 764 data): 766 REGISTER user@example.net 767 Contact: audio;text;speech-send;text- 768 receive;language="en" 770 At call time, a user who prefers to talk and get text in return in 771 English would set the Accept-Contact header field to: 773 Accept-Contact: *; audio; text; speech-receive; text-send; 774 language="en";q=0.8 775 Accept-Contact: *; text; language="en"; q=0.2 777 Note that the directions specified here are as viewed from the callee 778 side to match what the callee has registered. 780 A bridge arranged for invoking a relay service specifically arranged 781 for captioned telephony would register the following for supporting 782 calling users: 784 REGISTER ct@ctrelay.net 785 Contact: audio; text; speech-receive; 786 text-send; language="en" 788 A bridge arranged for invoking a relay service specifically arranged 789 for captioned telephony would register the following for supporting 790 called users: 792 REGISTER ct@ctrelay.net 793 Contact: audio; text; speech-send; text- 794 receive; language="en" 796 At call time, these alternatives are included in the list of possible 797 outcome of the call routing by the SIP proxies and the proper relay 798 service is invoked. 800 A.2.2. Caller Preferences for Asymmetric Language Tags 802 An alternative is to register new language tags for the purpose of 803 asymmetric language usage. 805 Instead of using "language=", six new language tags would be 806 registered: 808 humintlang-text-recv 809 humintlang-text-send 810 humintlang-speech-recv 811 humintlang-speech-send 812 humintlang-sign-recv 813 humintlang-sign-send 815 These language tags would be used instead of the regular 816 bidirectional language tags, and users with bidirectional 817 capabilities SHOULD specify values for both directions. Services 818 specifically arranged for supporting users with asymmetric needs 819 SHOULD specify only the asymmetry they support. 821 Author's Address 823 Randall Gellens 824 Core Technology Consulting 826 Email: rg+ietf@randy.pensive.org