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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 20, 2016 5 Expires: January 21, 2017 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-02 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 21, 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 . . . . . . . . . . . . . . . . . . . . . . 8 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 72 9. Changes from Previous Versions . . . . . . . . . . . . . . . 9 73 9.1. Changes from draft-ietf-slim-...-01 to draft-ietf- 74 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 9 75 9.2. Changes from draft-ietf-slim-...-00 to draft-ietf- 76 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 9 77 9.3. Changes from draft-gellens-slim-...-03 to draft-ietf- 78 slim-...-00 . . . . . . . . . . . . . . . . . . . . . . . 10 79 9.4. Changes from draft-gellens-slim-...-02 to draft-gellens- 80 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 10 81 9.5. Changes from draft-gellens-slim-...-01 to draft-gellens- 82 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 10 83 9.6. Changes from draft-gellens-slim-...-00 to draft-gellens- 84 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 10 85 9.7. Changes from draft-gellens-mmusic-...-02 to draft- 86 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 10 87 9.8. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 10 88 9.9. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 11 89 9.10. Changes from draft-gellens-...-02 to draft-gellens- 90 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 11 91 9.11. Changes from draft-gellens-...-01 to -02 . . . . . . . . 11 92 9.12. Changes from draft-gellens-...-00 to -01 . . . . . . . . 12 93 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 94 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 95 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 96 12.1. Normative References . . . . . . . . . . . . . . . . . . 12 97 12.2. Informational References . . . . . . . . . . . . . . . . 13 98 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 13 99 A.1. Use of Caller Preferences Without Additions . . . . . . . 14 100 A.2. Additional Caller Preferences for Asymmetric Needs . . . 16 101 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 16 102 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 17 103 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 105 1. Introduction 107 A mutually comprehensible language is helpful for human 108 communication. This document addresses the real-time, interactive 109 side of the issue. A companion document on language selection in 110 email [draft-tomkinson-multilangcontent] addresses the non-real-time 111 side. 113 When setting up interactive communication sessions (using SIP or 114 other protocols), human (natural) language and media modality (voice, 115 video, text) negotiation may be needed. Unless the caller and callee 116 know each other or there is contextual or out of band information 117 from which the language(s) and media modalities can be determined, 118 there is a need for spoken, signed, or written languages to be 119 negotiated based on the caller's needs and the callee's capabilities. 120 This need applies to both emergency and non-emergency calls. For 121 various reasons, including the ability to establish multiple streams 122 using different media (e.g., voice, text, video), it makes sense to 123 use a per-stream negotiation mechanism, in this case, SDP. 125 This approach has a number of benefits, including that it is generic 126 (applies to all interactive communications negotiated using SDP) and 127 not limited to emergency calls. In some cases such a facility isn't 128 needed, because the language is known from the context (such as when 129 a caller places a call to a sign language relay center, to a friend, 130 or colleague). But it is clearly useful in many other cases. For 131 example, someone calling a company call center or a Public Safety 132 Answering Point (PSAP) should be able to indicate if one or more 133 specific signed, written, and/or spoken languages are preferred, the 134 callee should be able to indicate its capabilities in this area, and 135 the call proceed using in-common language(s) and media forms. 137 Since this is a protocol mechanism, the user equipment (UE client) 138 needs to know the user's preferred languages; a reasonable technique 139 could include a configuration mechanism with a default of the 140 language of the user interface. In some cases, a UE could tie 141 language and media preferences, such as a preference for a video 142 stream using a signed language and/or a text or audio stream using a 143 written/spoken language. 145 Including the user's human (natural) language preferences in the 146 session establishment negotiation is independent of the use of a 147 relay service and is transparent to a voice service provider. For 148 example, assume a user within the United States who speaks Spanish 149 but not English places a voice call. The call could be an emergency 150 call or perhaps to an airline reservation desk. The language 151 information is transparent to the voice service provider, but is part 152 of the session negotiation between the UE and the terminating entity. 153 In the case of a call to e.g., an airline, the call could be 154 automatically handled by a Spanish-speaking agent. In the case of an 155 emergency call, the Emergency Services IP network (ESInet) and the 156 PSAP may choose to take the language and media preferences into 157 account when determining how to process the call. 159 By treating language as another attribute that is negotiated along 160 with other aspects of a media stream, it becomes possible to 161 accommodate a range of users' needs and called party facilities. For 162 example, some users may be able to speak several languages, but have 163 a preference. Some called parties may support some of those 164 languages internally but require the use of a translation service for 165 others, or may have a limited number of call takers able to use 166 certain languages. Another example would be a user who is able to 167 speak but is deaf or hard-of-hearing and requires a voice stream plus 168 a text stream (known as voice carry over). Making language a media 169 attribute allows the standard session negotiation mechanism to handle 170 this by providing the information and mechanism for the endpoints to 171 make appropriate decisions. 173 Regarding relay services, in the case of an emergency call requiring 174 sign language such as ASL, there are two common approaches: the 175 caller initiates the call to a relay center, or the caller places the 176 call to emergency services (e.g., 911 in the U.S. or 112 in Europe). 177 (In a variant of the second case, the voice service provider invokes 178 a relay service as well as emergency services.) In the former case, 179 the language need is ancillary and supplemental. In the non-variant 180 second case, the ESInet and/or PSAP may take the need for sign 181 language into account and bridge in a relay center. In this case, 182 the ESInet and PSAP have all the standard information available (such 183 as location) but are able to bridge the relay sooner in the call 184 processing. 186 By making this facility part of the end-to-end negotiation, the 187 question of which entity provides or engages the relay service 188 becomes separate from the call processing mechanics; if the caller 189 directs the call to a relay service then the human language 190 negotiation facility provides extra information to the relay service 191 but calls will still function without it; if the caller directs the 192 call to emergency services, then the ESInet/PSAP are able to take the 193 user's human language needs into account, e.g., by assigning to a 194 specific queue or call taker or bridging in a relay service or 195 translator. 197 The term "negotiation" is used here rather than "indication" because 198 human language (spoken/written/signed) is something that can be 199 negotiated in the same way as which forms of media (audio/text/video) 200 or which codecs. For example, if we think of non-emergency calls, 201 such as a user calling an airline reservation center, the user may 202 have a set of languages he or she speaks, with perhaps preferences 203 for one or a few, while the airline reservation center will support a 204 fixed set of languages. Negotiation should select the user's most 205 preferred language that is supported by the call center. Both sides 206 should be aware of which language was negotiated. This is 207 conceptually similar to the way other aspects of each media stream 208 are negotiated using SDP (e.g., media type and codecs). 210 2. Terminology 212 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 213 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 214 document are to be interpreted as described in RFC 2119 [RFC2119]. 216 3. Expected Use 218 This facility may be used by NENA and 3GPP. NENA has already 219 referenced it in NENA 08-01 (i3 Stage 3 version 2) in describing 220 attributes of calls presented to an ESInet, and may add further 221 details in that or other documents. 3GPP may reference this 222 mechanism in general call handling and emergency call handling. Some 223 CRs introduced in SA1 have anticipated this functionality being 224 provided within SDP. 226 4. Desired Semantics 228 The desired solution is a media attribute that may be used within an 229 offer to indicate the preferred language of each media stream, and 230 within an answer to indicate the accepted language. The semantics of 231 including multiple values for a media stream within an offer is that 232 the languages are listed in order of preference. 234 (While conversations among multilingual people sometimes involve 235 multiple languages, the complexity of negotiating multiple 236 simultaneous languages within an interactive media stream outweighs 237 the usefulness of this as a general facility.) 239 5. The existing 'lang' attribute 241 RFC 4566 [RFC4566] specifies an attribute 'lang' which appears 242 similar to what is needed here, but in considering its use the group 243 felt its semantics were ambiguous, noted that there was not much 244 evidence of its use (and thus less likelihood of conflict or 245 confusion in defining new attributes), and that there was value in 246 being able to specify language per direction (sending and receiving). 247 This document therefore defines two new attributes. 249 6. Proposed Solution 251 An SDP attribute seems the natural choice to negotiate human 252 (natural) language of an interactive media stream. The attribute 253 value should be a language tag per RFC 5646 [RFC5646] 255 6.1. Rationale 257 The decision to base the proposal at the media negotiation level, and 258 specifically to use SDP, came after significant debate and 259 discussion. From an engineering standpoint, it is possible to meet 260 the objectives using a variety of mechanisms, but none are perfect. 261 None of the proposed alternatives was clearly better technically in 262 enough ways to win over proponents of the others, and none were 263 clearly so bad technically as to be easily rejected. As is often the 264 case in engineering, choosing the solution is a matter of balancing 265 trade-offs, and ultimately more a matter of taste than technical 266 merit. The two main proposals were to use SDP and SIP. SDP has the 267 advantage that the language is negotiated with the media to which it 268 applies, while SIP has the issue that the languages expressed may not 269 match the SDP media negotiated (for example, a session could 270 negotiate video at the SIP level but fail to negotiate any video 271 media stream at the SDP layer). 273 The mechanism described here for SDP can be adapted to media 274 negotiation protocols other than SDP. 276 6.2. New 'humintlang-send' and 'humintlang-recv' attributes 278 Rather than re-use 'lang' we define two new media-level attributes 279 starting with 'humintlang' (short for "human interactive language") 280 to negotiate which human language is used in each (interactive) media 281 stream. There are two attributes, one ending in "-send" and the 282 other in "-recv": 284 a=humintlang-send: 285 a=humintlang-recv: 287 Each can appear multiple times in an offer for a media stream. 289 In an offer, 'humintlang-send' indicates the language(s) the offerer 290 is willing to use when sending using the media, and 'humintlang-recv' 291 indicates the language(s) the offerer is willing to use when 292 receiving using the media. The values constitute a list of languages 293 in preference order (first is most preferred). When a media is 294 intended for use in one direction only (such as a speech-impaired 295 user sending using text and receiving using audio), either 296 humintlang-send or humintlang-recv MAY be omitted. When a media is 297 not primarily intended for language (for example, a video or audio 298 stream intended for background only) both SHOULD be omitted. 299 Otherwise, both SHOULD have the same values in the same order. The 300 two SHOULD NOT be set to languages which are difficult to match 301 together (e.g., specifying a desire to send audio in Hungarian and 302 receive audio in Portuguese will make it difficult to successfully 303 complete the call). 305 In an answer, 'humintlang-send' is the accepted language the answerer 306 will send (which in most cases is one of the languages in the offer's 307 'humintlang-recv'), and 'humintlang-recv' is the accepted language 308 the answerer expects to receive (which in most cases is one of the 309 languages in the offer's 'humintlang-send'). 311 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 312 describes mechanisms for matching language tags. While RFC 5646 313 provides a mechanism accommodating increasingly fine-grained 314 distinctions, in the interest of maximum interoperability for real- 315 time interactive communications, each 'humintlang-send' and 316 'humintlang-recv' value SHOULD be restricted to the largest 317 granularity of language tags; in other words, it is RECOMMENDED to 318 specify only a Primary-subtag and NOT to include subtags (e.g., for 319 region or dialect) unless the languages might be mutually 320 incomprehensible without them. 322 In an offer, each language tag value MAY have an asterisk appended as 323 the last character (after the registry value). The asterisk 324 indicates a request by the caller to not fail the call if there is no 325 language in common. See Section 6.3 for more information and 326 discussion. 328 When placing an emergency call, and in any other case where the 329 language cannot be assumed from context, each media stream in an 330 offer primarily intended for human language communication SHOULD 331 specify both (or in some cases, one of) the 'humintlang-send' and 332 'humintlang-recv' attributes. 334 Note that while signed language tags are used with a video stream to 335 indicate sign language, a spoken language tag for a video stream in 336 parallel with an audio stream with the same spoken language tag 337 indicates a request for a supplemental video stream to see the 338 speaker. 340 Clients acting on behalf of end users are expected to set one or both 341 'humintlang-send' and 'humintlang-recv' attributes on each media 342 stream primarily intended for human communication in an offer when 343 placing an outgoing session, and either ignore or take into 344 consideration the attributes when receiving incoming calls, based on 345 local configuration and capabilities. Systems acting on behalf of 346 call centers and PSAPs are expected to take into account the values 347 when processing inbound calls. 349 6.3. Advisory vs Required 351 One important consideration with this mechanism is if the call fails 352 if the callee does not support any of the languages requested by the 353 caller. 355 In order to provide for maximum likelihood of a successful 356 communication session, especially in the case of emergency calling, 357 the mechanism defined here provides a way for the caller to indicate 358 a preference for the call failing or succeeding when there is no 359 language in common. However, the callee is NOT REQUIRED to honor 360 this preference. For example, a PSAP MAY choose to attempt the call 361 even with no language in common, while a corporate call center MAY 362 choose to fail the call. 364 The mechanism for indicating this preference is that, in an offer, if 365 the last character of any of the 'humintlang-recv' or 'humintlang- 366 send' values is an asterisk, this indicates a request to not fail the 367 call (similar to SIP Accept-Language syntax). Either way, the called 368 party MAY ignore this, e.g., for the emergency services use case, a 369 PSAP will likely not fail the call. 371 6.4. Silly States 373 It is possible to specify a "silly state" where the language 374 specified does not make sense for the media type, such as specifying 375 a signed language for an audio media stream. 377 An offer MUST NOT be created where the language does not make sense 378 for the media type. If such an offer is received, the receiver MAY 379 reject the media, ignore the language specified, or attempt to 380 interpret the intent (e.g., if American Sign Language is specified 381 for an audio media stream, this might be interpreted as a desire to 382 use spoken English). 384 A spoken language tag for a video stream in conjunction with an audio 385 stream with the same language might indicate a request for 386 supplemental video to see the speaker. 388 7. IANA Considerations 390 IANA is kindly requested to add two entries to the 'att-field (media 391 level only)' table of the SDP parameters registry: 393 +------------------------------+-----------------+-----------------+ 394 | Type | Name | Reference | 395 +------------------------------+-----------------+-----------------+ 396 | att-field (media level only) | humintlang-send | (this document) | 397 | att-field (media level only) | humintlang-recv | (this document) | 398 +------------------------------+-----------------+-----------------+ 400 Table 1: att-field (media level only)' entries 402 8. Security Considerations 404 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 405 use of that RFC). In addition, if the 'humintlang-send' or 406 'humintlang-recv' values are altered or deleted en route, the session 407 could fail or languages incomprehensible to the caller could be 408 selected; however, this is also a risk if any SDP parameters are 409 modified en route. 411 9. Changes from Previous Versions 413 9.1. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 415 o Deleted most of Section 5 and replaced with a very short summary 416 o Replaced "wishes to" with "is willing to" in Section 6.2 417 o Reworded description of attribute usage to clarify when to set 418 both, only one, or neither 419 o Deleted all uses of "IMS" 420 o Other editorial changes for clarity 422 9.2. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 424 o Editorial changes to wording in Section 5. 426 9.3. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 428 o Updated title to reflect WG adoption 430 9.4. Changes from draft-gellens-slim-...-02 to draft-gellens- 431 slim-...-03 433 o Removed Use Cases section, per face-to-face discussion at IETF 93 434 o Removed discussion of routing, per face-to-face discussion at IETF 435 93 437 9.5. Changes from draft-gellens-slim-...-01 to draft-gellens- 438 slim-...-02 440 o Updated NENA usage mention 441 o Removed background text reference to draft-saintandre-sip-xmpp- 442 chat-04 since that draft expired 444 9.6. Changes from draft-gellens-slim-...-00 to draft-gellens- 445 slim-...-01 447 o Revision to keep draft from expiring 449 9.7. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 450 slim-...-00 452 o Changed name from -mmusic- to -slim- to reflect proposed WG name 453 o As a result of the face-to-face discussion in Toronto, the SDP vs 454 SIP issue was resolved by going back to SDP, taking out the SIP 455 hint, and converting what had been a set of alternate proposals 456 for various ways of doing it within SIP into an informative annex 457 section which includes background on why SDP is the proposal 458 o Added mention that enabling a mutually comprehensible language is 459 a general problem of which this document addresses the real-time 460 side, with reference to [draft-tomkinson-multilangcontent] which 461 addresses the non-real-time side. 463 9.8. Changes from draft-gellens-mmusic-...-01 to -02 465 o Added clarifying text on leaving attributes unset for media not 466 primarily intended for human language communication (e.g., 467 background audio or video). 468 o Added new section Appendix A ("Alternative Proposal: Caller- 469 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 470 level. 472 9.9. Changes from draft-gellens-mmusic-...-00 to -01 474 o Relaxed language on setting -send and -receive to same values; 475 added text on leaving on empty to indicate asymmetric usage. 476 o Added text that clients on behalf of end users are expected to set 477 the attributes on outgoing calls and ignore on incoming calls 478 while systems on behalf of call centers and PSAPs are expected to 479 take the attributes into account when processing incoming calls. 481 9.10. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 483 o Updated text to refer to RFC 5646 rather than the IANA language 484 subtags registry directly. 485 o Moved discussion of existing 'lang' attribute out of "Proposed 486 Solution" section and into own section now that it is not part of 487 proposal. 488 o Updated text about existing 'lang' attribute. 489 o Added example use cases. 490 o Replaced proposed single 'humintlang' attribute with 'humintlang- 491 send' and 'humintlang-recv' per Harald's request/information that 492 it was a misuse of SDP to use the same attribute for sending and 493 receiving. 494 o Added section describing usage being advisory vs required and text 495 in attribute section. 496 o Added section on SIP "hint" header (not yet nailed down between 497 new and existing header). 498 o Added text discussing usage in policy-based routing function or 499 use of SIP header "hint" if unable to do so. 500 o Added SHOULD that the value of the parameters stick to the largest 501 granularity of language tags. 502 o Added text to Introduction to be try and be more clear about 503 purpose of document and problem being solved. 504 o Many wording improvements and clarifications throughout the 505 document. 506 o Filled in Security Considerations. 507 o Filled in IANA Considerations. 508 o Added to Acknowledgments those who participated in the Orlando ad- 509 hoc discussion as well as those who participated in email 510 discussion and side one-on-one discussions. 512 9.11. Changes from draft-gellens-...-01 to -02 514 o Updated text for (possible) new attribute "humintlang" to 515 reference RFC 5646 516 o Added clarifying text for (possible) re-use of existing 'lang' 517 attribute saying that the registration would be updated to reflect 518 different semantics for multiple values for interactive versus 519 non-interactive media. 521 o Added clarifying text for (possible) new attribute "humintlang" to 522 attempt to better describe the role of language tags in media in 523 an offer and an answer. 525 9.12. Changes from draft-gellens-...-00 to -01 527 o Changed name of (possible) new attribute from 'humlang" to 528 "humintlang" 529 o Added discussion of silly state (language not appropriate for 530 media type) 531 o Added Voice Carry Over example 532 o Added mention of multilingual people and multiple languages 533 o Minor text clarifications 535 10. Contributors 537 Gunnar Hellstrom deserves special mention for his reviews, 538 assistance, and especially for contributing the core text in 539 Appendix A. 541 11. Acknowledgments 543 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 544 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 545 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 546 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 547 Peter Saint-Andre, and Dale Worley for reviews, corrections, 548 suggestions, and participating in in-person and email discussions. 550 12. References 552 12.1. Normative References 554 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 555 Requirement Levels", BCP 14, RFC 2119, 556 DOI 10.17487/RFC2119, March 1997, 557 . 559 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 560 "Indicating User Agent Capabilities in the Session 561 Initiation Protocol (SIP)", RFC 3840, 562 DOI 10.17487/RFC3840, August 2004, 563 . 565 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 566 Preferences for the Session Initiation Protocol (SIP)", 567 RFC 3841, DOI 10.17487/RFC3841, August 2004, 568 . 570 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 571 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 572 July 2006, . 574 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 575 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 576 September 2009, . 578 12.2. Informational References 580 [draft-tomkinson-multilangcontent] 581 Tomkinson, N. and N. Borenstein, "Multiple Language 582 Content Type", draft-tomkinson-multilangcontent (work in 583 progress), April 2014. 585 [I-D.iab-privacy-considerations] 586 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 587 Morris, J., Hansen, M., and R. Smith, "Privacy 588 Considerations for Internet Protocols", draft-iab-privacy- 589 considerations-09 (work in progress), May 2013. 591 [I-D.saintandre-sip-xmpp-chat] 592 Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, 593 "Interworking between the Session Initiation Protocol 594 (SIP) and the Extensible Messaging and Presence Protocol 595 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- 596 chat-06 (work in progress), June 2013. 598 [RFC3066] Alvestrand, H., "Tags for the Identification of 599 Languages", RFC 3066, DOI 10.17487/RFC3066, January 2001, 600 . 602 Appendix A. Historic Alternative Proposal: Caller-prefs 604 The decision to base the proposal at the media negotiation level, and 605 specifically to use SDP, came after significant debate and 606 discussion. It is possible to meet the objectives using a variety of 607 mechanisms, but none are perfect. Using SDP means dealing with the 608 complexity of SDP, and leaves out real-time session protocols that do 609 not use SDP. The major alternative proposal was to use SIP. Using 610 SIP leaves out non-SIP session protocols, but more fundamentally, 611 would occur at a different layer than the media negotiation. This 612 results in a more fragile solution since the media modality and 613 language would be negotiated using SIP, and then the specific media 614 formats (which inherently include the modality) would be negotiated 615 at a different level (typically SDP, especially in the emergency 616 calling cases), making it easier to have mismatches (such as where 617 the media modality negotiated in SIP don't match what was negotiated 618 using SDP). 620 An alternative proposal was to use the SIP-level Caller Preferences 621 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 623 The Caller-prefs mechanism includes a priority system; this would 624 allow different combinations of media and languages to be assigned 625 different priorities. The evaluation and decisions on what to do 626 with the call can be done either by proxies along the call path, or 627 by the addressed UA. Evaluation of alternatives for routing is 628 described in RFC 3841 [RFC3841]. 630 A.1. Use of Caller Preferences Without Additions 632 The following would be possible without adding any new registered 633 tags: 635 Potential callers and recipients MAY include in the Contact field in 636 their SIP registrations media and language tags according to the 637 joint capabilities of the UA and the human user according to RFC 3840 638 [RFC3840]. 640 The most relevant media capability tags are "video", "text" and 641 "audio". Each tag represents a capability to use the media in two- 642 way communication. 644 Language capabilities are declared with a comma-separated list of 645 languages that can be used in the call as parameters to the tag 646 "language=". 648 This is an example of how it is used in a SIP REGISTER: 650 REGISTER user@example.net 651 Contact: audio; video; text; 652 language="en,es,ase" 654 Including this information in SIP REGISTER allows proxies to act on 655 the information. For the problem set addressed by this document, it 656 is not anticipated that proxies will do so using registration data. 657 Further, there are classes of devices (such as cellular mobile 658 phones) that are not anticipated to include this information in their 659 registrations. Hence, use in registration is OPTIONAL. 661 In a call, a list of acceptable media and language combinations is 662 declared, and a priority assigned to each combination. 664 This is done by the Accept-Contact header field, which defines 665 different combinations of media and languages and assigns priorities 666 for completing the call with the SIP URI represented by that Contact. 667 A priority is assigned to each set as a so-called "q-value" which 668 ranges from 1 (most preferred) to 0 (least preferred). 670 Using the Accept-Contact header field in INVITE requests and 671 responses allows these capabilities to be expressed and used during 672 call set-up. Clients SHOULD include this information in INVITE 673 requests and responses. 675 Example: 677 Accept-Contact: *; text; language="en"; q=0.2 678 Accept-Contact: *; video; language="ase"; q=0.8 680 This example shows the highest preference expressed by the caller is 681 to use video with American Sign Language (language code "ase"). As a 682 fallback, it is acceptable to get the call connected with only 683 English text used for human communication. Other media may of course 684 be connected as well, without expectation that it will be usable by 685 the caller for interactive communications (but may still be helpful 686 to the caller). 688 This system satisfies all the needs described in the previous 689 chapters, except that language specifications do not make any 690 distinction between spoken and written language, and that the need 691 for directionality in the specification cannot be fulfilled. 693 To some degree the lack of media specification between speech and 694 text in language tags can be compensated by only specifying the 695 important medium in the Accept-Contact field. 697 Thus, a user who wants to use English mainly for text would specify: 699 Accept-Contact: *;text;language="en";q=1.0 701 While a user who wants to use English mainly for speech but accept it 702 for text would specify: 704 Accept-Contact: *;audio;language="en";q=0.8 705 Accept-Contact: *;text;language="en";q=0.2 707 However, a user who would like to talk, but receive text back has no 708 way to do it with the existing specification. 710 A.2. Additional Caller Preferences for Asymmetric Needs 712 In order to be able to specify asymmetric preferences, there are two 713 possibilities. Either new language tags in the style of the 714 humintlang parameters described above for SDP could be registered, or 715 additional media tags describing the asymmetry could be registered. 717 A.2.1. Caller Preferences for Asymmetric Modality Needs 719 The following new media tags should be defined: 721 speech-receive 722 speech-send 723 text-receive 724 text-send 725 sign-send 726 sign-receive 728 A user who prefers to talk and get text in return in English would 729 register the following (if including this information in registration 730 data): 732 REGISTER user@example.net 733 Contact: audio;text;speech-send;text- 734 receive;language="en" 736 At call time, a user who prefers to talk and get text in return in 737 English would set the Accept-Contact header field to: 739 Accept-Contact: *; audio; text; speech-receive; text-send; 740 language="en";q=0.8 741 Accept-Contact: *; text; language="en"; q=0.2 743 Note that the directions specified here are as viewed from the callee 744 side to match what the callee has registered. 746 A bridge arranged for invoking a relay service specifically arranged 747 for captioned telephony would register the following for supporting 748 calling users: 750 REGISTER ct@ctrelay.net 751 Contact: audio; text; speech-receive; 752 text-send; language="en" 754 A bridge arranged for invoking a relay service specifically arranged 755 for captioned telephony would register the following for supporting 756 called users: 758 REGISTER ct@ctrelay.net 759 Contact: audio; text; speech-send; text- 760 receive; language="en" 762 At call time, these alternatives are included in the list of possible 763 outcome of the call routing by the SIP proxies and the proper relay 764 service is invoked. 766 A.2.2. Caller Preferences for Asymmetric Language Tags 768 An alternative is to register new language tags for the purpose of 769 asymmetric language usage. 771 Instead of using "language=", six new language tags would be 772 registered: 774 humintlang-text-recv 775 humintlang-text-send 776 humintlang-speech-recv 777 humintlang-speech-send 778 humintlang-sign-recv 779 humintlang-sign-send 781 These language tags would be used instead of the regular 782 bidirectional language tags, and users with bidirectional 783 capabilities SHOULD specify values for both directions. Services 784 specifically arranged for supporting users with asymmetric needs 785 SHOULD specify only the asymmetry they support. 787 Author's Address 789 Randall Gellens 790 Core Technology Consulting 792 Email: rg+ietf@randy.pensive.org