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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 Qualcomm Technologies Inc. 4 Intended status: Standards Track November 1, 2015 5 Expires: May 4, 2016 7 Negotiating Human Language in Real-Time Communications 8 draft-gellens-slim-negotiating-human-language-03 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 May 4, 2016. 43 Copyright Notice 45 Copyright (c) 2015 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 . . . . . . . . . . . . . . . . 5 65 6. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 6 66 6.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 6 67 6.2. New 'humintlang-send' and 'humintlang-recv' attributes . 7 68 6.3. Advisory vs Required . . . . . . . . . . . . . . . . . . 8 69 6.4. Silly States . . . . . . . . . . . . . . . . . . . . . . 9 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 72 9. Changes from Previous Versions . . . . . . . . . . . . . . . 10 73 9.1. Changes from draft-gellens-slim-...-02 to draft-gellens- 74 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 10 75 9.2. Changes from draft-gellens-slim-...-01 to draft-gellens- 76 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 10 77 9.3. Changes from draft-gellens-slim-...-00 to draft-gellens- 78 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 10 79 9.4. Changes from draft-gellens-mmusic-...-02 to draft- 80 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 10 81 9.5. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 11 82 9.6. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 11 83 9.7. Changes from draft-gellens-...-02 to draft-gellens- 84 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 11 85 9.8. Changes from draft-gellens-...-01 to -02 . . . . . . . . 12 86 9.9. Changes from draft-gellens-...-00 to -01 . . . . . . . . 12 87 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 88 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 90 12.1. Normative References . . . . . . . . . . . . . . . . . . 12 91 12.2. Informational References . . . . . . . . . . . . . . . . 13 92 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 13 93 A.1. Use of Caller Preferences Without Additions . . . . . . . 14 94 A.2. Additional Caller Preferences for Asymmetric Needs . . . 16 95 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 16 96 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 17 97 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18 99 1. Introduction 101 A mutually comprehensible language is helpful for human 102 communication. This document addresses the real-time, interactive 103 side of the issue. A companion document on language selection in 104 email [draft-tomkinson-multilangcontent] addresses the non-real-time 105 side. 107 When setting up interactive communication sessions (using SIP or 108 other protocols), human (natural) language and media modality (voice, 109 video, text) negotiation may be needed. Unless the caller and callee 110 know each other or there is contextual or out of band information 111 from which the language(s) and media modalities can be determined, 112 there is a need for spoken, signed, or written languages to be 113 negotiated based on the caller's needs and the callee's capabilities. 114 This need applies to both emergency and non-emergency calls. For 115 various reasons, including the ability to establish multiple streams 116 using different media (e.g., voice, text, video), it makes sense to 117 use a per-stream negotiation mechanism, in this case, SDP. 119 This approach has a number of benefits, including that it is generic 120 (applies to all interactive communications negotiated using SDP) and 121 not limited to emergency calls. In some cases such a facility isn't 122 needed, because the language is known from the context (such as when 123 a caller places a call to a sign language relay center, to a friend, 124 or colleague). But it is clearly useful in many other cases. For 125 example, someone calling a company call center or a Public Safety 126 Answering Point (PSAP) should be able to indicate if one or more 127 specific signed, written, and/or spoken languages are preferred, the 128 callee should be able to indicate its capabilities in this area, and 129 the call proceed using in-common language(s) and media forms. 131 Since this is a protocol mechanism, the user equipment (UE client) 132 needs to know the user's preferred languages; a reasonable technique 133 could include a configuration mechanism with a default of the 134 language of the user interface. In some cases, a UE could tie 135 language and media preferences, such as a preference for a video 136 stream using a signed language and/or a text or audio stream using a 137 written/spoken language. 139 Including the user's human (natural) language preferences in the 140 session establishment negotiation is independent of the use of a 141 relay service and is transparent to a voice service provider. For 142 example, assume a user within the United States who speaks Spanish 143 but not English places a voice call using an IMS device. It doesn't 144 matter if the call is an emergency call or not (e.g., to an airline 145 reservation desk). The language information is transparent to the 146 IMS carrier, but is part of the session negotiation between the UE 147 and the terminating entity. In the case of a call to e.g., an 148 airline, the call can be automatically handled by a Spanish-speaking 149 agent. In the case of an emergency call, the Emergency Services IP 150 network (ESInet) and the PSAP may choose to take the language and 151 media preferences into account when determining how to process the 152 call. 154 By treating language as another attribute that is negotiated along 155 with other aspects of a media stream, it becomes possible to 156 accommodate a range of users' needs and called party facilities. For 157 example, some users may be able to speak several languages, but have 158 a preference. Some called parties may support some of those 159 languages internally but require the use of a translation service for 160 others, or may have a limited number of call takers able to use 161 certain languages. Another example would be a user who is able to 162 speak but is deaf or hard-of-hearing and requires a voice stream plus 163 a text stream (known as voice carry over). Making language a media 164 attribute allows the standard session negotiation mechanism to handle 165 this by providing the information and mechanism for the endpoints to 166 make appropriate decisions. 168 Regarding relay services, in the case of an emergency call requiring 169 sign language such as ASL, there are two common approaches: the 170 caller initiates the call to a relay center, or the caller places the 171 call to emergency services (e.g., 911 in the U.S. or 112 in Europe). 172 In the former case, the language need is ancillary and supplemental. 173 In the latter case, the ESInet and/or PSAP may take the need for sign 174 language into account and bridge in a relay center. In this case, 175 the ESInet and PSAP have all the standard information available (such 176 as location) but are able to bridge the relay sooner in the call 177 processing. 179 By making this facility part of the end-to-end negotiation, the 180 question of which entity provides or engages the relay service 181 becomes separate from the call processing mechanics; if the caller 182 directs the call to a relay service then the human language 183 negotiation facility provides extra information to the relay service 184 but calls will still function without it; if the caller directs the 185 call to emergency services, then the ESInet/PSAP are able to take the 186 user's human language needs into account, e.g., by assigning to a 187 specific queue or call taker or bridging in a relay service or 188 translator. 190 The term "negotiation" is used here rather than "indication" because 191 human language (spoken/written/signed) is something that can be 192 negotiated in the same way as which forms of media (audio/text/video) 193 or which codecs. For example, if we think of non-emergency calls, 194 such as a user calling an airline reservation center, the user may 195 have a set of languages he or she speaks, with perhaps preferences 196 for one or a few, while the airline reservation center will support a 197 fixed set of languages. Negotiation should select the user's most 198 preferred language that is supported by the call center. Both sides 199 should be aware of which language was negotiated. This is 200 conceptually similar to the way other aspects of each media stream 201 are negotiated using SDP (e.g., media type and codecs). 203 2. Terminology 205 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 206 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 207 document are to be interpreted as described in RFC 2119 [RFC2119]. 209 3. Expected Use 211 This facility may be used by NENA and 3GPP. NENA has already 212 referenced it in NENA 08-01 (i3 Stage 3 version 2) in describing 213 attributes of calls presented to an ESInet, and may add further 214 details in that or other documents. 3GPP may reference this 215 mechanism in general call handling and emergency call handling. Some 216 CRs introduced in SA1 have anticipated this functionality being 217 provided within SDP. 219 4. Desired Semantics 221 The desired solution is a media attribute that may be used within an 222 offer to indicate the preferred language of each media stream, and 223 within an answer to indicate the accepted language. The semantics of 224 including multiple values for a media stream within an offer is that 225 the languages are listed in order of preference. 227 (While it is true that a conversation among multilingual people often 228 involves multiple languages, the usefulness of providing a way to 229 negotiate this as a general facility is outweighed by the complexity 230 of the desired semantics of the SDP attribute to allow negotiation of 231 multiple simultaneous languages within an interactive media stream.) 233 5. The existing 'lang' attribute 235 RFC 4566 specifies an attribute 'lang' which sounds similar to what 236 is needed here, the difference being that it specifies that 'a=lang' 237 is declarative with the semantics of multiple 'lang' attributes being 238 that all of them are used, while we want a means to negotiate which 239 one is used in each stream. This difference means that the existing 240 'lang' attribute can't be used and we need to define a new attribute. 242 The text from RFC 4566 [RFC4566] is: 244 a=lang: 245 This can be a session-level attribute or a media-level attribute. 246 As a session-level attribute, it specifies the default language 247 for the session being described. As a media- level attribute, it 248 specifies the language for that media, overriding any session- 249 level language specified. Multiple lang attributes can be 250 provided either at session or media level if the session 251 description or media use multiple languages, in which case the 252 order of the attributes indicates the order of importance of the 253 various languages in the session or media from most important to 254 least important. 255 The "lang" attribute value must be a single [RFC3066] language tag 256 in US-ASCII [RFC3066]. It is not dependent on the charset 257 attribute. A "lang" attribute SHOULD be specified when a session 258 is of sufficient scope to cross geographic boundaries where the 259 language of recipients cannot be assumed, or where the session is 260 in a different language from the locally assumed norm. 262 A recent search of RFCs and Internet Drafts turned up only one use of 263 the 'lang' attribute (in a now-expired draft), and that sole use was 264 coincidentally in exactly the way we need (erroniously assuming that 265 the attribute was used for negotiation). The sole use was in an 266 example in a draft not directly related to language, where the 267 initial invitation contains two 'a=lang' entries for a media stream 268 (for English and Italian) and the OK accepts one of them (Italian). 270 The example serves as evidence of the need for an SDP attribute with 271 the semantics as described in this document; unfortunately, the 272 existing 'lang' attribute is not it. 274 6. Proposed Solution 276 An SDP attribute seems the natural choice to negotiate human 277 (natural) language of an interactive media stream. The attribute 278 value should be a language tag per RFC 5646 [RFC5646] 280 6.1. Rationale 282 The decision to base the proposal at the media negotiation level, and 283 specifically to use SDP, came after significant debate and 284 discussion. From an engineering standpoint, it is possible to meet 285 the objectives using a variety of mechanisms, but none are perfect. 286 None of the proposed alternatives was clearly better technically in 287 enough ways to win over proponents of the others, and none were 288 clearly so bad technically as to be easily rejected. As is often the 289 case in engineering, choosing the solution is a matter of balancing 290 trade-offs, and ultimately more a matter of taste than technical 291 merit. The two main proposals were to use SDP and SIP. SDP has the 292 advantage that the language is negotiated with the media to which it 293 applies, while SIP has the issue that the languages expressed may not 294 match the SDP media negotiated (for example, a session could 295 negotiate video at the SIP level but fail to negotiate any video 296 media stream at the SDP layer). 298 The mechanism described here for SDP can be adapted to media 299 negotiation protocols other than SDP. 301 6.2. New 'humintlang-send' and 'humintlang-recv' attributes 303 Rather than re-use 'lang' we define two new media-level attributes 304 starting with 'humintlang' (short for "human interactive language") 305 to negotiate which human language is used in each (interactive) media 306 stream. There are two attributes, one ending in "-send" and the 307 other in "-recv" to indicate the language used when sending and 308 receiving media: 310 a=humintlang-send: 311 a=humintlang-recv: 313 Each can appear multiple times in an offer for a media stream. 315 In an offer, the 'humintlang-send' values constitute a list in 316 preference order (first is most preferred) of the languages the 317 offerer wishes to send using the media, and the 'humintlang-recv' 318 values constitute a list in preference order of the languages the 319 offerer wishes to receive using the media. In cases where the user 320 wishes to use one media for sending and another for receiving (such 321 as a speech-impaired user who wishes to send using text and receive 322 using audio), one of the two MAY be unset. In cases where a media is 323 not primarily intended for language (for example, a video or audio 324 stream intended for background only) both SHOULD be unset. In other 325 cases, both SHOULD have the same values in the same order. The two 326 SHOULD NOT be set to languages which are difficult to match together 327 (e.g., specifying a desire to send audio in Hungarian and receive 328 audio in Portuguese will make it difficult to successfully complete 329 the call). 331 In an answer, 'humintlang-send' is the accepted language the answerer 332 will send (which in most cases is one of the languages in the offer's 333 'humintlang-recv'), and 'humintlang-recv' is the accepted language 334 the answerer expects to receive (which in most cases is one of the 335 languages in the offer's 'humintlang-send'). 337 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 338 describes mechanisms for matching language tags. While RFC 5646 339 provides a mechanism accommodating increasingly fine-grained 340 distinctions, in the interest of maximum interoperability for real- 341 time interactive communications, each 'humintlang-send' and 342 'humintlang-recv' value SHOULD be restricted to the largest 343 granularity of language tags; in other words, it is RECOMMENDED to 344 specify only a Primary-subtag and NOT to include subtags (e.g., for 345 region or dialect) unless the languages might be mutually 346 incomprehensible without them. 348 In an offer, each language tag value MAY have an asterisk appended as 349 the last character (after the registry value). The asterisk 350 indicates a request by the caller to not fail the call if there is no 351 language in common. See Section 6.3 for more information and 352 discussion. 354 When placing an emergency call, and in any other case where the 355 language cannot be assumed from context, each media stream in an 356 offer primarily intended for human language communication SHOULD 357 specify one or both 'humintlang-send' and 'humintlang-recv' 358 attributes (to avoid ambiguity). 360 Note that while signed language tags are used with a video stream to 361 indicate sign language, a spoken language tag for a video stream in 362 parallel with an audio stream with the same spoken language tag 363 indicates a request for a supplemental video stream to see the 364 speaker. 366 Clients acting on behalf of end users are expected to set one or both 367 'humintlang-send' and 'humintlang-recv' attributes on each media 368 stream primarily intended for human communication in an offer when 369 placing an outgoing session, but either ignore or take into 370 consideration the attributes when receiving incoming calls, based on 371 local configuration and capabilities. Systems acting on behalf of 372 call centers and PSAPs are expected to take into account the values 373 when processing inbound calls. 375 6.3. Advisory vs Required 377 One important consideration with this mechanism is if the call fails 378 if the callee does not support any of the languages requested by the 379 caller. 381 In order to provide for maximum likelihood of a successful 382 communication session, especially in the case of emergency calling, 383 the mechanism defined here provides a way for the caller to indicate 384 a preference for the call failing or succeeding when there is no 385 language in common. However, the callee is NOT REQUIRED to honor 386 this preference. For example, a PSAP MAY choose to attempt the call 387 even with no language in common, while a corporate call center MAY 388 choose to fail the call. 390 The mechanism for indicating this preference is that, in an offer, if 391 the last character of any of the 'humintlang-recv' or 'humintlang- 392 send' values is an asterisk, this indicates a request to not fail the 393 call (similar to SIP Accept-Language syntax). Either way, the called 394 party MAY ignore this, e.g., for the emergency services use case, a 395 PSAP will likely not fail the call. 397 6.4. Silly States 399 It is possible to specify a "silly state" where the language 400 specified does not make sense for the media type, such as specifying 401 a signed language for an audio media stream. 403 An offer MUST NOT be created where the language does not make sense 404 for the media type. If such an offer is received, the receiver MAY 405 reject the media, ignore the language specified, or attempt to 406 interpret the intent (e.g., if American Sign Language is specified 407 for an audio media stream, this might be interpreted as a desire to 408 use spoken English). 410 A spoken language tag for a video stream in conjunction with an audio 411 stream with the same language might indicate a request for 412 supplemental video to see the speaker. 414 7. IANA Considerations 416 IANA is kindly requested to add two entries to the 'att-field (media 417 level only)' table of the SDP parameters registry: 419 +------------------------------+-----------------+-----------------+ 420 | Type | Name | Reference | 421 +------------------------------+-----------------+-----------------+ 422 | att-field (media level only) | humintlang-send | (this document) | 423 | att-field (media level only) | humintlang-recv | (this document) | 424 +------------------------------+-----------------+-----------------+ 426 Table 1: att-field (media level only)' entries 428 8. Security Considerations 430 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 431 use of that RFC). In addition, if the 'humintlang-send' or 432 'humintlang-recv' values are altered or deleted en route, the session 433 could fail or languages incomprehensible to the caller could be 434 selected; however, this is also a risk if any SDP parameters are 435 modified en route. 437 9. Changes from Previous Versions 439 9.1. Changes from draft-gellens-slim-...-02 to draft-gellens- 440 slim-...-03 442 o Removed Use Cases section, per face-to-face discussion at IETF 93 443 o Removed discussion of routing, per face-to-face discussion at IETF 444 93 446 9.2. Changes from draft-gellens-slim-...-01 to draft-gellens- 447 slim-...-02 449 o Updated NENA usage mention 450 o Removed background text reference to draft-saintandre-sip-xmpp- 451 chat-04 since that draft expired 453 9.3. Changes from draft-gellens-slim-...-00 to draft-gellens- 454 slim-...-01 456 o Revision to keep draft from expiring 458 9.4. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 459 slim-...-00 461 o Changed name from -mmusic- to -slim- to reflect proposed WG name 462 o As a result of the face-to-face discussion in Toronto, the SDP vs 463 SIP issue was resolved by going back to SDP, taking out the SIP 464 hint, and converting what had been a set of alternate proposals 465 for various ways of doing it within SIP into an informative annex 466 section which includes background on why SDP is the proposal 467 o Added mention that enabling a mutually comprehensible language is 468 a general problem of which this document addresses the real-time 469 side, with reference to [draft-tomkinson-multilangcontent] which 470 addresses the non-real-time side. 472 9.5. Changes from draft-gellens-mmusic-...-01 to -02 474 o Added clarifying text on leaving attributes unset for media not 475 primarily intended for human language communication (e.g., 476 background audio or video). 477 o Added new section Appendix A ("Alternative Proposal: Caller- 478 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 479 level. 481 9.6. Changes from draft-gellens-mmusic-...-00 to -01 483 o Relaxed language on setting -send and -receive to same values; 484 added text on leaving on empty to indicate asymmetric usage. 485 o Added text that clients on behalf of end users are expected to set 486 the attributes on outgoing calls and ignore on incoming calls 487 while systems on behalf of call centers and PSAPs are expected to 488 take the attributes into account when processing incoming calls. 490 9.7. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 492 o Updated text to refer to RFC 5646 rather than the IANA language 493 subtags registry directly. 494 o Moved discussion of existing 'lang' attribute out of "Proposed 495 Solution" section and into own section now that it is not part of 496 proposal. 497 o Updated text about existing 'lang' attribute. 498 o Added example use cases. 499 o Replaced proposed single 'humintlang' attribute with 'humintlang- 500 send' and 'humintlang-recv' per Harald's request/information that 501 it was a misuse of SDP to use the same attribute for sending and 502 receiving. 503 o Added section describing usage being advisory vs required and text 504 in attribute section. 505 o Added section on SIP "hint" header (not yet nailed down between 506 new and existing header). 507 o Added text discussing usage in policy-based routing function or 508 use of SIP header "hint" if unable to do so. 509 o Added SHOULD that the value of the parameters stick to the largest 510 granularity of language tags. 511 o Added text to Introduction to be try and be more clear about 512 purpose of document and problem being solved. 513 o Many wording improvements and clarifications throughout the 514 document. 515 o Filled in Security Considerations. 516 o Filled in IANA Considerations. 517 o Added to Acknowledgments those who participated in the Orlando ad- 518 hoc discussion as well as those who participated in email 519 discussion and side one-on-one discussions. 521 9.8. Changes from draft-gellens-...-01 to -02 523 o Updated text for (possible) new attribute "humintlang" to 524 reference RFC 5646 525 o Added clarifying text for (possible) re-use of existing 'lang' 526 attribute saying that the registration would be updated to reflect 527 different semantics for multiple values for interactive versus 528 non-interactive media. 529 o Added clarifying text for (possible) new attribute "humintlang" to 530 attempt to better describe the role of language tags in media in 531 an offer and an answer. 533 9.9. Changes from draft-gellens-...-00 to -01 535 o Changed name of (possible) new attribute from 'humlang" to 536 "humintlang" 537 o Added discussion of silly state (language not appropriate for 538 media type) 539 o Added Voice Carry Over example 540 o Added mention of multilingual people and multiple languages 541 o Minor text clarifications 543 10. Contributors 545 Gunnar Hellstrom deserves special mention for his reviews, 546 assistance, and especially for contributing the core text in 547 Appendix A. 549 11. Acknowledgments 551 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 552 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 553 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 554 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 555 Peter Saint-Andre, and Dale Worley for reviews, corrections, 556 suggestions, and participating in in-person and email discussions. 558 12. References 560 12.1. Normative References 562 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 563 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 564 RFC2119, March 1997, 565 . 567 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 568 "Indicating User Agent Capabilities in the Session 569 Initiation Protocol (SIP)", RFC 3840, August 2004. 571 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 572 Preferences for the Session Initiation Protocol (SIP)", 573 RFC 3841, August 2004. 575 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 576 Description Protocol", RFC 4566, July 2006. 578 [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying 579 Languages", BCP 47, RFC 5646, September 2009. 581 12.2. Informational References 583 [I-D.iab-privacy-considerations] 584 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 585 Morris, J., Hansen, M., and R. Smith, "Privacy 586 Considerations for Internet Protocols", draft-iab-privacy- 587 considerations-09 (work in progress), May 2013. 589 [I-D.saintandre-sip-xmpp-chat] 590 Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, 591 "Interworking between the Session Initiation Protocol 592 (SIP) and the Extensible Messaging and Presence Protocol 593 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- 594 chat-06 (work in progress), June 2013. 596 [RFC3066] Alvestrand, H., "Tags for the Identification of 597 Languages", RFC 3066, January 2001. 599 [draft-tomkinson-multilangcontent] 600 Tomkinson, N. and N. Borenstein, "Multiple Language 601 Content Type", draft-tomkinson-multilangcontent (work in 602 progress), April 2014. 604 Appendix A. Historic Alternative Proposal: Caller-prefs 606 The decision to base the proposal at the media negotiation level, and 607 specifically to use SDP, came after significant debate and 608 discussion. It is possible to meet the objectives using a variety of 609 mechanisms, but none are perfect. Using SDP means dealing with the 610 complexity of SDP, and leaves out real-time session protocols that do 611 not use SDP. The major alternative proposal was to use SIP. Using 612 SIP leaves out non-SIP session protocols, but more fundamentally, 613 would occur at a different layer than the media negotiation. This 614 results in a more fragile solution since the media modality and 615 language would be negotiated using SIP, and then the specific media 616 formats (which inherently include the modality) would be negotiated 617 at a different level (typically SDP, especially in the emergency 618 calling cases), making it easier to have mismatches (such as where 619 the media modality negotiated in SIP don't match what was negotiated 620 using SDP). 622 An alternative proposal was to use the SIP-level Caller Preferences 623 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 625 The Caller-prefs mechanism includes a priority system; this would 626 allow different combinations of media and languages to be assigned 627 different priorities. The evaluation and decisions on what to do 628 with the call can be done either by proxies along the call path, or 629 by the addressed UA. Evaluation of alternatives for routing is 630 described in RFC 3841 [RFC3841]. 632 A.1. Use of Caller Preferences Without Additions 634 The following would be possible without adding any new registered 635 tags: 637 Potential callers and recipients MAY include in the Contact field in 638 their SIP registrations media and language tags according to the 639 joint capabilities of the UA and the human user according to RFC 3840 640 [RFC3840]. 642 The most relevant media capability tags are "video", "text" and 643 "audio". Each tag represents a capability to use the media in two- 644 way communication. 646 Language capabilities are declared with a comma-separated list of 647 languages that can be used in the call as parameters to the tag 648 "language=". 650 This is an example of how it is used in a SIP REGISTER: 652 REGISTER user@example.net 653 Contact: audio; video; text; 654 language="en,es,ase" 656 Including this information in SIP REGISTER allows proxies to act on 657 the information. For the problem set addressed by this document, it 658 is not anticipated that proxies will do so using registration data. 659 Further, there are classes of devices (such as cellular mobile 660 phones) that are not anticipated to include this information in their 661 registrations. Hence, use in registration is OPTIONAL. 663 In a call, a list of acceptable media and language combinations is 664 declared, and a priority assigned to each combination. 666 This is done by the Accept-Contact header field, which defines 667 different combinations of media and languages and assigns priorities 668 for completing the call with the SIP URI represented by that Contact. 669 A priority is assigned to each set as a so-called "q-value" which 670 ranges from 1 (most preferred) to 0 (least preferred). 672 Using the Accept-Contact header field in INVITE requests and 673 responses allows these capabilities to be expressed and used during 674 call set-up. Clients SHOULD include this information in INVITE 675 requests and responses. 677 Example: 679 Accept-Contact: *; text; language="en"; q=0.2 680 Accept-Contact: *; video; language="ase"; q=0.8 682 This example shows the highest preference expressed by the caller is 683 to use video with American Sign Language (language code "ase"). As a 684 fallback, it is acceptable to get the call connected with only 685 English text used for human communication. Other media may of course 686 be connected as well, without expectation that it will be usable by 687 the caller for interactive communications (but may still be helpful 688 to the caller). 690 This system satisfies all the needs described in the previous 691 chapters, except that language specifications do not make any 692 distinction between spoken and written language, and that the need 693 for directionality in the specification cannot be fulfilled. 695 To some degree the lack of media specification between speech and 696 text in language tags can be compensated by only specifying the 697 important medium in the Accept-Contact field. 699 Thus, a user who wants to use English mainly for text would specify: 701 Accept-Contact: *;text;language="en";q=1.0 703 While a user who wants to use English mainly for speech but accept it 704 for text would specify: 706 Accept-Contact: *;audio;language="en";q=0.8 707 Accept-Contact: *;text;language="en";q=0.2 709 However, a user who would like to talk, but receive text back has no 710 way to do it with the existing specification. 712 A.2. Additional Caller Preferences for Asymmetric Needs 714 In order to be able to specify asymmetric preferences, there are two 715 possibilities. Either new language tags in the style of the 716 humintlang parameters described above for SDP could be registered, or 717 additional media tags describing the asymmetry could be registered. 719 A.2.1. Caller Preferences for Asymmetric Modality Needs 721 The following new media tags should be defined: 723 speech-receive 724 speech-send 725 text-receive 726 text-send 727 sign-send 728 sign-receive 730 A user who prefers to talk and get text in return in English would 731 register the following (if including this information in registration 732 data): 734 REGISTER user@example.net 735 Contact: audio;text;speech-send;text- 736 receive;language="en" 738 At call time, a user who prefers to talk and get text in return in 739 English would set the Accept-Contact header field to: 741 Accept-Contact: *; audio; text; speech-receive; text-send; 742 language="en";q=0.8 743 Accept-Contact: *; text; language="en"; q=0.2 745 Note that the directions specified here are as viewed from the callee 746 side to match what the callee has registered. 748 A bridge arranged for invoking a relay service specifically arranged 749 for captioned telephony would register the following for supporting 750 calling users: 752 REGISTER ct@ctrelay.net 753 Contact: audio; text; speech-receive; 754 text-send; language="en" 756 A bridge arranged for invoking a relay service specifically arranged 757 for captioned telephony would register the following for supporting 758 called users: 760 REGISTER ct@ctrelay.net 761 Contact: audio; text; speech-send; text- 762 receive; language="en" 764 At call time, these alternatives are included in the list of possible 765 outcome of the call routing by the SIP proxies and the proper relay 766 service is invoked. 768 A.2.2. Caller Preferences for Asymmetric Language Tags 770 An alternative is to register new language tags for the purpose of 771 asymmetric language usage. 773 Instead of using "language=", six new language tags would be 774 registered: 776 humintlang-text-recv 777 humintlang-text-send 778 humintlang-speech-recv 779 humintlang-speech-send 780 humintlang-sign-recv 781 humintlang-sign-send 783 These language tags would be used instead of the regular 784 bidirectional language tags, and users with bidirectional 785 capabilities SHOULD specify values for both directions. Services 786 specifically arranged for supporting users with asymmetric needs 787 SHOULD specify only the asymmetry they support. 789 Author's Address 791 Randall Gellens 792 Qualcomm Technologies Inc. 793 5775 Morehouse Drive 794 San Diego, CA 92121 795 US 797 Email: rg+ietf@randy.pensive.org