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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 July 4, 2015 5 Expires: January 5, 2016 7 Negotiating Human Language in Real-Time Communications 8 draft-gellens-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 routed 18 to a Public Safety Answering Point (PSAP) or call taker capable of 19 communicating with the user, or a translator or relay operator can be 20 bridged into the call during setup, but this applies to non-emergency 21 calls as well (as an example, when calling a company call center). 23 This document describes the need and expected use, and describes a 24 solution using new SDP stream 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 5, 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. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 5 64 4.1. Emergency Call from English Speaker in Spain . . . . . . 5 65 4.2. Emergency Call from Spanish/English Speaker in France . . 6 66 4.3. Call to Call Center from Russian Speaker in U.S. . . . . 6 67 4.4. Emergency Call from speech-impaired caller in the U.S. . 6 68 4.5. Emergency Call from deaf caller in the U.S. . . . . . . . 7 69 5. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 7 70 6. The existing 'lang' attribute . . . . . . . . . . . . . . . . 7 71 7. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 8 72 7.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 8 73 7.2. New 'humintlang-send' and 'humintlang-recv' attributes . 9 74 7.3. Advisory vs Required . . . . . . . . . . . . . . . . . . 10 75 7.4. Silly States . . . . . . . . . . . . . . . . . . . . . . 11 76 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 77 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 78 10. Changes from Previous Versions . . . . . . . . . . . . . . . 12 79 10.1. Changes from draft-gellens-slim-...-00 to draft-gellens- 80 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . 12 81 10.2. Changes from draft-gellens-mmusic-...-02 to draft- 82 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . 12 83 10.3. Changes from draft-gellens-mmusic-...-01 to -02 . . . . 12 84 10.4. Changes from draft-gellens-mmusic-...-00 to -01 . . . . 12 85 10.5. Changes from draft-gellens-...-02 to draft-gellens- 86 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . 12 87 10.6. Changes from draft-gellens-...-01 to -02 . . . . . . . . 13 88 10.7. Changes from draft-gellens-...-00 to -01 . . . . . . . . 13 89 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14 90 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 91 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 92 13.1. Normative References . . . . . . . . . . . . . . . . . . 14 93 13.2. Informational References . . . . . . . . . . . . . . . . 14 94 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 15 95 A.1. Use of Caller Preferences Without Additions . . . . . . . 15 96 A.2. Additional Caller Preferences for Asymmetric Needs . . . 17 97 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 17 98 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 19 99 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 101 1. Introduction 103 A mutually comprehensible language is helpful for human 104 communication. This document addresses the real-time, interactive 105 side of the issue. A companion document on language selection in 106 email [draft-tomkinson-multilangcontent] addresses the non-real-time 107 side. 109 When setting up interactive communication sessions (using SIP or 110 other protocols), human (natural) language and media modality (voice, 111 video, text) negotiation may be needed. Unless the caller and callee 112 know each other or there is contextual or out of band information 113 from which the language(s) and media modalities can be determined, 114 there is a need for spoken, signed, or written languages to be 115 negotiated based on the caller's needs and the callee's capabilities. 116 This need applies to both emergency and non-emergency calls. For 117 various reasons, including the ability to establish multiple streams 118 using different media (e.g., voice, text, video), it makes sense to 119 use a per-stream negotiation mechanism, in this case, SDP. 121 This approach has a number of benefits, including that it is generic 122 (applies to all interactive communications negotiated using SDP) and 123 not limited to emergency calls. In some cases such a facility isn't 124 needed, because the language is known from the context (such as when 125 a caller places a call to a sign language relay center, to a friend, 126 or colleague). But it is clearly useful in many other cases. For 127 example, someone calling a company call center or a Public Safety 128 Answering Point (PSAP) should be able to indicate if one or more 129 specific signed, written, and/or spoken languages are preferred, the 130 callee should be able to indicate its capabilities in this area, and 131 the call proceed using in-common language(s) and media forms. 133 Since this is a protocol mechanism, the user equipment (UE client) 134 needs to know the user's preferred languages; a reasonable technique 135 could include a configuration mechanism with a default of the 136 language of the user interface. In some cases, a UE could tie 137 language and media preferences, such as a preference for a video 138 stream using a signed language and/or a text or audio stream using a 139 written/spoken language. 141 Including the user's human (natural) language preferences in the 142 session establishment negotiation is independent of the use of a 143 relay service and is transparent to a voice service provider. For 144 example, assume a user within the United States who speaks Spanish 145 but not English places a voice call using an IMS device. It doesn't 146 matter if the call is an emergency call or not (e.g., to an airline 147 reservation desk). The language information is transparent to the 148 IMS carrier, but is part of the session negotiation between the UE 149 and the terminating entity. In the case of a call to e.g., an 150 airline, the call can be automatically routed to a Spanish-speaking 151 agent. In the case of an emergency call, the Emergency Services IP 152 network (ESInet) and the PSAP may choose to take the language and 153 media preferences into account when determining how to route and 154 process the call (i.e., language and media needs may be considered 155 within policy-based routing (PBR)). 157 By treating language as another attribute that is negotiated along 158 with other aspects of a media stream, it becomes possible to 159 accommodate a range of users' needs and called party facilities. For 160 example, some users may be able to speak several languages, but have 161 a preference. Some called parties may support some of those 162 languages internally but require the use of a translation service for 163 others, or may have a limited number of call takers able to use 164 certain languages. Another example would be a user who is able to 165 speak but is deaf or hard-of-hearing and requires a voice stream plus 166 a text stream (known as voice carry over). Making language a media 167 attribute allows the standard session negotiation mechanism to handle 168 this by providing the information and mechanism for the endpoints to 169 make appropriate decisions. 171 Regarding relay services, in the case of an emergency call requiring 172 sign language such as ASL, there are two common approaches: the 173 caller initiates the call to a relay center, or the caller places the 174 call to emergency services (e.g., 911 in the U.S. or 112 in Europe). 175 In the former case, the language need is ancillary and supplemental. 176 In the latter case, the ESInet and/or PSAP may take the need for sign 177 language into account and bridge in a relay center. In this case, 178 the ESInet and PSAP have all the standard information available (such 179 as location) but are able to bridge the relay sooner in the call 180 processing. 182 By making this facility part of the end-to-end negotiation, the 183 question of which entity provides or engages the relay service 184 becomes separate from the call processing mechanics; if the caller 185 directs the call to a relay service then the human language 186 negotiation facility provides extra information to the relay service 187 but calls will still function without it; if the caller directs the 188 call to emergency services, then the ESInet/PSAP are able to take the 189 user's human language needs into account, e.g., by routing to a 190 particular PSAP or call taker or bridging a relay service or 191 translator. 193 The term "negotiation" is used here rather than "indication" because 194 human language (spoken/written/signed) is something that can be 195 negotiated in the same way as which forms of media (audio/text/video) 196 or which codecs. For example, if we think of non-emergency calls, 197 such as a user calling an airline reservation center, the user may 198 have a set of languages he or she speaks, with perhaps preferences 199 for one or a few, while the airline reservation center will support a 200 fixed set of languages. Negotiation should select the user's most 201 preferred language that is supported by the call center. Both sides 202 should be aware of which language was negotiated. This is 203 conceptually similar to the way other aspects of each media stream 204 are negotiated using SDP (e.g., media type and codecs). 206 2. Terminology 208 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 209 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 210 document are to be interpreted as described in RFC 2119 [RFC2119]. 212 3. Expected Use 214 This facility may be used by NENA and 3GPP. NENA has already 215 referenced it in NENA 08-01 (i3 Stage 3 version 2) in describing 216 attributes of calls presented to an ESInet, and may add further 217 details in that or other documents describing Policy-Based Routing 218 (PBR) capabilities within a Policy-Based Routing Function. 3GPP may 219 reference this mechanism in general call handling and emergency call 220 handling. Some CRs introduced in SA1 have anticipated this 221 functionality being provided within SDP. 223 4. Example Use Cases 225 4.1. Emergency Call from English Speaker in Spain 227 Someone who speaks only English is visiting Spain and places an 228 emergency (112) call. The call offers an audio stream using English. 229 The ESInet and PSAP have policy-based routing rules that take into 230 account the SDP language request when deciding how to route and 231 process the call. The ESInet routes the call to a PSAP within Spain 232 where an English-speaking call taker is available, and the PSAP 233 selects an English-speaking call taker to handle the call. The PSAP 234 answers the offer with an audio stream using English. The call is 235 established with an audio stream; the caller and call taker 236 communicate in English. 238 Alternatively, the ESInet routes the call to a cooperating PSAP 239 within the U.K. The PSAP answers the offer with an audio stream 240 using English. The call is established with an audio stream; the 241 caller and call taker communicate in English. (This approach is 242 similar to that envisioned in REACH112 Total Conversation.) 244 4.2. Emergency Call from Spanish/English Speaker in France 246 Someone who speaks both Spanish and English (but prefers Spanish) is 247 visiting France and places an emergency (112) call. The call offers 248 an audio stream listing first Spanish (meaning most preferred) and 249 then English. The ESInet and PSAP have policy-based routing rules 250 that take into account the SDP language request when deciding how to 251 route and process the call. The ESInet routes the call to a PSAP 252 within France where a Spanish-speaking call taker is available, and 253 the PSAP selects a Spanish-speaking call taker to handle the call. 254 The PSAP answers the offer with an audio stream listing Spanish. The 255 call is established with an audio stream; the caller and call taker 256 communicate in Spanish. 258 Alternatively, the ESInet routes the call to a cooperating PSAP in 259 Spain or England. (This approach is similar to that envisioned in 260 REACH112 Total Conversation.) 262 Alternatively, there is no ESInet or the ESInet does not take 263 language into account in its PBR. The call is routed to a PSAP in 264 France. The PSAP ignores the language information in the SDP offer, 265 and answers the offer with an audio stream with no language or with 266 French. The UE continues the call anyway. The call taker answers in 267 French, the user tries speaking Spanish and perhaps English. The 268 call taker bridges in a translation service or transfers the call to 269 a multilingual call taker. 271 4.3. Call to Call Center from Russian Speaker in U.S. 273 A Russian speaker is visiting the U.S. and places a call to her 274 airline reservation desk to inquire about her return flight. The 275 airline call processing system takes into account the SDP language 276 request and decides to route the call to its call center within 277 Russia. 279 Alternatively, if the airline call processing system does not look at 280 SDP, it uses the SIP "hint" if present. 282 4.4. Emergency Call from speech-impaired caller in the U.S. 284 Someone who uses English but is speech-impaired places an emergency 285 (911) call. The call offers an audio stream listing English and a 286 real-time text stream also using English. The ESInet and PSAP have 287 policy-based routing rules that take into account the SDP language 288 and media requests when deciding how to route and process the call. 290 The ESInet routes the call to a PSAP with real-time text 291 capabilities. The PSAP answers the offer with an audio stream 292 listing English and a real-time text stream listing English. The 293 call is established with an audio and a real-time text stream; the 294 caller and call taker communicate in English using voice from the 295 call-taker to the caller and text from the caller to the call taker. 296 The audio stream is two-way, allowing the call taker to hear 297 background sounds. 299 4.5. Emergency Call from deaf caller in the U.S. 301 A deaf caller who uses American Sign Language (ASL) places an 302 emergency (911) call. The call offers a video stream listing ASL and 303 an audio stream with no language indicated. The ESInet and PSAP have 304 policy-based routing rules that take into account the SDP language 305 and media needs when deciding how to route and process the call. The 306 ESInet routes the call to a PSAP. The PSAP answers the offer with an 307 audio stream listing English and a video stream listing ASL. The 308 PSAP bridges in a sign language interpreter. The call is established 309 with an audio and a video stream. 311 5. Desired Semantics 313 The desired solution is a media attribute that may be used within an 314 offer to indicate the preferred language of each media stream, and 315 within an answer to indicate the accepted language. The semantics of 316 including multiple values for a media stream within an offer is that 317 the languages are listed in order of preference. 319 (While it is true that a conversation among multilingual people often 320 involves multiple languages, the usefulness of providing a way to 321 negotiate this as a general facility is outweighed by the complexity 322 of the desired semantics of the SDP attribute to allow negotiation of 323 multiple simultaneous languages within an interactive media stream.) 325 6. The existing 'lang' attribute 327 RFC 4566 specifies an attribute 'lang' which sounds similar to what 328 is needed here, the difference being that it specifies that 'a=lang' 329 is declarative with the semantics of multiple 'lang' attributes being 330 that all of them are used, while we want a means to negotiate which 331 one is used in each stream. This difference means that the existing 332 'lang' attribute can't be used and we need to define a new attribute. 334 The text from RFC 4566 [RFC4566] is: 336 a=lang: 337 This can be a session-level attribute or a media-level attribute. 338 As a session-level attribute, it specifies the default language 339 for the session being described. As a media- level attribute, it 340 specifies the language for that media, overriding any session- 341 level language specified. Multiple lang attributes can be 342 provided either at session or media level if the session 343 description or media use multiple languages, in which case the 344 order of the attributes indicates the order of importance of the 345 various languages in the session or media from most important to 346 least important. 347 The "lang" attribute value must be a single [RFC3066] language tag 348 in US-ASCII [RFC3066]. It is not dependent on the charset 349 attribute. A "lang" attribute SHOULD be specified when a session 350 is of sufficient scope to cross geographic boundaries where the 351 language of recipients cannot be assumed, or where the session is 352 in a different language from the locally assumed norm. 354 A recent search of RFCs and Internet Drafts turned up only one use of 355 the 'lang' attribute (in a now-expired draft), and that sole use was 356 coincidentally in exactly the way we need (erroniously assuming that 357 the attribute was used for negotiation). The sole use was in an 358 example in a draft not directly related to language, where the 359 initial invitation contains two 'a=lang' entries for a media stream 360 (for English and Italian) and the OK accepts one of them (Italian). 362 The example serves as evidence of the need for an SDP attribute with 363 the semantics as described in this document; unfortunately, the 364 existing 'lang' attribute is not it. 366 7. Proposed Solution 368 An SDP attribute seems the natural choice to negotiate human 369 (natural) language of an interactive media stream. The attribute 370 value should be a language tag per RFC 5646 [RFC5646] 372 7.1. Rationale 374 The decision to base the proposal at the media negotiation level, and 375 specifically to use SDP, came after significant debate and 376 discussion. From an engineering standpoint, it is possible to meet 377 the objectives using a variety of mechanisms, but none are perfect. 378 None of the proposed alternatives was clearly better technically in 379 enough ways to win over proponents of the others, and none were 380 clearly so bad technically as to be easily rejected. As is often the 381 case in engineering, choosing the solution is a matter of balancing 382 trade-offs, and ultimately more a matter of taste than technical 383 merit. The two main proposals were to use SDP and SIP. SDP has the 384 advantage that the language is negotiated with the media to which it 385 applies, while SIP has the issue that the languages expressed may not 386 match the SDP media negotiated (for example, a session could 387 negotiate video at the SIP level but fail to negotiate any video 388 media stream at the SDP layer). 390 The mechanism described here for SDP can be adapted to media 391 negotiation protocols other than SDP. 393 7.2. New 'humintlang-send' and 'humintlang-recv' attributes 395 Rather than re-use 'lang' we define two new media-level attributes 396 starting with 'humintlang' (short for "human interactive language") 397 to negotiate which human language is used in each (interactive) media 398 stream. There are two attributes, one ending in "-send" and the 399 other in "-recv" to indicate the language used when sending and 400 receiving media: 402 a=humintlang-send: 403 a=humintlang-recv: 405 Each can appear multiple times in an offer for a media stream. 407 In an offer, the 'humintlang-send' values constitute a list in 408 preference order (first is most preferred) of the languages the 409 offerer wishes to send using the media, and the 'humintlang-recv' 410 values constitute a list in preference order of the languages the 411 offerer wishes to receive using the media. In cases where the user 412 wishes to use one media for sending and another for receiving (such 413 as a speech-impaired user who wishes to send using text and receive 414 using audio), one of the two MAY be unset. In cases where a media is 415 not primarily intended for language (for example, a video or audio 416 stream intended for background only) both SHOULD be unset. In other 417 cases, both SHOULD have the same values in the same order. The two 418 SHOULD NOT be set to languages which are difficult to match together 419 (e.g., specifying a desire to send audio in Hungarian and receive 420 audio in Portuguese will make it difficult to successfully complete 421 the call). 423 In an answer, 'humintlang-send' is the accepted language the answerer 424 will send (which in most cases is one of the languages in the offer's 425 'humintlang-recv'), and 'humintlang-recv' is the accepted language 426 the answerer expects to receive (which in most cases is one of the 427 languages in the offer's 'humintlang-send'). 429 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 430 describes mechanisms for matching language tags. While RFC 5646 431 provides a mechanism accommodating increasingly fine-grained 432 distinctions, in the interest of maximum interoperability for real- 433 time interactive communications, each 'humintlang-send' and 434 'humintlang-recv' value SHOULD be restricted to the largest 435 granularity of language tags; in other words, it is RECOMMENDED to 436 specify only a Primary-subtag and NOT to include subtags (e.g., for 437 region or dialect) unless the languages might be mutually 438 incomprehensible without them. 440 In an offer, each language tag value MAY have an asterisk appended as 441 the last character (after the registry value). The asterisk 442 indicates a request by the caller to not fail the call if there is no 443 language in common. See Section 7.3 for more information and 444 discussion. 446 When placing an emergency call, and in any other case where the 447 language cannot be assumed from context, each media stream in an 448 offer primarily intended for human language communication SHOULD 449 specify one or both 'humintlang-send' and 'humintlang-recv' 450 attributes (to avoid ambiguity). 452 Note that while signed language tags are used with a video stream to 453 indicate sign language, a spoken language tag for a video stream in 454 parallel with an audio stream with the same spoken language tag 455 indicates a request for a supplemental video stream to see the 456 speaker. 458 Clients acting on behalf of end users are expected to set one or both 459 'humintlang-send' and 'humintlang-recv' attributes on each media 460 stream primarily intended for human communication in an offer when 461 placing an outgoing session, but either ignore or take into 462 consideration the attributes when receiving incoming calls, based on 463 local configuration and capabilities. Systems acting on behalf of 464 call centers and PSAPs are expected to take into account the values 465 when processing inbound calls. 467 7.3. Advisory vs Required 469 One important consideration with this mechanism is if the call fails 470 if the callee does not support any of the languages requested by the 471 caller. 473 In order to provide for maximum likelihood of a successful 474 communication session, especially in the case of emergency calling, 475 the mechanism defined here provides a way for the caller to indicate 476 a preference for the call failing or succeeding when there is no 477 language in common. However, the callee is NOT REQUIRED to honor 478 this preference. For example, a PSAP MAY choose to attempt the call 479 even with no language in common, while a corporate call center MAY 480 choose to fail the call. 482 The mechanism for indicating this preference is that, in an offer, if 483 the last character of any of the 'humintlang-recv' or 'humintlang- 484 send' values is an asterisk, this indicates a request to not fail the 485 call (similar to SIP Accept-Language syntax). Either way, the called 486 party MAY ignore this, e.g., for the emergency services use case, a 487 PSAP will likely not fail the call. 489 7.4. Silly States 491 It is possible to specify a "silly state" where the language 492 specified does not make sense for the media type, such as specifying 493 a signed language for an audio media stream. 495 An offer MUST NOT be created where the language does not make sense 496 for the media type. If such an offer is received, the receiver MAY 497 reject the media, ignore the language specified, or attempt to 498 interpret the intent (e.g., if American Sign Language is specified 499 for an audio media stream, this might be interpreted as a desire to 500 use spoken English). 502 A spoken language tag for a video stream in conjunction with an audio 503 stream with the same language might indicate a request for 504 supplemental video to see the speaker. 506 8. IANA Considerations 508 IANA is kindly requested to add two entries to the 'att-field (media 509 level only)' table of the SDP parameters registry: 511 +------------------------------+-----------------+-----------------+ 512 | Type | Name | Reference | 513 +------------------------------+-----------------+-----------------+ 514 | att-field (media level only) | humintlang-send | (this document) | 515 | att-field (media level only) | humintlang-recv | (this document) | 516 +------------------------------+-----------------+-----------------+ 518 Table 1: att-field (media level only)' entries 520 9. Security Considerations 522 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 523 use of that RFC). In addition, if the 'humintlang-send' or 524 'humintlang-recv' values are altered or deleted en route, the session 525 could fail or languages incomprehensible to the caller could be 526 selected; however, this is also a risk if any SDP parameters are 527 modified en route. 529 10. Changes from Previous Versions 531 10.1. Changes from draft-gellens-slim-...-00 to draft-gellens- 532 slim-...-01 534 o Revision to keep draft from expiring 536 10.2. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 537 slim-...-00 539 o Changed name from -mmusic- to -slim- to reflect proposed WG name 540 o As a result of the face-to-face discussion in Toronto, the SDP vs 541 SIP issue was resolved by going back to SDP, taking out the SIP 542 hint, and converting what had been a set of alternate proposals 543 for various ways of doing it within SIP into an informative annex 544 section which includes background on why SDP is the proposal 545 o Added mention that enabling a mutually comprehensible language is 546 a general problem of which this document addresses the real-time 547 side, with reference to [draft-tomkinson-multilangcontent] which 548 addresses the non-real-time side. 550 10.3. Changes from draft-gellens-mmusic-...-01 to -02 552 o Added clarifying text on leaving attributes unset for media not 553 primarily intended for human language communication (e.g., 554 background audio or video). 555 o Added new section Appendix A ("Alternative Proposal: Caller- 556 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 557 level. 559 10.4. Changes from draft-gellens-mmusic-...-00 to -01 561 o Relaxed language on setting -send and -receive to same values; 562 added text on leaving on empty to indicate asymmetric usage. 563 o Added text that clients on behalf of end users are expected to set 564 the attributes on outgoing calls and ignore on incoming calls 565 while systems on behalf of call centers and PSAPs are expected to 566 take the attributes into account when processing incoming calls. 568 10.5. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 570 o Updated text to refer to RFC 5646 rather than the IANA language 571 subtags registry directly. 572 o Moved discussion of existing 'lang' attribute out of "Proposed 573 Solution" section and into own section now that it is not part of 574 proposal. 575 o Updated text about existing 'lang' attribute. 576 o Added example use cases. 578 o Replaced proposed single 'humintlang' attribute with 'humintlang- 579 send' and 'humintlang-recv' per Harald's request/information that 580 it was a misuse of SDP to use the same attribute for sending and 581 receiving. 582 o Added section describing usage being advisory vs required and text 583 in attribute section. 584 o Added section on SIP "hint" header (not yet nailed down between 585 new and existing header). 586 o Added text discussing usage in policy-based routing function or 587 use of SIP header "hint" if unable to do so. 588 o Added SHOULD that the value of the parameters stick to the largest 589 granularity of language tags. 590 o Added text to Introduction to be try and be more clear about 591 purpose of document and problem being solved. 592 o Many wording improvements and clarifications throughout the 593 document. 594 o Filled in Security Considerations. 595 o Filled in IANA Considerations. 596 o Added to Acknowledgments those who participated in the Orlando ad- 597 hoc discussion as well as those who participated in email 598 discussion and side one-on-one discussions. 600 10.6. Changes from draft-gellens-...-01 to -02 602 o Updated text for (possible) new attribute "humintlang" to 603 reference RFC 5646 604 o Added clarifying text for (possible) re-use of existing 'lang' 605 attribute saying that the registration would be updated to reflect 606 different semantics for multiple values for interactive versus 607 non-interactive media. 608 o Added clarifying text for (possible) new attribute "humintlang" to 609 attempt to better describe the role of language tags in media in 610 an offer and an answer. 612 10.7. Changes from draft-gellens-...-00 to -01 614 o Changed name of (possible) new attribute from 'humlang" to 615 "humintlang" 616 o Added discussion of silly state (language not appropriate for 617 media type) 618 o Added Voice Carry Over example 619 o Added mention of multilingual people and multiple languages 620 o Minor text clarifications 622 11. Contributors 624 Gunnar Hellstrom deserves special mention for his reviews, 625 assistance, and especially for contributing the core text in 626 Appendix A. 628 12. Acknowledgments 630 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 631 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 632 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 633 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 634 Peter Saint-Andre, and Dale Worley for reviews, corrections, 635 suggestions, and participating in in-person and email discussions. 637 13. References 639 13.1. Normative References 641 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 642 Requirement Levels", BCP 14, RFC 2119, March 1997. 644 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 645 "Indicating User Agent Capabilities in the Session 646 Initiation Protocol (SIP)", RFC 3840, August 2004. 648 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 649 Preferences for the Session Initiation Protocol (SIP)", 650 RFC 3841, August 2004. 652 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 653 Description Protocol", RFC 4566, July 2006. 655 [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying 656 Languages", BCP 47, RFC 5646, September 2009. 658 13.2. Informational References 660 [I-D.iab-privacy-considerations] 661 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 662 Morris, J., Hansen, M., and R. Smith, "Privacy 663 Considerations for Internet Protocols", draft-iab-privacy- 664 considerations-09 (work in progress), May 2013. 666 [I-D.saintandre-sip-xmpp-chat] 667 Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, 668 "Interworking between the Session Initiation Protocol 669 (SIP) and the Extensible Messaging and Presence Protocol 670 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- 671 chat-06 (work in progress), June 2013. 673 [RFC3066] Alvestrand, H., "Tags for the Identification of 674 Languages", RFC 3066, January 2001. 676 [draft-tomkinson-multilangcontent] 677 Tomkinson, N. and N. Borenstein, "Multiple Language 678 Content Type", draft-tomkinson-multilangcontent (work in 679 progress), April 2014. 681 Appendix A. Historic Alternative Proposal: Caller-prefs 683 The decision to base the proposal at the media negotiation level, and 684 specifically to use SDP, came after significant debate and 685 discussion. It is possible to meet the objectives using a variety of 686 mechanisms, but none are perfect. Using SDP means dealing with the 687 complexity of SDP, and leaves out real-time session protocols that do 688 not use SDP. The major alternative proposal was to use SIP. Using 689 SIP leaves out non-SIP session protocols, but more fundamentally, 690 would occur at a different layer than the media negotiation. This 691 results in a more fragile solution since the media modality and 692 language would be negotiated using SIP, and then the specific media 693 formats (which inherently include the modality) would be negotiated 694 at a different level (typically SDP, especially in the emergency 695 calling cases), making it easier to have mismatches (such as where 696 the media modality negotiated in SIP don't match what was negotiated 697 using SDP). 699 An alternative proposal was to use the SIP-level Caller Preferences 700 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 702 The Caller-prefs mechanism includes a priority system; this would 703 allow different combinations of media and languages to be assigned 704 different priorities. The evaluation and decisions on what to do 705 with the call can be done either by proxies along the call path, or 706 by the addressed UA. Evaluation of alternatives for routing is 707 described in RFC 3841 [RFC3841]. 709 A.1. Use of Caller Preferences Without Additions 711 The following would be possible without adding any new registered 712 tags: 714 Potential callers and recipients MAY include in the Contact field in 715 their SIP registrations media and language tags according to the 716 joint capabilities of the UA and the human user according to RFC 3840 717 [RFC3840]. 719 The most relevant media capability tags are "video", "text" and 720 "audio". Each tag represents a capability to use the media in two- 721 way communication. 723 Language capabilities are declared with a comma-separated list of 724 languages that can be used in the call as parameters to the tag 725 "language=". 727 This is an example of how it is used in a SIP REGISTER: 729 REGISTER user@example.net 730 Contact: audio; video; text; 731 language="en,es,ase" 733 Including this information in SIP REGISTER allows proxies to act on 734 the information. For the problem set addressed by this document, it 735 is not anticipated that proxies will do so using registration data. 736 Further, there are classes of devices (such as cellular mobile 737 phones) that are not anticipated to include this information in their 738 registrations. Hence, use in registration is OPTIONAL. 740 In a call, a list of acceptable media and language combinations is 741 declared, and a priority assigned to each combination. 743 This is done by the Accept-Contact header field, which defines 744 different combinations of media and languages and assigns priorities 745 for completing the call with the SIP URI represented by that Contact. 746 A priority is assigned to each set as a so-called "q-value" which 747 ranges from 1 (most preferred) to 0 (least preferred). 749 Using the Accept-Contact header field in INVITE requests and 750 responses allows these capabilities to be expressed and used during 751 call set-up. Clients SHOULD include this information in INVITE 752 requests and responses. 754 Example: 756 Accept-Contact: *; text; language="en"; q=0.2 757 Accept-Contact: *; video; language="ase"; q=0.8 759 This example shows the highest preference expressed by the caller is 760 to use video with American Sign Language (language code "ase"). As a 761 fallback, it is acceptable to get the call connected with only 762 English text used for human communication. Other media may of course 763 be connected as well, without expectation that it will be usable by 764 the caller for interactive communications (but may still be helpful 765 to the caller). 767 This system satisfies all the needs described in the previous 768 chapters, except that language specifications do not make any 769 distinction between spoken and written language, and that the need 770 for directionality in the specification cannot be fulfilled. 772 To some degree the lack of media specification between speech and 773 text in language tags can be compensated by only specifying the 774 important medium in the Accept-Contact field. 776 Thus, a user who wants to use English mainly for text would specify: 778 Accept-Contact: *;text;language="en";q=1.0 780 While a user who wants to use English mainly for speech but accept it 781 for text would specify: 783 Accept-Contact: *;audio;language="en";q=0.8 784 Accept-Contact: *;text;language="en";q=0.2 786 However, a user who would like to talk, but receive text back has no 787 way to do it with the existing specification. 789 A.2. Additional Caller Preferences for Asymmetric Needs 791 In order to be able to specify asymmetric preferences, there are two 792 possibilities. Either new language tags in the style of the 793 humintlang parameters described above for SDP could be registered, or 794 additional media tags describing the asymmetry could be registered. 796 A.2.1. Caller Preferences for Asymmetric Modality Needs 798 The following new media tags should be defined: 800 speech-receive 801 speech-send 802 text-receive 803 text-send 804 sign-send 805 sign-receive 807 A user who prefers to talk and get text in return in English would 808 register the following (if including this information in registration 809 data): 811 REGISTER user@example.net 812 Contact: audio;text;speech-send;text- 813 receive;language="en" 815 At call time, a user who prefers to talk and get text in return in 816 English would set the Accept-Contact header field to: 818 Accept-Contact: *; audio; text; speech-receive; text-send; 819 language="en";q=0.8 820 Accept-Contact: *; text; language="en"; q=0.2 822 Note that the directions specified here are as viewed from the callee 823 side to match what the callee has registered. 825 A bridge arranged for invoking a relay service specifically arranged 826 for captioned telephony would register the following for supporting 827 calling users: 829 REGISTER ct@ctrelay.net 830 Contact: audio; text; speech-receive; 831 text-send; language="en" 833 A bridge arranged for invoking a relay service specifically arranged 834 for captioned telephony would register the following for supporting 835 called users: 837 REGISTER ct@ctrelay.net 838 Contact: audio; text; speech-send; text- 839 receive; language="en" 841 At call time, these alternatives are included in the list of possible 842 outcome of the call routing by the SIP proxies and the proper relay 843 service is invoked. 845 A.2.2. Caller Preferences for Asymmetric Language Tags 847 An alternative is to register new language tags for the purpose of 848 asymmetric language usage. 850 Instead of using "language=", six new language tags would be 851 registered: 853 humintlang-text-recv 854 humintlang-text-send 855 humintlang-speech-recv 856 humintlang-speech-send 857 humintlang-sign-recv 858 humintlang-sign-send 860 These language tags would be used instead of the regular 861 bidirectional language tags, and users with bidirectional 862 capabilities SHOULD specify values for both directions. Services 863 specifically arranged for supporting users with asymmetric needs 864 SHOULD specify only the asymmetry they support. 866 Author's Address 868 Randall Gellens 869 Qualcomm Technologies Inc. 870 5775 Morehouse Drive 871 San Diego, CA 92121 872 US 874 Email: rg+ietf@qti.qualcomm.com