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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 April 6, 2015 5 Expires: October 8, 2015 7 Negotiating Human Language in Real-Time Communications 8 draft-gellens-slim-negotiating-human-language-01 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 October 8, 2015. 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 . . . . . . . . . . . . . . . . . . . . . . 9 72 7.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 9 73 7.2. New 'humintlang-send' and 'humintlang-recv' attributes . 9 74 7.3. Advisory vs Required . . . . . . . . . . . . . . . . . . 11 75 7.4. Silly States . . . . . . . . . . . . . . . . . . . . . . 11 76 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 77 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 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 . . . . 13 84 10.4. Changes from draft-gellens-mmusic-...-00 to -01 . . . . 13 85 10.5. Changes from draft-gellens-...-02 to draft-gellens- 86 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . 13 87 10.6. Changes from draft-gellens-...-01 to -02 . . . . . . . . 14 88 10.7. Changes from draft-gellens-...-00 to -01 . . . . . . . . 14 89 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14 90 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 91 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 92 13.1. Normative References . . . . . . . . . . . . . . . . . . 15 93 13.2. Informational References . . . . . . . . . . . . . . . . 15 94 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 16 95 A.1. Use of Caller Preferences Without Additions . . . . . . . 16 96 A.2. Additional Caller Preferences for Asymmetric Needs . . . 18 97 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 18 98 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 19 99 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 101 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 is expected to be used by NENA and 3GPP. NENA is 215 likely to reference it in NENA 08-01 (i3 Stage 3) in describing 216 attributes of calls presented to an ESInet, and in that or other 217 documents describing Policy-Based Routing (PBR) capabilities within a 218 Policy-Based Routing Function. 3GPP may reference this mechanism in 219 general call handling and emergency call handling. Recent CRs 220 introduced in SA1 have anticipated this functionality being provided 221 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 Note that there are existing examples of it being used in exactly the 355 way we need. For example, draft-saintandre-sip-xmpp-chat-04 356 [I-D.saintandre-sip-xmpp-chat] contains an example where the initial 357 invitation contains two 'a=lang' entries for a media stream (for 358 English and Italian) and the OK accepts one of them (Italian), which 359 matches what we need: 361 Example: (F1) SIP user starts the session 363 INVITE sip:juliet@example.com SIP/2.0 364 To: 365 From: ;tag=576 366 Subject: Open chat with Romeo? 367 Call-ID: 742507no 368 Content-Type: application/sdp 370 c=IN IP4 s2x.example.net 371 m=message 7313 TCP/MSRP * 372 a=accept-types:text/plain 373 a=lang:en 374 a=lang:it 375 a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp 377 Example: (F2) Gateway accepts session on Juliet's behalf 378 SIP/2.0 200 OK 379 To: ;tag=534 380 From: ;tag=576 381 Call-ID: 742507no 382 Content-Type: application/sdp 384 c=IN IP4 x2s.example.com 385 m=message 8763 TCP/MSRP * 386 a=accept-types:text/plain 387 a=lang:it 388 a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp 390 The example serves as evidence of the need for an SDP attribute with 391 the semantics as described in this document; unfortunately, the 392 existing 'lang' attribute is not it. 394 7. Proposed Solution 396 An SDP attribute seems the natural choice to negotiate human 397 (natural) language of an interactive media stream. The attribute 398 value should be a language tag per RFC 5646 [RFC5646] 400 7.1. Rationale 402 The decision to base the proposal at the media negotiation level, and 403 specifically to use SDP, came after significant debate and 404 discussion. From an engineering standpoint, it is possible to meet 405 the objectives using a variety of mechanisms, but none are perfect. 406 None of the proposed alternatives was clearly better technically in 407 enough ways to win over proponents of the others, and none were 408 clearly so bad technically as to be easily rejected. As is often the 409 case in engineering, choosing the solution is a matter of balancing 410 trade-offs, and ultimately more a matter of taste than technical 411 merit. The two main proposals were to use SDP and SIP. SDP has the 412 advantage that the language is negotiated with the media to which it 413 applies, while SIP has the issue that the languages expressed may not 414 match the SDP media negotiated (for example, a session could 415 negotiate video at the SIP level but fail to negotiate any video 416 media stream at the SDP layer). 418 The mechanism described here for SDP can be adapted to media 419 negotiation protocols other than SDP. 421 7.2. New 'humintlang-send' and 'humintlang-recv' attributes 423 Rather than re-use 'lang' we define two new media-level attributes 424 starting with 'humintlang' (short for "human interactive language") 425 to negotiate which human language is used in each (interactive) media 426 stream. There are two attributes, one ending in "-send" and the 427 other in "-recv" to indicate the language used when sending and 428 receiving media: 430 a=humintlang-send: 431 a=humintlang-recv: 433 Each can appear multiple times in an offer for a media stream. 435 In an offer, the 'humintlang-send' values constitute a list in 436 preference order (first is most preferred) of the languages the 437 offerer wishes to send using the media, and the 'humintlang-recv' 438 values constitute a list in preference order of the languages the 439 offerer wishes to receive using the media. In cases where the user 440 wishes to use one media for sending and another for receiving (such 441 as a speech-impaired user who wishes to send using text and receive 442 using audio), one of the two MAY be unset. In cases where a media is 443 not primarily intended for language (for example, a video or audio 444 stream intended for background only) both SHOULD be unset. In other 445 cases, both SHOULD have the same values in the same order. The two 446 SHOULD NOT be set to languages which are difficult to match together 447 (e.g., specifying a desire to send audio in Hungarian and receive 448 audio in Portuguese will make it difficult to successfully complete 449 the call). 451 In an answer, 'humintlang-send' is the accepted language the answerer 452 will send (which in most cases is one of the languages in the offer's 453 'humintlang-recv'), and 'humintlang-recv' is the accepted language 454 the answerer expects to receive (which in most cases is one of the 455 languages in the offer's 'humintlang-send'). 457 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 458 describes mechanisms for matching language tags. While RFC 5646 459 provides a mechanism accommodating increasingly fine-grained 460 distinctions, in the interest of maximum interoperability for real- 461 time interactive communications, each 'humintlang-send' and 462 'humintlang-recv' value SHOULD be restricted to the largest 463 granularity of language tags; in other words, it is RECOMMENDED to 464 specify only a Primary-subtag and NOT to include subtags (e.g., for 465 region or dialect) unless the languages might be mutually 466 incomprehensible without them. 468 In an offer, each language tag value MAY have an asterisk appended as 469 the last character (after the registry value). The asterisk 470 indicates a request by the caller to not fail the call if there is no 471 language in common. See Section 7.3 for more information and 472 discussion. 474 When placing an emergency call, and in any other case where the 475 language cannot be assumed from context, each media stream in an 476 offer primarily intended for human language communication SHOULD 477 specify one or both 'humintlang-send' and 'humintlang-recv' 478 attributes (to avoid ambiguity). 480 Note that while signed language tags are used with a video stream to 481 indicate sign language, a spoken language tag for a video stream in 482 parallel with an audio stream with the same spoken language tag 483 indicates a request for a supplemental video stream to see the 484 speaker. 486 Clients acting on behalf of end users are expected to set one or both 487 'humintlang-send' and 'humintlang-recv' attributes on each media 488 stream primarily intended for human communication in an offer when 489 placing an outgoing session, but either ignore or take into 490 consideration the attributes when receiving incoming calls, based on 491 local configuration and capabilities. Systems acting on behalf of 492 call centers and PSAPs are expected to take into account the values 493 when processing inbound calls. 495 7.3. Advisory vs Required 497 One important consideration with this mechanism is if the call fails 498 if the callee does not support any of the languages requested by the 499 caller. 501 In order to provide for maximum likelihood of a successful 502 communication session, especially in the case of emergency calling, 503 the mechanism defined here provides a way for the caller to indicate 504 a preference for the call failing or succeeding when there is no 505 language in common. However, the callee is NOT REQUIRED to honor 506 this preference. For example, a PSAP MAY choose to attempt the call 507 even with no language in common, while a corporate call center MAY 508 choose to fail the call. 510 The mechanism for indicating this preference is that, in an offer, if 511 the last character of any of the 'humintlang-recv' or 'humintlang- 512 send' values is an asterisk, this indicates a request to not fail the 513 call (similar to SIP Accept-Language syntax). Either way, the called 514 party MAY ignore this, e.g., for the emergency services use case, a 515 PSAP will likely not fail the call. 517 7.4. Silly States 519 It is possible to specify a "silly state" where the language 520 specified does not make sense for the media type, such as specifying 521 a signed language for an audio media stream. 523 An offer MUST NOT be created where the language does not make sense 524 for the media type. If such an offer is received, the receiver MAY 525 reject the media, ignore the language specified, or attempt to 526 interpret the intent (e.g., if American Sign Language is specified 527 for an audio media stream, this might be interpreted as a desire to 528 use spoken English). 530 A spoken language tag for a video stream in conjunction with an audio 531 stream with the same language might indicate a request for 532 supplemental video to see the speaker. 534 8. IANA Considerations 536 IANA is kindly requested to add two entries to the 'att-field (media 537 level only)' table of the SDP parameters registry: 539 +------------------------------+-----------------+-----------------+ 540 | Type | Name | Reference | 541 +------------------------------+-----------------+-----------------+ 542 | att-field (media level only) | humintlang-send | (this document) | 543 | att-field (media level only) | humintlang-recv | (this document) | 544 +------------------------------+-----------------+-----------------+ 546 Table 1: att-field (media level only)' entries 548 9. Security Considerations 550 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 551 use of that RFC). In addition, if the 'humintlang-send' or 552 'humintlang-recv' values are altered or deleted en route, the session 553 could fail or languages incomprehensible to the caller could be 554 selected; however, this is also a risk if any SDP parameters are 555 modified en route. 557 10. Changes from Previous Versions 559 10.1. Changes from draft-gellens-slim-...-00 to draft-gellens- 560 slim-...-01 562 o Revision to keep draft from expiring 564 10.2. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 565 slim-...-00 567 o Changed name from -mmusic- to -slim- to reflect proposed WG name 568 o As a result of the face-to-face discussion in Toronto, the SDP vs 569 SIP issue was resolved by going back to SDP, taking out the SIP 570 hint, and converting what had been a set of alternate proposals 571 for various ways of doing it within SIP into an informative annex 572 section which includes background on why SDP is the proposal 573 o Added mention that enabling a mutually comprehensible language is 574 a general problem of which this document addresses the real-time 575 side, with reference to [draft-tomkinson-multilangcontent] which 576 addresses the non-real-time side. 578 10.3. Changes from draft-gellens-mmusic-...-01 to -02 580 o Added clarifying text on leaving attributes unset for media not 581 primarily intended for human language communication (e.g., 582 background audio or video). 583 o Added new section Appendix A ("Alternative Proposal: Caller- 584 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 585 level. 587 10.4. Changes from draft-gellens-mmusic-...-00 to -01 589 o Relaxed language on setting -send and -receive to same values; 590 added text on leaving on empty to indicate asymmetric usage. 591 o Added text that clients on behalf of end users are expected to set 592 the attributes on outgoing calls and ignore on incoming calls 593 while systems on behalf of call centers and PSAPs are expected to 594 take the attributes into account when processing incoming calls. 596 10.5. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 598 o Updated text to refer to RFC 5646 rather than the IANA language 599 subtags registry directly. 600 o Moved discussion of existing 'lang' attribute out of "Proposed 601 Solution" section and into own section now that it is not part of 602 proposal. 603 o Updated text about existing 'lang' attribute. 604 o Added example use cases. 605 o Replaced proposed single 'humintlang' attribute with 'humintlang- 606 send' and 'humintlang-recv' per Harald's request/information that 607 it was a misuse of SDP to use the same attribute for sending and 608 receiving. 609 o Added section describing usage being advisory vs required and text 610 in attribute section. 611 o Added section on SIP "hint" header (not yet nailed down between 612 new and existing header). 613 o Added text discussing usage in policy-based routing function or 614 use of SIP header "hint" if unable to do so. 615 o Added SHOULD that the value of the parameters stick to the largest 616 granularity of language tags. 617 o Added text to Introduction to be try and be more clear about 618 purpose of document and problem being solved. 620 o Many wording improvements and clarifications throughout the 621 document. 622 o Filled in Security Considerations. 623 o Filled in IANA Considerations. 624 o Added to Acknowledgments those who participated in the Orlando ad- 625 hoc discussion as well as those who participated in email 626 discussion and side one-on-one discussions. 628 10.6. Changes from draft-gellens-...-01 to -02 630 o Updated text for (possible) new attribute "humintlang" to 631 reference RFC 5646 632 o Added clarifying text for (possible) re-use of existing 'lang' 633 attribute saying that the registration would be updated to reflect 634 different semantics for multiple values for interactive versus 635 non-interactive media. 636 o Added clarifying text for (possible) new attribute "humintlang" to 637 attempt to better describe the role of language tags in media in 638 an offer and an answer. 640 10.7. Changes from draft-gellens-...-00 to -01 642 o Changed name of (possible) new attribute from 'humlang" to 643 "humintlang" 644 o Added discussion of silly state (language not appropriate for 645 media type) 646 o Added Voice Carry Over example 647 o Added mention of multilingual people and multiple languages 648 o Minor text clarifications 650 11. Contributors 652 Gunnar Hellstrom deserves special mention for his reviews, 653 assistance, and especially for contributing the core text in 654 Appendix A. 656 12. Acknowledgments 658 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 659 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 660 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 661 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 662 Peter Saint-Andre, and Dale Worley for reviews, corrections, 663 suggestions, and participating in in-person and email discussions. 665 13. References 667 13.1. Normative References 669 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 670 Requirement Levels", BCP 14, RFC 2119, March 1997. 672 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 673 "Indicating User Agent Capabilities in the Session 674 Initiation Protocol (SIP)", RFC 3840, August 2004. 676 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 677 Preferences for the Session Initiation Protocol (SIP)", 678 RFC 3841, August 2004. 680 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 681 Description Protocol", RFC 4566, July 2006. 683 [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying 684 Languages", BCP 47, RFC 5646, September 2009. 686 13.2. Informational References 688 [I-D.iab-privacy-considerations] 689 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 690 Morris, J., Hansen, M., and R. Smith, "Privacy 691 Considerations for Internet Protocols", draft-iab-privacy- 692 considerations-09 (work in progress), May 2013. 694 [I-D.saintandre-sip-xmpp-chat] 695 Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, 696 "Interworking between the Session Initiation Protocol 697 (SIP) and the Extensible Messaging and Presence Protocol 698 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- 699 chat-06 (work in progress), June 2013. 701 [RFC3066] Alvestrand, H., "Tags for the Identification of 702 Languages", RFC 3066, January 2001. 704 [draft-tomkinson-multilangcontent] 705 Tomkinson, N. and N. Borenstein, "Multiple Language 706 Content Type", draft-tomkinson-multilangcontent (work in 707 progress), April 2014. 709 Appendix A. Historic Alternative Proposal: Caller-prefs 711 The decision to base the proposal at the media negotiation level, and 712 specifically to use SDP, came after significant debate and 713 discussion. It is possible to meet the objectives using a variety of 714 mechanisms, but none are perfect. Using SDP means dealing with the 715 complexity of SDP, and leaves out real-time session protocols that do 716 not use SDP. The major alternative proposal was to use SIP. Using 717 SIP leaves out non-SIP session protocols, but more fundamentally, 718 would occur at a different layer than the media negotiation. This 719 results in a more fragile solution since the media modality and 720 language would be negotiated using SIP, and then the specific media 721 formats (which inherently include the modality) would be negotiated 722 at a different level (typically SDP, especially in the emergency 723 calling cases), making it easier to have mismatches (such as where 724 the media modality negotiated in SIP don't match what was negotiated 725 using SDP). 727 An alternative proposal was to use the SIP-level Caller Preferences 728 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 730 The Caller-prefs mechanism includes a priority system; this would 731 allow different combinations of media and languages to be assigned 732 different priorities. The evaluation and decisions on what to do 733 with the call can be done either by proxies along the call path, or 734 by the addressed UA. Evaluation of alternatives for routing is 735 described in RFC 3841 [RFC3841]. 737 A.1. Use of Caller Preferences Without Additions 739 The following would be possible without adding any new registered 740 tags: 742 Potential callers and recipients MAY include in the Contact field in 743 their SIP registrations media and language tags according to the 744 joint capabilities of the UA and the human user according to RFC 3840 745 [RFC3840]. 747 The most relevant media capability tags are "video", "text" and 748 "audio". Each tag represents a capability to use the media in two- 749 way communication. 751 Language capabilities are declared with a comma-separated list of 752 languages that can be used in the call as parameters to the tag 753 "language=". 755 This is an example of how it is used in a SIP REGISTER: 757 REGISTER user@example.net 758 Contact: audio; video; text; 759 language="en,es,ase" 761 Including this information in SIP REGISTER allows proxies to act on 762 the information. For the problem set addressed by this document, it 763 is not anticipated that proxies will do so using registration data. 764 Further, there are classes of devices (such as cellular mobile 765 phones) that are not anticipated to include this information in their 766 registrations. Hence, use in registration is OPTIONAL. 768 In a call, a list of acceptable media and language combinations is 769 declared, and a priority assigned to each combination. 771 This is done by the Accept-Contact header field, which defines 772 different combinations of media and languages and assigns priorities 773 for completing the call with the SIP URI represented by that Contact. 774 A priority is assigned to each set as a so-called "q-value" which 775 ranges from 1 (most preferred) to 0 (least preferred). 777 Using the Accept-Contact header field in INVITE requests and 778 responses allows these capabilities to be expressed and used during 779 call set-up. Clients SHOULD include this information in INVITE 780 requests and responses. 782 Example: 784 Accept-Contact: *; text; language="en"; q=0.2 785 Accept-Contact: *; video; language="ase"; q=0.8 787 This example shows the highest preference expressed by the caller is 788 to use video with American Sign Language (language code "ase"). As a 789 fallback, it is acceptable to get the call connected with only 790 English text used for human communication. Other media may of course 791 be connected as well, without expectation that it will be usable by 792 the caller for interactive communications (but may still be helpful 793 to the caller). 795 This system satisfies all the needs described in the previous 796 chapters, except that language specifications do not make any 797 distinction between spoken and written language, and that the need 798 for directionality in the specification cannot be fulfilled. 800 To some degree the lack of media specification between speech and 801 text in language tags can be compensated by only specifying the 802 important medium in the Accept-Contact field. 804 Thus, a user who wants to use English mainly for text would specify: 806 Accept-Contact: *;text;language="en";q=1.0 808 While a user who wants to use English mainly for speech but accept it 809 for text would specify: 811 Accept-Contact: *;audio;language="en";q=0.8 812 Accept-Contact: *;text;language="en";q=0.2 814 However, a user who would like to talk, but receive text back has no 815 way to do it with the existing specification. 817 A.2. Additional Caller Preferences for Asymmetric Needs 819 In order to be able to specify asymmetric preferences, there are two 820 possibilities. Either new language tags in the style of the 821 humintlang parameters described above for SDP could be registered, or 822 additional media tags describing the asymmetry could be registered. 824 A.2.1. Caller Preferences for Asymmetric Modality Needs 826 The following new media tags should be defined: 828 speech-receive 829 speech-send 830 text-receive 831 text-send 832 sign-send 833 sign-receive 835 A user who prefers to talk and get text in return in English would 836 register the following (if including this information in registration 837 data): 839 REGISTER user@example.net 840 Contact: audio;text;speech-send;text- 841 receive;language="en" 843 At call time, a user who prefers to talk and get text in return in 844 English would set the Accept-Contact header field to: 846 Accept-Contact: *; audio; text; speech-receive; text-send; 847 language="en";q=0.8 848 Accept-Contact: *; text; language="en"; q=0.2 850 Note that the directions specified here are as viewed from the callee 851 side to match what the callee has registered. 853 A bridge arranged for invoking a relay service specifically arranged 854 for captioned telephony would register the following for supporting 855 calling users: 857 REGISTER ct@ctrelay.net 858 Contact: audio; text; speech-receive; 859 text-send; language="en" 861 A bridge arranged for invoking a relay service specifically arranged 862 for captioned telephony would register the following for supporting 863 called users: 865 REGISTER ct@ctrelay.net 866 Contact: audio; text; speech-send; text- 867 receive; language="en" 869 At call time, these alternatives are included in the list of possible 870 outcome of the call routing by the SIP proxies and the proper relay 871 service is invoked. 873 A.2.2. Caller Preferences for Asymmetric Language Tags 875 An alternative is to register new language tags for the purpose of 876 asymmetric language usage. 878 Instead of using "language=", six new language tags would be 879 registered: 881 humintlang-text-recv 882 humintlang-text-send 883 humintlang-speech-recv 884 humintlang-speech-send 885 humintlang-sign-recv 886 humintlang-sign-send 888 These language tags would be used instead of the regular 889 bidirectional language tags, and users with bidirectional 890 capabilities SHOULD specify values for both directions. Services 891 specifically arranged for supporting users with asymmetric needs 892 SHOULD specify only the asymmetry they support. 894 Author's Address 896 Randall Gellens 897 Qualcomm Technologies Inc. 898 5775 Morehouse Drive 899 San Diego, CA 92121 900 US 902 Email: rg+ietf@qti.qualcomm.com