idnits 2.17.1 draft-gellens-slim-negotiating-human-language-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The exact meaning of the all-uppercase expression 'NOT REQUIRED' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. -- The document date (October 13, 2014) is 3475 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'I-D.iab-privacy-considerations' is defined on line 703, but no explicit reference was found in the text ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Obsolete informational reference (is this intentional?): RFC 3066 (Obsoleted by RFC 4646, RFC 4647) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). 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 October 13, 2014 5 Expires: April 16, 2015 7 Negotiating Human Language in Real-Time Communications 8 draft-gellens-slim-negotiating-human-language-00 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 April 16, 2015. 43 Copyright Notice 45 Copyright (c) 2014 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-...-00 to -01 . . . . . . . . 12 80 10.2. Changes from draft-gellens-...-01 to -02 . . . . . . . . 13 81 10.3. Changes from draft-gellens-...-02 to draft-gellens- 82 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . 13 83 10.4. Changes from draft-gellens-mmusic-...-00 to -01 . . . . 14 84 10.5. Changes from draft-gellens-mmusic-...-01 to -02 . . . . 14 85 10.6. Changes from draft-gellens-mmusic-...-02 to draft- 86 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . 14 87 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 88 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 89 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 90 13.1. Normative References . . . . . . . . . . . . . . . . . . 15 91 13.2. Informational References . . . . . . . . . . . . . . . . 15 92 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 16 93 A.1. Use of Caller Preferences Without Additions . . . . . . . 16 94 A.2. Additional Caller Preferences for Asymmetric Needs . . . 18 95 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 18 96 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 20 97 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 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 routed to 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 route and 152 process the call (i.e., language and media needs may be considered 153 within policy-based routing (PBR)). 155 By treating language as another attribute that is negotiated along 156 with other aspects of a media stream, it becomes possible to 157 accommodate a range of users' needs and called party facilities. For 158 example, some users may be able to speak several languages, but have 159 a preference. Some called parties may support some of those 160 languages internally but require the use of a translation service for 161 others, or may have a limited number of call takers able to use 162 certain languages. Another example would be a user who is able to 163 speak but is deaf or hard-of-hearing and requires a voice stream plus 164 a text stream (known as voice carry over). Making language a media 165 attribute allows the standard session negotiation mechanism to handle 166 this by providing the information and mechanism for the endpoints to 167 make appropriate decisions. 169 Regarding relay services, in the case of an emergency call requiring 170 sign language such as ASL, there are two common approaches: the 171 caller initiates the call to a relay center, or the caller places the 172 call to emergency services (e.g., 911 in the U.S. or 112 in Europe). 173 In the former case, the language need is ancillary and supplemental. 174 In the latter case, the ESInet and/or PSAP may take the need for sign 175 language into account and bridge in a relay center. In this case, 176 the ESInet and PSAP have all the standard information available (such 177 as location) but are able to bridge the relay sooner in the call 178 processing. 180 By making this facility part of the end-to-end negotiation, the 181 question of which entity provides or engages the relay service 182 becomes separate from the call processing mechanics; if the caller 183 directs the call to a relay service then the human language 184 negotiation facility provides extra information to the relay service 185 but calls will still function without it; if the caller directs the 186 call to emergency services, then the ESInet/PSAP are able to take the 187 user's human language needs into account, e.g., by routing to a 188 particular PSAP or call taker or bridging a relay service or 189 translator. 191 The term "negotiation" is used here rather than "indication" because 192 human language (spoken/written/signed) is something that can be 193 negotiated in the same way as which forms of media (audio/text/video) 194 or which codecs. For example, if we think of non-emergency calls, 195 such as a user calling an airline reservation center, the user may 196 have a set of languages he or she speaks, with perhaps preferences 197 for one or a few, while the airline reservation center will support a 198 fixed set of languages. Negotiation should select the user's most 199 preferred language that is supported by the call center. Both sides 200 should be aware of which language was negotiated. This is 201 conceptually similar to the way other aspects of each media stream 202 are negotiated using SDP (e.g., media type and codecs). 204 2. Terminology 206 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 207 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 208 document are to be interpreted as described in RFC 2119 [RFC2119]. 210 3. Expected Use 212 This facility is expected to be used by NENA and 3GPP. NENA is 213 likely to reference it in NENA 08-01 (i3 Stage 3) in describing 214 attributes of calls presented to an ESInet, and in that or other 215 documents describing Policy-Based Routing (PBR) capabilities within a 216 Policy-Based Routing Function. 3GPP is expected to reference this 217 mechanism in general call handling and emergency call handling. 218 Recent CRs introduced in SA1 have anticipated this functionality 219 being provided within SDP. 221 4. Example Use Cases 223 4.1. Emergency Call from English Speaker in Spain 225 Someone who speaks only English is visiting Spain and places an 226 emergency (112) call. The call offers an audio stream using English. 227 The ESInet and PSAP have policy-based routing rules that take into 228 account the SDP language request when deciding how to route and 229 process the call. The ESInet routes the call to a PSAP within Spain 230 where an English-speaking call taker is available, and the PSAP 231 selects an English-speaking call taker to handle the call. The PSAP 232 answers the offer with an audio stream using English. The call is 233 established with an audio stream; the caller and call taker 234 communicate in English. 236 Alternatively, the ESInet routes the call to a cooperating PSAP 237 within the U.K. The PSAP answers the offer with an audio stream 238 using English. The call is established with an audio stream; the 239 caller and call taker communicate in English. (This approach is 240 similar to that envisioned in REACH112 Total Conversation.) 242 4.2. Emergency Call from Spanish/English Speaker in France 244 Someone who speaks both Spanish and English (but prefers Spanish) is 245 visiting France and places an emergency (112) call. The call offers 246 an audio stream listing first Spanish (meaning most preferred) and 247 then English. The ESInet and PSAP have policy-based routing rules 248 that take into account the SDP language request when deciding how to 249 route and process the call. The ESInet routes the call to a PSAP 250 within France where a Spanish-speaking call taker is available, and 251 the PSAP selects a Spanish-speaking call taker to handle the call. 252 The PSAP answers the offer with an audio stream listing Spanish. The 253 call is established with an audio stream; the caller and call taker 254 communicate in Spanish. 256 Alternatively, the ESInet routes the call to a cooperating PSAP in 257 Spain or England. (This approach is similar to that envisioned in 258 REACH112 Total Conversation.) 260 Alternatively, there is no ESInet or the ESInet does not take 261 language into account in its PBR. The call is routed to a PSAP in 262 France. The PSAP ignores the language information in the SDP offer, 263 and answers the offer with an audio stream with no language or with 264 French. The UE continues the call anyway. The call taker answers in 265 French, the user tries speaking Spanish and perhaps English. The 266 call taker bridges in a translation service or transfers the call to 267 a multilingual call taker. 269 4.3. Call to Call Center from Russian Speaker in U.S. 271 A Russian speaker is visiting the U.S. and places a call to her 272 airline reservation desk to inquire about her return flight. The 273 airline call processing system takes into account the SDP language 274 request and decides to route the call to its call center within 275 Russia. 277 Alternatively, if the airline call processing system does not look at 278 SDP, it uses the SIP "hint" if present. 280 4.4. Emergency Call from speech-impaired caller in the U.S. 282 Someone who uses English but is speech-impaired places an emergency 283 (911) call. The call offers an audio stream listing English and a 284 real-time text stream also using English. The ESInet and PSAP have 285 policy-based routing rules that take into account the SDP language 286 and media requests when deciding how to route and process the call. 288 The ESInet routes the call to a PSAP with real-time text 289 capabilities. The PSAP answers the offer with an audio stream 290 listing English and a real-time text stream listing English. The 291 call is established with an audio and a real-time text stream; the 292 caller and call taker communicate in English using voice from the 293 call-taker to the caller and text from the caller to the call taker. 294 The audio stream is two-way, allowing the call taker to hear 295 background sounds. 297 4.5. Emergency Call from deaf caller in the U.S. 299 A deaf caller who uses American Sign Language (ASL) places an 300 emergency (911) call. The call offers a video stream listing ASL and 301 an audio stream with no language indicated. The ESInet and PSAP have 302 policy-based routing rules that take into account the SDP language 303 and media needs when deciding how to route and process the call. The 304 ESInet routes the call to a PSAP. The PSAP answers the offer with an 305 audio stream listing English and a video stream listing ASL. The 306 PSAP bridges in a sign language interpreter. The call is established 307 with an audio and a video stream. 309 5. Desired Semantics 311 The desired solution is a media attribute that may be used within an 312 offer to indicate the preferred language of each media stream, and 313 within an answer to indicate the accepted language. The semantics of 314 including multiple values for a media stream within an offer is that 315 the languages are listed in order of preference. 317 (While it is true that a conversation among multilingual people often 318 involves multiple languages, the usefulness of providing a way to 319 negotiate this as a general facility is outweighed by the complexity 320 of the desired semantics of the SDP attribute to allow negotiation of 321 multiple simultaneous languages within an interactive media stream.) 323 6. The existing 'lang' attribute 325 RFC 4566 specifies an attribute 'lang' which sounds similar to what 326 is needed here, the difference being that it specifies that 'a=lang' 327 is declarative with the semantics of multiple 'lang' attributes being 328 that all of them are used, while we want a means to negotiate which 329 one is used in each stream. This difference means that the existing 330 'lang' attribute can't be used and we need to define a new attribute. 332 The text from RFC 4566 [RFC4566] is: 334 a=lang: 335 This can be a session-level attribute or a media-level attribute. 336 As a session-level attribute, it specifies the default language 337 for the session being described. As a media- level attribute, it 338 specifies the language for that media, overriding any session- 339 level language specified. Multiple lang attributes can be 340 provided either at session or media level if the session 341 description or media use multiple languages, in which case the 342 order of the attributes indicates the order of importance of the 343 various languages in the session or media from most important to 344 least important. 346 The "lang" attribute value must be a single [RFC3066] language tag 347 in US-ASCII [RFC3066]. It is not dependent on the charset 348 attribute. A "lang" attribute SHOULD be specified when a session 349 is of sufficient scope to cross geographic boundaries where the 350 language of recipients cannot be assumed, or where the session is 351 in a different language from the locally assumed norm. 353 Note that there are existing examples of it being used in exactly the 354 way we need. For example, draft-saintandre-sip-xmpp-chat-04 355 [I-D.saintandre-sip-xmpp-chat] contains an example where the initial 356 invitation contains two 'a=lang' entries for a media stream (for 357 English and Italian) and the OK accepts one of them (Italian), which 358 matches what we need: 360 Example: (F1) SIP user starts the session 362 INVITE sip:juliet@example.com SIP/2.0 363 To: 364 From: ;tag=576 365 Subject: Open chat with Romeo? 366 Call-ID: 742507no 367 Content-Type: application/sdp 369 c=IN IP4 s2x.example.net 370 m=message 7313 TCP/MSRP * 371 a=accept-types:text/plain 372 a=lang:en 373 a=lang:it 374 a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp 376 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 383 c=IN IP4 x2s.example.com 384 m=message 8763 TCP/MSRP * 385 a=accept-types:text/plain 386 a=lang:it 387 a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp 389 The example serves as evidence of the need for an SDP attribute with 390 the semantics as described in this document; unfortunately, the 391 existing 'lang' attribute is not it. 393 7. Proposed Solution 395 An SDP attribute seems the natural choice to negotiate human 396 (natural) language of an interactive media stream. The attribute 397 value should be a language tag per RFC 5646 [RFC5646] 399 7.1. Rationale 401 The decision to base the proposal at the media negotiation level, and 402 specifically to use SDP, came after significant debate and 403 discussion. From an engineering standpoint, it is possible to meet 404 the objectives using a variety of mechanisms, but none are perfect. 405 None of the proposed alternatives was clearly better technically in 406 enough ways to win over proponents of the others, and none were 407 clearly so bad technically as to be easily rejected. As is often the 408 case in engineering, choosing the solution is a matter of balancing 409 trade-offs, and ultimately more a matter of taste than technical 410 merit. The two main proposals were to use SDP and SIP. SDP has the 411 advantage that the language is negotiated with the media to which it 412 applies, while SIP has the issue that the languages expressed may not 413 match the SDP media negotiated (for example, a session could 414 negotiate video at the SIP level but fail to negotiate any video 415 media stream at the SDP layer). 417 The mechanism described here for SDP can be adapted to media 418 negotiation protocols other than SDP. 420 7.2. New 'humintlang-send' and 'humintlang-recv' attributes 422 Rather than re-use 'lang' we define two new media-level attributes 423 starting with 'humintlang' (short for "human interactive language") 424 to negotiate which human language is used in each (interactive) media 425 stream. There are two attributes, one ending in "-send" and the 426 other in "-recv" to indicate the language used when sending and 427 receiving media: 429 a=humintlang-send: 430 a=humintlang-recv: 432 Each can appear multiple times in an offer for a media stream. 434 In an offer, the 'humintlang-send' values constitute a list in 435 preference order (first is most preferred) of the languages the 436 offerer wishes to send using the media, and the 'humintlang-recv' 437 values constitute a list in preference order of the languages the 438 offerer wishes to receive using the media. In cases where the user 439 wishes to use one media for sending and another for receiving (such 440 as a speech-impaired user who wishes to send using text and receive 441 using audio), one of the two MAY be unset. In cases where a media is 442 not primarily intended for language (for example, a video or audio 443 stream intended for background only) both SHOULD be unset. In other 444 cases, both SHOULD have the same values in the same order. The two 445 SHOULD NOT be set to languages which are difficult to match together 446 (e.g., specifying a desire to send audio in Hungarian and receive 447 audio in Portuguese will make it difficult to successfully complete 448 the call). 450 In an answer, 'humintlang-send' is the accepted language the answerer 451 will send (which in most cases is one of the languages in the offer's 452 'humintlang-recv'), and 'humintlang-recv' is the accepted language 453 the answerer expects to receive (which in most cases is one of the 454 languages in the offer's 'humintlang-send'). 456 Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 457 describes mechanisms for matching language tags. While RFC 5646 458 provides a mechanism accommodating increasingly fine-grained 459 distinctions, in the interest of maximum interoperability for real- 460 time interactive communications, each 'humintlang-send' and 461 'humintlang-recv' value SHOULD be restricted to the largest 462 granularity of language tags; in other words, it is RECOMMENDED to 463 specify only a Primary-subtag and NOT to include subtags (e.g., for 464 region or dialect) unless the languages might be mutually 465 incomprehensible without them. 467 In an offer, each language tag value MAY have an asterisk appended as 468 the last character (after the registry value). The asterisk 469 indicates a request by the caller to not fail the call if there is no 470 language in common. See Section 7.3 for more information and 471 discussion. 473 When placing an emergency call, and in any other case where the 474 language cannot be assumed from context, each media stream in an 475 offer primarily intended for human language communication SHOULD 476 specify one or both 'humintlang-send' and 'humintlang-recv' 477 attributes (to avoid ambiguity). 479 Note that while signed language tags are used with a video stream to 480 indicate sign language, a spoken language tag for a video stream in 481 parallel with an audio stream with the same spoken language tag 482 indicates a request for a supplemental video stream to see the 483 speaker. 485 Clients acting on behalf of end users are expected to set one or both 486 'humintlang-send' and 'humintlang-recv' attributes on each media 487 stream primarily intended for human communication in an offer when 488 placing an outgoing session, but either ignore or take into 489 consideration the attributes when receiving incoming calls, based on 490 local configuration and capabilities. Systems acting on behalf of 491 call centers and PSAPs are expected to take into account the values 492 when processing inbound calls. 494 7.3. Advisory vs Required 496 One important consideration with this mechanism is if the call fails 497 if the callee does not support any of the languages requested by the 498 caller. 500 In order to provide for maximum likelihood of a successful 501 communication session, especially in the case of emergency calling, 502 the mechanism defined here provides a way for the caller to indicate 503 a preference for the call failing or succeeding when there is no 504 language in common. However, the callee is NOT REQUIRED to honor 505 this preference. For example, a PSAP MAY choose to attempt the call 506 even with no language in common, while a corporate call center MAY 507 choose to fail the call. 509 The mechanism for indicating this preference is that, in an offer, if 510 the last character of any of the 'humintlang-recv' or 'humintlang- 511 send' values is an asterisk, this indicates a request to not fail the 512 call (similar to SIP Accept-Language syntax). Either way, the called 513 party MAY ignore this, e.g., for the emergency services use case, a 514 PSAP will likely not fail the call. 516 7.4. Silly States 518 It is possible to specify a "silly state" where the language 519 specified does not make sense for the media type, such as specifying 520 a signed language for an audio media stream. 522 An offer MUST NOT be created where the language does not make sense 523 for the media type. If such an offer is received, the receiver MAY 524 reject the media, ignore the language specified, or attempt to 525 interpret the intent (e.g., if American Sign Language is specified 526 for an audio media stream, this might be interpreted as a desire to 527 use spoken English). 529 A spoken language tag for a video stream in conjunction with an audio 530 stream with the same language might indicate a request for 531 supplemental video to see the speaker. 533 8. IANA Considerations 535 IANA is kindly requested to add two entries to the 'att-field (media 536 level only)' table of the SDP parameters registry: 538 +------------------------------+-----------------+-----------------+ 539 | Type | Name | Reference | 540 +------------------------------+-----------------+-----------------+ 541 | att-field (media level only) | humintlang-send | (this document) | 542 | att-field (media level only) | humintlang-recv | (this document) | 543 +------------------------------+-----------------+-----------------+ 545 Table 1: att-field (media level only)' entries 547 9. Security Considerations 549 The Security Considerations of RFC 5646 [RFC5646] apply here (as a 550 use of that RFC). In addition, if the 'humintlang-send' or 551 'humintlang-recv' values are altered or deleted en route, the session 552 could fail or languages incomprehensible to the caller could be 553 selected; however, this is also a risk if any SDP parameters are 554 modified en route. 556 10. Changes from Previous Versions 558 10.1. Changes from draft-gellens-...-00 to -01 560 o Changed name of (possible) new attribute from 'humlang" to 561 "humintlang" 563 o Added discussion of silly state (language not appropriate for 564 media type) 566 o Added Voice Carry Over example 568 o Added mention of multilingual people and multiple languages 569 o Minor text clarifications 571 10.2. Changes from draft-gellens-...-01 to -02 573 o Updated text for (possible) new attribute "humintlang" to 574 reference RFC 5646 576 o Added clarifying text for (possible) re-use of existing 'lang' 577 attribute saying that the registration would be updated to reflect 578 different semantics for multiple values for interactive versus 579 non-interactive media. 581 o Added clarifying text for (possible) new attribute "humintlang" to 582 attempt to better describe the role of language tags in media in 583 an offer and an answer. 585 10.3. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 587 o Updated text to refer to RFC 5646 rather than the IANA language 588 subtags registry directly. 590 o Moved discussion of existing 'lang' attribute out of "Proposed 591 Solution" section and into own section now that it is not part of 592 proposal. 594 o Updated text about existing 'lang' attribute. 596 o Added example use cases. 598 o Replaced proposed single 'humintlang' attribute with 'humintlang- 599 send' and 'humintlang-recv' per Harald's request/information that 600 it was a misuse of SDP to use the same attribute for sending and 601 receiving. 603 o Added section describing usage being advisory vs required and text 604 in attribute section. 606 o Added section on SIP "hint" header (not yet nailed down between 607 new and existing header). 609 o Added text discussing usage in policy-based routing function or 610 use of SIP header "hint" if unable to do so. 612 o Added SHOULD that the value of the parameters stick to the largest 613 granularity of language tags. 615 o Added text to Introduction to be try and be more clear about 616 purpose of document and problem being solved. 618 o Many wording improvements and clarifications throughout the 619 document. 621 o Filled in Security Considerations. 623 o Filled in IANA Considerations. 625 o Added to Acknowledgments those who participated in the Orlando ad- 626 hoc discussion as well as those who participated in email 627 discussion and side one-on-one discussions. 629 10.4. Changes from draft-gellens-mmusic-...-00 to -01 631 o Relaxed language on setting -send and -receive to same values; 632 added text on leaving on empty to indicate asymmetric usage. 634 o Added text that clients on behalf of end users are expected to set 635 the attributes on outgoing calls and ignore on incoming calls 636 while systems on behalf of call centers and PSAPs are expected to 637 take the attributes into account when processing incoming calls. 639 10.5. Changes from draft-gellens-mmusic-...-01 to -02 641 o Added clarifying text on leaving attributes unset for media not 642 primarily intended for human language communication (e.g., 643 background audio or video). 645 o Added new section Appendix A ("Alternative Proposal: Caller- 646 prefs") discussing use of SIP-level Caller-prefs instead of SDP- 647 level. 649 10.6. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 650 slim-...-00 652 o Changed name from -mmusic- to -slim- to reflect proposed WG name 654 o As a result of the face-to-face discussion in Toronto, the SDP vs 655 SIP issue was resolved by going back to SDP, taking out the SIP 656 hint, and converting what had been a set of alternate proposals 657 for various ways of doing it within SIP into an informative annex 658 section which includes background on why SDP is the proposal 660 o Added mention that enabling a mutually comprehensible language is 661 a general problem of which this document addresses the real-time 662 side, with reference to [draft-tomkinson-multilangcontent] which 663 addresses the non-real-time side. 665 11. Contributors 667 Gunnar Hellstrom deserves special mention for his reviews, 668 assistance, and especially for contributing the core text in 669 Appendix A. 671 12. Acknowledgments 673 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 674 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 675 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 676 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 677 Peter Saint-Andre, and Dale Worley for reviews, corrections, 678 suggestions, and participating in in-person and email discussions. 680 13. References 682 13.1. Normative References 684 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 685 Requirement Levels", BCP 14, RFC 2119, March 1997. 687 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 688 "Indicating User Agent Capabilities in the Session 689 Initiation Protocol (SIP)", RFC 3840, August 2004. 691 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 692 Preferences for the Session Initiation Protocol (SIP)", 693 RFC 3841, August 2004. 695 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 696 Description Protocol", RFC 4566, July 2006. 698 [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying 699 Languages", BCP 47, RFC 5646, September 2009. 701 13.2. Informational References 703 [I-D.iab-privacy-considerations] 704 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 705 Morris, J., Hansen, M., and R. Smith, "Privacy 706 Considerations for Internet Protocols", draft-iab-privacy- 707 considerations-09 (work in progress), May 2013. 709 [I-D.saintandre-sip-xmpp-chat] 710 Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, 711 "Interworking between the Session Initiation Protocol 712 (SIP) and the Extensible Messaging and Presence Protocol 713 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- 714 chat-06 (work in progress), June 2013. 716 [RFC3066] Alvestrand, H., "Tags for the Identification of 717 Languages", RFC 3066, January 2001. 719 [draft-tomkinson-multilangcontent] 720 Tomkinson, N. and N. Borenstein, "Multiple Language 721 Content Type", draft-tomkinson-multilangcontent (work in 722 progress), April 2014. 724 Appendix A. Historic Alternative Proposal: Caller-prefs 726 The decision to base the proposal at the media negotiation level, and 727 specifically to use SDP, came after significant debate and 728 discussion. It is possible to meet the objectives using a variety of 729 mechanisms, but none are perfect. Using SDP means dealing with the 730 complexity of SDP, and leaves out real-time session protocols that do 731 not use SDP. The major alternative proposal was to use SIP. Using 732 SIP leaves out non-SIP session protocols, but more fundamentally, 733 would occur at a different layer than the media negotiation. This 734 results in a more fragile solution since the media modality and 735 language would be negotiated using SIP, and then the specific media 736 formats (which inherently include the modality) would be negotiated 737 at a different level (typically SDP, especially in the emergency 738 calling cases), making it easier to have mismatches (such as where 739 the media modality negotiated in SIP don't match what was negotiated 740 using SDP). 742 An alternative proposal was to use the SIP-level Caller Preferences 743 mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. 745 The Caller-prefs mechanism includes a priority system; this would 746 allow different combinations of media and languages to be assigned 747 different priorities. The evaluation and decisions on what to do 748 with the call can be done either by proxies along the call path, or 749 by the addressed UA. Evaluation of alternatives for routing is 750 described in RFC 3841 [RFC3841]. 752 A.1. Use of Caller Preferences Without Additions 754 The following would be possible without adding any new registered 755 tags: 757 Potential callers and recipients MAY include in the Contact field in 758 their SIP registrations media and language tags according to the 759 joint capabilities of the UA and the human user according to RFC 3840 760 [RFC3840]. 762 The most relevant media capability tags are "video", "text" and 763 "audio". Each tag represents a capability to use the media in two- 764 way communication. 766 Language capabilities are declared with a comma-separated list of 767 languages that can be used in the call as parameters to the tag 768 "language=". 770 This is an example of how it is used in a SIP REGISTER: 772 REGISTER user@example.net 774 Contact: audio; video; text; 775 language="en,es,ase" 777 Including this information in SIP REGISTER allows proxies to act on 778 the information. For the problem set addressed by this document, it 779 is not anticipated that proxies will do so using registration data. 780 Further, there are classes of devices (such as cellular mobile 781 phones) that are not anticipated to include this information in their 782 registrations. Hence, use in registration is OPTIONAL. 784 In a call, a list of acceptable media and language combinations is 785 declared, and a priority assigned to each combination. 787 This is done by the Accept-Contact header field, which defines 788 different combinations of media and languages and assigns priorities 789 for completing the call with the SIP URI represented by that Contact. 790 A priority is assigned to each set as a so-called "q-value" which 791 ranges from 1 (most preferred) to 0 (least preferred). 793 Using the Accept-Contact header field in INVITE requests and 794 responses allows these capabilities to be expressed and used during 795 call set-up. Clients SHOULD include this information in INVITE 796 requests and responses. 798 Example: 800 Accept-Contact: *; text; language="en"; q=0.2 802 Accept-Contact: *; video; language="ase"; q=0.8 804 This example shows the highest preference expressed by the caller is 805 to use video with American Sign Language (language code "ase"). As a 806 fallback, it is acceptable to get the call connected with only 807 English text used for human communication. Other media may of course 808 be connected as well, without expectation that it will be usable by 809 the caller for interactive communications (but may still be helpful 810 to the caller). 812 This system satisfies all the needs described in the previous 813 chapters, except that language specifications do not make any 814 distinction between spoken and written language, and that the need 815 for directionality in the specification cannot be fulfilled. 817 To some degree the lack of media specification between speech and 818 text in language tags can be compensated by only specifying the 819 important medium in the Accept-Contact field. 821 Thus, a user who wants to use English mainly for text would specify: 823 Accept-Contact: *;text;language="en";q=1.0 825 While a user who wants to use English mainly for speech but accept it 826 for text would specify: 828 Accept-Contact: *;audio;language="en";q=0.8 830 Accept-Contact: *;text;language="en";q=0.2 832 However, a user who would like to talk, but receive text back has no 833 way to do it with the existing specification. 835 A.2. Additional Caller Preferences for Asymmetric Needs 837 In order to be able to specify asymmetric preferences, there are two 838 possibilities. Either new language tags in the style of the 839 humintlang parameters described above for SDP could be registered, or 840 additional media tags describing the asymmetry could be registered. 842 A.2.1. Caller Preferences for Asymmetric Modality Needs 844 The following new media tags should be defined: 846 speech-receive 848 speech-send 849 text-receive 851 text-send 853 sign-send 855 sign-receive 857 A user who prefers to talk and get text in return in English would 858 register the following (if including this information in registration 859 data): 861 REGISTER user@example.net 863 Contact: audio;text;speech-send;text- 864 receive;language="en" 866 At call time, a user who prefers to talk and get text in return in 867 English would set the Accept-Contact header field to: 869 Accept-Contact: *; audio; text; speech-receive; text-send; 870 language="en";q=0.8 872 Accept-Contact: *; text; language="en"; q=0.2 874 Note that the directions specified here are as viewed from the callee 875 side to match what the callee has registered. 877 A bridge arranged for invoking a relay service specifically arranged 878 for captioned telephony would register the following for supporting 879 calling users: 881 REGISTER ct@ctrelay.net 883 Contact: audio; text; speech-receive; 884 text-send; language="en" 886 A bridge arranged for invoking a relay service specifically arranged 887 for captioned telephony would register the following for supporting 888 called users: 890 REGISTER ct@ctrelay.net 892 Contact: audio; text; speech-send; text- 893 receive; language="en" 895 At call time, these alternatives are included in the list of possible 896 outcome of the call routing by the SIP proxies and the proper relay 897 service is invoked. 899 A.2.2. Caller Preferences for Asymmetric Language Tags 901 An alternative is to register new language tags for the purpose of 902 asymmetric language usage. 904 Instead of using "language=", six new language tags would be 905 registered: 907 humintlang-text-recv 909 humintlang-text-send 911 humintlang-speech-recv 913 humintlang-speech-send 915 humintlang-sign-recv 917 humintlang-sign-send 919 These language tags would be used instead of the regular 920 bidirectional language tags, and users with bidirectional 921 capabilities SHOULD specify values for both directions. Services 922 specifically arranged for supporting users with asymmetric needs 923 SHOULD specify only the asymmetry they support. 925 Author's Address 927 Randall Gellens 928 Qualcomm Technologies Inc. 929 5775 Morehouse Drive 930 San Diego, CA 92121 931 US 933 Email: rg+ietf@qti.qualcomm.com