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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-14) exists of draft-ietf-slim-multilangcontent-06 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Gellens 3 Internet-Draft Core Technology Consulting 4 Intended status: Standards Track February 26, 2017 5 Expires: August 30, 2017 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-08 10 Abstract 12 Users have various human (natural) language needs, abilities, and 13 preferences regarding spoken, written, and signed languages. This 14 document adds new SDP media-level attributes so that when 15 establishing interactive communication sessions ("calls"), it is 16 possible to negotiate (communicate and match) the caller's language 17 and media needs with the capabilities of the called party. This is 18 especially important with emergency calls, where a call can be 19 handled by a call taker capable of communicating with the user, or a 20 translator or relay operator can be bridged into the call during 21 setup, but this applies to non-emergency calls as well (as an 22 example, when calling a company call center). 24 This document describes the need and a solution using new SDP media 25 attributes. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on August 30, 2017. 44 Copyright Notice 46 Copyright (c) 2017 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 63 3. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5 64 4. The existing 'lang' attribute . . . . . . . . . . . . . . . . 5 65 5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 5.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 6 67 5.2. The 'hlang-send' and 'hlang-recv' attributes . . . . . . 6 68 5.3. No Language in Common . . . . . . . . . . . . . . . . . . 8 69 5.4. Undefined Combinations . . . . . . . . . . . . . . . . . 8 70 5.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 72 6.1. att-field Table in SDP Parameters . . . . . . . . . . . . 11 73 6.2. Warn-Codes Sub-Registry of SIP Parameters . . . . . . . . 12 74 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 75 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 76 9. Changes from Previous Versions . . . . . . . . . . . . . . . 13 77 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf- 78 slim-...-06 . . . . . . . . . . . . . . . . . . . . . . . 13 79 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf- 80 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 13 81 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf- 82 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 13 83 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf- 84 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 14 85 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf- 86 slim-...-00 . . . . . . . . . . . . . . . . . . . . . . . 14 87 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 88 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 14 89 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 90 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 14 91 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 92 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 14 93 9.9. Changes from draft-gellens-mmusic-...-02 to draft- 94 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 14 95 9.10. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 15 96 9.11. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 15 97 9.12. Changes from draft-gellens-...-02 to draft-gellens- 98 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 15 99 9.13. Changes from draft-gellens-...-01 to -02 . . . . . . . . 16 100 9.14. Changes from draft-gellens-...-00 to -01 . . . . . . . . 16 101 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16 102 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 103 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 104 12.1. Normative References . . . . . . . . . . . . . . . . . . 17 105 12.2. Informational References . . . . . . . . . . . . . . . . 17 106 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 108 1. Introduction 110 A mutually comprehensible language is helpful for human 111 communication. This document addresses the real-time, interactive 112 side of the issue. A companion document on language selection in 113 email [I-D.ietf-slim-multilangcontent] addresses the non-real-time 114 side. 116 When setting up interactive communication sessions (using SIP or 117 other protocols), human (natural) language and media modality 118 (spoken, signed, written) negotiation may be needed. Unless the 119 caller and callee know each other or there is contextual or out-of- 120 band information from which the language(s) and media modalities can 121 be determined, there is a need for spoken, signed, or written 122 languages to be negotiated based on the caller's needs and the 123 callee's capabilities. This need applies to both emergency and non- 124 emergency calls. For various reasons, including the ability to 125 establish multiple streams using different media (e.g., voice, text, 126 video), it makes sense to use a per-stream negotiation mechanism, in 127 this case, SDP. 129 This approach has a number of benefits, including that it is generic 130 (applies to all interactive communications negotiated using SDP) and 131 is not limited to emergency calls. In some cases such a facility 132 isn't needed, because the language is known from the context (such as 133 when a caller places a call to a sign language relay center, to a 134 friend, or colleague). But it is clearly useful in many other cases. 135 For example, it is helpful that someone calling a company call center 136 or a Public Safety Answering Point (PSAP) be able to indicate 137 preferred signed, written, and/or spoken languages, the callee be 138 able to indicate its capabilities in this area, and the call proceed 139 using the language(s) and media forms supported by both. 141 Since this is a protocol mechanism, the user equipment (UE client) 142 needs to know the user's preferred languages; a reasonable technique 143 could include a configuration mechanism with a default of the 144 language of the user interface. In some cases, a UE could tie 145 language and media preferences, such as a preference for a video 146 stream using a signed language and/or a text or audio stream using a 147 written/spoken language. 149 Including the user's human (natural) language preferences in the 150 session establishment negotiation is independent of the use of a 151 relay service and is transparent to a voice or other service 152 provider. For example, assume a user within the United States who 153 speaks Spanish but not English places a voice call. The call could 154 be an emergency call or perhaps to an airline reservation desk. The 155 language information is transparent to the voice service provider, 156 but is part of the session negotiation between the UE and the 157 terminating entity. In the case of a call to e.g., an airline, the 158 call could be automatically handled by a Spanish-speaking agent. In 159 the case of an emergency call, the Emergency Services IP network 160 (ESInet) and the PSAP may choose to take the language and media 161 preferences into account when determining how to process the call. 163 By treating language as another attribute that is negotiated along 164 with other aspects of a media stream, it becomes possible to 165 accommodate a range of users' needs and called party facilities. For 166 example, some users may be able to speak several languages, but have 167 a preference. Some called parties may support some of those 168 languages internally but require the use of a translation service for 169 others, or may have a limited number of call takers able to use 170 certain languages. Another example would be a user who is able to 171 speak but is deaf or hard-of-hearing and requires a voice stream plus 172 a text stream. Making language a media attribute allows the standard 173 session negotiation mechanism to handle this by providing the 174 information and mechanism for the endpoints to make appropriate 175 decisions. 177 Regarding relay services, in the case of an emergency call requiring 178 sign language such as ASL, there are currently two common approaches: 179 the caller initiates the call to a relay center, or the caller places 180 the call to emergency services (e.g., 911 in the U.S. or 112 in 181 Europe). (In a variant of the second case, the voice service 182 provider invokes a relay service as well as emergency services.) In 183 the former case, the language need is ancillary and supplemental. In 184 the non-variant second case, the ESInet and/or PSAP may take the need 185 for sign language into account and bridge in a relay center. In this 186 case, the ESInet and PSAP have all the standard information available 187 (such as location) but are able to bridge the relay sooner in the 188 call processing. 190 By making this facility part of the end-to-end negotiation, the 191 question of which entity provides or engages the relay service 192 becomes separate from the call processing mechanics; if the caller 193 directs the call to a relay service then the human language 194 negotiation facility provides extra information to the relay service 195 but calls will still function without it; if the caller directs the 196 call to emergency services, then the ESInet/PSAP are able to take the 197 user's human language needs into account, e.g., by assigning to a 198 specific queue or call taker or bridging in a relay service or 199 translator. 201 The term "negotiation" is used here rather than "indication" because 202 human language (spoken/written/signed) is something that can be 203 negotiated in the same way as which forms of media (audio/text/video) 204 or which codecs. For example, if we think of non-emergency calls, 205 such as a user calling an airline reservation center, the user may 206 have a set of languages he or she speaks, with perhaps preferences 207 for one or a few, while the airline reservation center will support a 208 fixed set of languages. Negotiation should select the user's most 209 preferred language that is supported by the call center. Both sides 210 should be aware of which language was negotiated. This is 211 conceptually similar to the way other aspects of each media stream 212 are negotiated using SDP (e.g., media type and codecs). 214 2. Terminology 216 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 217 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 218 document are to be interpreted as described in RFC 2119 [RFC2119]. 220 3. Desired Semantics 222 The desired solution is a media attribute (preferably per direction) 223 that may be used within an offer to indicate the preferred 224 language(s) of each (direction of a) media stream, and within an 225 answer to indicate the accepted language. The semantics of including 226 multiple values for a media stream within an offer is that the 227 languages are listed in order of preference. 229 (Negotiating multiple simultaneous languages within a media stream is 230 out of scope of this document.) 232 4. The existing 'lang' attribute 234 RFC 4566 [RFC4566] specifies an attribute 'lang' which appears 235 similar to what is needed here, but is not sufficiently specific or 236 flexible for the needs of this document. In addition, 'lang' is not 237 mentioned in [RFC3264] and there are no known implementations in SIP. 238 Further, it is useful to be able to specify language per direction 239 (sending and receiving). This document therefore defines two new 240 attributes. 242 5. Solution 244 An SDP attribute (per direction) seems the natural choice to 245 negotiate human (natural) language of an interactive media stream, 246 using the language tags of BCP 47 [RFC5646]. 248 5.1. Rationale 250 The decision to base the proposal at the media negotiation level, and 251 specifically to use SDP, came after significant debate and 252 discussion. From an engineering standpoint, it is possible to meet 253 the objectives using a variety of mechanisms, but none are perfect. 254 None of the proposed alternatives was clearly better technically in 255 enough ways to win over proponents of the others, and none were 256 clearly so bad technically as to be easily rejected. As is often the 257 case in engineering, choosing the solution is a matter of balancing 258 trade-offs, and ultimately more a matter of taste than technical 259 merit. The two main proposals were to use SDP and SIP. SDP has the 260 advantage that the language is negotiated with the media to which it 261 applies, while SIP has the issue that the languages expressed may not 262 match the SDP media negotiated (for example, a session could 263 negotiate video at the SIP level but fail to negotiate any video 264 media stream at the SDP layer). 266 The mechanism described here for SDP can be adapted to media 267 negotiation protocols other than SDP. 269 5.2. The 'hlang-send' and 'hlang-recv' attributes 271 This document defines two media-level attributes starting with 272 'hlang' (short for "human interactive language") to negotiate which 273 human language is used in each interactive media stream. There are 274 two attributes, one ending in "-send" and the other in "-recv", 275 registered in Section 6. Each can appear multiple times in an offer 276 for a media stream. 278 In an offer, the 'hlang-send' values are the language(s) the offerer 279 is willing to use when sending using the media, and the 'hlang-recv' 280 values are the language(s) the offerer is willing to use when 281 receiving using the media. The values from all instances of the 282 attribute constitute a list of languages in preference order (first 283 is most preferred). When a media is intended for interactive 284 communication using a language in one direction only (such as a user 285 sending using text and receiving using audio), either hlang-send or 286 hlang-recv MAY be omitted. When a media is not primarily intended 287 for language (for example, a video or audio stream intended for 288 background only) both SHOULD be omitted. Otherwise, both SHOULD have 289 the same values in the same order. The two SHOULD NOT be set to 290 languages which are difficult to match together (e.g., specifying a 291 desire to send audio in Hungarian and receive audio in Portuguese 292 will make it difficult to successfully complete the call). 294 In an answer, 'hlang-send' is the language the answerer will send 295 when using the media (which in most cases is one of the languages in 296 the offer's 'hlang-recv'), and 'hlang-recv' is the language the 297 answerer expects to receive in the media (which in most cases is one 298 of the languages in the offer's 'hlang-send'). 300 Each value MUST be a language tag per BCP 47 [RFC5646]. BCP 47 301 describes mechanisms for matching language tags. Note that [RFC5646] 302 Section 4.1 advises to "tag content wisely" and not include 303 unnecessary subtags. 305 In an offer, each language tag value MAY have an asterisk appended as 306 the last character. An asterisk appended to any value indicates a 307 request by the caller to not fail the call if there is no language in 308 common. See Section 5.3 for more information and discussion. 310 When placing an emergency call, and in any other case where the 311 language cannot be inferred from context, in an offer each media 312 stream primarily intended for human language communication SHOULD 313 specify both (or for asymmetrical language use, one of) the 'hlang- 314 send' and 'hlang-recv' attributes. 316 Note that while signed language tags are used with a video stream to 317 indicate sign language, a spoken language tag for a video stream in 318 parallel with an audio stream with the same spoken language tag 319 indicates a request for a supplemental video stream to see the 320 speaker. 322 Clients acting on behalf of end users are expected to set one or both 323 'hlang-send' and 'hlang-recv' attributes on each media stream 324 primarily intended for human communication in an offer when placing 325 an outgoing session, and either ignore or take into consideration the 326 attributes when receiving incoming calls, based on local 327 configuration and capabilities. Systems acting on behalf of call 328 centers and PSAPs are expected to take into account the values when 329 processing inbound calls. 331 Note that media and language negotiation might result in more media 332 streams being accepted than are needed by the users (e.g., if more 333 preferred and less preferred combinations of media and language are 334 all accepted). This is not a problem. 336 5.3. No Language in Common 338 A consideration with the ability to negotiate language is if the call 339 proceeds or fails if the callee does not support any of the languages 340 requested by the caller. This document does not mandate either 341 behavior, although it does provide a way for the caller to indicate a 342 preference for the call succeeding when there is no language in 343 common. It is OPTIONAL for the callee to honor this preference. For 344 example, a PSAP is likely to attempt the call even without an 345 indicated preference when there is no language in common, while a 346 call center might choose to fail the call. 348 The mechanism for indicating this preference is that, in an offer, if 349 the last character of any of the 'hlang-recv' or 'hlang-send' values 350 is an asterisk, this indicates a request to not fail the call. The 351 called party MAY ignore the indication, e.g., for the emergency 352 services use case, regardless of the absence of an asterisk, a PSAP 353 will likely not fail the call; some call centers might reject a call 354 even if the offer contains a language with an asterisk. 356 If the call is rejected due to lack of any languages in common, it is 357 suggested to use SIP response code 488 (Not Acceptable Here) or 606 358 (Not Acceptable) [RFC3261] and include a Warning header field 359 [RFC3261] in the SIP response. The Warning header field contains a 360 warning code of [TBD: IANA VALUE, e.g., 308] and a warning text 361 indicating that there are no mutually-supported languages; the text 362 SHOULD also contain the supported languages and media. 364 Example: 366 Warning: [TBD: IANA VALUE, e.g., 308] proxy.example.com 367 "Incompatible language specification: Requested languages not 368 supported. Supported languages are: es, en; supported media 369 are: audio, text." 371 5.4. Undefined Combinations 373 With the exception of the case mentioned in Section 5.2 (a spoken 374 language tag for a video stream in parallel with an audio stream with 375 the same spoken language tag), the behavior when specifying a spoken/ 376 written language tag for a video media stream, or a signed language 377 tag for an audio or text media stream, is not defined. 379 5.5. Examples 381 Some examples are shown below. Only the most directly relevant 382 portions of the SDP block are shown, for clarity. 384 An offer or answer indicating spoken English both ways: 386 m=audio 49170 RTP/AVP 0 387 a=hlang-send:en 388 a=hlang-recv:en 390 An offer or answer indicating American Sign Language both ways, and 391 requesting that the call proceed even if the callee does not support 392 the language: 394 m=video 51372 RTP/AVP 31 32 395 a=hlang-send:ase* 396 a=hlang-recv:ase* 398 An offer requesting spoken Spanish both ways (most preferred), spoken 399 Basque both ways (second preference), or spoken English both ways 400 (third preference). The offer further requests that the call proceed 401 even if the callee does not support any of the languages: 403 m=audio 49250 RTP/AVP 20 404 a=hlang-send:es* 405 a=hlang-recv:es* 406 a=hlang-send:eu* 407 a=hlang-recv:eu* 408 a=hlang-send:en* 409 a=hlang-recv:en* 411 An answer to the above offer indicating spoken Spanish both ways: 413 m=audio 49250 RTP/AVP 20 414 a=hlang-send:es 415 a=hlang-recv:es 417 An alternative answer to the above offer indicating spoken Italian 418 both ways (as the callee does not support any of the requested 419 languages but chose to proceed with the call): 421 m=audio 49250 RTP/AVP 20 422 a=hlang-send:it 423 a=hlang-recv:it 425 An offer of answer indicating written Greek both ways: 427 m=text 45020 RTP/AVP 103 104 428 a=hlang-send:gr 429 a=hlang-recv:gr 431 An offer requesting the following media streams: video for the caller 432 to send using Argentine Sign Language, text for the caller to send 433 using written Spanish (most preferred) or written Portuguese, audio 434 for the caller to receive spoken Spanish (most preferred) or spoken 435 Portuguese. The offer also requests that the call proceed even if 436 the callee does not support any of the languages: 438 m=video 51372 RTP/AVP 31 32 439 a=hlang-send:aed* 441 m=text 45020 RTP/AVP 103 104 442 a=hlang-send:sp 443 a=hlang-send:pt* 445 m=audio 49250 RTP/AVP 20 446 a=hlang-recv:sp 447 a=hlang-recv:pt* 449 An answer for the above offer, indicating text in which the callee 450 will receive written Spanish, and audio in which the callee will send 451 spoken Spanish: 453 m=text 45020 RTP/AVP 103 104 454 a=hlang-recv:sp 456 m=audio 49250 RTP/AVP 20 457 a=hlang-send:sp 459 An offer requesting the following media streams: text for the caller 460 to send using written English (most preferred) or written Spanish, 461 audio for the caller to receive spoken English (most preferred) or 462 spoken Spanish, supplemental video. The offer also requests that the 463 call proceed even if the callee does not support any of the 464 languages: 466 m=text 45020 RTP/AVP 103 104 467 a=hlang-send:en 468 a=hlang-send:sp 470 m=audio 49250 RTP/AVP 20 471 a=hlang-recv:en 472 a=hlang-recv:sp* 474 m=video 51372 RTP/AVP 31 32 476 An answer for the above offer, indicating text in which the callee 477 will receive written Spanish, audio in which the callee will send 478 spoken Spanish, and supplemental video: 480 m=text 45020 RTP/AVP 103 104 481 a=hlang-recv:sp 483 m=audio 49250 RTP/AVP 20 484 a=hlang-send:sp 486 m=video 51372 RTP/AVP 31 32 488 6. IANA Considerations 490 6.1. att-field Table in SDP Parameters 492 IANA is kindly requested to add two entries to the 'att-field (media 493 level only)' table of the SDP parameters registry: 495 Attribute Name: hlang-recv 497 Contact Name: Randall Gellens 499 Contact Email Address: rg+ietf@randy.pensive.org 501 Attribute Syntax: 503 hlang-value = Language-Tag [ asterisk ] 505 ; Language-Tag as defined in BCP 47 507 asterisk = "*" 509 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 511 Usage Level: media 513 MUX Category: NORMAL 515 Charset Dependent: No 517 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 519 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 521 Reference: TBD: THIS DOCUMENT 522 Attribute Name: hlang-send 524 Contact Name: Randall Gellens 526 Contact Email Address: rg+ietf@randy.pensive.org 528 Attribute Syntax: hlang-value 530 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 532 Usage Level: media 534 MUX Category: NORMAL 536 Charset Dependent: No 538 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 540 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 542 Reference: TBD: THIS DOCUMENT 544 6.2. Warn-Codes Sub-Registry of SIP Parameters 546 IANA is requested to add a new value in the warn-codes sub-registry 547 of SIP parameters in the 300 through 329 range that is allocated for 548 indicating problems with keywords in the session description. The 549 reference is to this document. The warn text is "Incompatible 550 language specification: Requested languages not supported. Supported 551 languages and media are: [list of supported languages and media]." 553 7. Security Considerations 555 The Security Considerations of BCP 47 [RFC5646] apply here. In 556 addition, if the 'hlang-send' or 'hlang-recv' values are altered or 557 deleted en route, the session could fail or languages 558 incomprehensible to the caller could be selected; however, this is 559 also a risk if any SDP parameters are modified en route. 561 8. Privacy Considerations 563 Language and media information can suggest a user's nationality, 564 background, abilities, disabilities, etc. 566 9. Changes from Previous Versions 568 RFC EDITOR: Please remove this section prior to publication. 570 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06 572 o Deleted Section 3 ("Expected Use") 574 o Reworded modalities in Introduction from "voice, video, text" to 575 "spoken, signed, written" 577 o Reworded text about "increasingly fine-grained distinctions" to 578 instead merely point to BCP 47 Section 4.1's advice to "tag 579 content wisely" and not include unnecessary subtags 581 o Changed IANA registration of new SDP attributes to follow RFC 4566 582 template with extra fields suggested in 4566-bis (expired draft) 584 o Deleted "(known as voice carry over)" 586 o Changed textual instanced of RFC 5646 to BCP 47, although actual 587 reference remains RFC due to xml2rfc limitations 589 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 591 o Added Examples 593 o Added Privacy Considerations section 595 o Other editorial changes for clarity 597 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 599 o Deleted most of Section 4 and replaced with a very short summary 601 o Replaced "wishes to" with "is willing to" in Section 5.2 603 o Reworded description of attribute usage to clarify when to set 604 both, only one, or neither 606 o Deleted all uses of "IMS" 608 o Other editorial changes for clarity 610 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 612 o Editorial changes to wording in Section 5. 614 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 616 o Updated title to reflect WG adoption 618 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 619 slim-...-03 621 o Removed Use Cases section, per face-to-face discussion at IETF 93 623 o Removed discussion of routing, per face-to-face discussion at IETF 624 93 626 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 627 slim-...-02 629 o Updated NENA usage mention 631 o Removed background text reference to draft-saintandre-sip-xmpp- 632 chat-04 since that draft expired 634 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 635 slim-...-01 637 o Revision to keep draft from expiring 639 9.9. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 640 slim-...-00 642 o Changed name from -mmusic- to -slim- to reflect proposed WG name 644 o As a result of the face-to-face discussion in Toronto, the SDP vs 645 SIP issue was resolved by going back to SDP, taking out the SIP 646 hint, and converting what had been a set of alternate proposals 647 for various ways of doing it within SIP into an informative annex 648 section which includes background on why SDP is the proposal 650 o Added mention that enabling a mutually comprehensible language is 651 a general problem of which this document addresses the real-time 652 side, with reference to [I-D.ietf-slim-multilangcontent] which 653 addresses the non-real-time side. 655 9.10. Changes from draft-gellens-mmusic-...-01 to -02 657 o Added clarifying text on leaving attributes unset for media not 658 primarily intended for human language communication (e.g., 659 background audio or video). 661 o Added new section ("Alternative Proposal: Caller-prefs") 662 discussing use of SIP-level Caller-prefs instead of SDP-level. 664 9.11. Changes from draft-gellens-mmusic-...-00 to -01 666 o Relaxed language on setting -send and -receive to same values; 667 added text on leaving on empty to indicate asymmetric usage. 669 o Added text that clients on behalf of end users are expected to set 670 the attributes on outgoing calls and ignore on incoming calls 671 while systems on behalf of call centers and PSAPs are expected to 672 take the attributes into account when processing incoming calls. 674 9.12. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 676 o Updated text to refer to RFC 5646 rather than the IANA language 677 subtags registry directly. 679 o Moved discussion of existing 'lang' attribute out of "Proposed 680 Solution" section and into own section now that it is not part of 681 proposal. 683 o Updated text about existing 'lang' attribute. 685 o Added example use cases. 687 o Replaced proposed single 'hlang' attribute with 'hlang-send' and 688 'hlang-recv' per Harald's request/information that it was a misuse 689 of SDP to use the same attribute for sending and receiving. 691 o Added section describing usage being advisory vs required and text 692 in attribute section. 694 o Added section on SIP "hint" header (not yet nailed down between 695 new and existing header). 697 o Added text discussing usage in policy-based routing function or 698 use of SIP header "hint" if unable to do so. 700 o Added SHOULD that the value of the parameters stick to the largest 701 granularity of language tags. 703 o Added text to Introduction to be try and be more clear about 704 purpose of document and problem being solved. 706 o Many wording improvements and clarifications throughout the 707 document. 709 o Filled in Security Considerations. 711 o Filled in IANA Considerations. 713 o Added to Acknowledgments those who participated in the Orlando ad- 714 hoc discussion as well as those who participated in email 715 discussion and side one-on-one discussions. 717 9.13. Changes from draft-gellens-...-01 to -02 719 o Updated text for (possible) new attribute "hlang" to reference RFC 720 5646 722 o Added clarifying text for (possible) re-use of existing 'lang' 723 attribute saying that the registration would be updated to reflect 724 different semantics for multiple values for interactive versus 725 non-interactive media. 727 o Added clarifying text for (possible) new attribute "hlang" to 728 attempt to better describe the role of language tags in media in 729 an offer and an answer. 731 9.14. Changes from draft-gellens-...-00 to -01 733 o Changed name of (possible) new attribute from 'humlang" to "hlang" 734 o Added discussion of silly state (language not appropriate for 735 media type) 736 o Added Voice Carry Over example 737 o Added mention of multilingual people and multiple languages 738 o Minor text clarifications 740 10. Contributors 742 Gunnar Hellstrom deserves special mention for his reviews and 743 assistance. 745 11. Acknowledgments 747 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 748 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 749 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 750 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 751 Peter Saint-Andre, and Dale Worley for reviews, corrections, 752 suggestions, and participating in in-person and email discussions. 754 12. References 756 12.1. Normative References 758 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 759 Requirement Levels", BCP 14, RFC 2119, 760 DOI 10.17487/RFC2119, March 1997, 761 . 763 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 764 A., Peterson, J., Sparks, R., Handley, M., and E. 765 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 766 DOI 10.17487/RFC3261, June 2002, 767 . 769 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 770 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 771 July 2006, . 773 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 774 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 775 September 2009, . 777 12.2. Informational References 779 [I-D.ietf-slim-multilangcontent] 780 Tomkinson, N. and N. Borenstein, "Multiple Language 781 Content Type", draft-ietf-slim-multilangcontent-06 (work 782 in progress), October 2016. 784 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 785 with Session Description Protocol (SDP)", RFC 3264, 786 DOI 10.17487/RFC3264, June 2002, 787 . 789 Author's Address 791 Randall Gellens 792 Core Technology Consulting 794 Email: rg+ietf@randy.pensive.org