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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) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 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 November 21, 2017 5 Expires: May 25, 2018 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-18 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 May 25, 2018. 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 1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5 65 4. The existing 'lang' attribute . . . . . . . . . . . . . . . . 5 66 5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 5.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 5 68 5.2. The 'hlang-send' and 'hlang-recv' attributes . . . . . . 6 69 5.3. No Language in Common . . . . . . . . . . . . . . . . . . 7 70 5.4. Usage Notes . . . . . . . . . . . . . . . . . . . . . . . 7 71 5.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 72 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 73 6.1. att-field Table in SDP Parameters . . . . . . . . . . . . 10 74 6.2. Warn-Codes Sub-Registry of SIP Parameters . . . . . . . . 11 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 76 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 77 9. Changes from Previous Versions . . . . . . . . . . . . . . . 12 78 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf- 79 slim-...-06 . . . . . . . . . . . . . . . . . . . . . . . 12 80 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf- 81 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 12 82 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf- 83 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 12 84 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf- 85 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 13 86 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf- 87 slim-...-00 . . . . . . . . . . . . . . . . . . . . . . . 13 88 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 89 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 13 90 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 91 slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 13 92 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 93 slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 13 94 9.9. Changes from draft-gellens-mmusic-...-02 to draft- 95 gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 13 96 9.10. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 14 97 9.11. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 14 98 9.12. Changes from draft-gellens-...-02 to draft-gellens- 99 mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 14 100 9.13. Changes from draft-gellens-...-01 to -02 . . . . . . . . 15 101 9.14. Changes from draft-gellens-...-00 to -01 . . . . . . . . 15 102 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 103 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 104 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 105 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 106 12.2. Informational References . . . . . . . . . . . . . . . . 16 107 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 109 1. Introduction 111 A mutually comprehensible language is helpful for human 112 communication. This document addresses the negotiation of human 113 (natural) language and media modality (spoken, signed, written) in 114 real-time communications. A companion document [RFC8255] addresses 115 language selection in email. 117 Unless the caller and callee know each other or there is contextual 118 or out-of- band information from which the language(s) and media 119 modalities can be determined, there is a need for spoken, signed, or 120 written languages to be negotiated based on the caller's needs and 121 the callee's capabilities. This need applies to both emergency and 122 non-emergency calls. For example, it is helpful for a caller to a 123 company call center or a Public Safety Answering Point (PSAP) to be 124 able to indicate preferred signed, written, and/or spoken languages, 125 and for the callee to be able to indicate its capabilities in this 126 area, allowing the call to proceed using the language(s) and media 127 forms supported by both. 129 For various reasons, including the ability to establish multiple 130 streams using different media (e.g., voice, text, video), it makes 131 sense to use a per-stream negotiation mechanism known as the Session 132 Description Protocol (SDP). Utilizing SDP enables the solution 133 described in this document to be applied to all interactive 134 communications negotiated using SDP, in emergency as well as non- 135 emergency scenarios. 137 By treating language as another SDP attribute that is negotiated 138 along with other aspects of a media stream, it becomes possible to 139 accommodate a range of users' needs and called party facilities. For 140 example, some users may be able to speak several languages, but have 141 a preference. Some called parties may support some of those 142 languages internally but require the use of a translation service for 143 others, or may have a limited number of call takers able to use 144 certain languages. Another example would be a user who is able to 145 speak but is deaf or hard-of-hearing and and desires a voice stream 146 to send spoken language plus a text stream to receive written 147 language. Making language a media attribute allows the standard 148 session negotiation mechanism to handle this by providing the 149 information and mechanism for the endpoints to make appropriate 150 decisions. 152 The term "negotiation" is used here rather than "indication" because 153 human language (spoken/written/signed) can be negotiated in the same 154 manner as media (audio/text/video) and codecs. For example, if we 155 think of a user calling an airline reservation center, the user may 156 have a set of languages he or she speaks, with perhaps preferences 157 for one or a few, while the airline reservation center will support a 158 fixed set of languages. Negotiation should select the user's most 159 preferred language that is supported by the call center. Both sides 160 should be aware of which language was negotiated. This is 161 conceptually similar to the way other aspects of each media stream 162 are negotiated using SDP (e.g., media type and codecs). 164 Since this is a protocol mechanism, the user equipment (UE client) 165 needs to know the user's preferred languages; while this document 166 does not address how clients determine this, reasonable techniques 167 could include a configuration mechanism with a default of the 168 language of the user interface; in some cases, a UE could tie 169 language and media preferences, such as a preference for a video 170 stream using a signed language and/or a text or audio stream using a 171 written/spoken language. 173 1.1. Applicability 175 Within this document, it is assumed that the negotiating endpoints 176 have already been determined, so that a per-stream negotiation based 177 on the Session Description Protocol (SDP) can proceed. 179 When setting up interactive communications sessions it is necessary 180 to route signaling messages to the appropriate endpoint(s). This 181 document does not address the problem of language-based routing. 183 2. Terminology 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 187 document are to be interpreted as described in RFC 2119 [RFC2119]. 189 3. Desired Semantics 191 The desired solution is a media attribute (preferably per direction) 192 that may be used within an offer to indicate the preferred 193 language(s) of each (direction of a) media stream, and within an 194 answer to indicate the accepted language. The semantics of including 195 multiple languages for a media stream within an offer is that the 196 languages are listed in order of preference. 198 (Negotiating multiple simultaneous languages within a media stream is 199 out of scope of this document.) 201 4. The existing 'lang' attribute 203 RFC 4566 [RFC4566] specifies an attribute 'lang' which appears 204 similar to what is needed here, but is not sufficiently specific or 205 flexible for the needs of this document. In addition, 'lang' is not 206 mentioned in [RFC3264] and there are no known implementations in SIP. 207 Further, it is useful to be able to specify language per direction 208 (sending and receiving). This document therefore defines two new 209 attributes. 211 5. Solution 213 An SDP attribute (per direction) seems the natural choice to 214 negotiate human (natural) language of an interactive media stream, 215 using the language tags of BCP 47 [RFC5646]. 217 5.1. Rationale 219 The decision to base the proposal at the media negotiation level, and 220 specifically to use SDP, came after significant debate and 221 discussion. From an engineering standpoint, it is possible to meet 222 the objectives using a variety of mechanisms, but none are perfect. 223 None of the proposed alternatives was clearly better technically in 224 enough ways to win over proponents of the others, and none were 225 clearly so bad technically as to be easily rejected. As is often the 226 case in engineering, choosing the solution is a matter of balancing 227 trade-offs, and ultimately more a matter of taste than technical 228 merit. The two main proposals were to use SDP and SIP. SDP has the 229 advantage that the language is negotiated with the media to which it 230 applies, while SIP has the issue that the languages expressed may not 231 match the SDP media negotiated (for example, a session could 232 negotiate a signed language at the SIP level but fail to negotiate a 233 video media stream at the SDP layer). 235 The mechanism described here for SDP can be adapted to media 236 negotiation protocols other than SDP. 238 5.2. The 'hlang-send' and 'hlang-recv' attributes 240 This document defines two media-level attributes starting with 241 'hlang' (short for "human interactive language") to negotiate which 242 human language is selected for use in each interactive media stream. 243 (Note that not all streams will necessarily be used.) There are two 244 attributes, one ending in "-send" and the other in "-recv", 245 registered in Section 6. Each can appear in offers and answers for 246 media streams. 248 In an offer, the 'hlang-send' value is a list of one or more 249 language(s) the offerer is willing to use when sending using the 250 media, and the 'hlang-recv' value is a list of one or more 251 language(s) the offerer is willing to use when receiving using the 252 media. The list of languages is in preference order (first is most 253 preferred). When a media is intended for interactive communication 254 using a language in one direction only (such as a user sending using 255 text and receiving using audio), either hlang-send or hlang-recv MAY 256 be omitted. When a media is not primarily intended for language (for 257 example, a video or audio stream intended for background only) both 258 SHOULD be omitted. Otherwise, both SHOULD have the same value. The 259 two SHOULD NOT be set to languages which are difficult to match 260 together (e.g., specifying a desire to send audio in Hungarian and 261 receive audio in Portuguese will make it difficult to successfully 262 complete the call). 264 In an answer, 'hlang-send' is the language the answerer will send if 265 using the media for language (which in most cases is one of the 266 languages in the offer's 'hlang-recv'), and 'hlang-recv' is the 267 language the answerer expects to receive if using the media for 268 language (which in most cases is one of the languages in the offer's 269 'hlang-send'). 271 Each value MUST be a list of one or more language tags per BCP 47 272 [RFC5646], separated by white space. BCP 47 describes mechanisms for 273 matching language tags. Note that [RFC5646] Section 4.1 advises to 274 "tag content wisely" and not include unnecessary subtags. 276 When placing an emergency call, and in any other case where the 277 language cannot be inferred from context, in an offer each media 278 stream primarily intended for human language communication SHOULD 279 specify both (or for asymmetrical language use, one of) the 'hlang- 280 send' and 'hlang-recv' attributes. 282 Clients acting on behalf of end users are expected to set one or both 283 'hlang-send' and 'hlang-recv' attributes on each media stream 284 primarily intended for human communication in an offer when placing 285 an outgoing session, and either ignore or take into consideration the 286 attributes when receiving incoming calls, based on local 287 configuration and capabilities. Systems acting on behalf of call 288 centers and PSAPs are expected to take into account the attributes 289 when processing inbound calls. 291 Note that media and language negotiation might result in more media 292 streams being accepted than are needed by the users (e.g., if more 293 preferred and less preferred combinations of media and language are 294 all accepted). This is not a problem. 296 5.3. No Language in Common 298 A consideration with the ability to negotiate language is if the call 299 proceeds or fails if the callee does not support any of the languages 300 requested by the caller. This document does not mandate either 301 behavior. 303 If the call is rejected due to lack of any languages in common, it is 304 suggested to use SIP response code 488 (Not Acceptable Here) or 606 305 (Not Acceptable) [RFC3261] and include a Warning header field 306 [RFC3261] in the SIP response. The Warning header field contains a 307 warning code of [TBD: IANA VALUE, e.g., 308] and a warning text 308 indicating that there are no mutually-supported languages; the text 309 SHOULD also contain the supported languages and media. 311 Example: 313 Warning: [TBD: IANA VALUE, e.g., 308] proxy.example.com 314 "Incompatible language specification: Requested languages not 315 supported. Supported languages are: es, en; supported media 316 are: audio, text." 318 5.4. Usage Notes 320 A sign language tag with a video media stream is interpreted as an 321 indication for sign language in the video stream. A non-sign 322 language tag with a text media stream is interpreted as an indication 323 for written language in the text stream. A non-sign language tag 324 with an audio media stream is interpreted as an indication for spoken 325 language in the audio stream. 327 This document does not define any other use for language tags in 328 video media (such as how to indicate visible captions in the video 329 stream). 331 In the IANA registry of language subtags per BCP 47 [RFC5646], a 332 language subtag with a Type field "extlang" combined with a Prefix 333 field value "sgn" indicates a sign language tag. The absense of such 334 "sgn" prefix indicates a non-sign language tag. 336 This document does not define the use of sign language tags in text 337 or audio media. 339 This document does not define the use of language tags in media other 340 than interactive streams of audio, video, and text (such as "message" 341 or "application"). Such use could be supported by future work or by 342 application agreement. 344 5.5. Examples 346 Some examples are shown below. For clarity, only the most directly 347 relevant portions of the SDP block are shown. 349 An offer or answer indicating spoken English both ways: 351 m=audio 49170 RTP/AVP 0 352 a=hlang-send:en 353 a=hlang-recv:en 355 An offer indicating American Sign Language both ways: 357 m=video 51372 RTP/AVP 31 32 358 a=hlang-send:ase 359 a=hlang-recv:ase 361 An offer requesting spoken Spanish both ways (most preferred), spoken 362 Basque both ways (second preference), or spoken English both ways 363 (third preference): 365 m=audio 49250 RTP/AVP 20 366 a=hlang-send:es eu en 367 a=hlang-recv:es eu en 369 An answer to the above offer indicating spoken Spanish both ways: 371 m=audio 49250 RTP/AVP 20 372 a=hlang-send:es 373 a=hlang-recv:es 375 An alternative answer to the above offer indicating spoken Italian 376 both ways (as the callee does not support any of the requested 377 languages but chose to proceed with the call): 379 m=audio 49250 RTP/AVP 20 380 a=hlang-send:it 381 a=hlang-recv:it 383 An offer or answer indicating written Greek both ways: 385 m=text 45020 RTP/AVP 103 104 386 a=hlang-send:gr 387 a=hlang-recv:gr 389 An offer requesting the following media streams: video for the caller 390 to send using Argentine Sign Language, text for the caller to send 391 using written Spanish (most preferred) or written Portuguese, audio 392 for the caller to receive spoken Spanish (most preferred) or spoken 393 Portuguese: 395 m=video 51372 RTP/AVP 31 32 396 a=hlang-send:aed 398 m=text 45020 RTP/AVP 103 104 399 a=hlang-send:sp pt 401 m=audio 49250 RTP/AVP 20 402 a=hlang-recv:sp pt 404 An answer for the above offer, indicating text in which the callee 405 will receive written Spanish, and audio in which the callee will send 406 spoken Spanish. The answering party had no video capability: 408 m=video 0 RTP/AVP 31 32 409 m=text 45020 RTP/AVP 103 104 410 a=hlang-recv:sp 412 m=audio 49250 RTP/AVP 20 413 a=hlang-send:sp 415 An offer requesting the following media streams: text for the caller 416 to send using written English (most preferred) or written Spanish, 417 audio for the caller to receive spoken English (most preferred) or 418 spoken Spanish, supplemental video: 420 m=text 45020 RTP/AVP 103 104 421 a=hlang-send:en sp 423 m=audio 49250 RTP/AVP 20 424 a=hlang-recv:en sp 426 m=video 51372 RTP/AVP 31 32 428 An answer for the above offer, indicating text in which the callee 429 will receive written Spanish, audio in which the callee will send 430 spoken Spanish, and supplemental video: 432 m=text 45020 RTP/AVP 103 104 433 a=hlang-recv:sp 435 m=audio 49250 RTP/AVP 20 436 a=hlang-send:sp 438 m=video 51372 RTP/AVP 31 32 440 Note that, even though the examples show the same (or essentially the 441 same) language being used in both directions (even when the modality 442 differs), there is no requirement that this be the case. However, in 443 practice, doing so is likely to increase the chances of successful 444 matching. 446 6. IANA Considerations 448 6.1. att-field Table in SDP Parameters 450 IANA is kindly requested to add two entries to the 'att-field (media 451 level only)' table of the SDP parameters registry: 453 Attribute Name: hlang-recv 455 Contact Name: Randall Gellens 457 Contact Email Address: rg+ietf@randy.pensive.org 459 Attribute Value: hlang-value 461 Attribute Syntax: 463 hlang-value = Language-Tag *( SP Language-tag ) 465 ; Language-Tag as defined in BCP 47 467 SP = 1*" " ; one or more space (%x20) characters 469 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 471 Usage Level: media 473 Mux Category: NORMAL 474 Charset Dependent: No 476 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 478 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 480 Reference: TBD: THIS DOCUMENT 482 Attribute Name: hlang-send 484 Contact Name: Randall Gellens 486 Contact Email Address: rg+ietf@randy.pensive.org 488 Attribute Value: hlang-value 490 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 492 Usage Level: media 494 Mux Category: NORMAL 496 Charset Dependent: No 498 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 500 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 502 Reference: TBD: THIS DOCUMENT 504 6.2. Warn-Codes Sub-Registry of SIP Parameters 506 IANA is requested to add a new value in the warn-codes sub-registry 507 of SIP parameters in the 300 through 329 range that is allocated for 508 indicating problems with keywords in the session description. The 509 reference is to this document. The warn text is "Incompatible 510 language specification: Requested languages not supported. Supported 511 languages and media are: [list of supported languages and media]." 513 7. Security Considerations 515 The Security Considerations of BCP 47 [RFC5646] apply here. In 516 addition, if the 'hlang-send' or 'hlang-recv' values are altered or 517 deleted en route, the session could fail or languages 518 incomprehensible to the caller could be selected; however, this is 519 also a risk if any SDP parameters are modified en route. 521 8. Privacy Considerations 523 Language and media information can suggest a user's nationality, 524 background, abilities, disabilities, etc. 526 9. Changes from Previous Versions 528 RFC EDITOR: Please remove this section prior to publication. 530 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06 532 o Deleted Section 3 ("Expected Use") 534 o Reworded modalities in Introduction from "voice, video, text" to 535 "spoken, signed, written" 537 o Reworded text about "increasingly fine-grained distinctions" to 538 instead merely point to BCP 47 Section 4.1's advice to "tag 539 content wisely" and not include unnecessary subtags 541 o Changed IANA registration of new SDP attributes to follow RFC 4566 542 template with extra fields suggested in 4566-bis (expired draft) 544 o Deleted "(known as voice carry over)" 546 o Changed textual instanced of RFC 5646 to BCP 47, although actual 547 reference remains RFC due to xml2rfc limitations 549 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 551 o Added Examples 553 o Added Privacy Considerations section 555 o Other editorial changes for clarity 557 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 559 o Deleted most of Section 4 and replaced with a very short summary 561 o Replaced "wishes to" with "is willing to" in Section 5.2 563 o Reworded description of attribute usage to clarify when to set 564 both, only one, or neither 566 o Deleted all uses of "IMS" 568 o Other editorial changes for clarity 570 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 572 o Editorial changes to wording in Section 5. 574 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 576 o Updated title to reflect WG adoption 578 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 579 slim-...-03 581 o Removed Use Cases section, per face-to-face discussion at IETF 93 583 o Removed discussion of routing, per face-to-face discussion at IETF 584 93 586 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 587 slim-...-02 589 o Updated NENA usage mention 591 o Removed background text reference to draft-saintandre-sip-xmpp- 592 chat-04 since that draft expired 594 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 595 slim-...-01 597 o Revision to keep draft from expiring 599 9.9. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 600 slim-...-00 602 o Changed name from -mmusic- to -slim- to reflect proposed WG name 604 o As a result of the face-to-face discussion in Toronto, the SDP vs 605 SIP issue was resolved by going back to SDP, taking out the SIP 606 hint, and converting what had been a set of alternate proposals 607 for various ways of doing it within SIP into an informative annex 608 section which includes background on why SDP is the proposal 610 o Added mention that enabling a mutually comprehensible language is 611 a general problem of which this document addresses the real-time 612 side, with reference to [RFC8255] which addresses the non-real- 613 time side. 615 9.10. Changes from draft-gellens-mmusic-...-01 to -02 617 o Added clarifying text on leaving attributes unset for media not 618 primarily intended for human language communication (e.g., 619 background audio or video). 621 o Added new section ("Alternative Proposal: Caller-prefs") 622 discussing use of SIP-level Caller-prefs instead of SDP-level. 624 9.11. Changes from draft-gellens-mmusic-...-00 to -01 626 o Relaxed language on setting -send and -receive to same values; 627 added text on leaving on empty to indicate asymmetric usage. 629 o Added text that clients on behalf of end users are expected to set 630 the attributes on outgoing calls and ignore on incoming calls 631 while systems on behalf of call centers and PSAPs are expected to 632 take the attributes into account when processing incoming calls. 634 9.12. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 636 o Updated text to refer to RFC 5646 rather than the IANA language 637 subtags registry directly. 639 o Moved discussion of existing 'lang' attribute out of "Proposed 640 Solution" section and into own section now that it is not part of 641 proposal. 643 o Updated text about existing 'lang' attribute. 645 o Added example use cases. 647 o Replaced proposed single 'hlang' attribute with 'hlang-send' and 648 'hlang-recv' per Harald's request/information that it was a misuse 649 of SDP to use the same attribute for sending and receiving. 651 o Added section describing usage being advisory vs required and text 652 in attribute section. 654 o Added section on SIP "hint" header (not yet nailed down between 655 new and existing header). 657 o Added text discussing usage in policy-based routing function or 658 use of SIP header "hint" if unable to do so. 660 o Added SHOULD that the value of the parameters stick to the largest 661 granularity of language tags. 663 o Added text to Introduction to be try and be more clear about 664 purpose of document and problem being solved. 666 o Many wording improvements and clarifications throughout the 667 document. 669 o Filled in Security Considerations. 671 o Filled in IANA Considerations. 673 o Added to Acknowledgments those who participated in the Orlando ad- 674 hoc discussion as well as those who participated in email 675 discussion and side one-on-one discussions. 677 9.13. Changes from draft-gellens-...-01 to -02 679 o Updated text for (possible) new attribute "hlang" to reference RFC 680 5646 682 o Added clarifying text for (possible) re-use of existing 'lang' 683 attribute saying that the registration would be updated to reflect 684 different semantics for multiple values for interactive versus 685 non-interactive media. 687 o Added clarifying text for (possible) new attribute "hlang" to 688 attempt to better describe the role of language tags in media in 689 an offer and an answer. 691 9.14. Changes from draft-gellens-...-00 to -01 693 o Changed name of (possible) new attribute from 'humlang" to "hlang" 694 o Added discussion of silly state (language not appropriate for 695 media type) 696 o Added Voice Carry Over example 697 o Added mention of multilingual people and multiple languages 698 o Minor text clarifications 700 10. Contributors 702 Gunnar Hellstrom deserves special mention for his reviews and 703 assistance. 705 11. Acknowledgments 707 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 708 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 709 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 710 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 711 Natasha Rooney, Brian Rosen, Peter Saint-Andre, and Dale Worley for 712 reviews, corrections, suggestions, and participating in in-person and 713 email discussions. 715 12. References 717 12.1. Normative References 719 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 720 Requirement Levels", BCP 14, RFC 2119, 721 DOI 10.17487/RFC2119, March 1997, . 724 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 725 A., Peterson, J., Sparks, R., Handley, M., and E. 726 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 727 DOI 10.17487/RFC3261, June 2002, . 730 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 731 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 732 July 2006, . 734 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 735 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 736 September 2009, . 738 12.2. Informational References 740 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 741 with Session Description Protocol (SDP)", RFC 3264, 742 DOI 10.17487/RFC3264, June 2002, . 745 [RFC8255] Tomkinson, N. and N. Borenstein, "Multiple Language 746 Content Type", RFC 8255, DOI 10.17487/RFC8255, October 747 2017, . 749 Author's Address 751 Randall Gellens 752 Core Technology Consulting 754 Email: rg+ietf@coretechnologyconsulting.com 755 URI: http://www.coretechnologyconsulting.com