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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 October 13, 2017 5 Expires: April 16, 2018 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-15 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 April 16, 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. Undefined Combinations . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . 11 77 9. Changes from Previous Versions . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . . . . . . . . . . 12 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 . . . . . 13 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 There are two attributes, one ending in "-send" and the other in 244 "-recv", registered in Section 6. Each can appear in offers and 245 answers for media streams. 247 In an offer, the 'hlang-send' value is a list of one or more 248 language(s) the offerer is willing to use when sending using the 249 media, and the 'hlang-recv' value is a list of one or more 250 language(s) the offerer is willing to use when receiving using the 251 media. The list of languages is in preference order (first is most 252 preferred). When a media is intended for interactive communication 253 using a language in one direction only (such as a user sending using 254 text and receiving using audio), either hlang-send or hlang-recv MAY 255 be omitted. When a media is not primarily intended for language (for 256 example, a video or audio stream intended for background only) both 257 SHOULD be omitted. Otherwise, both SHOULD have the same value. The 258 two SHOULD NOT be set to languages which are difficult to match 259 together (e.g., specifying a desire to send audio in Hungarian and 260 receive audio in Portuguese will make it difficult to successfully 261 complete the call). 263 In an answer, 'hlang-send' is the language the answerer will send if 264 using the media for language (which in most cases is one of the 265 languages in the offer's 'hlang-recv'), and 'hlang-recv' is the 266 language the answerer expects to receive if using the media for 267 language (which in most cases is one of the languages in the offer's 268 'hlang-send'). 270 Each value MUST be a list of one or more language tags per BCP 47 271 [RFC5646], separated by white space. BCP 47 describes mechanisms for 272 matching language tags. Note that [RFC5646] Section 4.1 advises to 273 "tag content wisely" and not include unnecessary subtags. 275 When placing an emergency call, and in any other case where the 276 language cannot be inferred from context, in an offer each media 277 stream primarily intended for human language communication SHOULD 278 specify both (or for asymmetrical language use, one of) the 'hlang- 279 send' and 'hlang-recv' attributes. 281 Note that while signed language tags are used with a video stream to 282 indicate sign language, a video stream in parallel with an audio 283 stream, both using the exact same (spoken) language tag, indicates a 284 request for a supplemental video stream to see the speaker. 286 Clients acting on behalf of end users are expected to set one or both 287 'hlang-send' and 'hlang-recv' attributes on each media stream 288 primarily intended for human communication in an offer when placing 289 an outgoing session, and either ignore or take into consideration the 290 attributes when receiving incoming calls, based on local 291 configuration and capabilities. Systems acting on behalf of call 292 centers and PSAPs are expected to take into account the attributes 293 when processing inbound calls. 295 Note that media and language negotiation might result in more media 296 streams being accepted than are needed by the users (e.g., if more 297 preferred and less preferred combinations of media and language are 298 all accepted). This is not a problem. 300 5.3. No Language in Common 302 A consideration with the ability to negotiate language is if the call 303 proceeds or fails if the callee does not support any of the languages 304 requested by the caller. This document does not mandate either 305 behavior. 307 If the call is rejected due to lack of any languages in common, it is 308 suggested to use SIP response code 488 (Not Acceptable Here) or 606 309 (Not Acceptable) [RFC3261] and include a Warning header field 310 [RFC3261] in the SIP response. The Warning header field contains a 311 warning code of [TBD: IANA VALUE, e.g., 308] and a warning text 312 indicating that there are no mutually-supported languages; the text 313 SHOULD also contain the supported languages and media. 315 Example: 317 Warning: [TBD: IANA VALUE, e.g., 308] proxy.example.com 318 "Incompatible language specification: Requested languages not 319 supported. Supported languages are: es, en; supported media 320 are: audio, text." 322 5.4. Undefined Combinations 324 With the exception of the case mentioned in Section 5.2 (an audio 325 stream in parallel with a video stream with the exact same (spoken) 326 language tag), the behavior when specifying a non-signed language tag 327 for a video media stream, or a signed language tag for an audio or 328 text media stream, is not defined in this document. 330 The problem of knowing which language tags are signed and which are 331 not is out of scope of this document. 333 5.5. Examples 335 Some examples are shown below. For clarity, only the most directly 336 relevant portions of the SDP block are shown. 338 An offer or answer indicating spoken English both ways: 340 m=audio 49170 RTP/AVP 0 341 a=hlang-send:en 342 a=hlang-recv:en 344 An offer indicating American Sign Language both ways: 346 m=video 51372 RTP/AVP 31 32 347 a=hlang-send:ase 348 a=hlang-recv:ase 350 An offer requesting spoken Spanish both ways (most preferred), spoken 351 Basque both ways (second preference), or spoken English both ways 352 (third preference): 354 m=audio 49250 RTP/AVP 20 355 a=hlang-send:es eu en 356 a=hlang-recv:es eu en 358 An answer to the above offer indicating spoken Spanish both ways: 360 m=audio 49250 RTP/AVP 20 361 a=hlang-send:es 362 a=hlang-recv:es 364 An alternative answer to the above offer indicating spoken Italian 365 both ways (as the callee does not support any of the requested 366 languages but chose to proceed with the call): 368 m=audio 49250 RTP/AVP 20 369 a=hlang-send:it 370 a=hlang-recv:it 372 An offer or answer indicating written Greek both ways: 374 m=text 45020 RTP/AVP 103 104 375 a=hlang-send:gr 376 a=hlang-recv:gr 378 An offer requesting the following media streams: video for the caller 379 to send using Argentine Sign Language, text for the caller to send 380 using written Spanish (most preferred) or written Portuguese, audio 381 for the caller to receive spoken Spanish (most preferred) or spoken 382 Portuguese: 384 m=video 51372 RTP/AVP 31 32 385 a=hlang-send:aed 387 m=text 45020 RTP/AVP 103 104 388 a=hlang-send:sp pt 390 m=audio 49250 RTP/AVP 20 391 a=hlang-recv:sp pt 393 An answer for the above offer, indicating text in which the callee 394 will receive written Spanish, and audio in which the callee will send 395 spoken Spanish. The answering party had no video capability: 397 m=video 0 RTP/AVP 31 32 398 m=text 45020 RTP/AVP 103 104 399 a=hlang-recv:sp 401 m=audio 49250 RTP/AVP 20 402 a=hlang-send:sp 404 An offer requesting the following media streams: text for the caller 405 to send using written English (most preferred) or written Spanish, 406 audio for the caller to receive spoken English (most preferred) or 407 spoken Spanish, supplemental video: 409 m=text 45020 RTP/AVP 103 104 410 a=hlang-send:en sp 412 m=audio 49250 RTP/AVP 20 413 a=hlang-recv:en sp 415 m=video 51372 RTP/AVP 31 32 417 An answer for the above offer, indicating text in which the callee 418 will receive written Spanish, audio in which the callee will send 419 spoken Spanish, and supplemental video: 421 m=text 45020 RTP/AVP 103 104 422 a=hlang-recv:sp 424 m=audio 49250 RTP/AVP 20 425 a=hlang-send:sp 427 m=video 51372 RTP/AVP 31 32 429 Note that, even though the examples show the same (or essentially the 430 same) language being used in both directions (even when the modality 431 differs), there is no requirement that this be the case. However, in 432 practice, doing so is likely to increase the chances of successful 433 matching. 435 6. IANA Considerations 437 6.1. att-field Table in SDP Parameters 439 IANA is kindly requested to add two entries to the 'att-field (media 440 level only)' table of the SDP parameters registry: 442 Attribute Name: hlang-recv 444 Contact Name: Randall Gellens 446 Contact Email Address: rg+ietf@randy.pensive.org 448 Attribute Value: hlang-value 450 Attribute Syntax: 452 hlang-value = Language-Tag *( SP Language-tag ) 454 ; Language-Tag as defined in BCP 47 456 SP = 1*" " ; one or more space (%x20) characters 458 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 460 Usage Level: media 462 Mux Category: NORMAL 464 Charset Dependent: No 466 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 468 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 470 Reference: TBD: THIS DOCUMENT 472 Attribute Name: hlang-send 474 Contact Name: Randall Gellens 475 Contact Email Address: rg+ietf@randy.pensive.org 477 Attribute Value: hlang-value 479 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 481 Usage Level: media 483 Mux Category: NORMAL 485 Charset Dependent: No 487 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 489 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 491 Reference: TBD: THIS DOCUMENT 493 6.2. Warn-Codes Sub-Registry of SIP Parameters 495 IANA is requested to add a new value in the warn-codes sub-registry 496 of SIP parameters in the 300 through 329 range that is allocated for 497 indicating problems with keywords in the session description. The 498 reference is to this document. The warn text is "Incompatible 499 language specification: Requested languages not supported. Supported 500 languages and media are: [list of supported languages and media]." 502 7. Security Considerations 504 The Security Considerations of BCP 47 [RFC5646] apply here. In 505 addition, if the 'hlang-send' or 'hlang-recv' values are altered or 506 deleted en route, the session could fail or languages 507 incomprehensible to the caller could be selected; however, this is 508 also a risk if any SDP parameters are modified en route. 510 8. Privacy Considerations 512 Language and media information can suggest a user's nationality, 513 background, abilities, disabilities, etc. 515 9. Changes from Previous Versions 517 RFC EDITOR: Please remove this section prior to publication. 519 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06 521 o Deleted Section 3 ("Expected Use") 523 o Reworded modalities in Introduction from "voice, video, text" to 524 "spoken, signed, written" 526 o Reworded text about "increasingly fine-grained distinctions" to 527 instead merely point to BCP 47 Section 4.1's advice to "tag 528 content wisely" and not include unnecessary subtags 530 o Changed IANA registration of new SDP attributes to follow RFC 4566 531 template with extra fields suggested in 4566-bis (expired draft) 533 o Deleted "(known as voice carry over)" 535 o Changed textual instanced of RFC 5646 to BCP 47, although actual 536 reference remains RFC due to xml2rfc limitations 538 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 540 o Added Examples 542 o Added Privacy Considerations section 544 o Other editorial changes for clarity 546 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 548 o Deleted most of Section 4 and replaced with a very short summary 550 o Replaced "wishes to" with "is willing to" in Section 5.2 552 o Reworded description of attribute usage to clarify when to set 553 both, only one, or neither 555 o Deleted all uses of "IMS" 557 o Other editorial changes for clarity 559 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 561 o Editorial changes to wording in Section 5. 563 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 565 o Updated title to reflect WG adoption 567 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 568 slim-...-03 570 o Removed Use Cases section, per face-to-face discussion at IETF 93 572 o Removed discussion of routing, per face-to-face discussion at IETF 573 93 575 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 576 slim-...-02 578 o Updated NENA usage mention 580 o Removed background text reference to draft-saintandre-sip-xmpp- 581 chat-04 since that draft expired 583 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 584 slim-...-01 586 o Revision to keep draft from expiring 588 9.9. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 589 slim-...-00 591 o Changed name from -mmusic- to -slim- to reflect proposed WG name 593 o As a result of the face-to-face discussion in Toronto, the SDP vs 594 SIP issue was resolved by going back to SDP, taking out the SIP 595 hint, and converting what had been a set of alternate proposals 596 for various ways of doing it within SIP into an informative annex 597 section which includes background on why SDP is the proposal 599 o Added mention that enabling a mutually comprehensible language is 600 a general problem of which this document addresses the real-time 601 side, with reference to [RFC8255] which addresses the non-real- 602 time side. 604 9.10. Changes from draft-gellens-mmusic-...-01 to -02 606 o Added clarifying text on leaving attributes unset for media not 607 primarily intended for human language communication (e.g., 608 background audio or video). 610 o Added new section ("Alternative Proposal: Caller-prefs") 611 discussing use of SIP-level Caller-prefs instead of SDP-level. 613 9.11. Changes from draft-gellens-mmusic-...-00 to -01 615 o Relaxed language on setting -send and -receive to same values; 616 added text on leaving on empty to indicate asymmetric usage. 618 o Added text that clients on behalf of end users are expected to set 619 the attributes on outgoing calls and ignore on incoming calls 620 while systems on behalf of call centers and PSAPs are expected to 621 take the attributes into account when processing incoming calls. 623 9.12. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 625 o Updated text to refer to RFC 5646 rather than the IANA language 626 subtags registry directly. 628 o Moved discussion of existing 'lang' attribute out of "Proposed 629 Solution" section and into own section now that it is not part of 630 proposal. 632 o Updated text about existing 'lang' attribute. 634 o Added example use cases. 636 o Replaced proposed single 'hlang' attribute with 'hlang-send' and 637 'hlang-recv' per Harald's request/information that it was a misuse 638 of SDP to use the same attribute for sending and receiving. 640 o Added section describing usage being advisory vs required and text 641 in attribute section. 643 o Added section on SIP "hint" header (not yet nailed down between 644 new and existing header). 646 o Added text discussing usage in policy-based routing function or 647 use of SIP header "hint" if unable to do so. 649 o Added SHOULD that the value of the parameters stick to the largest 650 granularity of language tags. 652 o Added text to Introduction to be try and be more clear about 653 purpose of document and problem being solved. 655 o Many wording improvements and clarifications throughout the 656 document. 658 o Filled in Security Considerations. 660 o Filled in IANA Considerations. 662 o Added to Acknowledgments those who participated in the Orlando ad- 663 hoc discussion as well as those who participated in email 664 discussion and side one-on-one discussions. 666 9.13. Changes from draft-gellens-...-01 to -02 668 o Updated text for (possible) new attribute "hlang" to reference RFC 669 5646 671 o Added clarifying text for (possible) re-use of existing 'lang' 672 attribute saying that the registration would be updated to reflect 673 different semantics for multiple values for interactive versus 674 non-interactive media. 676 o Added clarifying text for (possible) new attribute "hlang" to 677 attempt to better describe the role of language tags in media in 678 an offer and an answer. 680 9.14. Changes from draft-gellens-...-00 to -01 682 o Changed name of (possible) new attribute from 'humlang" to "hlang" 683 o Added discussion of silly state (language not appropriate for 684 media type) 685 o Added Voice Carry Over example 686 o Added mention of multilingual people and multiple languages 687 o Minor text clarifications 689 10. Contributors 691 Gunnar Hellstrom deserves special mention for his reviews and 692 assistance. 694 11. Acknowledgments 696 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 697 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 698 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 699 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 700 Natasha Rooney, Brian Rosen, Peter Saint-Andre, and Dale Worley for 701 reviews, corrections, suggestions, and participating in in-person and 702 email discussions. 704 12. References 706 12.1. Normative References 708 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 709 Requirement Levels", BCP 14, RFC 2119, 710 DOI 10.17487/RFC2119, March 1997, . 713 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 714 A., Peterson, J., Sparks, R., Handley, M., and E. 715 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 716 DOI 10.17487/RFC3261, June 2002, . 719 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 720 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 721 July 2006, . 723 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 724 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 725 September 2009, . 727 12.2. Informational References 729 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 730 with Session Description Protocol (SDP)", RFC 3264, 731 DOI 10.17487/RFC3264, June 2002, . 734 [RFC8255] Tomkinson, N. and N. Borenstein, "Multiple Language 735 Content Type", RFC 8255, DOI 10.17487/RFC8255, October 736 2017, . 738 Author's Address 740 Randall Gellens 741 Core Technology Consulting 743 Email: rg+ietf@coretechnologyconsulting.com 744 URI: http://www.coretechnologyconsulting.com