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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 14, 2017 5 Expires: April 17, 2018 7 Negotiating Human Language in Real-Time Communications 8 draft-ietf-slim-negotiating-human-language-16 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 17, 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . . . . . . . . . . 12 88 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 89 slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 12 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 . . . . . 13 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 . . . . . . . . 14 101 9.14. Changes from draft-gellens-...-00 to -01 . . . . . . . . 15 102 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 103 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 104 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 105 12.1. Normative References . . . . . . . . . . . . . . . . . . 15 106 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 Clients acting on behalf of end users are expected to set one or both 282 'hlang-send' and 'hlang-recv' attributes on each media stream 283 primarily intended for human communication in an offer when placing 284 an outgoing session, and either ignore or take into consideration the 285 attributes when receiving incoming calls, based on local 286 configuration and capabilities. Systems acting on behalf of call 287 centers and PSAPs are expected to take into account the attributes 288 when processing inbound calls. 290 Note that media and language negotiation might result in more media 291 streams being accepted than are needed by the users (e.g., if more 292 preferred and less preferred combinations of media and language are 293 all accepted). This is not a problem. 295 5.3. No Language in Common 297 A consideration with the ability to negotiate language is if the call 298 proceeds or fails if the callee does not support any of the languages 299 requested by the caller. This document does not mandate either 300 behavior. 302 If the call is rejected due to lack of any languages in common, it is 303 suggested to use SIP response code 488 (Not Acceptable Here) or 606 304 (Not Acceptable) [RFC3261] and include a Warning header field 305 [RFC3261] in the SIP response. The Warning header field contains a 306 warning code of [TBD: IANA VALUE, e.g., 308] and a warning text 307 indicating that there are no mutually-supported languages; the text 308 SHOULD also contain the supported languages and media. 310 Example: 312 Warning: [TBD: IANA VALUE, e.g., 308] proxy.example.com 313 "Incompatible language specification: Requested languages not 314 supported. Supported languages are: es, en; supported media 315 are: audio, text." 317 5.4. Undefined Combinations 319 The behavior when specifying a non-signed language tag for a video 320 media stream, or a signed language tag for an audio or text media 321 stream, is not defined in this document. 323 The problem of knowing which language tags are signed and which are 324 not is out of scope of this document. 326 5.5. Examples 328 Some examples are shown below. For clarity, only the most directly 329 relevant portions of the SDP block are shown. 331 An offer or answer indicating spoken English both ways: 333 m=audio 49170 RTP/AVP 0 334 a=hlang-send:en 335 a=hlang-recv:en 337 An offer indicating American Sign Language both ways: 339 m=video 51372 RTP/AVP 31 32 340 a=hlang-send:ase 341 a=hlang-recv:ase 343 An offer requesting spoken Spanish both ways (most preferred), spoken 344 Basque both ways (second preference), or spoken English both ways 345 (third preference): 347 m=audio 49250 RTP/AVP 20 348 a=hlang-send:es eu en 349 a=hlang-recv:es eu en 351 An answer to the above offer indicating spoken Spanish both ways: 353 m=audio 49250 RTP/AVP 20 354 a=hlang-send:es 355 a=hlang-recv:es 357 An alternative answer to the above offer indicating spoken Italian 358 both ways (as the callee does not support any of the requested 359 languages but chose to proceed with the call): 361 m=audio 49250 RTP/AVP 20 362 a=hlang-send:it 363 a=hlang-recv:it 365 An offer or answer indicating written Greek both ways: 367 m=text 45020 RTP/AVP 103 104 368 a=hlang-send:gr 369 a=hlang-recv:gr 371 An offer requesting the following media streams: video for the caller 372 to send using Argentine Sign Language, text for the caller to send 373 using written Spanish (most preferred) or written Portuguese, audio 374 for the caller to receive spoken Spanish (most preferred) or spoken 375 Portuguese: 377 m=video 51372 RTP/AVP 31 32 378 a=hlang-send:aed 380 m=text 45020 RTP/AVP 103 104 381 a=hlang-send:sp pt 383 m=audio 49250 RTP/AVP 20 384 a=hlang-recv:sp pt 386 An answer for the above offer, indicating text in which the callee 387 will receive written Spanish, and audio in which the callee will send 388 spoken Spanish. The answering party had no video capability: 390 m=video 0 RTP/AVP 31 32 391 m=text 45020 RTP/AVP 103 104 392 a=hlang-recv:sp 394 m=audio 49250 RTP/AVP 20 395 a=hlang-send:sp 397 An offer requesting the following media streams: text for the caller 398 to send using written English (most preferred) or written Spanish, 399 audio for the caller to receive spoken English (most preferred) or 400 spoken Spanish, supplemental video: 402 m=text 45020 RTP/AVP 103 104 403 a=hlang-send:en sp 405 m=audio 49250 RTP/AVP 20 406 a=hlang-recv:en sp 408 m=video 51372 RTP/AVP 31 32 410 An answer for the above offer, indicating text in which the callee 411 will receive written Spanish, audio in which the callee will send 412 spoken Spanish, and supplemental video: 414 m=text 45020 RTP/AVP 103 104 415 a=hlang-recv:sp 417 m=audio 49250 RTP/AVP 20 418 a=hlang-send:sp 420 m=video 51372 RTP/AVP 31 32 422 Note that, even though the examples show the same (or essentially the 423 same) language being used in both directions (even when the modality 424 differs), there is no requirement that this be the case. However, in 425 practice, doing so is likely to increase the chances of successful 426 matching. 428 6. IANA Considerations 430 6.1. att-field Table in SDP Parameters 432 IANA is kindly requested to add two entries to the 'att-field (media 433 level only)' table of the SDP parameters registry: 435 Attribute Name: hlang-recv 437 Contact Name: Randall Gellens 439 Contact Email Address: rg+ietf@randy.pensive.org 441 Attribute Value: hlang-value 443 Attribute Syntax: 445 hlang-value = Language-Tag *( SP Language-tag ) 447 ; Language-Tag as defined in BCP 47 449 SP = 1*" " ; one or more space (%x20) characters 451 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 453 Usage Level: media 455 Mux Category: NORMAL 457 Charset Dependent: No 459 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 461 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 463 Reference: TBD: THIS DOCUMENT 465 Attribute Name: hlang-send 467 Contact Name: Randall Gellens 469 Contact Email Address: rg+ietf@randy.pensive.org 471 Attribute Value: hlang-value 473 Attribute Semantics: Described in Section 5.2 of TBD: THIS DOCUMENT 474 Usage Level: media 476 Mux Category: NORMAL 478 Charset Dependent: No 480 Purpose: See Section 5.2 of TBD: THIS DOCUMENT 482 O/A Procedures: See Section 5.2 of TBD: THIS DOCUMENT 484 Reference: TBD: THIS DOCUMENT 486 6.2. Warn-Codes Sub-Registry of SIP Parameters 488 IANA is requested to add a new value in the warn-codes sub-registry 489 of SIP parameters in the 300 through 329 range that is allocated for 490 indicating problems with keywords in the session description. The 491 reference is to this document. The warn text is "Incompatible 492 language specification: Requested languages not supported. Supported 493 languages and media are: [list of supported languages and media]." 495 7. Security Considerations 497 The Security Considerations of BCP 47 [RFC5646] apply here. In 498 addition, if the 'hlang-send' or 'hlang-recv' values are altered or 499 deleted en route, the session could fail or languages 500 incomprehensible to the caller could be selected; however, this is 501 also a risk if any SDP parameters are modified en route. 503 8. Privacy Considerations 505 Language and media information can suggest a user's nationality, 506 background, abilities, disabilities, etc. 508 9. Changes from Previous Versions 510 RFC EDITOR: Please remove this section prior to publication. 512 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06 514 o Deleted Section 3 ("Expected Use") 516 o Reworded modalities in Introduction from "voice, video, text" to 517 "spoken, signed, written" 519 o Reworded text about "increasingly fine-grained distinctions" to 520 instead merely point to BCP 47 Section 4.1's advice to "tag 521 content wisely" and not include unnecessary subtags 523 o Changed IANA registration of new SDP attributes to follow RFC 4566 524 template with extra fields suggested in 4566-bis (expired draft) 526 o Deleted "(known as voice carry over)" 528 o Changed textual instanced of RFC 5646 to BCP 47, although actual 529 reference remains RFC due to xml2rfc limitations 531 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 533 o Added Examples 535 o Added Privacy Considerations section 537 o Other editorial changes for clarity 539 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 541 o Deleted most of Section 4 and replaced with a very short summary 543 o Replaced "wishes to" with "is willing to" in Section 5.2 545 o Reworded description of attribute usage to clarify when to set 546 both, only one, or neither 548 o Deleted all uses of "IMS" 550 o Other editorial changes for clarity 552 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 554 o Editorial changes to wording in Section 5. 556 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 558 o Updated title to reflect WG adoption 560 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- 561 slim-...-03 563 o Removed Use Cases section, per face-to-face discussion at IETF 93 565 o Removed discussion of routing, per face-to-face discussion at IETF 566 93 568 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- 569 slim-...-02 571 o Updated NENA usage mention 573 o Removed background text reference to draft-saintandre-sip-xmpp- 574 chat-04 since that draft expired 576 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- 577 slim-...-01 579 o Revision to keep draft from expiring 581 9.9. Changes from draft-gellens-mmusic-...-02 to draft-gellens- 582 slim-...-00 584 o Changed name from -mmusic- to -slim- to reflect proposed WG name 586 o As a result of the face-to-face discussion in Toronto, the SDP vs 587 SIP issue was resolved by going back to SDP, taking out the SIP 588 hint, and converting what had been a set of alternate proposals 589 for various ways of doing it within SIP into an informative annex 590 section which includes background on why SDP is the proposal 592 o Added mention that enabling a mutually comprehensible language is 593 a general problem of which this document addresses the real-time 594 side, with reference to [RFC8255] which addresses the non-real- 595 time side. 597 9.10. Changes from draft-gellens-mmusic-...-01 to -02 599 o Added clarifying text on leaving attributes unset for media not 600 primarily intended for human language communication (e.g., 601 background audio or video). 603 o Added new section ("Alternative Proposal: Caller-prefs") 604 discussing use of SIP-level Caller-prefs instead of SDP-level. 606 9.11. Changes from draft-gellens-mmusic-...-00 to -01 608 o Relaxed language on setting -send and -receive to same values; 609 added text on leaving on empty to indicate asymmetric usage. 611 o Added text that clients on behalf of end users are expected to set 612 the attributes on outgoing calls and ignore on incoming calls 613 while systems on behalf of call centers and PSAPs are expected to 614 take the attributes into account when processing incoming calls. 616 9.12. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 618 o Updated text to refer to RFC 5646 rather than the IANA language 619 subtags registry directly. 621 o Moved discussion of existing 'lang' attribute out of "Proposed 622 Solution" section and into own section now that it is not part of 623 proposal. 625 o Updated text about existing 'lang' attribute. 627 o Added example use cases. 629 o Replaced proposed single 'hlang' attribute with 'hlang-send' and 630 'hlang-recv' per Harald's request/information that it was a misuse 631 of SDP to use the same attribute for sending and receiving. 633 o Added section describing usage being advisory vs required and text 634 in attribute section. 636 o Added section on SIP "hint" header (not yet nailed down between 637 new and existing header). 639 o Added text discussing usage in policy-based routing function or 640 use of SIP header "hint" if unable to do so. 642 o Added SHOULD that the value of the parameters stick to the largest 643 granularity of language tags. 645 o Added text to Introduction to be try and be more clear about 646 purpose of document and problem being solved. 648 o Many wording improvements and clarifications throughout the 649 document. 651 o Filled in Security Considerations. 653 o Filled in IANA Considerations. 655 o Added to Acknowledgments those who participated in the Orlando ad- 656 hoc discussion as well as those who participated in email 657 discussion and side one-on-one discussions. 659 9.13. Changes from draft-gellens-...-01 to -02 661 o Updated text for (possible) new attribute "hlang" to reference RFC 662 5646 664 o Added clarifying text for (possible) re-use of existing 'lang' 665 attribute saying that the registration would be updated to reflect 666 different semantics for multiple values for interactive versus 667 non-interactive media. 669 o Added clarifying text for (possible) new attribute "hlang" to 670 attempt to better describe the role of language tags in media in 671 an offer and an answer. 673 9.14. Changes from draft-gellens-...-00 to -01 675 o Changed name of (possible) new attribute from 'humlang" to "hlang" 676 o Added discussion of silly state (language not appropriate for 677 media type) 678 o Added Voice Carry Over example 679 o Added mention of multilingual people and multiple languages 680 o Minor text clarifications 682 10. Contributors 684 Gunnar Hellstrom deserves special mention for his reviews and 685 assistance. 687 11. Acknowledgments 689 Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, 690 Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian 691 Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, 692 Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, 693 Natasha Rooney, Brian Rosen, Peter Saint-Andre, and Dale Worley for 694 reviews, corrections, suggestions, and participating in in-person and 695 email discussions. 697 12. References 699 12.1. Normative References 701 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 702 Requirement Levels", BCP 14, RFC 2119, 703 DOI 10.17487/RFC2119, March 1997, . 706 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 707 A., Peterson, J., Sparks, R., Handley, M., and E. 708 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 709 DOI 10.17487/RFC3261, June 2002, . 712 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 713 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 714 July 2006, . 716 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 717 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 718 September 2009, . 720 12.2. Informational References 722 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 723 with Session Description Protocol (SDP)", RFC 3264, 724 DOI 10.17487/RFC3264, June 2002, . 727 [RFC8255] Tomkinson, N. and N. Borenstein, "Multiple Language 728 Content Type", RFC 8255, DOI 10.17487/RFC8255, October 729 2017, . 731 Author's Address 733 Randall Gellens 734 Core Technology Consulting 736 Email: rg+ietf@coretechnologyconsulting.com 737 URI: http://www.coretechnologyconsulting.com