Network Working Group R. Gellens Internet-Draft Core Technology Consulting Intended status: Standards Track February 20, 2018 Expires: August 24, 2018 Negotiating Human Language in Real-Time Communications draft-ietf-slim-negotiating-human-language-24 Abstract Users have various human (natural) language needs, abilities, and preferences regarding spoken, written, and signed languages. This document adds new SDP media-level attributes so that when establishing interactive communication sessions ("calls"), it is possible to negotiate (communicate and match) the caller's language and media needs with the capabilities of the called party. This is especially important with emergency calls, where a call can be handled by a call taker capable of communicating with the user, or a translator or relay operator can be bridged into the call during setup, but this applies to non-emergency calls as well (as an example, when calling a company call center). This document describes the need and a solution using new Session Description Protocol (SDP) media attributes. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 24, 2018. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. Gellens Expires August 24, 2018 [Page 1] Internet-Draft Negotiating Human Language February 2018 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5 4. The existing 'lang' attribute . . . . . . . . . . . . . . . . 5 5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. The 'hlang-send' and 'hlang-recv' attributes . . . . . . 5 5.2. No Language in Common . . . . . . . . . . . . . . . . . . 7 5.3. Usage Notes . . . . . . . . . . . . . . . . . . . . . . . 7 5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6.1. att-field Table in SDP Parameters . . . . . . . . . . . . 10 6.2. Warn-Codes Sub-Registry of SIP Parameters . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11 9. Changes from Previous Versions . . . . . . . . . . . . . . . 11 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf- slim-...-06 . . . . . . . . . . . . . . . . . . . . . . . 12 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf- slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 12 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf- slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 12 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf- slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 12 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf- slim-...-00 . . . . . . . . . . . . . . . . . . . . . . . 13 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 13 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 13 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 13 9.9. Changes from draft-gellens-mmusic-...-02 to draft- gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 13 9.10. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 13 9.11. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 14 Gellens Expires August 24, 2018 [Page 2] Internet-Draft Negotiating Human Language February 2018 9.12. Changes from draft-gellens-...-02 to draft-gellens- mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 14 9.13. Changes from draft-gellens-...-01 to -02 . . . . . . . . 15 9.14. Changes from draft-gellens-...-00 to -01 . . . . . . . . 15 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.2. Informational References . . . . . . . . . . . . . . . . 16 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction A mutually comprehensible language is helpful for human communication. This document addresses the negotiation of human (natural) language and media modality (spoken, signed, written) in real-time communications. A companion document [RFC8255] addresses language selection in email. Unless the caller and callee know each other or there is contextual or out-of- band information from which the language(s) and media modalities can be determined, there is a need for spoken, signed, or written languages to be negotiated based on the caller's needs and the callee's capabilities. This need applies to both emergency and non-emergency calls. For example, it is helpful for a caller to a company call center or a Public Safety Answering Point (PSAP) to be able to indicate preferred signed, written, and/or spoken languages, and for the callee to be able to indicate its capabilities in this area, allowing the call to proceed using the language(s) and media forms supported by both. For various reasons, including the ability to establish multiple streams using different media (e.g., voice, text, video), it makes sense to use a per-stream negotiation mechanism known as the Session Description Protocol (SDP). Utilizing Session Description Protocol (SDP) [RFC4566] enables the solution described in this document to be applied to all interactive communications negotiated using SDP, in emergency as well as non-emergency scenarios. By treating language as another SDP attribute that is negotiated along with other aspects of a media stream, it becomes possible to accommodate a range of users' needs and called party facilities. For example, some users may be able to speak several languages, but have a preference. Some called parties may support some of those languages internally but require the use of a translation service for others, or may have a limited number of call takers able to use certain languages. Another example would be a user who is able to speak but is deaf or hard-of-hearing and and desires a voice stream Gellens Expires August 24, 2018 [Page 3] Internet-Draft Negotiating Human Language February 2018 to send spoken language plus a text stream to receive written language. Making language a media attribute allows the standard session negotiation mechanism to handle this by providing the information and mechanism for the endpoints to make appropriate decisions. The term "negotiation" is used here rather than "indication" because human language (spoken/written/signed) can be negotiated in the same manner as media (audio/text/video) and codecs. For example, if we think of a user calling an airline reservation center, the user may have a set of languages he or she speaks, with perhaps preferences for one or a few, while the airline reservation center will support a fixed set of languages. Negotiation should select the user's most preferred language that is supported by the call center. Both sides should be aware of which language was negotiated. In the offer/answer model used here, the offer contains a set of languages per media (and direction) that the offerer is capable of using, and the answer contains one language per media (and direction) that the answerer will support. Supporting languages and/or modalities can require taking extra steps, such as having a call handled by an agent who speaks a requested language and/or with the ability to use a requested modality, or bridging external translation or relay resources into the call, etc. The answer indicates the media and languages that the answerer is committing to support (possibly after additional steps have been taken). This model also provides knowledge so both ends know what has been negotiated. Note that additional steps required to support the indicated languages or modalities may or may not be in place in time for any early media. Since this is a protocol mechanism, the user equipment (UE client) needs to know the user's preferred languages; while this document does not address how clients determine this, reasonable techniques could include a configuration mechanism with a default of the language of the user interface; in some cases, a UE could tie language and media preferences, such as a preference for a video stream using a signed language and/or a text or audio stream using a written/spoken language. This document does not address user interface (UI) issues, such as if or how a UE client informs a user about the result of language and media negotiation. 1.1. Applicability Within this document, it is assumed that the negotiating endpoints have already been determined, so that a per-stream negotiation based on the Session Description Protocol (SDP) can proceed. Gellens Expires August 24, 2018 [Page 4] Internet-Draft Negotiating Human Language February 2018 When setting up interactive communications sessions it is necessary to route signaling messages to the appropriate endpoint(s). This document does not address the problem of language-based routing. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 RFC 8174 [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Desired Semantics The desired solution is a media attribute (preferably per direction) that may be used within an offer to indicate the preferred language(s) of each (direction of a) media stream, and within an answer to indicate the accepted language. The semantics of including multiple languages for a media stream within an offer is that the languages are listed in order of preference. (Negotiating multiple simultaneous languages within a media stream is out of scope of this document.) 4. The existing 'lang' attribute RFC 4566 [RFC4566] specifies an attribute 'lang' which appears similar to what is needed here, but is not sufficiently specific or flexible for the needs of this document. In addition, 'lang' is not mentioned in [RFC3264] and there are no known implementations in SIP. Further, it is useful to be able to specify language per direction (sending and receiving). This document therefore defines two new attributes. 5. Solution An SDP attribute (per direction) seems the natural choice to negotiate human (natural) language of an interactive media stream, using the language tags of BCP 47 [RFC5646]. 5.1. The 'hlang-send' and 'hlang-recv' attributes This document defines two media-level attributes starting with 'hlang' (short for "human language") to negotiate which human language is selected for use in each interactive media stream. (Note that not all streams will necessarily be used.) There are two attributes, one ending in "-send" and the other in "-recv", Gellens Expires August 24, 2018 [Page 5] Internet-Draft Negotiating Human Language February 2018 registered in Section 6. Each can appear in offers and answers for media streams. In an offer, the 'hlang-send' value is a list of one or more language(s) the offerer is willing to use when sending using the media, and the 'hlang-recv' value is a list of one or more language(s) the offerer is willing to use when receiving using the media. The list of languages is in preference order (first is most preferred). When a media is intended for interactive communication using a language in one direction only (e.g., a user with difficulty speaking but able to hear who indicates a desire to send using text and receive using audio), either hlang-send or hlang-recv MAY be omitted. Note that the media can still be useful in both directions. When a media is not primarily intended for language (for example, a video or audio stream intended for background only) both SHOULD be omitted. Otherwise, both SHOULD have the same value. Note that specifying different languages for each direction (as opposed to the same or essentially the same language in different modalities) can make it difficult to complete the call (e.g., specifying a desire to send audio in Hungarian and receive audio in Portuguese). In an answer, 'hlang-send' is the language the answerer will send if using the media for language (which in most cases is one of the languages in the offer's 'hlang-recv'), and 'hlang-recv' is the language the answerer expects to receive if using the media for language (which in most cases is one of the languages in the offer's 'hlang-send'). In an offer, each value MUST be a list of one or more language tags per BCP 47 [RFC5646], separated by white space. In an answer, each value MUST be one language tag per BCP 47. BCP 47 describes mechanisms for matching language tags. Note that [RFC5646] Section 4.1 advises to "tag content wisely" and not include unnecessary subtags. When placing an emergency call, and in any other case where the language cannot be inferred from context, in an offer each media stream primarily intended for human language communication SHOULD specify the 'hlang-send' and/or 'hlang-recv' attributes for the direction(s) intended for interactive communication. Clients acting on behalf of end users are expected to set one or both 'hlang-send' and 'hlang-recv' attributes on each media stream primarily intended for human communication in an offer when placing an outgoing session, and either ignore or take into consideration the attributes when receiving incoming calls, based on local configuration and capabilities. Systems acting on behalf of call Gellens Expires August 24, 2018 [Page 6] Internet-Draft Negotiating Human Language February 2018 centers and PSAPs are expected to take into account the attributes when processing inbound calls. Note that media and language negotiation might result in more media streams being accepted than are needed by the users (e.g., if more preferred and less preferred combinations of media and language are all accepted). This is not a problem. 5.2. No Language in Common A consideration with the ability to negotiate language is if the call proceeds or fails if the callee does not support any of the languages requested by the caller. This document does not mandate either behavior. When a call is rejected due to lack of any languages in common, the SIP response has SIP response code 488 (Not Acceptable Here) or 606 (Not Acceptable) [RFC3261] and a Warning header field [RFC3261] with a warning code of [TBD: IANA VALUE, e.g., 308] and a warning text indicating that there are no mutually-supported languages; the warning text SHOULD also contain the supported languages and media. Example: Warning: [TBD: IANA VALUE, e.g., 308] proxy.example.com "Incompatible language specification: Requested languages not supported. Supported languages are: es, en; supported media are: audio, text." 5.3. Usage Notes A sign-language tag with a video media stream is interpreted as an indication for sign language in the video stream. A non-sign- language tag with a text media stream is interpreted as an indication for written language in the text stream. A non-sign-language tag with an audio media stream is interpreted as an indication for spoken language in the audio stream. This document does not define any other use for language tags in video media (such as how to indicate visible captions in the video stream). In the IANA registry of language subtags per BCP 47 [RFC5646], a language subtag with a Type field "extlang" combined with a Prefix field value "sgn" indicates a sign-language tag. The absence of such "sgn" prefix indicates a non-sign-language tag. Gellens Expires August 24, 2018 [Page 7] Internet-Draft Negotiating Human Language February 2018 This document does not define the use of sign-language tags in text or audio media. This document does not define the use of language tags in media other than interactive streams of audio, video, and text (such as "message" or "application"). Such use could be supported by future work or by application agreement. 5.4. Examples Some examples are shown below. For clarity, only the most directly relevant portions of the SDP block are shown. An offer or answer indicating spoken English both ways: m=audio 49170 RTP/AVP 0 a=hlang-send:en a=hlang-recv:en An offer indicating American Sign Language both ways: m=video 51372 RTP/AVP 31 32 a=hlang-send:ase a=hlang-recv:ase An offer requesting spoken Spanish both ways (most preferred), spoken Basque both ways (second preference), or spoken English both ways (third preference): m=audio 49250 RTP/AVP 20 a=hlang-send:es eu en a=hlang-recv:es eu en An answer to the above offer indicating spoken Spanish both ways: m=audio 49250 RTP/AVP 20 a=hlang-send:es a=hlang-recv:es An alternative answer to the above offer indicating spoken Italian both ways (as the callee does not support any of the requested languages but chose to proceed with the call): m=audio 49250 RTP/AVP 20 a=hlang-send:it a=hlang-recv:it An offer or answer indicating written Greek both ways: Gellens Expires August 24, 2018 [Page 8] Internet-Draft Negotiating Human Language February 2018 m=text 45020 RTP/AVP 103 104 a=hlang-send:gr a=hlang-recv:gr An offer requesting the following media streams: video for the caller to send using Argentine Sign Language, text for the caller to send using written Spanish (most preferred) or written Portuguese, audio for the caller to receive spoken Spanish (most preferred) or spoken Portuguese: m=video 51372 RTP/AVP 31 32 a=hlang-send:aed m=text 45020 RTP/AVP 103 104 a=hlang-send:sp pt m=audio 49250 RTP/AVP 20 a=hlang-recv:sp pt An answer for the above offer, indicating text in which the callee will receive written Spanish, and audio in which the callee will send spoken Spanish. The answering party had no video capability: m=video 0 RTP/AVP 31 32 m=text 45020 RTP/AVP 103 104 a=hlang-recv:sp m=audio 49250 RTP/AVP 20 a=hlang-send:sp An offer requesting the following media streams: text for the caller to send using written English (most preferred) or written Spanish, audio for the caller to receive spoken English (most preferred) or spoken Spanish, supplemental video: m=text 45020 RTP/AVP 103 104 a=hlang-send:en sp m=audio 49250 RTP/AVP 20 a=hlang-recv:en sp m=video 51372 RTP/AVP 31 32 An answer for the above offer, indicating text in which the callee will receive written Spanish, audio in which the callee will send spoken Spanish, and supplemental video: m=text 45020 RTP/AVP 103 104 Gellens Expires August 24, 2018 [Page 9] Internet-Draft Negotiating Human Language February 2018 a=hlang-recv:sp m=audio 49250 RTP/AVP 20 a=hlang-send:sp m=video 51372 RTP/AVP 31 32 Note that, even though the examples show the same (or essentially the same) language being used in both directions (even when the modality differs), there is no requirement that this be the case. However, in practice, doing so is likely to increase the chances of successful matching. 6. IANA Considerations 6.1. att-field Table in SDP Parameters The syntax in this section uses ABNF per RFC 5234 [RFC5234]. IANA is kindly requested to add two entries to the 'att-field (media level only)' table of the SDP parameters registry: The first entry is for hlang-recv: Attribute Name: hlang-recv Contact Name: Randall Gellens Contact Email Address: rg+ietf@coretechnologyconsulting.com Attribute Value: hlang-value Attribute Syntax: hlang-value = hlang-offv / hlang-ansv ; hlang-offv used in offers ; hlang-ansv used in answers hlang-offv = Language-Tag *( SP Language-Tag ) ; Language-Tag as defined in BCP 47 SP = 1*" " ; one or more space (%x20) characters hlang-ansv = Language-Tag Attribute Semantics: Described in Section 5.1 of TBD: THIS DOCUMENT Usage Level: media Mux Category: NORMAL Charset Dependent: No Purpose: See Section 5.1 of TBD: THIS DOCUMENT O/A Procedures: See Section 5.1 of TBD: THIS DOCUMENT Reference: TBD: THIS DOCUMENT The second entry is for hlang-send: Gellens Expires August 24, 2018 [Page 10] Internet-Draft Negotiating Human Language February 2018 Attribute Name: hlang-send Contact Name: Randall Gellens Contact Email Address: rg+ietf@coretechnologyconsulting.com Attribute Value: hlang-value Attribute Syntax: hlang-value = hlang-offv / hlang-ansv Attribute Semantics: Described in Section 5.1 of TBD: THIS DOCUMENT Usage Level: media Mux Category: NORMAL Charset Dependent: No Purpose: See Section 5.1 of TBD: THIS DOCUMENT O/A Procedures: See Section 5.1 of TBD: THIS DOCUMENT Reference: TBD: THIS DOCUMENT 6.2. Warn-Codes Sub-Registry of SIP Parameters IANA is requested to add a new value in the warn-codes sub-registry of SIP parameters in the 300 through 329 range that is allocated for indicating problems with keywords in the session description. The reference is to this document. The warn text is "Incompatible language specification: Requested languages not supported. Supported languages and media are: [list of supported languages and media]." 7. Security Considerations The Security Considerations of BCP 47 [RFC5646] apply here. An attacker with the ability to modify signaling could prevent a call from succeeding by altering any of several crucial elements, including the 'hlang-send' or 'hlang-recv' values. RFC 5069 [RFC5069] discusses such threats. Use of TLS or IPSec can protect against such threats. Emergency calls are of particular concern; RFC 6881 [RFC6881], which is specific to emergency calls, mandates use of TLS or IPSec (in ED-57/SP-30). 8. Privacy Considerations Language and media information can suggest a user's nationality, background, abilities, disabilities, etc. 9. Changes from Previous Versions RFC EDITOR: Please remove this section prior to publication. Gellens Expires August 24, 2018 [Page 11] Internet-Draft Negotiating Human Language February 2018 9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06 o Deleted Section 3 ("Expected Use") o Reworded modalities in Introduction from "voice, video, text" to "spoken, signed, written" o Reworded text about "increasingly fine-grained distinctions" to instead merely point to BCP 47 Section 4.1's advice to "tag content wisely" and not include unnecessary subtags o Changed IANA registration of new SDP attributes to follow RFC 4566 template with extra fields suggested in 4566-bis (expired draft) o Deleted "(known as voice carry over)" o Changed textual instanced of RFC 5646 to BCP 47, although actual reference remains RFC due to xml2rfc limitations 9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03 o Added Examples o Added Privacy Considerations section o Other editorial changes for clarity 9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02 o Deleted most of Section 4 and replaced with a very short summary o Replaced "wishes to" with "is willing to" in Section 5.1 o Reworded description of attribute usage to clarify when to set both, only one, or neither o Deleted all uses of "IMS" o Other editorial changes for clarity 9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01 o Editorial changes to wording in Section 5. Gellens Expires August 24, 2018 [Page 12] Internet-Draft Negotiating Human Language February 2018 9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00 o Updated title to reflect WG adoption 9.6. Changes from draft-gellens-slim-...-02 to draft-gellens- slim-...-03 o Removed Use Cases section, per face-to-face discussion at IETF 93 o Removed discussion of routing, per face-to-face discussion at IETF 93 9.7. Changes from draft-gellens-slim-...-01 to draft-gellens- slim-...-02 o Updated NENA usage mention o Removed background text reference to draft-saintandre-sip-xmpp- chat-04 since that draft expired 9.8. Changes from draft-gellens-slim-...-00 to draft-gellens- slim-...-01 o Revision to keep draft from expiring 9.9. Changes from draft-gellens-mmusic-...-02 to draft-gellens- slim-...-00 o Changed name from -mmusic- to -slim- to reflect proposed WG name o As a result of the face-to-face discussion in Toronto, the SDP vs SIP issue was resolved by going back to SDP, taking out the SIP hint, and converting what had been a set of alternate proposals for various ways of doing it within SIP into an informative annex section which includes background on why SDP is the proposal o Added mention that enabling a mutually comprehensible language is a general problem of which this document addresses the real-time side, with reference to [RFC8255] which addresses the non-real- time side. 9.10. Changes from draft-gellens-mmusic-...-01 to -02 o Added clarifying text on leaving attributes unset for media not primarily intended for human language communication (e.g., background audio or video). Gellens Expires August 24, 2018 [Page 13] Internet-Draft Negotiating Human Language February 2018 o Added new section ("Alternative Proposal: Caller-prefs") discussing use of SIP-level Caller-prefs instead of SDP-level. 9.11. Changes from draft-gellens-mmusic-...-00 to -01 o Relaxed language on setting -send and -receive to same values; added text on leaving on empty to indicate asymmetric usage. o Added text that clients on behalf of end users are expected to set the attributes on outgoing calls and ignore on incoming calls while systems on behalf of call centers and PSAPs are expected to take the attributes into account when processing incoming calls. 9.12. Changes from draft-gellens-...-02 to draft-gellens-mmusic-...-00 o Updated text to refer to RFC 5646 rather than the IANA language subtags registry directly. o Moved discussion of existing 'lang' attribute out of "Proposed Solution" section and into own section now that it is not part of proposal. o Updated text about existing 'lang' attribute. o Added example use cases. o Replaced proposed single 'hlang' attribute with 'hlang-send' and 'hlang-recv' per Harald's request/information that it was a misuse of SDP to use the same attribute for sending and receiving. o Added section describing usage being advisory vs required and text in attribute section. o Added section on SIP "hint" header (not yet nailed down between new and existing header). o Added text discussing usage in policy-based routing function or use of SIP header "hint" if unable to do so. o Added SHOULD that the value of the parameters stick to the largest granularity of language tags. o Added text to Introduction to be try and be more clear about purpose of document and problem being solved. o Many wording improvements and clarifications throughout the document. Gellens Expires August 24, 2018 [Page 14] Internet-Draft Negotiating Human Language February 2018 o Filled in Security Considerations. o Filled in IANA Considerations. o Added to Acknowledgments those who participated in the Orlando ad- hoc discussion as well as those who participated in email discussion and side one-on-one discussions. 9.13. Changes from draft-gellens-...-01 to -02 o Updated text for (possible) new attribute "hlang" to reference RFC 5646 o Added clarifying text for (possible) re-use of existing 'lang' attribute saying that the registration would be updated to reflect different semantics for multiple values for interactive versus non-interactive media. o Added clarifying text for (possible) new attribute "hlang" to attempt to better describe the role of language tags in media in an offer and an answer. 9.14. Changes from draft-gellens-...-00 to -01 o Changed name of (possible) new attribute from 'humlang" to "hlang" o Added discussion of silly state (language not appropriate for media type) o Added Voice Carry Over example o Added mention of multilingual people and multiple languages o Minor text clarifications 10. Contributors Gunnar Hellstrom deserves special mention for his reviews and assistance. 11. Acknowledgments Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen, Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian Groves, Andrew Hutton, Hadriel Kaplan, Ari Keranen, John Klensin, Mirja Kuhlewind, Paul Kyzivat, John Levine, Alexey Melnikov, Addison Phillips, James Polk, Eric Rescorla, Pete Resnick, Alvaro Retana, Natasha Rooney, Brian Rosen, Peter Saint-Andre, and Dale Worley for reviews, corrections, suggestions, and participating in in-person and email discussions. Gellens Expires August 24, 2018 [Page 15] Internet-Draft Negotiating Human Language February 2018 12. References 12.1. Normative References [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, . [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, September 2009, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 12.2. Informational References [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002, . [RFC5069] Taylor, T., Ed., Tschofenig, H., Schulzrinne, H., and M. Shanmugam, "Security Threats and Requirements for Emergency Call Marking and Mapping", RFC 5069, DOI 10.17487/RFC5069, January 2008, . [RFC6881] Rosen, B. and J. Polk, "Best Current Practice for Communications Services in Support of Emergency Calling", BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013, . [RFC8255] Tomkinson, N. and N. Borenstein, "Multiple Language Content Type", RFC 8255, DOI 10.17487/RFC8255, October 2017, . Gellens Expires August 24, 2018 [Page 16] Internet-Draft Negotiating Human Language February 2018 Author's Address Randall Gellens Core Technology Consulting Email: rg+ietf@coretechnologyconsulting.com URI: http://www.coretechnologyconsulting.com Gellens Expires August 24, 2018 [Page 17]