Negotiating Human Language in Real-Time Communications
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|Replaced by||draft-ietf-slim-negotiating-human-language, RFC 8373|
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Network Working Group R. Gellens Internet-Draft Qualcomm Technologies Inc. Intended status: Standards Track October 13, 2014 Expires: April 16, 2015 Negotiating Human Language in Real-Time Communications draft-gellens-slim-negotiating-human-language-00 Abstract Users have various human (natural) language needs, abilities, and preferences regarding spoken, written, and signed languages. When establishing interactive communication ("calls") there needs to be a way 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 routed to a Public Safety Answering Point (PSAP) or 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 expected use, and describes a solution using new SDP stream 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 April 16, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. Gellens Expires April 16, 2015 [Page 1] Internet-Draft Negotiating Human Language October 2014 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Expected Use . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Emergency Call from English Speaker in Spain . . . . . . 5 4.2. Emergency Call from Spanish/English Speaker in France . . 6 4.3. Call to Call Center from Russian Speaker in U.S. . . . . 6 4.4. Emergency Call from speech-impaired caller in the U.S. . 6 4.5. Emergency Call from deaf caller in the U.S. . . . . . . . 7 5. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 7 6. The existing 'lang' attribute . . . . . . . . . . . . . . . . 7 7. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2. New 'humintlang-send' and 'humintlang-recv' attributes . 9 7.3. Advisory vs Required . . . . . . . . . . . . . . . . . . 11 7.4. Silly States . . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 10. Changes from Previous Versions . . . . . . . . . . . . . . . 12 10.1. Changes from draft-gellens-...-00 to -01 . . . . . . . . 12 10.2. Changes from draft-gellens-...-01 to -02 . . . . . . . . 13 10.3. Changes from draft-gellens-...-02 to draft-gellens- mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . 13 10.4. Changes from draft-gellens-mmusic-...-00 to -01 . . . . 14 10.5. Changes from draft-gellens-mmusic-...-01 to -02 . . . . 14 10.6. Changes from draft-gellens-mmusic-...-02 to draft- gellens-slim-...-00 . . . . . . . . . . . . . . . . . . 14 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 13.1. Normative References . . . . . . . . . . . . . . . . . . 15 13.2. Informational References . . . . . . . . . . . . . . . . 15 Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 16 A.1. Use of Caller Preferences Without Additions . . . . . . . 16 A.2. Additional Caller Preferences for Asymmetric Needs . . . 18 A.2.1. Caller Preferences for Asymmetric Modality Needs . . 18 Gellens Expires April 16, 2015 [Page 2] Internet-Draft Negotiating Human Language October 2014 A.2.2. Caller Preferences for Asymmetric Language Tags . . . 20 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction A mutually comprehensible language is helpful for human communication. This document addresses the real-time, interactive side of the issue. A companion document on language selection in email [draft-tomkinson-multilangcontent] addresses the non-real-time side. When setting up interactive communication sessions (using SIP or other protocols), human (natural) language and media modality (voice, video, text) negotiation may be needed. 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 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, in this case, SDP. This approach has a number of benefits, including that it is generic (applies to all interactive communications negotiated using SDP) and not limited to emergency calls. In some cases such a facility isn't needed, because the language is known from the context (such as when a caller places a call to a sign language relay center, to a friend, or colleague). But it is clearly useful in many other cases. For example, someone calling a company call center or a Public Safety Answering Point (PSAP) should be able to indicate if one or more specific signed, written, and/or spoken languages are preferred, the callee should be able to indicate its capabilities in this area, and the call proceed using in-common language(s) and media forms. Since this is a protocol mechanism, the user equipment (UE client) needs to know the user's preferred languages; a reasonable technique 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. Including the user's human (natural) language preferences in the session establishment negotiation is independent of the use of a relay service and is transparent to a voice service provider. For example, assume a user within the United States who speaks Spanish but not English places a voice call using an IMS device. It doesn't Gellens Expires April 16, 2015 [Page 3] Internet-Draft Negotiating Human Language October 2014 matter if the call is an emergency call or not (e.g., to an airline reservation desk). The language information is transparent to the IMS carrier, but is part of the session negotiation between the UE and the terminating entity. In the case of a call to e.g., an airline, the call can be automatically routed to a Spanish-speaking agent. In the case of an emergency call, the Emergency Services IP network (ESInet) and the PSAP may choose to take the language and media preferences into account when determining how to route and process the call (i.e., language and media needs may be considered within policy-based routing (PBR)). By treating language as another 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 requires a voice stream plus a text stream (known as voice carry over). 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. Regarding relay services, in the case of an emergency call requiring sign language such as ASL, there are two common approaches: the caller initiates the call to a relay center, or the caller places the call to emergency services (e.g., 911 in the U.S. or 112 in Europe). In the former case, the language need is ancillary and supplemental. In the latter case, the ESInet and/or PSAP may take the need for sign language into account and bridge in a relay center. In this case, the ESInet and PSAP have all the standard information available (such as location) but are able to bridge the relay sooner in the call processing. By making this facility part of the end-to-end negotiation, the question of which entity provides or engages the relay service becomes separate from the call processing mechanics; if the caller directs the call to a relay service then the human language negotiation facility provides extra information to the relay service but calls will still function without it; if the caller directs the call to emergency services, then the ESInet/PSAP are able to take the user's human language needs into account, e.g., by routing to a particular PSAP or call taker or bridging a relay service or translator. Gellens Expires April 16, 2015 [Page 4] Internet-Draft Negotiating Human Language October 2014 The term "negotiation" is used here rather than "indication" because human language (spoken/written/signed) is something that can be negotiated in the same way as which forms of media (audio/text/video) or which codecs. For example, if we think of non-emergency calls, such as 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. This is conceptually similar to the way other aspects of each media stream are negotiated using SDP (e.g., media type and codecs). 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Expected Use This facility is expected to be used by NENA and 3GPP. NENA is likely to reference it in NENA 08-01 (i3 Stage 3) in describing attributes of calls presented to an ESInet, and in that or other documents describing Policy-Based Routing (PBR) capabilities within a Policy-Based Routing Function. 3GPP is expected to reference this mechanism in general call handling and emergency call handling. Recent CRs introduced in SA1 have anticipated this functionality being provided within SDP. 4. Example Use Cases 4.1. Emergency Call from English Speaker in Spain Someone who speaks only English is visiting Spain and places an emergency (112) call. The call offers an audio stream using English. The ESInet and PSAP have policy-based routing rules that take into account the SDP language request when deciding how to route and process the call. The ESInet routes the call to a PSAP within Spain where an English-speaking call taker is available, and the PSAP selects an English-speaking call taker to handle the call. The PSAP answers the offer with an audio stream using English. The call is established with an audio stream; the caller and call taker communicate in English. Alternatively, the ESInet routes the call to a cooperating PSAP within the U.K. The PSAP answers the offer with an audio stream using English. The call is established with an audio stream; the Gellens Expires April 16, 2015 [Page 5] Internet-Draft Negotiating Human Language October 2014 caller and call taker communicate in English. (This approach is similar to that envisioned in REACH112 Total Conversation.) 4.2. Emergency Call from Spanish/English Speaker in France Someone who speaks both Spanish and English (but prefers Spanish) is visiting France and places an emergency (112) call. The call offers an audio stream listing first Spanish (meaning most preferred) and then English. The ESInet and PSAP have policy-based routing rules that take into account the SDP language request when deciding how to route and process the call. The ESInet routes the call to a PSAP within France where a Spanish-speaking call taker is available, and the PSAP selects a Spanish-speaking call taker to handle the call. The PSAP answers the offer with an audio stream listing Spanish. The call is established with an audio stream; the caller and call taker communicate in Spanish. Alternatively, the ESInet routes the call to a cooperating PSAP in Spain or England. (This approach is similar to that envisioned in REACH112 Total Conversation.) Alternatively, there is no ESInet or the ESInet does not take language into account in its PBR. The call is routed to a PSAP in France. The PSAP ignores the language information in the SDP offer, and answers the offer with an audio stream with no language or with French. The UE continues the call anyway. The call taker answers in French, the user tries speaking Spanish and perhaps English. The call taker bridges in a translation service or transfers the call to a multilingual call taker. 4.3. Call to Call Center from Russian Speaker in U.S. A Russian speaker is visiting the U.S. and places a call to her airline reservation desk to inquire about her return flight. The airline call processing system takes into account the SDP language request and decides to route the call to its call center within Russia. Alternatively, if the airline call processing system does not look at SDP, it uses the SIP "hint" if present. 4.4. Emergency Call from speech-impaired caller in the U.S. Someone who uses English but is speech-impaired places an emergency (911) call. The call offers an audio stream listing English and a real-time text stream also using English. The ESInet and PSAP have policy-based routing rules that take into account the SDP language and media requests when deciding how to route and process the call. Gellens Expires April 16, 2015 [Page 6] Internet-Draft Negotiating Human Language October 2014 The ESInet routes the call to a PSAP with real-time text capabilities. The PSAP answers the offer with an audio stream listing English and a real-time text stream listing English. The call is established with an audio and a real-time text stream; the caller and call taker communicate in English using voice from the call-taker to the caller and text from the caller to the call taker. The audio stream is two-way, allowing the call taker to hear background sounds. 4.5. Emergency Call from deaf caller in the U.S. A deaf caller who uses American Sign Language (ASL) places an emergency (911) call. The call offers a video stream listing ASL and an audio stream with no language indicated. The ESInet and PSAP have policy-based routing rules that take into account the SDP language and media needs when deciding how to route and process the call. The ESInet routes the call to a PSAP. The PSAP answers the offer with an audio stream listing English and a video stream listing ASL. The PSAP bridges in a sign language interpreter. The call is established with an audio and a video stream. 5. Desired Semantics The desired solution is a media attribute that may be used within an offer to indicate the preferred language of each media stream, and within an answer to indicate the accepted language. The semantics of including multiple values for a media stream within an offer is that the languages are listed in order of preference. (While it is true that a conversation among multilingual people often involves multiple languages, the usefulness of providing a way to negotiate this as a general facility is outweighed by the complexity of the desired semantics of the SDP attribute to allow negotiation of multiple simultaneous languages within an interactive media stream.) 6. The existing 'lang' attribute RFC 4566 specifies an attribute 'lang' which sounds similar to what is needed here, the difference being that it specifies that 'a=lang' is declarative with the semantics of multiple 'lang' attributes being that all of them are used, while we want a means to negotiate which one is used in each stream. This difference means that the existing 'lang' attribute can't be used and we need to define a new attribute. The text from RFC 4566 [RFC4566] is: a=lang:<language tag> Gellens Expires April 16, 2015 [Page 7] Internet-Draft Negotiating Human Language October 2014 This can be a session-level attribute or a media-level attribute. As a session-level attribute, it specifies the default language for the session being described. As a media- level attribute, it specifies the language for that media, overriding any session- level language specified. Multiple lang attributes can be provided either at session or media level if the session description or media use multiple languages, in which case the order of the attributes indicates the order of importance of the various languages in the session or media from most important to least important. The "lang" attribute value must be a single [RFC3066] language tag in US-ASCII [RFC3066]. It is not dependent on the charset attribute. A "lang" attribute SHOULD be specified when a session is of sufficient scope to cross geographic boundaries where the language of recipients cannot be assumed, or where the session is in a different language from the locally assumed norm. Note that there are existing examples of it being used in exactly the way we need. For example, draft-saintandre-sip-xmpp-chat-04 [I-D.saintandre-sip-xmpp-chat] contains an example where the initial invitation contains two 'a=lang' entries for a media stream (for English and Italian) and the OK accepts one of them (Italian), which matches what we need: Example: (F1) SIP user starts the session INVITE sip:email@example.com SIP/2.0 To: <sip:firstname.lastname@example.org> From: <sip:email@example.com>;tag=576 Subject: Open chat with Romeo? Call-ID: 742507no Content-Type: application/sdp c=IN IP4 s2x.example.net m=message 7313 TCP/MSRP * a=accept-types:text/plain a=lang:en a=lang:it a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp Example: (F2) Gateway accepts session on Juliet's behalf SIP/2.0 200 OK To: <sip:firstname.lastname@example.org>;tag=534 From: <sip:email@example.com>;tag=576 Call-ID: 742507no Content-Type: application/sdp Gellens Expires April 16, 2015 [Page 8] Internet-Draft Negotiating Human Language October 2014 c=IN IP4 x2s.example.com m=message 8763 TCP/MSRP * a=accept-types:text/plain a=lang:it a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp The example serves as evidence of the need for an SDP attribute with the semantics as described in this document; unfortunately, the existing 'lang' attribute is not it. 7. Proposed Solution An SDP attribute seems the natural choice to negotiate human (natural) language of an interactive media stream. The attribute value should be a language tag per RFC 5646 [RFC5646] 7.1. Rationale The decision to base the proposal at the media negotiation level, and specifically to use SDP, came after significant debate and discussion. From an engineering standpoint, it is possible to meet the objectives using a variety of mechanisms, but none are perfect. None of the proposed alternatives was clearly better technically in enough ways to win over proponents of the others, and none were clearly so bad technically as to be easily rejected. As is often the case in engineering, choosing the solution is a matter of balancing trade-offs, and ultimately more a matter of taste than technical merit. The two main proposals were to use SDP and SIP. SDP has the advantage that the language is negotiated with the media to which it applies, while SIP has the issue that the languages expressed may not match the SDP media negotiated (for example, a session could negotiate video at the SIP level but fail to negotiate any video media stream at the SDP layer). The mechanism described here for SDP can be adapted to media negotiation protocols other than SDP. 7.2. New 'humintlang-send' and 'humintlang-recv' attributes Rather than re-use 'lang' we define two new media-level attributes starting with 'humintlang' (short for "human interactive language") to negotiate which human language is used in each (interactive) media stream. There are two attributes, one ending in "-send" and the other in "-recv" to indicate the language used when sending and receiving media: a=humintlang-send:<language tag> Gellens Expires April 16, 2015 [Page 9] Internet-Draft Negotiating Human Language October 2014 a=humintlang-recv:<language tag> Each can appear multiple times in an offer for a media stream. In an offer, the 'humintlang-send' values constitute a list in preference order (first is most preferred) of the languages the offerer wishes to send using the media, and the 'humintlang-recv' values constitute a list in preference order of the languages the offerer wishes to receive using the media. In cases where the user wishes to use one media for sending and another for receiving (such as a speech-impaired user who wishes to send using text and receive using audio), one of the two MAY be unset. In cases where a media is not primarily intended for language (for example, a video or audio stream intended for background only) both SHOULD be unset. In other cases, both SHOULD have the same values in the same order. The two SHOULD NOT be set to languages which are difficult to match together (e.g., specifying a desire to send audio in Hungarian and receive audio in Portuguese will make it difficult to successfully complete the call). In an answer, 'humintlang-send' is the accepted language the answerer will send (which in most cases is one of the languages in the offer's 'humintlang-recv'), and 'humintlang-recv' is the accepted language the answerer expects to receive (which in most cases is one of the languages in the offer's 'humintlang-send'). Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646 describes mechanisms for matching language tags. While RFC 5646 provides a mechanism accommodating increasingly fine-grained distinctions, in the interest of maximum interoperability for real- time interactive communications, each 'humintlang-send' and 'humintlang-recv' value SHOULD be restricted to the largest granularity of language tags; in other words, it is RECOMMENDED to specify only a Primary-subtag and NOT to include subtags (e.g., for region or dialect) unless the languages might be mutually incomprehensible without them. In an offer, each language tag value MAY have an asterisk appended as the last character (after the registry value). The asterisk indicates a request by the caller to not fail the call if there is no language in common. See Section 7.3 for more information and discussion. When placing an emergency call, and in any other case where the language cannot be assumed from context, each media stream in an offer primarily intended for human language communication SHOULD specify one or both 'humintlang-send' and 'humintlang-recv' attributes (to avoid ambiguity). Gellens Expires April 16, 2015 [Page 10] Internet-Draft Negotiating Human Language October 2014 Note that while signed language tags are used with a video stream to indicate sign language, a spoken language tag for a video stream in parallel with an audio stream with the same spoken language tag indicates a request for a supplemental video stream to see the speaker. Clients acting on behalf of end users are expected to set one or both 'humintlang-send' and 'humintlang-recv' attributes on each media stream primarily intended for human communication in an offer when placing an outgoing session, but either ignore or take into consideration the attributes when receiving incoming calls, based on local configuration and capabilities. Systems acting on behalf of call centers and PSAPs are expected to take into account the values when processing inbound calls. 7.3. Advisory vs Required One important consideration with this mechanism is if the call fails if the callee does not support any of the languages requested by the caller. In order to provide for maximum likelihood of a successful communication session, especially in the case of emergency calling, the mechanism defined here provides a way for the caller to indicate a preference for the call failing or succeeding when there is no language in common. However, the callee is NOT REQUIRED to honor this preference. For example, a PSAP MAY choose to attempt the call even with no language in common, while a corporate call center MAY choose to fail the call. The mechanism for indicating this preference is that, in an offer, if the last character of any of the 'humintlang-recv' or 'humintlang- send' values is an asterisk, this indicates a request to not fail the call (similar to SIP Accept-Language syntax). Either way, the called party MAY ignore this, e.g., for the emergency services use case, a PSAP will likely not fail the call. 7.4. Silly States It is possible to specify a "silly state" where the language specified does not make sense for the media type, such as specifying a signed language for an audio media stream. Gellens Expires April 16, 2015 [Page 11] Internet-Draft Negotiating Human Language October 2014 An offer MUST NOT be created where the language does not make sense for the media type. If such an offer is received, the receiver MAY reject the media, ignore the language specified, or attempt to interpret the intent (e.g., if American Sign Language is specified for an audio media stream, this might be interpreted as a desire to use spoken English). A spoken language tag for a video stream in conjunction with an audio stream with the same language might indicate a request for supplemental video to see the speaker. 8. IANA Considerations IANA is kindly requested to add two entries to the 'att-field (media level only)' table of the SDP parameters registry: +------------------------------+-----------------+-----------------+ | Type | Name | Reference | +------------------------------+-----------------+-----------------+ | att-field (media level only) | humintlang-send | (this document) | | att-field (media level only) | humintlang-recv | (this document) | +------------------------------+-----------------+-----------------+ Table 1: att-field (media level only)' entries 9. Security Considerations The Security Considerations of RFC 5646 [RFC5646] apply here (as a use of that RFC). In addition, if the 'humintlang-send' or 'humintlang-recv' values are altered or deleted en route, the session could fail or languages incomprehensible to the caller could be selected; however, this is also a risk if any SDP parameters are modified en route. 10. Changes from Previous Versions 10.1. Changes from draft-gellens-...-00 to -01 o Changed name of (possible) new attribute from 'humlang" to "humintlang" 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 Gellens Expires April 16, 2015 [Page 12] Internet-Draft Negotiating Human Language October 2014 o Minor text clarifications 10.2. Changes from draft-gellens-...-01 to -02 o Updated text for (possible) new attribute "humintlang" 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 "humintlang" to attempt to better describe the role of language tags in media in an offer and an answer. 10.3. 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 'humintlang' attribute with 'humintlang- send' and 'humintlang-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. Gellens Expires April 16, 2015 [Page 13] Internet-Draft Negotiating Human Language October 2014 o Many wording improvements and clarifications throughout the document. 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. 10.4. 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. 10.5. 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). o Added new section Appendix A ("Alternative Proposal: Caller- prefs") discussing use of SIP-level Caller-prefs instead of SDP- level. 10.6. 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 [draft-tomkinson-multilangcontent] which addresses the non-real-time side. Gellens Expires April 16, 2015 [Page 14] Internet-Draft Negotiating Human Language October 2014 11. Contributors Gunnar Hellstrom deserves special mention for his reviews, assistance, and especially for contributing the core text in Appendix A. 12. 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, Paul Kyzivat, John Levine, Alexey Melnikov, James Polk, Pete Resnick, Peter Saint-Andre, and Dale Worley for reviews, corrections, suggestions, and participating in in-person and email discussions. 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller Preferences for the Session Initiation Protocol (SIP)", RFC 3841, August 2004. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 5646, September 2009. 13.2. Informational References [I-D.iab-privacy-considerations] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", draft-iab-privacy- considerations-09 (work in progress), May 2013. [I-D.saintandre-sip-xmpp-chat] Saint-Andre, P., Loreto, S., Gavita, E., and N. Hossain, "Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol Gellens Expires April 16, 2015 [Page 15] Internet-Draft Negotiating Human Language October 2014 (XMPP): One-to-One Text Chat", draft-saintandre-sip-xmpp- chat-06 (work in progress), June 2013. [RFC3066] Alvestrand, H., "Tags for the Identification of Languages", RFC 3066, January 2001. [draft-tomkinson-multilangcontent] Tomkinson, N. and N. Borenstein, "Multiple Language Content Type", draft-tomkinson-multilangcontent (work in progress), April 2014. Appendix A. Historic Alternative Proposal: Caller-prefs The decision to base the proposal at the media negotiation level, and specifically to use SDP, came after significant debate and discussion. It is possible to meet the objectives using a variety of mechanisms, but none are perfect. Using SDP means dealing with the complexity of SDP, and leaves out real-time session protocols that do not use SDP. The major alternative proposal was to use SIP. Using SIP leaves out non-SIP session protocols, but more fundamentally, would occur at a different layer than the media negotiation. This results in a more fragile solution since the media modality and language would be negotiated using SIP, and then the specific media formats (which inherently include the modality) would be negotiated at a different level (typically SDP, especially in the emergency calling cases), making it easier to have mismatches (such as where the media modality negotiated in SIP don't match what was negotiated using SDP). An alternative proposal was to use the SIP-level Caller Preferences mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841]. The Caller-prefs mechanism includes a priority system; this would allow different combinations of media and languages to be assigned different priorities. The evaluation and decisions on what to do with the call can be done either by proxies along the call path, or by the addressed UA. Evaluation of alternatives for routing is described in RFC 3841 [RFC3841]. A.1. Use of Caller Preferences Without Additions The following would be possible without adding any new registered tags: Potential callers and recipients MAY include in the Contact field in their SIP registrations media and language tags according to the joint capabilities of the UA and the human user according to RFC 3840 [RFC3840]. Gellens Expires April 16, 2015 [Page 16] Internet-Draft Negotiating Human Language October 2014 The most relevant media capability tags are "video", "text" and "audio". Each tag represents a capability to use the media in two- way communication. Language capabilities are declared with a comma-separated list of languages that can be used in the call as parameters to the tag "language=". This is an example of how it is used in a SIP REGISTER: REGISTER firstname.lastname@example.org Contact: <sip:email@example.com> audio; video; text; language="en,es,ase" Including this information in SIP REGISTER allows proxies to act on the information. For the problem set addressed by this document, it is not anticipated that proxies will do so using registration data. Further, there are classes of devices (such as cellular mobile phones) that are not anticipated to include this information in their registrations. Hence, use in registration is OPTIONAL. In a call, a list of acceptable media and language combinations is declared, and a priority assigned to each combination. This is done by the Accept-Contact header field, which defines different combinations of media and languages and assigns priorities for completing the call with the SIP URI represented by that Contact. A priority is assigned to each set as a so-called "q-value" which ranges from 1 (most preferred) to 0 (least preferred). Using the Accept-Contact header field in INVITE requests and responses allows these capabilities to be expressed and used during call set-up. Clients SHOULD include this information in INVITE requests and responses. Example: Accept-Contact: *; text; language="en"; q=0.2 Accept-Contact: *; video; language="ase"; q=0.8 This example shows the highest preference expressed by the caller is to use video with American Sign Language (language code "ase"). As a Gellens Expires April 16, 2015 [Page 17] Internet-Draft Negotiating Human Language October 2014 fallback, it is acceptable to get the call connected with only English text used for human communication. Other media may of course be connected as well, without expectation that it will be usable by the caller for interactive communications (but may still be helpful to the caller). This system satisfies all the needs described in the previous chapters, except that language specifications do not make any distinction between spoken and written language, and that the need for directionality in the specification cannot be fulfilled. To some degree the lack of media specification between speech and text in language tags can be compensated by only specifying the important medium in the Accept-Contact field. Thus, a user who wants to use English mainly for text would specify: Accept-Contact: *;text;language="en";q=1.0 While a user who wants to use English mainly for speech but accept it for text would specify: Accept-Contact: *;audio;language="en";q=0.8 Accept-Contact: *;text;language="en";q=0.2 However, a user who would like to talk, but receive text back has no way to do it with the existing specification. A.2. Additional Caller Preferences for Asymmetric Needs In order to be able to specify asymmetric preferences, there are two possibilities. Either new language tags in the style of the humintlang parameters described above for SDP could be registered, or additional media tags describing the asymmetry could be registered. A.2.1. Caller Preferences for Asymmetric Modality Needs The following new media tags should be defined: speech-receive speech-send Gellens Expires April 16, 2015 [Page 18] Internet-Draft Negotiating Human Language October 2014 text-receive text-send sign-send sign-receive A user who prefers to talk and get text in return in English would register the following (if including this information in registration data): REGISTER firstname.lastname@example.org Contact: <sip:email@example.com> audio;text;speech-send;text- receive;language="en" At call time, a user who prefers to talk and get text in return in English would set the Accept-Contact header field to: Accept-Contact: *; audio; text; speech-receive; text-send; language="en";q=0.8 Accept-Contact: *; text; language="en"; q=0.2 Note that the directions specified here are as viewed from the callee side to match what the callee has registered. A bridge arranged for invoking a relay service specifically arranged for captioned telephony would register the following for supporting calling users: REGISTER firstname.lastname@example.org Contact: <sip:email@example.com> audio; text; speech-receive; text-send; language="en" A bridge arranged for invoking a relay service specifically arranged for captioned telephony would register the following for supporting called users: Gellens Expires April 16, 2015 [Page 19] Internet-Draft Negotiating Human Language October 2014 REGISTER firstname.lastname@example.org Contact: <sip:email@example.com> audio; text; speech-send; text- receive; language="en" At call time, these alternatives are included in the list of possible outcome of the call routing by the SIP proxies and the proper relay service is invoked. A.2.2. Caller Preferences for Asymmetric Language Tags An alternative is to register new language tags for the purpose of asymmetric language usage. Instead of using "language=", six new language tags would be registered: humintlang-text-recv humintlang-text-send humintlang-speech-recv humintlang-speech-send humintlang-sign-recv humintlang-sign-send These language tags would be used instead of the regular bidirectional language tags, and users with bidirectional capabilities SHOULD specify values for both directions. Services specifically arranged for supporting users with asymmetric needs SHOULD specify only the asymmetry they support. Author's Address Randall Gellens Qualcomm Technologies Inc. 5775 Morehouse Drive San Diego, CA 92121 US Email: firstname.lastname@example.org Gellens Expires April 16, 2015 [Page 20]