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Versions: 00 01 02 draft-gellens-slim-negotiating-human-language

MMUSIC Working Group                                          R. Gellens
Internet-Draft                                Qualcomm Technologies Inc.
Intended status: Standards Track                       February 13, 2014
Expires: August 17, 2014


         Negotiating Human Language in Real-Time Communications
           draft-gellens-mmusic-negotiating-human-language-02

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 communicate and ideally match (i.e., negotiate) the caller's
   language preferences 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 plus an optional SIP "hint."

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 17, 2014.









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Copyright Notice

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   document authors.  All rights reserved.

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   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.  New 'humintlang-send' and 'humintlang-recv' attributes  .   9
     7.2.  Advisory vs Required  . . . . . . . . . . . . . . . . . .  10
     7.3.  SIP "hint"  . . . . . . . . . . . . . . . . . . . . . . .  11
     7.4.  Silly States  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Alternative Proposal: Caller-prefs  . . . . . . . . . . . . .  12
     8.1.  Use of Caller Preferences Without Additions . . . . . . .  12
     8.2.  Additional Caller Preferences for Asymmetric Needs  . . .  14
       8.2.1.  Caller Preferences for Asymmetric Modality Needs  . .  14
       8.2.2.  Caller Preferences for Asymmetric Language Tags . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. Changes from Previous Versions  . . . . . . . . . . . . . . .  16
     11.1.  Changes from draft-gellens-...-00 to -01 . . . . . . . .  16
     11.2.  Changes from draft-gellens-...-01 to -02 . . . . . . . .  17
     11.3.  Changes from draft-gellens-...-02 to draft-gellens-
            mmusic-...-00  . . . . . . . . . . . . . . . . . . . . .  17
     11.4.  Changes from draft-gellens-mmusic-...-00 to -01  . . . .  18
     11.5.  Changes from draft-gellens-mmusic-...-01 to -02  . . . .  18
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  18



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   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  19
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     14.2.  Informational References . . . . . . . . . . . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   When setting up interactive communication sessions (using SIP or
   other protocols), human (natural) language negotiation may be needed.
   When the caller and callee know each other or where context or out of
   band information implies the language, such negotiation is typically
   not needed.  In other cases, there is a need for spoken, signed, or
   written languages to be negotiated based on the caller's preferences
   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
   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



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   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.

   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,



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   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
   caller and call taker communicate in English.  (This approach is
   similar to that envisioned in REACH112 Total Conversation.)





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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.
   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



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   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>

      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



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      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:juliet@example.com SIP/2.0
           To: <sip:juliet@example.com>
           From: <sip:romeo@example.net>;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:juliet@example.com>;tag=534
           From: <sip:romeo@example.net>;tag=576
           Call-ID: 742507no
           Content-Type: application/sdp

           c=IN IP4 x2s.example.com
           m=message 8763 TCP/MSRP *



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           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.  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>

      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



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   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 7.2 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).

   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.

7.2.  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.





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   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.

7.3.  SIP "hint"

   SDP is used for stream negotiation, and emergency services based on
   NENA i3 have the ability to reference SDP within policy-based routing
   rules.  However, it is possible that some entities wishing to take
   the caller's language needs into account may lack this ability.
   Accordingly, a SIP header is provided to supply a "hint" regarding
   the caller's language needs.  This is merely a hint, not actual
   negotiation.

   Protocols other than SIP may be used to establish interactive
   communication sessions; this document does not provide a "hint"
   mechanism for any protocol other than SIP.

   TBD: The SIP header used for the "hint" is either a new header or
   caller preferences (RFC 3841), presumably Accept-Contact (where the
   caller sets media and language and optionally required; it's not yet
   clear if this matches our desired semantics.

   This SIP header is just a hint; it is RECOMMENDED to be sent; it is
   NOT REQUIRED to be sent or to be used on receipt.

   In the case of spoken languages using an audio stream, this "hint"
   regarding language may be sufficient to allow the callee to optimally
   handle the call, but since the "hint" only deals with language, not
   media type, it is not sufficient when the caller requests non-audio
   media such as text or video.

7.4.  Silly States






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   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.

   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.  Alternative Proposal: Caller-prefs

   An alternative proposal is to use the SIP-level Caller Preferences
   mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841] rather than
   the SDP-level mechanism described above.

   The Caller-prefs mechanism includes a priority system by which
   different combinations of media and languages can 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].

8.1.  Use of Caller Preferences Without Additions

   The following is 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].

   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:





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      REGISTER    user@example.net

      Contact:    <sip:user1@example.net> 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
   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.





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   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.

8.2.  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.

8.2.1.  Caller Preferences for Asymmetric Modality Needs

   The following new media tags should be defined:

      speech-receive

      speech-send

      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):



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      REGISTER    user@example.net

      Contact:    <sip:user1@example.net> 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    ct@ctrelay.net

      Contact:    <sip:ct1@ctreley.net> 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:



      REGISTER    ct@ctrelay.net

      Contact:    <sip:ct2@ctreley.net> 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.

8.2.2.  Caller Preferences for Asymmetric Language Tags

   An alternative is to register new language tags for the purpose of
   asymmetric language usage.



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   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.

9.  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

10.  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.

11.  Changes from Previous Versions

11.1.  Changes from draft-gellens-...-00 to -01




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   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

   o  Minor text clarifications

11.2.  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.

11.3.  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.





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   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.

   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.

11.4.  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.

11.5.  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 Section 8 ("Alternative Proposal: Caller-prefs")
      discussing use of SIP-level Caller-prefs instead of SDP-level.

12.  Contributors

   Gunnar Hellstrom deserves special mention for his reviews,
   assistance, and especially for contributing the text in Section 8 on
   the alternative proposal using SIP-level Caller-prefs.




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13.  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.

14.  References

14.1.  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.

14.2.  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
              (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.




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Author's Address

   Randall Gellens
   Qualcomm Technologies Inc.
   5775 Morehouse Drive
   San Diego, CA  92121
   US

   Email: rg+ietf@qti.qualcomm.com










































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