MMUSIC Working Group                                          R. Gellens
Internet-Draft                               Qualcomm Technologies, Inc.
Intended status: Standards Track                       February 24, 2013
Expires: August 26, 2013

                  Negotiating Human Language Using SDP


   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 needs, abilities, and preferences with the capabilities of
   the called party.  This is especially important with emergency
   calling, where a call can be routed to a 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 an airline
   reservation desk).

   This document describes the need and expected use, and discusses the
   solution using either an existing or new SDP attribute.

Status of this Memo

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   This Internet-Draft will expire on August 26, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Expected Use . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Desired Semantics  . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Proposed Solution  . . . . . . . . . . . . . . . . . . . . . .  5
     5.1.  Possibility: Re-Use existing 'lang' attribute  . . . . . .  5
     5.2.  Possibility: Define new 'humintlang' attribute . . . . . .  7
   6.  Silly States . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   9.  Changes from Previous Versions . . . . . . . . . . . . . . . .  7
     9.1.  Changes from -00 to -01  . . . . . . . . . . . . . . . . .  7
     9.2.  Changes from -01 to -02  . . . . . . . . . . . . . . . . .  8
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     11.1.  Normative References  . . . . . . . . . . . . . . . . . .  8
     11.2.  Informational References  . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9

1.  Introduction

   When setting up interactive communication sessions, human (natural)
   language negotiation is needed in some cases.  When the caller and
   callee are known to each other or where context implies language,
   such language negotiation may not be needed.  In other cases, there
   is a need for the caller to indicate language preferences, abilities,
   or needs, including specific spoken, signed, or written languages.
   This need exists when setting up SIP or other sessions (including
   emergency and non-emergency calling).  For various reasons, including
   the ability to establish multiple streams each using a different
   media (e.g., voice, text, video), it makes sense to use a per-stream

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   negotiation mechanism, using SDP.

   This approach has a number of benefits, including that it is generic
   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).  But it
   seems clearly useful in many other cases.  For example, it seems
   generally useful that someone calling a company call center be able
   to indicate if a specific sign and/or spoken language is needed.  The
   UE would need to set this, but could default to the language used for
   the interface with the user.

   Including the user's human (natural) language requirements 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
   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 ESInet and the PSAP may
   choose to take the language into account when determining how to
   route and process the call (e.g., language and media needs may be
   considered within policy-based routing).

   By treating language as another attribute that is negotiated along
   with other aspects of a media stream, it becomes possible to
   accommodate a wide 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

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   caller initiates the call to a relay center, or the caller places the
   call to emergency services (e.g., 911 or 112).  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 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,
   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 whichever language
   supported by the call center is most preferred by the user.  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",
   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 capabilities within a
   Policy-Based Routing Function (PCRF).  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.  Desired Semantics

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   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, it does not seem useful enough as a
   general facility to warrant complicating the desired semantics of the
   SDP attribute to allow negotiation of multiple simultaneous languages
   within an interactive media stream.)

5.  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 from RFC 4566 [RFC4566] or the IANA
   registry [IANA-lang-tags]

5.1.  Possibility: Re-Use 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 either the
   existing 'lang' attribute can't be used and we need to define a new
   attribute; or we finese/update the semantics of 'lang' such that the
   existing semantics apply to non-interactive streams (multiple 'lang'
   values means all are used), while for interactive streams, one is
   used; (or possibly the author of this memo has misunderstood RFC

   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
      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.

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      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.

   The question is: Can the 'lang' attribute be used for our purposes?
   Using it to negotiate the language for a media seems at first glance
   to violate its semantics as defined in RFC 4566 [RFC4566].  But 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/2.0
           To: <>
           From: <>;tag=576
           Subject: Open chat with Romeo?
           Call-ID: 742507no
           Content-Type: application/sdp

           c=IN IP4
           m=message 7313 TCP/MSRP *

      Example: (F2) Gateway accepts session on Juliet's behalf

           SIP/2.0 200 OK
           To: <>;tag=534
           From: <>;tag=576
           Call-ID: 742507no
           Content-Type: application/sdp

           c=IN IP4
           m=message 8763 TCP/MSRP *

   To re-use the existing 'lang' attribute, we'd update its registration
   to specify that for non-interactive media, multiple 'lang' values in
   an offer have the existing RFC 4566 [RFC4566] semantics (all
   languages are used in the media), while for interactive media
   streams, one of the values should be selected in the answer and that
   language used in the media stream.

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5.2.  Possibility: Define new 'humintlang' attribute

   Instead of re-using 'lang' we may define a new media-level attribute
   'humintlang' (short for "human interactive language") to negotiate
   which human language is used in each (interactive) media stream:

      a=humintlang:<language tag>

      This is a media-level attribute.  In an offer, it specifies the
      desired language(s) for the media.  Multiple "humintlang"
      attributes can be provided in an offer for a media stream, in
      which case the order of the attributes indicates the order of
      preference of the various languages from most preferred to least
      preferred.  When the "humintlang" attribute appears within an
      answer it indicates the accepted language for the media.

      The "humintlang" attribute value MUST be a language tag per RFC
      5646 [RFC5646].  A "humintlang" attribute SHOULD be specified for
      each media stream in an offer when placing an emergency call (to
      avoid ambiguity) and in any other case where the language cannot
      be assumed from context.

      When an offer includes media with one or more language tags, each
      accepted media in the answer MUST include one of the language tags
      offered for the media.  RFC 5646 describes mechanisms for matching
      language tags.

6.  Silly States

   It's 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).

7.  IANA Considerations


8.  Security Considerations


9.  Changes from Previous Versions

9.1.  Changes from -00 to -01

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   o  Changed name of (possible) new attribute from 'humlang" to

   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

9.2.  Changes from -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.  Acknowledgments

   Many thanks to Doug Ewell for his review and corrections/suggestions.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

11.2.  Informational References

              Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M. and R. Smith, "Privacy
              Considerations for Internet Protocols", Internet-Draft
              draft-iab-privacy-considerations-03, July 2012.


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              Saint-Andre, P., Gavita, E., Hossain, N. and S. Loreto,
              "Interworking between the Session Initiation Protocol
              (SIP) and the Extensible Messaging and Presence Protocol
              (XMPP): One-to-One Text Chat", Internet-Draft draft-
              saintandre-sip-xmpp-chat-04, October 2012.

              "IANA Language Subtag Registry", , <

   [RFC3066]  Alvestrand, H., "Tags for the Identification of
              Languages", RFC 3066, January 2001.

Author's Address

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


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