Negotiating Modality in Real-Time Communications
draft-hellstrom-slim-modalitypref-00

slim                                                        G. Hellstrom
Internet-Draft                                                   Omnitor
Intended status: Standards Track                            June 5, 2017
Expires: December 7, 2017

            Negotiating Modality in Real-Time Communications
                  draft-hellstrom-slim-modalitypref-00

Abstract

   When negotiating language for a real-time session, users may have
   very specific preferences for using one modality (spoken, written or
   signed) over other possible but less preferred modalities.  This
   specification introduces indication of modality preference to be used
   in session negotiation in combination with an earlier speified
   mechanism for language preference negotiation.

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   the Trust Legal Provisions and are provided without warranty as
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Modality Preference Indication  . . . . . . . . . . . . . . .   3
   4.  Interaction with Call Denial Indication . . . . . . . . . . .   4
   5.  Interaction with Simultaneity Indication  . . . . . . . . . .   4
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   A mechanism for negotiating human language for real-time
   communication is specified in
   [I-D.ietf-slim-negotiating-human-language].  The indication of
   language preference is expressed per media and specified in SDP
   [RFC4566] attributes 'hlang-send' and 'hlang-recv'.  Negotiation of
   language can take place by the answering part selecting from the
   languages, media and direction alternatives expressed by the offering
   part.  Languages are expressed by using language-tags as specified in
   BCP 47 [RFC5646].

   When starting a conversation in a media-rich environment, the users
   may have very specific preferences for using one modality (spoken,
   written or signed) over other possible but less preferred modalities.
   In traditional call establishment, it is the answering part who is
   expected to start the conversation by a greeting.  In the media-rich
   environment, the modality and language of this greeting sets the
   expectations for what modality and language to mainly use in the
   session.  Deviation from this initial expectation is usually possible
   during the session by mutual agreement between the participants, but
   may be time consuming and cause uncertainty.

   A way for the parties to not only indicate alternative languages and
   modalities for the communication directions in the session, but also
   indicate preference for specific modalities per direction provides
   the opportunity to more exactly describe the desired language
   communication for a session, while still providing information about
   less preferred alternatives.  This specification extends

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   [I-D.ietf-slim-negotiating-human-language] with a mechanism for
   indicating modality preference by a condensed notation integrated
   with the syntax of the language indications of
   [I-D.ietf-slim-negotiating-human-language].

   The expected application area is wide.  By old tradition, the most
   common modality for real-time interaction is spoken communication.
   In some settings, e.g. where silence is required, it may be desirable
   to express a preference for using written communication, while still
   leaving a possibility open for traditional spoken communication by an
   indication on lower preference level.  For persons having full
   ability to both use sign language and spoken language, but not
   wanting to force the other party to bring in a sign language
   interpreter in the call, it may be of importance to be able to
   indicate the sign language capability on a lower preference level and
   the spoken laanguage capability on a higher level.  Some persons with
   disabilities may strongly prefer to conduct a written conversation,
   while still wanting to express that a spoken conversation is possible
   as a last resort.  Many other situations exist in the media-rich
   communication environment when the media preference indication is of
   value for a smooth initiation of a real-time session.

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 [RFC2119].

3.  Modality Preference Indication

   This specification extends the use of the asterisk in the
   'hlang'send' and 'hlang-recv' SDP [RFC4566] attributes introduced by
   [I-D.ietf-slim-negotiating-human-language].

   In [I-D.ietf-slim-negotiating-human-language], the asterisk appended
   at the end of the attribute value indicates a preference to not get
   the call denied if no languages match.

   This specification adds the following meaning of the asterisk:

   In an offer or answer, a 'hlang-send' or 'hlang-recv' attribute value
   MAY have an asterisk appended as the final token.  An asterisk
   appended to a value in an offer indicates a the caller has higher
   preference for the corresponding modality to be used in the specified
   direction than other modalities for the indicated direction without
   an asterisk.  In an answer, the asterisk indicates a modality that is
   preferred by the callee to be used in the session.

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   A user may have a clear preference to use one specific modality in a
   direction, while use of other modalities may be acceptable but lower
   in preference.  This condition MAY be indicated by appending an
   asterisk as the last parameter in the corresponding 'hlang-' value.
   Note that the asterisk appended at the end of a 'hlang-' attribute
   value also should also be seen as a preference to not have the call
   denied even if no indicated languages are in common as specified in
   [I-D.ietf-slim-negotiating-human-language].

   When negotiating language use for a direction, languages and
   modalities specified together with the asterisk should be given
   preference to be selected for use.

   If there is no specific preference between modalities in the same
   direction, this condition should be indicated by appending an
   asterisk on all or no 'hlang-' values for that direction.

4.  Interaction with Call Denial Indication

   If no modality preference is indicated in any 'hlang-' attribute by
   no attached asterisk, this should also be taken as a preference by
   the caller to get the call denied if no languages are in common
   between the caller and the callee.

   A caller with language capabilities in multiple media, but no
   specific modality preferences should attach the asterisk to all
   'hlang-' attributes in at least one direction for indication that the
   call should not be denied.

   If there is a preference for denying the call when no languages
   match, no asterisk should be appended on any 'hlang-' attribute
   value, and then it is not possible to indicate any preferred modality
   at the same time.

5.  Interaction with Simultaneity Indication

   - - Interaction with simultaneity indication - -

6.  Examples

   An offer requesting the following media streams: audio for the caller
   to send using spoken English (most preferred modality) or American
   Sign Language (less preferred modality), audio for the caller to
   receive spoken English (most preferred modality) or American Sign
   Language (less preferred modality), supplemental text.  The offer
   also requests that the call proceed even if the callee does not
   support any of the languages.  The offer is likely from a hearing
   person with knowledge in sign language:

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      m=text 45020 RTP/AVP 103 104
      m=audio 49250 RTP/AVP 20
      a=hlang-recv:en *
      a=hlang-send:en *
      m=video 51372 RTP/AVP 31 32
      a=hlang-recv: ase
      a=hlang-send: ase

   An answer for the above offer, indicating video in which the callee
   will send and receive American Sign Language, because that callee had
   no capability for spoken English.  The text and audio streams are
   opened as supplementary streams.

      m=text 45020 RTP/AVP 103 104
      m=audio 49250 RTP/AVP 20
      m=video 51372 RTP/AVP 31 32
      a=hlang-send: ase
      a=hlang-recv: ase

   An offer requesting the following media streams: audio for the caller
   to send using spoken French (most preferred modality) or written
   French (less preferred modality), text for the caller to receive
   written French.  The offer also requests that the call proceed even
   if the callee does not support any of the languages.  Video is
   supplemental.The offer is likely from a hard-of-hearing person with
   no use of received spoken language and a preference to use spoken
   language rather than type French:

      m=text 45020 RTP/AVP 103 104
      a=hlang-send:fr
      a=hlang-recv:fr
      m=audio 49250 RTP/AVP 20
      a=hlang-send:fr *
      m=video 51372 RTP/AVP 31 32

   An answer for the above offer, indicating text in which the callee
   will send written French, and audio in which the callee is prepared
   to receive spoken French.  The video stream is opened as a
   supplementary stream.

      m=text 45020 RTP/AVP 103 104
      a=hlang-send: fr
      m=audio 49250 RTP/AVP 20
      a=hlang-recv: fr
      m=video 51372 RTP/AVP 31 32

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7.  Acknowledgements

   Thanks to Randall Gellens for providing the background for this
   extension.  Brian Rosen and Paul Kyzivat for thorough discussions and
   guidance.

8.  IANA Considerations

9.  Security Considerations

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <http://www.rfc-editor.org/info/rfc5646>.

10.2.  Informative References

   [I-D.ietf-slim-negotiating-human-language]
              Gellens, R., "Negotiating Human Language in Real-Time
              Communications", draft-ietf-slim-negotiating-human-
              language-10 (work in progress), May 2017.

Author's Address

   Gunnar Hellstrom
   Omnitor
   Hammarby Fabriksvag 23
   Stockholm  120 30
   Sweden

   Phone: +46 708 204 288
   Email: gunnar.hellstrom@omnitor.se

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