Negotiating Human Language Using SDP

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Document Type Active Internet-Draft (individual)
Author Randall Gellens 
Last updated 2013-02-16
Replaced by draft-gellens-slim-negotiating-human-language, RFC 8373, RFC 8373
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MMUSIC Working Group                                          R. Gellens
Internet-Draft                               Qualcomm Technologies, Inc.
Intended status: Standards Track                       February 15, 2013
Expires: August 17, 2013

                  Negotiating Human Language Using SDP


   Users have various human 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 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 17, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the

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   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  . . . . . . . . . . . . . . . . . . . . . .  4
     5.1.  Possibility: Re-Use existing 'lang' attribute  . . . . . .  4
     5.2.  Possibility: Define new 'humlang' attribute  . . . . . . .  6
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  6
     8.2.  Informational References . . . . . . . . . . . . . . . . .  7
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  7

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 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
   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.

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   Including the user's 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
   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 session attribute that is negotiated
   along with media, 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 bridged translation service for others.  The
   standard session negotiation mechanism handles this by providing the
   information and mechanism for the endpoints to make appropriate

   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 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 natural 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
   natural 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)

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   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 the session are negotiated using SDP
   (e.g., media 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

   The desired solution is a media attribute that may be used within an
   offer to indicate preferred language(s) 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.

5.  Proposed Solution

   An SDP attribute seems the natural choice to negotiate human
   (natural) language.  The attribute value should be an IANA  language
   tag from the registry
   registry [1]

5.1.  Possibility: Re-Use existing 'lang' attribute

   RFC 4566 [RFC4566] 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' (or possibly the author has misunderstood RFC 4566).

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   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.

      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

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           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 *

5.2.  Possibility: Define new 'humlang' attribute

   Instead of re-using 'lang' we may define a new media-level attribute
   'humlang' to negotiate which human language is used in each media

      a=humlang:<language tag>

      This is a media-level attribute.  In an offer, it specifies the
      desired language(s) for the media.  Multiple humlang 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.  Within
      an answer it indicates the accepted language for the media.

      The "humlang" attribute value must be a single [RFC3066] language
      tag in US-ASCII [RFC3066].  It is not dependent on the charset
      attribute.  A "humlang" attribute SHOULD be specified when placing
      an emergency call (to avoid ambiguity) or in any other case where
      the language cannot be assumed from context.

6.  IANA Considerations


7.  Security Considerations


8.  References

8.1.  Normative References

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

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

   [RFC4566]  Handley, M., Jacobson, V. and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

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8.2.  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.

              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.

Author's Address

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

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