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Versions: (draft-gellens-slim-negotiating-human-language) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

Network Working Group                                         R. Gellens
Internet-Draft                                Core Technology Consulting
Intended status: Standards Track                           July 14, 2017
Expires: January 15, 2018


         Negotiating Human Language in Real-Time Communications
             draft-ietf-slim-negotiating-human-language-13

Abstract

   Users have various human (natural) language needs, abilities, and
   preferences regarding spoken, written, and signed languages.  This
   document adds new SDP media-level attributes so that when
   establishing interactive communication sessions ("calls"), it is
   possible 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
   handled by a 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 a solution using new SDP media
   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 January 15, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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
     1.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Desired Semantics . . . . . . . . . . . . . . . . . . . . . .   5
   4.  The existing 'lang' attribute . . . . . . . . . . . . . . . .   5
   5.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  The 'hlang-send' and 'hlang-recv' attributes  . . . . . .   6
     5.3.  No Language in Common . . . . . . . . . . . . . . . . . .   7
     5.4.  Undefined Combinations  . . . . . . . . . . . . . . . . .   8
     5.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  att-field Table in SDP Parameters . . . . . . . . . . . .  10
     6.2.  Warn-Codes Sub-Registry of SIP Parameters . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  12
   9.  Changes from Previous Versions  . . . . . . . . . . . . . . .  12
     9.1.  Changes from draft-ietf-slim-...-04 to draft-ietf-
           slim-...-06 . . . . . . . . . . . . . . . . . . . . . . .  12
     9.2.  Changes from draft-ietf-slim-...-02 to draft-ietf-
           slim-...-03 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.3.  Changes from draft-ietf-slim-...-01 to draft-ietf-
           slim-...-02 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.4.  Changes from draft-ietf-slim-...-00 to draft-ietf-
           slim-...-01 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.5.  Changes from draft-gellens-slim-...-03 to draft-ietf-
           slim-...-00 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.6.  Changes from draft-gellens-slim-...-02 to draft-gellens-
           slim-...-03 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.7.  Changes from draft-gellens-slim-...-01 to draft-gellens-
           slim-...-02 . . . . . . . . . . . . . . . . . . . . . . .  13
     9.8.  Changes from draft-gellens-slim-...-00 to draft-gellens-
           slim-...-01 . . . . . . . . . . . . . . . . . . . . . . .  14
     9.9.  Changes from draft-gellens-mmusic-...-02 to draft-
           gellens-slim-...-00 . . . . . . . . . . . . . . . . . . .  14
     9.10. Changes from draft-gellens-mmusic-...-01 to -02 . . . . .  14



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     9.11. Changes from draft-gellens-mmusic-...-00 to -01 . . . . .  14
     9.12. Changes from draft-gellens-...-02 to draft-gellens-
           mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . .  14
     9.13. Changes from draft-gellens-...-01 to -02  . . . . . . . .  15
     9.14. Changes from draft-gellens-...-00 to -01  . . . . . . . .  16
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  16
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     12.2.  Informational References . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   A mutually comprehensible language is helpful for human
   communication.  This document addresses the negotiation of human
   (natural) language and media modality (spoken, signed, written) in
   real-time communications.  A companion document
   [I-D.ietf-slim-multilangcontent] addresses language selection in
   email.

   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 example, it is helpful for a caller to a
   company call center or a Public Safety Answering Point (PSAP) to be
   able to indicate preferred signed, written, and/or spoken languages,
   and for the callee to be able to indicate its capabilities in this
   area, allowing the call to proceed using the language(s) and media
   forms supported by both.

   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 known as the Session
   Description Protocol (SDP).  Utilizing SDP enables the solution
   described in this document to be applied to all interactive
   communications negotiated using SDP, in emergency as well as non-
   emergency scenarios.

   By treating language as another SDP 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



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   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.  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.

   The term "negotiation" is used here rather than "indication" because
   human language (spoken/written/signed) can be negotiated in the same
   manner as media (audio/text/video) and codecs.  For example, if we
   think of 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).

   Since this is a protocol mechanism, the user equipment (UE client)
   needs to know the user's preferred languages; while this document
   does not address how clients determine this, reasonable techniques
   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.

1.1.  Applicability

   Within this document, it is assumed that the negotiating endpoints
   have already been determined, so that a per-stream negotiation based
   on the Session Description Protocol (SDP) can proceed.

   When setting up interactive communications sessions it is necessary
   to route signaling messages to the appropriate endpoint(s).  This
   document does not address the problem of language-based routing.

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].








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3.  Desired Semantics

   The desired solution is a media attribute (preferably per direction)
   that may be used within an offer to indicate the preferred
   language(s) of each (direction of a) media stream, and within an
   answer to indicate the accepted language.  The semantics of including
   multiple languages for a media stream within an offer is that the
   languages are listed in order of preference.

   (Negotiating multiple simultaneous languages within a media stream is
   out of scope of this document.)

4.  The existing 'lang' attribute

   RFC 4566 [RFC4566] specifies an attribute 'lang' which appears
   similar to what is needed here, but is not sufficiently specific or
   flexible for the needs of this document.  In addition, 'lang' is not
   mentioned in [RFC3264] and there are no known implementations in SIP.
   Further, it is useful to be able to specify language per direction
   (sending and receiving).  This document therefore defines two new
   attributes.

5.  Solution

   An SDP attribute (per direction) seems the natural choice to
   negotiate human (natural) language of an interactive media stream,
   using the language tags of BCP 47 [RFC5646].

5.1.  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 a signed language at the SIP level but fail to negotiate a
   video media stream at the SDP layer).

   The mechanism described here for SDP can be adapted to media
   negotiation protocols other than SDP.



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5.2.  The 'hlang-send' and 'hlang-recv' attributes

   This document defines two media-level attributes starting with
   'hlang' (short for "human interactive language") to negotiate which
   human language is selected for use in each interactive media stream.
   There are two attributes, one ending in "-send" and the other in
   "-recv", registered in Section 6.  Each can appear in offers and
   answers for media streams.

   In an offer, the 'hlang-send' value is a list of one or more
   language(s) the offerer is willing to use when sending using the
   media, and the 'hlang-recv' value is a list of one or more
   language(s) the offerer is willing to use when receiving using the
   media.  The list of languages is in preference order (first is most
   preferred).  When a media is intended for interactive communication
   using a language in one direction only (such as a user sending using
   text and receiving using audio), either hlang-send or hlang-recv MAY
   be omitted.  When a media is not primarily intended for language (for
   example, a video or audio stream intended for background only) both
   SHOULD be omitted.  Otherwise, both SHOULD have the same value.  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, 'hlang-send' is the language the answerer will send if
   using the media for language (which in most cases is one of the
   languages in the offer's 'hlang-recv'), and 'hlang-recv' is the
   language the answerer expects to receive in the media (which in most
   cases is one of the languages in the offer's 'hlang-send').

   Each value MUST be a list of one or more language tags per BCP 47
   [RFC5646], separated by white space.  BCP 47 describes mechanisms for
   matching language tags.  Note that [RFC5646] Section 4.1 advises to
   "tag content wisely" and not include unnecessary subtags.

   In an offer, a list of language tags MAY have an asterisk appended at
   the end.  An asterisk appended to any value in any media in an offer
   indicates a request by the caller to the callee to not fail the call
   if there is no language in common.  See Section 5.3 for more
   information and discussion.

   An asterisk appended to any value in any media in an answer is
   undefined.

   Note that separate work may introduce additional information
   regarding language/modality preferences among media.




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   When placing an emergency call, and in any other case where the
   language cannot be inferred from context, in an offer each media
   stream primarily intended for human language communication SHOULD
   specify both (or for asymmetrical language use, one of) the 'hlang-
   send' and 'hlang-recv' attributes.

   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
   'hlang-send' and 'hlang-recv' attributes on each media stream
   primarily intended for human communication in an offer when placing
   an outgoing session, and 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 attributes
   when processing inbound calls.

   Note that media and language negotiation might result in more media
   streams being accepted than are needed by the users (e.g., if more
   preferred and less preferred combinations of media and language are
   all accepted).  This is not a problem.

5.3.  No Language in Common

   A consideration with the ability to negotiate language is if the call
   proceeds or fails if the callee does not support any of the languages
   requested by the caller.  This document does not mandate either
   behavior, although it does provide a way for the caller to indicate a
   preference for the call succeeding when there is no language in
   common.  It is OPTIONAL for the callee to honor this preference.  For
   example, a PSAP is likely to attempt the call even without an
   indicated preference when there is no language in common, while a
   call center might choose to fail the call.

   The mechanism for indicating this preference is that, in an offer, if
   the last token of any 'hlang-recv' or 'hlang-send' value for any
   media is an asterisk, this indicates a request to not fail the call.
   The called party MAY ignore the indication, e.g., for the emergency
   services use case, regardless of the absence of an asterisk, a PSAP
   will likely not fail the call; some call centers might reject a call
   even if the offer contains an asterisk.

   If the call is rejected due to lack of any languages in common, it is
   suggested to use SIP response code 488 (Not Acceptable Here) or 606



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   (Not Acceptable) [RFC3261] and include a Warning header field
   [RFC3261] in the SIP response.  The Warning header field contains a
   warning code of [TBD: IANA VALUE, e.g., 308] and a warning text
   indicating that there are no mutually-supported languages; the text
   SHOULD also contain the supported languages and media.

   Example:



      Warning:  [TBD: IANA VALUE, e.g., 308] proxy.example.com
         "Incompatible language specification: Requested languages not
         supported.  Supported languages are: es, en; supported media
         are: audio, text."

5.4.  Undefined Combinations

   With the exception of the case mentioned in Section 5.2 (a spoken
   language tag for a video stream in parallel with an audio stream with
   the same spoken language tag), the behavior when specifying a spoken/
   written language tag for a video media stream, or a signed language
   tag for an audio or text media stream, is not defined.

5.5.  Examples

   Some examples are shown below.  For clarity, only the most directly
   relevant portions of the SDP block are shown.

   An offer or answer indicating spoken English both ways:

      m=audio 49170 RTP/AVP 0
      a=hlang-send:en
      a=hlang-recv:en

   An offer indicating American Sign Language both ways, and requesting
   that the call proceed even if the callee does not support the
   language:

      m=video 51372 RTP/AVP 31 32
      a=hlang-send:ase
      a=hlang-recv:ase *

   An offer requesting spoken Spanish both ways (most preferred), spoken
   Basque both ways (second preference), or spoken English both ways
   (third preference).  The offer further requests that the call proceed
   even if the callee does not support any of the languages:

      m=audio 49250 RTP/AVP 20



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      a=hlang-send:es eu en
      a=hlang-recv:es eu en *

   An answer to the above offer indicating spoken Spanish both ways:

      m=audio 49250 RTP/AVP 20
      a=hlang-send:es
      a=hlang-recv:es

   An alternative answer to the above offer indicating spoken Italian
   both ways (as the callee does not support any of the requested
   languages but chose to proceed with the call):

      m=audio 49250 RTP/AVP 20
      a=hlang-send:it
      a=hlang-recv:it

   An offer or answer indicating written Greek both ways:

      m=text 45020 RTP/AVP 103 104
      a=hlang-send:gr
      a=hlang-recv:gr

   An offer requesting the following media streams: video for the caller
   to send using Argentine Sign Language, text for the caller to send
   using written Spanish (most preferred) or written Portuguese, audio
   for the caller to receive spoken Spanish (most preferred) or spoken
   Portuguese.  The offer also requests that the call proceed even if
   the callee does not support any of the languages:

      m=video 51372 RTP/AVP 31 32
      a=hlang-send:aed

      m=text 45020 RTP/AVP 103 104
      a=hlang-send:sp pt

      m=audio 49250 RTP/AVP 20
      a=hlang-recv:sp pt *

   An answer for the above offer, indicating text in which the callee
   will receive written Spanish, and audio in which the callee will send
   spoken Spanish.  The answering party had no video capability:

      m=video 0 RTP/AVP 31 32
      m=text 45020 RTP/AVP 103 104
      a=hlang-recv:sp

      m=audio 49250 RTP/AVP 20



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      a=hlang-send:sp

   An offer requesting the following media streams: text for the caller
   to send using written English (most preferred) or written Spanish,
   audio for the caller to receive spoken English (most preferred) or
   spoken Spanish, supplemental video.  The offer also requests that the
   call proceed even if the callee does not support any of the
   languages:

      m=text 45020 RTP/AVP 103 104
      a=hlang-send:en sp

      m=audio 49250 RTP/AVP 20
      a=hlang-recv:en sp *

      m=video 51372 RTP/AVP 31 32

   An answer for the above offer, indicating text in which the callee
   will receive written Spanish, audio in which the callee will send
   spoken Spanish, and supplemental video:

      m=text 45020 RTP/AVP 103 104
      a=hlang-recv:sp

      m=audio 49250 RTP/AVP 20
      a=hlang-send:sp

      m=video 51372 RTP/AVP 31 32

   Note that, even though the examples show the same (or essentially the
   same) language being used in both directions (even when the modality
   differs), there is no requirement that this be the case.  However, in
   practice, doing so is likely to increase the chances of successful
   matching.

6.  IANA Considerations

6.1.  att-field Table in SDP Parameters

   IANA is kindly requested to add two entries to the 'att-field (media
   level only)' table of the SDP parameters registry:

   Attribute Name:  hlang-recv

   Contact Name:  Randall Gellens

   Contact Email Address:  rg+ietf@randy.pensive.org




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   Attribute Value:  hlang-value

   Attribute Syntax:

      hlang-value =  Language-Tag *( SP Language-tag ) [ SP asterisk ]

                           ; Language-Tag as defined in BCP 47

      asterisk    =  "*"   ; an asterisk (%x2A) character

      SP          =  1*" " ; one or more space (%x20) characters



   Attribute Semantics:  Described in Section 5.2 of TBD: THIS DOCUMENT

   Usage Level:  media

   Mux Category:  NORMAL

   Charset Dependent:  No

   Purpose:  See Section 5.2 of TBD: THIS DOCUMENT

   O/A Procedures:  See Section 5.2 of TBD: THIS DOCUMENT

   Reference:  TBD: THIS DOCUMENT

   Attribute Name:  hlang-send

   Contact Name:  Randall Gellens

   Contact Email Address:  rg+ietf@randy.pensive.org

   Attribute Value:  hlang-value

   Attribute Semantics:  Described in Section 5.2 of TBD: THIS DOCUMENT

   Usage Level:  media

   Mux Category:  NORMAL

   Charset Dependent:  No

   Purpose:  See Section 5.2 of TBD: THIS DOCUMENT

   O/A Procedures:  See Section 5.2 of TBD: THIS DOCUMENT




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   Reference:  TBD: THIS DOCUMENT

6.2.  Warn-Codes Sub-Registry of SIP Parameters

   IANA is requested to add a new value in the warn-codes sub-registry
   of SIP parameters in the 300 through 329 range that is allocated for
   indicating problems with keywords in the session description.  The
   reference is to this document.  The warn text is "Incompatible
   language specification: Requested languages not supported.  Supported
   languages and media are: [list of supported languages and media]."

7.  Security Considerations

   The Security Considerations of BCP 47 [RFC5646] apply here.  In
   addition, if the 'hlang-send' or 'hlang-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.

8.  Privacy Considerations

   Language and media information can suggest a user's nationality,
   background, abilities, disabilities, etc.

9.  Changes from Previous Versions

   RFC EDITOR: Please remove this section prior to publication.

9.1.  Changes from draft-ietf-slim-...-04 to draft-ietf-slim-...-06

   o  Deleted Section 3 ("Expected Use")

   o  Reworded modalities in Introduction from "voice, video, text" to
      "spoken, signed, written"

   o  Reworded text about "increasingly fine-grained distinctions" to
      instead merely point to BCP 47 Section 4.1's advice to "tag
      content wisely" and not include unnecessary subtags

   o  Changed IANA registration of new SDP attributes to follow RFC 4566
      template with extra fields suggested in 4566-bis (expired draft)

   o  Deleted "(known as voice carry over)"

   o  Changed textual instanced of RFC 5646 to BCP 47, although actual
      reference remains RFC due to xml2rfc limitations





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9.2.  Changes from draft-ietf-slim-...-02 to draft-ietf-slim-...-03

   o  Added Examples

   o  Added Privacy Considerations section

   o  Other editorial changes for clarity

9.3.  Changes from draft-ietf-slim-...-01 to draft-ietf-slim-...-02

   o  Deleted most of Section 4 and replaced with a very short summary

   o  Replaced "wishes to" with "is willing to" in Section 5.2

   o  Reworded description of attribute usage to clarify when to set
      both, only one, or neither

   o  Deleted all uses of "IMS"

   o  Other editorial changes for clarity

9.4.  Changes from draft-ietf-slim-...-00 to draft-ietf-slim-...-01

   o  Editorial changes to wording in Section 5.

9.5.  Changes from draft-gellens-slim-...-03 to draft-ietf-slim-...-00

   o  Updated title to reflect WG adoption

9.6.  Changes from draft-gellens-slim-...-02 to draft-gellens-
      slim-...-03

   o  Removed Use Cases section, per face-to-face discussion at IETF 93

   o  Removed discussion of routing, per face-to-face discussion at IETF
      93

9.7.  Changes from draft-gellens-slim-...-01 to draft-gellens-
      slim-...-02

   o  Updated NENA usage mention

   o  Removed background text reference to draft-saintandre-sip-xmpp-
      chat-04 since that draft expired







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9.8.  Changes from draft-gellens-slim-...-00 to draft-gellens-
      slim-...-01

   o  Revision to keep draft from expiring

9.9.  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 [I-D.ietf-slim-multilangcontent] which
      addresses the non-real-time side.

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

9.11.  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.

9.12.  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.



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   o  Updated text about existing 'lang' attribute.

   o  Added example use cases.

   o  Replaced proposed single 'hlang' attribute with 'hlang-send' and
      'hlang-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.

   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.

9.13.  Changes from draft-gellens-...-01 to -02

   o  Updated text for (possible) new attribute "hlang" 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 "hlang" to
      attempt to better describe the role of language tags in media in
      an offer and an answer.




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

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

10.  Contributors

   Gunnar Hellstrom deserves special mention for his reviews and
   assistance.

11.  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.

12.  References

12.1.  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>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [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>.






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12.2.  Informational References

   [I-D.hellstrom-slim-modalitypref]
              Hellstrom, G., "Negotiating Modality in Real-Time
              Communications", draft-hellstrom-slim-modalitypref-02
              (work in progress), June 2017.

   [I-D.ietf-slim-multilangcontent]
              Tomkinson, N. and N. Borenstein, "Multiple Language
              Content Type", draft-ietf-slim-multilangcontent-08 (work
              in progress), June 2017.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

Author's Address

   Randall Gellens
   Core Technology Consulting

   Email: rg+ietf@coretechnologyconsulting.com
   URI:   http://www.coretechnologyconsulting.com



























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