wdiff rfc8373.alt-original rfc8373.txt

Network Working Group
Internet Engineering Task Force (IETF) R. Gellens
Internet-Draft
Request for Comments: 8373 Core Technology Consulting
Intended status:
Category: Standards Track February 20, 2018
Expires: August 24, April 2018
ISSN: 2070-1721

Negotiating Human Language in Real-Time Communications
draft-ietf-slim-negotiating-human-language-24

Abstract

Users have various human (natural) (i.e., natural) language needs, abilities,
and preferences regarding spoken, written, and signed languages.
This document adds defines new SDP media-level Session Description Protocol (SDP) media-
level attributes so that when establishing interactive communication
sessions ("calls"), it is possible to negotiate (communicate (i.e., communicate
and match) the caller's language and media needs with the
capabilities of the called party. This is especially important with for
emergency calls, where because it allows for a call can to be handled by a call
taker capable of communicating with the user, user or for a translator or
relay operator can to be bridged into the call during
setup, but setup. However,
this also applies to non-emergency calls as well (as an (for example, when calling calls to a
company call center).

This document describes the need and as well as a solution using that uses new Session
Description Protocol (SDP)
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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
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material or to cite them other than as "work in progress."

This Internet-Draft will expire on August 24, 2018.
https://www.rfc-editor.org/info/rfc8373.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2
1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4
3. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5 4
4. The existing Existing 'lang' attribute Attribute . . . . . . . . . . . . . . . . 5
5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. The 'hlang-send' and 'hlang-recv' attributes Attributes . . . . . . 5
5.2. No Language in Common . . . . . . . . . . . . . . . . . . 7 6
5.3. Usage Notes . . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9
6.1. att-field Table in Sub-Registry of SDP Parameters . . . . . . . . . . . . 10 9
6.2. Warn-Codes Warning Codes Sub-Registry of SIP Parameters . . . . . . . . 11 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
10. Contributors
9. References . . . . . . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgments . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . 15
12. References . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . 12
Contributors . . . . . . . . 16
12.2. Informational References . . . . . . . . . . . . . . . . 16 . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 13

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, or written) in real-time
communications. A companion document [RFC8255] addresses language
selection in email.

Unless the caller and callee know each other or there is contextual
or out-of- band 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 An example of a non-emergency call is helpful for when a
caller to contacts a company call center or center; an emergency call typically
involves a caller contacting a Public Safety Answering Point (PSAP) (PSAP).
In such scenarios, it is helpful for the caller to be able to
indicate preferred signed, written, and/or spoken languages, languages and for
the callee to be able to indicate its capabilities in capabilities; this
area, allowing allows 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., (i.e., voice, text, and/or video), it
makes sense to use a per-stream negotiation mechanism known as the
Session Description Protocol (SDP). Utilizing Session Description Protocol
(SDP) SDP [RFC4566] 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 called-party facilities. For
example, some users may be able to speak several languages, 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 they 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 hard of hearing and desires a voice stream to send spoken
language plus a text stream to receive written language. 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
be able to use a set of languages he or she speaks, with languages, perhaps with preferences for one
or a few, while the airline reservation center will may 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.

In the offer/answer model used here, the offer contains a set of
languages per media (and direction) that the offerer is capable of
using, and the answer contains one language per media (and direction)
that the answerer will support. Supporting languages and/or
modalities can require taking extra steps, such as bridging external
translation or relay resources into the call or having a call handled
by an agent who speaks a requested language and/or with has the ability to
use a requested modality, or bridging external translation
or relay resources into the call, etc. modality. The answer indicates the media and
languages that the answerer is committing to support (possibly after
additional steps have been taken). This model also provides
knowledge so both ends know what has been negotiated. Note that
additional steps required to support the indicated languages or
modalities may or may not be in place in time for any early media.

Since this is a protocol mechanism, the user equipment (UE client) (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 interface. In some cases, a UE client 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.

This document does not address user interface (UI) issues, such as if
or how a UE client informs a user about the result of language and
media negotiation.

1.1. Applicability

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

When setting up interactive communications sessions communication 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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 RFC 8174 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

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, stream and within an
answer to indicate the accepted language. The semantics of including When multiple languages
are included for a media stream within an offer is that within an offer, the languages are
listed in order of preference.

(Negotiating preference (most preferred first).

Note that negotiating multiple simultaneous languages within a media
stream is out of scope of this document.) document.

4. The existing Existing 'lang' attribute Attribute

RFC 4566 [RFC4566] specifies an attribute 'lang' which appears that is similar to
what is needed here, here but is not sufficiently specific or flexible for
the needs of this document. In addition, 'lang' is not mentioned in [RFC3264]
[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]. [BCP47].

5.1. The 'hlang-send' and 'hlang-recv' attributes Attributes

This document defines two media-level attributes starting attributes: 'hlang-send' and
'hlang-recv' (registered in Section 6). Both start with
'hlang' (short 'hlang',
short for "human language") language". These attributes are used to negotiate
which human language is selected for use in (each direction of) each
interactive media stream. (Note that not all streams will
necessarily be used.) There are two
attributes, one ending in "-send" and the other in "-recv",
registered in Section 6. Each can appear for media streams in offers
and answers for
media streams. answers.

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 only one direction only (e.g., a user in France with difficulty
speaking but able to hear who indicates a desire to send receive French
using text audio and receive send French using audio), text), either hlang-send 'hlang-send' or hlang-recv
'hlang-recv' MAY be omitted. Note that the media can still be useful
in both directions. When a media is not primarily intended for
language (for example, a video or audio stream intended for
background only) only), both SHOULD be omitted. Otherwise, both SHOULD
have the same value. Note that specifying different languages for
each direction (as opposed to the
same same, or essentially the same same,
language in different modalities) can make it difficult to complete
the call (e.g., specifying a desire to send audio in Hungarian and
receive audio in Portuguese).

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 if using the media for
language (which in most cases is one of the languages in the offer's
'hlang-send').

In an offer, each value MUST be a list of one or more language tags
per BCP 47 [RFC5646], [BCP47], separated by white space. In an answer, each value MUST
be one language tag per BCP 47. BCP 47 [BCP47]. [BCP47] describes mechanisms for
matching language tags. Note that [RFC5646] Section 4.1 of RFC 5646 [BCP47]
advises to "tag content wisely" and not include unnecessary subtags.

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

Clients acting on behalf of end users are expected to set one or both
of the 'hlang-send' and 'hlang-recv' attributes on each OFFERed 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 into account
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.

5.2. No Language in Common

A consideration with regarding the ability to negotiate language is if
whether 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.

When a call is rejected due to lack of any languages language in common, the
SIP response has SIP response code 488 (Not Acceptable Here) or 606
(Not Acceptable) [RFC3261] and a Warning header field [RFC3261] with
a warning code of [TBD: IANA VALUE, e.g., 308] 308 and a warning text indicating that there are no mutually-supported
mutually supported languages; the warning text SHOULD also contain
the supported languages and media.

Example:

Warning: [TBD: IANA VALUE, e.g., 308] 308 proxy.example.com "Incompatible language
specification: Requested languages not supported.

Supported languages are: es, en; supported media are:
audio, text."

5.3. Usage Notes

A sign-language tag with a video media stream is interpreted as an
indication for sign language in the video stream. A non-sign-
language tag with a text media stream is interpreted as an indication
for written language in the text stream. A non-sign-language tag
with an audio media stream is interpreted as an indication for spoken
language in the audio stream.

This document does not define any other use for language tags in
video media (such as how to indicate visible captions in the video
stream).

This document does not define the use of sign-language tags in text
or audio media.

In the IANA registry of for language subtags per BCP 47 [RFC5646], [BCP47], a language
subtag with a Type field "extlang" combined with a Prefix field value
"sgn" indicates a sign-language tag. The absence of such "sgn"
prefix indicates a non-sign-language tag.

This document does not define the use of sign-language tags in text
or audio media.

This document does not define the use of language tags in media other
than interactive streams of audio, video, and text (such as "message"
or "application"). Such use could be supported by future work or by
application agreement.

5.4. 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:

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):

m=audio 49250 RTP/AVP 20
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, and
audio for the caller to receive spoken Spanish (most preferred) or
spoken Portuguese:

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, Spanish and audio in which the callee will send
spoken Spanish. The (The answering party had has no video capability: 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
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, and supplemental video:

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 Sub-Registry of SDP Parameters

The syntax in this section uses ABNF per RFC 5234 [RFC5234].

IANA is kindly requested to add has added two entries to the 'att-field "att-field (media level only)' table only)" sub-
registry of the SDP parameters registry: "Session Description Protocol (SDP) Parameters"
registry.

The first entry is for hlang-recv: 'hlang-recv':

Attribute Name: hlang-recv
Long-Form English Name: human language receive
Contact Name: Randall Gellens
Contact Email Address: rg+ietf@coretechnologyconsulting.com
Attribute Value: hlang-value
Attribute Syntax:

hlang-value = hlang-offv / hlang-ansv
; hlang-offv used in offers
; hlang-ansv used in answers
hlang-offv = Language-Tag *( SP Language-Tag )
; Language-Tag as defined in BCP 47 [BCP47]
SP = 1*" " ; one or more space (%x20) characters
hlang-ansv = Language-Tag

Attribute Semantics: Described in Section 5.1 of TBD: THIS
DOCUMENT RFC 8373
Usage Level: media
Mux Category: NORMAL
Charset Dependent: No
Purpose: See Section 5.1 of TBD: THIS DOCUMENT RFC 8373
O/A Procedures: See Section 5.1 of TBD: THIS DOCUMENT RFC 8373
Reference: TBD: THIS DOCUMENT RFC 8373

The second entry is for hlang-send: 'hlang-send':

Attribute Name: hlang-send
Long-Form English Name: human language send
Contact Name: Randall Gellens
Contact Email Address: rg+ietf@coretechnologyconsulting.com
Attribute Value: hlang-value
Attribute Syntax:

hlang-value = hlang-offv / hlang-ansv
Attribute Semantics: Described in Section 5.1 of TBD: THIS
DOCUMENT RFC 8373
Usage Level: media
Mux Category: NORMAL
Charset Dependent: No
Purpose: See Section 5.1 of TBD: THIS DOCUMENT RFC 8373
O/A Procedures: See Section 5.1 of TBD: THIS DOCUMENT RFC 8373
Reference: TBD: THIS DOCUMENT RFC 8373

6.2. Warn-Codes Warning Codes Sub-Registry of SIP Parameters

IANA is requested to add a new has added the value in 308 to the warn-codes sub-registry "Warning Codes (warn-codes)" sub-
registry of SIP parameters in the 300 through 329 "Session Initiation Protocol (SIP) Parameters"
registry. (The value lies within the range that is allocated for indicating
problems with keywords in the session description. description.) The reference is
to this document. The warn text is "Incompatible language
specification: Requested languages not supported. Supported
languages and are [list of supported languages]; supported media are:
[list of supported languages and media]."

7. Security Considerations

The Security Considerations of BCP 47 [RFC5646] [BCP47] apply here. An attacker with
the ability to modify signaling could prevent a call from succeeding
by altering any of several crucial elements, including the 'hlang-send' 'hlang-
send' or 'hlang-recv' values. RFC 5069 [RFC5069] discusses such
threats. Use of TLS or IPSec IPsec can protect against such threats.
Emergency calls are of particular concern; RFC 6881 [RFC6881], which
is specific to emergency calls, mandates use of TLS or IPSec IPsec (in ED-57/SP-30). ED-
57/SP-30).

8. Privacy Considerations

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

12.

9. References

12.1.

9.1. Normative References

[BCP47] Phillips, A., Ed. and Mark. Davis, Ed., "Matching of
Language Tages", BCP 47, RFC 4647, DOI 10.17487/RFC464,
September 2006.

Phillips, A., Ed., and M. Davis, Ed., "Tags for
Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/
RFC5646, September 2009.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://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, <https://www.rfc-
editor.org/info/rfc3261>.
<https://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, <https://www.rfc-editor.org/info/rfc4566>.

[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, <https://www.rfc-
editor.org/info/rfc5234>.

[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
<https://www.rfc-editor.org/info/rfc5234>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

12.2. Informational

9.2. Informative References

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

[RFC5069] Taylor, T., Ed., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069,
DOI 10.17487/RFC5069, January 2008, <https://www.rfc-
editor.org/info/rfc5069>.
<https://www.rfc-editor.org/info/rfc5069>.

[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013,
<https://www.rfc-editor.org/info/rfc6881>.

[RFC8255] Tomkinson, N. and N. Borenstein, "Multiple Language
Content Type", RFC 8255, DOI 10.17487/RFC8255, October
2017, <https://www.rfc-editor.org/info/rfc8255>.

11. Acknowledgments

Acknowledgements

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,
Mirja Kuhlewind, Paul Kyzivat, John Levine, Alexey Melnikov, Addison
Phillips, James Polk, Eric Rescorla, Pete Resnick, Alvaro Retana,
Natasha Rooney, Brian Rosen, Peter Saint-Andre, and Dale Worley for
their reviews, corrections, suggestions, and participating participation in in-person and email
and in-person discussions.

10.

Contributors

Gunnar Hellstrom deserves special mention for his reviews and
assistance.

Author's Address

Randall Gellens
Core Technology Consulting

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