MMUSIC Working Group R. Gellens
Internet-Draft Qualcomm Technologies Inc.
Intended status: Standards Track July 07, 2013
Expires: January 06, 2014
Negotiating Human Language Using SDP
draft-gellens-mmusic-negotiating-human-language-00
Abstract
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 preferences with the capabilities of the called party. This
is especially important with emergency calls, where a call can be
routed to a Public Safety Answering Point (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 a company
call center).
This document describes the need and expected use, and describes a
solution using new SDP stream attributes plus an optional SIP "hint."
Status of this Memo
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Emergency Call from English Speaker in Spain . . . . . . . 5
4.2. Emergency Call from Spanish/English Speaker in France . . 5
4.3. Call to Call Center from Russian Speaker in U.S. . . . . . 6
4.4. Emergency Call from speech-impaired caller in the U.S. . . 6
4.5. Emergency Call from deaf caller in the U.S. . . . . . . . 6
5. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 7
6. The existing 'lang' attribute . . . . . . . . . . . . . . . . 7
7. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 8
7.1. New 'humintlang-send' and 'humintlang-recv' attributes . . 8
7.2. Advisory vs Required . . . . . . . . . . . . . . . . . . . 9
7.3. SIP "hint" . . . . . . . . . . . . . . . . . . . . . . . . 10
7.4. Silly States . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. Changes from Previous Versions . . . . . . . . . . . . . . . . 11
10.1. Changes from draft-gellens-...-00 to -01 . . . . . . . . 11
10.2. Changes from draft-gellens-...-01 to -02 . . . . . . . . 11
10.3. Changes from draft-gellens-...-02 to draft-gellens-
mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . 13
12.2. Informational References . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
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When setting up interactive communication sessions (using SIP or
other protocols), human (natural) language negotiation may be needed.
When the caller and callee know each other or where context or out of
band information implies the language, such negotiation is typically
not needed. In other cases, there is a need for spoken, signed, or
written languages to be negotiated based on the caller's preferences
and the callee's capabilities. This need applies to both emergency
and non-emergency calls. 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, in this case, SDP.
This approach has a number of benefits, including that it is generic
(applies to all interactive communications negotiated using SDP) 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, to a friend,
or colleague). But it is clearly useful in many other cases. For
example, someone calling a company call center or a Public Safety
Answering Point (PSAP) should be able to indicate if one or more
specific signed, written, and/or spoken languages are preferred, the
callee should be able to indicate its capabilities in this area, and
the call proceed using in-common language(s) and media forms.
Since this is a protocol mechanism, the user equipment (UE client)
needs to know the user's preferred languages; a reasonable technique
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.
Including the user's human (natural) language preferences 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 Emergency Services IP
network (ESInet) and the PSAP may choose to take the language and
media preferences into account when determining how to route and
process the call (i.e., language and media needs may be considered
within policy-based routing (PBR)).
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By treating language as another 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
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
caller initiates the call to a relay center, or the caller places the
call to emergency services (e.g., 911 in the U.S. or 112 in Europe).
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
negotiation 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 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).
2. Terminology
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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].
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 (PBR) capabilities within a
Policy-Based Routing Function. 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. Example Use Cases
4.1. Emergency Call from English Speaker in Spain
Someone who speaks only English is visiting Spain and places an
emergency (112) call. The call offers an audio stream using English.
The ESInet and PSAP have policy-based routing rules that take into
account the SDP language request when deciding how to route and
process the call. The ESInet routes the call to a PSAP within Spain
where an English-speaking call taker is available, and the PSAP
selects an English-speaking call taker to handle the call. The PSAP
answers the offer with an audio stream using English. The call is
established with an audio stream; the caller and call taker
communicate in English.
Alternatively, the ESInet routes the call to a cooperating PSAP
within the U.K. The PSAP answers the offer with an audio stream
using English. The call is established with an audio stream; the
caller and call taker communicate in English. (This approach is
similar to that envisioned in REACH112 Total Conversation.)
4.2. Emergency Call from Spanish/English Speaker in France
Someone who speaks both Spanish and English (but prefers Spanish) is
visiting France and places an emergency (112) call. The call offers
an audio stream listing first Spanish (meaning most preferred) and
then English. The ESInet and PSAP have policy-based routing rules
that take into account the SDP language request when deciding how to
route and process the call. The ESInet routes the call to a PSAP
within France where a Spanish-speaking call taker is available, and
the PSAP selects a Spanish-speaking call taker to handle the call.
The PSAP answers the offer with an audio stream listing Spanish. The
call is established with an audio stream; the caller and call taker
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communicate in Spanish.
Alternatively, the ESInet routes the call to a cooperating PSAP in
Spain or England. (This approach is similar to that envisioned in
REACH112 Total Conversation.)
Alternatively, there is no ESInet or the ESInet does not take
language into account in its PBR. The call is routed to a PSAP in
France. The PSAP ignores the language information in the SDP offer,
and answers the offer with an audio stream with no language or with
French. The UE continues the call anyway. The call taker answers in
French, the user tries speaking Spanish and perhaps English. The
call taker bridges in a translation service or transfers the call to
a multilingual call taker.
4.3. Call to Call Center from Russian Speaker in U.S.
A Russian speaker is visiting the U.S. and places a call to her
airline reservation desk to inquire about her return flight. The
airline call processing system takes into account the SDP language
request and decides to route the call to its call center within
Russia.
Alternatively, if the airline call processing system does not look at
SDP, it uses the SIP "hint" if present.
4.4. Emergency Call from speech-impaired caller in the U.S.
Someone who uses English but is speech-impaired places an emergency
(911) call. The call offers an audio stream listing English and a
real-time text stream also using English. The ESInet and PSAP have
policy-based routing rules that take into account the SDP language
and media requests when deciding how to route and process the call.
The ESInet routes the call to a PSAP with real-time text
capabilities. The PSAP answers the offer with an audio stream
listing English and a real-time text stream listing English. The
call is established with an audio and a real-time text stream; the
caller and call taker communicate in English using voice from the
call-taker to the caller and text from the caller to the call taker.
The audio stream is two-way, allowing the call taker to hear
background sounds.
4.5. Emergency Call from deaf caller in the U.S.
A deaf caller who uses American Sign Language (ASL) places an
emergency (911) call. The call offers a video stream listing ASL and
an audio stream with no language indicated. The ESInet and PSAP have
policy-based routing rules that take into account the SDP language
and media needs when deciding how to route and process the call. The
ESInet routes the call to a PSAP. The PSAP answers the offer with an
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audio stream listing English and a video stream listing ASL. The
PSAP bridges in a sign language interpreter. The call is established
with an audio and a video stream.
5. Desired Semantics
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, the usefulness of providing a way to
negotiate this as a general facility is outweighed by the complexity
of the desired semantics of the SDP attribute to allow negotiation of
multiple simultaneous languages within an interactive media stream.)
6. The 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 the existing
'lang' attribute can't be used and we need to define a new attribute.
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.
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Note that 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:juliet@example.com SIP/2.0
To: <sip:juliet@example.com>
From: <sip:romeo@example.net>;tag=576
Subject: Open chat with Romeo?
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 s2x.example.net
m=message 7313 TCP/MSRP *
a=accept-types:text/plain
a=lang:en
a=lang:it
a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp
Example: (F2) Gateway accepts session on Juliet's behalf
SIP/2.0 200 OK
To: <sip:juliet@example.com>;tag=534
From: <sip:romeo@example.net>;tag=576
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 x2s.example.com
m=message 8763 TCP/MSRP *
a=accept-types:text/plain
a=lang:it
a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
The example serves as evidence of the need for an SDP attribute with
the semantics as described in this document; unfortunately, the
existing 'lang' attribute is not it.
7. 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 per RFC 5646 [RFC5646]
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7.1. New 'humintlang-send' and 'humintlang-recv' attributes
Rather than re-use 'lang' we define two new media-level attributes
starting with 'humintlang' (short for "human interactive language")
to negotiate which human language is used in each (interactive) media
stream. There are two attributes, one ending in "-send" and the
other in "-recv" to indicate the language used when sending and
receiving media:
a=humintlang-send:<language tag>
a=humintlang-recv:<language tag>
Each can appear multiple times in an offer for a media stream.
In an offer, the 'humintlang-send' values constitute a list in
preference order (first is most preferred) of the languages the
offerer wishes to send, and the 'humintlang-recv' values constitute a
list in preference order of the languages the offerer wishes to
receive. Both SHOULD have the same values in the same order, because
otherwise it is harder to match desired resources.
In an answer, 'humintlang-send' is the accepted language the answerer
will send (which in most cases is one of the languages in the offer's
'humintlang-recv'), and 'humintlang-recv' is the accepted language
the answerer expects to receive (which in most cases is one of the
languages in the offer's 'humintlang-send').
Each value MUST be a language tag per RFC 5646 [RFC5646]. RFC 5646
describes mechanisms for matching language tags. While RFC 5646
provides a mechanism accommodating increasingly fine-grained
distinctions, in the interest of maximum interoperability for real-
time interactive communications, each 'humintlang-send' and
'humintlang-recv' value SHOULD be restricted to the largest
granularity of language tags; in other words, it is RECOMMENDED to
specify only a Primary-subtag and NOT to include subtags (e.g., for
region or dialect) unless the languages might be mutually
incomprehensible without them.
In an offer, each language tag value MAY have an asterisk appended as
the last character (after the registry value). The asterisk
indicates a request by the caller to not fail the call if there is no
language in common. See Section 7.2 for more information and
discussion.
When placing an emergency call, and in any other case where the
language cannot be assumed from context, each media stream in an
offer SHOULD specify both 'humintlang-send' and 'humintlang-recv'
attributes (to avoid ambiguity), and both SHOULD be set to the same
values in the same order.
7.2. Advisory vs Required
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One important consideration with this mechanism is if the call fails
if the callee does not support any of the languages requested by the
caller.
In order to provide for maximum likelihood of a successful
communication session, especially in the case of emergency calling,
the mechanism defined here provides a way for the caller to indicate
a preference for the call failing or succeeding when there is no
language in common. However, the callee is NOT REQUIRED to honor
this preference. For example, a PSAP MAY choose to attempt the call
even with no language in common, while a corporate call center MAY
choose to fail the call.
The mechanism for indicating this preference is that, in an offer, if
the last character of any of the 'humintlang-recv' or 'humintlang-
send' values is an asterisk, this indicates a request to not fail the
call (similar to SIP Accept-Language syntax). Either way, the called
party MAY ignore this, e.g., for the emergency services use case, a
PSAP will likely not fail the call.
7.3. SIP "hint"
SDP is used for stream negotiation, and emergency services based on
NENA i3 have the ability to reference SDP within policy-based routing
rules. However, it is possible that some entities wishing to take
the caller's language needs into account may lack this ability.
Accordingly, a SIP header is provided to supply a "hint" regarding
the caller's language needs. This is merely a hint, not actual
negotiation.
Protocols other than SIP may be used to establish interactive
communication sessions; this document does not provide a "hint"
mechanism for any protocol other than SIP.
TBD: The SIP header used for the "hint" is either a new header or
caller preferences (RFC 3841), presumably Accept-Contact (where the
caller sets media and language and optionally required; it's not yet
clear if this matches our desired semantics.
This SIP header is just a hint; it is RECOMMENDED to be sent; it is
NOT REQUIRED to be sent or to be used on receipt.
In the case of spoken languages using an audio stream, this "hint"
regarding language may be sufficient to allow the callee to optimally
handle the call, but since the "hint" only deals with language, not
media type, it is not sufficient when the caller requests non-audio
media such as text or video.
7.4. Silly States
It is 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.
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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).
8. IANA Considerations
IANA is kindly requested to add two entries to the 'att-field (media
level only)' table of the SDP parameters registry:
+------------------------------+-----------------+-----------------+
| Type | Name | Reference |
+------------------------------+-----------------+-----------------+
| att-field (media level only) | humintlang-send | (this document) |
| att-field (media level only) | humintlang-recv | (this document) |
+------------------------------+-----------------+-----------------+
9. Security Considerations
The Security Considerations of RFC 5646 [RFC5646] apply here (as a
use of that RFC). In addition, if the 'humintlang-send' or
'humintlang-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.
10. Changes from Previous Versions
10.1. Changes from draft-gellens-...-00 to -01
o Changed name of (possible) new attribute from 'humlang" to
"humintlang"
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
10.2. Changes from draft-gellens-...-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.
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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.
10.3. 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.
o Updated text about existing 'lang' attribute.
o Added example use cases.
o Replaced proposed single 'humintlang' attribute with 'humintlang-
send' and 'humintlang-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.
11. Acknowledgments
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Many thanks to Bernard Aboba, Harald Alvestrand, Flemming Andreasen,
Francois Audet, Eric Burger, Keith Drage, Doug Ewell, Christian
Groves, Gunnar Hellstrom, 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, 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.
12.2. Informational References
[I-D.iab-privacy-considerations]
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.
[I-D.saintandre-sip-xmpp-chat]
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.
[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
US
Email: rg+ietf@qti.qualcomm.com
Gellens Expires January 06, 2014 [Page 13]