I have reviewed draft-ietf-slim-negotiating-human-language-06.txt and
have composed a proposed edited version adjusted for my comments below,
and additionally for some minor editorial issues.
The attached version is a rough edit of the txt file version. Accepted
edits need to be re-done in the XML version.
Please use a diff to find all edit proposals. The main ones are listed
below with reference to sections in the files.
-------------------------------------------------------------------------------------------------
1. Inexact wording about the syntax of the new attributes.
Sections 5 and 5.2, .
The text sometimes indicate that the value of the attributes is a
language tag, and sometimes a language tag with an optionally appended
asterisk. The syntax shown in section 5.2 is also not in alignment with
the syntax shown in section 6. In 5.2 it is shown without the optional
asterisk, and in 6 with the optional asterisk.
Proposed action: Make the attribute syntax equal in sections 5.2 and 6.
Make sure that when "Language-Tag" is mentioned, it is only about the
language tag part of the attribute value, and when the attribute value
is mentioned, it is about the complete value, including the optional
modifier.
Changes:
Last line in 5. Change "be" to "contain"
Add [ asterisk ] last in both syntax lines in 5.2.
Multiple small changes in section 5.2. to adjust wording to be more
exact. - See attached draft.
--------------------------------------------------------------------------------------------------------------------------------
2. Reminiscense of earlier syntax.
In a couple of places, there is wording left over from a recently
abandoned syntax for the attributes. In an earlier version, each
attribute value could contain multiple language-tags. Now, there is just
one language-tag in each attribute value.
Changes:
At end of page 6:
Old: "The values constitute a list of languages in preference order"
New: "The values from multiple attributes constitute a list of languages
in preference order per direction"
At end of Section 5.3, the comparison with Accept-Language syntax is not
valid anymore.
Delete: "(similar to SIP Accept-Language syntax)"
----------------------------------------------------------------------------------------------------------------------------------
3. Inexact wording about O/A procedure in section 5.2
The answers are called "accepted language", but within paranthesis it is
mentioned that it is only in most cases that it is selected from the
offer. More suitable is then to just call it just "language":
Old:
" 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')."
New:
"In an answer, 'humintlang-send' indicates the language the answerer
will send (which in most cases is one of the languages in the offer's
'humintlang-recv'), and 'humintlang-recv' indicates the language
the answerer expects to receive (which in most cases is one of the
languages in the offer's 'humintlang-send')."
-----------------------------------------------------------------------------------------------
4. Inexact note at end of section 5.2.
The note at end of 5.2 has a short discussion about accepted media as if
it should possibly be influenced by the matching languages. This
discussion is not really valid. A media section is a request to set up a
media stream, unrelated to the language indications. The devices should
deny media because they are not needed for language communication. This
is made more clear in an extended note.
Old:
"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)."
New:
"Note that media and language negotiation might result in more media
streams being accepted than are needed by the users for language
exchange (e.g., if more preferred and less preferred combinations
of media and language are all accepted). This is normal and accepted,
because the humintlang attribute is not intended to restrict media
streams to be used only for language exchange."
---------------------------------------------------------------------------------
5. Make use of the asterisk modifier on media level with session scope
also for media level purposes
The asterisk modifier optionally appended on attribute values has in the
original -06 draft only a session effect. It is specified to indicate if
the call should be rejected or not if languages do not match. It can be
appended to any humintlang attribute in the whole SDP without any change
in effect. This independancy of placement indicates that it is wrongly
placed. With the current definition, it should be a single separate
session level attribute. Instead of specifying a separate session level
attribute, it is proposed that the asterisk gets an expanded definition,
so that its placement conveys meaning of value for the successful
language negotiation.
It has been discussed in the SLIM WG that the specification lacks two
functions, required by the specifications by other bodies who are
waiting for the results of SLIM real-time work. (e.g. 3GPP TS 22.228 and
ETSI TR 103 201). 3GPP TS 22.228 requires "The system should be able to
negotiate the user's desired language(s) and modalities, per media
stream and/or session, in order of preference." Thus negotiation
with preference indication within the session is required, not only
within each media.
ETSI TR 103 201 says "the Total Conversation user should be able to
indicate the preferred method of communication for each direction of the
session, so that the call-taker can be selected appropriately or an
appropriate assisting service be invoked. " Saying "preferred" means
that it should also be possible to indicate less preferred alternatives.
The most urgent of these functions can be fulfilled in a simple but
sufficient way by extending the meaning of the asterisk. That is the
possibility to indicate a difference in preference between languages in
different modalities. There is an apparent risk that many calls will
start and continue in an inconvenient modaity if this differentiation is
not introduced. See the proposed replaced section 5.3 and extended
examples in section 5.5.
Earlier discussions on this topic has not resulted in a sufficiently
simple mechanism. The extended use of the asterisk proposed here is
intended to introduce the required simplification, and yet meet the most
urgent needs.
Changes:
In 5.2
Old:
"In an offer, each language tag value MAY have an asterisk appended as
the last character (after the language tag). The asterisk indicates
a request by the caller to not fail the call if there is no language
in common."
New:
"In an offer or answer, each attribute value MAY have a modifier
appended as the last character (after the Language-Tag). This
specification defines one value for the modifier; an asterisk ("*"). The
asterisk included in a humintlang attribute value in the SDP indicates a
lower preference for the indicated language and a request by the caller
to not reject the call if there is no language in common."
In 5.3. The whole section replaced by:
"
5.3. Preferences within the session
It is of high importance for a smooth start of a call that the
answering party is answering the call using the best matching
language(s) and modality(ies) suitable for the continuation of the call.
Switching language and modality during the call by agreement between
the participants is often time consuming. Without support of detailed
language and modality negotiation the particiants may have a tendency
to continue the call in the initial language and modality even if a
more convenient common language and modality combination is available.
In order to support the decision on which of the available language(s)
and modality(ies) to use initially in the call, a simple two-level
preference indicator is specified here for inclusion as a modifier
in the humintlang attribute values. The preference indicator is also
used as an indicator that the call SHOULD be established even if no
language match is found.
The asterisk ("*") is used as a preference indicator within the session.
Low relative preference for a language and modality to be used in the
session SHOULD be indicated by appending an asterisk after the language
tag in the attribute value. This indication from the offering party
SHOULD be interpreted by the answering party as a request to use a
higher preferred language and modality when answering the call if
available, but otherwise accept a lower preferred language and
modality combination if that is available. When satisfying languages
and modalities in the offer is regarded to be so important that the
whole call SHOULD be rejected if no match can be provided in the
session in one or both directions, then the asterisk shall not be
appended on any indicated language in the whole session description.
For the case when no specific preference is desired, but the offering
party does not want the call to be rejected, all indicated languages
and modalities SHOULD have an asterisk appended.
In an answer, the language(s) and modality(ies) that the answering
party will use initially in the answer SHOULD be indicated without
an appended asterisk. Any language and modality available for later
use in the session MAY be indicated by a language tag with an
appended asterisk.
In the case when more than two parties participate in the call,
the language and modality indications provided to each party
SHOULD be the sum of the indications from the other parties.
The use of the preference indicator as specified above does
not provide for distinguishing between the case when two or
more language/modality combinations in the same direction
are desired for use simultaneously versus the case when two
or more language/modality combinations for the same directions
are provided as selectable alternatives without specific
preference differentiation. The context or other specifications
may introduce the possibility to distinguish between these cases.
When a party in a call has no indications that two or more
language/modality combinations for each direction are desired
simultaeously in the call, the party SHOULD assume that
satisfying one is sufficient.
Other specifications may add other attribute value modifiers than
the asterisk. If an unknown modifier is detected, the modifier
SHALL be ignored."
In section 6.
Reference to semantics in the attribute registrations are expanded from
5.2 to 5.2-5.3.
---------------------------------------------------------------------------------------------------
6. The cases in the "Silly states" section 5.4 are not all silly.
Section 5.4 contains some proposed interpretations of unusual language
indications.
They are not silly, but just unusual. Therefore change the name of the
section to
"5.4 Unusual indications"
The section contains too weak specification about what to do with the
unusual indications. That may cause a risk that a user who gets
accustomed to one behavior in contact with certain UAs, suddeenly gets
another behavior in contact with another UA.
Change:
Old:
"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)."
To:
"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 SHOULD
ignore the language specified."
Also add the following at the end of 5.4 to explain the choice of
interpretation of a spoken/written language tag in a video medium to be
a request to see the speaker rather than having text captions overlayed
on video.
"There is no difference between language tags for spoken and written
languages. The spoken or written language tag indicated for a video
stream could therefore be interpreted as a capability or request to
use text captions overlayed on the video stream. The interpretation
according to this specification SHALL however be to have a view of
the speaker."
-----------------------------------------------------------------------------------------------------------
7. Examples section 5.5 requires expansion
Section 5.5 Examples has very little explanations and show just a few
cases. The section is proposed to be expanded, with O/A examples with
descriptions and alternative outcomes in order to more thoroughly
describe the intended use.
See 5.5 in the the attached file for the proposed expansion.
------------------------------------------------------------------------------------------------------------
8. Include more fields for attribute registration from 4566bis
Section 6 has the form for attribute registration by IANA. There are a
couple of fields missing that will be important for use of the
specification in the WebRTC environment. Include these fields if that
is allowable according to current IANA procedures and if that does not
delay the publication of this draft. These fields are needed for use of
text media in WebRTC.
Change:
In two locations from:
"Usage Level: media"
to:
"Usage Level: media, dcsa(subprotocol)"
Insert in two locations in the registration forms:
"Mux Category: NORMAL"
---------------------------------------------------------------------------------------------------------------
With these proposed modifications accepted I am convinced that the
result will be useful for its purpose.
Regards
Gunnar Hellstrom
-----------------------------------------
Gunnar Hellström
Omnitor
gunnar.hellstrom@xxxxxxxxxx
+46 708 204 288
Den 2017-02-06 kl. 16:27, skrev The IESG:
The IESG has received a request from the Selection of Language for
Internet Media WG (slim) to consider the following document:
- 'Negotiating Human Language in Real-Time Communications'
<draft-ietf-slim-negotiating-human-language-06.txt> as Proposed
Standard
The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@xxxxxxxx mailing lists by 2017-02-20. Exceptionally, comments may be
sent to iesg@xxxxxxxx instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.
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 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 stream
attributes.
The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-slim-negotiating-human-language/
IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-slim-negotiating-human-language/ballot/
No IPR declarations have been submitted directly on this I-D.
The document contains these normative downward references.
See RFC 3967 for additional information:
draft-saintandre-sip-xmpp-chat: Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): One-to-One Text Chat (None - )
Note that some of these references may already be listed in the acceptable Downref Registry.
--
-----------------------------------------
Gunnar Hellström
Omnitor
gunnar.hellstrom@xxxxxxxxxx
+46 708 204 288
Network Working Group R. Gellens
Internet-Draft Core Technology Consulting
Intended status: Standards Track February 12, 2017
Expires: August 6, 2017
Negotiating Human Language in Real-Time Communications
draft-ietf-slim-negotiating-human-language-06gh
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 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 stream
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 August 6, 2017.
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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Desired Semantics . . . . . . . . . . . . . . . . . . . . . . 5
4. The existing 'lang' attribute . . . . . . . . . . . . . . . . 5
5. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. The 'humintlang-send' and 'humintlang-recv' attributes . 6
5.3. Preferences within the session . . . . . . . . . . . . . 8
5.4. Unusual indications . . . . . . . . . . . . . . . . . . . 8
5.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
9. Changes from Previous Versions . . . . . . . . . . . . . . . 10
9.1. Changes from draft-ietf-slim-...-04 to draft-ietf-
slim-...-06 . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. Changes from draft-ietf-slim-...-02 to draft-ietf-
slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 11
9.3. Changes from draft-ietf-slim-...-01 to draft-ietf-
slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 11
9.4. Changes from draft-ietf-slim-...-00 to draft-ietf-
slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 11
9.5. Changes from draft-gellens-slim-...-03 to draft-ietf-
slim-...-00 . . . . . . . . . . . . . . . . . . . . . . . 11
9.6. Changes from draft-gellens-slim-...-02 to draft-gellens-
slim-...-03 . . . . . . . . . . . . . . . . . . . . . . . 11
9.7. Changes from draft-gellens-slim-...-01 to draft-gellens-
slim-...-02 . . . . . . . . . . . . . . . . . . . . . . . 11
9.8. Changes from draft-gellens-slim-...-00 to draft-gellens-
slim-...-01 . . . . . . . . . . . . . . . . . . . . . . . 11
9.9. Changes from draft-gellens-mmusic-...-02 to draft-
gellens-slim-...-00 . . . . . . . . . . . . . . . . . . . 11
9.10. Changes from draft-gellens-mmusic-...-01 to -02 . . . . . 12
9.11. Changes from draft-gellens-mmusic-...-00 to -01 . . . . . 12
9.12. Changes from draft-gellens-...-02 to draft-gellens-
mmusic-...-00 . . . . . . . . . . . . . . . . . . . . . . 12
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9.13. Changes from draft-gellens-...-01 to -02 . . . . . . . . 13
9.14. Changes from draft-gellens-...-00 to -01 . . . . . . . . 13
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informational References . . . . . . . . . . . . . . . . 14
Appendix A. Historic Alternative Proposal: Caller-prefs . . . . 14
A.1. Use of Caller Preferences Without Additions . . . . . . . 15
A.2. Additional Caller Preferences for Asymmetric Needs . . . 17
A.2.1. Caller Preferences for Asymmetric Modality Needs . . 17
A.2.2. Caller Preferences for Asymmetric Language Tags . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
A mutually comprehensible language is helpful for human
communication. This document addresses the real-time, interactive
side of the issue. A companion document on language selection in
email [I-D.ietf-slim-multilangcontent] addresses the non-real-time
side.
When setting up interactive communication sessions (using SIP or
other protocols), human (natural) language and media modality
(spoken, signed, written) negotiation may be needed. 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 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.
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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. The call could be an emergency
call or perhaps to an airline reservation desk. The language
information is transparent to the voice service provider, 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 could be
automatically handled by 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 process the call.
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. 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 currently 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 a variant of the second case, the voice service
provider invokes a relay service as well as emergency services.) In
the former case, the language need is ancillary and supplemental. In
the non-variant second 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.
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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 assigning to a
specific queue or call taker or bridging in 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
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. Desired Semantics
The desired solution is a media attribute (preferably per direction)
that MAY be used within an offer to indicate the preferred language
of each (direction of a) 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.
(Negotiating multiple simultaneous languages within a media stream is
out of scope, as the complexity of doing so outweighs the
usefulness.)
4. The existing 'lang' attribute
RFC 4566 [RFC4566] specifies an attribute 'lang' which appears
similar to what is needed here, but is not sufficiently detailed for
use here. In addition, it is not mentioned in [RFC3264] and there
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are no known implementations in SIP. Further, there is value in
being able to specify language per direction (sending and receiving).
This document therefore defines two new attributes.
5. Proposed Solution
An SDP attribute (per direction) seems the natural choice to
negotiate human (natural) language of an interactive media stream.
The attribute value SHOULD contain a language tag per 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 video at the SIP level but fail to negotiate any video
media stream at the SDP layer).
The mechanism described here for SDP can be adapted to media
negotiation protocols other than SDP.
5.2. The 'humintlang-send' and 'humintlang-recv' attributes
This document defines two 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",
registered in Section 6 and described here:
a=humintlang-send:<Language-Tag>[asterisk]
a=humintlang-recv:<Language-Tag>[asterisk]
Each can appear multiple times in an offer for a media stream.
In an offer, each 'humintlang-send' attribute indicates a language the
offerer is willing to use when sending using the media, and
'humintlang-recv' indicates a language the offerer is willing to use when
receiving using the media. The Language-Tag values from multiple
attributes constitute a list of languages in preference order per direction
(first is most preferred).
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When a media is intended for language use in one direction only (such
as a user with speech-impairment is sending using text and receiving
using audio), either humintlang-send or humintlang-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 values in the same order. 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, 'humintlang-send' indicates the language the answerer
will send (which in most cases is one of the languages in the offer's
'humintlang-recv'), and 'humintlang-recv' indicates the language
the answerer expects to receive (which in most cases is one of the
languages in the offer's 'humintlang-send').
Each Language-Tag value MUST be a language tag per BCP 47 [RFC5646].
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 or answer, each attribute value MAY have a modifier appended as
the last character (after the Language-Tag). This specification defines one
value for the modifier; an asterisk ("*"). The asterisk included in a humintlang
attribute value in the SDP indicates a lower preference for the indicated
language and a request by the caller to not reject the call if there
is no language in common.
See Section 5.3 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 primarily intended for human language communication SHOULD
specify both (or in some cases as described above, one of) the
'humintlang-send' and 'humintlang-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
'humintlang-send' and 'humintlang-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 values
when processing inbound calls.
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Note that media and language negotiation might result in more media
streams being accepted than are needed by the users for language
exchange (e.g., if more preferred and less preferred combinations
of media and language are all accepted). This is normal and accepted,
because the humintlang attribute is not intended to restrict media
streams to be used only for language exchange.
5.3. Preferences within the session
It is of high importance for a smooth start of a call that the
answering party is answering the call using the best matching
language(s) and modality(ies) suitable for the continuation of the call.
Switching language and modality during the call by agreement between
the participants is often time consuming. Without support of detailed
language and modality negotiation the particiants may have a tendency
to continue the call in the initial language and modality even if a
more convenient common language and modality combination is available.
In order to support the decision on which of the available language(s)
and modality(ies) to use initially in the call, a simple two-level
preference indicator is specified here for inclusion as a modifier
in the humintlang attribute values. The preference indicator is also
used as an indicator that the call SHOULD be established even if no
language match is found.
The asterisk ("*") is used as a preference indicator within the session.
Low relative preference for a language and modality to be used in the
session SHOULD be indicated by appending an asterisk after the language
tag in the attribute value. This indication from the offering party
SHOULD be interpreted by the answering party as a request to use a
higher preferred language and modality when answering the call if
available, but otherwise accept a lower preferred language and
modality combination if that is available. When satisfying languages
and modalities in the offer is regarded to be so important that the
whole call SHOULD be rejected if no match can be provided in the
session in one or both directions, then the asterisk shall not be
appended on any indicated language in the whole session description.
For the case when no specific preference is desired, but the offering
party does not want the call to be rejected, all indicated languages
and modalities SHOULD have an asterisk appended.
In an answer, the language(s) and modality(ies) that the answering
party will use initially in the answer SHOULD be indicated without
an appended asterisk. Any language and modality available for later
use in the session MAY be indicated by a language tag with an
appended asterisk.
In the case when more than two parties participate in the call,
the language and modality indications provided to each party
SHOULD be the sum of the indications from the other parties.
The use of the preference indicator as specified above does
not provide for distinguishing between the case when two or
more language/modality combinations in the same direction
are desired for use simultaneously versus the case when two
or more language/modality combinations for the same directions
are provided as selectable alternatives without specific
preference differentiation. The context or other specifications
may introduce the possibility to distinguish between these cases.
When a party in a call has no indications that two or more
language/modality combinations for each direction are desired
simultaeously in the call, the party SHOULD assume that
satisfying one is sufficient.
Other specifications may add other attribute value modifiers than
the asterisk. If an unknown modifier is detected, the modifier
SHALL be ignored.
5.4. Unusual indications
It is possible to specify an unusual indicationn where the language
specified does not make sense for the media type, such as specifying
a signed language for an audio media stream.
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 SHOULD
ignore the language specified.
However, there are indications which look illogical, but can be
assigned valid interpretations.
A spoken language tag for a video stream in conjunction with an audio
stream with the same language indicates a request for
supplemental video to see the speaker.
There is no difference between language tags for spoken and written
languages. The spoken or written language tag indicated for a video
stream could therefore be interpreted as a capability or request to
use text captions overlayed on the video stream. The interpretation
according to this specification SHALL however be to have a view of
the speaker.
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5.5. Examples
Some informative examples are shown below. Only the most directly
relevant portions of the SDP block are shown, for clarity.
5.5.1 Preference for a spoken language and desire to fail the call if not met
A calling user does only want to use spoken Russian and want the call to
be rejected if this preference is not met. Video is also included in
the offer but not for language communication purpose.
m=audio 49170 RTP/AVP 0
a=humintlang-send:ru
a=humintlang-recv:ru
m=video 51372 RTP/AVP 34
The desire to get the call rejected if the language preferences are
not met is indicated by not appending any asterisk on any of the
humintlang attributes. The answering party has capability in spoken
Russian, but no video capability in the UE, so the answer
will contain the following:
m=audio 54000 RTP/AVP 0
a=humintlang-send:ru
a=humintlang-recv:ru
m=video 0 RTP/AVP 34
5.5.2 Preference for spoken language and capability in sign language
This SDP shows preference for spoken English both ways. The user
also has knowledge in American sign language but by indication of
the asterisks on these attribute values, the user does not prefer
that modality. Text is included in the offer but with no indication
to be used primarily for initial language exchange.
The call is also requested to not be rejected even if none of the
indicated languages can be provided.
m=audio 49170 RTP/AVP 0
a=humintlang-send:en
a=humintlang-recv:en
m=video 51372 RTP/AVP 31 32
a=humintlang-send:ase*
a=humintlang-recv:ase*
m=text 45670 RTP/AVP 100 102
5.5.3 Preference for spoken and capability for written languages
This offer shows preference for spoken Spanish and Basque in this
order, and at lower preference a capability for written Spanish,
Basque and also English. Video is include without any indication
of use for language communication purposes.
The call is also requested to not be rejected even if none of
these languages can be provided.
m=audio 49250 RTP/AVP 20
a=humintlang-send:es
a=humintlang-recv:es
a=humintlang-send:eu
a=humintlang-recv:eu
m=text 45020 RTP/AVP 103 104
a=humintlang-send:es*
a=humintlang-recv:es*
a=humintlang-send:eu*
a=humintlang-recv:eu*
a=humintlang-send:en*
a=humintlang-recv:en*
m=video 54332 RTP/AVP 32 96
A corresponding answer can indicate that the answering party
is only capable to make the call in written English.
The other media are accepted but not intended to be used for
any dominating language communication.
m=audio 60000 RTP/AVP 20
m=text 45040 RTP/AVP 103 104
a=humintlang-recv:en
a=humintlang-send:en
m=video 56000 RTP/AVP 96
5.5.4 Preference for speaking and receiving text
In this example a French user with hearing loss prefers to speak
and prefers to receive real-time text. The user also benefits
from receiving spoken French, but does not handle a conversation
in just spoken French well. The user also does not feel rapid
enough on the keyboard, so sending text is not an alternative.
The calling user would like to indicate that there is value to
receive spoken French together with the recieved text. The
current specification has no way to indicate that preference,
so only the lower preference for received spoken French as an
alternative is indicated.
The calling user want the call to go through even if the
languages do not match. This is indicated by the asterisk
appended on the lower preference attribute for received French.
When calling, the offer may be:
m=audio 49250 RTP/AVP 20
a=humintlang-send:fr
a=humintlang-recv:fr*
m=text 45020 RTP/AVP 103 104
a=humintlang-recv:fr
The answering party detects the two preferred attributes without
an asterisk to be the main preferred languages for the conversation,
and has capability for this combination. The answer will be:
m=audio 49300 RTP/AVP 20
a=humintlang-recv:fr
m=text 45600 RTP/AVP 103 104
a=humintlang-send:fr
The same user is customer of a relay service that can be invoked if
the answer does not satisfy the highest preference of the calling user.
In another call starting with the same offer, the initial answer may
be from a user who has no text capabilities. Instead the answering
party detects that answering with spoken French is an option even
if it is less preferred. The answer in this case indicates spoken
French in both directions.
m=audio 49300 RTP/AVP 20
a=humintlang-recv:fr
a=humintlang-send:fr
m=text 0 RTP/AVP 103 104
The answer is analyzed by the calling user's UE and the lack
of the preferred received French text is detected. The UE
invokes the relay service as a third party in the call, in order
to get the spoken French from the called user to be translated to
French text. The spoken French from the answering party will be
delivered to both the calling user and the relay service. The
invocation of the relay service is a separate application action
and the signaling not included here.
6. IANA Considerations
IANA is kindly requested to add two entries to the 'att-field (media
level only)' table of the SDP parameters registry:
Contact Name: Randall Gellens
Contact Email Address: rg+ietf@xxxxxxxxxxxxxxxxx
Attribute Name: humintlang-recv
Attribute Syntax:
humintlang-value = Language-Tag [ asterisk ]
; Language-Tag defined in RFC 5646
asterisk = "*"
Attribute Semantics: Described in Section 5.2-5.3 of TBD: THIS DOCUMENT
Usage Level: media, dcsa(subprotocol)
Charset Dependent: No
Purpose: See Section 5.2-5.3 of TBD: THIS DOCUMENT
Mux Category: NORMAL
O/A Procedures: See Section 5.2-5.3 of TBD: THIS DOCUMENT
Reference: TBD: THIS DOCUMENT
Contact Name: Randall Gellens
Contact Email Address: rg+ietf@xxxxxxxxxxxxxxxxx
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Attribute Name: humintlang-send
Attribute Syntax:
humintlang-value = Language-Tag [ asterisk ]
; Language-Tag defined in RFC 5646
asterisk = "*"
Attribute Semantics: Described in Section 5.2-5.3 of TBD: THIS DOCUMENT
Usage Level: media, dcsa(subprotocol)
Charset Dependent: No
Purpose: See Section 5.2-5.3 of TBD: THIS DOCUMENT
Mux Category: NORMAL
O/A Procedures: See Section 5.2-5.3 of TBD: THIS DOCUMENT
Reference: TBD: THIS DOCUMENT
7. Security Considerations
The Security Considerations of BCP 47 [RFC5646] apply here. 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.
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
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
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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 Appendix A ("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.
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.
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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 "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.
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.
9.14. 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. Contributors
Gunnar Hellstrom deserves special mention for his reviews,
assistance, and especially for contributing the core text in
Appendix A.
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.
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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>.
[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>.
12.2. Informational References
[I-D.ietf-slim-multilangcontent]
Tomkinson, N. and N. Borenstein, "Multiple Language
Content Type", draft-ietf-slim-multilangcontent-06 (work
in progress), October 2016.
[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>.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004,
<http://www.rfc-editor.org/info/rfc3840>.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, DOI 10.17487/RFC3841, August 2004,
<http://www.rfc-editor.org/info/rfc3841>.
Appendix A. Historic Alternative Proposal: Caller-prefs
The decision to base the proposal at the media negotiation level, and
specifically to use SDP, came after significant debate and
discussion. It is possible to meet the objectives using a variety of
mechanisms, but none are perfect. Using SDP means dealing with the
complexity of SDP, and leaves out real-time session protocols that do
not use SDP. The major alternative proposal was to use SIP. Using
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SIP leaves out non-SIP session protocols, but more fundamentally,
would occur at a different layer than the media negotiation. This
results in a more fragile solution since the media modality and
language would be negotiated using SIP, and then the specific media
formats (which inherently include the modality) would be negotiated
at a different level (typically SDP, especially in the emergency
calling cases), making it easier to have mismatches (such as where
the media modality negotiated in SIP don't match what was negotiated
using SDP).
An alternative proposal was to use the SIP-level Caller Preferences
mechanism from RFC 3840 [RFC3840] and RFC 3841 [RFC3841].
The Caller-prefs mechanism includes a priority system; this would
allow different combinations of media and languages to be assigned
different priorities. The evaluation and decisions on what to do
with the call can be done either by proxies along the call path, or
by the addressed UA. Evaluation of alternatives for routing is
described in RFC 3841 [RFC3841].
A.1. Use of Caller Preferences Without Additions
The following would be possible without adding any new registered
tags:
Potential callers and recipients MAY include in the Contact field in
their SIP registrations media and language tags according to the
joint capabilities of the UA and the human user according to RFC 3840
[RFC3840].
The most relevant media capability tags are "video", "text" and
"audio". Each tag represents a capability to use the media in two-
way communication.
Language capabilities are declared with a comma-separated list of
languages that can be used in the call as parameters to the tag
"language=".
This is an example of how it is used in a SIP REGISTER:
REGISTER user@xxxxxxxxxxx
Contact: <sip:user1@xxxxxxxxxxx> audio; video; text;
language="en,es,ase"
Including this information in SIP REGISTER allows proxies to act on
the information. For the problem set addressed by this document, it
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is not anticipated that proxies will do so using registration data.
Further, there are classes of devices (such as cellular mobile
phones) that are not anticipated to include this information in their
registrations. Hence, use in registration is OPTIONAL.
In a call, a list of acceptable media and language combinations is
declared, and a priority assigned to each combination.
This is done by the Accept-Contact header field, which defines
different combinations of media and languages and assigns priorities
for completing the call with the SIP URI represented by that Contact.
A priority is assigned to each set as a so-called "q-value" which
ranges from 1 (most preferred) to 0 (least preferred).
Using the Accept-Contact header field in INVITE requests and
responses allows these capabilities to be expressed and used during
call set-up. Clients SHOULD include this information in INVITE
requests and responses.
Example:
Accept-Contact: *; text; language="en"; q=0.2
Accept-Contact: *; video; language="ase"; q=0.8
This example shows the highest preference expressed by the caller is
to use video with American Sign Language (language code "ase"). As a
fallback, it is acceptable to get the call connected with only
English text used for human communication. Other media may of course
be connected as well, without expectation that it will be usable by
the caller for interactive communications (but may still be helpful
to the caller).
This system satisfies all the needs described in the previous
chapters, except that language specifications do not make any
distinction between spoken and written language, and that the need
for directionality in the specification cannot be fulfilled.
To some degree the lack of media specification between speech and
text in language tags can be compensated by only specifying the
important medium in the Accept-Contact field.
Thus, a user who wants to use English mainly for text would specify:
Accept-Contact: *;text;language="en";q=1.0
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While a user who wants to use English mainly for speech but accept it
for text would specify:
Accept-Contact: *;audio;language="en";q=0.8
Accept-Contact: *;text;language="en";q=0.2
However, a user who would like to talk, but receive text back has no
way to do it with the existing specification.
A.2. Additional Caller Preferences for Asymmetric Needs
In order to be able to specify asymmetric preferences, there are two
possibilities. Either new language tags in the style of the
humintlang parameters described above for SDP could be registered, or
additional media tags describing the asymmetry could be registered.
A.2.1. Caller Preferences for Asymmetric Modality Needs
The following new media tags should be defined:
speech-receive
speech-send
text-receive
text-send
sign-send
sign-receive
A user who prefers to talk and get text in return in English would
register the following (if including this information in registration
data):
REGISTER user@xxxxxxxxxxx
Contact: <sip:user1@xxxxxxxxxxx> audio;text;speech-send;text-
receive;language="en"
At call time, a user who prefers to talk and get text in return in
English would set the Accept-Contact header field to:
Accept-Contact: *; audio; text; speech-receive; text-send;
language="en";q=0.8
Accept-Contact: *; text; language="en"; q=0.2
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Note that the directions specified here are as viewed from the callee
side to match what the callee has registered.
A bridge arranged for invoking a relay service specifically arranged
for captioned telephony would register the following for supporting
calling users:
REGISTER ct@xxxxxxxxxxx
Contact: <sip:ct1@xxxxxxxxxxx> audio; text; speech-receive;
text-send; language="en"
A bridge arranged for invoking a relay service specifically arranged
for captioned telephony would register the following for supporting
called users:
REGISTER ct@xxxxxxxxxxx
Contact: <sip:ct2@xxxxxxxxxxx> audio; text; speech-send; text-
receive; language="en"
At call time, these alternatives are included in the list of possible
outcome of the call routing by the SIP proxies and the proper relay
service is invoked.
A.2.2. Caller Preferences for Asymmetric Language Tags
An alternative is to register new language tags for the purpose of
asymmetric language usage.
Instead of using "language=", six new language tags would be
registered:
humintlang-text-recv
humintlang-text-send
humintlang-speech-recv
humintlang-speech-send
humintlang-sign-recv
humintlang-sign-send
These language tags would be used instead of the regular
bidirectional language tags, and users with bidirectional
capabilities SHOULD specify values for both directions. Services
specifically arranged for supporting users with asymmetric needs
SHOULD specify only the asymmetry they support.
Gellens Expires August 6, 2017 [Page 18]
Internet-Draft Negotiating Human Language February 2017
Author's Address
Randall Gellens
Core Technology Consulting
Email: rg+ietf@xxxxxxxxxxxxxxxxx
Gellens Expires August 6, 2017 [Page 19]