Last Call Review of draft-ietf-slim-negotiating-human-language-06

Request Review of draft-ietf-slim-negotiating-human-language
Requested rev. no specific revision (document currently at 23)
Type Last Call Review
Team General Area Review Team (Gen-ART) (genart)
Deadline 2017-02-20
Requested 2017-02-06
Other Reviews Opsdir Last Call review of -08 by Mahesh Jethanandani (diff)
Secdir Last Call review of -22 by Taylor Yu (diff)
Genart Last Call review of -19 by Dale Worley (diff)
Review State Completed
Reviewer Dale Worley
Review review-ietf-slim-negotiating-human-language-06-genart-lc-worley-2017-02-17
Posted at
Reviewed rev. 06 (document currently at 23)
Review result Ready with Nits
Draft last updated 2017-02-17
Review completed: 2017-02-17


I am the assigned Gen-ART reviewer for this draft.  The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
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For more information, please see the FAQ at

Document:  draft-ietf-slim-negotiating-human-language-06
Reviewer:  Dale R. Worley
Review Date:  2017-02-17
IETF LC End Date:  2017-02-20
IESG Telechat date:  [unknown]

       This draft is basically ready for publication, but has nits
       that should be fixed before publication.

* Technical comments

A. Call failure

If a call fails due to no available language match, in what way(s)
does it fail?  Section 5.3 says

   If such an offer is received, the receiver MAY
   reject the media, ignore the language specified, or attempt to
   interpret the intent

But I suspect it's also allowed for the UAS to fail the call at the
SIP level.  Whether or not that is allowed (or at least envisioned)
should be described.  And what response code(s)/warn-code(s) should be
used for that?

B. Audio/Video coordination

   5.2.  New '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

And there's a similar paragraph in 5.4:

>    A spoken language tag for a video stream in conjunction with an audio
>    stream with the same language might indicate a request for
>    supplemental video to see the speaker.

I think this mechanism needs to be described more exactly, and in
particular, it should not depend on the UA understanding which
language tags are spoken language tags.  It seems to me that a
workable rule is that there is an audio stream and a video stream and
they specify exactly the same language tag in their respective
humintlang attributes.  In that case, it is a request for a spoken
language with simultaneous video of the speaker, and those requests
should be considered satisfied only if both streams can be

* The following three items are adjustments to the design which I'd
like to know have been considered.

C. "humintlang" seems long to me

Given the excessive length of SDP in practice, it seems to me that a
shorter attribute name would be desirable.  E.g., "humlang" as was
used in some previous versions.  Or is there a coordinated usage with
other names in the "hum*lang" pattern?

D. Use the Accept-Language syntax

It seems to me that it would better to use the Accept-Language syntax
for the attribute values.  This allows (1) specifiying the quality of
language experience, allowing clear description of bilingualism, (2) a
unified method of specifying whether or not arbitrary languages are
acceptable, and (3) abbreviating SDP descriptions.

In a way, the fact that the current proposal seems to require (but
does not directly specify) the coordinated absence/presence of an
asterisk on all of the repetitions of humintlang-send or
humintlang-recv is a warning that the syntax doesn't represent the
semantics as well as it might.

E. Have an attribute to abbreviate the bidirectionally-symmetric case

Note that all examples are bidirectionally symmetric, and the text
says that requests and responses SHOULD be bidirectionally symmetric.
So it would be a very useful abbreviation to define
"humintlang=<value>" to be equivalent to the combination of
"humintlang-send=<value>" and "humintlang-recv=<value>".

Combining proposals C, D, and E, the examples become

      m=audio 49170 RTP/AVP 0

      m=video 51372 RTP/AVP 31 32

      m=audio 49250 RTP/AVP 20

      m=text 45020 RTP/AVP 103 104

which requires about half as many characters as they have now.

* Editorial comments and nits


   This document describes the need and a solution using new SDP stream

I don't think the term "stream attribute" is used in RFC 4566.
Instead, it uses "media attribute".

1.  Introduction

   caller and callee know each other or there is contextual or out of
   band information from which the language(s) and media modalities can

I think this context, it's preferred to hyphenate "out-of-band" to
make it clearly be an adjective.

   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.

I think s/and not limited to/and is not limited to/ reads more smoothly.

   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.

I think s/preferred, the callee/preferred; the callee/ because the
sentence is the concatenation of two sentences.

Perhaps s/in-common/shared/.

   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. 

I think it's even broader than "transparent to a voice service
provider" -- it's transparent to any serivice provider, assuming that
the media are language-neutral.

   In the case of a call to e.g., an airline, the call could be
   automatically handled by a Spanish-speaking agent.

I think s/handled by/routed to/ is the usual usage.

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.

In this one instance, I think you want to use "language(s)" to drive
home that that multiple languages can be specified:  "within an offer
to indicate the preferred language(s)".

   (Negotiating multiple simultaneous languages within a media stream is
   out of scope, as the complexity of doing so outweighs the

You might want to say instead "(Negotiating multiple simultaneous
languages within a media stream is out of scope for this document.)"
to ensure that nobody decides to argue whether "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.

"for use here" isn't quite right.  Maybe "is not sufficiently specific
or flexible to satisfy the requirements".

   In addition, it is not mentioned in [RFC3264]

"it" is somewhat ambiguous here, perhaps change to "the 'lang' attribute".

5.  Proposed Solution

Perhaps /Proposed Solution/Solution/, since once this draft is
approved, it becomes the solution.

5.2.  New 'humintlang-send' and 'humintlang-recv' attributes

      a=humintlang-send:<language tag>
      a=humintlang-recv:<language tag>

This is presented as the generic form of the attributes, but there is
no indication of the posible asterisk.

   The values constitute a list of languages
   in preference order (first is most preferred).

"The values" isn't very clear, because the values are in successive
attributes.  You want to say something like "The sequence of values in
the occurrences of one of these attributes constitutes ...".  However,
see the technical comments above.

   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, one of) the 'humintlang-send' and
   'humintlang-recv' attributes.

Probably s/assumed/inferred/.

Could you be more accurate by
s/or in some cases/or for unidirectional streams/?

5.3.  Advisory vs Required

   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.

The construction of this paragraph isn't quite complete.  It says that
if an asterisk is present, a request shouldn't fail, but it doesn't
say that if no asterisk is present, a request should fail if there is
no language match.  And it's the latter condition that makes the
second sentence meaningful.  So I think you want to insert between the
two sentences one regarding the absence of an asterisk.

5.5.  Examples

Given that the combined audio/video mechanism is the only irregularity
in this system, there ought to be an example of it.  E.g.,

   An example of a supplemental video stream with a spoken language
   audio stream:

      m=video 51372 RTP/AVP 31 32

      m=audio 49250 RTP/AVP 20

6.  IANA Considerations

      humintlang-value =  Language-Tag [ asterisk ]
                          ; Language-Tag defined in RFC 5646
      asterisk         =  "*"

s/Language-Tag defined in RFC 5646/Language-Tag as defined in RFC 5646/

But perhaps also s/RFC 5646/BCP 47/, which ensures that "humintlang"
tracks the current version of language tags.

Appendix A.  Historic Alternative Proposal: Caller-prefs

   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).

"the media modality and language would be negotiated using SIP" isn't
quite the right way to say it because SIP isn't explicitly negotiating
the modality.  Better would be

   ... the language (and by implication the media modality) would be
   negotiated using SIP, and then the specific media (which inherently
   include the modalities and formats) would be negotiated at a
   different level ...