[Slim] Human-language Issue 26: Asterisk modifier scope

[Bernard Aboba <[e-mail]>]

Issue: https://trac.ietf.org/trac/slim/ticket/26

The remaining open aspect of Issue 26 relates to the scope of  the "*".

Paul Kyzivat summarized the problem in his post on February 13, 2017 (see:
  https://www.ietf.org/mail-archive/web/slim/current/msg00737.html)


   - The text needs to be improved simply to properly explain and define
   the syntax related to the "*" as you intend to use it.


   - the use of the "*" to indicate what it does is confusing. It is using
   a media level attribute "parameter" to signify a session level property.
   This has been brought up before, but simply rejected without (IMO) adequate
   justification. There seems to be some love for this particular syntax. ISTM
   that in part Gunnar is trying to adapt this syntax so that it both makes
   sense as a media-level attribute and simultaneously can satisfy the session
   level need that has been identified.

These concerns do not appear to have been addressed in
https://tools.ietf.org/html/draft-ietf-slim-negotiating-human-language-13

Section 5.2 states:

   In an offer, a list of language tags MAY have an asterisk appended at
   the end.  An asterisk appended to any value in any media in an offer
   indicates a request by the caller to the callee to not fail the call
   if there is no language in common.  See Section 5.3
<https://tools.ietf.org/html/draft-ietf-slim-negotiating-human-language-13#section-5.3>
for more
   information and discussion.


Section 5.3 states:

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

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


Some questions that come to mind:

1. Does the inclusion of an * represent a request for the callee to not
fail the call based on an inability to negotiate a common language only for
the particular hlang-recv or hlang-send line that contains the "*"?

That is, if an "*" is included on some hlang-recv/send lines but not other
ones, would it tell the callee that it can fail the call if a
common-language can't be negotiated for the lines without an "*"?

-OR-

2. Does the inclusion of an "*" on any hlang-recv/send line imply the
inclusion of an "*" on other hlang-recv/send lines, either within a given
m-line or on other m-lines?


-OR-


3. To provide clarity, should the "*" merely be considered an indication
that the offerer will accept "any language"?  If so, should it be valid
only for hlang-recv lines and can an Answer respond with a * in its
hlang-recv line?