Re: [Slim] Eric Rescorla's No Objection on draft-ietf-slim-negotiating-human-language-19: (with COMMENT)

Eric Rescorla <> Sun, 07 January 2018 14:35 UTC

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From: Eric Rescorla <>
Date: Sun, 07 Jan 2018 06:34:39 -0800
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To: Randall Gellens <>
Cc: The IESG <>,,,, Bernard Aboba <>
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Subject: Re: [Slim] Eric Rescorla's No Objection on draft-ietf-slim-negotiating-human-language-19: (with COMMENT)
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On Sat, Jan 6, 2018 at 7:22 PM, Randall Gellens <>

> At 5:39 PM -0800 1/6/18, Eric Rescorla wrote:
>  Document: draft-ietf-slim-negotiating-human-language-17.txt
>>  1. I'm not marking this first point DISCUSS, but I do think it's
>>  important it be addressed and I trust the AD will ensure that it is.
>>  This document is ambiguous about the contents of the answer
>>  attribute. Specifically, it says:
>>     In an answer, 'hlang-send' is the language the answerer will send if
>>     using the media for language (which in most cases is one of the
>>     languages in the offer's 'hlang-recv'), and 'hlang-recv' is the
>>     language the answerer expects to receive if using the media for
>>     language (which in most cases is one of the languages in the offer's
>>     'hlang-send').
>>  However, the next paragraph permits >1 tag, as does the ABNF in S 6.1.
>>     Each value MUST be a list of one or more language tags per BCP 47
>>     [RFC5646], separated by white space.  BCP 47 describes mechanisms for
>>     matching language tags.  Note that [RFC5646] Section 4.1 advises to
>>     "tag content wisely" and not include unnecessary subtags.
>>  So, how am I supposed to interpret an answer with >1 tag? Is this
>>  forbidden? I can imagine a number of semantics, but it's important
>>  it be clear in the document.
> Thank you for catching this.  I think the first paragraph is correct and
> the second paragraph and ABNF are in error, they were copied from the offer
> and not fixed.  The intent is that a single language per direction be
> arrived it per media stream.
>  2. The negotiation structure here does not match that which is
>>  conventionally used with SDP, where each side indicates the formats it
>>  is prepared to receive and the other side can send any of them. Why
>>  did you use this structure? One reason you might is that you expect
>>  the answer to resolve which language is in use, however because SIP
>>  supports early media (i.e., media which is delivered prior to the
>>  answer.)
> In light of my reply to (1), do you still feel that the negotiation
> structure doesn't match usual offer/answer behavior?

Yes. That doesn't necessarily mean it's wrong, of course. Conventions are
just that, conventions.


> --
> Randall Gellens
> Opinions are personal;    facts are suspect;    I speak for myself only
> -------------- Randomly selected tag: ---------------
> We do not stop playing because we grow old; we grow old because we stop
> playing.             --U.S. Supreme Court Justice Oliver Wendell Holmes