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

Randall Gellens <> Mon, 08 January 2018 17:41 UTC

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Date: Mon, 08 Jan 2018 09:41:16 -0800
To: Eric Rescorla <>
From: Randall Gellens <>
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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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At 5:56 PM -0800 1/7/18, Eric Rescorla wrote:

>  On Sun, Jan 7, 2018 at 5:22 PM, Randall Gellens 
> <<>> wrote:
>  At 6:36 AM -0800 1/7/18, Eric Rescorla wrote:
>   On Sat, Jan 6, 2018 at 7:31 PM, Bernard Aboba 
> <<mailto:<>><>> 
> wrote:
>   On Jan 6, 2018, at 6:55 PM, Eric Rescorla 
> <<mailto:<>><>> 
> wrote:
>   For disabled users, the capabilities may not be symmetric.
>   But this is true for ordinary SDP as well. I might be able to 
> receive H.264 but not send it.
>   [BA] Thanks. The draft should explain the reasoning. IMHO the 
> argument goes sonething like this:
>   A pure recv/recv negotiation will not necessarily disclose 
> beforehand what special services are needed for the call - services 
> (e.g. ASL interpretation or RTT handling) that could take time to 
> acquire.
>   Since the actual video media sent is not labelled as ASL even if 
> the answerer has ASL interpreters it can pull in and therefore 
> advertises in SDP ASL reception capability in video, a recv/recv 
> negotiation doesn't tell the Answerer that the Offerer will need 
> them, so the Answerer may need to (frantically) arrange for ASL 
> interpretation after initial receipt of media. In an emergency, 
> that can chew up valuable time.
>   Thanks. I think it would be helpful to put this logic in the draft.
>  I am not clear on what logic we want to add to the draft, or what 
> about the draft this logic is explaining.
>  It would be helpful to explain in the draft why you have deviated 
> from the otherwise near-universal SDP negotiation pattern of each 
> side advertising what it accepts.

I'm not clear on what you're referring to.  Are you talking about 
early offer versus late offer?  To my understanding, the draft 
follows a typical offer/answer model: the caller lists the media and 
languages it supports, and the callee answers with the media and 
languages it supports.

>   That said, as I noted in my review, it is still possible to get 
> some media (early media) prior to receiving the answer, so this 
> isn't a complete solution.
>  The draft provides a useful mechanism that will be helpful.  As an 
> example of the fact that others find it useful, NENA has included 
> it in it's next-generation emergency call architecture standards. 
> The draft does not try to solve all problems related to human 
> language in real-time calling.
>  I don't think I claimed it wasn't useful.
>  The rationale provided for this design is that you wish to have the 
> answerer notify the offerer of which language it would be 
> providing. The point I am making is that there is at least one 
> important case where this design does not provide that, which seems 
> like it's relevant to the design question.

I think I'm still not understanding your concern.  Even without 
providing a mechanism for the caller to know the languages used with 
any early media, the draft is still meeting a need.

Randall Gellens
Opinions are personal;    facts are suspect;    I speak for myself only
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Imagination is more important than facts. --Albert Einstein