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

Bernard Aboba <> Sun, 07 January 2018 03:31 UTC

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From: Bernard Aboba <>
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To: Eric Rescorla <>
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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 Jan 6, 2018, at 6:55 PM, Eric Rescorla <> 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.