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Re: [rtcweb] Fix for DSCP bleaching issue suggested

Bernard Aboba <bernard.aboba@gmail.com> Thu, 04 August 2016 13:30 UTC

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From: Bernard Aboba <bernard.aboba@gmail.com>
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Date: Thu, 04 Aug 2016 06:30:18 -0700
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To: Harald Alvestrand <harald@alvestrand.no>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Fix for DSCP bleaching issue suggested
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On Aug 2, 2016, at 01:23, Harald Alvestrand <harald@alvestrand.no> wrote:
> 
> My proposed text for the DSCP blocking/bleaching issue is here:
> 
> https://github.com/rtcweb-wg/rtcweb-transport/pull/30
> 
> Note that this differs from what was said at the IETF meeting - after
> considering, I didn't see a reason to recommend ICE restart.
> 
> The text does not contain MUST or SHOULD. This is implementation advice.
> Is this approprate, given the current state of our knowledge of the issue?
> 
> Diff:
> 
> @@ -344,6 +344,18 @@
>         of packets with certain DSCP markings. The detection of these
>         conditions is implementation dependent.</t>
> 
> +        <t>A particularly hard problem is when one media transport uses
> +        multiple DSCP code points, where one may be blocked and another
> may be
> +        allowed. This is allowed for video in <xref
> +        target="I-D.ietf-tsvwg-rtcweb-qos"/>. Implementations need to
> diagnose
> +        this scenario; one possible implementation is to send initial ICE
> +        probes with DSCP 0,

[BA]Seems reasonable.

> and send ICE probes on all the DSCP code points
> +        that are intended to be used once a candidate pair has been
> selected.

[BA] Not sure what "probe" means here - are you referring to keepalives and/or consent checks?

> +        If one or more of the DSCP-marked probes fail, the sender will
> switch
> +        the transport to using DSCP 0. This can be carried out
> simultaneously
> +        with the initial media traffic; on failure, the initial data
> may need
> +        to be resent.</t>

[BA] Losing a single consent check does not tell you much, and if some consent checks with a marking were responded to, changing markings based on a subsequent loss is most probably a bad idea. Does "resent" refer to RFC 4588 (RTX)? 

> +
>         <t>All packets carrying data from the SCTP association
> supporting the
>         data channels MUST use a single DSCP code point. The code point
> used
>         SHOULD be that recommended by <xref
> 
> Comments welcome, especially if they come today! - the item is on
> Thursday's telechat, and it would be nice to release a fixed version
> well before the telechat.
> 
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb

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