Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S

Sebastian Moeller <> Tue, 17 March 2020 15:07 UTC

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From: Sebastian Moeller <>
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Date: Tue, 17 Mar 2020 16:07:27 +0100
Cc: Jonathan Morton <>, Ingemar Johansson S <>, "" <>, "" <>
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To: Ingemar Johansson S <>
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Subject: Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S
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HI Ingemar,

> On Mar 17, 2020, at 08:02, Ingemar Johansson S <> wrote:
> Hi Jonathan
> Please see inline
> /Ingemar
> [...]
>> I've looked briefly at the code, and I think true SCE support could also
> be
>> implemented without difficulty; you already have sufficient ECN codepoint
>> feedback from the receiver.  You would need to apply the L4S response (or
>> something broadly equivalent) when noting ECT(1) codepoints, and the
>> conventional Multiplicative Decrease response when noting CE codepoints.
>> Obviously, this also means ECT(0) must be emitted at origin, not ECT(1).
>> I'd be happy to advise further on work in this direction, if you think
> it's
>> promising.
> [IJ] Surely possible. But like said before, I am not going there. I don't
> see that it is worth spending effort on this as it should be apparent by now
> that SCE would not give better performance than L4S .

	[SM] My prediction is, that both will give you more or less equal performance, because both offer the kind of fast feedback that you designed SCReAM to require. I do understand, that you do not want to change your test vehicle for yet another variant of ECN and that is fine and fair. But no matter which of the higher-temporal-fidelity, lower amplitude ECN schemes is left standing once the dust settles, any will work well for SCReAM (or rather better than rfc3168 ECN).

> I'd rather spend my
> time on improving SCReAM, or any other congestion control algorithm for low
> latency steaming media to utilize the potential with L4S better.

	[SM] That is obviously your prerogative, but it also IMHO makes SCReAM not really a helpful data point in the discussion about how to deploy 1/p-style congestion control to the internet, as it does not help to choose between the contenders. Unless I missed something, the discussion is less about "if" we should deploy 1/p fast congestion signaling and more about "how" and which variant.

> But the
> SCReAM code is of course available for anybody who wants to with it in any
> desired direction.

	[SM] Thanks for the open project!

Best Regards

>> - Jonathan Morton