Re: [tsvwg] Neal Cardwell's rationale for supporting ECT(1) as an input/L4S signal

[Jeremy Harris <[e-mail]>]

On 08/05/2020 16:19, Neal Cardwell wrote:
> - SCE is basically an extension of RFC3168 ECN: senders mark their packets
> ECT(0), and respond to CE like RFC 3168 says they should, by halving cwnd.
> This would not work well for large sites with a substantial installed base
> of shallow-threshold (DCTCP-style) ECN: if these sites marked their traffic
> with ECT(0) to try to use SCE, their local switches configured for
> shallow-threshold ECN would make CE marks at low queue occupancies, which
> would cause large RFC3681-style reductions in cwnd, which would cause
> underutilization. To the best of my knowledge this applies to several large
> Internet services.

Wait, that doesn't match my understanding.  In such an example site
using SCE I would expect ECT(0) marking only at "large" queue
occupancies (and resulting in cwnd halving when seen), but more
prevalently ECT(1) marking at "small" queue occupancies - resulting
in some smaller percentage (than 50) decrease in cwnd when seen.

What did I miss?

-- 
Cheers,
  Jeremy