[iccrg] IETF104 ICCRG TCP Prague presentation

[Sebastian Moeller <[e-mail]>]

I finally got around to see the TCP Prague presentation, nice, especially the part around slide 11 "Fallback to Reno-friendly on Classic ECN" caught my interest.

The claim made there is that L4S's inability to properly deduce the type of CE signal (normal ECN response expected versus DCTCP-like ECN response expected) would only matter in the case of ECN-marking single queue AQMs and not for flow-queueung AQMs, and I would like to argue that that should be measured rather than solved by declaration.


Consider the following case, that get's more and more common: traffic shaping for both ingress and egress somewhere on the end-customer side of an internet access link. For egress I agree with the rationale, that flow-queueing/fair-queueung should deal with flows that appear unresponsive sooner or later (but I note that this still will increase the memory required for the queueing and should not be considered ideal behavior).
But for ingress shaping downstream of the "true" bottleneck (I am simplifying over some details here) this rationale falls apart, the unexpected packets the L4S sender kept sending since it misinterpreted the CE mark, will still hog valuable bandwidth of the internet access link, and hence fair queuing on the home end of the true bottleneck will not isolate that homenet from the L4S misunderstanding.

I would be delighted to learn where my assumptions are wrong...

Regards
	Sebastian Moeller