[Bloat] incremental deployment, transport and L4S (Re: when does the CoDel part of fq_codel help in the real world?)

[Jonathan Morton]

> On 29 Nov, 2018, at 9:28 am, Mikael Abrahamsson <swmike at swm.pp.se> wrote:
> 
> This is one thing about L4S, ETC(1) is the last "codepoint" in the header not used, that can statelessly identify something. If anyone sees a better way to use it compared to "let's put it in a separate queue and CE-mark it agressively at very low queue depths and also do not care about re-ordering so a ARQ L2 can re-order all it wants", then they need to speak up, soon.

You are essentially proposing using ECT(1) to take over an intended function of Diffserv.  In my view, that is the wrong approach.  Better to improve Diffserv to the point where it becomes useful in practice.  Cake has taken steps in that direction, by implementing some reasonable interpretation of some Diffserv codepoints.

My alternative use of ECT(1) is more in keeping with the other codepoints represented by those two bits, to allow ECN to provide more fine-grained information about congestion than it presently does.  The main challenge is communicating the relevant information back to the sender upon receipt, ideally without increasing overhead in the TCP/IP headers.

 - Jonathan Morton