[Make-wifi-fast] On the 802.11 performance anomaly and an airtime fairness scheduler to fix it

[Jonathan Morton]

> On 3 Jul, 2016, at 10:06, David Lang <david at lang.hm> wrote:
> 
> do they delay the L2 Ack until the L4 ack comes back? If so, how does that work on long-latency connections where it takes a long time for the L4 ack to show up?

I’m pretty sure it’s only meant to work when the TCP endpoint is local to the receiving station, assuring low turnaround latency.  This is the typical case, so it’s a win.

With that said, there’s no fundamental reason why the piggybacked L4 ack need be the one corresponding to the L2 ack.  It just needs to be a small packet that won’t unduly extend the airtime occupied by the ack anyway, and which won’t mind being lost if the L2 ack gets squashed.  A scheme allowing a certain amount of slop in this way would accommodate remote TCP endpoints as well as local ones.

 - Jonathan Morton