[Make-wifi-fast] Thoughts on tackling airtime fairness

[Toke Høiland-Jørgensen]

Luca Muscariello <luca.muscariello at gmail.com> writes:

>  Do you happen to recall what precision you achieved or how much the
>  precision was really important? Several papers seem to assume that very
>  high precision is not terribly important since it all evens out in the
>  end, and I can see how that could be true; but would like to have it
>  confirmed :)
>
> what do you mean with precision?
> Do you mean in measuring the PHY rate? 
> Short term vs long term measurements? else?

Yes, in measuring the rate. Was this a per-packet thing, and were you
actually able to get information sufficiently accurate to achieve the
desired level of fairness? And by what mechanism? Was this in the driver
or higher up in the stack?

> The hard part was adaptiveness. Correlation between the speed of the
> STA, the PHY rate controller and quanta updates in SFQ.

Yes, that's what I though :)

> Ideally we were trying to approach something like 
> downlink channel scheduling in HSDPA where you have slotted time TX
> and polling. A slot in HSDPA (but also LTE) is a burst  of fixed time size of several packets.
> Similar to what you want to achieve in your email point 1.

Yeah, if we could just switch to TDMA a lot of things would be much
simpler...

> As a side note, there are several differences in aggregates in 802.11n
> and HSDPA/LTE as in the latter the scheduler can send an aggregate
> containing packets using different modulation/coding schemes to reach
> different stations with a single aggregate transmission.

Neat.

> For the records, this feature was rejected in the 802.11n amendement
> but discussed by the group as it makes the chip more expensive.

Right; not terribly surprised, but still a shame.

-Toke