[Bloat] Bufferbloat on 4G Connexion

[Luca Muscariello]

On Wed, Oct 23, 2019 at 2:27 PM Toke Høiland-Jørgensen <toke at redhat.com>
wrote:

> Rich Brown <richb.hanover at gmail.com> writes:
>
> >> On Oct 23, 2019, at 5:54 AM,<erik.taraldsen at telenor.com <mailto:
> erik.taraldsen at telenor.com>> wrote:
> >>
> >> If you could influence the 4G vendors to de-bloat their equipment,
> >> would you recommend BQL, L4S or codel/cake?
> >
> > I've been enjoying this discussion and wonder whether the work going
> > on in the make-wifi-fast
> > (https://lists.bufferbloat.net/pipermail/make-wifi-fast/) is relevant.
> >
> > I only have a 30,000 foot understanding of this work, but it seems the
> > use of AQL (Airtime Queue Limit) maps better onto the vagaries of
> > 4G/5G radio transmissions than BQL. Specifically, having a measurement
> > of the actual time it takes to transmit a packet might give additional
> > information about the current link speed, with the potential for
> > adjusting the codel target, etc.
>
> Indeed, I suspect something like AQL would work for LTE as well. At the
> right level; think this might need to be in the firmware (which in turn
> could push back on the host).
>
> > Separately, I also wonder whether the Air Time Fairness algorithm
> > might provide a benefit if the cellphone tower station manufacturers
> > chose to get into the game.
>
> LTE base stations already does TDMA scheduling (which they can do easily
> because they are centralised and own the license band); airtime fairness
> is about getting the same benefits into WiFi that LTE has been enjoying
> from the get-go :)
>

There is one main difference between ATF and the kind of TDMA
realized by an LTE scheduler (but also HSDPA/HSUPA).
Toke correct me if I'm wrong.

The current ATF scheduler for WiFi does airtime-DRR based on the current
PHY rates,
is that right? Side question, how do you measure current?

In LTE TDMA makes use of what is called multi-user diversity gain
by scheduling users when they are at their relative best radio condition.
Typically the user with the best current radio condition NORMALIZED
over the average radio conditions. The average can be based on a
moving average or a sliding window. This is the case of the widely used
David Tse's proportional fair scheduler.

This means that TDMA is still in place to share air-time fairly but the
scheduler will tend to avoid bad radio conditions.

>From a theoretical point of view if you do that the total capacity
of the AP can increase with the number of stations (I think logarithmically)
as the scheduler surfs across radio quality peaks and not the average radio
quality. Very smart.

In LTE this is doable as the scheduling time slot is 1ms and the feedback
channel
is as fast. Not all TDMAs are equal.
Maybe the current scheduler in WiFi can be improved to do that. Maybe.

Luca




>
> -Toke
>
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