On Thu, Oct 24, 2019 at 11:34 AM Toke Høiland-Jørgensen <t...@redhat.com> wrote:
> Luca Muscariello <muscarie...@ieee.org> writes: > > > On Wed, Oct 23, 2019 at 2:27 PM Toke Høiland-Jørgensen <t...@redhat.com> > > wrote: > > > >> Rich Brown <richb.hano...@gmail.com> writes: > >> > >> >> On Oct 23, 2019, at 5:54 AM,<erik.tarald...@telenor.com <mailto: > >> erik.tarald...@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? > > s/current/last/. The ATF scheduler does everything after-the-fact, by > accounting the actual TX time of a transmission after it has completed. > So no fancy scheduling or prediction tricks are needed; with the > tradeoff being coarser granularity of the fairness achieved (i.e., there > can be unfairness on short timescales). > > In the airtime queue limit work that's ongoing, we do ahead-of-time > airtime estimation to limit queueing in firmware. But this still just > uses the last TX rate recorded for the given station to calculate the > estimate. > > > 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. > > Yeah, the LTE MAC is pretty cool. Just a shame that the equipment is so > expensive :( > It looks like there is a positive correlation between the size of the specifications and the cost to build the associated product :) > > > Maybe the current scheduler in WiFi can be improved to do that. Maybe. > > I think 802.11ax is going in that direction. Nothing nearly as advanced, > but at least there's the possibility of a dedicated back channel... > That's right. ax does much better. > > -Toke > >
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