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 :( > 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... -Toke _______________________________________________ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat