Toke Høiland-Jørgensen, Michał Kazior, Dave Täht, Per Hurtig, Anna Brunstrom
2017 · arXiv
With more devices connected, delays and jitter at the WiFi hop become more prevalent, and correct functioning during network congestion becomes more important. However, two important performance issues prevent modern WiFi from reaching its potential: Increased latency under load caused by excessive queueing (i.e. bufferbloat) and the 802.11 performance anomaly. To remedy these issues, we present a novel two-part solution: We design a new queueing scheme that eliminates bufferbloat in the wireless setting. Leveraging this queueing scheme, we then design an airtime fairness scheduler that operates at the access point and doesn't require any changes to clients. We evaluate our solution using both a theoretical model and experiments in a testbed environment, formulating a suitable analytical model in the process. We show that our solution achieves an order of magnitude reduction in latency under load, large improvements in multi-station throughput, and nearly perfect airtime fairness for both TCP and downstream UDP traffic. Further experiments with application traffic confirm that the solution provides significant performance gains for real-world traffic.We develop a production quality implementation of our solution in the Linux kernel, the platform powering most access points outside of the managed enterprise setting. The implementation has been accepted into the mainline kernel distribution, making it available for deployment on billions of devices running Linux today.
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The "sparse" and "rounds" concepts also works really well as a per station wifi scheduler, where it is now the default for a plethora of chipsets in linux. Some plots of which I will forever be proud here: https://arxiv.org/pdf/1703.00064.pdf Before/After on an ath10k chip here: https://forum.openwrt.org/t/aql-and-the-ath10k-is-lovely/590...
The code shipped in lede 17.01 that january(2017) and also went Linux mainline at the same time. Everybody on linux using an ath9k and ath10 chip is benefiting today, and it (or a variant) is in multiple commercial products now. I kind of expect it to be in all new products leveraging these chips. Our writeup of how it works is here: https://arxiv.org/pdf/1703.00064.pdf - lots of pretty pictures. I recently had to shut down my lab for lack of funding.
And there's good news on the Wi-Fi front as well. Many of the same people who brought us fq_codel/cake have new algorithms for "Making Wi-Fi Fast". Their paper tells how they've reduced bufferbloat as well as increasing "airtime fairness" in the Wi-Fi stack. The paper, "Ending the Anomaly: Achieving Low Latency and Airtime Fairness in WiFi", is now available as a preprint at: https://arxiv.org/abs/1703.00064 The conclusion of the paper states: "We have developed a novel two-part solution to two large performance problems affecting WiFi: Bufferbloat and the 802.11 performance anomaly. "The solution consists of a new integrated queueing scheme tailored specifically to…
eliminating bufferbloat in WiFi, which reduces latency under load by an order of magnitude. Leveraging the queueing structure, we have developed a deficit based airtime fairness scheduler that works at the access point with no client modifications, and achieves close to perfect fairness in all the evaluated scenarios, increasing total throughput by up to a factor of 5. "Our solution reduces implementation complexity and increases accuracy compared to previous work, and has been accepted into the mainline Linux kernel, making it deployable on billions of Linux-based devices." Fun reading! Oh, and it's available in LEDE today.
Always nice to see you, john. 1) If we had sufficient backpressure in the ISPs provided router network driver, with "BQL" to manage the ringbuffers and fq_codel to do fq + aqm, we're mostly done, at least on the uplink. The hope has been, since most home routers run linux, that 5 years after RFC8920 entered mainline linux, it would appear in ISP gear. fq_codel is now the default on most linux distros but without the backpressure from bql or running below line rate it's not effective unless further configured or shaped. 2) I wish having your own shaper was not "a trend". bql and fq_codel are lightweight compared to shaping. 3) sch_cake solves a bunch of remaining problems:…
A) doing both flow and host based fairness at the same time, so your host frantically issuing http requests only gets 1/hosts the bandwidth. B) uses a deficit shaper that consistently runs at a rate slightly less than the (ubiquitous) token bucket shaper ISPs use. So it can share the same setpoint but control the queue. https://arxiv.org/abs/1804.07617 4) we have a lot of wifi devices now doing fq_codel by default. Very happy with the results. https://arxiv.org/pdf/1703.00064.pdf Perhaps on rfc970's 40th anniversary, we can view these problems as solved!
DOCSIS 3.1 devices mandate pie, which helps a lot, but it's not as good as fq_codel, nor do they do shaping from the isp, which is kind of needed for all the cable links in the USA I've tried. Get one if you can, though, they are better across the board in many other ways. pfsense has fq_codel. Anything (1000s of routers) from lede/openwrt has the most advanced bufferbloat-fighting stuff in it, followed by dd-wrt, tomato, etc. If you need high bandwidths the multi-core arms are the best. fq_codel is pre-configured on all links (ethernet/usb/fiber/wifi/whatever) but if you need shaping to the ISP provided rate you need to configure it. All the research that went into…
fixing bufferbloat queuing problems everywhere landed in openwrt and lede first. Most of the research that improved tcp everywhere came out of google. Most gaming routers now sold commercially have some variant of fq_codel in them in their trade name ISP "qos" system. Also fq_codel derived anti-bufferbloat work has landed in many commercial wifi routers on the wifi side (eero, google wifi, some ubnt products, meraki, many others). The paper behind all that was: https://arxiv.org/pdf/1703.00064.pdf - happily that work was "good enough" to enable by default, and boy, does it make a difference if wifi is your bottleneck. The current premier dsl router with cake is evenroute. I think there are several new models from several manufacturers that are going to get it right, soon. Not tracking FIOS (gpon fiber) closely at the moment. Yes, fiber networks have bufferbloat, but it's harder to hit, and generally smaller than on dsl and cable technologies. I configured cake on sonic fiber recently and got 60ms back. (going from 60ms latency under load to 3ms ) Regrettably shaper setup is finicky and requires a few minutes of testing with a site like dslreports or a tool like flent.org to get right. If more ISPs published their shapers' bitrate and burst rate settings, life would be easier here... but the hope has always been they'd just ship a router with this stuff on and remotely configured to be "right". In some ways, what are you doing about bufferbloat is
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