A couple cake notes below... On Fri, Dec 13, 2024 at 3:50 PM <sro...@ronan-online.com> wrote: > > Do you have an explanation for the question he asked? I am sure it would be > of interest to many here. > > Shane > > > On Dec 13, 2024, at 4:23 PM, L Sean Kennedy <l...@fedney.org> wrote: > > > > I replied to Dan off list to investigate. > > > > Any Prime Video quality issues reported to an ISP by customers or CDN > > issues can be sent directly to primevideo-isp...@amazon.com . > > > > Thanks, > > Sean > > > >>>> On Dec 13, 2024, at 3:52 PM, Daniel Sterling <sterling.dan...@gmail.com> > >>>> wrote: > >>> > >>> While streaming football last night from AT&T fiber (AS7018), I > >>> noticed the video quality went way down when I did a large download on > >>> another system. I have gigabit fiber but I'm using Linux tc to > >>> throttle my network traffic. I've configured cake with a 200mbit > >>> limit, and I also use a low BQL setting to further ensure low latency > >>> for low-bandwidth traffic.
OK there are several things about cake that seem to be conflated here. Glad you are using it! 1) BQL is for outbound traffic only and provides backpressure at the native rate of the interface. If you further apply cake's shaper to a rate below that, BQL hardly enters the picture. 2) Applying a 200Mbit inbound limit to a gig fiber connection is overkill. Worst case it should be at 50%, and we generally recommend 85%. People keep trying to go above 95% and that fails to control slow start. This does not account for how congested the backhaul is and we certainly see people trying desparately to figure that out - see the cake-autorate project for a 5g example. 3) By default cake is in triple-isolate mode which does per-host/per flow fq. This means if you have two devices asking for the bandwidth, one with 1 flow, the other with dozens, each device will get roughly half the bandwidth. fq_codel, on the other hand, shares on pure flow basis. We put per host fq in there because of torrent, and to some extent, web traffic (which typically opens 15 flows at a time). However, if cake is on a natted router the per host mode fails unless you apply the "nat" option on the invocation. Arguably we should have made nat the default. If you have demand for less bandwidth that your fair share, you experience near zero latency and no loss for your flow. At 200Mbit, assuming nat mode was on, your amazon flow (probably running below 20mbit) should have seen no congestion or loss at all while another machine merrily downloaded at 180, dropping the occasional packet to keep it under control. Anyway, moving on... > >>> IOW, my Linux router will drop packets across the board rather > >>> liberally in the face of large downloads, but I've always seen streams Arguably cake drops less packets than any other AQM we know of. It still does not early and fast enough to slow start on short RTTs. I keep trying to get people to deploy ecn. > >>> fight back for their share of the bandwidth -- except for amazon's. > >>> > >>> The live stream appears to use UDP on a non-standard port (not 443). > >>> Does anyone know what amazon has done to cause their congestion > >>> control algorithms to yield so much bandwidth and not fight for their > >>> fair share? Anyway, this is a good question, if that was the observed behavior. A packet capture showing it not recovering after a loss or delay would be interesting. > >>> > >>> Thanks, > >>> Dan -- Dave Täht CSO, LibreQos
