Thanks for the detail. It makes sense but it kind of feels like in some (maybe many) cases the router could know the internet link performance. Particularly home router-modems often monitor this already. Maybe that's just not exposed in any standardised way? I'm guessing if I was into openwrt I could maybe do something, but I prefer just to find something off the shelf with half decent SQM... If "auto configuration" isn't a feature then that answers my question and I can get on choosing the best option.
On Sat, Jun 3, 2023, 16:44 Jonathan Morton <[email protected]> wrote: > > On 3 Jun, 2023, at 4:56 pm, John D via Bloat < > [email protected]> wrote: > > > > On the website it says the following: > > > > CoDel is a novel “no knobs”, “just works”, “handles variable bandwidth > and RTT”, and simple AQM algorithm. > > > > • It is parameterless — no knobs are required for operators, > users, or implementers to adjust. > > • It treats good queue and bad queue differently - that is, it > keeps the delays low while permitting bursts of traffic. > > • It controls delay, while insensitive to round-trip delays, link > rates, and traffic loads. > > • It adapts to dynamically changing link rates with no negative > impact on utilization. > > > > But everywhere I have read about about hardware which implements SQM > (including the bufferbloat website) it describes the need to tune based on > actual internet connection speed. > > These seem to conflict especially that "handles variable bandwidth" bit. > Have I misunderstood or do the algorithms used in modern hardware just not > provide this part typically? My connection performance is quite variable > and I'm worried about crippling SQM to the lowest speed seen. > > SQM in practice requires three components: > > 1: Flow isolation, so that different flows don't affect each others' > latency and are delivered fairly; > > 2: Active Queue Management (AQM) to signal flows to slow down > transmissions when link capacity is exceeded; > > 3: Bandwidth shaping to match the queue to the available capacity. > > CoDel is, in itself, only the AQM component. It does indeed work pretty > well with no additional tuning - but only in combination with the other two > components, or when applied directly to the actual bottleneck. > Unfortunately in most consumer internet links, the actual bottleneck is > inaccessible for this purpose. Thus an artificial bottleneck must be > introduced, at which SQM is applied. > > The most convenient tool for applying all three SQM components at once is > Cake. This includes implementations of advanced flow isolation, CoDel AQM, > and a deficit-mode bandwidth shaper. All you really need to do is to tell > it how much bandwidth you have in each direction, minus a small margin to > ensure it becomes the actual bottleneck and can exert the necessary control. > > When your available bandwidth varies over time, that can be inconvenient. > There are methods, however, of observing how available capacity tends to > change over time (typically on diurnal and weekly patterns, if the > variations are due to congestion in the ISP backhaul or peering) and > scheduling adjustments on that basis. If you have more information on your > situation, we might be able to give more detailed advice. > > - Jonathan Morton
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