On 4 May 2015, at 12:33, Jonathan Morton <[email protected]> wrote:
> >> On 4 May, 2015, at 13:42, Neil Davies <[email protected]> wrote: >> >> Noting that, delay and loss is, of course, a natural consequence of having a >> shared medium > > Not so. Delay and loss are inherent to link oversubscription, not to > contention. Without ECN, delay is traded off against loss by the size of the > buffer; a higher loss rate keeps the queue shorter and thus the induced delay > lower. Sorry Jonathan - that’s not what we’ve observed. We’ve measured “excessive” delay on links that are averagely loaded << 0.1% (as measured over a 15 min period) - I can supply pointers to the graphs for that. > > You can have just as much delay and loss in a single flow on a dedicated, > point-to-point, full-duplex link (in other words, one that is *not* a shared > medium) as on the same link with multiple flows contending for it. A single flow can contend the medium just as much as a multiple ones - it is the total arrival pattern that is important, which may be related to the number of flows (in that there is more freedom in the system). > > Conversely, we can demonstrate almost zero flow-to-flow induced delay and > zero loss by adding AQM, FQ and ECN, even in a fairly heavy multi-flow, > multi-host scenario. > > AQM with ECN solves the oversubscription problem (send rates will oscillate > around the true link rate instead of exceeding it), without causing packet > loss (because ECN can signal congestion instead), and FQ further reduces the > most easily perceived delay (ie. flow-to-flow induced) as well as improving > fairness. > > Of course, loss can also be caused by poor link quality, but that’s an > entirely separate problem. It is a separate cause, agreed, but it has a similar effect... > > - Jonathan Morton > _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
