Ok thanks I think I will stay away from the quagmire of rating ISPs on buffer bloat. And first try to boil any bloat measurement down to an easy to understand letter grade between A+ and F, in a way that you guys think stands inspection of individual results. On Wed, Apr 29, 2015 at 11:39 AM, Jonathan Morton wrote: > These are pretty good questions, actually. But as pointed out, when you > want to start ranking, it's important to distinguish the performance of the > ISP itself from equipment under the subscriber's control, which itself > might be configured to hide faults in the ISP. > > Statistics is a hard subject. If you feel at all confused by what I > describe below, it might be a good idea to sit down with a real expert. The > basic calculations are not difficult; it's knowing WHAT to calculate and > what it means once you've done it. > > Notably, the upload queue usually depends much more on the CPE than on > anything the ISP controls directly. I don't think there are that many ISPs > left which absolutely insist on using their own modem, but most will supply > a preferred, preconfigured model on request, and many users will accept > that, not knowing better. Unfortunately, I can't think of an easy, robust > way to detect what CPE is in use our how it has been configured, so it's > hard to control for it statistically. > > In general, downstream queuing is much more under the ISP's control. To > account for the (growing?) subset of users who apply ingress shaping, you > could look at the upper percentiles of latency, since usually ingress > shaping will improve matters. Caveat: it's also possible for ingress > shaping to make things worse, either through accidental misconfiguration or > even maliciously, so don't just take the peak value. > > Initially I suggest you present a histogram of the results that fall into > particular grades. That'll help you get a feel for the statistics, and it's > easy to pick out a modal value by eye. Beware of trying to calculate a > modal value simplistically, since the histogram might not show a simple > mode if results tend to straddle two adjacent grades. (This is why the mode > is the least used of the three basic averages; it's hard to calculate it > such that it's reliably useful, even though it's often intuitively useful.) > > I also suggest you add a basic question to the user: are you using a > router with QoS features turned on (yes/no/dunno), with dunno as the > default. That'll give you a way to point out that most of the lower latency > results are probably a result of this. You could draw stacked or adjacent > histograms with this information colour coded. > > As for the single numbers to plug into the formula, this also requires > some care. > > For the idle/baseline, I suggest using only the samples from before the > bandwidth tests begin, rather than also including those from between and > afterwards. Then you should use the harmonic mean on these, to get a value > biased on the low end. > > For each of the load sets, you want a value biased high. Taking the 90th > percentile might be a reasonable approach here; it'll discard outliers and > brief transients that a good AQM acting alone (ie. without FQ) might leave, > but should still expose the sorts of obvious problems that we're trying to > tackle. > > I do think that the idle latency and the total loaded latency can usefully > be reported as frequencies. The total loaded latency can be taken to be the > idle latency plus the induced download latency plus the induced upload > latency, as an approximation of the latency when both directions are loaded > at once. > > As for ranking ISPs overall... this is hard to do in a way that's > perceived to be fair. My recommendation on this front would be to allow > your users to select criteria with weights. Some might consider download > and/or upload speed to be important as well as latency, while others might > see a choice between overall latency (important for games) and jitter > (important for VoIP). This makes it harder to claim that you're personally > presenting a controversial opinion on relative merits. > > - Jonathan Morton >