id summary reporter owner description type status priority milestone component version severity resolution keywords cc actualpoints parent points reviewer sponsor
4490 Sensitivity analysis of different ways to sample relay capacity for simulations arma arma "Since current Tor simulators can't handle the whole 2500 relays, they end up running simulations on a subset of relays that they hope is representative. Early papers chose their sample by choosing n relays weighted by capacity. Rob and Kevin both found that they could achieve more consistent results by breaking the relays into deciles, and choosing n/10 relays from the ""0-10%"" bucket, n/10 from the ""10-20%"" bucket, and so on.
But I suspect that it is not optimal to base these parameter choices on the number of fingers that primates have. In particular, Mike's graphs show that the ""0-5%"" bucket is quite different from the ""5-10%"" bucket. So I worry that different runs could see quite different outcomes.
Rob pointed out that if we want to match reality, we'll need to know what load to place on the network -- and even messier, how to scale down that load in a way that matches the scaling down of the relay population.
But I think there's still some good insight to be had here, by looking at how much variation we get for a variety of sampling algorithms for a given set of loads. If the results are consistent for a given set of loads while varying sampling algorithms, that would be a surprising and interesting result. And if the results for a given load change by sampling algorithm, we should get some better intuition about how much they change, and what parameters seem to influence the changes the most.
Alas, the part of this question that makes the number of simulation runs blow up is that we ought to do the tests for a variety of research questions, since maybe some research questions are quite sensitive to changes in capacity distribution and others not so much.
I bet we could get quite a bit of mileage here by just looking at the resulting capacity (and thus probability) distributions of various sampling algorithms, and leaving the ""Tor simulation"" component out entirely -- since using a full-blown Tor simulator to measure similarity of distribution is a mighty indirect approach." project closed Medium Metrics/Analysis implemented performance simulation SponsorF20121101 robgjansen kevin