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Yes in principle that is true. Blocking all other traffic is not really an option because the people hosting the probes would not really like it if we did that. The only way around this would be to use a router as a probe and *measure* the load which is present during the measurements; then one can take it into account. This is what some others like SamKnows do. We have decided against it because we want to avoid sniffing any traffic; our probes can be installed behind a switch port that do not see any user traffic. Our research shows that this is essential for quite a number of potential hosts, especially those in commercial environments. <br /><br />Also routers are a bit too expensive for us right now since we aim for 10s of thousands of probes eventually. However it would be great if in the future we can convince some router manufacturers to include measurment code in their software which users can enable if they choose to. But before considering this we want to get version 1 of the measurement network up and running.<br /><br />In the mean time we will try to take the network load into consideration by making many measurements from a number of probes. When doing that we can use heuristics like considering only the variance that is common to all measurements.