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Rate limiting is much harder to discover this than simple blocking. In some cases it will result in sudden increase in losses. For example ICTP turned on rate limiting at their bordeer in May-Jun 2008. This affected the losses measured from ICTP to almost all its remote hosts. On the left in the table below is an example plot of losses and RTT from ICTP to a host in Brazil Brazi. Itl shows the increase in hourly ping losses starting early in June 2008. On the right is the median loss from ICTP to 93 sites worldwide in June 2008 showing a steep increase on June 6th and 7th as rate limiting was applied.
Losses from ICTP to a Brazilian site | Median losses from ICTP to 93 sites worldwide |
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Another useful tool to spot anoamlous values is the motion bubble plot. In particular looking at min_RTT for countries seen from a monitoring site can quickly show impossibly small minimum RTTs and spot when they start and stop occuring.