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However the ping distributions are decidedly non-normal (see for example the figure below) have wide outliers, and are heavy tailed on the upper side (see https://www.slac.stanford.edu/comp/net/wan-mon/ping-hi-stat.html). This leads to large standard deviations (one to two order of magnitude greater than the IQR) in the RTT values. As can be seen from the table this results in low values of the Z-test and a false probability of no significant statistical difference. Using the IQRs of the frequency distributions instead generally leads to much higher values of the Z-test and hence a higher probability that the distributions of RTTs between two pairs of hosts are significantly different. Comparing the frequency distributions it is seen that there is indeed a marked offset in the RTT values of the peak frequencies and a resultant difference in the cumulative RTT distributions, Using the non-parametric Kolomogorov Smirnoff test (KS test) also indicated significant differences in the distributions.
It is interesting to note that The RTT measurements made from pinger.SLAC and pingerpinger-raspberry.SLAC TRIUMF to both TRIUMF to TRIUMF and CERN show that the average around 23ms and 151ms respectively. Despite this large difference in average RTTs', comparing the average RTTs from pinger.SLAC with those from pinger-raspberry.SLAC yields a difference of only ~0.35ms for both TRIUMF and CERN.
and median RTTs are about 0.4ms different even though the RTTs for TRIUMF are about 23ms whereas for CERN they are ~151ms. Looking at the traceroutes, using Matt's traceroute to measure the RTT to each hop indicates hop, indicates that this difference starts at the first hop and persists for later hops. See spreadsheet (MTR tab). We therefore made ping measurements from each SLAC MA to its loopback network interface. Themeasure The measurements were made at the sames same times to facilitate comparisons. . They indicate that the pinger-raspberry.SLAC is ~0.13ms lslower in responding than the pinger.SLAC MA. Thus approximately 1/3rd of the difference in average RTS tro TRIUMF measured by the two SLAC MAs is due to the MA platform itself.
Powerpoint of figures.
Kolmogorov-Smirnov Test
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