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<span style="color: #000000">The purpose of this study is to investigate the effectiveness of tiering</span> for [TULIP|http://www.slac.stanford.edu/comp/net/wan-mon/tulip/] (i.e we have a set of primary landmarks tier0 which will narrow down the target location to being in a particular region*\[1\] and then a denser set of secondary tier1 landmarks in the discovered region that can be used to get more accurate results). The use of tiering should enable us to reduce the network traffic (number of landmarks pinging a target) while retaining the accuracy of using all landmarks. |
Currently we are looking into two regions where we hope to use tiering, i.e. North America and Europe. The choice of these two regions is since we have a relatively large number of landmarks in these regions. Landmarks in all other regions will be considered as tier0. Thus TULIP will try and locate targets in two passes. The first just uses tier0 landmarks. If the target then appears to be in North America or Europe, then a second pass is made using all the landmarks in that region, otherwise the target is determined from the first pass. The purpose of the current study is to determine whether tiering is effective and how it should be used.
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Looking at the graph above of Alpha vs min_RTT from SLAC it appears there are two regimes separated at ~8ms. Above 8ms alpha is ~ 50km/ms, below it is more variable closer to ~10km/ms. One can use a smooth power function to predict alpha given the min_RTT as shown in the figure. However it is as easy and probably more accurate to use the two values.
We also calculated median alpha from SLAC which is ~ 46.5km/ms and IQR ~15.6km/ms or IQR/Median~ 33% or ~ +-16%
Faran uses the maximum alpha value in order to avoid underestimation which is ~ 62.98 km/ms in our case. Also Faran calculates alpha based on PingER historical data to all the world regions and in this study we only used the North American PingER sites. Looking at the frequency histogram of alpha for the SLAC landmark to Norther American sites it is seen that this is a reasonable maximum value.
Europe
Conclusion
References
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