Purpose
<span style="color: #000000"> The purpose of this study is to investigate the effectiveness of tiering</span> for TULIP
. (i.e we have a set of primary landmarks tier0 which will narrow down the location to a particular region*[1] and then more denser secondary tier1 landmarks can be used to get more accurrate results). Currently we are looking into two regions North America and Europe. We are trying to build heuristics which will enable us to find the region of a particular host.
North America
We selected 4 landmarks in North America for our study( SLAC, BNL, Ampath-Florida,TRIUMF-Canada). We pinged a set of know geographical sites from PingER database in US, Canada and Mexico. We also calculated the physical distances between them. The figure below shows the distribution. It appeared that all hosts were within 80ms of one another of the 4 monitors and 98.84 are < 70ms.
Here are graphs of data seen from four landmarks
As we can see from the first graph that some sites are replicated (root servers) and we ignore them in our results. It is also seen that some values for Mexico are aberrant for example min rtt >200 for a Mexican site from Florida. So it is a good idea not to include Mexico in this region. This region will comprise of Canada and US only.
The above graph shows how alpha varies with distance. Using a single alpha may fail for small RTTs (distances). This is probably since the min_RTT is dependent on router delays and where networks peer (so the routes may be very different from the Great Circle Distance (GCD) rather than global distance.
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
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. 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.
Europe
Conclusion
62.9841 |