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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&nbsp; 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). Currently we are looking into two regions where we hope to use tiering, i.e. North America and Europe.&nbsp; 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 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. The purpose of the current study is to determine whether tiering is effective and how it should be 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.

North America 

We selected 4 landmarks in North America for our study( SLAC, BNL, Ampath-Florida,TRIUMF-Canada). They were chosen to be reliable and to roughly be located close to the 4 corners of the region. We pinged a set of known geographical target sites in the US, Canada and Mexico. The coordinates of the sites were obtained from the PingER database. We also calculated the physical distances between the target sites and the landmarks. 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 within 70ms.

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 As we can see from the first graph that some sites are replicated (e.g. DNS root name servers, Yahoo) 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 therefore comprise of Canada and US only.

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