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Hosts that are on satellite links have very large delays. They cannot be located using the RTTs from a set of landmarks. Usually they have RTTs > 500ms. Most of the Central Asian countries (including Afghanistan) and some African countries use satellite links. Data from hosts in Kazakhistan, Burundi, Madagascar, Uganda, Afghanistan and Nigeria can be found here. The three best Landmarks chosen gives an RTT greater than 500ms. If the RTT from the three best landmarks is greater than 500ms then our algorithm returns the host as satellite link and does not perform trilateration. This figure may be changed latter.
Replicated Servers
There are two types of replicated servers. (i ) Replicated Servers with same IP address (ii) Replicated Servers with different IP addresses
( i) Replicated Servers with same IP address:
In some cases (i.e root servers in particular) the IP address of all the replicated servers are same. In this case case we select the 3 landmarks with minimum RTT and check if the circles intersect. If the circles do not intersect then its a replicated server.
(ii) Replicated Servers with different IP addresses:
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Replicated Servers
Trilateration VS Multilateration
Here is the data. This is a much simple case, we request all the PingER landmarks to get the IP address of the target. If all the IP address are same the server is no replicated otherwise the server is replicated. This will require making modifications to reflector.cgi to return the IP address of the target being queried.