Review - King: Estimating Latency between Arbitrary Internet End Hosts

There are many applications where latency measurements are valuable over the
wide-area network. King is a tool for measuring latency on the Internet
between to arbitrary hosts. It uses the existing DNS infrastructure to
estimate round-trip times via recursive lookups. In this way, King is able
to estimate network distances, achieving good accuracy, without the
cooperation of end nodes.

King operates by first determining the closest authoritative name server for
the two end nodes that it wishes to investigate. By requesting a recursive
name lookup from one server, observing the response time, and subtracting it
from the round-trip time to the queried server, an estimate of latency
between the two DNS servers can be obtained. The authors show that this
estimate is more accurate, is calculated more quickly and is easier to use
than previous methods.

Deficiencies in King become apparent on the last hop. The authors admit that
a host connected over a slow medium, such as a modem, DSL, satellite, etc.,
the will carry a significant last hop latency that is not reflected in the
King calculation. It is also stated in the paper that the hop latencies can
vary from tens to hundreds of milliseconds. King is also admittedly
inaccurate when there are multiple authoritative name servers.
Unfortunately, this is the typical case on the Internet and further
inaccuracies may be introduced.

Although it has several deficiencies, there are many relevant applications
where King can be beneficial. Specifically, this method has good accuracy in
preserving latency rank, which is important in applications where locating
the nearest server is needed. Here, absolute latency is not an issue.
Received on Thu Nov 03 2005 - 02:42:24 EST