  Round-trip times (RTTs) are an important metric for the operation of many
applications in the Internet. For instance, they are taken into account when
choosing servers or peers in streaming systems, and they impact the operation
of fault detectors and congestion control algorithms. Therefore, detailed
knowledge about RTTs is important for application and protocol developers. In
this work we present results on measuring RTTs between 81 PlanetLab nodes every
ten seconds, for ten days. The resulting dataset has over 550 million
measurements. Our analysis gives us a profile of delays in the network and
identifies a Gamma distribution as the model that best fits our data. The
average times observed are below 500 ms in more than 99% of the pairs, but
there is significant variation, not only when we compare different pairs of
hosts during the experiment, but also considering any given pair of hosts over
time. By using a clustering technique, we observe that links can be divided in
five distinct groups based on the distribution of RTTs over time and the losses
observed, ranging from groups of near, well-connected pairs, to groups of
distant hosts, with lower quality links between them.
