An important feature of Pathrate is that it is robust to cross traffic effects, meaning that it can measure the path capacity even when the path is significantly loaded. This is crucial, since the hardest paths to measure are the heavily loaded ones. For more information about how Pathrate works, you can read the following paper: ``Packet Dispersion Techniques and Capacity Estimation'' (to appear in the Transactions on Networking). An earlier version of this paper appeared at Infocom 2001 with the title: ``What do Packet Dispersion Techniques Measure?''.

Pathrate is based on the dispersion of packet pairs and packet trains. Pathrate uses many packet pairs (with packets of variable size) to uncover a set of possible "capacity modes". Then, it uses long packet trains to estimate the so called "Asymptotic Dispersion Rate" R. The capacity of the path will be larger than R, and so this gives a hint about which local modes to reject. From the modes that are higher than R, the one that is the strongest and narrowest is chosen.