Pathrate |
A measurement tool for the capacity of network paths |
We have developed a measurement methodology that can estimate the capacity of Internet paths. The methodology has been implemented in a tool called Pathrate. 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. To make a rather long story very short, we use many packet pairs (with packets of variable size) to uncover a set of possible "capacity modes". Then, we use long packet trains to estimate the so called "Asymptotic Dispersion Rate" R. We know that the capacity of the path will be larger than R, and so this gives us a hint about which local modes to reject. From the modes that are higher than R, we choose the one that is the strongest and narrowest.