Using self-clocking for passive estimation of TCP round-trip times
Veal, Bryan Edward
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Passive methods of measurement allow the examination of network properties without altering the ow of data, which could change the network properties being measured. Passive methods also allow a choice between online and o ine measurement using data traces. We propose a method to passively estimate round-trip times, an important network performance metric, for TCP data ows. The method works by observing repeating patterns of segment clusters caused by TCP's self-clocking mechanism. Estimates need not be taken at the end-points; they can be taken anywhere along the route between the sender and receiver. Also, since only one direction of ow is necessary, estimates can be taken when network routes are asymmetric. Furthermore, estimates can be taken throughout the lifetime of the transfer, allowing observation of changes in round-trip times. We evaluate this method using traces from the Internet and also a testbed with emulated network conditions.