On assessing unidirectional latencies in packet-switched networks

This report presents a method to collect statistics about unidirectional delays in packet-switched inter- and intranetworks. The necessary synchronization of the computer clocks on source and target host is performed via a new approach that first determines the relative clock drift between these hosts, i.e. the difference in the frequency drifts of the oscillators. This measure is used to adjust the clock timestamps delivered by the target host. Upon synchronization of the clock phases a very accurate time offset between the network hosts can be estimated. Finally, the time-stamps obtained via the exchanged probe packets can be re-evaluated to compute the one-way delays on both transmission paths between the respective hosts