A Methodology for Clock Benchmarking

Accurate timestamping is a basic need in traffic monitoring as well as distributed computing in the broad sense, and is destined to become increasingly important as network latency becomes a hard barrier to improved performance across networks. Software clocks need to be improved to meet this challenge, however evaluating their performance is non trivial, as they are imbedded inside computing systems. We present a methodology for clock validation which allows many of the difficult problems to be resolved. Our method involves a combination of external and internal validation strategies, and makes use of GPS synchronized DAG cards and system clocks. We illustrate in detail how it may be applied using real data collected from 3 clocks implemented in UNIX PCs.