Active measurement and time-domain characterization of IP packet jitter

摘要

Synchronization over packet-switched networks has been attracting increasing attention lately, e.g. due to migration to IP transport in GSM networks. Timing is distributed by sending packet flows with constant rate. At the receiver, timing is recovered mostly based on PLL schemes that equalize packet random delay. The performance of these schemes depends significantly on the statistics of packet jitter, thus yielding a growing interest for real data measurement. We developed an experimental setup to measure IP packet jitter by active probing, aiming at statistical characterization of packet jitter in real heterogeneous networks. We present some experimental results, measured in networks including bridges and routers. Contrary to previous studies in literature, we emphasize data analysis by means of Modified Allan Variance (MAVAR) and Maximum Time Interval Error (MTIE), two well-known time-domain quantities widely used for synchronization interface specification in international standards. Although our setup is simple, the noise floor is negligible, compared to the network jitter under measurement.