On packet selection criteria for clock recovery

Many packet-based clock recovery algorithms use only a subset of timing packet arrivals to discipline the local oscillator. One commonly used selection process is to partition the time into non-overlapping windows and, for each window, select only the one that had the smallest network transit time. This process is a non-linear filter, developed mostly based on intuition and widely accepted by many researchers and developers without much formal analysis. In this paper, we analyze the output statistics of such a filter, provide a closed-form expression for some commonly observed packet delay profiles, and back the results with experimental data. We also point out some network scenarios where usage of the filter is not well justified.