Mitigation of Asymmetric Link Delays in IEEE 1588 Clock Synchronization Systems

The IEEE 1588 standard defines the Precision Time Protocol (PTP) which provides mechanisms for synchronizing distributed clocks in packet-based networks. The accuracy of PTP synchronization depends on a number of factors such as the quality of the timestamps, packet delay variation, clock stability, and the asymmetry. In the latest update of the standard, IEEE 1588 version 2008, compensations for asymmetric delays have been introduced into the protocol. However, specific procedures for determining the asymmetry have not been specified. This paper analyzes various asymmetry mitigation measures for software timestamping and proposes a timestamp correction-based asymmetry compensation scheme. Measurements using WLAN synchronization hardware show that the proposed scheme can almost mitigate the link asymmetry without requiring any changes in PTP or additional messages.