Understanding Precision Time Protocol in Today's Wi-Fi Networks: A Measurement Study

Emerging mobile applications involving distributed control and sensing call for accurate time synchronization over wireless links. This paper systematically studies the performance of Precision Time Protocol (PTP) in today's Wi-Fi networks. We investigate both software and hardware PTP implementations. Our study uncovers the root causes of software PTP synchronization errors. We show that with fine-tuned system configurations and an online calibration procedure, software PTP can achieve reasonable accuracy with off-the-shelf Wi-Fi devices. Hardware PTP requires a PTP hardware timestamper clock not contained in Wi-Fi NICs. We propose a method to make use of the hardware TSF counter to emulate the PTP clock. Rigorous tests traversing various conditions show that both software and hardware PTP implementations can achieve a 1-µs level of accuracy in today's Wi-Fi networks.