Clockscalpel: understanding root causes of internet clock synchronization inaccuracy

Authors:
Chi-Yao Hong;Chia-Chi Lin;Matthew Caesar
Affiliations:
University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign
Venue:
PAM'11 Proceedings of the 12th international conference on Passive and active measurement
Year:
2011

Citing 8
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Abstract

Synchronizing clocks is an integral part of modern network and security architectures. However, the ability to synchronize clocks in modern networks is not well-understood. In this work, we use testbeds equipped with a high-accuracy GPS receiver to acquire ground truth, to study the accuracy of probe-based synchronization techniques to over 1861 public time servers. We find that existing synchronization protocols provide a median error of 2 - 5 ms, but suffer from a long-tail. We analyze sources of inaccuracy by decoupling and quantifying different network factors. We found that most inaccuracies stem from asymmetry of propagation delay and queueing delay. We discuss possible schemes to compensate these errors to improve synchronization accuracy.