Passive and Active Measurement

Volume 6579 of the series Lecture Notes in Computer Science pp 204-213

Clockscalpel: Understanding Root Causes of Internet Clock Synchronization Inaccuracy

  • Chi-Yao HongAffiliated withUniversity of Illinois
  • , Chia-Chi LinAffiliated withUniversity of Illinois
  • , Matthew CaesarAffiliated withUniversity of Illinois

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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.