Clock Synchronization using Packet Streams⋆

Recent distributed applications in the domains of digital audio and sensor networks require clock synchronization in the order of 10μs. The achievable precision depends on system properties like synchronization message delay and synchronization message pattern. These properties are often unknown or difficult to determine. Therefore we propose a new analysis for clock synchronization algorithms. The analysis is based on two properties: safe synchronization and optimal selective synchronization. We present two algorithms that use an arbitrary stream of synchronization messages to achieve clock synchronization over an asynchronous communication channel and on clocks with unknown and variable drift. The first algorithm needs no parameterization, is safe and optimal selective. The second algorithm improves the first with a drift compensation mechanism. It is safe. A parameter of the algorithm allows to choose between fast drift compensation and high probability of optimal selective behavior. Simulation results show that the algorithms can achieve 10μs precision on 802.11b wireless LAN in ad-hoc mode.