Using atomic broadcast to implement a posteriori agreement for clock synchronization

A clock synchronization algorithm was given by P. Verissimo et al. (1989), dubbed a posteriori agreement, a variant of the convergence nonaveraging technique. By exploiting the characteristics of broadcast networks, the effect of message delivery delay variance is largely reduced. In consequence, the precision achieved by the algorithm is drastically improved. Accuracy preservation is near to optimal. A particular materialization of this algorithm, implemented as a time service of the xAMp group communications system, is given here. The algorithm was implemented using some of the primitives offered by xAMp, which simplified the work and stressed its advantages. Performance results for this implementation obtained on two different infrastructures are presented. Timings validate the design choices and clearly show that the algorithm is able to provide improved precision without compromising accuracy and reliability