Virtual time synchronization over unreliable network transport

In parallel and distributed simulations, it is sometimes desirable that the application's time-stamped events and/or the simulator's time-management control messages be exchanged over a combination of reliable and unreliable network channels. A challenge in developing infrastructure for such simulations is to correctly compute simulation time advances despite the loss of some simulation events and/or control messages. The authors present algorithms for synchronization in distributed simulations, performed directly over best-effort network transport. The algorithms are presented in a sequence of progressive refinement, starting with all reliable transport and finishing with combinations of reliable and unreliable transport for both time-stamped events and time management messages. Performance results from a preliminary implementation of these algorithms are also presented. To our knowledge, this is the first work to solve asynchronous time synchronization performed directly over unreliable network transport.