We investigate the performance of the Time Warp kernel APSIS when running on various communication layers, in particular on a wide-area Grid. Several cancellation strategies are tried, among them the lazy cancellation and a little known bulk anti-messages optimisation. Our experiments with an Ising spin simulation indicate that the slowdown caused by high latency networks, while signi.cant, is not catastrophic, and that it can be significantly reduced using the lazy cancellation. Experiments suggest that further improvements can be expected if a more elaborate communication infrastructure is put in place.