Replicated state space approach for parallel simulation

Parallel processing offers the possibility of greatly increased performance for simulations which are computationally bound on existing machines. On shared memory machines, such as the BBN Butterfly, a natural approach is to allocate entities to be processed on different processors with locks used to prevent synchronization problems for a state space in global memory. Parallel processors having local memory only, such as the hypercube architectures, cannot use this approach. Such machines are potentially less expensive than shared memory architectures with similar local computational power, since the interconnection network is simpler. The most natural simulation paradigm for such machines, object oriented programming with interactions limited to messages, may become communications bound if the entities represented are tightly coupled. This paper presents an alternative approach based on use of replicated state spaces on each processor, and consolidation of these changes on a processor basis rather than an interaction basis to minimize message passing. The effect is to trade a parallel processing synchronization problem for a data consistency problem. The approach then relies only on a message broadcasting or passing architecture. For small degrees of parallelism, this requirement can be met by a variety of architectures. The method described is being applied to parallelize the CORBAN combat simulation for operation on a hypercube architecture as part of preliminary feasibility analysis concerning simulation support of Airland Battle Management (ALBM).