Simultaneous events and lookahead in simulation protocols

  • Authors:

  • Vikas Jha;Rajive Bagrodia

  • Affiliations:

  • Department of Computer Science, University of California at Los Angeles, 3532 Boelter Hall, Box 951596, Los Angeles, CA;Department of Computer Science, University of California at Los Angeles, 3532 Boelter Hall, Box 951596, Los Angeles, CA

  • Venue:
  • ACM Transactions on Modeling and Computer Simulation (TOMACS)
  • Year:
  • 2000

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Abstract

A discrete event simulation model may contain several events that have the same timestamp, referred to as simultaneous events. In general, the results of a simulation depend on the order in which simultaneous events are executed. Simulation languages and protocols use different, sometimes ad hoc, tie-breaking mechanisms to order simulataneous events. As a result, it may be impossible to reproduce the results of a simulation model across different simulators. This article presents a systematic analysis of the lookahead requirements for sequential and parallel simulation protocols, utilizing the process-oriented world view, with respect to their abililty to execute models with simultaneous events in a deterministic order. In particular, the article shows that most protocols, including the global event list protocol and commonly used parallel conservative and optimistic protocols, require that the simulation model provide some form of lookahead guarantee to enforce deterministc ordering of simultaneous events. The article also shows that the lookahead requirements for many protocols can be weakened if the model allows simultaneous events to be processed in a nondeterministic order. Finally, the lookahead properties that must be satisfied by a model in order for its execution to make guaranteed progress are derived using various simulation protocols.