Alongside event throughput, it is important to ensure that inter-entity message passing scales well with the number of entities. For simplicity of scheduling, many (inefficient) parallel simulation systems utilize kernel threads or processes to model entities, which can lead to severe degradation with scale.
The systems that we have considered do not exhibit this problem. ns2 is a sequential simulator, so this issue does not arise. Parsec, and therefore also GloMoSim, models entities using logical processes implemented in user space and use an efficient simulation time scheduler. JiST implements entities as concurrent objects and also uses an efficient simulation time scheduler. The overheads of both Parsec and JiST were empirically measured. They are both negligible and do not represent a scalability constraint.