Eliminating Queues from RT UML Model Representations

This paper concerns analyzing UML based models of distributed real time systems involving multiple active agents. In order to avoid the time-penalties incurred by distributed execution of synchronous operation calls, it is typically recommended to restrict inter-task communication to event-based communication through unbounded FIFO buffers. This means that such systems potentially have an infinite number of states, making them out of reach for analysis techniques intended for finite-state systems. We present a symbolic analysis technique of such systems, which can be tuned to give a finite, possibly inexact representation of the state-space. The central idea is to eliminate FIFO buffers completely, and represent their contents implicitly, by their effect on the receiving agent. We propose a natural class of protocols which we call mode separated, for which this representation is both finite and exact. This result has impact on both responsiveness and predictability of end-to-end latencies, as well for the protocol verification, enabling automatic verification methods to be applied.