Evaluation of the Optimal SRPT Strategy with Overhead

Abstract

Considering queueing systems in data networks, one can identify a special feature of the communication system: the service time, which is proportional to message length, is known in advance. This is a precondition for queueing strategies such as SPT (shortest processing time first) or SRPT (shortest remaining processing time first), which offers the shortest mean delay time among all conceivable strategies. For a practical evaluation of these strategies it is essential to include the influence of overhead time, especially for the Preemptive SRPT strategy. This paper analyzes SRPT with constant overhead time CV modified by a constant preemption gap <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CP \gcong CV</tex> for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M/G/1</tex> systems. The comparison of strategies for FIFO, SPT, SRPT, and RR (round robin) using different service time distributions with coefficients of variation >1 and overhead shows, for SRPT and for a combination of SRPT and RR, a considerable reduction of the mean delay time <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\overline{TD}</tex> , especially for service time distributions with high coefficients of variation. This result indicates the potential advantages of these strategies in data network applications.