Optimal buffer size for a stochastic processing network in heavy traffic

  • Authors:
  • Arka P. Ghosh;Ananda P. Weerasinghe

  • Affiliations:
  • Department of Statistics, Iowa State University, Ames, USA 50011-1210;Department of Mathematics, Iowa State University, Ames, USA 50011

  • Venue:
  • Queueing Systems: Theory and Applications
  • Year:
  • 2007

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Abstract

We consider a one-dimensional stochastic control problem that arises from queueing network applications. The state process corresponding to the queue-length process is given by a stochastic differential equation which reflects at the origin. The controller can choose the drift coefficient which represents the service rate and the buffer size b0. When the queue length reaches b, the new customers are rejected and this incurs a penalty. There are three types of costs involved: A "control cost" related to the dynamically controlled service rate, a "congestion cost" which depends on the queue length and a "rejection penalty" for the rejection of the customers. We consider the problem of minimizing long-term average cost, which is also known as the ergodic cost criterion. We obtain an optimal drift rate (i.e. an optimal service rate) as well as the optimal buffer size b *0. When the buffer size b0 is fixed and where there is no congestion cost, this problem is similar to the work in Ata, Harrison and Shepp (Ann. Appl. Probab. 15, 1145---1160, 2005). Our method is quite different from that of (Ata, Harrison and Shepp (Ann. Appl. Probab. 15, 1145---1160, 2005)). To obtain a solution to the corresponding Hamilton---Jacobi---Bellman (HJB) equation, we analyze a family of ordinary differential equations. We make use of some specific characteristics of this family of solutions to obtain the optimal buffer size b *0.