Stationary analysis of the "Shortest Queue First" service policy: the asymmetric case

TL;DR

This paper analyzes the stationary behavior of the Shortest Queue First policy for two asymmetric queues with exponential service times, deriving the workload distribution and queue empty probabilities.

Contribution

It extends previous symmetric queue analysis to asymmetric queues, providing a functional equation approach and series solutions for workload distributions.

Findings

Derived the bivariate Laplace transform of workloads.

Characterized empty queue probabilities.

Analyzed tail behavior of workload distributions.

Abstract

As a follow-up to a recent paper considering two symmetric queues, the \textit{Shortest Queue First} service discipline is presently analysed for two general asymmetric queues. Using the results previously established and assuming exponentially distributed service times, the bivariate Laplace transform of workloads in each queue is shown to depend on the solution $\mathbf{M}$ to a two-dimensional functional equation $$ \mathbf{M} = Q_1 \cdot \mathbf{M}\circ h_1 + Q_2 \cdot \mathbf{M}\circ h_2 + \mathbf{L} $$ with given matrices $Q_1$, $Q_2$ and vector $\mathbf{L}$ and where functions $h_1$ and $h_2$ are defined each on some rational curve; solution $\mathbf{M}$ can then represented by a series expansion involving the semi-group $< h_1, h_2 >$ generated by these two functions. The empty queue probabilities along with the tail behaviour of the workload distribution at each queue are characterised.