A 3-queue polling system with join the shortest-serve the longest policy

Efrat Perel, Nir Perel*, Uri Yechiali

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


In 1987, J.W. Cohen analyzed the so-called Serve the Longest Queue (SLQ) queueing system, where a single server attends two non-symmetric M/G/1-type queues, exercising a non-preemptive priority switching policy. Cohen further analyzed in 1998 a non-symmetric 2-queue Markovian system, where newly arriving customers follow the Join the Shortest Queue (JSQ) discipline. The current paper generalizes and extends Cohen's works by studying a combined JSQ–SLQ model, and by broadening the scope of analysis to a non-symmetric 3-queue system, where arriving customers follow the JSQ strategy and a single server exercises the preemptive priority SLQ discipline. The system states’ multi-dimensional probability distribution function is derived while applying a non-conventional representation of the underlying process's state-space. The analysis combines both Probability Generating Functions and Matrix Geometric methodologies. It is shown that the joint JSQ–SLQ operating policy achieves extremely well the goal of balancing between queue sizes. This is emphasized when calculating the Gini Index associated with the differences between mean queue sizes: the value of the coefficient is close to zero. Extensive numerical results are presented.

Original languageEnglish
Pages (from-to)1101-1120
Number of pages20
JournalIndagationes Mathematicae
Issue number5
StatePublished - Sep 2023


  • Gini index
  • Join the shortest queue
  • Matrix geometric
  • Polling systems
  • Probability generating functions
  • Serve the longest queue


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