Routing equal-size messages on a slotted ring

  • Authors:
  • Dariusz Dereniowski;Wiesław Kubiak

  • Affiliations:
  • Department of Algorithms and System Modeling, Gdańsk University of Technology, Gdańsk, Poland;Faculty of Business Administration, Memorial University, St. John's, Canada

  • Venue:
  • Journal of Scheduling
  • Year:
  • 2012

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Abstract

We deal with the problem of routing messages on a slotted ring network in this paper. We study the computational complexity and algorithms for this routing by means of the results known in the literature for the multi-slot just-in-time scheduling problem. We consider two criteria for the routing problem: makespan, or minimum routing time, and diagonal makespan. A diagonal is simply a schedule of ring links i=0,驴,q驴1 in q consecutive time slots, respectively. The number of diagonals between the earliest and the latest diagonals with non-empty packets is referred to as the diagonal makespan. For the former, we show that the optimal routing of messages of size k, is NP-hard in the strong sense, while an optimal routing when k=q can be computed in O(n 2log2 n) time. We also give an O(nlogn)-time constant factor approximation algorithm for unit size messages. For the latter, we prove that the optimal routing of messages of size k, where k divides the size of the ring q, is NP-hard in the strong sense even for any fixed k驴1, while an optimal routing when k=q can be computed in O(nlogn) time. We also give an O(nlogn)-time approximation algorithm with an absolute error 2q驴k.