Equivalent permutation capabilities between time-division optical omega networks and non-optical extra-stage omega networks

  • Authors:
  • Xiaojun Shen;Fan Yang;Yi Pan

  • Affiliations:
  • University of Missouri-Kansas City, Kansas City, MO;IBM Corporation 414/6-4, Poughkeepsie, NY;Georgia State University, Atlanta, GA

  • Venue:
  • IEEE/ACM Transactions on Networking (TON)
  • Year:
  • 2001

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Abstract

Because signals carried by two waveguides entering a common switch element would generate crosstalk, a regular N × N multistage interconnection network (MIN) cannot be directly used as an optical switch between N inputs and N outputs in an optical network. A simple solution is to use a 2N × 2N cube-type MIN to provide the N × N connections, which needs a much larger hardware cost. A recent research proposed another solution, called the time-domain approach, that divides the N optical inputs into several groups such that crosstalk-free connections can be provided by an N × N regular MIN in several time slots, one for each group. Researchers studied this approach on Omega networks and defined the class set θ to be the set of N-permutations realizable in two time slots on an Omega network. They proved that the size of θ is larger than the size of class Ω, where Ω consists of all N-permutations admissible to a regular N × N (nonoptical) Omega network. This paper first presents an optimal O(N log N) time algorithm for identifying whether a given permutation belongs to class θ or not. Using this algorithm, this paper then proves an interesting result that the class θ is identical to the class Ω + 1 which represents the set of N-permutations admissible to a nonoptical N × N one-extra stage Omega network.