Oblivious Routing Algorithms on the Mesh of Buses

  • Authors:
  • Kazuo Iwama;Eiji Miyano

  • Affiliations:
  • -;-

  • Venue:
  • IPPS '97 Proceedings of the 11th International Symposium on Parallel Processing
  • Year:
  • 1997

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Abstract

An optimal \lceil 1.5N^{1/2} \rceil lower bound is shown for oblivious routing on the mesh of buses, a two-dimensional parallel model consisting of N^{1/2}\times N^{1/2} processors, N^{1/2} row and N^{1/2} column buses but no local connections between neighbouring processors. Many lower bound proofs for routing on mesh-structured models use a single instance (adversary) which includes difficult packet-movement. This approach does not work in our case; our proof is the first which exploits the fact that the routing algorithm has to cope with many different instances. Note that the two-dimensional mesh of buses includes 2N^{1/2} buses and each processor can access two different buses. Apparently the three-dimensional model provides more communication facilities, namely, including 3N^{2/3} buses and each processor can access three different buses. Surprisingly, however, the oblivious routing on the three-dimensional mesh of buses needs more time, i.e., \Omega(N^{2/3}) steps, which is another important result of this paper.