Direct routing: Algorithms and complexity

  • Authors:
  • Costas Busch;Malik Magdon-Ismail;Marios Mavronicolas;Paul Spirakis

  • Affiliations:
  • Rensselaer Polytechnic Institute, Department of Computer Science, 110 8th Street, 12180, Troy, NY, USA;Rensselaer Polytechnic Institute, Department of Computer Science, 110 8th Street, 12180, Troy, NY, USA;University of Cyprus, Department of Computer Science, P.O. Box 20537, 110 8th Street, CY-1678, Nicosia, NY, Cyprus;University of Patras, Rion, Department of Computer Engineering and Informatics, P.O. Box 20537, 110 8th Street, 265 00, Patras, NY, Greece and Computer Technology Institute, 61 Riga Fereou Street, ...

  • Venue:
  • Algorithmica
  • Year:
  • 2006

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Abstract

Direct routing is the special case ofbufferless routing whereN packets, once injected into the network, must be delivered to their destinations without collisions. We give a general treatment of three facets of direct routing: 1. Algorithms. We present a polynomial-timegreedy direct algorithm which is worst-case optimal. We improve the bound of the greedy algorithm for special cases, by applying variants of this algorithm to commonly used network topologies. In particular, we obtainnear-optimal routing time for thetree, mesh, butterfly, andhypercube. 2. Complexity. By a reduction from Vertex Coloring, we show that optimal Direct Routing is inapproximable, unless P=NP. 3. Lower Bounds for Buffering. We show that certain direct routing problems cannot be solved efficiently; in order to solve these problems,any routing algorithm needs buffers. We give non-trivial lower bounds on such buffering requirements for general routing algorithms.