A simpler proof for O(congestion+dilation) packet routing

  • Authors:
  • Thomas Rothvoß

  • Affiliations:
  • MIT, Cambridge

  • Venue:
  • IPCO'13 Proceedings of the 16th international conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2013

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Abstract

In the store-and-forward routing problem, packets have to be routed along given paths such that the arrival time of the latest packet is minimized. A groundbreaking result of Leighton, Maggs and Rao says that this can always be done in time $O(\textrm{congestion} + \textrm{dilation})$, where the congestion is the maximum number of paths using an edge and the dilation is the maximum length of a path. However, the analysis is quite arcane and complicated and works by iteratively improving an infeasible schedule. Here, we provide a more accessible analysis which is based on conditional expectations. Like [LMR94], our easier analysis also guarantees that constant size edge buffers suffice. Moreover, it was an open problem stated e.g. by Wiese [Wie11], whether there is any instance where all schedules need at least $(1+\varepsilon)\cdot(\textrm{congestion}+\textrm{dilation})$ steps, for a constant ε0. We answer this question affirmatively by making use of a probabilistic construction.