Optimal multihop routing. An iterative approach to TWDM embedding

This paper introduces the concept of time slot synchronization in time-wave division multiplexed (TWDM) multihop lightwave networks. It is shown that the time slot assignments of the intermediate nodes in a multihop path have significant effect on the end-to-end message delay. This is different from traditional notions in routing, where the hop count and congestion control are the primary concerns. Assuming a TWDM embedding of a given logical topology already exists, we formulate the optimal routing problem for arbitrary propagation delays. We propose a graph unfolding technique which converts this problem into the shortest path routing problem for weighted graphs with well known solutions. We show a method to estimate the buffering cost at the intermediate nodes (in multihop routing) to accommodate high-bandwidth traffic (e.g., video). Next, we address the question: given a logical topology what should the TWDM embedding be so that the routing delays are optimized P This leads us to an iterative approach for TWDM embedding. Given an initial embedding an optimal route is estimated for each pair of nodes. A weighted average of these optimal route distances is used as a metric to evaluate the TWDM embedding. Using a heuristic the TWDM embedding is modified and the process iterated to improve along this metric. Preliminary performance results illustrating the improvement in routing delay are provided. For example, for a 4-cube network on average delay minimization of 10% to 20% is observed