Minimum-expected-delay alternate routing

The authors consider the problem of finding a routing strategy that minimizes the expected delay from every source to a single destination in a network in which each link fails and recovers according to a Markov chain. It is assumed that each node knows the current state of its own outgoing links and the state-transition probabilities for every link of the network. It is shown that the general problem is #P-complete, and two special cases are considered: case 1 assumes the network is a directed acyclic graph oriented toward the destination, and case 2 assumes that the link states are independent from slot to slot. For each case, it is proved that the optimal routing strategy has a simple state-independent representation. An efficient algorithm is presented for finding the optimal strategy.