  In optical WDM networks, since each lightpath can carry a huge mount of
traffic, failures may seriously damage the end user applications. Hence fault
tolerance becomes an important issue on these networks. The light path which
carries traffic during normal operation is called as primary path. The traffic
is rerouted on a backup path in case of a failure. In this paper we propose to
design a reliable and fault tolerant routing algorithm for establishing primary
and backup paths. In order to establish the primary path, this algorithm uses
load balancing in which link cost metrics are estimated based on the current
load of the links. In backup path setup, the source calculates the blocking
probability through the received feedback from the destination by sending a
small fraction of probe packets along the existing paths. It then selects the
optimal light path with the lowest blocking probability. Based on the
simulation results, we show that the reliable and fault tolerant routing
algorithm reduces the blocking probability and latency while increasing the
throughput and channel utilization.
