Recent papers in the literature on hybrid optical architectures combining path and packet switching have shown that it can be a good candidate for future optical networks. However, the optimization of the traffic splitting parameters by some metrics is vital to maximize the benefit by the hybrid architecture. Blocking rate is one of the most important performance metrics in a path switching network. In this paper, the authors propose an analytical method to compute both forward and backward blocking rates in path switching optical WDM networks with destination-initiated reservation. On a mesh topology they show that the results of their analytical method and simulations are close to each other.