Abstract: The advantages and disadvantages of the common four circuit routing algorithms were analyzed in details based on the methods of topologic, and thus the relationship between the routing algorithm and the availability of the links was described quantitatively. Then the relationship between the availability of the links, the transmission network structure as well as the bearing services, were given. A quantified formula to calculate the availability index of the links was presented. On the foundation of the availability index, a new routing algorithm was finally presented. The validity of the algorithm is verified through an example.

Key words: routing algorithm, usability, transmission network