Automatic ring protection provides simple and rapid fault protection and restoration in telecommunication networks. To implement the automatic ring protection in general wavelength-division multiplexing (WDM) optical networks, the lightpaths are partitioned into groups each of which can be carried in a simple cycle of the underlying network. As the electronic line terminals are the dominant cost factor in the deployment of WDM optical networks, we study how to generate these partitions with minimum electronic line terminals. This optimization problem is NP-hard. We develop two polynomial-time approximation algorithms, with performance guarantees between 1.5 and 1.6 and between 1.5 and 1.5 + epsilon, respectively. The second algorithm can be adapted, with the same performance guarantees, to the problem in which lightpaths are not prespecified and only the endpoints of each connection are given. Both algorithms can be easily adapted, with the same performance guarantees, to the problem in which only link protection is desired, and each group must be carried in a closed trail. The first algorithm matches and the second algorithm improves the approximation ratio obtained independently by Eilam et al. (2000).
