The diameter of a network, one of measures of network performance, must be small to make network delay small even after a link failure occurs. Therefore, the critical links whose failures degrade the performance must be protected by rapid recovery. In addition, the number of these protected links must be small to reduce the cost. Consequently, it is important to find the smallest number of the links to be protected so that the diameter of the network resulting from failures of non-protected links is not more than a threshold. First, we prove that the problem is generally NP-hard and present a polynomial-time algorithm when a failure pattern is restricted to a single link failure. Moreover, we present approximation algorithms with the approximation ratio of a fixed constant. In addition, we evaluate the number of protected links needed to keep the diameter of the networks small for actual network topology.
['Koji Imagawa', 'Takeshi Fujimura', 'Hiroyoshi Miwa']
Method for finding protected links to keep small diameter against failures