Network Design Method by Link Protection to Keep Connectivity and Communication Quality to Servers

Abstract

Information network must be sufficiently reliable. The most reliable method is to protect all links so that the failure probability of a link is sufficiently small by sufficient backup resource and rapid recovery system. However, as link protection needs much cost, it is necessary to find the smallest number of links to be protected so that a network resulting from failures of any non-protected links can provide sufficient connectivity. Especially, in content delivery services, a request from a user is navigated to one of the mirror servers so that small delay time and balance of loads can be achieved; the network topology must be designed so that the navigation can be efficiently achieved even after failure. In this paper, we focus on the problem of finding the protected links so that the conditions that include the stretch factor and the fragmentation factor are satisfied. First, we formulate this problem and prove that this problem is NP-hard. Next, we present a polynomial-time algorithm to solve the problem that the number of the simultaneous link failures is restricted to one. Furthermore, we present a polynomial-time approximation algorithm with the approximation ratio of a constant that is the number of the simultaneous link failures. In addition, we apply the approximation algorithms to the topology of actual networks and evaluate the approximation ratio.