Design of survivable VPN based VoIP networks

This paper addresses the issue of survivable voice over IP (VoIP) network design. In the applied model the whole VoIP network is divided into two logical components: the access network and the transport network. The access network consists of VoIP end-points, which connect to the transport network through edge routers serving as gateways. Thus, one task of the design process is to assign gateways to the VoIP end-points. To assure security and availability for the VoIP traffic, a virtual private network (VPN) is assumed as transport network in this paper; therefore, the other task is to specify the transport VPN in the most economical way, while also taking the possible failures of transport network elements into consideration. Assuming a single failure at a time, the survivability of the VoIP network can be assured by assigning two gateways, namely a primary and a backup one, to each VoIP end-point, and calculating two disjoint paths between each pair of gateways. The two tasks of survivable VoIP network design can be solved separately; however, in this paper, a novel solution is proposed in which the edge router assignment process takes both the objective function of VPN specification and the issues of survivability into consideration. Multiple methods realizing the novel approach are presented, which are based on the paradigms of evolutionary algorithms and simulated annealing. The performance of the presented methods is evaluated with the help of simulations, using a well-known greedy algorithm as reference. It is shown that the proposed methods outperform the reference algorithm significantly in the simulation scenarios investigated.