Flow optimization in IP networks with fast proactive recovery

The post-failure convergence of the shortest path routing (SPR) protocols used in IP networks can be too slow to meet the restrictive requirements (i.e., maximum allowable delay, jitter, etc.) of the multimedia services and therefore new restoration mechanisms combined with IP routing are of interest. The paper addresses optimization of three potential rerouting mechanisms based on the IP fast reroute mechanism proposed by Shand and Bryant [1]. The first mechanism takes advantage of equal-cost multiple (shortest) paths (ECMP) where two or more ECMP paths outgoing from one router can be used to protect one another in the IP fast reroute mechanism. Due to a limited number of the ECMP paths, the ECMP protection cannot be used as a stand-alone rerouting mechanism which assures protection against all link failures. Therefore, two other mechanisms, called loop-free alternate (LFA) and multi-hop repair path (MHRP) are considered. The LFA protection consists in determining an alternative next-hop address used in the case of a link failure. MHRP is a generalization of LFA which uses multi-hop tunnels to redirect packets from the failing link to a router that is able to send them to the destination based on a shortest path based forwarding. For each of the mechanisms we formulate an appropriate optimization problem as a mixed integer program (MIP). Moreover, we consider a combined approach where protection is assured through ECMP paths, LFA next-hop addresses, or MHRP paths. Thanks to the variety of protection mechanisms, the IP fast reroute technique is able to provide protection for any single link failure. The associated optimization problem (consisting in a simultaneous optimization of a weight system, LFA alternative next-hop addresses and MHRP paths) is difficult and is thus approached with a heuristic method. In our numerical experiments we evaluate effectiveness of this method.