A loop-free path-finding algorithm: specification, verification and complexity

The loop-free path-finding algorithm (LPA) is presented. LPA specifies the second-to-last hop and distance to each destination to ensure termination; in addition, it uses an inter-neighbor synchronization mechanism to eliminate temporary loops. A detailed proof of LPA's correctness is presented and its complexity is evaluated. LPA's average performance is compared by simulation with the performance of algorithms representative of the state of the art in distributed routing, namely an ideal link-state (ILS) algorithm and a loop free algorithm that is based on internodal coordination spanning multiple hops (DUAL). The simulation results show that LPA is a more scalable alternative than DUAL and ILS in terms of the average number of steps, messages, and operations needed for each algorithm to converge after a topology change. LPA is shown to achieve loop freedom at every instant without much additional overhead over that incurred by prior algorithms based on second-to-last hop and distance information.