Steady-state response of shortest-path routing algorithms

The steady-state response of link-state and loop-free distance-vector routing algorithms to multiple changes in the costs of links is investigated. A quantitative comparison of an ideal link-state algorithm similar to the one used in the open shortest path first (OSPF) and in the OSI intradomain routing protocol, and a new loop-free distance-vector algorithm, is made for several computer network topologies. A variety of quantities, including the length of messages and the average number of paths affected by routing loops, are computed as a function of time after a link or node change. Probabilities of various conditions, including the existence of loops, are also obtained as a function of time. The results show that in steady state, a loop-free distance-vector algorithm operates with essentially the same communication overhead as the ideal link state algorithm, and requires substantially fewer CPU cycles. The results also suggest that it may be possible to correlate the performance of the routing algorithms with various parameters that can be used to characterize networks.<>