Dynamic behavior of shortest path routing algorithms for communication networks

Abstract

Abstract-Several proposed routing algorithms for store and forward oscillations. This behavior is due to the fact that delay conlmunication networks, including one currently- in operation in the estimates used to choose routes are themselves affected by ARPANET. route messages along shortest paths computed by using some the route choice with a feedback effect resulting. To reset of link lengths. When these lengths depend on current traffic conditions a5 they must in an adaptive algorithm, dynamic behavior questions such as medy this situation it was decided on heuristic grounds to stabilitv, convergence, and speed of convergence are of interest. This paper introduce an additive factor, called bias, to the estimated is the first attempt to analyze sy-stematically these issues. It is shom that minimum queuing delay path algorithms tend to eshibit violent oscillaton behavior in the absence of a damping mechanism. The oscillations can be damped by means of several typs of schemes two of which are analyzed in this paper. In the first scheme a constant bias is added to the queuing delay thereby providing a preference towards paths with a small number of links. delay of each link. thereby building into the algorithm a preference towards paths with small number of hops to the destination [5]-[7]. This had a stabilizing effect albeit at the expense of considerable loss of sensitivity to traffic congestion. In the second scheme the effects of several past routings are averaged as for esample when the link lengths are computed and conmunicated ay nchronously throughout the network. The implementation of the minimum delay path idea in the original ARPANET algorithm had a number of flaws allowing, for example. the formation of loops. For this reason alternative schemes based on the same idea were I.