Dynamics of load-sensitive adaptive routing

Shortest path first (SPF) routing protocols, such as OSPF and IS-IS are currently the dominant intra-domain IP routing protocols and are widely used in the ISP backbones. Although the traffic on the Internet is highly dynamic, OSPF and IS-IS are not adaptive to the changing traffic, because the shortest path generated by these protocols are based on the link weights, which are fixed and usually can not be changed during network operation. This paper investigates a way of changing the weights in OSPF/IS-IS adaptively according to the changing traffic load on the links. The feedback effect and the stability issue of adaptive routing are analyzed from a control system point of view. The paper shows why minimal-delay adaptive routing, such as the routings in the early ARPANET, is not stable, and proposes some techniques to make our load-sensitive adaptive routing (LSAR) stable. Finally, the performance of LSAR is evaluated by simulation. The result shows that LSAR can significantly improve the QoS of the network by increasing network throughput and reducing packet drop ratio.

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