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 of Internet is highly dynamic, but OSPF and IS-IS are not adaptive to the changing traffic, because the shortest path generated by these protocols ate based on the link weights which are fixed and can not be changed during network operation. This paper investigates a way of changing the weights in OSPF/IS-IS adaptively to the changing traffic. The feed-back effect and the stability issue of adaptive routing are analyzed from a control point of view. The paper shows why Minimal-Delay Adaptive Routing, such as the routings in the early ARPANET, is not stable and what can be done to make Load-Sensitive Adaptive Routing (LSAR) stable. Finally, the performance of LSAR is evaluated by simulation. The result shows that LSAR can significantly improve QoS of the network by increasing throughput and reducing packet drop ratio.
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