On reducing the processing cost of on‐demand QoS path computation

Quality of Service (QoS) routing algorithms have become the focus of recent research due to their potential for increasing the utilization of an Integrated Services Packet Network (ISPN) serving requests with QoS requirements. While heuristics for determining paths for such requests have been formulated for a variety of QoS models, little attention has been given to the overall processing complexity of the QoS routing protocol. This paper deals with the processing complexity of determining QoS paths in link state based routing architectures. Although on‐demand path computation is very attractive due to its simplicity, many believe that its processing cost will be prohibitive in environments with high request rates. In this work, we first characterize the processing cost of QoS routing algorithms that use the widest‐shortest path heuristic. Then we study alternatives to on‐demand path computation that can reduce this processing overhead. In addition to the well known solution of path pre‐computation, we introduce and study path caching, an incremental modification of on‐demand path computation. By simulating realistic topologies and traffic conditions we investigate the performance of both alternatives. Our results show that caching is an effective alternative to path pre‐computation and that both path caching and pre‐computation can achieve significant processing cost savings without severely compromising routing performance.