Dynamic traffic controls for Web-server networks

Distributed Web-server systems have been widely used to provide effective Internet services. The management of these systems requires dynamic controls of the Web traffic. With the development of multimedia Web sites and increasingly diversified services, the existing load balancing approaches can no longer satisfy the requirements of either the service providers or the users. In this paper, a new reward-based control mechanism is proposed that can satisfy the dynamic content-based control requirement while avoiding congestion at the dispatcher. The core of the control algorithm is based on an MDP model. To minimize the system overhead, a centralized dispatching with decentralized admission (CDDA) approach is used to distribute the control related computation to each server pool. This cuts down the dimensions of the problem dramatically. We also propose a state-block scheme to further reduce the state space so that the algorithm becomes computationally feasible for on-line implementation. Simulation results demonstrate that the proposed state-block approach can not only reduce the computation time dramatically but also provide a good approximation of power-tailed request interarrival times common for Internet traffic. Finally, an implementation plan with system design is also proposed. (C) 2004 Elsevier B.V. All rights reserved