QoS restoration for dependable networks

QoS restoration, the capability of a network to help maintain the QoS above pre-defined minimum requirements in case of failures or load fluctuations, is proposed. If failures or load fluctuations occur, a network with QoS restoration reallocates surplus network resources from working connections as well as from pre-assigned spare capacity by using a distributed algorithm to restore the degraded connections. This distributed algorithm is composed of the flooding of failure or load fluctuation notification, working connection reconfiguration signaling, and a conventional self-healing or distributed algorithm against load fluctuations. Theoretical maximum restoration ratios for various failures were calculated by integer programming. These analytical evaluations show that resource reallocation allows high ratio of restoration from single-link failures having no spare resources, and double-link failures having spare resources prepared for single-link failures. Simulation results show that the proposed distributed algorithm achieves a restoration ratio close to the theoretical maximum regardless of whether pre-assigned spare capacity exists