Abstract
Network Survivability is defined as the ability of a network to support the committed Quality of Services (QoS) continuously in the presence of different failure scenarios. Both availability and performance degradation of a system in presence of failure are integral components of survivability evaluation. Therefore, a composite model is presented for network survivability that includes system availability analysis to find out the cost due to system downtime, and system failure impact analysis to find out the transient performance degradation when failure occurs. A new analytical technique is presented to evaluate the excess loss due to failure (ELF) as the transient performance degradation when the system is operating in gracefully degraded states. Single and multiple link failures as well as node failures are considered. An algorithm is proposed to carry out the steady state availability analysis of a network even when the available paths between a pair of nodes are non-disjoint. A recursive generalized form of the availability algorithm when there are multiple paths available between a pair of nodes is presented. The availability model and the performance model are combined to construct a hierarchical model to evaluate the network survivability performance. Simulation results are used to validate the proposed model. A WDM network with wavelength conversion is considered as an example for this evaluation.