System- and Element-Related Metrics Useful in the Evaluation of Resilience

Failures of network elements will undoubtedly continue to occur since it is impossible to eliminate all the factors responsible for them. However, the scale of the negative consequences of failure events is determined not only by the characteristics of the related challenges but also by the properties of the system architecture such as system topology, location of servers providing services to end users, transmission schemes, etc. This chapter aims to discuss the most important metrics useful in evaluating resilience. It starts with the analysis of properties of metrics dedicated to single elements of the system. Next, it explains the properties of the essential structural metrics and discusses the reasons for the diverse characteristics of system elements, the related irregular characteristics of the system topology, and the resulting potential challenges. After that, it elaborates on the major functional metrics, i.e., the ones useful for evaluating system performance at the network level and the packet level, as well as the subjective metrics referring to the satisfaction of users. The final part discusses the practical applications of the analyzed metrics in everyday use (e.g., in the configuration of routing protocols).