Novel availability metrics for network topologies

This paper presents two novel definitions for availability concerning communication networks. It is shown that currently used network availability metrics cannot fully describe the resiliency of a network. The aim of this paper is to provide metrics that enable network operators to compare different network topology designs assuming a given population distribution. A transport network is considered to be in down state when at least a certain percentage of all subscribers for at least 10 seconds have no connectivity, or have only poor performance. We also present another availability metric named Session Completion Ratio, which is a more user-centric performance indicator since any user with poor performance or no connectivity deteriorates the overall network performance. Simulation results are presented and different transport network topologies are compared based on their availability performance, followed by a case study, where the availability of a network is improved by allocating extra capacity on the links. The results proved that single link failure-tolerant capacity setting leads to high-availability. Finally a tool is presented that helps identifying those parts of the network that have the strongest influence on resiliency.