Formal Specification and Dependability Analysis of Optical Communication Networks

Network dependability reflects the ability to deliver continuous services even after failures, such as man-made or natural disturbances, e.g., storms, hurricanes, and floods, etc. In the last decade, optical networks have been increasingly deployed to provide multicast traffic in metropolitan areas. In this paper, we provide a formal specification of double-rings with dual attachments (DRDA) topologies of optical networks using Continuous-Time Markov Chains. Our formal modeling includes the concept of pre-configured protection cycles (p-cycles), which provide effective fault tolerance against link-failures in optical networks. Our approach is generic enough to handle networks of any size that are prone to any combinations of link failures. We formally specify several dependability properties using Continuous Stochastic Logic (CSL). We then provide a quantitative evaluation of these properties using the PRISM model checker. We observe that such formal analysis can provide critical information at early design stages to network operators for designing highly-dependable optical networks in metropolitan areas (e.g., availability on the order of 99.99% or 99.999%).