High availability tops the list of features desired for building a network. Various factors influencing path availability of optical networks with span restoration are investigated from the network design point of view. Network redundancy, number of backup routes, and dual span failure restorability can have important effects on path availability. A formulation to improve average path availability of a network by maximizing dual failure restorability is developed. We also introduce a practical method to optimize spare capacity and path availability of a network at the same time. A case study analyzes how much average dual-failure restorability can be improved in a long haul network with span restoration. Conclusions deduced from the computational and analytical results can help network planners to design a network with high performance and optimized cost and availability.
The foundation pillars of successful technical products are performance, cost, and reliability. The development of reliable components and the operation of highly available systems is a comprehensive engineering task combining probability theory, materials science, and experience. Components have to be as reliable as necessary in order to build systems that are dependable and cost efficient during the whole life cycle. Reliability engineering is an ongoing process starting at the conceptual phase of a product design and continuing throughout all phases of a product life cycle. Theprimary objective is to identify and eliminate potential reliability problems as early as possible. While it may never be too late to improve the reliability of a product, corrections are orders of magnitude less expensive in the early design phase rather than once the product is manufactured and in service. This paper comprises an introduction to basic reliability engineering terms, reliability analysis methods such as reliability block diagrams, failure mode and effects analysis, Markov processes, the concept of redundancy, failure rate prediction models and the physics of failure approach, qualification and accelerated reliability testing. Examples of electronic and optical components, as well as complex opto-electronic systems and networks are given for illustration.
This work is motivated by interest in analyzing and optimizing availability of optical networks under different protection strategies. Methodology dealing with availability calculation, protection strategies, spare capacity, redundancy and sensitivity analysis is described. A case study calculates the availability of all connections within a long haul US-network using three protection strategies: path protection, span protection and protection-cycles. The distributions of connection down time of the three protection strategies are given. The availability optimization potential is estimated based on analysis of its sensitivity on reliability input data. Advantages and disadvantages of each strategy are compared from the availability and spare capacity requirement points of view.