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.
The paper gives an overview of reliability, availability, and maintainability of fiber optical sensors, three key factors on which standards and validation should be based and which are required for successful industrialization. The examples given are based on two long term applications with fiber optical Bragg gratings - the surveillance of two bridges (civil engineering). However, similar reflections are required for any type of application and any optical fiber sensors. Recommendations are given to improve the confidence and acceptance of possible users in fiber optical sensing systems. It is shown that with proper installation lifetimes of 50 years are possible.
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.
Fiber optic sensors are potentially very well suited for condition monitoring of environment, materials, structures, and facilities. However, there is a long way from a laboratory prototype to a reliable industrial sensor system. Based on the examples of two fiber Bragg grating systems, both used for long term monitoring of strain and temperature on bridges, general sensor system reliability will be discussed. In addition, specific reliability considerations and lifetime tests, especially for optical fibers and Bragg gratings, coatings, and adhesives will be presented.
This paper describes analysis tools and characterization techniques for photonic components related materials analysis as well as functionality and reliability testing. Field failures and breakdowns of optical fibers and cables, fiber Bragg gratings, connectors, semiconductor lasers, opto-couplers, micro-optical elements, and others have to be analyzed and failure causes and mechanisms have to be found in order to improve future components. On the other hand, new materials used and new components for future all-optical networks may lead to new failure mechanisms, which have to be analyzed and modeled for lifetime predictions. In this paper some basic principles of instruments and techniques used for reliability and failure analysis rather than a deep treatise are given and may guide the reader to find appropriate methods for a specific problem. Illustrative examples are provided.
For the extension of existing optical fiber links to higher data transfer rates in the multi-gigabit range and the expected higher power density due to DWDM one must consider possible limitations of the deployed cables. Many investigations have identified polarization mode dispersion PMD as a crucial parameter especially for cables exposed to environmental stresses. Three aerial optical fiber cable links were characterized by measuring PMD, optical time domain reflectometry OTDR, polarization-OTDR, and bit error rate BER. Measurement results over several days are correlated to temperature data from weather stations along the cable lines.
Highly reliable and available systems in all-optical networks require the implementation of various types of redundancy. For reliability and availability analysis systems can be described by reliability block diagrams or diagrams describing system state transitions. Analytical calculations for characteristic reliability and availability parameters such as mean time to failure or average availability for complex, repairable systems containing redundancies rapidly become costly and intractable. Monte Carlo simulation and Markov process calculations are therefore deployed. Results of simulations and calculations show sufficient accuracy and high flexibility for sensitivity analysis. Sensitivity analysis is the quantitative identification of system parts dominating the overall system availability by systematical variation of calculation input data, i.e. failure and repair rates. This gives valuable input for possible system optimization comprising technical and economical aspects.
This contribution investigates mean time to failure, mean unavailability and mean down time of an optical cross connect described by a complex reliability block diagram. In addition a sensitivity analysis is performed. All Monte Carlo simulations and Markov calculations are done by using a commercial software tool.
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