Marcel Held

Connection Availability Analysis of Shared Backup Path-Protected Mesh Networks

Dual-span failures dominate the system unavailability in a mesh-restorable network with full restorability to single-span failures. Traditional availability analysis based on reliability block diagrams is not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of connection availability. A U.S. network consisting of 19 nodes and 28 spans yielding 171 bidirectional connections is investigated. We find that networks with shared backup path protection can have average connection unavailabilities of the same order of magnitude as those with dedicated automatic protection switching, however, with a much better capacity efficiency. The proposed method can exactly calculate the unavailability of a specific connection with known restoration details or the average connection performance without any restoration details by presuming the dual-span failures to be the only failure mode and an arbitrary allocation rule of spare capacity

Comparison and evaluation of newest failure rate prediction models: FIDES and RIAC 217Plus

The failure rate of an example avionics control unit with approximately 7000 electronic components is calculated with the latest state-of-the-art prediction models FIDES Guide 2004 and RIAC-Handbook-217Plus (2006). To allow comparison of the component prediction models a standard civil avionics profile was defined and used for both calculations. Results are compared supported by analysis of the influence of component and application specific parameters such as temperature, temperature cycles, humidity, and vibration. In addition predicted failure rates are compared to field data that has been collected for this unit during 15 years.

Consideration of connection availability optimization in optical networks

Availability calculations of generalized span and path protected connections based on reference failure and repair times are performed. A case study analyzes the availability of a connection within a long haul network using three protection strategies: path protection, span protection and protection-cycles. A sensitivity analysis shows the dependency of the achieved connection availabilities on reliability data and the resulting improvement and optimization potential. Optimization aspects are completed by an estimation of spare parts provisioning and corrective maintenance actions.

Analysis and optimization of connection availabilities of optical networks with different protection strategies

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.

Redundancy, Restorability and Path Availability in Optical Mesh Networks

A new calculation method to estimate path availability under dual failure scenarios for networks designed for 100% restorability against single span failures is presented. This method is applicable to all survivability schemes and considers their respective restoration or protection effect. A case study calculates the availability of all service paths within a long haul network under four protection/restoration strategies: dedicated automatic protection switching, shared backup path protection, span restoration and protection-cycles. The availability optimization potential is estimated based on measures for standard network redundancy and dual failure restorability. Assets and drawbacks of survivability schemes are compared from the availability and capacity efficiency point of view

Long-term monitoring of polarization-mode dispersion of aerial optical cables with respect to line availability

Physical and technical limits become important when trying to increase data transfer rates to tens of gigabits and higher for already installed optical cables. Polarization-mode dispersion (PMD) is one of the crucial transmission constraints, especially for aerial cables exposed to environmental stresses. Optical fibers in the laboratory and three aerial optical fiber cable links across the Swiss alps were characterized with respect to PMD. Long-term measurement results are correlated to weather data along the cables, and predictions regarding line availability are made.

AN INTRODUCTION TO RELIABILITY OF OPTICAL COMPONENTS AND FIBER OPTIC SENSORS

We shortly review general reliability engineering concepts and methods and attempt to discuss in how far these can be applied to optical components used for optical fiber sensors.

Connection availability analysis of span-restorable mesh networks

Dual-span failures are the key factor of the system unavailability in a mesh-restorable network with full restorability of single-span failures. Availability analysis based on reliability block diagrams is not suitable to describe failures of mesh-restorable networks with widely distributed and interdependent spare capacities. Therefore, a new concept of restoration-aware connection availability is proposed to facilitate the analysis. Specific models of span-oriented schemes are built and analyzed. By using the proposed computation method and presuming dual-span failures to be the only failure mode, we can exactly calculate the average connection unavailability with an arbitrary allocation rule for spare capacity and no knowledge of any restoration details, or the unavailability of a specific connection with known restoration details. Network performance with respect to connection unavailability, traffic loss, spare capacity consumption, and dual failure restorability is investigated in a case study for an optical span-restorable long-haul network.

Reliability, availability, and maintainability considerations for fiber optical sensor applications

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.

Availability Calculation and Simulation of Optical Network Systems

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.