Survivability stategies in all optical networks.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.Thesis (M.Sc.)-University of KwaZulu-Natal, 2006.Recent advances in fiber optics technology have enabled extremely high-speed transport of different forms of data, on multiple wavelengths of an optical fiber, using Dense Wavelength Division Multiplexing (DWDM). It has now become possible to deploy high-speed, multi-service networks using DWDM technology. As the amount of traffic carried has increased, any single failure can be catastrophic. Survivability becomes indispensable in such networks. Therefore, it is imperative to design networks that can quickly and efficiently recover from failures. Most research to date in survivable optical network design and operation focuses on single link failures, however, the occurrence of multiple-link failures are not uncommon in networks today. Multi-link failure scenarios can arise out of two common situations. First, an arbitrary link may fail in the network, and before that link can be repaired, another link fails, thus creating a multi-link failure sequence. Secondly, it might happen in practice that two distinct physical links may be routed via the same common duct or physical channel. A failure at that shared physical location creates a logical multiple-link failure. In this dissertation, we conduct an intensive study of mechanisms for achieving survivability in optical networks. From the many mechanisms presented in the literature the focus of this work was on protection as a mechanism of survivability. In particular four protection schemes were simulated and their results analyzed to ascertain which protection scheme achieves the best survivability in terms of number of wavelengths recovered for a specific failure scenario. A model network was chosen and the protection schemes were evaluated for both single and multiple link and node failures. As an indicator of the performance of these protection schemes over a period of time average service availability and average loss in traffic for each protection scheme was also simulated. Further simulations were conducted to observe the percentage link and node utilization of each scheme hence allowing us to determine the strain each protection scheme places on network resources when traffic in the network increases. Finally based on these simulation results, recommendations of which protection scheme and under what failure conditions they should be used are made.Recent advances in fiber optics technology have enabled extremely high-speed transpor

Aggregate planning for multi-product assembly lines with reconfigurable cells

This paper deals with aggregate planning of Reconfigurable Assembly Lines (RAL). The assembly line considered in this paper consists of hexagonal cells. These have multiple slots where processing modules can be inserted to perform certain operations. In addition, each cell has a single central slot where a central module can be inserted for inter-cellular and intra-cellular transportation of parts. Multiple products with different assembly sequences must be handled over multiple planning periods. An Integer Quadratic Programming (IQP) model is proposed to solve the following problems simultaneously: (i) assigning processing modules and a central module to the cells; (ii) installation of the cells and conveyors between the cells; and (iii) routing products, ensuring that availability of the resources is not exceeded. The assembly line should be reconfigured over time to adapt to possible product functionality and demand changes at minimum reconfiguration, operational and material handling costs while ensuring the demand is met within each period. The IQP model is implemented and solved for an illustrative problem and its extensions using Gurobi

Tangible mixed reality for remote design review: a study understanding user perception and acceptance

Background: The design review process is often expensive due to the need for face-to-face meetings between the involved parties. Distributed design collaboration is made possible by advances in networking techniques. A tangible Mixed Reality (MR)-based virtual design prototype was created as a distributed virtual environment (DVE) for the purpose of improving remote design review collaboration. This tangible MR system has been developed to a point that experimental evaluation is necessary in order to understand the strengths and weaknesses of various features of the system. Methods: In this paper, we evaluated the tangible MR system against a commercial 3D distributed design review system in three aspects: the investigation of how users experienced virtual models in the tangible MR system as compared with the commercial system, the measurement of the users’ attitude towards the effectiveness of the tangible MR system, and the discoveries of usability issues involved in the tangible MR interface through usability studies. Results: The findings from user feedback suggest that the tangible MR system may facilitate problem-solving and the quantity of work in a given amount of time and that virtual design displayed in the mixed scene was a useful aid in the design error detection task. Conclusion: These findings are useful for the improvement of future generations of the MR system. Also the suggestions can be further generalized to become usability guidelines for the MR developers in other applications and domains