In this research a suspected "gray" area in computer network performance that might exist between the network's optimum performance and complete network failure was investigated. Changes in performance were studied as seen by the application layer of the network as attenuation was introduced at the physical layer of the network. The network performance was measured for four groups of tests running over TCP and UDP. Various scripts emulating different network applications were used. Ultimately the performance was evaluated at different optical power levels, based on throughput, transaction rate, response time, and lost data. Additionally, the bit error rate characterization of the attenuated optical fiber link was analyzed. Ultimately, performance of the fiber optic ATM-based computer network as seen by the user was correlated with optical power degradation introduced in the physical layer. A decrease in performance was found as attenuation was increased, even in the range of "normal" operating conditions. As expected, TCP, although not immune to soft failures, performed better than UDP. A description of the investigation, tests, scripts, methods and results are included. / Master of Science

Real-time constraints place additional limitations on distributed memory computing systems. Message passing delay variance and maximum message delay are important aspects of such systems that are often neglected by performance studies. This thesis examines the performance of the spanning bus hypercube, dual bus hypercube, and torus topologies to understand their desirable characteristics for real-time systems. FIFO, TDM, and token passing link access protocols and several queueing priorities are studied to measure their effect on the system’s performance. Finally, the contribution of the message parameters to the overall system delay is discussed. Existing analytic models are extended to study delay variance and maximum delay in addition to mean delay. These models separate the effects of node and link congestion, and thus provide a more accurate method for studying multicomputer networks. The SLAM simulation language substantiates results obtained analytically for the mean and variance of message delay for the FIFO link access protocol, as well as providing a method for measuring the message delay for the other link access protocols and queueing priorities. Both analytic and simulation results for the various topologies, protocols, priorities, and message parameters are presented. / Master of Science

To create neural networks that work, one needs to specify a structure and the interconnection weights between each pair of connected computing elements. The structure of a network can be selected by the designer depending on the application, although the selection of interconnection weights is a much larger problem. Algorithms have been developed to alter the weights slightly in order to produce the desired results. Learning algorithms such as Hebb's rule, the Delta rule and error propagation have been used, with success, to learn the appropriate weights. The major objection to this class of algorithms is that one cannot specify what is not desired in the network in addition to what is desired. An alternate method to learning the correct interconnection weights is to evolve a network in an environment that rewards "good” behavior and punishes "bad" behavior, This technique allows interesting networks to appear which otherwise may not be discovered by other methods of learning. In order to teach a network the correct weights, this approach simply needs a direction where an acceptable solution can be obtained rather than a complete answer to the problem. / Master of Science

In this thesis, the design and performance issues of multicomputer interconnection networks are addressed. Analytic models are used to evaluate the performance of large scale multicomputer networks. Performance is measured as the average end-to-end delay between communicating nodes. The models consider the communication processing queueing delays experienced by packets at each node as well as delays associated with transmission of packets. A comparison study of message switching and cut-through switching is presented. It is shown, conforming to previous studies, that a network has superior performance when cut-through switching is used. Cut-through switching is most advantageous when the network load is low and degenerates to message switching performance under heavy network loads. The network model is used to develop a "Network Analyzer", an interactive program that allows analysis of different network designs and workloads. Torus and spanning bus hypercube networks are then analyzed by the program to study the effect of various network parameters, traffic patterns, and switching techniques on network delay performance. The Network Analyzer is relatively easy to learn and use, and once learned, it is easy to change network parameters to perform a trade-off study of design alternatives. The program can also be used to quickly generate listings and graphics to illustrate the results of the analysis. The program proved to be an efficient design tool. Hypercube topologies are the most popular for large scale parallel computers, particularly for computationally intensive applications. The torus and spanning bus hypercubes are implemented in our program and analyzed in detail. Results show that network topology has a mixed impact on system performance. Networks built of standard modules of spanning bus hypercubes are harder to expand, compared to a torus network, but they have lower connection cost per node. Communication delays are generally higher for spanning bus networks except at very low traffic loads. / M.S.

No description available.

No description available.

The Internet is a large-scale decentralized system that is composed of thousands of independent networks. In this system, there are two main components, interdomain routing and traffic, that are vital inputs for many tasks such as traffic engineering, security, and business intelligence. However, due to the decentralized structure of the Internet, global knowledge of both interdomain routing and traffic is hard to come by. In this dissertation, we address a set of statistical inference problems with the goal of extending the knowledge of the interdomain-level Internet. In the first part of this dissertation we investigate the relationship between the interdomain topology and an individual network's inference ability. We first frame the questions through abstract analysis of idealized topologies, and then use actual routing measurements and topologies to study the ability of real networks to infer traffic flows. In the second part, we study the ability of networks to identify which paths flow through their network. We first discuss that answering this question is surprisingly hard due to the design of interdomain routing systems where each network can learn only a limited set of routes. Therefore, network operators have to rely on observed traffic. However, observed traffic can only identify that a particular route passes through its network but not that a route does not pass through its network. In order to solve the routing inference problem, we propose a nonparametric inference technique that works quite accurately. The key idea behind our technique is measuring the distances between destinations. In order to accomplish that, we define a metric called Routing State Distance (RSD) to measure distances in terms of routing similarity. Finally, in the third part, we study our new metric, RSD in detail. Using RSD we address an important and difficult problem of characterizing the set of paths between networks. The collection of the paths across networks is a great source to understand important phenomena in the Internet as path selections are driven by the economic and performance considerations of the networks. We show that RSD has a number of appealing properties that can discover these hidden phenomena.

published_or_final_version / Business Administration / Master / Master of Business Administration

In recent years, a growing number of diagnostic examinations in a hospital are being generated by digitally formatted imaging modalities. The evolution of these systems has led to the development of a totally digitized imaging system, which is called Picture Archiving and Communication System (PACS). A high speed computer network plays a very important role in the design of a Picture Archiving and Communication System. The computer network must not only offer a high data rate, but also it must be structured to satisfy the PACS requirements efficiently. In this dissertation, a computer network, called PACnet, is proposed for PACS. The PACnet is designed to carry image, voice, image pointing overlay, and intermittent data over a 200 Mbps dual fiber optic ring network. The PACnet provides a data packet channel and image and voice channels based on Time Division Multiple Access (TDMA) technique. The intermittent data is transmitted over a data packet channel using a modified token passing scheme. The voice and image pointing overlay are transferred between two stations in real-time to support the consultive nature of a radiology department using circuit switching techniques. Typical 50 mega-bit images are transmitted over the image channel in less than a second using circuit switching techniques. A technique, called adaptive variable frame size, is developed for PACnet to achieve high network utilization and short response time. This technique allows the data packet traffic to use any residual voice or image traffic momentarily available due to variation in voice traffic or absence of images. To achieve optimal design parameters for network and interfaces, the PACnet is also simulated under different conditions.

This thesis is concerned with the design of a high-speed backbone network which provides a high bandwidth interconnection for various Personal Computer Networks (PC-Networks) with an integrated service of voice and data. With the advanced technology of optical fiber as the transmission medium, several different existing topologies and protocols are discussed for the backbone network design. The token ring protocol is simulated and evaluated to find out a suitable buffer size and the length of voice and data packet for backbone network. The Network II.5 simulation tool is applied to simulate the token ring simulation model with different parameters. The Network Interface Unit (NIU) is designed from the simulation results with a cost-effective consideration.