The role of the host in a cooperating mainframe and workstation environment, volumes 1 and 2

In recent years, advancements made in computer systems have prompted a move from centralized computing based on timesharing a large mainframe computer to distributed computing based on a connected set of engineering workstations. A major factor in this advancement is the increased performance and lower cost of engineering workstations. The shift to distributed computing from centralized computing has led to challenges associated with the residency of application programs within the system. In a combined system of multiple engineering workstations attached to a mainframe host, the question arises as to how does a system designer assign applications between the larger mainframe host and the smaller, yet powerful, workstation. The concepts related to real time data processing are analyzed and systems are displayed which use a host mainframe and a number of engineering workstations interconnected by a local area network. In most cases, distributed systems can be classified as having a single function or multiple functions and as executing programs in real time or nonreal time. In a system of multiple computers, the degree of autonomy of the computers is important; a system with one master control computer generally differs in reliability, performance, and complexity from a system in which all computers share the control. This research is concerned with generating general criteria principles for software residency decisions (host or workstation) for a diverse yet coupled group of users (the clustered workstations) which may need the use of a shared resource (the mainframe) to perform their functions

Mathematical problems for complex networks

Copyright @ 2012 Zidong Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is made available through the Brunel Open Access Publishing Fund.Complex networks do exist in our lives. The brain is a neural network. The global economy is a network of national economies. Computer viruses routinely spread through the Internet. Food-webs, ecosystems, and metabolic pathways can be represented by networks. Energy is distributed through transportation networks in living organisms, man-made infrastructures, and other physical systems. Dynamic behaviors of complex networks, such as stability, periodic oscillation, bifurcation, or even chaos, are ubiquitous in the real world and often reconfigurable. Networks have been studied in the context of dynamical systems in a range of disciplines. However, until recently there has been relatively little work that treats dynamics as a function of network structure, where the states of both the nodes and the edges can change, and the topology of the network itself often evolves in time. Some major problems have not been fully investigated, such as the behavior of stability, synchronization and chaos control for complex networks, as well as their applications in, for example, communication and bioinformatics

Towards a Formal Model for Quantifying Trust in Distributed Usage Control Systems

Distributed usage control is a form of usage control that spans over multiple domains and computer systems. As a result, usage control components responsible for evaluating policies, gathering information, executing actions and enforcing decisions are operated in the vicinity of different stakeholders with conflicting interests. In order to prevent malicious stakeholders from manipulating these components, remote attestation can be used to verify the integrity of their code base. However, in a distributed case it is not always apparent what sequence of attestations is necessary and which verifier should conduct them. Furthermore, it is unclear what impact a failed attestation has on the trustworthiness of the whole usage control system. To solve these questions, it is necessary to identify which agents need to trust each other in order to securely execute a certain usage control function. Then the sequence of remote attestations that occur across the distributed usage control system can be examined accordingly. In this work we develop a formal model that represents the trust relationships of distributed usage control systems with multiple collaborating actors. Based on the conducted attestations we define simple binary and non-binary trust metrics that quantify the trust level a data owner can expect at a certain point in time. Finally we show how the model can be used to determine the level of trust reached in a real-world scenario

Adaptive traffic signal control using approximate dynamic programming

This thesis presents a study on an adaptive traffic signal controller for real-time operation. An approximate dynamic programming (ADP) algorithm is developed for controlling traffic signals at isolated intersection and in distributed traffic networks. This approach is derived from the premise that classic dynamic programming is computationally difficult to solve, and approximation is the second-best option for establishing sequential decision-making for complex process. The proposed ADP algorithm substantially reduces computational burden by using a linear approximation function to replace the exact value function of dynamic programming solution. Machine-learning techniques are used to improve the approximation progressively. Not knowing the ideal response for the approximation to learn from, we use the paradigm of unsupervised learning, and reinforcement learning in particular. Temporal-difference learning and perturbation learning are investigated as appropriate candidates in the family of unsupervised learning. We find in computer simulation that the proposed method achieves substantial reduction in vehicle delays in comparison with optimised fixed-time plans, and is competitive against other adaptive methods in computational efficiency and effectiveness in managing varying traffic. Our results show that substantial benefits can be gained by increasing the frequency at which the signal plans are revised. The proposed ADP algorithm is in compliance with a range of discrete systems of resolution from 0.5 to 5 seconds per temporal step. This study demonstrates the readiness of the proposed approach for real-time operations at isolated intersections and the potentials for distributed network control

Gain tuning of proportional integral controller based on multiobjective optimization and controller hardware-in-loop microgrid setup

Proportional integral (PI) control is a commonly used industrial controller framework. This PI controller needs to be tuned to obtain desired response from the process under control. Tuning methods available in literature by and large need sophisticated mathematical modelling, and simplifications in the plant model to perform gain tuning. The process of obtaining approximate plant model conceivably become time consuming and produce less accurate results. This is due to the simplifications desired by the power system applications especially when power electronics based inverters are used in it. Optimal gain selection for PI controllers becomes crucial for microgrid application. Because of the presence of inverter based distributed energy resources. In the proposed approach, a multi-objective genetic algorithm is used to tune the controller to obtain expected step response characteristics. The proposed approach do not need simplified mathematical models. This prevents the need for obtaining unfailing plant models to maintain the fidelity of modelling. Microgrid system and the PI controller are modelled in different software, hardware platform and tuned using the proposed approach. Gain values for PI controller in these different platform are tuned using the same objective function and multi-objective optimization. This proves the re-usability, scalability, and modularity of the proposed tuning algorithm. Three different combination of software, hardware platform are proposed. First, the process and the PI controller are modelled in a computer based hardware. In order to increase the speed of the multi-objective optimization in the computer based hardware parallel computing is employed. This is a natural fit for paralleling the GA based optimization. Second, both the plant and control representation are modelled in the real time digital simulator (RTDS). Finally, a controller hardware in loop platform is used. In this platform, the plant will be modelled in RTDS and the PI controller will be modelled in an FPGA based hardware platform. Results indicate that the proposed approach has promising potentials since it does not need to simplify the switching model and can effectively solve the complicated tuning procedure using parallel computing. Similar advantage could be said for RTDS based tuning because RTDS simulates the models in real time

Design of feedback control systems with transport lag by parameter plane techniques

A method is presented for the exact determination of absolute and relative stability of linear feedback control systems containing transport or distributed lag. All results are in terms of two variable system parameters. The method utilizes an extension of modern parameter plane techniques that allows for the inclusion of transcendental functions in the system characteristic equation. The design of controllers in linear systems containing transport lag is then considered. A design technique is proposed that allows for the systematic determination of two variable controller parameters in order to meet frequency or time domain design specifications. The design technique is formulated in terms of the familiar dominant root concept for systems that do not contain transport lag. The proposed design technique gives the system designer at least as much control over the system response as conventional design procedures for systems without transport lag. The investigation of absolute and relative stability, as well as the proposed method for controller design, is no more complicated for multiloop feedback control systems than for single loop systems. This is because the characteristic equation of the closed-loop system transfer function is utilized rather than the conventional open-loop methods. Further, if a digital computer is used, high-order systems are dealt with as easily as low-order systems. A method of constructing the root-locus of systems containing transport lag is then proposed so that this familiar engineering tool can be utilized in conjunction with the proposed analysis and design technique. Finally, nonlinear systems containing transport lag are considered where describing function analysis is applicable. It is shown that the amplitude and frequency of limit cycles can he predicted where the describing function is real and is dependent upon the amplitude of the input signal to the nonlinearity

Performance of voice and data transmission using the IEEE 802.11 MAC Protocol

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 99-100).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.The IEEE 802.11 wireless LAN standard attempts to provide high throughput and reliable data delivery for stations transmitting over a lossy, wireless medium. To efficiently allocate resources for bursty sources, the 802.11 Medium Access Control (MAC) sublayer uses a type of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol called the Distributed Coordination Function (DCF). The MAC protocol also includes an optional polling scheme called the Point Coordination Function (PCF) to deliver near-isochronous service to stations. This thesis analyzes the performance of these two medium access mechanisms under real-time voice and asynchronous data transmissions. Using analytical and simulative methods, the efficiency and capacity of the 802.11 protocol is determined for each type of traffic individually, as well as for a traffic mix of the two types. It is shown that the upper bound of data efficiency for DCF is 65.43% percent when transmitting maximum-sized IP packets at 11 Mbps. Furthermore, due to the difference in packet size of the two traffic types, for each additional GSM voice call (approximately 11 kbps including voice activity) to be supported using DCF, the non-real-time traffic load must decrease by approximately 250 kbps. Voice receives very little real-time Quality of Service (QoS) when using DCF to contend with constantly sending data stations. In order for 802.11 to provide real-time QoS for voice packets despite all levels of asynchronous traffic data load, the PCF mechanism can be used. By only using PCF for voice traffic, voice packets will always take priority over asynchronous data packets and receive the required real-time QoS.by Jessica M. Yeh.M.Eng

Design and implementation of a laboratory computer: network for data acquisition and analysis, 1984

A Laboratory Data System (LDS) was implememented in the Chemistry Research Laboratory. The design of the system was a distributed local area network (LAN) of microcomputers. This LAN is based on a combination of the Corvus Constellation and OMNINET hardware and software. The LAN has a Bus topology with all attached computers having access to a 20 Mbyte Winchester Disk Drive. There are a total of seven computers currently in the LAN - three APPLE II systems, two LSI-11 systems, one LSI-11/23 system, and one IBM PC system. Four spectrophotometers were interfaced to the LSI-11/23 computer via a 12-bit Analog Input/Output System (16 channels ana 1og-to-digita 1 converter and 2 channels digita 1-1o-ana1og converter, DAC) and a real time clock (RTC). The instruments were a Varian Model 3700 Gas Chromatograph, a Cary 17 UV-VIS-NIR Spectrophotometer, a Beckman 42 40 Infrared (IR) Spectrophotometer, and a Durrum-Jasco J-20 Circular Dichroism (CD) Spectrophotometer. The two DAC channels were interfaced to an oscillose for real time graphics output and to a x-y plotter for hard copy graphics output. Subroutines which control the function of the two interface boards are written in MACRO-11 assembly language. Data aquisition programs were written in Fortran. Programs have been written for signal averaging and spectral smoothing. A sophisticated graphics program (AGRAPH) plots the data on a graphics terminal and a digital plotter. Furthermore, the LAN has a powerful intercomputer communication protocol allowing data collected from the instruments to be stored as a part of a created database

On-line monitoring of water distribution networks

This thesis is concerned with the development of a computer-based, real-time monitoring scheme which is a prerequisite of any form of on-line control. A new concept, in the field of water distribution systems, of water system state estimation is introduced. Its function is to process redundant, noise-corrupted telemeasurements in order to supply a real-time data base with reliable estimates of the current state and structure of the network. The information provided by the estimator can then be used in a number of on-line programs. In view of the strong nonlinearity of the network equations, two methods of state estimation, which have enhanced numerical stability, are examined in this thesis. The first method uses an augmented matrix formulation of a classical least-squares problem, and the second is based on a least absolute value solution of an over determined set of equations. Two water systems, one of which is a realistic 34-node network, are used to evaluate the performance of the proposed methods .The problem of bad data processing and its extension to the validation of network topology and leakage detection is also examined. It is shown that the method based on least absolute values estimation provides a more immediate indication of erroneous measurements. In addition, this method demonstrates the useful feature of eliminating the effects of gross errors on the final state estimate. The important question of water system observability is then studied. Two original combinatorial methods are proposed to check topological observability. The first one is an indirect technique which searches for a maximum measurement-to-branch matching and then attempts to build a spanning tree of the network graph using only the branches with measurement assignment. The second method is a direct search for an observable spanning tree. A number of systems are used to test both techniques, including a 34-node water supply network and an IEEE 118-bus power system. The problem of minimisation of distributed leakages is solved efficiently using a state estimation technique. Comparison of the head profile achieved for the calculated optimal valve controls with the standard operating conditions for a 25-node network indicates a major reduction of the volume of leakages. In the final part of this thesis a software package, which simulates the real-time operation of a water distribution system, is described. The programs are designed in such a way that by replacing simulated measurements with live telemetry data they can be directly used for. water network monitoring and control