Dynamic routing in circuit-switched non-hierarchical networks

This thesis studies dynamic routing in circuit-switched non-hierarchical networks based on learning automata algorithms. The application of a mathematical model for a linear reward penalty algorithm is explained. Theoretical results for this scheme verified by simulations shows the accuracy of the model. Using simulation and analysis, learning automata algorithms are compared to several other strategies on different networks. The implemented test networks may be classified into two groups. The first group are designed for fixed routing and in such networks fixed routing performs better than any dynamic routing scheme. It will be shown that dynamic routing strategies perform as well as fixed routing when trunk reservation is employed. The second group of networks are designed for dynamic routing and trunk reservation deteriorates the performance. Comparison of different routing algorithms on small networks designed to force dynamic routing demonstrates the superiority of automata under both normal and failure conditions. The thesis also considers the instability problem in non-hierarchical circuit-switched networks when dynamic routing is implemented. It is shown that trunk reservation prevents instability and increases the carried load at overloads. Finally a set of experiments are performed on large networks with realistic capacity and traffic matrices. Simulation and analytic results show that dynamic routing outperforms fixed routing and trunk reservation deteriorates the performance at low values of overload. At high overloads, optimization of trunk reservation is necessary for this class of networks. Comparison results show the improved performance with automata schemes under both normal and abnormal traffic conditions. The thesis concludes with a discussion of proposed further work including expected developments in Integrated Service Digital Networks

Formation and transmission of a dynamic graphics display

The NEC 7220 / GDC is a high resolution colour graphics display controller. It is programmable, and can generate lines, arcs and rectangles at high speeds with little intervention from the host computer. The GDC has interesting capabilities such as scrolling, DMA transfers and read and write of its display memory through the FIFO buffer. This thesis describes the GDC and its relation to the other components of a graphics terminal. Software programs are developed and implemented to show how the GDC's capabilities can be used to generate a dynamic graphics picture on the CRT screen. The programs are written in both Pascal and 8086 assembler. Two methods are presented for the transfer of a graphical display from one NEC/APC to another one. The first technique sends the display memory's pixels and the second one transfers the picture codes for the reconstruction of the image. For each of them software programs are developed and tested thoroughly and found to perform as stipulated