Throughput analysis of the IEEE 802.4 token bus standard under heavy load

It has become clear in the last few years that there is a trend towards integrated digital services. Parallel to the development of public Integrated Services Digital Network (ISDN) is service integration in the local area (e.g., a campus, a building, an aircraft). The types of services to be integrated depend very much on the specific local environment. However, applications tend to generate data traffic belonging to one of two classes. According to IEEE 802.4 terminology, the first major class of traffic is termed synchronous, such as packetized voice and data generated from other applications with real-time constraints, and the second class is called asynchronous which includes most computer data traffic such as file transfer or facsimile. The IEEE 802.4 token bus protocol which was designed to support both synchronous and asynchronous traffic is examined. The protocol is basically a timer-controlled token bus access scheme. By a suitable choice of the design parameters, it can be shown that access delay is bounded for synchronous traffic. As well, the bandwidth allocated to asynchronous traffic can be controlled. A throughput analysis of the protocol under heavy load with constant channel occupation of synchronous traffic and constant token-passing times is presented

Some issues related to simulation of the tracking and communications computer network

The Communications Performance and Integration branch of the Tracking and Communications Division has an ongoing involvement in the simulation of its flight hardware for Space Station Freedom. Specifically, the communication process between central processor(s) and orbital replaceable units (ORU's) is simulated with varying degrees of fidelity. The results of investigations into three aspects of this simulation effort are given. The most general area involves the use of computer assisted software engineering (CASE) tools for this particular simulation. The second area of interest is simulation methods for systems of mixed hardware and software. The final area investigated is the application of simulation methods to one of the proposed computer network protocols for space station, specifically IEEE 802.4

A Buffer insertion priority mechanism based on the IEEE 802.4 priority scheme

The focus of this thesis is to investigate a media access priority mechanism for a buffer insertion network so that it is better suited for use in real-time applications. This is done by examining a popular priority mechanism present in the IEEE 802.4 token bus standard, and Fiber Distributed Data Interface (FDDI) standard. Mathematical models for throughput and delay are presented for the IEEE 802.4 priority mechanism. These models are then used as a basis for developing the priority mechanism for the buffer insertion ring. Models for throughput and delay are also presented for the buffer insertion priority scheme so that the two media access techniques may be compared

Token bus LAN performance : modeling and simulation

A simulation model based on CSIM, a process oriented simulated language, to analyze the performance of the Token Bus protocol is developed. Performance measures such as throughput, average delay and maximum delay per packet are presented. System performance is analyzed for different loads, number of stations, network lengths, different physical and logical distribution of the stations with packet length as a parameter. Previous studies were based on the delay-throughput analysis with no discussion on the effect of variation of the logical and physical distribution of the stations on the performance of the model which is done in the present thesis. The load is offered to the network in the form of a stream of data packets with uniformly distributed inter-arrival times. A comparison of the Token Bus model with that of a CSNIA/CD model shows that the physical distribution of the stations has a minimum effect on the performance of the model in the case of the Token Bus model but has a considerable effect on that of the CSMA/CD model

Communication and control in an integrated manufacturing system

Typically, components in a manufacturing system are all centrally controlled. Due to possible communication bottlenecking, unreliability, and inflexibility caused by using a centralized controller, a new concept of system integration called an Integrated Multi-Robot System (IMRS) was developed. The IMRS can be viewed as a distributed real time system. Some of the current research issues being examined to extend the framework of the IMRS to meet its performance goals are presented. These issues include the use of communication coprocessors to enhance performance, the distribution of tasks and the methods of providing fault tolerance in the IMRS. An application example of real time collision detection, as it relates to the IMRS concept, is also presented and discussed

Analysis of exhaustive limited service for token ring networks

Token ring operation is well-understood in the cases of exhaustive, gated, gated limited, and ordinary cyclic service. There is no current data, however, on queueing models for the exhaustive limited service type. This service type differs from the others in that there is a preset maximum (omega) on the number of packets which may be transmitted per token reception, and packets which arrive after token reception may still be transmitted if the preset packet limit has not been reached. Exhaustive limited service is important since it closely approximates a timed token service discipline (the approximation becomes exact if packet lengths are constant). A method for deriving the z-transforms of the distributions of the number of packets present at both token departure and token arrival for a system using exhaustive limited service is presented. This allows for the derivation of a formula for mean queueing delay and queue lengths. The method is theoretically applicable to any omega. Fortunately, as the value of omega becomes large (typically values on the order of omega = 8 are considered large), the exhaustive limited service discipline closely approximates an exhaustive service discipline

The implementation of a LAN

Includes bibliography.The subject of this thesis concerns the development of a Local Area Network (LAN) for the Department of Electrical and Electronic Engineering at the University of Cape Town. Motivation for this project was as a result of the ever increasing demands placed on the department's micro-computer training facilities by larger student intakes. The original training system consisted of a PDP 11/23 mini-computer connected via 9600 baud asynchronous links to 11 U.C.T. built micro-computers. This network topology was limiting in three ways: 1. It was slow because of the 9600 baud links and because the PDP was doing a large proportion of the processing.2. High-leve 1 software development tools for the PDP were too expensive and would over-load the computer. Because the micro-computers have no operating system but only an "in-house" monitor program which is not able to support any high-level language utility, all high-level software tools would have to be individually developed for this particular environment. 3. Switching was impractical. Because the PDP was the hub of the network all communication between computers had. to pass through it. This switching would lead to a greater processing load on the PDP, thus further degrading its performance. A two pronged attack was used to overcome these weaknesses: firstly, by designing a high-speed (1 Mbps) LAN to provide communications between a PDP 11/23 and up to 30 U.C.T. built micro-computers, faster inter-computer communication as well as switching and resource sharing was facilitated. Secondly, by customizing an operating system for the micro-computers, standard high-level software development tools could be used on these computers, consequently reducing the PDP's processing load

Some aspects of a code division multiple access local area network

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