摘要:

A concept to improve the resilience to failures of the Cambridge Ring network is described. The ideas conceived should be applicable to any other ring network. Reliability issues are raised, and several existing fault-tolerant techniques are briefly discussed. The Centre-Switching Ring- Star concept is then described, detailing its design, operation and problems. The star connections are only brought into use when a fault is detected. This design is based on the automatic bypassing of faulty repeaters or cable sections. Any number of failures may be tolerated. The design allows the continual operation of the network whilst a new node is being added or removed. A laboratory model has been built and successfully tested.

DOI:10.1049/jiere.1986.0073

出版商:IERE    

年代:1986

数据来源: IET

摘要:

This paper describes a technique for reducing the delay of speech packets on Ethernet caused by collisions with other packets. The improvement is achieved by truncating the standard binary exponential back-off generated by nodes experiencing a collision. The technique is easily implemented using special-purpose v.l.s.i. Ethernet devices and ensures an even distribution of delay and packet loss between active nodes.

DOI:10.1049/jiere.1986.0074

出版商:IERE    

年代:1986

数据来源: IET

摘要:

Project Universe was a collaborative project to build a highspeed computer network linking local area networks (LANs) at a number of sites by broadcast satellite communication. This network was tested by a series of experiments in which a very wide range of traffic types, including those generated by conventional computer networking, by distributed computing and by real-time voice and video communication, were carried on the network.An important result from the experiment was the demonstration that a wide area network approaching the simplicity and performance of a local area network could be constructed. The project produced information on the characterization of the traffic types that a network providing fully integrated services would have to carry and gave some insight on how such a network would have to be constructed.

DOI:10.1049/jiere.1986.0076

出版商:IERE    

年代:1986

数据来源: IET

摘要:

The Distributed Secure System project being undertaken by the Royal Signals and Radar Establishment aims to provide distributed general-purpose computing systems capable of enforcing a variety of multi-level security policies. The project relies on the concept of synthesizing secure systems from standard untrusted components. These untrusted components are interfaced via small trustworthy security mechanisms to one or more local or wide area networks. The components are linked together in such a way that the total system is not only demonstrably secure, but is also very flexible and cost effective.

DOI:10.1049/jiere.1986.0078

出版商:IERE    

年代:1986

数据来源: IET

摘要:

The paper describes a novel development of the Viterbi algorithm detector that is suitable for the detection of a convolutionally coded digital signal. The technique enables a substantial reduction in equipment complexity to be achieved, relative to that of the Viterbi algorithm detector, with only a very small reduction in tolerance to noise. Results of computer-simulation tests are presented showing the performance of the system and giving also a measure of its complexity, for the particular case of a coded 8-level PSK signal. An outline is also presented of a possible implementation of the new detector for the given application.

DOI:10.1049/jiere.1986.0079

出版商:IERE    

年代:1986

数据来源: IET

摘要:

Synchronous frequency-hopped spread-spectrum systems using Einarsson's optimum addressing scheme areconsidered and an exact expression is derived for the word-error probability. The new expression for the error-probability is shown to be approximately an order of magnitude tighter than the upper bound results of Einarsson. Also, a relationship is derived between the average transmitter power, the number of allowed frequency channels and the number of users on the system.

DOI:10.1049/jiere.1986.0081

出版商:IERE    

年代:1986

数据来源: IET

摘要:

Two new coding schemes for bit-rate reduction of digital images are proposed. Both coding schemes are based on a new model which makes use of the conditional statistical properties of the image signals. These statistics are used to construct codebooks for the encoding and decoding of the digital images. In the first scheme, the code words are assigned in such a way as to provide a signal with long bit runs. Such a signal is then efficiently run-length coded using CCITT codes. In the second scheme, each picture element (PEL) value is coded by variable-length code words according to the values of previously transmitted PELs. The performance of both schemes in terms of entropy and bit-rate are compared with an optimum predictive coder. The simulation results indicate that the proposed schemes have a significant advantage over standard predictive encoders. A method to reduce the storage requirement for the encoder and decoder codebooks is also proposed.

DOI:10.1049/jiere.1986.0082

出版商:IERE    

年代:1986

数据来源: IET