distributed processing configurations enjoy a distinct advantage over a centralized approach due to their adaptability to a constantly changing environment. They also have many other positive characteristics, such as...
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distributed processing configurations enjoy a distinct advantage over a centralized approach due to their adaptability to a constantly changing environment. They also have many other positive characteristics, such as enhanced survivability, reconfigurability, and recoverability. Enhanced capabilities dictate effective production and operational control procedures in a difficult and complex environment, and it is thus viewed as essential that an overall philosophy be applied to system design, development, production, operation, and maintenance. Two models are proposed for use in demonstration of the 2 philosophies that can be adopted: 1. decentralized, or 2. centralized. The goal is to highlight the need at the higher echelons of the control hierarchy for a centralized philosophy for the effective coordination of locally identifiable subordinate control functions.
This paper describes a simple and yet versatile inter-process communication construct which has been implemented as part of a universal run time support system (UNI_RTSS) for distributed real-time and multi-tasking ap...
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This paper describes a simple and yet versatile inter-process communication construct which has been implemented as part of a universal run time support system (UNI_RTSS) for distributed real-time and multi-tasking applications. The communication facility permits processes to communicate through entities called ‘paths’. Messages are sent to paths owned by the destination processes. A process can choose the paths from which it wishes to receive messages at a given time. The inter-process communication facilities described have proven to be very useful in desingning distributed real-time and multi-tasking systems in a clear and modular fashion.
The background to and progress in the development of ‘distributed programs’ which execute on a distributed multiple-processor architecture are reviewed. Three basic concurrent programming methodologies are introduce...
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The background to and progress in the development of ‘distributed programs’ which execute on a distributed multiple-processor architecture are reviewed. Three basic concurrent programming methodologies are introduced and illustrated. The general problems associated with the use of distributed architectures are considered. Finally, the problems and techniques associated with implementing the various programming methodologies on different architectures are discussed. The implicit constraints imposed on the high-level software by the low-level communications architecture are then examined.
The paper describes an extensible communication system for Conic, an architecture for distributed embedded systems. Conic provides a high level programming language with interprocess communication primitives suited to...
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The paper describes an extensible communication system for Conic, an architecture for distributed embedded systems. Conic provides a high level programming language with interprocess communication primitives suited to both local and remote communication. These primitives are sufficiently powerful to be used for applications programming yet simple and efficient enough for programming system software. The communication system which supports these primitives is itself implemented in the Conic language. It provides a very simple datagram-like service, over interconnected local area networks. The configuration flexibility of Conic is exploited to allow extension of the basic communication system to give additional services such as virtual circuit or routing. The paper also relates the Conic communication system to the ISO Reference Model and indicates some of the problems of using the model. An earlier version of this paper was presented at the 5th IFAC Workshop on distributed Computer Control Systems, Sabi Sabi, South Africa, May 1983.
The reliability of distributed processing systems can be expressed in terms of the reliability of the processing components that run the programs, the reliability of the processing components holding the required file...
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The reliability of distributed processing systems can be expressed in terms of the reliability of the processing components that run the programs, the reliability of the processing components holding the required files, and the reliability of the communication ties used in file transfers. Two reliability measures are introduced, namely, distributed program reliability and distributed system reliability, to accurately model the reliability of distributed systems. The first measure characterizes the likelihood of successful execution of a distributed program that runs on some processing elements and needs to communicate with other processing elements for remote files. The 2nd measure describes the likelihood that all the programs of a given set can run successfully. The graph theory method, which is used to systematically generate file spanning trees to provide the needed connections, is general and can be used in a dynamic environment for efficient reliability evaluation.
Modula-2 is a recently developed concurrent programming language designed primarily for implementation on a mono-processor. This paper reports on the changes found necessary, both to the source language and to the sup...
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Modula-2 is a recently developed concurrent programming language designed primarily for implementation on a mono-processor. This paper reports on the changes found necessary, both to the source language and to the support environment, in order to allow the language to be used to program a tightly coupled, homogenous, distributed computing system. Specific areas covered are: the allocation of program code and data to processors, which is kept independent of the source code, allowing flexible re-allocation without re-compilation; the choice of an inter-processor communication mechanism, where the remote procedure call was considered to be the most flexible technique; and the selection of an inter-process communication mechanism, where, despite the distributed nature of the target, the monitor was found most suitable.
Many applications have a need for different degrees of fault tolerance in the same system. The paper presents the software architecture of a fault-tolerant distributed system which supports both cold and hot standby r...
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Many applications have a need for different degrees of fault tolerance in the same system. The paper presents the software architecture of a fault-tolerant distributed system which supports both cold and hot standby redundancy of selected software modules. Cold standby modules are created and activated by the system in order to replace failed modules, but no state information is preserved. Hot standby modules do preserve state information and provide transparent recovery from failures. A technique is used that allows modules to be programmed without fault-tolerance in mind; afterwards they can be transformed in order to achieve that capability. These two types of redundancy are supported by common mechanisms which provide for detection of failures and reconfiguration of the software modules of the application. Reconfiguration is also used to recover the reliability of the system by providing further standby modules to replace failed ones. We believe that this approach provides a simple, flexible, and practical approach for the provision of fault tolerance in distributed embedded systems.
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 ...
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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.
Growing reliance on computer systems means that organizations must ensure those systems are secure from external and internal interference. Government offices operate a very tight method of controlling access to files...
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Growing reliance on computer systems means that organizations must ensure those systems are secure from external and internal interference. Government offices operate a very tight method of controlling access to files. Security measures can only work if taken seriously by all involved. Many current crimes would not occur if they were likely to be detected quickly.
distributed systems allow greater overall availability. Standby redundancy can be incorporated into application software to improve availability in the event of a crash. The Tandem-16 is an example of crash-tolerant c...
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distributed systems allow greater overall availability. Standby redundancy can be incorporated into application software to improve availability in the event of a crash. The Tandem-16 is an example of crash-tolerant computers. Other examples include Prosur, intended for a hostile environment, and Demos M/P, which uses a broadcast network and a computer called the ‘recorder’. Local area networks can introduce greater vulnerability.
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