A system with storage hierarchy which handles large programs is considered and its performance is investigated. Compared with the systems treated traditionally, this sytem is more effective due to the greater locality...
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A system with storage hierarchy which handles large programs is considered and its performance is investigated. Compared with the systems treated traditionally, this sytem is more effective due to the greater locality of information. It is shown that analysis of this type of system is possible by using renewal theory. This method is useful in the performance evaluation of other systems. In addition, evaluation is made with respect to the number of programs in the system, and it is shown that there exists an optimal number of programs for a given system. The mean system response time is also given.
The technical problems of run-time scheduling to meet multiple deadlines in a hard real-time environment are discussed. It is shown that except for the case of a uniprocessor, optimal scheduling without a priori knowl...
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The technical problems of run-time scheduling to meet multiple deadlines in a hard real-time environment are discussed. It is shown that except for the case of a uniprocessor, optimal scheduling without a priori knowledge of the start-times of the tasks is impossible in general. Sufficient conditions are derived which will permit a set of tasks to be optimally scheduled at run-time.
This paper discusses a high level protocol for real-time voice communication over a packet switched computer communication network. First, the problems associated with real-time digital voice communication and its tra...
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This paper discusses a high level protocol for real-time voice communication over a packet switched computer communication network. First, the problems associated with real-time digital voice communication and its transmission through a packet switched network are discussed. These problems are addressed by the design objectives of the protocol introduced, then the most popular techniques for digital voice encoding (vocoding) are summarized. With this background, a specific NVP (Network Voice Protocol) which has been operational on the ARPANET is introduced. This protocol is then used as the basis for two higher level protocols. One of these protocols deals with multi-participant conferences, and the other with offline voice files.
Techniques for definition and verification of computer network protocols have progressed significantly in the past two years to the point where complex real world protocols can now be analyzed. This success is largely...
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Techniques for definition and verification of computer network protocols have progressed significantly in the past two years to the point where complex real world protocols can now be analyzed. This success is largely due to the combination of two apparently divergent approaches - state tramsitions, and assertion proofs - and to the greater automation of the verification process. This paper summarizes and compares some of the more recent work in this field, emphasizing the common underlying principals of different techniques.
The progress of one research effort in computer-automated protocol validation is summarized in this paper. It brings together in one place the results of a number of studies. Described are a formal representation, the...
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The progress of one research effort in computer-automated protocol validation is summarized in this paper. It brings together in one place the results of a number of studies. Described are a formal representation, the ″duologue″ , ″phase-diagram″ , and ″state-perturbation″ methods. These are discussed on the basis of a common example. Sample results from the validation of the International Telegraph and Telephone Consultative Committee (CCITT) X. 21 interface are explained as an indication of what these techniques can achieve.
Formal specification of program modules which control the access to resource shared among concurrent processes is considered. The state space of the program modules under consideration is constructed. Thus specificati...
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Formal specification of program modules which control the access to resource shared among concurrent processes is considered. The state space of the program modules under consideration is constructed. Thus specification assertations are statements about the states of the program modules. By giving careful considerations on the domain of discourse of the specification assertions, a concrete interpretation of the program module invariant and more specific formulation of the input and output assertions are obtained. These results can help the programmer in his endeavor to construct the formal specifications.
A protocol verifier using symbolic execution has been designed and implemented as part of a general verifier (oriented towards microcode). This paper describes how this method works for communication protocols involvi...
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A protocol verifier using symbolic execution has been designed and implemented as part of a general verifier (oriented towards microcode). This paper describes how this method works for communication protocols involving timing assumptions, state changes depending on message contents, unreliable medium, an arbitrary number of communicting processes, etc. The method can detect design errors such as deadlock and tempo-blocking; in addition the user can add his own assertions to express other desired properties.
Consideration of the pros and cons of writing distributed applications software. Most applications software is highly sequential due to the sharing of variables. Attention is focused on one such application: discrete-...
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Consideration of the pros and cons of writing distributed applications software. Most applications software is highly sequential due to the sharing of variables. Attention is focused on one such application: discrete-event siumulation. The authors show how to develop distributed software for this application by taking a radically different view of the application. Proofs are outlined that the authors distributed software is correct.
The shared memory requirements for implementing mutual exclusion of N asynchronous parallel processes are analyzed in a model where the only primitive communication mechanism is a generalized test-and-set operation. W...
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The shared memory requirements for implementing mutual exclusion of N asynchronous parallel processes are analyzed in a model where the only primitive communication mechanism is a generalized test-and-set operation. While two memory states suffice to implement mutual exclusion, it is shown that any solution which avoids possible lockout of processes requires at least (2N0** one-half - one-half states. A technical restriction on the model increases this requirement to (N plus 1)/2 states, while achieving bounded waiting ( ″fairness″ ) further increases the requirement to N plus 1 states. These bounds are nearly optimal. All the lower bounds apply alpha fortiori to the space requirements for weaker primitives such as P and V using busy-waiting.
Timer-based protocol mechanisms are developed for reliable and efficient transmission of both single-message and message-stream traffic. That is, correct data delivery is assured in the face of lost, damaged, duplicat...
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Timer-based protocol mechanisms are developed for reliable and efficient transmission of both single-message and message-stream traffic. That is, correct data delivery is assured in the face of lost, damaged, duplicate, and out-of-sequence packets. The protocol mechanisms seem particularly useful in a high-speed local network environment. Current reliable protocol design approaches are not well suited for single-message modes of communication appropriate, for example, to distributed network operating systems. The timer intervals that must be maintained for sender and receiver are developed along with the rules for timer operation, packet acceptance, and connection opening and closing. The underlying assumptions about network characteristics required for the timer-based approach to work correctly are discussed, particularly that maximum packet lifetime can be bounded. The timer-based mechanisms are compared with mechanisms designed to deal with the same problems using the exchange of multiple messages to open and close logical connections or virtual circuits.
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