Search

Slotted rings have been popular medium access control protocols for local area networks (LANs) since the early proposal of Cambridge and Owell rings. This paper provides a simple approximation technique for the performance analysis of a slotted ring based on a single-buffer model in which at most one packet can be stored at each node. The technique produces approximate values of the network throughput by using an assumption which is valid for large networks and a solution of a quadratic equation whose complexity does not depend on the number of nodes in the network. It is shown by numerical examples that the present technique also gives accurate performance dam for rather small networks to the extent that the relative error of the approximate throughout values is less than 0.3 percent of exact values. Since other performance measures for the single buffer model of a slotted ring can easily be calculated from the throughput, the proposed technique is very useful for evaluating the total performance of a slotted ring network. [ABSTRACT FROM AUTHOR]

In large-scale distributed systems such as communication protocol, FA, OA and sequence control system, several discrete processes evolve in parallel and asynchronously. It is desirable to establish a systematic method of design for such systems. The design methods presently employed for large-scale systems are characterized by bottom-up or top-down hierarchy. The former is to construct the whole system by combining several subsystems, and the latter is to start the design from the global framework of the system and to refine in a stepwise manner the detail descriptions. The Petri net is a model which can be used for qualitative analysis and verification of the distributed systems. The top-down hierarchical representation can easily be constructed by Petri net by successively replacing a part of the net by a net with a more detailed description. By employing the Petri net throughout from the specification to the verification of the system, a systematic design method will be realized. A problem in such a hierarchical representation is whether or not the liveliness and the boundedness is preserved before and after the refinement. This paper discusses this problem and specifies the condition in terms of the net structure and the initial token distributions so that those properties are preserved. It is indicated that the hierarchical representation by Petri net is useful in the verification and other problems in the large-scale distributed systems. [ABSTRACT FROM AUTHOR]

In the distributed processing applications, the dynamic load balancing is considered to be important. In most of the past studies concerning the dynamic load balancing, where the load is distributed based on the information during the job execution by the system, the load of a computer is defined as the number of jobs in execution on the computer. In other words, the computer resources are given little consideration. Even if the computer resources are considered, the model is defined as a homogeneous system composed of computers of the same performance, which seems to deviate from reality. From such a viewpoint, CPU and the input/output units such as disk are considered as the computer resources, and are represented by the load vector in this paper. A relatively simple dynamic load balancing algorithm using the load vector is proposed. The method is extended so that it is applicable to the non-homogeneous system composed of computers with the same function bat with different speeds. The proposed method is simulated by a model in which computers are connected through a bus-type network. As a result, various effects were recognized, such as the decrease of the mean response time, the decrease of the variation of the response time, and the effective use of a high-speed computer in the heterogeneous system. [ABSTRACT FROM AUTHOR]

University and other educational computer systems may have several thousands to several tens of thousands of users, and several hundreds to several thousands of terminals. When the scale of the system is enlarged, not only is the burden of management increased, but various problems are produced in the system configuration and administration due to the character of the educational system, in which many identical manipulations are performed at the same time. This study was performed in the educational computer system of the Osaka University Information Processing Education Center (now the Cybermedia Center). Through the design and development of a system to support smooth administration of the computer system and classroom activities in the center, the functions needed for support were organized and practical problems were identified, together with methods for their solution. The new system was operated at the Osaka University Information Processing Education Center and was found to contribute greatly to classroom and administration support. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(9): 42–52, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10180 [ABSTRACT FROM AUTHOR]