Object model of application for simulation of cyclic queueing systems

In this paper, we consider the problem of developing the application for simulation of cyclic queueing systems. Cyclic (polling) systems is a class of queuing systems in which servers cyclically connect to various buffers (or inputs) to serve customers from these buffers. In the study of cyclic systems, in most cases, analytical results cannot be obtained, therefore, the development and using software programs for the simulation of such systems is an important problem. In the paper, the following model of cyclic queuing systems is considered. The system has K > 1 inputs where incoming customers arrive. All customers from the input number k go to a single buffer connected to this input. Also, the system has N > 1 servers that periodically connect to the buffers, take customers from them and serve the customers according to the specified service laws. When a service is complete, customers leave the system. In the case of the number of servers N > 1, different versions of their group behavior (disciplines) is possible. In the paper, we consider such group disciplines as a hard group, single devices and a flexible group. Also, there are disciplines of two types for connecting of separate or grouped servers to buffers: time-sharing or exhaustive. Moreover, when the server or group of servers have completed a service of one buffer and they need to switch to the next buffer, it maybe requires a certain switching time. In addition, in the case of the exhaustive discipline, this time should be greater than zero. We use libraries of software package ODIS as a framework for the application implementation. This framework designed for simulation of queuing networks. The main classes of the framework that used in the work are the following: Element which is an abstract parent of all elements of the simulation model. Source which simulates arrivals of customers, Server which implements the service unit, PassiveBuffer which is a buffer with queue organized for customers in it, Call which implements a customer. In addition, the following special classes for simulation of cyclic systems is designed in the work: InputSource combines two objects - a Source instance and a PassiveBuffer one; ConnectionMannager is an object which implements the logic of connecting servers to buffers; Session is an object which is created at the instant when servers pool is connecting to a buffer, it responds for the duration of the connection and controls the movements of incoming customers, customers in the buffer and in servers. Special technique of system events is designed to realize the simulation based on the discrete event model. This technique implements mechanisms of generation, logging and processing of system events. For the simulation of the cyclic systems, it is identified five types of the system events: start of simulation; customer arrival in a particular input; the end of switching time period (if it set that switching requires some time); customer service completion; the end of the session (for time-sharing connection discipline). Processing procedures for scenarios of all these events was designed and implemented. An application was implemented on the designed basis. The application is used for investigations in the field of queuing theory.

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