Data performance of modified pushout+ppd mechanism with elastic and deterministic traffic sources with priorities



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3. SIMULATION MODEL

In the literature, the ATM switch is approximated usually as a single server queue with different priority disciplines [4]. Our ATM switch also differentiates many types of traffic sources. Queue length is assumed 76 waiting places. Cell serving rate is 2.7 us (=155 Mbps). Serving discipline is FIFO (First Input First Output) with and without priorities. Figure 1 shows the main structure of the simulation model. For elastic traffic the servicing discipline is without priorities the queue acts as pure FIFO. In other case we apply priority schema the queue is FIFO for different types of priority classes (fig. 1) due to the nature of the pushout mechanism. High-level priority cells overcome all low level priority cells.



The simulation model is single server queue and is encoded on GPSS (General Purpose Simulation System). Load of the queue system varies among 0.7 and 1.1 . All types of traffic sources in the model have different representation and weight during the simulation. Ratio of high- to low priority cells varies among 3:1, 1:1 and 1:3. The ATM line interface serves only one cell at given moment. New cell arriving at the same moment waits in the queue or is lost in case of full queue.


Figure 1. The simulation model with priorities


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