Study of a space priority mechanism for ATM networks using both analytical and simulation techniques

Priority mechanisms have been shown to improve the throughput of asynchronous transfer mode (ATM) networks. This paper describes a study of an approximated version of the priority mechanism partial buffer sharing (PBS), using an exact fluid flow analysis and a cell-rate ATM network simulator. PBS, a two priority level scheme, discards low priority cells accessing a buffer when it has reached a threshold. The approximated version of PBS does not consider queueing above the threshold, and is applied in both the analytical technique and the cell-rate simulator. The cell-rate simulation method is used, as it accurately models the burst scale queueing behaviour and leads to speed increases of up to four orders of magnitude, when compared with cell level simulation. Low cell loss probabilities can thus be measured within reasonable computing times. The fluid flow model has the particular characteristic of considering changes in the buffer in discrete steps and it models an on-off traffic source accessing a finite queue. Firstly, the paper explains how the approximated version of PBS was added, both to the analysis and the simulator. It then presents cell loss results obtained with the two approaches, that show the precision of the prioritised simulator. The agreement between the two approaches is particularly significant for low priority cell loss. This study produces a simple and relatively accurate way of helping to foresee the behaviour of a real ATM network in the presence of a priority mechanism