Most of the existing analytical models for multistage ATM switching fabric are not accurate in the presence of a non-uniform traffic at the input of the switch. In this paper, we discuss the issues in modeling a multistage ATM switching fabric, and investigate the effect of independence assumptions in two previous analytical models. A highly accurate 4-state Markov chain model for evaluating the performance of ATM switching fabrics based on multistage switches with 22 finite output-buffered SEs is proposed. The proposed model correctly reflects the correlation of cell movements between two subsequent cycles and states of the buffers of two adjacent stages. By comparing the results obtained from the oroposed model, existing models and simulations, it has been shown that the proposed model is much more accurate than existing models in the presence of a non-uniform traffic in the switch. The results from the existing models are unsatisfactory in the presence of an increased blocking in the switch arising from a non-uniform traffic in the switch. On the contrary, the proposed model is very robust even under severe blocking in the switch.

The emerging, ATM network will support permanent, semi-permanent and switched virtual channel connections (SVCC). A number of simulation studies have been carried out to study the performance of SVCCs using empirical data. The absence of an analytical model has prevented the study of SVCCs under known traffic distributions. In this paper, we develop a new delayed vacation model to facilitate the performance study of SVCCs with configurable inactivity timer in the ATM network interface card (NIC). Comparison with simulation results indicates that the proposed model is very accurate and can be effectively used to optimise the performance of SVCCs by selecting an appropriate inactivity timer.

Random Early Detection (RED), an active queue management scheme, has been recommended by the Internet Engineering Task Force (IETF) for the next generation routers. RED suffers from a number of performance problems, such as low throughput, large delay/jitter, and induces instability in networks. Many of the previous attempts to improve the performance of RED have been based on optimizing the values of the RED parameters. However, results have shown that such optimizations resulted in limited improvement in the performance. In this paper, we propose Double Slope RED (DSRED), a new active queue management scheme to improve the performance of RED. The proposed scheme is based on dynamically changing the slope of the packet drop probability curve as a function of the level of congestion in the buffer. Results show that our proposed scheme results in better performance than original RED.