A COMPARATIVE STUDY OF DYNAMIC QUEUE CONTROL FUNCTIONS IN ATM ABR SWITCH SCHEMES

Abstract

The ATM (Asynchronous Transfer Mode) is the chosen technology for implementing B-ISDN (BroadBand Integrated Services Digital Network). The ABR service in ATM can be used to transport data traffic with minimum rate guarantee. ABR uses closed loop feedback to control the source rates The source sends periodically an RM (Resource Management) cell to gather information from the network. The RM cells are turned around at the destination. The switches along the path indicate the rate, which they can currently support. When the source receives the backward RM cell, it adjusts its allowed rate based. on the explicit rate indicated in the RM cell. Switches maintain queue of packets and based on this decide the rate to be permitted (stamped in the RM cell). In most schemes a simple threshold function is used for queue control. Better control of the queue and hence delay can be achieved by using sophisticated queue control functions. It is very important to design and analyze such queue control functions. In this dissertation queue control functions like step, linear and inverse hyperbolic is analyzed with respect to various parameters (deviation, convergence time, efficiency). Analytical explanation and simulation results consistent with analysis are presented. From the study, it is concluded that inverse hyperbolic is the best queue control function. Performance of these functions is far better than the initial system without using these functions in terms of queue length, deviation, throughput and channel efficiency. Results of comparison between model using these queue control functions and the model not using these functions show that the previous model is better than the later one with respect to all parameters considered in this dissertation. To reduce the complexity, linear control function can be used since it performs satisfactorily in most of the cases.