PARAMETER ENGINEERING FOR CONGESTION AVOIDANCE IN ATM NETWORKS

Abstract

The transport mechanism for ISDN (STM) has been found to face fundamental problems like complex switching and rigid channel structure when considered for B-ISDN. As a result a new standard, the Asynchronous Transfer Mode (ATM) has been suggested for use as a transport mechanism for B-ISDN. ATM is expected to greatly simplify network architecture and management functions. ATM is an evolving technology with signaling mechanisms , protocols yet to be standardised. One of the most active areas of research in ATM networks is congestion control. Congestion control in ATM is difficult because of high link speeds, diverse service requirements and diverse traffic characteristics. Issues like call admission control, source rate control, link scheduling, priorities, discarding policies etc., present a need for a complex interaction amongst themselves rather than the individual optimisation. Nevertheless with the use of optical fiber technology, fast switching units and other -features ATM. is a promising solution to the user network interface for B-ISDN. We present a study of a simple two level scheme operating at call level and cell level to prevent congestion in ATM networks. Parameter engineering and sizing algorithms for optimal link allocation are developed. Finally modelling of the real time traffic at the user network interface (Route Pacer) is studied and its performance analysed. A sizing algorithm is also suggested for the same. By using link sizing algorithms, traffic is regulated at the network entrance itself. This will ensure a congestion free environment in the backbone network with a guaranteed grade of service in terms of cell loss and delay. The backbone node is simplified because of the removal of the traffic control protocol from the backbone. Now the backbone node will involve only in call management functions (call set up/release).