STUDY OF STATE-DEPENDENT PRIORITY SCHEMES IN ATM NETWORKS

Abstract

Synchronous Transfer Mode (STM), the transport mechanism for Integrated Services Digital Network (ISDN), has been found to face fundamental problems like complex switching and rigid channel structure when considered for broad band access :o ISDN. So Asynchronous Transfer Mode (ATM) was chosen as switching and multiplexing technique by CCITT for the broadband access to ISDN. The User Network Interface (UNI) offers one physical channel over which connections are multiplexed using short, fixed length packets called cells. ATM is connection oriented. Cells are self routed based on their header information. In this way, ATM networks can transmit various types of information in a flexible way. However, without appropriate traffic control measures, these high speed, networks may easily get congested. 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. Call admission control, source rate control, buffer management schemes and priorities, discarding policies etc. are schemes which operate at various levels for congestion control. For optimized congestion control it is essential that these schemes -work together and not in isolation. Optimized congestion control is not achieved if each of these schemes are optimized at their respective levels. Instead, it is obtained by the cumulative effect of all these schemes. iii We present a study of a buffer management scheme using two different prioritized state-dependent service disciplines to improve the cell delay for each traffic class and reduce the cell loss rate of loss-sensitive traffic class. An attempt was made to compare two state-dependent priority schemes through performance analysis. Simulation of the same was done for two types of traffic models, i.e., random traffic model and bursty traffic model. The Longest Line First (LLF), the Shortest Line First (SLF) and the Oldest Customer First (OCF) schemes are simulated and their performances compared with the ARBSD and the RSD priority schemes.