Simulação e análise de mecanismos de controle de fluxo para serviço ABR em redes ATM.

Abstract

This present work analyses the mechanisms of flow control for ABR services on ATM networks. The aim of ABR service is to adjust the transmission rate of the cells, directly onto the data source, owing to the charge condicion of the network. On ABR service, the ATM switch may adopt two different mechanisms - the binary mechanism and the ER (Explicit Rate) one. Under the binary mechanism soon after detecting the congestion, the switch will mark every cell which passes by, as congested one, having the source to accomplish the procedure of transmission rate reduction. On the ER mechanism, which shows several varations, the ATM switch is able to broadcast the network traffic and calculate the transmission rate which can be tolerated by the network and, subsequently, inform this rate to the source through the RM cells (Resource Management). In this work the binary flow control mechanism EFCI (Explicit Forward Congestion Indication) and two ER mechanisms - the EPRCA (Enhaced Proportional Rate Control Algoritm) and NIST ER, are discussed. These mechanism were simulated and their results were analysed and compared. A shareware version of the NIST ATM was used as a simultion tool. The following performance measurements are shown on regards to time: ACR (Allowed Cell Rate), buffer occupation and link utilization. Other measurements such as average value of ACR, throughput and fairness, are also shown. The fairness measurement allows to verify how fair the simulated mechanisms are in bandwidth allocation.