TCP Performance in ATM Networks: ABR Parameter Tuning and ABR/UBR Comparisons

This paper explores two issues on TCP performance over ATM networks: ABR parameter tuning and performance comparison of binary mode ABR with enhanced UBR services. Of the fifteen parameters defined for ABR, two parameters dominate binary mode ABR performance: Rate Increase Factor (RIF) and Rate Decrease Factor (RDF). Using simulations, we study the effects of these two parameters on TCP over ABR performance. We compare TCP performance with different ABR parameter settings in terms of throughputs and fairness. The effects of different buffer sizes and LAN/WAN distances are also examined. We then compare TCP performance with the best ABR parameter setting with corresponding UBR service enhanced with Early Packet Discard and also with a fair buffer allocation scheme. The results show that TCP performance over binary mode ABR is very sensitive to parameter value sett,ings, and that. a poor choice of parameters can result in ABR performance worse than that of the much less expensive UBR-EPD scheme.