Improving the Performance of TCP over the ATM-UBR service

TL;DR

This paper investigates methods to enhance TCP performance over ATM UBR networks by analyzing switch and end-system policies, demonstrating improvements through simulation of various congestion control strategies and buffer management techniques.

Contribution

It introduces and evaluates specific switch and end-system policies, including Early Packet Discard and per-VC accounting, to improve TCP throughput and fairness over ATM UBR.

Findings

Early Packet Discard improves throughput under congestion.

Per-VC buffer management reduces unfairness.

TCP congestion control policies impact performance significantly.

Abstract

In this paper we study the design issues in improving TCP performance over the ATM UBR service. ATM-UBR switches respond to congestion by dropping cells when their buffers become full. TCP connections running over UBR can experience low throughput and high unfairness. Intelligent switch drop policies and end-system policies can improve the performance of TCP over UBR with limited buffers. We describe the various design options available to the network as well as to the end systems to improve TCP performance over UBR. We study the effects of Early Packet Discard, and two per-VC accounting based buffer management policies. We also study the effects of various TCP end system congestion control policies including slow start and congestion avoidance, fast retransmit and recovery and selective acknowledgments. We present simulation results for various small and large latency configurations with varying buffer sizes and number of sources.