A problem in sending TCP traffic over ATM network is that the loss of even one ATM cell will corrupt the whole TCP packet.In order to resolve such a problem

it has been proposed that an ATM switch is used to intelligently discard selective cells when congested.Intelligent discarding policies such as EPD can improve the performance of TCP over ATM network with limited buffer.To analyze its performance

a fluid flow model has been introduced in this paper.The joint distribution of aggregate source state and buffer occupancy is obtained.Based on these results

upper and lower bounds of packet loss probability in an EPD system are derived.The analytical comparison between EPD and oncontrol case has shown that the performance of an EPD system with the threshold set at the buffer size is better than or at least equal to the performance of an uncontrolled system.