Abstract: TCP suffers from low performance over Asynchronous Transfer Mode network. This is mainly because during phase of congestion, ATM drops cells without taking into account the effect this has on the upper layer protocols. We propose the enhancement of cell discarding method in RED algorithm supporting TCP over ATM traffic with and UBR service. We call this method TCD (Tightening of Cell Discarding)-RED. The proposed method uses the advantage of RED to keep the average queue size as low as possible. The TCD method is optimal for discarding cells in a TCP over ATM network to overcome shortcomings of RED. In this paper we propose an TCD-RED that improves TCP performance dramatically on congested networks and guarantees fairness among multiple connections.