Abstract: In today's heterogeneous internet, bandwidth available to TCP flows is often variable. However, current TCP cannot perform optimally under such dynamically varying bandwidth conditions. This paper addresses this problem by introducing a new architecture to improve TCP performance with explicit bandwidth notification (EBN). It uses a normalized bandwidth feedback method to provide accurate and timely bandwidth estimations. Then, a new TCP control algorithm (TCP-EBN) is proposed to promptly respond to any bandwidth changes. Our simulation results have shown that TCP-EBN performs much better than several other variations of TCP.