In this paper

we propose an analytical model for the dropping behavior at the network bottleneck where large number of TCP (Transmission controd protocol) connections exist.The inevitable congestion and buffer overflow at the bottleneck is the main reason of the packet loss in networks

which has great influence on the network performance.This model predicts the packet loss rate and transmission interruption rate of the sustained TCP connections sharing the bottleneck link.If most packet-losses are caused by network congestion

our models can give close approximations to the real networks that always contain many connections.The analytical model is useful in studying the effects of TCP

finding new effective algorithm of congestion control

and determining how TCP needs to be modified in the long term for efficient operation over emerging networks.