Abstract: In wired network, the packet loss is caused by network congestion. TC;P protocol was designed for wired network. But it isn't adapted to the wired-wireless networks anymore because packet loss is mainly caused by link errors in wireless networks. So it proposed a new protocol (named TCP-Ackflag) based on TC;P. It judges network congestion according to trend of relative time delay in receiver. Then the receiver sends an ACK with network congestion flag bit(NCF) to the sender. For the maximum throughput, the sender checks the NCF in ACK which is received recently when it has found the packet loss. It will deal with network congestion or fast retransmit according to network congestion flag bit in ACK. The simulation results show the accuracy and sensitivity in this programs on the network congestion to determine arc greatly improved, and on this basis to ensure the network transmission performance.

Key words: Heterogeneous networks,TCP,Network congestion