Research Of Congestion Control Algorithm On TCP/IP Communication Protocol

With development of the Internet and computer technology, the network has become an integral part of society. In the network, generation of network congestion will cause some big problems, such as increased network transmission delay, increased packet loss rate, or even a meltdown of the network. Therefore, network congestion control mechanism is required in the network communication protocol on the main part.This paper has a study about the TCP network congestion control mechanism of TCP/IP communication protocol for network transmission.The main work of this paper is described as follows:First, this paper analyses the current TCP congestion control algorithm. And then by analyzing, this paper makes the view that improving the slow-start or timeout retransmission can better the information transmission efficiency.Second, the paper analyses the original mechanism in the slow start algorithm, then comes to two problems that slow-start anaphase can easily lead to a large number of packet loss and slow-start threshold value is set too fixed. Based on a new phase-divided TCP slow start mechanism, utilizing bandwidth measuring method to detect the real-time network path bandwidth, which is used to calculate corresponding slow-start threshold value and the congestion window growth. Combining the two, for the characteristics of TCP data transmission, the paper comes to a new sender's algorithm which is a bandwidth measurement based and phase-divided TCP slow start mechanism. And then a detailed theoretical analysis is carried out. Using NS-2 simulation experiments compares the improved and the original slow-start algorithm for packet loss rate, current bottleneck link queue length and the congestion window instantaneous changes, the results show that the improved algorithm can reduce the packet loss rate, increase network processing capacity and enhance network utilization.Finally, this paper analyses the timeout retransmission of the original congestion control mechanism, and puts forward the view that the reaction of the original timeout retransmission mechanism could easily lead to unstable network throughput and low network utilization. The paper puts forward a new timeout retransmission algorithm, referencing the fast retransmit and recovery mechanism for congestion control. When retransmission timer timeout between the data transmission, the new algorithm makes use of a more smooth sending rate reduction mechanisms, compared with the original algorithm. And then a detailed theoretical analysis is carried out. Using NS-2 simulation experiments compares the improved and the original timeout retransmission algorithm for the congestion window instantaneous changes. The results show that the improved algorithm can handle a faster restoration of network capacity, improve network utilization and reduce the oscillation of the network throughput.Experiments show that the improved slow start algorithm and timeout retransmission algorithm can adapt to network changes better, reduce network jitter and improve the efficiency of network transmission. More importantly, the two algorithms are based on the source side, it is easy to implement for control system.At the end of this paper, in the real network, the improved congestion control algorithm is verified, that through the information transmission, in the improved and the former congestion control mechanism, the transmitter transfers the same data package, and by the analysis and comparison of the data obtained through the packet transmission delay, we can get that improved algorithm can improve the information transmission efficiency.