Study On Congestion Control Of TCP Based On Bidirectional Path

TCP is an important file transfer protocol based on the Internet. And network congestion is the major factor of data loss that causing reduction of QOS. TCP congestion control mechanism can effectively avoid the data loss causing by congestion and so that the quality of QOS can be improved. On the other hand, when TCP being linked conveys numerous data unidirectionally, it will assume similar state with the congestion. And standard TCP congestion control mechanism can't tell apart them. Accordingly, this situation brings about frequently starting of the congestion control and reduces the efficiency of QOS.RTT is the base of realization of the TCP protocol, and is also a very important parameter of judging degree of the network congestion. And in this paper, the measure theory of traditional RTT has been stated, the structure of RTT has been analysed , the differences between bi-directional symmetry path and asymmetry path has been pointed out, and the limitation of traditional RTT, which under the condition of not changing the structure of standard TCP, also has been analysed when transmit large volume of data unilaterally (multicast)and delay sensitivity(wireless network based on controlled energy),at the same time, a kind of transmit and control arithmetic of optimization—RTT arithmetic based on bi-directional asymmetry path that suit to the network circumstance of unilateral large data transmit and delay sensitive has been put forward, it could effective distinguish the unilateral large data transmit and network congestion. The simulation shows that it could improved effectively the QOS. The main ones to study are as follows:(1)On the basis of analysis to the he symmetry of the RTT measurement and additionally to analyze the current situation and demands of network so as to show the urgent requirement of symmetric two-way network identification.(2)By detailed-analyzing the method of RTT measurement and the structure of RTT deferring, the thesis is to discourse upon the category congestion caused by those kinds of unilateral asymmetric network with large volume of data transmission, such as network video and wireless network, and thereby to bring forward the threshold RTT algorithms method based on the discovery of bidirectional asymmetric route. This algorithms method can effectively limit the congestion control caused by the frequent congestion false and also enhance the network QOS while without affecting the standard TCP.(3)By utilizing the network simulation software OPNET and based on the network with large volume of data transmission (multicast) unilaterally and wireless network with deferring sensitivity, we can confirm the validity of threshold RTT algorithm through the emulational experimentation of the threshold RTT algorithm which is based on the bidirectional asymmetric route.Through the test of network it shows that the wireless networks which are based on the multicast protocol-based networks and energy control can distinguish congestion and normal data transmission effectively, therefore it is an effective way of enhancing QOS. Meanwhile, it has a good interoperability with the current RTT measurement.