| Since it has many functions and effects, Internet has been developed rapidly and become an important basic of today's social life. Because of the great requirement of network applications, the network systems often result in the status of congestion. Although the CPU of the network equipments become more quickly and the bandwidth of networks continue increasing, the networks can not satisfy the more increase of application requirement. For the IP networks have the characteristics, such as connectionless and packet switch, they can not avoid the congestion indeed. So the schemes of congestion control are very important for the robusticity and stability of the IP networks. Currently, there are two kinds of the schemes of network's congestion control. The first is congestion control strategies in hosts, such as the algorithms of TCP congestion control. The second is congestion control strategies in subnet, such as the scheme of Active Queue Management (AQM).A good scheme of congestion control should base on the exact description of the network system. For not understanding the dynamic characteristic of the network system, the current schemes of congestion control most came from expert's experience and lack of the support in theory. This thesis proposes a dynamic model for a simple IP network with a single bottle-neck link. First we decompose the simple network into several basic parts and set up the corresponding dynamic models. Then the model of the whole network can be easily combined. On the base of experimental analysis, we did the researches on control objects and algorithm designing of the schemes of queue management.Currently, the congestion control algorithm of TCP is dominant in network system. To solve the problem that multiple packets were lost from the same window in TCP connections, this thesis proposes the Instant Recovery algorithm, A New recovery algorithm for TCP congestion control. With the developing of Internet, the real-time applications, such as multimedia, have continuously increased. Commonly, real-time network applications use UDP to transmit data in constant rate, which may affect the performance of the other transmissions such as TCP connections, and result in severe network congestion. To solve this problem, this thesis proposes a new UDP congestion control scheme basing on explicit rate, which is TCP-friendly.In general, the main contents and contributions in this thesis could be summarizedas below:(1) To solve the problem that multiple packets were lost from the same window in TCP connections, this thesis proposes the Instant Recovery algorithm. Through dynamically setting the threshold for exiting the recovery period, the Instant Recovery algorithm can recover the first lost packets and the packets lost later in the recovery period. The simulation results show that the performance of this algorithm is much better than TCP New-Reno, and is not worse than SACK TCP.(2) Proposed a new UDP congestion control scheme based on explicit rate. In the new scheme, the end-systems get the fair bandwidth of the bottleneck link in the connection, with the support of the routers in networks. Then the sender regulates the send-rate to this fair bandwidth smoothly. The new UDP congestion control scheme has better performance than the other UDP congestion control scheme such as TCP-Friendly Rate Control (TFRC) protocol, especial in the throughput and TCP-friendliness.(3) Based on the fluid-based data transmission, this thesis proposes a dynamic model for a simple IP network with a single bottle-neck link. We decompose the simple network into several basic parts and set up the corresponding dynamic models. And then the model of the whole network can be easily combined.(4) A hybrid system is used to describe the data transmission process of TCP congestion control scheme. Combining the dynamic model for IP networks, we got the model description of data transmission process in TCP/IP network system. This model is well validated by comparing the analytical results with the NS simulati...
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