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Study on Network Congestion Control Method Based on TCP/IP Protocol

Author: SunXu
Tutor: LiDengDao
School: Shandong University of Science and Technology
Course: Applied Computer Technology
Keywords: Congestion control Available bandwidth estimates Slow start congestion avoided Opnet simulation
CLC: TP393.06
Type: Master's thesis
Year: 2011
Downloads: 74
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Abstract

Recently, with the development of the computer network technology, Internet users has dramatically increased, network scale grows at an alarming rate and network traffic also increases dramatically. But when overmuch packet can not be timely precessed, some problems will arise subsequently. Such as network throughput will be low, and the performance will fall subsequently, this phenomenon calls congestion. Network congestion problem has become the bottleneck problem of restricting network development and application.Through summarizing the previous work, the paper studies network congestion control strategy based on TCP/IP protocol, analyses some shortcomings and puts forward some improvement measures. Main job of this paper as follows:(1) The paper researches estimation algorithm of available bandwidth, and puts forward a new bandwidth estimation method which expands sampling cycle. In this way, the bandwidth estimate value can reflect the network actual transmission ability better.(2) The paper analyses the limits of the TCP congestion control in slow start stage, and improves slow start algorithm. Adjust slow start threshold value and congestion window values according to the improved bandwidth estimate value. This way can improve the network utilization rate. On the other hand, in slow start last cycle the window numbers of one-time sending to the network are too large. Such a large size easily makes the network oscillate. So the paper puts forward Slow Start Late Deceleration Algorithm (SSLD), which can slow the send speed in slow start late, make network transition to congestion avoid stage with more smooth speed.(3) By analysis, in congestion avoid stage the window numbers of sending to the network are appropriate. The paper puts forward improved algorithm which extends the time of the congestion avoid phase, makes the network stays in congestion avoid stage for long time. The network utilization is improved(4) The paper analyses the grouping discard strategy of IP layers and proposes Predict Early Postpone Sending strategy on the basis of RED algorithm. This algorithm can predict in advance the behavior of cast grouping of purpose routers; take measures to postpone sending grouping in certain probability. This way can reduce the probability of lost package, reduce retransmission frequency. (5) In view of the above algorithms thought, the paper builds the simulation experiment platform, analyses the performance of the modified algorithm. The results show, improved available bandwidth estimation algorithm can better predict the use of network bandwidth. The paper simulates SSLD algorithm also. The result shows that when the number of packet growth to a certain amount, the improved algorithm packet loss rate is less than the original algorithm. So the measures are effective.

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