Improvement On TCP Over High Speed Satellite & Internet Network

In recent years, along with the satellite communication technology inceasing improvement and enhancement, many kinds of new services like multimedia, Internet, distance learning and the medical service and so on have already replaced the traditional television, telephone business, these new services become the main satellite transmission business. Among them, satellite and the Internet is particularly noticeable. Satellite communication coverage wide area, communication costs has nothing to do with distance, away from the impact of natural disasters, these advantages fit the rapid development of the Internet business. However, a combination of both, there are still some problems, one of the main problems is the protocol. Currently Internet data flow widely uses TCP protocol, this TCP protocol originally designed to be the major consideration in the ground cable channel transmission, and satellite channel has different characteristics with terrestrial cable channel, when apply TCP to satellite, Its performance will be decreased by a number of factors, resulting in lower throughput. In this context, The author analysis the characteristics of high-speed satellite channel and its impact on TCP performance, Presents a satellite link with TCP improved algorithm for the simulation and analysis.In this paper, The author take a thorough analysis on the TCP in the satellite Internet. In the satellite transmission, some random factors (such as attenuation, etc.) in the wireless channel make it very easy to access the burst error, thus leading to a satellite channel bit error rate is higher than that of cable channel. Because TCP is impossible to distinguish congestion caused by the loss and by the errors. it is only an assumption that one packet loss and congestion caused by the congestion. And then use a type of plot-control mechanism to reduce the size of the window to ease network congestion. When the satellite channel error occurred and the packet loss, TCP would think that congestion is caused by the loss, This larger error rate would trigger the mechanism of window reduction to early, thus reducing the throughput. In addition, the delay of satellite channel is longer, particularly in theGEO system, the RTT in more than 500ms. This delay makes TCP slow start to spend a very long time. Congestion control mechanism should also spend some more time.Currently, there are many of the TCP improvements on satellite and Internet, and the author's method is mainly for the improvement of TCP-SACK version. In SACK version, some new mechanism has been adapted to the larger error rate, the large delay satellite channel. Although errors can be recoverd through a rapid Retransmission, but in rapid recover which after the congestion phase, The slow growth of the window is still a large impact on the throughput. This paper presents the basic idea of improving algorithm as follows, As the satellite channel transmission errors caused by the packet loss probability than congestion caused by the probability of packet loss, Therefore, when the error recovery, we can change the fast recovery algorithm, increase the window growth rate useing of the new algorithm, and avoid entering the stage of avoid congestion too early. This improved algorithm has the advantage of smaller changes from TCP, simplicity, while raising throughput.To achieve certification and improved algorithm In this paper, we use the present widely used network simulator ----NS2 (Network Simulator ) on TCP in high-speed satellite channel on the performance simulation. NS2 is an open source network simulation software, initially developed with UC Berkeley. It is used to study large-scale networks, future network protocols and the development of interaction. It provides a strong support on wireline and wireless network TCP, and the multicast routing protocols. NS2 is an open source project, all source code is open, and anyone can use and modify the source code. Because of this, around the world, researchers are daily updating and expanding its functions, adding new support for the protocols and functional modules. It is currently one of the most popular network simulation software.In the process of improved algorithms implementation, the author carefully study the NS2 standard TCP mechanism for the program. Amend the protocol through the C + + source code, and add this improved algorithm to TCP protocol.After the Linux compiler generate a separate TCP protocol module, the author eventually add this module to the NS2 software.The author construct a simple point-to-point GEO satellite systems by NS2 software. The sending and receiving earth stations are Daejeon, Korea (127.55 east longitude, latitude 36.70). and Harbin, China (126.8 east longitude, latitude 46.30). The channel transmission rate of GEO satellite (128.2 N) is 100MB/s. Using the existing TCP modules in NS2, the author construct the TCP Tahoe. Reno and SACK TCP Protocol Module, By changing the channel packet loss rate to compare various versions of TCP performance. Simulation results show that in the simulation of high-speed satellite Internet environment, improved algorithm has the better performance than the other versions. The throughput in improved algorithm increased by about 10% more than TCP-SACK. And about 26% more than TCP-Reno. with the channel transmission rate increases, improved TCP throughput has been increased.Currently, many domestic and foreign researchers has been studying ways to improve TCP, They have done a lot of work on TCP applications for satellite communications. TCP has been constantly improved and updated, I believe that with future technological advances and applications will increase demand for TCP more demanding, TCP performance will be greatly improved. The reaearch on TCP improvements against satellite network features , will be a long-term study on satellite and Internet.