Research On The Dynamic Graph Based DTN Routing Algorithm For Satellite Network

Since the beginning of 21 st century, some countries have been working on the plan of developing a new generation of satellite coverage network due to the rapid development of computer hardware,software technology and the growing demand of the economic and military. For example, China and Russia are developing the system "happy star" which a global satellite Internet system. To deal with the mass of data and support multi-media technology, the satellite network has to be more complicated and need to increase its size. And many researchers are working on the subject of optimizing the transmission, reducing transmission cost, reducing the packet delivering time and balancing the network payload. DTN, a network protocol system,which inherits the idea of TCP/IP Protocol and CCSDS protocol is compatible for many underlying protocols. By using BP Protocol(Bundle) Protocol and LTP Protocol(Licklider Transmission Protocol), it can solve the data transmission problems in challenging environment.A practical protocol system is the necessary premise to transmit data between nodes. There are many problems in communication in the environment of satellite network, such as intermittent connection, high error rate and dynamic link features which make it impossible to use ground Internet protocols. At present there are three types of the satellite Internet protocol architectures to be studying: IP space protocols, CCSDS protocols and the DTN(Delay/Disrupt-Tolerant Network).Comparing with IP space protocols and CCSDS protocols, DTN protocol architecture has a good performance in integration of the traditional network and satellite network. Its the Routing strategy CGR(Contact Graph Routing) can transmit data in the challenging network by intermittent transmission.The main purpose of this paper is to study the DTN protocol in the application of satellite network. At first,we analyze the characteristics and mechanism of BP and LTP in the data transmission. As a result, we find that CGR routing strategy does not select the optimal path in routing decision by ignoring the orbit information of satellite. We analyze the transmission of LTP layer segments the mathematical model of satellite channel.We establish new indicators to choose the transmission path in routing decision which include both the cost of bandwith and expected retransmission rate. The indicators also need to consider the value of packet loss rate and the possible round-trip time. As the BER(bit error rate) is time-varying in the channel of satellite network, it is necessary to study the mathematical model of channel. As a result,it is found that BER is mainly affected by the link distance. Then the study is to find the time-varying model of the space channel. We use a machine learning strategy to forecast the BER in transmission. And all the ideas are put into practice as software programs in BP protocol. The BP uses the improved route algorithm in data transmission.Finally, we simulate the idea on the platform of ION. The space environment is simulated by configuring parameters of network cards. We compare the parameters of channel model and the result of machine learning strategy. And by comparing the improved routing algorithm with CGR strategy, we analyze the improved performance of throughput in transmission.