Design And Simulation Of TCP/IP And CCSDS Protocol Conversion For Space-earth Interconnection

As China’s deep space exploration activities continue to progress,the interconnection between heaven and earth is a key link to ensure the smooth implementation of space missions.At present,the ground network generally uses TCP/IP protocol,while the space network generally uses CCSDS standard protocol,and the two protocol systems are independent of each other.In order to use mature terrestrial communication protocols in space networks,this thesis carries out research on the protocol conversion scheme of IP over CCSDS,i.e.using the CCSDS AOS protocol to transmit IP packets in space links,and carries out detailed design from the link layer,network layer and transport layer of the interconnected network between heaven and earth.In the link layer,for the problem of AOS protocol carrying IPv4 packets,AOS encapsulation is used to solve the problem,and the structure of AOS transmission frames is designed;for the problem of the length of IP packets during the data interaction between heaven and earth,the cut and splice operation is adopted to solve the problem based on the actual length of the packets.In addition,in order to solve the problem of fast transmission of emergency information in the heaven and earth interconnection network,a data priority sending method is introduced in the Mac protocol of the link layer.In the network layer,mobile IP technology is used to compensate for the lack of conventional IP technology in space and to reduce link interruption times,in response to the problem of link interruptions caused by spacecraft movement and the inability to send packets properly.In the transport layer,in response to the performance degradation of the TCP protocol caused by the high BER of the space link,the SCPS-TP protocol is used to replace the TCP protocol,which is partially extended in the TCP protocol prefix option,and solves the problems of throughput degradation,packet loss rate increase and smaller congestion window of the conventional TCP protocol in the space network by means of SACK and SNACK in the data retransmission mechanism and the use of Vegas in the congestion control algorithm.In this thesis,a simulation of the Earth-Moon network was created using OMNe T++ to fully validate the above study.The results show that: from the link layer,the unencapsulated IP packets on the sender side and the packets on the receiver side after AOS encapsulation and parsing are identical,verifying the feasibility of the AOS protocol and the correctness of the packet processing process,while the simulation results using data priority show that the number of collisions between different data sources is reduced by more than 50%,and the transmission delay is reduced by more than 2s after using this method.From the network layer,the use of mobile IP technology solves the problem of link interruption inability to send packets,and the link interruption time is also reduced by about 3s;from the transport layer,SCPS-TP protocol improves about 150 bps in throughput and 15-20 MSS in congestion window than TCP protocol,the above results show that SCPS-TP protocol outperforms TCP protocol in space network.The above results show that the SCPS-TP protocol outperforms the TCP protocol in spatial networks and is more suitable for the protocol conversion mode of IP over CCSDS.This thesis has some implications for the design of interconnection protocols between heaven and earth for the development of near-Earth space and Earth-Moon communication and data interaction in China,and gives theoretical and technical help for future exploration of space communication systems.