Research And Improvement Of Transmission Control Protocol For Satellite Communication Systems

Congestion control mechanism of Transport Communication Protocol has two categories which are packet loss-based congestion control mechanism and delay-based congestion control mechanism.Traditional TCP protocols use packet loss-based congestion control mechanism.TCP Vegas and other improved protocols use delay-based congestion control mechanism.In this paper,the Transport Communication Protocol is on research from the perspective of improving the communication throughput and channel utilization,reducing transmission delay for LEO satellite communication systems and deep space communication systems.Firstly,in this paper,SCPS-TP is deeply researched.SCPS-TP is a standard transport protocol for space communication.Although SCPS-TP uses a variety of strategies to adapt to the satellite communication environment,there are still many problems,such as asymmetric channel bandwidth problem,the stability problem,bandwidth competition and fairness problem and problems caused by routing switch.A protocol named SNACK-block protocol for LEO satellite communication system is proposed to solve the problems of SCPS-TP.The SNACK-block protocol consists of the quick start algorithm,the congestion control algorithms and fast reconstruction algorithm.The window growth in quick start algorithm is based on the number of rounds.The round number leads the window strategies.Congestion control algorithm is based on the SNACK mechanism,and the concept of dropping hole is furthermore proposed,the lost packets in an ACK packet segment are identified to discriminate,classify the congestion phase to extend the period of congestion avoidance,thereby enhancing the channel utilization rate.Fast reconstruction algorithm is based on the ACK sequence replacement by the redefinition of RTO events.ACK sequence is cached in normal communication,and ACK sequence replacement is performed when RTO event occurs.Secondly,an error tolerance congestion control algorithm based on the packet loss rate called PLRM algorithm for deep space communications is proposed in this paper.The algorithm extends the concept of packet loss to packet loss rate,so it can cope with the effects of the harsh environment of deep space.The algorithm divides the entire communication process into three sections by measuring the rate of loss,and each section performs different congestion window strategies.Thus the algorithm has a higher communication throughput in high link error rate of the space environment.In addition,in order to enhance the transmission efficient,the algorithm also defines a new packet format.Thirdly,ad-PLRM algorithm which is an adaptive algorithm on the basis of PLRM algorithm is proposed in the paper.The error tolerance changes to adaptive processing mode.Adaptive congestion window directly depends on the size of the packet loss rate instead of segmenting the communications,this method increases the stability of the algorithm.Finally,mathematical modeling and a simulation software called OPNET are used to accomplish the mentioned algorithms.Mathematical modeling results show that the channel utilization of SNACK-block protocol,PLRM algorithm and ad-PLRM algorithm are 16.88%,19.6%and 16.4%higher than TCP Reno protocol.The stability of SNACK-block protocol,PLRM algorithm and ad-PLRM algorithm are 48.02%,29.45%and 39.84%higher than TCP Reno protocol.The OPNET software simulation is measured from three aspects of congestion window,transmission delay and retransmission delay.SNACK-block protocol,PLRM algorithm and ad-PLRM algorithm are simulated compared to TCP Reno protocol.The results show that the proposed protocol and algorithms in this paper is better than TCP Reno protocol in the aspects of improving communication throughput and channel utilization,reduce transmission delay.So the research of SCPS-TP for LEO satellite communication systems and deep space communication systems is complished.