A Study Of Transmission Performance Of DTN Protocol For Space Communication

Space network will provide necessary guarantee for future space science exploration,space information application,military and civil emergency rescue and other fields in China with the development of aerospace and satellite payload technology.The environment and link characteristics of space communication are different from those of terrestrial network.There are dynamic changes in topology and heterogeneous systems in space network.Communication links characteristics such as high error rate,long transmission delay,asymmetric link and frequent stochastic interruption bring some obstacle to space tasks and data transmission.Moreover,the mature technology of terrestrial Internet is not applicable.Protocol architecture and transmission scheme are the key factors affecting the transmission performance of space networks.It is necessary to achieve interconnection,collaboration,integration,unified processing among heterogeneous networks,and to effectively cope with the bad characteristics of space links,with compatibility and scalability.Delay/Disruption-Tolerant Network(DTN)is a new network technology that can overcome space communication environment and provide reliable transmission solutions for intermittent and dynamic networks.Aiming at the development status and requirements of space network,this paper systematically studies the transmission performance of DTN network key protocols and combinations of different protocols in space network environment through mathematical modeling,simulation and theoretical analysis,which provides theoretical support for the practical application of related protocols in future space missions.The main contributions of this paper are as follows:1.Evaluating the transtmission performance of DTN space applications based on Hardware-in-the-loop Simulation platform.This paper focuses on the constraints of the characteristics of space transmission links on the performance of the protocol.This paper mainly studies two kinds of protocol structures,i.e.Bundle Protocol(BP)with custody-based retransmission disable/Licklider Transport Protocol(LTP)with red data transmission and BP with custody-based retransmission disable/TCP The effects of space link delay,bit error rate and link asymmetry on the reliable transmission performance of the protocol are studied in two typical space communication application scenarios of near-Earth and deep-space exploration below GEO in space-time perspective.2.The modeling of transmission performance and optimization setting of retransmission timer-out(RTO)for BP.For space communication,especially deep space communication,there is inherent long propagation delay in the link.The solution of setting up retransmit timer using terrestrial Internet is not applicable,which is not conducive to the optimization of network performance.Aiming at the link characteristics of long propagation delay and high packet loss rate in space communication,the RTO of retransmit timer is modeled and optimized according to the maximum transmission performance of BP and the minimum end-to-end transmission delay to maximize the transmission performance.The performance evaluation of the model shows that the retransmit timer RTO has a vital impact on reliable delivery of transmission performance.The validity of the model is verified by the real data stream of the hardware-in-the-loop simulation platform,which provides an effective method for DTN application and protocol performance prediction.3.Assessing the impact of link stochastic interruption on LTP reliable transmission performance and LTP queuing delay on protocol performance The high bit error rate and dynamic topology of space link cause communication link interruption,which seriously affects the transmission performance and even loses the effectiveness of communication.This paper models the reliable file delivery delay basing on the application of reliable file delivery with aiming at the link characteristics of high bit error rate and random interruption in space link,and studies the effect of random interruption on LTP reliable transmission performance.The queuing delay of LTP is increased for forwarding nodes with the bad communication environment and link characteristics according to the reliable delivery mechanism of LTP In this paper,the queuing delay of LTP layer is modeled according to LTP data transmission and reliable delivery process,and the effect of queuing delay on LTP reliable transmission performance is studied.The model is evaluated and validated.4.Optimizing the cross-layer packet size of DTN.The protocol standard does not explain the cross-layer packet of DTN protocol structure.But the size of the cross-layer packet has an important impact on the protocol transmission performance.In this paper,the bundle size of Bundle Protocol(BP)layer,the block size of LTP layer,the number of session and the segment size are given respectively.The bundle size of BP layer is discussed separately according to whether the custody-based retransmission is enabled.LTP cross layer packet size is studied mainly for reliable transmission,i.e.the optimal size of block with red data transmission.The number of sessions is determined by weighing link resource(bandwidth delay product)and LTP process storage resource.Then considering the overhead cost and data loss to determine segment size.