Research On Congestion Control Of Satellite Link Based On Dynamic Confirmation Mechanism

With the development of information technology and the popularization of computing concepts such as big data and artificial intelligence,intangible assets such as public facilities,energy facilities and environmental protection in daily life are increasing,and human society is gradually entering the era of big data.In order to meet such a huge demand,adapt to the development prospects of the market,and solve the problem that it is difficult to lay and cover the ground network in special environment areas,providing services with high throughput,low delay and strong stability becomes the key.In the construction of a global interconnected integrated information network,satellite communication has been widely concerned and applied due to its advantages of wide coverage,large communication capacity,and freedom from terrain constraints.However,in the face of the requirements of high-precision service and the construction of the interconnection between heaven and earth,the high dynamics and instability of satellite networks make it difficult for existing congestion control algorithms to ensure the reliability of data transmission,resulting in poor link communication performance.Aiming at the above problems,this thesis improves the traditional TCP Vegas algorithm and proposes a DCM-Vegas algorithm which can accurately determine the forward and backward congestion.This algorithm mainly adjusts the working mechanism of traditional transmission protocols from three perspectives.Firstly,a new mechanism that takes timeout as the critical point and adopts two different methods to determine positive and negative congestion is added instead of the original strategy of adjusting the congestion window based on the change of time delay.Before timeout,combined with ECN,determine the degree of forward congestion and adjust the congestion window according to the number of ACKs with ECE received.After the timeout,the congestion location is further determined by calculating the number of packets in the reverse cache queue.If it is determined to be reverse congestion,focus on optimizing the congestion avoidance mechanism after retransmitting the data packet.Otherwise,continue to observe whether the last received ACK carries congestion markers,so as to confirm whether the packet loss is caused by the bit error rate or serious forward congestion,and make corresponding adjustments.Secondly,optimize the congestion avoidance phase of traditional algorithms.First,the sender calculates the forward and reverse queuing delay and the minimum transmission delay according to the confirmation information and the timestamp.Then,the reverse queuing delay is removed from the total delay,and the actual throughput of the link is updated.At the same time,the minimum forward and backward transmission delay obtained for the first time is used as the initial value of base RTT in the calculation of the expected throughput,which is then adjusted in real time according to the network condition.Finally,the combination of the two can obtain a more accurate value of diff,which makes the adjustment of congestion window more accurate and reduces the impact of reverse link congestion on transmission efficiency.Third,added a method to classify congestion levels according to the current status of communication networks.The estimated round-trip delay jitter is obtained from the average delay of multiple groups of data,and compared with the experimental data when the network is normal to obtain the congestion factor and define the degree of congestion.Finally,under different congestion levels,according to the characteristics of each confirmation mechanism,the acknowledgement information sending mechanism used in reverse link is adjusted adaptively,the transmission rate of acknowledgement packets is reasonably adjusted,so as to relieve the pressure of the link and make it more suitable for the communication characteristics of the satellite network bandwidth asymmetry.In this thesis,OPNET software is used for simulation,and the simulation model is built according to the real communication environment.Then,the traditional Vegas algorithm and the improved DCM-Vegas algorithm are compared with the same index under different parameters.The statistical results show that the peak throughput is increased by about 20%,and the packet loss rate is reduced by up to 7‰,which effectively improves the utilization rate of bandwidth resources.The feasibility and applicability of the new algorithm in satellite network are verified.