Measurement And Optimization Of Network Protocols In Cellular Networks In High Speed Mobility Scenarios

With the rapid popularization and development of high speed railway,the demand for acceptable QoE of network service in the high-speed mobility scenarios has been unprecedentedly strong.However,the performance and behavior of commonly used network protocols,such as TCP and UDP,have not been fully and profoundly studied in such scenarios.We urgently need to measure these network protocols,find existing problems,and propose solutions.For this purpose,this paper has conducted a large-scale measurement study on TCP,and Skype,a voice/video call application based on UDP,in 3G/4G networks on high speed rails with a peak speed of 310km/h in China.Finally,multipath transmission with multiple carriers is proposed to improve performance.The main contributions are as follows:1)Innovative measurement and analysis methods.We have developed a measurement tool that can automatically collect the information of many influencing factors,such as terrain,speed,network type,handoff,network disconnection etc.We have designed an analytical method that can analyze the independent influences of each factor quantitatively.In addition,when measuring Skype,to overcome the challenge that Skype is proprietary software,and there is very limited public information about its encoding and transmission algorithms,we bring in two reference flows to detect network condition and evaluate the efficiency of Skype.2)A comprehensive and in-depth measurement on TCP.The measurement lasted three years and we collected 500 GB of data.It was found that RTT and packet loss rate increased sharply,and throughput decreased significantly in high speed mobility.Many key operations of TCP,such as retransmission,congestion control connection,and establishment/closure show serious abnormal behavior.It was found that big flows suffer much more significant performance degradation than small flows.3)A comprehensive and in-depth measurement on Skype.The measurement lasted eight months and we collected 50 GB of data.Various objective performance metrics(including RTT,sending rate and call setting time)and a subjective performance metric(QoE)were found to be significantly reduced.Many key operations of Skype show serious abnormal behavior,including routing in application layer,rate control,state updates and call termination.4)It is proposed to improve the performance through multi-path transmission with multiple cellular carriers.A mature multi-path transport protocol,MPTCP,was measured on high speed rails.During a 22-month period,we collected more than2.7 TB of data.It is found that although MPTCP can improve robustness,it is not efficient.In order to improve the efficiency,we designed a new protocol,MPTCP HSR.Experiment results show that MPTCP HSR performs much better than MPTCP LIA.