Multipathing In Embedded Operating Systems Research And Design Of TCP

As the Internet technology is more and more widely used,stable and high-speed data transmission protocols are widely concerned.Transmission Control Protocol(TCP)has been used for reliable message sending and file transfer due to its high reliability,but TCP protocol can only use one physical interface for communication.Nowadays,embedded devices are widely equipped with multiple types of network interfaces and have the demand for parallel communication with multiple interfaces,so the traditional TCP transmission protocol can hardly meet the everchanging communication environment and user requirements.At the same time,the Internet is a very complex heterogeneous network with huge performance differences between paths.Multipath Transmission Control Protocol(MPTCP)technology is one of the effective methods and approaches to solve the above problems,and realizing parallel transmission of multiple network interfaces and efficient data scheduling among multiple paths has become an urgent problem and research hotspot for researchers at home and abroad.The main work of this thesis is as follows.1.Adaptive Packet Data Scheduling Scheme(AGDS): This thesis proposes a multi-path TCP data scheduling algorithm based on the problem of buffer blocking at the receiving end due to packets arriving out of order in a heterogeneous network environment.The algorithm is based on adaptive grouping to make packets arrive in order as much as possible,reduce the number of outof-order packets,and reduce the risk of buffer blocking.The main idea of the algorithm is to first evaluate the data transmission rate of each path before packet allocation and dynamically preallocate the appropriate number of packets to each transmission path;predict the packet arrival time based on half of the packet transmission time RTT and use it to allocate the packet sequence number;meanwhile,in view of the real-time change in transmission performance of each path,the preallocation is modified according to the actual change in RTT of each path.The packet sequence number is assigned according to the actual change of RTT of each path.The results show that the AGDS scheduling algorithm outperforms the other two algorithms by comparing with the shortest transmission time first(STTF)scheduling algorithm and the shortest delay first(LRF)scheduling algorithm respectively,while the status of each path remains unchanged.2.Multipath TCP protocol design,implementation and verification: Based on the characteristics of the embedded operating system,the overall framework of the protocol,the main data structures used in the system,and the core technical points of the protocol stack upper and lower interfaces are designed by analyzing the requirements of the MPTCP protocol in the network protocol stack.At the same time,the core functional flow of the protocol,including connection establishment,subflow establishment,message construction,data transmission,data reception,multipath data reassembly,and connection closure,is elaborated and explained.On this basis,the MPTCP protocol using the AGDS algorithm proposed in this thesis is applied to the Vx Works embedded operating system and compared with the single-path TCP transport protocol and the MPTCP protocol based on the LRF and STTF scheduling algorithms.The experimental results show that the MPTCP protocol outperforms other protocols in terms of reliable transmission redundancy and data transmission performance under the condition of parallel data transmission using both Ethernet and Wi-Fi interfaces.