Linux-based Embedded System Real-time Communication Technologies

The embedded system itself requires high real-time performance, and it is used in network system more and more frequently, so it is vital to improve the embedded system's real-time communication ability. Linux is an open source operating system, and its kernel can be customized freely according to users' request. Therefore, Linux provides an excellent platform for the embedded system to be transplanted and modified. So we do our work in Linux operating system.In the field of embedded application which needs high real-time ability, the real-time performance of traditional TCP/IP stack can't satisfy us very much, because traditional TCP/IP stack concentrates on details such as the reliability of data transmission, data flow control and so on. Traditional TCP/IP stack has a great number of code and poor real-time performance, therefore, it doesn't adapt to use in embedded system. In this paper, we modify the main data structure of TCP/IP stack and bring up a light embedded TCP/IP stack without going against the existed protocol standard. The modules of TCP,ICMP, UDP and TCP are emphasized, then the paper discusses some questions that should be considered carefully ,such as the design mode of TCP/IP stack; decreasing the times of data copy; optimizing the management of buffer and memory; puting forword an interface layer between OS and the stack.In order to assure the embedded system to keep high real-time performance when communication flow increasing, we should consider carefully congestion control in embedded communication system. However, traditional congestion control algorithm is not suitable for embedded communication system. Thus this thesis gives a modified scheme for congestion control algorithm in two aspects, one is adjusting the buffer dynamically, the other is data dispatching based on two-dimensional table. Adjusting the buffer dynamically refers to dispatching the memory according to the quantity of small TCP connections; data dispatching based on two-dimensional table is calculating the priority of data packet in term of its size and importance through a two-dimensional table, the method of data dispatching is to assure the small and important data packet can be dispatched preferentially.The paper constructs a test platform, and designs two schemes to test the modules of IP, ICMP,TCP, UDP and the modified embedded congestion control algorithm.After analyzing the experimental data, we can get the conclusion:the real-time communication capability of embedded system is enhanced remarkably with the modified TCP/IP stack and embedded congestion control algorithm.Finally, on the basis of the summarization of the research work, some problems which should be discussed deeply are put forward. The paper gives some suggestions for the further research as well.