计算校验和

　　命令行：check_sum infile

其中check_sum是程序名，infile是数据文件名

　　输出：数据文件的校验和。

目的是通过数据链路层与介质访问控制层的学习，根据数据链路层的基本原理，针对普遍应用的Ethernet帧，通过构造一个具体的帧，深入理解网络协议的基本概念与网络问题处理的一般方法。-calculated checksum command line : check_sum infile which check_sum procedures, and infile data output file name : data files, the checksum. The purpose of the data link layer and the MAC layer of learning, according to the data link layer to the basic principles of universal application against the Ethernet frame, and by constructing a concrete frames, in-depth understanding of network protocols and the basic concepts of network issues to deal with the general approach.