说明：  计算机网络的数据链路层协议保证通信双方在有差错的通信线路上进行无差错的数据传输，是计算机网络各层协议中通信控制功能最典型的一层协议。 为了更好地掌握“滑动窗口”技术，要求在一个数据链路层的模拟实现环境中，用C/C++语言实现“退回到N重发”的滑动窗口协议（协议5）和“选择重发”的滑动窗口协议（协议6）。
(Computer network data link layer protocol to ensure that there are errors in communication between the two sides in the communication line on the error-free data transmission, all floors of the agreement is the computer network communication control protocol layer of the most typical. In order to better grasp the sliding window technology, the requirements in a data link layer of the simulation environment, with C/C++ Language back to the N re-issued, the sliding window protocol (Protocol 5) and choice of re-issued, the sliding window protocol (protocol 6).)