c语言模仿滑动窗口协议，源代码。（1）　　编写滑动窗口协议的发送程序，令序号长度N=3，窗口最大尺寸=4；

（2）　　发送程序需要处理的三个事件：网络层分组到达、计时器超时、确认到达可以通过外部输入来模拟；而发送程序应送往对等方的帧直接输出，便于检查程序的正确性。

-c language to imitate the sliding window protocol, the source code. (1) the preparation of the sliding window protocol to send a program, so that the serial number length N = 3, the maximum window size = 4　(2) send the program needs to handle three events: the network layer packet arrives, the timer timeout, confirm arrival external inputs to simulate　and send the program should be sent to the side frame directly output, easy to check the correctness of the program.