数据链路层的选择性重传协议的编写。在仿真环境下编程实现有噪音信道环境下

两站点之间无差错双工通信。信道模型为8000bps 全双工卫星信道，信道传播时延270毫秒，信道误码率

为10-5，信道提供字节流传输服务，网络层分组长度固定为256字节-The data link layer selective retransmission protocol preparation. In the simulation environment, programming environment, the noise channels between the two sites error-free duplex communication. Channel model for 8000bps full duplex satellite channel, the channel propagation delay 270 milliseconds, the channel bit error rate of 10-5, the channel to provide byte-stream transport service, the network-layer packet length is fixed to 256 bytes