实现多级节点的停止等待ARQ，算出吞吐量-To achieve the multi-stage node Stop and Wait ARQ, calculated throughput

非持续性CAMA是一种冲突避免的CSMA协议，如果终端检测到信道状态空闲，则立即进行数据传输，而信道状态忙，则停止载波监听，并随机在等待一段时间后再进行载波监听。-Non-durable CAMA avoid CSMA protocol is a kind of conflict, if the end channel state idle, detected immediately for data transmission, the channel state is busy, stop t