▍1. Signal
接收器必须具有某种方法能够知道数据流中字节的起始和结束。在异步通信中，字节边界由起始和停止位指示。在同步通信中，定时机制帮助发送器和接收器处于同步状态。(The receiver must have some way to know the data stream in bytes of the start and end. In asynchronous communication, the byte boundary from the start and stop bit instructions. In synchronous communication, the timing mechanism to help the transmitter and receiver are in sync.)
