1. 请求发送/清除发送：
RTS/CTS，顾名思义，是一种流机制，其中数据终端设备 (DTE) 即主机资产或将 RTS 发送到数据通信设备 (DCE)。这样做只是为了表明主机已准备好发送数据，调制解调器可以启动或形成通信通道。然后 DCE 进一步断言或发送 CTS 以授予权限，即您可以发送数据。 RTS 只是表明主机想要发送一些数据，而 CTS 只是表明是的，您可以开始发送数据。这里，主机可以是计算机或任何其他设备，DCE 可以是调制解调器。
2. 数据终端就绪/数据集就绪：
DTR/DSR，顾名思义，是一种流机制，其中 DTE 即主机断言或发送 DTR 到 DCE 即调制解调器，只是为了指示主机已准备好进行通信并且调制解调器可以启动或创建通信通道。 DCE 然后进一步资产 DSR 以简单地指示接收器已准备好进行通信。
RTS/CTS 和 DTR/DSR 的区别：
| RTS/CTS | DTR/DSR |
|---|---|
| While using RTS/CTS, there is a lot of buffering by hardware. | While using DTR/DSR flow control, there is no buffering. |
| It is used in different fields such as Academic, Vending, Industrial, etc. | It is used in different fields such as POS (Point of Sale), Printers, EPOS (Electronic Point of Sale), etc. |
| It can also be used for controlling flow of data among host and device. | It can also be used for controlling flow of data, handshaking as well as providing power also. |
| RTS simply indicates that it wants to send data to device that is being connected. | DTR simply indicates that device that is being connected is ready to receive data. |
| RTS only start and stop communication. | DTR also indicates that there are some equipment present. |
| RTS/CTS lines are not driven by firmware. Instead, they are controlled and driven by hardware. | DTR/DSR lines are generally driven be firmware in adapters. |