1.请求发送/清除发送：
顾名思义，RTS / CTS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，并且调制解调器可以启动或形成通信通道。然后DCE进一步声明或发送CTS授予许可，即可以发送数据。 RTS只是表明主机要发送一些数据，而CTS只是表明是，您可以开始发送数据。在这里，主机可以是计算机或任何其他设备，而DCE可以是调制解调器。
2.数据终端就绪/数据集就绪：
顾名思义，DTR / DSR是一种流机制，其中DTE(即主机声明)或将DTR发送到DCE(即调制解调器)只是为了表明主机已准备好进行通信，而调制解调器可以启动或创建通信通道。 DCE随后会增加资产DSR，以简单地指示接收器已准备好进行通信。
RTS / CTS和DTR / DSR之间的区别：
| 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. |