Check serial of mid-low end router with display interface command, what is the meaning of DCD/DTR/DSR/RTS/CTS?
1、DCD Data Carrier Detect
DTR Data Terminal Ready
DSR Data Set Ready
RTS Request To Send
CTS Clear To Send
For the five control signaling, DTR and RTS are sent by DTE device (such as router). DSR, CTS and DCD are sent by DCE device (such as MODEM).
2、The negotiation mechanism of five control signals:
(1)、For the serial of the router does not configure flow control, as long as it is power on, DTR and RTS (Although it is power on, these two states are up.) When the router checks DSR, CTS and DCD sent by the opposite, the physical state of serial is UP(Anyone of physical signal is invalid, the physical state is not up.).
If the serial configures NO DETECT DSR-DTR command, DTE will not detect DSR and CTS signal sent by the opposite. As long as DCD signal is checked , the physical layer is UP.
(2)、If the serial configures flow control (flowcontrol auto), RTS and CTS are used for flow control (the transmission and receiving flow control between serial and Modem). If the data is not handled in time, two control signals are DOWN.