How do SeaLINK Ethernet serial servers transmit modem control signals in serial tunneling mode?
SeaLINK Ethernet serial servers use RFC-2217, the Telnet COM port control protocol, to transmit modem control signals in serial tunneling mode. Since SeaLINK Ethernet serial servers are DTE devices, they follow standard null-modem conventions to tunnel output modem control signals. This is done in two parts as explained below.
Setting the output modem control signals on the remote serial server
The remote SeaLINK serial server sets output modem control signals on the output serial port when it receives the matching RFC-2217 command:
- Set DTR ON
- Set DTR OFF
- Set CTS ON
- Set CTS OFF
Receiving input modem control signals on the local serial server
When input modem control signals are set on the input serial port, the local SeaLINK Ethernet serial server will send the RFC-2217 commands to set DTR or CTS as follows:
- When a SeaLINK device sees either the DSR or DCD input is ON, it sends the RFC-2217 command to set DTR ON.
- When a SeaLINK device sees both the DSR and DCD inputs are OFF, it sends the RFC-2217 command to set DTR OFF.
- When a SeaLINK device sees the CTS input is ON, it sends the RFC-2217 command to set RTS ON.
- When a SeaLINK device sees the CTS input is OFF, it sends the RFC-2217 command to set RTS OFF.
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