WebNMS CLI API provides Serial Communication as one of the standard protocol implementations for connecting network devices such modems, routers, printers and others. The serial communication can be carried out by plugging the devices to serial port using the null-modem cable.
The serial port "serializes" data, i.e. it takes a byte of data and transmits the 8 bits in the byte one at a time.
The serial port needs only one wire to transmit the 8 bits. Before each byte of data, a serial port sends a start bit, which is a single bit with a value of 0. After each byte of data, it sends a stop bit to signal that the byte is complete. It may also send a parity bit.
Serial ports, also called communication (COM) ports are bidirectional. The bidirectional communication allows each device to receive data as well as transmit it. Serial devices use different pins to receive and transmit data using the same pins would limit communication to half-duplex, using different pins allows for full-duplex communication.
An important aspect of serial communications is the concept of flow control. This is the ability of one device to tell another device to control the sending data for a while. The commands Request to Send (RTS), Clear To Send (CTS), Data Terminal Ready (DTR), and Data Set Ready (DSR) are used to enable flow control.