The DB9F-TO-RJ45 Adapter plugs into a normal DSub-9 male serial port. This way it allows to use a Cat5 cable for data transmission. This is very effective when using RS422 or RS485 operation, since the differential signals are located on the paired wires. The matching adapter DB9M-TO-RJ45 at the other end of the Cat5 cable reverses the conversion, the standard signal assignment is valid again. But customers may use their own connection on the other side.