The simplest method is to use a null modem cable (Item# CA213), which reverses the transmit and receive signals between the serial devices. This method only works for short distances.
For distances over 50 feet, a better method is to use a pair of Sealevel Ethernet Serial Servers and configure them for “serial tunneling”. This allows asynchronous serial devices to communicate over an Ethernet network eliminating costly upgrades to application programs or serial devices. Barcode scanners, RFID readers, scales, sensors, and other serial devices can be located remotely on the network, yet communicate with a host serial device as though they were directly connected to a local serial port.
Sealevel Ethernet Serial Servers support serial tunneling and can be configured via a simple web interface.