Ethernet to serial converters can be placed on the network.The Serial Port can be accessed using a IP address and Port Number to create a TCP socket connection. Software such as Telnet, or HyperTerminal's TCP/Winsock can be used to make that socket connection to an end device.Software that ships with the Ethernet to serial converter allows you to create a Virtual Com port on your computer that will appear as a standard com port on the PC. Software on your PC can then open up the com port number that was created. Two Ethernet to serial converters can be used to create a serial data tunnel.
This is know as data tunneling or paired mode.
It acts like a Virtual Serial cable of unlimited length.