Ethernet Encapsulation is the ability to communicate directly with terminal servers. Many latest generation prodcuts have this build in now.....

If you want to gather data from each machine on the plant floor, and you want it quick. Your Manager thinks this will be easy since site has dictated that Ethernet cabling everywhere. BUT your existing PLCs only have serial connections (RS323).

To address this, you may need to use terminal servers from companies like Digi and Comtrol. A terminal server is essentially a virtual serial port. More importantly, a virtual serial port that can sit on your existing Ethernet network.

In this way you can connect all of your controllers which have serial port to your ethernet. Now You can place a terminal server next to each machine gathering operational data directly from the serial ports of the controller, and bring that data back to you via commonly used Ethernet cabling.
Many vendors supply accompanying software that allows the terminal server to appear like a serial port to your operating system. This software can make using a terminal server quite easy.

But in some cases timing is critical. User also usually seen and reported frequent communications errors, continuous breaks in the communications, and long delays while the supplied software reconnects to the terminal server. All of these problems can make your use of a terminal server less than ideal.

In this type of scenario, produts/software which has Ethernet Encapsulation incorporated (the functions needed to directly connect to a serial device connected to an Ethernet based terminal server), are best way to go....