TN5250

TN5250 stands for Telnet 5250. TN5250 is a protocol that provides remote terminal access to an IBM AS/400 and iSeries computers.  The TN5250 protocol allows this communication via a TCP/IP network instead of an SNA network. 

The computer that acts as a terminal is called the TN5250 client and the computer that acts as the host is called the TN5250 server. The TN5250 client computer must run an TN5250 client application (like TN3270 Plus) and the telnet server must run a telnet server application. The TN5250 client received data streams from the host computer and displays them in a terminal emulation Windows. The contents of terminal emulation window mimic the screen of an IBM 5250 terminal. 

The TN5250 protocol is based on the IBM 5250 terminal device which was sold with the IBM System/34 computer systems. The 5250 terminal was a block-oriented terminal similar to the IBM 3270 terminal.

IBM 5250 - Wikipedia.com

RFC1205 - 5250 Telnet interface

RFC2877 - 5250 Telnet Enhancements