Telnet to HIS = TCP or UDP?

I’m not entirely sure I understand the problem we’re experiencing at the moment but I’ve hit a brick wall and really have no idea where to go from here.

We have an HIS that has some (telnet?) sessions on it. When we connect in with a terminal emulator called WinVV (closed source developed back in the day by British Rail) we get a session that was specified inside the WinVV config and hey presto it talks to the 3270 mainframe.

I’d like to use an open source telnet client rather than the WinVV one, and my problem is that they don’t seem to work. To investigate this I tried a simple telnet to the HIS server, expecting an error back stating it couldn’t understand 3270 streams, but the telnet connection simply times out. This seems really odd because I thought that anything that connected to a (telnet?) session needed to use telnet.

Investigating further I captured the packets sent whilst connecting with WinVV. It seems they are UDP packets with a destination port of 22102. I’m really puzzled as to where to go from here.