Function key mappings in telnet session to Universe Application

Our client uses Termtek terminals to connect to their Universe platform. More terminals needed and we can't get any. The alternative is to get winboxes and run wintegrate or try and get a Linux terminal working. Configured xterm with keybindings that I need for the F1-F5 keys. In xterm session these bindings work, however when I connect via telnet to the Universe sessions, they don't. For F1 I get ^[OP. I need EX and return. F2 I need + and return and so forth. I have been trawling the net with not much luck. Indications are it's to to do with the terminal settings rather than on the host side however I can't seem to find anything concrete. I found that the the backspace button did not work(even though worked in terminal session) and used a script I found on this forum to run with the telnet command. This tends to suggest that the terminal keyboard mappings need to change for Telnet sessions. The supplier has set up the universe platform for us to test but only have 10 days before it expires. Hope I can get some help before then