the protocol is called 3270, runs on port 23 but isn't telnet, and there's several emulators depending on the account... bluezone 3270, ibm personal communications, reflections workspace, x3270/ws3270, there's a few...
@JourneymanGeek this works too, until you are in the middle of a crisis, middle management is pinging you nonstop and the client loses a few thousand dollars per minute the system is down...