In transparent mode, the only function key available is the PA1 attention key. It is used to invoke a TELNET subcommand. If there is more than one nested TELNET session, the PA1 key is used to invoke a TELNET subcommand for the first TELNET session.

See PA1—Send the PA1 keystroke to a host for information about how to send the PA1 keystroke to the foreign host session.