Closing an open PPP line involves using the pppclose command.
Run the built-in C_INIT command, pppclose, on the target system:
host% rsh target pppclose device
pppd device:info: Terminating on signal 15.
pppd device:notice: Connection terminated, connected for 2 minutes
pppd device:info: Exit.
where device is either /dev/tty01 or /dev/tty02.