AT&T SYSTEM 25 Manual page 189

If the PC is connected to System 25 over a STARLAN NETWORK, do not turn off or reboot
the PC to end the call. If you do, the call will remain connected for another fifteen (15)
minutes.
Normally the BREAK key should be pressed twice to end a data call. If the "Recall sequence"
data port option is set to "Long Break", a long break signal must be sent from the terminal.
Consult the data terminal user guide for instructions on sending a long break signal.
The data session is terminated when the
Ending a Data Call
DISCONNECTED
message is displayed.
Ending a Data Call 4-15