This read-write enabled/disabled setting, DURABLE across reboots, when enabled makes the unit automatically detect the baud rate of incoming calls by watching for a modem's connect indication strings, and adjust this port's baud rate to match. An admin enables this so a serial port can accept calls at varying baud rates without manual reconfiguration for each connection. For example, enabling auto-negotiate lets the same serial port correctly handle both a 9600 baud and a 33600 baud incoming modem connection without the admin changing settings between calls.