Android, Serial USB connection and terminal commands

High-level summary: an external device is usually being setup using a Windows PC and connecting the PC via a USB cable to the device, sending a text file to the device and executing some simple terminal commands. That external device usually connects using a standard "AT91 USB to serial driver" as used by many AT91 compatible devices. We want to be able to establish such serial USB connection from an Android smartphone and via this connection send standard terminal commands and a configuration text file from the Android smartphone to the external device and also store responses which the external device giv es back in return to the terminal commands.