Build a program to send and receive ASCII to M2M via secure portal

The program will reside on a web server (raspberry pi initially). The program will allow the user to send and receive queries to the remote equipment via a M2M terminal. These commands will have a certain packet format eg. A?PQLV. And will need to look up commands from a table to interpret the message (payload) and its meaning or intent. The physical connection is via serial cable RS232 or RS485 to the remote transceiver, then over the network and to the service provider secure gateway. The gateway can handle the messages through https and will distribute the incoming and outgoing stream in XML. The program may need to be revised and or modified in the future to accommodate the varying manufacturers and upgrades of the remote equipment (ie. look up table modifications, packet format changes). This is a technical brief, and I am open to other design suggestions.