Hello,

Packet Radio is used by Ham-radio people. This protocol is derived from X25 and is named AX25.
This is a 1200 or 9600 bauds application and allow to connect any other modem using RF. An existing networks of BBS is implemented all around the world using this protocol.

I suppose Mercedes want to use this mode in order to interface its module with existing equipment and/or to connect on the Ham Packet network.

I had also in mind to design a such project. Check AX25 protocol resources on the web. I've found the whole document explaining the protocol. It's available on my website in the projects pages :
http://perso.wanadoo.fr/rs-rey/el...essources/

However, the whole protocol is quite heavy to code whereas you probably need a few commands to transmit and received information. So this document is quite too complex to use for coding.

The best is to look resources on internet on a "light" AX25 implementation. There is many links on it. Try a google search.
If you find it I'm also very interrested.

concerning the way to develop I fully agree with Erik and others. Try first to code the protocol using RS232. Once it will work and be validated you could add the RF link and it should work as it.

Regards
Stephane, F1TJJ