GSM modem problems

We use CSD data
Do not use SMS or GPRS

We have tried 2 different types of modem:
Falcom model “Twist”
Wavecom model “M1306B”

We use this modem to connect a cash register to a software package that downloads sales once a day. The cash register saves each sale transaction as a separate file, so it transmits each sale separately, the sale transaction files are very small but there could be 300-400 each day. When we dial the GSM modem, we connect at 14400 and the cash register starts downloading each of it’s sales.

We periodically get “corrupt data” messages, in which case the software requests that the cash register re-transmits the file.

Then sometimes it just all stops, and even though we are still connected, there are no more sales files transmitted. In this case sometimes the connection times out, sometimes it just sits there forever and doesn’t hang up the call, and sometimes after a long period of time e.g. 2 minutes, the cash register resumes sending sales files.

Worst case scenario is the communication software crashes big time and we lose a whole pile of sales.

We commonly connect to these cash registers with standard land line modems and there are no problems.
We know of a site in Australia using the exact same software and hardware that is working correctly.