The Wavecom modem I use has a 'multiplex mode', which enables the application to send and receive AT commands (and responses) as well as data, without context switching. This is really useful for unattended applications, because it enables you to set up the modem to send unsolicited result codes that indicate the network status. So if and when the connection is dropped, the application will be notified immediately and can take the neccessary steps to re-establish the connection.


I have and I was ;o))


Yep, that's what my client does. With a projected 2500 (possibly up to 5000) devices in the field, that's well worth it.


There is absolutely nothing magical about the so-called reliablility of TCP! It is simply a timeout-and-retry mechanism. The only 'trick' is that this is inherent in the TCP layer, so normally the application does not need to worry about it. The same method of keeping tag of timeouts and resending the message if needed can easily be applied to UDP as well, making it just as reliable as TCP.

Rob.