We have done some more testing and will be upgrading the firmware of the ublox module as it is a development kit. Like almost all development kits the modules and kits don’t have the latest firmware.
The ublox modem has a setting to turn off power saving. We did turn it off in the past but it didn’t have an effect until we moved it to the front of the AT command queue. Voila. It now seems to work more without losing connection after a while. (We have not tested this to death yet, but we suddenly can connect and reconnect for 10 minutes or so without hassles)
We homed in the problem by opening and closing a connection every 500ms then we gradually increased the sleep time between attempts.
We are not entirely convinced that we have solved the issue but it may be that when the ublox want to go to sleep it sends back some commands that may upset PPP or it simply just goes to sleep. Our ublox representative did inform us that there were changes on the particular ublox module in terms of sleeping.
Our engineer came across another potential problem with clock drifting and synching between Embedded master and Ublox. We will investigate further. In our application it must be able to run 24/7.
I do find that the TCP/IP socket.Connect that don’t timeout to be a big problem. I have built in a module reset to force a restart but nonetheless it is a very harsh way to deal with a reality, and that is that connect attempts will fail more often than desired.
Thanks for the help. Something else to note is that like all other GPRS modems the UBLOX start up sequence seems to be very finiky.