3G/GPRS connection goes down and does not recover again

= Error Definition =
 * After a duration of successful communication, 3G/GPRS connection goes down and does not recover again.

= Components To Be Checked =
 * Make sure your sim-card's data quota is still enough to connect to the internet. Contact your operator to check this.
 * Check if PPP is enabled in the firmware or not. You can use AT+INCLUDE=? and see if "PPP=1" exists ( on Mikroterminal). If PPP is disabled check the CSQ level(AT+CSQ=?) and simcard state (AT+SIM=?)

= Possible Solutions =
 * Sometimes GSM operators resets the line. If you are using a PPP(Point to Point) enabled firmware you need to set the "LwipTmo" value other that zero to recover the connection back again. "LwipTmo" can be set through a special register on the device via MODBUS. Modbus register address "15" keeps that value. A value like "120" will be fine for most of the applications. After a "120 seconds" timeout the device will clear the line and reset the connection.