I am using SIM 900 modem to enable GSM connection wirh my product.
Micro-controller Communicates with SIM900 modem through a SET AT commands over UART.
My product is time critical and i need to have updated time even after power failure.
To achieve this I am using inbuilt RTC of SIM900 modem.
After each power ON I send following sequence to modem:

* AT+CFUN=0
* AT+CFUN=1

After this I am supposed to get +PSUTTZ string from modem which has timestamp in it and it indicated that modem has synchronized its time with network.After this after this I send AT+CCLK? command periodically to modem to read its RTC.

The problem is sometimes I does receive +PSUTTZ string from modem with some Service providers. With BSNL(in India) service provider I never able to get this string.

Anyone has Idea that how to make sure that +PSUTTZ will always receive without fail?
(May be some different AT commands or something?)