Creating a forbidden list of networks in SIM



It is possible to create forbidden PLMN list to avoid WCPU® from registering to a network/networks. Using the AT+CRSM command it is possible to write 4 PLMNs to the FPLMN Elementary file using the UPDATE BINARY command.

Read through the example illustrated below:
Initially the SIM has certain PLMNs in the EF-FLMN. We can read it from using the AT+CRSM command in READ BINARY mode.

AT+CRSM = 176,28539,0,0,12 -> Where 176 : read binary
28539: is 6F7B in hexa is the id of the elementary file for FLPMN .
+CRSM: 144,0,“04350804052804453004F444”

From the response of CSRM command: the FPLMNS are
043508 -> 405803 -> Airtel
040528 - > 405820 -> uninor
044530 -> 405034 -> unknown
04F444 -> 40444 -> Spice telecomm

The same PLMNs can be seen as forbidden can be deciphered from the AT+COPS=? response as well.

+COPS: (2,“AirTel”,"",“40445”),(3,“Airtel”,“Airtel”,“405803”),(3,"","",“405034”),(3,“uninor”,“UNITECH”,“405820”),(3,“Spice Telecom”,“SPICE”,“40444”),(0,1,4)

The FPLMN list can be updated using the same AT+CRSM command.
If we want to add 40445 to the FPLMN list, so that WCPU® doesn’t try to clamp on that PLMN:
AT+CRSM=214,28539,0,0,12,“04544404052804453004F444” //where 214 is UPDATE BINARY command, 28539 is EF-HPLMN id
+CRSM: 144,0

Now if we see the response of AT+COPS=? , it can be seen that the PLMN status of 40445 PLMN is forbidden.
+COPS: (3,“IND airtel”,“airtel”,“40445”),(3,“Airtel”,“Airtel”,“405803”),(3,"","",“405034”),(3,“Spice Telecom”,“SPICE”,“40444”),(3,“uninor”,“UNITECH”,“405820”),(0,1, 4),(0,1,2)