When the mobile is switched on it will select the registered PLMN in the mobile if there exist one. If there is no registered GSM PLMN or the registered PLMN is not available (no coverage) then the GSM mobile will try to select another GSM PLMN either automatically or manually depending on it mode.
AUTOMATIC MODE PLMN Selection GSM
The automatic mode uses a list of GSM PLMNS in an order of priority. The priority will be :
- The last network on which you were registered.
- Home PLMN.
- Each PLMN stored in the SIM card in priority order.
- Other PLMN with signal level above -85 dBm in random order.
- All other PLMN in decreasing signal strength.
MANUAL MODE PLMN Selection GSM
In the manual mode PLMN Selection the mobile will try to connect to the Home PLMN first. If it is unsuccessful then it will provide a list of available PLMN and ask the user to choose one. If the second chosen PLMN is not successful then the mobile will make an indication to the user to select another GSM PLMN.
Until the users selects another network a message “No access” will be displayed. If there is no GSM or DCS coverage at all then a message “No Network” will be displayed.