for the inetrnet key in roaming, when roamer comes to our network he try to connect inetrnet by using his inetrnet key, in automatique mode he finds only our competitor coverage, but in manual mode he can reach our network, i tried to check his preferred PLMN file in his SIM card but it was crypted, can you please explain to me how the SIM card chosse the VPLMN (basing on the preferred PLMN or level of signal)
Which summarize very nicely the principles of selection.
“the home PLMN operator and the user can prioritise by means of lists the available PLMNs/Access technologies combinations for roaming. If only networks for which no priority is defined are available, then those networks with sufficient radio quality are chosen at random, then the rest are chosen in order of decreasing signal strength. Furthermore the home PLMN operator has control over the periodicity the UE attempt to register on a PLMN with higher priority than the current registered one.”