| CPC H04W 12/72 (2021.01) [H04W 8/183 (2013.01)] | 20 Claims |
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1. A communications system, comprising a communications device and a network device, wherein a subscriber identification module (SIM) card is installed in the communications device, wherein:
the communications device is configured to:
determine that the SIM card is removed;
send alarm information to the network device, wherein the alarm information indicates that the SIM card in the communications device is removed, and wherein security protection is performed on the alarm information based on security context stored in the communications device; and
delete the security context, wherein deleting the security context comprises:
receiving a security-protected acknowledgment message from the network device; and
deleting the security context after performing security deprotection on the security-protected acknowledgment message by using the security context; and
the network device is configured to:
receive the alarm information; and
store the alarm information.
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