FIELD: wireless communication.
SUBSTANCE: network mobility control element determines whether a terminal accessing the network meets a predetermined condition, where the predetermined condition includes that the terminal uses a CIoT 5GS control plane optimization function. The mobility control network element sends to the terminal, when the terminal meets a predetermined condition, a downlink NAS message in which NAS security protection is performed using the NAS security context, wherein the downlink NAS message includes a truncated 5G-S-TMSI parameter.
EFFECT: increased security of information transmission.
39 cl, 15 dwg
