Handover method, core network device, access network device, and terminal device

A device, comprising:

• a non-transitory memory storing executable instructions;
• and
• a processer configured to execute the executable instructions to perform operations comprising:
• receiving an update message, wherein the update message instructs a terminal device to update at least one of a non-access stratum (NAS) type or a key of the terminal device;
• and
• updating the at least one of the NAS type or the key of the terminal device from a first NAS type or a first key used for communication with a second core network device to a second NAS type of a second key used for communication with a first core network device.

A handover method, comprising:

• receiving, by an access network device, a change instruction message, wherein the change instruction message instructs the access network device to instruct a terminal device to perform an update;
• generating, by the access network device, an update message, wherein the update message instructs the terminal device to perform an update;
• and
• sending, by the access network device, the update message to the terminal device.