A、HANDOVER REQUIRED、HANDOVER REQUEST、HANDOVER COMMAND、HANDOVER REQUEST ACKNOWLEDGE
B、HANDOVER REQUEST、HANDOVER REQUIRED、HANDOVER COMMAND、HANDOVER REQUEST ACKNOWLEDGE
C、HANDOVER REQUEST、HANDOVER REQUIRED、HANDOVER REQUEST ACKNOWLEDGE、HANDOVER COMMAND
D、HANDOVER REQUIRED、HANDOVER REQUEST、HANDOVER REQUEST ACKNOWLEDGE、HANDOVER COMMAND