MICO(Mobile Initiated Connection Only) is a mode of operation for the UEs, e.g. the NB-IoT UEs registered in the 5GCN (5G Core Network). The 5G network cannot initiate a connection with the devices operating in MICO mode . In other words, the UE operating in MICO mode is not reachable for MT(Mobile Terminated) data and it will only receive MT data when it initiates transition from the Idle state (CM_Idle) to the Connected state (CM_Connected).
The UE, e.g. NB-IoT UE in MICO mode may stop any AS(Access Stratum) procedures . This operation mode conserve the device’s battery power and as result the battery can last for very long time.
During Initial Registration or Mobility Registration Update procedure, e.g. a NB-IoT UE can request the AMF to enable MICO mode using Registration Request message. The AMF determines whether MICO mode is allowed for the UE and indicates it to the UE using Registration Accept message.
To enable UE power saving and to enhance MT reachability in the Idle state while using MICO mode, e.g. for CIoT (Cellular IoT), the AMF can send MICO mode indication with Active Time in the Registration Accept message.
Here I try to depict how MICO mode can be activated by the UE when MICO mode indication with Active Time is sent to the UE during registration procedure.