ally carries a request to establish one or more PDU sessions, security context, UE radio and security capabilities, mobility restriction list, allowed NSSAI, etc. 8. Access stratum (AS) security between UE and gNB is activated and Data Radio Bearers (DRBs) are set up (details are not shown for brevity). The gNB informs the AMF that the procedure is completed using the Initial Context Setup Response. It typically carries the information (e.g. transport tunnels) of the estab- lished PDU sessions and the list of PDU sessions that failed to be established. NAS transport and UE context management messages use UE-associated signaling, like most other NG-AP messages (except for those used for interface management). This means that there is a UE association in a gNB and an AMF, identified by a pair of temporary identifiers: AMF UE NG Application Protocol (NGAP) ID and RAN UE NGAP ID. These identifiers are present in every UE-associated message, with the exception of the Initial UE Message, which is used to initiate the UE association and carries only the RAN UE NGAP ID. When a new UE association needs to be created, a gNB allocates a new RAN UE NGAP ID and sends it to an AMF in the Initial UE Message. The AMF, in its turn, allocates a new AMF UE NGAP ID and sends it back (together with the received RAN UE NGAP ID) in the Initial Context Setup Request message. After that, the UE association in gNB and AMF is established. 3.3.3.1.3 UE Mobility Mobility procedures are used primarily for connected mode UE mobility (i.e. handover). The messages are: Handover preparation (between source NG-RAN node and AMF) Handover Required Handover Command Handover Preparation Failure Handover resource allocation (between target NG-RAN node and AMF) Handover Request Handover Request Acknowledge Handover Failure Handover notification (from target NG-RAN node to AMF) Handover cancelation (between source NG-RAN node and AMF) Handover Cancel Handover Cancel Acknowledge Other Path Switch Request Uplink/Downlink RAN Status Transfer. The usage of s