ons such as the Authentication Server Function [AUSF] and Unified Data Management [see below]) perform mutual authentication. As an AMF typically serves part of a network only, UEs inform the network when they enter an area that may be served by a different AMF by performing a mobility registration. To enable the network to keep track of which UEs are still registered with the network, UEs perform periodic registrations. Connection management: to exchange signaling messages with the network (e.g. to request 5GC to establish a data session), UE and AMF need to first establish a secure signaling channel, also known as a NAS signaling connection. Establishing and releasing the NAS signaling connection is referred to as connection management. Reachability management: while UE and AMF have an active NAS signaling connection, i.e. while the UE is in CM-CONNECTED state, AMF is aware of the actual NG-RAN cell serving the UE and can directly exchange signaling messages with the UE. However, to save power and network resources, the NAS signaling connection is typically released when no further data or signaling is to be exchanged between UE and network. Without NAS signaling connection the UE is in CM-IDLE state. In this state the network is not aware of the exact location of the UE. To bring the UE back into CM-CONNECTED state, e.g. to deliver downlink data or to send signaling messages to the UE, the AMF triggers NG-RAN to broadcast paging messages for this UE. To send and receive data, also referred to as protocol data units (PDUs), UEs need to first request establishment of a PDU session toward a data network. In 5GC, the Session Manage- ment Function (SMF) is in charge of establishing, modifying, and releasing PDU sessions. 5GS supports PDU sessions for IPv4, IPv6, Ethernet, and unstructured data. The key difference between session management in 5GC and EPC is as follows: while in EPC session management functionality is split across two functions, the SGW and the PDN Gateway (PGW), 5GC session management functionality