5G MM is 5G Mobility Management is involved mainly in the NAS (Non-Access Stratum) registration process. It is mostly associated with the N1/N2 interface. The major functionality of 5G MM include Registration, de-registration, call inactivity procedure, connected mode procedure and connection management procedure. The mobility management functionality enables the possibility for identification of the UE, security and serves as a message transport for other communication between 5GC and the UE. The Aim of 5GC is to act as a converged core network for any access technology.
5GMM related procedures are divided into three categories depending on the purpose of the procedure and how they can be initiated: common procedures - can always be initiated when the UE is in CM-CONNECTED state, Specific procedures - only one UE initiated specific procedure can be running for each of the Access types, Connection management procedures - used to establish a secure signalling connection between the UE and the network.
The mobility management procedures can only be performed if a NAS signalling connection has been established between the UE and the AMF. if there is not any Active signalling connection, the 5G MM layer has to initiate the establishment of the NAS signalling connection.