System Architecture Evolution

It is responsible for idle mode User Equipment (UE) paging and tagging procedure including retransmissions.

The Non Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs.

The MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management.

The Serving Gateway routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and Packet Data Network Gateway).

It manages and stores UE contexts, e.g. parameters of the IP bearer service, network internal routing information.

The Packet Data Network Gateway (PDN Gateway, also PGW) provides connectivity from the User Equipment (UE) to external packet data networks (PDNs) by being its point of exit and entry of traffic.

Another key role of the Packet Data Network Gateway is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMAX and 3GPP2 (CDMA 1X and EvDO).

The functions of the HSS include mobility management, call and session establishment support, user authentication and access authorization.

The main function of the ePDG is to secure the data transmission with a UE connected to the EPC over untrusted non-3GPP access, e.g. Wi-Fi calling (VoWiFi).

For this purpose, the ePDG acts as a termination node of IPsec tunnels established with the UE.

The EPS (Evolved Packet System) Mobility Management (EMM) protocol provides procedures for the control of mobility when the User Equipment (UE) uses the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).

Types of ESM procedures: ESM involves different types of procedures such as: The MME maintains EMM context and EPS bearer context information for UEs in the ECM-IDLE, ECM CONNECTED and EMM-DEREGISTERED states.

The integrated data plane stack for these interfaces consists of IP, UDP, eGTP-U.

The 3GPP delivers standards in parallel releases, which compose consistent sets of specifications and features.