4GKernnetz

The 4G-Kernnetz, also known as the Evolved Packet Core (EPC), is the core network of the LTE mobile communications standard. It provides packet-switched data services, supports voice over LTE (VoLTE) via IP Multimedia Subsystem (IMS), and handles mobility, session management, and policy control for the radio access network.

The EPC comprises several functional nodes, notably the Mobility Management Entity (MME), Serving Gateway (S-GW), and Packet Data Network Gateway (P-GW). The Home Subscriber Server (HSS) stores subscriber data used for authentication and profile information. Optional components include the Policy and Charging Rules Function (PCRF) and related interfaces.

Key interfaces connect these components: S1-MME and S1-U between the eNodeB and EPC, S5/S8 between S-GW and P-GW; Gx links PCRF to P-GW; other interfaces may include Diameter-based signaling with the HSS. The architecture is designed to separate control plane from user plane while maintaining interworking with external networks.

Functions include mobility management, session management, IP address allocation, and policy-based charging. The EPC provides a single IP-based core for data services, enables roaming, and anchors user plane traffic while enabling seamless handovers between eNodeBs. It also supports voice services through VoLTE and interworks with external networks for Internet access and enterprise connectivity.

In evolution terms, the EPC is the 4G core and is gradually complemented or replaced by 5G core networks (5GC) in mixed deployments. LTE voice traffic uses IMS for signaling, while data traffic is routed through the EPC to external networks.