4G Core Network (Evolved Packet Core)

4G Core Network (Evolved Packet Core)

As name signifies, EPC is the evolved flat architecture focused on delivering packet services. For circuit switch services, it has to either inter-work with legacy CS core network (termed as fallback) or with IP Multimedia System IMS (Voice over IP/LTE).

To get access to the network, user is first authenticated, registered and then move across different areas/technologies - the key core node to do this function is MME (Mobility Management Entity). MME continuously interact with HSS (Home Subscriber Server), which stores and updates the database containing all the user subscription information including User identification. If services are allowed in the HSS for the user, then only user can access to those services.

After control plane, there is a user plane interface establishing between RAN and core network and core node that comes in picture is SGW (Serving Gateway) - Packet forwarding/routing is done here. Then comes the PGW (Packet data network gateway), which provides connectivity to external packet data networks (e.g. internet) by being the point of exit and entry of traffic for the UE. PCRF (Policy charging and rule function) is responsible for making policy decisions and charging rules and interacts with PGW. PCRF can be integrated with different platforms like billing, rating, charging, and subscriber database or can be deployed as a standalone entity.

Above mentioned nodes have many other functions and are highlighted below. (Ref - 3GPP)

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