The Evolved Packet Core (EPC) is a key component of the LTE (Long-Term Evolution) system, commonly known as 4G LTE. It represents the core network architecture in LTE, designed to handle data traffic and manage mobile connectivity. The EPC is also known as the System Architecture Evolution (SAE) core network.

Here are the main components and functionalities of the EPC:

MME (Mobility Management Entity):

  • Responsible for the management of mobility.
  • Handles the signaling between the user equipment (UE) and the network.
  • Manages the tracking area lists and sends paging messages when data is waiting to be delivered to a UE.
  • Manages bearer paths and sets them up or modifies them as needed.

SGW (Serving Gateway):

  • Routes and forwards user data packets.
  • Acts as the mobility anchor for user equipment (UE) when moving between eNodeBs.
  • Manages and stores UE contexts, such as parameters of the IP bearer service, network internal routing information, and S1-U (user plane) configuration.

PGW (PDN Gateway):

  • Represents the UE’s entry and exit point to and from the network.
  • Allocates IP addresses to UEs.
  • Performs QoS (Quality of Service) enforcement and flow-based charging.
  • Acts as the mobility anchor for inter-network mobility (e.g., between LTE and other 3GPP technologies like 2G or 3G).

HSS (Home Subscriber Server):

  • A central database that contains information about subscribers.
  • Handles authentication and authorization of users.
  • Stores the subscription profiles, current locations, and other relevant information about each subscriber.

PCRF (Policy and Charging Rules Function):

  • Decides how to handle data traffic for individual subscribers.
  • Determines QoS decisions and manages the policy enforcement.
  • Handles charging rules, i.e., how data usage is billed.


  • While technically part of the radio network and not the EPC, the eNodeB interfaces directly with both the MME and the SGW in the EPC.
  • It handles the radio communications with the UE and manages resources at the radio layer.


  • The EPC components communicate through well-defined interfaces. For instance, the S1 interface connects the eNodeB to both the MME and the SGW. The S11 interface connects the MME to the SGW, and the S5/S8 interfaces connect the SGW to the PGW.

The EPC’s architecture allows for scalability and flexibility. It can handle a wide variety of data traffic, from traditional internet browsing to voice over LTE (VoLTE) and video streaming. As 5G networks evolve, the next generation of core network, known as the 5G Core, is expected to build on the principles established by the EPC but offer even more capabilities and flexibility.