The Evolved Packet Core (EPC) is the mobile core network that 3GPP defined in 2007 to connect LTE the 4G radio network technology, to. The EPC is characterized for being a simplified IP based mobile core network with a flat architecture and supporting packet switching only.

In Release 15 3GPP is defining 5G and its core network which is referred to as the Next Generation Core. Beside the definition of diverse name for the functionalities there is consensus that the Next Generation Core is an evolution of the EPC to incorporate SDN principles like user and control plane separation and support for Layer 2 connections as well as varied transport protocols beyond GTP; also the support of heterogeneous networks in a more consistent way is an aspect being addressed and some other non-major innovations. The main principles and functions of the EPC are still valid and worth understanding.

In Release 8, 3GPP finalized the standardization of LTE access which was immediately followed by the standardization of LTE-Advanced (LTE-A) foreseen as the first truly 4G access network. Additionally, a new all-IP core network architecture was defined as System Architecture Evolution (SAE) or Evolved Packet Core (EPC), which was further evolved up. The EPC is a novel network architecture that combines the advantages of 3GPP 2G, 3G, 4G mobile broadband solutions with the cost-cutting pragmatism of wireless environments based on standard IETF protocols – WiFi. 3GPP EPC defines a variety of functions including gateways, charging and QoS policy engines and enforcers, mobility enablers, all with a service offering differentiation at subscriber level.

  • The Gateways – forward the data traffic of mobile devices and ensure that access control, gating, QoS and mobility management is enforced according to the rules provided by the decision entities. The access network specific gateways – Serving Gateway (SGW), the evolved Packet Data Gateway (ePDG) and the generic Access Network Gateway (ANGw) – provide the interconnection with the various Radio Access Technologies (RATs). The Packet Data Network Gateway (PGW) is the mobility anchor point for the user-data plane traffic of the mobile devices in the core network, the “routing” functionality towards the PDN and provides also the main charging point.
  • The Control Entities – the Mobility Management Entity (MME), the Serving GPRS Support Node (SGSN), the Policy and Charging Rules Function (PCRF) and the Access Network Discovery and Selection Function (ANDSF) are control plane functions that make policy based decisions for the connectivity, the access control and the resources allocated for mobile devices. The Policy Charging and Enforcement Function (PCEF),  as well as the Base Stations and User Endpoints (UE) control and enforce the QoS and charging policies per individual traffic flows.
  • The subscription data entities – the Home Subscriber Server / Service Profile Repository (HSS/SPR) and the AAA Server/Proxy replace the aging Home Location Register (HLR) concepts, store update, and transmit notifications on the subscription profile of the users towards the other EPC authorization entities and are supplying information and mechanisms for the authentication of mobile devices.

In order to provide a network layer mobility concept, EPC specifications include a large variety of IP-based protocols and their correspondent entities such as the GPRS Tunneling Protocol (GTP) and multiple Mobile IP (MIP) variants. The mobility management is enabled by the gateway components, which ensure a transparent IP connection for mobile devices while roaming through the wireless environment.

The QoS and charging control is based on the 3GPP Policy and Charging Control (PCC) architecture, including the PCRF as policy based decision entity, which communicates using the Diameter protocol with the BBERF located within the access network specific gateways and the PCEF in the PGW, ensuring as such the signaling and enforcement of QoS, gating and charging policies on the data path.

The interconnection with applications is provided on the user-data plane by the PGW which breaks out the data traffic to the PDN through the SGi interface (e.g. the IP service domain, typically the Internet, but not limited to). The PCRF offers a signaling interface based on Diameter which allows the various service platforms and applications to share information on the data flows exchanged with the mobile devices, permitting dynamic QoS management and also service adaptation to the wireless link conditions.

The access control and the resource management for the LTE access is controlled through the MME and is considering a dynamically selected data path including the eNodeB of the access technology and an MME selected SGW. Enforcing QoS rules at a bearer level is also achieved by signaling between the aforementioned components.

For legacy mobile radio technologies, EPC integrates also with the SGSN functions, in architecture more or less aligned to the high-capacity demanded for example by the latest 3.X G upgrades and advances.

For providing the telephony services the MSC function handles the legacy 2G/3G domains, including SMS. For the LTE domain IMS takes over on this functionality, providing the VoLTE capabilities, potentially integrating in the future with the legacy domains through SRVCC.

For updated materials, training and custom tutorial sessions on LTE, EPC, as well as application enablers like IMS, presented directly by the researchers and developers of OpenEPC and OpenIMSCore, please contact us at info@openepc.com