The Evolved Packet Core

In Release 8, 3GPP finalized the standardization of LTE access which was immediately followed by the standardization of LTE-Advanced 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 which was then further evolved in Release 9 and Release 10. The EPC is a novel network architecture that eliminates the shortcomings of IP communication for the wireless environment based on standard IETF protocols. 3GPP’s EPC defines a variety of entities with multiple functional components including subscription data entities, control entities and gateways.

• The subscription data entities – the Home Subscriber Server / Service Profile Repository (HSS/SPR) and the AAA Server store, update and transmit notifications on the subscription profile of the users and are supplying the information for the authentication and authorization of the mobile devices.
• The control entities – the Policy and Charging Rules Function (PCRF), the Mobility Management Entity (MME) and the Access Network Discovery and Selection Function (ANDSF) make policy based decisions for the connectivity, the access control and the resources allocated for mobile devices.
• The gateways – forward the data traffic of mobile devices and ensure the access control, gating, QoS and mobility management is enforced according to the rules provided by the decision entities. The access network specific gateways (Serving GW (S-GW), the evolved Packet Data Gateway (ePDG) and the generic Access Network Gateway (ANGw)) provide the interconnection with the various access network technologies. The Packet Data Network Gateway (PDN GW) is the anchor point for the data traffic of the mobile devices in the core network and provides also the main charging functionality.

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 ensuring a transparent IP connection for mobile devices 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 Bearer Binding and Event Report Function (BBERF) located within the access network specific gateways and the Policy and Charging Enforcement Function (PCEF) in the PDN GW, ensuring as such the enforcement of QoS, gating and charging policies on the data path.

The interconnection with applications is ensured by the PDN GW which breaks out the data traffic to the IP service domain. 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 S-GW.

For more details on current status of the standard development of the 3GPP Evolved Packet Core please refer to the tutorial provided here