The Evolved Packet Core (EPC)

This article looks at the Evolved Packet Core (EPC), the core network of the LTE system, giving an overview of the architecture of the core network, describing some of its key elements.

The EPC is the latest evolution of the 3GPP core network architecture.

In GSM, the architecture relies on circuit-switching (CS). This means that circuits are established between the calling and called parties throughout the telecommunication network (radio, core network of the mobile operator, fixed network). This circuit-switching mode can be seen as an evolution of the “two cans and a string”. In GSM, all services are transported over circuit-switches telephony principally, but short messages (SMS) and some data is also seen.

In GPRS, packet-switching (PS) is added to the circuit-switching. With this technology, data is transported in packets without the establishment of dedicated circuits. This offers more flexibility and efficiency. In GPRS, the circuits still transport voice and SMS (in most cases). Therefore, the core network is composed of two domains: circuit and packet.
In UMTS (3G), this dual-domain concept is kept on the core network side. Some network elements have evolved but the concept remains very similar.

When designing the evolution of the 3G system, the 3GPP community decided to use IP (Internet Protocol) as the key protocol to transport all services. It was therefore agreed that the EPC would not have a circuit-switched domain anymore and that the EPC should be an evolution of the packet-switched architecture used in GPRS/UMTS.
This decision had consequences on the architecture itself but also on the way that the services were provided. Traditional use of circuits to carry voice and short messages needed to be replaced by IP-based solutions in the long term.