WHAT IS THE COMPOSITION OF EPC?

Evovled Packet Core (EPC) also known as core network is made up of control plane node called Mobility Management Entity (MME) and two other nodes named as Serving Gateway (SGW) and Packet Data Network abberviated as PGW.

As shown below.

Non-Roaming Case: In non-roaming case, the S-GW and P-GW functionalities are both located within one operators network and can be implemented in a combined S and P-GW.