Evolved Packet Core (EPC) is the main component of SAE (System Architecture Evolution). EPC is pure packet switched network rather circuit switched network. In EPC, the full connectivity will work on IP(Internet Protocol). The main components of EPC are:-
1. MME (Mobility Management Entity)
2. Serving Gateway aka S-Gateway
3. PDN Gateway aka P-Gateway

MME is responsible for all control messages, mobility management, tracking of user equipment and paging. It is connected with HSS and responsible for user authentication.
Serving gateway acts a anchor point and responsible for the forwarding of user data packets.
PDN gateway provides direct connectivity with the external IP network and APN is stored in P-Gateway which is being looked up by the S-Gateway. It also does the DPI and LI functionality.