Evolved Packet Core or EPC is the core network for LTE. In LTE all communication is packet based. In Earlier architecture (3G and 2 G), core network have both packet and circuit based network. The voice call uses ISUP based circuit switched signaling for voice transmission and data network uses packets based network. Evolved packet core has reduces the hierarchy of network elements used in data core. EPC architecture is standardized in 3GPP release 8.
For LTE the access network is E-UTRAN. But the EPC can connect to other 3GPP access technology as well e.g UTRAN and GERAN. Epc can connect to other access network types e.g WIFI. This makes possible to have single network for 2g, 3G and others technology e.g DSL.
Evolved Packet core Network Nodes:
MME in LTE:
When a subscriber roams. It uses two types of core networks , one is home network and another is roaming network. MME is a node in LTE network located in roaming network. When a subscriber attaches to the network in LTE, MME does signaling to the home network. MME does signaling with HSS in home network over diameter protocol. S6a is application interface for diameter protocol between HSS and MME.
MME does authentication and location management with the home over a wired interface. On another side it connects to the UE via eNodeB. Interface between UE and eNodeB is wireless.
This node manages data between eNodeB and PGW. S1-U interface between EURAN and SGW. S5 is interface between PGW and SGW.
This node is in home network. Interface SGW and external PDN. Authenticates a mobile user for data and create a pdp session. This is corresponding to GGSN in 3G/2G.
A central data base for 4G subscriber. Authenticate a user based on authentication vectors. Vectors are generated by the AuC. Store EPS subscription profile for data.