EPC was first introduced by 3GPP in release 8 of the standard.
It was set to achieve a "flat architecture". the change is to handle the payload (the data traffic) expeditiously from performance and prices perspective. Few network nodes are included within the handling of the traffic and protocol conversion is avoided.
It was also set to separate the user data (also referred to as the user plane) and therefore the signalling (also recognize as the control plane) to form the scaling independent. because of this business split, the operators will dimension and adapt their network simply.
Figure 2 shows a really basic design of the EPS when the User equipment (UE) is connected to the EPC over E-UTRAN (LTE access network). The Evolved NodeB (eNodeB) is the base station for LTE radio. As is shown in the figure, the EPC consists of 4 network elements: the Serving gateway (Serving GW), the PDN gateway (PDN GW), the MME and the HSS. The EPC is connected to the external networks, which may embody the ip multimedia Core Network subsystem (IMS).
Basically, the HSS (for Home Subscriber Server) could be a database that contains user-related and subscriber-related data. It conjointly provides support functions in mobility management, call and session setup, user authentication and access authorization.
It is stems from the pre-3GPP release 4 - Home Location Register (HLR) and Authentication Centre (AuC).
The gateways (Serving GW and PDN GW) take charge of the user plane. They transport the ip data traffic between the User equipment (UE) and the external networks.
The Serving GW is the access point of interconnect between the radio-side and the EPC. As its name indicates, this entry serves the UE by routing the incoming and outgoing science packets.
It is the anchor point for the intra-LTE mobility (i.e. just in case of interaction between eNodeBs) and between LTE and different 3GPP accesses.
It is logically connected to the opposite entry, the PDN GW.
The PDN GW is the point of interconnect between the EPC and the external ip networks. These networks areknown as PDN (Packet data Network), therefore the name. The PDN GW routes packets to and from the PDNs.
The PDN GW also performs other functions like ip address / ip prefix allocation or policy control and charging.
3GPP specifies these gateways seperately but in practice they'll be combined in a very single "box" by network vendors.
The MME (for mobility Management Entity) deals with the control plane. It handles the signalling associated withmobility and security for E-UTRAN access.
The MME is taking charge of the tracking and the paging of UE in idle-mode. it's the termination entry of the Non-Access Stratum (NAS).