LTE-EPC – MME in LTE  –

Evolved Packet Core or EPC is the core network for LTE or 4G.  3GPP release 8 has specifications for the EPC network. LTE is the packet-switched only network. The packet only means, there is no voice circuit/truck reservation for a call. Earlier generation (3G or 2 G), the core network has both packet and circuit network.  A voice call uses ISUP based circuit-switched signaling for voice transmission and data network uses packets based network for internet services. LTE belongs to the fourth generation for mobile communication. Which brings more data speed to the mobile user. To achieve high speed, the Evolved packet core has reduced the hierarchy of network elements used in a data core.

LTE EPC can connect to the non-3GPP access network e.g WiFi.  This is one of the major differences from past generations of mobile networks.

Evolved Packet core Network Components:

MME in LTE:

When a subscriber roams. It uses two types of core networks, one is a home network and another is the roaming network. MME is a node in the LTE network located in the 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 an application interface for the 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. The interface between UE and eNodeB is wireless.

S-GW

This node manages data between eNodeB and PGW. S1-U interface between EURAN and SGW. S5 is an interface between PGW and SGW.

P-GW

This node is in the 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.

HSS: 

A central database for 4G subscribers. Authenticate a user based on authentication vectors. Vectors are generated by the AUC.  Store the EPS subscription profile for data.

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