LTE Network Topology

EPC:

• Evolved Packet Core (EPC), also knows as the System Architecture Evolution (SAE) core.
• Its a simplified all-IP network architecture.
• It supports higher throughput and lower latency.
• It supports mobility between legacy 3GPP-based systems, but also non-3GPP systems like WiMax and CDMA2000.

MME:

• Mobility Management Entity (MME), It controls the signalling between the UE and the core network.
• It handles the establishment, maintenance and release of radio bearer services.
• It is also responsible for paging and tracking the UE between calls and selecting of proper S-GW upon connection.
• It acts as the termination point for ciphering protection, and is therefore the point of lawful interception of signalling.

S-GW:

• The serving gateway (S-GW), This routes data packets; maintains the data connection for inter eNodeB handovers, as well as, inter system handovers between LTE and GSM/UMTS networks.
• It stores UE contexts, for example bearer service parameters and routing information.
• It is the main junction between the radio access network (RAN) and the core network(CN).

P-GW:

• Packet-Data Network (PDN) Gateway, It provides connectivity for the UE to external packet data networks.
• It allocates IP addresses for the UE and enforces QOS(Quality of Service).
• It maintains the mobility connection between LTE/UMTS/GSM systems and non-3GPP systems like WiMax and CDMA2000.

eUTRAN:

• The enhanced UTRAN is simply a collection of eNodeBs networked together.
• It's responsible for radio resource management, header compression, security and connectivity to the evolved packet core.

eNodeB:

• The enhanced NodeB, contains the radio and antenna equipment to link the UE and the LTE core network via the RF air interface.
• It is practically equivalent to the BTS in GSM and the NodeB in UMTS, however functionality is more robust in LTE.
• The Radio Controller functionality now resides in the eNodeB resulting in a more efficient, less latent network... For example, mobility is governed by the eNodeB instead of the BSC or RNC.

HSS:

• Home Subscriber Service (HSS), is a database similer to HLR in GSM/UMTS core network that contains subscriber-related information supporting call control and session management.
• Its primarily involved in authentication, authorization, security ciphering and also can provide use location details.

PCRF:

• The Policy control and Charging Rules Function (PCRF), is responsible for policy control decision making.
• It provides the QOS authorization to decide how data will be treated with respect to the user's subscription.

SGSN:

• The Serving GPRS Support Node (SGSN), It interconnects the LTE, UMTS and GSM networks for increased mobility.