LTE NETWORK TOPOLOGY AND ARCHITECTURE

 
There is a new approach in the inter-connection between radio access network and core network. The EPS architecture is made up of an EPC (Packet Core Network, also referred as EPC) and an eUTRAN Radio Access Network (also referred as LTE)

There are no circuit switched components in LTE/EPC . 

The CN provides access to external packet IP networks and performs a number of CN related functions (e.g. QoS, security, mobility and terminal context management) for idle (camped) and active terminals. The RAN performs all radio interface related functions.

The LTE/EPC radio access network - Evolved UTRAN (E-UTRAN) - will only contain Node Bs. No RNC is provided anymore. This means, that the evolved Node Bs take over the radio management functionality.

This will make radio management faster and the network architecture simpler. E-UTRAN exclusively uses IP as transport layer. Behind the EPC follow one or more IP networks.
Evolved Packet Core:
- Also known as the System Architecture Evolution (SAE) core;
- Simplified , all-IP network architecture;
- Supports higher throughput and lower latency;
- Supports mobility between legacy 3GPP-based systems, but also non-3GPP systems like WiMAX and CDMA2000.

Mobility Management Entity – MME:
- Controls the signaling between the UE and the core network;
- Establishment, maintenance and release of radio bearer services;
- Responsible for paging and tracking the UE between calls and selecting of proper S-GW upon connection;
- Acts the termination point for ciphering protection, and therefore is the point of lawful interception of signaling.

LTE NETWORK ARCHITECURE

Serving Gateway – SGW:
- Routes data packets, maintains the data connection for inter-eNodeB handovers, as well as, inter-system handovers between LTE and GSM/UMTS;
- Store UE contexts, for example bearer service parameters and routing information;
- Is the main junction between the radio access network and the core network.

Packet Switched Data Network Gateway – PGW:
- Provides connectivity for the UE to exernal packet data networks;
- Allocates IP addresses for UE and QOS enforcement;
- Maintains the mobility connection between LTE/UMTS/GSM systems and non-3GPP systems like WiMAX and CDMA2000.

Enhanced UTRAN – eUTRAN:
- Simply a collection of eNodeBs networked together;
- Responsible for radio resource management, header compression, security, and connectivity to the evolved packet core.

Enhanced NodeB – eNodeB:
- Contains the radio and antenna equipment to link the UE and the LTE core network via the RF air interface;
- Practical equivalent to the BTS in GSM and the NodeB in UMTS, however functionality is more robust in LTE;
- 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.

Home Subscriber Service – HSS:
- database similar to the HLR in GSM / WCDMA core network that contains subscriber-related information supporting call control and session management;
- Primarily involved in authentication, authorization, security ciphering, and can provide user locations details.

Policy Control and Charging Rules Functions – PCRF:
- Responsible for policy control decision making;
- Provides the QOS authorization to decide how data will be treated with respect to the user’s subscription.

Serving GPRS Support Node – SGSN:
- Interconnects the LTE, UMTS, and GSM networks for increased mobility.