LTE (Long Term Evolution) is mainly designed for high speed data applications both in the uplink and downlink. LTE network offers about 300Mbps data rate in the downlink and about 75 Mbps in the uplink.

Its basis stands in the GSM/EDGE and UMTS/HSPA network technologies, with changes in terms of an increased capacity and higher speed by simplifying the core network and using a different radio interface.

Fig:LTE network architecture:

As shown in the figure LTE network architecture consists of UE, eNodeB and EPC. The basic LTE architecture contains the following network elements:

1)EUTRAN (Evolved Universal Terrestrial Radio).

2) Evolved Packet Core (EPC).

• 1) E-UTRAN: E-UTRAN is a new air interface system.It is a radio access network standard meant to be a replacement of the UMTS, HSDPA and HSUPA. It provides higher data rates, lower latency and is optimized for packet data.

E-UTRAN comprises of:

a) User Equipment (UEs).

b) Evolved Node B basestations (eNodeBs).

c) The Evolved Universal Terrestrial Radio Access (E-UTRA).

- 2) EPC:

EPC is the LTE core network.EPC has a “flat” IP architecture that allows the network to handle a great amount of data traffic in an efficient and cost-effective manner.

EPC comprises of:

a) Mobility Management Entity (MME)

b) Serving Gateway (SGW)

c) Packet Data Network Gateway (PGW)

d) Home Subscriber Server (HSS)

e) Policy and Charging Rules Function (PCRF)

f) Policy and Charging Enforcement Function (PCEF)

a) Mobility Management Entity (MME): The MME is a control entity. MME handles all of the signaling exchanges between the UEs and the EPC, as well as those between the eNodeBs and the EPC. MME is also responsible for SGSN (Serving GPRS Support Node) selection during LTE to 2G/3G handovers. MME connects to the eNodeB through the S1-AP interface and performs authentication. It connects to the HSS and requests the authentication information for the subscriber trying to connect to the network.UE is also authenticated by MME.MME is also responsible for bearer management functions including establishment of dedicated bearers for all signaling traffic flow.

b) Serving Gateway (SGW): Serving gateway terminates the interface towards EUTRAN. S-GW also handles mobility between LTE and other CS networks. For idle state UEs, the S-GW maintains the UEs’ context, and generates paging requests when the UE receives downlink data. eNB is responsible for uplink packet marking, SGW is responsible for downlink packet marking.

c) Packet Data Network Gateway (PGW): PGW is responsible for all IP packet based operations such as deep packet inspection, UE IP address allocation, Transport level packet marking in uplink and downlink, accounting.Another key role of the P-GW is to act as the anchor for mobility between 3GPP and non-3GPP technologies.

d) Home Subscriber Server (HSS): HSS is a central database that contains user-related and subscription-related information. Functions of the HSS include mobility management, call and session establishment support, user authentication and access authorization. It holds information about the PDNs to which the user can connect. HSS also holds dynamic information such as the identity of the MME to which the user is currently attached or registered. HSS integrates the authentication center (AUC) which generates the vectors for authentication and security keys.

e) Policy and Charging Rules Function (PCRF): PCRF is a combination of the Charging Rules Function (CRF) and the Policy Decision Function (PDF). PCRF provides the QoS authorization and bit rates that decides how a certain data flow will be treated in the PCEF and ensures that it is in accordance with the user's subscription profile.

f) Policy and Charging Enforcement Function (PCEF): PCEF performs policy enforcement and service data flow detection, which allows data to flow through the implemented P-GW. PCEF enforces rules which allows data packets to pass through the gateway. It is also responsible for the QoS on IP packets in the P-GW.