8 4G. LTE.

NETWORK ARCHITECTURE

Introduction

IntroductionLTE has been designed to support only Packet-Switched (PS) services. LTE (Long-Term Evolution) (Evolved-UTRAN, E-UTRAN). (Evolved Packet Core, EPC), SAE (System Architecture Evolution). LTE and SAE Evolved Packet System (EPS).

Overall Architectural OverviewNetwork is comprised of:the access network (i.e. E-UTRAN) = set of evolved NodeB (eNodeB), which connects to the UEs;the CN (i.e. EPC) = all other logical nodes.

The Core Network (EPC)EPC:PCRF (Policy Control and Charging Rules Function) is responsible for policy control decision-making. PCRF provides QoS authorization that decides how a certain data flow will be threated in the P-GW and ensures that this is in accordance with the users subscription profile.P-GW (PDN Gateway) is responsible for IP address allocation for the UE, as well as QoS enforcement and flow-based charging according to rules from PCRF (filtering of downlink user IP packets into the different QoS-based bearers). P-GW is also the mobility anchor for inter-working with non-3GPP technologies;S-GW (Serving Gateway). All user IP packets are transferred through the S-GW. S-GW retains the information about the bearers when UE is in idle state; buffers downlink data while MME initiates paging; is local mobility anchor for data bearers when the UE moves between eNodeBs. S-GW is mobility anchor for inter-working with other 3GPP technologies. In visited network S-GW collect information for charging.

The Core Network (EPC)EPC:MME(Mobility Management Entity) is the control node which processes the signaling between the UE and the CN (Non-Access stratum (NAS) protocols). Functions: bearer management (establishment, maintenance and release), connection management (establishment of connection and security between CN and UE) and others.HSS (Home Subscriber Server) contains users subscription data and holds the identity of the MME to which UE is currently attached. The HSS may also integrate the AuC.E-SMLC (Evolved Serving Mobile Location Centre) manages the overall coordination and scheduling of resources required to find the location of a UE.GMLC (Gateway Mobile Location Centre) contains functionalities required to support LoCation Services (LCS).

The Access Network (E-UTRAN)E-UTRAN functions:Radio Resource management;Header Compression;Security;Positioning (provides necessary measurements to the E-SMLC);Connectivity to the EPC (signaling towards the MME and bearer path towards the S-GW)

Functional split between E-UTRAN and EPC

Roaming ArchitectureA network run by one operator in one country is known as a PLMN (Public Land Mobile Network). HPLMN Home PLMN. VPLMN Visited PLMN.

QoS and EPS BearersA bearer is an IP packet flow with a defined Quality of Service (QoS). Two bearers categories:Minimum Guaranteed Bit Rate (GBR) bearers for applications such as VoIP;Non-GBR bearers for applications such as web browsing and FTP transfer.

QoS and EPS BearersPacket filtering into different bearers is based on Traffic Flow Templates (TFTs), which use IP header information (source and destination IP addresses, port numbers, ). UpLink TFT (UL TFT) in the UE.DownLink TFT (DL TFT) in the P-GW.

Bearer establishment procedure example

Inter-Working with other RATsP-GW anchor for all non-3GPP technologies (WiMAX);S-GW anchor for other 3GPP technologies (UMTS, GPRS).

Inter-Working with other RATsVoice in LTE:VoIP (using IMS services);Circuit-Switched FallBack (CSFB).

S1 InterfaceInitiation over S1:The initialization of the S1-MME starts with the identification of the MME to which the eNodeB must connect.Establishment of the SCTP association between eNodeB and MME.S1 SETUP procedure initiated by the eNodeB

S1 InterfaceContext Management over S1:UE is associated to one particular MME for all its communications.This MME create a context for the UE.When the UE becomes active, the MME provides this context information to eNodeBBearer Management over S1For each bearer requested to be set up, the eNodeB provided all necessary information.

S1 InterfacePaging over S1:In order to re-establish a connection towards a UE in idle mode, the MME distributes a Paging Request message to the relevant eNodeBsWhen receiving this request, the eNodeB sends a page over the radio interface.Load Management over S1Trace FunctionDelivery of Warning Messages

S1 InterfaceMobility over S1:Intra-LTE mobilityInter-LTE mobilityMobility towards Home eNodeB

X2 InterfaceThe X2 interface may be established between eNodeBs.Two types of information may need to be exchanged over X2 to drive the establishment of an X2 interface:Load or interference related informationHandover related information.

X2 InterfaceMobility over X2Handover via the X2 interface is triggered by default (unless there is no X2 interface established or the source eNodeB is configured to use the S1-handover).

X2 InterfaceLoad and Interference Management over X2The exchange of load information between eNodeBs is of key importance in the flat architecture used in LTE, as there is no central RRM node (as RNC in UMTS).Two purposes:Load balancingInterference coordination

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