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LTE Network Architecture

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LTE Network Architecture

LTE Network architecture is structured to provide:

� “Smart platform for 4G services and applications”

� “Natural” IP connectivity to IP based networks,

services and applications

� Easy integration of network elements from

different vendors

� Easy integration of third party services and

applications

� Allows sophisticated charging schemes

� Scalability

� Tight QoS control

� “Build in” QoS mechanisms and interfaces

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3G Vs. LTE Network Architecture

NodeB

Radio Network Controller

Packet Switch Core

CircuitSwitch Core

NodeB

Packet Data

Networks

3rd Generation

Circuit

Switch

Networks

eNodeB

Packet Switch Core

eNodeB

Packet Data

Networks

IMS

Radio Access Network - RAN

LTE

Circuit

Switch

Networks

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The Bigger Picture

The LTE-EPS is part of a bigger picture of next generation network architecture

for IP based services and call control where the IMS plays a central role:

�Common authentication, authorization and accounting framework

�Common media control and network management

- Common policy enforcement rules

�Can easily serve roaming subscribers

�Open application development framework

2G, 3G

Non 3GPPAccess

“IP networks”

CS networks

“User Mgmt”

Circuit Core

IMS Domain

Core Network

Applications

LTEeUTRAN

Evolved Packet Core

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LTE/SAE Terminology

• EPS- Evolved Packet System

–The EPS provides access to external packet IP networks and performs CN (Core Network) related functions. The EPS is sometimes called: SAE – System Architecture Evolution

• EPC- Evolved Packet Core

–No circuit switched components

–Direct connection between the base station (eNB) and the Core Network (No RNC)

• eUTRAN – LTE Radio Access Network

• UE – User Equipment

eUTRAN

EPC

IMS/PDN

EPS/SAEUE

eNB eNB

UE

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LTE Architecture Elements and Interfaces

E-UTRAN Evolved Packet Core-EPC

eNB

eNB MMEPCRF

X2

S1-U

S11

S5/S8 SGi

GxS1-MME

S6a

Rx+

Serving Gateway

PDN Gateway

HSSHome Subscriber Server

SAE Gateway

Uu

Uu

PDN

Separation between control and data entities and interfacesAllows separate scale up for data increase and for increase in subscriber numberAllows distribution of data supporting entities while centralizing control supporting entities

Policy and Charging Rule

Function

Packet Data Network

S1-UX2

SPRSp

Gxa

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A UE May Connect to Multiple PDN’s

PDN Gateway

PDN# 1

Serving Gateway

PDN Gateway

PDN# 2

Internet

Operator Portal

Facebook

YouTube

Others

Music

Video

Games

PDN Gateway

PDN# 3

IMS SMS

Voice

Others

IP Address #1

IP Address #2

IP Address #3

� A PDN is established when the UE attaches to the network

� The UE uses APN (Access Point Name) to define the required PDN

� Otherwise, the network assigns the default APN of the UE (stored in the HSS)

� For each APN connection the UE have different IP address

� Each PGW serves a single PDN

� A PDN may be served by multiple PGW’s

UE E-NodeB

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LTE Architecture Elements and InterfacesE-UTRAN

eNB

MME

PCRF

X2

Serving Gateway

PDN Gateway

HSSHome Subscriber Server

Uu

Uu

PDN 1

Packet Data Network 1

eNB

eNB MME

Serving Gateway

PDN Gateway

PDN 2

Packet Data Network 2

AF

PCRF

AF

SPR

X2

X2

1. Most system elements are not “hard nailed“ to each other but can be routed to support different portions of the system.

2. Supports Pooling, weight factoring, load balancing

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PDN

IP

IPIP IP

IP

Layer1Layer1Layer1

Layer2 Layer2Layer2

PDN GW

RouterServing GW

Application layer

UE IP Connection

Application layer

PDN Connection layer

Transport layer

UE

� Two IP layers:

� PDN connection IP layer (EPS entities as UE, PDN GW etc.)

� Transport IP layer (routers, switches etc.)

� The PDN connection is not aware to the transport IP layer network

techniques as required (Diffserv etc.)

PDN Connectivity and the Transport Layer

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LTE Roaming – Home Routed Traffic

Case 1: Home Routed Traffic

Access of the UE to the PDN is routed through the Home

Network. Also called “Remote Breakout”.

CelleNBUE

MME

S-GW

S1-U

S1-MMES11

LTE-Uu

HSS

SGi

Gx

Rx+

PDN

P-GW

PCRF

S6a S8

Home NetworkhPLMN

Visited NetworkvPLMN

Home Network

Provides Data

connectivity

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LTE Roaming - “Local Breakout”

Case 2: “Local Breakout”

UE can access the PDN network directly from the vPLMN rather than traffic being

routed through the hPLMN.

� The hPCRF communicates the allowed services and the authorization of

resources to the vPCRF.

� Th evPCRF may accept or reject but not change the hPCRF authorized services

HSS

Rx+

hPCRF

S6a S9

Home NetworkhPLMN

Visited NetworkvPLMN

CelleNBUE

MME

S-GWS1-U

S1-MMES11

SGi

Gx

Rx+

PDNP-GW

S5

vPCRFLTE-Uu

Home Network

Provides Policy

AF

AF may be associated with eithr the hPCRF or vPCRF