02 LTE Architecture Summary 25min

8/3/2019 02 LTE Architecture Summary 25min

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Eiko Seidel


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3GPP Network Evolution

Directions

Simple, flat, IP based architecture low complexity, low latency

IP based low cost network, reuse of backhaul

Separate control and user plane scalability, low latency

Move all radio into base station only very fast adaptations

LTE Architecture Summary2


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LTE Architecture/Terminology

MME Serving Gateway

S1- S1

S1-

S1-MME

S1-

S1-U

EPC

(Evolved packet Core)

MME

(Mobility Management

Entity)


eNB eNB

eNB

ME

-

UME

X2

X2

X2

E-UTRAN

U

(Evolved UMTS Terrestrial

Radio Access Network)

EPS(Evolved Packet

System)

eNB(evolved Node B)

UE

User Equipment


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Logical and physical interfaces

X2 interface is a logical interface !

Physical path might look very different



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Topologies

Traditional 2G/3G hierarchy

One to many relation top down

Changed from UMTS Rel. 5

Iu Flex option

GGSN

PDN GW

Flexible topology

Avoids single point of failure

Load balancing and scalability

Reduction of relocations in ACTIVE


SGSN

NB

RNC

eNB

Serving GW

MME


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Pooling concept

Pools of nodes are created to have some centralized control Node selection is done at registration within the pool nodes

Stateful network elements with UE context in every node



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Overload protection

Active load balancing between network nodes possible Node specific weight factors also influence the node selection



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Overall LTE Architecture


HSS Home Subscriber ServerHLR Home Location RegisterAuC Authorization CenterPCRF Policy and Charging Rules FunctionPDN Packet Data Network


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PDNGW

ServingGW

PeerEntity

UE eNB

End-to-end Service

InternetE-UTRAN EPC

LTE/SAE QoS Architecture

Service Data

Flow(s)

Service Data

Flow(s)Application

EPS Bearer

Radio Bearer S1 Bearer

External Bearer

Radio S5/S8S1 Gi

S5/S8 Bearer


UL Packet

Filter(s) DL Packet

Filter(s)

Information about EPS Bearer Parameter from PCRF

(e.g. IP flows, QoS description, labels)


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User Plane Architecture

GTP-UGTP-U

UDP/IP UDP/IP

RelayPDCP

RLC

IP

Application

UDP/IP

GTP-U

IP

RLC UDP/IP

PDCP GTP-U

Relay


Serving GW PDN GW

S5/S8

22

L1 L1L1

2

L1

SGiS1-ULTE-Uu

eNodeB

2

L1 L1

UE

GTP GPRS Tunnel ProtocolPDCP Packet Data Convergence ProtocolRLC Radio Link ControlMAC Medium Access Control


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Control Plane Architecture

S1-AP S1-AP

NAS

RRCRRC

NASRelay

Constrained in terms of security, reliability and data

loss to provide reliable control procedures


SCTP

L2L1

IPL2L1

IPSCTP

S1-MMEeNodeB

MME

MAC

L1

RLCPDCP

UE

MAC

L1

RLCPDCP

LTE-Uu


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S1-MME Interface Procedures

SAE Bearer Service Management function Setup, release and modification

Mobility (handover) functions for UEs in LTE_ACTIVE

Intra-LTE Handover Inter-3GPP-RAT Handover

Paging function for UEs in LTE_IDLE Paging within the Tracking Area (set of cells)

NAS Signalling Transport function S1-interface management functions Other functions

Error indication Network Sharing Function

Roaming and Area Restriction Support Function NAS Node Selection Function Initial Context Setup Function MME Load Balancing Overload Function



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X2 Control Plane (X2-C)

Logical point to point interfacebetween eNBs

Interface between eNodeBmight not be a physical interface

Only point to pointSCTP

X2-AP

-

Reliable transport (PER < 10-8)

Flow control

Typical delay ca. 5 ... 20ms


IP

Data link layer

Physical layer


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X2-C Interface Procedures

User specific procedures Mobility procedures to support handover

Handover request to prepare handover

PDCP status report during handover for lossless handoverDelete context after completion of the procedure

Global procedures Setting up X2 interfaces and resetting

Including security and exchange of eNB configuration data eNB configuration update

Change of the served cell IDs, global ID, group ID for pooling etc

Load management between eNBsRegular load measurement exchange

Support of intercell interference coordination

Handover procedures in active mode

Error indication



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Self-Organizing Networks

Term is used for many, many different things

LTE supports various SON functions to automate network configuration/optimization processes

reduce need for centralized planning and human intervention

SON functions are enabled by exchange of messages between neighbour eNBs (mostly X2)

exchange of messages between eNBs and MMEs (partly S1)

UE reporting measurements to the eNBs (partly Uu air)



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Standardised SON functions

Automatic Neighbor Relation (ANR) functioneNB automatically builds and maintains its neighbour relations based on

UE reports

Automatic Physical Cell Identity (PCI) selectioneNB automatically selects its own PCI based on UE reports and

information received from neighbour eNBs

Dynamic configuration of X2/S1 interfaceseNB dynamically configures the S1MME interface with the serving MMEs

and the X2 interface with neighbour eNBs

RACH parameters optimizationeNBs exchange information about their used PRACH resources to avoid

interference and RACH collisions

Mobility parameters optimization

eNBs automatically adapts mobilityrelated parameters to enhance mobility

robustness or for loadbalancing reasons


Documents

02 LTE Architecture Summary 25min