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Bearers in LTE

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Introduction

Multiple applications may be running in a

UE at the same time

each one having different QoS requirements In order to support multiple QoS

requirements

different bearers are set up within EPS each being associated with a QoS

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Bearers

Categories

Minimum Guaranteed Bit Rate (GBR) bearers

Non-GBR bearersClassification is based on the nature of the

QoS the bearers provide

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Bearers

GBR bearers

can be used for applications such as VoIP

an associated GBR value for which dedicated transmission resources are

permanently allocated at bearer 

establishment/modification

Bit rates higher than the GBR may be allowed if resources are available

a Maximum Bit Rate (MBR) parameter 

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Bearers

Non-GBR bearers

do not guarantee any particular bit rate

can be used for applications such as webbrowsing or FTP transfer 

no bandwidth resources are allocated

permanently to the bearer 

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Bearers

Each bearer hasan associated QoS Class Identifier 

QCI

an Allocation and Retention Priority

 ARP

QCI

characterized by priority, packet delay budget

and acceptable packet loss

The QCI label for a bearer determines the

way it is handled in the eNodeB

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Bearers

 ARPThe ARP of a bearer is used for call

admission control

To decide whether or not the requested bearer 

should be established in case of radio congestion

Governs the prioritization of the bearer 

for pre-emption with respect to a new bearer 

establishment request

Once a bearer is successfully established

a bearer’s ARP does not have any impact on the

bearer-level packet forwarding treatment

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Bearers

 An EPS bearer has to cross multiple

interfaces

the S5/S8 interface from the P-GW to the S-GW,

the S1 interface

from the S-GW to the eNodeB,

the radio interface

from the eNodeB to the UE

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Bearers

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Bearers IP packets mapped to the same EPS

bearer 

receive the same bearer-level packet

forwarding treatment

e.g. scheduling policy, queue management policy

Providing different bearer-level QoS thus

requires

a separate EPS bearer is established for eachQoS flow

user IP packets must be filtered into the

different EPS bearers.

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Bearers

Traffic Flow Templates: TFTs

Packet filtering into different bearers is based

on TFTsUse IP header information to filter packets

e.g. source and destination IP addresses,

Transmission Control Protocol (TCP) port numbers

Each packet can be sent down the respectivebearers with appropriate QoS

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Bearers

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Bearers

 An UpLink TFT

UL TFT: associated with each bearer in the

UE

filters IP packets to EPS bearers in the uplinkdirection

 A DownLink TFT

DL TFT: in the P-GW filters IP packets to EPS bearers in the downlink

direction

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Bearer Establishment Procedure