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HUAWEI TECHNOLOGIES Co., Ltd.

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HUAWEI Confidential

Security Level: internal

Huawei eRAN3.0

CSFB Feature Introduction

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

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eRAN2.2 eRAN3.0 eRAN2.1

CSFB to UTRAN • PS HO

• PS redirection

CSFB to GERAN • PS HO

• PS redirection

• CCO

CSFB to

CDMA2000 1xRTT

Flash CSFB to

UTRAN

Flash CSFB to

GERAN

CSFB to GERAN • CCO with NACC

Next Evolutions

Adaptive blind

CSFB

CSFB Steering

CSFB with eMPS

CSFB to UTRAN

with LAI

CSFB to GERAN

with LAI

Released

Planning

Planned

Huawei CSFB Feature Roadmap


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Chapter One：Feature Introduction

Architecture and functionalities

Mobile Originating call

Mobile Terminating call

SMS

Emergency call

Page 3


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Page 4

CSFB: brief introduction

Circuit Switched Fallback (CSFB, 3GPP TS23.272)

The CS fallback in EPS enables the provisioning of voice and other

CS-domain services (e.g. SMS/ LCS) by reuse of CS infrastructure

when the UE is served by E-UTRAN.

This function is only available in case E-UTRAN coverage is

overlapped by either GERAN coverage or UTRAN coverage.


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Page 5

CSFB: Architecture and functionalities

S1-MME

S1-U

S11

E-UTRAN

MME

S-GW

S5

SGSN

HSS/HLR

S6a

S4

S3

S12

Iu-ps

Gb

PDN-GW

SGi

S7

MSC/VLR

A

Iu-cs

Gr

SGs

G/U/L handset

•Multi-mode G/U/L

•CSFB capable

•Support of procedures:

Combined EPS/IMSI

Attach, Update, Detach.

•Deriving a VLR number and LAI

from the TAI of the current cell, or

using a default VLR number and

LAI.

•Maintaining SGs association with

MSC/VLR for EPS/IMSI Attached

UE

•Triggering paging to eNodeB

(when MSC-S pages the UE)

•Initiating IMSI Detach at EPS

Detach

GERAN

UTRAN

•Need to be R8 ready

•Maintaining SGs

association with MME

•Forwarding paging request for CS

domain to the UE.

•Directing the UE to the target CS

capable cell. (PS HO/redirection

with or without SIBs).

C/D

PCRF

Rx

Internet / intranet /

Operators & 3rd

Party Applications

Gs

for the mobility

management and

paging procedures

between EPS and

CS domain.


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CSFB: Mobile Originating call

RAT change (and selection) is under full network control (eNodeB triggers the

RAT change towards to 2G/3G based on the UE’s capability\measurement\SPID

indication from MME.)

NodeB RNC

eNodeB SAE-GW

3G

LTE

MSC-VLR

SGs

HSS/HLR

Inte

r-s

ys

tem

ch

an

ge

6.Initiate voice call

MME

7.IAM

1. Ext Service RQ

(CSFB indicator)

SGSN

5. eNB direct the UE to

G/U

3.optional measurement


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CSFB: Mobile Terminating call

NodeB RNC

eNodeB SAE-GW

3G

LTE

MSC-VLR

SGs

2. Paging RQ

(Domain indicator:

CS)

HSS/HLR

Inte

r-s

ys

tem

ch

an

ge

9.Voice call establishment

MME

1.IAM

SGSN

7. eNB direct the UE to G/U

5.measurement

3. Ext Service RQ (CSFB

indicator)


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Page 8

MMERNCeNodeBUE MSC SGSN

Handover

Command

1. Extended Service Request

(containing a CS Fallback Indicator)

Handover Command

S1-AP Response Message

3. Optional measurement report

4. PS handover preparation phase

5.CS call establishment procedure with LAU or combined RAU/LAU

6.PS handover execution phase

2. S1-AP Message



3. S1-AP message with CS Fallback indicator

2.Extended Service Request


Service

Request

S-GW

P-GW

Paging

1.Paging Request

4. Subsequent procedure similar to that in a mobile-originated case, with the CS

call establishment procedure replaced with a Paging Response message

CSFB to UMTS (PS HO)

MO call MT call


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CSFB to UMTS (PS RRC Redirection w/o RIM)

MO call (R8: without RIM)


2.S1-AP Message with CS Fallback Indicator



S1-AP Reponse Message

3.Optional measurement report

5. LAU, combined RAU/LAU, or RAU and LAU

6.CS call establishment procedure

S1 UE context release

4. RRC Connection Release with UTRAN frequency


2.S1-AP Message with CS Fallback Indicator





5. LAU, combined RAU/LAU, or RAU and LAU



4. RRC Connection Release with UTRAN

frequency\cell id\cell System information

MO call (R9: with RIM)

*MT call’s procedure is same.

PS Suspend PS Suspend


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CSFB to GERAN (PS HO)

MO call MT call

MMEBSCeNodeBUE MSC SGSN

Handover

Command

1. Extended Service Request


Handover Command


3. Optional measurement report

4a. PS handover preparation phase

4b.Suspend

5.CS call establishment procedure with LAU or combined RAU/LAU

6.PS handover execution phase

S-GW

P-GW

Update

Bearers

2. S1-AP Message



3. S1-AP message with CS Fallback indicator



Service

Request

S-GW

P-GW

Paging

1.Paging Request

4. Subsequent procedure similar to that in a mobile-originated case, with the CS

call establishment procedure replaced with a Paging Response message

BSC

In case GERAN or UE can’t support DTM (Dual transfer Mode) the PS service will be suspended


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CSFB to GERAN (PS RRC Redirection w/o RIM)


2.S1-AP Message

(containing a CS Fallback

Indicator)





6.Suspend

5.LAU, combined RAU/LAU, or RAU and LAU



4. RRC Connection Release with GERAN frequency group


2.S1-AP Message






6.Suspend




4. RRC Connection Release with GERAN frequency

group\Cell id\Cell system information

MO call (R8: without RIM) MO call (R9: with RIM)


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Page 12

CSFB to GERAN (CCO w/o RIM)

MO call (w/o RIM)


4. MobilityFromEUTRACommand

(CCO optionally with NACC)

2.S1-AP Message






7.Suspend



5. S1 UE context release

In case GERAN or UE can’t support DTM (Dual transfer Mode) the PS service will be suspended


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Page 13

CSFB to UTRAN: Three mechanisms

R8 PS Handover: base on the

inter-RAT PS handover procedures

R8 PS redirection: RRC release with

“redirectedCarrierInfo”IE to UE

R9 PS redirection: RRC release with a

carrier frequency and UTRAN cell’s SIBs

acquired by RIM procedures before CSFB.


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Page 14

CSFB to GERAN: Four mechanisms

R8 PS Handover: base on the

inter-RAT PS handover procedures

R8 PS redirection: RRC release with

“redirectedCarrierInfo”IE to UE

R9 PS redirection: RRC release with a

carrier frequency list and cell’s SIBs

acquired by RIM procedures before CSFB.

R8 CCO with NACC: HandoverCommand

With target cell and SI


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Page 15

CSFB: SMS

UE is EPS/IMSI attached and the CS

access domain is chosen by the UE

and/or the home PLMN for delivering

short messages.

SMS support is based on the

connectionless SGs reference point

between the MME and the MSC

Server and use of NAS signalling

between the UE and the MME.

The MO SMS and MT SMS are

signalled over SGs and do not cause

any CS Fallback to GERAN/UTRAN

RATs, and consequently does not

require any overlapped

GERAN/UTRAN coverage.

UE MME MSC HLR SMSC

1.EPS/IMSI attach

2.UE triggered Service Request

3. Uplink NAS

Transport

4.Uplink Unitdata

5.Forward Short Message

4a.Downlink Unitdata

4a.Downlink NAS Transport

6.Delivery report

No CS Fallback is performed for SMS


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Page 16

CSFB: Emergency call

E-UTRAN may use the emergency indication for selecting a particular radio access

network (2G or 3G) for CS emergency handling.

If PS handover is initiated, E-UTRAN may indicate priority level of the CSFB to the

target RAT, in order to prepare radio resource at target RAT in appropriate way, e.g.

priority allocation of the RAB resource.

UE MME MSC RNC

Extended Service Request with

Emergency Call Indication

S1-AP message with

Emergency Call

Indication

eNB indicates in the Source RNC to Target RNC

Transparent container that PS handover was

triggered due to CSFB and emergency purpose

eNB


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Chapter Two: CSFB Algorithm at eNB

是

否

CSFB触发：

是否盲切换

收到CS Fallback Indicator

开始

CSFB测量

CSFB决策

CSFB执行

结束

测量超时或异常

Triggering phase

The eNodeB receives a CS Fallback Indicator from the

MME. If the eNodeB supports blind handovers to an inter-

RAT system, it performs a blind handover without

delivering the measurement configuration to the UE.

Otherwise, the eNodeB delivers the measurement

configuration to the UE. Compared with measurement-

based handovers, blind handovers can reduce the access

delay. Therefore, blind handovers take precedence over

measurement-based handovers. Blind handovers,

however, have an impact on the handover success rate.


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The eNodeB delivers

the inter-RAT

measurement

configuration, and the

UE performs inter-RAT

measurements

accordingly.

In abnormal cases, eNB

performs blind

procedure.

The eNodeB executes

CSFB to enable the UE

to initiate the voice call

in the target cell.

The ongoin2g PS

services of the UE might

be handed over to the

target cell or suspended

in the source cell.

The eNodeB checks

the measurement

results and

generates a list of

candidate cells.


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R8 CSFB

eRAN2.0/2.1

Blind Scenario：

A list of candidate cells is generated on the basis of the blind handover priorities, which are determined by both

the RAT-specific priorities and the cell-specific priorities.

The RAT-specific priorities used in blind handovers for CSFB are defined through the InterRatHighestPri,

InterRatSecondPri, and InterRatLowestPri parameters.

Measure Scenario：

eNB sends the UE the measurement configuration, according to which the UE performs measurements on the

specified system. The measurement configuration sent to the UE contains the configuration information for only the

RATs and frequencies that are supported by the UE.

eNB selects the best cell from UE’s measurement report.

Mn is the measurement result of the neighboring cell.

Ofn is the frequency-specific offset for the frequency of the neighboring

cell.

Hys is the hysteresis for event B1.

Thresh is the threshold for event B1. The values of Thresh are set on

the basis of the measurement quantities of each RAT.

The Received Signal Code Power (RSCP) threshold for CSFB to

UTRAN, Ec/No threshold for CSFB to UTRAN, threshold for CSFB to

GERAN, and threshold for CSFB to CDMA2000 1xRTT are specified

through the CsfbHoUtranB1ThdRSCP, CsfbHoUtranB1ThdECN0,

CsfbHoGeranB1Thd, and CsfbHoCDMAB1ThdPS parameters

respectively.

ThreshHysOfnMn B1 entering condition:


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Flash CSFB ( R9 redirection with SIBs）

2G/3G

Access

LTE

Access

RIM : RAN

information

exchanging

SGSN

GSM/UMTS

Core

MME

LTE Core

Flash CSFB:

• Saving 1s for UMTS compare with R8

CSFB

• Saving 2s for GSM compare with R8

CSFB

Frequency and

target cell

system

information

Key Point:

1. eNB request system information from BSC/RNC when

establish Inter-RAT neighbor relation;

2. BSC/RNC reply system information. If system

information update，BSS/RNC notify eNodeB and

send the latest information;

3. Core Network doesn’t handle the message, only

forward;

4. eNB doesn’t translate message from BSC/RNC，send

to UE directly;

5. eNB fill out the target frequency and related neighbor

cell information in RRC_Release message.

BSC/RNC

RA

N

info

rma

tion

RA

N info

rma

tion

requ

est

eRAN2.2

http://mobile.younet.com/files/22/22305.html


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CSFB to UTRAN/GERAN with LAI

LAI Based CSFB:

1. Priority to select target GU cells with same

LAC as UE registered in GU NW during

CSFB to avoid LAU (0.5s~3s).

2. Support National Roaming Ue to select

suitable fallback RAT/Cell bases on LAI

Indicator among multi-PLMNs.

TA3/LA1

TAI/L

AI

MME

LTE

Core

GUL

GUL

GUL

TA1/LA1

TA2/LA2

Select same LA to

CSFB

CSFB to

LA1

eRAN3.0

Step1: eNB receives “Registered LAI” from MME

MME sends “Registered LAI” to eNB via “Initial

Context Setup Request” or “UE Context

Modification Request” message.

Step2: eNB selects target network with LAI

consideration

1> Blind case: following the priority below.

1>Neighboring cell with the same LAI with

“Registered LAI”;

2>Neighboring cell with the same PLMN with

“registered LAI”;

3>Neighboring cell with the same PLMN with

the UE current serving PLMN.

2>Measurement case:

1>if any of the neighboring frequency’s cell

PLMN is the same with “Registered LAI”, or if any

of the neighboring frequency’s cell PLMN is the

same with the UE current serving PLMN, and the

UE supports the RAT and the frequency, eNB will

send these frequency to UE for measuring.

2>eNB will choose the same LAI from the

measurement reports.

http://mobile.younet.com/files/22/22305.html


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CSFB key parameters

MO Parameter ID Description

CSFallBackBlindHoCfg InterRatHighestPri Indicates the high-priority system to be considered in blind handovers for CS

fallback. It is UTRAN by default.

CSFallBackBlindHoCfg InterRatSecondPri Indicates the medium-priority system to be considered in blind handovers for CS

fallback. It is GERAN by default. If this parameter is set to null, the system with the

medium blind handover priority is not specified. In this case, only the blind

handovers to the high-priority system are applicable.

CSFallBackBlindHoCfg InterRatLowestPri Indicates the low-priority system to be considered in blind handovers for CS fallback.

It is CDMA2000 by default. If this parameter is set to null, the system with the low

blind handover priority is not specified. In this case, only the blind handovers to the

high- and medium-priority systems are applicable.

CSFallBackBlindHoCfg UtranLcsCap Indicates the Location Services (LCS) capability of the UTRAN.

CSFallBackBlindHoCfg GeranLcsCap Indicates the Location Services (LCS) capability of the GERAN.

CSFallBackBlindHoCfg CdmaLcsCap Indicates the Location Services (LCS) capability of the CDMA2000.

CSFallBackHo CsfbHoUtranTimeToTrig Indicates the time-to-trigger for event B1 that is used in CS fallback to

UTRAN/GERAN/CDMA2000. When CS fallback to UTRAN/GERAN/CDMA2000 is

applicable, this parameter is set for UEs and used in the evaluation of whether to

trigger event B1. When detecting that the signal quality in at least one

UTRAN/GERAN/CDMA2000 cell meets the entering condition, the UE does not

send a measurement report to the eNodeB immediately. Instead, the UE sends a

report only when the signal quality continuously meets the entering condition during

the time-to-trigger. This parameter helps decrease the number of occasionally

triggered event reports, the average number of handovers, and the number of wrong

handovers, and thus helps prevent unnecessary handovers. For details, see 3GPP

TS 36.331. CSFallBackHo CsfbHoGeranTimeToTrig

CSFallBackHo CsfbHoCDMATimeToTrig


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MO Parameter ID Description

CSFallBackHo CsfbHoUtranB1ThdRSCP Indicates the RSCP threshold for event B1, which is used in CS fallback to UTRAN.

When CS fallback to UTRAN is applicable, this parameter is set for UEs and used

in the evaluation about whether to trigger event B1. This parameter indicates the

RSCP requirement for the UTRAN cells to be included in the measurement report.

A UE sends a measurement report related to event B1 to the eNodeB when the

RSCP in at least one UTRAN cell exceeds this threshold and other triggering

conditions are met. For details, see 3GPP TS 36.331.

CSFallBackHo CsfbHoUtranB1ThdECN0 Indicates the Ec/No threshold for event B1, which is used in CS fallback to UTRAN.

When CS fallback to UTRAN is applicable, this parameter is set for UEs and used

in the evaluation about whether to trigger event B1. This parameter indicates the

Ec/No requirement for the UTRAN cells to be included in the measurement report.

A UE sends a measurement report related to event B1 to the eNodeB when the

Ec/No in at least one UTRAN cell exceeds this threshold and other triggering

conditions are met. For a cell with large signal fading variance, set this parameter

to a large value to prevent unnecessary handovers. For a cell with small signal

fading variance, set this parameter to a small value to ensure that the handover is

performed in time. For details, see 3GPP TS 36.331.

CSFallBackHo CsfbHoGeranB1Thd Indicates the RSSI threshold for event B1 that is used in CS fallback to GERAN. A

UE sends a measurement report related to event B1 to the eNodeB when the RSSI

in at least one GERAN cell exceeds this threshold and other triggering conditions

are met. For details, see 3GPP TS 36.331.

CSFallBackHo CsfbHoCDMAB1ThdPS Indicates the pilot strength threshold related to event B1, which is used in CS

fallback to CDMA2000. A UE sends a measurement report related to event B1 to

the eNodeB when the pilot strength in at least one CDMA2000 cell exceeds this

threshold and other triggering conditions are met. For details, see 3GPP TS

36.331.


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MO Parameter ID Default Value Actual Unit MML Command

CSFallBackBlindHoCf

g

InterRatHighestPri UTRAN UTRAN, GERAN,

CDMA2000

UTRAN, GERAN,

CDMA2000

None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G

CSFallBackBlindHoCf

g

InterRatSecondPri GERAN UTRAN, GERAN,

CDMA2000, NULL

UTRAN, GERAN,

CDMA2000, NULL

None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G

CSFallBackBlindHoCf

g

InterRatLowestPri CDMA2000 UTRAN, GERAN,

CDMA2000, NULL

UTRAN, GERAN,

CDMA2000, NULL

None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G

CSFallBackBlindHoCf

g

UtranLcsCap OFF(Off) OFF(Off), ON(On) OFF, ON None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G

CSFallBackBlindHoCf

g

GeranLcsCap OFF(Off) OFF(Off), ON(On) OFF, ON None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G

CSFallBackBlindHoCf

g

CdmaLcsCap OFF(Off) OFF(Off), ON(On) OFF, ON None MOD

CSFALLBACKBLINDHOCF

G

LST

CSFALLBACKBLINDHOCF

G


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MO Parameter ID Default Value Actual Unit MML Command

CSFallBackHo CsfbHoUtranTim

eToTrig

40ms 0ms, 40ms, 64ms,

80ms, 100ms, 128ms,

160ms, 256ms, 320ms,

512ms, 480ms, 640ms,

1024ms, 1280ms,

2560ms, 5120ms

0ms, 40ms, 64ms,

80ms, 100ms,

128ms, 160ms,

256ms, 320ms,

512ms, 480ms,

640ms, 1024ms,

1280ms, 2560ms,

5120ms

ms MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoGeranTim

eToTrig

40ms ms MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoCDMATi

meToTrig

40ms ms MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoUtranB1T

hdRSCP

-106 -120~-25 -120~-25 dBm MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoUtranB1T

hdECN0

-13 -48~0 -24~0 0.5dB MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoGeranB1

Thd

-103 -110~-48 -110~-48 dBm MOD CSFALLBACKHO

LST CSFALLBACKHO

CSFallBackHo CsfbHoCDMAB1

ThdPS

-34 -63~0 -31.5~0 0.5dB MOD CSFALLBACKHO

LST CSFALLBACKHO

Switches are not shown here. Please refer to CSFB FPD.

HUAWEI TECHNOLOGIES Co., Ltd. HUAWEI Confidential Page 26

Chapter Three: Algorithm Relationship

LOFD-001033 CS Fallback to UTRAN depends on LOFD-001019 PS Inter-RAT Mobility between

E-UTRAN and UTRAN.

LOFD-001034 CS Fallback to GERAN depends on LOFD-001020 PS Inter-RAT Mobility

between E-UTRAN and GERAN.

LOFD-001035 CS Fallback to CDMA2000 1xRTT depends on LOFD-001021 PS Inter-RAT

Mobility between E-UTRAN and CDMA2000.

LOFD-001052 Flash CS Fallback to UTRAN depends on LOFD-001033 CS Fallback to UTRAN.

LOFD-001053 Flash CS Fallback to GERAN depends on LOFD-001034 CS Fallback to GERAN.

LOFD-001068 CS Fallback with LAI to UTRAN depends on LOFD-001033 CS Fallback to

UTRAN.

LOFD-001069 CS Fallback with LAI to GERAN depends on LOFD-001034 CS Fallback to

GERAN.

Page 26


Chapter Four: Use Case

G/U coverage

LTE

coverage UL dual

mode UE

Camping (LTE) Voice (G/U) Back to LTE

PLMN selection indicator

in SIM card

Frequency priority in

network system

information broadcast

CSFB to G/U to make

the CS call

Idle UE:

Frequency priority in G/U

system information broadcast

Active UE:

PS redirection

PS HO based on service

Deployment Scenario

No IMS support in LTE/SAE or roaming.

E-UTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.


Thank You