Huawei eRAN3.0
CSFB Feature Introduction
www.huawei.com
Node B Products of Huawei
Apr. 2006
HUAWEI TECHNOLOGIES CO., LTD.
Huawei CSFB Feature Roadmap
Released
CSFB to UTRAN
• PS HO
• PS redirection
CSFB to GERAN
• PS HO
• PS redirection
• CCO
Flash CSFB to
UTRAN
CSFB to UTRAN
with LAI
Adaptive blind
CSFB
Flash CSFB to
GERAN
CSFB to GERAN
with LAI
CSFB Steering
CSFB with eMPS
CSFB to GERAN
• CCO with NACC
CSFB to
CDMA2000 1xRTT
eRAN2.1
eRAN2.2
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eRAN3.0
Huawei Confidential
Next Evolutions
Planned
Planning
Chapter One：Feature Introduction

Architecture and functionalities

Mobile Originating call

Mobile Terminating call

SMS

Emergency call
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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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CSFB: Architecture and
functionalities
•Need to be R8 ready
•Maintaining SGs
association with MME
for the mobility
management and
paging procedures
between EPS and
CS domain.
MSC/VLR
A
Gs
SGSN
Iu-cs
GERAN
Gb
C/D
Gr
UTRAN
•Multi-mode G/U/L
•CSFB capable
•Support of procedures:
Combined EPS/IMSI
Attach, Update, Detach.
HSS/HLR
SGs
Iu-ps
S3
S6a
•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
S12
PCRF
S4
MME
S11
S5
SGi
S1-U
G/U/L handset
E-UTRAN
Rx
S7
S1-MME
S-GW
Internet / intranet /
Operators & 3rd
Party Applications
PDN-GW
•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).
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CSFB: Mobile Originating call
7.IAM
Inter-system change
6.Initiate voice call
NodeB
MSC-VLR
RNC
HSS/HLR
SGSN
SGs
3G
LTE
MME
1. Ext Service RQ
(CSFB indicator)
3.optional measurement
eNodeB
5. eNB direct the UE to
G/U
SAE-GW
 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.)
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CSFB: Mobile Terminating call
1.IAM
9.Voice call establishment
NodeB
RNC
MSC-VLR
Inter-system change
SGSN
3G
SGs
LTE
MME
2. Paging RQ
(Domain indicator:
CS)
3. Ext Service RQ (CSFB
indicator)
5.measurement
eNodeB
SAE-GW
7. eNB direct the UE to G/U
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HSS/HLR
CSFB to UMTS (PS HO)
MO call
UE
eNodeB
MT call
RNC
MME
MSC
SGSN
UE
eNodeB
RNC
1. Extended Service Request
(containing a CS Fallback Indicator)
MME
MSC
SGSN
S-GW
P-GW
1.Paging Request
Paging
2. S1-AP Message
(containing a CS Fallback Indicator)
2.Extended Service Request
(containing a CS Fallback Indicator)
S1-AP Response Message
Service
Request
3. Optional measurement report
3. S1-AP message with CS Fallback indicator
4. PS handover preparation phase
Handover Command
4. Subsequent procedure similar to that in a mobile-originated case, with the CS
call establishment procedure replaced with a Paging Response message
Handover
Command
5.CS call establishment procedure with LAU or combined RAU/LAU
6.PS handover execution phase
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CSFB to UMTS (PS RRC Redirection w/o RIM)
MO call (R9: with RIM)
UE
eNodeB
RNC
MO call (R8: without RIM)
MME
MSC
1.Extended Service Request
(containing a CS Fallback Indicator)
SGSN
UE
eNodeB
RNC
MME
MSC
1.Extended Service Request
(containing a CS Fallback Indicator)
2.S1-AP Message with CS Fallback Indicator
2.S1-AP Message with CS Fallback Indicator
S1-AP Reponse Message
S1-AP Reponse Message
3.Optional measurement report
3.Optional measurement report
4. RRC Connection Release with UTRAN
frequency\cell id\cell System information
4. RRC Connection Release with UTRAN frequency
S1 UE context release
S1 UE context release
5. LAU, combined RAU/LAU, or RAU and LAU
PS Suspend
5. LAU, combined RAU/LAU, or RAU and LAU
PS Suspend
6.CS call establishment procedure
6.CS call establishment procedure
*MT call’s procedure is same.
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SGSN
CSFB to GERAN (PS HO)
MO call
UE
eNodeB
MT call
BSC
MME
MSC
SGSN
S-GW
P-GW
1. Extended Service Request
(containing a CS Fallback Indicator)
UE
eNodeB
RNC
BSC
2. S1-AP Message
(containing a CS Fallback Indicator)
MME
MSC
SGSN
S-GW
P-GW
1.Paging Request
Paging
S1-AP Response Message
2.Extended Service Request
(containing a CS Fallback Indicator)
3. Optional measurement report
Service
Request
4a. PS handover preparation phase
3. S1-AP message with CS Fallback indicator
Handover Command
Handover
Command
4b.Suspend
Update
Bearers
4. Subsequent procedure similar to that in a mobile-originated case, with the CS
call establishment procedure replaced with a Paging Response message
5.CS call establishment procedure with LAU or combined RAU/LAU
6.PS handover execution phase
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)
MO call (R9: with RIM)
UE
eNodeB
BSC
MO call (R8: without RIM)
MME
MSC
SGSN
UE
eNodeB
1.Extended Service Request
(containing a CS Fallback Indicator)
BSC
MME
MSC
1.Extended Service Request
(containing a CS Fallback Indicator)
2.S1-AP Message
(containing a CS Fallback
Indicator)
2.S1-AP Message
(containing a CS Fallback Indicator)
S1-AP Reponse Message
S1-AP Reponse Message
3.Optional measurement report
3.Optional measurement report
4. RRC Connection Release with GERAN frequency
group\Cell id\Cell system information
4. RRC Connection Release with GERAN frequency group
S1 UE context release
S1 UE context release
5.LAU, combined RAU/LAU, or RAU and LAU
5.LAU, combined RAU/LAU, or RAU and LAU
6.Suspend
6.Suspend
7.CS call establishment procedure
7.CS call establishment procedure
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SGSN
CSFB to GERAN (CCO w/o RIM)
MO call (w/o RIM)
UE
eNodeB
BSC
MME
MSC
SGSN
1.Extended Service Request
(containing a CS Fallback Indicator)
2.S1-AP Message
(containing a CS Fallback Indicator)
S1-AP Response Message
3.Optional measurement report
4. MobilityFromEUTRACommand
(CCO optionally with NACC)
5. S1 UE context release
6.LAU, combined RAU/LAU, or RAU and LAU
7.Suspend
8.CS call establishment procedure
In case GERAN or UE can’t support DTM (Dual transfer Mode) the PS service will be suspended
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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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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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CSFB: SMS
UE
MME
HLR
MSC
SMSC
1.EPS/IMSI attach
 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.
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
 UE is EPS/IMSI attached and the CS
access domain is chosen by the UE
and/or the home PLMN for delivering
short messages.
 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.
No CS Fallback is performed for SMS
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CSFB: Emergency call
UE
eNB
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
 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.
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Chapter Two: CSFB Algorithm at eNB
 Triggering phase
开始
The eNodeB receives a CS Fallback Indicator from the
收到CS Fallback Indicator
MME. If the eNodeB supports blind handovers to an interRAT system, it performs a blind handover without
CSFB触发：
是否盲切换
是
delivering the measurement configuration to the UE.
Otherwise, the eNodeB delivers the measurement
否
CSFB测量
测量超时或异常
CSFB决策
configuration to the UE. Compared with measurementbased handovers, blind handovers can reduce the access
delay. Therefore, blind handovers take precedence over
measurement-based handovers. Blind handovers,
CSFB执行
however, have an impact on the handover success rate.
结束
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
The eNodeB delivers

The eNodeB checks
The eNodeB executes
the inter-RAT
the measurement
CSFB to enable the UE
measurement
results and
to initiate the voice call
configuration, and the
generates a list of
in the target cell.
UE performs inter-RAT
candidate cells.
measurements

The ongoin2g PS
services of the UE might
accordingly.


be handed over to the
In abnormal cases, eNB
target cell or suspended
performs blind
in the source cell.
procedure.
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eRAN2.0/2.1
R8 CSFB
 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.
B1 entering condition:
Mn  Ofn  Hys  Thresh
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.
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eRAN2.2
Flash CSFB ( R9 redirection with SIBs）
GSM/UMTS
Core
RIM :
RAN
information
exchanging
LTE Core
Key Point:
SGSN
RAN
information
BSC/RNC
RAN information
request
1. eNB request system information from BSC/RNC when
MME
establish Inter-RAT neighbor relation;
Frequency and
target cell
system
information
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
2G/3G
Access
LTE
Access
Flash CSFB:
to UE directly;
5. eNB fill out the target frequency and related neighbor
cell information in RRC_Release message.
• Saving 1s for UMTS compare with R8
CSFB
• Saving 2s for GSM compare with R8
CSFB
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eRAN3.0
CSFB to UTRAN/GERAN with LAI
LTE
Core
Step1: eNB receives “Registered LAI” from MME
MME sends “Registered LAI” to eNB via “Initial
Context Setup Request” or “UE Context
Modification Request” message.
TA1/LA1
MME
GUL
TAI/L
AI
CSFB to
LA1
Select same LA to
CSFB
GUL
TA3/LA1
TA2/LA2
GUL
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
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.
Indicator among multi-PLMNs.
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CSFB key parameters
MO
Parameter ID
CSFallBackBlindHoCfg InterRatHighestPri
CSFallBackBlindHoCfg UtranLcsCap
Description
Indicates the high-priority system to be considered in blind handovers for CS
fallback. It is UTRAN by default.
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.
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.
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
CSFallBackHo
CsfbHoGeranTimeToTrig
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
CsfbHoCDMATimeToTrig
CSFallBackBlindHoCfg InterRatSecondPri
CSFallBackBlindHoCfg InterRatLowestPri
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MO
CSFallBackHo
Parameter ID
Description
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
CSFallBackBlindHoCf InterRatHighestPri UTRAN
UTRAN, GERAN,
g
CDMA2000
Actual
UTRAN, GERAN,
CDMA2000
Unit
None
CSFallBackBlindHoCf InterRatSecondPri GERAN
g
UTRAN, GERAN,
CDMA2000, NULL
UTRAN, GERAN,
CDMA2000, NULL
None
CSFallBackBlindHoCf InterRatLowestPri CDMA2000
g
UTRAN, GERAN,
CDMA2000, NULL
UTRAN, GERAN,
CDMA2000, NULL
None
CSFallBackBlindHoCf UtranLcsCap
g
OFF(Off)
OFF(Off), ON(On)
OFF, ON
None
CSFallBackBlindHoCf GeranLcsCap
g
OFF(Off)
OFF(Off), ON(On)
OFF, ON
None
CSFallBackBlindHoCf CdmaLcsCap
g
OFF(Off)
OFF(Off), ON(On)
OFF, ON
None
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MML Command
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MOD
CSFALLBACKBLINDHOCF
G
LST
CSFALLBACKBLINDHOCF
G
MO
Parameter ID
Default Value
CSFallBackHo
CsfbHoUtranTim 40ms
eToTrig
CSFallBackHo
CsfbHoGeranTim40ms
eToTrig
CSFallBackHo
CsfbHoCDMATi 40ms
meToTrig
CSFallBackHo
CsfbHoUtranB1T -106
hdRSCP
CSFallBackHo
Actual
0ms, 40ms, 64ms,
80ms, 100ms, 128ms,
160ms, 256ms, 320ms,
512ms, 480ms, 640ms,
1024ms, 1280ms,
2560ms, 5120ms
Unit
MML Command
0ms, 40ms, 64ms, ms
80ms, 100ms,
128ms, 160ms,
256ms, 320ms,
ms
512ms, 480ms,
640ms, 1024ms,
1280ms, 2560ms,
5120ms
ms
MOD CSFALLBACKHO
LST CSFALLBACKHO
-120~-25
-120~-25
dBm
MOD CSFALLBACKHO
LST CSFALLBACKHO
CsfbHoUtranB1T -13
hdECN0
-48~0
-24~0
0.5dB
MOD CSFALLBACKHO
LST CSFALLBACKHO
CSFallBackHo
CsfbHoGeranB1 -103
Thd
-110~-48
-110~-48
dBm
MOD CSFALLBACKHO
LST CSFALLBACKHO
CSFallBackHo
CsfbHoCDMAB1 -34
ThdPS
-63~0
-31.5~0
0.5dB
MOD CSFALLBACKHO
LST CSFALLBACKHO
MOD CSFALLBACKHO
LST CSFALLBACKHO
MOD CSFALLBACKHO
LST CSFALLBACKHO
Switches are not shown here. Please refer to CSFB FPD.
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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.
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Chapter Four: Use Case
 Deployment Scenario
No IMS support in LTE/SAE or roaming.
E-UTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.
G/U
coverage
UL dual
mode UE
Camping (LTE)
Voice (G/U)
 PLMN selection indicator
in SIM card
 Frequency priority in
network system
information broadcast
 CSFB to G/U to make
the CS call
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LTE
coverage
Back to LTE
Idle UE:
 Frequency priority in G/U
system information broadcast
Active UE:
 PS redirection
 PS HO based on service
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Thank You
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