eRAN CS Fallback Feature Parameter Description

eRAN
CS Fallback Feature Parameter Description
Issue 02
Date 2015-06-30
HUAWEI TECHNOLOGIES CO., LTD.

Copyright © Huawei Technologies Co., Ltd. 2015. All rights reserved.
No part of this document may be reproduced or transmitted in any form or by any means
without prior written consent of Huawei Technologies Co., Ltd.
Trademarks and Permissions
and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.
All other trademarks and trade names mentioned in this document are the property of their
respective holders.
Notice
The purchased products, services and features are stipulated by the contract made between
Huawei and the customer. All or part of the products, services and features described in this
document may not be within the purchase scope or the usage scope. Unless otherwise
specified in the contract, all statements, information, and recommendations in this document
are provided "AS IS" without warranties, guarantees or representations of any kind, either
express or implied.
The information in this document is subject to change without notice. Every effort has been
made in the preparation of this document to ensure accuracy of the contents, but all
statements, information, and recommendations in this document do not constitute a warranty
of any kind, express or implied.
Huawei Technologies Co., Ltd.
Address:
Huawei Industrial Base Bantian, Longgang Shenzhen 518129 People's Republic
of China
Website: http://www.huawei.com
Email: support@huawei.com
Contents
1 About This Document
1.1 Scope

1.2 Intended Audience
1.3 Change History
1.4 Differences Between eNodeB Types
2 Overview
2.1 Overview
2.2 Benefits
2.3 Architecture
3 CSFB to UTRAN
3.1 Basic CSFB to UTRAN
3.1.1 Handover Measurement
3.1.2 Blind Handover
3.2 Flash CSFB to UTRAN
3.3 Ultra-Flash CSFB to UTRAN
3.4 CS Fallback with LAI to UTRAN
3.5 E-UTRAN to UTRAN CS Steering
3.6 CS Fallback Steering to UTRAN
3.7 Load-based CSFB to UTRAN
3.8 Handover Decision
3.8.1 Basic Handover Decision
3.8.2 Flash Redirection Decision
3.9 Handover Execution
3.9.1 Handover Policy Selection
3.9.2 Ultra-Flash CSFB to UTRAN
3.9.3 Redirection-based CSFB Optimization for UEs in Idle Mode
3.9.4 CSFB Admission Optimization for UEs in Idle Mode

3.10 RIM Procedure Between E-UTRAN and UTRAN
3.10.1 RIM Procedure Through the Core Network
3.10.2 RIM Procedure Through the eCoordinator
3.11 CSFB to UTRAN
3.11.1 Combined EPS/IMSI Attach Procedure
3.11.2 CSFB Based on PS Handover
3.11.3 Signaling procedure of redirection to CDMA2000 1xRTT
3.11.4 Flash CSFB
3.11.7 CSFB for SMS
3.11.8 Emergency Call
3.11.9 CSFB for LCS
4 CSFB to GERAN
4.1 Basic CSFB to GERAN
4.2 Flash CSFB to GERAN
4.3 CS Fallback with LAI to GERAN
4.4 CS Fallback Steering to GERAN
4.5 Ultra-Flash CSFB to GERAN
4.8 RIM Procedure Between E-UTRAN and GERAN
4.9 CSFB to GERAN

4.9.3 CSFB Based on CCO/NACC
4.9.4 CSFB Based on Redirection
4.9.5 Flash CSFB
4.9.6 Ultra-Flash CSFB to GERAN
4.9.7 CSFB for SMS
4.9.9 CSFB for LCS
5 Related Features
5.1 Features Related to LOFD-001033 CS Fallback to UTRAN
5.2 Features Related to LOFD-001052 Flash CS Fallback to UTRAN
5.3 Features Related to LOFD-070202 Ultra-Flash CSFB to UTRAN
5.4 Features Related to LOFD-001068 CS Fallback with LAI to UTRAN
5.5 Features Related to LOFD-001088 CS Fallback Steering to UTRAN
5.6 Features Related to LOFD-001078 E-UTRAN to UTRAN CS/PS Steering
5.7 Features Related to LOFD-001034 CS Fallback to GERAN
5.8 Features Related to LOFD-001053 Flash CS Fallback to GERAN
5.9 Feature Related to LOFD-081283 Ultra-Flash CSFB to GERAN
5.10 Features Related to LOFD-001069 CS Fallback with LAI to GERAN
5.11 Features Related to LOFD-001089 CS Fallback Steering to GERAN
6 Network Impact
6.1 LOFD-001033 CS Fallback to UTRAN
6.2 LOFD-001052 Flash CS Fallback to UTRAN
6.3 LOFD-070202 Ultra-Flash CSFB to UTRAN
6.4 LOFD-001068 CS Fallback with LAI to UTRAN
6.5 LOFD-001088 CS Fallback Steering to UTRAN

6.6 LOFD-001078 E-UTRAN to UTRAN CS/PS Steering
6.7 LOFD-001034 CS Fallback to GERAN
6.8 LOFD-001053 Flash CS Fallback to GERAN
6.9 LOFD-081283 Ultra-Flash CSFB to GERAN
6.10 LOFD-001069 CS Fallback with LAI to GERAN
6.11 LOFD-001089 CS Fallback Steering to GERAN
7 Engineering Guidelines
7.1 LOFD-001033 CS Fallback to UTRAN
7.1.1 When to Use CS Fallback to UTRAN
7.1.2 Required Information
7.1.3 Requirements
7.1.4 Precautions
7.1.5 Data Preparation and Feature Activation
7.1.5.1 Data Preparation
7.1.5.2 Using the CME to Perform Batch Configuration for Newly Deployed eNodeBs
7.1.5.3 Using the CME to Perform Batch Configuration for Existing eNodeBs
7.1.5.4 Using the CME to Perform Single Configuration
7.1.5.5 Using MML Commands
7.1.6 Activation Observation
7.1.7 Deactivation
7.1.8 Performance Monitoring
7.1.9 Parameter Optimization
7.2 RIM Procedure from E-UTRAN to UTRAN
7.2.1 When to Use RIM Procedure from E-UTRAN to UTRAN

7.2.3 Requirements
7.2.4 Precautions
7.2.7 Deactivation
7.3 LOFD-001052 Flash CS Fallback to UTRAN
7.3.1 When to Use Flash CS Fallback to UTRAN
7.3.3 Requirements
7.3.4 Precautions
7.3.7 Deactivation

7.4 LOFD-070202 Ultra-Flash CSFB to UTRAN
7.4.1 When to Use Ultra-Flash CSFB
7.4.3 Requirements
7.4.4 Precautions
7.4.7 Deactivation
7.5 LOFD-001068 CS Fallback with LAI to UTRAN
7.5.1 When to Use CS Fallback with LAI to UTRAN
7.5.3 Requirements
7.5.4 Precautions

7.5.7 Deactivation
7.6 LOFD-001088 CS Fallback Steering to UTRAN
7.6.1 When to Use CS Fallback Steering to UTRAN
7.6.3 Requirements
7.6.4 Precautions
7.6.7 Deactivation
7.7 LOFD-001078 E-UTRAN to UTRAN CS/PS Steering
7.7.1 When to Use E-UTRAN to UTRAN CS/PS Steering

7.7.3 Requirements
7.7.4 Precautions
7.7.7 Deactivation
7.8 LOFD-001034 CS Fallback to GERAN
7.8.1 When to Use CS Fallback to GERAN
7.8.3 Requirements
7.8.4 Precautions
7.8.5.5 Using Feature Operation and Maintenance on the CME

7.8.7 Deactivation
7.9 RIM Procedure from E-UTRAN to GERAN
7.9.1 When to Use RIM Procedure Between E-UTRAN and GERAN
7.9.3 Requirements
7.9.4 Precautions
7.9.7 Deactivation
7.10 LOFD-001053 Flash CS Fallback to GERAN
7.10.1 When to Use Flash CS Fallback to GERAN
7.10.3 Requirements
7.10.4 Precautions

7.10.7 Deactivation
7.11 LOFD-081283 Ultra-Flash CSFB to GERAN
7.11.1 When to Use This Feature
7.11.3 Requirements
7.11.4 Precautions
7.11.7 Deactivation
7.12 LOFD-001069 CS Fallback with LAI to GERAN
7.12.1 When to Use CS Fallback with LAI to GERAN

7.12.3 Requirements
7.12.4 Precautions
7.12.7 Deactivation
7.13 LOFD-001089 CS Fallback Steering to GERAN
7.13.1 When to Use CS Fallback Steering to GERAN
7.13.3 Requirements
7.13.4 Precautions

7.13.7 Deactivation
7.14 Troubleshooting
7.14.1 CSFB Calling Procedure Failure
7.14.2 eNodeB Receiving No Measurement Report
7.14.3 CSFB Blind Handover Failure
7.14.4 CSFB Handover Failure
8 Parameters
9 Counters
10 Glossary
11 Reference Documents
1 About This Document
1.1 Scope
This document describes circuit switched fallback (CSFB), including its technical principles,
related features, network impact, and engineering guidelines.
This document covers the following features:
 LOFD-001033 CS Fallback to UTRAN
 LOFD-001052 Flash CS Fallback to UTRAN
 LOFD-070202 Ultra-Flash CSFB to UTRAN
 LOFD-001068 CS Fallback with LAI to UTRAN
 LOFD-001088 CS Fallback Steering to UTRAN
 LOFD-001078 E-UTRAN to UTRAN CS/PS Steering
 LOFD-001034 CS Fallback to GERAN
 LOFD-001053 Flash CS Fallback to GERAN
 LOFD-001069 CS Fallback with LAI to GERAN
 LOFD-001089 CS Fallback Steering to GERAN
 LOFD-081283 Ultra-Flash CSFB to GERAN
If Huawei devices are used in the GERAN or UTRAN to which CS fallback is performed,
refer to the following documents to obtain details about CSFB implementation in the
corresponding network:

 For the GERAN, see CSFB in GBSS Feature Documentation.
 For the UTRAN, see Interoperability Between UMTS and LTE in RAN Feature
Documentation.
Any managed objects (MOs), parameters, alarms, or counters described herein correspond to
the software release delivered with this document. Any future updates will be described in the
product documentation delivered with future software releases.
This document applies only to LTE FDD. Any "LTE" in this document refers to LTE FDD,
and "eNodeB" refers to LTE FDD eNodeB.
This document applies to the following types of eNodeBs.
eNodeB Type Model
Macro 3900 series eNodeB
Micro BTS3202E
BTS3203E
LampSite DBS3900
1.2 Intended Audience
This document is intended for personnel who:
 Need to understand the features described herein
 Work with Huawei products
1.3 Change History
This section provides information about the changes in different document versions. There
are two types of changes:
 Feature change
Changes in features and parameters of a specified version as well as the affected
entities
 Editorial change
Changes in wording or addition of information and any related parameters affected by
editorial changes. Editorial change does not specify the affected entities.
eRAN8.1 02 (2015-06-30)
This issue includes the following changes.

Change Type Change Description Parameter Change Affected
Entity
Feature
change
Added the measurement-specific
DRX configuration for Ultra-Flash
CSFB to GERAN. For details, see 4.5
Ultra-Flash CSFB to GERAN.
None Macro,
micro, and
LampSite
eNodeBs
Added the random procedure
selection optimization for CSFB. For
details, see 7.1.5.1 Data Preparation.
Added the
RsvdSwPara1_bit23
option in the reserved
parameter
eNBRsvdPara.
RsvdSwPara1.
Macro,
micro, and
LampSite
eNodeBs
Editorial
change
None None -
eRAN8.1 01 (2015-03-23)
This issue includes the following changes.
Change
Type
Change Description Parameter Change Affected
Entity
Feature
change
Added the UE
compatibility risk
optimization for Ultra-
flash CSFB. For details,
see 7.11.5.1 Data
Preparation.
Added the UltraFlashCsfbComOptSw
option to the
GlobalProcSwitch.UeCompatSwitch
parameter.
Macro,
micro, and
LampSite
eNodeBs
Editorial
change
None None -
eRAN8.1 Draft A (2015-01-15)
Compared with Issue 06 (2014-12-30) of eRAN7.0, Draft A (2015-01-15) of eRAN8.1
includes the following changes.
Chan
ge
Type
Change Description Parameter Change Affecte
d
Entity
Featur
e
chang
e
Supported the cell-level
blind handling switch for
CSFB in CS Fallback to
UTRAN or GERAN and
Flash CS Fallback to
UTRAN or GERAN
Added the
CellHoParaCfg.HoModeSwitch
parameter.
Macro,
micro,
and
LampS
ite
eNode
Bs

Chan
ge
Type
d
Entity
scenarios.
 For details about the
switch, see 3.1 Basic
CSFB to UTRAN
and 3.1.2 Blind
Handover.
 For details about
handover policy
selection, see 3.9.1
Handover Policy
Selection.
scenario-specific
parameter
preparations, see
section "Data
Preparation" in
engineering
guidelines.
scenario-specific
configurations, see
"Using the CME to
Perform Batch
Configuration for
Newly Deployed
eNodeBs" and
"Using MML
Commands" in
section "Activation"
in engineering
guidelines.
Added the feature LOFD-
081283 Ultra-Flash CSFB to
GERAN.
feature description,
see 4.5 Ultra-Flash
CSFB to GERAN.
signaling procedure,
see 4.9.6 Ultra-Flash
 Added the
GeranExternalCell.UltraFlashCsf
bInd parameter.
 Added the
GeranUltraFlashCsfbSwitch option
in the
ENodeBAlgoSwitch.HoAlgoSwitc
h parameter.
Macro,
micro,
and
LampS
ite
eNode
Bs

Chan
ge
Type
d
Entity
CSFB to GERAN.
related features and
network impact, see
5.9 Feature Related
to LOFD-081283
Ultra-Flash CSFB to
GERAN and 6.9
LOFD-081283 Ultra-
Flash CSFB to
GERAN.
engineering
guidelines, see 7.11
LOFD-081283 Ultra-
Flash CSFB to
GERAN.
Added the configuration of
the round-robin function for
L2U blind redirections.
switch, see 3.1.2
Blind Handover.
scenario-specific
data preparations, see
7.1.5.1 Data
Preparation.
function activation,
see 7.1.5.5 Using
MML Commands.
Added the
CSFallBackBlindHoCfg.UtranCsfbBlind
RedirRrSw parameter.
Macro,
micro,
and
LampS
ite
eNode
Bs
Added SPID-based mobility
management. For details
about the function, see 3.1.2
Blind Handover, 3.8.1 Basic
Handover Decision, and
3.8.2 Flash Redirection
Decision.
None Macro,
micro,
and
LampS
ite
eNode
Bs
Ultra-flash CSFB to
GERAN uses the DRX-
Added the
CellDrxPara.DrxForMeasSwitch
Macro,
micro,

Chan
ge
Type
d
Entity
based measurement, which
is controlled by the
CellDrxPara.DrxForMeas
Switch parameter.
parameter, see 4.5
Ultra-Flash CSFB to
GERAN.
 For details about data
preparations and
MML
configurations, see
related sections in
7.11 LOFD-081283
Ultra-Flash CSFB to
GERAN.
parameter. and
LampS
ite
eNode
Bs
Editor
ial
chang
e
Changed "blind handling" to
"blind handover". For
details, see descriptions of
blind handover in this
document.
None -
1.4 Differences Between eNodeB Types
The features described in this document are implemented in the same way on macro, micro,
and LampSite eNodeBs.
2 Overview
In an early phase of evolved packet system (EPS) construction, operators who own a mature
UTRAN or GERAN can protect their investments in legacy CS networks and reduce their
investments in the EPS by using legacy CS networks to provide CS services such as the voice
service, short message service (SMS), location service (LCS), and emergency calls.
Currently, CSFB and voice over IP (VoIP) over IP multimedia subsystem (IMS) are the two
standard solutions to provide voice services for E-UTRAN UEs. After the technological
maturity, industry chain, and deployment costs of the two methods are well weighed, CSFB
is chosen to serve as an interim solution for voice service access before mature commercial
use of IMS.
2.1 Overview

With the CSFB solution, when a UE initiates a CS service, the MME instructs the UE to fall
back to the legacy CS network before the UE performs the service. CSFB is a session setup
procedure. UEs fall back to CS networks before CS sessions are set up, and they always stay
in the CS networks during the CS sessions. For details, see 3GPP TS 23.272 V8.5.0.
The eNodeB handles the CSFB for different types of CS services in a uniform way such as
the voice service, SMS, LCS, and emergency calls.
2.2 Benefits
CSFB brings the following benefits:
 Facilitates voice services for the LTE network.
 Helps operators reduce costs by reusing legacy CS networks and not deploying an
IMS network.
2.3 Architecture
CSFB is applicable to scenarios where the CS network of the UTRAN/GERAN has the same
or larger coverage area than E-UTRAN.
The network architecture for CSFB is simple. To implement CSFB, all mobile switching
centers (MSCs) that serve overlapping areas with the E-UTRAN coverage must be upgraded
to support functions involving the SGs interface. The SGs interface is between an MSC and a
mobility management entity (MME), and functions involving the SGs interface include
combined attach, combined TAU/LAU (TAU is short for tracking area update, and LAU is
short for location area update), paging, and SMS. If the live network uses an MSC pool, only
one or multiple MSCs in the MSC pool need to be upgraded to support the SGs interface.
Figure 2-1 shows the network architecture for CSFB to UTRAN/GERAN.

Figure 2-1 Network architecture for CSFB to UTRAN/GERAN
Table 2-1 describes the elements of the network architecture in Figure 2-1.
Table 2-1 Elements of the network architecture for CSFB to UTRAN/GERAN
Element Function
SGs interface  Is an interface between the MME and the MSC server.
 Assists mobility management and paging between the EPS and
the CS network.
 Transmits mobile originated (MO) and mobile terminated (MT)
SMS messages.
 Transmits messages related to combined attach and combined
TAU/LAU.
UE  Is capable of accessing the EPS and accessing the UTRAN,
GERAN, or both.
 Supports combined EPS/IMSI (IMSI is short for international
mobile subscriber identity) attach, combined EPS/IMSI detach,
and combined TAU/LAU.
 Supports CSFB mechanisms, such as PS redirection and PS
handover.
NOTE:
CSFB-capable UEs must support SMS over SGs, but UEs that support
SMS over SGs are not necessarily CSFB-capable.
MME  Supports the SGs interface to the MSC/VLR.
 Selects the VLR and location area identity (LAI) based on the
tracking area identity (TAI) of the serving cell.
 Forwards paging messages delivered by the MSC.

Element Function
 Performs public land mobile network (PLMN) selection and
reselection.
 Supports combined EPS/IMSI attach, combined EPS/IMSI
detach, and combined TAU/LAU.
 Routes CS signaling.
 Supports SMS over SGs.
 Supports RIM, which is required when flash CSFB or CCO with
NACC is used as the CSFB mechanism. (CCO is short for cell
change order and NACC is short for network assisted cell
change.)
MSC  Supports combined EPS/IMSI attach.
 Supports SMS over SGs.
 Forwards paging messages transmitted through the SGs interface.
E-UTRAN  Forwards paging messages related to CSFB.
 Selects target cells for CSFB for E-UTRAN UEs.
 Supports one or more of the following functions:
o PS redirection to UTRAN or GERAN, if PS redirection is
used as the CSFB mechanism.
o PS handover to UTRAN or GERAN, if PS handover is
used as the CSFB mechanism.
o CCO without NACC to GERAN, if CCO without NACC
is used as the CSFB mechanism; RIM for acquiring the
system information of GERAN cells, if NACC is used as
the CSFB mechanism.
o RIM for acquiring the system information of UTRAN or
GERAN cells, in addition to PS redirection, if flash CSFB
is used as the CSFB mechanism.
UTRAN/GERAN Supports one or more of the following functions:
 Incoming handovers from the E-UTRAN, if PS handover is used
as the CSFB mechanism.
 RIM for delivering the system information of GERAN cells to
eNodeBs, if CCO with NACC is used as the CSFB mechanism.
 RIM for delivering the system information of UTRAN or
GERAN cells to eNodeBs, in addition to PS redirection, if flash
CSFB is used as the CSFB mechanism.
NOTE:
The UTRAN and GERAN do not need to provide extra functions to
support PS redirection. The GERAN does not need to provide extra
functions to support CCO without NACC.
SGSN  Supports the follow-up procedures performed for the PS

Element Function
handover, including data forwarding, path switching, RAU, and
encryption and authentication.
 Supports RIM, which is required when flash CSFB or CCO with
NACC is used as the CSFB mechanism.
eCoordinator Is a network element provided by Huawei, and is optional. The
eCoordinator supports the RIM procedure.
3 CSFB to UTRAN
CSFB to UTRAN can be implemented in different ways, and this section covers the
following features/functions:
 LOFD-001033 CS Fallback to UTRAN
 LOFD-001052 Flash CS Fallback to UTRAN
 LOFD-070202 Ultra-Flash CSFB to UTRAN
 LOFD-001068 CS Fallback with LAI to UTRAN
 LOFD-001078 E-UTRAN to UTRAN CS/PS Steering
 LOFD-001088 CS Fallback Steering to UTRAN
 Load-based CSFB to UTRAN
The triggering conditions for different features are different. Basically the procedure for
CSFB to UTRAN is as follows:
1. Selecting a target cell or frequency
In a measurement-based handover, the eNodeB generates a candidate cell list based
on inter-RAT measurement results and selects a target cell from the list.
In a blind handover, the eNodeB selects a target cell based on the blind handover
priorities of neighboring cells or selects a target frequency based on the frequency
priorities.
2. Handover decision
In the handover decision phase, the eNodeB checks the target cell list.
3. Handover execution
The eNodeB controls the UE to be handed over from the serving cell to the target cell.
3.1 Basic CSFB to UTRAN

This section describes the optional feature LOFD-001033 CS Fallback to UTRAN. For
details about the engineering guidelines for this feature, see 7.1 LOFD-001033 CS Fallback
to UTRAN. The UtranCsfbSwitch option in the ENodeBAlgoSwitch.HoAlgoSwitch
parameter specifies whether to enable this feature.
When a UE initiates a CS service in the E-UTRAN, the MME sends an S1-AP message
containing CS Fallback Indicator to the eNodeB, instructing the eNodeB to transfer the UE as
well as the CS service to a target network.
The eNodeB determines whether to trigger UTRAN measurements or blind handling for
CSFB to UTRAN based on the status of the blind handling switch first. The blind handover
switch is controlled by the BlindHoSwitch option in the eNodeB-level parameter
ENodeBAlgoSwitch.HoModeSwitch and the BlindHoSwitch option in the cell-level
parameter CellHoParaCfg.HoModeSwitch. The blind handover function takes effect only
if the eNodeB-level BlindHoSwitch and cell-level BlindHoSwitch options are selected.
 If this option is selected, the eNodeB triggers blind handover directly.
 If this option is cleared, the eNodeB determines whether to trigger inter-RAT
measurements or blind handover based on the UE capability:
o If the UE supports UTRAN measurements, the eNodeB triggers inter-RAT
measurements.
o If the UE does not support UTRAN measurements, the eNodeB triggers a
blind handover.
3.1.1 Handover Measurement
Measurement Triggering Reason
During CSFB, the eNodeB starts a UTRAN measurement after it receives a CS Fallback
Indicator. The measurement configuration is the same as that for coverage-based handover
from E-UTRAN to UTRAN. For details, see Inter-RAT Mobility Management in Connected
Mode.
Figure 3-1 shows the measurement object selection procedure.

Figure 3-1 Measurement object selection procedure
The configurations involved in Figure 3-1 are as follows:
 Neighboring UTRAN frequencies are added by running the ADD UTRANNFREQ
command.
 The frequency priority is specified by the UtranNFreq.ConnFreqPriority
parameter. A larger value indicates a higher priority.
 The cell measurement priorities of neighboring UTRAN cells can be automatically
optimized by ANR. The UTRAN_SWITCH option in the

ENodeBAlgoSwitch.NCellRankingSwitch parameter is used to enable this
function. This option is recommended to be selected if ANR is enabled.
o If this option is selected, the eNodeB automatically optimizes the setting of the
UtranNCell.NCellMeasPriority parameter for the cell. This parameter
cannot be modified manually. For details, see ANR Management.
o If this option is cleared, the cell measurement priorities are specified by the
UtranNCell.CellMeasPriority parameter, which needs to be configured
manually.
 The number of frequencies or cells that the eNodeB can randomly select for
measurement is always equal to the allowed maximum number.
 The maximum number of frequencies is specified by the
CellUeMeasControlCfg.MaxUtranFddMeasFreqNum parameter.
 For details about the maximum number of neighboring cells in a measurement
configuration message, see section 6.4 "RRC multiplicity and type constraint values"
in 3GPP TS 36.331 V10.1.0.
Triggering of CSFB
During the measurement procedure, CSFB is triggered by event B1. The principle of
triggering CSFB by event B1 is the same as that of triggering the coverage-based inter-
frequency handover by event B1. For details, see Inter-RAT Mobility Management in
Connected Mode.
They have different thresholds and time-to-trigger. Table 3-1 lists the thresholds and time-to-
trigger related to event B1 for CSFB to UTRAN. Other parameters are the same as those
related to event B1 for coverage-based inter-frequency handovers.
Table 3-1 Parameters related to event B1 for CSFB to UTRAN
Parame
ter
Name
Parameter ID Parameter Description
CSFB
UTRAN
EventB
1 RSCP
Trigger
Thresho
ld
CSFallBackHo.CsfbHoUtranB1
ThdRscp
The
InterRatHoComm.InterRATHoUtranB1
MeasQuan parameter determines which
threshold is to be used.
CSFB
UTRAN
EventB
1 ECN0
Trigger
Thresho
ld
CSFallBackHo.CsfbHoUtranB1
ThdEcn0
CSFB
Utran
CSFallBackHo.CsfbHoUtranTim
eToTrig
N/A

Parame
ter
Name
Parameter ID Parameter Description
EventB
1 Time
To Trig
3.1.2 Blind Handover
Triggering of Blind Handover
The blind handover switch is controlled by the BlindHoSwitch option in the
ENodeBAlgoSwitch.HoModeSwitch parameter and the BlindHoSwitch option in the
CellHoParaCfg.HoModeSwitch parameter. The blind handover function takes effect only
if the eNodeB-level BlindHoSwitch and cell-level BlindHoSwitch options are selected.
When an E-UTRAN coverage area is larger than a UTRAN coverage area and E-UTRAN
and UTRAN base stations are co-sited, adaptive-blind-handover-based CSFB estimates the
signal strength of the neighboring UTRAN cell based on the signal strength of the serving E-
UTRAN cell.
 If the UE is located in the center of the E-UTRAN cell, the eNodeB performs the
blind handover.
 If the UE is located at the edge of the E-UTRAN cell, the eNodeB performs a
measurement-based handover.
When the blind handover function takes effect:
 If adaptive-blind-handover-based CSFB is disabled, the eNodeB directly enters the
blind handover procedure.
 If adaptive-blind-handover-based CSFB is enabled, the eNodeB delivers measurement
configurations for event A1.
o If the eNodeB receives an event A1 report and determines that the UE is
located in the center of the E-UTRAN cell, it directly enters the blind
handover procedure.
o If the eNodeB does not receive an event A1 report and determines that the UE
is located at the edge of the E-UTRAN cell, it enters the measurement
procedure.
The event A1 threshold is specified by the CSFallBackHo.BlindHoA1ThdRsrp
parameter, and other event-A1-related principles are the same as these in coverage-
based handover from E-UTRAN to UTRAN. For details, see Inter-RAT Mobility
Management in Connected Mode.
Target RAT Selection
During a blind handover for CSFB, the eNodeB selects the target RAT based on the RAT
priorities specified by the following parameters:

 CSFallBackBlindHoCfg.InterRatHighestPri: specifies the RAT with the highest
priority.
 CSFallBackBlindHoCfg.InterRatSecondPri: specifies the RAT with the second
highest priority.
 CSFallBackBlindHoCfg.InterRatLowestPri: specifies the RAT with the lowest
priority.
If CSFallBackBlindHoCfg.InterRatHighestPri is set to UTRAN(UTRAN), the eNodeB
performs CSFB to UTRAN.
 When selecting target cells for blind handover, the eNodeB excludes the following
neighboring cells:
o Blacklisted neighboring cells
o Neighboring cells with a handover prohibition flag
o Neighboring cells that have a different PLMN from the serving cell in the
neighboring cell list. If the inter-PLMN handover switch is turned on, such
cells are not excluded.
o Cells in the areas indicated by the Handover Restriction List IE in the
INITIAL CONTEXT SETUP REQUEST message sent from the MME
After the preceding exclusion, the eNodeB excludes cells from the neighboring cell
list based on SPID-based mobility management in connected mode. For details, see
LOFD-00105401 Camp and Handover Based on SPID in Flexible User Steering
Feature Parameter Description.
 When selecting target frequencies for blind redirection, the eNodeB filters frequencies
based on the RATs supported by the UE and PLMN information corresponding to
frequencies.
After the preceding exclusion, the eNodeB filters cells from the neighboring cell list
based on SPID-based mobility management in connected mode. For details, see
LOFD-00105401 Camp and Handover Based on SPID in Flexible User Steering
During blind handover, the target selection procedure is different, depending on whether
neighboring UTRAN cells are configured.
 If neighboring UTRAN cells are configured, the target selection procedure is shown
in Figure 3-2.
o The blind handover priority of a neighboring UTRAN cell is specified by the
UtranNCell.BlindHoPriority parameter. A larger value indicates a higher
priority.
o The priority of a neighboring UTRAN frequency is specified by
UtranNFreq.ConnFreqPriority parameter. A larger value indicates a higher
priority.
 If no neighboring UTRAN cell is configured, neighboring UTRAN frequencies are
configured, and the UE performs CSFB based on redirection, the target selection
procedure is shown in Figure 3-3.
o Neighboring UTRAN frequencies are configured in UtranNFreq MOs.

o The PLMN information of the neighboring UTRAN frequencies is contained
in the configured UtranRanShare or UtranExternalCell MOs.
Figure 3-2 Target cell selection (configured with a neighboring UTRAN cell)

Figure 3-3 Target cell selection (configured with no neighboring UTRAN cell)
When a UE performs a blind redirection, the eNodeB preferentially selects the frequency
with the highest priority. If multiple frequencies are of the same priority, the eNodeB selects
the blind redirection frequency in a round-robin manner. This ensures that the UE accesses
each frequency equally. This function is specified by the
CSFallBackBlindHoCfg.UtranCsfbBlindRedirRrSw parameter.
3.2 Flash CSFB to UTRAN
This section describes the optional feature LOFD-001052 Flash CS Fallback to UTRAN. For
details about the engineering guidelines for this feature, see 7.3 LOFD-001052 Flash CS
Fallback to UTRAN. The UtranFlashCsfbSwitch option of the
ENodeBAlgoSwitch.HoAlgoSwitch parameter specifies whether to enable this feature.
This feature is an enhancement to the optional feature LOFD-001033 CS Fallback to
UTRAN. After this feature is activated. the eNodeB obtains the UTRAN cell information
through the RIM procedure and then sends the LTE-to-UMTS redirection message including
the obtained UTRAN cell information to the UE. In this case, the UE can access a UTRAN
cell without obtaining the UTRAN cell information. This reduces the access delay. For
details about how the UTRAN cell information is delivered to the eNodeB through the RIM
procedure, see Interoperability Between UMTS and LTE.

This feature requires that the eNodeB can obtain UTRAN cell information through the RIM
procedures and the networks and UEs involved must support 3GPP Release 9 or later. For
details about the RIM procedure, see 3.10 RIM Procedure Between E-UTRAN and UTRAN.
Other procedures are the same as those in CSFB to UTRAN. For details, see 3.1 Basic CSFB
to UTRAN.
3.3 Ultra-Flash CSFB to UTRAN
This section describes the optional feature LOFD-070202 Ultra-Flash CSFB to UTRAN. For
details about the engineering guidelines for this feature, see 7.4 LOFD-070202 Ultra-Flash
CSFB to UTRAN. The UtranUltraFlashCsfbSwitch option in the
This feature is a Huawei-proprietary feature. To enable this feature, the MME, MSC, and
RNC must all provided by Huawei and support this feature.
When a UE initiates a CS service setup request in an LTE cell that does not support VoIP,
this feature enables the eNodeB to hand over the UE to the UTRAN through the SRVCC
handover procedure. This shortens the access delay for CS fallbacks by 1 second.
The measurement procedure and blind handover procedure for this feature are the same as
those in CSFB to UTRAN. For details, see 3.1 Basic CSFB to UTRAN.
NOTE:
The following table describes the parameters that must be set in the
GLOBALPROCSWITCH MO to turn on the UE compatibility switch when UEs do not
support Ultra-Flash CSFB, resulting in UE compatibility problems.
3.4 CS Fallback with LAI to UTRAN
This section describes the optional feature LOFD-001068 CS Fallback with LAI to UTRAN.
For details about the engineering guidelines for this feature, see 7.5 LOFD-001068 CS
Fallback with LAI to UTRAN. This feature is under license control and is not controlled by a
switch.
This feature mainly applies to the following scenarios:
 In a multi-PLMN or national roaming scenario
An LAI consists of a PLMN ID and a LAC. In the CSFB with LAI function, the
PLMN ID identifies the CS network that the UE has registered with and will fall back
to after fallback.
If the serving E-UTRAN cell has multiple neighboring UTRAN or GERAN cells with
different PLMN IDs and the InterPlmnHoSwitch option of the
ENodeBAlgoSwitch.HoAlgoSwitch parameter is selected, or the serving PLMN

differs from the target PLMN, the operator can use CSFB with LAI to achieve
fallback to a specified target network.
 In a tracking area (TA) that overlaps multiple location areas (LAs)
The eNodeB selects a CSFB target cell with the same LAC as that mapped to the
network to which the UE has attached. An LAU is not required after CSFB, and
therefore the CSFB delay does not include the LAU time.
UTRAN. With this feature, the eNodeB selects a target frequency or cell for measurement or
blind handover based on the LAI sent by the MME.
 In a measurement procedure, the eNodeB selects only an inter-RAT frequency on
which the PLMN ID of a neighboring cell is the same as that in the LAI received. The
follow-up measurement procedure is similar to that in CS Fallback to UTRAN. For
details, see 3.1.1 Handover Measurement.
The difference is that the eNodeB sorts neighboring cells in the following order after
receiving measurement reports from a UE:
1. Neighboring cells with PLMN IDs and LACs the same as those in the LAI
2. Neighboring cells with PLMN IDs the same as that in the LAI but LACs
different from that in the LAI
If no frequency or neighboring cell can be selected based on the LAI, the processing
is the same as that when no LAI is received.
 In a blind handover procedure, the eNodeB first selects a target cell for blind
handover.
If no neighboring UTRAN cell is configured, the eNodeB preferentially selects the
UTRAN frequencies whose PLMN ID is the same as that in the LAI. The follow-up
procedure is the same as that described in 3.1.2 Blind Handover.
If neighboring UTRAN cells are configured, the eNodeB preferentially selects the
operating UTRAN frequencies of the neighboring UTRAN cells whose PLMN ID is
the same as that in the LAI. The eNodeB then sorts the frequencies based on the blind
handover priorities of the neighboring cells and frequency priorities for connected
mode. For details, see 3.1.2 Blind Handover.
The eNodeB selects a target cell in the following order of preference:
1. Neighboring cell whose PLMN ID and LAC are the same as those in the LAI
2. If no neighboring cells described in 1 exist, the eNodeB selects the
neighboring cells with PLMN IDs the same as that in the LAI but LACs
different from that in the LAI.
3. If no neighboring cells described in 1 and 2 exist, the eNodeB selects the
neighboring cells with PLMN IDs the same as the serving PLMN ID of the
UE.

If the InterPlmnHoSwitch option of the
ENodeBAlgoSwitch.HoAlgoSwitch parameter is selected, the eNodeB also
selects cells whose PLMN IDs are in the target PLMN list.
3.5 E-UTRAN to UTRAN CS Steering
This section describes the CS steering function in the optional feature LOFD-001078 E-
UTRAN to UTRAN CS/PS Steering. For details about the engineering guidelines for this
function, see 7.7 LOFD-001078 E-UTRAN to UTRAN CS/PS Steering. For details about the
PS steering function in this feature, see Inter-RAT Mobility Management in Connected Mode.
This feature applies to a scenario where service steering is required in a UTRAN with
multiple UTRAN frequencies. By setting CS service priorities for UTRAN frequencies, the
operator can achieve CSFB from E-UTRAN only to the UTRAN frequency that has a high
CS service priority.
CS Steering in CSFB
This function is an enhancement to the CS Fallback to UTRAN feature. The enhancements
are as follows:
 During inter-RAT measurement on the UTRAN, frequencies with a high CS service
priority are preferentially measured.
The UtranFreqLayerMeasSwitch option of the
ENodeBAlgoSwitch.FreqLayerSwtich parameter specifies whether to enable this
function.
If the option is selected, the eNodeB preferentially selects frequencies with a high CS
service priority specified by the UtranNFreq.CsPriority parameter as the
measurement targets. A larger value of this parameter indicates a higher priority. If
this parameter is set to Priority_0(Priority 0) for a frequency, the eNodeB does not
select this frequency as the measurement target. The follow-up measurement
procedure is the same as that in CS Fallback to UTRAN. For details, see 3.1.1
Handover Measurement.
 During blind handover, cells working on frequencies with a high CS service priority
are preferentially selected.
The UtranFreqLayerBlindSwitch option of the
ENodeBAlgoSwitch.FreqLayerSwtich parameter specifies whether to enable this
function.
If the option is selected, the eNodeB preferentially selects cells working on
frequencies with a high CS service priority specified by the UtranNFreq.CsPriority
parameter. A larger value of this parameter indicates a higher priority. If this
parameter is set to Priority_0(Priority 0) for a frequency, the eNodeB does not select
cells working on this frequency. The follow-up blind handover procedure is the same
as that in CS Fallback to UTRAN. For details, see 3.1.2 Blind Handover.

LAI-based CS Steering in CSFB
This function is an enhancement to the CS Fallback with LAI to UTRAN feature. The
enhancements are as follows:
 Enhancement in measurement
1. The eNodeB selects inter-RAT frequencies on which the PLMN ID of a
neighboring cell is the same as the PLMN ID in the LAI.
2. Among the selected frequencies, the eNodeB selects a frequency with a high
CS service priority specified by the UtranNFreq.CsPriority parameter.
3. The follow-up measurement procedure is similar to that in CS Fallback to
UTRAN. For details, see 3.1.1 Handover Measurement.
The difference is that the eNodeB sorts neighboring cells in the following
order after receiving measurement reports from a UE:
4. Neighboring cells with PLMN IDs and LACs the same as those in the LAI
5. Neighboring cells with PLMN IDs the same as that in the LAI but LACs
different from that in the LAI
6. Neighboring cells with PLMN IDs the same as the serving PLMN ID of the
UE
 Enhancement in blind handover
1. The eNodeB selects frequencies whose PLMN ID is the same as the PLMN ID
in the LAI.
2. Among the selected frequencies, the eNodeB selects a frequency with a high
CS service priority specified by the UtranNFreq.CsPriority parameter.
3. The eNodeB selects a neighboring cell whose PLMN ID and LAC are the
same as those in the LAI.
4. If such a neighboring cell is unavailable, the eNodeB selects a neighboring
cell whose PLMN ID is the same as that in the LAI but LAC is different from
that in the LAI.
5. The follow-up blind handover procedure is the same as that in CS Fallback to
UTRAN. For details, see 3.1.2 Blind Handover.
3.6 CS Fallback Steering to UTRAN
This chapter describes the optional feature LOFD-001088 CS Fallback Steering to UTRAN.
Fallback Steering to UTRAN. The UtranCsfbSteeringSwitch option of the
This feature is an enhancement to the optional feature LOFD-001033 CSFB to UTRAN. In
terms of the UE status at the time when the UE initiates a CS service, you can configure the
target RAT and handover policy flexibly. There are two types of UEs:
 CS-only UE
CS-only UE If the MME uses the INITIAL CONTEXT SETUP REQUEST message
to send the CSFB indicator to the eNodeB, the eNodeB determines that the UE is in

idle mode at the time when the UE initiates the CS service. This UE is called a CS-
only UE.
 CS+PS UE
If the MME uses the UE CONTEXT MODIFICATION REQUEST message to send
the CSFB indicator to the eNodeB, the eNodeB determines that the UE is performing
PS services at the time when the UE initiates the CS service. This UE is called a
CS+PS UE.
CS-only UE
If the UE is a CS-only UE, the eNodeB selects the target RAT based on the RAT priorities
for CSFB of CS-only UEs. The priorities are specified by the following parameters:
 CSFallBackBlindHoCfg.IdleCsfbHighestPri: specifies the highest-priority RAT
for CSFB of CS-only UEs.
 CSFallBackBlindHoCfg.IdleCsfbSecondPri: specifies the second-highest-priority
RAT for CSFB of CS-only UEs.
 CSFallBackBlindHoCfg.IdleCsfbLowestPri: specifies the lowest-priority RAT
for CSFB of CS-only UEs.
The eNodeB can select a neighboring cell or frequency with a lower-priority RAT only if no
neighboring cell or frequency with higher-priority RATs is configured.
If the target system with the highest priority is UTRAN, the eNodeB selects the target
frequencies based on the setting of the UtranNFreq.CsPriority parameter. For details, see
3.5 E-UTRAN to UTRAN CS Steering.
The eNodeB selects the handover policy for CSFB of CS-only UEs based on the setting of
the CSFallBackPolicyCfg.IdleModeCsfbHoPolicyCfg parameter. PS HO and redirection
are selected in descending order.
CS+PS UE
The eNodeB selects the target RAT based on the RAT priorities specified by the following
parameters:
 CSFallBackBlindHoCfg.InterRatHighestPri: specifies the RAT with the highest
priority.
 CSFallBackBlindHoCfg.InterRatSecondPri: specifies the RAT with the second-
highest priority.
 CSFallBackBlindHoCfg.InterRatLowestPri: specifies the RAT with the lowest
priority.
The eNodeB can select a neighboring cell or frequency with a lower-priority RAT only if no
neighboring cell or frequency with higher-priority RATs is configured.
If the target system with the highest priority is UTRAN, the eNodeB selects the target
frequencies based on the setting of the UtranNFreq.CsPsMixedPriority parameter. The

UtranNFreq.CsPsMixedPriority and UtranNFreq.CsPriority parameters have similar
setting principles. For details, see 3.5 E-UTRAN to UTRAN CS Steering.
The eNodeB selects the handover policy for CSFB based on the setting of the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter. PS HO and redirection are selected in
descending order.
3.7 Load-based CSFB to UTRAN
This chapter describes load-based CSFB to UTRAN. This function is an enhancement to the
CS Fallback to UTRAN feature. For details about the engineering guidelines for this feature,
see 7.1 LOFD-001033 CS Fallback to UTRAN. The CSFBLoadInfoSwitch option of the
ENodeBAlgoSwitch.HoAlgoSwitch parameter specifies whether to enable this function.
In load-based CSFB to UTRAN, the eNodeB uses the RIM procedure in Multiple Report
mode to obtain the load information about UTRAN cells. For details about the RIM
procedure, see 3.10 RIM Procedure Between E-UTRAN and UTRAN. After receiving the
load information about UTRAN cells, the eNodeB saves the information and uses the
information to determine the target UTRAN cell for the CSFB.
In load-based CSFB to UTRAN, the measurement and blind handover procedures are the
same as those in the CS Fallback to UTRAN feature. For details, see 3.1 Basic CSFB to
UTRAN.
When the eNodeB selects the target UTRAN cell for the CSFB based on the load status of
UTRAN cells, the eNodeB considers UTRAN cells in descending order as follows: cells
whose load status is normal, cells whose load status is congested, and cells whose load status
is overloaded.
Load-based CSFB to UTRAN affects the target cell selection at a later phase. If measurement
is performed, the eNodeB does not select a low-priority frequency because all UTRAN cells
on the high-priority frequency are overloaded.
3.8.1 Basic Handover Decision
When the handover policy is PS HO, SRVCC, or redirection (excluding flash redirection), the
eNodeB does not need to obtain system information of the peer and performs the basic
handover decision.
In the handover decision phase, the eNodeB checks the candidate cell list. Based on the check
result, the eNodeB determines whether a handover needs to be initiated and, if so, to which
cell the UE is to be handed over. If the eNodeB receives measurement reports about different
RATs, it processes the reports in an FIFO manner.
The eNodeB excludes the following cells from the neighboring cell list:
 Blacklisted neighboring cells

 Neighboring cells with a handover prohibition flag
 Neighboring cells that have a different PLMN from the serving cell in the neighboring
cell list
If the inter-PLMN handover switch is turned on, such cells are not excluded.
 Neighboring cells in the areas indicated by the IE Handover Restriction List in the
INITIAL CONTEXT SETUP REQUEST message sent from the MME
After the preceding exclusion, the eNodeB excludes cells from the neighboring cell list based
on SPID-based mobility management in connected mode. For details, see LOFD-00105401
Camp & Handover Based on SPID in Flexible User Steering Feature Parameter
Description.
The eNodeB then sends a handover request to the target cell at the top of the filtered
candidate cell list. If the handover request fails, the eNodeB sends the handover request to the
next target cell, as described in Table 3-2.
Table 3-2 Sequence of handover requests to be sent by the eNodeB
Candidate Cell List
Generated by
Sequence of Handover Requests
Measurement A handover request is sent to the cell with the best signal quality.
Blind handover A handover request is sent to a cell or frequency that has the
highest priority. If multiple cells have the highest priority, the
eNodeB randomly selects a cell for blind handover.
If the handover request fails in all candidate cells:
 For a measurement procedure, the eNodeB waits until the UE sends the next
measurement report.
 For a blind handover procedure, the eNodeB finishes the handover attempt.
3.8.2 Flash Redirection Decision
When the handover policy requires the eNodeB to obtain system information about the peer,
for example, flash redirection, handover decision based on system information is performed.
If the handover decision is based on system information, the eNodeB includes system
information of the target cell of the corresponding RAT. Therefore, the time for reading cell
system information is not required so that the UE can quickly access the target network.
Decision based on system information adheres to the following principles:
 In blind handover scenarios:
1. The target cell list for blind handover is selected, including other cells under
the target frequency for redirection. The UTRAN_SWITCH option of the
ENodeBAlgoSwitch.NCellRankingSwitch parameter specifies the
sequence of adding other cells.

When this option is selected, the eNodeB adds other cells in the target
frequency according to UtranNCell.NCellMeasPriority in descending
order.
When this option is cleared, the eNodeB adds other cells in the target
frequency according to UtranNCell.CellMeasPriority in descending order.
2. Basic handover decision is applied. For details, see 3.8.1 Basic Handover
Decision.
3. Cells whose system information is not obtained are filtered out.
4. The eNodeB excludes cells from the neighboring cell list based on SPID-
based mobility management in connected mode. For details, see LOFD-
00105401 Camp & Handover Based on SPID in Flexible User Steering
 In measurement scenarios:
1. Cells in the candidate cell list generated by measurement are selected, plus
cells that are not in measurement reports but work on the target frequency for
redirection. The UTRAN_SWITCH option of the
ENodeBAlgoSwitch.NCellRankingSwitch parameter specifies the
sequence of adding other cells.
2. Basic handover decision is applied. For details, see 3.8.1 Basic Handover
Decision.
3. Cells whose system information is not obtained are filtered out.
You can specify the number of UTRAN cells contained in the redirection message by setting
the InterRatHoComm.CellInfoMaxUtranCellNum parameter. Assume that this parameter
is set to N.
 If the number of target cells after flash redirection decision is greater than N, the
eNodeB selects the first N cells.
 If the number of target cells after flash redirection decision is smaller than N, the
eNodeB selects target cells after flash redirection decision.
The eNodeB obtains system information of target cells in the RAN information management
(RIM) procedure. If a target cell does not support the RIM procedure, the eNodeB cannot
obtain system information of that cell.
3.9.1 Handover Policy Selection
When a UE in an LTE system needs to perform voice service but the LTE system does not
support VoIP, a CSFB to an inter-RAT network is triggered.
CSFB from E-UTRAN to UTRAN can be based on PS handover, redirection, or flash
redirection, as shown in Figure 3-4. This handover policy selection procedure is based on the
assumption that neighboring frequency and neighboring cell configurations are proper.

During a CSFB based on blind PS handover, if the target cell with the highest blind handover
priority fails to prepare the handover, the eNodeB attempts another cell with the second
highest blind handover priority. The eNodeB can attempt a maximum of eight cells. If all
these cells fail in preparation, the eNodeB performs CSFB based on redirection.

Figure 3-4 E-UTRAN-to-UTRAN CSFB policy selection procedure
The parameters mentioned in the preceding figure are described as follows:

 The timer length is specified by the CSFallBackHo.CsfbProtectionTimer
parameter. If the UE stays in the area covered by the eNodeB before the timer expires,
the eNodeB performs the CSFB based on the blind redirection,
o The eNodeB preferentially selects a system that the UE has not measured. For
example, if the UE has measured the UTRAN, the eNodeB preferentially
selects the GERAN for redirection.
o If a cell to which the eNodeB has never attempted to hand over the UE is
reported, the eNodeB preferentially selects the operating frequency of the cell
for redirection.
o The eNodeB selects the target cell for redirection as it does during blind
handover. For details about how the eNodeB performs target selection during
blind handover, see 3.1.2 Blind Handover.
o If there is not target frequency available for redirection, the eNodeB stops the
procedure.
o If flash CSFB is enabled in this situation, redirection-based CSFB performed
by the eNodeB is referred to as CSFB emergency redirection. In this scenario,
you need to set the InterRatHoComm.UTRANCellNumForEmcRedirect
parameter to specify the maximum number of UTRAN cell system
information messages that can be transmitted during a CSFB emergency
redirection procedure.
 The blind handover switch is controlled by the BlindHoSwitch option in the eNodeB-
level parameter ENodeBAlgoSwitch.HoModeSwitch and the BlindHoSwitch
option in the cell-level parameter CellHoParaCfg.HoModeSwitch. The blind
handover function takes effect only when the eNodeB-level BlindHoSwitch and cell-
level BlindHoSwitch options are selected.
 The adaptive-blind-handover-based CSFB switch is controlled by the
CsfbAdaptiveBlindHoSwitch option of the ENodeBAlgoSwitch.HoAlgoSwitch
parameter.
 If PS handover for CSFB is required, select the UtranPsHoSwitch option of the
ENodeBAlgoSwitch.HoModeSwitch parameter and the PS_HO option of the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter. If either option is cleared, PS
handover for CSFB is invalid. The eNodeB selects the redirection policy. If the
redirection policy is invalid and the CSFB protection timer expires, the eNodeB enters
the blind redirection procedure.
 If blind redirection for CSFB is required, select the REDIRECTION option of the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter.
 The CSFB policy is specified by different parameters, depending on whether LOFD-
001088 CS Fallback Steering to UTRAN is enabled.
If this feature is enabled:
o The CSFB policy for UEs in idle mode is specified by the
CSFallBackPolicyCfg.IdleModeCsfbHoPolicyCfg parameter.
o The CSFB policy for UEs in connected mode is specified by the
If this feature is not enabled, the CSFB policy is specified by the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter, regardless of whether UEs are
in idle or connected mode.

This section describes the optional feature LOFD-070202 Ultra-Flash CSFB to UTRAN. For
details about the engineering guidelines for this feature, see 7.4 LOFD-070202 Ultra-Flash
CSFB to UTRAN. The UtranUltraFlashCsfbSwitch option in the
This feature is a Huawei-proprietary feature. To enable this feature, the MME, MSC, and
RNC must all provided by Huawei and support this feature.
When a UE initiates a CS service setup request in an LTE cell that does not support VoIP,
this feature enables the eNodeB to hand over the UE to the UTRAN through the SRVCC
handover procedure. This shortens the access delay for CS fallbacks by 1 second.
The measurement procedure and blind handover procedure for this feature are the same as
those in CSFB to UTRAN. For details, see 3.1 Basic CSFB to UTRAN.
support VoIP, the eNodeB decides to perform ultra-flash CSFB if LOFD-070202 Ultra-Flash
CSFB to UTRAN is enabled. Figure 3-5 shows ultra-flash CSFB to UTRAN by using the
SRVCC procedure after the eNodeB performs a measurement or blind handover decision. For
details about how to select other CSFB policies, see 3.9.1 Handover Policy Selection.

Figure 3-5 Ultra-Flash CSFB to UTRAN
The preceding figure is described as follows:
 The ultra-flash CSFB to UTRAN switch is controlled by the
UtranUltraFlashCsfbSwitch option of the ENodeBAlgoSwitch. HoAlgoSwitch
parameter.
 At least one neighboring UTRAN cell's RNC support ultra-flash CSFB to UTRAN.
o If all neighboring UTRAN cells' RNCs support ultra-flash CSFB to UTRAN,
no configuration is required.
o If some neighboring UTRAN cells' RNCs do not support ultra-flash CSFB to
UTRAN, the following configurations are required:
Select the UtranSepOpMobilitySwitch option of the
ENodeBAlgoSwitch.MultiOpCtrlSwitch parameter.
For RNCs that do not support ultra-flash CSFB to UTRAN, do not select the
corresponding UltraFlashCsfbCap option of the
UtranNetworkCapCfg.NetworkCapCfg parameter.

To speed up CSFB for UEs in idle mode by shortening end-to-end delays and to reduce the
CSFB failure rate due to initial context setup failures, redirection-based CSFB for UEs in idle
mode is optimized.
The optimization is performed after the eNodeB decides to perform blind handover, as shown
in Figure 3-6.
Figure 3-6 Redirection-based CSFB optimization for UEs in idle mode
The optimization switch is controlled by the IdleCsfbRedirectOptSwitch option of the
GlobalProcSwitch.ProtocolMsgOptSwitch parameter.
For details about how to decide between redirection and flash redirection, see 3.9.1 Handover
Policy Selection.
For the signaling procedure, see 3.11.6 Redirection-based CSFB Optimization for UEs in Idle
Mode.
3.9.4 CSFB Admission Optimization for UEs in Idle Mode
UEs in idle mode only have a default bearer for data service, and the allocation/retention
priority (ARP) of the default bearer is generally lower. When a UE in idle mode needs to

perform CSFB but the target cell is congested or cannot accommodate more UEs, this UE
cannot preempt resources in the target cell.
To ensure the CSFB success rate in the preceding scenario, the eNodeB can preferentially
admit CSFB UEs. This function is controlled by the
CSFallBackPolicyCfg.CsfbUserArpCfgSwitch parameter.
A larger value of the CsFallbackPolicyCfg.NormalCsfbUserArp parameter indicates a
higher probability of admission of CSFB UEs in idle mode. For details about the admission
procedure, see Admission and Congestion Control.
3.10 RIM Procedure Between E-UTRAN and UTRAN
The RIM procedure exchanges information between the E-UTRAN and UTRAN through the
core networks.
In CSFB procedures, the eNodeB obtains the load information of external UTRAN cells from
RNCs through the RIM procedure if the parameter
GlobalProcSwitch.UtranLoadTransChan is set to BASED_ON_RIM.
In flash CSFB procedures, the eNodeB obtains the system information (SI) of external cells
from RNCs through the RIM procedure. For details about related parameters, see 3.10.1 RIM
Procedure Through the Core Network and 3.10.2 RIM Procedure Through the eCoordinator.
The RIM procedure includes the following two information exchange modes:
 Single Report
In Single Report mode, the source sends a request, and then the target responds with a
single report.
When flash CSFB to UTRAN is triggered, the eNodeB sends a RIM message to the
RNC and then includes the obtained SI in a redirection message to send to the UE. If
the SI fails to be obtained from the RNC, the eNodeB no longer attempts the RIM
request.
 Multiple Report
In Multiple Report mode, the target responds with a report after receiving a request
from the source, and the target also sends a report to the source each time information
about the target changes.
When flash CSFB to UTRAN is triggered, the eNodeB sends RIM messages to all
neighboring UTRAN cells every four seconds no matter whether the eNodeB has
CSFB services.
To ensure that the SI of the target cell can be obtained successfully, the eNodeB starts
a four-second timer when it sends a RIM message.

o If the eNodeB receives a response to the RIM message before the timer
expires, the eNodeB saves the obtained SI.
o If the eNodeB receives a response to the RIM message after the timer expires,
the eNodeB considers that an exception occurs and discards the SI.
o If the eNodeB does not receive a response to the RIM message when the timer
expires, the eNodeB sends the RIM message and starts the timer again (called
a retry) two hours later. If the eNodeB still does not receive a response after 10
retries, the RIM request fails. The interval between the nth and (n+1)th retries
is twice the interval between the (n-1)th and nth retries. For example, the first
retry occurs two hours after the first SI acquisition fails, the second retry
occurs four hours after the first retry fails, and the third retry occurs six hours
after the second retry fails. For each retry, the eNodeB sends a RIM message
and restarts the timer.
The eNodeB may obtain incorrect SI due to the abnormalities in the UTRAN, core
network, or transport network. To avoid this situation, the eNodeB selects a time point
randomly every day from 02:00 a.m. to 04:00 a.m and deletes all the obtained SI.
Then, the eNodeB requests the SI of UTRAN cells through the RIM procedure again.
If a neighboring UTRAN cell is faulty or deactivated, the RNC sends an END
message to notify the eNodeB of stopping the RIM procedure. In this case, the
eNodeB deletes the obtained SI and requests SI again in the next RIM procedure.
Currently, the eNodeB triggers a RIM procedure in Multiple Report mode only if
MMEs comply with 3GPP Release 9 or later.
The RIM procedure can be performed through the core network or eCoordinator.
3.10.1 RIM Procedure Through the Core Network
If ENodeBAlgoSwitch.RimOnEcoSwitch is set to OFF(Off), the RIM procedure is
performed through the core network As shown in Figure 3-7, the RIM procedure involves the
eNodeB, MME, SGSN, and RNC Among these NEs, the MME and the SGSN transfer but do
not resolve information. For details, see section 8c "Signalling procedures between RIM
SAPs" in 3GPP TS 48.018 V10.0.0.
Figure 3-7 Performing the RIM procedure through the core network
The preceding figure is described as follows:
 The RIM procedure between EUTRAN and UTRAN is controlled by the
UTRAN_RIM_SWITCH option of the ENodeBAlgoSwitch.RimSwitch parameter.

If this option is selected, the eNodeB uses the RIM procedure in Multiple Report
mode to obtain the system information of external UTRAN cells.
 Whether multiple UTRAN operators can use different mobility policies is specified
by the UtranSepOpMobilitySwitch option of the
ENodeBAlgoSwitch.MultiOpCtrlSwitch parameter.
 The RIM procedure for obtaining SI is controlled by the SiByRimCapCfg option of
the UtranNetworkCapCfg.NetworkCapCfg parameter.
Figure 3-8 Information exchange mode selection for the RIM procedure
3.10.2 RIM Procedure Through the eCoordinator
If ENodeBAlgoSwitch.RimOnEcoSwitch is set to ON(On), the RIM procedure is
performed through the eCoordinator. As shown in Figure 3-9, the RIM procedure through the
eCoordinator involves the eNodeB, eCoordinator, and RNC. Among these NEs, the MME
and the SGSN transfer but do not resolve information.

Figure 3-9 RIM procedure through the eCoordinator
The RIM procedure through the eCoordinator requires that the corresponding switches of all
NEs involved to be switched on.
During the RIM procedure through the eCoordinator, the eNodeB does not send RIM
messages to the EPC or process RIM messages from the EPC.
The information exchange mode for the eCoordinator-based RIM procedure is controlled by
UTRAN_RIM_SWITCH under the ENodeBAlgoSwitch.RimSwitch parameter.
 If this switch is on, the eNodeB uses the RIM procedure in Multiple Report mode to
obtain the system information of external UTRAN cells.
 If this switch is off, the eNodeB uses the RIM procedure in Single Report mode.
3.11 CSFB to UTRAN
The combined EPS/IMSI attach procedure is performed by exchanging NAS messages.
Therefore, this procedure is transparent to the eNodeBs. After a CSFB-capable UE is
powered on in the E-UTRAN, the UE initiates a combined EPS/IMSI attach procedure, as
shown in Figure 3-10.
Figure 3-10 Combined EPS/IMSI attach procedure
HSS: home subscriber server VLR: visitor location register

NOTE:
The symbols that appear in signaling procedure figures throughout this document are
explained as follows:
 An arrow denotes the transmission of a message.
 A plain box denotes a mandatory procedure.
 A dashed box denotes an optional procedure.
The combined EPS/IMSI attach procedure is described as follows:
1. The UE sends a Combined attach request message to the MME, requesting a
combined EPS/IMSI attach procedure. This message also indicates whether the CSFB
or SMS over SGs function is required.
2. The EPS attach procedure is performed in the same way as it is performed within the
LTE system. For details, see section 5.3.2 in 3GPP TS 23.401 V9.2.0.
3. The MME allocates an LAI to the UE, and then it finds the MSC/VLR for the UE
based on the LAI. If multiple PLMNs are available for the CS domain, the MME
selects a PLMN based on the selected PLMN information reported by the eNodeB.
Then, the MME sends the MSC/VLR a Location update request message, which
contains the new LAI, IMSI, MME name, and location update type.
4. The MSC/VLR performs the location update procedure in the CS domain.
5. The MSC/VLR responds with a Location update accept message that contains
information about the VLR and temporary mobile subscriber identity (TMSI). The
location update procedure is successful.
6. The UE is informed that the combined EPS/IMSI attach procedure is successful. If the
network supports SMS over SGs but not CSFB, the message transmitted to the UE
contains the information element (IE) SMS-only. The message indicates that the
combined EPS/IMSI attach procedure is successful but only SMS is supported.
During CSFB based on PS handover, the UE is transferred from the E-UTRAN to the
UTRAN by performing a PS handover. It then initiates a CS service in the UTRAN.
Call procedure
Figure 3-11 shows the procedure for CSFB to UTRAN based on PS handover for mobile-
originated calls.

Figure 3-11 CSFB to UTRAN based on PS handover for mobile-originated calls
1. The UE sends the MME an NAS message Extended Service Request to initiate a CS
service.
2. The MME sends an S1-AP message to instruct the eNodeB to initiate a CSFB
procedure. If the MME supports the LAI-related feature, the MME also delivers the
LAI to the eNodeB.
3. If the MME supports the LAI-related feature, the MME also delivers the LAI to the
eNodeB.
4. The eNodeB initiates the preparation phase for a PS handover. If the preparation is
successful, the eNodeB instructs the UE to perform a handover.
NOTE:
For details about how the eNodeB selects a target cell and a CSFB policy, see 3.8
Handover Decision and 3.9 Handover Execution.
5. After the handover, the UE may initiate a CS call establishment procedure with an
LAU or combined RAU/LAU procedure in the UTRAN.
6. The follow-up procedures are performed for the PS handover. These procedures
include data forwarding, path switching, and RAU. This step is performed together
with 5.
CSFB Procedure for Mobile-terminated Calls
Figure 3-12 shows the procedure for CSFB to UTRAN based on PS handover for mobile-
terminated calls.

Figure 3-12 CSFB to UTRAN based on PS handover for mobile-terminated calls
1. The MSC sends a Paging Request message from the CS domain to the MME over the
SGs interface. Then, either of the following occurs:
o If the UE is in idle mode, the MME sends a Paging message to the eNodeB.
Then the eNodeB sends a Paging message over the Uu interface to inform the
UE of an incoming call from the CS domain.
o If the UE is in active mode, the MME sends the UE an NAS message to
inform the UE of an incoming call from the CS domain.
2. The UE sends an Extended Service Request message containing a CS Fallback
Indicator after receiving the paging message from the CS domain.
3. The MME instructs the eNodeB over the S1 interface to perform CSFB.
4. The subsequent steps are similar to steps 3 through 6 in the procedure for CSFB to
UTRAN based on PS handover for mobile-originated calls. The only difference is that
the UE sends a Paging Response message from the UTRAN cell.
3.11.3 Signaling procedure of redirection to CDMA2000 1xRTT
During CSFB based on PS redirection, the eNodeB receives a CS Fallback Indicator, and
then it sends an RRC Connection Release message to release the UE. The message contains
information about a target UTRAN frequency, reducing the time for the UE to search for a
target network. After selecting the UTRAN, the UE acquires the system information of a
UTRAN cell. Then, the UE performs initial access to the cell to initiate a CS service. For the
UTRAN, the UE is an initially accessing user.
Call procedure
Figure 3-13 shows the procedure for CSFB to UTRAN based on redirection for mobile-
originated calls.

Figure 3-13 CSFB to UTRAN based on redirection for mobile-originated calls
service.
LAI to the eNodeB.
eNodeB.
4. The eNodeB sends an RRC Connection Release message to instruct the UE to
perform a redirection. The message contains information about a target UTRAN
frequency. Then, the eNodeB initiates an S1 UE context release procedure.
NOTE:
5. The UE may initiate an LAU, a combined RAU/LAU, or both an RAU and an LAU in
the target cell.
6. The UE initiates a CS call establishment procedure in the target UTRAN cell.
In a mobile-terminated call, the MSC sends a Paging request message from the CS domain to
the MME over the SGs interface, and then the MME or eNodeB initiates a paging procedure
for the UE. The paging procedure is similar to that for UTRAN described in 3.11.2 CSFB
Based on PS Handover. The subsequent steps are the same as the steps in the procedure for
CSFB to UTRAN based on PS handover for mobile-originated calls.

3.11.4 Flash CSFB
During the flash CSFB procedure, the eNodeB receives a CS Fallback Indicator, and then it
sends an RRC Connection Release message to release the UE. The message contains
information about a target UTRAN frequency, as well as one or more physical cell identities
and their associated system information. In this way, the UE can quickly access the target
UTRAN without the need to perform the procedure for acquiring system information of the
target UTRAN cell. Then, the UE can directly initiate a CS service in the UTRAN cell.
Call procedure
Figure 3-14 shows the procedure for CSFB to UTRAN based on flash redirection for mobile-
originated calls.
Figure 3-14 CSFB to UTRAN based on flash redirection for mobile-originated calls
service.
LAI to the eNodeB.
eNodeB.
4. The eNodeB sends an RRC Connection Release message to instruct the UE to
perform a redirection. The message contains information about a target UTRAN
frequency, as well as one or more physical cell identities and their associated system
information. Then, the eNodeB initiates an S1 UE context release procedure.
NOTE:

Handover Decision and 3.9 Handover Execution. The system information of the target
cell is acquired during the RIM procedure.
5. The UE may initiate an LAU, a combined RAU/LAU, or both an RAU and an LAU in
the target cell.
6. The UE initiates a CS call establishment procedure in the target UTRAN cell.
CSFB to UTRAN based on PS handover for mobile-originated calls.
CSFB Procedure for Mobile-Originated Calls
Figure 3-15 shows the procedure of ultra-flash CSFB to UTRAN for mobile-originated calls.
Compared with the standard procedure described in chapter 6 "Mobile Originating Call" in
3GPP TS 23.272 V10.9.0 and 3GPP TS 24.008 V11.0.0, Huawei ultra-flash CSFB to
UTRAN for mobile-originated calls:
 Excludes the authentication procedure because the UE has been authenticated in the
LTE system before CSFB to UTRAN.
 Excludes the ciphering procedure because the UE has performed ciphering as
instructed during SRVCC.
 Excludes the IMEI check procedure because the MME has sent the IMEI to the MSC
during the preparation for SRVCC.
 Excludes the CS resource setup procedure because the UTRAN system has prepared
CS resources during SRVCC and therefore the UE does not need to reestablish the CS
resource after SRVCC.

Figure 3-15 Flash CSFB to UTRAN for mobile-originated calls
CSFB Procedure for Mobile-Terminated Calls
Figure 3-16 shows the procedure of ultra-flash CSFB to UTRAN for mobile-terminated calls.
Ultra-flash CSFB for mobile-terminated calls excludes the same procedures as ultra-flash
CSFB for mobile-originated calls. For details about the standard procedure, see chapter 6
"Mobile Originating Call" in 3GPP TS 23.272 V10.9.0 and 3GPP TS 24.008 V11.0.0.

Figure 3-16 Ultra-flash CSFB to UTRAN for mobile-terminated calls
After the NodeB receives an initial context setup request with a CS Fallback Indicator from
the MME, the eNodeB does not perform the UE capability query, Uu security mode
command, or RRC connection reconfiguration procedure with dashed lines in the following
figure:

Figure 3-17 Redirection-based CSFB optimization for UEs in idle mode
3.11.7 CSFB for SMS
SMS services are unknown to the eNodeB because SMS messages are encapsulated in NAS
messages. During interworking with the UTRAN, SMS messages are exchanged between the
MME and the MSC over the SGs interface. Because a UE does not require fallback to the
UTRAN to perform an SMS service, the SMS over SGs function can be used in a place
covered only by the E-UTRAN.
As the SMS service is transparent to the eNodeB, the procedure is not described in this
document. For details about the procedure, see section 8.2 in 3GPP TS 23.272 V10.0.0.
The CSFB procedure for an emergency call is the same as the CSFB procedure for a normal
mobile-originated voice service. The UE sends an RRC Connection Request message over
the Uu interface or the MME sends an Initial Context Setup Request or UE Context
Modification Request message, which contains an IE to inform the eNodeB of the service
type. Emergency calls take precedence over other services in the eNodeB.
If PS handover is used for CSFB for emergency calls, the eNodeB does not restrict the cells
in the handover restriction list when selecting the target cell. The eNodeB sends the RNC a
handover request with the IE CSFB high priority in the IE Source to Target Transparent

Container. This request informs the RNC that a CSFB procedure is required for an
emergency call. Upon receiving the information, the RNC preferentially processes this call
when using related algorithms such as admission control.
If redirection is used for CSFB for emergency calls, the RRC Connection Request message
that the UE sends when accessing the UTRAN contains the indication of a CS emergency
call.
The UTRAN will treat this call as a common CS emergency call. For details about admission
and preemption of emergency calls, see Emergency Call.
3.11.9 CSFB for LCS
After a UE initiates an LCS request, the MME performs an attach or combined TAU/LAU
procedure to inform the UE of the LCS capability of the EPS. If the EPS does not support
LCS, the UE falls back to the UTRAN to initiate LCS under the control of the EPS. The
CSFB procedure is the same as the procedure for CSFB to UTRAN for mobile-originated
calls.
If the UTRAN initiates an LCS request towards a UE camping on an E-UTRAN cell, the
MSC sends an LCS indicator to the MME over the SGs interface. Then, the MME instructs
the eNodeB to perform CSFB for the UE. The CSFB procedure is the same as the procedure
for CSFB to UTRAN for mobile-terminated calls. The UE performs the LCS service after the
fallback to the UTRAN.
For details about the CSFB procedure for LCS, see section 8.3 in 3GPP TS 23.272 V10.0.0
and LCS.
4 CSFB to GERAN
CSFB to GERAN can be implemented in different ways, and this section covers the
following features/functions:
 LOFD-001034 CS Fallback to GERAN
 LOFD-001053 Flash CS Fallback to GERAN
 OFD-001069 CS Fallback with LAI to GERAN
 LOFD-001089 CS Fallback Steering to GERAN
 LOFD-081283 Ultra-Flash CSFB to GERAN
The triggering condition for different features are different. Basically the procedure is as
follows:
1. Target cell/frequency selection
For a measurement, the eNodeB generates a candidate cell list based on inter-RAT
measurement results.
For a blind handover, the eNodeB selects a blind handover target based on the blind
handover priority or frequency priority of neighboring cells.

2. Handover decision
In the handover decision phase, the eNodeB checks the candidate cell list. Based on
the check result, the eNodeB determines whether a handover needs to be initiated and,
if so, to which cell the UE is to be handed over.
3. Handover execution
The eNodeB controls the UE to be handed over from the serving cell to the target cell.
4.1 Basic CSFB to GERAN
This section describes the optional feature LOFD-001034 CS Fallback to GERAN. For
details about the engineering guidelines for this feature, see 7.8 LOFD-001034 CS Fallback
to GERAN. The GeranCsfbSwitch option in the ENodeBAlgoSwitch.HoAlgoSwitch
parameter specifies whether to enable this feature.
The blind handover switch is controlled by the BlindHoSwitch option in the eNodeB-level
parameter ENodeBAlgoSwitch.HoModeSwitch and the BlindHoSwitch option in the cell-
level parameter CellHoParaCfg.HoModeSwitch. The blind handover function takes effect
only when the eNodeB-level BlindHoSwitch and cell-level BlindHoSwitch options are
selected.
This feature has the same principle as CSFB to UTRAN, except the parameters mentioned
below in this section. For details about the principle of CSFB to UTRAN, see 3.1 Basic
CSFB to UTRAN.
Handover Measurement
The frequency priority used during target frequency selection is specified by the
GeranNfreqGroup.ConnFreqPriority parameter. A larger value indicates a higher
priority.
During the GERAN frequency selection for measurement that is different from the UTRAN
frequency selection, if the total number of the GERAN frequencies that can be delivered in
the frequency group with the highest priority and the frequencies that have been delivered
exceeds the allowed maximum number 32, all frequencies in this frequency group cannot be
delivered. The eNodeB determines whether the GERAN frequencies in the frequency group
with the second highest priority can be delivered until the number of delivered frequencies is
less than or equal to the maximum number of GERAN frequencies allowed for measurement
or all frequency groups are determined.
In GERAN, no cell measurement priority is configured. If the number of cells working on a
frequency exceeds the specification, the eNodeB randomly measures certain cells.
Blind Handover
If CSFallBackBlindHoCfg.InterRatHighestPri is set to GERAN(GERAN), the eNodeB
performs CSFB to GERAN.

During blind handover, the target selection procedure is different, depending on whether
neighboring GERAN cells are configured.
 If neighboring GERAN cells are configured:
o The blind handover priority of a GERAN neighboring cell is specified by the
GeranNcell.BlindHoPriority parameter. A larger value indicates a higher
priority.
o The GERAN frequency group with the highest priority (specified by the
GeranNfreqGroup.ConnFreqPriority parameter) is selected for blind
handover. A larger value indicates a higher priority.
o If the priorities of neighboring GERAN cells or frequencies are the same, the
eNodeB randomly selects a target cell or frequency. Due to uncertainty of
random selection, to increase the probability of a successful blind handover,
you are not advised to set an identical priority for neighboring GERAN cells
or frequencies.
 If no neighboring GERAN cell is configured:
o Neighboring GERAN frequencies are configured in GeranNfreqGroup MOs.
o The PLMN information of the neighboring GERAN frequency is contained in
the configured GeranRanShare or GeranExternalCell MOs.
4.2 Flash CSFB to GERAN
This section describes the optional feature LOFD-001053 Flash CS Fallback to GERAN. For
details about the engineering guidelines for this feature, see 7.10 LOFD-001053 Flash CS
Fallback to GERAN. The GeranFlashCsfbSwitchh option of the
GERAN. After this feature is activated, the eNodeB obtains the GERAN cell information
through the RIM procedure and then sends the LTE-to-GSM redirection message including
the obtained GERAN cell information to the UE. The
InterRatHoComm.CellInfoMaxGeranCellNum parameter specifies the maximum
number of GERAN cells that can be contained in the redirection message, which is
configurable.
In this case, the UE can access a GERAN cell without obtaining GERAN cell information.
This reduces the access delay. For details about how the GERAN cell information is
delivered to the eNodeB through the RIM procedure, see Interoperability Between GSM and
LTE.
This feature has the same principle as flash CSFB to UTRAN. For details, see 3.2 Flash
CSFB to UTRAN.
4.3 CS Fallback with LAI to GERAN
This section describes the optional feature LOFD-001069 CS Fallback with LAI to GERAN.

Fallback with LAI to GERAN. This feature is under license control and is not controlled by a
switch.
This feature has the same principle as CS fallback with LAI to UTRAN. For details, see 3.4
CS Fallback with LAI to UTRAN.
4.4 CS Fallback Steering to GERAN
This chapter describes the optional feature LOFD-001089 CS Fallback Steering to GERAN.
Fallback Steering to GERAN. The GeranCsfbSteeringSwitch option of the
The principles of this feature are similar to the principles of the CS Fallback Steering to
UTRAN feature. For details about the principles, see 3.6 CS Fallback Steering to UTRAN.
The eNodeB selects a handover policy for CSFB of a CS-only UE based on the setting of the
CSFallBackPolicyCfg.IdleModeCsfbHoPolicyCfg parameter. The eNodeB selects PS
HO, CCO, and redirection in descending order.
The eNodeB selects a handover policy for CSFB of a CS+PS UE based on the setting of the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter. The eNodeB selects PS HO, CCO,
and redirection in descending order.
4.5 Ultra-Flash CSFB to GERAN
This section describes the optional feature LOFD-081283 Ultra-Flash CSFB to GERAN. The
GeranUltraFlashCsfbSwitch option in the ENodeBAlgoSwitch.HoAlgoSwitch parameter
specifies whether to enable this feature. This feature is a Huawei-proprietary feature. To
enable this feature, the MME, MSC, and eNodeB must be all provided by Huawei and
support this feature.
When a UE initiates a voice setup request in an LTE cell that does not support VoIP, this
feature enables the eNodeB to transfer the UE to the GERAN through the SRVCC handover
procedure. This shortens the access delay for CS fallbacks by 2 seconds.
 The measurement procedure and blind handover procedure for this feature are the
same as those in CSFB to GERAN. For details, see 3.1 Basic CSFB to UTRAN.
 The SRVCC handover policy for this feature is the same as that for ultra-flash CSFB
to GERAN. For details, see 3.9.2 Ultra-Flash CSFB to UTRAN.
This feature requires that external GERAN cells support ultra-flash CSFB to GERAN.
 If all external GERAN cells support ultra-flash CSFB to GERAN, no configuration is
required.
 If some external GERAN cells do not support ultra-flash CSFB to GERAN, the
following configurations are required:
o Set UltraFlashCsfbInd to BOOLEAN_FALSE for external GERAN cells
that do not support ultra-flash CSFB to GERAN.

o The ultra-flash CSFB to GERAN capability for external GERAN cells is
specified by the GeranExternalCell.UltraFlashCsfbInd parameter.
When the UE completes voice services on the E-UTRAN after the Ultra-Flash CSFB to
GERAN, you can enable the Fast Return to LTE feature on the GSM side so that the UE
quickly returns to the E-UTRAN. After the UE completes voice services on the GERAN, the
UE carries the LTE frequency information in a Channel Release message and selects a proper
LTE cell to camp on based on the frequency information to accelerate the return to the E-
UTRAN.
When IratMeasCfgTransSwitch in the GlobalProcSwitch.ProtocolMsgOptSwitch parameter
is set to ON, the eNodeB filters LTE frequencies supported by the UE based on the UE
capability to obtain a frequency set. During the SRVCC handover, the eNodeB sends a
Handover Required message containing the frequency set to the BSC of the target cell and
provides reference for the UE to accelerate the return to the E-UTRAN after the UE
completes voice services on the GERAN.
When the CellDrxPara.DrxForMeasSwitch parameter is set to ON(On), the eNodeB
delivers the DRX and gap-assisted measurement configurations if the following conditions
are met. The UE uses the DRX measurement preferentially and makes more use of DRX
sleep time continuously to accelerate the measurement and decrease the delay.
 The UE cannot perform the gap-assisted measurement. In this case, the
AutoGapSwitch option of the ENODEBALGOSWITCH.HoModeSwitch
parameter is set to OFF(Off) or the interRAT-NeedForGaps option for the GSM
frequency of the UE capability is set to TRUE(True).
 The gap-assisted measurement is not configured for the UE.
 The UE supports DRX.
 The BlindHoSwitch option of the ENODEBALGOSWITCH.HoModeSwitch
parameter is set to OFF(Off).
After the DRX measurement is used, you need to set longer sleep time for measurements.
Therefore, the UE is easier to enter the sleep time, affecting the scheduling by decreasing the
cell throughput.
For details about how to configure measurement-specific DRX troubleshooting and related
parameters, see DRX and Signaling Control.
NOTE:
The following table describes the parameters that must be set in the
GLOBALPROCSWITCH MO to turn on the UE compatibility switch when UEs do not
support Ultra-Flash CSFB, resulting in UE compatibility problems.
The handover decision for CSFB to GERAN is the same as that for CSFB to UTRAN. For
details, see 3.8 Handover Decision.

support VoIP, a CSFB to an inter-RAT network is triggered.
CSFB from E-UTRAN to GERAN can be based on PS handover, CCO/NACC, redirection,
or flash redirection, as shown in Figure 4-1. This handover policy selection procedure is
based on the assumption that neighboring frequency and neighboring cell configurations are
proper.
During a CSFB based on blind PS handover, if the target cell with the highest blind handover
priority fails to prepare the handover, the eNodeB attempts another cell with the second
highest blind handover priority. The eNodeB can attempt a maximum of eight cells. If all
these cells fail in preparation, the eNodeB performs CSFB based on redirection.

Figure 4-1 E-UTRAN-to-GERAN handover policy selection procedure

The parameters mentioned in the preceding figure are described as follows:
 The timer length is specified by the CSFallBackHo.CsfbProtectionTimer
parameter. If the UE stays in the area covered by the eNodeB before the timer expires,
the eNodeB performs the CSFB based on the blind redirection,
o The eNodeB preferentially selects a system that the UE has not measured. For
example, if the UE has measured the UTRAN, the eNodeB preferentially
selects the GERAN for redirection.
o If there is not target frequency available for redirection, the eNodeB stops the
procedure.
 The BlindHoSwitch switch under the ENodeBAlgoSwitch.HoModeSwitch
parameter and the BlindHoSwitch switch under the
CELLHOPARACFG.HoModeSwitch parameter specify whether to enable blind
handover. The CSFB blind handover is triggered only when eNodeB- and cell-level
blind handover switches are enabled.
 The adaptive-blind-handover-based CSFB switch is controlled by the
CsfbAdaptiveBlindHoSwitch option of the ENodeBAlgoSwitch.HoAlgoSwitch
parameter.
 The CSFB policy switches are controlled by the options of the
ENodeBAlgoSwitch.HoModeSwitch parameter:
o The PS handover supporting capability is specified by GeranPsHoSwitch.
o The CCO supporting capability is specified by GeranCcoSwitch.
o The NACC supporting capability is specified by GeranNaccSwitch.
When CSFB to GERAN is based on CCO/NACC, the eNodeB obtains SI of
external cells from RNCs through the RIM procedure. For details about the
RIM procedure, see 4.8 RIM Procedure Between E-UTRAN and GERAN.
 The CSFB policy is specified by different parameters, depending on whether LOFD-
001089 CS Fallback Steering to GERAN is enabled.
If this feature is enabled:
o The CSFB policy for UEs in idle mode is specified by the
CSFallBackPolicyCfg.IdleModeCsfbHoPolicyCfg parameter.
o The CSFB policy for UEs in connected mode is specified by the
If this feature is not enabled, the CSFB policy is specified by the
CSFallBackPolicyCfg.CsfbHoPolicyCfg parameter, regardless of whether UEs are
in idle or connected mode.
4.8 RIM Procedure Between E-UTRAN and GERAN
The principles of the RIM procedure between E-UTRAN and GERAN are the same as those
for UTRAN described in 3.10 RIM Procedure Between E-UTRAN and UTRAN.
The RIM procedure between E-UTRAN and GERAN is enabled by default because there is
no switch for selecting a load information transfer channel.

If ENodeBAlgoSwitch.RimOnEcoSwitch is set to OFF(Off), the RIM procedure is
performed through the core network. If ENodeBAlgoSwitch.RimOnEcoSwitch is set to
ON(On), the RIM procedure is performed through the eCoordinator. The two RIM
procedures select information exchange modes in the same way.
Figure 4-2 shows the procedure of information exchange mode selection for the RIM
procedure.
 The preceding figure is described as follows: The RIM procedure between EUTRAN
and GERAN is controlled by the GERAN_RIM_SWITCH option of the
ENodeBAlgoSwitch.RimSwitch parameter.
If this option is selected, the eNodeB uses the RIM procedure in Multiple Report
mode to obtain the system information of external GERAN cells.
 If external GERAN cells do not support the Multiple Report mode, they do not notify
the eNodeB of any system information change after the initial request.
Figure 4-2 Information exchange mode selection for the RIM procedure

4.9 CSFB to GERAN
The combined EPS/IMSI attach procedure for CSFB to GERAN is the same as that for CSFB
to UTRAN. For details, see 3.11.1 Combined EPS/IMSI Attach Procedure.
During CSFB based on PS handover, the UE is transferred from the E-UTRAN to the
GERAN by performing a PS handover. It then initiates a CS service in the GERAN. If the
GERAN or UE does not support dual transfer mode (DTM, in which CS and PS services run
simultaneously), the ongoing PS services of the UE are suspended before a CS service is set
up.
Call procedure
Figure 4-3 shows the procedure for CSFB to GERAN based on PS handover for mobile-
originated calls.
Figure 4-3 CSFB to GERAN based on PS handover for mobile-originated calls
The procedure is described as follows:
1. The UE sends the MME a NAS message Extended service request to initiate a CS
service.

2. The MME instructs the eNodeB to initiate a CSFB procedure. If the MME supports
the LAI-related feature, the MME also delivers the LAI to the eNodeB.
3. The eNodeB determines whether to perform blind handover based on the UE
capabilities, parameters settings, and algorithm policies.
4. The eNodeB initiates the preparation phase for a PS handover. If the preparation is
successful, the eNodeB instructs the UE to perform a handover. If the GERAN or UE
does not support DTM, the ongoing PS services of the UE are suspended, and the
SGSN update bearers with the S-GW/P-GW.
NOTE:
5. After the handover, the UE may initiate a CS call establishment procedure with an
LAU or combined RAU/LAU procedure in the GERAN.
6. The follow-up procedures are performed for the PS handover. These procedures
include data forwarding, path switching, and RAU, which are performed together with
step 5.
CSFB Procedure for Mobile-Terminated Calls
CSFB to GERAN based on PS handover for mobile-originated calls.
4.9.3 CSFB Based on CCO/NACC
During CSFB based on CCO/NACC, the eNodeB receives a CS Fallback Indicator from the
MME, and then it sends a Mobility From EUTRA Command message to the UE over the Uu
interface. The message contains information about the operating frequency, ID, and system
information of a target GERAN cell. The UE searches for a target cell based on the
information it received, and then it performs initial access to the cell to initiate a CS service.
It then initiates a CS service in the GERAN.
Call procedure
Figure 4-4 shows the procedure for CSFB to GERAN based on CCO/NACC for mobile-
originated calls.

Figure 4-4 CSFB to GERAN based on CCO/NACC for mobile-originated calls
service.
LAI to the eNodeB.
eNodeB.
4. The eNodeB sends a Mobility From EUTRA Command message over the Uu
interface to indicate the operating frequency and ID of the target GERAN cell. If the
source cell has the system information of the target cell, the system information is
also carried in the message.
NOTE:
5. The UE initiates an LAU, a combined RAU/LAU, or both an RAU and an LAU in the
target cell.
6. If DTM is not supported by the UE or GERAN, the ongoing PS services of the UE are
suspended.
7. The UE initiates a CS call establishment procedure in the target GERAN cell.
8. The eNodeB initiates an S1-based UE context release procedure.

eRAN CS Fallback Feature Parameter Description

eRAN CS Fallback Feature Parameter Description

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Andere mochten auch

Andere mochten auch (17)

Ähnlich wie eRAN CS Fallback Feature Parameter Description

Ähnlich wie eRAN CS Fallback Feature Parameter Description (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

eRAN CS Fallback Feature Parameter Description