Voice Services in LTE -CSFB Rev B

Voice Services in LTECS Fall Back Feature

HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

www.huawei.com

By: Sherjil Bari

CSFB Circuit-switched fallback CSFB relies on a temporary inter-system that switches between LTE and a

system where circuit-switched voice calls can be served, the solution is based

on the fact that LTE terminals register in the circuit-switched domain when

powered on and attaching to LTE, This is handled through an interaction

between the MME and the MSC server in the CS domain.

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

services by reuse of CS infrastructure when the UE is served by E-UTRAN. A

HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential Page 2

services by reuse of CS infrastructure when the UE is served by E-UTRAN. A

CS fallback enabled terminal, connected to E-UTRAN may use GERAN or

UTRAN to connect to the CS-domain. This function is only available in case E-

UTRAN coverage is overlapped by either GERAN coverage or UTRAN

coverage.

It can be assumed that operators initially deploying CSFB may over time

migrate towards the MMTel (IMS) + SRVCC solution.

CS fallback in EPS architecture


CS Call Request in E-UTRAN, Call in GERAN/UTRAN


CS Page in E-UTRAN, Call in GERAN/UTRAN


LTE -> UMTS/GERAN CSFB SETTINGS IN VDCLTE Parameter MML Command Recommended value Comments

HoAlgoSwitch MOD

ENODEBALGOSWI

TCH

UtranCsfbSwitch:

On

UtranCsfbSwitch: On Enable CSFB to Utran switch

HoAlgoSwitch GeranCsfbSwitch:

On

GeranCsfbSwitch: On Enable CSFB to Geran switch

HoModeSwitch BlindHoSwitch:On BlindHoSwitch:On Enable blind handover switch to do CSFB to Utran/GERAN

without measurement

InterRatHighestPri MOD

CSFALLBACKBLIN

DHOCFG

UTRAN UTRAN Indicates the high-priority system to be considered in

blind handovers for CS fallback.

It is UTRAN by default.

InterRatSecondPri GERAN GERAN Indicates the medium-priority system to be considered in


blind handovers for CS fallback.

CsfbHoUtranB1ThdR

scp

MOD

CSFALLBACKHO

-106 -106dBm RSCP threshold for event B1

CsfbHoUtranTimeToT

rig

40 40ms Time-to-trigger for event B1 that is used in CS fallback to UTRAN.

CsfbHoGeranB1Thd -103 -103dBm RSSI threshold for event B1 that is used in CS fallback to GERAN

CsfbHoGeranTimeTo

Trig

40 40ms Time-to-trigger for event B1 that is used in CS fallback to GERAN

(higher than Utran to do CSFB to

Utran first).

CS FB FEATURE

IMPROVEMENTS IN ERAN3.0


IMPROVEMENTS IN ERAN3.0

Low Latency - Flash CSFB (R9 Redirection

with SIB)RIM :RAN

Information

Management

SGSN

GSM/UMTS GSM/UMTS

CoreCore

M

ME

LTE CoreLTE Core

BSC/RNC eNodeB

RAN

information RAN information

requestRRCConnectionRele

ase(Frequency and

target cell system

information)

RRCConnectionRele

ase(Frequency and

target cell system

information)

CSFB to G/UCSFB to G/U Core Network Support

Both GSM/UMTS and LTE core network support

R9 RIM procedure

Terminal Support

SGSN MME


GSM/UMTS LTE

eNodeB saves UTRAN/GERAN

neighbor cell system information (RIM: MME&RNC)

eNodeB saves UTRAN/GERAN

neighbor cell system information (RIM: MME&RNC)

eNodeB receives command of CSFB

from MME

eNodeB receives command of CSFB

from MME

eNodeB selects Redirection to CSFB based on

capability and strategy

eNodeB selects Redirection to CSFB based on

capability and strategy

eNodeB fills out target frequency and related neighbor cell

information in RRCConnectionRelease messageU: 1 Freq, 16 Cell ID; G: 1 Freq Group, 32 Cell ID)

eNodeB fills out target frequency and related neighbor cell

information in RRCConnectionRelease messageU: 1 Freq, 16 Cell ID; G: 1 Freq Group, 32 Cell ID)

Terminal support R9 redirection with SIB

(System Info Block)

Latency Reduced

Saving 1s for UMTS compare with R8 CSFB

Saving 2s for GSM compare with R8 CSFB

TAI/LAI

(PLMN+L

AC)

MM

E

LTE CoreLTE Core

GSM/UMTS

TA1/LA1

CSFB to LA1

LAI based CSFB to

UMTS without LAU

LAI based CSFB to

UMTS without LAU

LAI based CSFB toLAI based CSFB to

CSFB to UMTS with LAU

CSFB

1~2s

2~3s

LA: Location Area

LAI: Location Area

Indicator

LAC: Location Area

Code

LAU: Location Area

Update

TAI: Tracking Area

Indicator

LAI Based CS Fallback further optimized

latency


1. Priority to select target GU cells with same LAC as

UE registered in GU network during CSFB.

2. Support National Roaming UE to select suitable

fallback RAT/Cell bases on LAI Indicator among

multi-PLMNs.

TA3/LA1GSM/UMTSLTE

TA2/LA2

Select same LA to

CSFB

LAI based CSFB to

GSM without LAU

LAI based CSFB to

GSM without LAU

CSFB to GSM with LAUCSFB to GSM with LAU

Latency

The optimized CSFB process of eNB can avoid unnecessary LAU and reduce the CSFB E2E

latency 1~3 second(s)

LAI Based CSFB:

THANK YOU


THANK YOU

Documents

Voice Services in LTE -CSFB Rev B