Radio Link Re-Establishment

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Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

WCDMA Call Re-

Establishment

Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved. Page1

Contents

1. Call Re-Establishment Overview

2. Call Re-Establishment Causes

a) Downlink RL failure

b) Uplink RL failure

c) SRB Reset

d) UE SRB Reset

3. Related Configuration

4. Case Analysis


Call Re-Establishment Overview

Call reestablishment is a function by which radio links (RLs) are reestablished when a

service interruption or an access failure occurs due to bad RF environment. that cause

significant signal quality fluctuation.

Call reestablishment can be initiated by a UE or the RAN.

Call reestablishment initiated by a UE: The UE sends a call reestablishment request to the

network to restore services upon detecting a downlink RL failure or a signaling radio bearer

(SRB) reset.

Call reestablishment initiated by the RAN: The RAN informs the UE to start call reestablishment

upon detecting a service interruption or an access failure.

Benefits

Call reestablishment improves user experience by increasing the radio access bearer (RAB) setup

success rate and reducing the call drop rate.

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Contents





c) SRB Reset

d) UE SRB Reset


4. Case Analysis


Call Re-Establishment Causes

The possible causes of a service interruption or an access failure that may result

in call re-establishment are :

Downlink RL failure

Uplink RL failure

SRB reset

UE SRB reset

Before releasing RLs due to the preceding causes in those processes, the RAN

detects the service interruption or access failure and initiates call

reestablishment,..

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Contents





c) SRB Reset

d) UE SRB Reset


4. Case Analysis


Downlink RL failure Downlink RL Failure Detection

UE monitors downlink RL quality.

UE receives N313 number of "out-sync" indications

UE starts the T313 timer and didn’t receive N315 "in-sync" indications within it

(as if so UE will not send Cell Update message)

Downlink RL Failure Call Reestablishment Triggering

UE will enter in call reestablishment procedure

Downlink RL Failure Call Reestablishment Implementation

UE transmits the Cell Update message with cause value "Radio Link Failure" to

the RNC for call reestablishment.

Meanwhile, the UE starts T314 timer for CS services or the T315 timer for PS

services which is maximum allowed time for UE to try to send Cell Update

message

UE can resend Cell Update message if he didn’t have a reply from network

every T302 time for maximum N302 number of times

If faulty RLs are restored before T314/T315 expires, the call reestablishment is

successful. Interrupted services are restored or UE access succeeds.

If faulty RLs are not restored before T314/T315 expires, the call reestablishment

fails. And UE access fails.

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N313

T313

N315

Cell Update

Cell Update Confirm

Physical CH Reconfig CMP

CELL_B

100

T314+T302*N302

RL Setup Req

RL Setup Rsp

RL Del Req

RL Del Rsp

CELL_A


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c) SRB Reset

d) UE SRB Reset


4. Case Analysis


Uplink RL failure Uplink RL Failure Detection

NodeB monitors uplink RL quality.

NodeB receives NOUTSYNCIND number of "out-sync" indications

NodeB starts the TRlFailure timer

NodeB didn’t receive NINSYNCIND "in-sync" indications within

TRlFailure timer (as if so the NodeB stops and resets the timer)

RNC activates a synchronization timer

NodeB does not detect uplink RL synchronization before synchronization

timer expires

Uplink RL Failure Call Reestablishment Triggering

RNC sends to NodeB the Radio Link Activation Command message

containing IE "deactivate“

NodeB stops downlink power transmission for the UE's RL sets

RNC starts the timer for call reestablishment (RsvdPara2 timer for CS

services and RsvdPara3 timer for PS services)

If RNC receives Cell Update message from UE before previous timer

expires, the RNC stops the timer and initiates call reestablishment. (as if

received after, call drops or UE access fails)

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Uplink RL failure (Cont.) Uplink RL Failure Call Reestablishment

Implementation

After the NodeB stops downlink power transmission for a UE's RLs, UE

will receive N313 number of "out-sync" indications

UE starts the T313 timer and didn’t receive N315 "in-sync"

indications within it (as if so UE will not send Cell Update message)

UE transmits the Cell Update message with cause value "Radio Link

Failure" to the RNC for call reestablishment.

Meanwhile, the UE starts T314 timer for CS services or the T315

timer for PS services which is maximum allowed time for UE to try

to send Cell Update message

UE can resend Cell Update message if he didn’t have a reply from

network every T302 time for maximum N302 number of times

If faulty RLs are restored before T314/T315 expires, the call

reestablishment is successful. Interrupted services are restored or UE

access succeeds.

If faulty RLs are not restored before T314/T315 expires, the call

reestablishment fails. Services are released or UE access fails.

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c) SRB Reset

d) UE SRB Reset


4. Case Analysis


SRB Reset

SRB Reset Detection

AMRlcDiscardMode parameter is set to NO_DISCARD

RNC sends a signaling message in acknowledged mode (AM) to UE

RNC does not receive a response from the UE before the number of SRB RLC

PDU retransmissions reaches the value of the NoDiscardMaxDAT parameter.

RNC triggers an SRB reset and sends the Reset PDU message to the UE to

reestablish RLC entities on both sides

SRB Reset Call Reestablishment Triggering

Same as UL RL Failure

SRB Reset Call Reestablishment Implementation


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c) SRB Reset

d) UE SRB Reset


4. Case Analysis


UE SRB Overlap

UE SRB Detection

UE SRB occurred

UE SRB Call Reestablishment Triggering

RNC does not send the Radio Link Activation Command message containing the

"deactivate" IE to the NodeB. Therefore, the NodeB does not stop downlink power

transmission for the UE's RL sets.

Instead, the RNC initiates call reestablishment upon receiving the Cell Update message

from the UE.

UE SRB Call Reestablishment Implementation


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UE SRB RESET

Cell Update( UE SRB RESET)

Cell Update Confirm

Physical CH Reconfig CMP

CELL_B

100

T314+T302*N302

RL Setup Req

RL Setup Rsp

RL Del Req

RL Del Rsp

CELL_A

Iu Release Req


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c) SRB Reset

d) UE SRB Reset


4. Case Analysis


Related Configuration Call reestablishment is controlled by service switch, process switch, and cause switch

parameters. Enable the corresponding service switch before enabling a process switch or

a cause switch

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Parameter Name Sub-Parameter

Name

Huawei

Default value

Recommen

ded Value

Remark

Service

Switch

RSVDBIT1_BIT24 Disabled Enabled Switch that controls call reestablishment for CS services (CS+PS combined services is also

controlled by this switch)

RSVDBIT1_BIT25 Disabled Enabled Switch that controls call reestablishment for PS services

Cause

Switch

RSVDBIT1_BIT22 Disabled Enabled Switch that controls call reestablishment triggered by SRB resets

RSVDBIT1_BIT23 Disabled Enabled Switch that controls call reestablishment triggered by RL failures


Related Configuration (Cont.)

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Parameter Name Huawei Default

value

Recommended

Value

Remark

NOutsyncInd 50 8 Times of successive out-sync indications required for starting the radio link failure timer.

NInsyncInd 5 8 Times of successive in-sync indications required for the NodeB to trigger the radio link recovery process

TRlFailure 5sec 5sec NodeB starts the timer after it receives successive out-of-sync indications of the number defined by NOutsyncInd.

The NodeB shall stop and reset the timer after receiving successive in-sync indications of the number defined by

NInsyncInd.

RsvdPara1:RSVD

BIT1_BIT28 1 0 Switch that controls Synchronization Timer for CS reestablishment triggered, 1:RlRstrTmr,0:T313

RlRstrTmr 11000msec 11000msec A timer to RNC wait for radio link restoration indication in the radio link procedure.

RsvdPara2 0msec 15000msec CS Timer for Enhanced Call Reestablishment, start after RNC send the RL Active CMD , stop after RNC receives

cell update message.

RsvdPara3 0msec 30000msec PS Timer for Enhanced Call Reestablishment, , start after RNC send the RL Active CMD , stop after RNC receives

cell update message.

N313 50 20 Maximum number of successive "out of sync" indications received from L1

N315 1 1 Maximum number of successive "in sync" indications received from L1 when T313 is activated

T313 3sec 3sec T313 is started after the UE detects consecutive N313 "out of sync“ indications from L1. T313 is stopped after the

UE detects consecutive N315 "in sync" indications from L1

T314 0sec 12sec T314 is started when the criteria for CS radio link failure are fulfilled and only radio bearers associated with T314

exist.T314 is stopped after the Cell Update procedure has been completed. (must be greater than T302*N302)

T315 0sec 30sec T315 is started when the criteria for PS radio link failure are fulfilled, and only radio bearer associated with T315

exists.T315 is stopped after the Cell Update procedure has been completed (must be greater than T302*N302)

N302 3 3 Maximum number of retransmissions of CELL UPDATE/URA UPDATE

T302 2000msec 1400msec CELL UPDATE/URA UPDATE will be resent upon expiry of the timer if V302 less than or equal to N302


Related Configuration (Cont.)

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Parameter Name Huawei Default

value

Recommended

Value

Remark

HoAsuTmr 5000msec 10000msec A timer to RNC wait for the response to active set update in soft handover procedure.

HoCellUpdateRspTmr 5000msec 10000msec A timer to RNC wait for the response to the cell update confirm from UE in forward handover procedure.

HoPhychRecfgTmr 5000msec 10000msec A timer to RNC wait for the response to physical channel reconfiguration in hard handover procedure

RbSetupRspTmr 5000msec 10000msec A timer to RNC wait for the RB setup response from UE in the RB procedure.

RbRecfgRspTmr 5000msec 10000msec Timer used to wait for the RB reconfiguration response from UE in the RB procedure

RsvdPara1:RSVDBIT1_BI

T26

Disabled Enabled To enable to perform call reestablishment If the RNC receives the Cell Update message containing the

cause value "RLC Unrecoverable Error" from the UE


Contents





c) SRB Reset

d) UE SRB Reset


4. Case Analysis


Case Analysis (Overview)

This feature have been implemented and gave good results in

following Countries / Operators:

M1 in Singapore

3GIS in Switzerland

X operator in Spain

X operator in Norway

Turkcell in Turkey

DU in UAE

Etisalat in Egypt

Vodafone in Egypt

…

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Case Analysis (1)

From below two RNCs’ CS&PS CDR trend, after activating the Call Re-establishment we

could see that CDR has step improvement.

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Case Analysis (2)

From RNC analysis, found that most call drop happens due to RL Failure

So we activated Call Re-establishment which improved CDR Rate

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Row Labels Count of count

DropCall_CombinedService 1

DropCall_DueTo_BadCoverage 30

DropCall_DueTo_CNRelated 4

DropCall_DueTo_High_RTWP 28

DropCall_DueTo_IU_Related 4

DropCall_DueTo_IUR_Related 4

DropCall_DueTo_MISSING_NEIGHBOR 8

DropCall_DueTo_RadioResCong 5

DropCall_DueTo_RAN 3

Dropcall_Dueto_RL_Failure 82

DropCall_DueTo_Slow_SHO 23

DropCall_InterFreq/InerRat Related 2

DropCall_Pilot_Pollution 20


Case Analysis (3)

From below RNC PS CDR trend, after activating the Call Re-establishment we could see

that CDR has step improvement.

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Thank you www.huawei.com

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Radio Link Re-Establishment