RAN13 Call Reestablishment Feature Delivery Summary Report

Call Reestablishment Feature Delivery

Summary Report

Huawei Technologies Co., Ltd.

All rights reserved

2013-12-17 HUAWEI Confidential Page I, Total 14

Call Reestablishment Feature Delivery Summary Report Internal

Contents

CONTENTS...........................................................................................................................................2

1 APPLICATION SCOPE.......................................................................................................................3

2 OVERVIEW OF CALL RESTABLISHEMENT FEATURE...........................................................3

2.1 Introduction.....................................................................................................................................3

2.2 Benefits............................................................................................................................................3

2.3 Description.......................................................................................................................................4

3 SOLUTION FOR ACTIVATING CALL REESTABLISHMENT FEATURE...............................7

3.1 Enable the switches that control the call reestablishment feature........................................7

3.2 Timer related parameters configuration for call reestablishment....................................................9

4 TRIAL ON LIVE NETWORK..........................................................................................................12

4.1 Script for Activating the Feature...................................................................................................12

4.2 Effect Evaluate...............................................................................................................................12

4.3 KPIs Monitoring............................................................................................................................13

5 CONCLUSION...................................................................................................................................14

6 Attachments.........................................................................................................................................14

2013-12-17 HUAWEI Confidential Page 2, Total 14


1 Application Scope

This document describes the feature Call Reestablishment feature for RAN13, which is

used to improve user experience by increasing the radio access bearer (RAB) setup success rate

and reducing the call drop rate.

The trial of this document was performed in XXX Operator for the sole purpose of delivering

PIP#1 feature project. Information contained in this document shall not be disclosed to any party

unless it is expressly authorized by Huawei.

The solution of this document is suit for RAN 13 or later version, the version of trial network

is,

Product Version

NodeB V200R013C00SPC521

RNC BSC6900

V900R013C00SPH558

2 Overview of Call Restablishement feature

2.1 Introduction

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

interruption or an access failure occurs in temporary coverage holes and in tunnels, elevators, and

buildings 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.

2.2 Benefits

The RAN detects a service interruption or an access failure before a UE does and stops

downlink power transmission to initiate call reestablishment. Call reestablishment improves user

experience by increasing the radio access bearer (RAB) setup success rate and reducing the call



drop rate

2.3 Description

Call re-establishment function is targeting drops saving and make further improvement on

user experience. According to 3GPP specification, an AM RLC or a failure radio link on UE side

can be re-established by CELL UPDATE procedure.

Figure 2-1 shows the call re-establishment signaling procedure.

Figure 2-1 Re-establish signaling procedure: call re-establish from NodeB 1 to NodeB 2

Below scenarios can trigger the call reestablishment.

1) RLC unrecoverable error

If the UE detects RLC unrecoverable error in an AM RLC entity with RBn (n>4), UE

initiate cell update using the cause "RLC unrecoverable error“ to re-establish a new RLC

entity for corresponding RBn.

If the CELL UPDATE message indicates that this error occurred on RB2, RB3, or RB4 in

the UE, the RNC directly releases the RRC connection of the UE.

2) Radio link failure

If the UE in CELL_DCH state detects that the criteria for radio link downlink failure are met,

the UE performs cell update with the cause "radio link failure” to re-establishes a new radio link.

For example,

UE detects consecutive N313 "out of sync" indications from L1 and starts T313.

T313 expires without consecutive N315 "in sync" indications from L1.

UE will re-select to a suitable cell and send CELL UPDATE to RNC indicates Radio

Link failure.

RRC will be re-established with cell update confirmed and radio link synchronization

restored



Figure 2-2. Example of Radio link failure

3) SRB on UE side

When Cell Update of UE SRB

Reset is received (e.g. from CELL_B), RNC

will re-establishes the RL and send “Cell Update Confirm ” to UE instead of sending “Iu Release

Req” to CN.

Figure 2-3. SRB reset on UE side

4) UL RL Failure

RNC receives UL radio

link failure indication from NodeB.

RNC starts timer “RlRstrTmr” and waits for “RL Restore Indication”.

If no “RL Restore Indication” and the timer expires, RNC will send “RADIO LINK

ACTIVATION COMMAND” with IE “deactivate” to NodeB instead of sending “Iu

Release Req” to CN.

NodeB will shut down when the UE DL transmits power.

UE will detect “DL Radio Link Failure” and trigger Call Re-establishment.



2.4 Script for Activating

the Feature

%%% AS_KUM_RNC01

SET URRCTRLSWITCH: RsvdPara1=RSVDBIT1_BIT22-0&RSVDBIT1_BIT23-

0&RSVDBIT1_BIT24-0&RSVDBIT1_BIT25-0&RSVDBIT1_BIT26-0&RSVDBIT1_BIT28-0;

SET UCONNMODETIMER: T302=D1400, N302=3, T313=3, N313=D50, N315=D20,

T314=D12, T315=D30;

MOD UCELL: CellId=xxxx, NInsyncInd=8, NOutsyncInd=8, TRlFailure=50;

SET UCACALGOSWITCH: RsvdPara2=15000, RsvdPara3=30000;

Figure 1. Procedure for active re-establishment

5) SRB reset on RNC

RNC receives “SRB Reset” from RLC layer, RNC will send “RADIO LINK

ACTIVATION COMMAND” with IE “deactivate” to NodeB instead of sending “Iu

Release Req” to CN.

NodeB will shut down when the UE DL transmits power.

UE will detect “DL Radio Link Failure” and trigger Call Re-establishment.



Figure 2-5. Improvement for

RNC SRB Reset

3 Solution for Activating

Call Reestablishment Feature

333Enable the switches that control the call reestablishment feature

Enable the switch to control use which synchronization timer to initiate RL establishment.

Run the SET URRCTRLSWITCH command to set the RSVDBIT1_BIT28.under Reserved

parameter 1 to 0

Enable the switches that control the call reestablishment feature for CS and PS services

Run the SET URRCTRLSWITCH command and set RSVDBIT1_BIT24 and

RSVDBIT1_BIT25 under Reserved parameter 1 to 0.

Enable the switches that control the call reestablishment feature triggered by RL failures

and SRB resets

Run the SET URRCTRLSWITCH command and set RSVDBIT1_BIT22 and

RSVDBIT1_BIT23 under Reserved parameter 1 to 0.

Enable the switch that to permit RNC reestablishes radio links for a UE if the UE reports

to the RNC cell update caused by SRB reset.

Run the SET URRCTRLSWITCH command and set RSVDBIT1_BIT26 under Reserved

parameter 1 to 0.



Detail meanings for these switches show as below,

Switch Meaning and impact

RSVDBIT1_BIT24

When the switch is turned on, for UEs using CS services, the RNC does not trigger cell update

with the cause value "RL Failure" reported by a UE, if the RNC detects interrupted downlink

transmission on SRB2, or if the associated NodeB reports to the RNC that all radio links for the

UE experience synchronization loss.

When the switch is turned off, for UEs using CS services, the RNC triggers cell update with the

cause value "RL Failure" reported by a UE and reestablishes radio links, if the RNC detects

interrupted downlink transmission on SRB2, or if the associated NodeB reports to the RNC that all

radio links for the UE experience synchronization loss.

RSVDBIT1_BIT25

When the switch is turned on, for UEs using PS services only, the RNC does not reestablish radio

links for a UE if the RNC detects interrupted downlink transmission on SRB2, or if the associated

NodeB reports to the RNC that all radio links for the UE experience synchronization loss.

When the switch is turned off, for UEs using PS services only, the RNC triggers cell update with

the cause value "RL Failure" reported by a UE and reestablishes radio link, if the RNC detects

interrupted downlink transmission on SRB2, or if the associated NodeB reports to the RNC that all

radio links for the UE experience synchronization loss.

RSVDBIT1_BIT22

When the switch is turned on, the RNC does not trigger cell update with the cause value "RL

Failure" if the RNC detects interrupted downlink transmission on SRB2.

When the switch is turned off, the RNC triggers cell update with the cause value "RL Failure" and

reestablishes radio links if the RNC detects interrupted downlink transmission on SRB2.

RSVDBIT1_BIT26

When the switch is turned on, the RNC does not reestablish radio links for a UE if the UE reports

to the RNC cell update caused by SRB reset.

When the switch is turned off, the RNC reestablishes radio links for a UE if the UE reports to the

RNC cell update caused by SRB reset.

RSVDBIT1_BIT23

When the switch is turned on, the RNC does not trigger cell update with the cause value "RL

Failure" reported by a UE if the associated NodeB reports to the RNC that all radio links for the

UE experience synchronization loss.

When the switch is turned off, the RNC triggers cell update with the cause value "RL Failure"

reported by a UE and reestablishes radio links, if the associated NodeB reports to the RNC that

all radio links for the UE experience synchronization loss.

RSVDBIT1_BIT28

When the switch is turned on, for UEs using CS services, if a NodeB reports to the RNC that all

radio links for a UE experience synchronization loss, the RNC starts the RL Restore timer whose

duration is specified by the RlRstrTmr parameter in the SET USTATETIMER command. After the

timer has expired, the RNC triggers cell update with the cause value "radio link failure" and

reestablishes radio links for the UE.

When the switch is turned off, for UEs using CS services, if a NodeB reports to the RNC that all

radio links for a UE experience synchronization loss, the RNC starts the RL Restore timer whose

duration is specified by the T313 parameter in the SET UCONNMODETIMER command. After the

timer has expired, the RNC triggers cell update with the cause value "radio link failure" and

reestablishes radio links for the UE.



3.2 Timer related parameters configuration for call reestablishment

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

T313 timer if the number of "out-sync" indications received consecutively from Layer 1 reaches

the value of the N313 parameter. The higher the value of the N313 parameter, the harder it will be

for the UE to detect an RL failure and the longer the UE stays on the verge of RL failure.

2) If the number of "in-sync" indications received consecutively from Layer 1 does not reach

the value of the N315 parameter before the T313 timer expires, the UE transmits the Cell Update

message with the cause value "Radio Link Failure" to the RNC for call reestablishment.

Meanwhile, the UE starts the T302 timer as well as the T314 timer for CS services or the T315

timer for PS services.

3) If the UE does not receive the Cell Update Confirm message from the RAN side after the

T302 timer expires, the UE retransmits the Cell Update message until the T314/T315 timer

expires: (The number of retransmissions is determined by the value of the N302 parameter.). 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.

Set these parameters appropriately so that UEs can quickly detect RL failures and then

perform call reestablishment procedure. Suggest configuring these parameters follow below

experience value.

Parameter Current ValueRecommend

Value

T302(ms) D2000 D1400

N302 3 3

T313(s) 3 3

N313 D50 D50

N315 D1 D20

T314(s) D0 D12

T315(s) D0 D30

4) The NodeB monitors uplink RL quality. If the number of "out-sync" indications received

by the NodeB reaches the value of the NOUTSYNCIND parameter, the NodeB starts the

TRlFailure timer. The detection process continues according to the situation:

If the number of "in-sync" indications received by the NodeB reaches the value of the

NINSYNCIND parameter before the TRlFailure timer expires, the NodeB stops and resets the

TRlFailure timer.

If the number of "in-sync" indications received by the NodeB does not reach the value of the

NINSYNCIND parameter before the TRlFailure timer expires, the NodeB considers that an RL

failure has occurred and identifies the RL set where the failure is located. (An RL set contains all

the RLs of a UE under a NodeB.)

The higher the value of the NOUTSYNCIND parameter, the harder it will be for RL failures

to be triggered. The higher the value of the NINSYNCIND parameter, the harder it will be for RLs

to be synchronized. If either parameter is set to a high value, RLs will be on the verge of RL



failure for a long time, and user experience will be poor for both CS and PS services.

Set NOUTSYNCIND to a value less than the default and NINSYNCIND to a value higher

than the default. This way, RL failures are easily triggered for call reestablishment to improve user

experience. Suggest configuring these parameters follow below experience value.


Value

NoutsyncInd 50 8

NInsyncInd 5 8

TRlFailure(0.1s) 50 50

5) If the NodeB does not detect uplink RL synchronization before the RlRstrTmr or T313

timer expires, the RNC sends to the NodeB the Radio Link Activation Command message

containing the information element (IE) "deactivate." Upon receiving the message, the NodeB

stops downlink power transmission for the UE's RL sets. Then, the RNC starts the timer for call

reestablishment (RsvdPara2 timer for CS services and RsvdPara3 timer for PS services).


Value

RsvdPara2(ms) 15000 15000

RsvdPara3(ms) 35000 30000

Meanings for these parameters show as below table,

Parameter Meaning and impact

T302(ms)

Meaning: T302 is started after the UE transmits the CELL UPDATE/URA UPDATE

message and stopped after the UE receives the CELL UPDATE CONFIRM/URA

UPDATE CONFIRM message. CELL UPDATE/URA UPDATE will be resent upon the

expiry of the timer if V302 less than or equal to N302; otherwise, the UE will enter idle

mode. Protocol default value is 4000.

N302Meaning: Maximum number of retransmissions of CELL UPDATE/URA UPDATE.Protocol

default value is 3.

T313(s)

Meaning: 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. It indicates Radio Link (RL) failure upon expiry. Protocol default value is 3.

N313Meaning: Maximum number of successive "out of sync" indications received from L1.

Protocol default value is 20.

N315Meaning: Maximum number of successive "in sync" indications received from L1 when

T313 is activated. Protocol default value is 1.

T314(s)

Meaning: T314 is started when the criteria for radio link failure are fulfilled and only radio

bearers (RBs) associated with T314 exist.T314 is stopped after the Cell Update

procedure has been completed. Protocol default value is 12.

In case of the RL failure when the UE is in CELL_DCH state, If the RL cannot be

successfully reconfigured by CELL UPDATE CONFIRM before the expiry of the

corresponding T314 (or T315), CELL UPDATE will be resent for RL reconfiguration (this

operation relates to T302 and N302). It is recommended that T314 be set to greater than



T302*N302. The smaller the value of T314 is, the higher the call drop rate of the

corresponding service is. When T314 expires and the UE is performing a CS service, or

T315 expires and the UE is performing a PS service,the RNC releases the RRC

connection.

T315(s)

Meaning: T315 is started when the criteria for radio link failure are fulfilled, and only the

radio bearer associated with T315 exists.T315 is stopped after the Cell Update procedure

has been completed. Protocol default value is 180.

In case of the RL failure when the UE is in CELL_DCH state, T315 (or T314) is started

and CELL UPDATE is sent. If the RL cannot be successfully reconfigured by CELL

UPDATE CONFIRM before the expiry of the corresponding T315 (or T314), CELL

UPDATE will be resent for RL reconfiguration (this operation relates to T302 and N302). It

is recommended that T315 be set to greater than T302*N302. The smaller the value of

T315 is, the higher the call drop rate of the corresponding service is. When T314 expires

and the UE is performing a CS service, or T315 expires and the UE is performing a PS

service,the RNC releases the RRC connection.

NoutsyncInd

Meaning: This parameter defines the times of successive in-sync indications required for

starting the radio link failure timer. When the radio link set is in the synchronized state,

the 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.When the timer

expires, the NodeB triggers the radio link failure process, and indicates which radio link

set is out-of-sync.

NInsyncInd

Meaning: This parameter defines the times of successive in-sync indications required for

the NodeB to trigger the radio link recovery process.The radio link set remains in the

initial state until it has received a certain number (the number is defined by NInsyncInd) of

successive in-sync indications from L1, and then the NodeB triggers the radio link

recovery process, which indicates that the radio link set has been synchronized. Once the

radio link recovery process is triggered, the radio link set is considered to be in the

synchronized state. In the radio link maintenance process, NInsyncInd is used together

with the successive out-of-sync indication counter.

TRlFailure(0.1s)

Meaning: Radio link failure timer duration. When the radio link set is in the synchronized

state, the 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. When the timer

expires, the NodeB triggers the radio link failure process, and indicates which radio link

set is out-of-sync.

RsvdPara2(ms) CS Traffic, timer for RNC Waiting for UE to select cell

RsvdPara3(ms) PS Traffic, timer for RNC Waiting for UE to select cell



4 Trial on live network

4.1 Effect Evaluate

Main KPIs and counters for monitoring the feature performance show as below,

KPIs & counters Expected Result

CS Call drop rate Decrease

PS DROP RATE( with PCH) Decrease

HSDPA Service Drop rate( with PCH) Decrease

HSUPA Service Drop rate( with PCH) Decrease

CS RAB setup success rate Similar

PS RAB setup success rate Similar

4.2 KPIs Monitoring

Implemented the feature in RNC AS_KUM_RNC01, we can see from below table and

pictures that the CS CDR decreased about 0.18%, PS CDR decreased about 0.3%, PS CDR with

PCH decreased about 0.04%, HSDPA CDR with PCH decreased about 0.03%, HSUPA CDR with

PCH decreased about 0.03%, CS and PS RAB SSR decreased because some cells were not

available on 09/06/2013,



Time RNC Integrity

CS RAB Setup

Success Ratio (RNC)(%

)

CS Call Drop

Ratio(RNC)(%)

PS RAB Setup

Success Ratio

(RNC)(%)

PS Call Drop

Ratio(RNC)(%)

PS Service

Drop Ratio

with PCH (RNC)(%)

HSDPA Service

Drop Ratio with

PCH(RNC

HSUPA Call Drop

Ratio with PCH (RNC)(%)

08/26/2013 AS_KUM_RNC01 100% 99.59 0.60 99.55 0.94 0.30 0.29 0.27

08/27/2013 AS_KUM_RNC01 100% 99.54 0.65 99.56 1.00 0.31 0.30 0.28

08/28/2013 AS_KUM_RNC01 100% 99.58 0.61 99.57 1.02 0.30 0.30 0.27

08/29/2013 AS_KUM_RNC01 100% 99.59 0.69 99.56 1.04 0.31 0.31 0.28

08/30/2013 AS_KUM_RNC01 100% 99.49 0.63 99.56 0.99 0.30 0.30 0.28

08/31/2013 AS_KUM_RNC01 100% 99.60 0.65 99.55 1.04 0.32 0.32 0.30

09/01/2013 AS_KUM_RNC01 100% 99.66 0.66 99.55 0.92 0.29 0.29 0.28

09/02/2013 AS_KUM_RNC01 100% 99.34 0.63 99.56 1.02 0.31 0.30 0.29

09/03/2013 AS_KUM_RNC01 100% 99.50 0.63 99.49 1.06 0.31 0.31 0.30

09/04/2013 AS_KUM_RNC01 100% 99.56 0.61 99.48 1.10 0.32 0.32 0.30

99.54 0.64 99.54 1.01 0.31 0.30 0.28

09/05/2013 AS_KUM_RNC01 99% 99.31 0.52 99.46 0.76 0.28 0.28 0.25

09/06/2013 AS_KUM_RNC01 99% 97.98 0.48 99.22 0.80 0.29 0.28 0.26

09/07/2013 AS_KUM_RNC01 100% 99.64 0.44 99.55 0.64 0.25 0.25 0.23

09/08/2013 AS_KUM_RNC01 100% 99.65 0.49 99.53 0.64 0.25 0.25 0.24

09/09/2013 AS_KUM_RNC01 100% 99.21 0.48 99.53 0.72 0.27 0.27 0.24

09/10/2013 AS_KUM_RNC01 100% 99.37 0.47 99.51 0.75 0.28 0.28 0.26

09/11/2013 AS_KUM_RNC01 100% 99.36 0.45 99.45 0.72 0.28 0.28 0.25

09/12/2013 AS_KUM_RNC01 100% 99.44 0.43 99.51 0.72 0.27 0.27 0.26

09/13/2013 AS_KUM_RNC01 99% 99.49 0.43 99.54 0.72 0.26 0.27 0.24

09/14/2013 AS_KUM_RNC01 100% 99.61 0.44 99.52 0.71 0.26 0.27 0.24

09/15/2013 AS_KUM_RNC01 100% 99.59 0.47 99.54 0.66 0.25 0.25 0.23

99.33 0.46 99.49 0.71 0.27 0.27 0.25

average before activating the feature

averageafter activating the feature



5 Conclusion

After implemented the feature in one RNC of xxx operator, the CS/PS /HSPA CDR all

decreased, and we have suggested the customer to implement the feature in whole network.

6 Attachments


Documents

RAN13 Call Reestablishment Feature Delivery Summary Report