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Master’s Thesis, Mikko Nieminen Espoo, February 14th, 2006. TROUBLESHOOTING IN LIVE WCDMA NETWORKS. Supervisor: Professor Heikki Hämmäinen. Background to the Study. The number of live WCDMA networks is growing quickly.

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Master’s Thesis, Mikko Nieminen Espoo, February 14th, 2006

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Master s thesis mikko nieminen espoo february 14th 2006 l.jpg

Master’s Thesis, Mikko NieminenEspoo, February 14th, 2006

TROUBLESHOOTING IN LIVE WCDMA NETWORKS

Supervisor: Professor Heikki Hämmäinen


Background to the study l.jpg

Background to the Study

  • The number of live WCDMA networks is growing quickly.

  • The first commercial Third Generation Partnership Project (3GPP) compliant network, J-phone, was opened in December 2002.

  • By October of 2005, there were 80 live commercial WCDMA networks and the amount of subscribers was nearly 40 million. By that time, around 140 licenses had been awarded for WCDMA, the current WCDMA license holders having more than 500 million subscribers in their Second Generation (2G) networks.

  • Especially in Europe and Asia, WCDMA network deployment after successful field trials and service launches has entered a new critical stage: the phase of network optimisation and network troubleshooting.


Research problem l.jpg

Research Problem

  • As the amount of WCDMA subscribers quickly increases, operators and equipment vendors are facing big challenges in maintaining and troubleshooting their networks.

    • We may raise the question of how one can efficiently narrow down the root causes of the problems when there is a huge amount of subscribers and traffic in a live WCDMA network.

    • What are the principles of examination of the fault scenarios and narrowing down the problem investigation into logical manageable pieces?

    • Which are the tools and methods that are in practice used in WCDMA network troubleshooting today?

  • In order tackle these questions and challenges, this Thesis presents a Framework for KPI-triggered troubleshooting in live WCDMA networks.

  • The applicability of the Framework is demonstrated by applying it to a selection of real troubleshooting cases that have occurred in commercial WCDMA networks.


Scope of the study l.jpg

Scope of the Study

  • This study concentrates on the KPI-triggered problems in live WCDMA networks.

  • In general, the faults can be classified into three categories

    • Critical, which are emergency problems that require immediate actions,

    • Major (which we refer in this study as KPI-triggered problems)

    • Minor which do not affect the services of the network.

  • The viewpoint of is from the equipment vendor’s side, the main objective being to create guidelines for troubleshooting experts and technical support personnel of WCDMA network manufacturers in order to perform troubleshooting and narrow the problems down following a defined logic.

  • This Thesis mainly concentrates on WCDMA network troubleshooting from a Radio Access Network perspective. The reasoning behind this approach is that the UTRAN covers most of the WCDMA specific functionality and intelligence, and therefore brings the majority of the troubleshooting challenges also.


Research methods l.jpg

Research Methods

  • This Thesis is mainly based on the study of various technical specifications and interviews of WCDMA network troubleshooting experts.

  • The main literature sources are the 3GPP specifications of release 99, since the majority of the live WCDMA networks were based on 3GPP release 99 during the writing of this Thesis.

  • It can be noted that 3GPP release 4 networks are currently gaining foothold in the live WCDMA networks. However, there are only minor differences in the Radio Access functionality of the afore-mentioned two 3GPP specification releases.


Structure of the thesis l.jpg

Structure of the Thesis

  • Introduction to WCDMA Networks

  • UTRAN Protocols

  • Call Trace Analysis

  • Key Performance Indicators

  • Framework for KPI-Triggered Troubleshooting

  • Cases from Live WCDMA Networks


Wcdma network architecture l.jpg

WCDMA network architecture

PSTN

INTERNET

GMSC

GGSN

AuC

CORE

NETWORK

HLR

EIR

SGSN

MSC/VLR

UTRAN

RNC

RNC

Node B

Node B

Node B

Node B

cell

cell

cell

cell

cell

cell

cell

cell

UE

ME

USIM


Utran architecture l.jpg

UTRAN architecture

UTRAN

Core Network (CN)

Iu-CS

Node B

3G

MSC

RNC

Node B

Uu

Iub

Iur

Node B

SGSN

RNC

User Equipment

(UE)

Node B

Iu-PS


Umts bearer services l.jpg

Radio Access Bearer

Non-Access Stratum

Signalling connection

RRC

RRC connection

Iu connection

Access Stratum

Radio bearer service

Iu bearer service

: SAP

UE

RAN

CN

Uu

Iu

UMTS Bearer Services


Summary of protocols cs user plane l.jpg

Summary of Protocols (CS user plane)

Iub

Iu

Uu

CS

application and

coding

CS

application

and

coding

RLC

RLC

MAC

MAC

Iu-UP

protocol

Iu-UP

protocol

WCDMA

L1

WCDMA L1

FP

FP

AAL2

AAL2

AAL2

AAL2

ATM

ATM

ATM

ATM

PDH/SDH

PDH/SDH

PDH/SDH

PDH/SDH

UE

Node B

RNC

MSC


Summary of protocols ue control plane l.jpg

Summary of Protocols (UE control plane)

Iub

Iu

Uu

NAS

NAS

RRC

RRC

RANAP

RANAP

RLC

RLC

SCCP

SCCP

MAC

MAC

MTP3b

MTP3b

SSCF-NNI

SSCF-NNI

WCDMA L1

WCDMA L1

FP

FP

SSCOP

SSCOP

AAL2

AAL2

AAL5

AAL5

ATM

ATM

ATM

ATM

PDH/SDH

PDH/SDH

PDH/SDH

PDH/SDH

UE

Node B

RNC

CN


Overview of wcdma call setup l.jpg

Overview of WCDMA Call Setup

MT Call

MO Call

Paging

RRC

Connection

Establishment

Radio Access

Bearer

Establishment

User Plane

Data Flow


Slide13 l.jpg

RRC

RRC

RRC

RRC

RRC

RRC

D-NBAP

C-NBAP

C-NBAP

D-NBAP

C-NBAP

C-NBAP

ALCAP

ALCAP

ALCAP

ALCAP

RRC connection establishment (DCH)

UE

Node B

RNC

1. RRC CONNECTION REQUEST

2. Admission

Control

3. RADIO LINK SETUP REQUEST

4. Start RX

5. RADIO LINK SETUP ESPONSE

6. ESTABLISH REQUEST

7. ESTABLISH CONFIRM

8. UPLINK & DOWNLINK SYNC

FP

FP

9. Start TX

10. RRC CONNECTION SETUP

11. L1 SYNCH

12. RL RESTORE INDICATION

13. RRC CONNECTION SETUP COMPLETE


Protocol analysers l.jpg

Protocol Analysers


Rrc connection events and kpis l.jpg

Access phase

Active phase

Sum of RRC_CONN_ACC_COMP

RRC Establishment Complete Rate =

x 100 %

Sum of RRC_CONN_STP_ATT

RRC Connection Events and KPIs

UE

RNC

CN

RRC CONNECTION REQUEST

Event 1

Event 1

RRC_CONN_ATT_EST

Setup phase

incremented

RRC CONNECTION SETUP

Event 2

RRC_CONN_ATT_COMP

Event 2

incremented

Event 3

RRC_CONN_ACC_COMP

incremented

RRC CONNECTION SETUP COMPLETE

Event 3

Event 4

RRC_CONN_ACT_COMP

incremented

Event 4

IU RELEASE COMMAND

Sum of RRC_CONN_STP_COMP

RRC Setup Complete Rate =

x 100 %

Sum of RRC_CONN_STP_ATT

Sum of RRC_CONN_ACT_COMP

RRC Retainability Rate =

x 100 %

Sum of RRC_CONN_ACC_COMP


Rrc connection phases l.jpg

RRC connection Phases

Phase:

Setup

Access

Active

Access

Active

Setup

Complete

Complete

complete

Success

Access

Active

Release

Active

Failures

RRC Drop

Attempts

Access Failures

Setup Failures, Blocking


Other wcdma network kpis l.jpg

Other WCDMA network KPIs

Sum of RAB_STP_COMP

x 100 %

RAB Setup Complete Rate =

Sum of RAB_STP_ATT

Sum of RAB_ACC_COMP

x 100 %

RAB Establishment Complete Rate =

Sum of RAB_STP_ATT

Sum of RAB_ACT_COMP

RAB Retainability Rate =

x 100 %

Sum of RAB_ACC_COMP

Sum of RAB_ACC_COMP

CSSR =

x 100 %

Sum of RRC_CONN_STP_ATT

Sum of RAB_ACT_COMP

CCSR =

x 100 %

Sum of RRC_CONN_STP_ATT


Fault classification l.jpg

Fault Classification


Framework for kpi triggered troubleshooting l.jpg

Framework for KPI-Triggered Troubleshooting

  • Framework is designed for investigating and soelving B-MAJOR level i.e. “KPI-triggered” faults

  • Before applying the Framework

    • The general alarm status of the network has been checked. No clear network alarms pointing to the root cause of the fault can be detected.

    • Traces from external interfaces of RNC have been taken with a protocol analyser in order to record the fault scenario. Also RNC internal trace has been taken when the fault took place.

    • The basic fault scenario has been analysed and clarified.


Slide20 l.jpg

P

C

A

H

G

I

D

B

Q

F

R

O

N

M

E

L

K

J

Is the problem new in the operator network?

No

Yes

  • Perform simulation of the fault

  • in test bed.

  • Does the fault still occur?

New SW, HW, parameters, UE

model or feature introduced?

No

Yes

No

Yes

Is the fault operator

specific?

Perform simulation of the fault

with reference conditions.

Does the fault still occur?

Yes

No

Yes

No

  • Has average network load increased

  • significantly and/or does the

  • problem occur at a specific time of day?

  • Analyse and

  • investigate the

  • differences between

  • the working and faulty

  • conditions.

Yes

No

Use RNC Performance Tester to generate load

in test bed and perform analysis.

Analyse the traces. Investigate fault scope.

CN

specific

RNC

specific

Node B

specific

Transmission

specific

Service

specific

Country

specific

UE

specific

  • Analyse network element and interface specific alarms, parameters, capacity, logs

  • and traces. Take specific actions depending on problem scope

  • (refer to detailed Framework notes).

  • In case of MVI environment, check IOT results and contact foreign vendor.

  • Investigate own vendor’s default parameters and compare implementation

  • againts 3GPP specifications.

  • Compare own default parameters with other default parameters of other vendors.

  • Execute air interface protocol analysis and drive tests.


Case increased amr call drop rate l.jpg

Case: Increased AMR call drop rate

  • A decrease in RAB Retainability Rate KPI for AMR telephony service was experienced during the last three months in an operator network.

  • The decrease was around 2% on each RNC compared to the time when the network was performing well. Actions that had already been taken with no positive effect:

    • Soft reset for all Node Bs and for all RNCs

    • Hard reset and re-commissioning of Node Bs

    • Alarms checked and no major alarms found


Slide22 l.jpg

A

C

G

E

Case: Increased AMR call drop rate

Is the problem new in the operator network?

I.

Yes

New SW, HW, parameters, UE

model or feature introduced?

II.

Yes

Perform simulation of the fault

in reference conditions.

Does the fault still occur?

III.

No

  • Analyse and

  • investigate the

  • differences between

  • the working and faulty

  • conditions.

IV.


Case increased amr call drop rate23 l.jpg

Case: Increased AMR call drop rate

  • Solution

    • The short term solution was that the parameter for planned maximum downlink transmission power of all the Node Bs in the operator network was changed to the default value of 34 dBm. In this way, the problem disappeared in the operator network.

    • The long term solution was to implement a fix of the bug into the next software release of the Node B.


Results l.jpg

Results

  • As a result of thorough research conducted for this Thesis, a Framework for KPI-triggered troubleshooting for live WCDMA networks was developed.

  • The Framework is mainly targeted for WCDMA network equipment vendors, to help them in solving major service affecting faults occurring in the live WCDMA networks of today.

  • Troubleshooting cases from live WCDMA networks were solved using the Framework developed, in order to verify the results and test the applicability and practicality of the Framework.


Assessment of the results l.jpg

Assessment of the results

  • The applicability and relevance of the troubleshooting Framework was tested against three different fault cases from live WCDMA networks.

  • The results were fairly promising since all the cases were successfully solved by utilising the Framework. The Framework was found to be quite practical and suitable for solving KPI-triggered problems in live WCDMA networks.

  • However, it must be taken into account that the Framework was tested with a limited number of cases, because of time and resource limitations. If more extensive testing and verification with a large number of cases would be applied, there is a possibility that optimisations and improvements to the Framework could be done.

  • Still, the basic logic of the Framework was proven with reasonable relevance. The results presented in this study can be easily tested in the future against a number of cases in order to verify the results with more extensive statistical reliability.


Exploitation of the results l.jpg

Exploitation of the results

  • The results of this study will be used as source material in the development of UTRAN troubleshooting competence development and advanced learning solution creation, targeted for troubleshooting experts and customer support engineers of one of the leading WCDMA network equipment vendors.

  • Also, the results of the Thesis will be used as an input in creation of customer documentation for UTRAN troubleshooting.

  • There is also an intention to further test the relevance and reliability of the results of this Thesis by applying it in the 24/7 RAN technical support operator service of the equipment vendor in question.


Future research l.jpg

Future Research

  • The significance of Performance Indicator based troubleshooting is increasing continuously in live WCDMA networks.

  • Once the PI and KPI specifications become more mature, more extensive study of the most relevant Performance Indicators used in WCDMA network troubleshooting is essential.

  • Also, there is a need to develop a Framework and logic for solving emergency problems in WCDMA networks.

  • As the growth of complexity of telecommunication networks increases, effective and efficient troubleshooting procedures are essential in order to manage the diversity of network technologies and the increasing quality requirements of the operators.


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