9 problem investigation methodology

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Company Confidential

1 2006 Nokia Problem Investigation Methodology.ppt / 2006-12--20 / JVi / MNi

PROBLEM INVESTIGATION METHODOLOGY


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Contents

Problem investigation steps

Searching for common and difference Framework for KPI triggered troubleshooting an example model


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Problem investigation steps

Understand what is the exact problem and when it appeared

Understand the scope of the problem

Get scenario/monitorings that show the problem

Search what is common for failures and what is different compared to

successful case

Make a conclusion and plan next step


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What is the problem when did the problem appear

What is the problem

Is this problem KPI issue Is this end-to-end problem

What kind of tools and logs are needed

What is the RRC or RAB phase: setup/access/active/release

When did the problem appear? It was there from the beginning

After software upgrade

It has increased little by little

After HW upgrade

Something else?


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Understand the scope of the problem

Is this problem:

Country specific problem? Customer specific problem?

Core specific problem?

One RAN specific problem?

One BTS/Cell specific problem?

RAB type specific problem? UE type specific problem?

Something else..


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Get monitorings that show the problem

If problem is end-to-end problem

Arrange drive test When the problem appears, stop monitorings

If problem is KPI issue

Collect ICSU monitorings when the problem is on

Search for problem cases

Search for similar successful cases


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Search common and difference

Search similar problems scenarios

What is common for the cases Search for scenarios, objects or affecting parameters

Example:

Typically the problem appears when Ue makes HHO

Typically related to one cell

Typically related to a call making Iur HO

Typically related to particular RAB type


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Search common and difference

Success Failures cases: 1, 2, 3 & 4

#1

#1

#1

#1

#1

#4#3

#3

#2

#2

#2

#2

#4

#4

#4

#4

Search

difference

Searchcommon


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Framework for KPI triggered troubleshooting onemodel

When a drop in a certain KPI is detected, the PIs of the KPI in question arefurther analysed, in order to find out the exact scenario where the fault takesplace.

Before applying the Framework presented in the following slides, these faultinvestigation steps should be performed and the following conditions should bemet.

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

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

The basic fault scenario has been analysed and clarified.

More information on this model can be found from Masters Thesis of Mikko

Nieminen: Troubleshooting in Live WCDMA Networks


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Yes

No

No

Use RNC Performance Tester to generate load

in test bed and perform analysis.

Has average network load increased

significantly and/or does the

problem occur at a specific time of day?

Is the problem new in the operator network?

No Yes

Yes

Analyse and

investigate the

differences between

the working and faulty

conditions.

NoYes

Yes

Perform simulation of the fault

in test bed.

Does the fault still occur?

No

Yes

No

New SW, HW, parameters, UE

model or feature introduced?

Is the fault operator

specific?

Analyse the traces. Investigate fault scope.

Perform simulation of the fault

with reference conditions.

Does the fault still occur?

A

B C

D

F

H

G

I

E


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Transmissionspecific

Node Bspecific

Servicespecific

RNCspecific

CNspecific

Countryspecific

UEspecific

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

Investigate own vendors 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.

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

and traces. Take specific actions depending on problem scope

(refer to detailed Framework notes).

J

Q

K L M N O

R

P

Analyse the traces. Investigate fault scope.I


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