12.omd000301 gsm bsc trouble shooting issue2.2

7/27/2019 12.Omd000301 Gsm Bsc Trouble Shooting Issue2.2

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Huawei Confidential. All Rights Reserved

ISSUE 2.2

OMD000301 GSM BSC Trouble

Shooting



Internal Use

Objectives

Upon completion this course, you will be

able to: Know how to find faults in BSC

Know the common fault types

Grasp BSC fault disposal method

Know how to prevent BSC fault



Internal Use

Chapter 1 General Introduction

Chapter 2 Typical Cases

Chapter 3 BSC fault prevention



Internal Use


1.1 The ways to find faults

1.2 Common fault types

1.3 Basic disposal method



Internal Use


Alarm

Alarm console

Alarm box

OMC Shell

Traffic statistics

Drive test

Routine inspection

Customer complain



Internal Use

Locating fault equipment

If BSC has fault, usually it will affect some Sites or all of Sites

If BTS has fault, usually it just affect itself and the handover

successful rate of adjacent cells

During implementation or expansion, we can ―Interchange ‖ BTS

and judge the fault is because of BSC or BTS During maintenance, BSC faults don’t just affect one BTS


http://slidepdf.com/reader/full/12omd000301-gsm-bsc-trouble-shooting-issue22 7/82Internal Use








Operation and maintenance fault

OMC

Software Loading

BSC fault

Voice Link

Interconnection

Clock

BTS fault

Antenna & Feeder

transmission

RNO fault

Access Call drop

Congestion

Handover



Basic disposal method

Analyzing the Alarm Information

Alarm information come from the BSS alarm system, indicatedusually through sound, light, LED, and screen output, etc

It includes the detailed description of the abnormality, possible

causes and restoration suggestions, involves the hardware, link,

trunk and CPU loading ratio, etc.. It is a gist for the fault analysis

and location

Analyzing the Indicator Status Indicators can indicate the work status of circuit, link, optical path,

node and active/standby mode besides that of the corresponding

boards, usually used along with the alarm information generally

Analyzing Traffic Statistics Result

It is the most useful method for locating RNO fault.




Analyzing Apparatus & Meter Test Result

It reflects the fault nature with the visual and quantified data

Some common Apparatus & Meter

Signaling Analyzer, Test phone, Sitemaster , etc.

Tracing the Interface

It is applied in locating the failure causes of subscriber call connection

and inter-office signaling cooperation, etc. The trace result can help to find the cause of call failure directly and

locate the problem or to get the index for the subsequent analysis

Calling Test

It is a simple and quick method to judge whether the call processing

function and relative modules of the BSS are normal or not




Comparison/Interchange

Comparison: compare the faulted components or phenomenon with the

normal ones, and find the differences so as to find the problem It is usually used in the situation with simple fault range

Interchange: if the fault can not be located even after the standby

components are replaced, you can interchange the normal components

(such as board, optical fiber, etc.) with the potential faulted components,

and to compare the work status so as to specify the fault range or part

It is usually used in the situation with complicated fault range Switching/Resetting

It can not locate the fault cause accurately, and due to the randomness

of software running, the fault may be not able to recur, thus it is difficult

to know the real fault and solve the problem

This method is just an emergency method, applicable only in the

emergent situation




Contacting the Technical Support Engineers of Huawei

Before you call, please collect information as follow

Detailed name of the office or site

Linkman and telephone

Time of fault occurring

Software version of the office or site

Detailed description of fault

Alarm files, interface tracing files, traffic statistic result

Actions performed after the fault’s occurring and the

results

Problem level and the time you wish to solve the

problem



Summary

General Procedures of Troubleshooting

Finding fault－

>Judging Fault－

>locating fault－

>Removing Fault Basic Methods of Fault Judgment and Location

For simple fault

Analyzing the Alarm Information and the Indicator status

Comparison/Interchange

For complex fault Analyzing Traffic Statistics Result

Analyzing Apparatus & Meter Test Result

Tracing the Interface, Calling Test

For restoring system

Switching/Resetting




2.1 OMC fault

2.2 Link fault

2.3 Access fault

2.4 Communication fault



2.1 OMC fault

Working principle of OMC system: OMC shell When running OMC shell on WS, the system will try to connect

with OMC Server. OMC server will do authentication to judge

whether it’s a legal user and get the operation right. Then when

user selects the node in OMC shell, system will get configuration

information of this node from OMC Server and realizeconnection with BAM

WS OMC Server BAM Host



2.1 OMC fault

Working principle of OMC system: OMC LocalWS When running OMC LocalWS on WS, the system will ask

for the IP address of the BAM. After system get the

configuration information of the BAM, it will connect directly

with BAM

WS BAM Host



2.1 OMC fault

Fault 1: OMC Shell can’t connect with OMC Server

Fault 2: OMC Server can’t connect with BAM Fault 3: BAM can’t connect with host



2.1 OMC fault 1

Description

After start OMC Shell, it can not pop up the window of log-in. After

a while, it will show ―communication with OMC Server timeout‖ in

status bar.

Process of disposal

Step1: check hardware connection between WS and OMC Server

Step2: Use command ―ping (OMC Server IP address)‖

If system feed back: request time out, please check relative

equipment such as HUB, Ethernet cable, network adaptor

If system feed back: reply from (IP address of OMC server),

then go to next step



2.1 OMC fault1 1

Process of disposal

Step3: check initial file of OMC system (OMC.ini) in WS

There are three relative configuration parameters

– [WS CommDrv]

Switch IP= OMC Server IP address

– [Stat Report]SvrIP= OMC Server IP address

– [WarnDB]

SvrIP= OMC Server IP address

These three parameters must equal to IP address of

OMC Server – If not equal, modify them and restart OMC Shell

– If equal, go to next step



Internal Use

2.1 OMC fault 1

Process of disposal

Step4: check processes in OMC server In OMC Server, there are 8 relative processes, and only all of

them have already startup normally, then the OMC Server

can realize its functions. If some processes don’t startup

normally, it need startup them manually

These 8 relative processes are

– Timesvrd Newswitchsvr

– Newcommdriver Newlogmanager

– Alarmbam Sumserver

– Mssvr newserverd

Check status of processes – ps –ef|grep omc (check the first 7 processes startup

normally or not)

– ps –ef|grep newserverd (check the last one process

startup or not)



Internal Use

2.1 OMC fault 1

Process of disposal Step5: check Sybase database in OMC server

Check status of database

– su – sybase (switch to sybase user)

– Showserver (check the database has already

startup or not)

If the database don’t startup normally, it need to startup

it manually

– md /etc/rc2.d(switch over to the directory of

database auto-startup file S98sybserver)

– su – (switch to super user) – ./s98sybserver start (execute startup database

manually)



Internal Use

2.1 OMC fault 2

Description

In OMC Shell, there is a cross on the relative BSC node



Internal Use

2.1 OMC fault 2

Process of disposal Step1: check hardware connection between OMC server and

BAM

Step2: Use command ―ping (OMC Server IP address)‖

If system feed back: request time out, please check relative

equipment such as HUB, Ethernet cable, network adaptor If system feed back: reply from (IP address of OMC server),

then go to next step

Step3: check configuration information of corresponding BSC

node

In the feature of BSC node, there is one field for IP address of BAM

– If it’s wrong, then modify, this fault will be recover

– If it’s right, then go to next step



Internal Use

2.1 OMC fault 2

Process of disposal:

Step4: check initial file of BAM (bam.ini) in BAM

There is only one relative configuration parameter

– [NetWork]

ServerAddress = OMC Server IP address

This parameter must equal to IP address of OMC

Server

– If not equal, modify it and restart BAM software

Step5: check processes in OMC server

If some processes don’t startup normally, it need startup

them manually

Step6: check Sybase database in OMC server

If the database don’t startup normally, it need to startup

it manually



Internal Use

2.1 OMC fault 3

Description of fault:

The first red indicator on BAM task bar is on and displays"Communication between BSC and BAM interrupted―

BAM keeps beeping and the boards cannot be loaded

the corresponding BSC node on OMC SHELL displays a red

slant line, and operations at the maintenance console can not

be performed



Internal Use

2.1 OMC fault 3

Process of disposal: Communication channel between BAM and BSC is as follows

AM

– BAM-MCP-Loading Cable-MCB-GMCC0-GMCC1-other

boards of AM/CM

BM – BAM-MCP-Loading Cable-MCB-GMCCM-GMCCS-

GSNT-GFBI-Optical Fiber-GOPT-GNET-GMC2-GMPU

Possible causes

Hardware: MCP, backboard, GMCC, GSNT, etc.

Cable: loading cable, optical fiber

Software version is incorrect



Internal Use


2.1 OMC fault

2.2 Link fault

2.3 Access fault




Internal Use

Signaling path

Antenna CDU 2.0TRX FPU

TMU3.0TRX

42BIEHW

E1

LAPDm

LAPD

NO.7

2.0

3.0 DBUS

32BIENETLAPDMPUHWHW

TTBIENETLPN7

HWHW

E3MTCSM£ M̈SM£ ©MSCE1E1E1

MS



Internal Use

Common faults

SS7 link fault Link interrupted

Link unstable

RSL link fault

OML link fault



Internal Use

2.2 Link fault

Fault 1: SS7 Signaling Link can’t establish

Fault 2: LAPD link disconnection Fault 3: Signaling Link between AM/CM and BM Cannot Be Located

2 2 i k f l 1



Internal Use

2.2 Link fault 1

Description Corresponding indicator lights of LPN7 is not on

Enter BSC Maintenance Console, SS7 Maintenance-Status

query, system feed back is not correct

SS7 link is established as follows

MPU<－－>LPN7<－－>GNET <－－> TTBIE <－－

>E3M

<－－>TCSM <－－>MSC

2 2 Li k f lt 1



Internal Use

2.2 Link fault 1

Process of disposal Step1: check transmission

Transmission between MSC and MSM

– View indicator of MSM(E11-E14), normal status

should be off

Transmission between MSM and E3M – View Indicator of MSM(E10), normal status should be

off

Transmission between E3M and TTBIE

– View indicator of TTBIE(LIU1-LIU6), normal status

should be off

2 2 Li k f lt 1



Internal Use

2.2 Link fault 1

Process of disposal Step2: Self-loop at MSM, and view the indicator of LPN7

If status of LPN7 indicator is 10~12 second flash on (flash

twice after every 10~12 seconds on), then you can judge

the fault isn’t in BSC, and is on the inter-connection

between BSC and MSC. So you need check accordanceof BSC and MSC SPC,TS which is used to transmit

signaling, SLC, network indication, and so on

If status of LPN7 indicator is still flash, then go to next

step

2 2 Li k f lt 1



Internal Use

2.2 Link fault 1

Process of disposal Step3: Self-loop at TTBIE, and view the indicator of LPN7

If status of LPN7 indicator is 10~12 second flash on

(flash twice after every 10~12 seconds on), then you

can judge the fault is between TTBIE and MSM

If status of LPN7 indicator is still flash, then you can judge the fault is in BM. Then you should check GMPU,

LPN7, GNET, TTBIE (DIP switches) and so on

2 2 Li k f lt 2



Internal Use

2.2 Link fault 2

Description Enter BSC maintenance console, Control-LAPD link

maintenance, system feed back is not ―multi-frame

establishment‖

There are two kinds of LAPD signaling

RSL: the channel of signaling message between TRXand BSC

OML: the operation and maintenance link between BSC

and BTS

LAPD link is established as follows

BTS<

－－

>BIE<－－

>GNET <－－

> GLAP <－－

>GMPU

2 2 Li k f lt 2



Internal Use

2.2 Link fault 2

Process of disposal Step1: check transmission

Transmission between BTS and BSC

– View indicator of BIE(LIU1-LIU6), normal status should

be off

Step2: check data configurationRelative data tables include

– [site description]

– [TRX description]

– [LAPD signaling link table]

– [LAPD semi-fixed connection table]

Common Data error

– 900M? 1800M?

2 2 Li k f lt 3



Internal Use

2.2 Link fault 3

Description In BSC maintenance console, device control can’t show the

information of BM

In BSC maintenance console, BM module’s state is inactive

Inter-module signaling is established as following:GMCCS <－－> GSNT <－－> GFBI <－－> GOPT <－－>

GNET

<－－> GMC2 <－－> GMPU

2 2 Li k f lt 3



Internal Use

2.2 Link fault 3

Process of disposal Step1: check the connection between GFBI and GOPT

View the indicator of GFBI and GOPT, the normal status

should be off

Step2 check the corresponding signaling between GFBI and

GOPTView the indicator of GMC2 (F0), normal status should be

on

Summary



Internal Use

Summary

Judging link faults according to signaling path

For No.7 link fault, self-loop test is very useful

No. Possible causes Remarks

1 Transmission trouble

Interrupted transmission may cause link interruption.

Intermittent transmission, bit error and bad trunk cable connection may cause

higher link error rate and more messages retransmissions between BSC and

MSC. This may result in frequent initial establishments, link congestion and

link unstableness.

2 Trunk board (TTBIE, E3M,

MSM) troubleThis may cause link interruption, link unstableness and link congestion.

3 Signaling link blocked

manually at the remote end

4 Data configuration unsuitable

When the MTP data SLC and DPC is not consistent with that at the peer end,

the link cannot pass the Layer-3 signaling link test after initial establishment.This may result in so many link establishments that the link becomes unstable



Internal Use


2.1 OMC fault

2.2 Link fault

2.3 Access fault


Common fault



Internal Use

Common fault

MS Cannot Find a Network MS Cannot Access a Network

MS Drops from the Network Frequently

MS Finds a Network but Cannot Call

Access fault



Internal Use

Access fault

Fault1: MS is Difficult to Access a Network Fault2: MSC Cell Data Result in MS Access Network Difficultly

Fault3: CGI Result in MS Drops from Network

Access fault 1



Internal Use

Description

MS could not access a network though MS is near to the BTS B,which could be seen by the subscriber

Process of disposal

Performed drive test over the BTS B in the positions where the

BTS could be seen. The MS receive signal level was high and

ranged between -80~-90dBm when it was in the positions lower

than the BTS and low when it was in the positions about 500m

vertically higher than the BTS. It was also found that the MS

could not access a network when it was on the roadside nearer

to the mountain

Access fault 1

Access fault 1



Internal Use

Process of disposal

BTS B was an omni BTS and its main lobe was in the planeparallel to the ground; therefore, its upward-radiated power was

very low. Since the MS antenna was not very far from the ground,

its receive signal might suffer from much attenuation from the

ground. That was the reason why MS in the high position

(especially on the roadside nearer to the mountain) could not

access a network though the subscriber could see the BTS This was caused by the characteristics of radio wave propagation.

It had nothing to do with the BTS performance. We can increase

the height of the antenna to improve this fault

Access fault 1

Access fault 2



Internal Use

Description

There was a BTS A. MS under it could receive signal very welland make calls; however, later the MS displayed "Network

failure" or "No networks". The MS became normal when it was

powered off and then on. However, later the trouble appears

again

Access fault 2

Access fault 2



Internal Use

Analysis For a trouble that sometimes occurs and sometimes does not,

the most probable problem is because of transmission failure.

That BTS used microwave for transmission; therefore, it should

be checked whether the BER was too high

The BTS clock accuracy should also be considered. That BTS

was in the second hierarchy; therefore, it should be checkedwhether the TMU was OK

The problem also may be in periodic location updating failure,

that may be caused by data configuration error

Access fault 2

Access fault 2



Internal Use

Process of disposal Via test, the possibility of transmission failure was excluded at

first

checked the TMU clock status and found it was normal

It was noticed that there were two sites B and C near the BTS A,

and they were in the same location area as A Used a test MS to scan all frequencies and found that the MS

could receive signals from B and C, access a network and make

calls. Later it detected stronger signals (from A). Then it

performed cell reselection and selected the cell under A.

However, its periodic location updating was rejected by MSC.

Data in BSC and MSC might be erroneous

Access fault 2

Access fault 2



Internal Use

Process of disposal Checked the MSC data and found that the CGI of the cell under

A had not been defined. In this case, periodic location updating

initiated in the cell under A would be rejected by MSC, because

the CGI could not be found. It was no wonder that MS dropped

from the network

Added the CGI of the cell under A to the MSC data configuration.

The trouble disappeared

Access fault 2

Access fault 3



Internal Use

Description There was a BTS. MS under it could not normally access a

network. The MS sometimes could receive signals and

sometimes could not even when it was near to the BTS. It

became normal when it was powered off and then on

Access fault 3

Access fault 3



Internal Use

Process of disposal

The temperature in the equipment room reached 40°C and the

air conditioner could not work normally, the engineer doubted it

was the high temperature that caused the BTS trouble. However,

after correction, the trouble was not removed yet

Replaced the BTS TRX and then performed a test. However, the

trouble still existed. The possibility of TRX failure was excluded Viewed the MSC Location Area & Cell Table and found that the

GCI settings of the three cells at MSC were identical while

inconsistent with the corresponding CGI settings at BSC.

Modifing the GCI in MSC. The trouble disappeared

Access fault 3

Summary



Internal Use

Summary

MS Cannot Find a Network Mainly because of signal faintly, or the MS trouble

MS Cannot Access a Network

Mainly because of signal faintly, or CGI data error

MS Drops from the Network Frequently

Mainly because of signal faintly, interference, or unreasonable LAconfiguration

MS Finds a Network but Cannot Call

Mainly because of circuit data error



Internal Use


2.1 OMC fault

2.2 Link fault

2.3 Access fault


Summary



Internal Use

Summary

Summary

Send

short message

How to judge “MS Cannot Access a Network”

or “MS Finds a Network but Cannot Call” ???

Voice path



Internal Use

Voice path

E3M E3

CTN

FBIFBI

OPT OP

NET

32BI E

TCSM TCS

AM/CM

BM

Processing of Voice Trouble



Internal Use


Analysis: reducing the range of trouble gradually

Judge whether it occurs inside MSC or only out of MSC

Only the path via which the call between two MSs (not

including prepaid MS) in a MSC goes can be ensured to be

in the MSC

For a fault out of MSC, check relevant outgoing equipment

and data. If correct, it shall be a fault of outgoing equipment

For a fault inside MSC, it can be located as followStep1: Judge whether the fault occurs to one site or several

sites

Step2: If the fault only occurs to one site, perform dial-and-

test on all carriers of the site to check whether a time slot, a

frequency or the whole site has such problem

– If it is a frequency fault, it may be caused by

interference

– If it is a site fault, check the transmission path from this

site to GNET (including boards, lines, trunk

transmission equipment etc.)




Internal Use


Analysis: reducing the range of trouble gradually

Step3: If the fault occurs to several sites, check how these

sites are distributed as per data configuration and see

whether they share the same transmission path, the same

BIE, the same BM, the same SM or the same MSC.

– If a special transmission path gets faulty, check the

corresponding transmission equipment, cables andoptical fibers

– If the faulty sites share the same BIE, check the BIE

and HW between BIE and GNET

– If the fault occurs to a BM, check the boards and

cables between GNET and GCTN

– If the fault occurs in the total BSC, check the boards

and cables between GCTN and MSC, especially FTC

and its DIP switch

Procedures to locate fault



Internal Use

Use two test MSs and activate the functions ―Call Holding‖ and ―Call

Waiting‖ for them. Lock their frequencies to a BTS and record the

software version of the BTS. Perform the dial-and-test at night and

enable user interface tracking of MSC to trace the A interface

message. When fault occurs, don’t hook on and execute the

following operations

Step1: Record the CIC of the calling and the called parties as

per the tracked A interface message, record the correspondingfrequency and channel No. according to the message displayed

on the two test MSs. Check whether the recorded CIC and the

corresponding time slots are on a FTC and a TRX respectively





Internal Use

Step2: If the functions Call Holding and Call Waiting are

activated for the two test MSs, this step shall be executed,

otherwise go to the next step

When MS A fails to communicate with MS B, use MS C to

originate a call to the faulty MS (assuming it is MS A). MS A

accepts the new call, and at this time the original call is held.

Since the resource used by MS A didn’t change at all duringthe two calls, if fault still exists during the second

conversation, MS A might be faulty (you may use MS C to

originate a call to MS B for confirmation). Contrarily, if the

trouble disappears during the second conversation, it could

be concluded that MS B might be faulty





Internal Use

Step3: Hand over GCTN of BSC during conversation. If fault

remains, proceed the following operations. If it disappears, the

GCTN may be faulty, and switch over it back to check whether

fault still exists

Step4: According to the CIC recorded in the A interface

message find the corresponding BSC module No. in ―trunk

circuit table‖ of the BSC data management console. Switch over

the GNET of the BSC module (if the two MSs correspond todifferent modules, the two relevant GNETs shall be switched

over). If the fault still exists, proceed the following operations; If

the trouble disappears, the GNET of BSC or the HW connected

with the active GNET gets faulty. Switch over the board back to

check whether the fault still remains




Internal Use

Step5: find the BIE group the BTS which be tested. Switch over

BIE board. If the fault remains, proceed the following operations;

if the trouble disappears, the trouble may be caused by BIE.

Switch over them back for further test

Step6: Use the test MS to implement forced handover. Hand

over the MS to the cell of another adjacent site and check

whether the fault disappears. If possible, inter-BSC switchover

test can be implemented




Internal Use

Fault 1: Voice abnormally (one way or silence)

Fault 2: Echo Fault 3: Voice quality badly (Voice Discontinuity, Noise)

2.4 fault 1: Voice abnormally (one way or silence)



Internal Use

y ( y )

Description One way (Single pass): during conversation only one subscriber

can hear the voices sent from the opposite, but the other can

hear nothing

Silence (No pass): both subscribers cannot hear each other

Analysis Voice process is established as following

MS — antenna system — TRX — TMU — (E1) —

BTS_DDF —Trunk transmission — BSC_DDF — (E1) —

BIE — (HW) — GNET — (HW) — OPT — (Optical fiber) —

GFBI — GCTN — E3M — (E1 or transmission equipment) —

M S M — F T C — M S M — M S C




Internal Use

Analysis

As per voice circuit procedure in the system, the two type troublesmay be caused by

Radio problem

– Radio environment, e.g., imbalance between

uplink/downlink levels resulting in voice of poor quality and

interference to one party BTS fault

– Hardware: Board (e.g., CDU, TRX, TMU etc.) fault, error of

the switching network table of TMU

– Software: Data configuration error. For instance, time slot

No. In [Radio Channel Configuration Table] are configured

incorrectly. Trunk mode No. in [Site BIE Trunk Mode

Description table] are inconsistent with those in [Site BIE

Configuration Table], which causes the situation that the

cascaded BTS cannot converse normally

y ( y )




Internal Use

Analysis

Abis interface fault

– Poor quality devices between BTS and BIE (includingthe trunk transmission equipment), connectors and

cables as well as bit error of transmission line may

cause voice of poor quality to one party

BSC fault

– Hardware: All boards and cables between BIE andGCTN (including the backboard)

– Software: Time slot and HW configuration of BIE

A interface fault

– Hardware

» Board fault: such as E3M, MSM, FTC, DT at MSCetc.

» Cable fault: such as crossover cable and crossed

pair of cables.

» Setting error of DIP switch: If DIP switches of FTC

are set incorrectly, it may cause one way or silence

– Software: CIC configuration




Internal Use

Analysis

MSC Sometimes a faulty MS may cause such troubles

– Receiver is fault

– The User adjust the volume to minimum

2.4 Fault 2: Echo



Internal Use

Description ECHO: when a digital MS originates a call to another digital MS

or a fixed-line phone, one subscriber can hear the voices from

itself

Voice loop-back: when a digital MS originates a call to another

digital MS or a fixed-line phone, one subscriber only can hear

the voices from itself while the other party can hear nothing

2.4 Fault 2: Echo



Internal Use

Analysis

Echo occurring in case of conversation between two MSs Such echo is a kind of acoustic echo. As the acoustic isolation

performance of some MSs cannot accord the requirement of

GSM protocol, the voices received by the receiver can be sent

to the microphone easily. Then these voices are sent to BTS

after decoding, and finally to the opposite MS. Such echo is

caused by the local MS and brought to the system, and finallyheard by the opposite MS

Acoustic echo has nothing to do with time slots of FTC, carrier

time slots of BTS and reloading of data but is related to MS

type

The following method can be used confirm the opposite MSgenerates acoustic echo

– Adjust the tone of the opposite MS and the local party can

feel the change of echo tone apparently

2.4 Fault 2: Echo



Internal Use

Analysis

Echo occurring in case of conversation between MS and telephone Such echo is a kind of electrical echo. Impedance mismatch of

the hybrid converter at PSTN causes the situation that the

transmitted signal is coupled to the receiving line, thus echoes

occur at the 4-wire end

Voice loop-back

If an intra-office call is looped back, usually it results from

hardware loop-back owing to wrong connection of A interface

trunk cable. If a outgoing call is looped back, it may be caused

by hardware loop-back occurring to the outgoing trunk

If GNET or GCTN of BSC or MSC gets faulty, time slot

switching error even loop-back may be caused

2.4 Fault 2: Echo



Internal Use

Process of disposal Echo occurring in case of conversation between two MSs

Acoustic echo is related to the voice propagation

environment in which the MS is located (e.g., background

noise, surrounding barrier, space size and climate etc.).

Therefore, echoes don’t always occur to the MS that may

generate echoes

2.4 Fault 2: Echo



Internal Use

Process of disposal Echo occurring in case of conversation between MS and fixed-

line phone

Such kind of echo is called acoustic echo, which may result

from lack of Echo Cancellor (EC). Search the

corresponding route data of the call to ensure the data is

correct. If correct, check whether the EC of the

corresponding mobile network equipment is configured

accurately according to the principle that EC is placed near

PSTN

2.4 Fault 2: Echo



Internal Use

Process of disposal

Voice loop-back

when a intra-office call is looped back, block the A interface circuit and

make 32 circuits of only one trunk idle. Then perform dial-and-test on

each trunk of the A interface in sequence to check whether loop-back

exists. If it exists, check whether the corresponding trunk is connected

incorrectly

If only the outgoing call is looped back, perform dial-and-test on the

outgoing trunk to check whether loop-back exists. If it exists, check thecorresponding trunk is connected incorrectly

If all trunks are connected correctly after the above operations,

(however, it cannot be ensured that other offices corresponding to the

outgoing route are connected correctly), the trouble still remains. Try to

switch over GNET and GCTN at MSC

If the trouble still cannot be eliminated after the above operations andit is confirmed the outgoing call was looped back, check whether the

equipment and cables of other offices involved in the outgoing route

are in a normal state

2.4 Fault 3: bad quality (Voice Discontinuity, Noise)



Internal Use

Description Voice Discontinuity: Some instances of the conversation are lost,

or in worse condition, the entire conversation becomes difficult for

both parties

Noise: Bubbles, clicks and metallic sounds heard during a

conversation are called noises. In worse condition, only noisesinstead of voices can be heard




Internal Use

Analysis

Usually, voice discontinuity is because of Um interfacesignal faintly

Frequent handover: Since GSM system supports hard

handover. The handover from a source channel to the

destination channel can cause loss of Abis interface

downlink voice frames, so voice discontinuity resulting from

handover during conversation is inevitable. Frequent

handover occurring at cell edges or due to cell overlap may

cause discontinuity of conversation

Radio link interference: Interference may increase the BER

over the radio link and cause voice discontinuity. In addition,

the conversation may be of poor quality owing to signalfluctuation at cell edges




Internal Use

Analysis

Generally, noises are caused owing to bit error The fault of boards, connectors or cables on the path

Grounding error

Interference

Clock fault

Wrong setting of DIP switch




Internal Use

Analysis

Generally, noises are caused owing to bit error different error bits may cause different impacts

– The error bits on the line from A interface to MSC impact

on PCM sample, as a result, the noises generated are

relatively even because the noises and voices are in a

overlap relationship

– The error bits on the line from A interface to BSC impact

on the compressed voice signals which should be

decoded before being heard although these bits are also

well-proportioned. Consequently, the noises generated,

such as bubbles, sense of discontinuity and metallic

sounds – Slip frame or loss of frame caused by clock un-

synchronization is regular in time, therefore, noises

appear regularly during a conversation



Internal Use







Internal Use

nip the fault

in the bud




Internal Use

Hardware: installation specifications is important give mo re attent ion to E1 connector

Confirming the grounding and lightning protection Data Configuration

Data con f igurat ion speci f icat ion s is mo st impo rtant

Data configuration is the same as hardware configuration

Confirming the host data is the same as the data stored in

BAM and flash memory

Giving more attention to the A interface interconnection data




Internal Use

Checking Running status

Alarm console

If there are alarms, confirm the cause of every alarm BSC maintenance console

Checking BSC hardware status, CPU usage, clock status,

circuits of A interface and No.7 links. If it is abnormal, confirm

the causes

BSC traffic statistic consoleRegistering necessary tasks after expansion, upgrade, or

building a new BSC

– BSC measurement: 2 tasks

– Cell measurement: 5 tasks

– CPU usage measurement: 1 task Do calling test for every timeslot and every circuit



H i C fid ti l All Ri ht R d

12.omd000301 gsm bsc trouble shooting issue2.2

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