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Chapter 2

2.0 Training Experiences

2.1 Radio Access Network

Having considered the radio network communication, to enhance the performance and

efficiency of the mobile

Environment, it has been evolving into 4 generations and furthers more. The evolution can be

named as follow

1G- Analog

2G- GSM (Global System for Mobile Communication)

2.5G- GPRS (General Packet Radio Access)

2.75- EDGE (Enhanced Data rates for GSM Evolution)

3G- UMTS (Universal Mobile Telecommunication System)

3.5G-HSDPA (High-Speed Downlink Packet Access)

3.75G- HSPA+ (High Speed Packet Access)

4G- LTE (Long Term Evolution)

1G -Analog

2G GSM 3G 4G

WCDMA OFDMA

TDMA/FDMA

2.5 GPRS 2.75 EDGE 3.5 HSDPA 3.75 HSPA

Figure 2.1: Radio network

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2.1.1. What Is Radio Access Network (RAN)

Keep an eye on to the mobile telecommunication system; Radio Access Network (RAN) is

key sector of the system, which implements radio access technology as the underlying

physical connection method for a radio based communication network. Conceptually, RAN

resides between mobile phone and connection with its core.

Types of Radio Access Network (RAN)

GSM Radio Access Network

EDGE packet service with GSM Radio Access Network

UMTS GSM Radio Access Network

LTE high speed and low latency Radio Access Network

GSM Radio Access Network

Having considered the GSM architecture, the circled area in the figure called as GRAN

which links the mobile station with Network Switching Subsystem (NSS) or core and MSC.

GRAN comprises with Mobile Station (MS), BTS and BSC.

Base Station Subsystem Network Switching Subsystem

Figure 2.2 :2G Architecture

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Mobile Station (MS)

Having considered the GSM network the initial point, mobile station (MS), which grants the

access for the mobile subscriber to connect GSM network through air interface, comprises

with Subscriber Identity Module (SIM). Being attached the International Mobile station

Equipment Identity (IMEI), Mobile Termination conducts several operations such as speech

encoding and decoding, radio transmission and handover, Error detection and correction,

signaling and access to the SIM.

Base Transceiver Station (BTS)

To communicate between Mobile Station and operator network, it composes several physical

components such as transceivers (TRX) which control transmission and reception of signals

to or from higher network singletons such as Base Station Controller (BSC), power amplifiers

which use to amplify signals through antennas, duplexers which use to separate transmitting

and receiving signals, combiners which use to combine several TRXs to send out from a

single antenna to reduce number of antennas, alarm extension system which uses to gather

status of units in the BTS and extends them to operation and maintenance (O&M) monitoring

stations, and antenna which is an external part of the BTS.

Dialog has been using Huawei and Ericsson BTSs.

Base Station Controller (BSC)

Having the ability to control several BTSs, BSC communicates with the higher level, MSC,

to keep up the information overflow which impacts the MSC efficiency. As key functions

BSC controls and manages the timeslot allocation implemented by the BTSs, handles inter

cell handovers within BSS area, perform basic switching functions, handles paging data, and

identifies the mobile stations within the cell and informs MSC/VLR.

Mobile Switching Center (MSC)

Having known as the centerpiece of Network Switching Subsystem (NSS), MSC acts as the

interface between radio part and fixed part of the GSM network. The difference between

fixed line switching center and MSC can be distinguished as the ability of handling mobility

of subscriber by storing and updating the location of mobile station in Visitor Location

Registry (VLR) and Home Location Registry (HLR). Being controlled several Base Station

Subsystems (BSS), MSC associates with switching functions such as routing SMS and voice

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calls, call setup and release. The A-interface is known as the interface between BSC and

MSC which is connected using fiber cables

Home Location Registry (HLR)

The database which stores permanent data about subscribers such as service profile, location

information, and activity status, it stores the information about the subscription whenever

customer buys a subscription in the form of SIM.

Visitor Location Registry (VLR)

Having integrated with MSC, VLR keeps information relating to the subscribers with in the

particular MSC and associates with few location areas. When mobile station registers in a

new location area, the subscriber‟s details are copied from HLR into the VLR for that area.

If the subscriber subsequently moves into a location area controlled by a different VLR, the

details are deleted from the old VLR and added to the new VLR. When a call setup is needed,

without accessing HLR, by using the local copy of subscriber details the efficiency is

acquired.

Authentication Centre (AUC)

The security related information such as copy of the secret key stored in each subscriber‟s

SIM card which uses for authentication and encryption of the radio channel are kept in the

database of AUC.

Core

The data sent from BSC is transmitted to core while voice is sent to MSC. Core has two main

parts GGSN (Gateway GPRS Support Node) where Control Plane (CP) data is sent and

SGSN (Serving GPRS support node) where User Plane (UP) data is sent. The transmission is

done through Gb interface.

EDGE with GSM Radio Access Network

Though GERAN is essentially the same as GRAN, it specifies the inclusion of EDGE packet

radio services.

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UMTS GSM Radio Access Network

Having regarded the 3G architecture, the circled area in the figure is known as the UTRAN

which comprises User Equipment (UE), Node B and Radio Network Controller (RNC). It

differs from the 2G network slightly such as the BTS is named as Node B, BSC is named as

RNC, Abis and interfaces are named as IUB and IU-CS interfaces respectively.

RNC

The Radio Network Controller (or RNC) is a governing element in the UMTS radio access

network (UTRAN) and is responsible for controlling the Node Bs that are connected to it.

The RNC carries out radio resource management, some of the mobility

management functions and is the point where encryption is done before user data is sent to

and from the mobile. The RNC connects to the Circuit Switched Core Network through

Media Gateway (MGW) and to the SGSN (Serving GPRS Support Node) in the Packet

Switched Core Network.

SGSN

The Serving GPRS Support Node (SGSN) is a main component of the GPRS network,

which handles all packet switched data within the network, e.g. the mobility management

and authentication of the users.

Figure 2.3 : 3G Architecture

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MGW

A media gateway is a translation device or service that converts media streams between

disparate telecommunications technologies (2G,3G)

LTE Radio Access Network

Functions of eNodeB

Cell control and MME pool support

Mobility control

Control and User Plane security

Shared Channel handling

Segmentation/Concatenation Measurements and reporting

Figure 2.4 : 4G Architecture

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Functions of MME (Mobility Management Entity) The MME is in charge of all the Control plane functions related to subscriber and session management.

Idle mode UE (User Equipment) tracking Process

Paging Process.

Bearer activation/deactivation process

Core Network (CN) node relocation at time of intra-LTE handover

Security key management

SGW

Serving Gateway is handling the user data transmission between eNodeB and PGW. It is

responsible to initiate the connection with PGW during the initial UE attachment process.

Core network structure

Figure 2.5: Core network structure

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2.1.2 Frequency Allocation for GSM

GSM 900

In order to the frequency allocation provided by TRCSL for GSM 900 communication 880 –

960 MHz frequency range, is granted for all operators in Sri Lanka. With 35 MHz guard

band, the total bandwidth is bisected to 2 parts for uplink and downlink. Dialog has

purchased two 7.5 MHz bands separately for uplink and downlink communication.

Figure 2.6: Frequency allocations for GSM 900

GSM 1800

In order to the frequency allocation provided by TRCSL for GSM 1800, which is known as

Digital Cellular System (DCS) communication 1710 – 1880 MHz frequency range, is granted

for all operators in Sri Lanka. With 20 MHz guard band, the total bandwidth is bisected to 2

parts for uplink and downlink. Dialog has purchased two 15 MHz bands separately for uplink

and downlink communication

As DCS operates in a higher frequency than GSM 900, the path loss is higher in DCS to lead

its smaller coverage area in comparison to GSM 900. Since the one sector comprises with

both DCS & GSM 900, GSM 900 signals travel longer than DCS. Therefore from the

network, it gives priority to select DCS when both DCS & GSM 900 receive to mobile

station, increasing the capacity in GSM for mobile stations which are out of DCS coverage

area.

Figure 2.7: Frequency allocations for GSM 1800

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Frequency hopping

According to interferences explained above we want use huge frequency channels to

overcome that problem. But according to limited radio frequency band we can‟t use that

much of channels. So frequency hopping is use to save limited available frequency band. In

that case,

The BCCH channel frequency is fixed.

Change other TRXs frequencies randomly. To do that they allocate two parameters

to each cell called HSN (Hopping Sequence Number) & MAIO (Mobile Allocation

Index Offset). If that two parameters are allocate correctly there is no available in

adjacent or Co channels between neighbor cells.

2.2 Introduction to BTS Operation Division

This division is responsible for maintenance of Base Transceiver Stations (BTS) all

around the country. For the purpose of accuracy and easiness, the country is divided

into regions and BTS maintenance and operations in those regions are conducting

separately in those regions. Alarms and faults of BTSs are informed to relevant

regions by NOC and then the team working in that region takes the necessary actions

to fix those faults and maintain.

During my training I had chances to visit sites for microwave link installments,

VLAN ID configurations, PAT (Preliminary Acceptance Test), Fault corrections, etc.

It is really interesting to see an installation of a microwave link. I also got the

opportunity at several times to climb up to the towers when I training period.

The main objective of this division is to implementation and maintains these network

paths properly. Failure of a main link may cause a number of sites to be down.

Therefore the fault handling and maintenance should be done in an effective manner

in Dialog Transmission division.

Main Functions of a BTS Operation Division

Maintenances – maintaining equipments in BTS cabinets, Antennas and Shelters

Connecting Generators – generators should be connected to important sites

(hubs, mux) which are without in mount generators

and stand by batteries when power failures happened.

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Connecting Stand by Batteries – connect batteries to sites.

Site Commissions – commissioning newly implemented sites and pass or reject

the PAT

Troubleshooting – the main function, replacing faulty equipments and

troubleshooting the faults when occurred.

2.2.1 GSM Antennas (Sector Antennas)

Figure 2.8 :Basic Structure of BTS site

Figure 2.9: Sector Antennas

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A sector antenna is a type of directional microwave antenna with a sector-

shaped radiation pattern. There are 3 types of antennas.

Single Band. (Only one band of 900MHz or 1800MHz)

Dual Band (Both 900MHz and 1800MHz bands)

Tri Band. (For 900MHz, 1800MHz and 2100MHz )

Single Band

Having been compatible with one frequency range, to transmit

2G, DCS and 3G signals we need to have separate antennas.

These antennas only have two RF cable ports in bottom side.

Dual Band

Since the dual band antennas are compatible with two

frequency ranges, instead of two single band antennas we can

use only one dual band antenna. These antennas have four RF

cable ports in bottom side for two frequency ranges which are

clearly indicated by using different colors to stop

misunderstanding.

Tri Band

Though tri band antennas are compatible with two frequency

ranges, in contrast to dual band antenna this type has four

ports, both DCS band and 3G band together with GSM band.

Due to that, one Tri band antenna can be used instead of three

single band antennas. These antennas have six RF cable ports

in bottom side.

Figure 2.10: Single Band antennas

Figure 2.11: Dual Band antennas

Figure 2.12: Tri band Antennas

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These antennas are used for transmit the 3 bands used in mobile communication- 900MHz,

1800MHz and 2100MHz frequencies. 900MHz is for long distance 2G coverage, 1800MHz

is for short distance 2G coverage and 2100MHz is for 3G coverage.

The angle of the antenna can be changed in two different methods.

Mechanical Tilt- In Mechanically changeable tilt, we can change angle with loosen or

tighten at the top of antenna. It has 18 optional angles.

Electrical Tilt- In electrically changeable tilt, antenna transmits waves in relevant

Angle itself. It has 10 optional angles.

It is required to keep antennas in proper angles and directions to reach more efficiency

by direct them towards populated areas, main roads etc.

2.2.2 Micro wave link

Microwave links is establish by placing radio antennas directed to each other called “Line of

Sight”. The antennas transmit in microwave range and separate bands are used to uplink

and downlink. They are Microwave Antenna & ODU (Out Door Unit) and IDU (Indoor

Door Unit) and Feeder Cable (Coaxial Cable)

Figure 2.13: Transmission Equipment‟s

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2.2.3 Outdoor Unit (ODU)

ODU is the intermediate unit between IF stage and RF stage. ODU receives IF stage

signals from the IDU. IF signals are up converted and feed in to the antenna through a

wave guide. Microwave frequencies are sub banded and spectrum is distributed

among operators. Up link and downlink of the link is maintained by two frequency

bands. The radio units are categorized as upper band unit and lower band unit in the

sub band. There may be placed more than one radio link in a tower. So it is a

convention that using either upper band or lower band radio unit in the same site

ODU used in dialog

Huawei

Ericsson

ZTE

2.2.4 Indoor Unit (IDU)

The IDU contains much of the intelligence of the system. Main functions of the IDU

include Providing the Data interface, Error correction, Modulation and Demodulation,

Alarm status monitoring and Site-to-site communications. An IDU located in an

equipment shelter to interface with the operator interface and is connected to a close

coupled ODU Antenna assembly on the tower by a single coaxial cable.

Figure 2.14: Huawei ODU

Figure 2.15: Huawei IDU

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Process of installing IDU

First power was switched off from the breakers

Then IDU power cable was connected to the breakers

Next IDU was installed in proper place

Installing the protection grounding cable

Other end of power cable was connected the IDU and then switched on the IDU

Finally configured the IDU

2.2.5Antenna Alignment

The purpose of the alignment of antennas is to ensure that maximum signal strength is

present at both ends of the link. This is achieved by aiming the signal from each antenna

directly at the center of the opposite antenna. Electromagnetic signals consist of lobes as

Shown below. During my training period I participated and have experience of antenna

Alignment project in Hambanthota.

.

During antenna alignment, changed the direction vertically or horizontally meanwhile, used a

multimeter to test the RSS at the receiving end. Then could see the voltage wave was

displayed in multimeter. The peak point of the voltage wave indicates the main lobe position

in the vertical or horizontal direction.

Figure 2.16: Lobes of the microwave signal

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Alignment Steps

First we have to remove the ODU protective cap of the RSSI (Received Signal

Strength Indication) interface.

Then the voltmeter should be connected to the BNC connector of the RSSI interface.

In the next step the antenna mount (horizontal angle) should be loosen.

Then the antenna is adjusted to the azimuth position for maximum BNC voltage.

To ensure that the voltage observed is the maximum, we have to pan the antenna

Finally. If there are no other values greater than the voltage observed the antenna is

not mistakenly aligned to a side-lobe and hence aligned in the correct manner.

Figure 2.18: Microwave Antenna Alignment

Figure 2.17 :Antenna alignment using voltmeter

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2.2.6 Operation and Maintenance Software

Transmission unit equipment‟s in all brands come with compatible software for operation and

maintenance. Dialog use this software .This software provides an interface for users to

configure units. One such software is „iManager U2000 Web LCT‟ from Huawei for their

IDU RTN family. This software is installed to the laptop PC which is used to configure the

IDU. This is also used for fault handling. If there is a fault in the system IDU shows an alarm.

When we logged on to the iManager it shows the faulty cards highlighted. Then the type of

the fault can also be found. The most important advantage of software like this is the

graphical user interface. All we have to do is repair or replace the faulty card.

2.2.7 Base Transceiver Station (BTS)

BTS stands for Base Transceiver Station. It is the most important node in the access network.

It directly access to the mobile station and control the radio interface to the MS. Base

Transceiver Station (BTS). It contains components such as antennas, transceivers, and other

components that necessary to serve to the MS s.

A BTS is usually placed in the center of a cell. Its transmitting power defines according to the

size of a cell. Each BTS has in between 1 to 16 transceivers, depending on the density of

users in the cell. Encoding, encrypting, multiplexing, modulating, and feeding the RF signals

to the antenna are done by BTS

Figure 2.19: out door bts cabinet

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Currently Dialog has BTS cabinets from 2 vendors.

Ericsson

Huawei

ZTE

Functions of a BTS

Provide communication between user and network.

Broadcast/receive to/from MS either signaling and traffic signals.

Modulate/demodulate signals to be broadcasted through air interfaces.

Multiplex the information to be transmitted over each carrier.

Measure the quality of the signaling and traffic signals in downlink and uplink

channels.

2.2.8 VSWR measurements using Site Master

During the training period I had a chance to learn how to measure the VSWR (voltage

standing wave ratio) with a Site Master. It was used to identify the reason for a VSWR alarm

of a Huawei BTS at Negombo-pitipana site.

.

Steps for SWR Test,

Calibrate the Site Master.

Disconnect the jumper cable from the CDU.

Connect it to the Refl Test port of the Site Master.

Set the scale by using AMPLITUDE key.

Observe the trace in the frequency range according to the correct band.

Site Master

CDU jumper Feeder

Antenna Jumper

Figure 2.20 Passive antenna system connected for VSWR Test

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If the trace does not go over the value 1.30 for any frequency in the range, it is considered as

a normal VSWR level. This test should be done for two jumper cables separately

2.2.9 Distance to Fault (DTF) Test

The purpose of this test is to verify that there are no bad connections or other faults (for

example sharp bends) in the antenna feeder system. Following are the steps to test the DTF.

Connect the jumper cable to the Site Master.

Set the Mode into DTF – SWR.

Set the distance range according to the total length of the feeder system.

Set the scale with the maximum value 1.3.

Wait while the Site Master is calculating.

Observe the waveform and check that no reflections are above 1.05 SWR.

By this test we can identify the location of the fault. Then the fault should be identified and

repaired. However at the end of all, the DTF test should not over take the value 1.03. If there

is any fault in the system it can be easily identified because the Site Master gives the distance

to fault.

Figure 2.21 DTF Test result of a faulty system.

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2.2.10 Site visits

Mostly I involved that kind of jobs in my training period of dialog .Site visit means visiting to

of the network. ,Nodes (BTS ,Node B) for different reasons .That kind of some reasons are

clear alarms (Power/Site down/Sector down) ,PAT (Primary acceptance test) ,Rearrange

exciting supporting systems ( Power/ Cooling/ Serge/ protecting earthling /Power back up )

,Testing ,Survey and Audit and Other reason.

2.2.11 Clear Alarms

As a regional office most numbers of site visits are included in that category ,since that kind

of alarms occur generally in sites .According to the alarm basically We followed following

check lists to trouble shoot and resolve the issue after we were informed about the alarm by

the NOC.

2.2.12 Site down/Sector down

Site down alarms occurred in different situations .It may be caused power down for long

time. Ethernet of E1 cable failure etc. Sector down occurred basically card faults or cable

damaged .In sector down situation we followed following steps. Observed LED indicates on

the GTMU card or WMPP card according to the alarm occurred in 2G or 3G.Inter changed

fiber cables were observed the LED indicates .Cable were changed if the issue was issued

with the cable .That means issue on the cable or issue on the card.

2.2.13 Site Commissioning

Site commissioning is done for newly installed sites. Installed equipment‟s are checked to

identify defects and connections are observed. During the training period I was able to take

part in a several site commissioning at Badulla region. Installations are done by Huawei

personals. There are rules and conditions in site commissioning document, so those

conditions should be passed before to power up of the device. The test is done by an Engineer

or a technical officer

Configurations were checked using a laptop connected to the BTS equipment.

The transmission unit was a Huawei Optix RTN product. Its configurations

were also checked.

Mains power levels were checked with a multimeter.

Antenna directions were checked using a compass.

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Proper functionality of alarms

Antenna tilts were checked.

Grounding cable connections were checked and proper labeling of cables

Check whether all equipment‟s are operational. If it is OK the site

commissioning is done.

2.2.14 Routers

Routers are the network devices that operate at Layer-3 of OSI model of

communication.

As layer-3 protocols have access to logical address (IP addresses) so routers have

the capability to forward data across networks.

Sometimes routers are also known as layer-3 switches.

Routers maintain routing table for data forwarding.

Console Port

All configurations did with this port. We can use the Console cable to configure the

router. Also we can use serial cable to configure the router

2.2.15 Router Configuration

I configured few brand of routers Huawei & Cisco routers. To configure the router we used

console cable and SequreCRT Software. If power on correctly router and connect the

console cable to port and other side to computer.

Router > enable //This will give enable mode

Router # Configure terminal //This will give config mode

Router (Config) # hostname <Name for the router > //Set hostname of the router

Router (config) #interface Ethernet 0

Router (config-if) #ip address 195.1.2.1 255.255.255.0 //Enter the IP address and

subnet mask of the interface using the ip address ip address subnet mask command

Router (config-if) # no shutdown //This port up

Router (config)#interface serial 0

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Router (config-if) #ip address 192.168.10.1 255.255.255.0

Router (config-if) # no shutdown//This port up

Router (config) #router ospf 1 //Enter the router ospf command

Router(config-router) #network network 192.168.10.1 255.255.255.0 area 0

Router (config) # enable password ******

Router (config) # line console 0

Router (config-line) # password ******

Router (config-line) #login //console terminal for access

Router (config) # line vty 0 4

Router (config-line) # password ******

Router (config-line) #login //virtual terminal for remote console access.

Router # copy running-config startup-config //save the configuration

2.2.16 Drive Tests

Drive Test is a method of measuring and assessing the coverage, capacity and Quality

of Service (QoS) of a mobile radio network. The technique consists of using a motor

vehicle containing mobile radio network air interface measurement equipment that

can detect and record a wide variety of the physical and virtual parameters of mobile

cellular service in a given geographical area.

By doing a drive test we can collect following data of the network. Signal intensity

Signal quality

Interference

Dropped calls

Anomalous events

Call statistics

Service level statistics

Quality of Service information

Handover information

Neighboring cell information

Figure 2.22: Drive Test Equipment

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Coverage test consist of following equipment

TEMS investigation software installed laptop,

GPS receiver

Mobile Phone with TEMS pocket installed

These equipment are connecting as following figure,

2.2.17 Drive Test legend

Figure 2.23 Equipment connection of a Drive test

Figure2.24 Drive test legend

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There are two modes of drive tests .They are idle mode and dedicated mode is To measure

signal coverage In the idle mode the drive test is done without taking a phone call. This mode

is used to measure the receive level. And Dedicated mode is to measure call quality In the

dedicated mode the drive test is done with taking a call.

2.2.18 TEMS Investigator

TEMS Investigation is the industry standard tool for troubleshooting, verification,

optimization and maintenance of wireless networks. TEMS Investigation supports all major

technologies from GSM to 4G, making it the ideal testing tool at every stage of the network‟s

life cycle.

Before starting test we inform RNO section and NOC section for doing monitoring part of

drive test. After we took the plots and other data by doing those tests mentioned above, we

have analyze the data into a user friendly mode, (Map views, presentation, etc.) Analyzing

log files is main task done at RNO & Network Planning because all decisions are taken from

the results we got after analyzing.

Figure 2.25 TEMS Investigator Interface

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3. Conclusion

Industrial training period is the most valuable period .I was completed my training in Dialog

Axiata PLC. After two year spent in classroom with lectures and practical‟s this six month in

the industry was great opportunity to see the difference between it. After six month of period,

I have no hesitation to recommend Dialog Axiata PLC, one of the leading companies in

srilanka in the telecommunication field. It gives me that chance to be directly involved with

the industry and shows the first step of the long path of a challenging engineer.

During the 6 months of training period I was able to work as a trainee in Access Network

operation Division & Transmission Division. I have gained new knowledge and skills. It was

one of the greatest opportunities to work in a company like this because I got the chance to

work freely with the tools and software‟s.

Dialog is a concerning company about the trainees also they conducting some of lecture

sessions in every Tuesday to introduce each divisions and their duties, in access network

operation I do more configuration using the software, site upgrade, trx change, E1 checking,

cpich and etc. Though I was able to have on experience in Hambanthota and Badulla site

commissioning. I was able to participated many site visits and Drive test.

As an organization the Managers, Engineers, Technicians in the company are very friendly.

They work as a very powerful team without regarding the job titles honoring and helping to

each other. As a trainee I also joined to the team work done in the company and I understood

how to be a team member. In my training period they joined me to their works and hand over

to do works in my own responsibility under their guidance. At trouble situations and when I

need technical help they provided help to me. They shared their past experiences and the

gathered knowledge with me. I personally understood that own practicing is the best way to

study. We worked as a group of professionals, I had the opportunity to improve project

management, team working, problem solving, analyzing, communication and soft skills. In

conclusion, Regarding the ATI and NAITA, they had taken various steps to arrange a useful

training period for students. NAITA played responsible role in training establishment.

NAITA is the resource place that communicates with the companies to have the training

places. It was very easy to us all legal works (Training contract) are carried out by NAITA.

At the beginning of the training period NAITA informed us about how to maintain daily

diary and guided us to adopt by our self to the company.

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It would be better at is NAITA and the training division present at the training places at the

very beginning of the training period. That would be better to trainees to identify their week

points at the very beginning of the training period and successfully complete the overall

session. It is better is there is a regular training program within the company. According to

my knowledge the training sections and program varies from time to time I thank that. Dialog

is now planning standard training program to use trainees for the optimum use to the

company and provide the best to the trainees.

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References

1. Company Website: http://www.dialog.lk/

2. Annual Reports Dialog Axiata PLC 2013, 2014

3. HedEx Lite Huawei Documentation

4. Alex Ericsson Documentation

5. Presentations and articles received from the Dialog Axiata PLC.

6. Cisco Systems, Inc. 2015. Cisco Systems, Inc. Available at:

http://www.cisco.com/c/en/us/products/routers/.html