ABSTRACT
The efficient task of network management which ensure proper monitoring and
controlling of certain network parameters to enable performance evaluation is a
primary concern of the services providers in global system of mobile
telecommunication. A sampled of Celtel network traffic data in Lagos area, indicating
subscriber’s demands and responses for a period of six months were collected and
studied. From the review of the network performance analysis presented and the
subsequent application of such vital component of these parameters, it was shown
that the mobile switching centres in Victoria Island exhibit low network performance
for first two months of the year 2006 and the situation became worst in the month of
March and April of the same year. However, considerable improvements were
recorded in the months of May and June. Relative improvements were also observed
in the Lagos main land and other areas. Essential parameters, including the grade of
service clearly indicated this. This is a clear case of congestion or fault. However,
those mobile switching centres located in the Main Island were fair and on the other
areas due to their present capacities have better performance.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of Contents vii
List of Acronyms ix
List of Symbols xi
List of Tables xii
List of Figures xiii
CHAPTER ONE: INTRODUCTION 1
1.1 General 1
1.2 Network Overview 3
1.3 Problem Definition & Methodology 7
1.4 Thesis Outline 8
CHAPTER TWO: TELECOMMUNICATIONS TRAFFIC THEORY 9
2.1 General 9
2.2 Literature Review 10
2.3 Traffic Characteristics & Models 14
2.4 Congestion Theory 15
2.5 Multi-Switching Network Traffic 21
2.6 Dimensioning Circuit-Switched Network 26
CHAPTER THREE: GSM NETWORK DATA 28
3.1 General 28
3.2 Measurement of Traffic 28
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3.3 Call Handling Systems 31
3.4 Network Data 32
CHAPTER FOUR: TRAFFIC ANALYSIS 40
4.1 General 40
4.2 Circuit Occupancy 40
4.3 Attempted Calls 40
4.4 Completed Calls 41
4.5 Network Performance Parameters 41
4.6 Analysis of Results 48
CHAPTER FIVE: CONCLUSION & RECOMMENDATIONS 51
5.1 Introduction 51
5.2 Conclusions 51
5.3 Contributions 52
5.4 Limitations 53
5.5 Area of For the work 54
REFERENCES 55
APPENDIX A: Graphical representation of calculated parameters 58
APPENDIX B: Graphical representation of individual parameters 70
APPENDIX C: The standard value of certain parameters in Celtel 73
CHAPTER ONE
INTRODUCTION
1.1 General
The purpose of any communication system is to convey a message
from one point to another. The originating input is referred to as a source
whereas the terminating end is the sink. If the message is understandable,
then information has been conveyed from the source to the destination. The
nature of the message can take on a variety of forms. It can be a continuous
time-varying quantity such as speech, a discrete signal that only takes on
fixed levels or values such as transmission of data by a digital computer, a
continuous spatial varying quantity such as the image on a TV camera tube,
or a combination of some of them [16].
The International Telecommunication Union (ITU) and the International
Standardization Organization (ISO) have jointly defined a concept for
standardizing protocols for monitoring and management of telecommunication
equipment, called Telecommunication Management Network (TMN). This
concept encompasses all issues related to system management of
telecommunication systems. It provides support and tools for planning,
provisioning, installing, maintaining, operating and administering these
systems. The main area of interest in this work is performance management
in communication networks with specific interest on the Mobile Switching
Centre of Celtel limited Lagos area [17].
Telecommunications traffic simply referred to the amount of telephone
calls or data conveyed over a network. However, due to a lot of factors it is
not every initiated call that actually arrives at its destination. Any attempt
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either by the customer or equipment to re-initiate the call greatly increases the
loading on switching equipment and adds to the overall traffic volume.
Today, the Global System for Mobile Communication (GSM) Network
operators are the most popular in the country. They have many subscribers
and large networks but do not provide quality services to customer’s
satisfaction. There are frequent cases of call failures, handoff failures, network
congestions, link failures, busy tones, which to date do not have total solution.
The overall result is complete frustration on the part of the users, degrades
the network quality and performance, and un-necessary efforts by network
managers.
Monitoring and controlling the entire network in order to detect and
avoid the resulting service degradation is a difficult work, but it is increasingly
being undertaken by many of the worlds telecommunications services
providers. Results of such studies have indicated by various models that
under peak periods the effectiveness of switching centre is at its lowest level.
It becomes imperative that early detection and analysis of these factors is as
good as ability to maintain controls over the entire network.
The most common parameter used to study network performance in a
circuit switched network is the traffic load over a period of time. To serve the
purpose of switch management, the monitoring of these parameters needs to
be done frequently, thereby giving the managers a real-time perception of the
system.
Switching equipment is the brain of the cellular system. It consists of
two major parts, the switch and the processor. The switch is no different from
that used in the conventional telephone systems. The processor used in
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cellular systems is a special-purpose computer. It controls all the functions
which are specific for cellular systems, such as frequency assignment,
decisions regarding handoff (including decisions regarding new cells for
handoff), and monitoring of traffic. The smaller the cell, the more handoffs
involved, and that explains why the traffic load will be greater thereby
justifying needs to put in place facilities to reduce failure rate. The processor
can be programmed to correct its own errors and to optimize system
performance [18].
1.2 Network Overview
As Econet wireless Nigeria, Vee Network limited trading as Vmobil
Nigeria and now Celtel was one of the three winners of the highly competitive
Nigeria’s GSM license bid in 2001. It pioneered GSM telephone services in
the country with a rollout on August 6, 2001, two days ahead of competition
and three days ahead of the regulatory deadline.
A truly Nigerian Company, Celtel is fully owned by indigenous investors
including three state governments, banks and other institutional investors. The
company was unveiled to Nigerian public on the 15th of March 2004. Since its
inception, Celtel has continued to make good milestones, recording its one
million subscribers in December of 2003.
The company has built a reputation for being a truly reliable network
and one that cares for the community. Its aim has been:
To provide first-rate communications services to the people of Nigeria,
thus empowering them with the power of communication.
To this end, Celtel continues to expand improve on its network,
guaranteeing excellent services.
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Celtel has acquired fairly good coverage through an aggressive rollout
strategy. It presently operates in more than hundreds of cities and over
thousands of communities with over 6 million active subscribers. Celtel was
first to launch in Lagos, Port Harcourt, Uyo, Warri, Kano and Ibadan.
Since the commencement of its operations, the company has
resolutely embarked on an aggressive pursuit of service and professional
excellence, mindful of its place in the history of GSM telephone operation in
Nigeria. It is therefore, imperative to study its operational performance in this
case study with specific reference to the Mobile Switching Centres located in
Lagos areas.
A basic cellular system consists of three parts: a mobile unit, a cell site,
and a Mobile Telephone Switching Office (MTSO), as Fig. 1.1 shows, with
connections to link the three subsystems.
Mobile Units: a mobile telephone unit contains a control unit, a
transceiver, and an antenna system.
Site: The cell site provides interface between the MSC and the mobile
units. It has control unit, radio cabinets, antennas, a power plant, and
data terminals.
MSC: The switching office, the central coordinating element for all cell
sites, contains the cellular processor and cellular switch. It interfaces
with land lines, controls call processing, and handles billing activities.
Connections: The radio and high-speed data links connect the three
subsystems. Each mobile unit can only use one channel at a time for
its communication link. But the channel is not fixed; it can be any one in
the entire band assigned by the serving area, with each site having
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multi-channel capabilities that can connect simultaneously to many
mobile units.
The MSC is the heart of the cellular mobile system. its processor
provides central coordination and cellular administration.
The cellular switch, which can be either analog or digital, switches calls
to connect mobile subscribers to other mobile subscribers and to the
international telephone network. It uses voice trunks similar to land lines
exchange centres voice trunks. It also contains data links providing
supervision links between the processor and the switch and between the cell
sites and the processor. The radio link carries the voice and signaling
between the mobile unit and the cell site. The high-speed data links cannot be
transmitted over the standard telephone trunks and therefore must use either
micro links or T-carriers (wire lines). Microwave radio links or T-carriers carry
both voice and data between the cell site and the MSC [3].
Land lines Network
Voice circuits
Voice & Data Link
Cell Sites (Radio Base Station Sites)
Fig1.1 Cellular System
The general GSM network architecture is presented in Fig 1.2. All the
Switches and processor
MOBILE SWITCHING CENTRE
Cell 1
Cell 2
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interfaces are standard which permits a fierce competition among the vendors
and a multi vendor network.
Um Abis
Fig 1.2 Architecture of the GSM network
SIM: Subscriber Identity Module contains the International Mobile
Subscriber Identity (IMSI) used to identify the subscriber to the system, a
secret key for authentication.
ME: Mobile Equipment
BTS: Base Transceiver Station handles the radio-link protocols with the
Mobile Station.
BSC: Base Station Controller handles radio-channel setup, frequency
hopping, and handovers.
HLR: Home Location Register –all the administrative information of each
subscriber, and the current location of the mobile.
VLR: Visitor Location Register contains selected information, for call
control and services for mobiles located in its geographic area.
MSC: Mobile services Switching Centre – normal switching node of the
SIM
ME
BTS
BTS
BSC
BSC
MSC
HLR VLR
EIR AuC
PSTN
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PSTN (Public Switched Telephone Network), plus functionality for
registration, authentication, location updating, handovers, and call routing
to a roaming subscriber.
EIR: Equipment Identity Register
AuC: Authentication Center stores a copy of the secret key of each
subscriber’s SIM card, used for authentication and encryption.
1.3 Problem Definition and Methodology
Telecommunication development plans and investments are current
network performance based. The major aim of this thesis is to study the
performance and efficiency of the nine mobile switching centres in Lagos
area. A good network ensures proper usage of the available capacities to
deliver traffic demands at all time. To achieve this, a proper monitoring,
analysis and forecasting are essential tools.
Traffic profiles on different routes vary greatly according to the nature
of the route and its users. Highly peaked and busy hour oriented profiles can
be problematic for network operators as congestion and faults will be highly
likely and as a whole there will be little network use [1]. It is hoped that the
study will reveal the right control mechanisms by which recommendations for
possible optimization and dimensioning of the network under typical normalday
loading conditions will be achieved. This endeavour falls under the trunk
and traffic analysis administration in multi-exchange networks.
The methodology adopted in the study includes first collection of data
for such parameters as:
Traffic intensity
Total number of calls completed, total number of calls attempted
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Total number of minutes of usage.
and there after the analysis of this network data was conducted.
The analysis of Erlang formulae will be used for a statistical analysis of
the network data.
1.4 Thesis Outline
Chapter One is the introduction, which covers the fundamental
theories, past works, objective of the study, and the chosen approach.
Chapter Two reviewed the general concept of the telecommunication traffic
theory with relevant laws and proofs. Chapter Three describes the specific
nature of GSM network data relating to the Celtel in Lagos area. Chapter Four
is the analysis of the data to arrive at certain parameters that were used to
predict the Mobile Switching Centre performance behaviour. Chapter Five
simply outlines conclusion drawn, recommendations, limitations and
significance of the research work.
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