Memoire Online - The impact of fiber optic transmission in multiservices networks in rwanda

I certify that the project report titled «THE IMPACT OF FIBER OPTIC TRANSMISSION IN MULTISERVICE NETWORK IN RWANDA» Case Study NUR Fiber Optic Network is the bonafide work done by Mr. NIYITEGEKA Théogène (Ug10105802) In a partial fulfillment of the requirements for the award of Bachelor?s degree in Electronics and Communication System Engineering and I certify that to the best of my knowledge the work reported is my own work and it has not been submitted anywhere for the award of any Degree.

Submitted for University examination held in October/ 2011 at National University of Rwanda, University Avenue 117, Butare, Rwanda.

ABSTRACT

Fiber Optic is a flexible and transparent fiber made of very pure glass not much bigger than a human hair that acts as light pipe to transmit light between the two ends of the fiber. In this project, we assess the Network of National University of Rwanda and the impact of the fiber optic in this network. The fiber optics, as seen in our project have changed the daily life of many workers in this university throughout the high bandwidth available with fiber optic connectivity.

We have seen that the company?s provider of network in Rwanda can implement fiber optic in order to deliver a reliable service to their customer.

However the bandwidth of fiber optic is usually greater than other media cables and depending on the properties of a pure glass of the core which make easy the total internal reflection of light inside the core and the cladding of the fiber. The fiber optic grounded wire are allowed to transfer more data and does not radiate electromagnetic wave in space.

DEDICATION

ACKNOWLEDGEMENT

I owe much thanks to the almighty God for his help and guidance may this simple word express my respect to him.

I would also like to express my appreciation to Dr. Celestin TWIZERE for his tireless efforts to guide us and supervise my work and make it a success through encouragement and advices.

I am very grateful to my mother NTABUGI JEANNINE for her kindly moral and financially support.

With respect, I express my special thanks to lectures and staffs members of the faculty of Applied Sciences at National University of Rwanda; My sincere thanks go also to Mr. NDUSHABANDI JEAN BOSCO for his collaborating efforts to provide needed information to the achievement of this project.

I wish to extend my sincere gratitude thanks to all classmates and relatives who have directly or indirectly helped me and rendered great moral encouragement.

LISTS OF FIGURES

Figure 6 : Emission block of fiber optical signal and laser diodes as the source 13

LIST OF SYMBOLS

CATV: Cable Television DMUX: Demultiplexing DWDM: Dense Wavelength Division Multiplexing

FTTB: Fiber To The Building FTTC: Fiber To The Cabinet GPON :Gigabyte Passive Optical Network

LASER : Light Amplification by Stimulated Emission Radiation LED: Light Emitting Diode

UTP: Unshielded Twisted Pair VLAN: Virtual Local Access Network VSAT: Very Small Aperture Terminal WDM: Wave Division Multiplexing

CHAPTER ONE: GENERAL INTRODUCTION

1.1 BACKGROUND

An optical fiber is a flexible and transparent fiber made of very pure glass (silica) not much bigger than a human hair that acts as a waveguide or light pipe to transmit light between the two ends of the fiber.

Fiber optics though used extensively in the modern world is a fairly simple and old technology, of guiding light by refraction this principle makes fiber optics possible.

The laser was introduced as an efficient source of light and the concept was to show that masers could be made to operate in optical and infrared regions. Basically, light is reflected back and forth in an energized medium to generate amplified light as opposed to excited molecules of gas amplified to generate radio waves as is the case with the maser. Laser stands for light amplification by stimulated emission of radiation.

When the light passes from air into water, the refracted ray is bent towards the perpendicular, When the ray passes from water to air it is bent from the perpendicular if the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all, it will be totally reflected at the surface, The angle which marks the limit where total reflection begins is called the limiting angle of the medium, For water this angle is 48°27', Unpigmented human hairs have also been shown to act as an optical fiber.

Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index appeared later in the decade Development then focused on fiber bundles for image transmission.[1]

In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities also the Photophone was invented for transmission of voice signals over an optical beam.

The British company Standard Telephones and Cables (STC) was the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), making fibers a practical communication medium, he proposed that the attenuation in fibers

available at the time was caused by impurities that could be removed, rather than by fundamental physical effects such as scattering, he correctly and systematically theorized the light-loss properties for optical fiber, and pointed out the right material to use for such fibers, silica glass with high purity, attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70-150 kilometers.[2]

Today , Fiber optic systems have many attractive features that are superior to electrical systems, These include improved system performance, immunity to electrical noise, signal security, and improved safety and electrical isolation that why we encourage each Telecommunications services provider of network in Rwanda to implement fiber optics in their services for better communication.

In Rwanda we have five available fiber optics network such as: RDB Fiber ,MTN Fiber ,TIGO fiber, EWSA Fiber and Rwandatel fiber.

1.2 PROBLEM STATEMENT

When you compare the fiber optic with other media (copper cables, space media) which are often used in Rwanda especially at NUR for signal transmission those media causes the problem of electromagnetic interference, small bandwidth which affect the signal transmission performance.

In addition fiber optic reduce the effect of electromagnetic field radiation on human being which causes incurable illness( e.g.cancer...).

1.3 INTEREST AND RELEVANCE OF THE CHOICE OF THE TOPIC

Fiber optics has advantages in improving System efficient by Greatly increasing bandwidth and capacity, improving safety and electrical isolation ,reduced size and weight, environmental protection, Lower signal attenuation (loss), Immunity to Electrical Noise (electromagnetic interference and radio-frequency interference), No crosstalk ,Lower bit error rates, Nonconductive (does not radiate signals), Resistant to radiation and corrosion ,Resistant to temperature variations.

Fiber optics network has contribute very much in improvement of internet connections in Rwanda especially in National University of Rwanda.

1.4 RESEARCH HYPOTHESIS

This work will help the companies provider of networks in Rwanda and the entire society to understand well the good benefits of using fiber optic connection.

> To evaluate the advantages or benefits that fiber optics has contribute in telecommunication field in Rwanda focus will be put on NUR Network.

1.5. RESEARCH METHODS

> Observation methods: we will observe how the fiber optic is implemented in NUR. > Library: books related to our topic will be checked.

> Documentation: We will use the books and notes relative to the fiber optics transmission and same field will be done at National University of Rwanda where that technology is in use and being implemented.

1.6 LIMITATION OF THE TOPIC

1.7 STRUCTURE OF THE WORK

Besides conclusion and recommendations our work will include Four chapters which have General introduction as the first chapter where include the evolution of media cables technology fiber optic leading to transmission improvement will be illustrated, the second chapter is titled as optical fiber transmission this chapter we will deal with how optical fiber transmit signal using light, Reflection and it will contain General Information about the transmission media then comes The third chapter, The analysis of fiber optic network in NUR where Special emphasis will be put on fiber optic networks as passive and active link and its performance and evaluation and this will guide us to the Fourth chapter titled Discussion and interpretation of the results, we will analysis data collected on parameters used to test the effectiveness of that technology and comparison will be made before fiber optic implementation and in nowadays where has been implemented.

CHAPTER TWO: FIBER OPTIC TRANSMISSION

2.1 GENERAL INFORMATION ON THE TRANSMISSION MEDIA

A transmission media are the physical pathways that connect one point to another point. We will discuss about two different ways of transmission which are:

It relates also primarily to the explanation of various alternatives of these transmission resources, some common characteristics gives us an outline on the choice of optical fiber. [2]

2.1.1 COMMON CHARACTERISTICS

2.1.1.1 Bandwidth

Bandwidth is the amount of data that can be transmitted along a channel during a specified period of time. In most cases it is measured in bits per second (bps).

2.1.1.2 Impedance characteristics

The characteristic impedance, Z0, of a line is the input impedance of an infinite length of the line.[3]

G is the conductance of the dielectric per unit length, C is the capacitance per unit length,

2.1.1.3 Coefficient of velocity

The coefficient of velocity is a size which measures the propagation velocity of the signal in a media. It is also the relationship between the propagation velocity real and the speed of the light (c=3.10⁸m/s).

2.1.2 GUIDED MEDIA

2.1.2.1 The twister pair

Twisted pair cabling is a type of wiring in which two conductors; the forward and return conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference from external sources.

Generally several pairs are gathered under an envelope called sheath to form a cable, The signals transmitted in this type of medium can according to their characteristics traverse several tens of kilometers without amplification or regeneration, Beyond these distances rearrangement of the numerical signals in baseband and the amplification of the analogical signals in modulation are necessary.[3]

> UTP (unshielded twisted pair) is most commonly used in LAN's with maximum cable length of 100m.

2.1.2.2 Coaxial cable

Another current medium of transmission is the coaxial cable, it has better protection than the twisted pair which enables him to offer flow raised on long distances, Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses, is also sometimes used by telephone companies from their central office to the telephone poles near users.

Copper mesh: It is like a pipe or tube of copper that surrounds the insulator which in turn surrounds the copper wire.

The coaxial cable offers at the same time a broad bandwidth and an excellent immunity against the noise, his bandwidth depends on the quality of the cable, its length and the signal to noise ratio, this type of cable was largely employed within the telephone system on the trunk lines but it is now replaced by optical fiber, especially on the long distance. It however still very much used for the cable television and on the underground railway networks.

The major disadvantages of copper are a strong attenuation and a speed transmission relatively low which limits the maximum distance between two stations or two apparatuses of interconnection

2.1.2.3 Waveguide

Waveguides are metallic transmission lines that are used at microwave frequencies, typically to interconnect transmitters and receivers

Waveguide has a number of advantages over coax, it is completely shielded and excellent isolation between adjacent signals can be obtained, it can transmit extremely high peak powers and it has very low loss often almost negligible at microwave frequencies.[4]

One disadvantage of waveguide is its high cost, Manufacturing volumes are low and waveguide materials such as copper and silver are relatively expensive other disadvantages include unwieldy size and mass particularly at lower frequencies.

2.1.2.4. Fiber optic

An optical fiber is a flexible, transparent fiber made of very pure glass silica not much bigger than a human hair that acts as a waveguide, or light pipe used to transmit light between the two ends of the fiber.

The optical fiber is used more depend on its exceptional properties and particularly a very high bandwidth and a very weak attenuation ,it offers a flow of information definitely higher than that of coppers and supports a network broadband by which can as well forward television, telephony, the videoconference or the data information.[5]

The influence of optical fiber is the subject of our study, particularly in a network multiservice and a deepening is reserved to him in this chapter.

2.1.3 UNGUIDED MEDIA

2.1.3.1 Microwave link

A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit information between two fixed locations on the Earth. They are crucial to many forms of communication and impact a broad range of industries. Broadcasters use microwave links to send programs from the studio to the transmitter location which might be miles away, microwave links carry cellular telephone calls between cell sites and Wireless Internet service providers use microwave links to provide to their clients with high-speed Internet access without the need for cable connections and Telephone companies transmit calls between switching centers over microwave links, Although fairly recently they have been largely supplanted by fiber optic cables

2.1.3.2 Satellite

In communications, satellite is a specialized wireless receiver and transmitter that is launched by a rocket and placed in orbit around the earth they are used for such diverse purposes as weather forecasting, television broadcast, amateur radio communications, Internet communications, and the Global Positioning System, (GPS).

After having given a general idea on the various media of transmission, we will approach in the following the processes of optical fiber for the routing with very great range of significant flows of information integrated on the same line of transmission.

2.2 OPTICAL FIBER CABLE

To guide signals carrying information from a transmitter to a receiver, the technique of telecommunications uses primarily two means such as:

> Material support between the transmitter and the receiver; > Transmission by radio waves.

Among the transmission material medium, best adapted for significant traffics to high flow is the optical fiber; this is why, this chapter is devoted to the meticulous treatment of this transmission resource.

2.2.1 Definition

Fiber optics are long, thin strands of very pure glass about the diameter of a human hair, They are arranged in bundles called optical cables and used to transmit light signals over long distances that light contains information which are being transmitted, the basic structure of an optical fiber consists of three parts; the core, the cladding, and the coating or buffer. The core is a cylindrical rod of dielectric material, Dielectric material conducts no electricity, Light propagates mainly along the core of the fiber, The core is generally made of glass, the core is described as having a radius and an index of refraction. The core is surrounded by a layer of material called the cladding, even though light will propagate along the fiber core without the layer of cladding material, the cladding does perform some necessary functions.[6]

The cladding layer is made of a dielectric material with an index of refraction; the index of refraction of the cladding material is less than that of the core material. The cladding is generally made of glass or plastic, the cladding performs the following functions it Reduces loss of light from the core into the surrounding air, reduces scattering loss at the surface of the core ,Protects the fiber from absorbing surface contaminants

For extra protection, the cladding is enclosed in an additional layer called the coating or buffer. The coating or buffer is a layer of material used to protect an optical fiber from physical damage, the material used for a buffer is a type of plastic. [6]

2.2.2 Principle of optical transmission.

The fiber carries a signal encoded beam of light by virtue of total internal reflection (TIR). TIR occurs at the interface of a transparent medium with another medium, if the transparent medium has a higher index of refraction than the surrounding medium, TIR occurs. This makes the optical fiber a waveguide for frequencies in the range 10¹⁴ to 10¹⁵ Hz, covering the visible and part of the Infrared spectrum

The figure above illustrate the principle of total internal reflection as used in fiber optical communications, Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.

So the critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees.

Let's consider two different media creatively named medium i (incident medium) and medium r (refractive medium). The critical angle is the èi that gives a è_r value of 90-degrees. If this information is substituted into Snell's Law equation, a generic equation for predicting the critical angle can be derived. The derivation is shown below.[7]

Two stages transducers thus should be added (the equipment intended to convert the signals), one at the beginning, to ensure conversion electricity/light; the other on arrival for opposite conversion. In the first case, it is about a laser diode or LED diode ; in the second a photo diode.

By convention, an impulse of light indicates a bit to 1 and the absence of light to 0, But as any ray whose incidence reaches the critical angle undergoes an internal reflection, many rays are propagated under various angles in optical fiber. it is said that each one has a different mode a fiber presenting this property is thus called fiber multimode.[8]

However, if the diameter of fiber is tiny in proportions such as only one luminous ray can there be propagated, then the fiber acts like a guide of waves and the light can be propagated only in straight line without reflection is called a monomode fiber, it is more expensive than fiber multimode but is largely used at longer distances because it transmit data to 50 Gbit/s out of 100 km without amplification.

2.2.3 Schrödinger wave equation

The Schrödinger equation is the fundamental equation of physics for describing quantum mechanical behavior, it is also often called the Schrödinger wave equation, and is a partial differential equation that describes how the wave function of a physical system evolves over time.[9]

where i is the imaginary unit, is the time-dependent wave function, is h-bar, V(x) is the potential, and is the Hamiltonian operator, However the equation can be separated into temporal and spatial parts using separation of variables to write

Setting each part equal to a constant then gives the time independent Schrodinger equation for one dimension:

2.2.4 Emission

The figure bellow shows the Emission block of fiber and LASER diode as the source

Figure 6 : Emission block of fiber optical signal and laser diodes as the source.

The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and LASER diodes, the difference between LEDs and LASER diodes is that LEDs produce incoherent light, while LASER diodes produce coherent light, for use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, reliable and directly modulated at high frequencies.

The power emitted by the LASER diode is calculated as follow: P=h(I-Is) for I>Is and I<Is ,P=0 (2.9)
Where:

In an emissive transition, the energy of the photon created in LED diode is given by the difference of the energy levels Ei (initial level of energy ) and Ef (final level of energy ).

The main component of an optical receiver is a photo-detector which converts light into electricity using the photoelectric effect, the photo-detector is typically a semiconductor-based photodiode.

The significant parameters which characterize a photodiode are : sensitivity, obscurity current , the response time, we can remove obscurity current which circulates in the junction , in absence of illumination, thus that current is not provident by photons transmitted by the fiber ,they can have many sources like thermal generation in the intrinsic zone, currents of surface.

The expression of the total current in photodiode is given by the equation. Iph=S.Popt+Iobs (2.10)

2.2.6 TYPES OF FIBER OPTIC

According to the modes of propagations which they use, the optical fiber can be classified in three categories such as: [8]

2.2.6.1 Single mode fiber optic

The diameter of fiber being smaller, it transmits the signal on only one luminous way, it is especially used for very long distances.

This type of fiber presents the greatest performances but its cost is relatively high compared to multimode fiber.

Diameter of core 5 with 10um, cladding 125um;Very high bandwidth and Very weak attenuation 0.5dB/km with 13um and 0.2dB/km with 1.5um very delicate connections.

2.2.6.2 Multimode step index fiber optic

The figure bellow corresponds to multimode propagation with a refractive index profile that is called step index, when light enters the fiber optic cable on the left, it propagates down toward the right in multiple rays or multiple modes, the light is reflected angularly (in Zig-zag) .

This type of fiber contains : Diameter of the core 50um or 62.5um generally cladding 1,25um Bandwidth of 60MHz.km and Weak attenuation:3dB/km with jump 0,85um.

For step index fiber the numerical aperture NA the angle which light comes out of or goes into an optical fiber and acceptance angle èA are given by the following formula [10]:

Where n1 is the index of core and n2 is the index of the cladding èA= sin^-1(NA)

2.2.6.3 Multimode graded index fiber optic

A graded-index fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the fiber axis because the core parts is closer to the fiber axis and have a higher refractive index than the parts near the cladding then light rays follow sinusoidal paths down the fiber.[10]

It has the following characteristics: Diameter of the core is about 50um or 62,5um, cladding of 125um,Bandwidth is several GHz.km and Attenuation is 3 dB/km with 0,85 um or 1,3um .

2.2.7 ADVANTAGES AND DISADVANTAGES OF OPTICAL TRANSMISSION

2.2.7.1 The advantages

The optical fiber present different advantages such as Low transmission loss , Enormous Bandwidths, Immunity to cross talk and Electrical Isolation, Small size and weight , Signal security, Ruggedness and flexibility, Low cost and availability Reliability

2.2.7.2 The disadvantages

Difficulties of connection between 2 fibers, Difficult Derivations, Difficulties on wave multiplexing, High cost of installation Fragility.

2.2.8 APPLICATION OF FIBER OPTIC

Medical Used as light guides, imaging tools and also as lasers for surgeries Data Used for data transmission

Telecommunications Fiber is laid and used for transmitting and receiving purposes Networking Used to connect users and servers in a variety of network settings and help increase the speed and accuracy of data transmission

Industrial/Commercial Used for imaging in hard to reach areas, as wiring where EMI is an issue, as sensory devices to make temperature, pressure and other measurements and as wiring in automobiles and in industrial settings

Broadcast/cable companies are using fiber optic cables for wiring CATV,HDTV, internet video on-demand and other applications.

2.2.9 FIBER OPTIC CONNECTION

> The transmitting source with optical fiber. > The optical fiber to optical fiber.

2.2.10 THE PRINCIPLE STRUCTURE OF FIBER OPTIC

2.2.10.1. Fiber optical multiplexing

Optical multiplexing also called Wavelength Divided Multiplexing (WDM) or Dense Wavelength Divisions Multiplexing (DWDM) as presented on the following figure actual this technology of WDM was born from the idea of simultaneously injection of several trains of numerical signals at the same speed of modulation into same optical fiber each one with distinct wavelength.

The DWDM is the short form of Dense Wavelength Division Multiplexing DWDM is an important technology in nowadays for fiber optic network, DWDM use WDM technology to

arrange several fiber optic lights to transmit simultaneously via the same single fiber optic cable, DWDM is usually used on fiber optic backbones and long distance data.

2.2.10.2 Fiber optical modulation

We need a carrier signal high frequency for transmitting a signal because a low level signal less power can not transmit over a long distance, So modulation means to change some parameters (e.g phase, frequency and amplitude) of the carrier in accordance to the message signal.

Analogue modulation( e.g Frequency modulation amplitude and phase and Digital modulation(e.g pulse width modulation ,pulse code modulation...)

2.2.11 Maintenance of an optical link.

You will need to perform a visual inspection of the connector endface, using either a handheld optical microscope or a fiber optic video probe, this procedure will determine the type of action needed to repair the connector, If the connector only has minor damage, e.g: scratches, small chips, or small pits, then re-polishing the connector will usually fix the problem if the visual inspection determines that the connector is shattered or there is no continuity then either a pigtail assembly will have to be spliced onto the cable or the cable will need to be replaced utilizing a redundant spare fiber for line level repair.

CHAPTER THREE: THE ANALYSIS OF FIBER OPTIC NETWORK IN NUR

3.1 INTRODUCTION

Fiber optics uses light signals to transmit data as this data moves across fiber there needs to be a way to separate it so that it gets to the proper destination, There are two important types of systems that make fiber to the home broadband connections possible, these are active optical networks and passive optical networks each offers ways to separate data and route it to the proper place

3.2 THE FIBER OPTIC LINK

A fiber optic link is a transmission media which connect two points, at NUR the fiber optic comes from Kigali where the is a backbone office to our campus at the NUR ICT CENTER, when we send signal from one customer to the other we use that interconnection which consists of the sending station that converts electrical signals into light signals and the receiving station that convert the light signals back into electrical signals those signals contains the information or data. [11]

In addition links are also described in terms of their ability to send and receive signals they are divided into simplex and duplex system.

Simplex means that the link can only send at one end and receive at the other end, the signals travels in one way and example can be the signals from the Radio station.

Duplex stand for a link which can allow signals to be transmitted and received at each terminates. It can be broken down into half-duplex and full-duplex: half-duplex allows the signals to go only one way at a time where full-duplex allows users to send and receive signals at the same time for example a telephone communication.[11]

This following figure 13 shows the parts of an optical link and the function of each components are illustrated below:

Transmitter that convert the electrical signal input which can be data pulse or analogue signals into variations of optical power at the desired wavelength and send the light into the fiber ,the device to perform the task is the light emitting diode LED or LASER diode .

The optical fiber that carries the light which provides the communication medium. it can be single mode or multi-mode at our campus we use single mode because it transmit data at long distance without attenuation .

Receiver which converts the received optical power from the optical fiber back to the electrical signal and the device which performs the tasks is the optical detector. and the signal is amplified to increase its amplitude

Furthermore we have also what we call The connectors that couple the optical fiber to the transmitter and receiver an example can be pig-tails a short length of optical fiber with a connector fitted at one end and the other end in intimate optical contact with the source.[11]

3.3 PASSIVE OPTICAL NETWORK.

A passive optical network (PON) is defined as optical access networks that starts from an operator central office in my case study are MTN fiber optic and RDB fiber to the individual homes here it is our campus NUR ICT CENTER .

PONs are characterized by the absence of on any active components it uses optical splitters to separate and collect optical signals when they move through the network.

Furthermore PONs are also systems that brings all signals to the customers according on where the PONs terminates.

The figure 14 above explains how fiber optic arrives to the end users whom can be The students
in the computer labs or on their laptops or staff in their offices named home in the structure from

the central office called OLT ( Optical line termination) MTN or RDB Central operators offices to the ONUs optical network unit According where the fiber goes here it may be a cabinet distribution located at NYANZA or same where else along the way from central offices all users have access to the services offered by the network through the network terminal NT and to the optical network through ONU or ONT. This OLT is the interface between all users connected to the given PON.

Hence we have also ODN Optical distribution network which works as the PON splitters they are used to share resources to the other users in the same network by creating the link to the other customers they can be arranged in star, ring or tree configurations to increase reliability.[12]

In addition according to the general structure of PON shown above ,PONs can be deployed in a FTTH fiber to home where an ONU is provided at the subscriber?s premises or FTTB fiber to the building where the optical fiber terminates before actually reaching the subscriber?s living or working space itself , FTTC Fiber to the curb or cabinet this is installed in a street along way side cabinet and is used as the connection between the OLT the central office and the ONU which is the cabinet the local access network of the fiber .[13]

3.3.1 ETHERNET PASSSIVE OPTIC NETWORK

Ethernet passive optical network EPON consists of an Optical Line Termination (OLT) at the communication company's office and a number of Optical Network Units (ONUs) near end users which are the cabinet distribution centers and up to 32 ONUs can be connected to an OLT.

This figure 15 the data from the OLT to be sent to the different ONUs must queue with no time delay between them in the EPON where this serves as a trunk ,fiber optic link between a larger system and the home Ethernet user hence splitter is used to separate packets according to theirs respective destination .[14]

Downstream signals coming from the central office is broadcast to each customer premises sharing a fiber and data Encryption is used to prevent eavesdropping to keep the information out of the hands of unauthorized people.

We have also the following figure for upstream data flow in the EPON which shows as how packets are putted or uploaded on the network.

The customer which is represented by an ONUs may need to upload or sent packets to the other user in same or different network, Upstream signals are combined using a multiple access protocol usually time division multiple access (TDMA) then the OLTs range the ONUs packets in order to provide time slot assignments for upstream communication without collisions and packets fragmentation .[14]

3.3.2 BROADBAND PASSIVE OPTIC NETWORK

Broadband passive optical network is a wide band of frequencies in the fiber optic connection which are available to transmit information at high speed data rate and the information to be sent are multiplexed before being put into the fiber. BPON systems can support downlink performance of 155 to 622Mbit/s and uplink performance of 155 Mbit/s.[15]

3.3.3 GIGABIT PASSIVE OPTIC NETWORK

Gigabit Passive Optical Network GPON is an upgrade of BPON with high speed data rates and this types of fiber is used to provider network to the home .GPON is a point to multipoint access mechanism Its main characteristic is the use of passive splitters in the fiber distribution network enabling one single feeding fiber from the provider's central office to serve multiple homes and small businesses at different places.

GPON has a downstream capacity of 2488 Mbits/s and an upstream capacity of 1244 Mbit/s that is shared among users and Encryption is used to keep each user's data secured and private from other users[16]

3.4 ACTIVE OPTICAL NETWORK

An active optical network (AON) is a system that uses electrical powered switching equipment such as router and switch to manage signal distribution and direct signals to specific customers.

At the termination point of the fiber at the NUR ICT CENTER there is a semiconductor which converts optical signal into electrical signal then a signal amplifier which increase the amplitude of the signal in order to avoid signal attenuation that can cause the data to be loss hence comes switch which divide the network into different parts depending on how they wants to use it .

The most common type of active optical networks are called active Ethernet this Active Ethernet uses optical Ethernet switches to distribute the signal means that the internet network all over it is needed at Ruhande.

This switch opens and closes in various ways to direct the incoming and outgoing signals to the proper place in such a system a customer may have a dedicated fiber running to his building.

Active optical network is a fiber to the building, this is NUR ICT CENTER as optical network termination where all fibers connections ends from the operators offices OLT before being distributed to the users of the internet connections. User can also download and upload depending on his need.[17]

3.5 SONET TECHNOLOGY

When data is transmitted over a communications medium a number of things must be provided on the link including framing of the data, error checking and the ability to manage the link. for optical communications these functions have been standardized by the ANSI T1X1.5 committee as Synchronous Optical Networking (SONET)

The information is sent over an optical fiber by turning the light off and on in the fiber suppose that the presence of light is indicated by «1» while the absence of light is indicates by «0» we can

send and receive bits across an optical link and extract the information from those bits by using SONET .

SONET is defined as the low level framing , rules which governs the optical links By framing this means a block of bits (or octets) that have a structure and which utilizes some technique to allow us to find the boundaries of that frame structure ,Same parts of the block may be devoted to overhead the network in order to provide the use of network management and another parts will be dedicated to carrying payload or information we want to communicate. [18]

3.6 FIBER OPTIC LOSSES 3.6.1 TYPES OF LOSSES

The word loss means attenuation or loss of optical power in fiber optic itself, losses is valuable in designing and choosing components in a fiber optic communications system, losses are also important variables in the network design phase. There are different reasons for light losses which may occur during transmission of light signal inside the fiber or during the interconnection process of two fibers. [19]

Losses are expressed in decibels per kilometer (dB/km), in terms of particular length L of a fiber the loss is expressed as:

The loss may be arise from different sources same are fiber intrinsic loss which means that they occur due to the nature of the core material and others are attenuation losses which may be caused by different reasons.

3.6.1.2 Absorption Loss

This is due to the impurity such as metal particles or moisture in the fiber and it can block some of the light energy which caused absorption loss. it absorbs light and dissipate it in the form of heat energy

The solution to this problem is to use ultra pure glass and add Impurity chemicals to minimize impurities manufacturing so that Light can travels best in clear substance .

Absorption loss are due to the absorption of energy by impurity ions that forms the core and hydroxyl radicals present in the core in addition this causes the loss of signal means information along the transmission.[19]

3.6.1.3 Rayleigh Scatter

Rayleigh scatter occurs when there are small changes in the refractive index of materials in which the light signal travels, this loss is caused by the miniscule variation in the composition and density of the optical glass material itself.

Figure 19 Rayleigh Scatter loss, The light can also be loosed into the cladding or back scattered light that are caused by obstacle like bunching of atoms in the core of the fiber .

3.6.1.4 Bending Loss

Bending losses occurs when a cable is bent and it disrupts the path of the light signal the tighter the bends of a cable the greater it is of the light loss.

Figure 20 shows the bending radius of an optical fiber that result in light displacement caused by pinching or squeezing the fiber. Bending deform the fiber's core slightly causing light to escape at these deflections, The bend curvature creates an angle that is too sharp for the light to be reflected back into the core and some of it escapes through the fiber cladding hence the result is the optical power loss which increases rapidly as the radius is decreased to an inch or less.[20]

3.6.1.5 Insertion Loss

Insertion loss is the most important performance indicator of a fiber optic interconnection. this is the loss of light signal, measured in decibels (dB) during the insertion of a fiber optic connector. Some of the common causes of insertion losses includes: the misalignment of ferrules during connection, the air gap between two mating ferrules and absorption loss from impurities such as scratches and oil contamination

Insertion loss can be minimized by proper selection of interconnect materials ,good polishing and termination process of fiber connectors. [19]

3.6.1.6 Return Loss

Return loss which is also known as back reflection is the loss of light signal that is reflected back to the original light source. this occurs as the light is reflected off the connector and travels back along the fiber to the light source It occurs also when there are changes in the refractive index of materials in which the light travels such as the fiber core and the air gap between fiber interconnection. When light passes through these two different refractive indexes some of the light signal is reflected back. [19]

CHAPTER FOUR: DISCUSSION AND INTERPRETATION OF THE RESULTS

4.1 DISCUSSION OF THE NETWORK IN NUR

Before we were using the internet connection through satellite which was in communication with an Earth Antenna VSAT(Very Small Aperture Terminals ) this is type of antenna is chosen because is directional and very focus in terrestrial signal transmission here it is a dish located at NUR main library near NUR ICT center it?s bandwidth was about 2.5 Mbps download and 1.5 Mbps upload at that time connection was faster without interruption but the cost was high and the bandwidth was small to serve all people in need of internet connection at our campus it was shared by staffs only and few students labs.

Nowadays, we have moved to the fiber optic network which is a grounded optical fiber cable ,the first fiber being implemented was Rwandatel which is no longer in use at this time then MTN this is currently used and RDB pipeline which is for government sponsor and is connected to other fibers of the regions in order to provide high connectivity all over the world and soon it will be operational in our campus the implementation phase has finished now it?s time for putting data or signal inside the pipeline .

In addition the type of fiber optic network used at NUR is single mode fiber optic network because it transmit at long distances without the attenuation in addition it has Very high bandwidth and Very weak attenuation 0.5dB/km with 13um and 0.2dB/km with 1.5um very delicate connections the attenuation occurs at each 100km this is where we can put a repeater in order to increase signal amplitude and to avoid signal loss during the transmission phase.

The fiber optic has contribute so much in the increasing of bandwidth in NUR internet connection through cables and wireless connection now we have the bandwidth of about 54Mbps upload and download and all over our campus students and staffs can access the resources offered by the network.

4.2 FIBER OPTIC RESULTS IN BANDWIDTH AND YEARS IN NUR NETWORK 7 1E0U4.1: U18 5 UNS 1' : , ' 7 + US 1' U 6311

YEARS	UPLOAD	DOWNLOAD	ISP PROVIDER
2005	1.5 Mbps	2.5 Mbps	SATELLITE CONNECTION
2006	1.5 Mbps	2.5 Mbps	SATELLITE CONNECTION
2007	2.5 Mbps	6 Mbps	RWANDATEL FIBER OPTIC CABLE
2008	2.5 Mbps	6 Mbps	RWANDATEL and MTN FIBER OPTIC CABLE
2009	2.5 Mbps	6 Mbps
2010(2Qtr)	2.5Mbps	6 Mbps
2010(3Qtr)	17 Mbps	17 Mbps
2010(4Qtr)	27 Mbps	27 Mbps
2011(1Qtr)	17 Mbps	17 Mbps	MTN FIBER OPTIC CABLE
2011(2Qtr)	54 Mbps	54 Mbps

This table 4.1 shows us that by the time fiber optic being installed in NUR the bandwidth has increased rapidly from 1.5 Mbps/2.5 Mbps by 2005 to 54 Mbps/54 Mbps by 2011(2Qtr) this is great positive impact of the optical fiber transmission on the NUR network and this has been achieved with the internet service provider ISP called MTN fiber optic cable.

4.3 THE INCREASE IN BANDWIDTH CHART OF NUR INTERNET

This portion of a communications link is used for the transmission of signals or data from NUR to a satellite or to a fiber optic link.

This bandwidth is used by end users who can be a student or a staff to get information from the internet.

These two figures: figure 21 and figure 22; we noticed that the uplink speed is roughly equal to the downlink but at our campus we need more to download than to upload because students are doing research and it is often that we can upload sometimes we may need to send e-mails and files which does not require us a huge bandwidth.

4.4 THE TRAFFIC MONITORING OF NUR INTERNET LINK

This explains us the use of the bandwidth from 28/05/2011 at 11:39:11 to 28/07/2011 at 11:39:11 within two months ago where we see the white from the week axis it was the problem of the fiber such as cut off or other fiber losses in addition the green one shows the inbound maximum mean the used bandwidth it was 5.72 Mbps and the outbound maximum means the unused bandwidth was 572.10Kbps Where the peak is too high means the internet users are many on the network and this occurs within the working hours of students and staffs, this chart get automatic updates after each five minutes for any components to work properly tit needs current which played a important role in the transmission of data or any information through any medium.

CONCLUSION AND RECOMMENDATIONS

CONCLUSION

The main objective of this project was to evaluate the advantages or benefits and the impact of fiber optics network that has contribute in telecommunication field in NUR and this has been achieved accurately.

Used effectively, the fiber optic network grounded wire has a dramatic effect on the way of communication without any effect on the human being because it does not radiate electromagnetic waves in space.

Today, fiber optic is used to the system great performance and high data rate because of it s properties of conductivity which uses total internal reflection of light inside the core with low loss of signal and immunity to electromagnetic interference then low bit error rate and high bandwidth towards the infinite .

Every Telecommunication company in Rwanda which need to implement the fiber optic cable in our country has to dig and I see this as challenge and I suggest that they could use one fiber for transmission in order to do not loose resources for the same purpose.

My purpose in this domain in the next research ,people must study the maintenance of this fiber because when it got trouble we need special trained people in this domain and same times are from outside the country and are high costly.

Furthermore my satisfaction in this project was the better transmission of the fiber optic cable and low attenuation of this media cable.

> To NUR staffs especially those from NUR ICT CENTER to provide easily full and rich

> To Internet Service Provider ISP in Rwanda to use fiber optic transmission connection in

> To Rwanda government to put much effort in the implementation of this fiber optic network in order to achieve broadband communication with others countries in the world and also SFAR to provide certain sponsors for students who are doing their memories.

> To NUR Library to provide many books related to fiber optic transmission because they are few.

> To the faculty of Applied Sciences to provide the laboratories accessibility that could help the students in their research and for other needed knowledge.

The impact of fiber optic transmission in multiservices networks in rwanda

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