Day 1: 1. OVERVIEW OF ICT

• 1.1. Definition of ICT• I.C.T. stands for Information and Communications Technology.

It replaces the term I.T. (Information Technology) because many machines, including computers, now allow users to communicate with other people and machines, as well as to retrieve information

• However, apart from explaining an acronym, there is not a universally accepted definition of ICT? Why? Because the concepts, methods and applications involved in ICT are constantly evolving on an almost daily basis. It’s difficult to keep up with the changes - they happen so fast.

• A good way to think about ICT is to consider all the uses of digital technology that already exist to help individuals, businesses and organizations use information.

• ICT covers any product that will store, retrieve, manipulate, transmit or receive information electronically in a digital form. For example, personal computers, digital television, email, robots.

• So ICT is concerned with the storage, retrieval, manipulation, transmission or receipt of digital data. Importantly, it is also concerned with the way these different uses can work with each other.

• ICTs are the key enabler of the knowledge society. Those who have easy and affordable access to ICTs and Communication networks can participate fully, while those without have fewer opportunities, and remain trapped in pre-knowledge economy forms of economic activity.

• The phenomenon of differential access to ICTs is often labeled the “digital divide”. This is often assumed to be about the presence of ICT infrastructure and equipment.

1.2. Role of ICT in National Development

• Information and communication Technology refers to technologies and systems supporting the collection processing, dissemination, access, and prevention of data or information.

• Information Communication Technology is widely recognized as a potentially powerful tool in the fight against poverty, with a capacity to provide developing countries unprecedented opportunities to meet vital developmental goals far more effectively than ever before.

• The possibilities of applying ICT for socioeconomic development purposes are limitless. The use of information technology can improve the provision of

• Health care, promote educational achievements, increase agriculture production, facilitate participatory government and secure other socioeconomic developments as indicated below:

1.2.1. ICT for Agriculture• ICT applications can be used to facilitate wide access to

information and intensive sharing of knowledge among planners, policy makers, practitioners and researchers in the agriculture sector;

• ICT can assist farmers on such areas as input supply, extension and use of local knowledge;

• Efficient marketing of agricultural products through information and telecommunication networks;

• Provision of equitable access to new techniques for improving agricultural production;

• Reduced food storage losses through more efficient distribution.

1.2.2. ICT for Health• The application of innovations such as virtual

medicine and telemedicine make it possible for patients located in rural areas to have access to medical experts located thousands of miles away;

• Enhancement of health administration and management through medical information system;

• Establishment of information “health profiles” and decision support system on regional, national, rural and district levels.

1.2.3. ICT for Education and Research• Provide equitable remote access to resources in support of both

distance education and the strengthening of local educational capacity;

• Connecting schools, universities and research centers to national and international databases, libraries, research laboratories and computing facilities;

• Reducing communication and administrative costs by building communication networks linking all educational establishments;

• Promoting and supporting collaboration among teachers and researchers;

• Extending the reach of educational facilities in informal learning, especially to community level.

1.2.4. ICT for Trade and Commerce• Today’s technological advances have not only opened new

opportunities to advance human development but have also entirely changed the global economic and business systems. Advances in ICT have helped accelerate economic globalization that is rapidly unifying world markets. ICT-based innovations such as e-commerce have now emerged as a future way of doing business and are projected to dominate world trade in the future. The opportunities, which ICT can provide for businesses, include:

• Linking chamber of commerce, trade associations and enterprises to both national and global trade;

• Reduced commercial transaction costs;• Online trade related information and import/export opportunities;• Development and marketing of new products through electronic

networks.

1.2.5. ICT for Good Governance • ICT is a powerful tool that can be used to facilitate macroeconomic and public sector

management. Efforts to stabilize the macroeconomic environment, and strengthen the efficiency, accountability, and the transparency of government can benefit a great deal from the introduction of information technology applications. Information system, which can help the government design, implementation, and assess policy reforms are now powerful instruments of public policy. Such information systems could increase the speed, volume, quality, transparency and accountability of government transactions; yielding large productivity increases in government services.

• ICT is among the most potent democratization tools that can be used to enhance participation in the democratic process. ICT can be used to open the government to the public and can also provide the citizens with the ability to enhance their interactions with each other and with the government. Citizens can be invited to send in comments and their views to government officials or parliament. By so doing, their views can be taken into account before laws are passed and policies made. This can have the effect of making government more transparent, accessible, and accountable to its constituents and can reduce public cynicism about the political process.

1.2.6. ICT for Environmental Management• Increase agricultural productivity by providing farmers with information on

weather forecasts;• Implementing networks which, as far as possible, provide access to

telecommunications in areas threatened by environmental degradation and natural disasters;

• Facilitate the use of low cost terrestrial and satellite radio communication systems in emergency situations where there is no access to adequate telecommunications;

• Establishing problem monitoring information systems using geographic information system (GIS) technologies, remote sensing and satellite early warning systems which provide tools to anticipate such problems in advance and enable governments and international organizations to be more proactive and to respond more effectively when the need arises;

• GIS can combine information on soils, hydro-geology and rainfall with socio-economic data, allowing early warnings.

1.2.7 ICT for Tourism• Attracting more tourists and other visitors by

offering high-quality information and telecommunication services in tourist resorts;

• Reducing the costs of international promotions for attracting tourists;

• Improving the image of the country through on-line promotional campaigns;

• Provision of tourism related information and indicators that encourage and facilitate investment in tourism projects.

• 1.2.8. ICT for Gender• Improve the rights of women through access to

information and indicators which may be used for tracking gender issues and elimination of stereotypes;

• Ensure equitable access of women to information, technology and technological education;

• Enhance the role of modern communications media to promote awareness of equality between women and men.

1.2.9. ICT for Culture • Making national museums accessible to all

parts of the regions as well as to the rest of the world;

• Electronic preservation and documentation of manuscripts and artifacts;

• Increasing accessibility of rare manuscripts and artifacts to researchers and the general public through the development of cultural CDROM products.

2. ONGOING ICT DEVELOPMENT PROJECTS IN ETHIOPIA

• In recognition of the critical role of ICT for sustainable development, democratization and good governance, the Ethiopian Government has taken bold and aggressive initiatives on several fronts in the development of ICT both at the federal and regional levels. In the context of the national ICT policy the Government recognizes the need to implement e-government and governance structure to bring the government closer to the people and the networked globe. The different ICT national initiatives are outlined as below:

• 2.1 E-Government• In recognition of the critical role of ICT for democratization and good

governance, the Ethiopian government has taken wide-ranging measures for its development both at the federal and regional levels. Within the framework of PSCAP, the government initiated series of measures to make the civil and public service more efficient and effective in the delivery of government services, along with institutional reforms, improvements in working processes and procedures, and altitudinal changes.

• The program is being carried out within this framework of what has come to be known as electronic government (E-government).

• The broad objectives of Ethiopian e-government program are:• Improve administrative efficiency, effectiveness and productivity as

well as information provision and service delivery to the public at the federal and regional levels of government;

• Reduce administrative, operational and transactional costs of federal and regional governments, administrative activities, service delivery functions and operations by reducing operational inefficiencies, redundant spending and unnecessary excessive paperwork;

• Increase the ability of the federal and regional governments to serve citizens and businesses better by enhancing and improving responsiveness to citizens and businesses;

• Transform government systems into a citizen-centered government as will facilitate the process of bringing government closer to the people and making it easy for citizens to obtain services and interact better with government machinery and agencies at the federal and regional level;

• Develop and implement information and communication infrastructure to support federal and regional level intra and inter-agency electronic service delivery and information exchange and;

• Provide access to information and government services by the public and enhance good governance and strengthen the democratic process.

• 2.1.1 Woreda-net• Woreda-net is a terrestrial and satellite-based

network whose primary objective is to provide ICT services such as video conferencing, directory services, mail services, voice services, and Internet connectivity at the federal, regional and lowest levels of government.

• • The Woreda net consist a government intranet,

which connects 3 federal offices, 11 regional offices and 634 Woredas (districts).

• The objectives of Woreda-net include:• To bridge the technology gap between

urban and rural communities; • To provide knowledge and information to

citizens;• To build organizational capacity at all

levels of government;• To provide the lowest level of government

with accurate and timely information.

• 2.1.2. School-net• School net arises from the need to integrate ICT

into Ethiopia's school system. It connects about 600 secondary schools of the country through a wide area network and making Internet and on line education possible in these schools. The network will also facilitate the effective administration and service delivery within the school system of the country.

• 2. 2 CONTENTS AND APPLICATION DEVELOPMENT

• In order to obtain maximum benefits from opportunities provided by ICT, appropriate ICT content and application need to be developed and tailored to user needs and local conditions. The government is committed to the development of locally relevant ICT content and application consistent with specific local situations and that are sure to add value to the daily lives of communities.

• The components under this initiative include:• Localize the existing global knowledge and content for

use at the national and local levels• Develop government portal and messaging solutions and

interoperability between national and local languages in order for citizens to have unhindered and transparent access to government services;

• Develop content for preserving the values, wisdom and acquired knowledge of traditional communities and cultures;

• Promote initiatives for content and application development based on local languages, mass communication and information delivery;

• In this line, the Government is determined to develop and implement appropriate sector based content and application in priority areas but spanning over eleven executing Agencies. These are public administration and service delivery, agriculture and rural development, trade and industry, health and education, economic development, public finance and statistics, archive and documentation and road transport.

• Five languages will be used during the first phase of program development and implementation including Amharigna, Oromifa, Tigrigna, Afarigna and Somaligna.

• The development of government portal and messaging solutions as well as interoperability between local languages will be the components of the current program.

• Contents and applications to be developed in priority areas are classified into common and specific contents and applications.

• 2.3. ICT HUMAN RESOURCE DEVELOPMENT• The basic objective of the ICT human resource

development project is to facilitate the development of the required ICT human resource for the nation through an appropriate mix, quality and quantity. With developments in ICT

• driven initiatives, the demand for ICT skilled professionals is expected to rise substantially in the future. Human resource development is therefore a challenge that needs to be addresses as matter of urgency, because there can be no sustainable ICT development without adequate human resource base.

The planned activities under this project are:• To develop national ICT human resource development strategy by

identifying the ICT human resource need of the country;• To improve the overall ICT human resource and skill base within the civil

and public service;• To train professionals within the civil and public sector to operate and

manage computer systems in government ministries and agencies;• To increase the supply of adequately trained ICT personnel;• To develop national curricula for ICT education at all levels in collaboration

with concerned stake holders; • To designate ICT center of excellence from among ICT training centers and

institutions in the public and private sectors; • To setup and implement an accreditation system for ICT education; and

training centers and institutions in the public and private sectors;• Establish ICT career structure for ICT professionals; • Promote ICT Research and development; • Promote ICT awareness and Literacy.

2.4 ICT FOR COMMUNITY • The aim of this initiative is to promote citizens' access to

data/ information by creating conducive environment for development.

The planned activities under this project include:• Formulation of ICT for Community Development

Strategy;• Facilitate the exploitation and application of ICT- based

services within communities;• Co-ordinate development efforts in local regions for

increased efficiency and effectiveness;• Promote the development of public information kiosks;• Conduct study on Local/ Indigenous Knowledge;

2.5 ICT FOR PRIVATE SECTOR DEVELOPMENT

• The Ethiopian Government considers the private sector as an engine of growth in ICT development and a strategic partner. Since the private sector plays a crucial role in accelerating the process of transforming Ethiopia into a

• knowledge and information economy and society the Government is committed to removing obstacles constraining its development.

This initiative includes:• Stimulate the private sector as a key driver in the

development of ICT;• Encourage the private sector to develop a globally

competitive ICT industry and services;• Establish business incubators to assist entrepreneurs in

ICT and related business to translate ideas into productive and marketable ventures;

• Promote the development of ICT parks with focus on local and export markets;

• Promoting and developing electronic commerce,

2.6 REGULATORY FRAMEWORKS AND STANDARDS

• The exploitation and application of ICT requires an appropriate legal and regulatory environment. In view of dynamic developments in the global and national ICT environment, urgent reforms are needed to ensure equitable, reliable, and affordable access to ICT. The exploitation and application of ICT also requires appropriate standards.

The components under this initiative include:• Establish appropriate legal and regulatory frameworks to facilitate

the development, utilization and application of ICT at all spheres.• Review and improve upon existing polices, laws and regulations to

facilitate the exploitation of ICT;• Establish standards and guidelines harmonized at national and

regional levels for the deployment and exploitation of ICT in the country;

• Establish standards for hardware, software development, localization, content and document management.

• Introduce character setting and keyboard layout for local language computerization and adopt UNICODE technology.

2.7 INFORMATON SECURITY• The exploitation and application of ICT

requires secure environment.• The objective of this initiative is to ensure that

systems are dependable in the• face of threats that are becoming increasingly

sophisticated worldwide. • Therefore measures should be taken to

develop systems and guidelines aimed at unconstrained use of ICT in the public and private sectors.

The components under this initiative include:• Address national security implications arising

from the widespread application of ICT within the economy and society,

• Introduce and enforce appropriate legal measures against misuse of systems and data;

• Protect the existing government networks, data and information systems against attacks and unauthorized access, and protect the rights of citizens;

3. THE WOREDANET ICT NETWORK

3.1 BACKGROUND:• WoredaNet is a terrestrial and satellite-based network whose

primary objective is to provide ICT services such as video conferencing, directory services, mail services, voice services, and Internet connectivity to the federal-level, regional-level and woreda-level government entities. From conception, the WoredaNet was established to leverage its infrastructure so as to establish a three tier structure for the provision of government based quality ICT service to the pubic sector driven by user requirements. This was to be achieved by harmonizing efforts undertaken by other government institutions in terms of ICT capacity building or service delivery by use of and/or extension of the WoredaNet infrastructure.

3.2 CONCEPTUALIZATION:• How does The Government Architecture look like? What should be the

pattern of the aggregated network infrastructure?• The WoredaNet ICT Network is instituted as an infrastructure frame

(Skeleton) that goes in line with the FDRE’s Federal and Regional government’s hierarchy. The upgrading works of this system are designed to cover the government’s administrative, legislative and executive organs hierarchical structure.

• There is one National Data Center, NDC, with high speed Fiber optic Network connectivity with the Ethiopian Telecom Broad band Metro Network (BBMN). NDC has redundant and failover systems by design.

• The 3 Federal Data Centers (Ministry of Capacity Building, The Prime Ministers Office and Ministry of Federal Affairs); Regional Systems except that of Afar, Benihshangul Gumuz and Gambella are all connected via a Terrestrial connectivity to the ETC BBMN. The Rest of the Woredas are connected via satellite VSAT (Very Small Aperture Terminals).

• The following two diagrams shall demonstrate FDRE’s Federal and Regional government hierarchy.

Voice IP Gateway Router Cisco2600

ETC PSTN

DMZ

Mail Relay

Content Engine

ETC 7500

IP MPLS

IP MPLS

Starbak server

Web Server

(AD Backup)

Video Confer. Bridge

Call Manager

MS Exchange

server

Intranet server

(Primary AD) Media

Exchange

Manager

Federal & Regions

IP MPLSIP MPLS

7206

IDSID

S

Cisco 6509

Broad BandMetro

PrinterIP T

Workstation

Mic

IP T

Satellite dish

Router

Switch

3 Regions, 311 Woredos

IP T

Workstation

Mic

IP T

Satellite dish

Router

Switch

43 X Auxiliary

Printer

IP T

Workstation

Mic

IP T

Satellite dish

Router

Switch

3 Federal Offices & 8 Regions

42" Plasma Display

42" Plasma Display

42" Plasma Display

3.3 VISION OF THE WOREDANET PROJECT:

• The vision of the of WoredaNet ICT Network is to establish a multi-service IP-based service by the use of Broadband Terrestrial and VSAT infrastructure for the delivery of services to government and civil society. This vision is part of a broader ICT initiative to drive development through a massive program to rollout, develop, and utilize ICT for the mass empowerment of Ethiopian society and its people. The vision can be summarized as follows:

• To bridge the digital divide between urban and rural communities • To create information affluence by dismantling the information

have’s and have -nots • To build the organizational capacity on the three levels of

government by use of ICTs• To impact the drive for ethics and transparency through the

availability on public Information on a timely and visible platform• To assist in the empowerment of the lowest level of government by

the virtue of accurate, timely, and consistent information

3.4 WOREDANET SERVICES:• The WoredaNet is capable of delivering the following core services to all of

the federal regional and Woreda sites that are included within its scope:Web Service: • To provide wider access to content available on the Internet for education,

health, agriculture and governance by civil servants. Such service will contribute in the bridging the digital divide currently experienced between unequal distribution of Web access between urban and rural and between densely populated towns and thinly populated remote areas.

Voice over IP ( IP-Telephony) Service: • To establish a common and singular voice over IP (Internet Protocol)

communication infrastructure between Federal, Regional, and Woreda sites which can be stated to be non-existent at the present.

• This particular service is expected to contribute largely to the increase of the tele-density of the country by providing an aggregated telephone access service especially to remote woredas without having to traverse the traditional telephone exchanges.

Directory Service: • To establish a government wide catalogue of digital resources for managing

of government folders, files, users, computers, and enforcing of a coherent usage policy in the sharing of such resources. The directory service can greatly impact the alignment of government goals from a top down approach as well as across lateral approach by the design and implementation of policy across a network such as WoredaNet.

Messaging:• The role of structured messaging service is very important; In order to

create a consistent and true collaboration environment, whereby free flow of mail messages can take place The messaging service shall be secured and structured electronic messaging service that goes inline with the government’s hierarchical structure. Contact details of a specific resource at a woreda, e.g. an email address administrator@akobo.gambella.gov.et can be published, and common experiences can be posted and shared among the three tiers/levels of government.

Video Conferencing:• To reduce distance, time, and cost and to

substitute the value of face-to-face meeting by use of IP based Videoconferencing devices as tools for conducting meetings. The value of such a tool is not only for holding up a one to one meetings but also in conducting group meetings and broadcasting recorded sessions, programs or television content to the remote woredas.

4. INTRODUCTION TO COMPUTERS

• 4.1 What are Computers?• A computer is an electronic machine that

receives data from an input device, carries out arithmetic and logical processing according to a previously complied set of instructions, stores the proceed data, sends the processed data to an output device.

• Schematically, a computer can be represented as follows

Input Device

CPUMain memory: ROM +RAM

ControlArithmeticUnit Unit

Out Put Device

External (Secondary) Memory Diskettes Hard Disk

• Computers are not very intelligent devices, but they handle instructions flawlessly and fast. They must follow explicit directions from both the user and computer programmer. Computers are really nothing more than a very powerful calculator with some great accessories. Applications like word processing and games are just a very complex math problem.

• One of the great strengths of computer platform, which has led to its overwhelming success in the marketplace, is its modularity. Most computers are made up of many different individual components, which can be mixed and matched in thousands of different configurations. This lets you customize the PC you either buy or build to meet your exact needs.

• 4.2 PC PRIMARY COMPONENTS• Fundamentally, a computer is a lot like the human body.

The human body contains a brain, organs to help the body function properly, and skin to protect the internal organs. And everything works together to create a fully functional human being. Well, the microcomputer has analogous components to create a fully functional machine.

• The aim of this Topic is simply to take a look inside the computer, identify the main components, give operating principles, and discover how everything works together.

In this section, you'll be introduced to the following components:

• Mother boards• Microprocessors • Memory• The bus system• Input devices• Hard disk drives and interfaces• Output device• Power supplies

4.2.1 MOTHERBOARDSThe Components on the MotherboardIn addition to the motherboard, processor, and CMOS, you need to

know the components listed below. These components are usually found inside the system unit. After they are installed, they are considered a part of the motherboard's sphere of control.

• BIOS and CMOS • Bus architectures • Cache memory • Microprocessors • Memory • Storage devices • Power supply • I/O ports

• Part of understanding the operation of the motherboard is understanding its bus structure. Most of the motherboard exam questions are about bus architectures. This section provides you with a brief overview of the bus structures on the motherboard.

• The CPU moves data values and signals around the computer on a network of fine wires that interconnect it to all the other components on the motherboard. This network is called the bus.

• The lines that move data within the computer form the internal bus.

• The lines that communicate with peripherals and other devices attached to the motherboard form the external bus.

• You can find four primary types of bus structures on most motherboards:

• Address: The components on the motherboard pass memory addresses to one another over the address bus.

• Control: Used by the CPU to send out signals to coordinate and manage the activities of the motherboard components.

• Data: Because the primary job of the computer is to process data, logically the data must be transferred between peripherals, memory, and the CPU. Obviously, the data bus can be a very busy hallway.

• Power: The power bus is the river of life for the motherboard's components, providing each with the electrical power it needs to operate.

• The number of wires in a bus controls the number of bits that can be transferred over the bus. For example, a 32-bit bus must have 32 wires.

• A Personal Computer motherboard is a large printed circuit board that's home to many of the essential parts of the computer, including the microprocessor, chipset, cache, memory sockets, expansion bus, parallel and serial ports, mouse and keyboard connectors, and IDE, EIDE, or SCSI controllers.

• The motherboard is often referred to as a system board. IBM has always called its motherboard a system board. Apple Computer calls its motherboard a logic board, while a few others refer to theirs as a planar board. These terms are still around today; for the most part, they are interchangeable.

• The motherboard binds the PC's operational components together. Even devices (such as printers, hard drives, and CD-ROMs) are either connected to or controlled by the devices or controllers on the motherboard.

• Manufacturers attempt to set their motherboards apart from the others and increase their value by incorporating more or fewer controllers, expansion buses, processor sockets, external connectors, and memory slots.

• For consumers, a wide range of motherboards with a deep list of features is available to fit into an even wider range of PCs. However, if you don't do your homework before buying a new motherboard, this wide range of selection can be bad news, and you can end up wit lower-quality components than you want.

• A typical Pentium motherboard; most of the capabilities of a computer are contained within this component.

• Motherboards and system boards are manufactured under a number of competing standards. Each was designed to solve a particular design, engineering, or marketing problem. Motherboards come in every size — from tiny to huge. Some styles even divide the motherboard into several interconnecting pieces.

2.2 MICROPROCESSORS• The microprocessor, or CPU, is a single

computer chip about the size of a matchbook (see Figure). It’s many legs or pins are inserted into the motherboard. The CPU is responsible for storing and retrieving information on disks and other storage media. It also handles moving information from one part of the computer to another. Other chips and circuitry support it, but the CPU is the most important determinant of computer speed.

2.2.1 Types of Microprocessors• With the system case open, you should be able to tell what type of

CPU your system contains by reading the information that's printed on the top of the chip. You'll probably see a combination of numbers and letters that includes the numbers 386, 486, or 586, or the words Pentium or Pentium Pro, Pentium I, Pentium II, Pentium III or Pentium 4. The higher the microprocessor number, the more quickly it can process information, and the more megabytes of RAM it can address.

• The type of CPU that a computer contains determines its processing power-how fast it can execute various instructions. These days, most CPUs can execute on the order of millions of instructions per second. The type of CPU also determines the precise repertoire of instructions the computer understands and therefore which programs it can run.

• After you locate the chip designator; look in the same spot for an indication of the chip's speed, which is expressed in megahertz and gigahertz. Basically, the speed of the chip defines the number of commands it can perform per second. The higher the number, the faster the CPU (and thus, your computer) can perform

2.2.2 How Microprocessors Work• The CPU is kind of like a traffic cop. Information is constantly

flowing back and forth between the various parts of the PC and the CPU. The CPU stands in the middle, deciding what goes where. One of the CPU's jobs, then, is control of information flow. When you type at the keyboard, the CPU receives every keystroke and redirects it to the right place. When you print a letter, the CPU takes the characters from the screen or the disk and sends them streaming through the cable that connects your PC to your printer.

• Every once in a while, the CPU notices that some of the data flowing by is actually a command to perform a mathematical calculation. It stops the traffic for a second and performs the calculation. Then it returns to its traffic-control duties.

• The CPU gets its orders from the software program that is loaded into the computer's memory. Some of the information being shuttled around by the CPU takes the form of program commands.

• The CPU directs your keystrokes to the computer's electronic memory, or RAM. Your PC's RAM constantly cycles through millions of characters that may need the CPU's attention. In order to process the characters stored in RAM, the CPU must move data to and from RAM at an incredible pace. The faster the CPU and the more efficiently it moved data to and from RAM, the more processing power in the computer.

• The CPU isn't the only microprocessor in PCs. Coprocessors on graphics, 3-D accelerator and sound cards juggle display and sound data to relieve the CPU of part of its burden. And special processors, such as the one inside your keyboard that handles the signals generated whenever you press a key, perform specialized tasks designed to get data into or out of the CPU.

• One of the most important changes is in the arithmetic logic unit (ALU). The ALU handles all the data juggling that involves integers, or whole numbers, such as 1,23,610, or 234. The Pentium is the first Intel processor to have two ALUs so that it can crunch two sets of numbers at the same time. Like the 486, the Pentium has a separate calculation unit that's optimized for handling floating-point numbers or numbers with decimal fractions, such as 1.2 or 33.8942.

• 2.3 MEMORY• You might assume that when you run a program, the CPU fetches instructions from

the hard disk one at a time and executes them, returning to the disk drive every time it finishes a single step. If this were actually the way computers worked, they would be so slow as to be unusable.

• Most personal computer CPUs are capable of executing between one million and one hundred million instructions per second. But because it is mechanical-that is, composed of moving parts-the disk drive cannot deliver program instructions anywhere near that fast. Reading an instruction from the disk involves both rotating the disk so that the proper section is below one of the read/write heads and then moving the head closer to or farther from the center of the disk until it is positioned directly above the spot where the instruction is recorded. Even on a hard-disk drive, this process generally takes between 9 and 25 milliseconds.

• Now if the CPU can execute millions of instructions per second and the disk drive can only deliver, say, one hundred thousand instructions per second, you have the equivalent of an assembly line in which one person on the line (the CPU) is moving somewhere between 10 and 100 times faster than the previous one (the disk drive). If this were really the way your computer worked, the speed of the CPU would be wasted while it waited for the disk drive to deliver the next instruction.

• For the computer to function efficiently, it therefore needs some repository of information that is capable of keeping pace with the CPU. This extra piece is called random access memory, usually referred to as RAM or simply memory for short.

• Physically, RAM consists of a set of separate integrated circuits (each of which looks something like a small CPU chip) which are often mounted on fiber-glass boards called SIMMs (Single Inline Memory Modules) in practice, however, memory is treated as a single, contiguous set of storage bins.

• The figure shows two types of SIMMs. One uses a 30-pin configuration, and the other, larger SIMM uses a 72-pin configuration. Some newer motherboards accept a 168 pin dual in line module (DIMM).

• RAM is a type of short-term memory; when power is turned off, the information is lost. (This is why you must save your work to a floppy or hard disk before you turn off your computer.) RAM speed is measured in nano-seconds, with a smaller number indicating faster performance. Most systems today use RAM speeds between 60-100ns.

• Memory chips come in different shapes and sizes. DRAM (dynamic random-access memory) chips are the most common type of computer memory, and they need to be energized hundreds of times per second to hold the information.

• Another type of RAM chip, usually found in higher-end systems, is called a DIMM (Dual Inline Memory Module). DIMMs effectively pack twice as much memory in one package compared to SIMMs, although DIMMs are slightly longer than SIMMs.

• Like the CPU chip, memory chips store and transmit information electronically. Sending an instruction from memory to the CPU is therefore a simple matter of transmitting electrical impulses. There is no waiting for a disk to spin or a read/write head to move to the proper position.

• Because the CPU can move information in and out of memory so quickly, it uses memory as a kind of electronic desktop-the place it stores whatever it is working on this instant or plans to work with shortly. When you tell your computer that you want to use a particular program, for example, the first thing it does is find the program on your hard disk and copy it into memory. This process is known as loading a program. This gets the comparatively slow process of reading instructions from disk over with at the start. Once the entire program has been loaded, the CPU can quickly read instructions from memory as needed.

• Upgrading System Memory• Memory is one of the most important components of your computer. In order to run a

program or make changes to a file, that program or file must first be placed into memory. Once the file is in memory, the computer can read the data and perform tasks with it.

• When you run many programs at one time (which is easy to do with Windows), you can quickly use up your computer's available memory. Sometimes running only one complex program with a large file can use up all your available memory. When Windows runs out of memory, it starts copying the oldest data out of memory to a temporary holding area on the hard drive called virtual memory. From there, if the data is later needed back in memory, Windows copies the data back. As you can imagine, this whole process of copying data in and out of memory slows down your computer a considerable amount. The only solution is to run fewer programs at the same time, to use smaller data files, or to add more memory.

• When installing memory, you need to consider many things. For example, memory comes in several flavours: DIP, SIMM, DIMM and RAMBUS. DIP memory chips are inserted individually, making them more difficult to install. SIMM and DIMM memory chips are contained on a small board and inserted into special sockets (slots) on the motherboard, making them simple to install.

• RAM is a crucial system component. If it isn't installed properly or isn't the right type for your system, your system probably won't boot.

2.7 HARD DISK DRIVES AND INTERFACES

• Now we're getting to the real storage. The hard drive is essentially several non-removable rigid floppy disks stacked together with a drive built around them. Because the disks are rigid, the read/write heads can be positioned much more accurately, allowing more information to be written (higher density). Another advantage is the disks can spin much faster, thousands of RPM (Revolutions per Minute). As a result of higher recording density and faster spinning, hard drives can write and retrieve information much faster than floppy drives. The most important measure associated with a hard drive is the capacity, how many megabytes it can store.

• So exacting are the tolerances in a hard drive- the gaps between the heads and the platters aren't big enough to admit a human hair-that it's a wonder the drive can perform its work at all without constant disasters. Instead, it keeps on plugging away as the repository of perhaps years of work-with surprisingly few failures.

• The capacity, size, and performance of hard drives have changed dramatically since the introduction in the early 1980s of the first IBM XT with a hard drive.

• Back then, a capacity of 10 mega bytes was considered generous. The hard drive was 3 to 4 inches thick and filled a 5.25-inch drive bay. An access time of 87 milliseconds was warp speed compared to the access times of floppy drives. A decade later, hard drives that hold 3-4 gigabytes (3,000-4,000 megabytes), smaller than a 3.5-inch floppy drive, and with access speeds of 8 milliseconds are inexpensive and commonplace. Some hard drives pack scores of megabytes on removable disks no larger than a matchbox. In the future, the size and prices of drives will continue to decrease at the same time that their capacities increase.

• The price of hard storage is becoming so inexpensive that synchronized groups of hard drives, called drive arrays, are becoming affordable for small businesses and home offices that want the benefits of speed and dependability that the arrays provide.

• One thing about hard drives will stay the same. Unlike other PC components that obey the commands of software without complaint, the hard drive chatters and groans as it goes about its job. Those noises arc reminders that the hard drive is one of the few components of a personal computer that is mechanical as well as electronic. The drive's mechanical components make it the slowest component in your PC. But they also mean that the hard drive, in more ways than one, is where the action is.

• The disk uses the same characters whether it records a great novel or this week's grocery list. Another common element is the scheme that determines how the data on the disk is organized. The computer's operating system, which on most personal computers is Windows95 or MS DOS, determines the scheme. Even in Windows 95, the older DOS is still there, hidden beneath Windows's graphic interface. The operating system controls so many of a PC's operations that many PC users forget that DOS stands for disk operating system and that, originally, it’s primary function was to control disk drives.

• Before any information can be stored on a magnetic disk, the disk must first be formatted. Formatting creates a road map that allows the drive to store and find data in an orderly manner. The road map consists of magnetic codes that are embedded in the magnetic film on the surface of the disk. The codes divide the surfaces of the disk into sectors (pie slices) and tracks (concentric circles). These divisions organize the disk so tint data can be recorded in a logical manner and accessed quickly by the read/write heads that move back and forth over the disk as it spins. The number of sectors and tracks that fit on a disk determines the disk capacity.

• After a disk's formatted, writing or reading even the simplest file is a complicated process. This process involves your software, operating system, the PC's BIOS (basic input/output system), soft- ware drivers that tell the operating system how to use add-on hardware such as a SCSI drive or a tape drive and the mechanism of the disk drive itself.

• There are 2 interfaces you can go with drives: IDE or SCSI

• IDE• IDE is the most common and least expensive. If you have a 586 system, odds are that you have the controller

built into the motherboard so you won't need to buy a card. IDE, however, is slower and puts a greater load on your CPU. If you are running multiple drives they are difficult to configure and slower.

• EIDE• Extended Integrated Drive Electronics (sometimes called Enhanced IDE)EIDE is defined an improved version of

IDE/AT Attachment, with faster Data rates, 32-bit transactions, and (in some drives) DMA (direct Memory Access-the device speaks directly to memory bypassing the CPU). EIDE was named by Western Digital around 1994, and the standard is also referred to as ''Fast ATA-2'', based on its ANSI designation.

• The IDE ''bus'' only supports two devices - master and slave per controller. But the advantages are much lower price and equal or greater speeds than many SCSI drives. Also IDE drives are the de facto standard for PC's. Everything is compatible with IDE, whereas you can run into some problems configuring SCIS devices with some games and the like.

• SCSI• SCSI is much better, faster, and cooler. You can get some pretty buge sizes without difficulty, it is capable of 7

drives on one card and you can plug multiple cards into your system. If you have a SCSI card you can plug in SCSI hard drives, SCSI scanners, SCSI brain surgery Kits--anything SCSI. Oh. It's pronounced Skuzzy. A good SCSI controller will put less of a load on your CPU too. Fast SCSI(SCSI-2) is even faster, and fast-wide SCSI (sometimes incorrectly called SCSI-3) is faster yet. A note on fast-wide SCSI: you can plug 14 devices into it; the data path is twice as wide; it won't speed up anything unless you have a bunch of SCSI devices plugged in (i.e. 6 SCSI devices on a fast-wide system will go faster than 6 devices on a regular system, but 1 device will run the same speed on both--usually!).

• Disk terms are either relevant to a hard drive or to a drive interface. For drives, you’ll hear the terms summarized in the following table.

• 2.8 POWER SUPPLYS• The power supply is the black or silver box in the back of the PC with the large yellow label telling

you in five languages not to open the box up and warning you that it is dangerous• The basic function of a power supply is to convert the 220 volt AC 50Hz source from your wall

outlet into something the computer can use, specifically +5 v, -5 v, +12 v, -12v, and sometimes 3.3 v. The reason for all of the different voltages is due to the need of the PC components in the system. Components, such as disk drive motor and other motors use the +12 v signal and components like the motherboard and other circuit boards use the +5 v signal from the power supply. In newer PC's the negative voltages are not used very much. Due to a couple of standards on the ISA bus, these voltages are required to maintain backward compatibility.

• The power supply also has built-in self test that prevent it from running unless the required voltages are present. The power supply sends to the motherboard a special signal called Power_Good. If this signal is not present than the computer will not run. If your system has ever seemed dead when the power switch is on and the fan and hard disks are running, you know the effects losing the Power_Good signal. This process normally only takes 0.1 to 0.5 seconds after you turn on the power supply switch.If there is not a Power_Good signal then the timer chip continuously resets the processor, which prevents the system from running under bad or unstable power conditions, which could cause data corruption.

• On newer systems with ATX or LPX form factor motherboards, they also include a special signal called PS_ON which can be used to turn the power supply off via software. This is evident when you shut down the computer in Windows XP and then the system will completely shut down and not display a message like it's safe to shut down the computer. This is sometimes called a soft-off feature.

• 2.9 INPUT DEVICES• Input devices are parts of the computer that let you input information and data into the

computer. The keyboard, mouse, and joystick are examples of input devices. Scanners and cameras are also input devices, but are not used as often. Disk drives and modems can also be used as input devices.

• Disk Drives• Disk drives are a very important part of the computer, but choosing them is relatively

easy. There are several types of disk drives: Hard drives, Floppy disk drives, CD ROM drives, Tape backups, and Zip drives.

• Floppy Disk Drive• Every computer comes with a floppy disk drive. They are the main way of putting

information on to the hard drive. They also allow you to save information on a disk, which is an easy way to transport files and data between different computers. There are two different sizes of floppy drives. The 5.25” floppy disk is not used very often any more. It has been replaced by the 3.5” disk, which is smaller and can hold more information. A 3.5” high-density disk can hold 1.44 megabytes of data.

• The media is contained within a rigid case but is itself flexible. Thus, this is not a hard drive but a floppy drive. NEVER touch the media or the disk will be ruined. To view the actual media, slide open the metal door and look through the read/write window.

• The back of the drive has power and data connections. Some 3.5" floppy drives have non-standard connectors and must have adapters to connect with the data cable. The power connector will normally attach only one way. This makes it difficult to plug power in wrong. Pin one of the data connector is usually at the end of the connector next to the power connector. Wire one on the ribbon cable is most often marked with a different color, usually red, from the others and the connector has a small arrow or triangle-marking pin one of the connector. This information should help if you are installing a used floppy to an existing system or if you have no documentation.

• • CD ROM Drive• Most computers now come standard with a CD ROM drive. Most programs and games now come

on CD. Many programs are being put on CD’s because they can hold over 600 megabytes of data on a single disk. A CD ROM drive reads data from a CD that looks much similar to a music CD, except it holds data rather than music. Much like music CD’s, CD ROMs cannot be written to, so you cannot save information to a CD ROM. CD’s make it possible to add sound and video to games and programs. The CD ROM drive comes in several different speeds. Speeds vary from double speed to 52X speed.

• A double speed CD ROM is the minimum. It is still functional but the video and sound are more likely to be a bit jumpy. The faster a CD ROM can read a CD the smoother the video and sound becomes. Faster is better, but for most users an 8X speed will work just fine. CD writers are now available. CD writers allow you to write information to a CD. You have to buy blank CD’s to write to. Once written, these CD’s can be read by any CD ROM drive. This may sound like a good solution to your storage problems, but they can be tricky to use. You may waste a few CD’s while learning how to use it.

• CD-ROM (Compact Disk Read Only Memory) drives are very popular, and for good reason. The drives have become inexpensive to buy and the disks are cheap to make (figure under two dollars to press a disk). A software maker can put information onto software that looks at the disk and verifies that it is being accessed from the CD. This can be used to prevent software piracy. CD-ROM disks can hold 640 Megabytes of data, more than any application on the market today is likely to need. You don't need 16 3.5" high-density disks to load up your favorite suite of office apps.

• The disks require special care. Like 5.25" floppies the media is exposed. Unlike floppies, you can clean them. Refer to your CD-ROM drive manual for sections on cleaning the disks. Soft, lint-free, clean cloths only should be used. While I don't recommend it for software CD's, I have put my music CD's under the tap and washed them in dish soap, then dried them using a soft, clean, lint-free towel. While it worked great, I don't recommend it. It could void a warranty.

• The attachments for a CD-ROM drive are nearly identical to those for a 3.5" floppy, and with the same layout. In addition, a sound cable attaches to the CD and runs to a sound card. To get the drive to work properly, you may be called on to move a jumper to master or slave selection as required by your system. Again, refer to your manufacturer's manual for proper installation and troubleshooting.

• DVD Drive• The latest in mass storage is the DVD drive. DVD stands for digital video

disk. The DVD technology is still developing. A dual layer, dual sided version of this disk can hold up to 17 gigabytes. The current version, which is single layer, single sided holds 4.7 gigabytes. Since this technology is still relatively new, there are not a lot of products that support it. DVD will soon replace the CD.

• Keyboard• Using the keyboard is the primary way of inputting data into many of your

programs. we are sure you know what a keyboard is so I will not go into much detail to describe it, but we will tell you of a few different kinds of keyboards. Keyboards are usually described by the number of keys they have. This keyboard comes standard on most computers. There are also ergonomic keyboards. These keyboards look like they are broken in half, and are supposed to make typing less stressful on your wrists. Some keyboards come with a built in trackball or finger pad. Picking a keyboard is just a matter of preference. For most everybody, the standard 101 keyboard will work just fine.

• Mouse• The mouse is a very important input device because it makes getting around in your computer

easier. The mouse controls and arrow which can be moved anywhere on the screen. The mouse is good for doing tasks such as moving and pointing to objects on the screen. There are several types of mice, and several input devices similar to mice. Alternatives to the mouse include: the trackball, touchpad, and touch-screen.

• A mouse can have two or three buttons. A two button mouse is usually standard.• Another thing to note about your mouse is how it plugs into the computer. A serial mouse plugs

into a 9 pin serial port in the back of the computer. Most computers now come with an input for a bus mouse, also referred to as a PS/2 mouse. The PS/2 mouse has a round connector similar to that of the keyboard. This mouse is a better choice, because more computers are using it now.

• The trackball is very similar to the mouse, except the ball is on top instead of underneath. You move the ball with your thumb or palm. This is sometimes easier for children to use because they can let go of the ball to click the buttons. This is good because the arrow will not move when you try to click on something. With the mouse, if you let go of it to click a button, it will usually move. Choosing between the mouse and the trackball is just a matter of preference.

• The touch pad and touch screen are very similar. For both you use your finger to move the cursor on the screen. With the touch pad you move your finger on a pad. With the touch screen you move your finger directly on the screen. These may be fun additions to your computer, but I prefer the mouse or trackball.

• Scanners• Scanners are useful if you need to copy written page or

pictures directly into your computer. If you are using your computer for business, a scanner could be more useful. There are three basic types of scanners: Hand scanners, Page scanners, and Flatbed scanners. Both types come in black and white or color, with color being more expensive. A hand scanner is held in the hand and dragged across the page being scanned. A page scanner feeds paper through it similar to a printer, but instead of printing, it scans in whatever is on the paper. A flatbed scanner looks and works like a copy machine. You put the object to be scanned in the scanner, and then it scans it into the computer.

2.10 OUTPUT DEVICES

MONITORS and VIDEO CARDS

• A video display system has 2 major components: a display monitor and a video card.

VIDEO CARDS• Your system's video card is responsible for what you see on your monitor

screen, the video card is the part of the computer that sends the images to the monitor. Video cards are also referred to as video accelerators. Video cards usually contain their own memory chips. This memory helps the computer to load images faster. A video card should contain at lest 32 megabyte of memory, but 64 megabytes is becoming standard. 128 megabytes is quite a bit more expensive, but is even better.

• Besides video cards, video may be integrated on the motherboard. Having it included on the motherboard eliminates the possibility of choosing a card to meet your needs. Many have an option by jumper or BIOS setting to disable the on-board video when updating and adding a true video acceleration card. Usually this video does not render high resolution large screen graphics.

• The video processor, along with the system CPU, manipulates this data to change the screen image and the RAMDAC reads it and sends it to the monitor.

• RAMDAC (Random Access Memory Digital-Analog Converter): The screen image information stored in the video memory (RAM) is digital, because computers operate on digital numbers The patterns of ones and zeros control the colour and intensity of every pixel (dot) on the screen.

• The monitor, however, doesn't use digital information. it is analog. In order to display the image on the screen, the information in video memory must be converted to analog signals and sent to the monitor. The device that does this is called the RAMDAC.

• PCI vs AGP Video Cards: There are cards for a PCI slot as well as AGP (Accelerated Graphics Port). AGP was designed by Intel in 1997, specifically for the video subsystem. It is a new technology. It is considered a port not a bus. The idea behind AGP is to create a faster, dedicated interface between the video chipset and the system processor. The interface is only between these two devices. It makes it easier to implement the port, makes it easier to increase AGP in speed, and makes it possible to put enhancements into the design that are specific to video. AGP motherboards have a single expansion card slot for the AGP video card, and usually one less PCI slot, and are otherwise quite similar to PCI motherboards.

THE MONITOR• A display monitor is a video output device capable of displaying text and

graphics. • In a very basic Cathode Ray Tube (CRT) a beam of electrons is focused

and aimed by electromagnets, then the electron beam strikes a phosphorescent surface at the other end of the tube. Light is given off by the phosphor at the end of the CRT. The entire tube is kept at as close to vacuum as possible so that the electron stream is not deflected.

• This basic CRT would be a monochrome(one color) monitor. By raising the number of electrons that strike the screen, the display is made brighter. Relate this to a black and white television or an amber or a green screen computer monitor. On a computer monitor, each individual dot is addressed individually to make part of a shape or character. This dot is called a pixel.

• Color CRT type monitors have three kinds of phosphors to produce Red, Green and Blue (RGB) light. All of the colors that humans can see can be produced by some combination of these colors. The first color monitors used only two brightnesses of red, green and blue to produce colors. Red could be off, on or on high. A total of only sixteen colors (to include black) could be displayed because all colors had to match in intensity.

• The VGA monitor can display any color. Any limitation is in the video card used. While early VGA video cards were limited to sixteen colors displayed, they improved on EGA video cards both in resolution and in pallet depth. The sixteen colors were chosen from 256 basic colors.

• Since that time, true color VGA adapters have allowed the VGA and Super VGA monitor to display true color. This is the industry name for 24 bit color. With eight bits per color per pixel, there are 256 levels of red, green or blue per dot. 1677216 colors to choose from. It would take a 1295 by 1295 pixel monitor to display all of the colors possible! The largest industry standard monitor these days measures 1280 by 1024 pixels.

• Common VGA or SVGA monitors may be capable of 640x480, 800x600, 1024x768 and 1280x1024 pixels. This is horizontal dots by vertical dots. At 640 by 480, the number of pixels is (640x480=) 307200. The 1280 by 1024 display shows 1,310,720. At 16 colors, each dot has 4 bits of information. At true color, each dot holds 24 bits. So a monitor showing 640x480 dots at 16 colors has (640x480x4=) 1,228,800 bits of information, while a true color 1280x1024 video card holds 31,457,280 bits of information! This is why the newer, better video adapter cards demand so much memory.

• Screen savers came along because of a problem with cathode ray tubes. Recall from the basic CRT description above, the electrons hitting the phosphor coating on the front of the CRT. As each electron strikes, it may knock loose an atom! This is called sputter. When this happens, the phosphor in that spot being gone, there is less light given off. A display constantly showing the same image will concentrate this effect, producing screen burn.

• In an early solution to this problem, computer input inactivity would shut off the video monitor. Activity would start it right back up. However, thinking the computer off, it often happened that users would mess something up. Someone wanting to use the computer might think that, well, if this switch position is OFF, then that way must be ON. Screen savers, then, must not completely shut off the screen, but minimize the portion in use when the computer is not active. Now any program that starts to change screen characteristics after a period of inactivity may call itself a screen saver.

• Internal to the monitor is the CRT (Cathode Ray Tube). A CRT is a display device in computer monitors as well as television sets. A CRT consists of a glass vacuum tube that contains one electron gun for a monochrome display, or three RGB (red, green, blue) electron guns for a color display. Electron beams from these guns sweep rapidly across the inside of the screen from the upper-left to the lower right of the screen.

• The inside of the screen is coated with thousands of phosphor dots that glow when they are struck by this beam. The beams sweep rate is between 43 and 87 times per second (refresh rate) and is measured in Hz (hertz).

• Like televisions, screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally. Several sizes of monitors are available. The most common are the 14 or 15 inch monitor. There are also 17 and 21 inch monitors available.

• Sound Cards• Most computers comes standard with a sound card. A sound card

allows your computer to reproduce music, sounds, and voice. This is a definite necessity if you are going to play multimedia games. If you are just using your computer for business, then you may not need a sound card. The market standard for sound cards is the Sound Blaster. Be sure to get a computer with a Sound Blaster compatible sound card. There are also different quality of sound cards. Most computers now come with 16 bit sound cards. The next step up would be a 32 bit sound card. Some sound cards have a wave table, which means that it reproduces actual instruments rather than synthesized sound. Most sound cards also have an input for a microphone so that you can record your own voice. My choice would be the Sound Blaster awe32. This is a good quality sound card and it should work with almost all of your games.

• Modems• The modem comes standard on most computers. If you want to send faxes

or get on the internet, then this is what you need. The modem allows the computer to communicate with other computers through the telephone lines. Most modems come with faxing capabilities. Modems are available in different speeds. The standard speed is 56.6 Kbps. Kbps stands for kilo bauds per second, which is just the speed of the modem. The 56.6 modem is also refered to as V.90.  This is the name for the standard on which all 56.6 modems are built.  The 56.6 Kbps modem replaced the 33.6 Kbps modem as the standard.  33.6 and 28.8 modems are still widely used, but if you spend a lot of time on the Internet, you'll appreciate the speed of the 56.6.  The 14.4 modem is now outdated.  It's just too slow for most people.  Another choice you have with modems is external or internal. If you buy a new computer it should come with an internal modem. Internal means that it goes inside your computer, external means that is plugs into your computer and sits on the desk. Internal modems are usually less expensive than external modems. The quality between the two is about the same, so it is just a matter of preference.

• PRINTERS• All printers whether dot matrix, ink-jet or

LaserJet accomplish essentially the same task: They create a pattern of dots on a sheet of paper. The dots may be sized differently or composed of different inks that are transferred to the paper by different means, but all of the images for text or graphics are made up of dots. The smaller the dots, the more attractive the printout.

DOTMATRIX PRINTERS• The dot-matrix printer- noisy, slow, and crude - is a dying

technology. Laser printers are faster and produce more attractive documents. Ink-jet printers cost little more than a dot-matrix, but produce beautiful color and resolution. The only thing a dot matrix printer has on its cousins is that it can handle multi-layer forms - carbons - while the others can’t. That’s because a dot- matrix printer is, like a typewriter, an impact printer. It prints by pounding ink onto paper. But carbons being, themselves, a sort of retry technology, even that advantage is dubious.

• Impact printers with 24 or more pins produce documents that rival the laser printer, and some dot-matrix printers call interpret commands from PostScript or another page description language. But most impact printers are simple things, designed to work with another ancient technology, bitmapped type controlled by ASCII codes sent to the printer from a PC.

LASER JET PRINTERS• Every time you send a page 10 your laser printer, you're selling in motion a

complex, inter locked series of steps as efficiently organized as a factory and as precisely choreographed as a ballet. At the heart of the printer is the print engine-the mechanism that transfers a black powder to the page, which is a device that owes its ancestry to the photocopier. Its operation includes technologies Gutenberg never imagined, including laser imaging, precise paper movement, and microprocessor control of all its actions.

• To create the nearly typeset-quality output that is characteristic of a laser printer, the printer must control five different operations at the same time:

• It must interpret the signals coming from a computer, • Translate those signals into instructions that control the firing and movement

of a laser beam, • Control the movement of the paper, • Sensitize the paper so that it will accept the black toner that makes up the

image, An• Fuse that image to the paper.

• The result is no-compromise printing. Not only does the laser printer produce hard copy faster than most any other type of printer, but the laser printed pages are more sharply detailed. With the introduction of color laser printers, the five-ring circus turns into a 20-ring bazaar. For the foreseeable future, the laser is the standard for high end, day in, day out office printing.

• COLOR PRINTING• There have been two revolutions in computer printing in the last

decade. One was the laser printer, which brings typeset quality printing of text and graphics to the masses. The second was the development of inexpensive, fast, high quality color printing.

• The complexity of color printing, of course, means trade-offs. At the low-price end is the color ink-jet printer. It is in some ways a dot-matrix printer without the impact and with four times the colors. A color ink jet costs barely more than a black and white ink-jet. The visual detail approaches that of laser printers, in some printers surpassing it. But ink-jet technology is relatively slow and you always have to fuss with cleaning and replacing the ink-filled print beads. Color ink jets are the ideal printer for the home, where printing volume is small, a budget maybe nonexistent, and the flash of color in a school report or a greeting card is worth the extra wait.

• For the office there are different color printing solutions that match the budget of a small business or home office and solutions that give the most fussy graphic artists the speed, color-matching, and details they need to create professional results. The crucial difference among color printers is how they get ink on the paper. Because it involves four colors of ink to achieve full color printing, a printer must either make multiple passes over the same sheet of paper-as happens with laser and thermal wax color printers- or it must manage to transfer all of the colors more or less simultaneously, which is what happens with solid-ink printers, whose results are almost photograph-quality.

• A common office color printing device is the color thermal printer The process provides vivid colors because the inks it uses don't bleed into each other or soak into specially coated paper. But its four-pass method is slow and wastes ink. The color laser printer provides the most precise detail but is slow, complicated, and expensive because it requires four separate print engines that must each take their turn to apply colored toner to the page.

• Two other color-printing methods provide speed and photographic dazzle: dye sublimation-also called dye diffusion thermal transfer (D2T2) - and solid ink. By controlling not only how many dots of color they put on the page but the intensity of the dots, they produce continuous tone printing. The result is virtually indistinguishable from a color photograph even through its actual resolution maybe no more than the 300 dots per inch of the old laser printer. If the results you're trying to get with color printing are really important, these technologies arc well worth the cost.

Day 2-3: 5. NETWORKING

5.1 Network Fundamentals• Imagine 20 years ago working in an office with little or no computer equipment. It’s hard to

imagine now, isn’t it? One could say that we take for granted a lot of what we have gained in technology the past few decades. Now, imagine having to send a memo to everyone in the company. Back then we used interoffice mail; today we use e-mail. This is one form of communication that only became available due to the introduction and growth of networks.

• Stand-alone personal computers (See Figure 1.1), first introduced in 1970s, gave users the ability to create documents, spreadsheets, and other types of data and save them for future use. For a small business user or home computer enthusiast, this was great. For large companies and organizations, however, it was not enough. The larger the company, the greater the need to share information between offices, and sometimes over greater distances. The stand-alone computer was not enough for the following reasons:

• Their small hard drive capacities were inefficient.• To print, each computer required a printer attached locally.• Sharing documents was cumbersome. People grew tired of having to save a diskette, then taking

that diskette to the recipient. • There was no e-mail. Instead, there was interoffice mail, which was not reliable and frequently

was not delivered in a timely manner.• To address these problems, networks were born. A network links two or more computers

together to communicate and share resources.

What is a Computer Network?• A computer network is a group of computers and

associated peripheral devices connected by a communication channel capable of sharing files and other resources among several users. A network can range from a small network connecting a small number of users in an office or department, to a Local Area Network connecting many users over permanently installed cables and dial-up lines, to a Metropolitan Area Network or Wide Area Network connecting users on several net-works spread over a wide geographic area.

• If the computer shown in Figure 1.1 was to be connected to other computers, then, it could share data with the other computers or send documents to a printer. This connecting together of computers and other devices is called a network, and the concept of connected computers sharing resources is called networking. (See Figure 1.2)

• A simple computer network

• Benefits of Computer Networking

• application programs that are installed centrally in one location (application server). Software (application) that is installed centrally can be managed and upgraded centrally. Such systems are mostly common in financial system where the main application is stored centrally and users in different sections of the finance department are able to run the system from the network.

• It is effective for several reasons• Less disk storage space is required because the program is stored

only once on the server, instead of being stored on the hard disks of multiple stand alone computers

• When a new version of the software is released, it is easier to update on copy of the program on the server than to update many copies stored on stand alone computer.

• Purchasing a software license for a network can be less expensive than purchasing a single-user license for every workstation on the network

In short sharing programs on a network

• Saves disk space

• Reduces maintenance

• Reduce licensing cost

• Sharing Hardware • Computer networks enable us to share expensive hardware

resource among several computers. A typical example of shared resource is printer. For example, a company may prefer to acquire one expensive printer and connect it to the network to provide high quality printing to users. This avoids the need to have separate printer for each computer in the office.

• Central Disk storage – Network system provide the possibility of using a dedicated file server to store all the company data in one location. Users will be able to access their data over the network from their workstations. Using central disk storage system facilitates data backup operations from a central location guarantying complete data recovery in case of system failures.

Sharing Information/dataUsers in a certain network environment have the liberty of sharing data and information

across the network. Data sharing enables different users to work on a certain file concurrently. Few examples of data sharing are:

• Database: - databases are often managed centrally and several users can have access to the database at same time. For example, in a networked banking system, different bank branches can have access to the central account database. This enables bank clients to carry their transactions on any branch bank office.

• E-mail: email communication can be achieved over the network enabling networked users in the company to communicate messages across the network using email.

• Intranet: Intranets are similar to World Wide Web (WWW) where centrally stored hypertext documents can be accessed using the web. Unlike the WWW, intranets are available only to user with in the company network system. Intranet is a very common service in large networked organizations.

• Extranet: Although similar to intranet, extranet provides selected users from outside the organization to access data from the internal network. Extranets are commonly used by suppliers to provide data to company clients.

• By making information available for sharing, networks can reduce the need for paper communication, increase efficiency, and make nearly any type of data available simultaneously to every user who needs it. Managers can use these utilities to communicate quickly and effectively with large numbers of people and to organize and schedule meetings with people drawn from an entire company or business enterprise far more easily than was previously possible.

Centralizing Administration and Support• Networking computers can simplify support tasks as well. It is far more

efficient for technical personnel to support one version of one operating system or application and to set up all computers in the same manner than to support many individual and unique systems and setups

• Even if your computer is physically connected to a network, you cannot typically use network resources until you log into the network. When you log in, you formally identify yourself to the network by providing your ID and password.

• Your user ID and password are the basis for your user account. A user account provides access to network resources and accumulates information about your network use by tracking when you log in and log out.

• For such network environment a network administrator/supervisor is required who is responsible for setting up user accounts and maintains a network. The network administrator provides each new user with a user ID and starter password. In this way centralized administration and support can be achieved.

Types of Network Nodes Relationships• Fundamentally, at any given moment, the computer is either acting as a

client or as a server. A server is a computer that shares its resources across the network, and a client is one that access shared resources.

• Another way to understand this relationship is to visualize an information interchange that can best be described as request- response. That is, a client requests information, and s server responds to such a request by providing the requested information (or by denying the request). This relationship, called the client/server relationship.

• In some networking environments, certain computers take on specialized roles and function more or less exclusively as servers, while ordinary user’s machines tend to function more or less exclusively as clients. Such network environments are called client/server networks.

• Based on how the computers in a network are configured and how they access information, networks are classified into three types: peer-to-peer client-server and hybrid.

The difference between peer-to-peer and server-based networks is important because each type possesses different capabilities. The type of network you choose to implement will depend on factors such as the:

• Size of the organization • Level of security required • Type of business • Level of administrative support available • Amount of network traffic • Needs of the network users• Network budget

Peer-to-Peer Networks• In a peer-to-peer network, there are no

dedicated servers, and there is no hierarchy among the computers. All the computers are equal and therefore are known as peers. Each computer functions as both a client and a server, and there is no administrator responsible for the entire network. The user at each computer determines what data on that computer is shared on the network. Figure 1.4 shows a peer-to-peer network in which each computer functions as both a client and a server.

Size• Peer-to-peer networks are also called workgroups. The

term "workgroup" implies a small group of people. There are typically 10 or fewer computers in a peer-to-peer network.

Cost• Peer-to-peer networks are relatively simple. Because

each computer functions as a client and a server, there is no need for a powerful central server or for the other components required for a high-capacity network. Peer-to-peer networks can be less expensive than server-based networks.

Operating Systems• In a peer-to-peer network, the networking software does not require the same standard of

performance and level of security as the networking software designed for dedicated servers. Dedicated servers function only as servers and not as clients or workstations. They are discussed in more detail later in the next section.

• Peer-to-peer networking is built into many operating systems. In those cases, no additional software is required to set up a peer-to-peer network.

Implementation• In typical networking environments, a peer-to-peer implementation offers the following

advantages:• Computers are located at users' desks. • Users act as their own administrators and plan their own security. • Computers in the network are connected by a simple, easily visible cabling system.• Peer-to-peer networks are good choices for environments where:• There are 10 users or fewer. • Users share resources, such as files and printers, but no specialized servers exist. • Security is not an issue. • The organization and the network will experience only limited growth within the foreseeable

future. • Where these factors apply, a peer-to-peer network will probably be a better choice than a server-

based network.

Peer-to-Peer Network Considerations• Although a peer-to-peer network might meet the needs of small

organizations, it is not appropriate for all environments. The rest of this section describes some of the considerations a network planner needs to address before choosing which type of network to implement.

Administration• Network administration tasks include:• Managing users and security. • Making resources available. • Maintaining applications and data. • Installing and upgrading application and operating system software. • In a typical peer-to-peer network, no system manager oversees

administration for the entire network. Instead, individual users administer their own computers.

Sharing Resources• All users can share any of their resources in any manner they

choose. These resources include data in shared directories, printers, fax cards, and so on.

Server Requirements• In a peer-to-peer environment, each computer must:• Use a large percentage of its resources to support the user at the

computer, known as the local user. • Use additional resources such as hard-disk space and memory, to

support the user's accessing resources on the network, known as the remote user.

• While a server-based network relieves the local user of these demands, it requires at least one powerful, dedicated server to meet the demands of all the clients on the network.

Security• On a computer network, security (making computers and

data stored on them safe from harm or unauthorized access) consists of setting a password on a resource, such as a directory, that is shared on the network. All peer-to-peer network users set their own security, and shared resources can exist on any computer rather than on a centralized server only; consequently, centralized control is very difficult to maintain. This lack of control has a big impact on network security because some users may not implement any security measures at all. If security is an issue, a server-based network might be a better choice.

Server-Based Networks• As a network grows, a peer-to-peer network will

probably no longer be able to meet the increased demand on shared resources. To accommodate the increased demand and provide additional functionality, most networks have dedicated servers. A dedicated server functions as a server only, not as a client. The configuration of these servers is optimized to process requests from network clients.

Client-server networks (see Figure 1.5) have become standard models for networking.

• Figure 1.5 Server-based network

• As networks increase in size due to the number of connected computers and the physical distance and traffic between them, more than one server is usually needed. Distributing the network tasks among several servers ensures that each task is performed as efficiently as possible. Also, with the servers performing the network tasks, the workload on the individual computers is reduced.

• Advantages of Server-Based Network • Although it is more complex to install, configure, and

manage, a server-based network has many advantages over a simple peer-to-peer network. The following are some of the advantages:

• Sharing Resources• A server is designed to provide access to many files and

printers while maintaining performance and security for the user.

• Server-based data sharing can be centrally administered and controlled. Because these shared resources are centrally located, they are easier to find and support than resources on individual computers.

• Security• Security is often the primary reason for

choosing a server-based approach to networking. In a server-based environment, one administrator who sets the policy and applies it to every user on the network can manage security. Figure 1.6 depicts security being centrally administered.

• Backup• Backups can be scheduled several times a day or once

a week depending on the importance and value of the data. Server backups can be scheduled to occur automatically, according to a predetermined schedule, even if the servers are located on different parts of the network.

• Redundancy• Through the use of backup methods known as

redundancy systems, the data on any server can be duplicated and kept online. Even if harm comes to the primary data storage area, a backup copy of the data can be used to restore the data.

• Number of Users• A server-based network can support thousands of users. This type

of network would be impossible to manage as a peer-to-peer network, but current monitoring and network-management utilities make it possible to operate a server-based network for large numbers of users.

• Hybrid Networks• In fact it is not unusual to find networks in which workstations

function as peers on peer-to-peer networks and as client on server-based networks. Such networks are called hybrid networks sometimes called combination networks. These networks, partake of the advantages of both peer-to-peer and server-based network. And they incur the disadvantages of server based networks in their entirely and those of peer-to-peer networks only to the degree that peer-to-peer capabilities are exercised.

• Table 1.1 Comparisons of Network TypesConsiderationPeer-to-Peer NetworkServer-Based NetworkSizeGood for 10 or fewer computersLimited only by server and network hardware capacitySecuritySecurity established by the user of each computerExtensive and consistent resource and user securityAdministrationIndividual users responsible for their own administration; no full-time administrator necessaryCentrally located for network control; requires at least one knowledgeable administrator

5.2 Network Media• Data signal must enter and leave a computer at a point

to allow networked communication to occur. The data signal travels through transmission media.

• Transmission media is a medium or a material through which data can be transmitted over the long distances. The speed or rate at which data is transmitted over a communication channel is denoted by a parameter called bandwidth. Transmission media having higher bandwidths are used now -a -days for better performance.

• Transmission media is categorized as:• Bounded (guided) transmission media• Unbounded (unguided) transmission media

Guided Transmission Media• Guided transmission media uses a cabling system that

guides the data signals along a specific path. The data signals are bound by the cabling system. Guided media is also known as bound media. "Cabling" is meant in a generic sense, and is not meant to be interpreted as copper wire cabling only.

• The three major categories of cables or guided transmission medium that connect most networks are:

• Coaxial cable • Twisted-pair cable • Fiber-optic cable

Coaxial Cable• Coaxial cable consists of a copper wire core surrounded by

insulation, a braided metal shielding, and an outer cover. Figure 2.1 shows the various components that make up a coaxial cable.

• The term shielding refers to the woven or stranded metal mesh (or other material) that surrounds some types of cabling. Shielding protects transmitted data by absorbing stray electronic signals, called noise, so that they do not get onto the cable and distort the data. Cable that contains one layer of foil insulation and one layer of braided metal shielding is referred to as dual shielded. For environments that are subject to higher interference, quad shielding is available. Quad shielding consists of two layers of foil insulation and two layers of braided metal shielding.

• The core of a coaxial cable carries the electronic signals that make up the data. This wire core can be either solid or stranded. If the core is solid, it is usually copper.

• Surrounding the core is a dielectric insulating layer that separates it from the wire mesh. The braided wire mesh acts as a ground and protects the core from electrical noise and crosstalk. (Crosstalk is signal overflow from an adjacent wire).

• The conducting core and the wire mesh must always be kept separate from each other. If they touch, the cable will experience a short, and noise or stray signals on the mesh will flow onto the copper wire. An electrical short occurs when any two conducting wires or a conducting wire and a ground come into contact with each other. This contact causes a direct flow of current (or data) in an unintended path. In the case of household electrical wiring, a short will cause sparking and the blowing of a fuse or circuit breaker. With electronic devices that use low voltages, the result is not as dramatic and is often undetectable. These low-voltage shorts generally cause the failure of a device; and the short, in turn, destroys the data.

• A non-conducting outer shield—usually made of rubber, Teflon, or plastic—surrounds the entire cable.

• Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling. Attenuation is the loss of signal strength that begins to occur as the signal travels farther along a copper cable. (See the following figure).

• The stranded, protective sleeve absorbs stray electronic signals so that they do not affect data being sent over the inner copper cable. For this reason, coaxial cabling is a good choice for longer distances and for reliably supporting higher data rates with less sophisticated equipment.

Types of Coaxial Cable• There are two types of coaxial cable:• Thin (thinnet) cable • Thick (thicknet) cable

Thinnet Cable Thinnet cable is a flexible coaxial cable about 0.64 centimeters thick. Because this type of coaxial cable is flexible and easy to work with, it can be used in almost any type of network installation.

• Thinnet coaxial cable can carry a signal for a distance of up to approximately 185 meters before the signal starts to suffer from attenuation.

• Thicknet Cable Thicknet cable is a relatively rigid coaxial cable about 1.27 centimeters in diameter. Figure 2.3 shows the difference between thinnet and thicknet cable. Thicknet cable's copper core is thicker than a thinnet cable core.

• The thicker the copper core, the farther the cable can carry signals. This means that thicknet can carry signals farther than thinnet cable. Thicknet cable can carry a signal for 500 meters. Therefore, because of thicknet's ability to support data transfer over longer distances, it is sometimes used as a backbone to connect several smaller thinnet-based networks.

• Thinnet vs. Thicknet: As a general rule, the thicker the cable, the more difficult it is to work with. Thin cable is flexible, easy to install, and relatively inexpensive. Thick cable does not bend easily and is, therefore, harder to install. This is a consideration when an installation calls for pulling cable through tight spaces such as conduits and troughs. Thick cable is more expensive than thin cable, but will carry a signal farther.

• Coaxial-Cable Connection Hardware• Both thinnet and thicknet cable use a connection component, known as a

BNC connector, to make the connections between the cable and the computers. There are several important components in the BNC family, including the following:

• The BNC cable connector: The following figure shows a BNC cable connector. The BNC cable connector is either soldered or crimped to the end of a cable.

• The BNC T connector: The following figure shows a BNC T connector. This connector joins the network interface card (NIC) in the computer to the network cable.

• The BNC barrel connector: The following figure shows a BNC barrel connector. This connector is used to join two lengths of thinnet cable to make one longer length.

• The BNC terminator: The following figure shows a BNC terminator. A BNC terminator closes each end of the bus cable to absorb stray signals. Otherwise, the signal will bounce and all network activity will stop.

• NOTE: The origin of the acronym "BNC" is unclear, and there have been many names ascribed to these letters, from "British Naval Connector" to "Bayonet Neill-Councelman." Because there is no consensus on the proper name and because the technology industry universally refers to these simply as BNC-type connectors, in this manual we will refer to this family of hardware simply as BNC

• It is less susceptible to interference than twisted-pair cable.

• Transmit data for greater distances than is possible with less expensive cabling.

• Transmit voice, video, and data

• Offer a familiar technology with reasonable data security.

Disadvantages of Coaxial Cable

• There are many types of coaxial cables, each suited for one, or at most, a small number of LAN systems.

• Due to its high metallic content, coaxial cable is usually more expensive than other cable types.

Twisted-Pair Cable• Twisted-pair cable consists of two insulated strands of

copper wire twisted around each other.Types of twisted pair cable• There are two types of twisted-pair cable:• Unshielded twisted-pair cables (UTP cables)• Shielded twisted-pair cables (STP cables)• A number of twisted-pair wires are often grouped

together and enclosed in a protective sheath to form a cable. The total number of pairs in a cable varies. The twisting cancels out electrical noise from adjacent pairs and from other external sources such as motors, relays, and transformers.

Unshielded Twisted-Pair (UTP) Cable• UTP, using the 10BaseT (“10” indicates bandwidth of the

cable in Mbps, “Base” refers the type of transmission i.e. baseband transmission, and “T” indicates the type of the cable which is twisted pair) specification, is the most popular type of twisted-pair cable and is becoming the most popular LAN cabling. The maximum cable length segment is 100 meters (after 100 meters, the signal gets weaker and weaker as the result the receiving computer will not recognize whether it is noise or not).

• Traditional UTP cable consists of two insulated copper wires. UTP specifications govern how many twists are permitted per foot of cable; the number of twists allowed depends on the purpose to which the cable will be put.

There are 7 standard categories of UTP:• Category 1 This refers to traditional UTP telephone cable that can

carry voice but not data transmissions. • Category 2 This category certifies UTP cable for data transmissions

up to 4 megabits per second (Mbps). It consists of four twisted pairs of copper wire.

• Category 3 This category certifies UTP cable for data transmissions up to 16 Mbps. It consists of four twisted pairs of copper wire.

• Category 4 This category certifies UTP cable for data transmissions up to 20 Mbps. It consists of four twisted pairs of copper wire.

• Category 5 This category certifies UTP cable for data transmissions up to 100 Mbps. It consists of four twisted pairs of copper wire.

• Category 5e Improved version of CAT 5 category. The bandwidth is 1000Mbps

• Category 6 Similar to CAT 5 wire, but contains a physical separator between the 4 pairs to further reduce electromagnetic interference.

Shielded Twisted-Pair (STP) Cable• STP cable uses a woven copper-braid jacket

that is more protective and of a higher quality than the jacket used by UTP. Figure 2.9 shows a two-twisted-pair STP cable. STP also uses a foil (very thin sheet of metal) wrap around each of the wire pairs. This gives STP excellent shielding to protect the transmitted data from outside interference, which in turn allows it to support higher transmission rates over longer distances than UTP.

• Twisted-Pair Cabling Components• While we have defined twisted-pair cabling by the number of twists

and its ability to transmit data, additional components are necessary to complete an installation. As it is with telephone cabling, a twisted-pair cable network requires connectors and other hardware to ensure proper installation.

• Connection hardware Twisted-pair cabling uses RJ-45 telephone connectors to connect to a computer. These are similar to RJ-11 telephone connectors. An RJ-45 connector is shown in Figure 2.10 Although RJ-11 and RJ-45 connectors look alike at first glance, there are crucial differences between them.

• The RJ-45 connector is slightly larger and will not fit into the RJ-11 telephone jack. The RJ-45 connector houses eight cable connections, while the RJ-11 houses only four.

Figure 2.10 RJ-45 connector and jack

• Distribution racks and rack shelves Distribution racks and rack shelves can create more room for cables where there isn't much floor space. Using them is a good way to organize a network that has a lot of connections.

• Expandable patch panels These come in various versions that support up to 96 ports and transmission speeds of up to 100 Mbps.

• Jack couplers These single or double RJ-45 jacks snap into patch panels and wall plates and support data rates of up to 100 Mbps.

• Wall plates these support two or more couplers.

Advantages UTP • It has a large installed base and is a

familiar technology.• It is relatively inexpensive and easy to

install.• Most LAN systems are readily capable of

running over UTP.• It does not require bonding and grounding.• Easy to install.

Disadvantages of UTP • High-quality UTP systems require specialized

installation procedures.• UTP is potentially more sensitive to external

electromagnetic interference, crosstalk, and attenuation than other media.

• Not recommended for LAN that requires a high level of security and you must be absolutely sure of data integrity.

• Not suitable for transmitting data over long distances at high speeds.

Advantage of STP • Provides better performance than UTP in

environments with high noise levels—high levels of unwanted electrical signals.

Disadvantages STP • It is more labor-intensive than UTP to install.• Not all LAN systems work readily over STP.• Susceptible to ground faults through the shield.

Fiber-Optic Cable• In fiber-optic cable, optical fibers carry digital

data signals in the form of modulated pulses of light. This is a relatively safe way to send data because, unlike copper-based cables that carry data in the form of electronic signals, no electrical impulses are carried over the fiber-optic cable. This means that fiber optic cable cannot be tapped, and its data cannot be stolen.

• Fiber-optic cable is good for very high-speed, high-capacity data transmission because of the purity of the signal and lack of signal attenuation.

Fiber-Optic Cable Composition• An optical fiber consists of an extremely thin cylinder of glass, called

the core, surrounded by a concentric layer of glass, known as the cladding. The fibers are sometimes made of plastic. Plastic is easier to install, but cannot carry the light pulses for as long a distance as glass.

• Because each glass strand passes signals in only one direction, a cable includes two strands in separate jackets. One strand transmits and one receives. A reinforcing layer of plastic surrounds each glass strand, and Kevlar fibers provide strength. See Figure 2.12 for an illustration of fiber-optic cable. The Kevlar fibers in the fiber-optic connector are placed between the two cables. Just as their counterparts (twisted-pair and coaxial) are, fiber-optic cables are encased in a plastic coating for protection.

• Optical fiber strands are thin filaments of glass consisting of an inner core and an outer cladding. Both the core and the cladding are glass, and each has a different refractive index. Signals are transmitted as light pulses through the core of the optical fiber. When these light pulses strike the cladding they are reflected back into the core because the cladding has a lower refractive index than the core. This keeps the transmitted signal within the core as it travels down the fiber.

• Fiber-optic cable transmissions are not subject to electrical interference and are extremely fast, currently transmitting about 100 Mbps with demonstrated rates of up to 1 gigabit per second (Gbps). They can carry a signal—the light pulse—for many miles.

Fiber-Optic Cabling Considerations

Advantages of Fiber-Optic• Optical signals through glass encounter less loss than

electrical signals through copper. This translates into lower attenuation and higher bandwidth than copper, allowing transmission to occur over longer distances and/or at greater speeds.

• High level of immunity to electromagnetic interference since signals are sent as light and not as electricity.

Disadvantage of Fiber-Optic • Due to the required conversions between light and

electricity, more expensive electronics are required than with copper-based systems.

• Requires specialized installation procedures.

Unguided Transmission Media• Although the majority of LANs connect devices using a physical

cable, there are instances where it is difficult or impossible to install cable—such as in historical properties or when there is no right-of-way access between adjacent buildings. In such cases, wireless transmission can be used to connect network devices. Additionally, certain users within an organization may be required to be mobile and still have access to the LAN through the use of a laptop or hand-held computer, such as nurses on their rounds or warehouse employees. Wireless systems do not physically connect network devices since the links between the devices are invisible.

• To conclude, unguided transmission media consists of a means for the data signals to travel but nothing to guide them along a specific path. The data signals are not bound to a cabling media and are therefore often called unbound media.

• The three most common types of unguided transmission medium are• Infrared• Radio Frequency• Microwave• Infrared links• LAN devices connected to each other using infrared light signals work in the

same manner as remote control unit work with television sets. These systems consist of a base unit connected to the server and device connections to the stations. The base unit has two optical nodes—one to receive signals from the station and one to send signals to the station.

• Since the system depends on infrared light to transmit, a requirement is that the base unit and the station connections are in a direct line-of-sight to each other. Alternatively, some of these systems use a reflective surface positioned between the base unit and the station for the purpose of redirecting the signal.

Radio links• This second type of unguided (wireless) media uses

radio waves to transmit information between the server and the stations. Most of these systems use spread spectrum technology where data is transmitted at low density over a given frequency range.

• Systems based on radio links also work with two components—a control module connected to the server and user modules connected to the stations.

• The control module and the user module do not have to be in direct line-of sight with each other. The radio signals are capable of passing through most office building doors and walls.

Microwave

• A cableless medium that use high frequency radio signals to send data or information through the air.

Advantages of Unguided (Wireless) Transmission• Can be used in situations where it is difficult or

impossible to install cable.• Portability• ConvenienceDisadvantages Unguided (Wireless) Transmission• Typically, such systems are not able to meet the

performance demands of large or busy networks.• Transmission can only occur over limited distances and

at limited bit rates.

Networking Equipments and Instruments

Network Interface Card• Network interface card (NICs,) also known as

network adapters provide the interface between cables, and computers. The cards are installed in an expansion slot in each computer and server on the network. After the NIC has been installed, the network cable is attached to the card’s port to make the actual physical connection between the computer and the rest of the network. (See figure 4.1, which is the sample NIC).

Role of Network Interface Cards• The network adapter performs the following

functions:• Prepare data from the computer for the network

cable. • Send the data to another computer. • Control the flow of data between the computer

and the cabling system. • Receive incoming data from the cable and

translate it into bytes that can be understood by the computer's central processing unit (CPU).

• To provide to the growing networking needs of an organization, you need to expand the size or improve the performance of a network. You cannot make networks larger just by adding new computers and more cable. Each network topology or architecture has limits. You can, however, install components to increase the size of the network within its existing environment.

• Components that enable you to expand the network include:• Modem• Repeaters and Hubs• Bridges• Switches• Routers• Gateways

• You can also expand a network by allowing users to connect to the network from a remote location. To establish a remote connection, the three components required are a remote access client, a remote access server, and physical connectivity. Network operating systems enable remote client computers to connect to remote access servers by using:

• Public Switched Telephone Network (PSTN) • Integrated Services Digital Network (ISDN) • Asymmetric Digital Subscriber Line (ADSL)

Modem • A modem is a device that makes it possible for computers to

communicate over a telephone line.• When computers are too far apart to be joined by a standard

computer cable, a modem can enable communication between them. In a network environment, modems serve as a means of communication between networks and as a way to connect to the world beyond the local network.

• Computers cannot simply be connected to each other over a telephone line, because computers communicate by sending digital electronic pulses (electronic signals), and a telephone line can send only analog waves (sound).

• As shown in Figure 4.2, the modem at the sending end converts the computer's digital signals into analog waves and transmits the analog waves onto the telephone line. A modem at the receiving end converts the incoming analog signals back into digital signals for the receiving computer.

• In other words, sending modem MOdulates digital signals into analog signals, and receiving modem DEModulates analog signals back into digital signals.

Repeaters and Hubs

• You can use repeaters and hubs to expand a network by adding two or more segments of cabling. These commonly used devices are inexpensive and easy to set up.

Repeaters • Repeaters receive signals and retransmit them

at their original strength and definition. This increases the practical length of a cable. (If a cable is very long, the signal weakens and become unrecognizable.) Installing a repeater between cable segments enables to travel farther. Figure 4.3 shows how repeaters regenerate weak signals.

• Repeaters do not translate or filter signals. For a repeater to work, both segments connected to the repeater must use the same access method. For example, a repeater cannot translate an Ethernet packet into a token ring packet.

• Repeaters do not act as filters to restrict the flow of problem traffic. Repeaters send every bit of data from one cable segment to another, even if the data consists of malformed packets or packets not destined for a computer on another segment.

Use a repeater to:• Connect two segments of similar or dissimilar cabling.• Regenerate the signal to increase the distance

transmitted. • Transmit all traffic in both directions.• Connect two segments in the most cost-effective

manner.Do not use a repeater when:• There is heavy network traffic. • Segments are using different access methods. • Data filtering is needed.

• As shown in Figure 4.4, repeaters can move packets from one kind of physical media to another. They can take an Ethernet packet coming from a thinnet coaxial-cable segment and pass it on to a fiber-optic segment, provided the repeater is capable of accepting the physical connections.

Hubs • Hubs are connectivity devices that connect

computers in a star topology. Hubs contain multiple ports for connecting to network components. If you use a hub, a break in the network does not affect the entire network; only the segment and the computer attached to that segment fail. A single data packet sent through a hub goes to all connected computers. Figure 4.5 shows method of hub communication.

There are two basic types of hubs:• Passive Hubs. Send the incoming signal directly through

their ports without any signal processing. These hubs are usually wiring panels.

• Active Hubs. Sometimes called multiport repeaters, receive incoming signals, process the signals, and retransmit them at their original strengths and definitions to the connected computers or components.

• Hybrid Hubs. Advanced hubs that will accommodate several different types of cables are called hybrid hubs. The following figure shows a main hub (the hybrid) with three sub-hubs.

Use a hub to:

• Easily change and expand wiring systems

• Use different ports to accommodate a Varity of cable types

• Enable central monitoring of network activity and traffic

Bridges• A bridge is a device that passes data packets

between multiple network segments that use the same communications protocol. A bridge passes one signal at a time. If a packet is destined for a computer within the sender's own network segment, the bridge retains the packet within that segment. If the packet is destined for another segment, it passes the packet to that segment. Figure 4.7 shows a bridge connecting two network segments.

MAC Addresses• As traffic passes through the bridge, information about the sending

computers' MAC addresses is stored in the bridge's memory. The bridge uses this information to build a table based on these addresses. As more data is sent, the bridge develops a bridging table that identifies each computer and its location on network segments. When the bridge receives a packet, the source address is compared to the source address listed in the table. If the source address is not present in the table, it is added to the table. The bridge then compares the destination address with the destination address listed in the table. If a bridge recognizes the location of the destination address, it forwards the packet to this address. If it does not recognize the destination address, it forwards the packet to all segments.

Use a bridge to:• Expand the length of a segment. • Provide for an increased number of computers on the

network. • Reduce traffic bottlenecks resulting from an excessive

number of attached computers. • Split an overloaded network into two separate networks,

thereby reducing the amount of traffic on each segment and making each network more efficient.

• Link dissimilar physical cables, such as twisted-pair and coaxial Ethernet cables.

Switches• Switches are similar to bridges but offer a more direct network

connection between the source and destination computers. When a switch receives a data packet, it creates a separate internal connection, or segment, between any two of its ports and forwards the data packet to the appropriate port of the destination computer only, based on information in each packet's header. This insulates the connection from the other ports and gives the source and destination computers access to the full bandwidth of a network.

• Unlike a hub, switches are comparable to a telephone system with private lines. In such a system, if one person calls someone, the operator or telephone switch connects them on a dedicated line. This allows more conversations to take place at any one time. The following figure illustrates a switched network.

Use a switch to:

• Send a packet directly from the source computer to the destination computer.

• Provide for a greater rate of data transmission.

Router• A router is a device that acts like a bridge or

switch but provides more functionality. In moving data between different network segments, routers examine a packet header to determine the best path for the packet to travel. A router knows the path to all of the segments on the network by accessing information stored in the routing table. Figure 4.9 shows a router connecting two network segments. Routers enable all users in a network to share a single connection to the Internet or a WAN.

• Router allows you to segment your network into what are called subnets. A subnet is a network connected to another network via a router. The following figure shows a network divided into subnets using routers.

Use a router to:• Send packets directly to a destination computer on another

networks or segment. • Routers use a more complete packet address than do bridges, for

example, to determine which router or client should next receive each packet. Routers ensure that packets travel the most efficient paths to their destinations. If a link between two routers fails, the sending router can determine an alternate route to keep traffic moving.

• Reduce stress on the network. • Routers read addressed network packets only and pass information

only if the network address is known. Therefore, they do not pass corrupted data. This ability to control the data passing through the router reduces the amount of traffic between networks and enables routers to use these links more efficiently than bridges can.

Gateways• Gateways enable communication between different

network architectures. A gateway takes the data from one network and repackages it, so that each network can understand the other network's data.

• A gateway is like an interpreter. For example, if two groups of people can physically talk to each other but speak different languages, they need an interpreter to communicate. Similarly, two networks can have a physical connection but need a gateway to translate network communication.

Use a gateway to link two systems that do not use the same:

• Architecture.

• Set of communication rules and regulations.

• Data-formatting structures.

Public Switched Telephone Network• Public Switched Telephone Network (PSTN)

refers to the international telephone standard based on using copper wires for transmitting analog voice data. This standard was designed to carry only the minimal frequencies necessary to distinguish human voices. Because PSTN was not designed for data transmissions, there are limits to the maximum data transmission rate of a PSTN connection. In addition, analog communication is susceptible to line noise that causes a reduction in the data transmission rate.

Integrated Service Digital Network (ISDN)• Integrated Services Digital Network (ISDN) is an

international communications standard for sending voice, video, and data over digital telephone lines and standard telephone wires. ISDN has the ability to simultaneously deliver two connections over a single pair of telephone lines. The two connections may be in any combination of data, voice, video, or fax. The single line uses an ISDN subscriber service, which is called Basic Rate Interface (BRI). BRI has two channels, called B channels, at 64 Kbps each, which carry the data, and one data channel at 16 Kbps for control information. The two B channels can be combined to form a single 128 Kbps connection.

Asymmetric Digital Subscriber Line (ADSL)

• Asymmetric digital subscriber line (ADSL) is a technology that allows more data to be sent over existing copper telephone lines. ADSL accomplishes this by using the portion of a telephone line's bandwidth not utilized by voice, thereby allowing for simultaneous voice and data transmission.

• Typical remote access users receive much more information than they send. The asymmetric nature of the ADSL connection fits well with most Internet and remote business use. When receiving data, ADSL supports data rates from 1.5 to 9 Mbps. When sending data, ADSL supports data rates from 16 to 640 Kbps. Although ADSL provides higher data transmission rates than do PSTN and ISDN connections, the client computer can receive data at a faster rate than it can send data.

5.4 Network Topologies

• A network topology is the arrangement of computers, cables, and other components on a network. It is a map of the physical network. The type of topology you use affects the type and capabilities of the network's hardware, its management, and possibilities for future expansion.

• Generally, there are two types of topologies, which are Physical and Logical topologies.

Logical topology• Logical topology is the method used to pass the

information between the computers. In other words, looking at that same room, if you were to try to see how the network works with all the computers talking (think of the computers generating traffic and packets of data going everywhere on the network) you would be looking at the logical part of the network. The way the computers will be talking to each other and the direction of the traffic is controlled by various protocols.

Physical topology• The physical topology of a network refers to the layout of cables,

computers and other peripherals. Try to imagine yourself in a room with a small network, you can see network cables coming out of every computer that is part of the network, then those cables plug into a hub or switch. What you're looking at is the physical topology of that network.

• The physical topology describes the layout of the network, just like a map shows the layout of various roads, and the logical topology describes how the data is sent across the network or how the cars are able to travel (the direction and speed) at every road on the map.

• The most common types of standard physical topologies are Bus, Star, Ring, Mesh and Hybrid.

Bus Topology• In a bus topology, all of the computers in a network are

attached to a continuous cable, or segment, that connects them in a straight line (See Figure 3.1). In this straight-line topology, a packet is transmitted to all network adapters on that segment.

• An advantages of the bus topology are those use of cable is economical, media is inexpensive and easy to work with, system is simple and reliable and is easy to extend.

• Because of the way electrical signals are transmitted over this cable, the ends of the cable must be terminated by hardware devices called terminators, which act as the boundaries for the signal and define the segment.

• If there is a break anywhere in the cable or if an end is not terminated, the signal will travel back and forth across the network and all communication will stop.

• The number of computers attached to a bus also affects network performance. The more computers there are on the bus, the greater the backup of computers waiting to put data on the bus, and consequently, the slower the network. In addition, because of the way computers communicate in a bus topology, there may be a lot of noise. Noise is the traffic generated on the network when computers attempt to communicate with each other simultaneously. An increase in the number of computers results in an increase in noise and a corresponding decrease in network efficiency.

Star Topology• In a star topology, cable segments from each

computer on the network are connected to a central component, or hub (See Figure 3.2). A hub is a device that connects several computers together. In a star topology, signals are transmitted from the computer, through the hub, to all computers on the network. On a larger scale, multiple LANs can be connected to each other in a star topology.

• An advantage of the star topology is that if one computer on the star topology fails, only the failed computer is unable to send or receive data. The remainder of the network functions normally.

• The disadvantage of using this topology is that because each computer is connected to a hub, if the hub fails, the entire network fails. In addition, noise is created on the network in a star topology.

Ring Topology• In a ring topology, computers are connected on a single

circle of cable (See Figure 3.3). Unlike the bus topology, there are no terminated ends. The signals travel around the loop in one direction and pass through each computer, which acts as a repeater to boost the signal and send it to the next computer. On a larger scale, multiple LANs can be connected to each other in a ring topology by using ThickNet coaxial or fiber-optic cable.

• The advantage of a ring topology is that each computer acts as a repeater, regenerating the signal and sending it on to the next computer, thereby preserving signal strength.

• The method of transmitting data around the ring is called token passing. A token is a special series of bits that contains control information. Possession of the token allows a network device to transmit data to the network. Each network has only one token.

• The sending computer removes the token from the ring and sends the requested data around the ring. Each computer passes along the data until the packet finds the computer that matches the address on the data. The receiving computer then returns a message to the sending computer indicating that the data has been received. After verification, the sending computer creates a new token and releases it to the network.

• The advantage of a ring topology is that it can handle high-traffic environments better than bus networks. In addition, the impact of noise is reduced in the ring topology.

• The disadvantage of a ring topology is that only one computer at a time can send data on a single token ring. Also, ring topologies are usually more expensive than bus technologies.

Mesh Topology• In a mesh topology, each computer is connected

to every other computer by a separate cable (See Figure 3.4). This arrangement provides redundant paths through the network so that if one cable fails, another carries the traffic and the network continues to function. On a larger scale, multiple LANs can be connected to each other in a mesh topology by using leased telephone lines, ThickNet coaxial cable, or fiber-optic cable.

• An advantage of a mesh topology is its back-up capabilities by providing multiple paths through the network. Because redundant paths require more cable than is needed in other topologies, a mesh topology can be expensive.

Hybrid Topologies• In a hybrid topology, two or more topologies are

combined to form a complete network design. Networks are rarely designed using only one type of topology. For example, you may want to combine a star with a bus topology to benefit from the advantages of each.

• Two types of hybrid topologies are commonly in use: star-bus topology and star-ring topology. (See Figure 3.5)

Star-BusIn a star-bus topology, several star topology networks are linked to a bus connection. After a star configuration is full, you can add a second star and use a bus connection to connect the two star topologies.

• In a star-bus topology, if a single computer fails, it will not affect the rest of the network. However, if the central component, or hub, that attaches all computers in a star fails, all computers attached to that component fail and are unable to communicate.

Star-Ring• In the star-ring topology, the computers are

connected to a central component as in a star network. These components, however, are wired to form a ring network.

• Like the star-bus topology, if a single computer fails, it will not affect the rest of the network. By using token passing, each computer in a star-ring topology has an equal chance of communicating. This allows for greater network traffic between segments than in a star-bus topology.

5.5 Network Hardware and Architecture

• It is possible to use different network technologies to communicate between computers within LANs and WANs. You may use a combination of technologies to get the best cost-benefit and maximum efficiency from your network design.

• Different network technologies are available, one of the ways in which these technologies differ is the set of rules that each uses to place data onto the network cable and to remove data from the cable. This is called access method. When data moves on the network, these various access methods regulate the flow of network traffic.

Ethernet • Ethernet is a popular LAN technology that uses

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) between clients over a variety of cable types. Ethernet is passive, which means it requires no power source of its own, and thus does not fail unless the cable is physically cut or improperly terminated. Ethernet is connected by using a bus topology in which the cable is terminated at both ends.

Token ring • Token ring networks are implemented in a ring

topology. The physical topology of a token ring network is the star topology, in which all computers on the network are physically connected to a hub. The physical ring is wired through a hub called a multistation access unit (MSAU). The logical topology represents the token's path between computers, which is similar to a ring.

Asynchronous Transfer Mode (ATM) • Asynchronous transfer mode (ATM) is a packet-

switching network that sends fixed-length packets over LANs or WANs, instead of the variable-length packets used in other technologies. Fixed-length packets, or cells, are data packets that contain only basic path information, allowing switching devices to route the packet quickly. Communication occurs over a point-to-point system that provides a permanent and virtual data path between each station.

Fiber Distributed Data Interface (FDDI)• A Fiber Distributed Data Interface (FDDI)

network provides high-speed connections for various types of networks. FDDI was designed for use with computers that required speeds greater than the 10 Mbps available from Ethernet or the 4 Mbps available from existing token ring architectures. An FDDI network can support several low-capacity LANs that require a high-speed backbone.

• An FDDI network consists of two similar streams of data flowing in opposite directions around two rings. One ring is called the primary ring and the other is called the secondary ring. If there is a problem with the primary ring, such as a ring failure or a cable break, the ring reconfigures itself by transferring data to the secondary ring, which continues transmitting.

Frame relay• Frame relay is a packet-switching network that sends

variable-length packets over LANs or WANs. Variable length packets, or frames, are data packets that contain additional addressing and error handling information necessary for delivery.

• Communication occurs over a network that provides a permanent and virtual data path between each station. This type of network uses wide area digital or fiber-optic links and gives you quick access to data transfer that you pay for only as you need it.

• Packet switching is a method used to send data over a WAN by dividing a large package of data into smaller pieces (packets). These pieces are sent through a packet switch, which sends the individual packets across the WAN using the best route currently available. Although these packets may travel along different paths, the receiving computer can reassemble the pieces into the original data frame.

• However, you could have a permanent virtual circuit (PVC) established, which would use the same path for all of the packets. This allows for a faster transmission than by normal frame relay networks and eliminates the need for packet disassembly and reassembly.

Network Standards and Protocols

• Network client software operates at many different levels within the sending and receiving computers. Each of these levels, or tasks, is governed by one or more protocols (set of rules). These protocols, or rules of behavior, are standard specifications for formatting and moving the data. When the sending and receiving computers follow the same protocols, communication is assured.

• With the rapid growth of networking hardware and software, a need arose for standard protocols that could allow hardware and software from different vendors to communicate.

Open Systems Interconnection (OSI) Reference Model• Most networks are a combination of hardware and

software from a variety of vendors. This ability to combine the products manufactured by different vendors is made possible by the existence of industry standards (International Organization for Standardization) (ISO). ISO is responsible for standardizing the methods by which computers communicate worldwide. To do so, ISO created a model for network communication, called the Open Systems Interconnection (OSI) reference model, or the OSI model.

• In 1978, the International Organization for Standardization (ISO) released a set of specifications that described network architecture for connecting dissimilar devices. The original document applied to systems that were open to each other because they could all use the same protocols (the procedures used to control the orderly exchange of information between stations on a data communication network) and standards to exchange information.

• The OSI reference model is the best-known and most widely used guide for visualizing networking environments. Manufacturers adhere to the OSI reference model when they design network products. It provides a description of how network hardware and software work together in a layered fashion to make communications possible. The model also helps to troubleshoot problems by providing a frame of reference that describes how components are supposed to function.

• The OSI reference model architecture divides network communication into seven layers. Each layer covers different network activities, equipment, or protocols. Table 5.1 represents the layered architecture of the OSI reference model. (Layering specifies different functions and services as data moves from one computer through the network cabling to another computer.) The OSI reference model defines how each layer communicates and works with the layers immediately above and below it.

• Each layer provides some service or action that prepares the data for delivery over the network to another computer. The lowest layers—1 and 2—define the network's physical media and related tasks, such as putting data bits onto the network interface cards (NICs) and cable. The highest layers define how applications access communication services. The higher the layer, the more complex its task.

• The layers are separated from each other by boundaries called interfaces. All requests are passed from one layer, through the interface, to the next layer. Each layer builds upon the standards and activities of the layer below it.

Relationships among OSI Reference Model Layers• Each layer provides services to the next-higher layer and

shields the upper layer from the details of how the services below it are actually implemented. At the same time, each layer appears to be in direct communication with its associated layer on the other computer. This provides a logical, or virtual, communication between peer layers, as shown in Figure 5.1. In reality, actual communication between adjacent layers takes place on one computer only. At each layer, software implements network functions according to a set of protocols.

• Before data is passed from one layer to another, it is broken down into packets, or units of information, which are transmitted as a whole from one device to another on a network. The network passes a packet from one software layer to another in the same order as that of the layers. At each layer, the software adds additional formatting or addressing to the packet, which is needed for the packet to be successfully transmitted across the network.

• At the receiving end, the packet passes through the layers in reverse order. A software utility at each layer reads the information on the packet, strips it away, and passes the packet up to the next layer. When the packet is finally passed up to the application layer, the addressing information has been stripped away and the packet is in its original form, which is readable by the receiver.

• With the exception of the lowest layer in the OSI networking model, no layer can pass information directly to its counterpart on another computer. Instead, information on the sending computer must be passed down through each successive layer until it reaches the physical layer. The information then moves across the networking cable to the receiving computer and up that computer's networking layers until it arrives at the corresponding layer. For example, when the network layer sends information from computer A, the information moves down through the data-link and physical layers on the sending side, over the cable, and up the physical and data-link layers on the receiving side to its final destination at the network layer on computer B.

• In a client/server environment, an example of the kind of information sent from the network layer on computer A to the network layer on computer B would be a network address, with perhaps some error-checking information added to the packet.

• Interaction between adjacent layers occurs through an interface. The interface defines the services offered by the lower networking layer to the upper one and further defines how those services will be accessed. In addition, each layer on one computer appears to be communicating directly with the same layer on another computer.

• The following sections describe the purpose of each of the seven layers of the OSI reference model, and identify the services that each provides to adjacent layers.

Memorizing the OSI Reference Model

• Memorizing the layers of the OSI reference model and their order is very important, especially when preparing to take a computer networking exam. Table 5.2 provides two ways to help you recall the seven layers of the OSI reference model.

Network Protocol• To ensure that computers in a network are able to communicate,

they must share a common language known as a protocol. A protocol is a set of rules or standards that enables communication between computers in a network.

• Protocols are rules and procedures for communicating. The term "protocol" is used in a variety of contexts. For example, diplomats from one country adhere to rules of protocol designed to help them interact smoothly with diplomats from other countries. Rules of protocol apply in the same way in the computer environment. When several computers are networked, the rules and technical procedures governing their communication and interaction are called protocols.

• In general protocols are software and must be installed on network components that need them. Computers can communicate with each other only if they use the same protocol. If the protocol used by a computer in a network is not compatible with the protocol used by another computer, the two computers cannot exchange information. A variety of protocols are available for use in specific network environments. Although each protocol facilitates basic network communication, each has a different function and accomplishes different tasks.

Keep the following three points in mind when you think about protocols in a network environment:

• There are many protocols. While each protocol facilitates basic communications, each has different purposes and accomplishes different tasks. Each protocol has its own advantages and restrictions.

• Some protocols work only at particular OSI layers. The layer at which a protocol works describes its function. For example, a protocol that works at the physical layer ensures that the data packet passes through the network interface card (NIC) and out onto the network cable.

• Protocols can also work together in a protocol stack, or suite. Just as a network incorporates functions at every layer of the OSI reference model, different protocols also work together at different levels in a single protocol stack. The levels in the protocol stack "map," (you will study in the next sub section) or correspond, to the layers of the OSI reference model.

How Protocols Work?• The entire technical operation by which data is

transmitted over the network has to be broken down into discrete, systematic steps. At each step, certain actions take place that cannot take place at any other step. Each step includes its own rules and procedures, or protocol.

• The protocol steps must be carried out in a consistent order that is the same on every computer in the network. In the sending computer, these steps must be executed from the top down. In the receiving computer, these steps must be carried out from the bottom up.

The Sending Computer• Protocols at the sending computer:• Break the data into smaller sections, called

packets that the protocol can handle. • Add addressing information to the packets so

that the destination computer on the network can determine that the data belongs to it.

• Prepare the data for transmission through the NIC and out onto the network cable.

The Receiving Computer• Protocols at the receiving computer carry out the same series of

steps in reverse order. They:• Take the data packets off the cable. • Bring the data packets into the computer through the NIC. • Strip the data packets of all the transmitting information that was

added by the sending computer. • Copy the data from the packets to a buffer for reassembly. • Pass the reassembled data to the application in a usable form. • Both sending and receiving computers need to perform each step in

the same way so that the data will have the same structure when it is received as it did when it was sent.

Protocol stacks• The OSI model defines distinct layers related to packaging, sending, and

receiving data transmissions in a network. A layered set of related protocols actually carries out these services. This layered set of protocols running on a network is called a protocol stack. Together, the protocols in the stack handle all tasks required in packaging, sending, and receiving transmissions.

• Several protocol stacks are designated as standard protocol models. Some of the common protocol stacks are TCP/IP, IPX/SPX, and AppleTalk. Protocols exist at each layer of these stacks, performing the tasks specified by that layer. Generally, however, the responsibility for performing specific communication tasks in the network is assigned to protocols working as one of three types: application protocols, transport protocols, and network protocols.

• Application Protocols • Transport Protocols • Network Protocols

• Application protocols provide data exchange between applications in a network. Examples of common application protocols include File Transfer Protocol (FTP) and Simple Mail Transfer Protocol (SMTP).

• Transport protocols provide for communication sessions between computers and ensure that data moves reliably between computers. A common transport protocol is Transmission Control Protocol (TCP).

• Network protocols provide what are called link services. These protocols define the rules for communicating in a particular network environment. A common protocol that provides network services is Internet Protocol (IP).

Types of Protocols• Two types of protocols are available today: open and

vendor-specific.Open Protocols• Open protocols are protocols that are written to publicly

known industry standards. A protocol that adheres to these industry standards is compatible with other protocols written to the same standards. Open protocols are nonproprietary (not privately owned). A common example of an open protocol is Transmission Control Protocol/Internet Protocol (TCP/IP), which is used as the standard for communication over the Internet.

Vendor-Specific Protocols• Vendor-specific protocols are proprietary

and have been developed by different vendors for use in specific environments. For example, Novell provides a set of protocols, such as Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX), developed specifically for its NetWare architecture.

Common Protocols• Different protocols are needed for

communication with systems, devices, and computers in various environments. Some protocols are routable, and others are not. Based on which protocols are used by a client computer, you can determine whether or not that computer can communicate with other computers in network.

The common network protocols are:

• Transmission Control Protocol/Internet Protocol (TCP/IP)

• Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)

• NetBIOS Enhanced User Interface (NetBEUI)

• AppleTalk

Transmission Control Protocol/Internet Protocol (TCP/IP)• TCP/IP is an industry-standard protocol stack (a layered set of

protocols) that enables communication in different networking environments. Because of the interoperability of TCP/IP among different types of computers, most networks support TCP/IP.

• TCP/IP supports routing and enables computers to communicate across network segments. Because of this feature, TCP/IP is the standard protocol for communications over the Internet. Its reliable delivery and global use have made TCP/IP a necessity for accessing worldwide information networks, such as the Internet. However, you must configure TCP/IP on all computers with which you want to use the protocol to communicate.

Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)

• Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) is a protocol stack developed specifically for NetWare architecture. The IPX/SPX stack includes IPX and SPX. IPX defines the addressing schemes used on a NetWare network, and SPX provides security and reliability to the IPX protocol. IPX is a network-layer protocol that is equivalent to the IP of the TCP/IP protocol stack. SPX provides reliable service at the transport layer.

• IPX/SPX has the following characteristics:• It is used on networks with NetWare servers. • It is routable. IPX/SPX enables computers in a routed networking

environment to exchange information across segments.

NetBIOS Enhanced User Interface (NetBEUI)• NetBIOS Enhanced User Interface (NetBEUI) was one of

the earliest protocols available for use on networks composed of personal computers. It was designed around the Network Basic Input/Output System (NetBIOS) interface to be a small, efficient protocol for use in department-sized LANs of 20 to 200 computers, which would not need to be routed to other subnets.

• At present, NetBEUI is used almost exclusively on small, non-routed networks consisting of computers running a variety of operating systems.

The advantages of NetBEUI include:• Small stack size • No configuration requirement • High speed of data transfer on the network • The major disadvantage of NetBEUI is that

it does not support routing. Because of this, computers running NetBEUI can communicate only with other computers in the same network segment.

AppleTalk• AppleTalk is Apple Computer's proprietary protocol stack designed

to enable Apple Macintosh computers to share files and printers in a network environment.

• Some of the characteristics of the AppleTalk protocol are:• It enables Macintosh clients to access a server running Windows or

UNIX system. • It is routable. Computers running AppleTalk can communicate

across segments in a routed network environment. • It enables Macintosh clients to access print services provided by a

server running Windows or UNIX system if Print Server for Macintosh is installed on the server.

5.8 INTERNET AND E-MAIL

• If you're new to the Internet Technologies or a little unsure about how to use e-mail, this training can help you get started. The New Technologies the lecture explains many Internet and e-mail concepts and provides step-by-step instructions on using these new technologies.

• Language of the Internet • The Net, The Information Superhighway: The

Internet • The Web, WWW, W3, W3: The World Wide Web

• Web Page: A single Web document. Everything you can see in your browser window at one time (including what you can see by scrolling) makes up one Web page.

• Browser, Web Browser: The piece of software that runs on your computer and allows you to view Web pages. The most common browsers are Netscape and Internet Explorer.

• Web Site: A set of Web pages that are logically connected. They usually have a consistent look and feel, and are all related to the same theme.

• Home Page: The starting, introductory or welcome page for a Web site. A person's own home page is a Web page that describes all about them.

• Link, Hot Link, Hyper Link: A part of a Web page that can be clicked to get somewhere else. Links usually turn up a different colour and/or underlined in your Web browser.

• Broken Link: A link that references a page that no longer exists. If you click on a broken link you will get some kind of "Page not found - Error 404" message.

• Hypertext: Text that can contain links.• HTML: Stands for Hypertexts Markup Language. This is the language that

all Web pages are written in. • URL: Stands for Uniform Resource Locator. This is the address of a Web

page - for example http://www.Geocities.com/Ggiday is the URL of this Web page.

• Web server, Web Server: A Web server is a computer which holds a number of Web pages, and 'serves' them out to computers that request them. There is nothing very special about the actual computer - it's just an ordinary computer (though usually a fairly powerful one) running special software.

• Surf: "Surfing the Web" means casually using the Web - not really having any direction, just clicking the links that look interesting to find yourself in weird and interesting places.

• Cyber: Virtual - not real but existing only in the context of the Internet. • Cyberspace: A conceptual place that doesn't actually physically exist - but you can

roam around in it, visit places, meet other people there, chat to them, go shopping ... Cyberspace is a real world metaphor for the Internet.

• Newbie: A person who is new to the Internet, or new to a particular aspect of the Internet such as a service (IRC, Usenet) or a particular group (a specific mailing list or newsgroup).

• Post: When you send a message to a discussion forum, you're posting. This word can be used as a verb ("I posted a message") or a noun ("that was a nice post").

• FAQ: Stands for Frequently Asked Questions. They originate from online discussion forums where more experienced users got sick of answering the same "newbie" questions over and over again. So they started writing lists of frequently asked questions and their answers so newbies could refer to those. The concept has grown, and now a FAQ is more general - designed as an introduction to a certain topic.

• http://www.faqs.org/faqs/faqs/about-faqs

• Snail Mail: Traditional mail using paper, pen, envelope and stamp. • Remote: Not on your own computer or on a computer directly connected

with yours, but far away out in the Internet somewhere. • Local: On your own computer, or on a computer connected closely with

yours (a local network). • Download: Download a file means transferring that file from a remote

computer to your own computer. Technically, you are downloading a Web page (and all the elements, such as pictures contained on it) every time you view it, but the word is usually persevered to describe saving a file permanently on your own computer.

• Shareware: Software that you can use for free on a trial basis. It can often be downloaded from the Web.

• ISP: Stands for Internet Service Provider. They are companies who provide you with Internet access (for example Ehio-Net or ETC). Usually you use your telephone connected to a modem to dial up and connect your computer to your ISP.

• Interactive: Refers to any program which lets the user make decisions that affect the way the program operates in some way. It could be as simple as clicking a hypertext link, or more complicated like answering a quiz question and getting feedback.

• Bandwidth: It has a technical definition, but it is mostly used to describe how much data you can fit through a single connection at a time, and is related to how fast your Internet connection is.

• E-Anything: You can prefix the letter E to any activity to make it mean doing that activity over the Internet. "E-learning" and "E-commerce","E-government" are common examples of this. This practice has evolved from the word "Email" (in which the E stands for Electronic). "E" seems to have taken over from "Cyber" as the prefix-du-jour.

5.8. 1 History of the Internet

• The Internet had its origins in the cold war between Russia and America during the 1960's. Concerned about the survivability of its communications in the event of a nuclear strike, the US air force needed to ensure that it could still communicate with its forces.

• The RAND corporation proposed a system with no centralized authority, as any centralized system would be a target of any possible attack.

• The proposed system, developed by Paul Baran, suggested a decentralized system that would still operate even if parts of it were destroyed.

• All interconnections in the network could send and receive messages, forwarding them onto other interconnection points (called nodes) until the message reached its destination.

• Information would be sent in little packets (groups), each packet would be self-contained and have its own address information. Packets would travel from node to node, each node deciding how to send the packet to the next available node. Even if some nodes were destroyed, an alternative route could still send the message.

• In this way, the network would withstand a nuclear strike. After implementing the network, it was known as ARPANET and used by the US military and US universities. Gradually, as more and more connections were made, it has evolved to the Internet.

• It was created nearly thirty years ago as a project for the U.S. Department of Defense (DOD). Its goal was to create a method for widely separated computers to transfer data efficiently even in the event of a nuclear attack. From a handful of computers and users, today the Internet has grown to thousands of regional networks that can connect millions of users. Any single individual, company, or country does not own this global network.

The History of the Internet in Ethiopia• The Internet connection become Functional Starting From January

1,1997(1989). The EthioNet is connected to the Global Internet at Washington DC through a SPRINT link connection with 256 Kbps bandwidth. The Gateway and the domestic routers at the various locations are connected to the 7500-gateway router in turn.

• The EthioNet Presently provided the following Internet Services to its customers.

• Email• World Wide Web (WWW)• File Transfer Protocol (FTP)• Telnet to any Internet Host• USE NET and So on.

• By setting Up Eight Servers through out the Country and it's planning to provide Various Domain names and related Services to its Customers in the near future.

• At the moment the EthioNet Possess more than 15 thousand Customers and there is a plan to double the number of customers and the Server Capacity in the Future.

5.8.2 What is the Internet?

• The Internet is a computer network made up of thousands of networks worldwide. No one knows exactly how many computers are connected to the Internet. It is certain, however, that these number in the millions and are increasing at a rapid rate.

• No one is in charge of the Internet. There are organizations, which develop technical aspects of this network and set standards for creating applications on it, but no governing body is in control. The Internet backbone, through which Internet traffic flows, is owned by private companies.

• All computers on the Internet communicate with one another using the Transmission Control Protocol/Internet Protocol suite, abbreviated to TCP/IP. Computers on the Internet use client/server architecture. This means that the remote server machine provides files and services to the user's local client machine. Software can be installed on a client computer to take advantage of the latest access technology.

• An Internet user has access to a wide variety of services: electronic mail, file transfer, vast information resources, interest group membership, interactive collaboration, multimedia displays, real-time broadcasting, shopping opportunities, breaking news, and much more.

• The Internet consists primarily of a variety of access protocols. Many of these protocols feature programs that allow users to search for and retrieve material made available by the protocol.

• In simple terms, the Internet is many computers linked together. When we use the Internet we pass data from computer to computer across a vast network of wires, fiber optic cables (cables which contain thin glass wires that transmit data using light pulses) and satellite links

•The Internet's best-known feature, the World Wide Web, links together millions of documents called Web Pages. You view Web pages using a Web browser (a software program that allows you to find, view and send information over the Internet), such as Netscape or Microsoft Internet Explorer and so on.

Advantages of Internet:• Send and receive messages all over the world: You can send and

receive electronic mail to or from anyone who also has access to the Internet, anywhere in the world in just seconds.

• Participate in discussion groups: Thousands of special interest communities, or newsgroups, provide access to Internet-based discussions on topics from astrology to zoology.

•Find and access information: You can access information from Ethiopian Historical tips to New Zealand weather forecasts and the latest women's health research from South Africa. Millions of documents are available from libraries, museums, governments, educational institutions, the media, private corporations and individuals, not to mention your favorite music group.

• Retrieve files: On the Internet, you can access files that contain software programs, graphic images, music and other types of information, often for free.

• Do your banking and shopping: Today many banks have web sites that enable you to check your accounts, pay bills and even make investments using the Internet. There are also an ever-increasing number of products and services available for purchase right over the web.

• Accessing the Internet• There are several ways to access the Internet. The two most common

methods are through a modem connection or a network connection. • Modem Connection• A modem is a device that adapts a computer to a telephone line. It converts

the computer's digital pulses into audio frequencies for the telephone system and converts the audio frequencies back into pulses at the receiving side (the computer). Most home computers use a modem and a phone line to dial into an Internet Service Provider's (ISP in our case Tele) computer, which provides access to the Internet. Internet Service Providers will typically charge a monthly fee for a certain number of hours of access to the Internet, or, in some cases, for an unlimited number of hours. The speed of the Internet connection depends on the speed of your computer's modem.

5.8.3 Dial-up connection procedure

• To establish a conventional dial-up connection to the Internet, you will need the following:

• An account with an Internet Access Provider (in Ethiopia, at present, Ethiopian Telecommunication Corporation (ETC) is the only Internet Access Provider). The account can be either TCP/IP or Shell.

• A telephone connection.• A computer with serial port (for External modems) or an expansion

slot (for Internal modems)• A modem (External/Internal)• A communication (or terminal emulation) software. SLIP/PPP

(TCP/IP) account holders will require browser software (Internet Mail, Netscape Messenger, Eudora, etc.) For shell account holders, the browser software (Lynx) and the e-mail software (Pine) are available on the Shell account menu.

What is a Modem?• It is a device used to convert digital (computer) data to analog

(telephone) data and vice versa• This is modulation and demodulation respectively.• A modem is required to send digital data over an analogue

connection such as a dial up telephone line. Modems change the digital data to analogue tones that fit within the frequency range of the voice channel. A modem can also convert these analogue tones back to the original digital data.

• Nowadays, it is common for the home user to access the Internet via a dial up telephone connection using a modem. Typically, these modems run at 28.8Kbps or 33.3Kbps, although 56.6Kbps modems are now becoming available.

• Web Browser a browser is a software program that acts as an interface between the user and the World Wide Web. The browser sends requests for information that is available on the Internet and displays the information for the user. There are many different types of browsers. A text-based browser shows a user text only (Lynx). A graphical browser allows the user to see more of what the WWW has to offer, such as graphics, photographs and multimedia.

• Domain Name A domain name is a way to identify and locate computers connected to the Internet. A domain name must be unique; no two organizations on the Internet can have the same domain name.

• A domain name always contains two or more components separated by periods called “dots” .The major categories for the top-level domain names are:

• .com for commercial enterprises• .edu for educational institutions• .net organizations directly involved in Internet operation or for

network• .org miscellaneous organizations that don’t fit any other category,

such as non profit organizations.• .gov for government entities • .mil for military service• .int for organizations established by international treaty• .country codes a two letter abbreviation for particular country

such as “et “ for Ethiopia “ fr” for France” it” for Italy and so on

Dial up Internet Configuration

• You will get a New connection wizard and following the instruction in the wizard when you click next you will get options to select and choose the second option which says connect to the network at my workplace, then click Next and select dialup connection next it asks for name of your company and Next step is to put the telephone number you will use for the dialup connection. Last step of the wizard is to select option that asks to use the connection for anyone or for this computer only you can choose either of the two. After you finish the wizard you will get the following window.

• In this window in the Dial text box you will give the number 900. And then click on Dialing rules to provide the rules of dialing like Areal Code of your area for example 01 is for Addis Ababa.

• When you get this window click on Edit after giving the area code and you will get the following window

• In this window you will provide the country name and dialing type i.e. pulse.

Step-4

• You will get this window in your network connection and you can right click on the name of the connection you created and to connect or dial you double-click on the icon and get this window

• After this you can click on the Dial button and get connected to the internet.

Network Connection• A network connection means that the computer

is part of a network of computers, printers and other devices. This network has a direct, high-speed connection to the Internet. Universities, governments and larger companies usually have this kind of Internet connection, which provides fast and reliable access to the Internet, but is expensive, to set up and maintain.

Web browser • Web browser is a computer program that allows you to

connect to and browse the Internet. • To connect to the Internet, you may have to complete a

log on sequence. Logging on means that you have to enter a user name and a password (a series of letters and/or numbers that the Internet Service Provider sets up for you).

• From the Windows Start menu, choose your browser (for example, Internet Explorer or Netscape Communicator).

• If necessary, enter your user ID and password in your Internet Service Provider's dialog box.

• Your browser will open with the home page displayed.

5.8.4 What is a website?

• A Web site is a collection of digital documents called Web pages that can be viewed using a piece of software called a Web browser. Typically the first page of a Web site is called the home page, from which other pages branch off. The first page you see when you start your browser is also called your home page.

When you are viewing a Web page, the page's address appears in the Address bar in the browser.

• Each Web page has a unique address, sometimes known as a URL (Uniform Resource Locator). You can type the address into the browser's Address bar to go directly to the page. An address (URL) typically starts with a protocol name, followed by the location on the Internet where the Web site can be found, followed by the name of the organization that maintains the Web site, and ending with a suffix that identifies the kind of organization it is.

• For example, the address http://www.EICTDA.gov.et/ provides the following information:

• http://  The Protocol http stands for Hypertext Transfer Protocol. A protocol is a set of rules and standards that enable computers to exchange information.

• www The Server A Server is a computer that provides World Wide Web services on the Internet. The “www” in the Internet address shows that this Web site is located on the World Wide Web (www).

• EICTDA The Domain The Domain is usually the name of the company or organization. This indicates that the Ethiopian ICT Development Agency (EICTDA)) maintains the Web site.

• . Gov.et The Suffix The letters at the end of the address are used to indicate what kind of site it is. For example, the .et in this address indicates that it is a Ethiopian Web site. Generally, governmetal organization, for commercial site addresses end with .com, and the addresses for many educational institutions end with .edu.

• If the address links to a specific page within a Web site, additional information will be included after the suffix. For example, the address for the press release page on the EICTDA Web site looks like this:

http://www.EICTDA.gov.et/press_Release.• As you scroll down a Web page you will often see underlined or

colored words and phrases. These are called text links (or hyperlinks). Links are text items or images on a Web page that have addresses coded into them that can bring you to other Web sites and pages. Clicking the link takes you to the new page. Surfing the Web is browsing, or exploring, from link to link.

• You can tell whether an item is a link by moving the mouse cursor over the item. If the pointer changes to a hand, the item is a link. After you click a text link to go to another page, the colour of the link changes. This allows you to tell the difference between links you have and have not viewed. Typically, text links that you have not viewed yet are blue and viewed links are purple.

5.8.5 What is a browser?• Browsers are computer programs that allow us to look at the

Internet. There are many different Browsers. They all do similar things, such as allow you to follow links, go back to sites you have visited before, type in URLs and add bookmarks.

• The main differences between the browsers are how the above things are done and what the Internet looks like on your screen.

• Browsers can be roughly divided into two types: – Text Browsers and – Graphical Browsers.

• I'll explain the main differences between the two types of Browsers below. The best way by far, to see how they are different is to look at the same Internet site in both a Text and a Graphical Browser and compare them. This has been set up and you will have the chance to do this at the end of the course.

Text Browsers • 'Text browsers' allow only the text (writing) on the pages of the

Internet to be seen, not the graphics (graphs, charts, pictures, diagrams, maps etc). The site you are viewing is the same one; the only difference is that graphics can't be seen with a text browser.

• Text browsers can be run on any computer. • An example of a text browser is Lynx. Graphical Browsers • 'Graphical Browsers' are Internet browsers that allow you to see

everything on the pages of the Internet, which includes text (writing) and graphics (graphs, charts, pictures, diagrams, maps etc).

• There are many graphical browsers, including Mosaic, the Explorer and Netscape. They usually can only be used if the computer has the program 'Windows' on it.

Internet Explorer (IE) seems to be the most popular graphical browser.

• Remember, the site on the Internet is exactly the same one, regardless of which browser it is viewed through. The difference is how it looks on your screen.

• Notice what the page looks like, then go to the demonstration computer and see what the site looks like with a text browser.

• Sometimes you will see a page, which says something like:

• (A) THIS SITE IS BEST VIEWED THROUGH A GRAPHICAL BROWSER

• This means the site was made with Graphical browsers in mind. This is common for sites, which have a lot of graphics, which often do not look very nice with text browsers.

• Other times you may see something like: • (B) FOR TEXT BROWSERS, CLICK HERE or • FOR GRAPHICAL BROWSERS, CLICK HERE • This means the person who made the site has made two different

sites- one for text browsers and another one for graphical browsers. This is sometimes done when the people likely to visit this site will be using both types of browsers and the site designer realizes that a site with lots of graphics will not look good to text browsers.

• Also, a text browser can be useful if you are accessing the Internet over a slow or noisy line. You can get the essential information without having to wait ages for graphics to arrive.

• However, the tendency in Web page design is to use more and more graphics and some pages have essential information contained in the graphics that you can't see with a text browser.

5.8.6 The Internet Corporation for Assigned Names and Numbers (ICANN)

• ICANN exists to provide top-level coordination and management of key naming, addressing, and protocol systems for the Internet. These systems -- the Domain Name System, for example -- require some degree of centralized technical administration in order to function properly. At the same time, authority over these critical systems necessitates not just technical competence, but also credibility in the global policy arena.

• Internet Corporation for Assigned Names and Numbers • Non-profit, private sector Corporation • Formed in October 1998 • Coalition of technical, academic, business, user

communities

• IANA• The authority originally responsible for the oversight of IP

address allocation, assignment of protocol parameters and DNS management.

• Now under ICANN, IANA continues to play a limited role – primarily handling delegations and redelegations to managers.

• ICANN’s Purpose• Take over functions previously handled by the US govt • Coordination of the DNS • To set policy • In a transparent way • Collaborative • Consensus

• Globally representative• Four core functions• Domain Name System (DNS) • Allocation of IP addresses • Management of the root server system • Coordinating protocol number assignment • Previously run by the US government using contractors and

volunteers • At Large membership• Designed for Internet users worldwide, to have a voice in ICANN’s

policymaking structure for DNS & numbering systems; • Membership • open to any individual wishing to join • Online application • Active email address • Physical residence verified by postal mail address

• Using Help

• Both Netscape Communicator and Microsoft Internet Explorer have a built-in Help feature that you can use to learn more about the browser's features and to view step-by-step instructions for the functions that can be performed with the software.

• To use the browser's Help feature:• Click the Help command on the menu bar. • The Help menu opens. Click Contents and Index. • The Help window opens with the Contents tab on top.

Click a section title or icon (book) to view the topics for that section.

• Click a topic to view that information in the right pane of the Help window.

• You can also click the Index tab to search for topics using an index of Help subjects, or click the Search tab to use full-text search and look for specific words or phrases.

• In addition, you can use the other commands on the browser's Help menu to connect directly to the web sites operated by the browser's manufacturer. These sites typically provide access to technical resources, new product upgrades and additional information.

• Using a browser to navigate• Moving between different web pages is called

"navigating." There are several ways to go to a different Web page from the page you are currently viewing.

• Navigating Using Web Addresses (URLs) • Each Web page has a unique address or Uniform

Resource Locator (URL) that provides your computer with the information it requires to locate the page on the World Wide Web. When you open a Web page its address appears in the Address bar at the top of the browser.

• To navigate to a web site using its address (URL):• Click your cursor in the Address field and then type the

URL (address) of the Web page you want to view. • Press the ENTER key on your keyboard.

• Navigating Using Links and the Toolbar• Links provide a simple and fast way to navigate or "surf" the Web• To navigate using links:• Click any link on the current page. A link can be a picture, a 3-D

image, or colored text (usually underlined). You can tell whether an item is a link by moving the mouse cursor over the item. If the pointer changes to a hand, the item is a link.

• The browser retrieves and displays the Web page for that link. • To navigate using the Forward and Back buttons: • The buttons on the browser's Toolbar help you navigate the Web.

• Back Button• If you want to go back to the last page you viewed, click the Back

button on the toolbar. To go more than one page back, you can click the small down arrow next to the button and then click a Web page on the list.

Forward Button.• Once you have gone backward using the Back button, the Forward

button becomes available. Click the Forward button to go to the next page in a series of pages you have already visited. To go more than one page forward, you can click the small down arrow next to the button and then click a Web page on the list.

• 5.8.7 Searching the Web• Finding Things on the Web

• The Web is a very big and much disorganized place. Just about any information you would ever want to know (and a whole lot more that you wouldn't) exists on the Web somewhere. But finding it is another story.

• The reason for this is that it was never designed as a global information retrieval system, hence there is no central place monitoring where or how information is stored. The added complication of hypertext makes it very easy to lose your focus and get lost.

• Ways to find information on the Internet• There are a number of basic ways to access information on the Internet: • Join an e-mail discussion group or Usenet newsgroup • Go directly to a site if you have the address • Browse • Explore a subject directory • Conduct a search using a Web search engine • Explore the information stored in live databases on the Web, known as the

"deep Web"

Search Tools• Trailblazer Pages (Links Pages) • These are lists of links to other sites related to a

particular subject. The most useful trailblazer pages have links divided into categories and descriptions of why each site is useful.

• Enthusiastic amateurs often construct trailblazer pages. Some librarians are creating trailblazer pages to help people find information,

• Trailblazer pages can be very useful in your Web searching. You will often find links to pages that don't show up in search engines or directories. However, it can be frustrating to jump from one trailblazer page to another without finding any pages with actual content!

Subject Trees (Directories) • A subject tree is a broad list of categories that

branch off into sub-categories, such as that found in Yahoo. These are not organized by librarians so the subject classification doesn't conform to any established system. They aren't in any way complete - pages are usually only added to the directory when the writer of the page requests is.

Search Engines • These are computer programs that 'whiz around'

the Internet to find documents that contain key words which you type in. Search engines have different ways of searching which means that they will return different results and may be more or less successful for different searches.

• There are wonderful search engines like Alta Vista, Infoseek, Webcrawler, Excite, Hotbot, Google, Dogpile and Lycos. (All follows www.name of the engine.com)

Limitations of Search Engines • The ambiguities of language mean that the list of

retrieved documents may contain a high percentage of irrelevant material.

• Some search only document titles and others search the entire document.

• Being electronic, they can't discriminate between valuable documents and ones of dubious quality.

• With millions of people using the Internet they sometimes become overloaded.

• Search Strategies

• Directories or Trailblazer pages are usually more successful when you are searching for a site with some general information about a topic, for instance:

• Fairy tales • Pets • Insects • Weather • Poetry • Public speaking • Science fiction

• Search engines are more useful when looking for very specific or obscure information, for instance:

• The history of the settlement of the Gambella. • The myth of Internet. • Pictures of baby chicks. • The Musicians of Bremen' fairy tale. • Sometimes you will find the information you want almost

immediately - other times you will be led on a wild goose chase through page after page of links. Don't give up too easily though, persistence usually pays off.

• Search Tips• Understand the search engine you are using. Read the 'search tips'

or 'help' for the search engine - for instance Alta Vista's Help. • Use a variety of key words, use synonyms. • Search engines often match the first word first so put the most

important word or the broadest category at the beginning. • Use quotation marks to search for a phrase. Searching for rock and

roll will return documents with any of the words rock, and or roll. Searching for "rock and roll" will only return documents with the whole phrase (read the search engine 'help' to see if it supports phrases).

• Try different arrangements of key words eg. if you are looking for indigenous women poets try "women writers" AND indigenous. This is a combination of a phrase and a single word. Remember though, that in North America they use native rather than indigenous - think of how your key words will be written on the document.

• Some search engines are case sensitive. Most search engines will match both upper and lower case if lower case letter are entered, but only upper case if upper case letters are entered. For instance "behafta berhe" will match both "behafta berhe" and "Behafta Berhe", but "Behfta Berhe" will only match "Behafta Berhe".

• Most search engines will match part or whole of a word - eg. sing will retrieve singer, single, singe etc.

• Think of common misspellings - take into account American spellings eg. theater, center.

• Most search engines will search for documents with any of the words you enter - eg. a search for christmas carols will find documents with just the word christmas, as well as documents with just the word carols. Documents with both of the words will appear earlier on in the results. You can use operators to restrict your search futher (check the 'help' to find out which operators the search engine uses).

• Results are returned in order of relevance. If there is nothing useful in the first few pages, chances are there won't be anything useful in any of the others. Change your search query or use another search tool.

• Web Searching Activity• Practice your search strategies and share your insight with others

by completing this activity. • Pick one of these to do your search on: • A general site about conservation for your students to use as a

reference in a piece of their writing. • A page with information about Website that you can adapt into a

worksheet for your students. • A site containing facts on endangered species from around Ethiopia

and the world. • Information on why the Endod tree is dying out. • A site about Ethiopia or New Zealand flora and fauna.

5.8.8 Why people use the Internet?

• To find general information about a subject• The Web is like a huge encyclopaedia of information - in some ways

it's even better. The volume of information you'll find on the Web is amazing. For every topic that you've ever wondered about, there's bound to be someone who's written a Web page about it. The Web offers many different perspectives on a single topic.

• In fact you can even find online encyclopaedias. Many of these are now offering a subscription service, which lets you search through the complete text of the encyclopaedia. There are also many free encyclopaedias that may give you a cut-down version of what you would find in a complete encyclopaedia. – http://www.britannica.com– http://encarta.msn.com– http://www.encyclopedia.com

To access information not easily available elsewhere

• one of the great things about the Web is that it puts information into your hands that you might otherwise have to pay for or find out by less convenient means.

•  http://www.timeanddate.com/worldclock- current local times for cities all over the world - even knows about daylight savings.http://www.xe.net/currency/table.htm - get a table with exchange rates to and from any other currency.

To correspond with faraway friends• Email offers a cheap and easy alternative to traditional

methods of correspondence. It's faster and easier than writing snail mail and cheaper than using the telephone. Of course, there are disadvantages too. It's not as personal as a handwritten letter - and not as reliable either. If you spell the name of the street wrong in a conventional address, it's not too difficult for the post office to work out what you mean. However if you spell anything wrong in an email address, your mail won't be delivered (you might get it sent back to you or you might never realise).

To meet people• The Web is generally a very friendly place. People love

getting email from strangers, and friendships are quick to form from casual correspondence. The "impersonal" aspect of email tends to encourage people to reveal surprisingly personal things about themselves. When you know you will never have to meet someone face-to-face, you may find it easier to tell them your darkest secrets. Cyber-friendships have often developed into real life ones too. Many people have even found love on the Net, and have gone on to marry their cyber-partner.

To discuss their interests with like-minded people

• Did you think you were alone in your obsession with a singer, TV programme, author, and hobby? Well, chances are there's group of people like you discussing every little detail of your obsession on the Internet right now.

To have fun

• There’s no doubt that the Internet is a fun place to be. There's plenty to keep you occupied on a rainy day.

•   Here are just a few of the many frivolous things to do on the Web:

• http://postcards.wired2000.net/

• http://www.ethio.com

To learn• On-line distance education courses Universities

can give you an opportunity to gain a qualification over the Internet.

To read the news• www.dekialula.com•    www.ethiopiancommentator.com• Www.ethiozena.net• www.cnn.com

To find software• The Internet contains a wealth of useful

downloadable shareware. Some pieces of shareware are limited versions of the full piece of software, other are time limited trials (you should pay once the time limit is up). Other shareware is free for educational institutes, or for non-commercial purposes.

• www.shareware.com

To buy things• The security of on-line shopping is still questionable, but

as long as you are dealing with a reputable company or Web Site the risks are minimal.

• www.amazon.com

• Amazon Books is a huge American book store (they exist only on the Web and are very reputable). Their prices are very good - it's can be much cheaper to buy books from here than from ET book stores, especially if you buy several at once to keep the shipping cost down.

Why do people put things on the Web?• To advertise a product• Most company Web sites start up as a big advertisement for their

products and services. It may be hard to see why anyone would willingly visit a 10 page ad - but these advertisements are very useful to anyone genuinely interested in finding out about their products. Companies may also give away some information for free as an incentive for people to visit their pages. www.adobe.com - a good way to find out the facts about the excellent software that Adobe offers.

• To sell a product• Internet shopping (e-commerce) is still in its infancy - it takes a very

good marketing strategy to actually make money out of selling items over the Web, but that doesn't stop lots of people from trying.

• Amazon Books - one of the most successful (perhaps the most successful) e-businesses.

To make money • A popular way to make money out of the Web is from advertising

revenue. Popular sites have banners at the top of the page enticing people to click them and be taken to the advertiser's Web site. These banners are generally animated and very appealing, with mysterious messages to make users wonder where they will be taken. For each person that clicks the ad, the host site gets commission. Making money this way is only successful if the sit gets lots of visitors (thousands a day); so the sites must be very useful and offer something of real value to their visitors.

• The Alta Vista Search Engine is an example of a site that makes money from banner advertisements.

• www.imdb.com-offers a very useful and fun service - it's financed by advertising and sponsorship.

To share their knowledge with the world• Many individuals write Web pages to share

information about their interests or hobbies. They don't expect to make any money out of it - they just feel that the Web has given them so much information that the least they can do is put something into it that may be useful for others. Other rewards come from the prestige of having their site recognized as something good and the contact inspired by their pages with others sharing the same interest.

Evaluating Web Resources • People often assume that any information they

find on a computer is correct. This is a dangerous assumption regarding the WWW, where anyone can publish any information they like, without editorial intervention. Some information may be perfectly reliable, but other information may range from out-of-date, unreliable and inaccurate to biased, misleading or deliberately false.

Pointers for conducting research on the Web: • Be clear on what you want. Keep your purpose clearly in focus. • Be selective, critical, and use a useful set of evaluation criteria. • Don't take anything you find as undisputed fact. • Shop around - find a wide range of sites on your topic, don't stop at

the first useful looking page. • Use your common sense when judging how much faith you should

put into the information you find. • The World Wide Web is made up of millions of Web sites covering

almost every subject under the sun. If you want to find specific information and you don't have a list of Web addresses or "URLs”, then you need to conduct a Web search.

• You can search for information on the Web in a variety of ways.

To search using the Search button:• 1. On the Toolbar, click the Search button. • 2. The Search window is displayed on the left side of the

window. Type the word or phrase you're looking for into the text box at the top of the Search window, and then click Search.

• 3. A list of search results is displayed in the Search window. Click any link in the list to display that Web page in the right side of the browser window.

• Note: You can close the Search window by clicking the Search button on the Toolbar again or by clicking the Close button at the top of the Search window.

To search using a Search Engine:• A search engine is a service that indexes and

organizes Web sites. Search engines are set up by organizations that continually scan the Web. When new pages are found, they are classified in databases so you can easily search for information on any topic of interest. You can use a search engine by typing in its Web address.

• Although each search engine appears slightly different, each has a box in which you can enter a search word or phrase and a button for you to click to begin your search. This is called a text box.

• The list below provides the addresses of some popular search engines that you can try:

• Alta Vista: www.altavista.com • Excite: www.excite.com • Hotbot: www.hotbot.com • Infoseek: www.infoseek.com • Lycos: www.lycos.com • Yahoo!: www.yahoo.com • Yahooligans!: www.yahooligans.com • Webcrawler: www.webcrawler.com etc• No search engine keeps track of all the content on the Web, so try

several search engines to see which produce the most useful results for the type of information you're looking for.

• Boolean Searching on the Internet• Boolean searching is based on a system of symbolic

logic developed by George Boole, a 19th century English mathematician. Most keyword searchable computer databases support Boolean searches. Boolean search techniques may be used to perform accurate searches without producing many irrelevant documents. When you perform a Boolean search, you search the computer database for the keywords that best describe your topic. The power of Boolean searching is based on combinations of keywords with connecting terms called operators. The three basic operators are the terms AND, OR, and Not.

• The operator AND narrows a search by combining terms and retrieves every document that contains both of the words specified. e.g.

• To locate general information on computer Virus problem computer virus AND data protection

• When the computer searches its database it retrieves every record containing both of the words computer virus and data protection, and the records from the intersection will be retrieved as the end result. Practice by searching information on the relationship between poverty and crime.

• Several keywords may be used to narrow searches with the AND operator.

• The OR operator broadens or widens a search to include documents containing either keyword. The OR search is particularly useful when there are several common synonyms for a concept or variant spellings of a word.

• Computer virus OR data protection• The computer searches for all documents containing

computer virus and all documents containing body building and the union of all documents represented by both terms will be retrieved. OR searches often produce large numbers of documents. E.g. car or automobile

• Combining search terms with the NOT operator narrows a search by excluding unwanted terms. To find information on gambling but not the lottery use:

• Examples:• gambling NOT lottery• cats not dogs• and so on

• The term is sometimes stretched to include searches using other operators like “near”. E.g. Fashion NEAR show may produce results on London Fashion Show, New York, etc. but not designers, producers, etc.

• Boolean search terms may be combined in various ways to carefully refine searches.

• Examples:• Oceans OR lakes AND pollution• Nurses AND malpractice NOT doctors• Children NOT infants AND psychology• Note: By default, Goggle only returns pages that include all of

your search terms. There is no need to include Boolean operators between terms. If a common word is essential to getting the results you want, you can include it by putting a "+" sign in front of it. (Be sure to include a space before the "+" sign.)

Truncations• Truncations are character substitutes that could be used to retrieve

variant spellings and allow the searcher to insert a truncation symbol, usually the $ sign, an * or ?

• Examples:• The search term teen* will locate the terms teens, teenagers, and

teenaged.• By placing the $ sign at the end of the root word work like work$,

you will retrieve all words beginning with that root (work, worker, workforce, workplace, etc.).

• Be careful using truncation! If you want to retrieve items about cats, don’t truncate the word cat. If you do, you will also retrieve cataclysm, catacomb, catalepsy, catalog, etc., etc. It’s best to use the Boolean operator “or” in these instances (cat or cats)

• Some databases and search engines automatically truncate your search terms to find plurals, -ing, or –ed endings.

• Wild Cards• Some databases allow for wild cards to be embedded

within a word to replace a single character. For instance, you can also use $, *, or ? within a word to replace characters, such as, comp$tion and find composition, competition, computation, etc.

• You can also limit the number of characters that the wild card symbol represents such as theat$2 and find theater or theatre, but not theaters, theatrical, etc.

Saving, Copying and Downloading Information From Internet

• Saving and Copying Information • The Internet is not only to be surfed. We can copy and

save information, text or graphics, which we see on a web page to a floppy diskette and/or make printouts.

• To copy graphics• You can copy or save any graphic that you see on a web

page.• Click on the graphic you want to copy.• Right mouse clicks and choose Copy from the drop-

down menu.

To save graphics• Click on the graphic you want to save.• Right mouse click and choose Save Picture As from the drop-down

menu

To copy text.• Position the mouse pointer at the beginning of the text you want to

copy. The mouse pointer changes from an arrow to an “I” beam.• Drag to select the text.• Right mouse click and choose Copy from the drop-down menu:• The text is copied into the clipboard and can be pasted into a blank

word document.• Note: If there is a large quantity of text, then choose select All from

the drop-down menu.

To save text• You can save any document that Internet Explorer can display.• Choose Save As from the File menu. The Save As dialog box is

displayed. The file name is already placed in the dialog box. You can change this if you want to:

• There are two ways of saving a file:• As text enables you to paste the text into Word, Excel, PowerPoint

or Access. You are recommended to use this option.• As HTML keeps all the HTML source code in the page. This option

is not recommended unless you write web pages.• Click on the Save button

Saving favorite web pages• As you navigate from Web site to Web site, it soon becomes

impossible to remember the path you took to get to a specific site or its exact address or URL . Fortunately, you can use the Favorites feature of your browser to save a list of your favorite Web sites so that you can easily revisit them in the future. [Note: In Netscape this feature is called Bookmarks.]

To add a Web page to your list of favorite pages:• Go to the page you want to add to your list of favorite pages. • Click the Favorites command on the menu bar at the top of the

browser. • On the Favorites menu, click Add to Favorites. • The Add Favorite dialog box opens. Type a new name for the page

in the Name field if you want to. Click OK to add the page.

To view a favorite Web site:

• On the Toolbar, click the Favorites button.

• The Favorites window appears on the left side of the screen. Click a folder or page to display the Web page.

• Note: You can hide the Favorites window by clicking the Favorites button on the Toolbar again.

Downloading files• On the Internet, you can access files that contain software programs,

graphic images, music and other types of information, often for free. You can download (or save) these files onto your computer using your browser.

When you click on an Internet file or program that can be downloaded, your browser will give you two options: to open the file or to save it to a disk (for example, onto your computer's hard drive or to a floppy disk).

You should note that some files can contain viruses. A virus is a software program that is buried within an existing program or file. When you open that program or file, the virus copies itself onto your computer. The virus may be a simple prank that pops up a message on your computer screen but does no serious damage. However, other viruses are quite destructive and may destroy programs and data on your computer. Therefore, it is recommended that you save any file or program you wish to download to disk. This allows you to check the file with a virus detection program (such as McAfee Virus Scan or Trend Anti-Virus)before you open it.

• For more information on virus protection, you can link to one or two popular virus detection program Wesites:

• McAfee Virus Scan • http://www.mcafee.com/

Trend Anti-Virus • http://www.trend.com/

The amount of time it will take to download a file will depend on the size of the file and the speed of your Internet connection.

To download a file or program:• Click on the file or program you wish to download. • The File Download dialog appears. Click the Save this file to disk

option and click OK. • The Save As dialog appears. Choose a location on your computer

where you'd like to save the file and then click OK. • A dialog appears showing you the status of the download. When the

file or program has finished downloading, you should check the file with a virus scanner before opening or installing it.

• Note: If you're downloading a program file, note any installation instructions provided. Once you have finished downloading the program, install it according to the instructions on the original Web page.

E- mail• Electronic mail (e-mail) is one of the oldest and most

popular services on the Internet. With e-mail, you can send messages and documents down the hall, across town or around the world. You can also receive information through your personal e-mail mailbox, or "Inbox."

• To send and receive e-mail you need an e-mail account. You can get this through an Internet Service Provider (ISP in our case tele). In most cases, if you have purchased Internet services from an ISP, your monthly fee includes e-mail service.

• You also need a piece of software that will create an Inbox on your computer for messages that you receive. When you check your e-mail, new messages are downloaded (through the Internet) from your ISP's computer into your Inbox. You must be connected to the Internet (or to your organization's network) to send a message or to check if you have new mail. Most Web browsers include features that allow you to send and receive messages, or they enable you to link to another program that handles e-mail. To send e-mail, you have to know the recipient's e-mail address. E-mail addresses consist of a user ID followed by a domain name (usually the name of an organization), just like a Web address. In the example below, the user ID is Abebe and the domain name is @EICTDA.gov.et.

• Abebe@EICTDA.gov.et.• In many cases, a user ID will be the first initial of the user's name followed

by seven or more characters of their last name. However, many Internet Service Providers allow their clients to choose their own user ID, so you will often see e-mail addresses such as:

• Abeba@freemail.et

12.1 Sending e-mail• Most Web browsers include features that allow you to send and

receive e-mail messages, or they enable you to link to another program that handles e-mail.

For example, Microsoft's two main e-mail software packages, Outlook and Exchange, can be used on their own or with the Web browser Microsoft Internet Explorer. You must be connected to send an e-mail message over theInternet.

While most e-mail software packages follow the same basic structure, specific tools and menus vary. Internet Explorer will be used as the examples in the e-mail demonstrations and practice exercises in this training.

• Click on the ‘Compose new message’ button on the toolbar. You will get an empty mail form, which will have the following parts.

• ‘To’ – Enter the e-mail address of the person(s) to whom the message is sent.

• ‘Cc’ – The carbon Copy field is for the e-mail address of the person(s) .any addresses included here will be listed in all outgoing copies of the message.

• 'BCc': This blind carbon copy field unlike address listed in the Cc field address listed in the BCc.

• Note: Commas must separate multiple addresses; The Cc and BCc field may be left blank.

• ‘Subject’ – Enter a brief description as to what the message is about.

• ‘Body’ – Enter the actual message here.

• Some mail programs have the facility to send blind copies. If this feature is available, the other recipients of the mail will not know that you have sent a blind copy to another person. Almost all e-mail programs have the following features: address book, signature feature, and attachment facility. Now we will see how to make use of these features.

To send an e-mail message from within Internet Explorer:• Click the Mail button on the browser's Toolbar. • Click New Message/write message/compose. • The New Message window opens. In the To box, type the

recipient's e-mail address. (The recipient is the person to whom you're sending the message.) If you wish to send the message to more than one recipient separate each name with a semicolon. If you wish, you can enter a name(s) into the Cc(Carbon copy) box to send copies of the message to additional people. Bcc (Blind carbon Copy)

• Click the Subject box and then type a short description of what the message is about.

• Click the message area and then type your message. • Click the Send icon to send the message to the recipient(s).

12.2 Receiving E-mail

• To receive e-mail you need an e-mail account. You can get this through an Internet Service Provider or "ISP”. In most cases, if you have purchased Internet services from an ISP, your monthly fee includes e-mail service.

• To check if you have received any new e-mail messages, you must open your mail program and enter your mail account password. After you enter your password, the program checks for new messages and then download these from the ISP's computer to your computer. These messages will appear in your mail program's Inbox.

• You can use the Mail button in your browser to open your mail program and check for new mail.

To check for new messages from within Internet Explorer:

• Click the Mail button on the browser's Toolbar. • Click Read Mail. • A mail password dialog appears. Enter your user

ID and password. • The IEl program opens. New messages will

appear in bold text in the right pane of the Exchange window. Double-click on a message to open it.

12.3 Attaching a file to a message

• You can send more than simple text in your e-mail messages. You can also attach a variety of computer files – including word-processor documents, spreadsheets, graphics, and video clips – to an e-mail message. E-mail is a useful way to share files with other people. You can attach a file located on your hard disk, on a floppy disk, or on the network to an e-mail message.

To attach a file into an e-mail message: • For yahoo• Create the message into which you want to attach • click attach file. • Then click browse to open dialog box. Locate and click the file you

want to attach. The name of the file will appear in the File Name box of the dialog.

• An Attach file into the e-mail message. • Click OK/open. • For Email.com• click browse to open dialog box. Locate and click the file you want

to attach. The name of the file will appear in the File Name box of the dialog.

• Click OK/open• Click attach

• Many e-mail software packages have an Address Book feature. The Address Book allows you to create a list of e-mail addresses that you can use to quickly and correctly address the e-mail messages that you send. You can add and delete names to your Address Book

12.4 Using the Address Book

To address a message using the Address Book feature: • Open a New message. • Click the To: button. • The Address Book window appears. In the Show

Names From: box, select the Address list where the name you want to find is located.

• To select a name from the address list, type the name or the first part of the name in the Type Name Or Select From List: box. The list scrolls to match the letters you type.

• To add a selected name to an address box, click either the To or Cc button.

• Click OK.

Day 4:6. VIDEO CONFERENCING

6.1 INTRODUCTION • With the ever-increasing reach of the Internet, corporations are

taking advantage of its flexibility and cost-effectiveness to expand and enhance their traditional IP-based enterprise networks and

• Applications. This increases demand for greater capacities across the Internet.

• It has also been discovered that the value of IP-based, real-time voice and video applications is massive.

• As these applications become more commonplace, network managers are creating networks that overlay voice and video applications on top of the traditional enterprise network.

• When real-time, media-rich applications are merged with traditional enterprise applications and networks, several key issues must be addressed, including latency, jitter, security, NAT and firewalls.

6.2 VIDEOCONFERENCING DEFINITION AND OVERVIEW

What is videoconferencing? • Videoconferencing is defined as: "Conducting a conference

between two or more participants at different sites by using computer networks to transmit audio and video data. For example, a point-to-point (two-person) video conferencing system works much like a video telephone. Each participant has a video camera, microphone, and speakers mounted on his or her computer. As the two participants speak to one another, their voices are carried over the network and delivered to the other's speakers, and whatever images appear in front of the video camera appear in a window on the other participant's monitor."

• Videoconferencing is an interactive tool that incorporates audio, video, and computing, and communications technologies to allow people in different locations to electronically collaborate face-to-face, in real time, and share all types of information including data, documents, sound and picture. In essence videoconferencing removes the barrier of distance that separates us.

• "Multipoint videoconferencing allows three or more participants to sit in a virtual conference room and communicate as if they were sitting right next to each other. Until the mid 90s, the hardware costs made videoconferencing prohibitively expensive for most organizations, but that situation is changing rapidly. Many analysts believe that videoconferencing will be one of the fastest-growing segments of the computer industry in the latter half of the decade."

• Expanding this definition slightly to include not only computer network-based videoconferences but those that utilize ISDN telecommunications links as well.

• Also, the multimedia nature of modern videoconferencing technology provides for more than just audio/video conferencing. It provides for true multimedia conferencing that includes the sharing of data between applications as well. Lastly, we would like to emphasize the interactive nature of videoconferencing.

• Thus we might say: Videoconferencing is

• “Conducting an interactive conference between two or more participants at different sites by using computer networks or ISDN telecommunication links to transmit audio, video, and data. “

6.3 THE BASICS• Videoconferencing can conveniently be broken down into 3 components: • -the conference environment, i.e. the room or studio;• -the conference equipment, which generates sound and vision signals from

the participants and converts these into a format that enables transmission to a remote site over the network;

• -the conference network that links the sites together. • All videoconferences must have these three basic elements - however

simple or complex, the conference can always be divided into environment, equipment and network. Conferencing is not limited to talking heads (i.e. the participants).

• Still images, e.g. 35mm slides or overhead transparencies, can be introduced to illustrate a particular point. Moving sequences from a video cassette may be replayed. An application running on a PC, e.g. PowerPoint or Word, can also be relayed.

• It is even possible for a PC application running at one site to be shared with another site so that the remote site can annotate and take control of the software. When PC documents are shared in this way it is termed “data sharing”.

6.4 Technology:• Videoconferencing actually encompasses a range of technologies

used in a wide range of situations, often it is not just video and audio that is transmitted, but also data, allowing collaborative working though shared applications. Videoconferencing may be:-

• One-to-one meetings, also known as point-to-point communications, usually involving full two-way audio and video.

• One-to-many involving full audio and video broadcast from the main site, where other sites may be able to send audio. For example in a lecture situation, students could ask questions.

• Many-to-many, known as multi-point communication, provides audio and video between more than two sites. With most multi-point systems only one site in a conference can be seen at time, with switching between sites either controlled manually or voice activated (i.e., the loudest site is on screen).

6.5 VIDEOCONFERENCING PROTOCOLS

• In order to ensure that systems are able to work with each other independent of brand and or system type, a number of standards have been developed by the International Telecommunications Unit (ITU). You’ll see and hear these standards referred to by different equipment manufacturers when describing their products.

• The following are ITU Videoconferencing standards.• The Umbrella Protocol H.323 provides specifications for

voice and video communication over an IP network.• H.320 provides specifications for voice and video

communication over ISDN lines.• H.324 provides specifications for voice and video

communication over traditional phone lines.

• COMPARISON OF PROTOCOLS:• H.323 versus H.320 • As described above, there are a number of

videoconferencing technologies in use. In this presentation we shall concentrate on two that are in popular: H.320 and H.323-based videoconferencing technologies.

• H.320

This is a protocol that defines how real-time multimedia communications and conferencing are handled over switched or dedicated ISDN telecommunication links.

• The protocol is an international standard of the International Telecommunications Union (ITU), and it was adopted in 1990. Multimedia refers to the fact that the standard covers voice, video, and data. The standard is an umbrella standard and includes many other protocols that describe, as an example, how to encode and decode voice and data, how to setup calls between terminals, and how to handle data connections.

• The above definition of H.320 is rather complex. Lets see if we can describe it in simpler terms. Lets assume we have a H.320 compliant terminal that has a microphone, a speaker system, a display, a camera, an ISDN connection to the public telephone network, and the necessary electronics to implement the H.320 protocols. Assume another similar terminal exists at a remote site.

• The local user can dial the ISDN telephone number of the remote terminal, and the H.320 protocols handle the call setup between the terminals. The local terminals microphone and camera picks up the audio and video from the local user, decodes and compresses the audio/video stream, and sends it to the remote site all using the protocols as defined in the H.320 standard. The digital stream is transmitted via the ISDN telecommunication lines to the remote site where it is uncompressed, decoded, and displayed and heard by the remote user.

• A similar audio/video stream is formed at the remote site and sent to the local site where the audio and video from the remote site can be heard and seen by the local user. A fully interactive videoconference can thus be held between the two sites.

• H.320-based videoconferencing is considered to be "traditional", and has been around for a number of years. The problem is that H.320 terminals are expensive, and they normally are implemented in videoconferencing rooms that are, in themselves, very expensive to construct. Vendors have not made H.320 equipment that is applicable to desktop videoconferencing. In addition, ISDN telecommunications lines are expensive to install and incur rather large operating costs. However, there are a lot of H.320 rooms still in use, and thus H.320 is still an important part of the videoconferencing implementations over the world.

• H.323

• With the advent of the Internet, a new low-cost communication medium became available for communication between sites both local and remote users. Perhaps we should qualify this and say that at least the incremental cost to the end user to use the Internet is low-cost. There are generally no usage costs for the Internet, the bandwidth, at least between potential user sites, is quite high, and the reliability is very good. This motivated developers to create a videoconferencing technology that uses the Internet to interconnect sites. H.323 is the resulting protocol they developed.

• H.323 is an umbrella set of standards defining real-time multimedia communications and conferencing over packet switched networks.

Fig1. H.323 standard as defined in the OSI layer.

• H.323 Version 1 was adopted by the ITU in 1996 and Version 2 was finalized in 1998. Like H.320, it is a part of a family of H.32X standards. H.323 borrowed many of the H.32X standards used by H.320, especially those for encoding/decoding the audio/video streams and the data sharing protocol (T.120), but it defined a new set for handling communication over the Internet.

• Like H.320, vendors have produced a wide array of compatible H.323 compliant products. Unlike H.320, the H.323 products cover a much wider spectrum of capabilities.

• Videoconferencing has thus moved into the "do it yourself" category and no longer requires expensive videoconferencing rooms. This low entry cost for equipment, the ease of interconnecting H.323 equipment over the Internet, and the fact that equipment exists that allows H.320 and H.323 terminals to interoperate in the same videoconference has led to a rapid deployment of H.323 equipment for videoconferencing in the educational environment.

6.6 Broadband VSAT Network

• ETC’s Broadband VSAT Network implements a high level of VSAT system so as to provide broadband services throughout Ethiopia, where there is no alternative (terrestrial link). The introduction of broadband VSAT in Ethiopia will have a great role and it worth describing its significance for the nation with no access to terrestrial link.

1.2. Satellite communication1.2.1. Satellite coverage•

As it is clear on the footprint of the satellite used by the broadband VSAT network, covers almost all Africa and will have a great importance regarding delivery of broadband services across Africa for nations who need this service. Moreover, it will help deploy faster services almost immediately even in urban areas with terrestrial link, since the satellite covers every part of Ethiopia with a strong beam.

• Satellite facts• Huge Geographical Coverage• No ‘line-of-site’ problems• Extremely reliable (99.9% Up time)• Reliable data broadcast or multicast• Single Vendor• Easy to deploy• Supports multiple applications:• Video• Data• Voice

• Advantages of Broadband VSAT• Simple• Standard platform at every location• Scaleable• Easy to add further applications on demand almost anytime. It is also easy to manage

the necessity of additional sites.• Rapid Deployment• Services can be initiated anywhere almost immediately. Here comes the advantage of

VSAT for even provision of services in urban areas.• The very nature of VSAT is to provide the application of variable communication services in areas

like:• There is no means of alternative link other than satellite;• The necessity of immediate and fast implementation of communication services.• Generally it is the only means in giving a connection for rural areas in developing

countries, since most of the developing countries infrastructure doesn’t have sufficient microwave and fiber links so that to provide connection all over the country.

• * This is the very reason to bring VSAT technology in our country, Ethiopia.• Broadband VSAT Services

• Broadband VSAT provides an all-in-one or integrated Digital Data, Video Multicast, Internet, and Video Conference services.

• And these capabilities will make Broadband VSAT great contributor for our country regarding the development of ICT. Aiming at reaching every nation in an equitable level as of the country’s vision. Cumulatively, it will enable to achieve or contribute for the development of the awareness of IT over the rural areas and/or woreda’s.

• Broadband Sections:• ETC’s Broadband VSAT Network has three Network Groups:• School Net Network Group• Wereda Net Network Group• Agri Net Network Group

REMOTE SITE VIEW• Generally, two types of remotes are available for

School-Net, Receive Only and TX/RX.• And there is one type of TX/RX for Woreda-Net.

The PES remote equipment consists of the • Radio Frequency Transceiver (RFT), which is

located outdoors, • An Interfacility Link (IFL) and • The Indoor Unit (IDU), which is located indoors

at the point of customer interface.• Fig. PES Remote Equipment Overview

• Radio Frequency Transceiver (RFT): The Radio Frequency Transceiver (RFT) is comprised of: An antenna, and An Outdoors Digital Unit (ODU)

Antennas • The antennas have an offset of 22.3 degrees that helps prevent snow and ice from

collecting on the reflector.• The antenna’s azimuth/elevation (AZ/EL) pointing assembly is attached to the top of a

vertical pipe or mast. The AZ/EL assembly permits adjustment of the antenna’s beam angle over 360 degrees in azimuth and 5 to 45 degrees in elevation. The antenna reflector is directly attached to this structure.

• The feed support arm, which supports the ODU electronics package, is attached to the AZ/EL assembly to avoid any distortion of the reflector during the periods of high wind loading.

• The PES remote incorporates a pointing feature that enables the installer to view the strength of the received signal and the “lock” status of the demodulator at the ODU.

• In order to accommodate for the different frequencies supported, ISBN uses different kinds of antennas.

• For systems using the C-band frequency, a 1.8 or 2.4 meter conical antenna is used.• Fig. PES C-band Antenna

Outdoor Unit (ODU)• The ODU is a compact combination of• Down Converter (LNB), and • Power amplifier (SSPA, Solid State Power Amplifier), which is powered from the

indoors-electronic unit. • ODU has the following features:• Monitor and control of the ODU is exercised from the IDU.• Controls the uplink and downlink frequency as well as the uplink power.• The ODU processor communicates across the interfacility link (IFL) with the indoor

unit IFM • The PES ODU is mounted on the antenna’s feed support arm and is directly attached

to the antenna feed horn. Aperture blockage is minimized by the offset-fed design of the antenna.

• A 2.0-watt (at 1 dB Compression) Solid State Power Amplifier (SSPA) is available as an option. The PES C-band incorporates a 5-watt SSPA.

• Both the receiver and the transmitter are stabilized using a common RF source. This source is stabilized using a frequency locking technique referenced to the outroute signal from the hub, eliminating frequency drift.

Interfacility Link• The Interfacility Link (IFL) connects the ODU

with the IDU using a single coaxial cable. This cable carries:

• DC power (for the ODU)• Transmit and Receive IF signals• Transmitter control signals• ODU status signals• Reference frequency signal• A frequency division multiplexing technique is

used to combine these signals.

Indoor Unit• The IDU contains the satellite modem and

synthesizers, and a number of interface cards as required for data and voice, and decoders for TV broadcast reception. Includes a one-way indoor unit that supports high-speed TCP/IP applications that is Internet and e-mail. Each ODU can only operate when connected to the proper corresponding PES IDU.

Common Codes Interpretations

Common Codes for DW1000• Commonly the normal state is either 06 or 07

depending of the configuration, if it is rebooting, displaying 02, 03 and then coming to 06 or 07 on the LED display.

• If there is no LED display, inform to the technical operator

• Power indicator-Illuminates when downloading software; when blinking, DW is not ready to operate.

Common Codes for PES5000/OkemoHow to Interpret PES 5000/Okemo LED Displays: - The PES

5000/Okemo has two LED displays side by side or layer by layer respectively. The LED display on the right is referred to as the PC LED/upper layer. The LED on the left/lower layer is referred to as the IF LED.

PC LED State/Status Display: -Most of the time, each remote card will display two LED codes that flash alternately at one second intervals. These codes indicate the current condition (state/status) of the card. The state and status can be distinguished by the fact that:

• The state code is a single character.• The status code is a single character followed a dot.• This alternating display will be indicated by the state and status

separated by a slash (/): State/Status.

Normal State blank • Online (blank/blank.): - State blank is the normal

operating state of the remote. In this state, the downloaded user code is running and performing its protocol–specific functions with the user equipment. Minor alarms are posted by all blank states except:

• blank/0. and• blank/blank. Online the blank LED code state is

entered when all code is in memory; no alarms have occurred; and outroute and SFH sync are attained. This is the normal operating state of the remote, during which it can pass user data.

• and distribution system in the headend (see figure 1 below) digitally compresses and distributes eight active video channels. Each video channel is accompanied by two AES digital audio channels. A single hot standby encoder is employed to provide redundancy for the eight primary encoders in the event of any anomaly. All content provided to the encoding system uses an SDI interface for the Video and AES/EBU interface for the audio.

• Head end

ATM

Encoder # 2

Encoder # 4

RTM 3310Multiplexer

RTM3310RedundantMultiplexer

16X16 SDIVideo

2 StereoAES/EBU

StatisticalMultiplexer

NetworkManagement

System

Matrix

Encoder # 5

Encoder # 6

Encoder # 7

Encoder # 8

ASI

E1000Encoder # 1

Encoder # 3

Audio BroadcastReceiver ABR200

Monitor IRD2600

Video 2

Video 3

Video 4

Video 5

Video 6

Video 7

Video 8

Redundant Encoder

ASI

ATM Vision 1

RSW7200Switch

ASI

E3

Video 1

ASI

for monitoring

PVC

ASI

• The eight digitally encoded signals are statistically multiplexed and the variable bit rate streams are then sent to a multiplexer to be multiplexed into a single ASI transport stream. A single backup multiplexer is provided for redundancy management in the event of any anomalies in the primary multiplexer. A redundancy switch is employed to switch to the redundant multiplexer in the event of an anomaly. The network management system (NMS) monitors and controls the redundancy switch. One output of the multiplexer is provided to support monitoring the performance of the system. The multiplexed ASI stream is next converted into ATM and delivered across an ATM network from the headend to the uplink site.

Satellite Link (Sululta Earth Station)• The 34Mb carrier that is linked to ITMC is directly connected to

Sululta’s ATM Vision and will be converted to ASI back (as it is formatted first to carrier level at ITMC). And further multiplexed with a traffic that is processed by Satellite Gateway. The resulting multiplexed ASI out will be forwarded to the modem. The IF out from modem goes to the RF Subsystem in such a way to transmit to Satellite.

• The diagram shown below can be viewed as follows:• The ATM signal from the Head end is received at the uplink site and

converted back to ASI (see figure 2). A Multiplexer at the uplink site multiplexes the ASI signal from the Head end with data stream from a HNS IP Encapsulator Gateway. The Multiplexed signal is then modulated by HNS equipment for Satellite distribution.

The System Block Diagram (Sululta Side)

ATM SDH

ATM Vision 1 RTM 3304Multiplexer

DVB ASI Signal fromDirecWay Satellite Gateway

ATMASIATM ASI

NetworkManagement

System

E3PVC

Monitor IRD2600

Audio BroadcastReceiver ABR200

QPSK signal

ATM Vision• The 34Mb link that is from ITMC will go directly to ATM Vision. The

ATM (Asynchronous Transmission Module) situated at Sululta is different from the EMA side one. The ATM at Sululta side performs the conversion of the 34Mb carrier to an ASI format, in such a way that to retrieve the ASI, which carries the combined 8 Channels. And will be combined with the Satellite Gateway traffic to multiplexer. Then the multiplexed output will be linked to the Redyn Modulator, which has ASI interface that modulates it with the desired IF frequency and transmitted to RFT (Radio Frequency Terminal).

• *Though the ATM at Sululta side performs the inverse process, i.e., it converts back the 34M input from EMA to ASI format, same principle and future underlies with the ATM that discussed at EMA side.

6.7 Point-to-Point Videoconferencing

• Consider two client terminals that are connected to the Internet. (See Figure 2) An example of a client terminal or end point is a VCON end point Falcon IP or Polycom's Viewstation SP. This terminals and its associated peripherals allow the user to make a call to another client, send the local audio/video stream to the remote client, and hear/view the received audio/video stream on a local speaker/monitor that is connected to it.

• Figure2. Point-to-point VC

• Assume one user (the local user) uses a Falcon IP to call a user at a remote Falcon IP (client terminal) by entering the IP address of the remote Falcon IP. The clients setup a call between the stations following the specifications of the H.323 protocol. Once the call is setup, the clients exchange audio/video streams over the Internet. The point-to-point videoconference continues until one of the users "hangs up" the call.

• One of the problems with this type of video call is that IP numbers are used for the call. IP numbers are difficult to remember; some users have dynamically assigned (DHCP) IP numbers that can change every time they boot their system; there are problems in using IP addressing when different vendor systems are used. Although it is occasionally used, the use of IP dialing for creating videoconferencing sessions is not recommended.

• To alleviate the problem of IP dialing, the H.323 standard defines the use of a gatekeeper. (See Figure 3) The gatekeeper is a system that connects to the Internet just like the client terminals. The IP address of the gatekeeper is configured into the client terminals and when the clients "power up", they communicate with the gatekeeper and transfer certain information to the gatekeeper that describes the client. This process is known as registration; the client registers with the gatekeeper.

Figure 3. Use of gatekeeper

• Two identifiers are assigned to and configured in each client terminal. One is a H.323 Alias. It is usually descriptive of the particular client terminal and usually contains alphanumeric characters. The other descriptor is the H.323 Extension. It usually consists of several numbers and can be thought of as being the video telephone number of the client. While it is possible to use either the H.323 Alias or the H.323 extension for dialing, it is difficult to dial alphanumeric characters on most clients; it is the H.323 extension that is normally used for dialing.

• When the clients register with the gatekeeper, they pass their IP numbers, H.323 alias, and H.323 extension to the gatekeeper where it is stored. This allows a local user to dial a remote user by entering the remote users H.323 extension (video telephone number) rather than an IP address. The local client terminal communicates the H.323 extension to the gatekeeper. The gatekeeper then checks to see if the remote client is registered with the gatekeeper. If it has, the gatekeeper sets up the call between the two clients; if it is not registered, the call is rejected. Once the call has been setup, the audio/video streams flow directly between the clients over the Internet. The gatekeeper can perform a number of other management functions as well.

6.8 MULTIPOINT VIDEOCONFERENCING

• To this point we have only considered point-to-point videoconferences. These are conferences between two client terminals. The question can then be raised, "what if we have users at three or more clients that want to hold a videoconference". To handle this situation, the H.323 standard introduces the concept of a Multipoint Control Unit (MCU). The MCU (See Figure 4) is an endpoint that can be thought of as a "video bridge". The MCU connects to the Internet as does any other endpoint and registers with the gatekeeper, as does any other endpoint.

Fig 4. Multipoint Videoconferences

• MCU, depending on its design capacity, can handle a certain number of simultaneous videoconferences each with each videoconference being logically separate from the others and with each having a specified number of users. System administrators define "services" on the MCU where each service has certain characteristics that contrast it from other defined services on the MCU. As an example, a service of 75 to 700 might be defined that allows for several simultaneous videoconferences to be created where each have a maximum size of, say, five sites (clients) and where all must encode their audio/video streams at 384 Kbps. A specific videoconference on service 75 is then defined by the service number and by a conference "password" (e.g. 751234). Each of the simultaneous videoconferences that are held on service 75 is then defined by the service number (75) and by a different password.

• When users want to join a particular videoconferencing session, they dial the service number/password combination. The gatekeeper checks to see if that service has been registered by a MCU. If it has, the gatekeeper completes the call by connecting the client to the specified videoconference on the MCU; if the service has not been registered, the call is rejected.

• Once the call has been connected, the client's audio/video stream is then sent over the Internet from the client to the MCU. Similarly, other clients connect to the session and send their audio/video streams to the MCU. The MCU selects one of the audio/video streams on the videoconference and returns that audio/video stream to all of the clients (that is all except the client whose stream was selected).

• There are several methods for selecting an audio/video stream. Audio switching and chairman control are two alternatives. Typically, the method that is chosen is audio switching where the MCU selects the stream that currently has active audio (someone is talking or is talking the loudest). We frequently refer to this selection process by saying that this particular stream (client) has "captured" the MCU.

• Lets assume that we have several clients connected to a single videoconferencing session on a MCU. The assumption is that no users want to have the MCU send them back video of themselves and no site wants to receive an audio stream that contains their own audio. So the MCU sends the selected video stream to all the clients except the client whose stream was selected; the MCU sends the video from the last site that was selected to the currently selected site. All of the audio streams are aggregated together and sent back to each site except with their audio removed. Thus each site gets a unique audio stream. Each stream only contains the audio from the other sites.

• As the user(s) at one site stop talking and the user(s) at another site start to talk, they capture the MCU. The process is repeated with the video from the newly selected site now being sent to all the other sites, and the newly selected site getting the video from the previously selected site.

6.9 VIDEO STREAMING:

• To participate in a H.323 videoconference, users must have appropriate videoconferencing client terminals and have Internet connectivity with sufficient bandwidth to support the videoconference.

• Some users may not have these capabilities but would still like to be able to participate even if that meant that they could only see and hear conference participants but not be able to interact with them. This can be accomplished if the videoconference session is captured, encoded in an appropriate format, and streamed over the Internet although this capability is not a part of the H.323 standard.

Figure 5 streaming

• To accomplish the streaming, a H.323 client must be connected to the conference session to be streamed. This station will be able to capture and decode the audio/video that the MCU has currently selected. This decoded audio/video can then be re-encoded and streamed over the Internet.

• There are two popular encoding standards that are currently being used: Real Video and Microsoft Windows Media.

• The encoded audio/video can then be either streamed on the Internet by a server or archived on a disk file for later viewing or both. The system consists of a H.323 client, an encoder, a server, and an archive storage system.

• Users can receive the stream using a browser on a computer. They enter the URL of the server, and the server starts the encoded audio/video stream over the Internet to the computer. Plug-Ins for the browser exist that are capable of decoding both Real Video and Windows media streams. The user can thus see and hear the participants in the streamed videoconference in near real-time. Alternatively, a user can connect to the server at a latter date and view the archived version of the videoconference.

6.10 IP MULTICASTING

• IP Multicasting is a new technological phenomenon that contributes a great deal of investment benefits in delivering videoconferencing sessions to multiple users. It is a way of delivering content to multiple users by utilizing the bandwidth only once at a time.

• It provides more bandwidth economy than unicast content delivery.

• Based on TCP/IP multicast theory, using a common class D multicast group address, an initiating multicast system (Chairman) is able to call multiple endpoints and broadcast audio and video data to them simultaneously. Unlike unicast transmission, which would require central MCU hardware or software, multicast operates with single streams of video and audio, reducing the overall bandwidth required for the conference.

• In a unicast call, between two endpoints on the network, the amount of bandwidth utilized must be doubled, as there is video and audio data being transmitted by both endpoints simultaneously.If this conference is expanded (through centralized MCU hardware or software), the bandwidth used on the network increases by a factor of 2 for each endpoint added to the conference.

• With multicast, the video and audio data is a one-way transmission, and therefore, the overall bandwidth of the conference never changes, regardless of the number of endpoints that join.

• Interactive Multicast takes this theory one step further - although multicast is very useful for one-way communication, by adding small, direct unicast channels between the receiving stations and the chairman, it is possible to send requests and messages between participants. This communication 'back channel' thus provides us with a control method for switching off the multicast at one station and switching it on at another, effectively switching the source of transmission amongst participants as required.

• For instance VCON’s Interactive Multicasting technology is an exclusive software package available for most VCON LAN end-points and provides the ability to broadcast audio and video streams from any Interactive Multicast enabled end-point on the network.

Videoconferencing among different protocols

• So far we have discussed H.323 videoconferencing capabilities. However, many sites have videoconferencing rooms that implement the H.320 standard that uses telecommunication lines (e.g. dial-up or dedicated ISDN lines).

6.11 GATEWAYS

• H.323 standard was developed after the H.320 standard and uses many of the encoding/decoding protocols originally developed for H.320. The H.320 systems can be considered to be legacy systems, but since many of them still exist, it is important that we continue to support H.320.

• In addition to supporting pure H.320 videoconferences using H.320 MCUs, gateways between the two protocols can be provided.

• A gateway provides a path between H.320 and H.323 systems. It translates H.320 commands and audio/video streams to H.323 audio/video streams and vice versa. Users with H.320 client terminals dial the gateway over ISDN lines. The H.320 client then needs to input a service/password combination for the selected session, and the gateway connects the H.320 terminal to the selected session. All H.323-based users can see and hear the H.320-based users as if they were on H.323 terminals, and similarly the H.320-based users can see and hear the H.323 users as if the were on H.320-based terminals. Multiple H.320 connections can be made to the gateway up to the capacity of the gateway.

• One other benefit of the gateway is that it can accept calls from standard telephones. (See Figure 7)

• Fig. 8 Use of Gateways in making telephone calls to a network

• In the above picture A user with a standard telephone dials the ISDN telephone number and is connected to the gateway. The telephone user then enters a series of digits to indicate the service/password combination of the desired videoconferencing session. The user can then hear the entire audio from the videoconference and can also interact with others in the conference. The gateway is able to simultaneously connect multiple telephone calls and can even connect to a telephone bridge that could allow participation by a large number of audio only users.

BANDWIDTH CONSIDERATIONS

• The H.323 client terminals encode the selected audio (usually from a microphone) and video (usually from a camera) inputs. The encoded and video are then compressed into a single audio/video stream and sent to the remote end point (another client terminal or a MCU).

• Different rates can be selected for the encoding process. As an example, an encoding rate of 384 Kbps might be selected. 64 Kbps is reserved for the audio and 320 Kbps is reserved for the video. The 384 Kbps stream is compressed (redundancy is removed) and sent to the remote end point. Similarly a 384 Kbps stream is received from the remote end point. Thus approximately twice 384 Kbps in bandwidth (less any bandwidth saved because of compression) is required to support the videoconference for this end point. If there is a lot of motion in the video, very little compression is achieved. If there is almost no motion in the video, the savings approaches about 50%. Since we must design for the worst case, assume a bandwidth requirement of twice 384 Kbps.

• Faster encoding rates can be selected. Most client terminals support rates up to 768 Kbps. Some proprietary implementations can encode at speeds up to 2 Mbps.The higher the encoding rate, the better the quality of the video. However, higher encoding rates also mean higher bandwidth requirements, greater impact on the network, and greater impact on the MCU capacity. Lower encoding speeds can also be selected down to about 128 Kbps. This of course means lower video quality. 384 Kbps is a good compromise between quality on one hand and resource impact on the other. 384 Kbps will support 30 frames per second video. Lower encoding speeds yields lower frame rates and choppy video. There is a discernable but small improvement in quality between 384 Kbps and 768 Kbps.

• Physically, the most common scenarios of videoconferencing are: • Desktop videoconferencing - usually a small camera is located on

top of the PC or workstation monitor. The actual video is usually displayed in a small window, and shared applications, such as a shared whiteboard are often used.

• Studio-based systems - a studio is specially equipped for videoconferencing.

• This will normally include one or more cameras, microphones, one or more large monitors, and possibly other equipment such as an overhead camera for document viewing. Usually used for more formal meetings In practice a 'studio' may not be a dedicated room, but a standard meeting room with portable equipment that can be set up when required.