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Topic: Data communication

Data communications refers to the transmission of digital data between two or more computers.

This refers to the electronic transmission of information that has been encoded digitally (as for storage and processing by computers) from source to destination.

Or; It is the high speed data exchange between computers and other electronic devices via cable or wireless.

COMPONENTS OF DATA COMMUNICATION

Message. This is data/information to be communicated. This can be text, numbers, audio or video or any combination of these types

SENDER

A sender is a device that sends the data message. This can be a computer, workstation, telephone handset, video camera or mobile phone.

MEDIUM

The conduits/channels/media are the physical paths that telecommunications signals use to move from place to place. The various types of conduits of data include cables, fiber optics, satellite, and cellular.

RECEIVER

A device that receives the messages. It be a computer, workstation, telephone handset, television set or mobile phone.

protocol; is a setoff rules and procedures that govern data communication.

FEEDBACK.

Feedback can be an oral or a written message, an action or simply silence. .

Data communication tools

These are devices that allow the user to send and receive messages. These can be electronic or manual. Examples of electronic communication tools include; computers, mobile phones and internet etc.

Manual communication tools include; manual drums, bells and messengers.

Data Transmission Modes

There are three ways for transmitting data from one point to another.

Simplex: is a mode of transmission where data flows in only one direction between the two communicating devices e.g. broadcast on radio, TV and transmission between keyboard and the monitor, fire alarms.

Half-duplex: is a mode of transmission where data signals can flow in both directions but not at the same time. E.g. walkie talkie communication well known as radio calls.

Full-duplex: is a mode of data transmission where data signals can flow in both directions at the same time. E.g. telephone communication.

Use of full-duplex line improves the efficiency as the line turn-around time required in half-duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.

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Communication media /Transmission Media

Is a path/ways/channels/route through which data signal are transferred / conveyed from one point to another.

Types of transmission media

Wired/cabled/bounded or guided (Coaxial, fiber optics, twisted pair/untwisted pair)

Wireless/unbounded or unguided (radio waves, infrared & micro waves)

Classes of transmission media

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Physical transmission media

It uses wires, cables and other tangible materials to send communication signals. These include;

Twisted-pair cable

Coaxial cable

Fibre-optics cable

Twisted-pair cable

Twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together.

Twisted-pair cable comes in two forms: unshielded and shielded

The twisting helps to reduce the interference (noise) and crosstalk.

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Unshielded Twisted-pair (UTP) cable

Any medium can transmit only a fixed range of frequencies!

UTP cable is the most common type of telecommunication medium in use today.

The range is suitable for transmitting both data and video.

Advantages of UTP are its cost and ease of use. UTP is cheap, flexible, and easy to install

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Shielded Twisted (STP) Cable

STP cable has a metal foil or braided-mesh covering that enhances each pair of insulated conductors.

The metal casing prevents the penetration of electromagnetic noise.

Materials and manufacturing requirements make STP more expensive than UTP but less susceptible to noise.

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Applications

Twisted-pair cables are used in telephone lines to provide voice and data channels.

The DSL lines that are used by the telephone companies to provide high data rate connections also use the high-bandwidth capability of unshielded twisted-pair cables.

Local area networks, such as 10Base-T and 100Base-T, also used UTP cables

Coaxial Cable. A coaxial cable has a single copper conductor at its centre. A plastic layer provides insulation between the centre conductor and braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

Coaxial cables have bandwidths of up to 1 Gbps. They are installed in a network to form the network backbone ( link that connects two or more separate local area networks)

Advantages

It is highly resistant to signal interference

It can support greater cable lengths between network devices than twisted pair cable.

Disadvantages

It is difficult to install

Coaxial Cable standards:

RG-8, RG-9, RG-11 are

used in thick Ethernet

RG-58 Used in thin Ethernet

RG-59 Used for TV

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Optic fibre cable

Optic fibre cable uses light signals to transmit data from one point to another on the network. The electrical signals from the source are converted to light signals which are then propagated along the fibre optic cable. This eliminates the problem of electrical interference.

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials.

Advantages of fibre optic cables

Can transmit signals over much longer distances than coaxial and twisted pair

They are not affected by electrical interference such as lighting and power surges

They are thinner and lighter than coaxial cables

They provide greater security because they are difficult to tap into.

They have a high transmission speed and a low arror rate

They can carry thousands of separate signals.

Disadvantages

They are expensive

They are difficult to install and modify

Unguided media (wireless communication). This is a type of media that is used to transmit data from one point to another without a physical link established between two or more devices.

Wireless media re used when it is inconvenient, impractical, or impossible to install cables.

Or a type of media that transports electromagnetic waves without using a physical conductor. Instead, signals are broadcast through air (or, in a few cases, water), and thus are available to anyone who has a device capable of receiving them.

Types of wireless communication media

Infrared rays. This is a wireless transmission medium that sends signals using infrared light waves.

Infrared transmission requires a line of sight transmission that is the sender and receiver must be aligned so that nothing obstructs the path of infrared light wave. Communication devices should be close to each other (about 5 metres)

Radio waves. Radio waves are used to transmit television and radio signals. They can penetrate through walls and structures alike. The power of radio waves decreases sharply as they cover long distance unlike micro wave. Bluetooth technology also uses radio waves.

Micro waves. Microwaves are extremely high frequency radio waves. Unlike radio waves, microwave signals must be transmitted in a straight line with no obstructions between microwave antennas. Because micro waves travel in straight lines, both sender and receiver must be aligned to be strictly in line of sight.

Advantages of wireless transmission media

Wireless medium is flexible in operation as compared to wired medium i.e. devices can be moved around without losing access to the network.

Wireless network covers large geographical areas easily.

Can take place via satellite even in very remote areas that do not have high cost physical infrastructure like telephone lines

Disadvantages

It is relatively difficult to establish or configure

The initial cost is very high.

Signals can be easily blocked by thick material.

FACTORS THAT AFFECT DATA TRANSMISSION

Frequency:

This Refers to the cycle of waves per second. The amount of data that can be transmitted depends on the wave frequency. Frequency is expressed in hertz

Band width:

This is the difference between the highest and lowest frequency (+max 2 –min).The higher the bandwidth the higher the rate of data transmission.

Transmission impairments:

Such as attenuation and electro magnetic interference

Topic: Internet and the world wide web

Sub topic: internet

Internet refers to the global interconnection of computer networks. Computers within a laboratory or office can be connected together using transmission media such as cables to form a local area network (LAN). Several LANs can be connected to form Wide Area Networks (WANs), which constitute the global Internet. The Internet enables millions of computers to communicate and share resources globally.

History of the Internet:

In 1969 the U.S. Department of Defense commissioned the Advanced Research Projects Agency Network (ARPANET). The purpose was to provide communication links between supercomputers located at various regional sites (Universities and defense bases) within the United States. It is this ARPANET that evolved into the Internet after computer networks were connected to it in different parts of the world. By1992, more than 1 million hosts existed on the Internet

Connecting to the Internet

Requirement

A computer or PDA or cell phone

An account with an ISP (Internet Service Provider)

A modem (modulator/demodulator) for dial-up services or a NIC (Network Interface Card) for DSL/Cable services

Connection Types

• Dial-up Services. This method requires users to link their phone lines to a computer in order to access the internet

• Modem (Modulator/demodulator) A device that converts analog signal to digital (modulation) and vice versa (demodulation).

• ISDN (Integrated Services Digital Network). This allows users to send data, voice and audio content over digital telephone lines. The installation of ISDN adapters require at both ends of transmission an ISP.

• DSL (Digital Subscriber Line). A technology that provides digital data transmission over unused frequencies on traditional telephone lines.

• Cable network. A technology that provides digital data transmission over cable TV infrastructure

• Satellite. A technology that provide digital data transmission over satellites. Need a satellite dish

• Broadband Services. This is a high speed internet connection method that is provided through either a cable or telephone companies.

• Wi-Fi (Wireless Fidelity). A wireless technology that connects computers without cables

• Access Point (AP). A device (base station) that connects wireless devices together. usually connected to a wired-network. ESSID (Extended Service Set ID) A “name” for the AP, eg. mobilenet

• Hotspots. These are sites that offer internet access over a wireless local area network by use of a router that connects to an ISP

Advantages and disadvantages of using the Internet

Advantages of the Internet:

• Communication: By sending an e-mail, we can contact a person who is physically present thousand miles away within the fraction of a second’s time.

• E-commerce is the idea that is implemented for any form of business transactions that entails transmission of data from one corner of the world to another. E-commerce has become a fantastic option through which you can shop anything.

• Online Chat: There are many ‘chat rooms’ on the web.

• Downloading Software: This is one of the most happening and fun things to do via the Internet.

• Online learning. It facilitates long distance learning.

• Entertainment. A wide variety of entertainment including video games, music, movies, chat room, news and others can be accessed through the Internet.

• The biggest benefit offered by the Internet is information. It functions as a valuable resource of information. You can find any type of information on any subject with the help of the search engines like Yahoo and Google.

• Formation of communities. Internet helps in formation of communities or forums. Here a number of people can participate in different types of debates and discussions express their views and gather valuable knowledge.

• A variety of other advantages offered via Internet, include: job searching, online banking, buying movie tickets, hotel reservations and consultation services etc.

Disadvantages of the Internet:

• Pornography: This is a very serious issue concerning the Internet, especially when it comes to young children.

• Spamming: This refers to sending unsolicited e-mails in bulk, which serve no purpose.

• Virus threat. Virus is a program that interrupts the usual operation of your personal computer system. PCs linked to the Internet have high probability of virus attacks and as a result of this your hard disk can crash, giving you a lot of trouble.

• Theft of personal details while using the Internet, there is high probability that your personal details like name, address and credit card number may be accessed by con artists and used for fraudulent purposes.

• Some people are getting addicted to the internet and thus causing problems with their interaction of friends and loved ones

• It provides a lot of wrong information. This is because any one can post anything and much of it is garbage.

Factors that determine internet speed.

• Internet traffic; the server speed of the site you are visiting determines the speed of the internet.

• Device hardware; your computer’s resources like speed, memory etc also determine the internet speed i.e. if they are inadequate, the speed will be low.

• Viruses and malware; these consume significant resources like memory and adversely affect internet speed.

• Number of applications running; multiple programs using internet like downloading music with ITUNES and surfing the web using Firefox will reduce the overall speed.

• Number of devices connected; multiple laptops, tablets, smart phones reduce the overall speed of each device on the internet.

Internet service provider (ISP) . A company that provides internet access to individuals and business. Examples; Info com, Mai web, communication companies like MTN, AIRTEL, AFRICELL etc.

Services provided by ISP include; internet access, Domain name registration, E-mail accounts, web hosting, Ip addresses and ranges.

Factors to consider when selecting an ISP

Price; one should select an ISP whose price is friendly.

Technical support; Be sure the ISP you select provides technical support that meets your organization's requirements or that can offer help incase things go wrong.

Viability; when selecting an ISP, do some checking to see how long the company has been in existence, track of records and whether or not they received an award.

Performance; whether you are paying for a high speed connection or just using dial up, you should check the ISP’s track records for such things as uptime and overall throughout.

Internet communication services

These are computer software programs that help to accomplish specific tasks related to telecommunications. A variety of examples of application software for communications include:

-Telnet–enables users to use the resources of a computer in another part of the world. This is done by remotely logging to the distant computer which iscalled the host.

-Email–It allows the transfer of messages, documents, and pictures among others, across the Internet.

-Mailing list –This is based on the email protocol. As an electronic mailing listit is very convenient when somebody wants to send a message or newsletter, for example, to many people in one go.

-Internet Telephony or Voice over IP: Real-time voice conversations transmitted between computers on the Internet.

-Web Directory: A listing of Web sites and their URLs, categorized by topic.

-Electronic Commerce/e-commerce: Conducting commercial activities on the Internet.

-Social Networking. A type of service where users can seek others who share their interests, find out what's going on in their areas of concern, and share information with one

another (e.g. Facebook, Twitter)

-Internet Relay Chat (IRC) –A live interactive discussion in which parties on the network exchange ideas and observation electronically. Chats are usually organized in what we call chat rooms.

-File Transfer Protocol –The standard method for transferring files, whether downloading or uploading, to and from your computer with another computer on the Internet.

-Newsgroups –Worldwide discussion areas where notices can be posted for anyone to view. They are equivalent to a discussion group or an electronic bulletin board. There are newsgroups for every conceivable topic and more, e.g. educational technology.

-World Wide Web –This refers to the global collection of websites consisting of linked electronic documents called Webpagesstored on internet servers all over the world.The www is the most exciting service that has revolutionized the Internet, people use this service to browse for information.

-Instant Messaging: A combination of real-time chat and e-mail by which short text messages are rapidly exchanged over the Internet, with messages appearing on recipient’s display screen immediately upon arrival.

-Usenet: A system of worldwide discussion groups.

-Cloud Computing: A service in which computer software, hardware and data are used remotely over the Internet, instead of acquiring and using them on a local computer.

-Search Engines: Software programs that look through the Web to locate sites matching a keyword entered by the user. Keyword: A string of letters or words that indicates the subject to be searched.

Email Services

Electronic mail (or e-mail) is an Internet service that allows those people who have an e-mail address (accounts) to send and receive electronic letters.

Advantages of email:

Cost .Email is cheap: businesses can save large amounts of money using e-mail, in lieu of long-distance phone calls and postal deliveries.

Time .Email will reach its destination across the world in a few seconds as opposed to days or even weeks with the postal service.

Convenient .Email doesn't worry about crossing time zones or that colleagues are not in their offices to take telephone calls.

Email can be sent to groups of people at the same time. This facilitates collaborative working and efficient dissemination of information.

Doesn't use any paper (good for the environment).

Can attach large documents and other files with a click of a button (and without using up resources like paper).

Unlikely to be lost

Faster to arrive

Allows sending messages to several people at a time

Cheaper in terms of costs incurred

Less prone to illegal access

Allows sending multimedia format document

Several documents can be sent at once

Disadvantages of emails:

User has to open email website or email program to read the message. If you do not login, unread messages can remain unread forever.

Socially, writing a letter and talking over a phone is thought to bring you closer to the recipient compared to writing an email through a computer.

Alot of unwanted emails from spammers can fill your email inbox and important emails may not get delivered.

Email attachments can bring virus into your computer if not scanned by the network or virus program on your computer.

Emails cannot really be used for official business documents.

Less hand-writing practice.

Can be bad for your eyes if you spend too long sending e-mails on your computer.

Messages may be misinterpreted easily.

Components of an e-mail

1. Headers : The message headers contain information concerning the sender and recipients. The exact content of mail headers can vary depending on the email system that generated the message. Generally, headers contain the following information:

– Subject. The theme of the email message

– Sender (From). This is the senders Internet email address.

– Date and time received (On). The time the message was received.

– Recipient (To :). First/last name of email recipient, as configured by the sender.

– CC: “Carbon copy” enables copies of the email message to be sent to third party while acknowledging other recipients. Carbon copy: here you type the addresses of those to whom you are sending carbon copies.

– Bcc: Enables copies of the mail message to be sent to the third party without acknowledging nay other recipients. Blind carbon copies: here you type the addresses as in cc, but the recipients will not know whether the other has received the copy.

– Reply-to. This is the Internet email address that will become the recipient of your reply if you click the Reply button.

2. Body:

– The body of a message contains text that is the actual content.

– The message body also may include signatures or automatically generated text that is inserted by the sender's email system.

3. Attachments

– Attachments are optional and include any separate files that may be part of the message

Other internet communication services/tools

Instant messaging; this type of online chat which offers real time text transmission over the internet.

Video conferencing; this is a technology that allows users in different loctions to hold face-to-face meetings on the internet. It involves transmission of audio and video data.

Equipments for video conferencing

Computers, web cam, a microphone, skype, speakers, high speed internet, video conferencing software

Advantages of video conferencing

It can take place without leaving the office

It minimizes travel costs

Meetings can be called instantly

Delegates can still attend the meeting even if they are physically unable

It saves time

Increases productivity by sharing of data.

Disadvantages

Confidential documents that need to be viewed and signed in person may not be used.

It is more expensive

It is limited to certain number of participants

Stability of connection requires complex technology

Chat room; this is a software application in which participants can engage in real time discussions about a specific topic with one another.

News group. This is an internet based discussion about a particular topic. It ranges from transport, cars, investments etc.

Cloud computing; In cloud computing a type of Internet-based computing," where different services — such as servers, storage and applications — are delivered to an organization's computers and devices through the Internet.

Or the practice of using a network of remote servers hosted on the internet to store and manage resources. Examples include; e-mail communication, online storage such as Google drive, Drop box, web hosting services etc

Sub topic: The World Wide Web

(Abbreviated as WWW commonly known as the web) is a system of interlinked hypertext documents accessed over a network

Or it’s a vast collection of linked documents held on computers all over the world and is accessible via the internet.

The Web (World Wide Web) consists of websites hosted on servers on the internet globally. Websites contain information organized into Web pages. Webpagesare electronic documents with text and graphic images, written in Hyper Text Markup Language (HTML). It contains hypertext links, or highlighted keywords and images that lead to related information. A collection of linked Web pages that has a common theme or focus is called a Web site.

The main page that all of the pages on a particular Web site are organized around and link back to is called the site’s home page.

TERMS USED

Web browser

Web Browser is a software tool or program that allows you to navigate through the web.

Or it’s an application software that allows users to access/connect to the internet or

It’s a tool that allows you to view web pages and interact on the internet.

Examples of web browsers include: Google Chrome, Mozilla Firefox, Internet Explorer, (Opera, and (Safari, Konqueror, Flock , etc.

Search engine

Search engine. It’s a program or web site that can be used to search for keywords on web pages throughout the World Wide Web.

A web search engine is a type of website that helps computer user find specific information on the Internet.

Search engines include: Google, Yahoo!, , Forestle, Bing and (Alta Vista.

Searches for information from the Web

Uses search engine syntax.

Website Addresses

Each computer on the internet does have a unique identification number, called an IP (Internet Protocol) address. The IPv4 addressing system uses a four-part number. For example, 106.29.242.17. Most web browsers do not use the IP address to locate Web sites and individual pages. They use domain name addressing.

A domain name is a unique name associated with a specific IP address by a program that runs on an Internet host computer. This program, which coordinates the IP addresses and domain names for all computers attached to it, is called DNS (Domain Name System ) software.

Uniform Resource Locators

The IP address and the domain name each identify a particular computer on the Internet. However, they do not indicate where a Web page’s HTML document resides on that computer. To identify a Web pages exact location, Web browsers rely on a Uniform Resource Locator (URL). URL is a four-part addressing scheme that tells the Web browser:

¬What transfer protocol to use for transporting the file

¬The domain name of the computer on which the file resides

¬The pathname of the folder or directory on the computer on which the file resides

¬The name of the file

Structure of a Uniform Resource Locator

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READING WEB ADDRESSES

Let's look at the parts of a typical URL:

•



•

Here's what it all means:

•

"http"means hypertext transfer protocol and refers to the rules used to transfer and deal with information

•

"www"stands for World Wide Web and is the general name for the host server that supports text, graphics, sound files, etc. (It is not an essential part of the address, and some sites choose not to use it)

•

"sc"is the second-level domain name and usually designates the server's location, in this case, the University of South Carolina

•

"edu"is the top-level domain name (see below)

•

"beaufort"is the directory name

•

"library"is the sub-directory name

•

"pages" and "bones" are the folder and sub-folder names

•

"lesson1"is the file name

•

"html"is the file type extension and, in this case, stands for “hypertext mark-up language" (that's the language the computer reads).

Website

Web site is the location of a web domain name in a computer somewhere on the internet.

Collection of related web pages.

Types of Websites

Static websites

In static Websites, the information does not change, and the same information is displayed to all visitors.

Mostly coded in HTML so easier to build.

Most commonly used for simple sites.

Updating is difficult.

Cannot do complex tasks, such as providing user interactivity.

Dynamic websites; Dynamic website pages are able to accept input data (fill-in forms) and store that information in a database on the server, allowing a visitor to cre ate a user profile and personalized experience.

In Dynamic Websites, the information may change at any given time and according to the visitor. Mostly built in scripting languages like Javascript, and can be more difficult to build.

Used for large sites with a lot of content, sites that need extensive updates, use real time services (e.g. online stores), and/or require automatic changes (e.g. blogs). Updating is easy.

Personal Websites

A platform for individuals to provide information about themselves, promote themselves, create an online CV and/or portfolio, keep in touch with family and friends, share photos and videos, expand hobbies and interests, and express thoughts and ideas.

Commercial/Business Websites

A platform for companies or organizations to provide information about themselves, market or sell their products and/or services, and provide customer support

Informative Websites

These are dedicated to providing information. They may include news websites, online encyclopedias, educational websites, and websites providing topic-specific information like sports data, medical information, weather reports, stock market quotes and analysis, and TV guides.

Search Engines/Directories

These are search engines index material on the web that automatically respond to a search query with links to relevant websites.

Directories list businesses by different categories and/or locations.

Wikis

A wiki is a specialized form of content-managed web site designed to support the easy collaborative creation of web pages by groups of users.

Wikis differ from blogs and other cms options in that wikis allow all users to change the content of the wiki pages, not just to post comments about the content.

Examples of wiki are Wikipedia, online encyclopaedia can be publicly accessible and edited by any user.

Blogs

Web logs, or blogs, are the most popular, inexpensive, and widespread form of web content management. Blog software such as Blogger, Roller, or WordPress allows nontechnical users to combine text, graphics, and digital media files easily into interactive web pages.

Blog – online journal used to express ideas/opinions

E-Commerce website – platform to sell products online

Forum – promotes discussions among people with mutual interests

Media-Sharing Website – where people can share pictures, videos, music, etc.

Review Websites – where people can write and/or view reviews of products, services, etc.

Social Networking Website – where people can meet, interact and share multi-media.

Webmail – provides e-mail services

Why an institution should own a website

Your business will gain credibility

It saves you money in the long term

Customers can be kept informed

A website is always accessible

A website enables you to target a wider audience

It provides a medium to showcase your work

A website saves you time

A website can improve customer service

Netiquettes

Refers to the do's and don'ts of online communication

Or rules and regulations governing online communication

Here are some of the Best Rules of Netiquette

o Keep messages brief and use proper grammar and spellings

o Never read someone’s private email

o Respect other people’s privacy

o Know where you are in cyberspace. Understand the group of people you are interacting with. When you join a new group, first understand its likes and dislikes before giving your full contribution

o Post only acceptable information that has no harm to the public

o Minimize use of uppercase in text when sending messages

o Be forgiving of other’s people’s mistakes like spelling error, a stupid question or unnecessary long answers because experts on internet were once beginners.

o Respect other people’s time and bandwidth. Ensure that time and bandwidth people spend reading your posting is not wasted. Send a well prepared message and ensure that its sent to right recipient.

o Make yourself look good online

o Avoid impersonation

o Be ethical and aim at acting within the laws of society and cyberspace

• Don't spam. That is, don't repeatedly post the same advertisement for products or services. Most sites have strict and specific rules about who is allowed to post ads and what kind of ads they are.

• Remember that your posts are public. They can be read by your partner, your children, your parents, or your employer.

• Do not post copyrighted material to which you do not own the rights.

• Treat others as you would like to be treated.

TOPIC: COMPUTER NETWORKS

What is a Network?

A network is the connection of two or more devices for a function or purpose

A computer network is a connection of two or more computers in order to share resources, exchange files, or allow electronic communications.

The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

Requirements for setting up a computer network

A computer

Cables/ transmission media

Communication devices (router,Switch,Network interface card)

Server

Network resources like printers

Network software

TYPES OF NETWORKS

The two basic types of networks include: LAN, MAN and WAN.

Local Area Network (LAN) is a computer network that interconnects computers within a limited area such as a room of a building like school, laboratory, university campus or office building.

note; A wireless LAN (WLAN) is a LAN that does not use physical wires, but uses wireless media such as radio waves.

Wide Area Network (WAN)

Wide Area Networks (WANs) connects larger geographic areas, such as London, the UK, or the world. In this type of network dedicated transoceanic cabling or satellite uplinks may be used.

OTHER NETWORKS INCLUDE

Metropolitan Area Network (MAN)

Metropolitan Area Network (MAN) covers relatively larger geographic areas, such as cities. Often used by local libraries and government agencies to connect to citizens and private industries

CAMPUS AREA NETWORK (CAN); this covers a relatively small geographical area of buildings close to each other like in a hospital, university, hotel, etc

Personal Area Network (PAN); this involves a personal computer connected to other devices (like modem, printer, loud speaker, etc) to form a network,

Intranet; is a private network that allows access to organization data/information to only members of the organization. It is a smaller version of internet that uses similar protocols like internet.

Extranet; is a private network that allows access to organization data/information to members within the organization and some authorized outsiders like suppliers. This is also a version of internet connection that uses the same protocols of internet.

Networking hardware

Networking hardware are Communications devices that enable two or more computers to exchange items such as data, instructions, and information with each other.

Examples include: a server computer, clients/work stations, network interface card, modems, Hub/Switch, repeater, Router, etc.

SERVER

A server is the host or central computer that manages the resources on a network.

A server provides a centralized storage area for programs, data, and information.

This is a very fast processor computer dedicated to providing specific services for other computers connected in a network.

A dedicated server is a server that performs a specific task. Examples of dedicated Servers include: file server, print server, database server, and a network server

Roles of Dedicated Servers

A file server stores and manages files on a network

A print server manages printers and print jobs.

A database server stores and provides access to a database

A network server (e.g., a DNS) manages network traffic.

Requirements of a server computer

It needs a computer with very high processing speed

It needs large amounts of RAM

It needs a very big storage capacity

It needs a very fast Network interface card

It needs network operating system such as Novell Netware, Windows NT Server or Apple Share

Expansion abilities.

Functions of a Server

Administration of client computers.

Security of files and applications.

Managing printer Jobs.

Data bank.

Software and Applications handling.

Client computers

These are computers sharing resources and capable of sending and receiving data signals to and from the server.

A Client is a computer that accesses remote service on another computer (server). All of the computers connected to the file server on a network are called workstations

NETWORK INTERFACE CARD

A network card, also called network interface card (NIC), is a device that enables the computer or device that does not have built-in networking capability to access a network.

Examples include: adapter card, PC Card, USB network adapter, flash card e.t.c

MODEMS (signal converters)

This is a hardware device which transforms digital signals into analog signals (Modulation) to facilitates their transmission into air space, and vice versa (demodulation)

HUBS and SWITCHES

These are devices that provide a central connection point for cables from workstations, servers, and peripherals.

A hub, (also called a multi-station access unit (MAU)) is a device that provides a central point for cables in a network.

A switch does not broadcast the data to all the computers, it sends the data packets only to the destined computer.

REPEATER

This is a device which accepts transmitted signals, amplifies them, and rebroadcasts them back on the network media.

As a signal travels over a long distance, it undergoes a reduction in strength, an occurrence called attenuation.

A ROUTER

This is a device used to link more than two different network configurations to communicate one another.These networks can be of different protocols.

A Router connects multiple networks and routs communications traffic to the appropriate network using the fastest available path.

A router allows multiple computers to share a single high-speed Internet connection such as through a cable modem

A router translates information from one network to another.

NETWORK BRIDGE

A network bridge is device that connects two networks making each accessible to the other. A bridge knows all of the addresses on each side of the bridge and can send information accordingly. These networks are of the same protocol.

MULTIPLEXER

This is a hardware device which merges several low speed transmissions into one high-speed transmission.

A multiplexer is a device that combines two or more input signals from various devices into a single stream of data and then transmits it over a single transmission medium.

By combining the separate data streams into one, a multiplexer increases the efficiency of communications and reduces the need for using multiple separate transmission media.

Concentrator

This is a network device which enables several client computers to share a single line.

Gateway

This is a device (interface) used to link two different networks to communicate with one another.

Bridge:

This is a device used to link two similar networks to communicate to one another, making each accessible to the other.

NOTE: To Connect to or create a home or small office (SOHO) network, you need the following components:

Computers

Network Adapter/Network Interface Card

Hub/Switch

Cables

Modem

Internet Service Provider (ISP)

Network models or architecture

A network architecture refers to the construction of computers on the network. These are majorly two are:

Peer-to-Peer and Client/Server

Peer-to-Peer. In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks. AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems.

Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers.

However, they do not have a file server or a centralized management source (See fig. 1).

[pic]

Fig. 1. Peer-to-peer network

Advantages of a peer-to-peer network:

Less initial expense - No need for a dedicated server.

Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations.

Disadvantages of a peer-to-peer network:

Decentralized - No central repository for files and applications.

Security - Does not provide the security available on a client/server network.

Client/Server

A server is a centralized computer that controls the shared resources on the network while a client computer is a computer that sends requests to the server and it is dependant on the server.

Client/server network allows the network to centralize functions and applications in one or more dedicated file servers (See fig. 2).

[pic]

Fig. 2. Client/server network

Advantages of a client/server network:

Centralized - Resources and data security are controlled through the server.

Scalability - Any or all elements can be replaced individually as needs increase.

Flexibility - New technology can be easily integrated into system.

Interoperability - All components (client/network/server) work together.

Accessibility - Servers can be accessed remotely and across multiple platforms.

Disadvantages of a client/server network:

Expense - Requires initial investment in dedicated servers.

Maintenance - Large networks will require a staff to ensure efficient operation.

Dependence - When server goes down, operations will cease across the network.

Client-server model

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Advantages of computer Networks

Speed. Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files (referred to as sneaker-net) is very time-consuming.

Cost. Networkable versions of many popular software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations.

Security. Files and programs on a network can be designated as "copy inhibit," so that you do not have to worry about illegal copying of programs. Also, passwords can be established for specific directories to restrict access to authorized users.

Centralized Software Management. One of the greatest benefits of installing a network at a school is the fact that all of the software can be loaded on one computer (the file server). This eliminates the need to spend time and energy installing updates and tracking files on independent computers throughout the building.

Resource Sharing. Sharing resources is another area in which a network exceeds stand-alone computers. Most schools cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users.

Electronic Mail. The presence of a network provides the hardware necessary to install an e-mail system. E-mail aids in personal and professional communication for all school personnel, and it facilitates the dissemination of general information to the entire school staff. Electronic mail on a LAN can enable students to communicate with teachers and peers at their own school. If the LAN is connected to the Internet, students can communicate with others throughout the world.

Flexible Access. School networks allow students to access their files from computers throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network.

Workgroup Computing. Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently. For example, educators located at various schools within a county could simultaneously contribute their ideas about the new curriculum standards to the same document and spreadsheets.

Disadvantages of computer Networks

Expensive to Install. Although a network will generally save money over time, the initial costs of installation can be prohibitive. Cables, network cards, and software are expensive, and the installation may require the services of a technician.

Requires Administrative Time. Proper maintenance of a computer network requires considerable time and expertise. Many schools have installed networks, only to find that they did not budget for the necessary administrative support.

File Server May Fail. Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire school may lose access to necessary programs and files.

Cables May Break. The Topology chapter presents information about the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network.

Other disadvantages of networks

Server faults stop applications being available

Network faults can cause loss of data.

Network fault could lead to loss of resources

User work dependent upon network

System open to hackers

Decisions tend to become centralised

Could become inefFicient

Could degrade in performance

Resources could be located too far from user

Network topology

The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology is the method used to pass information between workstations.

Main Types of Network Topologies In networking, the term "topology" refers to the layout of connected devices on a network.

Network topologies include the following:

Star Topology. Star topology

A topology in which all the nodes are connected to a central hub. Each node has an equal right of transmission of data.

A sketch diagram of a star topology

Hub/Concentrator/Server/Switch

Advantages of a Star Topology

Easy to install and wire.

No disruptions to the network when connecting or removing devices.

Easy to detect faults and to remove parts.

Failure in any star network cable will only take down one computer's network access and not the entire LAN.

Disadvantages of a Star Topology

Requires more cable length than a linear topology.

If the hub fails, however, the entire network also fails.

More expensive than linear bus topologies because of the cost of the concentrators.

a star network generally requires more cable,

Ring Topology. Ring Layout/topology

A ring topology is a network layout in which each node has exactly two neighbours connected to it for communication purposes. For each node to communicate, it must make a request for a token be able to send a signal along the path.

A failure in any cable or device breaks the loop and can take down the entire network.

A sketch diagram of a ring topology

Cable

Bus Topology: Bus or linear topology

A topology in which each node is connected in series along a single conduit or main cable called a bus.

A sketch diagram of a bus topology

Main Advantage: It's easy to connect a computer or device and typically it requires less cable than a star topology.

Bus networks are relatively inexpensive and easy to install for small networks.

Main Disadvantage: The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.

Advantages of a Linear Bus Topology

Easy to connect a computer or peripheral to a linear bus.

Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

Entire network shuts down if there is a break in the main cable.

Terminators are required at both ends of the backbone cable.

Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand-alone solution in a large building.

.

Tree Topology

Tree network topology is also known as a the hierarchical network topology.

This is because it contains different levels of hierarchy.

[pic]

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level),

Each of the second level nodes will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it.

The hierarchy of the tree is symmetrical - Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy.

It usually has three layers: the core layer, the distribution layer and the Access layer.

Mesh Topology: A network topology in which at least each node has two or more paths between them.

A sketch diagram of a mesh topology

Main Advantage: In a star network, one malfunctioning node doesn't affect the rest of the network.

Main Disadvantage: If the central computer fails, the entire network becomes unusable.

Extended Star/Tree/Hybrid topology

It’s a combination of two or more topology

The same network topology to be distributed in different segiments

It’s the extended star Or a combination of two or more star topology

Or. it’s a combination of two or more topologies

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Factors to consider When Choosing a Topology

Cost.

Future growth:

Length of cable needed.

Number of computers to be connected

Level of security required

Networking Operating System

A network operating system (NOS) is the system software that organizes and coordinates the activities on a network. The principal functions of NOS include network control, access control, transmission control, error detection/correction, and network security.

System maintenance tasks such as backup

File management tasks

Prioritizing print jobs on the network

Examples of NOSs include:

Novell NetWare

Microsoft Windows server 2003 and 2008.

AppleShare

Unix /NFS

Sun Solaris

Apple Talk

Linux

IBM OS/2 Wrap

Mac OS

Windows OS (Win NT, Win XP, Win 7, and Win 8 etc.)

Client/Server Linux

Network Protocols

This refers to a set of rules and procedures governing transmission between components in a computer network.

The principal functions of protocol in a network include:

identifying each device in the communication path;

securing the attention of the other device;

verifying correct receipt of the transmitted message;

determining that a message requires retransmission if it is incomplete or has errors;

performing recovery when errors occur.

Common protocols

Simple Mail Transfer Protocol (SMTP) - an internet protocol for transferring of e-mails.

File Transfer Protocol (FTP): It allows files containing text, programs, graphics, numerical data, and so on to be downloaded off or uploaded onto a network.

Internet Protocol (IP) - does the packet forwarding and routing.

Transmission Control Protocol/Internet Protocol (TCP/IP) is a network standard that defines how messages (data) are routed from one end of a network to the other, ensuring the data arrives correctly.

Transmission Control Protocol (TCP) - responsible for delivery of data over the network.

Hypertext Transfer Protocol (HTTP): It allows Web browsers and servers to send and receive Web pages.

Simple Network Management Protocol (SNMP): It allows the management of networked nodes to be managed from a single point.

Telnet Protocol: It provides terminal emulation that allows a personal computer or workstation to act as a terminal, or access device, for a server.

Sequential Packet Exchange (IPX/SPX) - works with the Novell's internet work' packet / sequential exchange; responsible for delivery of sequential data over the network

Packets and Packet Switching

When a computer sends data over the Internet, the data is divided into small pieces called packets.

Each packet contains the data, as well as the recipient (destination), the origin (sender), and the sequence information used to reassemble the data at the destination.

Each packet travels along the fastest individual available path to the recipient's computer via communications devices called routers.

This technique of breaking a message into individual packets, sending the packets along the best route available, and then reassembling the data is called packet switching.

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