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Computer Networks & Internetworking

Published on May 2018 | Categories: Documents | Downloads: 19 | Comments: 0



Resource Sharing: a computer network allows sharing of resources such as hardware and software e.g. if there are four people in a family, each having their own computer, they will require four modems for the Internet Inter net connection and four printers, pr inters, if they want want to use the resources at the same time. A computer network, on the other hand, provides a cheaper alternative by the provision of resource sharing, In this way, all the four computers can be interconnected, using a network, network, and just one modem and printer can efficiently eff iciently pro provide the services to all four members. The facility f acility of shared shared folders can also be availed availed by family members. me mbers. Centralized Software Management: a computer network allows installation of software software on one computer (the file server), server), this eliminates that need to spend time and energy energy installing updates and tracking files on independent computers thr t hroughout oughout the building. building. Communication medium: a computer network can provide a powerful communication medium among people spread widely at different physical locations, It acts as a powerful powerful communication medium when it comes to sharing information and resources across the world.

Data Security and Management :In a business environment, a computer network allows the administrators to much better manage the company's critical data. Instead of having this data spread over dozens or even hundreds of small computers in a haphazard fashion as their users create it, data can be centralized on shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information. Speed: Sharing and transferring files within Networks are very fast. Networks provide a very rapid method for sharing and transferring files. The sharing of data with the other users in a stand-alone environment requires physical transfer of data. This can be done by copying the data on a floppy disk or taking a printout. This requires more time and is inconvenient as compared to sharing the data over a network.

Disadvantages of the computer Network Expensive Set Up: The initial set up cost of a computer network can be high depending on the number of computers to be connected. Costly devices like routers, switches, hubs, software etc. can add up to the bills of a person trying to install a computer network and the installation may require the services of a technician. .

•Data Security: If a network is implemented properly, it is possible to greatly improve the security of important data, in contrast a poorly secured network puts critical data at risk exposing it to the potential problems associated with hackers or unauthorized access. •Rapid Spread of Computer Viruses: If any computer system in a network gets affected by a computer virus there is a possible threat of other systems getting affected too. Viruses get spread on a network easily because of the interconnectivity of workstations, such spread can be dangerous if the computers have important database which can get corrupted by the virus. •Server failure or cable breakage: In case the main Server of a computer network breaks down, the system becomes useless also cables may break interfering with the effective operation of the network.

CLASSIFICATION OF COMPUTER NETWORKS Computer Networks may be classified according to a wide variety of characteristics such as geographical coverage,ownership,size ,physical architecture etc. Local area network(LAN) • A LAN is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building or closely positioned group of buildings. •Each computer or device on the network is called as a node. •LAN’s usually use only one type of transmission media and organized using bus, ring or star topologies. Personal area network (PAN) • A PAN is a computer network used for communication among computer and different information technological devices such as personal computers, printers, fax machines, telephones, PDAs, scanners close to one person. • A PAN may include wired and wireless devices. •The reach of a PAN typically extends to 10 meters. •] A wired PAN is usually constructed with USB and Firewire connections  while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

PAN(Personal Area Network)

Bluetooth trademark sign

Metropolitan area network (MAN)

 A large computer network that usually spans a city. It usually interconnects a number of local area networks (LANs) using a highcapacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.

Mombasa Rd Branch

Rongai Branch

Githurai Branch

Westlands Branch

 Wide area network (WAN) 

 A WAN is a computer network that covers a large geographic area such as a country, a continent or the whole  world using a communications channel that combines many types of media such as telephone lines, cables, and air  waves.

The Internet The term Internet is an acronym that stands for International Network. The Internet is a global system of interconnected governmental, academic, corporate, public, and private computer networks based on the networking technologies of the TCP/IP protocol. It is defined as a world-wide computer network linking countless thousands of computer networks, through a mixture of private and public computer networks. Internet is just like a wide highway in a cyber space (space of electronic movement of data) that moves data and information. Therefore, the terms Cyber Space and Information Super Highway are frequently used to refer to Internet .

Internet Services Some of the most common uses of Internet are: 

World Wid e Web (WWW) – This is a vast virtual space of the internet where information pages called web pages are installed. A collection of web pages stored as a file in a special type of a computer called web server is called a Website. Every website is accessed using Uniform Resource Locator (URL) e.g. KSTC’s http://www.uonbi.ac.ke Commun ication - You can exchange information with your family and friends anywhere in the world through e-mails, chat rooms and newsgroups ETC. E-commerce – Today you can access cyber shops for online purchasing, windowshopping and pay for the services through electronic funds transfer (EFT), cheque and credit cards. Research - Researchers and scholars use Internet to access digital (virtual) libraries for the latest information and archives. Entertainment - You can watch Web TVs, online videos and play games, in Internet you will almost get anything you need to keep you entertained. E-learni ng – Academic materials for all levels of education are readily available on the Internet.

Telnet – Logging into remote computer & work on it as your local computer.

FTP – Transferring files to a remote computer or from remote comp. to a local comp.

Internet Connectivity Requirements: ◦

 A computer, a PDA or WAP enabled mobile phones) – these devices are used

to access the internet data either through the physical or wireless means. ◦

Transmission media – This is a physical (copper wires) or wireless (radio

frequencies) pathway used to the medium for transferring data/information from one computer to another. ◦

 Internet Service Provider - These are licensed commercial or non-commercial

organizations that provide access to internet. Examples are Access Kenya, Swift Kenya, Nairobi net, Africa online, Wananchi, Celtel, Safaricom etc. 

Software – The main categories of internet software are: ◦

Browser Software - This lets you access the Internet resources examples are Internet explorer, Netscape Navigator, Opera, Monzila FireFox, Mosaic etc. Email Software enables you to receive, compose and send emails e.g. Outlook express, Eudora Light, Pegasus Mail, Yahoo mail etc. Search Engines – These are search agent programs that enable one to quickly search and access internet resources. They provide a catalogue of all information available over the internet for quick access. They all provide a search form where one types key words of the information he/she wants to access. Examples are: Yahoo, Google, Inforseek, Alta Vista, Lycos etc.

MODEM (Modular-Demodulator) - Transforms digital data signals from a

computer into analog data signals (a form that can travel over the transmission

Internet Connection Types There are two principal ways of connecting to the Internet, that is; Direct and Dial – up connection


1. ◦

In this, the user has a fixed or dedicated link (physical line/wireless)to the ISP.

Direct connections provide continuous, “always on” access to the Internet.

 A direct connection can be obtained in many ways e.g. Local Area Network (LAN) – A LAN can be connected to the Internet through a special hardware component called a router which is connected to another router at the ISP by a high-speed line.

 Advantages: ◦

High speed connection  You do not need a modem but a router It is convenient as one does not have to keep on dialing up.

Disadvantage: ◦

It is expensive to maintain the connection

Only economical for large corporation/organizations.

Internet Connection Types Dial-up

2. ◦

In this you connect your computer by use of a modem and/or phone line/wireless only when you want to use Internet.

The user gains Internet access when he/she contact the ISP and the ISP transfers him/her to Internet. When he/she finishes, they disconnect from the ISP. The speed with which you can access the Internet is determined primarily by the speed of your modem.

To gain faster dial-up connections, you can install an Integrated Service Digital Network (ISDN) line which is a digital line provided by the local phone company.

 Advantage: ◦

Initial connection fee is less as compared to direct connection

Cost can be controlled by reducing connection time

Connection done only when there is a need

Disadvantages: ◦

May be disappointing in case of resource contention/traffic jam during dial up process as one has to keep on dialing up.

Electronic Mail (E-mail) 

Electronic Mail refers to the sending and receiving of electronic letters and documents on the Internet.

 Advantages Over the Traditional Paper Mail/‘Snail Mail’ ◦

It is fast

It is cheap

It is convenient

Easy to send one mail to many recipients by use of carbon copies

Mail can be saved for future retrieval

Easy to reply mails

Mails can easily be forwarded to another recipient

Document created using other application can easily be attached to the mail etc.

Reliable if all email etiquette and netiquette is observed.

Disadvantages ◦

Security of message may not be guaranteed – due to tapping while on transit.

Not yet accessible to every body due to the connectivity limitations

Requires some ICT literacy to use and enjoy

It is boring to read ‘junk mails’

E-mail Address 

For one to send and receive an email, he/she must have an email address.

Email address directs the computers on the Internet on where to deliver the email message.

A typical email address has this format: [email protected] e.g. [email protected] i.e. the email parts are: ◦

Pekyalo – This is the user name that identifies the owner of the email address.

@ - Separates the username from the rest of the address parts

Yahoo – The name of the host computer on the Internet in to which the email account is hosted.

The period (.) – read as dot. Separates different parts of the email address. Com – The domain. Identifies the type of Institution that owns the host computer.

E-mail Address Commonly Used Domains

.com – commercial organizations .co – company/commercial organization .org – NGOs .go – government .edu – educational institution .ac – academic/educational institution etc Country Domains are: .ke – Kenya.

.tz – Tanzania

.uk – United Kingdom

.ug - Uganda


Load the e-mail program that you are using e.g. for yahoo mail account holders, type ‘www.mail.yahoo.com’ in address bar of your browser to load the mail program.

In the username text box, type your user name .e.g. pkmulwa

In the password text box, type the password. The password appears encrypted for security.

Click on Sign in command button and wait as your mails window is opened

Composing and sending Email Steps: 

Load email application program/Email Editor

Log in/Sign in if required by typing your user name and password.

Click on compose command button – mail editor window appears as shown on the left.

Type email address of the recipient in the TO: text box.

To sent Carbon Copies (Cc) & Blind Carbon Copies (Bcc) type the addresses in the Cc: & Bcc: textboxes respectively. Separate two or more addresses by commas. Bcc recipients don’t see the identity of other recipients.

Type the subject/title of your message in the Subject: text box.

Type the message and format it as you want in the message text area.

Click on send command button to send mail.

The computer confirms on sending the mail.

File Attachment

Steps: 

Load email application program/Email Editor

Log in or sign in as expected to access your account by supplying your username and password.

Compose your mail as usual.

Click on Attach Files command button.

From the dialog box that appears, browse to specify the file/s to attach from your computer.

Click on Open command button from the ‘Choose file’ dialog box after choosing the file to attach.

The attachment progress bar appears. Wait as the file/s is/are attached to you mail.

 An attachment bar is inserted in the mail  window with the name of the attached file.

Click on send command to send the mail.

Receiving/Replying/Forwarding mail Steps: 

Load email application program/Email Editor

Log/sign in if required to access your email account by supplying your username and password.


Click on ‘check mail’ command button

Click on Inbox to view the mails received as shown on the left.

To read a mail, click on its subject/title from the list of received mails. To read an attachment, click on the attachment icon & follow the instructions that follow.

To reply the mail, simply click on Reply tab/command and type the reply message then click on send command to send it.

To forward the mail, click on ‘Forward’ tab, type the address of the person whom you


 want to forward the mail to, click on send.

Saving an E-mail

a) With the mail window opened, click on file menu  b) Click on save as from the pull down menu c) Select the location to save the mail and type the file name d) Click on save

Deleting and Spamming mails

a) From the inbox window, select the mail to delete or spam  b) Click on the delete or spam command button to delete or spam the mail  NB: For deleting, confirm the deletion

Printing Mails a) Open the mail that you want to print  b) Click on the file menu c) Click on print from the pull down menu d) Specify the printer and the number of copies e) Click on print.

Sign Out/Log Off  •Once you have read your mail, it is advisable to sign out or log off to ensure that unauthorized users do not read the mail. •To sign out or log off, click on the sign out or log off command button.

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