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Computer Networks. Why Computer Networks ?. Sharing Resources Sharing Data & Software Efficient Communication Using one database Saving time. Disadvantages of a Computer Networks. High cost to establish Spreading virus soon Need experts to maintain the network - PowerPoint PPT Presentation
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Computer Networks
Why Computer Networks ?- Sharing Resources
- Sharing Data & Software
- Efficient Communication
- Using one database
- Saving time
Disadvantages of a Computer Networks
- High cost to establish
- Spreading virus soon
- Need experts to maintain the network
- Server down effect the whole network
Aims of a Computer Networks
- Resource Sharing
- Remote Computability
- High Reliability
- Ensure the data consistency
- Message Passing
- Data Security
- Save money
Classification Of Network
- Wide Area Network – (WAN)
By Geographical Setup
Spread to unlimited
area
Eg:- Internet
Classification Of Network
- Metropolitan Area Network – (MAN)
By Geographical Setup
Spread in a City or Country Eg:- Network within town
- Campus Area Network – (CAN)
By Geographical Setup
Spread in a site like School,
Campus Eg:-
Network within a school
Classification Of Network
- Local Area Network – (LAN)
By Geographical Setup
Spread in a Building
Eg:- Network within a Building
Classification Of Network
- Home Area Network – (HAN)
By Geographical Setup
Spread in a House
Eg:- Network within a home
Classification Of Network
- Personal Area Network – (PAN)
By Geographical Setup
Computer and its components
Classification Of Network
- Client Sever
By Functional Relationship
Clients work under Server
Classification Of Network
- Peer to Peer (P2P)
By Functional Relationship
All the Computer have same capabilities
Classification Of Network
- Bus Network
By Network Topology Classification Of Network
- Star Network
By Network Topology Classification Of Network
- Ring Network
By Network Topology Classification Of Network
- Tree Network
By Network Topology Classification Of Network
- Mesh Network
By Network Topology Classification Of Network
- Hybrid Network
By Network Topology Classification Of Network
Server – Manages all the other computers in the network..
Common Network Elements
Client – Work under the server
Communication Media – Trough which computers are connected.
Network Operating System (NOS) – Software installed to the server
Shared Resources – Devices shared among network clients
Modem – Device used to get the internet
Hub/ Switch – Device used to connect all the computer
Common Network Elements
Server
Clients
Communication Media
Network Operating
Shared Resources
Modem
Hub/ Switch
Hub
Hub sends messages to all computers
Hub Vs Switch
A B C D
Switch sends messages to destination computer only
Switch
1. Dedicated Line
Line Connections
2. Lease Line
3. Switch line (Dial Up connection)
Simplex
Transmission Modes
Duplex
Half Duplex
Guided Media
Communication Media
Radiated Media
Guided Media
Coaxial Cables Guided Media
Twisted pair cables Guided Media
Fiber Optic Cables Guided Media
Radiated Media
Radio Transmission Radiated Media Media
Infrared Transmission Radiated Media Media
Microwave Transmission Radiated Media Media
Satellite Transmission Radiated Media Media
Data Transmission Types
Serial Transmission
Parallel Transmission
0 1 1 0 0 0
0110
Network Interface Card
Make the physical Connection between the computer and network wire
What is a Network Protocol ?
It is an agreement on transferring Data between computers in a network
Eg:-
TCP/IP, IPX/SPX, X.25
Backbone Network Components Components that several networks link together.
TCP/IP TCP/IP
Devices
Hub Bridge
Backbone Network Components Components that several networks link together.
TCP/IP IPX/SPX
Devices
Router Gateway
InternetWide Network spread all over the world to transfer electronic data.
Today Internet is used for….
Business, Education, communication
Resources in the internet
Information, Pictures, Sounds, Vedio, on line exams, Games, Chatting
Necessaries for Getting Internet
A Computer, Modem, Telephone line, internet browser
Why a modem is needed….
To convert digital signals Analog and vise versa
Analog Signals
Digital Signals
DAC - Modulation
ADC - Demodulation
Internet Browsers
The Application Software through which we access to the internet Eg :-
Internet explorer Netscape Navigator
Fire Fox
Safari
World Wide Web (WWW)
Collection of Web pages throughout the world
WWW. Rupavahini.lk WWW. Defence.lk
www.Rupavahini.lk
Web Address = URL (Uniform Resource Locator)
It is essential to separate web pages each other
http: // WWW. Defence.lk /News
Protocol
Hyper Text Transfer Protocol
The server
Where this information is?
Path name
Location of an item on the server
Domain Name
www.Rupavahini.lk
www.Youtube.com
www.Wickipedia.org
www. Carrer.edu
Classification of web sites according to their contents.
Domain Type What it Means
.com a commercial business, organization, or company
.edu an educational institution
.int an international organization
.gov a nonmilitary government entity
.mil a military organization
.net a network administration, often Internet-related
.org other organizations: nonprofit, nonacademic
.uk, .au, ca, jp, nz, etc. country codes denoting servers found in other countries
Search Engines
A web page that helps us to find information on web pages when we don’t know the exact name of the Web.
Eg:- WWW. Google.com, Yahoo.com ….
Popularity of Search Engines
What is download & Upload
Internet SeversHome Computer
Downloading…
Uploading
Computer Virus
Computer Virus
It is a software that is very harm to computer.
• Replicate itself
• Join with another programs
• Do unintended actions
Why Virus ?
• Hacking
• Avoid of copying software
• Revenge
• To break security systems
• to defeat competitors
Etc…..
How Virus enter ?
Characteristics of Virus ?
• If computer take long time than normal to open a program
• If it Read the hard disks, Floppy disks often
• If Unknown files are visible• If unnecessary beep codes activate• If Unnecessary messages & pictures visible
Kinds of Virus ?
• Boot virus
• File Virus
• Macro Virus
• Trojan horse
• Warms
• Spyware
+
Format Fonts
+
• Spam Unsolicited email, often of a commercial nature, sent indiscriminately to multiple mailing lists or individuals.
• Spyware This is software that secretly gathers information about a user while he/she navigates the Internet. This information is normally used for advertising purposes. Spyware can also gather information about email addresses and even passwords and credit card numbers.
• Trojan horse This is a program that disguises itself as another program. Similar to a virus, these programs are hidden and cause an unwanted effect. They differ from viruses because they are normally not designed to replicate like a virus.
• Virus A computer virus is a piece of code that is secretly introduced into a system in order to corrupt it or destroy data. Often viruses are hidden in other programs or documents and when opened, the virus is let loose.
• Worm This is a special type of virus that spreads without any user interaction, typically by exploiting a flaw in popular software.
Prevent from virus ?
• Use Anti virus Software
Prevent from virus ?
• Use Firewalls
Prevent from virus ?
• Avoiding of using unexamined CD, Floppy, Software
Virus G
uard
E-mail (Electronic Mail)
• Sending electronic data by using a network
E-mail Addresses
samantha [email protected] - wrong (Space between username)
samantha#[email protected] - wrong (Special Symbols)
samantha@[email protected] - duplicated @ sign
[email protected] - wrong (Capital Letters)
samantha_ [email protected] - Correct (Underscore can be use)
[email protected] - Correct (numbers can be use)
E-mail Addresses
We can create email accounts through….
www.google.com – [email protected]
www.yahoo.com – [email protected]
www.esrilanka.lk – [email protected]
Through Telecom – [email protected]
