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Computer Networks

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Why Computer Networks ? - Sharing Resources - Sharing Data & Software - Efficient Communication - Using one database - Saving time

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Disadvantages of a Computer Networks - High cost to establish - Spreading virus soon - Need experts to maintain the network - Server down effect the whole network

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Aims of a Computer Networks - Resource Sharing emote Computability - High Reliability -E-Ensure the data consistency - Message Passing - Data Security -S-Save money

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Classification Of Network - W- Wide Area Network (WAN) By Geographical Setup Spread to unlimited area Eg:- Internet

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Classification Of Network - M- Metropolitan Area Network (MAN) By Geographical Setup Spread in a City or Country Eg:- Network within town

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- C- Campus Area Network (CAN) By Geographical Setup Spread in a site like School, Campus Eg:- Network within a school Classification Of Network

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- L- Local Area Network (LAN) By Geographical Setup Spread in a Building Eg:- Network within a Building

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- H- Home Area Network (HAN) By Geographical Setup Spread in a House Eg:- Network within a home

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- P- Personal Area Network (PAN) By Geographical Setup Computer and its components

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-C-Client Sever By Functional Relationship Clients work under Server

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-P-Peer to Peer (P2P) By Functional Relationship All the Computer have same capabilities

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-B-Bus Network By Network Topology

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-S-Star Network By Network Topology

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-R-Ring Network By Network Topology

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-T-Tree Network By Network Topology

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-M-Mesh Network By Network Topology

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-H-Hybrid Network By Network Topology

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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

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Common Network Elements Server Clients Communication Media Network Operating Shared Resources Modem Hub/ Switch

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Hub Hub sends messages to all computers Hub Vs Switch ABC D Switch sends messages to destination computer only Switch

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1. Dedicated Line Line Connections 2. Lease Line 3. Switch line (Dial Up connection)

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Simplex Transmission Modes Duplex Half Duplex

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Guided Media Communication Media Radiated Media

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Guided Media

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Coaxial Cables Guided Media

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Twisted pair cables

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Fiber Optic Cables

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Radiated Media

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Radio Transmission Radiated Media Media

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Infrared Transmission

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Microwave Transmission

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Satellite Transmission

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Data Transmission Types Serial Transmission Parallel Transmission 011000 0 1 1 0

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Network Interface Card Make the physical Connection between the computer and network wire

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What is a Network Protocol ? It is an agreement on transferring Data between computers in a network Eg:- TCP/IP, IPX/SPX, X.25

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Backbone Network Components Components that several networks link together. TCP/IP Devices Hub Bridge

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Backbone Network Components Components that several networks link together. TCP/IP IPX/SPX Devices Router Gateway

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Internet Wide Network spread all over the world to transfer electronic data.

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Today Internet is used for. Business, Education, communication

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Resources in the internet Information, Pictures, Sounds, Vedio, on line exams, Games, Chatting

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Necessaries for Getting Internet A Computer, Modem, Telephone line, internet browser

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Why a modem is needed. To convert digital signals Analog and vise versa Analog Signals Digital Signals DAC - Modulation ADC - Demodulation

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Internet Browsers The Application Software through which we access to the internet Eg :- Internet explorerNetscape Navigator Fire Fox Safari

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World Wide Web (WWW) Collection of Web pages throughout the world WWW. Rupavahini.lkWWW. Defence.lk www.Rupavahini.lk

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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

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Domain Name www.Rupavahini.lk www.Youtube.com www.Wickipedia.org www. Carrer.edu Classification of web sites according to their contents. Domain TypeWhat it Means.coma commercial business, organization, or company.eduan educational institution.intan international organization.gova nonmilitary government entity.mila military organization.neta network administration, often Internet-related.orgother organizations: nonprofit, nonacademic.uk,.au, ca, jp, nz, etc.country codes denoting servers found in other countries

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Search Engines A web page that helps us to find information on web pages when we dont know the exact name of the Web. Eg:- WWW. Google.com, Yahoo.com .

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Popularity of Search Engines

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What is download & Upload Internet Severs Home Computer Downloading Uploading

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Computer Virus

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Computer Virus It is a software that is very harm to computer. Replicate itself Join with another programs Do unintended actions

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Why Virus ? Hacking Avoid of copying software Revenge To break security systems to defeat competitors Etc..

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How Virus enter ?

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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

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Kinds of Virus ? Boot virus File Virus Macro Virus Trojan horse Warms Spyware + Format Fonts +

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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.

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Prevent from virus ? Use Anti virus Software

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Prevent from virus ? Use Firewalls

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Avoiding of using unexamined CD, Floppy, Software V i r u s G u a r d

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E-mail (Electronic Mail) Sending electronic data by using a network

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E-mail Addresses samantha perera@gmail.com - wrong (Space between username) samantha#?perera@gmail.com - wrong (Special Symbols) samantha@perera@gmail.com - duplicated @ sign SAMANTHAPERERA@gmail.com - wrong (Capital Letters) samantha_ perera@gmail.com - Correct (Underscore can be use) samanthaperera1981@gmail.com - Correct (numbers can be use)

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E-mail Addresses samantha@gmail.com We can create email accounts through. www.google.com username@gmail.com www.yahoo.com username@yahoo.com www.esrilanka.lk username@esrilanka.lk Through Telecom username@slt.lk

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