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Computer Networks

August 7, 2009

i). Networking is the practice of linking computing devices together with hardware and software that supports data communications across these devices.

ii). It can also be defined as an interconnection of a group of computers used for file sharing,data transfer etc.
Network Security:
i). Protection of networks and their services from unwanted intruders.Users are assigned an ID number and password that allows them access to information and programs within their authority.
ii). Network Security is controlled by the network administrator.
How can we share a file within a network?

This diagram illustrates the file sharing between two computers.A Simple network is commonly used for file sharing.Two computers make a direct connection with each and communicate over a wire or cable.Now-a-days,some people still use CD-ROM/DVD-ROM disks and USB keys for transfering the photos and videos,but networks give you more flexible options.
File sharing with Microsoft windows:
Microsoft windows contain built-in features for file sharing.File folders can be shared across a LAN or the Internet using Explorer interface and network drive mappings.
FTP (File transfer Protocol):
File Transfer Protocol is used to share files on the internet.FTP is a method used to transfer files across the internet using an FTP client program.FTP is an application protocol that uses the Internet’s TCP\IP protocols.
A central computer called FTP Server holds all the files to be shared.All modern operating systems contain in-built FTP client software and popular web browsers like Internet explorer can also be configured to run FTP clients.Security option can be set on the FTP server requiring clients to supply a valid login name and password.
Peer to peer File sharing:
Peer to peer File sharing is used for swapping large files on the internet,particularly music and videos.P2P file sharing systems do not use any central servers like FTP.It allow all computers on the network to function both as a client and a server.It also allow all computers to communicate and share resources as equals.
Files can be transfered from person to person over a network using email software.Emails can travel across the Internet or within a company intranet.Like FTP systems,email systems use a client/server model.
Online sharing devices:
Number of web sites built for community file sharing exist on the internet.Members post or upload their files to the site using a web browser,and others can download the copies of these files using their browser.Some community file sharing sites charge member fees,while others are free.
Types of Networks:
Local Area Network (LAN):

This diagram illustrates LAN with Printer which enables the user to access the printer across the network.A network covering a small geographic area like a home,office or building.Current LAN¬タルs are mostly based on Ethernet technology.
Metropolitan Area Network (MAN):
A Metropolitan area Network is a network that connects two or more Local area networks together but does not extend beyond the boundaries of the town,city or metropolitan area.Multiple routers,switches & hubs are connected to create a MAN.
Wide Area Network (WAN):

This diagram illustrates a Wide Area Network (WAN) configuration.WAN covers a large geographic area like a city, a country or multiple countries.The Internet is an example of a WAN that joins local and metropolitan area networks across most of the world.WAN technologies generally function at the lower three layers of the OSI reference model : the Physical layer,the Data link layer and the Network layer.
A network device called a router connects LANs to a WAN.In IP networking,the router maintains both a LAN address and a WAN address.
Wired Networks:

This diagram illustrates several common forms of wiring in computer networks.Twisted pair Ethernet cables are often used to connect computers in many homes.Phone or cable TV lines in turn connect the home LAN to the ISP(Internet Service Provider).Twisted pair and coaxial cable can also be used in remote areas.
Wireless Networks:

This diagram illustrates several common forms of wireless networks.Wi-Fi is the standard technology for building wireless home networks and other LANs. The Microsoft Windows, Apple Mac OS X and open source Unix and Linux operating systems support Wi-Fi to different extents.The coverage of one or more interconnected access points is called a hotspot.Hotspot service has been replaced by the new wireless services, Resnet and Eduroam.Businesses and communities also use the same Wi-Fi technology to set up public hotspots.Cellular technology supports voice communications over mobile phones.
Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, personal computers, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency.
Bluetooth enables these devices to communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, as long as the received transmission is powerful enough.
Maximum Permitted Power
Class 1
100 mW (20 dBm)
~100 meters
Class 2
2.5 mW (4 dBm)
~10 meters
Class 3
1 mW (0 dBm)
~1 meter
Other Area Networks:
ᅡᄋ WLAN-Wireless Local Area Network
ᅡᄋ SAN-Storage Area Network,Server Area Network or sometimes Small Area Network.
ᅡᄋ CAN-Campus Area Network,Controller Area Network or sometimes Cluster Area Network.
ᅡᄋ PAN-Personal Area Network
ᅡᄋ DAN-Desk Area Network
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