Slide 1Networks

Networks

“Each time you use the telephone you use the world’s largest computer network – the telephone system”

Slide 2Networks

A Computer Network

• A system of linked computers that allow messages to be transmitted from one to another

• Messages can be text, sound, video and graphics

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Purpose of Networks

• Allows sharing of hardware• Allows sharing of software• Allows easy exchange and

sharing of data between different locations– Tele-working– Video Conferencing– Electronic data interchange (EDI)

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Components of a Network

• Hardware– A sending device– A communications link– A receiving device

• Communications software

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Network Terms• Node

– A point on a network to which a device is attached

• Channel– The path over which data is

transmitted

• Host Computer (Server)– A computer that manages the

network

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Types of Networks

• There are 2 basic types of networks– LAN – Local Area Network– WAN – Wide Area Network

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LAN

• ‘Hardwired’ within the same building– Components are in fixed positions– Computers are in close ‘proximity’ to

each other– Computers have immediate access to

CPU – no dial-up required– Terminals/computers are directly linked

to each other and to the host computer

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WAN

• Uses a telecommunications service to link computers over a distance

• Needs a modem to convert signals from digital to analog for transmission

• May use a combination of telecommunications services

• Connects many types of computers

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Hardware Required

• Network Card• Cables/wires for

interconnection• Modem to convert signals• Satellites to relay data• Microwave stations to relay

data

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Network Card (NIC)

• Network card also called a Network Interface Card (NIC)

• NICs are needed to connect the network cable to the computer

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Communications Channel

• The route for digital information to pass through the network– Wired and wireless– The channel capacity is the number

of bits of information it can transmit per second

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How is Data Transmitted?

• Both LANS and WAN use the following to link computers – Twisted pair wire– Coaxial Cable– Fiber-optic cable

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Twisted Pair Wire• Two copper wires are twisted

together to form a cable and then insulated– Inexpensive– Used in normal telephone lines

so are already in place in buildings

– Susceptible to noise or interference

– Slow data transmission

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Coaxial Cable

• Used to connect computers and terminals in a LAN

• Heavily insulated single wire • Can be laid underground or

under the sea• Much faster data transmission

than twisted wire• Less interference than twisted

wire

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Fiber Optic Cable

• Fiber optic technology uses light, not electricity, to send data

• Cables are made of glass fibers that guide light beams for miles

• Fiber optics is faster, lighter, and less expensive than wire cables

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Fiber Optics

• Used higher frequencies so less interference

• Has high bandwidth thus faster transmission of data

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Modem

• Modems convert digital signals to analog and analog signals to digital

• Modem is short for Modulate/Demodulate

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Modem Speeds

• Modem speed is measured in bits per second

• This is how many bits per second (bps) are being transmitted over the channel

• Current speed for modems is 56.6 kbps

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ISDN

• ISDN (Integrated Services Digital Network) is designed to transmit a computer’s digital signal directly over a network

• The entire network is digital

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Benefits of ISDN

• No digital to analog conversion• Speed—data can be transmitted

at 128,000bps much faster than modem

• Voice and data transmission can happen at same time

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•Disadvantages of ISDN

• High initial costs• On-going monthly fees• Possibly, a newer phone line is needed• Not available in some geographic areas• Newer technologies like DSL now

becoming available

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Microwave Transmission

• Data is sent as signals through the atmosphere from one relay station to another

• Line-of-sight transmission only

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Microwave Transmission

• Since signals cannot bend - needs relay stations (in high places) about 30 miles apart to continue transmission

• Microwave transmissions are fast and cost-effective

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Satellites

• This form of communications link requires earth stations and transponders

• Earth stations send and receive signals. Transponders amplify the signal, change the frequency, and retransmit the data to a receiving earth station

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Satellite Transmission

• Requires– Earth Stations - which send and

receive signals– Transponders – receives the signal

from an earth station, amplifies it, changes the frequency and sends it on to another earth station near the destination

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Wireless Networks

• Use radio waves and/or microwaves to maintain communication channels between computers

• The data is beamed out over the airwaves

• Advantages of wireless include mobility and elimination of unsightly cables

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Advantages of Wireless

• Users with personal digital assistant (PDA) handheld computers such as Palm Pilots or with laptops can use wireless technology to allow them to move about while maintaining their network connectivity

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Advantages of Wireless

• The ability for users to network desktop computers at various locations without the trouble or expense of wiring

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Disadvantages of Wireless

• Slower than wired networks• Equipment more expensive• Wireless networks are affected by

obstructions such as walls etc in their vicinity

• Interference from other wireless devices such as cell-phones

• Interference from weather

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Mix and Match

• Most networks will be a combination of the many technologies that have been looked at here