Transcript NETWORKS

Networks
“Each time you use the telephone you
use the world’s largest computer
network – the telephone system”
Networks
Slide 1
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
Networks
Slide 2
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)
Networks
Slide 3
Components of a
Network
• Hardware
– A sending device
– A communications link
– A receiving device
• Communications software
Networks
Slide 4
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
Networks
Slide 5
Types of Networks
• There are 2 basic types of
networks
– LAN – Local Area Network
– WAN – Wide Area Network
Networks
Slide 6
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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Slide 7
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
Networks
Slide 8
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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Slide 9
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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Slide 10
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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Slide 11
How is Data
Transmitted?
• Both LANS and WAN use
the following to link
computers
– Twisted pair wire
– Coaxial Cable
– Fiber-optic cable
Networks
Slide 12
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
Networks
Slide 13
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
Networks
Slide 14
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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Slide 15
Fiber Optics
• Used higher frequencies so
less interference
• Has high bandwidth thus
faster transmission of data
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Slide 16
Modem
• Modems convert digital signals to
analog and analog signals to
digital
• Modem is short for
Modulate/Demodulate
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Slide 17
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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Slide 18
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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Slide 19
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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Slide 20
•Disadvantages of
ISDN
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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
Networks
Slide 21
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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Slide 22
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
Networks
Slide 23
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
Networks
Slide 24
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
Networks
Slide 25
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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Slide 26
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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Slide 27
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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Slide 28
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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Slide 29
Mix and Match
• Most networks will be a
combination of the many
technologies that have been looked
at here
Networks
Slide 30