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
Networks
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
Networks
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
Networks
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
Networks
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
Networks
Slide 15
Fiber Optics
• Used higher frequencies so
less interference
• Has high bandwidth thus
faster transmission of data
Networks
Slide 16
Modem
• Modems convert digital signals to
analog and analog signals to
digital
• Modem is short for
Modulate/Demodulate
Networks
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
Networks
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
Networks
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
Networks
Slide 20
•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
Networks
Slide 21
Microwave Transmission
• Data is sent as signals
through the atmosphere
from one relay station to
another
• Line-of-sight transmission
only
Networks
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
Networks
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
Networks
Slide 27
Advantages of Wireless
• The ability for users to network
desktop computers at various
locations without the trouble or
expense of wiring
Networks
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
Networks
Slide 29
Mix and Match
• Most networks will be a
combination of the many
technologies that have been looked
at here
Networks
Slide 30