331: STUDY DATA COMMUNICATIONS AND
NETWORKS
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1. Discuss computer networks (5 hrs)
2. Discuss data communications (15 hrs)
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PERFORMANCE STANDARD
◦ Given a network system, identify and illustrate the
different data communications components clearly
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Objectives:
◦ Define elements of a communication system
◦ Define data communications
◦ Discuss various types of transmission media and
their characteristics
◦ Discuss encoding of information tor transmission
◦ Discuss types of signal & their characteristics
◦ Relate data capacity of a channel and bandwidth
◦ Classify media based on bandwidth
◦ Discuss channel organization
Discuss various types
of transmission media
and their
characteristics
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twisted pair – telephone cable
coaxial cable –Thick black cable used for
higher bandwidth communications than
twisted pair (i.e. Optus cable)
fibre optic – data transferred through pulses
of light. Extremely fast.
Non cable methods such as satellite,
microwave, wireless and Bluetooth
Twisted pair
cable
Twisted pair cable application
 Most common medium
 Telephone network
◦ Between house and local exchange (subscriber
loop)
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Within buildings
◦ To private branch exchange (PBX)
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For local area networks (LAN)
◦ 10Mbps or 100Mbps
Twisted pair cable pro and contra
Advantages
 Cheap
 Easy to work with
Disadvantages
 Low data rate
 Short range
Twisted pair Transmission Characteristics
 Analog
◦ Amplifiers every 5km to 6km
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Digital
◦ Use either analog or digital signals
◦ repeater every 2km or 3km
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Limited distance
Limited bandwidth (1MHz)
Limited data rate (100MHz)
Susceptible to interference and noise
Twisted pair (UTP and STP)
 Unshielded Twisted Pair (UTP)
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Ordinary telephone wire
Cheapest
Easiest to install
Suffers from external EM interference
Shielded Twisted Pair (STP)
◦ Metal braid or sheathing that reduces interference
◦ More expensive
◦ Harder to handle (thick, heavy)
The Electronic Industries Association (EIA) has
developed standards to grade UTP.
1.
Category 1. The basic twisted-pair cabling used
in telephone systems. This level of quality is fine
for voice but inadequate for data transmission.
2.
Category 2. This category is suitable for voice
and data transmission of up to 2Mbps.
3.
Category 3.This category is suitable for data
transmission of up to 10 Mbps. It is now the
standard cable for most telephone systems.
4.
Category 4. This category is suitable for data
transmission of up to 20 Mbps.
5.
Category 5. This category is suitable for data
transmission of up to 100 Mbps.
Category
Bandwidth
Data Rate
Digital/Analog
Use
1
very low
< 100 kbps
Analog
Telephone
2
< 2 MHz
2 Mbps
Analog/digital
T-1 lines
3
16 MHz
10 Mbps
Digital
LANs
4
20 MHz
20 Mbps
Digital
LANs
5
100 MHz
100 Mbps
Digital
LANs
6 (draft)
200 MHz
200 Mbps
Digital
LANs
7 (draft)
600 MHz
600 Mbps
Digital
LANs
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The most common UTP connector is RJ45 (RJ
stands for Registered Jack).
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Coaxial Cable (or coax)
Coaxial cable carries signals of higher
frequency ranges than twisted-pair cable.
Coaxial Cable standards:
◦ RG-8, RG-9, RG-11 are used in thick Ethernet
◦ RG-58 Used in thin Ethernet
◦ RG-59 Used for TV
Coaxial Cable
 Used for cable television, LANs, telephony
 Has an inner conductor surrounded by a
braided mesh
 Both conductors share a common center
axial, hence the term “co-axial”
Coax
Layers
outer jacket
(polyethylene)
shield
(braided wire)
insulating material
copper or aluminum
conductor
Coaxial Cable Applications:
 Most versatile medium
 Television distribution
◦ Ariel to TV
◦ Cable TV
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Long distance telephone transmission
◦ Can carry 10,000 voice calls simultaneously
◦ Being replaced by fiber optic
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Short distance computer systems links
Local area networks
Coaxial Cable - Transmission Characteristics
 Analog
◦ Amplifiers every few km
◦ Closer if higher frequency
◦ Up to 500MHz
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Digital
◦ Repeater every 1km
◦ Closer for higher data rates
Fiber Optic Cable
 Relatively new transmission medium used by
telephone companies in place of longdistance trunk lines
 Also used by private companies in
implementing local data communications
networks
 Require a light source with injection laser
diode (ILD) or light-emitting diodes (LED)
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consists of three concentric sections
plastic jacket
glass or plastic
cladding
fiber core
Fiber Optic Cable
 Metal cables transmit signals in the form of
electric current.
 Optical fiber is made of glass or plastic and
transmits signals in the form of light.
 Light, a form of electromagnetic energy,
travels at 300,000 Kilometers/second
(186,000 miles/second), in a vacuum.
 The speed of the light depends on the density
of the medium through which it is traveling
(the higher density, the slower the speed).
Optical Fiber
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multimode step-index fiber
◦ the reflective walls of the fiber move the light
pulses to the receiver
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multimode graded-index fiber
◦ acts to refract the light toward the center of the
fiber by variations in the density
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single mode fiber
◦ the light is guided down the center of an
extremely narrow core
fiber optic multimode
step-index
fiber optic multimode
graded-index
fiber optic single mode
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greater capacity (bandwidth of up to 2 Gbps)
smaller size and lighter weight
lower attenuation
immunity to environmental interference
highly secure due to tap difficulty and lack of
signal radiation
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expensive over short distance
requires highly skilled installers
adding additional nodes is difficult
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Unguided media, or wireless communication,
transport electromagnetic waves without
using a physical conductor.
Instead the signals are broadcast though air
or water, and thus are available to anyone
who has a device capable of receiving them.
The section of the electromagnetic spectrum
defined as radio communication is divided
into eight ranges, called bands.
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Electrical conductor (or system of..) used to radiate
electromagnetic energy or collect electromagnetic
energy
Transmission
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Radio frequency energy from transmitter
Converted to electromagnetic energy
By antenna
Radiated into surrounding environment
Reception
◦ Electromagnetic energy impinging on antenna
◦ Converted to radio frequency electrical energy
◦ Fed to receiver
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Same antenna often used for both
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transmission and reception are achieved by
means of an antenna
directional
◦ transmitting antenna puts out focused beam
◦ transmitter and receiver must be aligned
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omnidirectional
◦ signal spreads out in all directions
◦ can be received by many antennas
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Directional Antennas provide great efficiency
of power transmission because the power can
be focused into a narrow beam directed
toward the station of interest.
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Omnidirectional Antenna is widely used
for radio broadcasting antennas, in mobile
devices that use radio such as cell
phones, FM radios, walkie-talkies, wireless
computer networks, cordless phones, GPS
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Radio technology considers the earth as surrounded
by two layers of atmosphere: the troposphere and
the ionosphere.
The troposphere is the portion of the atmosphere
extending outward approximately 30 miles from the
earth's surface.
The troposphere contains what we generally think of
as air. Clouds, wind, temperature variations, and
weather in general occur in the troposphere.
The ionosphere is the layer of the atmosphere above
the troposphere but below space.
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Ground propagation: radio waves travel through
the lowest portion of the atmosphere, hugging the
earth. These low-frequency signals emanate in all
directions from the transmitting antenna and
follow the curvature of the planet. The distance
depends on the power in the signal.
In Sky propagation, higher-frequency radio waves
radiate upward into the ionosphere where they
are reflected back to earth. This type of
transmission allows for greater distances with
lower power output.
In Line-of-Sight Propagation, very high frequency
signals are transmitted in straight lines directly
from antenna to antenna.
Band
Range
Propagation
Application
VLF
3–30 KHz
Ground
Long-range radio navigation
LF
30–300 KHz
Ground
Radio beacons and
navigational locators
MF
300 KHz–3 MHz
Sky
AM radio
HF
3–30 MHz
Sky
Citizens band (CB),
ship/aircraft communication
VHF
30–300 MHz
Sky and
line-of-sight
VHF TV,
FM radio
UHF
300 MHz–3 GHz
Line-of-sight
UHF TV, cellular phones,
paging, satellite
SHF
3–30 GHz
Line-of-sight
Satellite communication
EHF
30–300 GHz
Line-of-sight
Long-range radio navigation
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Satellite is relay station
Satellite receives on one frequency, amplifies
or repeats signal and transmits on another
frequency
Requires geo-stationary orbit
◦ Height of 35,784km
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Television
Long distance telephone
Private business networks
QUESTION?