Download Telecommunications

Chapter 6
Information Technology in
Business:
Telecommunications and
Networks
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Telecommunications:

Transmittal of data from one computer
to another over a distance
 Telecommunications has improved
business in three main ways:
Better communication
 Higher efficiency
 Better distribution of data

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What is the Different between
Communication
and
Telecommunication ?
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What is Data Communications?
 Data Communications is Any
transfer of data



within a computer,
between a computer and another device,
or between two computers
 Two Basic Modes


Parallel transmission
Serial transmission
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Communication Direction
 Three Modes of Communication
Between Devices

Simplex


Half-Duplex


One-way in one direction
One-way in two directions
Full-Duplex

Two-way in two directions
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Asynchronous Communication


In asynchronous transmission, the devices are
not synchronized by any timing aids.
Advantage of asynchronous transmission


Does not need sophisticated and expensive timing
hardware
Disadvantage of asynchronous transmission

Overhead, time spent transmitting bits that are not a
part of the primary data
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Synchronous Communication

In synchronous communication, data are
transmitted using timing devices.

Messages are transmitted in packets.

Advantage of synchronous communication

Overhead in synchronous communication is
significantly smaller than in asynchronous
communication.
Synchronous transmission
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Channels and Media
 Media

A medium is any
means by which data
can be transmitted.
 Transmission speed

A medium’s capacity
is determined by the
range of bits per
second at which it can
operate.
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Channels and Media
 Twisted Pair

Telephone line made of a pair of copper wires
twisted to reduce electromagnetic interference
(EMI)
 Coaxial Cable

Commonly used for cable television transmission



More expensive than twisted pair
Greater transmission rate than twisted pair
Much less susceptible to EMI
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Channels and Media
 Microwaves

High-frequency, short radio-frequency
(RF) waves


Terrestrial microwave
Satellite microwave
 Optical Fiber

Fiber-optic technology uses light
instead of electricity to transmit data.
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Channels and Media
Characteristics of channel media
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SPEEDS & COST OF MEDIA
MEDIUM
TWISTED WIRE
SPEED
300 BPS - 10 MBPS
MICROWAVE
256 KBPS - 100 MBPS
SATELLITE
256 KBPS - 100 MBPS
COAXIAL CABLE
56 KBPS - 200 MBPS
FIBER OPTICS
500 KBPS - 10 GBPS
BPS : BITS PER SECOND
KBPS: KILOBITS PER SECOND
MBPS: MEGABITS PER SECOND
GBPS: GIGABITS PER SECOND
COST
LOW
HIGH
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OTHER SERVICES:
 DIGITAL SUBSCRIBER LINE (DSL):
enhancing capacity over copper telephone lines
 CABLE MODEM: modem for cable TV for
high-speed access to Internet
 T1 LINE: dedicated telephone connection, 24
channels @ 1.544 megabits per second
*
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Analog vs. Digital
Analog signals: A continuous series of waves
 Digital signals: A series of discrete bits

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MODEM
Devices that modulate and demodulate signals

Modulation: Modification of a digital signal
into an analog signal

Demodulation: Modification of an analog
signal into a digital signal
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Modulation
 Amplitude Modulation
(AM)
 Frequency Modulation
(FM)
Figure 6.8 Signal modulation
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Multiplexers
 Devices
that allow several telephones
or computers to transmit data through
a single line
 Frequency division multiplexing
 Time-division multiplexing
Multiplexing
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Networks
 LANs (Local Area Networks)

Networks within a building, or within a group of
adjacent buildings
 WANs (Wide Area Networks)

Networks that cross organizational boundaries or
reach outside the company
Value-added networks (VANs)
 Wireless communication

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Where wireless LANs are a good choice
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Networks
 Network Topology

Physical layout of the nodes in a network
Star
 Ring
 Bus
 Tree

Network topologies
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Protocols
 Communication protocols

Rules governing the communication between
computers or between computers and other
computer-related devices
 Network protocols

Rules governing a network of devices
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Protocols
Some communications software allows a user to establish protocols: bit rate, parity, number of
data bits, stop bits, and a handshake procedure.
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Protocols
Figure 6.14 The seven layers of the OSI model
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Switching Techniques and
Transfer Modes
 Circuit Switching:Message is communicated in its entirety
from the transmitting computer to the receiving computer
 Packet Switching:Message is divided into packets of bytes
and transmitted via several nodes
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The Changing Business
Environment
 Cellular Phones
 Teleconferencing
 Voice Mail
 Facsimile
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Ethical and Societal Issues
Telecommuting: Pros and Cons
Pros
Saves travel cost and time
 Decreases pollution
 May reduce unemployment.
 Productivity higher among telecommuters

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Ethical and Societal Issues
Telecommuting: Pros and Cons
Cons

Employers tend to pressure telecommuters
to work harder than workers in the office.

May negatively impact some segments of the
economy
Restaurants
 Downtown business and industries

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