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Alternatives and Sourcesof Data Transmission
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Data Transmission
The transportation of anykind of information, from
one place to another by
physical means.
In computer terminology,this means sending
streams of bits or bytes
from one location to
another location usingtechnologies such as
copper wire, fiber optics,
lasers, radio, or infrared
light.
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Data Transmission
Data transmission
involves the
communication of digitalmessages between digital
devices. Signals are sent
via a network to external
devices, such as printersor other computers.
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Example of Data Transmission
EmailsA form of data transfer very
popular because virtually
free, but not secure.
Its possibilities in terms oftransmission / reception are
limited to a few megabytes
(usually up to 5 megabytes
or exceptionally up to 10Megabytes).
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The Data Communications Channel
A communications
channel is the medium
through which digital
information must pass. Same as line, link, or pipe
Requires special hardware
that transmits the digital
information betweencomputers
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Transmission Channels
Transmission channels are pathways that transfer dataThree Transmission Modes used to exchange data:
1. Simplex
Data flows in only one direction from the
transmitter device to the receiver device2. Half-duplex
Half-duplex mode allows data to move in eitherdirection, but each device must take turns in using
the line3. Full-duplex mode
With full-duplex transmission, data can flow inboth directions simultaneously.
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Transmission Channels
Three TransmissionModes used to
exchange data:
1. Simplex2. Half-duplex
3. Full-duplex mode
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Transmission Media: Twisted-Pair Wire
Twisted-pair wirecontains two insulatedcopper wires twistedaround each other
One twisted-pair lineprovides POTS
Plain old telephoneservice: analog line that
permits voice serviceAnother service is DSL
Digital subscriber line
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Transmission Media: Coaxial Cable
Coax: the cable in cabletelevision
Minimum signal
distortionHas a very wide pipe
Hundreds of times faster
than POTS
100 times faster than
ISDN
Need a cable modem
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Transmission Media: Wireless
Communication
Carries data viamicrowave or radiosignals
Transmission is line-of-sight
Use transceivers/repeaterstations
Satellites Eliminates line-of-sight
limitation
Geosynchronous orbit setat 22,300 miles aboveearth
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Transmission Media: Fiber Optic Cable
Carries data as laser-
generated pulses of light
Foundation transmission
medium for Internet
backbone
Better for data security
Future technology lookslike very big pipe
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Controlling Transmissions over
Communications Channels
Communication protocols
Rules that govern the
way data are
transmitted
TCP/IP (Transmission
Control
Protocol/Internet)Protocol
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Asynchronous and Synchronous
Asynchronous Transmission uses start and stop bits to signify the
beginning and end of a transmission.
The start and stop bits must be of oppositepolarity. This allows the receiver to recognize
when the second packet of information is
being sent.
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Asynchronous Transmission
Synchronous Transmission
Low speed
Modem needed
Transmitted as needed
Start/stop bits used
High speed
Source and destination in
synch
No start/stop bits needed
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