DATA COMMUNICATION HARDWARE
DATA TRANSFER IN DIGITAL CIRCUITS
Data can travel within the computer distances from a few thousandths of a centimeter,
as within a single IC, to 10s of centimeters along the main circuit board.
Over small distances, digital data can be transferred directly as two-level electrical
signals over simple copper conductors
Frequently, however, data must be sent beyond the local circuitry that constitutes a
computer. In many cases, the distances involved may be enormous.
Unfortunately, as the distance between the source of a message and its destination
increases, accurate transmission becomes increasingly difficult. This results from the electrical
distortion of signals traveling through long conductors, and from noise added to the signal as
it propagates through a transmission medium.
TRANSFER OVER MEDIUM DISTANCES
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COMMUNICATIONS CHANNEL
DATA COMMUNICATIONS
concerns the transmission of digital messages to devices external to the message source.
"External" devices are generally thought of as being independently powered circuitry that
exists beyond the chassis of a computer or other digital message source (NETWORKS).
As a rule, the maximum permissible transmission rate of a message is directly proportional to
signal power, and inversely proportional to channel noise.
It is the aim of any communications system to provide the highest possible
transmission rate at the lowest possible power and with the least possible noise.
is the medium through which digital information must pass to get from one location to
another.
It may be defined by a physical wire that connects communicating devices, or by a radio,
laser, or other radiated energy source that has no obvious physical presence.
Information sent through a communications channel has a source from which the
information originates, and a destination to which the information is delivered.
Although information originates from a single source, there may be more than one
destination, depending upon how many receive stations are linked to the channel and how
much energy the transmitted signal possesses.
In a digital communications channel, the information is represented by individual data bits
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Any communications channel has a direction associated with it:
Data can be transmitted between 2 points in 2 ways:
SERIAL
PARALLEL
In Serial Transmission, data is sent bit by bit.
10010101
sender
10010101
media
receiver
In Parallel Transmission, all bits are sent at once, and each bit is sent on a
separate wire
bit 0
bit 1
bit 2
bit 3
bit 4
bit 5
bit 6
bit 7
sender
bit 0
bit 1
bit 2
bit 3
bit 4
bit 5
bit 6
bit 7
media
The message source is the transmitter, and the destination is the receiver.
A channel whose direction of transmission is unchanging is referred to as a simplex channel.
For example, a radio station is a simplex channel because it always transmits the signal to
its listeners and never allows them to transmit back.
receiver
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A half-duplex channel is a single physical channel in which the direction may be reversed.
Messages may flow in two directions, but never at the same time, in a half-duplex system.
In a telephone call, one party speaks while the other listens. After a pause, the other
party speaks and the first party listens. Speaking simultaneously results in garbled sound
that cannot be understood.
A full-duplex channel allows simultaneous message exchange in both directions. It really
consists of two simplex channels, a forward channel and a reverse channel, linking the
same points.
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TRANSMISSION MEDIA
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COAXIAL CABLE (otherwise known as the cable TV):
A variety of communications channels, some with wires, some without, carry digital
signals between computers
Contains electrical cable (usually copper wire)
Permits high-speed data transmission with minimum signal distortion
Each channel is rated by its CHANNEL CAPACITY, or BANDWIDTH.
Laid along the ocean floor for intercontinental data transmission
The channel capacity is the number of bits a channel can transmit per second (baudrate).
TWISTED-PAIR WIRE
Has a high capacity channel – can carry digital data of up to 10 M bps
POTS (Plain Old Telephone Services): regular analog phone line –
permits voice data transmission
traditional lines permit data transmission rates of 56 K bps
WIRELESS COMMUNICATION:
ISDN (Integrated Services Digital Network): terminates at an ISDN modem.
permits faster data transmission, max. 192 K bps for Basic
Rate Interface or BRI.
(2 M bps for Primary Rate Interface or PRI)
Signal travels in a straight line from source to destination – transceivers are placed on top
of high mountains…
or geosynchronous orbits…
Data can also be transmitted using microwave signals or radio signals.
DSL (Digital Subscriber Line): much faster transmission rate achieved by new technology
about 1.5 – 9 M bps
requires special modem
Internet access via satellite is available at speeds up to 48 M bps.
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WIRELESS COMMUNICATION
THROUGH MICROWAVES
FIBER OPTIC CABLES:
Carries data as laser-generated pulses of light.
(LASER: Light Amplification by Stimulated Emission of Radiation)
Carry data more inexpensively and much more quickly than copper wires –
PLUS provides data security – harder to intercept a beam of light!!!
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COMMON CARRIERS
DATA COMMUNICATIONS HARDWARE
A PRIVATE LINE, or LEASED LINE is a dedicated data communications channel between
any two points in a computer network.
The charge for a private line is based on channel capacity (bps) and distance.
A SWITCHED LINE, or DIAL-UP LINE, is available on a time- and distance charge, like a
phone call.
Data communications, or telecommunications, is the electronic collection and distribution
of information between two points.
Data communications hardware is used to transmit digital information between terminals
and computers, or between computers and other computers.
Host computer
Concentrators
Front-end processor
Hubs
Multiplexer
Network Interface Cards
Router
Modem
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A SIMPLIFIED COMMUNICATION MODEL
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THE MODEM
If your computer is not connected to a LAN, it is still possible to establish a link with
other computers if
-You have access to a telephone line
-Your PC is equipped with a modem
NETWORK INTERFACE CARDS
An add-on board that enables and controls the exchange of data within a LAN.
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MULTIPLEXING AND THE MULTIPLEXER
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ROUTER
The concept of multiplexing is fundamental to computer
networks.
Multiplexing allows several transmitting sources to share a larger
transmission capacity, thereby making more efficient use of
communication lines.
A multiplexer (MUX) is a device that is used to transmit multiple
connections over a single physical link, thereby minimizing the no.
of transmission lines required.
Multiplexers operate at higher bit rates than individual terminal
rates.
Networks use a variety of communications protocols and operating systems
Therefore, incompatible networks cannot directly “talk” to each other
Routers are the primary hardware/software technology used to connect incompatible
networks. They carry out the necessary protocol conversions.
BACKBONE
Interconnections of computer networks are done over a backbone, the system of
routers and the transmission media (cables, wires, links).
The Internet backbone refers to the main 'trunk' connections of the Internet.
It is made up of a large collection of interconnected commercial, government,
academic and other high-capacity data routes and routers that carry data
across the countries, continents and oceans of the world.
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