Transcript CISCO, Semester 1, Chapter 1

Electronics and Signals
Chapter 4
Parts of an Atom
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nucleus - the center part of the atom,
formed by neutrons and protons
protons - particles have a positive charge,
and
along with
neutrons,
form the nucleus
neutrons – particles
have no charge
(neutral), and along
with protons, form
the nucleus
electrons - particles have a negative
charge, and orbit the nucleus
Types of Electrical Materials
insulators—high resistance to electrical
current
 plastic, glass, air, wood, paper, rubber
 conductors—conducts the flow of electrons
 Copper, silver, gold
 semiconductors—control the flow of
electrons
 carbon, silicon
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Measuring Electricity
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Voltage (V)—electrical force or pressure that
occurs when electrons and protons are
separated
 The force that is created pushes toward the
opposite charge and away from the like
charge.
 Voltage can also be created by friction
(static electricity), by magnetism (electric
generator), or by light (solar cell).
 unit of measurement is VOLT
Measuring Electricity
Current (I)—the measurement of electron
flow in an electrical circuit
 unit of measurement is AMPERE (amp)
 Resistance (R)—amount of opposition to
current
 unit of measurement is the OHM ()
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ELECTRICITY FUNDAMENTALS
Measuring Electricity
Electricity is brought to your home, school,
and office by power lines. The power lines
carry electricity in the form of alternating
current (AC). Another type of current,
called direct current (DC) can be found in
flashlight batteries, car batteries, and as
power for the microchips on the
motherboard of a computer. It is important
to understand the difference between
these two types of current.
Measuring Electricity
Alternating Current (AC)
 flows in two directions
 Direct Current (DC)
 flows in one direction only
 Impedance--(Z)—unit of measurement ()
 total opposition to current flow (due to AC
and DC voltages)
 resistance--generally used when referring
to DC voltages
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Measuring Electricity
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current flows through closed loops called
circuits
 These circuits must be composed of
conducting materials and have sources of
voltage.
 The three required parts of an electrical
circuit are source or battery, complete
path, load or resistance.
 Voltage causes current to flow while
resistance and impedance oppose it.
Measuring Electricity
Measuring Electricity
For AC and DC electrical systems, the flow
of electrons is always from a negatively
charged source to a positively charged
source.
 For the controlled flow of electrons to occur,
a complete circuit is required.
 Electrical current generally follows the path
of least resistance.
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Measuring Electricity
 Because
metals such as copper provide
little resistance, they frequently are used
as conductors for electrical current.
 Materials such as glass, rubber, and
plastic provide more resistance; they are
not good conductors and are generally
used as insulators.
Measuring Electricity
The purpose of connecting the safety
ground to exposed metal parts of
computing equipment is to prevent such
metal parts from becoming energized
with a hazardous voltage from a wiring
fault inside the device.
Using a Multimeter to Make
Resistance Measurements
A multimeter can use used to measure
 voltage
 resistance
 continuity
Using a Multimeter to Make
Resistance Measurements
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If you intentionally make a path into a lowresistance path for use by two connected
electrical devices, then the path has continuity.
If a path is made unintentionally into a lowresistance path, then it is called a short circuit.
The unit of measurement for both is the OHM
().
Continuity refers to the level of resistance of a
path.
Using a Multimeter to Make
Resistance Measurements
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You can perform measurements on the
following:
 CAT 5 cable
 Terminated CAT 5 cable
 Terminated coaxial cable
 Telephone wire
 CAT 5 jacks
 Switches
 Wall outlets
Using a Multimeter to Make
Voltage Measurements
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Two types of voltage measurements exist: DC
and AC.
 The meter must be set to DC when measuring
DC voltages. This includes the following:
 batteries
 outputs of computer power supplies
 solar cells
 DC generators
Using a Multimeter to Make
Voltage Measurements
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Two types of voltage measurements exist: DC
and AC.
 The meter must be set to AC when you
measure AC voltages.
 If you measure a wall socket, you must
assume that line voltage is present.
 Line voltage is 120 V AC in the US and
220 V AC in most other places around the
world.
Signals and Noise in
Communication Systems
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The term signal refers to a desired electrical
voltage, light pattern, or modulated electromagnetic
wave.
Signals can be created as
 electrical pulses that travel over copper wire
 pulses of light that travel through strands of glass
or plastic
 radio transmissions that travel over the airwaves
 as laser or satellite transmissions
 as infrared pulse
Signals and Noise in
Communication Systems
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Two main types of signaling
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analog
 change
gradually and continuously (will have a
continuously varying voltage-versus-time graph)
 typical of things in nature
 used widely in telecommunications for more than 100
years
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digital
 change
one state to another almost instantaneously,
without stopping at an in-between state
 discrete or jumpy
 typical of technology instead of nature
Measuring Analog Signals
Analog signals are measured in cycles, with
one cycle representing the change from high
to low and back again.
 Three characteristics are measured:
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amplitude
 frequency
 phase
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Digital and Analog Signaling
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Digital signaling is the most appropriate format
for transmitting computer data, and most
networks use digital signaling methods for that
reason.
Because it is a simpler technology, digital
signaling has some advantages over analog:
generally less expensive to make digital
equipment
 generally less vulnerable to errors caused by
interference because the discrete state of on and
off is not as easily affected by a small distortion
as is a continuous waveform
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Digital and Analog Signaling
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Analog signals also have advantages:
Signals can be easily mutilplexed; that is signals
can be combined to increase bandwidth.
 Signals are less vulnerable to the problem of
attenuation (signal loss due to surroundings)
because of distance so they can travel farther
without becoming too weak for reliable
transmission. However, when an analog signal is
amplified, the noise is amplified with the signal.
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Digital connectivity solutions generally offer
better security, faster performance, and higher
reliability.
Simplex, Half-Duplex, and FullDuplex Transmission
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Simplex Transmission
Unidirectional—signal travels in only one
direction
 Television is an example.
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Half-Duplex Transmission
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Signal can travel in both directions but not at the
same time.
Full-Duplex Transmission
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Signal can travel in both directions at the same
time.
Baseband and Broadband
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The entire capacity of an Ethernet cable is used for
transmitting the data in one channel.
This makes Ethernet a BASEBAND technology.
A channel is an allocated portion of the media’s
available bandwidth.
The signal has the benefit of having the entire
bandwidth to itself.
BASEBAND is usually associated with digital
signaling (although it can be used with analog).
Most computer communications are baseband.
BASEBAND signal is bidirectional; the signal can
flow both ways so you can transmit and receive on
the same cable.
Baseband and Broadband
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BROADBAND technologies allow for dividing
the capacity of a link into two or more channels,
each of which can carry a different signal.
All channels can send simultaneously.
ISDN is an example of BROADBAND
technology because multiple signals can be
carried over separate channels on a single wire.
DSL is another example of a BROADBAND
technology because data and voice can travel
simultaneously over the same line.
Signaling and Communications
Problems
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Propagation
 travel
time; speed depends upon medium
 As data transmission rates increase, you must
sometimes take into account the amount of
time it takes the signal to travel.
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Attenuation
 loss
of signal over distance due to
surroundings
 can affect a network because it limits the
length of network cabling over which you can
send a message
Signaling and Communications
Problems
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Reflection
 caused
by discontinuities in the medium
 occurs in electrical signals; can be a result of
kinks in cable or poorly terminated cables
 networks should have a specific impedance to
match the electrical components in the NICs
 The result of impedance mismatch is reflected
energy.
Signaling and Communications
Problems
Noise
 unwanted
additions to optical/electromagnetic
signals
 Crosstalk—electrical noise from other wires
in a cable
 EMI (electromagnetic interference) can be
caused by electric motors.
 Cancellation of signals can be avoided
through the twisting of wire pairs to provide
self-shielding within the network media.
Signaling and Communications
Problems
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Timing problem
 Dispersion—signal
broadens in time
 can be fixed by proper cable design,
limiting cable lengths, and finding the
proper impedance
 Jitter—source and destination not
synchronized
 can be fixed through hardware and software
including protocols
 Latency—delay of network signal
Signaling and Communications
Problems
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Collisions
 occurs
when two bits from different
communicating computers are on a shared
medium at the same time
 excessive collisions can slow the network
Encoding Networking Signals
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Encoding means to convert the binary data
into a form that can travel on a physical
communications link such as an electrical
pulse on a wire, a light pulse on an optical
fiber, or an electromagnetic wave in space.
 two methods for encoding
 TTL—high signals or low signals
 Manchester—more complex and more
immune to noise and better at
remaining synchronized (includes
NRZs and 4B/5B
Encoding Networking Signals
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Modulation means using the binary data
to manipulate an analog wave.
 taking a wave and changing it so that it
carries information
 AM
 FM
 PM