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Analog Transmission
Depending on the data formats that may be utilized to transfer
digital data over analog media, there are two situations
...
A filter's "bandpass" is the range of
frequencies it can pass
...
The process of turning digital data into a bandpass analog signal
is known as digital-to-analog conversion
...
Digital-to-Analog Conversion
Data from one computer is transformed into analog signals
before being transferred from that computer to another through
an analog carrier
...
The three properties of an analog signal are amplitude,
frequency, and phase
...
•
When binary data represents digit 1, the amplitude is
held; otherwise it is set to 0
...
Frequency Shift Keying
In this conversion technique, the frequency of the
analog carrier signal is modified to reflect binary data
...
One of
them, for example f1, is chosen to represent binary
•
•
digit 1 and the other one is used to represent binary
digit 0
...
Phase Shift Keying
In this conversion scheme, the phase of the original
carrier signal is altered to reflect the binary data
...
Amplitude and frequency of the
original carrier signal is kept intact
...
This is done in two different phases
...
The serial data is converted in to parallel in
both sub-streams and then each stream is converted to
digital signal using NRZ technique
...
Analog-to-Analog Conversion
Analog data is represented by modified analog signals
...
Bandpass requires
analog modulation, hence it must be used
...
•
Amplitude modulation is implemented by means of a
multiplier
...
The frequency and phase of carrier signal remain
unchanged
...
•
The amplitude and phase of the carrier signal are not
altered
...
Phase modulation is practically similar to Frequency
Modulation, but in Phase modulation frequency of the
carrier signal is not increased
...
Transmission Media in Computer Network
The transmission media is nothing but the physical media over
which communication takes place in computer networks
...
Despite the fact that it may seem
outdated in today's high-speed internet environment, magnetic
media is nevertheless used when the size of the data is quite
large
...
The WAN links may not support such high speed, and
even if they do, the cost would be too high for the bank to afford
if it needed to store a lot of backup data
...
Twisted Pair Cable
Twisted together to create a single media, two copper wires with
plastic insulation make up a twisted pair cable
...
In order to lessen noise (electromagnetic
interference) and crosstalk, the cables are twisted
...
This makes it more indifferent to noise and crosstalk
...
In
computer networks, Cat-5, Cat-5e, and Cat-6 cables are mostly
used
...
Coaxial Cable
Coaxial cable has two wires of copper
...
The core is enclosed in
an insulating sheath
...
This
all is covered by plastic cover
...
The wrapped
structure provides it a good shield against noise and cross talk
...
There are three categories of coax cables namely, RG-59 (Cable
TV), RG-58 (Thin Ethernet), and RG-11 (Thick Ethernet)
...
Cables are connected using BNC connector and BNC-T
...
Power Lines
Power Line communication (PLC) is Layer-1 (Physical Layer)
technology which uses power cables to transmit data signals
...
The receiver on the
other end de-modulates and interprets the data
...
PLC works in halfduplex
...
They can be
spread over several kilometers
...
8 – 250 MHz)
...
Fiber Optics
Fiber Optic works on the properties of light
...
This property
has been used in fiber optic
...
From one end of it light is emitted,
it travels through it and at the other end light detector detects
light stream and converts it to electric data
...
It comes in two
modes, one is single mode fiber and second is multimode fiber
...
Fiber Optic also comes in unidirectional and bidirectional
capabilities
...
These can be Subscriber Channel (SC),
Straight Tip (ST), or MT-RJ
...
Wireless
communication involves no physical link established between
two or more devices, communicating wirelessly
...
When an antenna is attached to electrical circuit of a computer
or wireless device, it converts the digital data into wireless
signals and spread all over within its frequency range
...
A little part of electromagnetic spectrum can be used for wireless
transmission
...
Radio waves can have wavelength from 1 mm – 100,000 km
and have frequency ranging from 3 Hz (Extremely Low
Frequency) to 300 GHz (Extremely High Frequency)
...
Radio waves at lower frequencies can travel through walls
whereas higher RF can travel in straight line and bounce
back
...
High frequency radio waves have more
power
...
Radio waves of high frequencies are prone to be absorbed by
rain and other obstacles
...
High frequency radio waves such as HF and VHF
bands are spread upwards
...
Microwave Transmission
Electromagnetic waves above 100 MHz tend to travel in a
straight line and signals over them can be sent by beaming those
waves towards one particular station
...
Microwaves can have wavelength ranging from 1 mm – 1 meter
and frequency ranging from 300 MHz to 300 GHz
...
As shown in picture above, multiple antennas can be aligned
to reach farther
...
Microwave transmission depends highly upon the weather
conditions and the frequency it is using
...
It has wavelength of 700-nm to 1-mm and
frequency ranges from 300-GHz to 430-THz
...
Infrared travels in a
straight line hence it is directional by nature
...
Light Transmission
Highest most electromagnetic spectrum which can be used for
data transmission is light or optical signaling
...
Because of frequency light uses, it tends to travel strictly in
straight line
...
Because laser transmission is unidirectional, at both
ends of communication the laser and the photo-detector needs
to be installed
...
Laser works as Tx (transmitter) and photo-detectors works as Rx
(receiver)
...
Additionally, laser beam is distorted by wind, atmosphere
temperature, or variation in temperature in the path
...
Multiplexing in Computer Network
Multiplexing is a technique by which different analog and digital
streams of transmission can be simultaneously processed over a
shared link
...
Communication is possible over the air (radio frequency), using
a physical media (cable), and light (optical fiber)
...
When multiple senders try to send over a single medium, a
device called Multiplexer divides the physical channel and
allocates one to each
...
Frequency Division Multiplexing
When the carrier is frequency, FDM is used
...
FDM divides the spectrum or carrier bandwidth in
logical channels and allocates one user to each channel
...
All channels are divided in such a way that
they do not overlap with each other
...
Guard band is a frequency which is not used by
either channel
...
In TDM the shared channel is divided
among its user by means of time slot
...
Digital signals are
divided in frames, equivalent to time slot i
...
frame of an optimal
size which can be transmitted in given time slot
...
Both ends, i
...
Multiplexer
and De-multiplexer are timely synchronized and both switch to
next channel simultaneously
...
As
soon as the channel A’s time slot expires, this side switches to
channel B
...
Signals
from different channels travel the path in interleaved manner
...
In fiber optic mode,
multiple optical carrier signals are multiplexed into an optical
fiber by using different wavelengths
...
Further, on each wavelength time division multiplexing can be
incorporated to accommodate more data signals
...
FDM divides the frequency
in smaller channels but CDM allows its users to full bandwidth
and transmit signals all the time using a unique code
...
Each station is assigned with a unique code, called chip
...
The receiver knows in advance the chip code signal it
has to receive