Introduction to Data Communication concepts

Data Communication
V Sem B.E. Computer Sc. & Engg
Department of Computer Science & Engineering
Priyadarshini Bhagwati College of Engineering,
Nagpur
(Odd 2021)
K N Hande
Head of the Department

Text Books
1. Data Communications and Networking by
Behrouz A. Forouzan, 4thEdition, Tata
McGraw Hill
2. Packet guide to core network protocol by
Bruce Hartpence, Oreilly
Bruce Hartpence, Oreilly
3. Electronic Communication Systems by
Kennedy
4. Understanding Data Communications
and Networks by William A. Shay, 2nd
Edition, Vikas Publishing House.
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UNIT I - CONTENTS
1. Analog And Digital Signals
2. Periodic And Non Periodic Signals
3. Composite Signals
4. Frequency Spectrum And Bandwidth
4. Frequency Spectrum And Bandwidth
5. Transmission Modes
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Data and Signals
• One of the major functions of the physical
layer is to move data in the form of
electromagnetic signals across a transmission
medium.
medium.
• Transmission media work by conducting
energy along a physical path
• To be transmitted, data must be
transformed to electromagnetic signals.
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Analog and Digital
• The term communications refers to the
sending, receiving and processing of
information by electronic means.
• Both data and the signals that represent
• Both data and the signals that represent
them can be either analog or digital in form.
• The term analog data refers to information
that is continuous; digital data refers to
information that has discrete states.
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Communication System
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Analog and Digital Signals
• An analog signal has infinitely many levels of
intensity over a period of time.
• A digital signal, on the other hand, can have
only a limited number of defined values.
only a limited number of defined values.
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Periodic and Non-periodic Signals
• A periodic signal completes a pattern within a
measurable time frame, called a period
• A nonperiodic signal changes without
exhibiting a pattern or cycle that repeats over
exhibiting a pattern or cycle that repeats over
time.
• Both analog and digital signals can be periodic
or nonperiodic.
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Periodic Analog Signals
• Periodic analog signals can be classified as simple or
composite. A simple periodic analog signal, a sine
wave, cannot be decomposed into simpler signals. A
composite periodic analog signal is composed of
multiple sine waves.
multiple sine waves.
• The sine wave is the most fundamental form of a
periodic analog signal.
• Each cycle consists of a single arc above the time axis
followed by a single arc below it.
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Sine Wave
• A sine wave can be represented by three parameters:
the peak amplitude, the frequency, and the
phase.
• The peak amplitude of a signal is the absolute value of
its highest intensity, proportional to the energy it
its highest intensity, proportional to the energy it
carries. For electric signals, peak amplitude is
normally measured in volts.
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Period and Frequency
• Period refers to the amount of time, in seconds, a signal needs
to complete 1 cycle.
• Frequency refers to the number of periods in 1 second.
• Period is the inverse of frequency, and frequency is the inverse
of period
f= 1/ T T=1/f
• Period is formally expressed in seconds. Frequency is
formally expressed in Hertz (Hz), which is cycle per
second.
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More about Frequency
• Frequency is the rate of change with respect to
time. Change in a short span of time means high
frequency. Change over a long span of time means
low frequency.
• If the value of a signal changes over a very short
• If the value of a signal changes over a very short
span of time, its frequency is high. If it changes
over a long span of time, its frequency is low.
• If a signal does not change at all, its frequency
is zero. If a signal changes instantaneously, its
frequency is infinite.
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Phase
• The term phase describes the position of the
waveform relative to time O. If we think of the wave
as something that can be shifted backward or
forward along the time axis, phase describes the
amount of that shift.
amount of that shift.
• A phase shift of 360° corresponds to a shift of a
complete period; a phase shift of 180° corresponds to
a shift of one-half of a period; and a phase shift of 90°
corresponds to a shift of one-quarter of a period
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Wavelength
• Wavelength binds the period or the frequency of a
simple sine wave to the propagation speed of the
medium
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Time and Frequency Domains
• We have been showing a sine wave by using what is
called a time-domain plot.
• The time-domain plot shows changes in signal
amplitude with respect to time (it is an amplitude-
versus-time plot)
versus-time plot)
• To show the relationship between amplitude and
frequency, we can use what is called a frequency-
domain plot. A frequency-domain plot is concerned
with only the peak value and the frequency.
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Time and Frequency Domains Plots
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Time and Frequency Domains
• A complete sine wave is represented by one spike.
The position of the spike shows the frequency; its
height shows the peak amplitude.
• A complete sine wave in the time domain can be
represented by one single spike in the frequency
domain.
• The frequency domain is more compact and useful
when we are dealing with more than one sine wave.
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Composite Signals
• We need to send a composite signal to communicate
data.
• A composite signal is made of many simple sine
waves.
• A single frequency sine wave is not useful in data
• A single frequency sine wave is not useful in data
communications; we need to send a composite signal,
a signal made of many simple sine waves.
• In the early 1900s, the French mathematician Jean-
Baptiste Fourier showed that any composite signal
is actually a combination of simple sine waves with
different frequencies, amplitudes, and phases.
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Composite Signals
• A composite signal can be periodic or nonperiodic.
• A periodic composite signal can be decomposed into
a series of simple sine waves with discrete
frequencies, frequencies that have integer values
• A nonperiodic composite signal can be decomposed
• A nonperiodic composite signal can be decomposed
into a combination of an infinite number of simple
sine waves with continuous frequencies, frequencies
that have real values.
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Composite Signals- Example
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Composite Signals
• The frequency of the sine wave with frequency f is the
same as the frequency of the composite signal; it is
called the fundamental frequency, or first
harmonic.
• The sine wave with frequency 3f has a frequency of 3
• The sine wave with frequency 3f has a frequency of 3
times the fundamental frequency; it is called the third
harmonic.
• Note that the frequency decomposition of the signal is
discrete; it has frequencies f, 3f, and 9f Because f is
an integral number, 3f and 9f are also integral
numbers.
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Non-Periodic Composite Signals
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Bandwidth
• The range of frequencies contained in a composite
signal is its bandwidth.
• The bandwidth of a composite signal is the difference
between the highest and the lowest frequencies
contained in that signal.
• The bandwidth is normally a difference between two
numbers.
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Digital Signals
• Information can also be represented by a digital
signal.
• A digital signal can have more than two levels.
• In general, if a signal has L levels, each level needs
log L bits.
log2L bits.
• Bit Rate: Most digital signals are nonperiodic, and
thus period and frequency are not appropriate
characteristics.
• The bit rate is the number of bits sent in 1 sec,
expressed in bits per second (bps).
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Bit Length
• The bit length is the distance one bit occupies on the
transmission medium.
• Bit length =propagation speed * bit duration
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Performance
• Bandwidth: bandwidth in hertz and bandwidth in
bits per second.
• The term bandwidth can also refer to the number of
bits per second that a channel, a link, or even a
network can transmit.
network can transmit.
• Basically, an increase in bandwidth in hertz means an
increase in bandwidth in bits per second.
• The throughput is a measure of how fast we can
actually send data through a network.
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Bandwidth Delay Product
• Bandwidth delay product is calculated as the product
of the link capacity of the channel and the round –
trip delay time of transmission.
• The bandwidth-delay product defines the number of
bits that can fill the link.
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Transmission Modes
• The transmission of binary data across a link can be
accomplished in either parallel or serial mode.
• In parallel mode, multiple bits are sent with each
clock tick. In serial mode, 1 bit is sent with each clock
tick.
tick.
• While there is only one way to send parallel data,
there are three subclasses of serial transmission:
Asynchronous, synchronous, and isochronous
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Parallel Transmission
• Binary data, consisting of 1s and 0s, may be organized
into groups of n bits each.
• By grouping, we can send data n bits at a time
instead of 1. This is called parallel transmission.
• The mechanism for parallel transmission is a
• The mechanism for parallel transmission is a
conceptually simple one: Use n wires to send n bits at
one time.
• The advantage of parallel transmission is speed.
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Parallel Transmission
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Serial Transmission
• In serial transmission one bit follows another, so we
need only one communication channel rather than n
to transmit data between two communicating devices
• The advantage of serial over parallel transmission is
that with only one communication channel, serial
that with only one communication channel, serial
transmission reduces the cost of transmission over
parallel by roughly a factor of n.
• Serial transmission occurs in one of three ways:
asynchronous, synchronous, and isochronous.
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Asynchronous Transmission
• Asynchronous transmission is so named because the
timing of a signal is unimportant.
• Instead, information is received and translated by
agreed upon patterns.
• Without synchronization, the receiver cannot use
• Without synchronization, the receiver cannot use
timing to predict when the next group will arrive.
• In asynchronous transmission, we send 1 start bit
(0) at the beginning and 1 or more stop bits (1s) at
the end of each byte. There may be a gap between
each byte.
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• Asynchronous here means "asynchronous at the
byte level”, but the bits are still synchronized; their
durations are the same.
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Synchronous Transmission
• In synchronous transmission, the bit stream is
combined into longer "frames," which may contain
multiple bytes.
• In synchronous transmission, we send bits one after
another without start or stop bits or gaps. It is the
another without start or stop bits or gaps. It is the
responsibility of the receiver to group the bits.
• The advantage of synchronous transmission is speed.
• Although there is no gap between characters in
synchronous serial transmission, there may be
uneven gaps between frames.
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Synchronous Transmission
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Isochronous Transmission
• In real-time audio and video, in which uneven delays
between frames are not acceptable, synchronous
transmission fails.
• The isochronous transmission guarantees that the
data arrive at a fixed rate.
data arrive at a fixed rate.
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Data Flow
• The transmission mode defines the direction of
signal flow between two connected devices.
• There are three modes of transmission, namely:
simplex, half duplex, and full duplex.
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Simplex Mode
• The communication between sender and receiver
occurs in only one direction. The sender can only
send the data, and the receiver can only receive the
data. The receiver cannot reply to the sender.
• Simplex transmission can be thought of as a one-way
• Simplex transmission can be thought of as a one-way
road in which the traffic travels only in one direction
• To take a keyboard / monitor relationship as an
example, the keyboard can only send the input to the
monitor, and the monitor can only receive the input
and display it on the screen.
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Half-Duplex Mode
• The communication between sender and receiver
occurs in both directions in half duplex transmission,
but only one at a time.
• Half duplex is still considered a one-way road, in
which a vehicle traveling in the opposite direction of
which a vehicle traveling in the opposite direction of
the traffic has to wait till the road is empty before it
can pass through.
• For example, in walkie-talkies, the speakers at both
ends can speak, but they have to speak one by one.
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Full-Duplex Mode
• In full duplex transmission mode, the communication
between sender and receiver can occur
simultaneously.
• The sender and receiver can both transmit and
receive at the same time.
receive at the same time.
• For example, in a telephone conversation, two
people communicate, and both are free to speak and
listen at the same time.
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Signal To Noise Ratio
• Noise is another cause of impairment.
• Several types of noise, such as thermal noise,
induced noise, crosstalk, and impulse noise, may
corrupt the signal.
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• We need to know the ratio of the signal power to the
noise power.
• We need to consider the average signal power and the
average noise power because these may change with
time.
• SNR is actually the ratio of what is wanted (signal) to
what is not wanted (noise).
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• A high SNR means the signal is less corrupted by
noise; a low SNR means the signal is more corrupted
by noise.
• Because SNR is the ratio of two powers, it is often
described in decibel units.
• The deciBel, dB utilizes a logarithmic scale based to
compare two quantities. It is a convenient way of
comparing two physical quantities like electrical
power, intensity, or even current, or voltage.
• The deciBel, dB or deci-Bel is actually a tenth of a Bel
- a unit that is seldom used.
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Solved
examples based
examples based
on Topics
Covered
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Example: Given the frequencies listed below, calculate the
corresponding periods.
a. 24Hz
b. 8 MHz
c. 140 KHz
a) T = 1/f = 1/(24 Hz)= 0.0417 s =41.7 x 10-3 s = 41.7 msec
b) T = 1/f = 1/(8 MHz)= 0.000000125 s =0.125 x 10-6 s = 0.125 µsec
b) T = 1/f = 1/(140 KHz)= 0.00000714 s =7.14 x 10-6 s = 7.14 µsec
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Example: Given the following periods, calculate the
corresponding frequencies.
a. 5 s
b. 12 µsec
c. 220 ns
a) f = 1/T = 1/(5s)= 0.2 Hz
b) f = 1/T = 1/(12µs )= 83333 Hz=83.333 x 103 Hz= 83.33 KHz
c) f = 1/T = 1/(220 ns)= 4550000 Hz= 4.55 x 106 Hz = 4.55 MHz
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Example: What is the bit rate for each of the following
signals?
a. A signal in which 1 bit lasts 0.001 s
b. A signal in which 1 bit lasts 2 ms
c. A signal in which 10 bits last 20 µs
a) Bit rate= 1 / Bit duration = 1/ (0.001 s)= 1000 bps= 1 Kbps
b) Bit rate= 1 / Bit duration = 1/ (2ms)= 500 bps
c) Bit rate= 1 / Bit duration = 1/ (20 µs)= 500 Kbps
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Example: A device is sending out data at the rate of 1000 bps.
a. How long does it take to send out 10 bits?
b. How long does it take to send out a single character (8 bits)?
c. How long does it take to send a file of 100,000 characters?
a) (10/1000)s = 0.01 s
b) (8/1000)s = 0.008 s= 8 ms
b) (8/1000)s = 0.008 s= 8 ms
c) ((100,000x8)/1000s) = 800 s
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Example: A TV channel has a bandwidth of 6 MHz. If we send a digital
signal using one channel, what are the data rates if we use one
harmonic, three harmonics, and five harmonics?
a) Using the first harmonics, the data rate =2x6 MHz = 12 Mbps
b) Using the three harmonics, the data rate =(2x6 MHz)/3 = 4 Mbps
c) Using the five harmonics, the data rate =(2x6 MHz)/5 = 2.4 Mbps
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Example: If the bandwidth of the channel is 5 Kbps, how
long does it take to send a frame of 100,000 bits out of this
device?
Answer : 100000 / 5 Kbps = 20 s
Example :A file contains 2 million bytes. How long does it
take to download this file using a 56-Kbps channel? 1-Mbps
channel?
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channel?
Answer : The file contains 2,000,000x8 = 16,000,000 bits
With a 56 Kbps channel it takes 16,000,000/56,000= 286 s
With a 1 Mbps channel it takes 16,000,000/1,000,000=16 s

Example: What is the transmission time of a packet sent by
a station if the length of the packet is 8 million bytes and
the bandwidth of the channel is 200 Kbps?
Answer : Transmission Time = (Packet Length) / (bandwidth)
= (8,000,000) / (200,000) = 40 s
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Example: What is the length of a bit in a channel with a propagation
speed of 2 x 108 m/s if the channel bandwidth is
a. 1 Mbps?
h. 10 Mbps?
c. 100 Mbps?
Answer : Bit length = (Propagation speed) x (Bit duration)
Bit duration is a inverse of a bandwidth
a) Bit length = (2 x 108 ) x (1/ 1 Mbps) = 200 meter. This means a bit
occupies 200 meter in a channel
b) Bit length = (2 x 108 ) x (1/ 10 Mbps) = 20 meter. This means a bit
c) Bit length = (2 x 108 ) x (1/ 100 Mbps) = 2 meter. This means a bit
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Example: How many bits can fit on a link with a 2 ms delay if
the bandwidth of the link is
a. 1 Mbps?
h. 10 Mbps?
c. 100 Mbps?
Answer :
a) No of bits = Bandwidth x delay = 1 Mbps x 2 ms = 2000 Bits
a) No of bits = Bandwidth x delay = 1 Mbps x 2 ms = 2000 Bits
b) No of bits = Bandwidth x delay = 10 Mbps x 2 ms = 20,000 Bits
c) No of bits = Bandwidth x delay = 100 Mbps x 2 ms = 200,000 Bits
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Example: What is the total delay (latency) for a frame of size 5 million bits that
is being sent on a link with 10 routers each having a queuing time of 2 µs and a
processing time of 1 µs . The length of the link is 2000 Km. The speed of light
inside the link is 2 x 108 m/s. The link has a bandwidth of 5 Mbps. Which
component of the total delay is dominant? Which one is negligible?
Answer : We have latency = Processing Time + Queuing Time + Transmission Time +
Propagation Time
Processing Time = 10 x 1 µs = 10 µs = 0.000010 s
Queuing Time = 10 x 2 µs = 20 µs = 0.000020 s
Transmission Time = 5,000,000 / 5 Mbps = 1 s
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Transmission Time = 5,000,000 / 5 Mbps = 1 s
Propagation Time = (2000 Km) / (2 x 108 m/s) = 0.01 s
Latency = 0.000010 + 0.000020 + 1 + 0.01 = 1.01000030 s
The transmission time is dominant here because packet size is
huge.

Summary of Unit I
• Data must be transformed to electromagnetic
signals to be transmitted.
• Data can be analog or digital. Analog data are
continuous and take continuous values. Digital data
have discrete states and take discrete values.
have discrete states and take discrete values.
• Signals can be analog or digital. Analog signals can
have an infinite number of values in a range; digital
,signals can have only a limited number of values.
• In data communications, we commonly use periodic
analog signals and nonperiodic digital signals.
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Summary of Unit I
• Frequency and period are the inverse of each other.
• Frequency is the rate of change with respect to time.
• Phase describes the position of the waveform
relative to time 0.
domain.
• A single-frequency sine wave is not useful in data
communications; we need to send a composite
signal, a signal made of many simple sine waves.
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Summary of Unit I
• According to Fourier analysis, any composite signal is
a combination of simple sine waves with different
frequencies, amplitudes, and phases.
• The bandwidth of a composite signal is the difference
• Noise is the external energy that corrupts a signal.
bits that can fill the link.
K N Hande

Introduction to Data Communication concepts

Introduction to Data Communication concepts

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