Digital Electronics

1. Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423 603
(An Autonomous Institute, Affiliated to Savitribai Phule Pune University, Pune)
NACC ‘A’ Grade Accredited, ISO 9001:2015 Certified
Department of Computer Engineering
(NBA Accredited)
Prof. S.A.Shivarkar
Assistant Professor
E-mail : shivarkarsandipcomp@sanjivani.org.in
Contact No: 8275032712
Subject- Digital Electronics and Data Communications(CO204)
Unit 6- Data Communication

2. 1. Data communication changing the way we do business and we live.
2. Quick decision!!
3. Why to wait for report?
4. Business rely on
1. Computer Network
5. Revolution is occurring in data communication.
6. Technological advancement make it possible for communication link
to carry more and faster signals.
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3. • Communication can be a
• Local or
• Remote
• Local communication
• Face to face
• Remote communication
• Communication over a long distance.
• The term telecommunication includes
• Telephony
• Telegraphy
• Television
• Tele is a Greek for “far”..
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4. • Data refers to information presented in whatever form is agreed
upon by the parties creating and using the data.
• Data communications are the exchange of data between two devices
via some form of transmission medium such as a wire cable.
• The effectiveness of data communication system depends on..
• Delivery
• Accuracy
• Timeliness
• Jitter
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• Indicate how data flow on transmission link..
• It indicate direction of data flow between two devices.
• There are 3 mode
• Simplex
• Half Duplex
• Full Duplex

7. • Communication is unidirectional..
• Data can flow only in one direction.
• Example
• One way street
• Only one device on link can transmit and
other can only receive.
• Keyboard, Traditional monitor are
example of simplex devices.
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8. • Communication is bidirectional but not
at same time..
• Each station can both transmit as well as
receive but not at same time
• Entire capacity of channel is taken over
by the device which is transmitting at
given time.
• Walkie-talkies is a example of half duplex
devices.
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9. • Communication is bidirectional and
occurs at same time..
• Both station can transmit and receive
simultaneously.
• Capacity of channel is shared between
signals flowing in both direction.
• Telephone network is a example of full
duplex devices.
• When two people are communicating by a
telephone line, both can talk and listen at the
same time.
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10. • Data Element is smallest entity that can represent a piece of
information.
• This is bit.
• In digital data communication a signal element carries the data
element.
• A signal element is shortest unit of digital signal.
• Data elements are being carried.
• Signal elements are carriers.
• Let us define ratio r which is number of data elements carried by each
signal element.
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12. • The data rate defines the number of data elements (bits) sent in 1 s.
• The unit is bits per second (bps).
• The data rate is sometimes called the bit rate;
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13. • The signal rate is the number of signal elements sent in 1 s.
• The unit is the baud.
• The signal rate is sometimes called the pulse rate, the modulation
rate, or the baud rate.
• Goal in data communications is to increase the data rate while
decreasing the signal rate.
• Increasing the data rate increases the speed of transmission.
• Decreasing the signal rate decreases the bandwidth requirement.
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14. • Signals travel through transmission media, which are not perfect. The
imperfection causes signal impairment. This means that the signal at
the beginning of the medium is not the same as the signal at the end
of the medium. What is sent is not what is received. Three causes of
impairment are attenuation, distortion, and noise.
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16. • It means loss of energy.
• When signal travels through the medium it loses some of its energy..
But why??
• in overcoming resistance of the medium.
• That is why wire carrying electric signals gets warm after a while..
• Some of its electrical energy gets converted into heat..
• So to compensate this loss we need amplifier.

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18. Decibel
• To show that a signal has lost or gained strength, engineers use the
unit of the decibel. The decibel (dB) measures the relative strengths
of two signals or one signal at two different points.
• Note that the decibel is negative if a signal is attenuated and positive
if a signal is amplified.
• dB=10log10(P2/P1)

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• Several types of noise
• Thermal noise
• Random motion of electron in wire creates extra signal which is not part of signal sent by
transmitter.
• Induced noise
• Comes from sources such as motors, appliances..
• Crosstalk
• It is effect of one wire on the other wire.
• Impulse noise
• It is a spike that comes from power lines, lightening etc.

22. • SNR = (average signal power) / (average noise power)
• SNR is actually the ratio of what is wanted (signal) to what is not
wanted (noise).
• A high SNR means the signal is less corrupted by noise.
• A low SNR means the signal is more corrupted by noise.
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23. • Baseband transmission means sending digital signal over a channel
without changing the digital signal to analog signal.
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25. • Baseband transmission of a digital signal that preserves the
shape of the digital signal is possible only if we have a low-pass
channel with an infinite or very wide bandwidth.
• An example of a dedicated channel where the entire bandwidth of
the medium is used as one single channel is a LAN. Almost every
wired LAN today uses a dedicated channel for two stations
communicating with each other. In a bus topology LAN with
multipoint connections, only two stations can communicate with each
other at each moment in time (timesharing); the other stations need
to refrain from sending data. In a star topology LAN, the entire
channel between each station and the hub is used for communication
between these two entities.
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26. • If the available channel is a band pass channel, we cannot send
the digital signal directly to the channel;
we need to convert the digital signal to an analog signal before
transmission.
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28. • An example of broadband transmission using modulation is the
sending of computer data through a telephone subscriber line, the
line connecting a resident to the central telephone office. These lines
are designed to carry voice with a limited bandwidth. The channel is
considered a bandpass channel. We convert the digital signal from
the computer to an analog signal, and send the analog signal. We can
install two converters to change the digital signal to analog and vice
versa at the receiving end. The converter, in this case, is called a
modem
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• Located below Physical layer.
• It is anything that carry information from source to destination.
• Example
• Two people talking to one another. Which is transmission medium?
• Air
• For written message
• Truck, Airplane

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• In data communication transmission medium is usually
• Free space
• Metallic cable
• Fiber-optic cable
• The use of electrical signals for long distance communication started with invention of
telegraphy.
• This communication was slow and dependent on metallic medium.
• Extending the range of human voice become possible after invention of telephone in
1869.
• This communication required metallic medium to carry electrical signals.
• Communication was unreliable due to poor quality of wires.
• Lines were often busy.
• Wireless communication started in 1895.

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• Today huge change in communication..
• Better metallic media.
• Optical fibers
• Free space (air, water, vacuum)
• Signals to represent data!
• These signals are transmitted from one device to other in form of electromagnetic energy
which is propagated through transmission media.

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33. Guided media, which are those that provide a conduit from one device to
another, include twisted-pair cable, coaxial cable, and fiber-optic cable.
• Twisted-Pair Cable, Coaxial Cable
• Use metallic conductor that accept and
transport signals in form of electric signals..
• Fiber-Optic Cable
• Accept and transport signals in form of light..
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• Consist of two conductors / wires(normally copper)..
• Each conductor has insulation..
• Twisted together..
• One wire carries signal to receiver!!
• Other wire is used as ground reference!!
• The receiver use difference between the two..
• Why Twisted??
• Noise may affect both wire and create unwanted signals..
• If wires parallel then effect of noise signals is not same in both
wires because they will be at different location relative to the
noise. So receiver will not get correct data..
• By twisting pairs, balance is maintained..
• Suppose in one twist one wire is closer to noise source and other is
farther. In next twist the reverse is true.
• So both wire are equally affected..

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49. Unguided media transport electromagnetic waves without using a
physical conductor. This type of communication is often referred to as
wireless communication.
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53. Wireless transmission waves
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54. Radio waves are used for multicast communications, such as radio and
television, and paging systems.
 They can penetrate through walls.
Highly regulated.
Use omni directional antennas.
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56. Microwaves are used for unicast communication such as cellular
telephones, satellite networks, and wireless LANs.
Higher frequency ranges cannot penetrate walls.
Use directional antennas - point to point line of sight
communications.
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58. Infrared signals can be used for short-range communication in a
closed area using line-of-sight propagation.
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59.  Are subject to a lot more errors than guided media channels.
 Interference is one cause for errors, can be circumvented with high
SNR.
 The higher the SNR the less capacity is available for transmission
due to the broadcast nature of the channel.
 Channel also subject to fading and no coverage holes.
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1. Fourauzan B., "Data Communications and Networking", Tata
McGraw- Hill.