Transcript Data Communication - Dr. Rajiv Srivastava

Unit 1
Lecture 1
Introduction to Data communication
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Syllabus of Unit 1
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Data Communication: Introduction
Components
Data representation
Data flow and basic model
Serial & Parallel transmission
Modes of data transmission
Encoding: Unipolar, Polar, Bipolar
Line & Block codes
Data compression
Lossy & Lossless techniques
Review of analog & digital
Transmission methods.
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A Foreword
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What is Data?
What is Communication?
What is Data Communication?
What is the need of Data Communication?
What is Data?
Data
• Data is defined as the entities that convey
meaning or information. Signals are electric or
electromagnetic representation of data.
• Data can be two types :
1. Analog data
2. Digital data
Analog data :
• Analog data is the type of data that varies
continuously (smoothly) with respect to time.
Voice and Video are the best examples of
analog data. The other examples are
temperature, pressure etc.
Digital data :
• Digital data is the type of data that can take on
discrete(clearly fixed) values. The examples of
digital data are text and integers.
What is data communication?
• The aim of data communication and networking is
to facilitate the exchange of data such as audio,
text, video between any points in the world
• The word Data refers to the information which is
presented in a form that is agreed by the users and
creators of data.
• Data communication is the exchange of data
between two devices via some form of transmission
medium, e.g. Computer to Computer, Computer to
printer, sending email, browsing internet sites such
as Facebook, Instagram, twitter & LinkedIn etc.
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Components of Data communication?
It has the following five components
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Message
Sender
Medium
Receiver
Protocol
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Figure 1.1
Five components of data communication
1 Message
• Message is nothing but information or data
which is to be sent from one point to the other
• A message can be in the form of sound, text,
number, picture, video or combination of them.
2 Sender
• Sender is the device which sends the message.
3 Medium
• It is the physical path over which the message
travels from the sender to the receiver, it can be
wired or wireless.
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4 Receiver
It is the device which receives the message.
5 Protocol
• Protocol is defined as the set of rules which
govern data communication.
• The connection of two devices takes place via
the communication medium, but the actual
communication between them will take place
with the help of protocol.
Fundamentals characteristics of Data communication?
The fundamental characteristics of a Data
communication system are:
1. Delivery
2. Accuracy
3. Timeliness
1. Delivery
The data should be delivered to the correct
destination. It should reach only to the intended
user and not to any other.
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2. Accuracy
• There is a possibility of data alternation or corruption
when it is travelling over a communication medium.
This will affect the accuracy of the received data.
• The data communication system should be such that
it should deliver data accurately.
3. Timelines
• For the audio and video data, the system should
deliver the data in a timely manner i.e. deliver as it is
produced without any time delay.
• Such a data delivery is called as real-time
transmission of data.
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Definition of communication channel
• It is also called as communication medium.
• The communication channel is the medium used for
transmission of electronic signal from one place to
other.
• The communication medium can be conducting
wires, cables, optical fiber or free space
atmosphere.
• Depending on the type of communication medium
we define , two types of communication systems.
1. Wired communication or line communication.
2. Wireless communication or radio communication
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Model of Communication System
Figure
Description of model of data communication
• Suppose that the input device and transmitter are
the components of a personal computer. The user of
this PC wants to send a message to another m PC.
• Then the message m will be in the form of a digital
bit stream and labeled as input data as shown in
figure.
• The sender PC is connected to some transmission
medium such as a local network or a telephone line,
by an input/output device such as a local network
transceiver or a modem.
• The input data are transferred to an transmitter as a
sequence of voltage shifts that represent bits on a
transmission cable or communication bus.
• The transmitter is connected directly to the medium
and converts the incoming digital bit stream into an
analog single suitable for transmission over the
communication cable.
• The analog transmitter signals travels on the
transmission medium and is subjected to a number
of impairments, before reaching the receiver.
• Due to this impairments, the receiver signal may be
different from the transmitted signal.
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• The receiver tries to estimate the original
signal based on the distorted received signal,
and the knowledge of transmission medium.
• A sequence of digital bits is produced at the
output of the receiver.
• These bits are then sent to the destination
which is another PC. The signal m represent
the output information which is represented to
the user and can be seen on the computer
screen or printed using a printer.
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