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CHAPTER 3
DATA COMMUNICATION
DATA
The collection of raw facts and figures is called data. The word data is derived from
the Latin language and it is plural of Datum. The text, numbers, symbols, images,
voice, and video which are processed by computers and digital devices are called data.
Data can be considered as unprocessed information.
COMMUNICATION
Communication is the process of sharing a message. A conversation between two
people is an example of communication.
DATA COMMUNICATION
Data Communication is the process of transferring data electrically from one place to
another. It is the process of exchange of data and information between two parties
such as humans and electronic or computing devices.
COMPONENTS OF COMMUNICATION SYSTEM
A Communication system has the following five components.
 Message
It is the information or data to be communicated. Common forms of information
include text, numbers, pictures, audio, and video.
 Sender
It is the device that generates and sends a message. It can be a computer,
telephone handset, etc.
 Receiver
Any particular digital electronic device can receive data in form of a message.
The location of receiving computer is generally different from the sending
computer. Like the sender, it can also be a computer, telephone handset, etc.
 Medium
It is the channel or path through which the message is carried from the sender to
the receiver. Some examples include twisted-pair cable, coaxial cable, radio
waves, etc.
 Protocol
Protocols are the rules and procedures by which computers exchange data on the
network. The sender and receiver follow the same protocols to communicate with
each other. In other words, a protocol is an agreement between two parties or
vendors, using communication devices.

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STANDARDS
Standards are the set of rules for data communication that are needed for the exchange
of information among devices. It is important to follow Standards that are created by
various Standard Organizations like IEEE, ISO, ANSI, etc.
OR
Standards are rules that define the appearance, functionality, or protocols of some
equipment. They are essential for network communication. Network standards define
rules of communications among computing devices. This ensures that companies (i.e.
Cisco and IBM) that manufacture computing and networking products follow these
uniform standards. By following standards, all hardware becomes compatible with the
network, allowing efficient networking to take place.
CHARACTERISTICS OF DATA TRANSMISSIONS
Data communication has several characteristics but some are discussed below:
1. Signal type
2. Transmission mode
3. Direction of transmission
1. SIGNAL
A signal is an electromagnetic or electrical current that carries data from one system
or network to another.
TYPES OF SIGNAL
There are two types of signals discussed below:
 Analog Signals
Analog signals are continuously varying signals or waves that change with time
and are used to represent data. An analog signal can be used to measure
changes in some physical quantities such as light, sound, pressure, or
temperature.
Example
An example of an analog signal is the human voice. When we speak, we use air
to transmit an analog signal. An electrical signal from an audio tape can also be
in analog form.
 Characteristics Of Analog Signals
 Amplitude
The amplitude of a signal refers to the height of the signal. It is equal to
the vertical distance from a given point on the waveform to the
horizontal axis. It is measured in volts.
 Frequency
Frequency refers to the number of periods in one second or the number
of cycles per second. Frequency is measured in Hertz (Hz).

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 Digital Signals
A digital signal is an electrical signal that is converted into a pattern of bits to
represent a sequence of discrete values, at any given time. It can only be one of
the finite numbers represented as 0 or 1.
Examples
Examples of digital signals are Computers, Digital Phones, Digital pens, etc.
DIFFERENCE BETWEEN ANALOG AND DIGITAL SIGNAL
PARAMETERS ANALOG SIGNAL DIGITAL SIGNAL
Definition
An analog signal is a
continuous wave that
changes over time.
A digital signal is a discrete
wave that carries information
in binary form.
Range
The Analog signal has no
fixed range.
Digital signal has an infinite
number i.e. 0 and 1.
Flexibility
Analog hardware is not
flexible.
Digital hardware is flexible in
implementation.
Representation
An analog signal is
represented by a sine wave.
A digital signal is represented
by square waves
Examples
The human voice is an
example of an analog signal.
Signals used by the computer
are the digital signal.
2. TRANSMISSION MODES (Asynchronous And Synchronous)
Transmission is the action of transferring or moving something from one position or
person to another. It is a mechanism for transferring data between two devices
connected using a network. It is also called communication Mode. In computer
networking there are two types of transmission:
 Synchronous transmissions
 Asynchronous transmissions
 ASYNCHRONOUS TRANSMISSION
In Asynchronous Transmission, data is sent in form of a byte or character. This
transmission is the half-duplex type transmission. In this transmission start bits and
stop bits are added with data. It does not require synchronization.

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EXAMPLE
 Email
 Forums
 Letters etc.
 SYNCHRONOUS TRANSMISSION
In Synchronous Transmission, data is sent in form of blocks or frames. This
transmission is the full-duplex type. Between sender and receiver, synchronization is
compulsory. In Synchronous transmission, There is no gap present between data. It is
efficient and more reliable than asynchronous transmission to transfer a large amount
of data.
EXAMPLE
 Chat Rooms
 Telephonic Conversations
 Video Conferencing etc.
DIFERENCES BETWEEN SYNCHRONOUS AND ASYNCHRONOUS
TRANSMISSION
SYNCHRONOUS
TRANSMISSION
ASYNCHRONOUS
TRANSMISSION
In Synchronous transmission, data is
sent in form of blocks or frames.
In Asynchronous transmission, data is
sent in form of bytes or characters.
Synchronous transmission is fast. Asynchronous transmission is slow.
Synchronous transmission is costly Synchronous transmission is costly
In Synchronous transmission, the time
interval of transmission is constant.
In Asynchronous transmission, the time
interval of transmission is not constant,
it is random.
In this transmission, users have to
wait till the transmission is complete
before getting a response back from
the server.
Here, users do not have to wait for the
completion of transmission to get a
response from the server.
In Synchronous transmission, there is
no gap present between data.
In Asynchronous transmission, there is
a gap present between data.
Efficient use of transmission lines is
done in synchronous transmission.
While in Asynchronous transmission,
the transmission line remains empty
during a gap in character transmission.
The start and stop bits are not used in
transmitting data.
The start and stop bits are used in
transmitting data that imposes extra
overhead.
Synchronous transmission needs Asynchronous transmission does not

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precisely synchronized clocks for the
information of new bytes.
need synchronized clocks as a parity
bit is used in this transmission for
information of new bytes.
3. DIRECTION OF TRANSMISSION
Another characteristic of data transmission is direction Data may flow in more than
one direction. There are three types of transmission modes. They are:
 Simplex Mode
 Half-duplex Mode
 Full-duplex Mode
 Simplex Mode
Simplex is the data transmission mode in which the data can flow only in one
direction, i.e., the communication is unidirectional. In this mode, a sender can
only send data but can not receive it, and vice versa.
OR
In simplex mode, Sender can send the data but the sender can’t receive the data.
It is unidirectional communication.
Example
Radio and TV transmission, keyboard, mouse, etc.
Advantages
 It utilizes the full capacity of the communication channel during data
transmission.
 It has the least or no data traffic issues as data flows only in one direction.
Disadvantages
 It is unidirectional having no inter-communication between devices.
 There is no mechanism for information to be transmitted back to the
sender(No mechanism for acknowledgment).
 Half-Duplex Mode

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In half-duplex mode, each station can both transmit and receive, but not at
the same time. When one device is sending, the other can only receive it, and
vice versa. The half-duplex mode is used in cases where there is no need for
communication in both directions at the same time.
OR
In half-duplex mode, Sender can send the data and also can receive the data
one at a time. It is two-way directional communication but one at a time.
Example
Walkie-talkie in which message is sent one at a time and messages are sent in
both directions.
Advantages
 Speed is a big advantage of a full-duplex.
 The device can receive and send data, but not at the same time.
 Troubleshooting is very easy
 Data is transmitted on both sides
Disadvantages
 In a half Duplex, more data cannot be transmitted on both sides at the same
time.
 When one device sends data, the device on the other hand only receives data.
 It is slow in data transmission.
 Delay in data transmission.
 Full-Duplex Mode
In full-duplex mode, both stations can transmit and receive simultaneously.
In full-duplex mode, signals going in one direction share the capacity of the

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link with signals going in another direction, this sharing can occur in two
ways:
 Either the link must contain two physically separate transmission paths,
one for sending and the other for receiving.
 Or the capacity is divided between signals traveling in both directions.
OR
In full-duplex mode, Sender can send the data and also can receive the data
simultaneously. It is two-way directional communication simultaneously.
Example:
Telephone Network in which there is communication between two persons by a
telephone line, through which both can talk and listen at the same time.
Advantages
 Performance of full-duplex mode is much better than half and simplex mode.
 The speed of full-duplex mode is high than simplex and half-duplex mode.
 Data can be sent and received on both sides, which increases the
performance of the network.
 No delay in communication, because both devices send and receive data at
the same time.
Disadvantages
 No proper bandwidth utilization as the same line is used for sending and
receiving data at the same time.
 It is more complex than a simplex and half-duplex mode.
DIFFERENCES BETWEEN THE TYPES OF TRANSMISSION MODES
PARAMETERS
SIMPLEX
MODE
HALF DUPLEX
MODE
FULL-DUPLEX
MODE
Direction Of
Communication
Simplex mode is a
uni-directional
communication.
Half Duplex mode
is a two-way
directional
communication but
one at a time.
Full-Duplex mode
is a two-way
directional
communication
simultaneously.
Sender And
Receiver
In simplex mode,
Sender can send
the data but the
sender can’t
In Half-duplex
mode, Sender can
send the data and
also can receive
In Full-duplex
mode, Sender can
send the data and
also can receive

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receive the data. the data one at a
time.
the data
simultaneously.
Channel Usage
Usage of one
channel for the
transmission of
data.
Usage of one
channel for the
transmission of
data.
Usage of two
channels for the
transmission of
data.
Performance
The simplex mode
provides less
performance than a
half duplex and a
full duplex.
The Half-duplex
mode provides less
performance than
the full duplex.
Full-duplex
provides better
performance than
simplex and half-
duplex modes.
Bandwidth
Utilization
Simplex utilizes
the maximum of a
single bandwidth.
The Half-duplex
involves lesser
utilization of single
bandwidth at the
time of
transmission.
The Full-duplex
doubles the
utilization of
transmission
bandwidth.
Examples
Keyboard and
monitor Walkie-
talkie
The walkie-talkie
is an example of
half-duplex mode.
The telephone
network is an
example of a full-
duplex mode.