CHAPTER 3 DATA COMMUNICATION TERMINOLOGIES DATA COMMUNICATION DATA COMMUNICATION COMPONENTS OF THE COMMUNICATION SYSTEM Message Sender Receiver Medium Protocol STANDARDS CHARACTERISTICS OF DATA TRANSMISSIONS SIGNAL TYPES OF SIGNAL Analog Signals With Example Characteristics Of Analog Signals Amplitude Frequency Digital Signals With Examples DIFFERENCE BETWEEN ANALOG AND DIGITAL SIGNAL TRANSMISSION MODES (Asynchronous And Synchronous) ASYNCHRONOUS TRANSMISSION WITH EXAMPLE SYNCHRONOUS TRANSMISSION WITH EXAMPLE DIFFERENCES BETWEEN SYNCHRONOUS AND ASYNCHRONOUS TRANSMISSION DIRECTION OF TRANSMISSION Simplex Mode With Example, Advantages And Disadvantages Half-Duplex Mode With Example, Advantages And Disadvantages Full-Duplex Mode With Example, Advantages And Disadvantages DIFFERENCES BETWEEN THE TYPES OF TRANSMISSION MODES DATA COMMUNICATION SPEED AND MEDIA DATA COMMUNICATION SPEED BANDWIDTH Narrowband Voice band Broadband DATA COMMUNICATION MEDIA Twisted-Pair Cable With Reason for twisting Coaxial Cable Fiber Optics Cable With Advantages And Disadvantages Microwaves Terrestrial Satellite COMMUNICATION HARDWARE MODEM OSI MODEL Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

1. 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 the 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 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 THE 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.

2. 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 communication 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).

3.  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 to the data. It does not require synchronization.

4. 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.
DIFFERENCES 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
Here, users do not have to wait for the
completion of transmission to get a
response from the server.

5. 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
precisely synchronized clocks for the
information of new bytes.
Asynchronous transmission does not
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.

6.  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
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.

7.  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
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 Simplex mode is a Half Duplex mode Full-Duplex mode

8. Communication uni-directional
communication.
is a two-way
directional
communication but
one at a time.
is a two-way
directional
communication
simultaneously.
Sender And
Receiver
In simplex mode,
Sender can send
the data but the
sender can’t
receive the data.
In Half-duplex
mode, Sender can
send the data and
also can receive
the data one at a
time.
In Full-duplex
mode, Sender can
send the data and
also can receive
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 a
half-duplex mode.
The telephone
network is an
example of a full-
duplex mode.
DATA COMMUNICATION SPEED AND MEDIA
BANDWIDTH
Bandwidth is the maximum rate at which data transfer occurs across any particular
path of the network. OR
The data handling capacity of a media is referred to as its bandwidth. Bandwidth is
the range of frequencies that is available for the transmission of data. There are
some types of bandwidth are discussed below:
 Narrowband
The media communicate data at a relatively slow speed. Examples are
telegraph lines.
 Voice band
These media are faster than narrowband. Most telephone lines that are used
to carry microcomputer transmissions are voice bands.
 Broadband
These media transmit large volumes of data at high speed via microwave,
satellite, coaxial cable, and fiber optics cable. It is also called a wind band.
COMMUNICATION MEDIAS
Communication media refers to the medium through which data transmission from
the transmitter to the receiver takes place. The most common media for data

9. communications are twisted-pair cable, coaxial cable, fiber optics cable, microwave,
and satellite.
 Twisted-Pair Cable
Twisted pair cables were one of the earliest directed transmission media. A
twisted pair cable is made up of two individual, insulated copper wires that
are twisted together and run parallel. Usually 1mm in diameter, copper wires.
Data is transmitted through one wire while ground reference is provided by
the other.
Reason for twisting
All transmissions frequently experience noise, interference, and crosstalk.
When the wires are twisted, some of the noise signals move together with the
data signals while the other parts move in the other direction. The outside
waves are canceled out by the unique twists. By computing the voltage
difference between the two wires, the receiver can recover data. As a result,
noise immunity is significantly improved.
 Coaxial Cable
An electrical cable containing a copper conductor, an insulator covering it,
and a braided metal mesh that reduces crosstalk and signal interference is
known as a coaxial cable. Coax is another name for coaxial cable.
Coaxial cable offers much higher bandwidths and supports transmission
speeds up to 10 megabits per second (Mbps). It can carry more data than
older types of twisted pair cable. However, it is also expensive.
 Fiber Optics Cable
A fiber optic cable is made of glass or plastic and transmits signals in the
structure of light signals. It involves an inner glass core surrounded by a
glass cladding that reflects the light into the core. Each fiber is encircled by
a plastic jacket.
Semiconductor lasers transmit data in the form of light along with hair-thin
glass fiber optic cables at the speed of light with no significant loss of
intensity over very long distances. The system includes fiber optic cables
that are made of tiny threads of glass or plastic.
Advantages of Fiber Optic Cables
The advantage of fiber optics cable are listed below:
 Small Size and Lightweight
The size of the optical fiber optic cables is minimal.
 Easily available and low cost
Silica glass is the substance used to make fiber optic cables. As a result,
fiber optic cables are less expensive than cables with metallic conductors.
 No electrical or electromagnetic interface
The signal is unaffected by electrical or electromagnetic interference
since the transmission uses light rays.
 Large Bandwidth
The fiber optic cable bandwidth is exceptionally wide since the light
arrays operate at very high frequencies in the GHz range. This makes it
possible to transmit more channels. As a result, a fiber optic cable has a
substantially larger information-carrying capacity than a coaxial wire.
Disadvantages of Fiber Optic Cables
The disadvantage of fiber optics cable are listed below:
 High Cost

10. In comparison to other guided media, the cost of the cable and interfaces
is higher.
 Unidirectional light propagation
Two-way communication requires either two fiber optic cables or two
frequency bands on a single fiber because optical transmission is by
nature unidirectional.
 Installation and Maintenance
fiber is different technology requiring skills; most engineers do not
occupy. It is defined as fixed point-to-point ground installations.
 Microwaves
Microwave transmission is a line-of-sight transmission i.e. the sending and
receiving antennas need to be properly aligned with each other. The distance
covered by the signal is directly proportional to the height of the antenna.
These are mostly used for mobile phone communications towers and
television broadcasts. Terrestrial and Satellite are two types of microwave
transmissions.
 Terrestrial
Terrestrial microwaves have both stations having antennas on earth.
 Satellite
In a satellite system, some antennas are on satellites in orbit and others
are on stations on earth. They work at remote places so they can be used
on mobile devices.
COMMUNICATION HARDWARE
MODEM
A modem is short for Modulator and Demodulator. Modulation is the process of
converting digital signals into analog signals. Demodulation is quite opposite; it
converts analog signals into digital signals. The modem can send and receive signals
that allow computers to share information. This sharing of information is possible
over phone lines, cables, or satellite connections.
Modulation
Demodulation
OSI MODEL
The Open Systems Interconnection model is a
conceptual model developed by ISO. It characterizes
and standardizes the communication functions of a
telecommunication and computing network. Its goal is
the interoperability of different communication
systems with standard communication protocols. This
model divides a communication system into seven abstraction layers.
 Application Layer
This layer enables users to access the network with applications such as
email, file transfer, etc. These applications produce the data, which is
transferred over the network.
 Presentation Layer
It receives information from the application layer and converts it to a uniform
network format (ASCII or Unicode) which is acceptable by the rest of the
OSI model and destination. Encryption and decryption are also the

11. responsibility of this layer. This layer also reduces the number of transfer bits
by compression.
 Session Layer
This layer establishes, maintains, and ends a session or logical connection
between applications on two computers. It manages who can transmit data at
a certain time and for how long. This layer adds checkpoints. If the session
fails only data after the most recent checkpoint need to be transmitted.
 Transport Layer
It ensures the reliable transmission of data. The transport layer manages error
control, ow control, and quality of the service. If the data is not properly
transmitted it requests to be resent.
 Network Layer
The function of this layer is the selection of the shortest and most suitable
path from source to destination, from the number of routes available. It is
also responsible to convert logical addresses (IP addresses) to physical
addresses (MAC addresses).
 Data Link Layer
This layer is responsible to transmit data using physical addresses. The data
link layer ensures error free transmission of packets. The packet in this layer
is referred to as the frame.
 Physical Layer
It is responsible for converting electrical signals into bits. It also defines the
cable types to be used as transmission media, cards, topology, and other
physical aspects.