Data communication and computer networks are fundamental concepts in the fields of computer

science and information technology, involving the transmission of data between devices or
points. Data communication refers to the process of transferring data from one device to another
via any transmission medium, such as wires, optical fibers, or wireless. Computer networks, on
the other hand, involve multiple computers and devices connected together to share resources,
information, and data.

Basic Elements of a Communication System

To understand data communication, it is crucial to first recognize the basic elements that make
up any communication system. These include:

1. Transmitter:
● The transmitter is the device that sends data signals. It converts the information
into a signal that is suitable for transmission over the communication channel or
medium. For example, in a computer network, this could be a computer or a
mobile device sending data.
2. Receiver:
● The receiver is the device that receives the transmitted signals. It converts the
signals back into a usable form. In the context of data communications, the
receiver would be another computer, server, printer, or mobile device that
interprets the incoming data.
3. Medium (Communication Channel):
● The communication medium is the physical path by which a message travels from
sender to receiver. This can include a variety of transmission media, such as
twisted-pair cables, coaxial cables, fiber optic cables, or electromagnetic waves
like radio, microwave, and infrared in the case of wireless communication.
4. Message:
● The message is the information (data) to be communicated. It can consist of text,
numbers, pictures, sound, or video or a combination of these. Messages are
generated by the source, and sent to the destination through the network.
5. Protocol:
● A protocol is a set of rules that governs the data communication. It defines how
the data is formatted, transmitted, and received, ensuring that the transmitter and
the receiver are performing their tasks in a synchronized manner. Protocols are
crucial for successful communication in networks, ensuring that connected
devices can understand each other and exchange data efficiently and correctly.

Additional Components

In more complex systems, additional elements might be included, such as:

 ● Encoding:
● Conversion of the message into signals suitable for the transmission medium.
Encoding can involve the conversion of analog to digital data or vice versa.
● Decoding:
● The reverse of encoding, performed by the receiver to interpret the signals back
into the original message format.
● Modulation/Demodulation:
● In cases where signals are transferred as analog waves, modulation and
demodulation are essential for encoding digital data into analog signals and
decoding analog signals back to digital data, respectively. This is typically
handled by modems.
● Multiplexer/Demultiplexer:
● Multiplexing involves combining multiple signals for transmission over a single
communication line, whereas demultiplexing is the process of separating those
signals at the receiver's end.

These basic elements form the backbone of any data communication system, and their effective
integration ensures that data can be transmitted from one place to another reliably and efficiently.
Understanding these components is fundamental to grasping how computer networks operate,
enabling data exchange and connectivity among different devices in a network.

Data Communication Modes

In data communications, the terms simplex, half duplex, and full duplex refer to the modes of
communication between two devices, defining how data is transmitted between them. Each mode
offers different capabilities regarding the direction and timing of data flow.

1. Simplex Mode

Simplex mode is the simplest type of communication in which data flows in only one direction.
Once the communication link is established, the sender can only send data, and the receiver can
only receive, with no capability for role reversal. Simplex systems are inherently unidirectional
and do not allow the receiver to send data back to the sender.

● Examples: A traditional television or radio broadcast where the station sends audio or
video signals and the audience merely receives them without sending signals back.

2. Half Duplex Mode

Half duplex mode allows for data transmission in both directions, but not simultaneously.
Communication can flow both ways between the sender and receiver, but only one device can
send at a time while the other must wait to respond. This requires the devices to switch between
sending and receiving modes.
 ● Examples: A walkie-talkie, where one person must push a button to speak and release it
to listen. This mode is often used in settings where simultaneous communication is not
critical but bidirectional flow is necessary.

3. Full Duplex Mode

Full duplex mode enables simultaneous two-way data transmission. Both the sender and receiver
can communicate with each other at the same time, improving the efficiency of the
communication link. Full duplex systems require two separate transmission paths: one for
sending and the other for receiving.

● Examples: A telephone conversation where both parties can talk and listen at the same
time without interference. Another common example is modern Ethernet connections in a
computer network, which use separate pairs of wires for sending and receiving data,
allowing for simultaneous communication.
●

Types of Transmission Media

In data communication terminology, a transmission medium is a physical path between the
transmitter and the receiver i.e. it is the channel through which data is sent from one place to
another. Transmission Media is broadly classified into the following types:

1. Guided Media: It is also referred to as Wired or Bounded transmission media. Signals being
transmitted are directed and confined in a narrow pathway by using physical links.
Features:

High Speed
Secure
Used for comparatively shorter distances
There are 3 major types of Guided Media:

(i) Twisted Pair Cable –

It consists of 2 separately insulated conductor wires wound about each other. Generally, several
such pairs are bundled together in a protective sheath. They are the most widely used
Transmission Media. Twisted Pair is of two types:

Advantages:
⇢ Better performance at a higher data rate in comparison to UTP

⇢ Eliminates crosstalk

⇢ Comparatively faster

Disadvantages:

⇢ Comparatively difficult to install and manufacture

⇢ More expensive

⇢ Bulky

(ii) Coaxial Cable –

It has an outer plastic covering containing an insulation layer made of PVC or Teflon and 2
parallel conductors each having a separate insulated protection cover. The coaxial cable
transmits information in two modes: Baseband mode(dedicated cable bandwidth) and Broadband
mode(cable bandwidth is split into separate ranges). Cable TVs and analog television networks
widely use Coaxial cables.

Advantages:

High Bandwidth
Better noise Immunity
Easy to install and expand
Inexpensive
Disadvantages:

Single cable failure can disrupt the entire network

Applications:

Radio frequency signals are sent over coaxial wire. It can be used for cable television signal
distribution, digital audio (S/PDIF), computer network connections (like Ethernet), and feedlines
that connect radio transmitters and receivers to their antennas.
(iii) Optical Fiber Cable –
It uses the concept of refraction of light through a core made up of glass or plastic. The core is
surrounded by a less dense glass or plastic covering called the cladding. It is used for the
transmission of large volumes of data.

The cable can be unidirectional or bidirectional. The WDM (Wavelength Division Multiplexer)
supports two modes, namely unidirectional and bidirectional mode.

Advantages:

Increased capacity and bandwidth

Lightweight
Less signal attenuation
Immunity to electromagnetic interference
Resistance to corrosive materials
Disadvantages:

Difficult to install and maintain

High cost
Fragile
Applications:

Medical Purpose: Used in several types of medical instruments.

Defence Purpose: Used in transmission of data in aerospace.
For Communication: This is largely used in formation of internet cables.
Industrial Purpose: Used for lighting purposes and safety measures in designing the interior and
exterior of automobiles.

2. Unguided Media:
It is also referred to as Wireless or Unbounded transmission media. No physical medium is
required for the transmission of electromagnetic signals.

Features:

The signal is broadcasted through air

Less Secure
Used for larger distances
There are 3 types of Signals transmitted through unguided media:
(i) Radio waves –
These are easy to generate and can penetrate through buildings. The sending and receiving
antennas need not be aligned. Frequency Range:3KHz – 1GHz. AM and FM radios and cordless
phones use Radio waves for transmission.

Further Categorized as (i) Terrestrial and (ii) Satellite.

(ii) Microwaves –
It 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. Frequency Range:1GHz – 300GHz. These are majorly used for mobile phone
communication and television distribution.

microwave transmission
Microwave Transmission

(iii) Infrared –
Infrared waves are used for very short distance communication. They cannot penetrate through
obstacles. This prevents interference between systems. Frequency Range:300GHz – 400THz. It
is used in TV remotes, wireless mouse, keyboard, printer, etc.