The document provides an overview of data communications, detailing the elements of communication systems, types of data transmission modes (simplex, half-duplex, full-duplex), and various data transmission media (bounded and unbounded). It explains essential concepts such as analog versus digital signaling, modulation techniques, and details on transmission media including coaxial cables, twisted-pair cables, fiber-optics, and wireless technologies like radio waves and microwaves. The document serves as a foundational guide to understanding how data is transmitted and the technologies involved in computer networking.

1. UNIT 4
DATA COMMUNICATIONS
Computer application in management

2. Unit Outline
4.1 Introduction
4.2 Basic Elements of a Communication System
4.2.1 Data Transmission Modes
4.2.2 Transmission Basics
4.3 Types of Data Transmission Media
4.3.1 Bounded Media
4.3.2 Unbounded Media
4.4 Modulation Techniques
4.4.1 Modems
4.4.2 Analog versus Digital Transmission
4.5 Multiplexing
4.5.1 Time Division Multiplexing (TDM)
4.5.2 Frequency Division Multiplexing (FDM)

3. 4.1 Introduction
Data Communications
concerns the transmission of
digital messages to devices
external to the message
source.

4. 4.2 Basic Elements of a Communication System
Communication is the
process of transferring
messages and data from one
point to another.

5. The three basic elements of any
communication process are:
1) A sender (source) which creates the
message to be transmitted.
2) A medium which carries the message.
3) A receiver (Sink) which receives the
message.

6. For example
when we speak to our friend over
telephone we are sender,
the telephone line through which our
voice is transmitted is a medium and
our friend is a receiver.
This is a simple example of voice
communication. The same concept
holds for the data communication also.

8. 4.2.1 Data Transmission Modes
Data transmission, whether
analog or digital, may also be
characterized by the direction
in which the signals travel over
the media.

10. 1. Simplex:
Data is sent from sender to
receiver.
Signals may travel in only one
direction.
Simplex is sometimes called
one-way, or unidirectional
communication.

11. Real-life examples of full communication
include:
 Radio broadcasting
Television broadcasting
Computer to print
Monitor output
Mouse /keyboard to computer
Loud speaker

12. •Advantage of simplex mode
 simplex mode is the easiest and mos reliable
mode of communication
 Is cost-effective mode
 No need for coordination b/n the transmitting
and receiving devices which simplifies the
communication

13. •Disadvantage of simplex mode
 Only one way communication is possible.
 There is no way to verify if the transmitted
data has been received correctly.
 Simplex mode is not suitable for application
that require bidirectional communication

15. 2. Half Duplex
 Data can transmit both ways, but not
simultaneously
Signals may travel in both directions
over a medium but in only one
direction at a time.
Half-duplex systems contain only one
channel for communication, and that
channel must be shared for multiple
nodes to exchange information.

16. Real-life examples of full
communication include:
A two-way radio that has a
push-to-talk button
Browsing the internet(requests
and responses)
Universal Serial Bus (USB)

17. •Advantage of Half-duplex mode
 Half-duplex mode allows for bidirectional
communication, which is useful in situations
where devices need to send and receive data.
 it is a more efficient mode of communication
than simplex mode, the channel can be used for
both transmission and reception.
 Half-duplex mode is less expensive than full-
duplex mode, as it only requires one
communication channel.

18. •Disadvantage of Half-duplex mode
 Half-duplex mode is less reliable than full-
duplex mode, as both devices cannot transmit at
the same time.
 There is delay b/n transmission and reception,
which can cause problems in some application.
 There is need for coordination b/n the
transmitting and receiving devices, which can
complicate the communication process.

20. 3. Full-Duplex
Signals are free to travel in both
directions over a medium
simultaneously.
Data can transmit both ways at the
same time.
Full duplex may also be called
bi-directional transmission or
sometimes, simply duplex.

21. Real-life examples of full
communication include:
 Video calls/video conferencing
 Audio calls
 Live chats

22. Advantage of Full-duplex mode
Full-duplex mode allows for simultaneous
bidirectional communication, which is ideal for
real-time application such as video conferencing
or online gaming.
It is the most efficient mode of communication,
as both devices can transmit and receive data
simultaneously.
Full-duplex mode provides a high level of
reliability and accuracy, as there is no need for
error correction mechanisms.

23. Disadvantage of Full-duplex mode
Full-duplex mode is the most expensive mode,
as it requires two communication channels.
It is more complex than simplex and half-duplex
mode, as it requires two physically separate
transmission paths or a division of channel
capacity.
Full-duplex mode may not suitable for all
applications, as it requires a high level of
bandwidth and may not be necessary for some
type of communication.

25. A channel is a distinct communication
path between two or more nodes.

26. 4.2.2 Transmission Basics
In data networking, the term
transmission has two meanings.
First, it can refer to the process of
issuing data signals on a medium.
Second, it can also refer to the
progress of data signals over a
medium from one point to another.

27. Analog and Digital Signalling
One important characteristic of
data transmission is the type of
signalling involved.
 On a data network, information
can be transmitted via one of
two signalling methods:

28. i. Analog
ii. Digital

29. Both types of signals are
generated by electrical
current, the pressure of which
is measured in volts.
The strength of an electrical
signal is directly proportional
to its voltage.

30. The essential difference
between analog and digital
signals is the way voltage
creates and sustains the
signal.

31. 1. Analog Signaling
In analog signals, voltage varies continuously.
In digital signals, voltage turns off and on
repeatedly, pulsing from zero voltage to a specific
positive voltage.
An analog signal’s voltage appears as a
continuous wave when graphed over time,
because voltage is varied and imprecise in analog
signals,
Analog transmission is more
susceptible/disposaed to transmission flaws such
as noise than digital signals.

32. 2. Digital Signaling
Unlike analog signals where there
is a smooth curve, digital signals
jump directly to the next value.
When digital signals can exist in
only one of two values, they go
directly to the next value, typically
changing between 0 and 1.

33. The jump from one value to
another is known as a
transition.
Data rate is measured in bits
per second (bps).

36. Data rate: This is the rate, in bits
per second (bps), at which data can
be communicated.
Bandwidth: This is the maximum
bandwidth of the transmitted signal
as constrained by the nature of the
transmission medium or
transmission channel, expressed in
cycles per second, or hertz (Hz).

37. Noise: The average level of
noise over the communications
path.
Error rate: The rate at which
errors occur, where an error is
the reception of a 1 when a 0
was transmitted or the reception
of a 0 when a 1 was transmitted.

38. 4.3 TYPES OF DATA TRANSMISSION MEDIA
Data Transmission Media is
divided into two types
1) Bounded Media
2) Unbounded Media

39. 4.3.1 Bounded Media
Bounded Media is also known
as guided media.
Bounded media are great for
LANs because they offer high
speed, good security, and low
cost.

40. Three common types of bounded media
are:
a) Coaxial
b) Twisted pair
c) Fiber optic

41. a) Coaxial Cable
Coaxial cable consists of a
central copper core surrounded
by an insulator, a braided metal
shielding, called braiding, and an
outer cover, and called the
sheath or jacket.

42. Because of its insulation and
protective braiding, coaxial cable has
a high resistance to interference
from noise.
Coaxial cable is also less desirable
than twisted-pair because it
supports lower throughput.

44. b) Twisted-Pair Cable
The most popular network cabling
right now is twisted pair.
It is lightweight, easy to install,
inexpensive, and supports many
different types of networks.
It can also supports speeds of up
to 100Mbps.

45. Twisted-pair cabling is made up of
pairs of solid or stranded copper
twisted around each other.
The twists are done to reduce the
vulnerability to EMI and cross talk.
The number of pairs in the cable
depends on the type.
The copper core of the cable is usually
22-AWG or 24-AWG, as measured on
the American Wire Gauge standard.

46. Twisted-pair (TP) cable is
similar to telephone wiring and
consists of color-coded pairs of
insulated copper wires, each
with a diameter of 0.4 to 0.8
mm, or 22-24 AWG (American
Wire Gauge) standard copper
wires.

48. C. Fiber-Optic Cable
Fiber-optic cable, or simply fiber,
contains one or several glass fibers at
its center, or core.
Data are transmitted via pulsing light
sent from a laser or light-emitting
diode (LED) through the central fibers.
Surrounding the fibers is a layer of
glass called cladding.

50. 4.3.2 Unbounded Media
Unbounded, or wireless, media does not
use any physical connectors between the
two devices communicating.
Usually the transmission is sent through
the atmosphere, but sometimes it can be
just across a room.
Wireless media is used when a physical
obstruction or distance blocks the use of
normal cable media.

51. Following are the types of unbounded media:
1. Radio Waves
i. Short-wave
ii. Very-high frequency (VHF)
television and radio
iii. Ultra-high frequency (UHF)
television and radio Micro waves
2. Microwaves
i. Terrestrial Microwaves
ii. Satellite Microwaves
3. Infrared
i. Point-to-point
ii. Broadcast

52. 1. Radio Waves
Radio waves have
frequencies between 10 KHz
and 1GHz.

53. Radio waves include the following types:
i. Short-wave
ii. Very-high frequency (VHF) television and
radio
iii. Ultra-high frequency (UHF) television and
radio Micro waves

54. Most radio frequencies in the US
and Canada are regulated.
To gain permission to use a
regulated frequency can take a long
time and a large amount of money.
The good news is that there are
some frequencies that are not
regulated and anyone can use.

55. The problem with unregulated
frequencies is that they can get
saturated.
To ease this, there have been
limits set on the amount of
power that devices can
broadcast in these frequencies.

56. 2. Microwaves
Microwaves travel at higher frequencies
than radio waves and provide better
throughput as a wireless network media.
Microwave transmissions require the
sender to be within sight of the receiver.
These systems use licensed frequencies,
which makes them more costly than radio
wave systems.

57. Microwaves are utilized on the following two types of
communication systems:
i. Terrestrial Microwaves
Terrestrial microwave transmissions are used to
transmit wireless signals across a few miles.
ii. Satellite Microwaves
Satellite microwave transmissions are used to transmit
signals throughout the world.

58. 3. Infrared
Infrared frequencies are just
below visible light.
These high frequencies allow
high-speed data transmissions.

59. These transmissions fall into the following two
categories:
i. Point-to-point Infrared
Point-to-point infrared
transmissions utilize highly
focused beams to transfer signals
directly between two systems.

60. ii. Broadcast infrared
Broadcast infrared transmissions
use a spread signal, one broadcast
in all directions, instead of a direct
beam.