This document provides an overview of key concepts in data communication and networks. It defines common terminology like data, information, communication, networks, and nodes. It describes what data communication is and its main components, including the message, sender, receiver, medium, and protocols. It discusses data representation, data flow modes (simplex, half-duplex, full-duplex), network criteria like performance and reliability, and different physical network topologies like bus, star, and ring. The document serves as an introductory lecture on data communication fundamentals.

1. Data Communication and
Networks
Lecture 1

2. Terminologies
 Data: The collection of facts and figures upon
which we can not take certain decision is called
data. It will always be in raw form.
 Information: The processed form of data upon
which we can take certain decision is called
information.
 Communication: The exchange of data or
information from one place to another place or
from one device to another device is called
communication.

3. Terminologies
 Network: When different devices are
interconnected with each others in such a way
that they can exchange data or information is
called Network.
 Networking: The way in which different networks
establish is called networking.
 Node: Any device that may be used in
establishing a computer network is called a node.
It may be a computer, switch, router, Hub or any
other device which send or receive the data.

4. What is Data communication?
 The exchange of data or information between two
nodes via some medium is called data
communication.
 The medium may be a wire cable in case of wired
network while it may be radio waves in case of
wireless network.
 The transmission of data from one device to
another device in the same or another computer
network with the help of some medium is also
called data communication.

5. Con’t
 The communication devices must be part of
the communication system made up of
combination of hardware and software.
 The communication between devices must
be effective so that the data reach from one
device to another device must be correct
and accurate.

6. Characteristics of effective
communication
 The following are the three main
characteristics of an effective communication
system
 Delivery: The system must deliver data to the
correct destination. Data must be received by
the intended device or user.
 Accuracy: The system must deliver accurate
data. Data that have been altered or changed
in transmission and left uncorrected are
unusable.

7. Con’t
 Timeliness: The system must deliver data in a
timely manner. Data delivered late are useless. In
case of video and audio, timely delivery means,
delivering data as they are produced, in the same
order as they are produced and without significant
delay. This kind of transmission is called real Time
transmission.
 Jitter: Jitter refers to the variation in the packet arrival
time. It is the uneven delay in the audio video packets. It
should be avoided in effective communication.

8. Data Comm Components
The following are the main components of
data communication system.
1.Message: The information or data that we
want to communicate is called message. It
consist of text, number, picture, sound, video or
any combination of these.
2.Sender: The device that send the data
message is called sender. It can be a computer,
workstation, telephone handset, video camera
etc.

9. Data Comm Components
3. Receiver: The device that receives the data
message is called Receiver. It can be a
computer, Workstation, telephone handset,
television etc.
4. Medium: The physical path by which a
message travels from sender to the receiver is
called Medium. It can be twisted pair wires or
radio waves or satellite micro waves.

10. Data Comm Components
5. Protocol: The set of rules designed to
manage the data communication process is
called protocol. It is a sort of agreement
between the communicating devices.
Without protocol two or more devices may
be connected but would not be able to
communicate with each others and would
not be able to understand each others.

11. Key elements of Protocol
The following are the three basic and key
elements of a protocol.
1.Syntax
2. Semantic
3.Timing

12. Syntax
 The term syntax refers to the structure or
format of data, meaning the order in which
they are presented. For example, a simple
protocol might expect the first 8-bits of data
to be the address of sender, the second 8-
bits to be the address of the receiver and
the rest of the stream to be the message
itself.

13. Semantic
 The word semantic refers to the meaning of
each stream of bits, how is a particular
pattern to be interpreted and what action to
be taken based on that interpretation.
 For example does an address identify the
route to be taken or the final destination of
the message.

14. Timing
 The Term timing refers that when data
should send to the destination and how its
flow can be controlled.
 For example if a sender produces data at
100Mbps but the receiver process the data
at only 10Mbps then the transmission will
overload the receiver and some data will
lost.

15. Data Comm Components

16. Data Representation
 The type of data used to present or transmit information
from one place to another is called data representation.
Data can be represented in the following ways.
1. Text: In data communication text is represented as a
sequence of bits called bit pattern. The number of bits in bit
pattern depends on the number of symbols used in a
language. Different sets of bit patterns have been designed
to represent text symbols. Each set is called a code.

17. Data Representation
2. Numbers: These are also represented by using bit
patterns.
3. Images: Images also represented by bit patterns.
However, the mechanism is different. In its simpler
form, an image is divided into a matrix of pixels
where each pixel is a small dot. The size of pixel
depends on what is called resolution.

18. Data Representation
4. Audio: It is the representation of sound. It is
different from text, number and images. It is
continuous and not discrete. First we convert audio
to digital or analog signal before transmission.
5: Video: It can be produced as continuous entity or
can be a combination of images each a discrete
entity.

19. Data Representation

20. Data flow
 The mechanism through which the data is
transmitted from one place to another place is
called data transmission mode or data flow.
The following are the three different modes of
data flow or data transmission.
1.Simplex mode of transmission
2. Half duplex mode of transmission
3. Full duplex mode of transmission

21. Data Flow

22. Simplex mode of transmission
 In Simplex mode of transmission the
communication is unidirectional. It means that one
device on the communication link can transmit and
the other device can only receive the data. e.g TV
and remote, Keyboard and CPU, CPU and Monitor.

23. Half Duplex mode of transmission
 In half duplex mode of transmission each
station can both transmit and receive but not
at the same time. When one device is
sending, the other can only receive and vice
versa.

24. Full Duplex mode of transmission
 In full duplex mode of transmission both
station can transmit and receive at the same
time i:e simultaneously. Example is
telephone

25. Networks
 A network is a set of nodes/devices
connected by communication link. A node
can be computer, printer, switch, router or
Hub, capable of sending and receiving
data generated by other nodes on the
network.
 Most networks are distributed processing
in which a task is divided among multiple
computers.

26. Network Criteria
A network must be able to meet a certain
number of criteria. The most important of
these are
1. Performance
2. Reliability
3. Security

27. Performance
 It can be measured in term of transit time and
response time. The amount of time required for a
message to travel from one device to another
device is called transit time. The elapsed time
between an inquiry and a response is called
response time. Besides these, performance
depends on the following factors.
 Number of users, type of transmission medium,
capabilities of connected hardware and efficiency
of the software.

28. Reliability and Security
 The network reliability is measured by the
frequency of failure, the time it takes to
recover from a failure and the network
robustness in catastrophe or disaster.
 By network security we mean how to protect
the data from unauthorized access and
prevent the network resources from Diffrent
type of attacks.

29. Network Attributes
Type of Connection:
 A network is two or more devices connected together
through links. A link is a communication pathway that
transfers data from one device to another. For
communication to occurs, two devices must be
connected in some way to the same link at the same
time. There are two possible type of connections
1. Point to point
2. Multi point

30. Point to point Connection
 It provides a dedicated link between two
devices. The entire capacity of the link is
reserved for transmission between those two
devices. P2P connection uses an actual
length of wires or microwave or satellite link.
Example TV and Remote

31. P2P Connection

32. Multipoint Connection
 That type of connection in which more that two
devices share the communication link and
then start transmitting and receiving of data is
called multipoint connection.

33. Physical Topology
 The way in which the computers or other
devices are interconnected is called
physical topology. The following are the
different ways to connect the computers.

34. Bus Topology
 A bus is a multipoint connection. One long cable act as a backbone to link
to the entire devices in the network. In this topology all the computers are
connected in series to one cable.
 Nodes are connected to the bus cable by drop lines and taps.
 A drop line is the connection between the device and the main cable.
 A tap is a connector that connect the drop line and main cable.

35. Star Topology
 In star topology each device has a point to point connection with a central
Controller usually called Hub.
 In star topology the devices are not directly linked with each. The controller
act as an exchange. If one device want to send data to another device,
first it will send to the central controller which then transmit the data to
other connected devices.
 When the data reach to the central controller then it retransmit it to all the
devices (in broadcast star network) or only to destination computer (in
switch star network)

36. Ring Topology
 In Ring topology each node has a dedicated point to point connection with
only to the two devices on either sides of it.
 A signal is passed along the ring in one direction, from device to device
until it reach to its destination.
 Each device in the ring incorporate a repeater. When a device a receive a
signal intended for another device, its repeater generates a bit and passes
them along.

37. Mesh Topology
 In mesh topology each device has a dedicated point to point connection
with each other device in the network.
 Dedicated means that the link carries traffic only between the two devices
it connects.
 If n is the number of nodes in mesh topology then the total number of
dedicated links can be calculated by the formula as under
Links= n(n-1)/2

38. Standards
 Why we have standards?
 Some countries require you to drive on the left side of the road while
some on the right. But never it is left up to the individual choice. Although
individual choice is highly desirable in many areas of the human activity.
Still there are areas in where we should accept the standards for the
common good.
It provides guidelines to manufacturers, vendors,
government agencies, and other service providers to
ensure the kind of interconnectivity necessary in today’s
marketplace and in international communication.
It provides guideline for manufacturer to produce an
equipment according to those standards defined by ISO.

39. Data Communication Standards
 Data communication standards falls in two categories.
De facto: Those standards that have not been approved by an organized
body but have been adopted as standards because of its widespread
use and are called De facto standards.
Such standards are often established by manufacturer who seeks to
define the functionality of the new product or technology.
The main drawback of such standards is that it is in the control of one
company and can be changed any time without taking an account the
interest of the other parties.
De Jure: De jure means legislated. In computer Science field it means
standards designed by a standard setting body. Since every one
knows the rules and these rules can not be changed with out industry
vote on it.

40. Standard organization and standards
 Standard are developed through the cooperation of standard Creation Committee,
forums and government agencies (Federal Communication Commission “FCC”)
 International Standard Organization (ISO):
Open System Interconnect (OSI) reference model of Networking.
 Institute of Electrical and Electronics Engineers (IEEE):
802.3 Committee governs the Ethernet
802.5 Committee governs the Token Ring
802.11 Committee governs the Wireless LAN’s
 American National Standards Institute (ANSI):
ASCII character code and FDDI
 International Telephone Union-Telecommunication Standard Sector(ITU-T):
V series modem, X series data communiation protocol and Voice over IP protocol
 Internet Engineering Task Force (IETF):
TCP/IP and all internet protocols