This document provides an overview of a lecture on data communication and computer networks. It defines key concepts like data communication, components of a communication system, transmission modes (simplex, half-duplex, full-duplex), characteristics of networks, types of networks (LAN, MAN, WAN), applications of networks, and a brief history of the Internet and World Wide Web. The document is presented as part of a lecture on introduction to computer networks.

1. Introduction to Computer
Lecture # 13
Course Instructor : Sehrish Rafiq
Govt. Girls Degree College Maneri Swabi
Higher Education Department KP

2. Lecture Overview
 Data Communication
 Components of a data communication system
 Characteristics of a data communication system
 Transmission Mode
 Network
 Network Criteria
 Applications of Networks
 Types of Networks

3. Data Communication
 “Data Communication is the exchange of information from one entity to
another using a transmission medium”.
 The word data refers to facts, concepts and instructions presented in
whatever form is agreed upon by the parties creating and using the data.
 In the context of Computer information Systems
 Data is represented by binary information units(or bits) produced and
consumed in the form of 0’s and 1’s.
 “Data Communication is the exchange of data (in the form of 0’s and
1’s) between devices(computers) via some form of transmission
medium(such as a wire cable)”.
 For data communication to occur the communicating devices must be part
of a communication system.

4. Components of a Data communication system

5. Components of a
Data Communication System
 Message
 Message is the information /data to be communicated.
 Popular forms of information is text, audio, image and video.
 Sender
 Sender can be any device that has the ability to send information.
 It can be a computer, telephone handset, video camera etc.
 Receiver
 A receiver can be any device that has the ability to receive information.
 It can be a computer, telephone handset, television, radio set etc.

6. Continued…
 Transmission medium
 Transmission medium is the physical pathway by which a message travels
from sender to receiver.
 Transmission medium can be wired(e.g. coaxial cable , twisted pair cable,
fiber optic) or wireless (e.g. radio waves, micro waves etc. )
 Protocol
 Protocol is the set of rules which governs data communication.
 It represents an agreement between the communicating devices.
 Without a protocol two devices may be connected but not communicating just
as a person speaking French cannot be understood by a person who speaks
only Japanese.

7. Characteristics of a Data Communication
System
• The effectiveness of a data communication system depends on three
fundamental characteristics:
 Delivery
 Accuracy
 Timeliness

8. Transmission Mode
 The term Transmission Mode is used to define the direction of signal flow
between two linked devices.
 Simplex
 Half-duplex
 Full-duplex

9. Simplex Mode
 In simplex mode the communication is uni-directional as on a one-way
street.
 Only one of the two stations on a link can transmit, the other can only
receive.
 Examples: Keyboard, Monitor, Mouse

10. Half Duplex
 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.
 The half-duplex mode is like a one-lane road with two-directional traffic.
 The entire capacity of the communication channel is taken over by
whichever of the two devices is transmitting at the time.
 e.g. walkie-talkie

11. Full duplex
 In full-duplex mode both stations can transmit and receive
simultaneously.
 The full duplex mode is like a two-way street with traffic flowing in both
directions at the same time.
 In full duplex mode signals going in either direction share the capacity of
the link.
 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 of the channel is divided between signals
traveling in opposite directions.

12. Network
 A network is a set of devices(often referred to as nodes) connected by
media links.
 A node can be a computer, printer or any other device capable of sending
and/or receiving data generated by other nodes on the network.
 Media links can be wired or wireless communication channels.

13. Network Criteria
 For a network to be considered effective & efficient, It must meet the
following criteria.
 Performance
 Reliability
 Security

14. Performance
 Performance can be measured in many ways including transit time and
response time.
 Transit time: The amount of time required for a message to travel from one
device to another.
 Response time: The elapsed time between an inquiry and a response.
 Performance of a network depends on a number of factors including:
 Number of users
 Type of transmission medium
 The capabilities of the connected hardware
 The efficiency of software

15. Reliability
 In addition to accuracy of delivery, network reliability is also
important for an effective network.
 Reliability measures
 Frequency of failure
 Recovery time after a failure
 Catastrophe

16. Security
 Network security issues include protecting data from unauthorized
access and viruses.
 Unauthorized access
 Lowest level
 Highest level
 Virus protection

17. Applications of Networks
 Data communication networks have been indispensable part of business,
industry & entertainment.
 Marketing & Sales:
 Marketing Professionals use them to collect, exchange and analyze data
relating to customer needs and product development cycles.
 E-Commerce:
 Because of computer networks many companies and business firms sell
their products online which save customer time and money.
 Financial Services:
 Financial services include credit card, foreign exchange and investment
services, EFT and ATM.

18. Continued…
 Manufacturing:
 Computer networks are used today in many aspects of manufacturing
including the manufacturing process itself.
 Two applications that use network services CAD and CAM allow multiple
users to work on a project simultaneously.
 Electronic Messaging:
 The most widely used network application.
 Electronic messaging allow users to type messages at their local nodes and
then send to someone on the network. Examples include email programs
and instant chat applications.
 Information Services:
 Network information services include Information publishing services,
products information etc.

19. Continued…
 Teleconferencing:
 Teleconferencing allow conferences to occur without participants being in
the same place.
 Cellular Telephone:
 Cellular telephones provide the facility of wireless based voice and text
communication between its customers over large distances.
 Cable Television:
 Cable television is also a common application of networks which provide
transmission of different channels to its customers. It also include services
like video on request and marketing.

20. Types of Network
 In to which category a network falls is determined by its size, its ownership,
the distance it covers and its physical architecture.

21. LAN(Local Area Network)
 A local Area network is usually privately owned.
 It usually links the devices in a single office, building or campus.
 LAN size is limited to a few kilometers.
 LAN’s are designed to allow resources to be shared between personal
computers or work stations.
 In addition to size, LANs are distinguished from other types of networks
by their transmission media and topology.
 Most common topologies: Bus, Ring & Star.

22. LAN(Local Area Network)

23. MAN(Metropolitan Area Network)
 A MAN is designed to extend over an entire city.
 It may be a single network such as cable television network or it may
be a means of connecting a number of LANs in to a larger network
so that resources may be shared LAN-to-LAN.
 A MAN may be wholly owned and operated by a private company
such as local telephone company.

24. MAN(Metropolitan Area Network)

25. WAN(Wide Area Network)
 A WAN provides long distance transmission of voice, data, image
and video information over large geographic areas.
 The area a WAN covers may comprise a country, a continent or
even the whole world.
 WANs may utilize public, leased or private communication devices
and media and can therefore span an unlimited number of miles.
 Usually a WAN lacks a single owner, in fact it has many stack
holders.
 A WAN that is wholly owned and used by a single company is often
referred to as enterprise network.

26. WAN(Wide Area Network)

27. Internetworks
 When two or more networks are connected, they became an internetwork
or internet.
 The Internet from “I” is a Wide area network while the internet from “i”
refers to the interconnection of networks.
 Internet can be thought as internet but the reverse is not necessarily true.

28. History of Internet
 1960, A project of ARPA of US department of Defense
 Stanford Research Institute
 University of California at Los Angeles
 University of California at Santa Barbara
 University of Utah
 Features
 Redundant lines
 Decentralized Computing
 1980, NSF and other Government agencies
 1991,Commercial traffic
 April 1995,US government action
 2017,4156 million users

29. World Wide Web
 WWW stands for "World Wide Web.“
 Web is a collection of hypertext documents which consists of pages that
can be accessed using a Web browser.
 Each page has its own unique address known as Universal Resource
Locator (URL).
 The Hyper-Text Transfer Protocol (HTTP) is the method used to transfer
Web pages to your computer.
 With hypertext, a word or phrase can contain a link to another Web site.
 These links are known as hyper links.
 All Web pages are written in the hyper-text markup language (HTML),
which works in conjunction with HTTP.