This document provides an overview of computer networks including: - Defining a computer network as interconnected hardware and computers that allow sharing of resources and information. - Describing the main types of transmission in networks as simplex (one-way), half duplex (one direction at a time), and full duplex (two-way simultaneous communication). - Discussing common network transmission media like twisted pair cable, coaxial cable, fiber optic cable, and wireless; outlining their advantages and disadvantages.

1. Computer Networks
Presentation By:
Nabendu Maji
Ritu Parna Jain
Noopur Tomar
nabendu.maji@gmail.com
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2. Abbreviations
O ANSI: American National Standards
Institute
O WWW: World Wide Web
O CPU: Central Processing Unit
O HDX: Half Duplex
O FDX: Half Duplex
O CB radio: Citizens' Band radio
O UTP : Unshielded twisted pair
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3. Computer Networking
Definition:
O A computer network, often simply
referred to as a network, is a collection of
hardware components and computers
interconnected by communications
channels that allow sharing of resources
and information.
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4. Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files,
databases)
Search Capability (WWW)
Communication
Email
Message broadcast
Remote computing
Distributed processing (GRID Computing) 4

5. Advantages
O File sharing.
O Resource sharing.
O Increase storage capacity.
O Increase cost efficiency.
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6. Disadvantages
O Security issues.
O Rapid spread of computer
virus.
O Expenses set-up.
O Dependency of main file
server. 6

7. Type Of Transmission
O Simplex
O Half Duplex
O Full Duplex
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8. Simplex
Simplex communication refers to communication that occurs in
one direction only.
O ANSI definition: A simplex circuit is one where all signals can
flow in only one direction. These systems are often employed
in broadcast networks, where the receivers do not need to
send any data back to the transmitter/broadcaster.
Examples
O Commercial Radio Broadcast (not walkie-talkies, etc.)
O Television Broadcast
O Keyboard to CPU communication
O One-way communications from a launcher to a guided missile,
where the launcher (airplane, ship, etc.) sends commands to
the missile, but does not receive any information sent back. 8

9. Simplex (Continued..)
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10. Half Duplex
Definition:
O A half-duplex (HDX) system provides
communication in both directions, but only one
direction at a time (not simultaneously).
Typically, once a party begins receiving a signal, it
must wait for the transmitter to stop transmitting,
before replying.
Example: Walkie-talkie
Fax Machine
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11. Full-Duplex
O A full-duplex (FDX), or sometimes double-
duplex system, allows communication in both directions,
and, unlike half-duplex, allows this to happen
simultaneously.
It is a system composed of two connected parties or
devices that can communicate with one another in both
directions. (The term multiplexing is also used when
describing communication between more than two parties
or devices.)
Examples: Land-line telephone networks are full-duplex,
since they allow both callers to speak and be heard at the
same time. A good analogy for a full-duplex system would
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be a two-lane road with one lane for each direction.

12. Full-Duplex
Examples:
O Telephone networks
O Mobile phone networks
O CB radio
O Internet
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13. How many kinds of Networks?
We can classify networks in different ways…
• Based on Transmission Media: Wired (UTP, coaxial cables,
fiber-optic cables) and Wireless
• Based on Network Size: LAN and WAN (and MAN)
• Based on Management Method: Peer-to-peer and
Client/Server
• Based on Topology (connectivity): Bus, Star, Ring, Mesh,
Hybrid…
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14. Transmission Media
O Twisted Pair Cable
O Coaxial cables
O Fiber-optic cables
O Wireless
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15. Twisted Pair Cable
O Twisted pair cabling is a type of wiring in which
two conductors (the forward and return
conductors of a single circuit) are twisted together
for the purposes of cancelling out electromagnetic
interference (EMI) from external sources; for
instance, electromagnetic radiation from
unshielded twisted pair (UTP) cables,
and crosstalk between neighbouring pairs. It was
invented by Alexander Graham Bell.
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16. Twisted Pair Cable
Advantages:
O High availability—More than 1 billion telephone
subscriber lines based on twisted-pair have been
deployed, and because it's already in the ground it can
be used.
O Low cost of installation on premises—The cost of
installing twisted-pair on premises is very low.
O It is a thin, flexible cable that is easy to string between
walls.
O More lines can be run through the same wiring
ducts.
O UTP costs less per meter/foot than any other type of
LAN cable. 16
O Electrical noise prevented- Electrical noise going into
or coming from the cable can be prevented.

17. Twisted Pair Cable
Disadvantages:
O Limited frequency spectrum—The total usable
frequency spectrum of twisted-pair copper cable is
about 1MHz.
O Limited data rates—The longer a signal has to travel
over twisted-pair, the lower the data rate. At 30 feet
(100 m), twisted-pair can carry 100Mbps, but at 3.5
miles (5.5 km), the data rate drops to 2Mbps or less.
O Short distances required between repeaters—
More components need to be maintained, and those
components are places where trouble can arise,
which leads to higher long-term operational costs.
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O High error rate—Twisted-pair is highly susceptibility
to signal interference.

18. Coaxial Cables
O Coaxial cable, or coax, is an electrical cable with
an inner conductor surrounded by a flexible,
tubular insulating layer, surrounded by a tubular
conducting shield. The term coaxial comes from
the inner conductor and the outer shield sharing
the same geometric axis. Coaxial cable was
invented by English engineer and
mathematician Oliver Heaviside, who patented the
design in 1880.
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19. Coaxial Cables
Advantages:
O Broadband system: Coax has a sufficient frequency range to
support multiple channels, which allows for much greater
throughput.
O Greater bandwidth: Compared to twisted-pair, coax provides
greater bandwidth, and it also offers greater bandwidth for
each channel. As it has greater bandwidth per channel, it
supports a mixed range of services. Voice, data, and even
video and multimedia can benefit from the enhanced capacity.
O Lower error rates: Because the inner conductor is in a shield
insulator, noise immunity is improved, and coax has lower
error rates and therefore slightly better performance than
twisted-pair. The error rate is generally 10-9 (i.e., 1 in 1 billion)
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bps.

20. Coaxial Cables
Disadvantages:
O Problems with the deployment architecture: The
bus topology in which coax is deployed is susceptible
to congestion, noise, and security risks.
O High installation costs: Installation costs in the local
environment are high.
O Bidirectional upgrade required: In countries that
have a history of cable TV, the cable systems were
designed for broadcasting, not for interactive
communications. Before they can offer to the
subscriber any form of two-way services, those
networks have to be upgraded to bidirectional systems.
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21. Fiber-Optic Cables
O An optical fiber cable is a cable containing one or
more optical fibers. The optical fiber elements are
typically individually coated with plastic layers and
contained in a protective tube suitable for the
environment where the cable will be deployed.
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22. Fiber-Optic Cables
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23. Fiber-Optic Cables
Advantages:
O Extremely high bandwidth – No other cable-based
data transmission medium offers the bandwidth that
fiber does.
O Resistance to electromagnetic interference – Fiber
has a very low rate of bit error (10 EXP-13), as a result
of fiber being so resistant to electromagnetic
interference. Fiber-optic transmission are virtually noise
free.
O Early detection of cable damage and secure
transmissions – Fiber provides an extremely secure
transmission medium. By constantly monitoring an
optical network and by carefully measuring the time 23 it
takes light to reflect down the fiber, splices in the cable
can be easily detected.

24. Fiber-Optic Cables
Disadvantages:
O Installation costs are still high – Despite the fact that fiber
installation costs are dropping by as much as 60% a year, still
installing fiber optic cabling is relatively costly.
O Special test equipment is often required – The traditionally
used test equipment are of no use. Equipment such as an
OTDR (Optical Time Domain Reflectometer) are used.
O Susceptibility to physical damage – Fiber is a small and
compact cable, and it is highly susceptible to becoming cut or
damaged during installation or construction activities.
O Wildlife damage to fiber optic cables – Fibre optic cable
(fiber cable jackets particularly) is made of using many
Wildlife materials such as Bird’s nest.
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25. Wireless
O Wireless network refers to any type of computer
network that is not connected by cables of any
kind. It is a method by which homes,
telecommunications networks and enterprise
(business) installations avoid the costly process of
introducing cables into a building, or as a
connection between various equipment locations.
Wireless telecommunications networks are
generally implemented and administered using a
transmission system called radio waves.
Example: WiMAX (Wireless MAN)
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26. Wireless
Wireless communications can be via:
O Radio frequency communication
O Microwave communication, for example long-range line-
of-sight via highly directional antennas, or short-range
communication,
O Infrared (IR) short-range communication, for example
from consumer IR devices such as remote controls.
O Wi-Fi is a wireless local area network that enables
portable computing devices to connect easily to
the Internet. Standardized as IEEE 802.11 a,b,g,n,
Example: Internet access at private homes, within
offices, and at public hotspots.
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27. Wireless
O Cellular data service offers effective coverage within a range
of 10-15 miles from the nearest cell site. Speeds have
increased as technologies have evolved, from earlier
technologies such as GSM, CDMA and GPRS, to 3G networks
such as W-CDMA, EDGE or CDMA2000.
O Mobile Satellite Communications may be used where other
wireless connections are unavailable, such as in largely rural
areas or remote locations. Satellite communications are
especially important
for transportation, aviation, maritime and military use.
O Bluetooth is a proprietary open wireless technology standard
for exchanging data over short distances (using short
wavelength radio transmissions in the ISM band from 2400-
2480 MHz) from fixed and mobile devices, creating personal
area networks(PANs) with high levels of security. Created by
telecoms vendor Ericsson in 1994, it was originally conceived
as a wireless alternative to RS-232 data cables. It can connect
several devices, overcoming problems of synchronization. 27

28. Network Tropology
Definition: The network topology defines the way in
which computers, printers, and other devices are
connected. A network topology describes the layout of
the wire and devices as well as the paths used by data
transmissions
Types:
O Bus Tropology
O Ring Tropology
O Star Tropology
O Mesh Tropology
O Hybrid Tropology
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29. Bus Tropology
O A bus network topology is a network architecture
in which a set of clients are connected via a
shared communications line, called a bus. There
are several common instances of the bus
architecture, including one in the motherboard of
most computers, and those in some versions of
Ethernet networks.
Bus 29
Topology

30. Ring Tropology
O A ring network is a network topology in which
each node connects to exactly two other nodes,
forming a single continuous pathway for signals
through each node - a ring. Data travels from node
to node, with each node along the way handling
every packet.
Ring Topology
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31. Star Tropology
O Star networks are one of the most
common computer network topologies. In its
simplest form, a star network consists of one
central switch, hub or computer, which acts as a
conduit to transmit messages. This consists of a
central node, to which all other nodes are
connected; this central node provides a common
connection point for all nodes through a hub.
Star
Topology
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32. Mesh Tropology
O The type of network topology in which some of
the nodes of the network are connected to more
than one other node in the network with a point-
to-point link – this makes it possible to take
advantage of some of the redundancy that is
provided by a physical fully connected mesh
topology without the expense and complexity
required for a connection between every node in
the network.
Mesh
Topology
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33. Hybrid Tropology
O Hybrid networks use a combination of any two or
more topologies in such a way that the resulting
network does not exhibit one of the standard
topologies (e.g., bus, star, ring, etc.).
For example, a tree network connected to a tree
network is still a tree network topology. A hybrid
topology is always produced when two different
basic network topologies are connected. Two
common examples for Hybrid network are: star ring
network and star bus network
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34. Hybrid Tropology (Continued…)
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35. LAN (Local Area Network)
O A local area network (LAN) is a computer
network that interconnects computers in a limited
area such as home, school, computer laboratory
or office building.
It allows resource sharing between computers
within a limited area.
Example: Intranet of IMED.
Wifi Network of my House.
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36. MAN (Metropolitan Area Network)
O A metropolitan area network (MAN) is a computer
network that usually spans a city or a large campus.
A MAN usually interconnects a number of local area
networks (LANs) using a high-capacity backbone
technology, such as fiber-optical links, and provides
up-link services to wide area networks (or WAN)
and the Internet.
Example: Many Telcom Company provide a popular
MAN service called SMDS (Switched Multimegabit Data Services).
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37. 37

38. WAN (Wide Area Network)
O A wide area network (WAN) is a
telecommunication network that covers a broad
area (i.e., any network that links across
metropolitan, regional, or national boundaries).
Business and government entities utilize WANs to
relay data among employees, clients, buyers, and
suppliers from various geographical locations. In
essence this mode of telecommunication allows a
business to effectively carry out its daily function
regardless of location.
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39. WAN (Wide Area Network)
(Cont.…)
WAN 39

40. Internet
O The Internet is a global system of
interconnected computer networks that use the
standard Internet Protocol Suite (TCP/IP) to serve
billions of users worldwide. It is a network of
networks that consists of millions of private, public,
academic, business, and government networks, of
local to global scope, that are linked by a broad
array of electronic, wireless and optical networking
technologies.
O Example: World Wide Web
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41. INTERNET
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42. Intranet
O An intranet is a computer network that
uses Internet Protocol technology to securely
share any part of an organization's information
or network operating system within that
organization.
Sometimes the term refers only to the
organization's internal website.
Example: Intranet Of Bharati Vidyapeeth University
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43. Extranet
O An extranet is a computer network that allows
controlled access from the outside, for specific
business or educational purposes. An extranet
can be viewed as an extension of a
company's intranet that is extended to users
outside the company, usually partners, vendors,
and suppliers.
Example: Bank’s Internet Banking
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45. Thank You
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46. ?
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