Networking concepts by Sachidananda M H

SACHIDANANDA M H. MCA
Lecturer in Computer Science

Introduction
 A network is an interconnected connection of autonomous
computers.
 Two computers are said to be interconnected if they are capable
of exchanging the information.

Networking goals
 Resource Sharing: The aim is to make all the programs, data
and peripherals available to anyone on the network.
 Reliability: A file can have copies on two or three different
machines, so if one of them is unavailable, the other copies
could be used. Ex. Military, banking.
 Cost Factor: PCs have better price/performance ratio than
microcomputers.
 Communication Medium: The changes at one end can be
immediately noticed.

Need for Networking
 File sharing provides grouping and sharing of data files over
the network.
 Print Sharing of computers such as hard disks and printers etc..
 Remote access around the globe.
 Email tools for communication.
 Sharing the database to multiple users at the same time.

ARPANET
 The Advanced Research Projects Agency Network(ARPANET)
was one of the world’s first operational packet switching
networks, the first network to implement TCP/IP.
 It was initially funded by ARPA within U.S. Department Of
Defense for use by its projects at universities and research
laboratories in the US.

2.6
Figure 2.1 Tasks involved in sending a letter

OSI Reference Model
Physical Layer :
 The physical layer of the OSI model defines connector and
interface specifications, as well as the medium(cable)
requirements.
 Electrical, mechanical, functional, and procedural
specifications are provided for sending a bit stream on a
computer network.
 The physical layer defines what it means to transmit and to
receive data.

The Data Link Layer
 Allows a device to access the network to send and receive
messages
 Offers a physical address so a device’s data can be sent on the
network
 Works with a device’s networking software when sending and
receiving messages
 Provides error-detection capability.

Networking Layer
 The network layer controls the operation of the subnet.
 The main function is to determine how packets are routed from
source to destination.

Transport Layer
 The transport layer is the layer in the open system
interconnection (OSI) model responsible for end-to-end
communication over a network.
 The basic function of transport layer is to accept data from
above layer and split up into smaller units if needed, and pass
these to the network layer and ensure that the pieces all arrive
correctly at the other end.
 It also determines type of services to provide to the session
layer.

Session Layer
 The session layer allows users on different machines
to establish sessions between them.
 It includes dialog control, token management and
synchronization.

Presentation Layer
 The primary goal of this layer is to take care of the syntax and
semantics of the information exchanged between two
communicating systems.
 It takes care that the data is sent in such a way that the receiver
will understand the information (data) and will be able to use
the data.

Application Layer
 The Application layer contains a variety of protocols that are
commonly needed by the user.
 Example: HTTP(Hyper Text Transfer Protocol).
 It provides services for an application program to ensure that
effective communication with another application program in a
network is possible.

TCP/IP(Transmission Control Protocol/Internet Protocol)

Networking concepts by Sachidananda M H

 TCP/IP is a two-layer program.
 The higher layer, Transmission Control Protocol, manages
the assembling of a message or file into smaller packets
that are transmitted over the Internet and received by a
TCP layer that reassembles the packets into the original
message.
 The lower layer, Internet Protocol, handles the address
part of each packet so that it gets to the right destination.
 Each gateway computer on the network checks this
address to see where to forward the message.

 Even though some packets from the same message are routed
differently than others, they'll be reassembled at the
destination.
 TCP/IP uses the client/server model of communication in
which a computer user (a client) requests and is provided a
service (such as sending a Web page) by another computer (a
server) in the network.
 Information is transferred as a sequence of “datagrams”.
 Each of these datagrams is sent through the network
individually.

NOTE
 A datagram is a unit of data, which is what the protocols deal
with.
 A packet is a physical thing, appearing on an Ethernet or some
wire.

Hypertext Transfer Protocol
 HTTP is an application level protocol with the lightness and
speed necessary for distributed, collaborative, hypermedia
information systems.
 HTTP functions as a request-response protocol in the client-
server computing model.
 It allows an open-ended set of methods to be used to indicate
the purpose of a request. It builds on the discipline of reference
provided by the Uniform Resource Identifier(URI), as a
location URL or name (URN) for indicating the resource
indicating the resource on which a method is to be applied.
 Messages are passed to HTTP in a format similar to that used
by internet mail and Multipurpose Internet Mail
Extension(MIME).

FTP(File Transfer Protocol)
 One of the original services on the internet was designed to
allow for transferring files from one system to another.
 Files of any type can be transferred, although you may have to
specify whether the file is an ASCII or Binary file.
Advantages of FTP
 It is very useful to transfer the files from one network to
another.
 It is an effective way to get a geographically dispersed group to
co-operate on a project.
 It is a popular way to share information over the internet.FTP
works as a client-server process.

SLIP/PPP(Serial Line Internet Protocol)
 Serial line IP(SLIP) was the first protocol for relaying the IP
packets over dial-up lines.
 It defines the encapsulation mechanism, but little else.

PPP(Point to Point Protocols)
 PPP is the internet standard for transmission of IP packets over
serial lines.
 PPP is currently the best solution for dial-up internet
connections, including ISDN.
 PPP is a layered protocol, starting with a link control
protocol(LCP).

The Internet
 The Internet is a worldwide network of computer networks that
evolved from the first network ARPAnet.
 The internet is made up of many networks each run by a
different company and interconnected at peering points.

The Interspace
 Interspace is a client/server software program that allows
multiple users to communicate online with real-time audio,
video and text chat in dynamic 3D environments.
 It provides the most advanced form of communication
available on the internet today.

Elementary Terminology of networks
 Let us have a look at some typical hardware components of the
network.
Nodes(Workstations)
o The term node refers to the computer that are attached to a
network and are seeking to share the resources of the
network.
Server
o Servers can be of two types :
1. Non-dedicated servers
2. Dedicated servers

Types of servers
 Non-dedicated servers
• On small networks, a workstation that can double as a server is
known as non-dedicated server since it is not completely
dedicated to the cause of serving.
• Such servers can facilitate the resource-sharing among the
workstations on a proportionately smaller scale.
• Since one computer works as a work station and as well as
server, it is slower and requires more memory.
• The networks using such a server are known as PEER-TO-
PEER networks.

 Dedicated Servers
• On bigger network installations, there is a computer
reserved for server’s job and its only job is to help
workstations access data, software and hardware
resources.
• It does not double-up as a workstations and such a
server is known as dedicated server.
• The networks using such a server is known as
MASTER-SLAVE networks.

 There may be a server exclusively for serving the file related
requests like storing files. This server is known as file server.
 Similarly there may be printer server and modem server.
 The Printer server takes care of the printing requirements of a
number of workstations.
 The modem server helps a group of network users use a
modem to transmit long distance messages.

TYPES OF NETWORKS
 Networks vary in size, complexity and geographical spread.
 Mostly computers are classified basis of geographical spread
and on this basis, there can be 3 types of networks:
 Local Area Networks (LANs)
 Wide Area Networks (WANs)
 Metropolitan Area Networks (MANs)

LANs
 Small computer networks that are confined to a localized area
(eg., an office, a building or a factory) are known as LANs.
 A local area network (LAN) is a computer network that
interconnects computers within a limited area such as a
residence, school, laboratory, or office building.
 For instance, LAN users can share data, information, programs,
printer, hard disks, monitor etc..

MANs
 MANs are the networks spread over a city.
 Example: Cable TV network.

WANs
 The networks spread across the countries are known as
WANs.
 It can even be a group of LANs that are spread across
several locations.
 The largest WAN in existence is the internet.

Difference between LAN and WAN
LAN WAN
 Diameter of not more than a
few kilometers.
 A total data rate of at least
several mbps.
 Complete ownership by a
single organization.
 Very low error rates.
 Span entire countries.
 Data rate less than one mbps.
 Owned by multiple
organization.
 Comparatively higher error
rates.

Network topologies
 The actual appearance or layout of networking.

Star topology
 This topology consists of a central node to which all other
nodes are connected by a single path.
 It is the technology used in most existing information networks
involving data processing or voice communications.
Advantages
 Ease of service.
 One device per connection

The Bus or linear topology
 a bus topology is a network setup in which each computer and
network device are connected to a single cable or backbone.
 This consists of the single length of the transmission
medium(normally coaxial cable) onto which the various nodes
are attached.
 The bus has the terminators at either end which absorb the
signal, removing it from the bus.
 Data is transmitted in small blocks, known as packets. Each
packet has some data bits, plus a header containing its
destination address.

 Advantages
o It works well when you have a small network.
o Easiest network topology for connecting computers or peripherals in
a linear fashion.
o Requires less cable length than a star topology.
o Easy to extend.
Disadvantages
o Difficult to identify the problems if the whole network goes
down.
o It can be hard to troubleshoot individual device issues.
o Not great for large networks.
o If a main cable is damaged, the network fails or splits into two

Ring or circular topology
 A network topology is set up in a circular fashion in such a way
that they make a closed loop.
 Each node is connected to two and only two neighboring nodes
and is transmitted onwards to another.
 Data travels in only one direction.
 After passing through each node, it returns to the sending node,
which removes it.

Advantages
 Short cable length. (Less connection is needed, which will in
turn increase network reliability.
Disadvantages
 Node failure causes network failure.
 Difficult to diagnose faults.
 Network reconfiguration is difficult.

Tree topology
 A variation of bus topology is the tree topology.
 The shape of an inverted tree with the central root branching
and sub branching to the extremities of the network.
 Transmission takes place in the same way as in the bus
topology.
 In both the cases, there is no need to remove packets from the
medium because when a signal reaches the end of the medium,
it is absorbed by the terminators.
 It is a hybrid technology because it is a modification of a pure
network topology, bus topology.

Graph topology
 In this topology, nodes are connected together in an arbitrary
fashion.
 If a path can be established in two nodes via one or more links
is called connected graph.

Mesh topology
 In this topology, each node is connected to more than one node
to provide an alternative root in the case the host is either down
or too busy. It is an extension to P-P network.
 Mesh topology is excellent for long distance networking
because it provides extensive backup, rerouting and pass
through capabilities.
 However, this topology is commonly used for wireless
networks.
 If there is a direct link between each host, then the network is
said t be fully connected.

Transmission medium
 By transmission media or communication channels of
network, it is meant that the connecting media are being talked
about.
 The cables that connect two or more workstations are the
communication channels.

TWISTED PAIR CABLE
 The most common form of wiring is data communication
application is the twisted pair cable.
 As a Voice Grade Medium (VGM), it is the basis for most
internal office telephone wiring. It consists of two identical
wires wrapped together in a double helix.
 Twisted-pair cable will have two common things.
a. The wires come in pairs.
b. The pairs of wires are twisted around each other.

Advantages
• It is simple and physically flexible.
• It can be easily connected.
• Easy to install and maintain.
• Low weight and very inexpensive.
Disadvantages
• Low bandwidth capability.
• Because of high attenuation, it is incapable carrying a
signal over long distances without the use of repeaters.

Types
I. Unshielded Twisted Pair (UTP) cable: UTP cabling is used
for variety of electronic communications. CAT1 to CAT 5 are
the categories. The UTP cables can have maximum segment
length of 100 mts.
II. Shielded Twisted Pair (STP) cable: This type of cable comes
with shielding of the individual pairs of wires, which further
protects it from external interference. It is heavier and
costlier than UTP.

Types of coaxial cables.
 Thicknet: This form of coaxial cable is thicker than thinet. The
thicknet coaxial cable segments can be upto 500 meters long.
 Thinnet: This form of coaxial cable is thinner and it can have
maximum segment length of 185 meters.

Optical fibers
 Optical fibers consists of thin strands of glass or glass like
material which are so constructed that they carry light from
source at one end of the fiber to a detector at the other end.
 The light sources used are either light emitting diodes(LEDs)
or laser diodes(LD).

Advantages
• It is highly suitable for harsh industrial environments.
• It guarantees source transmission and has a very high
transmission capacity.
• It is immune to electric and magnetic interference.
• Fiber optic fibers can be used for broadband
transmission where several channels are handled in
parallel.

Disadvantages
• Microwave propagation is susceptible to weather
effects like rains, thunder, storms etc.
• Bandwidth allocation is extremely limited.
• The cost of deign, implementation and maintenance
of microwave links is high.

Radio Wave
 The transmission making use of radio frequencies is
termed as radio-wave transmission. Any radio setup
has two parts:
 The transmitter
 The receiver
 The transmitter takes some sort of messages, encodes
it onto a sine wave and transmits it with radio waves.
 The receiver receives the radio waves and decodes the
messages from the sine wave it receives

Advantages
• Radio wave transmission offers mobility.
• It offers case of communication over difficult terrain.
Disadvantages
 It is an insecure communication.
 It is susceptible to weather effects like rain, thunder,
s torms etc.

Satellite(Satellite microwave)
 When the frequency of radio wave is more than 3 GHz, it is
named microwave.
 Satellite communication is special case of microwave relay
system. It uses synchronous satellite to relay the radio signal
transmitted from ground station.
 In satellite communication, the earth station consists of a
satellite dish that functions as an antenna and communication
equipment to transmit and receive data from satellites passing
overhead.

Advantages
 The area coverage through satellite communication is quite
large.
 The heavy usage of intercontinental traffic makes the satellite
commercially attractive.
Disadvantages
 The high investment cost and insurance cost.
 High atmospheric losses above 30 GHz limit carries
frequencies.

Other unguided media
Infrared
o This type of transmission uses infrared light to send the data.
o The infrared light transmits data through the air and can
propagate throughout a room. It is considered as a secure one.
o Example: PDAs, Handheld devices
Laser
 The laser transmission requires direct line-of-sight.
 It is unidirectional like microwave, but has much higher speed
than microwaves. This transmission requires laser trasnmitter
and a photo sensitive receiver.

Switching Techniques
 Circuit Switching
 Packet Switching
 Message Switching.

Circuit Switching
 In this technique, first the complete physical connection
between two computers is established and the data are
transmitted from source computer to destination computer.
 The important property of this switching technique is to setup
an end to end path(connection) between computers before any
data can be sent.

Message switching
 In message switching, the whole message is treated as a data
unit and is switching/transferred in its entirety.

Packet switching
 With message switching, there is no limit on block size, in
contrast, packet switching places a tight upper limit on block
size.
 A fixed size of packets which can be transmitted across the
network is specified.

Communication modes
 The communication mode defines in which data can flow
depending upon the type media used.
 Simplex
 Half duplex
 Full duplex

Simplex
 On this panel there is only one interface is a
transmitter and all other interfaces is a receiver.E
Ex: Radio, TV uses simplex channels.
Half duplex
 On this channel each interface works as transmitter
and receiver, but only one interface can transmit at a
time. Ex: Walkie-Talkies

Full duplex
 This channel has two ends, each serving as transmitter and
receiver.
 Each interface can transmit and receive at the same time.
Ex: Modern telephone system.

NETWORKING DEVICES
MODEM (MODULATOR and DEMODULATOR)
• Modems allow you to combine the power of you computer
with the global reach of the telephone system.
• Ordinary telephone lines cannot carry digital information, a
modem changes the digital data from your computer into
analog data, a format that can be carried by a telephone line.
• In a similar manner, the modem receiving the call then changes
the analog signal back into digital data to the computer.
• This shift of digital data into analog data back again, allows
two computers to communicate with one another called
Modulation and Demodulation

Working on Modem
 Modem converts digital signals to A/F(audio frequency) tones
which are in the frequency range that the telephone lines can
transmit and also it can also convert transmitted tones back to
digital information.
 After the power is turned on in DTE(Data Terminal
Equipment) and DCE(Data Communication Equipment), the
terminal runs for self check, it asserts the Data Terminal
Ready(DTR) Signal to tell the modem that it is ready.

Types of modem
 Internal Modems: Modems that are fixed within the
computer.
 External Modems: Modems that are connected externally to a
computer as other peripherals are connected.
Ethernet Card
 Ethernet is a LAN architecture developed by Xerox Corp in
association with DEC an Intel. Ethernet uses bus or star
topologies and can support data transfer rates of up to 10 mbps.
 The computers that are part of Ethernet have to install a
special card called Ethernet Card.

Hub
• A hub is a hardware device used to connect several computers
together.
• A hub that contains multiple independent but connected
modules of network and internetworked equipment.
• Hubs can be either passive or active.
1. Active Hubs: Electrically amplify the signal as it moves from
one connected device to another.
2. Passive Hubs: Allow the signals to pass from one computer
to another without any change.

Switch
 A switch is a device that is used to segment networks into
different sub networks called subnets or LAN segments.
 A switch is responsible for filtering i.e, transforming data in a
specific way and for forwarding packets between LAN
segments. Switch supports any packets protocol.
 LANs that are segmented through switches are called switched
LANs. In case of Ethernet Lans, switched Ethernet LANs.
How a switch functions?
• To insulate the transmission from the other ports, the switch
establishes a temporary connection between the source and
destination and then terminates the connection once the
conversation is done.

Repeater
 A repeater is a device that amplifies a signal being transmitted
on the network. It is used in long network lines, which exceed
the maximum rated distance for a single run.
 Kinds of Repeaters: amplifier and signal repeater.
Bridge
 A bridge is a device that lets link two networks together.
 Bridges are smart enough to know which computers are on
which side of the bridge, so they allow only those messages
that need to get to the other side of the bridge.

Router
 A device that works like a bridge but can handle different
protocols is known as a router. For example, a router can link
Ethernet to a mainframe.
How a router functions?
 Routers use a more complete packet address to determine
which router or workstation should receive each packet next.
 Based on a network road map called a routing table, routers can
help ensure that packets are travelling the most efficient paths
to their destinations.

Gateway
 A gateway is a device that connects dissimilar networks. A
gateway operates at the highest layer of network abstraction.
 It expands the functionality of routers by performing the data
translation and protocol conversion.
 It is needed to convert Ethernet traffic from the LAN. To
SNA(System Network Architecture) traffic on a legacy system.
 It then routes the SNA traffic to the mainframe. When the
mainframe answers, the reverse process occurs.

Wireless vs Mobile Computing
 Wireless refers to the method of transferring information
between a computing device and, such as PDA and a data
source, such as an agency data base server, without physical
connection.
 Mobile simply describing a computing device that is not
restricted to a desktop.
 Wireless communication is simply a data communication
without the use of Landlines.
 Mobile computing means that the computing device is not
continuously connected to the base or central network.

GSM
 GSM is short for Global System for Mobile communications,
which is one of the leading digital cellular systems.
 The GSM standard for digital cell phones was established in
the mid 1980s.
 GSM uses simply Switch Subscriber Identification
Module(SIM) cards.
 GSM operates in the 900 MHz and 1800 MHz bands.

What is a SIM card?
 Subscriber Identity Module (SIM) is a chip card, the size of a
postage stamp.
 A SIM is a tiny computer chip that gives a cellular device its
unique phone number.
 It has memory, processor and the ability to interact with the
user.

CDMA
 CDMA is a short Code Division Multiple Access, a digital
cellular technology that uses spread spectrum techniques.
 It is a form of spread spectrum, which simply means that data
is sent in small pieces over a number of the discrete frequencies
available for use at any time in the specified range.
WLL (Wireless in Local Loop)
• WLL is meant to server subscriber at homes or offices.
• The WLL system can operate with GSM handsets/mobile units,
as well as GSM compatible subscriber units.
Advantages
 Do not significantly suffer from weather damage, vandalism
and accidents.
 Offers better bandwidth than traditional telephone system.

GPRS
 GPRS is the abbreviation for General Packet Radio Service.
 It is used for wireless communication using a mobile device.
How does a GPRS work?
 The information is split into the smaller units or packets and
sent through the network and is reassembled at the receiving
end.
 GPRS provides a high speed data transfer between 56 kbps to
114 kbps.

WLL(Wireless in local loop)
 WLL is meant to server subscribers at homes or offices.
 WLL system can operate with GSM handsets/mobile units, as
well as with GSM compatible subscriber units.
Advantages
 Do not significantly suffer from weather damage, vandalism
and accidents.
 Offers better bandwidth than traditional telephone systems.

1G, 2G, 3G, 4G and 5G Networks
 The “G” in wireless networks refers to the “generation” of the
underlying wireless network technology.
1G networks
o (NMT, C-Nets, AMPS, TACS) are considered to be the first
analog cellular systems, which started early 1980s. There were
radio telephone systems even before that.
2G networks
o (GSM, CDMAOne, D-AMPS) are the first digital cellular
systems launched early 1990s, offering improved sound
quality, better security and higher total capacity.

3G Networks
 3G is a specification for the third generation(analog cellular
was the generation, digital PCS the second) of mobile
communication technology.
4G networks
 Support for Multiple Applications and Services
 Quality of Service
 Network Detection and Network Selection

5G Network
 The cellular concept was introduced in 5G technology stands for 5th
Generation Mobile Technology.
 5G technology has changed the means to use cell phones within very
high bandwidth.
Features
 5G technology offers high resolution for crazy cell phone user and
bi-directional large bandwidth shaping.
 It offers subscribers supervision tools for fast action.
 The high quality services of 5G technology based on Policy to avoid
error.
 The uploading and downloading speed of 5G technology is touching
the peak.

EDGE
 Enhanced Data rates for Global Evolution(EDGE) are a ratio
based mobile high speed data transfer. It allows data
transmission speeds of 384 kbps to be achieved when all time
slots are used.
 EDGE was formally called GSM384.
Applications in networking
SMS
Chat
Video Conferencing

SMS
 Short Message Service is the transmission of short text
messages to and from a mobile phone, fax machine and/or IP
address.
 Message must be no longer than some fixed number of alpha-
numeric characters and contains no images and graphics.
Chat
 Chatting is the most fantastic thing on internet. It is like a text
phone.
Video Conferencing (Video Phone)
 People who have a multimedia PC with camera and video
compression hardware, access to internet over an ordinary
telephone line , and videophone software can see each other
while talking, which is what is called VideoConferencing.

Wi-Fi
 Wireless Fidelity, line frohich lets you connect to the internet
without a direct linefrom your PC to ISP.
 For Wi-Fi to work you need:
 A broadband internet connection.
 A wireless router.
 A laptop or desktop with a wireless internet card or external
wireless adapter.
Wi –Fi hotspots
 A hotspot is a venue that offrers Wi-Fi access.
 There are Wi-Fi hotspots in thousands of locations around the
world.

WiMax
 WiMax is a wireless digital communication system.
 WiMax can provide Broadband Wireless Access (BWA) upto
30 miles for fixed stations and 3-10 miles for mobile stations.
 WiMax requires the tower called WiMax Base station, which is
connected to the internet using a standard wired high speed
connection.
 The internet connectivity to an end user is provided through
microwave link between the tower and the user end-point,
known as WiMax subscriber unit.

Network Security
 The problems encountered under network security can be
summarized as follows:
1. Physical Security Holes. When individuals gain unauthorized
physical access to a computer and temper with files.
2. Software Security Holes: When badly written programs or
’privileged’ software are compromised into doing things that
they should not be doing.
3. Inconsistent usage holes: When a system administrator
assembles combination of hardware and software such that
the system is seriously flawed from a security point of view.

Protection Methods
1. Authorization: It determines whether the service provider has
granted access to the web service to the requester.
2. Authentication: Authentication involves accepting credentials from
the entity and validating them against an authority. Also termed as
Password Protection.
3. Encrypted Smart cards: An encrypted smart card is a handheld
smart card that can generate a token that a computer system can
recognize. Every time a new and different token is generated,
which even though cracked or hacked, cannot be used later.
4. Bio Metric systems: They form the most secure level of
authorization. It involve some unique aspects of a person’s body
such as fingerprints, retinal patterns etc to establish his/her identity.

5. Firewall:
 A system designed to prevent unauthorized access to or from a
private network is called a firewall.
 They can be implemented in both hardware and software or
combination of both.
 There are several types of firewall techniques:
I. Packet Filter: Looks as each packet entering or leaving the network
and accepts or rejects it based on user defined rules.
II. Application Gateway: It applies security mechanism to specific
applications such as FTP and Telnet services.
III. Circuit Level Gateway: It applies security mechanism when a
connection is established.
IV. Proxy Server:It effectively hides the true network addresses.

Cookies
 Cookies are the messages that a web server transmits to a web
browser so that a web server can keep track of the user’s
activity on a specific web site.
Hackers and Crackers
 The crackers are the malicious programmers who break into
secure systems where as hackers are more interested in gainig
the knowledge about computer systems.
Cyber law: It is generic term, which refers to all the legal and
regulatory aspects of internet and the www.

India’s IT act
 In India the cyber laws are contained in the information
technology act, 2000 which was notified on 17 october 2000.
 The act aims to provide the legal infrastructure for ecommerce
in India by governing the transactions through the internet and
other electronic medium.

Viruses
 Computer Virus is a malicious program that requires a host
and is designed to make a system sick, just like real virus.
 They can replicate themselves.
Types of viruses:
1. File Infectors-Either infect executable files or attach
themselves to a program file and create duplicate files.
2. Boot Sector virus-Install themselves on the beginning tracks
of a hard drive or the Master boot record.
3. Macro Viruses: Infect data files such as electronic
spreadsheets or database of several software packages.
4. Network viruses- Use protocols and commands of computer
network to spread themselves on the network.

Virus Prevention
 Never use a foreign disk or CD without scanning for viruses.
 Always scan files downloaded from the internet or other
sources.
 Never boot your PC from a floppy unless you are certain that it
is virus free.
 Write protect your disks.
 Use licensed software.
 Password Protect your PC.
 Install and use antivirus software.
 Keep antivirus software up to date.

Reference: NCERT book and Internet source

Networking concepts by Sachidananda M H

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