01 computer communication and networks v

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Communication And Network Concepts
Network:-Network is an interconnected collection of autonomous computer.
Two computers are said to be interconnected if they are capable to exchanging
information. Autonomous means that no computer on network can start, stop, or
control another.

Network

Need for Networking:-
(a) Resource sharing (b) Reliability(c) Cost factor (d) Communication medium
(e) Access to Remote Database
Evolution of Networking:-
Evolution of networking started way back in 1969 by the development of first
network called APRANET, which led to the development of Internet.
(i) ARPANET:- The acronym of ARPANET is Advanced Research Projects
NETwork, was started to connect computers at U.S. Department of Defense and
Universities.
In 1980s, National Science Foundation started to make a high capacity network
called NSFnet to be used strictly for academic and engineering research.

Prepared By Sumit Kumar Gupta, PGT Computer Science

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In 1990s the internetworking of ARPANET, NSFnet and other private networks
resulted into Internet.
(ii)The Internet:-The Internet is a super-network which connects the worldwide
smaller networks together and allows all the computers to exchange the information.
Internet uses TCP/IP protocols (Transmission control Protocol/ Internet Protocol)
for communication.
(iii)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 3-D environments.

Switching Techniques

*Switching techniques are used for transmitting data across networks.

There are a number of ways to perform switching:

 Circuit Switching
 Packet Switching
 Message Switching
 Cell Switching

Circuit Switching-

This method involves the physical interconnection of two devices. A good example
of circuit switching involves the Public phone network. A data example would be
the classic A/B switch!

Packet Switching-


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Packet Switching techniques switch packets of data between destinations.
Traditionally, this applied to X.25 techniques, but this also applies to TCP/IP and
IPX/SPX routers also. Proprietary Frame Relay switches can switch voice signals.

Message Switching-

Message Switching techniques were originally used in data communications. An
example would be early "store and forward" paper tape relay systems. E-Mail
delivery is another example of message switching. In voice systems, you can find
Voice Mail delivery systems on the Internet. The classic "forward voice mail"
example.

Cell Switching-

Cell Switching is similar to packet switching, except that the switching does not
necessarily occur on packet boundaries. This is ideal for an integrated environment
and is found within Cell-based networks, such as ATM. Cell-switching can handle
both digital voice and data signals.

Data Communications Terminologies:-

1. Data Channel- a channel is the medium to carry information or data from one
point to another.
2. Baud-It is the unit of measurement for the information carrying capacity of a
communication channel. The Baud is synonymous with bps (bits per second).


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3. Bandwidth-Technically the bandwidth refers to the difference between the
highest and lowest frequencies of a transmission channel. High bandwidth
channels are called broadband and low bandwidth channels are called
narrowband.

*The speed of bandwidth is represented by bits per second (bps).

*Frequency of bandwidth is measured in cycles per second i.e., hertz.
1 Kilohertz (KHz) =1000Hz 1Megahertz (MHz) =1000 KHz.

1Gigahertz (MHz) =1000MHz. 1Terahertz (MHz) =1000GHz.

4. Data Transfer Rates:-The transfer rate represents the amount of data
transferred per second by a communication channel.

*Data rate measured in units of bits per second (bps), bytes per second (Bps) or
baud.

1 KB=210=1024 bytes 1 MB=1024 KB

1 GB=1024 MB 1 TB=1024 GB

Transmission media: - It means the physical materials that are used to transmit data
between computers.
Communication media are categorized into two types.
1. Guided Media(Cables)


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2. Unguided Media(Waves)

1. Guided Media-

Cable

For communications between computers that are linked by cable, there are three
choices.

Twisted (phone line) It consists of two identical wires wrapped
Pair together in a double helix. It is of two types-unshielded
Cable Twisted Pair Cable (UTP) ,and Shielded Twisted Pair
Cable(STP).

Advantage: i) It is simple, easy to install &
maintain.
ii) It is physically flexible and very
cheap.
iii) It has low weight & can be easily
connected.

Disadvantage: i) It is incapable carrying a signal
over long distances without the
use of repeaters.
ii) It is not suitable for broadband
application due to low
bandwidth( 1 MBPS to 10
MBPS)


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Coaxial (round insulated wire) It consists of a solid wire core
cable surrounded by one or more foil or wire shields, each
separated by some kind of plastic insulator.it is widely used
for television signals.

Advantage: i)Data transfer characteristics is better than
twisted-pair cables.
ii) it can be used for broadband
transmission due to higher bandwidth(upto
400 MBPS)

Disadvantage: i) Expensive compare to twisted
pair cables.
ii) It is not compatible with twisted
pair cables.

Fiber (glass fibers) The data to be transmitted is modulated onto
optic line the light beam using frequency modulation techniques.
Advantage: Smaller
Lighter
Faster (speed of light)
No interference

Disadvantage: Expensive
Harder to install and modify


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2.Unguided Media-

Broadcast

For longer distances or when cables are not practical, other transmission media come
into play. We're getting really high tech here.

It may seem odd to call microwaves, radio waves, or light a "physical" medium. All
are electromagnetic in nature. Sometimes they are treated by scientists like streams
of teeny, tiny particles and other times like waves on the beach. In their "particle"
life, they do behave like a bunch of physical particles. So it's not quite as odd as it
first appears. (But all those electromagnetic things are plenty odd.)

Radio Any Radio setup has two parts. i) Transmitter. ii) Receiver
wave Both transmitter & Receiver use antennas to radiate &
capture the radio signal.
Advantage: Flexible
Cheaper
Portable
Ease of communication
Disadvantage: Slower data transfer than hard-wired
methods
Insecure communication

Microwave Microwave signals are used to transmit data without the
use of cables. It is similar to radio & television signals for
long distance communication. It consists of transmitter,
receiver and atmosphere.


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Advantage: Speed of light
ease of communication.
Disadvantage: Insecure communication.
High cost of design & maintenance.

Satellite The smart phase of communication of global standard is
made possible with the aid of satellites. Signals are
retransmitted back to the receiver at different frequencies
on a global basis.

Advantage: Always in sight
Disadvantage: Expensive uplink and downlink facilities

Infrared This type of transmission uses infrared light to send data.
Like TV remotes, wireless speakers.
Advantage: Flexible
Cheaper
Secure communication
Portable
Ease of communication
Disadvantage: Slower data transfer than
hard-wired methods

Network Devices:-

• 1. Modem:- Allows computers to communicate over a telephone line


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• Enable communication between networks or connecting to the world beyond
the LAN

Cannot send digital signal directly to telephone line

Sending end: MODulate the computer’s digital signal into analog signal and
transmits

Receiving end: DEModulate the analog signal back into digital form

Modems come in two varieties:

1. Internal modems the modems are fixed within the computer.
2. External modems the modems that are connected externally to a
computer as other peripherals are connected.

RJ-45:-RJ-45 is short for Registered Jack -45 is an eight wire connector, which is
used to connect computers on the local area networks i.e., LANs especially
Ethernets.


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Ethernet Card:-The computers that are part of Ethernet have to install a special
card called Ethernet Card. An Ethernet card contains connections for either coaxial
or twisted pair cables. Ethernet cards are sometimes known as network interface
cards (NICs).
Hub:-A hub is a hardware device used to connect several computers together. Hubs
can be either passive or active.
Active hubs electrically amplify the signal as it moves from one connected device to
another. It works like Repeaters.
Passive hubs allow the signal from one computer to another without any change.


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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.

Hub 3.3Mbps
10Mbps
3.3Mbps
Switch
3.3Mbps
10Mbps
10Mbps

Repeater:-It is a network device that amplifies and restore signals from long
distance transmission.

Bridge:-A bridge is a network device that establishes an intelligent connection
between two local networks with the same standard but with different types of
cables.
Router:-A router is a network device that is used to separate different segments in a
network to improve performance and reliability. It works like a bridge but can
handle different protocols.
Gateway:-A gateway is a network device that connects dissimilar networks. It
establishes an intelligent connection between local network and external networks
with completely different structures.


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A gateway node often acts as proxy server and a firewall.
Different topologies:-
There are four basic types of LAN topology.

 STAR
 BUS
 TREE

Linear Bus-

A linear bus topology consists of a main run of cable with a terminator at each end
(See fig. 1). All nodes (file server, workstations, and peripherals) are connected to
the linear cable. Ethernet and Local Talk networks use a linear bus topology.

Fig. 1. Linear Bus topology

Advantages of a Linear Bus Topology

 Easy to connect a computer or peripheral to a linear bus.
 Requires less cable length than a star topology.


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Disadvantages of a Linear Bus Topology

 Entire network shuts down if there is a break in the main cable.
 Terminators are required at both ends of the backbone cable.
 Difficult to identify the problem if the entire network shuts down.
 Not meant to be used as a stand-alone solution in a large building.

Star -

A star topology is designed with each node (file server, workstations, and
peripherals) connected directly to a central network hub or concentrator (See fig.
2).Data on a star network passes through the hub or concentrator before continuing
to its destination. The hub or concentrator manages and controls all functions of the
network. It also acts as a repeater for the data flow. This configuration is common
with twisted pair cable; however, it can also be used with coaxial cable or fiber optic
cable.

Fig. 2. Star topology


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Advantages of a Star Topology

 Easy to install and wire.
 No disruptions to the network then connecting or removing devices.
 Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

 Requires more cable length than a linear topology.
 If the hub or concentrator fails, nodes attached are disabled.
 More expensive than linear bus topologies because of the cost of the
concentrators.

The protocols used with star configurations are usually Ethernet or LocalTalk.
Token Ring uses a similar topology, called the star-wired ring.

Tree-

A tree topology combines characteristics of linear bus and star topologies. It consists
of groups of star-configured workstations connected to a linear bus backbone cable
(See fig. 4). Tree topologies allow for the expansion of an existing network, and
enable schools to configure a network to meet their needs.


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Fig. 4. Tree topology

Advantages of a Tree Topology

 Point-to-point wiring for individual segments.
 Supported by several hardware and software venders.

Disadvantages of a Tree Topology

 Overall length of each segment is limited by the type of cabling used.
 If the backbone line breaks, the entire segment goes down.
 More difficult to configure and wire than other topologies.

Types of Networks:-

1.Local-area networks (LANs):-
->Operate within limited (local) geographical area


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->Allow multi-access to high bandwidth media
->Control network privately under local administration
->Provide full-time connectivity
Connect physically adjacent devices

Some common LAN technologies are:

 Ethernet

 Token Ring

 FDDI

2.Wide-area networks (WANs):-
->Operate over a large geographical area
->Use serial interfaces (e.g. modem) operating at lower speeds
->Provide full-time and part-time connectivity
->Connect devices separated over wide areas

Some common WAN technologies are:

 Modems

 Digital Subscriber Line (DSL)

 Cable modem

3.Metropolitan Area Network(MAN):-MAN are the networks spread over a
city. For example, cable TV networks.


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Protocols:-It is a set of rules which govern data communication. It is formal
description of message formats and the rules that two or more machines must follow
to exchange those messages.
1.FTP(File Transfer Protocol):-
FTP allows you to transfer files between two computers on the Internet. FTP is a
simple network protocol based on Internet Protocol and also a term used when
referring to the process of copying files when using FTP technology.

Advantages:-
i) It is very useful to transfer files from one network in an
organizatrion to another.
ii) It is an effective way to get a geographically dispersed group to co-
operate on a project.
iii) It is a potent and popular way to share information over the internet.
Objectives of FTP:-
i) to prompt sharing of files
ii) to encourage indirect or implicit use of remote computers.
2.TCP/IP(Transmission control protocol/Internet protocol):-
Transmission Control Protocol (TCP) and Internet Protocol (IP) are two distinct
network protocols, technically speaking. TCP and IP are so commonly used
together, however, that TCP/IP has become standard terminology to refer to either or
both of the protocols.

IP corresponds to the Network layer (Layer 3) in the OSI model, whereas TCP
corresponds to the Transport layer (Layer 4) in OSI. In other words, the term TCP/IP


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refers to network communications where the TCP transport is used to deliver data
across IP networks.

TCP/IP application use 4 layers.

i) an application protocol such as mail.
ii) A protocol such as TCP that provides services need by many
applications.
iii) IP, which provides the basic services of getting datagrams to their
destination.
iv) The protocols needed to manage a specific physical medium,such as
Ethernet or a point to point line.

*Datagram is a collection of the data that is sent as a single message.

3.HTTP(Hypertext Transfer Protocol):-
It is an application –level protocol with the lightness and speed necessary for
distributed ,collaborative hypermedia systems.
4.SLIP/PPP:-
SLIP(Serial Line Internet Protocol) /PPP(Point to Point Protocols)
provide the ability to transport TCP/IP traffic ever serial line between two
computers.
Telnet(TErminaL NETwork):-Telnet is an Internet utility that lets you log onto
remote computer systems.


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Wireless/Mobile communication:- This is simply 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(Globle System for Mobile):- uses narrowband TDMA(Time Division
Multiple access) which allows eight simultaneous calls on the same radio
frequency.
CDMA(Code Division Multiple Access):-uses a speed –spectrum technique
where data is sent in small pieces over a number of discrete frequencies available
for use. Each user’s signal is spread over the entire bandwidth by unique
spreading code. At the receiver end the same unique code is used to recover the
signal.

WLL(Wireless in Local Loop):-It is a system that connects subscribers to the
public switched telephone(or PBX) network using radio signal as a substitute for
other connecting media.

3G(third Generation):-3G mobile communication technology is a broadband,
packet-based transmission of text, digitized voice, video and multimedia at data rates
up to and possibly higher than 2Mbps provides set of services to mobile computer
and phone users.1

SMS(Short Message Service):-It is the transmission of short text messages to
and from a mobile phone ,fax machine and/or IP address.

Voice Mail:-It refers to e-mail system that supports audio.

Email(Electronic mail):-It is sending and receiving message s by computer.


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Advantages of email:-i) low cost.

ii) Speed

iii) Waste reduction.

Chat:-Online textual talk,in real time, is called Chatting.

Video Conferencing:- A two-way videophone conversation among multiple
participants is called Video Conferencing.

Network Security Concepts:-

1.Cyber Law:- Cyber law (also referred to as Cyberlaw) is a term used to describe
the legal issues related to use of communications technology, particularly
"cyberspace", i.e. the Internet.. In essence, cyber law is an attempt to apply laws
designed for the physical world to human activity on the Internet.

Cyber law is impotant because it touches almost all aspects of transactions activities
on aaand concerning the Inernet ,the World Wide Web and Cyberspace.

Virus threats and prevention:- Today’s threats bring us any combination of
Trojans, worms, and viruses in one tidy package.Antivirus software is must-have
protection. Keep it installed, enabled, and up-to-date at all times. But though
antivirus software is critical, alone it's not enough to keep you protected. Follow

sound security practices, install a firewall, and use other adjunct protection in
combination with your own common sense.


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Cookies:- are messages that Web server transmits to a Web browers so that Web
server can keeo track of the user’s activity on a specific Web site.It is a text sent by
a server to a web client (usually a browser) and then sent back unchanged by the
client each time it accesses that server.

Cookies have six parameters that can be passed to them:-

Name,Value,expiration date ,path,domain and secure server for Cookies..

Hackering:-

Hacker (computer security), someone who breaks computer and network security.

Hacker is a person who enjoys learning programming languagees and computer
systems and can often be considered an expert on the subject.Hackers themselves
maintain that the proper term for such individual is cracker.

Thus Crackers are the malicious parogrammers who break into secure systems
whereas Hackers are more interested in gaining knowledge about computer systems
and possibly using this knowledge for playful pranks.

Firewall:-The system designed to prevent unathorized to or from a private network
is called Filewall.

XML (eXtensible Markup Language) : -Xml is a markup language for
documents containing structured information.

HTML(Hypertext Markup Language) :-It is a language which is use to web
page design.It is ajust page-layoand hyperlink specificationut .


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DHTML ( Dynamic Hypertext Markup Language): - DHTML is a TERM
describing the art of making dynamic and interactive web pages.it is HTML
extension that will enable a Web page to react to user input without sending request
to the web server.

URL(Uniform Resource Locator):-Internet addresses in a special format called
a URL.

i.e. http:/www.yahoo.com.

DNS(Domain Name System):- An Internet address which is character based is
called a DNS.
Website:- A location on a net server is called Web Site.A document that uses
HTTP is called Web Page.
Web browser:-It is a WWW(World Wide Web) client that navigates through the
WWW and displays web pages.
Web server:-It is a WWW server that responds to the requests made by web
browsers.

Web hosting:-It is a means of hosting a web-server application on a computer
system through which electronic content on the internet is readily available to any
web-browser client.

*The computer system providing the web-hosting is known as web-server or the
web-host.


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Solved Questions of AISSE Computer Science (2008)
Q 1.What is modem?
Q.2Expand the following term
PPP
GSM
XML
HTTP
Q.3 how is Hacker different from Cracker?
Q4.China Middleton Fashion is planning to expand their network in India, Starting
with two cities in India to provide infrastructure for distribution of their product. The
company has planned to set up their main office units in Chennai at three different
location and have named their offices as “Production Unit” “Finance Unit” and
“Media Unit”. The company has its corporate unit in Delhi.
A rough layout of the same is as follow:


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INDIA
Corporate unit
(DELHI)
Production unit

Finance unit

Media unit

Approximate distance between these Units as follow:

From TO Distance
Production unit Finance Unit 70 Mtr
Production unit Media Unit 15 KM
Production unit Corporate Unit 2112 KM
Finance Unit Media Unit 15KM

In continuation of the above, The company expert have planned to install the
following number of computers in each of their office units

Production 150
Unit


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Finance Unit 35
Media Unit 10
Corporate Unit 30

(i) Suggest the kind of network required(out of LAN,MAN,WAN)for
connecting each of the following office units:

 Production nit and Media unit
 Production Unit and Finance Unit

(ii) Which one of the following Device s will you suggest for connecting all
the Computers within each of their office units?
 Switch/Hub
 Modem
 Telephone

(iii) Which of the following communication media , will you suggest to be
produced by the company for connecting their local office units in
Chennai for very effective (High Speed) communication.
 Telephone Cable
 Optical Fiber
 Ethernet Card
(iv) Suggest a cable/wiring layout for connecting the Company’s S local office
units located in Chennai .Also suggest an effective method/technology for
connecting the company’s office unit located in Delhi.

Solved Answer of 2008

Q.1 Modem:-Modem is a Modulation Demodulation device that convert analog
signal to digital signal and vice versa.


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Q.2 Hackers are the ones who get into someone’s code or computer without any
malicious intention ,where as Crackers are the one’s who get into someone’s code
or computer with malicious intention.

Q.3
PPP(Point to point Protocol)
GSM(Global System for Mobile)
XML(eXtensible Markup Language)
HTTP(Hyper Text Transfer Protocol)

Q.4
(i) Production nit and Media unit: MAN
Production Unit and Finance Unit: LAN
(ii)Switch/Hub
(iii)Optical fiber

INDIA

Satellite
Antenna

Satellite
Signal Production unit

Optical
FiberQuestions:-
Corporate unit
Questions:-(iv)Optical Fiber/Star Topology
(DELHI)
Wireless/Satellite Link/Leased Line
Ethernet Finance unit
Media
Cable


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Very Short Questions:-
 What is Network? Why is it needed
 Explain Communication Channel
 Explain Different types of Network?
 Explain LAN topology?
 What is Bandwidth? How is it measured?
 What is the role of modem in communication?
 What is the different between Hub and Switch?
 Explain the Protocols?
 What is web hosting?
 What is video conferencing?
 What is Firewall?
 What is hacking?
Short Questions:-
 Discuss the various types of network?
 What is the difference between Internet and Intranet?
 Define network security. What is its need?
 Compare the Fiber and Coaxial Transmission Media.
 What is difference between Hackers and Crackers
 Expand and explain the following terms:
 XML,HTML,DHTML,GSM,HTTP,WWW,WLL,ISP,CDMA,SMS,FTP
 What is URL
 What is Protocols?
 Define the following term
Bridge, Repeater, mail, chatting TCP/IP,TELNET, Cookies

LONG ANSWER QUESTIONS:-

Q .1 The Great Brain Organization has set up its new Branch at Shrinagar for its
office and web based activities .It has 4 wings to building as shown in the diagram


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Wing Z Wing Y

Wing X Wing U

Center to center distance between various blocks
Wing X To Wing Z 50 m
Wing Z To Wing Y 70 m
Wing Y To Wing X 125 m
Wing Y To Wing U 80 m
Wing X To Wing U 175 m
Wing Z To Wing U 90 m
Number of computers

Wing X 50
Wing Z 30
Wing Y 150
Wing U 15

(i) Suggest a suitable layout of connection between the wings and topology.
(ii) Suggest a suitable place (i.e. wing) to house the server of this organization
with a suitable reason with justification
(iii) Suggest the placement of the following devices with justification.
(a)Repeater (b) Hub/Switch


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(iv) The Organization is planning to link its head office situated in the Delhi with
the offices of Shrinagar.Suggest a economic way to connect it: if the company is
ready to compromise on the speed of connectivity .Justify your Answer.

Ans: -
( i) BUS Topology

Wing Z Wing Y

Wing X Wing U

(ii) The most suitable place to house the server is Wing Y as it has the most number
of computers thus cabling cost will be reduced and traffic will be local
(iii) Repeater
(iv)Dial-up or Broadband.

Q.2. K.V. No1 in Bhubaneswar is setting up the network between its
different wings. There are wings named as CRPF(S),MANCHESWAR
(J),CUTTACK(A) and PURI(H).

Distance between various wings is given below:-

Wing A To Wing S 100 m
Wing A To Wing J 200 m
Wing A To Wing H 400 m


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Wing S To Wing J 300 m
Wing S To Wing H 100 m
Wing J To Wing H 450 m
Number of computers

Wing A 20
Wing S 200
Wing J 100
Wing H 50

(i) Suggest a suitable Topology for Networking the Computer of all Wings.
(ii) Name the wing where the server is to be installed
(iii) Suggest the placement of Hub/Switch in the network.
(iv) Mention an economic technology to provide internal accessing to all wings

Ans:-
(i)star topology
(ii)wing S
(iii)Hub/Switch will be required in all the wings
(iv)dial-up network

Submitted by :
Ramesh Singh (K.V. Bondamunda)
Deepa Behera(K.V. Rourkela)
Kusum Kumari(K.V.Hinoo, Ranchi)


01 computer communication and networks v

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