Networking and Internet I-109
The advantages of mesh topology are as follows:
• If one link becomes unusable, the entire system does not get disabled.
• The use of large number of links eliminates network congestion.
The disadvantages of mesh topology are as follows:
• The amount of cabling required is very large.
• As every node is connected to the other, installation and reconfiguration are very difficult.
• The amount of hardware required in this type of topology makes it expensive to implement.
3. Write a short note on LAN, MAN and WAN.
Ans: A network can be as few as several personal computers on a small network or as large as the
Internet, a worldwide network of computers. Today, when talking about networks, we are generally
referring to three primary categories: Local Area Network (LAN), Metropolitan Area Network (MAN)
and Wide Area Network (WAN).
Local Area Network (LAN)
A LAN is a computer network that covers only a small geographical area (usually within a square mile
or less) such as an office, home or building (Figure 6.6). In a local area network, connected computers
have a network operating system installed onto them. One computer is designated as the ‘file server’,
which stores all the software that controls the network. It also stores the software that can be shared by
the computers attached to the network. Other computers connected to the file server are called ‘worksta-
tions’. The workstations can be less powerful than the file server and they may have additional software
on their hard drives. On most LANs, cables are used to connect the computers. Generally, LAN offers
a bandwidth of 10–100 Mbps.
Figure 6.6 Local Area Network
Metropolitan Area Network (MAN)
A MAN is a network of computers spread over a ‘metropolitan’ area such as a city and its suburbs. As the
name suggests, this sort of network is usually reserved for metropolitan areas where the city bridges its
local area networks with a series of backbones, making one large network for the entire city (Figure 6.7).
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I-110 Computer Fundamentals
It may be a single network such as a cable television network or it may be a means of connecting a number
of LANs. Note that MAN may be operated by one organization (a corporate with several offices in one
city) or be shared and used by several organizations in the same city.
D E L H I
D E L H I
Figure 6.7 Metropolitan Area Network
Wide Area Network (WAN)
A WAN is a system of interconnecting many computers over a large geographical area such as cities,
states, countries or even the whole world (Figure 6.8). These kinds of networks use telephone lines, sat-
ellite links and other long-range communications technologies to connect. Such networks are designed
Figure 6.8 Wide Area Network
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to serve an area of hundreds or thousands of miles such as public and private packet switching networks
and national telephone networks. For example, a company with offices in New Delhi, Chennai and
Mumbai may connect the LANs for each of those locations to each other through a WAN. Although a
WAN may be owned or rented by private business, it is usually a public network designed to connect
small- and intermediate-sized networks together. The largest WAN in existence is the Internet.
4. List any four advantages offered by WAN.
Ans: WAN offers many advantages to the business organizations. Some of these advantages are as
follows:
• It offers flexibility of location because not all the people needing to use the same data have to work
at the same site.
• Communication between branch offices can be improved using e-mail and file sharing.
• It facilitates a centralized company-wide data backup system.
• Companies located in a number of small, interrelated offices can store files centrally and access
each other’s information.
5. Explain various hardware devices used in computer network. Also give their functions.
Ans: Networks are becoming more complicated and more pervasive every day. Therefore, to reduce
the complexity, various network devices have been developed. ‘Network devices’ (or ‘hardware devices’)
are those devices that help nodes to get connected in a network for efficient communication. Network
devices include network interface card (NIC), repeater, hub, bridge, switch, router and gateway.
Network Interface Card (NIC)
It is a hardware device that connects clients, servers and peripherals to the network through a port.
Most network interfaces come as small circuit board that can be inserted onto one of the computer
motherboard’s slots. Alternatively, modern computers sometimes include the network interface as part
of their main circuit boards (motherboards). Each network interface is associated with a unique address
called its ‘media access control’ (MAC) address. The MAC address helps in sending information to
the intended destination. Network interface cards are the major factor in determining the speed and
performance of a network. It is a good idea to use the fastest network card available for the type of
workstation one is using.
Repeater
It is the most basic device on a network. Signals that carry information within a network can travel a fixed
distance before attenuation endangers the integrity of the data. A repeater installed on the link receives
signal, regenerates it and sends the refreshed copy back to the link. Doing this means that the new signal
is clean, free from any background noise introduced while travelling down the wire. Repeaters are most
commonly used to extend a network. All network cable standards have maximum cable length specifica-
tion. If the distance between two network devices is longer than this specification, a repeater is needed
to regenerate the signal. Without the repeater, the signal will be too weak for the computers on each end
to reliably understand. A good example of the use of repeaters would be in a LAN using a star topology
with unshielded twisted pair cabling. The length limit for unshielded twisted pair cable is 100 metres. The
repeater amplifies all the signals that pass through it allowing for the total length of cable on the network
to exceed the 100 metres limit. Nonetheless, repeaters have no in-built intelligence and they do not look at
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I-112 Computer Fundamentals
the contents of the packet while regenerating the signal. Thus, there is no processing overhead in sending
a packet through a repeater. However, a repeater will repeat any errors in the original signal.
Hub
It is a small box that connects individual devices on a network, so that they can communicate with one
another. The hub operates by gathering the signals from individual network devices, optionally ampli-
fying the signals and then sending them onto all other connected devices. Amplification of the signal
ensures that devices on the network receive reliable information. A hub can be thought of as the centre
of a bicycle wheel, where the spokes (individual computers) meet.
Nowadays, the terms repeater and hub are used synonymously, but actually they are not same.
Although at its very basic level, a hub can be thought of as a multi-port repeater. Typically, hubs have
anywhere from 4 to over 400 ports. When a signal is received on one port of the hub, it is regenerated
out to all the other ports. It is most commonly used to connect multiple machines to the same LAN.
Administrators connect a computer to each port on the hub, leaving one port free to connect to another
hub or to a higher-level device such as a bridge or a router.
Bridge
This device allows the division of a large network into two or more smaller and efficient networks.
It monitors the information traffic on the both sides of the network, so that it can pass packets of infor-
mation to the correct location. Most bridges can ‘listen’ to the network and automatically figure out the
address of each computer on both sides of the bridge. A bridge examines each packet as it enters though
one of the ports. It first looks at the MAC address of the sender and creates a mapping between the port
and the sender’s MAC address. It then looks at the address of the recipient, comparing the MAC address
to the list of all learned MAC addresses. If the address is in the list, the bridge looks up the port number
and forwards the packet to the port where it thinks the recipient is connected. If the recipient’s MAC
address is not in the list, the bridge then does a flood; it sends the signal to all the ports except the one
from where it was received. As a result, a bridge reduces the amount of traffic on a LAN by dividing it
into two segments. It inspects incoming traffic and decides whether to forward or discard it.
Bridges can be used to connect networks with different types of cabling or physical topologies. They
must, however, be used between networks employing the same protocol. Since a bridge examines the
packet to record the sender and lookups the recipient, there is overhead in sending a packet through a
bridge. On a modern bridge, this overhead is miniscule and does not affect network performance.
Switch
It is a multi-port bridge. It connects individual devices on a network, so that they can communicate with
one another. The behaviour of a switch is same as that of a bridge. It is capable of inspecting the data
packets as they are received, determining the source and destination device of that packet and forwarding
that packet appropriately. The difference is that most switches implement these functions in hardware
using a dedicated processor. This makes them much faster than traditional software-based bridges.
Router
It is an essential network device for interconnecting two or more networks. The router’s sole aim is to
trace the best route for information to travel. As network traffic changes during the day, routers can
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Networking and Internet I-113
redirect information to take less congested routes. A router creates and/or maintains a table, called a
routing table, which stores the best routes to certain network destinations. While bridges know the
addresses of all computers on each side of the network, routers know the addresses of computers,
bridges and other routers on the network. Routers can even ‘listen’ to the entire network to determine
which sections are the busiest. They can then redirect data around those sections until they clear up.
Routers are generally expensive and difficult to configure and maintain. They are critical components
of a network and if they fail, the network services will be significantly impaired. Most routers operate
by examining incoming or outgoing signals for information at the network layer. In addition, they can
permit or deny network communications with a particular network.
Gateway
It is an internetworking device, which joins networks operating on different protocols together. It is also
known as ‘protocol converter’. A gateway accepts the packet formatted for one protocol and converts
the formatted packet into another protocol. For example, a gateway can receive e-mail message in one
format and convert it into another format. A gateway can be implemented completely in software, hard-
ware or as a combination of both. One can connect systems with different protocols, languages and
architecture using a gateway.
6. Define Internet. Write a brief history of Internet.
Ans: The word ‘Internet’ is derived from two words: Interconnection and Networks. Also referred
to as ‘the Net’, Internet is a worldwide system of computer networks, that is, a network of networks,
which allows the participants (users) to share information. It consists of thousands of separately
administered networks of various sizes and types. Each of these networks comprises tens of thousands
of computers. Moreover, the total number of users of the Internet is known to be in millions. This
high level of connectivity encourages an unparalleled degree of communication, resource sharing and
information access.
The Internet traces its origin back to the 1960s, when it grew out of an experiment conducted by the
US Department of Defense. They wanted to create a computer network that could continue to function
in the event of a disaster, such as a nuclear war. Even if a part of the network was damaged or destroyed,
the rest of the system would continue to work. That network was known as ‘ARPANET’ (Advanced
Research Projects Agency Network), which linked US scientific and academic researchers. It is the
forerunner of today’s Internet.
By the 1970s, ARPA (Advanced Research Projects Agency) helped in the development of a new pro-
tocol known as TCP/IP (Transmission Control Protocol/Internet Protocol) for transferring data between
the networks. The TCP/IP is the core of the Internet. Internet really took off in the 1980s when National
Science Foundation (NSF) used ARPANET to link its five regional super computer centres at major
universities, so that many users could share their work. Later on, NSF created ‘NSFNET’ (National
Science Foundation Network) a series of networks for research and education and communication.
Initially, NSFNET allowed only academic research. Over the time, this network expanded to include
sites for business, universities, government etc. and finally becoming a network consisting of millions
of computers, now known as the Internet.
In the 1980s, Usenet newsgroups and Electronic Mail (e-mail) came into picture. To keep track of
the information on the Internet, indices such as Archie and the Wide Area Information Server (WAIS)
were also created in this decade. To give users an easy-to-use interface to work with, the University of
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