1. What is a network ? What are its goals and applications ?

 A network is an interconnected collection of autonomous

computers that can share and exchange information and resources.

Major goals and applications of networks are :

a) Resource Sharing — Through a network, data, software and

hardware resources can be shared irrespective of the physical
location of the resources and the user.
b) Reliability — A file can have its copies on two or more
computers of the network, so if one of them is unavailable, the
other copies could be used. That makes a network more reliable.
c) Reduced Costs — Since resources can be shared, it greatly
reduces the costs.
 d) Fast communication — With networks, it is possible to
exchange information at very fast speeds.
2. Briefly explain how Internet evolved.

 In 1969, ARPANET was started by U.S. Department of Defense to

connect computers at U.S. defense & different universities. In 1980s,
the National Science Foundation started NSFnet to make a high
capacity network to be used strictly for academic and engineering
research.

In 1990s, many private companies built their own networks, which

were later interconnected along with ARPANET and NSFnet to form
Internet. Later, the commercial Internet services came into picture,
which are running the Internet.

3. Write a short note on ARPAnet.

 ARPAnet (Advanced Research Projects Agency NETwork) is
regarded as the first computer network. It was started by the U.S.
Department of Defense in 1969 with the goal of connecting the
computers at different universities and U.S. defense. It laid the
foundations of today's internet. The users of this system began
exchanging data and messages on it. They were also able to play
long distance games and socialize with people who shared their
interests leading to its rapid expansion. The original ARPANET was
shut down in 1990.

4. How does Internet work ?

 In Internet, most computers are not connected directly to the

Internet. Rather they are connected to smaller networks, which in turn
are connected through gateways to the Internet backbone.

Internet functions in the following manner:

 a) At the source computer, the message or the file/document to
be sent to another computer is firstly divided into very small parts
called packets.
b) Each packet is given a number serial wise e.g., 1, 2, 3.
c) All these packets are then sent to the address of destination
computer.
d) The destination computer receives the packets in random
manner. If a packet is garbled or lost, it is demanded again.
e) The packets are reassembled in the order of their number and
the original message/file/document is obtained.
Every computer connected to the internet uses communication
protocols — Transmission Control Protocol(TCP) and Internet
Protocol (IP).

5. Write a short note on 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.

The Interspace is a vision of what the Internet will become, where

users cross-correlate information in multiple ways from multiple
sources. It is an applications environment for interconnecting spaces
to manipulate information.

6. What is a network ? What are necessary network elements ?

 A network is an interconnected collection of autonomous

computers that can share and exchange information and resources.

The necessary network elements are :

a) Hosts/Nodes
 b) Servers
c) Clients
d) Network hardware
e) Communication channel
f) Software
g) Network services
7. How is circuit switching different from message switching ?

 In circuit switching, a complete physical connection is established

between the sender and the receiver and then data is transmitted
from the source computer to the destination computer.

In message switching, no physical copper path is established in

advance between sender and receiver. Instead when the sender has
a block of data to be sent, it is stored in first switching office, then
forwarded later, one jump at a time until the data is delivered to the
destination computer. It works on the store and forward principle.
8.How does transmission take place across networks?

 Switching techniques are used for transmitting data across

networks. The switching techniques used are as follows:

a) Circuit switching — A complete physical connection is

established between the sender and the receiver and then data
are transmitted from the source computer to the destination
computer.
b) Message switching — In this form of switching no physical
copper path is established in advance between sender and
receiver. Instead when the sender has a block of data to be sent, it
is stored in first switching office, then forwarded later, one jump at
a time until the data is delivered to the destination computer.
c) Packet switching — A fixed size of packet which can be
transmitted across the network is specified. The message is
divided into packets and packets travel across hops.
9. What are communication channels ? Discuss various
communication channels available for networks.

 A communication channel is a means of communication between

two devices or workstations i.e., it refers to the medium used to carry
information or data from one point to another.

Communication channels can be grouped in two categories:

a) Guided media — These media include cables. There are

three basic types of cables :
i. Twisted-Pair Cables — These cables consist of two insulated
copper wires twisted around each other. These are also used
for short and medium range telephone communication.
ii. Coaxial Cables — A coaxial cable consists of one or more
small cables in protective covering. These are more expensive
than twisted pair cables but perform better.
 iii. Fiber-optic Cables — These cables are made of plastic or
glass and are about as thick as human hair. These cables are
highly durable and offer excellent performance but are
expensive.
b) Unguided media — These include waves through air, water or
vacuum. Unguided communication media are as follows:
i. Microwaves — The microwaves are similar to radio and
television signals and are used for long distance
communication. Microwave transmission consists of a
transmitter, receiver and the atmosphere.
ii. Radio-waves — The transmission making use of radio
frequencies is termed as radio-wave transmission.
iii. Satellites — Satellite communication use the synchronous
satellite to relay the radio signal transmitted from ground
station.
10.
i. Write some advantages and disadvantages of optical fibres.

Some advantages of optical fibres are:

a) It is immune to electrical and magnetic interference.

b) It is highly suitable for harsh industrial environments.
c) It guarantees secure transmission and has a very high
transmission capacity.
d) Fiber optic cables can be used for broadband transmission.
Some disadvantages of optical fibres are:

a) Fiber optic cables are quite fragile and may need special care to
make them sufficiently robust.
b) Connecting either two fibers together or a light source to a fiber
is a difficult process.
c) In order to incept the signal, the fiber must be cut and a detector
inserted.
 d) Light can reach the receiver out of phase.
e) Connection losses are common problems.
f) They are more difficult to solder.
g) They are the most expensive of all the cables.
ii. Write some advantages and disadvantages of coaxial cables.

Some advantages of coaxial cables are:

a) The data transmission characteristics of coaxial cables are

considerably better than that of twisted-pair cables.
b) They can be used as the basis for a shared cable network.
c) They can be used for broadband transmission.
d) They offer higher bandwidths — upto 400 Mbps.
Some disadvantages of coaxial cables are:

a) They are expensive as compared to twisted pair cables.

 b) They are not compatible with twisted pair cable.
iii) Write some advantages and disadvantages of twisted pair
cables.

Some advantages of twisted pair cables are:

a) It is simple.
b) It is easy to install and maintain.
c) It is physically flexible.
d) It has a low weight.
e) It can be easily connected.
f) It is very inexpensive.
Some disadvantages of twisted pair cables are:

a) It is incapable of carrying a signal over long distances without

the use of repeaters.
 b) It is unsuitable for broadband applications due to its low
bandwidth capabilities.
c) It supports maximum data rates of 1 Mbps without conditioning
and 10 Mbps with conditioning.
iv) Write some advantages and disadvantages of radio waves.

Some advantages of radio waves are:

a) Its transmission offers mobility.

b) It proves cheaper than cables.
c) It offers freedom from land acquisition rights.
d) It offers ease of communication over difficult terrain.
Some disadvantages of radio waves are:

a) Communication is highly insecure.

b) Its propagation is susceptible to weather effects like rains,
thunder storms etc.
v) Write some advantages and disadvantages of micro waves.

Some advantages of micro waves are:

a) It proves cheaper than cables.

b) It offers freedom from land acquisition rights.
c) It offers ease of communication over difficult terrain.
d) Microwaves have the ability to communicate over oceans.
Some disadvantages of micro waves are:

a) It is an insecure communication.
b) Signals from a single antenna may split up and propagate by
slightly different paths to the receiving antenna. When these out-of-
phase signals recombine, they interfere, reducing the signal
strength.
c) Its propagation is susceptable to weather effects like rains,
thunder storm, etc.
 d) Bandwidth allocation is extremely limited in case of microwaves.
e) The cost of design, implementation, and maintenance of
microwave links is high.
vi) Write some advantages and disadvantages of satellites.

Some advantages of satellites are:

1. The area coverage is quite large.

2. The laying and maintenance of intercontinental cable is difficult
and expensive and this is where the satellite proves to be the best
alterative.
3. The heavy usage of intercontinental traffic makes the satellite
commercially attractive.
4. Satellites can cover large areas of the Earth. This is particularly
useful for sparsely populated areas.
Some disadvantages of satellites are:
 a) Technological limitations preventing the deployment of large,
high gain antennas on the satellite platform.
b) Over-crowding of available bandwidths due to low antenna
gains.
c) The high investment cost and insurance cost associated with
significant probability of failure.
d) High atmospheric losses above 30 GHz limit carrier
frequencies.
11. What are types of twisted pair cables ?

The types of twisted pair cables are as follows :

a) Unshielded Twisted Pair (UTP) cable

b) Shielded Twisted Pair (STP) cable
12. What are types of coaxial cables ?

 The types of coaxial cables are as follows :

 a) Thicknet coaxial cable
b) Thinnet coaxial cable
13. What are the types of fiber optic cables ?

Answer

 The types of fiber optic cables are as follows :

a) Single mode fiber cable

b) Multimode fiber cable
14. What is bandwidth ? How is it measured ?

 Bandwidth refers to the width of allocated band of frequencies to a

channel. It is the difference between the highest and lowest frequencies
of a transmission channel. Bandwidth is directly proportional to the
amount of data transmitted or received per unit time.
In digital systems, bandwidth is data speed in bits per second (bps),
bytes per second (Bps), mega bytes per second (MBps).

In analog systems, bandwidth is measured in cycles per second —

kilohertz (kHz), megahertz (mHz), gigahertz (GHz) and terahertz (THz).

15. What do you understand by data transfer rates ?

 The data transfer rate represents the amount of data transferred per
second by communications channel or a computing or storage device.

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

16.In initial years, a modem providing a data rates of 56 kbps for

downloading and 14.4 kbps for uploading was considered a good
modem. How many bits per second could it download and
upload ?
 For downloading: 56 kbps = 56,000 bits per second (1 kilo bit = 1000
bits)

For uploading: 14.4 kbps = 14,400 bits per second

So, the modem could download data at a rate of 56,000 bits per second
and upload data at a rate of 14,400 bits per second.

17. Discuss and compare various types of networks.

 Based on geographical spread, networks can be of four types:

a) LAN (Local Area Network) — Small computer networks that
are confined to a localised area such as a building or factory, are
known as Local Area Networks (LANs). LANs have geographical
spread of upto 1 km.
b) WAN (Wide Area Network) — The networks spread across
countries or on a very big geographical area are known as WANs.
 The WANs link computers to facilitate fast and efficient exchange of
information at lesser costs and higher speeds. The largest WAN in
existence is the Internet.
c) PAN (Personal Area Network) — It is the interconnection of
information technology devices within the range of an individual
person, typically within a range of 10 meters. PAN could also be
interconnected without wires to the Internet or other networks.
d) MAN (Metropolitan Area Network) — MAN refers to a network
that is spread over an area as big as a city.
Based on component roles, network can be of two types:

a) Peer-to-Peer networks — Computers in peer-to-peer network

can act as both servers sharing resources and as clients using the
resources. A peer-to-peer network has upto ten computers.
b) Client/Server Networks — Server-based networks provide
centralized control of network resources and rely on server
computers to provide security and network administration. A client
 computer requests and utilizes network resources and a server is
dedicated to processing client requests. Bigger networks prefer to
have this type of network with centralized control.
18. Identify the network type from the following characteristics :

 used in personal space of a person

 covers range of 10-15 metres
 uses bluetooth/infrared or wifi etc. for connections.
 The network type that matches the given characteristics is the
Personal Area Network (PAN).

19. Identify the network type from the following characteristics :

 no outside connection
 interconnected devices within a factory or a building
 very high speeds
 secure network
  The network type that matches the given characteristics is the
Local Area Network (LAN).

20. Identify the network type :

 Mostly used in homes

 All computers are connected with each other
 Data exchange without any dedicated servers
 Limited number of computers
 The network type that matches the given characteristics is the
Peer-to-Peer Network (P2P).

21. Identify the network type :

 Big area geographically (countries/continents)

 Result of interconnected networks
  The network type that matches the given characteristics is the
Wide Area Network (WAN).

22. Explain various mostly used topologies.

 The most used topologies are as follows:

a) Bus or Linear topology — In this topology, all devices on
network are connected to a single continuous cable called a bus.
Transmission from any station travels the length of the bus in both
directions and can be received by all other stations. The destination
device, on identifying the address on data packet copies the data
onto its disk. When the data packet reaches at either end the
terminator on that end absorbs the signal, removing it from the bus.
This topology can be used for smaller networks.
b) Ring Topology — In this topology, each node is connected to
two and only two neighbouring nodes. Data is accepted from one of
the neighbouring nodes and is transmitted onwards to another.
 Thus data travels in one direction only, from node to node around
the ring. After passing through each node, it returns to the sending
node, which removes it.
c) Star Topology — In this topology each workstation is directly
linked to a central node. Devices can be easily plugged or
unplugged to the central node, as need dictates. Any
communication between the stations must pass through the central
node.
d) Tree Topology — In this topology the network is shaped as an
inverted tree with the central root branching and sub-branching to
the extremities of the network. Transmission in this topology takes
place in the same way as in bus topology.
e) Mesh topology — In this topology, each node is connected to
more than one node to provide an alternative route in the case the
host is either down or too busy.
f) Fully Connected topology — When in a network each host is
connected to other directly i.e., there is a direct link between each
 host, then the network is said to be fully connected. This
characteristic is termed as full connectivity.
23. Discuss the factors that govern the selection of a topology for
a network.

 The factors that govern the selection of a topology for a network are
as follows:

a) Cruciality of Work — How crucial the continuity of work is a

very important factor. For instance, military networks must not fail at
any cost thus fully connected topology is preferred for military
networks.
b) Cost — Keeping in mind the budget, the topology should be
decided based on cost. A linear bus topology network may be the
least expensive way to install a network. Fully connected is the
most expensive way of creating a network.
 c) Length of cable needed — Sometimes, length of cable must
be saved. The linear bus topology network uses shorter lengths of
cable.
d) Future growth — If a network has to grow in future, then the
topology must support expansion. With a star topology, expanding a
network is easily done by adding another concentrator.
e) Communication Media — Sometimes, difficult terrains like hilly
areas do not allow use of regular cables. For such conditions, linear
bus topologies are not possible. The most common cable in schools
is unshielded twisted pair, which is most often used with star
topologies.
24. i) Compare and contrast Star and Bus topologies.
 Star topology Bus topology

All the devices in the network are connected All the devices in this network are connected to a
by a central hub in the star topology. single cable - which acts as the backbone.

The entire network would fail in case the The entire network would fail in case the network
central hub fails in the network. cable fails.

It requires more cables. It requires less cables.

It is non-linear in nature.It is comparatively much

It is linear in nature.
easier to detect faults in the system.

Various devices can be added using this The network only allows the addition of a limited
configuration. number of devices.

Data transmission is comparatively slower. Data transmission is comparatively faster.

ii) Compare and contrast Star and Tree topologies.

Star topology Tree topology

All the devices in the network are connected by a It is in the shape of an inverted tree with the central root branchi
central hub in the star topology. sub-branching to the extremities of the network.

It is less complex. It is more complex.

It is cheaper. It is expensive.

Failure of one node doesn't affect entire network

Failure of higher node can affect next level node performance.
communication.

It is easy to install and maintain. It is difficult to install and maintain.

Data transmission rate is high. Data transmission rate is comparatively low.

iii) Compare and contrast Bus and Ring topologies.

Bus topology Ring topology

All the devices in this network are connected to a single cable - which acts as All the nodes are connected in the form
the backbone. or loop.

The addition of a new node disrupts the

A new node can be easily added using a connector.
network.

The chances of data collisions are very high. The chances of data collisions are low.

Node failure breaks the ring and commu

Failure of one node does not affect the entire network.
stops.