Applications of Information and
Communication Technologies
Lecture 12
Presented By
Dr. Muhammad Umar Javed
Assistant Professor
Department of Computer Science
Types of Network
Computer networks are divided into the following types
based on the size and physical area or distance covered by
the network
Local Area Network (LAN)
Wide Area Network (WAN)
Metropolitan Area Network (MAN)
Local Area Network (LAN)
Covers a small area. (limited to building or group of adjacent buildings)
Consists of limited number of computers.
Designed to share different resources (such as printers, scanners,
storage devices, and application programs)
Examples:
Computer network in laboratory of a college
Network of computers in an office building
Connected using cables or wireless transmission medium and Network
Interface Card (NIC).
Fast data transmission rate: from 10 Mbps to 1000 Mbps.
Local Area Network (LAN)
Wide Area Network (WAN)
Covers a large area such as different cities of the country or different
countries of the world.
Typically, consists of many LANs connected across a wide geographical area.
Example:
An organization has a LAN at each site.
LANs of all sites are connected to WAN.
World’s largest WAN is Internet
Computers and other devices are connected through telephone lines.
Can also be connected through leased lines, microwave, or satellite
systems.
Expensive and transmission rate slower.
Metropolitan Area Network (MAN)
Covers an area of a single city or town.
Usually, connects two or more LANs in a city or town.
Larger than LAN and smaller than WAN.
Fiber optic cables are used as communication media.
That’s why, very high speed network.
Examples
Cable TV network in a city.
Mobile phones (cellular) systems.
Internet Service Providers network in a city.
The network connecting different branches of a company in the same
city.
Network Topologies
In networking, term topology is the way of connecting
computers or nodes on a network
There are many ways in which computers can be
connected together in a computer network
Way in which computers or other devices are connected in
a network is called network topology
Shortly term network topology refers to the physical
layout or shape of network
Network Topologies
Commonly used network topologies
Bus topology
Star topology
Ring topology
Tree topology
Mesh topology
Bus Topology
In a Bus topology, all nodes are connected to a common
communication medium or central single cable
This central cable is the backbone cable.
This cable is called as Bus
The devices or nodes are connected to the Bus through an interface
connector
Both ends of the cable are closed with terminators
A terminator is a special small device that absorbs data signals (or
prevents data signals)
It is also known as terminating resistance
Bus topology is suitable for small networks
Bus Topology
Bus Topology - Working
When a sending computer wants to send a message, it has to determine whether the media is in
use or free
If no other device is transmitting the data, it sends a message to the
destination computer
Address of the destination computer is also attached to the message
This message moves from one computer to another through the bus
Each computer connected to the network receives the message, checks the attached address
If the attached message matches with the address of the computer, then it accepts the message
Otherwise, the message moves toward the next computer
When message reaches the destination computer, it accepts the message
Bus Topology
Pros
Very simple network
Easy to install and to maintain
Less expensive because it requires a single cable to connect devices
When nodes are added and removed in the network, network is not affected
If one node fails in the network, other nodes are not affected
Cons
Entire network fails if there is any problem with the bus (central cable)
It supports only a small number of nodes. So it is not suitable for a large
network
Star Topology
In a star network, all nodes are directly connected to a
central device, called Hub or Switch
This central device controls all the traffic
Usually, nodes are connected to the Hub with unshielded
twisted pair (UTP).
Shape of the Star network looks like a star.
Star topology is most commonly used in LAN
Many home networks use the star
topology.
Star Topology-Working
Computers communicate with each other through a
central device i.e. hub
Sending computer sends data to the central device
Central device sends data to the receiving computer
In this way, data is transferred from one computer to
another in the Star network
Star Topology- Advantages
Easy to install and to maintain
Nodes can easily be added or removed without affecting
the network
If any node or cable fails then the rest of the network is
not affected
It is easy to detect and remove faults in the network
It is suitable for small and large networks
Star Topology- Disadvantages
This type of network depends upon the central device If
this device fails, whole network breaks down
It requires more cables than any other networks.
So it becomes more costly.
Ring Topology
In a ring topology, each node is connected to next node and last node is
connected to first
Thus, shape of the network is formed just like a ring
Ring Topology - Working
In Ring topology, a token is passed around the network
Computer that has control of the token can transmit data/message
When a computer sends a message to another computer on the network,
message flows from one computer to the next computer
Every computer receives a message from previous computer and retransmits
it to the next computer until the destination computer receives the message
Destination computer sends an acknowledgment of receiving a message to the
sender computer
Sender computer then releases the token back to the network
This method of controlling access to shared network cable is called token
passing
Ring Topology - Advantages
Less expensive to implement
Easy to install and to maintain
All computers have equal access to the network
Every computer regenerates/refreshes the data signal
that’s why it can travel over a longer distance
Ring Topology - Disadvantages
If one node fails (or the ring is broken at any point), the
entire network stops functioning
Adding or removing a computer in the network affects the
whole network.
Tree Topology
Tree topology has combined features of both bus and star
topologies
Whole network is divided into segments
Each segment represents a Star topology
All segments (i e Star topologies) are combined through
central cable or bus
Thus, Bus topology works as the backbone of the Tree
network
Tree network looks like a tree structure
Tree Topology
Tree Topology - Working
In Tree topology network, usually, multiple hubs are used
Each hub controls the nodes directly connected to it and exchanges data
among them
It also exchanges data to other devices connected to the other hubs
Advantages
Can be expanded very easily.
Segments easily managed and maintained.
One segment fails, other segments are not affected.
Easy errors detection and correction.
Tree Topology
Disadvantages
More expensive (more hubs are required)
Relies on the central cable or bus.
Mesh Topology
Each node is directly connected to every other node
Involves the concept of routes.
Rarely used in LAN. Mostly used in WANs like Internet.
Working
In Mesh topology, each node can send a message to the destination through
multiple paths
It means that each node of the Mesh network has several possible paths to
send or to receive a message, but in Bus, Star, and Ring topologies each node
has only one path
Data always travels through the best suited path
Mesh Topology
Mesh Topology - Advantages
It provides multiple routes If one route is blocked, then another suitable
route can be used for data communication
Its performance is not affected by the heavy load of data transmission
It ensures data privacy or security
Troubleshooting of this topology is easy as compared with other networks
Disadvantages
It becomes very expensive because a large number of cabling and I/O ports
are required
It is difficult to install and configure.
Its maintenance is also difficult.
Hybrid Topology
A hybrid topology is a type of network topology that uses two or
more differing network topologies.
These topologies can include a mix of bus topology, mesh
topology, ring topology, star topology, and tree topology.
For Example
A department uses a Bus network, second department uses the
ring network, third department uses the Mesh network and
fourth department uses the star network.
All networks of different departments can be connected
through a central hub.
Hybrid Topology
Hybrid Topology
Advantages
Flexibility in design
Potentially easier to manage
Potentially easier to add or remove nodes
Suitable for larger networks
Disadvantages
Difficult to design and maintain
Costly
Communication Devices
An electronic device that is used for sending and receiving
data between the sending device and receiving device is
called a communication device
Most of the communication devices have the ability to
convert the digital signal of the computer into an analog
signal so that the signals can be transmitted on the
communication line to another end
The reverse is also true
NIC
NIC stands for Network Interface Card
NIC is a communication device that is used to connect a
computer to a LAN
It is also called a LAN card
NIC is a circuit board which is installed on the motherboard
A computer must have a network card ( to connect to the LAN
Nowadays, most computer systems have built in network card
into the motherboard
HUB & Switch
Hub and Switch are communication devices
Both provide a central connection point for connecting
computers/nodes together in a computer network
Typically, Hub does not manage any of the traffic that comes through it
It broadcast data packets to every computer/node
Only the receiver computer/node accepts the message and other
computers/nodes ignore the message
A switch is like a Hub but it is more intelligent than the Hub
It records the addresses of the computers connected to it in a table
It sends a message to the receiver computer/node only
Modem
Modem stands for modulator & demodulator
It is a commonly used communication device that converts
digital signals into analog signals and vice versa
It is used to send and receive data between two
computers through the telephone line
Both sending and receiving computers must have modems
Data is stored inside the digital computers in digital form
However, data is transmitted over the telephone line in
the form of analog signals
Modem
The sender computer sends data to the receiving computer as follows
Modulator
Dialup modem of sending a computer converts digital signals into analog
signals and sends it to the receiving computer through a telephone line
The process of converting digital signals into analog signals is called
modulation
Demodulator
Modem of receiving computer receives data from the telephone line in the
form of analog signals.
It converts these signals into digital signals and enters in the computer.
The process of converting the analog signals into digital form is called
demodulation
Modulator/ Demodulator
Router
A router is a communication device that connects multiple computers/devices
or other routers together and transmits data to its correct destination on a
network
Typically, routers are used to connect two or more different or similar
networks and transfers data packets from one network to another
Networks can be LANs or WANs
Router stores addressing information (routing information) of each computer
on the connected networks
When a router receives a packet of data, it looks at the address attached with
the data packet where the packet of data is to be sent
It determines the best route (path) to forward the data packet at its
destination and then sends it accordingly
Router
Gateway
A gateway is a communication device (or networking device)
It is used to connect two different types of networks (i e networks that use different protocols)
It is an intelligent device
It translates data from one format to the other
Different networks may have different types of data and of different formats
Gateway receives a data packet from one type of network
It reads the address of the computer on the networks where the data packet is to be sent
It converts the data packet into a format that the destination computer can understand
For example, computers connected to a LAN require a gateway to access the Internet
Bridge
A bridge is a communication electronic device that is used to connect two
similar network segments
A segment is a part of a network
It also controls the data flow between them
When a bridge receives a message, it reads the addresses of both the sender
and receiver
If the sender and receiver are in the same network segment, the bridge does
not pass the message to the other network segment
The message is directly sent to the receiver
The bridge, therefore, reduces network traffic
So the performance of the network is increased
Lecture End
