Lecture ONE
Computer Networks and Data Communication
Introduction To Computer Networks
And Data Communication
Brief History
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Communicating
with
people
over
a
distance
is
known
as telecommunication.
The first forms of telecommunication were smoke signals, drums or
fire torches, running etc.
The major disadvantage with these communication systems was that
only a set of pre-determined messages could be transmitted.
This was overcome in the 18th and 19th century through development
of telegraphy and Morse code.
Invention of telephone and establishment of commercial telephony in
1878 marked a turnaround in communication systems and real
telecommunication was born.
Now we had the communication technology to connect with people
physically located thousands of kilometers away.
Telephones slowly gave way to television, videophone, satellite and
finally computer networks.
Computer networks have revolutionized modern day communication
and communication technologies.
Outline
• Computer Networks
– Overview
– Types
– Classification
– Application
– Topologies
• Data Communication
– Overview
– X-tics
– Components
– Protocols and Standards
Computer Networks
Overview
• A computer network is a system of
interconnected computers and computerized
peripherals such as printers.
• This interconnection among computers
facilitates information sharing among them.
• Computers may connect to each other by
either wired or wireless media.
Network Engineering
• Networking engineering is a complicated task,
which involves software, firmware, chip level
engineering, hardware, and electric pulses.
• To ease network engineering, the whole
networking concept is divided into multiple
layers.
• Each layer is involved in some particular task
and is independent of all other layers. But as a
whole, almost all networking tasks depend on all
of these layers.
• Layers share data between them and they
depend on each other only to take input and
send output.
Computer Networks
• Computer network connects two or more autonomous
computers.
• The computers can be geographically located anywhere.
Introduction to Computer Networks
Types of Computer Networks
• PAN (Personal Area Network)
• LAN (Local Area Network)
• MAN (Metropolitan Area Network)
• WAN (Wide Area Network)
• Discussed in the subsequent slides.
PAN
• A Personal Area Network (PAN) is
smallest network which is very personal to
a user.
• This may include Bluetooth enabled
devices or infra-red enabled devices.
• PAN has connectivity range up to 10
meters. PAN may include wireless
computer keyboard and mouse, Bluetooth
enabled headphones, wireless printers,
and TV remotes.
PAN
LAN
• A computer network spanned inside a building
and operated under single administrative system
is generally termed as Local Area Network
(LAN).
• Usually, LAN covers an organization offices,
schools, colleges or universities. Number of
systems connected in LAN may vary from as
least as two to as much as 16 million.
• LAN provides a useful way of sharing the
resources between end users. The resources
such as printers, file servers, scanners, and
internet are easily sharable among computers.
LAN
• LANs are composed of inexpensive networking and
routing equipment.
• It may contains local servers serving file storage and
other locally shared applications.
• It mostly operates on private IP addresses and does not
involve heavy routing. LAN works under its own local
domain and controlled centrally.
• LAN uses either Ethernet or Token-ring technology.
• Ethernet is most widely employed LAN technology and
uses Star topology, while Token-ring is rarely seen.
• LAN can be wired, wireless, or in both forms at once.
LAN
MAN
• The Metropolitan Area Network (MAN) generally
expands throughout a city such as cable TV network. It
can be in the form of Ethernet, Token-ring, ATM, or Fiber
Distributed Data Interface (FDDI).
• Metro Ethernet is a service which is provided by ISPs.
This service enables its users to expand their Local Area
Networks.
• For example, MAN can help an organization to connect
all of its offices in a city.
• Backbone of MAN is high-capacity and high-speed fiber
optics.
• MAN works in between Local Area Network and Wide
Area Network. MAN provides uplink for LANs to WANs
or internet.
MAN
WAN
• As the name suggests, the Wide Area Network (WAN)
covers a wide area which may span across provinces
and even a whole country.
• Generally, telecommunication networks are Wide Area
Network. These networks provide connectivity to MANs
and LANs.
• Since they are equipped with very high speed backbone,
WANs use very expensive network equipment.
• WAN may use advanced technologies such as
Asynchronous Transfer Mode (ATM), Frame Relay, and
Synchronous Optical Network (SONET).
• WAN may be managed by multiple administration.
WAN
WAN
Classification of Computer
Networks
• Computer networks are classified based
on various factors.
• Geographical span
• Inter-connectivity
• Administration
• Architecture
Geographical Span
• Geographically a network can be seen in one of the
following categories:
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It may be spanned across your table, among Bluetooth
enabled devices, Ranging not more than few meters.
It may be spanned across a whole building, including
intermediate devices to connect all floors.
It may be spanned across a whole city.
It may be spanned across multiple cities or provinces.
It may be one network covering whole world.
Inter-Connectivity
• Components of a network can be connected to each
other differently in some fashion.
• By connectedness we mean either logically, physically,
or both ways.
• Every single device can be connected to every other
device on network, making the network mesh.
• All devices can be connected to a single medium but
geographically disconnected, created bus-like structure.
• Each device is connected to its left and right peers only,
creating linear structure.
• All devices connected together with a single device,
creating star-like structure.
• All devices connected arbitrarily using all previous ways
to connect each other, resulting in a hybrid structure.
Administration
• From an administrator’s point of view, a
network can be private network which
belongs a single autonomous system and
cannot be accessed outside its physical or
logical domain.
• A network can be public, which is
accessed by all.
Network Architecture
• Computer networks can be discriminated into various
types such as Client-Server, peer-to-peer or hybrid,
depending upon its architecture.
• There can be one or more systems acting as Server.
Other being Client, requests the Server to serve
requests. Server takes and processes request on behalf
of Clients.
• Two systems can be connected Point-to-Point, or in
back-to-back fashion. They both reside at the same level
and called peers.
• There can be hybrid network which involves network
architecture of both the above types.
Introduction to Computer Networks
Applications of Networks
• Resource Sharing
– Hardware (computing resources, disks, printers)
– Software (application software)
• Information Sharing
– Easy accessibility from anywhere (files, databases)
– Search Capability (WWW)
• Communication
– Email
– Message broadcast
• Remote computing
• Distributed processing (GRID Computing)
Applications of Networks
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Internet Radios
E-Commerce
News Groups
IP phones
– Calls via Internet VoIP
• Video conferences
– Zoom
– Skype
• Parallel computing
– Muti-tasking of processors
• Instant messaging
– Text messages
Introduction to Computer Networks
Network Topologies
• A Network Topology is the arrangement with which
computer systems or network devices are connected to
each other on a network.
• The network topology defines the way in which
computers, printers, and other devices are connected.
• A network topology describes the layout of the wire and
devices as well as the paths used by data transmissions.
• Topologies may define both physical and logical aspect
of the network.
• Both logical and physical topologies could be same or
different in a same network.
Network Topology Types
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Point-to-Point
Bus
Star
Tree/Extended Star
Mesh
Ring
Daisy Chain
Hybrid
Point-to-Point Topology
• Point-to-point networks contains exactly two hosts
such as computer, switches, routers, or servers
connected back to back using a single piece of
cable.
• Often, the receiving end of one host is connected to
sending end of the other and vice versa.
• If the hosts are connected point-to-point logically,
then may have multiple intermediate devices.
• But the end hosts are unaware of underlying
network and see each other as if they are
connected directly.
Point-to-Point Topology
Introduction to Computer Networks
Bus Topology
• Commonly referred to as a linear bus, all the devices on a
bus topology are connected by one single cable.
• In case of Bus topology, all devices share single
communication line or cable. Bus topology may have
problem while multiple hosts sending data at the same time.
• Therefore, Bus topology either uses CSMA/CD technology
or recognizes one host as Bus Master to solve the issue. It
is one of the simple forms of networking where a failure of a
device does not affect the other devices. But failure of the
shared communication line can make all other devices stop
functioning.
• Both ends of the shared channel have line terminator. The
data is sent in only one direction and as soon as it reaches
the extreme end, the terminator removes the data from the
line.
Bus Topology
Introduction to Computer Networks
Star Topology
• The star topology is the most commonly used architecture
in Ethernet LANs.
• When installed, the star topology resembles spokes in a
bicycle wheel.
• All hosts in Star topology are connected to a central
device, known as hub device, using a point-to-point
connection.
• That is, there exists a point to point connection between
hosts and hub.
• The hub device can be any of the following:
– Layer-1 device such as hub or repeater
– Layer-2 device such as switch or bridge
– Layer-3 device such as router or gateway
Star Topology
Tree/Extended Star Topology
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Larger networks use the extended star topology also called tree
topology.
Also known as Hierarchical Topology, this is the most common form
of network topology in use presently.
This topology imitates as extended Star topology and inherits
properties of Bus topology.
This topology divides the network into multiple levels/layers of
network. The middle layer is known as distribution layer, which
works as mediator between upper layer and lower layer.
The highest layer is known as core layer, and is central point of the
network, i.e. root of the tree from which all nodes fork.
When used with network devices that filter frames or packets, like
bridges, switches, and routers, this topology significantly reduces
the traffic on the wires by sending packets only to the wires of the
destination host.
All neighboring hosts have point-to-point connection between them.
Similar to the Bus topology, if the root goes down, then the entire
network suffers even though it is not the single point of failure.
Tree/Extended Star Topology
Comparison of Bus, Star and
Tree Topologies
• As in Bus topology, hub acts as single point of failure. If
hub fails, connectivity of all hosts to all other hosts fails.
• Every communication between hosts takes place
through only the hub.
• Star topology is not expensive as to connect one more
host, only one cable is required and configuration is
simple.
• For Tree Topology, if the root goes down, then the entire
network suffers even though it is not the single point of
failure. Every connection serves as point of failure, failing
of which divides the network into unreachable segment.
Introduction to Computer Networks
Ring Topology
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Each host machine connects to exactly two other machines, creating a
circular network structure.
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When one host tries to communicate or send message to a host which
is not adjacent to it, the data travels through all intermediate hosts.
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To connect one more host in the existing structure, the administrator
may need only one more extra cable.
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A frame travels around the ring, stopping at each node. If a node wants
to transmit data, it adds the data as well as the destination address to
the frame.
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The frame then continues around the ring until it finds the destination
node, which takes the data out of the frame.
– Single ring – All the devices on the network share a single cable.
– Dual ring – The dual ring topology allows data to be sent in both
directions.
Ring Topology
Dual ring Topology
Introduction to Computer Networks
Mesh Topology
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Here, a host is connected to one or multiple hosts. This topology
has hosts in point-to-point connection with every other host or may
also have hosts which are in point-to-point connection with few
hosts only.
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The mesh topology connects all devices (nodes) to each other for
redundancy and fault tolerance.
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It is used in WANs to interconnect LANs and for mission critical
networks like those used by banks and financial institutions.
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Implementing the mesh topology is expensive and difficult.
Mesh Topology
• Mesh technology comes into two types:
• Full Mesh: All hosts have a point-to-point connection to
every other host in the network.
• Thus for every new host n(n-1)/2 connections are required.
It provides the most reliable network structure among all
network topologies.
• Partially Mesh: Not all hosts have point-to-point
connection to every other host. Hosts connect to each other
in some arbitrarily fashion.
• This topology exists where we need to provide reliability to
some hosts out of all.
Mesh Topology
Daisy Chain Topology
• This topology connects all the hosts in a linear
fashion. Similar to Ring topology, all hosts are
connected to two hosts only, except the end hosts.
• Means, if the end hosts in daisy chain are
connected then it represents Ring topology.
• Each link in daisy chain topology represents single
point of failure.
• Every link failure splits the network into two
segments. Every intermediate host works as relay
for its immediate hosts.
Daisy Chain Topology
Hybrid Topology
• A network structure whose design contains more
than one topology is said to be hybrid topology.
• Hybrid topology inherits merits and demerits of
all the incorporating topologies.
• The combining topologies may contain attributes
of Star, Ring, Bus, and Daisy-chain topologies.
• Most WANs are connected by means of DualRing topology and networks connected to them
are mostly Star topology networks.
• Internet is the best example of largest Hybrid
topology.
Hybrid Topology
Factors that Affect Choice of a Network Topology
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Cost: Installation cost is a very important factor in overall cost of setting
up an infrastructure. So cable lengths, distance between nodes,
location of servers, etc. have to be considered when designing a
network.
Flexibility: Topology of a network should be flexible enough to allow
reconfiguration of office set up, addition of new nodes and relocation of
existing nodes.
Reliability: Network should be designed in such a way that it has
minimum down time. Failure of one node or a segment of cabling
should not render the whole network useless.
Scalability: Network topology should be scalable, i.e. it can
accommodate load of new devices and nodes without perceptible drop
in performance.
Ease of installation: Network should be easy to install in terms of
hardware, software and technical personnel requirements.
Ease of maintenance: Troubleshooting and maintenance of network
should be easy
Introduction to Computer Networks
Network Components
• Physical Media
• Interconnecting Devices
• Computers
• Networking Software
• Applications
Introduction to Computer Networks
Networking Media
• Networking media can be defined simply as the means
by which signals (data) are sent from one computer to
another (either by cable or wireless means).
Introduction to Computer Networks
Networking Devices
• Network devices or networking hardware, are physical
devices that are required for communication and interaction
between hardware on a computer network.
• HUB, Switches, Repeater, Routers, Wireless Access Points,
Modems, Ethernet card, Gateway, Wi-Fi Card. etc.
• Will be discussed more in Lect. 2
Introduction to Computer Networks
Computers: Clients and Servers
• In a client/server network arrangement, network services
are located in a dedicated computer whose only function
is to respond to the requests of clients.
• The server contains the file, print, application, security,
and other services in a central computer that is
continuously available to respond to client requests.
Introduction to Computer Networks
Networking Protocol: TCP/IP
Data Communication
Overview
• In Data Communications, data generally are
defined as information that is stored in digital
form.
• Data communications is the process of
transferring digital information between two or
more points.
• Information is defined as the knowledge or
intelligence.
Overview cont’d
• Data communications is summarized as the
transmission, reception, and processing of
digital information.
• For data communications to occur, the
communicating devices must be part of a
communication system.
• A communication system is made up of a
combination of hardware (physical equipment)
and software (programs).
X-tics and Data Commn.
• The effectiveness of a data communications
system depends on four fundamental
characteristics:
1. Delivery
2. Accuracy
3. Timeliness
4. Jitter.(small delays in network
transmissions)
Components of a Data Communication
System
The five components of a data communication System include;
1. Message: The message is the information (data) to be
communicated. Popular forms of information include text,
numbers, pictures, audio, and video.
2. Sender: The sender is the device that sends the data
message. It can be a computer, workstation, telephone handset,
video camera, and so on.
3. Receiver: The receiver is the device that receives the
message. It can be a computer, workstation, telephone handset,
television, and so on.
Components of a Data Communication
System cont’d
4. Transmission medium: The transmission
medium is the physical path by which a message
travels from sender to receiver. Some examples of
transmission media include twisted-pair wire,
coaxial cable, fiber-optic cable, and radio waves.
5. Protocol: A protocol is a set of rules that govern
data communications. It represents an agreement
between the communicating devices.
Protocols and Standards of Data
Communication
• A protocol is a set of rules that govern data
communications.
• It represents an agreement between the
communicating devices.
· Syntax
· Semantics
· Timing
Protocols and Standards of Data
Communication
• An association of organizations,
governments, manufacturers and users
form the standards organizations and are
responsible for developing, coordinating
and maintaining the standards. The intent is
that all data communications equipment
manufacturers and users comply with these
standards.
Standards Organizations
• The primary standards organizations for data communication
are:
1. International Standard Organization (ISO)
ISO is the international organization for standardization on a
wide range of subjects.
• It is comprised mainly of members from the standards
committee of various governments throughout the world.
• It is even responsible for developing models which provides
high level of system compatibility, quality enhancement,
improved productivity and reduced costs.
• The ISO is also responsible for endorsing and coordinating
the work of the other
standards organizations.
Standards Organizations
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2. International Telecommunications Union-Telecommunication
Sector(ITU-T)
ITU-T is one of the four permanent parts of the International
Telecommunications Union based in Geneva, Switzerland.
It has developed three sets of specifications:
the V series for modem interfacing and data transmission over telephone
lines,
the X series for data transmission over public digital networks, email and
directory services;
the Iand Q series for Integrated Services Digital Network (ISDN) and its
extension Broadband ISDN.
ITU-T membership consists of government authorities and
representatives from many countries and it is the present standards
organization for the United Nations.
Standards Organizations
• 3. Institute of Electrical and Electronics Engineers
(IEEE)
IEEE is an international professional organization founded
in United States and is compromised of electronics,
computer and communications engineers.
• It is currently the world’s largest professional society with
over 200,000 members.
• It develops communication and information processing
standards with the underlying goal of advancing theory,
creativity, and product quality in any field related to
electrical engineering.
Standards Organizations
• 4. American National Standards Institute (ANSI)
ANSI is the official standards agency for the United
States and is the U.S voting representative for the
ISO.
• ANSI is a completely private, non-profit organization
comprised of equipment manufacturers and users of
data processing equipment and services.
• ANSI membership is comprised of people form
professional societies, industry associations,
governmental and regulatory bodies, and consumer
goods.
Standards Organizations
• 5. Electronics Industry Association (EIA)
EIA is a non-profit U.S. trade association that
establishes and recommends industrial
standards.
• EIA activities include standards development,
increasing public awareness, and lobbying and it
is responsible for developing the RS
(recommended standard) series of standards for
data and communications.
General Information
• Assessment: CW + Virtual mini practical
Assignment (40%), final exam(60%).
• Coursework and Assignments will be done
either in groups or individual basis as will
be instructed by the lecturer.
• Practical will be done on virtual platform of
packet tracer.
Questions
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