Introduction to Computer Networks 

Introduction to Computer Networks:- A computer network is a group of devices connected with each other through a transmission medium such as wires, cables, etc. These devices can be computers, printers, scanners, Fax machines etc. Each device in the network connects to other devices using common physical media such as wires or cables. Each node can transmit or receive data to any other node on the network.

The network makes it possible to transfer data from one location to another in a very short amount of time. For example, if someone sends an email message from his computer to his coworkers computer using the internet, the message will be transmitted over the internet from one computer to the other. Once the message reaches the other computer it will be received and saved in the hard drive of the co worker’s computer. This process is called data transmission and is an integral part of a computer network.

cables connected to ethernet ports
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Table of Contents

What is Data Communication? 


  • Refers to information 
  • Presented in any form 
  • Agreed upon by the parties ( creating & using) 


  • Means sharing information 
  • Local (face to face) or remote (over distance) 


  • Telephone, telegraph, and television 
  • This means communication at a distance 
  • Tele is Greek for far 

Data communication: It is the sharing of information between two devices via some form of the transmission medium (wire cable). Local communication occurs face to face, while remote communication takes place over a distance. 


A data communication system is made up  of five components

Introduction To Computer Networks

1. Message: It is the information (data) to be  communicated 

– Consist of text, numbers, pictures, audio, or video

2. Sender: It is the device that sends the data message – Computer, workstation, telephone handset, video  camera 

3. Receiver: It is the device that receives the message – Computer, workstation, telephone handset, television

4. Medium: The physical path by which a message  travels from sender to receiver 

– twisted pair, coaxial cable, fiber-optic, radio waves

close up photo of plugged cables
Photo by Brett Sayles on

5. Protocol: A set of rules that govern data communications 

– An agreement between the communicating devices.

– Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

Effectiveness of Data Communication  System 

  • A communication system made up of a combination of  hardware and software 

The effectiveness of the data communication system depends  on: 

1. Delivery: The system must deliver data to the correct destination. That is, data should be received by the indented user only 

2. Accuracy: The system must deliver data accurately (no change). 

• Data changed & uncorrected is unusable

3. Timeliness: The system must deliver data in timely  manner 

• Data arrived late are useless 

• In the same order (video and audio) & without delay (Real-time  transmission) 

4. Jitter: Variation in the packet arrival time (uneven  quality in the video is the result)

Data Representation 

  1. Text 
  2. Numbers 
  3. Images
  4. Audio 
  5. Video 


  • It is represented as a bit pattern, a sequence of bits (0s or 1s)
  • Different sets of bit patterns have been designed to represent text symbols. Each set is called a code. 
  • The ASCII (American Standard Code for Information  Interchange) code is a 7-bit code. Constitutes 127 symbols/  characters. 
  • Today the most common coding system is Unicode. It uses 32  bits to represent a symbol or character in any language
close up photo of computer codes
Photo by Markus Spiske on


  • They are represented by bit patterns
  • The number is directly converted to a binary number.


  • Represented by bit patterns 
  • It is composed of a matrix of pixels, where each pixel is a small dot. 
  • The size of the pixels depends upon the resolution. 
  • High resolution: more memory is needed. For example; An image can be divided into 1000 pixels or 10,000  pixels. In the second case, there is a better representation of the  image (better resolution), but more memory is needed to store the  image 
  • Each pixel is assigned a bit pattern 


  • Audio refers to the recording of sound or music.
  • It is different from text, numbers, or images.
  • It is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal 


  • Recording of a picture or movie

Data Flow 

Communication between two devices can be:

  • Simplex 
  • Half-Duplex 
  • Full-Duplex

Simplex (one-way street) 

  • The communication is unidirectional 
  • Only one device on a link can transmit; the other  can only receive 
  • Use the entire capacity of the channel to send data
  • Example: Keyboards, Monitors 
Introduction to Computer Networks 
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Half-Duplex (one-lane with two-directional traffic)

  • Each station can both transmit and receive, but not  at the same time 
  • When one device is sending, the other can only  receive, and vice versa 
  • The entire capacity of a channel is taken over by  the transmitting device 
  • Example: Walkie-talkies 
Introduction to Computer Networks 
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Full-Duplex (Duplex) (two-way street) 

  • Both stations can transmit and receive at the same time
  • Signals going in either direction sharing the capacity  of the link 
  • Example: Telephone network 
Introduction to Computer Networks 
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What is a Network? 

Network : It is a set of devices (nodes)  connected by communication links 

Node: computer, printer, or any other device capable of  sending or receiving the data 

Distributed Processing :  

– Most networks use it 

– Task is divided among multiple computers instead of  one single large computer responsible for all the work

Network Criteria  

A network must meet a certain number of criteria – The most important of the network criteria are: –

  • Performance 
  • Reliability 
  • Security

1. Performance –

It is measured using transit time and response time

  • Transit time: Amount of time required for a message to travel  from one device to another 
  • Response time: Elapsed time between an inquiry and a  response  

Performance depends on : 

  1. The number of users: large number and slow response time.
  2. Type of transmission medium: fiber-optic cabling faster than other cables. 
  3. Capabilities of the connected hardware: affect both the speed and capacity of transmission. 
  4. The efficiency of the software

Performance is evaluated by two contradictory  networking metrics: 

  1. Throughput (high): a measure of how fast we can  actually send data through a network 
  2. Delay (low) 

Why contradictory? 

Sending more data to the network may increase  throughput, but the delay will also be increased because  of traffic congestion in the network

2. Reliability 

Reliability is measured by: 

  1. Frequency of failure 
  2. Recovery time of a network after a failure 
  3. Network’s robustness in a catastrophe: protect by a good  back up a network system 
  4. Security 


  • Protecting data from unauthorized access 
  • Protecting data from damage and development
  • Implementing policies and procedures for recovery from  breaches and data losses (Recovery plan)

Physical Structures

Type of connection 

  • Network: Two or more devices connected through  links 
  • Link: Communication pathway that transfers data from one device two another Two devices must be connected in some way to the same link at the same time.  

There are two possible types of connection: 

  1. Point-to-Point 
  2. Multipoint

1. Point-to-Point 

  • There is a dedicated link between the two devices. 
  • Dedicated means that the entire capacity of the link is reserved  for transmission between those two devices 
  • Example: For changing TV channels: A television remote control is used by establishing a point-to-point connection between the remote control and a TV.
Introduction to Computer Networks 
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  • There is a shared link between more than two devices.
  • Either the link is shared by the devices at the same time, or the devices can use the link by taking turns i.e. not use the link at the same time.
Introduction to Computer Networks 
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Physical Topology 

The way a network is laid out physically is known as the topology of the network. Four topologies: Mesh, Star, Bus, and Ring

Introduction to Computer Networks 
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  • Every link is a dedicated point-to-point link
  • The term dedicated means that the link carries  traffic only between the two devices it connects
  • To link n devices fully connected mesh has: n ( n – 1) / 2 physical channels (Full-Duplex) 
  • Every Device on the network must have n – 1 port 
  • Example: 8 devices in mesh has links: n(n-1) / 2 = 8 (8-1)/2 = 28 number of ports per device = n – 1 = 8 –1 = 7
Introduction to Computer Networks 
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  • Each connection carries its own data load, therefore there are  no traffic problems 
  • A mesh topology is robust. If one link becomes unusable, it does not stop the functioning of the entire network. 
  • There is privacy/ security in this topology. As every message travels along a dedicated link, only the intended recipient can see it, thus ensuring privacy.  
  • Easy fault identification and fault isolation


  • A big amount of cabling is required as every device must be connected to every other device.  
  • Installation and reconnection are difficult. 
  • The hardware required to connect each link (I/O ports and cable)  could be expensive.


  • Dedicated point-to-point link to a central controller (Hub). 
  • Devices are not directly linked to one another i.e. there is no direct traffic between devices. 
  • This type of topology is used in LAN
Introduction to Computer Networks 
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  • Less expensive than mesh (1 Link + 1 port per device) 
  • Easy to install and reconfigure 
  • Less cabling 
  • Robustness: If one link fails, it does not affect others
  • Easy fault identification and fault isolation 


  • Dependency of the whole topology on one single point (hub)
  • More cabling than other topologies ( ring or bus)


  • It is multipoint  
  • One long cable acts as a backbone.  
  • Nodes are connected to the bus cable using drop lines and taps.
  • Used in the design of early LANs, and Ethernet LANs
Introduction to Computer Networks 
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  • Easy to install.  
  • Fewer cables than mesh, star topology: Backbone cable can be laid along the path and then nodes can be connected to the cable using taps and drop lines. In this way, less cabling is needed than mesh, star topologies 


  • Adding a new device requires modification of the backbone
  • Fault or break stops all transmission


  • Each device has a dedicated point-to-point connection with only  the two devices on either side of it 
  • A signal is passed along the ring in one direction from device to  device until it reaches its destination 
  • Each device incorporates a Repeater
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  • Easy to install and reconfigure 
  • To add or delete a device, changing only two connections is required as each device is connected to its immediate neighbors only. 
  • Fault isolation is easy. 


  • One broken device can disable the entire network as it is unidirectional

Hybrid Topology 

Example: Having a main star topology with  each branch connecting several stations in a  bus topology

Categories of Networks

There are three categories of networks depending upon their size:

1. LAN (Local Area Network):  

  • The size of this network is limited to a few kilometers.  
  • It is privately owned 
  • It is used to link devices in the same office, building, or campus
  • Example of a simple LAN: 2 PCs & 1 printer in home or office. 

2. MAN (Metropolitan Area Network):  

  • The size of this network is between the size of LAN and WAN.
  • It is used to link devices inside a town or a city 
  • Example: the part of the telephone company network that can  provide a high-speed DSL to the customer 

3. WAN (Wide Area Network):

It is used to link devices worldwide i.e.  it provides long-distance transmission of data over large geographic  areas (country, continent, world)

Wireless LAN (WLAN) 

WLAN is a network that allows devices to connect and communicate wirelessly via Wi-Fi. Unlike a traditional wired LAN, in which devices communicate over Ethernet cables. 

Personal Area Network (PAN) 

A personal area network (PAN) is the interconnection of information technology devices such as computers, smartphones, tablets, and personal digital assistants within the range of an individual person, typically within a range of 10 meters using some form of wireless (Bluetooth) or wired (USB) technology. When Wireless technology is used, it is known as WPAN. 

A wireless personal area network (WPAN) is a PAN carried over a low-powered, short-distance wireless network technology such as IrDA, Wireless USB, Bluetooth, or ZigBee. The reach of a WPAN varies from a few centimeters to a few meters. 

A wired PAN is a PAN in which the connections are wired using a USB.

Private network, Public network, Virtual Private Network (VPN) 

  1. A public network is a network to which anyone can connect. The best example of such a network is the Internet. 
  2. A private network is any network to which access is restricted. A corporate network or a network in a school are examples of private networks. Also, the private network uses private IP address space. 
  3. A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across public networks as if their computing devices were directly connected to the private network. In other words, VPN gives you online privacy and anonymity by creating a private network from a public internet connection.

Types of Network 

There are many types of computer networks that are used worldwide these days. Some of the popularly used types of networks are: 

  • LAN – Local Area Network 
  • WAN – Wide Area Network 
  • MAN – Metropolitan Area Network 
  • WLAN – Wireless Local Area Network 
  • PAN – Personal Area Network 
  • WPAN – Wireless Personal Area Network 
  • Private Network 
  • Public Network 
  • VPN – Virtual Private Network

Interconnection of Networks:  Internetworks 

Introduction to Computer Networks 
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The Internet 

  • The Internet has revolutionized many aspects of our daily lives. 
  • It has affected the way we do business as well as the way we spend our leisure time. 
  • The Internet is a communication system that has brought a wealth of  information to our fingertips and organized it for our use
  • An internet (the lowercase letter i) is 2 or more networks that can  communicate with each other 
  • The Internet (the uppercase letter I) is a collaboration of more than  hundreds of thousands of interconnected networks
  • It is made up of many LANs and WANs. 
  • Every day new networks are added and removed. 
  • Internet Services Providers (ISPs) offer Internet services to the end users. 

There are levels of ISPs : 

  1. International ISPs: They are at the top of the hierarchy that connects nations together. 
  2. National ISPs: They are at the second level of hierarchy and provide services within a nation. 
  3. Regional ISPs: They are smaller ISPs that are connected to one or more national ISPs. 
  4. Local ISPs: They provide direct service to the end users. Local ISPs are connected to regional ISPs or directly to national ISPs.

Intranet vs. Extranet vs. Internet 

  • Intranet is shared content accessed by members within a single organization. 
  • Extranet is shared content accessed by groups through cross enterprise boundaries. 
  • Internet is global communication accessed through the Web

What are The Differences Between Intranet vs. Extranet vs. Internet 

DescriptionThe Internet is defined as a  global system of interconnected computer networks that uses the standard  Internet  Protocol Suite  (TCP/IP) to serve billions of users worldwide.An intranet is defined as a  private computer network designed to share any part of an organization’s information within that organization.  It is designed for a specific group of users within an organization. An extranet is a part of a  company’s intranet that is extended to users outside the company,  via the Internet. It can be used to share information with clients  (suppliers and vendors). 
Size Of The  NetworkInternet is the largest network as far as the number of connected devices is concerned. It is a small network with a few numbers of connected devices. It is a small network with a  few numbers of connected devices. 
PurposeThe Internet is a  means of sharing information throughout the world. An intranet is a  means of sharing sensitive or confidential information throughout the organization. An extranet is a  means of conveying information between members of the organization and external members. 
Regulation It is not regulated by any Authority.It is regulated by a specific Organization.It is regulated by multiple Organizations.
Content On The NetworkContent in the network is readily accessible to everyone who is connected. The content in the network is accessible only to members of the organization. The content on the network is accessible to members of the organization and external members with access to the network. 
OwnershipThe Internet has no known ownership. Ownership of the intranet is by a single organization. Ownership of extranet is by single or multiple organizations. 
AccessUsers have unrestricted access and can access the internet anonymously. An intranet may be accessible from the internet, but it is protected by a password and accessible only to authorized users. An extranet may be accessible from the internet,  but it is protected by a  password and accessible only to authorized users. 
InformationThe Internet contains different sources of information and is available for all. The intranet contains only specific group information. The extranet contains only specific group information. 
ExampleAn example of the Internet is the network you use to google words. An example intranet is a  company like  ExxonMobil using an internal network for its business operations. An example of an extranet is when companies like HP, Intel, and  Lenovo decide to use the same network for related business operations.
Differences Between Intranet vs. Extranet vs. Internet 

Client-Server Network 

The Client-Server network model is a widely used network model.  Here, the Server is a powerful system that stores the data or information in it.  On the other hand, the Client is the machine that let the users access the data on the remote server. 

Introduction to Computer Networks 
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The system administrator manages the data on the server. The client machines and the server are connected through a network. It allows the clients to access data even if the client machine and server are far apart from each other. 

In the Client-Server model, the client process on the client machine sends the request to the server process on the server machine. When the server receives the client request, it lookouts for the requested data and sends it back with the reply. 

As all the services are provided by a centralized server, there may be chances of the server getting bottlenecked, slowing down the efficiency of the system.

Peer-to-Peer Network 

Unlike Client-Server, the Peer-to-Peer model does not distinguish between client and server. Instead, each node can either be a client or a server depending on whether the node is requesting or providing the services. Each node is considered a peer

Introduction to Computer Networks 
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To become a part of peer-to-peer, a node must initially join the network.  After joining it must start to provide services to and must request the services from other nodes in the peer-to-peer system. There are two  ways to know which node provides which services; they are as follows: 

• When a node enters the peer-to-peer system, it must register the services it will be provided, into a centralized lookup service on the network. When a node desires any specific service it must contact centralized lookup services to check out which node will provide the desired services. The rest of the communication is done by the desiring node and the service-providing node. 

• A node desiring specific services must broadcast the request for services to all other nodes in the peer-to-peer system. The node providing the requested service will respond to the node making the request. 

Peer-to-Peer network has the advantage over client-servers in that the server is not bottlenecked as the services are provided by the several nodes distributed in a peer-to-peer system.

Difference Between Client-Server and Peer-to-Peer Network:

S.NoClient-Server NetworkPeer-To-Peer Network
01. In Client-Server Network, clients and servers
are differentiated. The client sends the request
to the server and the server responds
to the services which are requested by the client.
In Peer-to-Peer networks,
clients and servers are not
differentiated. Each node
can both request the
services and respond to the
02.It focuses on information
It focuses on connectivity.
03.A centralized server is used to
store the data.
Each peer has its own data.
04.When several clients request
for the services
simultaneously, a server can
get bottlenecked.
As the services are
provided by several
servers distributed in
the peer-to-peer system, a
server in not
05.It is costlier than Peer-to-Peer
It is less costly than Client-
Server Network.
06.It is more stable than Peer-to-Peer NetworksIt is less stable if number of peers is Increased.
07.It can be used for both small and
large networks.
It is suited for small
networks with fewer than
10 computers.
Difference Between Client-Server and Peer-to-Peer Network:

Protocols and Standards

  • Protocol synonymous with rule 
  • Standards: agreed-upon rules 


  • A protocol is a set of rules that govern data  communications 
  • Defines What, How, and When it is communicated

Elements of a protocol: 

  1. Syntax: structure or format of data Example: 8-bits address of the sender, 8-bits address of the receiver 
  2. Semantics: meaning of each section of bits Example: Does the address is a route to be taken or the  final destination of the message 
  3. Timing: when data should be sent and how fast they  can be sent 
  4. Example: sender produces data at 100 Mbps but the  receiver can process data at only 1 Mbps ⇒ overload and  data lose

Also Read

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Frequently Asked Questions?

01. Is WLAN the same as Wi-Fi?

Wi-Fi and WLANs are not the same things at all. Wi-Fi refers
to wireless communication, while a WLAN uses that communication in
a local area network, hence the name Wireless Local Area Network.

02. Is LAN faster than Wi-Fi?

A Wi-Fi connection transmits data via wireless signals, while
an Ethernet connection used in LAN, transmits data over cable.
An Ethernet connection is generally faster than a Wi-Fi connection and
provides greater reliability and security.

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