Computer Network and Communication

Computer Network

A computer network is a group of two or more computers and devices that are connected to share data, resources, and messages. Examples:
• Computers in a school lab sharing files
• Office computers using the same printer

Telecommunications

The word 'tele' means large distance and 'communication' means sharing of ideas, views and information with other individuals or machines.

Telecommunication means sending and receiving information over long distances with the help of electronic devices.

Examples:
• Making a phone call
• Watching TV or sending SMS

Bandwidth (Maximum Capacity)

Bandwidth is the maximum amount of data that can be transmitted over a network in a given time.

Measured in bps (bits per second)

Common units:

Kbps (Kilobits per second)
Mbps (Megabits per second)
Gbps (Gigabits per second)

Higher bandwidth = more data can flow at once

Determines the capacity of a network

Throughput (Actual Performance)

Throughput is the actual amount of data successfully transmitted over a network in a given period of time.

Faster downloads

Video streaming without buffering

Better online gaming and browsing experience

Features of Throughput

Shows the real performance of a network

Always less than or equal to bandwidth

Measured in Mbps (Megabits per second) or Gbps (Gigabits per second)

Throughput is affected by:

Network congestion

Signal interference

Hardware limitations

Distance from the network source

Number of connected users

Note: Higher throughput means faster and smoother network performance

Bandwidth vs Throughput

Bandwidth	Throughput
Maximum data capacity	Actual data transferred
Theoretical value	Practical value
Fixed by network design	Changes based on conditions
Not affected by traffic	Affected by congestion
Example: Road width	Example: Actual cars moving

Broadband:

Broadband is a high-speed data transmission method that can carry multiple signals or large amounts of data at the same time using a wide range of frequencies.

Provides fast and continuous Internet access
Uses multiple channels/frequencies
Always ON (no need to dial like old connections)
Supports voice, data, and video at the same time
Much faster than traditional dial-up connections

Types of Broadband connection:

DSL: Internet through telephone linesExample: Home internet using landline
Cable: Internet through TV cableExample: Internet from cable TV provider
Fiber-optic: Very fast internet using optical cablesExample: High-speed internet in cities/offices
Wireless: Internet using signals (no wires)Example: Wi-Fi, mobile data
Satellite: Internet using satellitesExample: Internet in remote areas

Broadband vs Baseband

Broadband	Baseband
Sends multiple signals at the same time	Sends only one signal at a time
Uses wide range of frequencies	Uses single frequency
Uses analog/modulated signals	Uses digital signals
High speed	Lower speed
Multiple channels	Single channel
Suitable for long distance	Suitable for short distance
More complex	Simple
Expensive	Cheap
Eg: Wifi,TV cable, 5G, 4G	Eg: Ethernet, USB

Frequency

Frequency is the number of signals sent per second in a communication channel.

It decides how fast and clearly data travels.

Mobile Network Generations (3G, 4G, and 5G)

3G (Third Generation Network)

3G is the third generation of mobile network technology. It was the first generation to provide real mobile internet and changed phones into smart devices. It was first launched in 2001.

Features

Faster internet browsing (up to 2 Mbps)
Multimedia messaging (photos and videos)
Enables video calling
Supports mobile apps, email, and social media
Global roaming (use mobile services in different countries)

Applications of 3G

Video communication
Mobile internet browsing
Social media usage
Online maps and navigation

Examples

Video calls on Skype
Browsing Facebook on mobile
Watching YouTube (low quality)
Using Google Maps

4G (Fourth Generation Network)

4G is the fourth generation of mobile network technology. It is much faster and more reliable than 3G and turned mobile phones into powerful devices for entertainment and work. It was launched in 2009.

Features

Very high speed (up to 1 Gbps)
Low latency (less delay)
HD video streaming
Better online multiplayer gaming
Fast downloads and uploads
High-quality video conferencing

Applications of 4G

Mobile internet browsing
HD video streaming
Online multiplayer gaming
Video conferencing for education and work
Social media usage
Mobile banking and e-commerce

Examples

Watching HD videos on YouTube
Playing online games like PUBG and Free Fire
Video meetings on Zoom or Microsoft Teams
Using apps like TikTok and Instagram smoothly

5G (Fifth Generation Network)

5G is the fifth and latest generation of mobile network technology. It is much faster, smarter, and supports a large number of connected devices. It was launched in 2019.

Features

Very high speed (up to 10 Gbps)
Very low latency (near real-time response)
Supports many devices at the same time
High reliability and strong connection
Enables advanced technologies

Applications of 5G

Smart homes and smart cities
Self-driving cars (autonomous vehicles)
Remote surgery and telemedicine
AR/VR applications
Internet of Things (IoT) devices
Industrial automation (smart factories)

Data Transmission Mode

Data transmission mode is the method of transmitting data from one location to another. There are three types of transmission modes:

1. Simplex Mode

In simplex mode, data transmission takes place in only one direction. Devices can either send or receive data at one time.

Examples

Radio
Television (TV)
Newspapers

2. Half Duplex Mode

In half duplex mode, data travels in both directions, but only one direction at a time. Devices can alternatively send or receive data.

Examples

Walkie-talkie
Pager
Wireless handset

3. Full Duplex Mode

In full duplex mode, data travels in both directions simultaneously. Devices can send and receive data at the same time.

Examples

Telephone
Mobile phones
Internet communication

Guided Media

Guided media is a communication medium that uses physical cables or wires to transmit data between devices. Data travels through a fixed path, making it faster, more secure, and reliable.

Types of Guided Media

CAT6 (Category 6) Cable
Optical Fiber Cable

CAT6 (Category 6) Cable

CAT6 (Category 6) is a type of Ethernet cable used to connect computers, routers, and switches in a network. It provides faster and more reliable communication than older cables like CAT5e.

Features

Supports 1 Gbps up to 100 meters
Supports 10 Gbps for short distances
Bandwidth up to 250 MHz
Contains four twisted copper wire pairs
Reduces interference and crosstalk
Uses RJ45 connector

Applications

Home internet connections
Office LAN (Local Area Network)
School and college computer labs
Data centers

Figure: CAT6 cable showing twisted wire pairs inside a protective covering.

Optical Fiber Cable

Optical fiber is a high-speed communication cable that uses light signals to transmit data through thin strands of glass or plastic.

Features

Very high-speed communication (1 Gbps to 100+ Gbps)
Supports long-distance communication
No EMI (Electromagnetic Interference)
Very low signal loss
High reliability and efficiency

Applications

Fiber internet by ISP (Internet Service Provider)
Telecommunication networks
Undersea cables between countries
Cable TV transmission
Medical equipment (endoscopy)

Connectors

ST (Straight Tip)
SMA (Screw Mounted Adapter)
SC (Subscriber Connector)

Unguided Media

Unguided media is a communication medium that transmits data without cables using electromagnetic waves such as radio waves.

Types of Unguided Media

Wi-Fi (Wireless Fidelity)
Bluetooth
RFID (Radio Frequency Identification)
Satellite Communication

Wi-Fi (Wireless Fidelity)

Wi-Fi is a wireless technology that allows devices to connect to the internet using radio signals.

Features

Works on 2.4 GHz and 5 GHz frequency bands
Connects multiple devices at once
Uses routers and access points
Provides high-speed internet
Uses beamforming and channel bonding

Applications

Home and office internet
Online classes and learning
Public Wi-Fi in cafes and airports
Streaming and gaming

Bluetooth

Bluetooth is a short-range wireless communication technology used to connect devices and exchange data.

Features

Range of 10–30 feet
Low power consumption
Uses FHSS (Frequency Hopping Spread Spectrum)
Secure and stable connection
Easy pairing

Applications

Wireless headphones and speakers
Smartwatches and fitness bands
File sharing between phones
Keyboard and mouse connection
Car hands-free systems

RFID (Radio Frequency Identification)

RFID is a wireless technology that uses radio waves to identify and track objects using tags and readers.

Features

Uses RFID tags and readers
No need for direct contact
Works without line of sight
Tags can be passive or active
Fast and automatic data collection

Applications

ID cards in schools and offices
Inventory management
Access control systems
Contactless payment cards
Parcel and goods tracking

RJ-45 Connector

RJ-45 stands for Registered Jack-45. It is a plastic connector used with UTP (Unshielded Twisted Pair) cables in computer networking.

Features

• Looks similar to a telephone connector
• Has 8 pins inside the connector
• Can be inserted in only one direction
• Follows standard wiring schemes
• Used in Ethernet and LAN connections

Uses

• Connecting computers in a LAN
• Internet connection
• Connecting switches, routers, and hubs

Advantages

• Easy to install
• Reliable communication
• Supports high-speed data transfer

Media Converter

A media converter is a network device that connects two different types of communication media such as copper cable and fiber optic cable.

Working Principle

• Converts electrical signals into light signals
• Converts light signals back into electrical signals

Uses

• Connecting fiber optic cable with Ethernet cable
• Extending network distance
• Improving network speed and performance

Media Converter is Useful When

Copper cable distance is not enough
Fiber optic cable is required for faster communication

Advantages

• Long-distance communication
• Faster data transmission
• Reduced signal loss
• Cost effective

Networking Devices

Networking devices are hardware devices used to connect computers and other devices in a network for communication and data sharing.

Common Networking Devices

• Repeater
• Hub
• Switch
• Bridge
• Router

Repeater

A repeater is a networking device that receives weak signals, regenerates them, and sends them forward.

Functions

• Boosts/amplify weak signals (increase the strength of signal)
• Extends network distance
• Helps long-distance data communication

Advantages

• Improves signal strength
• Increases network coverage

Disadvantage

• Cannot separate noise from data

Hub

A hub is a network device with multiple ports used to connect computers in a network. When a computer sends data to a hub, the hub does not check the destination. Instead, it sends the data to all connected devices. Every device receives the signal, but only the intended computer accepts it.

Features

• Works in star topology
• Broadcasts data to all connected computers
• Simple and low-cost device
• Also called a multiport device

Advantages

• Easy to install
• Cheap networking device

Disadvantages

• Slower performance
• Sends data to all computers unnecessarily
• Less secure

Switch

A switch is a networking device used to connect multiple computers in a LAN and send data directly to the correct destination device. A switch reads the MAC address of devices and forwards data only to the intended computer instead of broadcasting to all devices.

Features

• Keeps track of device addresses
• Sends data to the correct destination only
• Faster than a hub
• Reduces network traffic

Advantages

• High speed
• Better security
• Efficient communication

Bridge

A bridge is a networking device used to connect two similar LAN networks and allow communication between them.

Features

• Connects similar LANs
• Uses physical address for filtering
• Decides whether to forward or discard data

Advantages

• Reduces unnecessary traffic
• Improves network efficiency

Router

A router is an intelligent networking device that connects multiple wired or wireless networks and determines the best path for data transmission.

Features

• Uses IP address
• Connects similar and dissimilar networks
• Finds the best route for data
• Supports wired and wireless communication

Advantages

• Fast communication
• Smart routing
• Internet sharing
• Better network management

Network Topologies

Network topology is the physical layout or geographical arrangement of computers and other devices in a network. It shows how computers are connected to each other and how data flows from one device to another in the network. Different topologies are used according to the size, cost, performance and reliability of the network.

Types of Network Topology

1. Bus Topology

Bus topology is a type of network arrangement in which all computers and devices are connected to a single main cable called bus cable or trunk cable in a linear form. Data sent from one computer travels through the main cable and reaches all connected computers. Terminators are attached at both ends of the cable to stop data signals from escaping. It is simple, cheap and mostly suitable for small networks such as school laboratories and small offices.

Features

• Uses one main cable called trunk or bus cable
• Terminators are attached at both ends
• All computers share the same communication line
• Simple structure and low cost
• Suitable for small networks

Advantages

Easy to setup and install
Requires less number of cables
Cheap and cost effective
Easy to implement and extend
Terminators prevent data loss

Disadvantages

Entire network depends on a single cable
Collision occurs when many devices send data together
Performance decreases when more computers are added
Difficult to troubleshoot faults
Not suitable for large geographical areas
Failure of main cable stops the whole network

2. Ring Topology

Ring topology is a network arrangement in which all computers are connected in a circular path forming a closed loop. Each computer is connected to two neighboring computers. Data usually travels in one direction from one computer to another until it reaches the destination. Every computer acts like a repeater to pass the signal to the next device. Ring topology provides equal access to all computers and performs better under heavy traffic conditions.

Features

• Forms a circular loop structure
• Data travels in one direction
• Each node acts as a repeater
• Equal access for all computers
• Reduces chances of collision

Advantages

High speed communication
Equal access for all computers
Better performance under heavy traffic
Can cover greater distance using repeaters
Less collision compared to bus topology

Disadvantages

Entire network depends on a single cable
Failure of one computer or cable affects the whole network
Difficult to add or remove computers
Troubleshooting is difficult
Network modification is complex

3. Star Topology

Star topology is a network arrangement in which all computers and devices are connected to a centrally located device called hub or switch. All communication between computers passes through the central device. Each computer has a separate cable connection with the hub or switch. It is one of the most popular and reliable topologies because failure of one computer does not affect the other computers in the network.

Features

• Uses central hub or switch
• Each computer has separate connection
• Easy to manage and maintain
• Failure of one node does not affect others
• Provides better performance

Advantages

Easy to add or remove computers
Failure of one computer does not affect others
Easy fault detection and troubleshooting
Reliable and efficient network
Provides better performance

Disadvantages

Entire network depends on central device
Failure of hub or switch stops the whole network
Requires more cables
More expensive than bus topology
Performance depends on central device

4. Hybrid Topology

Hybrid topology is a network topology formed by combining two or more different topologies such as bus, star and ring topology. It combines the features and advantages of different topologies into a single network. Hybrid topology is flexible, scalable and suitable for large organizations where different departments may use different topologies according to their needs.

Features

• Combination of two or more topologies
• Flexible network design
• Scalable and reliable
• Supports large networks
• Reduces network congestion

Advantages

Flexible and scalable
Reliable network
Easy to expand
Better performance
Combines advantages of different topologies

Disadvantages

Expensive to install
Complex network design
Difficult maintenance
Requires skilled manpower
Troubleshooting becomes difficult in large networks

Bus Topology	Ring Topology	Star Topology	Hybrid Topology
Uses single cable	Circular connection	Uses hub/switch	Combination of topologies
Cheap	Moderate cost	Expensive	More expensive
Easy setup	Difficult modification	Easy management	Complex structure
Failure of cable stops network	Failure affects network	One node failure does not affect others	More reliable
Slow in heavy traffic	Better performance	Fast communication	Better performance

Network Based on Coverage Area

Computer networks are classified according to the geographical area they cover. The main types are PAN, LAN, MAN and WAN.

1. PAN (Personal Area Network)

A Personal Area Network (PAN) is a small network used for communication between personal devices within a very short distance, usually up to 10 meters. It connects devices like smartphones, laptops, smartwatches, wireless headphones and tablets using Bluetooth, USB or infrared.

Advantages

• Easy to set up and use.
• Very low cost.
• Wireless communication is possible.
• Useful for personal device connection.

Disadvantages

• Very limited range.
• Low number of devices can be connected.
• Lower security if not properly managed.
• Not suitable for large data transfer systems.

2. LAN (Local Area Network)

A Local Area Network (LAN) is a network that connects computers within a small area such as a room, building, school or office. It is used to share files, printers and internet. It uses cables like CAT5 or fiber optic and provides high-speed communication within a limited area (up to about 10 km).

Advantages

• High speed data transfer.
• Easy resource sharing.
• Easy to install and manage.
• More secure than larger networks.

Disadvantages

• Limited geographical area.
• Initial setup cost can be high.
• Needs proper maintenance.
• Depends on networking devices.

3. MAN (Metropolitan Area Network)

A Metropolitan Area Network (MAN) is a network that covers a city or large town. It connects multiple LANs together to form a larger network. It is commonly used by banks, government offices or companies with branches in the same city. It covers up to around 100 km.

Advantages

• Connects multiple LANs easily.
• Covers large city area.
• Good speed compared to WAN.
• Useful for organizations with branches.

Disadvantages

• Expensive to install and maintain.
• Requires skilled technicians.
• Slower than LAN.
• Difficult to manage when large.

4. WAN (Wide Area Network)

A Wide Area Network (WAN) is a network that covers a very large area such as countries or the whole world. It connects many LANs and MANs together. It uses satellites, fiber optics and microwave signals. The Internet is the best example of WAN.

Advantages

• Covers very large geographical area.
• Enables global communication.
• Supports internet and online services.
• Allows remote access to data.

Disadvantages

• Very expensive to set up.
• Slower than LAN.
• Requires skilled maintenance.
• Security risks are higher.

Comparison of PAN, LAN, MAN and WAN

Basis	PAN	LAN	MAN	WAN
Full Form	Personal Area Network	Local Area Network	Metropolitan Area Network	Wide Area Network
Coverage Area	Very short (up to 10m)	Small area (room/building/campus)	City or district	Country or world
Speed	Low to medium	Very high	Medium	Low
Cost	Very low	Medium	High	Very high
Connection Type	Wireless/USB	Wired/Wireless	Fiber/Wireless	Satellite/Internet
Example	Bluetooth devices	School lab network	City bank branches	Internet

Network Architecture (Models of Computer Network)

Network model means how the computers interact and communicate in a network. The arrangement of computers in a network based on the computing model is called network architecture.

Types of Network Architecture

• Client/Server Network
• Peer-to-Peer Network

1. Client/Server Network

In client/server architecture, computers are connected to a device called server. The server controls all clients and provides services, resources and data to them. Clients send requests to the server and the server processes and responds to those requests. This architecture is widely used in offices, banks, schools and large organizations because it provides better security and centralized management.

Advantages

• It covers large geographical areas.
• It is more secure.
• It reduces traffic occurring in the network.
• It is more efficient type of network.
• Provides centralized data management.

Disadvantages

• Overload may occur in the server computer.
• Skilled manpower is needed for maintenance.
• It is more expensive.
• If server fails, the whole network may be disturbed.
• Depends on dedicated server.

2. Peer-to-Peer Network

Peer-to-Peer (P2P) network is a group of computers which function both as servers and workstations to share data, information and other resources. In this type of architecture, there is no dedicated server. Each computer acts both as a client and a server. All computers have equal responsibility and rights in the network. It is less expensive but also less efficient compared to client/server architecture.

Advantages

• Easy to setup.
• Cheaper than client/server architecture.
• Easy to troubleshoot.
• All computers have equal rights.
• Suitable for home, office and small organizations.

Disadvantages

• Less secure than client/server model.
• Expansion of network is limited.
• It becomes slow under heavy loads.
• Installing required software consumes more time.
• Difficult to manage large networks.

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

Client/Server Network	Peer-to-Peer Network
There is a specific server and specific clients connected to the server.	Clients and servers are not distinguished; each node acts as both client and server.
It is more secure.	It is less secure.
It is more reliable.	It is less reliable.
Overload may occur in server computer.	There is no dedicated server.
Client depends on server computer.	All computers have equal responsibilities.
Data is stored in centralized server.	Each peer has its own data.
Expensive to implement.	Less expensive to implement.

Network Protocols and IP Addressing

Network Protocols

A network protocol is a set of rules used for communication and data exchange between computers in a network. It defines how data is sent, received, and processed.

Common Network Protocols

Protocol	Full Form	Purpose
TCP/IP	Transmission Control Protocol / Internet Protocol	Used for communication over the Internet
HTTP	Hyper Text Transfer Protocol	Transfers web pages (HTML documents) on the World Wide Web
HTTPS	Hyper Text Transfer Protocol Secure	Secure version of HTTP that protects data from hackers
DHCP	Dynamic Host Configuration Protocol	Automatically assigns IP addresses to devices on a network
SMTP	Simple Mail Transfer Protocol	Used for sending e-mails
FTP	File Transfer Protocol	Transfers files between computers

Concept of IP Addressing

An IP Address is a unique address assigned to each device connected to a network.

The Internet Protocol (IP) helps:

Identify devices
Route data correctly from source to destination

There are two versions of IP:

IPv4
IPv6

IPv4 (Internet Protocol Version 4)

IPv4 is the most commonly used version of the Internet Protocol. It is a 32-bit numeric address divided into four parts, i.e., 4 octets.
It produces numbers from 0 to 255 in each octet. So, the total length is 8 × 4 = 32 bits.
i.e., N.N.N.N = XXXXXXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX

WHERE X = 1 OR 0

IPv4 can produce about 4 billion (2³²) unique connected device addresses.

Example

192.34.244.1

Features of IPv4

Uses 32-bit addresses
Supports about 4.3 billion addresses
Written in decimal format separated by dots (.)
Address format: 192.168.1.1
Suffers from address exhaustion
Uses techniques like:

NAT (Network Address Translation)
Private IP ranges

IPv6 (Internet Protocol Version 6)

IPv6 was developed to solve the limitations of IPv4. it is a 128 bit binary address displayed as 32 hexadecimal digits so 16×8=128 bit.

Features of IPv6

Uses 128-bit addresses
Provides a huge number of addresses (0-FFFF) i.e. 65535
Written in hexadecimal format and separated by colon (:)
Supports:

Auto configuration
Built-in security
Multicast communication

Example

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Difference Between IPv4 and IPv6

IPv4	IPv6
IPv4 uses 32-bit addresses.	IPv6 uses 128-bit addresses.
IPv4 addresses are written in decimal notation.	IPv6 addresses are written in hexadecimal notation.
IPv4 supports manual and DHCP configuration.	IPv6 supports automatic configuration.
IPv4 has limited address space.	IPv6 has a very large address space.
IPv4 provides less security.	IPv6 provides better security with encryption and authentication.
IPv4 header size ranges from 20 to 60 bytes.	IPv6 has a fixed header size of 40 bytes.
IPv4 does not easily support end-to-end integrity.	IPv6 supports end-to-end integrity.

Internet, Intranet, and Extranet

1. Internet

The Internet is a worldwide network that connects millions of computers and devices. It is also called "Network of networks". It allows users to share information and communicate globally using protocols like TCP/IP.

Features

Publicly accessible
Connects users worldwide
Provides services like:

Web browsing
E-mail
Social media
Online shopping

Uses wired and wireless communication
Less secure compared to private networks

2. Intranet

An Intranet is a private network used inside an organization for communication, collaboration, and sharing information among employees.

Features

Accessible only to authorized employees
More secure than the Internet
Improves internal communication
Supports file sharing and collaboration
Uses Internet technologies like TCP/IP and HTTP

3. Extranet

An Extranet is a controlled private network that allows limited access to external users such as clients, suppliers, or business partners.

Features

Provides secure communication with outsiders
Allows controlled external access
Supports collaboration between organizations
Uses authentication and security systems
Shares selected information only

Comparison among Internet, Intranet, and Extranet

Internet	Intranet	Extranet
It is open for everyone.	It is used only inside an organization.	It is used by organization and selected outsiders.
It is accessible from anywhere.	It is accessible only by employees.	It is accessible with permission.
It is used for global communication.	It is used for internal communication.	It is used for external collaboration.
It is less secure.	It is more secure.	It is securely controlled.
It has no single owner.	It is owned by an organization.	It is shared between organizations.
Examples: Google, YouTube	Examples: Office portal	Examples: Online banking system, supplier system

Chapter 1 Computer Network and Communication

Computer Network and Communication