Introduction to Computer Networks
IGCSE Computer Science
Dr. Jyotsna Sharma
NETWORKING FUNDAMENTALS
IGCSE SYLLABUS
What is a Network?
A network is a group of two or more
computer systems linked together to share
resources and communicate effectively.
Networks have become the backbone of
modern computing.
Key Benefits
• Resource Sharing: Access printers,
scanners, and internet connections
across multiple devices
• Communication: Enable email, instant
messaging, and Voice over Internet
Protocol (VOIP)
• Data Sharing: Centralised file storage
allows teams to access and collaborate
on documents from anywhere
Network Hardware
To build a network, we need specialized hardware:
NIC (Network Interface Card):
Router
• Allows a device to connect to a network.
• Router: Forwards data packets between different
networks
• (e.g., your home LAN to the Internet)
Hub vs. Switch
• Hubs send data to everyone;
•
Switches send data to the specific intended device
(more efficient)
• Hubs are largely obsolete now!
LAN vs WAN
Local Area Network (LAN):
Wide Area Network (WAN):
• Covers a small geographic area (e.g., a school, office,
• Covers a large geographic area (e.g., countries or
or home).
• High data transfer speeds; usually owned by the
organization.
continents).
• The Internet is the largest example of a WAN.
• Often uses third-party infrastructure (satellites,
undersea cables).
Wired vs. Wireless Connectivity
Wired (Ethernet/Fibre Optic):
Wireless (Wi-Fi):
• Pros: Faster, more secure, more reliable.
• Pros: Easy to connect multiple devices, high mobility.
• Cons: Not portable, expensive to install cabling.
• Cons: Signal can be blocked by walls; less secure
(requires encryption).
Network Topologies (Layouts)
How devices are physically or logically arranged:
• Bus Topology: All devices connected to a single central cable.
• Ring Topology: All devices connectedin a closed circular loop, with each node linked to exactly two neighboring
devices.
• Star Topology: All devices connect to a central hub/switch. (Most common in modern LANs).
• Mesh Topology: Every device is connected to every other device (High redundancy).
Client-Server vs. Peer-to-Peer
Client-Server:
Peer-to-Peer (P2P):
A central server manages security and files; "clients"
Every computer has equal status; files are shared directly
(your PC) request services. (Used in schools).
between workstations. (Used for small home networks).
Data Transmission & Packets
Data isn't sent in one big chunk; it’s broken into Packets.
A Packet contains:
• Sender’s IP address.
• Receiver’s IP address.
• Packet sequence number.
• The actual data (payload).
• Error checking code (Checksum).
Network Security
How do we keep networks safe?
• Firewalls: Monitors incoming and outgoing traffic to block unauthorized access.
• Encryption: Scrambling data so it can’t be read without a key.
• User IDs and Passwords: The first line of defense for access control.
Thank You!