Big picture
A computer network is two or more devices (computers, phones, printers, servers) connected so they can share data and resources. Your school lab, your home Wi-Fi and the internet are all networks, differing in size and the devices used to build them.
For the Informatics Practices board paper, you need to classify networks by size, know what each network device does, compare topologies, and answer a case study on designing a network for an organisation.
Learning goals
Explain the meaning and advantages of a computer network.
Distinguish PAN, LAN, MAN and WAN with examples.
Explain the function of each network device.
Compare star, bus, tree and mesh topologies.
Choose suitable wired or wireless media.
Solve network design case studies.
Core ideas
1. Why networks?
Resource sharing: many computers share one printer, scanner or internet connection.
Data sharing: files and databases are accessible from many places.
Communication: email, chat, video calls.
Cost saving: expensive hardware and software are shared.
Reliability: data can be backed up on other computers in the network.
Each device on a network is called a node. A computer that provides services (files, web pages, databases) is a server; computers that use those services are clients.
2. Types of networks
Type | Spread | Example | Typical ownership |
|---|---|---|---|
PAN (personal area network) | Around one person, about 10 m | Smartphone, smartwatch and earbuds connected by Bluetooth; laptop connected to a phone hotspot | Individual |
LAN (local area network) | A room, building or campus, up to about 1 km | School computer lab; office network | Single organisation |
MAN (metropolitan area network) | A city or town, up to about 30–50 km | City-wide cable TV network; network linking a bank's branches in one city | Organisation or government |
WAN (wide area network) | Across states, countries and continents | The internet; a railway reservation network across India | Many organisations |
LANs offer high speed and low cost; WANs cover huge distances but are slower and costlier, often using leased lines and satellites.
3. Network devices
Device | What it does | Where it is used |
|---|---|---|
NIC (network interface card) | Connects a computer to the network; has a unique MAC address | Every networked computer |
Modem | Converts digital signals to analog and back (modulation and demodulation) for transmission over telephone or cable lines | Connecting a home or office to the internet |
Hub | Connects computers in a LAN and sends every incoming packet to all ports | Small, simple LANs |
Switch | Connects computers in a LAN and sends each packet only to the destination port | Most modern LANs |
Repeater | Regenerates a weak signal to extend the length of a cable (about 100 m for Ethernet) | Long cable runs |
Router | Connects different networks and chooses the best path for packets using IP addresses | Connecting a LAN to the internet; linking networks |
Gateway | Connects networks that use different protocols, translating between them | Entry and exit point of a network |
Wi-Fi access point | Lets wireless devices join a wired network | Offices, homes, campuses |
4. Network topologies
Topology is the arrangement (layout) of nodes and links in a network.
Topology | Layout | Advantages | Disadvantages |
|---|---|---|---|
Star | Every node connects to a central hub or switch | Easy to install and add nodes; failure of one node doesn't affect others; easy fault detection | Needs more cable; failure of the central device stops the network |
Bus | All nodes connect to a single backbone cable | Uses the least cable; cheap and simple for small networks | Backbone failure stops the whole network; difficult to find faults; slows down with many nodes |
Tree | Groups of star networks connected to a backbone, in a hierarchy | Easy to expand; suits large organisations with departments | Depends on the backbone; more cabling and setup |
Mesh | Every node is connected to every other node (or many others) | Very reliable: if one link fails, data takes another path; no traffic problems | Very expensive; lots of cabling; complex to install |
For n nodes in a full mesh, the number of links is n(n − 1)/2. With 5 nodes, that is 10 links.
5. Transmission media
Medium | Type | Notes |
|---|---|---|
Twisted pair cable | Wired | Cheap, common in LANs; up to about 100 m |
Coaxial cable | Wired | Better shielding; used in cable TV |
Optical fibre | Wired | Light signals; highest speed and distance; immune to electrical interference; costly |
Radio waves | Wireless | Wi-Fi and mobile networks; can pass through walls |
Microwaves | Wireless | Line of sight between towers; long-distance links |
Infrared | Wireless | Very short range; can't pass through walls (remote controls) |
Satellite | Wireless | Covers huge areas; used for TV, GPS and remote internet |
6. Network design case study
Example. An educational trust has four buildings: Admin (100 computers), Library (40), Science Block (60) and Hostel (25). Distances: Admin–Library 50 m, Admin–Science 110 m, Admin–Hostel 90 m, Library–Science 70 m, Science–Hostel 150 m.
Question | Answer and reasoning |
|---|---|
Where should the server be? | Admin, because it has the most computers, so most traffic stays within that building |
Suggest a cable layout | A star layout with Admin at the centre, connecting each building directly to Admin |
Where is a repeater needed? | On the Admin–Science link (110 m), because Ethernet cable signals weaken beyond about 100 m |
Which device connects computers within each building? | A switch |
Which device connects the network to the internet? | A router (with a modem) |
Which medium suits a fast link between buildings? | Optical fibre, for speed, distance and immunity to interference |
The trust opens a branch in another state. What type of network links them? | A WAN |
A reliable approach to questions
Classify the network by area: person (PAN), building or campus (LAN), city (MAN), country or world (WAN).
Name the device by its job: connect computers in a LAN (switch), regenerate signals (repeater), connect networks (router), different protocols (gateway), analog line (modem).
For topology questions, think about what happens if one node or the centre fails.
In case studies, put the server where the most computers are, use a star layout from there, add repeaters beyond 100 m, and pick optical fibre for long or fast links.
Connections that matter
Internet and web explains the services that run over these networks.
Computer Science: computer networks covers the same topics with protocols and switching.
Societal impacts discusses cyber safety on networks.
Common mistakes
Saying a hub sends data only to the destination. That is a switch.
Calling a mesh topology cheap. It is the most expensive.
Using a router where a repeater is needed, or the reverse.
Treating a city-wide network as a LAN.
Revision checklist
I can explain the advantages of networks and the roles of servers and clients.
I can classify PAN, LAN, MAN and WAN.
I can explain each network device.
I can compare star, bus, tree and mesh topologies.
I can choose transmission media.
I can solve a network design case study.