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1. Introduction

A computer network is a collection of computers and other devices connected together so that they can share resources and exchange information. The devices, called nodes, communicate with each other over a transmission medium such as cables or radio waves, guided by a set of rules known as protocols. Networking is the technology behind everything from a small home Wi-Fi setup to the global Internet, and every student of informatics needs a solid understanding of how these systems are built.

Networks are classified by their geographical reach into PAN, LAN, MAN, and WAN, and by their physical layout into topologies such as bus, star, ring, mesh, and tree. The hardware that builds these networks, including hubs, switches, routers, modems, and gateways, each has a distinct role, and the transmission media that carries the signals, from twisted pair cables to optical fibres and satellite links, differ in speed, cost, and reliability.

This chapter introduces the essential vocabulary and concepts of computer networks. We will study the categories of networks, the characteristics of each topology, the major transmission media, the key network devices, the two principal switching techniques, and the common protocols that govern data exchange. Special attention is paid to choosing the right topology or medium for a given scenario, since such reasoning questions appear regularly in the examination.

2. Network Basics and Terminology

3. Types of Networks

3.1 PAN (Personal Area Network)

A PAN covers the smallest area, typically a few metres, connecting personal devices such as a smartphone, laptop, and wireless earbuds. Bluetooth and infrared are common technologies used to build a PAN.

3.2 LAN (Local Area Network)

A LAN connects computers within a limited geographical area such as a school, office, or building. It is owned by a single organisation, offers high speed, and is relatively inexpensive to set up. A school's computer laboratory is the classic example of a LAN.

3.3 MAN (Metropolitan Area Network)

A MAN spans a city or a large campus, typically tens of kilometres. It connects several LANs, often using optical fibre, and is larger than a LAN but smaller than a WAN. Cable television networks and city-wide Wi-Fi grids are examples.

3.4 WAN (Wide Area Network)

A WAN covers a very large geographical area, possibly a country or the whole world, connecting LANs and MANs across long distances. The Internet is the largest WAN. WANs rely on leased telephone lines, satellites, and optical fibres, and have the lowest speed per connection but the greatest reach.

4. Network Topologies

The arrangement of nodes and connections in a network is called its topology.

4.1 Bus Topology

All nodes are connected to a single backbone cable called the bus. Data travels in both directions along the bus. A break in the backbone disables the whole network, but the cost is low and wiring is simple.

4.2 Star Topology

Every node connects directly to a central device, usually a hub or switch. Data passes through the central device. If one node's cable fails, only that node is affected, but the central device is a single point of failure. The star is the most common LAN topology.

4.3 Ring Topology

Nodes are connected in a closed loop, and data travels in one direction around the ring, passing through each node. Each node regenerates the signal. One failing node can disrupt the entire ring.

4.4 Mesh Topology

Every node is connected to every other node. The mesh provides multiple paths between any two nodes, so it is highly fault tolerant and reliable, but it requires a large number of cables and is expensive. The Internet's core uses a mesh-like structure.

4.5 Tree Topology

A tree combines several star networks connected by a common backbone bus, forming a hierarchy. It is suitable for organisations with departments, but the failure of the backbone affects all connected star segments.

5. Transmission Media

5.1 Wired Media

5.2 Wireless Media

6. Network Devices

7. Switching Techniques

Switching decides how data is routed from source to destination.

8. Common Network Protocols

The categories of networks can be represented simply in Python, for example by mapping each network type to its approximate coverage:

network_types = {"PAN": 10, "LAN": 1000, "MAN": 100000, "WAN": 10000000}
for name, meters in network_types.items():
    print(name, "covers up to", meters, "metres")

Such a model helps to compare the scale of each network at a glance and reinforces the ordering PAN, LAN, MAN, WAN.

Quick Revision Tables

Table 1: Types of Networks

Type Area Example
PAN A few metres Bluetooth devices
LAN A building / campus School computer lab
MAN A city Cable TV network
WAN Country or world The Internet

Table 2: Network Topologies and Their Features

Topology Central Device Best Feature Main Disadvantage
Bus None (backbone) Cheap, simple Backbone failure stops all
Star Hub / Switch Fault tolerant per node Central device failure
Ring None (loop) Orderly data flow One node fails the ring
Mesh None Highly reliable Expensive, many cables
Tree Root backbone Hierarchical expansion Backbone failure

Mind Map

graph TD A["Computer Networks"] --> B["Types"] A --> C["Topologies"] A --> D["Transmission Media"] A --> E["Devices"] A --> F["Switching"] A --> G["Protocols"] B --> B1["PAN, LAN"] B --> B2["MAN, WAN"] C --> C1["Bus, Star, Ring"] C --> C2["Mesh, Tree"] D --> D1["Twisted pair, Coaxial, Optical fibre"] D --> D2["Radio, Microwave, Infrared, Satellite"] E --> E1["Modem, Hub, Switch"] E --> E2["Repeater, Router, Gateway"] F --> F1["Circuit switching"] F --> F2["Packet switching"] G --> G1["TCP/IP, HTTP, FTP"] G --> G2["SMTP, POP3, Telnet"]

Important Diagrams (SVG)

Diagram 1: Network Types by Coverage

Network Types by Area Covered PAN A few metres Personal devices Bluetooth, phone Smallest LAN Building or campus School computer lab High speed Single owner MAN A city or campus Connects LANs Cable TV networks Tens of km WAN Country or whole world Connects LANs and MANs across long distances The Internet is the largest WAN Largest coverage, lowest per-connection speed Golden Rule As the covered area grows from PAN to WAN, the number of machines and the cost increase

Diagram 2: Star and Bus Topology Comparison

Star vs Bus Topology Star Topology Bus Topology Switch node 1 node 2 node 3 node 4 every node connects to the centre backbone bus nodes tapped on one cable Star: Pros and Cons One cable fails, only that node stops Central switch is single point of failure Bus: Pros and Cons Simple and cheap wiring Break in backbone stops whole network Golden Rule The central device of a star is its single point of failure, just as the backbone is for a bus

Common Mistakes

  1. Calling the Internet a LAN; the Internet is a WAN because it spans the entire globe.
  2. Confusing a hub with a switch: a hub broadcasts to all nodes while a switch sends data only to the intended destination.
  3. Believing that ring topology data flows in both directions; in a ring it normally travels in one direction only.
  4. Forgetting that star topology has a single point of failure in its central device, even though it is otherwise fault tolerant.
  5. Using "coaxial cable" when referring to optical fibre's speed advantage, or vice versa; they differ greatly in bandwidth and immunity to interference.
  6. Thinking packet switching needs a dedicated path; that is the feature of circuit switching.
  7. Mixing up LAN, MAN, and WAN by area: LAN for a building, MAN for a city, WAN for a country.
  8. Believing a modem is used in a LAN; it converts digital to analogue for telephone lines, a WAN technology.
  9. Forgetting that a repeater does not route data, it only amplifies or regenerates the signal.

Exam Tips

  1. Practise one-line definitions of PAN, LAN, MAN, and WAN, since 1-mark definition questions are common.
  2. Memorise a pro and a con for each topology so you can answer "which topology and why" questions confidently.
  3. Learn to match scenarios to media: long distance and high speed means optical fibre; short-range device pairing means Bluetooth.
  4. Remember the ordering of network sizes: PAN less than LAN less than MAN less than WAN.
  5. Be able to distinguish circuit switching (telephone) from packet switching (Internet) with one example each.
  6. Know the classic devices by role: modem connects to telephone line, router joins networks, switch directs within a LAN, gateway translates protocols.
  7. In reason-based questions, name the topology first and then justify it with one advantage relevant to the situation described.

Conclusion

Computer networks bring computers together to share data and resources, and a firm grasp of their vocabulary is essential for understanding how the Internet works. Networks are classified by area into PAN, LAN, MAN, and WAN, and by layout into bus, star, ring, mesh, and tree topologies, each with its own trade-offs between cost, reliability, and simplicity. Data travels through twisted pair, coaxial, optical fibre, or wireless media such as radio, microwave, and satellite links, and is directed by devices including modems, hubs, switches, routers, repeaters, and gateways. Packet switching, the technology behind the Internet, and the protocol families such as TCP/IP, HTTP, FTP, and SMTP, define how that data actually moves. Together these ideas prepare the student for the final chapters on the Internet and the Web.