# Computer Networks Basics — Types, Topologies and Devices

Source: https://skills101.in/learn/computer-networks/computer-networks-basics — Skills101 free tutorial (Computer Networks). Updated 2026-11-09.

A **computer network** is two or more devices connected so they can share data. Your phone on Wi-Fi, an office of laptops and the whole internet are all networks — just of different sizes.

## 1. Types by size

| Type | Covers | Example |
|---|---|---|
| **PAN** (Personal) | a few metres | phone ↔ earbuds over Bluetooth |
| **LAN** (Local) | a home, office, college building | college computer lab, home Wi-Fi |
| **MAN** (Metropolitan) | a city | a city-wide cable network |
| **WAN** (Wide) | countries, the world | the internet, a bank's branch network |

## 2. Topologies: how devices are connected

![Star (devices around a central switch), bus (all on one cable) and ring (each device connected to two neighbours) topologies](https://skills101.in/learn-img/computer-networks/topologies.svg)

| Topology | Pros | Cons |
|---|---|---|
| **Star** | easy to add devices; one broken cable affects one device | the central switch is a single point of failure |
| **Bus** | cheap, little cable | one break stops the whole network; collisions |
| **Ring** | orderly data flow | one break can stop everything (unless dual ring) |
| **Mesh** | very reliable — many paths | expensive, lots of cabling |
| **Tree / hybrid** | scales well | more complex |

Most modern LANs are **star** (everything connects to a switch); the internet backbone is closer to a **mesh**.

## 3. Network devices

![Comparison: a hub (layer 1) sends to all ports; a switch (layer 2) sends only to the right port using MAC addresses; a router (layer 3) connects different networks using IP addresses](https://skills101.in/learn-img/computer-networks/devices.svg)

| Device | What it does |
|---|---|
| **NIC** (network card) | connects a device to the network; has a **MAC address** |
| **Hub** | repeats data to every port (dumb, obsolete) |
| **Switch** | learns which MAC address is on which port and sends frames only there |
| **Router** | connects **different networks** and picks the path using **IP addresses** |
| **Modem** | converts digital data to signals for the phone line / fibre / cable and back |
| **Access point** | gives Wi-Fi access to a wired network |
| **Firewall** | filters traffic using security rules |

Your home "Wi-Fi router" is usually a **modem + router + switch + access point + firewall** in one box.

## 4. Key words you'll hear

- **Bandwidth** — maximum data per second (e.g. 100 Mbps).
- **Latency** — delay for data to travel (ms). Gaming and video calls care about this.
- **Throughput** — what you actually get.
- **Protocol** — agreed rules for communication (HTTP, TCP, IP).
- **Client–server** — clients request, servers respond (websites). **Peer-to-peer** — every device can be both (torrents).

## 5. Transmission modes

- **Simplex** — one way only (TV broadcast).
- **Half duplex** — both ways, one at a time (walkie-talkie).
- **Full duplex** — both ways at once (phone call).

## Common mistakes

- Saying "switch and router are the same". A switch connects devices **in** a network; a router connects **networks**.
- Confusing bandwidth (capacity) with speed experienced (throughput, latency).

## Quick recap

- PAN < LAN < MAN < WAN by area.
- Topologies: star (most common), bus, ring, mesh, hybrid.
- Hub (all ports), switch (MAC, right port), router (IP, between networks).
- Bandwidth = capacity; latency = delay.


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