Unit 5 · Session 3
Network Types and Topologies
🎯 Learning Objectives
By the end of this session, you will be able to:
- ✅ Define what a computer network is.
- ✅ Differentiate between a Local Area Network (LAN) and a Wide Area Network (WAN).
- ✅ Describe the common network topologies: Bus, Star, and Ring.
Networking Basics: Network Types and Topologies
What is a Computer Network?
A computer network is a collection of two or more computers and other hardware devices connected together to share resources and exchange data.
Think of it as a digital team, where each member can communicate and share tools.
- Components: Computers, printers, routers, switches.
- Purpose: Share files, printers, internet access, and more.
Network Types 📊
Networks are most often classified by their geographical scope.
Local Area Network (LAN)
Covers a small, limited area like a single building or campus.
Wide Area Network (WAN)
Covers a broad geographical area, like a city, country, or the entire globe.
Deep Dive: Local Area Network (LAN)
A network that connects computers within a limited geographical area, such as a single building or a school campus.
- Scope: Small (office, home, lab)
- Purpose: Share resources like printers and files.
- Speed: Typically very fast.
Example: The computer network in your university library, connecting all the PCs, printers, and servers together.
Deep Dive: Wide Area Network (WAN)
A network that covers a broad geographical area, often by connecting multiple LANs together.
- Scope: Large (city, country, global)
- Structure: A network of networks.
- Speed: Slower than a LAN due to distance.
The most famous example of a WAN is the Internet itself!
📏 Beyond LAN and WAN: PAN and MAN
Networks come in four common sizes, from your body to the whole planet:
| Type | Covers | Example |
|---|---|---|
| PAN (Personal Area Network) | A few metres around one person | Your phone linked to a smartwatch and wireless earbuds by Bluetooth |
| LAN (Local Area Network) | A room, building or campus | A college computer lab |
| MAN (Metropolitan Area Network) | A whole city | A city's traffic-camera network, or a university with campuses across one city |
| WAN (Wide Area Network) | A country or the world | A bank's national branch network, or the internet |
Bigger networks are usually built by joining smaller ones together.
A city-sized network: Kathmandu at night
🎯 Quick-Fire: PAN, LAN, MAN or WAN?
Call out your answer before each one is revealed.
| 1. Your smartwatch sending step counts to your phone | PAN |
| 2. A hospital's network across three buildings on one site | LAN |
| 3. CCTV cameras at junctions across Kathmandu, linked to one control room | MAN |
| 4. A company linking its offices in Kathmandu, Dubai and London | WAN |
| 5. Wireless earbuds playing music from your laptop | PAN |
| 6. Ten PCs and a printer in a small travel agency | LAN |
🖥️ Who's in Charge? Client–Server vs Peer-to-Peer
Client–Server
- Powerful central computers (servers) store data and provide services.
- Users' devices (clients) ask the servers for what they need.
- Examples: mobile banking, email, Netflix, your college's student portal
- ✅ Easy to secure, back up and control
- ⚠️ If the server fails, everyone is affected
Peer-to-Peer (P2P)
- Every device is equal and shares directly with the others.
- There's no central server.
- Examples: AirDrop or Quick Share between phones, BitTorrent, two PCs sharing a folder at home
- ✅ Cheap and simple for small groups
- ⚠️ Hard to secure and manage as it grows
Think: Why does every bank use client–server, not peer-to-peer?
🎬 Client–Server vs Peer-to-Peer
What is Network Topology? 🔍
Network Topology refers to the physical layout or arrangement of the devices on a network. It's the network's blueprint.
We'll explore the three most common historical and modern topologies:
🔍 The Main Topology Shapes
Bus Topology
All devices are connected to a single central cable, called the bus or backbone.
How it works:
- Data is sent down the entire cable.
- All devices see the data, but only the intended recipient accepts it.
- Simple and inexpensive to set up.
Major Disadvantage ⚡
If the main cable fails, the entire network goes down.
The T-connector that made a bus
Ring Topology
All devices are connected in a closed loop or ring. Data travels around the ring, typically in one direction.
How it works:
- Each device receives data and passes it along to the next one.
- Prevents data collisions since data flows in one direction.
Major Disadvantage ⚡
A failure in one device or cable can break the loop and take down the entire network.
Star Topology ⭐
All devices are connected to a central device, like a hub or a switch. This is the most common topology in modern LANs.
How it works:
- All data passes through the central hub/switch.
- Easy to add or remove devices.
- Easy to troubleshoot.
Key Advantage ✅
If one cable fails, only that single device is affected. The rest of the network remains functional.
🕸️ Mesh Topology
Each device connects to several others, so data has more than one path. In a full mesh, every device connects to every other device.
How many cables for a full mesh?
Links = n × (n − 1) ÷ 2, where n is the number of devices
- 5 devices: 5 × 4 ÷ 2 = 10 links
- 10 devices: 10 × 9 ÷ 2 = 45 links
- 50 devices: 50 × 49 ÷ 2 = 1,225 links
Key Advantage ✅
If one link fails, data simply takes another path.
Major Disadvantage ⚡
Lots of cables and ports make it expensive.
Where it's used: the internet's backbone between cities, and home "mesh Wi-Fi" systems with several units that pass the signal between them.
🕸️ A Real Mesh: The 1992 Internet Backbone
🌳 How Real Networks Look: Tree and Hybrid
Real networks rarely use just one shape.
Tree topology
Stars connected in layers, like branches on a tree. For example, on a college campus:
- A main switch in the server room connects to
- a switch in each building, which connects to
- a switch on each floor, which connects to the PCs.
Hybrid topology
Two or more topologies combined. The internet is the biggest example:
- a mesh of fibre links between cities and countries
- stars at the edge, in every home and office
Designers mix shapes to balance cost against reliability.
🔧 Activity: What Breaks?
For each failure, who loses their connection: one device, or the whole network?
| 1. Bus: the main backbone cable is cut | The whole network |
| 2. Star: one PC's cable is unplugged | Only that PC |
| 3. Star: the central switch loses power | Everyone. The switch is a single point of failure |
| 4. Ring: one computer in a simple ring breaks down | The whole ring |
| 5. Full mesh: one cable between two devices is cut | Nobody. Data takes another path |
Follow-up: How could an office protect itself from failure 3?
Keep a spare switch, put the switch on a UPS (backup battery), or use two linked switches.
📊 Topology Comparison
| Bus | Ring | Star | Mesh | |
|---|---|---|---|---|
| Cabling cost | Lowest | Low | Medium | Highest |
| One cable fails | All down | All down | One device down | No one affected |
| Adding a device | Disrupts the network | Breaks the loop | Easy: plug into the switch | Needs many new links |
| Troubleshooting | Hard | Hard | Easy | Complex |
| Used today | Rarely | Rarely in LANs | Almost every LAN | Backbones, mesh Wi-Fi |
Star wins for offices because it balances cost, reliability and ease of management.
🎬 Why the Internet Survives Failures
Networking in Nepal: Real-World Examples
LAN Example
A branch of a commercial bank like NIC Asia in Pokhara. All the teller computers, manager's PC, and printers are connected in a LAN, likely using a Star topology with a central switch.
WAN Example
The network of an Internet Service Provider like WorldLink. They connect their LANs in various cities (Kathmandu, Biratnagar, Nepalgunj) across the country using a wide-area fiber optic network. This forms a national WAN.
🎯 Activity: Design the Network
An accounting firm has 12 PCs, 2 printers and a file server on one floor in Kathmandu, and a new 4-person branch in Butwal. Staff also use their phones in the office. In groups:
- Which network type does each office need, and what links the two offices?
- Which topology would you use inside the Kathmandu office?
- What is your single point of failure, and how would you protect it?
- Client–server or peer-to-peer for the firm's files? Why?
Model answer: Each office has a LAN, and the offices are linked over a WAN (the internet). Inside, use a star with a central switch, plus a Wi-Fi access point for phones. The switch is the single point of failure, so keep a spare and put it on a UPS. Use client–server, because client files must be secured and backed up centrally.
Summary & Key Takeaways 🎯
- A network is a group of connected computers that share resources.
- Networks are classified by size: LANs are local (office), and WANs are wide-area (Internet).
- Topology is the physical layout of a network (its "map").
- While Bus and Ring were used historically, the Star topology is the reliable, modern standard for LANs.
Image & Video Credits
Images
- "NetworkTopologies.svg": Maksim, derivative work by Malyszkz, public domain — https://commons.wikimedia.org/wiki/File:NetworkTopologies.svg
- "BNC Tee connector, with Ethernet cable connected": Raimond Spekking, CC BY-SA 4.0 — https://commons.wikimedia.org/wiki/File:BNC_Tee_connector,_with_Ethernet_cable_connected-92166.jpg
- "Netgear Gigabit Switch 5-port": Simon A. Eugster, CC BY-SA 3.0 — https://commons.wikimedia.org/wiki/File:Netgear_Gigabit_Switch_5-port.jpg
- "NSFNET-backbone-T3": Merit Network, Inc., CC BY-SA 3.0 — https://commons.wikimedia.org/wiki/File:NSFNET-backbone-T3.png
- "Central Ridge Library Computer Rm 2026": Rachelb ABC, CC0 — https://commons.wikimedia.org/wiki/File:Central_Ridge_Library_Computer_Rm_2026.jpg
- "Thamel at Night - Kathmandu, Nepal (1)": Saddam Hussain Ansari, CC BY 4.0 — https://commons.wikimedia.org/wiki/File:Thamel_at_Night_-_Kathmandu,_Nepal_(1).jpg
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Videos (YouTube)
- PowerCert Animated Videos, "Network Topologies (Star, Bus, Ring, Mesh, Ad hoc, Infrastructure, & Wireless Mesh Topology)" (3:23 to 4:43)
- Professor Messer, "Client Server and Peer-to-Peer Networking - CompTIA Network+ N10-005: 3.5" (0:03 to 1:33)
Exam Practice 📝
Short answer
- What is a computer network? List three benefits.
- Differentiate between LAN and WAN.
- What is mesh topology? Where is it used?
Long answer
- Explain different network topologies with their advantages and disadvantages.
- A company has offices on three floors of a building. Suggest a suitable network type and topology, and justify your answer.
Revise the answers in the full note linked on the last slide.
Thank You
Questions before we wrap this hour?
Next: Unit 5 · Session 4 — Protocols, Hardware, and Wireless Networking