Network Topology
Topology is the arrangement (layout) of devices and connections in a network. The choice of topology affects performance, cost, and reliability.
Learning Objectives
- 11.6.1.2 Describe bus, ring, star, and mesh topologies
Conceptual Anchor
The Road System Analogy
Think of network topology like road layouts. A bus is a single main road with houses along it. A ring is a circular road. A star is a roundabout with roads radiating out. A mesh is a city grid where every intersection connects to many others.
Rules & Theory
1. Bus Topology
┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐
│ PC 1 │ │ PC 2 │ │ PC 3 │ │ PC 4 │
└──┬───┘ └──┬───┘ └──┬───┘ └──┬───┘
│ │ │ │
══════╪═════════╪═════════╪═════════╪══════ ← Main cable (backbone)
T T
(terminators at both ends)| Advantages | Disadvantages |
|---|---|
| Cheap — uses least cable | If backbone fails, entire network goes down |
| Easy to set up for small networks | Performance drops as more devices are added |
| No central device needed | Difficult to troubleshoot |
2. Ring Topology
┌──────┐
│ PC 1 │
└──┬───┘
╱ ╲
┌──────┐ ┌──────┐
│ PC 4 │ │ PC 2 │
└──┬───┘ └──┬───┘
╲ ╱
┌──────┐
│ PC 3 │
└──────┘
Data travels in ONE direction around the ring| Advantages | Disadvantages |
|---|---|
| Equal access — no collisions | If one device fails, the ring breaks |
| Data travels in one direction (predictable) | Adding/removing devices disrupts network |
| Good performance under heavy load | Slower — data must pass through each device |
3. Star Topology
┌──────┐ ┌──────┐
│ PC 1 │─────────│ PC 2 │
└──────┘ │ └──────┘
╲ │ ╱
┌──────────┐
│ Switch │ ← Central device
└──────────┘
╱ │ ╲
┌──────┐ │ ┌──────┐
│ PC 4 │─────────│ PC 3 │
└──────┘ └──────┘| Advantages | Disadvantages |
|---|---|
| If one cable fails, only that device is affected | If central device fails, entire network goes down |
| Easy to add/remove devices | Requires more cable than bus |
| Easy to troubleshoot | Central device is a single point of failure |
| Good performance (dedicated connections) | More expensive (switch/hub costs) |
4. Mesh Topology
┌──────┐─────────┌──────┐
│ PC 1 │╲ ╱│ PC 2 │
└──┬───┘ ╲ ╱ └──┬───┘
│ ╳ │
│ ╱ ╲ │
┌──┴───┐╱ ╲┌──┴───┐
│ PC 4 │─────────│ PC 3 │
└──────┘ └──────┘
Every device connects to every other device| Advantages | Disadvantages |
|---|---|
| Highly reliable — multiple paths | Expensive (lots of cable and ports) |
| No single point of failure | Complex to set up and manage |
| Fast — direct connections | Not practical for large networks |
Most Common Today
Star topology is by far the most common in modern LANs. Most home and office networks use a star layout with a central router/switch. The internet itself uses a mesh topology for redundancy and reliability.
Common Pitfalls
Topology = Physical Layout
Students sometimes confuse logical topology (how data flows) with physical topology (how cables are arranged). A network can be physically a star but logically a ring (e.g., Token Ring).
Tasks
Draw diagrams for bus, ring, star, and mesh topologies.
Explain why star topology is the most popular choice for modern LANs.
A school has 3 computer labs with 15 computers each. Recommend a topology for each lab and explain your choice.
Compare bus and star topologies in terms of cost, reliability, and scalability. Which would you recommend for a growing business? Why?
Self-Check Quiz
Q1: Which topology has a single point of failure at the central device?
Q2: In which topology does data travel in one direction?
Q3: Which topology uses the most cabling?