Roads and journeys
Look at a map of a town. You see the roads: where they are and how they join. That is one picture.
Now look at a bus timetable. It shows the journeys people really make, which may not follow the roads you expect. A cabled site has both pictures too.
Key words
| Word | What it means |
|---|---|
| Topology | the shape of a network: how its parts are joined |
| Physical topology | the real layout of cables and devices |
| Logical topology | the path data takes, whatever the cables look like |
| Star | every device has its own cable to one central device |
| Bus | all devices share one long cable |
| Ring | devices joined in a circle, each to the next |
| Mesh | many devices joined to many others |
| Hierarchical | arranged in layers, like a tree |
| Network | devices joined so they can share data |
| Switch | a device that sends each frame only to the right port |
| Hub | an old device that repeats every signal to every port |
| Ethernet | the common way to join wired devices in an office |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can describe the main topologies, and explain the difference between a physical topology and a logical one.
Starter: what you know
Have a go
Starter: what you know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Physical topology: the real layout
A physical topology shows where the cables really run.
In a star, each device has its own cable to a central switch. In a bus, one long cable passes every device. In a ring, each device joins the next in a circle. In a mesh, devices have several links, so there is more than one path.
The topologies compared
| Topology | Good point | Weak point |
|---|---|---|
| Star | One broken cable stops one device. Easy to add to | The central switch is a single weak spot |
| Bus | Uses little cable | One break can stop all. Hard to fault-find |
| Ring | Even use of the circle | One break can stop the circle unless it is double |
| Mesh | Very reliable: many paths | Costly. Many cables to fit and label |
| Hierarchical | Neat, easy to grow by floors and buildings | The top layer must be strong |
The cells students fill in are left blank in this preview.
Logical topology: the path data takes
A logical topology describes how data moves. It can differ from the cable layout.
Old Ethernet with a hub was a physical star, but data went to every port, like a bus. So it was a logical bus. Today a switch sends each frame to one port, so a star is a star in both senses.