Bus Topology
Picture a bus route along one long road. Every stop is on the same road, and the bus passes every stop. A bus network works the same way: one cable, and every computer sits on it.
1What a bus topology is
Send a message first with everything working. Watch which computers it passes.
2How data travels on a bus
When PC A sends a message, it goes onto the backbone and travels in both directions, all the way to both ends. It passes every computer on the way, and every computer receives it. Each one checks who the message is addressed to: the addressee keeps it, the rest ignore it.
At each end, a terminator soaks up the signal. Without it, the signal would bounce back off the end of the cable and crash into the next message.
3When the backbone breaks
In the lab, cut PC C’s own short cable: only PC C is lost. Now cut the backbone. The cut leaves two cable ends without terminators, signals bounce back from them, and the whole network stops — not just the computers beyond the cut.
4Advantages and disadvantages
- Uses the least cable, so it is cheap.
- Simple to set up for a few computers.
- Easy to add a computer: connect it to the backbone.
- No central device is needed.
- If the backbone fails, the whole network fails.
- Hard to find where a fault is along a long cable.
- Gets slower as more computers are added.
- Every computer receives every message, which is less secure.
5Check yourself
In a bus topology, the main cable that all computers connect to is called the…
What is the job of a terminator in a bus network?
PC A sends a message to PC D on a bus. Which computers receive it?