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Data paths in a network

Start a set of 8
Step 3 of 9

Predict before changing a link: can data still get from S to T? Set each control to 0 for OFF or 1 for ON. Try all four combinations. An OFF link disappears. S–A and S–B always work; A and B can forward data. The readout counts the two possible routes in this model, not the fastest route

Two possible routes: S–A–T and S–B–T. The controls remove or restore the last link of each route; all four devices remain in place. Visible connections: S–A, S–B, A–T, B–TSABT
Working S-to-T routes
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With A–T OFF and B–T ON, which path remains?

Year 7, Chapter 1, 3 difficulty levels, No calculatorBuild a worksheet

Working connections and possible paths

Follow the links that actually work, not the spaces between nearby devices

  1. A line is one direct connection A network connects devices so they can exchange data. In these diagrams, each circle is a device and each solid line is a working two-way link. A device in this model can pass data to another linked device
  2. Check every step For S → A → T to work, both S–A and A–T must work. Being close on the page does not create a connection
  3. Look for another route One failed link can block a route without blocking every route. Start again at the source and follow the remaining working links
  4. Keep the model's limits This diagram shows possible paths, not physical distances or speeds. A possible path does not tell us which path a real network will choose or guarantee delivery

Worked example

Each circle is a labelled device. A solid line is a working connection that data can use in either direction. Each device in this model can pass data along its working connections. Line length does not show distance or speed

Network devices A, B, C, D, E and F. Working connections: A–B, B–C, D–E, A–D, B–E, C–F.ABCDEF

All shown connections currently work. If just one listed connection fails, which failure leaves no working path from A to F? All devices and other connections still work

  1. Remove C–F: A can reach only A, B, C, D, E, so F cannot be reached

  2. Remove A–B: a working path is A → D → E → B → C → F

  3. Remove D–E: a working path is A → B → C → F

  4. The answer is C–F

Common mistakes

Direct is not the same as reachable
✕\(\displaystyle \text{No path}\)✓\(\displaystyle \text{Check links}\)
There may be an indirect path through another device even when there is no direct link
One failure need not stop everything
✕\(\displaystyle \text{All blocked}\)✓\(\displaystyle \text{Try a route}\)
Follow the remaining working connections. An alternative route may still reach the destination

Difficulty levels

introRead direct connections and check supplied paths. Eight fixed cases
standardRecheck paths and reachability after a link fails. Eight fixed cases
challengePredict which link change restores or blocks access. Eight fixed cases

Questions about this topic

Do all real computers forward other devices' data?+

No. These questions explicitly give the model's devices that role. Real networks use particular devices and protocols; we will study those separately

Does a possible path guarantee that data arrives?+

No. This model checks connections only. Actual delivery also depends on devices, protocols and conditions that are not modelled here

Are the practice questions unlimited?+

No. There are 24 fixed network cases, eight at each level. Changing the answer order does not create a new case. Repeats are useful revision, not fresh mastery evidence

Does this assess a complete network explanation or project?+

No. It checks choices about a supplied model. Constructing and explaining your own network, investigating real transmission and completing projects require additional evidence

Can I use a calculator?+

No. This topic is practised without a calculator

Which year level and chapter is this?+

Year 7 Digital Technologies, chapter 1: Digital systems

In this chapter

Hardware specifications for a stated taskData paths in a networkPackets and reassemblyProtecting an accountChecking account messages