← ACARA Digital Technologies Years 7–8

Redundant routes keep a network working

A spare path between devices. If one link or router fails, packets are sent another way so data keeps flowing. It costs more because extra cables and routers are needed.

Part of: ACARA Digital Technologies Years 7–8 — Wired and Wireless Networks — Module 49, WA Computer Science ATAR Year 11 — Network Communications — Module 92

Understanding Redundant routes keep a network working in ACARA Digital Technologies Years 7–8

What it does: The code shows the failover idea: when the main link fails, the network switches to the other path. The spare path adds to the total cost, because the extra equipment must be bought and set up. With only one path, a cut cable breaks the connection. A second path lets data keep flowing. A backup link is there for safety. It is not there to boost speed. Routers choose a route for each packet, so packets can go around a failed router if another path exists. Spare paths mean buying and setting up more equipment, so redundancy costs more. One path means one point of failure. If it breaks, nothing gets through.

Common mistakes: The backup link should only be used when the main link is down. Using = up would switch to the backup when nothing has failed. It should be IF mainLink = down THEN. Data can only be rerouted if the cable is cut AND a backup route exists. OR would try to reroute even when there is no backup. It should be IF cableCut AND backup THEN.

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This module's key terms are also in a printable crossword (Modules 69–124) and word search (Modules 69–152).

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Learning

Duo

A network has two different paths between a school and the internet. One cable is cut. What happens?

All data stops until the cable is fixedPackets are sent along the other path and data keeps flowing

Matches

Only one path: A -> Router -> B Cable cut. Data still arrives.

↓

With only one path there is no redundant route, so a cut cable stops the data. A second path is needed for data to keep flowing.

Applying

Meanings

Term

redundant route

Meaning

A spare path between devices. If one link or router fails, packets are sent another way so data keeps flowing. It costs more because extra cables and routers are needed.

Practice

IF main cable is cut THEN

Testing

Gaps

IF mainLink = "failed"

Check Answer

Spots

1mainLink ← up

2IF mainLink = up THEN

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Quick Questions

1. A network has two different paths between a school and the internet. One cable is cut. What happens?

A. All data stops until the cable is fixed

B. Packets are sent along the other path and data keeps flowing ✓

A redundant route is a spare path. When one link fails, packets are sent another way.

2. Which network is better at coping with one cable being cut?

A. A network with two paths between devices ✓

B. A network with only one path between devices

With only one path, a cut cable breaks the connection. A second path lets data keep flowing.

3. What is a backup link?

A. A spare connection that is used if the main link fails ✓

B. A link that makes the main cable faster

A backup link is there for safety. It is not there to boost speed.

4. Why can packets use a different path when a router fails?

A. Each packet is routed separately, so it can be sent another way ✓

B. All packets must follow the same fixed path

Routers choose a route for each packet, so packets can go around a failed router if another path exists.

5. Why does adding redundant routes make a network cost more?

A. It uses up all the packets

B. It needs extra cables and routers ✓

Spare paths mean buying and setting up more equipment, so redundancy costs more.

Match the Pairs

redundant route → A spare path between devices that packets can use if the main path fails

backup link → An extra cable or connection that stays ready to carry packets if the main link is cut

If one cable is cut, packets are sent another way so data keeps flowing → main link DOWN -> use backup route

Redundancy costs more because a network needs extra cables and routers → cost = main_path + spare_path

Only one path: A -> Router -> B Cable cut. Data still arrives. → With only one path there is no redundant route, so a cut cable stops the data. A second path is needed for data to keep flowing.

Spare cables and routers make a network cheaper. → Redundancy makes a network cost more, because extra cables and routers must be bought. The benefit is that data keeps flowing when something fails.

Key Term

redundant route

A spare path between devices. If one link or router fails, packets are sent another way so data keeps flowing. It costs more because extra cables and routers are needed.

Fill in the Blanks

1. IF mainLink = "failed" THEN send(packet, backupLink) END IF

Hint: Type the keyword that begins the action to take when the condition is true

2. IF mainLink = "failed" THEN send(packet, backupLink) END IF

Hint: Type the name of the spare path the packet is sent along when the main one fails

3. routes ← 2 IF routes > 1 THEN PRINT "Data flows"

Hint: Type the comparison operator that checks for more than one route

4. extraCables ← 3 extraRouters ← 1 cost ← extraCables + extraRouters

Hint: Type the operator that adds the extra equipment together to show redundancy costs more

5. IF cable1 = "cut" THEN use(route2) ELSE use(route1)

Hint: Type the keyword for what happens when the cable is not cut

Spot the Error

Question 1

A mainLink ← up

B IF mainLink = up THEN

C SEND packet VIA backupLink

D END IF

Line B — The backup link should only be used when the main link is down. Using = up would switch to the backup when nothing has failed. It should be IF mainLink = down THEN.

Question 2

A cableCut ← true

B backup ← true

C IF cableCut OR backup THEN

D SEND packet VIA backup

E ELSE

F DISPLAY 'Data stops'

Line C — Data can only be rerouted if the cable is cut AND a backup route exists. OR would try to reroute even when there is no backup. It should be IF cableCut AND backup THEN.

Question 3

A paths ← 2

B IF paths = 1 THEN

C redundant ← true

Line B — A network is redundant only when there is more than one path between devices. One path is not a spare. It should be IF paths > 1 THEN.

Question 4

A router1 ← failed

B router2 ← working

C SEND packet VIA router1

Line C — router1 has failed, so packets cannot go through it. They must be sent another way, via the working router2. It should be SEND packet VIA router2.

Question 5

A mainCost ← 100

B backupCost ← 40

C total ← mainCost + backupCost

D IF total < mainCost THEN

E DISPLAY 'Costs more'

Line D — Redundancy costs more because the extra cables and routers are added to the main cost. The total should be greater than the main cost. It should be IF total > mainCost THEN.

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