AP CSP Day 29: Fault Tolerance & Redundancy
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Network redundancy is measured by counting how many connections must fail before some node becomes unreachable. A minimum cut is the smallest set of connections whose removal disconnects the network. AP CSP review questions on fault tolerance typically show a labeled network diagram and ask students to determine whether the network remains connected after specified connections fail. Counting all available alternative paths between nodes is the core skill tested in these diagram-analysis questions.
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Fault Tolerance Review: Network Diagrams
Path Counting
To evaluate fault tolerance between two specific nodes, count all distinct paths between them. A network tolerates k simultaneous failures between those nodes if there are at least k+1 distinct paths with no shared links.
Most Vulnerable Node
The most vulnerable node in a network is the one with the fewest connections, or the one that all paths between two regions must pass through (a bridge node). Removing a bridge node splits the network.
Practice Question
A school network connects the main building to the library through two independent paths: a fiber optic cable and a wireless link. Which of the following best describes the benefit of having both paths?
Redundant paths provide fault tolerance. If the fiber optic cable is damaged, the wireless link can still carry traffic, and vice versa. This ensures continued connectivity even when one component fails.
A) Redundancy provides reliability, not necessarily doubled speed. Load balancing can improve throughput but the primary purpose of redundancy is resilience. C) Energy efficiency is not the purpose of network redundancy. D) Either path alone can handle traffic — both being active simultaneously is not required.
Students think the primary benefit of redundancy is speed rather than reliability. The key advantage is that the system continues working when a component fails.
Redundancy = backup systems for reliability. On the AP exam, the correct answer about redundancy almost always relates to continued operation during failures, not performance improvement.
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