AP CSP Day 65: Fault Tolerance in Network Topologies | Cycle 3
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A fault-tolerant network can continue to transmit data even when one or more connections fail. Redundancy (multiple paths between devices) is the key. If every pair of communicating devices has at least two independent paths, the network can survive a single connection failure.
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Redundancy and Path Analysis
Redundant Paths
Two paths are independent if they share no connections in common. A network is fault tolerant to a single failure if, for every possible single connection removal, all devices can still reach all other devices.
Bridge Connections
A bridge connection is one whose removal disconnects the network. If a connection is the ONLY path between two groups of devices, it is a bridge and the network is NOT fault tolerant to its failure.
Practice Question
A network has four devices: W, X, Y, and Z. The connections are: W—X, W—Y, X—Y, X—Z, and Y—Z.
Which of the following connections, if removed, would still allow every device to communicate with every other device?
I. Removing W—X
II. Removing X—Z
III. Removing W—Y
Remove W—X: W reaches X through W→Y→X. All connected. Remove X—Z: Z reaches X through Z→Y→X. All connected. Remove W—Y: W reaches Y through W→X→Y. All connected. All three removals are survivable.
B) Incorrectly excludes removing W—Y. After that removal, W still connects to X directly. C) Incorrectly excludes removing W—X. W still connects through Y. D) All three removals leave the network connected.
Students see a triangle (W-X-Y) and recognize redundancy there, but then panic about Z, forgetting Z has two connections (X—Z and Y—Z) providing its own redundancy.
For network fault tolerance questions, identify the connection in question and then check: can every device still reach every other device through a different path?
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