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Networking Fundamentals · Foundational

Electromagnetic Interference (EMI)

Unwanted electrical noise from external sources, such as motors, fluorescent lights and power lines, that disrupts signals on copper cabling.

Definition

EMI causes CRC errors, retransmissions and intermittent connectivity. Mitigations include routing data cable away from power cables, crossing power at 90 degrees, using shielded cable, or using fiber, which is immune. Radio-frequency interference (RFI) is a subset affecting radio frequencies.

Example

A cable run alongside an elevator motor shows high CRC errors.

Exam tip

Fiber is immune to EMI; STP reduces it; UTP relies on twists alone.

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