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Networking Fundamentals · Foundational

Attenuation

The loss of signal strength as it travels through a medium, measured in decibels.

Definition

Attenuation increases with cable length and signal frequency for copper and with distance, splices, connectors and bends for fiber. It is why Ethernet over twisted pair is limited to 100 m. Fiber attenuation is typically about 0.35 dB/km at 1310 nm on single-mode and about 3 dB/km at 850 nm on multimode.

Example

A 120 m copper run fails because attenuation exceeds the standard's limit.

Exam tip

Too-long cable runs cause attenuation; the fix is a shorter run, a repeater/switch, or fiber.

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