What is Attenuation?

Attenuation is the reduction in signal power as a wave travels through a medium. In copper, this is caused by electrical resistance and skin effect. In fiber, it is caused by absorption, scattering (Rayleigh scattering), and micro-bending.

Attenuation is measured in dB per kilometer.

Copper vs. Fiber: The Distance Wall

Copper cabling (like Cat6a) is limited by its high attenuation at high frequencies. This is why Ethernet is strictly capped at 100 meters. Beyond this distance, the SNR drops below the threshold required for successful decoding.

In contrast, Single Mode Fiber has extremely low attenuation, often as low as 0.2 dB/km at the 1550nm wavelength, allowing for runs of 80km or more without repeaters.

Calculating the 'Link Budget'

A 'Link Budget' is the calculation of all gains and losses from the transmitter to the receiver.

If $P_{RX}$ is lower than the receiver's threshold, the link will either fail or suffer from high Packet Loss.

Understanding the physical layer is the foundation of Cabling Infrastructure Standards and long-term network stability.