Signal-to-noise ratio

Signal-to-noise ratio (SNR) compares the power of the wanted signal with the background noise, normally in decibels. As the ratio falls, errors rise, frames have to be sent again, and wireless systems step down to slower, more robust encodings, so usable throughput drops even when nominal bandwidth has not changed. The ISC2 exam outline lists it among network performance metrics, beside bandwidth, latency, jitter and throughput.

In Wi-Fi and other radio networks, SNR is shaped by distance, walls, interference from other devices and deliberate jamming. Jamming is an availability attack that works by adding noise until the ratio is too low for communication, which is why it can succeed against a network whose encryption is sound. Damaged cable or electrical interference does the same on wired media. Security operations borrows the term for the share of SIEM alerts that reflect real threats rather than false positives; this entry uses the network sense.

Exam relevance: a scenario that describes a wireless link slowing and dropping without any change in load is likely to point to a falling SNR, and one with deliberate interference to jamming. Candidates are expected to see that encryption does not protect against a loss of signal quality.