Link flap is a condition where a communications link alternates between ''up'' and ''down'' states. Link flap can be caused by
end station reboots, power-saving features, incorrect duplex configuration or marginal connections and
signal integrity
Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. However, digital signals are fundamentally analog in nature, ...
issues on the link.
References
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Computer networking