Introduction to Data Communications
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Dropouts are sudden loss of signal amplitude greater than 12 db that last longer than 4 mSec. They cause more errors than any other type of transients. Telephone company standards allow no more than 1 dropout for every 30 minute interval. Dropouts would be heard on a voice conversation similar to call waiting, where the line goes dead for a 1/2 second. This is a sufficient loss of signal for some digital transfer protocols such as SLIP, that the connection is lost and would have to be re-established.

iv. Phase Hits

Phase Hits are sudden large changes in the received signal phase (20 degrees) or frequency lasting longer than 4 mSec. Phase Hits generally occur when switching between Telcos, common carriers or transmitters. FSK and PSK are particularly sensitive to Phase Hits. The data may be incorrect until the out of phase condition is rectified. The telephone company standard allows no more than 8 phase hits in any 15 minutes.

Introduction to Data Communications
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