We investigate, theoretically and experimentally, how inherent defects and miniscule imperfections in fiberoptic
cables degrade entanglement between two photons transmitted over fibers. We show that the loss of
entanglement could be either gradual or surprisingly abrupt. In addition, we suggest a novel way to compensate for
adverse effects that occur during propagation in fibers. Finally, we define the range of fiber parameters over which
entanglement remains sufficient for secure communication.