In a communications network, a node receives a transit packet. The technique effects survivability and security of the optical networks by encompassing conventional electronic security with an optical security layer by generating replicated versions of the input data payload at the input node, and the transmission of each of the replicated versions over a corresponding one of the plurality of links. The device may apply a 1-D transform twice to accomplish a 2-D transform. The inter-pair difference calculation unit calculates a difference between the first difference and the second difference as an amount of block distortion of the extracted pixel region. The test rows are located near bit line driver circuitry to insure the highest exposure to bit line voltages that may disturb memory cells in the array.