What is the idea used in the B8ZS scrambling technique?

Answer 1

B8ZS (Bipolar 8-Zero Substitution) Line Coding is used as a technique to maintain 1's density in telecommunications. It isn't really used for scrambling, though it does change specific bits to insert a bipolar violation when a frame of 8 consecutive 0's is transmitted. B8ZS is typically used on DS1 signals, and has become the standard line coding option for most modern telecom equipment involving T1 circuits. Equipment using DS1 signalling depends on a certain number of 1's (referred to as 1's density) to maintain synchronization, since the timing circuits will often derive clocking based on the rising voltage of a digital '1' pulse. Since a digital 0 is represented by a lack of a pulse, the receiving device cannot use 0's to help maintain clocking. A device optioned for B8ZS replaces a frame of eight 0's with one containing four 1's in a specific pattern, including a bipolar violation, which a receiving device (also optioned for B8ZS) will recognize, and will then translate that frame back into eight 0's. But this also helps maintain timing between those devices, due to the 1's being transmitted instead of all zero's.