A scrambler(SCR) is a pseudo-random generator used to scramble binarysignals quasi-randomly. It is a multi-stage shift register in which the output signals of the individual flip stages are logically linked and fed back to the input of the scrambler.
The quasi-random sequence results from the linkage and the number of toggle stages of the shift register. Since the pseudo-random function is known, the digital signal can be converted back to the original signal after transmission in a descrambler.
A scrambler avoids constant signal patterns such as those that occur in idle state and provides a better distribution of signal energy over the frequency range. The scrambler turns each signal into a random sequence. Scramblers are used in most modems of the V-recommendations, for example in V.28, V. 29, V. 32, V. 34 and V.42.