scrambling

[albatros]

Recently i was studying about the ATM protocol and i met the term"scrambling".
Does anybody know what does it mean?
Here is the whole sentence:
Scrambling and
Descrambling are to be done in the
information field of a cell before the
transmission and reception respectively
to protect the cell delineation
mechanism.

[juniper]

In ATM they use scrambling for clocking so that there is not a long string of all 1's or 0's in the pattern. This is the same as like B8ZS (Bipolar with 8-Zero Substitution) signaling on a T1. google B8ZS and it will make a lot of sense why they do this.