Complex sentence: To ensure that there are enough signal transitions for clock recovery to occur in the bitstream, a bit stuffing technique is applied to the data stream: an extra 0 bit is insert into the data stream after any occurrence of six consecutive 1 bits.
Split into simpler sentences: To ensure that there is enough signal transitions for clock recovery to occur in the bitstream, bit stuffing techniques is applied to the data stream. This is via inserting extra 0 bit into the data stream after any appearance of six consecutive 1 bits.