In order to force a transition from 1 to 0 on a regular basis, a technique called bit stuffing is used. The transmitting circuitry, being fed a stream of bits from the processor, counts the number of 1s or 0s in a row and if there are too many, it inserts the opposite. In Fig. 23.2.4 we see a bit stuffing mechanism where 5 1's are always followed by a 0. The receiver counts the number of 1s and if there are 5, it removes the following 0.