In Distributed Queue Dual Bus (DQDB), each network node has two counters: the Request Counter (RC) and the Countdown Counter (CC). The Request Counter is a reservation counter that counts each individual transmit request and increments the values. If an unoccupied time slot
passes the station, the RC counter is set back by one digit. If the station has a transmit request, it sets the RC counter to zero and transfers the count to the countdown counter.