In the event that a digital circuit is silent, i.e. there is no active data transmission, the channel service unit (CSU) that interfaces the circuit to the customer's data communications equipment (DCE) will regularly transmit a one (1) bit, collectively known as keep alive bits, to ensure that there are electrical pulses on the circuit with at least a minimal density.This process ensures that the various circuit terminating equipment and repeaters remain synchronized and, in some cases, powered. See also CSU, DCE, ones density, repeater, and synchronize.