A protocol family that includes protocols used on T1 in the USA, Hong Kong, and Taiwan. The protocol uses one-bit signaling, two-bit signaling, or presence or absence of current, and owes its name to the wink (brief presence of current or variation of the signaling bit) that the inbound side uses to acknowledge line seizure. Register signaling is performed by in-band DTMF or MF tones, or by out-of-band decadic pulses.