During digital transmission, a message packet is sent as bit data flow over the signal line. From the receiver's point of view, such a bit data flow looks like a sequence of pulses varying in length. To reconvert the pulse sequence into the original digital state, the receiver must know when the transmitted signals are valid, i.e. When they represent a bit and when not. To accomplish this, the transmitter and the receiver must be synchronized during transmission. The different data transmission methods solve this task either by
Providing clock-synchronous data transmission or
Performing asynchronous, time-controlled sampling.