To ensure data interpretation on the receiving side, a clock signal must be transmitted to the receiver or it obtains it from the transmitted data. The latter has the advantage in terms of transmission technology that no separate clock signal has to be transmitted. If the clock signal is derived from the data signal, this is referred to as clock recovery. Only with the clock signal is it possible to decode the received data signal.
Compared to asynchronous transmission, clock recovery has the advantage that a longer synchronism is guaranteed between transmitter and receiver. It uses the signal edges to derive the clock signal. Since many transmission methods transmit longer signal sequences consisting of several zeros (000000) or ones (111111), such signal sequences must be coded by appropriate channel coding with alternating 01 combinations or by coding methods in which additional edges are inserted.
The type of clock recovery also depends on the stability of the transmitting and receiving clock generators. The more stable they are, the fewer signal edges are required for clock recovery.