ANONYMOUS wrote: The sender and receiver of messages need to agree of two things: - what data is being exchanged (the 1s and 0s), and - how many bits are arriving The 1st requirement is met by using encoding schemes that use the amplitude, or change in amplitude, to represent the values of the data. However if, for example, a long sequence of bits was transmitted (e.g. a long sequence of 0s with NRZ-L), then the receiver can find/determine the beginning and ending of that sequence, but not how many (seemingly identical) bits there were. Senders and receivers use clocks (oscillators on the network interface card, not the OS) to know the passage of time (from their perspective) and the receiver uses the anticipated transmission speed and the elapsed time to determine how many bits were transmitted. To achieve this, the sender and receive need very similar clock rates, to agree on the rate at which they are communicating. The endpoints are agreeing/synchronising their perception of the speed involved. Hope this helps,