Fig. 1 : Information Sending/Receiving : Place of Synchronization Problem

　　When a message has to be transmitted between two points (i.e. two cities), the internal clock in the sender will control the frequency of information sent from this node (f1). A second clock located on the receiver node will control the frequency at which received data is read (f2).

The basic principle of synchronization is that the two frequencies must be exactly the same in order to allow the receiver to interpret the digital signal properly.

Should f1> f2, the sender will transmit information faster than the receiver can "understand" it, this will "miss" information (" slips of deletion ").

Should f2> f1, the sender is slower than the receiver, this will duplicate a part of received information (" slips of repetition) .