signal. To achieve a data transmission without synchronization, an agreement (hand- shake) between the transmitter and the receiver should be made prior to start of the data transfer. As an example, a specific bit pattern can be used to prepare the receiving mecha- nism for the reception and registration of a symbol (start symbol), and a stop symbol can be employed to bring the receiving mechanism to rest in preparation for the reception of the next symbol. The efficiency of an asynchronous transmission will depend on the number of addi- tional bits that are sent together with the information. Synchronization is still present at the bit level in an asynchronous transmission. This is because the receiver needs to know the timing of each bit within each group of bytes. Besides, a timer is usually needed to detect the length of the transmitted group of information bytes. This kind of data transmission might need higher processing power at the receiver to accurately identify the beginning and end of each datastream. Because of this operation, the transmission might be slower com- pared to a synchronous transmission. However, this procedure might be cheaper to imple- ment because synchronization is not needed. Asynchronous transmission applications can be observed in simple keyboard-to-computer communications, where each character typing is converted in a binary transmission. In synchronous serial transmission (see Figure 2.5), the transmitter is in charge of assign- ing a specific time to the bytes to be sent through the channel. In this case no gaps exist in the transmission link and the channel is totally occupied. In serial transmission, the reason is that even if just a group of bits is required to be sent through the channel, rather than allowing the bytes to travel through the channel in an ad hoc manner, a longer "frame" is assigned to these bits, which corresponds to multiple bytes. An analogy is a transport rail- road train carrying passengers as an alternative to several cars carrying different groups of pe