The term synchronous is used to describe a data transfer method in which a continous stream of data signals is accompanied by timing signals to ensure that the transmitter and the receiver are synchronized with one another. These types of connections are used when large amount of data must be transferred very quickly from one location to the other. The speed of the synchronous connection is attained by transferring data in large blocks instead of individual characters.A block of bits is transmitted in a steady stream without start and stop bits. Data or information is moved from one place to another at instants in time that are measured against the clock signal being used. This signal is usually comprised of one or more high frequency rectangular shaped waveforms are connected to all the devices that operate synchronously, allowing them to start and stop operations with respect to clock waveform.
In synchronous transmission, each block begins with a preamble bit pattern and generally ends with a postamble bit pattern. In addition, there are some other bits that convey control information. The data with the preamble, postamble, and control information are termed as frame.