SYNCHRONOUS TRANSMISSION AND ASYNCHRONOUS TRANSMISSION
WHAT IS SYNCHRONOUS TRANSMISSION?
The term synchronous is used to describe a continuous and consistent timed transfer of data blocks.
Synchronous data transmission is a data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals.
Synchronous transmission modes are used when large amounts 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.
Synchronous transmission synchronizes transmission speeds at both the receiving and sending end of the transmission using clock signals built into each component. A continual stream of data is then sent between the two nodes.
The data blocks are grouped and spaced in regular intervals and are preceded by special characters called syn or synchronous idle characters. See the following illustration.
Difference between Synchronous and Asynchronous Transmission
One of the major differences is that in Synchronous Transmission, the sender and receiver should have synchronized clocks before data transmission. Whereas Asynchronous Transmission does not require a clock, but it adds a parity bit to the data before transmission.
Furthermore, the synchronous transmission uses synchronization characters while asynchronous method employs start/stop bits, in order to alert the modem when data are being sent and when are these transmissions are completed are known as message characters.
Synchronous transmission interfaces are generally about 20 percent faster and somewhat more reliable than comparable asynchronous interfaces.
Both Synchronous and Asynchronous Transmission have their advantages and disadvantages. Asynchronous is simple, economical and used for transmitting a small amount of data. Conversely, Synchronous Transmission is used for transferring the bulk of data as it is efficient and has less overhead. Hence, we conclude that both Synchronous and Asynchronous Transmission are necessary for data transmission.
