9.3 Synchronous Transmission

In synchronous transmission, the clocks of the transmitter and receiver are synchronized.

One way to achieve this is to transmit the transmitter clock to the receiver using a separate channel.

The receiver uses the received clock to sample the data signal. The disadvantages of this approach are:

		Using a separate channel for the clock can be expensive.
		The clock signal might be subject to transformations (e.g. due to interference) causing timing errors.

An alternative synchronous transmission approach is to embed the timing information in the transmitted data signal.

This can be accomplished by using techniques such as Manchester and Differential Manchester encoding.

As described in Lecture 7, an inversion at the middle of each bit (0 or 1) is enforced by Manchester and Differential Manchester encoding.

Such inversion is used to at the receiver side to identify each bit in the signal, thus achieving synchronization.

9.3 Synchronous Transmission

To allow the receiver to identify the start and end of each block of data, a stream of preamble and postamble bits are used to mark the beginning and end of each block.

Synchronous transmission is more efficient than asynchronous transmission when large blocks of data are communicated.

		This is the case as there is no need in synchronous transmission to transmit a stop bit after every eight bit block.
		Preamble and postamble bits are only sent at the start and end of the block representing the whole data to be communicated.