Modes of signal transmission

Hello mates,
We have seen about the speech signals and the standards used for transmitting them in the previous post. Now, we will move the mode of transmission.

There are two modes of transmission
-Synchronous
-Asynchronous

Synchronous mode of transmission takes place in such a way that the data is synchronised with the clock. To be even more specific, consider the sampling of voice signal by your phone. The microphone will take the voice signals every 125 microseconds. How is this possible? There will be a clock running at a frequency of 125 microseconds. The clock will have the positive transition every 125 microseconds. At every positive transition of clock, the data is accepted and it is held till the next positive transition. If this sampled data is transmitted to the receiver maintaining the timing and the receiver receives the data with the same timing, then we call it synchronous mode of communication.
In short, the data is synchronised with the clock in synchronous mode of communication.

Whereas in asynchronous, the sampled data are sent without maintaining the timing info and all that. In short, the data transmission involves no clock and is packetised.

E1, DS1, SDH, SONET, PDH are synchronous transmission standards whereas Ethernet is asynchronous. In other words, we call the synchronous signals as TDMised signals.