Principles of Synchronous Digital Hierarchy

101

5

Clock

The most signicant difference in the digital communication systems as

compared with their analog counterparts is the presence of “clock” in the

digital systems. In digital systems, the events happen with the advancement

of clock step by step. If the clock stops, the digital communication world

would stop. The clock in the digital systems has the same function as the

normal clock (or watch) in our daily life. As in our daily life, all the events

such as getting up, going to the ofce, eating, sleeping, etc. are governed by

the time of the day, which is maintained by the clock, and so it is in the world

of digital commun ...