synchronous signal definition

[khatus]

It is probably a very simple question 

1) In telecommunication signaling within a network or between networks, synchronous signals are those that occur at the same clock rate when all clocks are based on a single reference clock. (Plesiochronous signals are almost but not quite in synchronization and asynchronous signals are those that run from different clocks or at a different transition rate.)
https://whatis.techtarget.com/definition/synchronous

What does it mean by 'based on a single reference clock'?? Can anybody explain?

[LapTop006]

Probably easiest to understand by example.

Take two function generators.

Set both to 1MHz exactly.

If you look at the output on a scope you'll almost certainly see one waveform move relative to the other.

This is because both generators have slightly different references.

If you essentially remove one of the references, and have both generators use the same signal for frequency reference, that stops happening, and this is exactly what's done in synchronous networks (which, outside cellular networks, and some very specific scientific use cases, are obsolete), as well as many RF labs.

[ejeffrey]

If you look at the back of a lot of better test equipment, especially RF stuff, it will have a 10 MHz input and possibly a 10 MHz output for synchronizing their internal clocks.  In our lab we use a SRS rubidium clock as a source plus some distribution amplifiers to synchronize a bunch of arbitrary waveform generators that need to start at the same time.  If they weren't synchronized, then there would be +/- 1 clock cycle uncertainty when each generator started.  The rubidium source is actually overkill for the most part, the only important thing is that all the generators start at the same time.