[Asterisk-Users] T1 Sync clarification

[Rich Adamson]

> > To complete this rather lengthy topic... what happens if you ignore all of
> > this and just slap a bunch of systems together with no regard to a master
> > sync source?  The quality and stability of your network will likely not be
> > as good as what it could be. If your clocks (in each device) happen to be
> > running very very close to what is expected, your network might run just
> > fine. But, if one of the clock's frequency drifts around, it could impact
> > quality via frame slippage and other unwanted events, and if off by a
> > large amount could even be the source of failures. (Your milage will vary
> > directly with the stability of your clocks.)

> What are the practical effects with in-correct clock sync
> -like to you hear odd buzzing, or dropped voice or gaps of audio ??

As mentioned earlier, it depends entirely upon how far off one clock is
from the clock at the other end of the T1.

If they are off by a little bit, you would see frame slips but probably
not hear any quality differences.

As the slip rate increases (to some unknown value since I've not tried
personally to qualify this), the audio would be infrequently interrupted
from the lost frames. I would expect you to hear it as repetitive clicks 
of some sort that might be construed as noise. The exact noise would again 
depending upon how far off the clocks really were. Each audio channel 
consists of 8,000 voice samples per second (on a normal US T1), so if the 
slip occurred once/second on average and then recovered, one would probably 
not hear 1/8000 second of a hickup.

If the slips were 100/sec average, it's likely the end nodes would have
a hard time recovering from it (best guess), and I would expect noise to
be apparent.

Others that have more experience correlating slip rates to noise levels
might have a better description of the noise vs slip rate.

Rich