01-28-2010 10:48 AM
01-29-2010 08:07 AM
This is the classic problem with ALL synchronous telephony!
When the clocks differ, you get underflow, or overflow, and a "frame slip."
There are specifications for how often a frame slip is allowed (in a PABX), so go find out.
Make the buffer exactly some number of frames, I think exactly one frame is best, perhaps two.
When you slip, you should re-establish frame sync as fast as possible, so you do not cause too long an outage (or loss of voice, or data on the E1).
The signals should all be synchronous (the internal 16.384 MHz should be the output of a 'Stratum 4 clock', which is traking (following) the frequency of one of the E1 inpts to the system).
Any E1 (or T1) terminal (end-point) equipment should be using the received clock frequency to generate all outgoing clocks. This is supposed to be the function of the terminal clock (Stratum 4). When no input reference is available, it should fall back to +/-50 ppm ONLY.
In the E1 system, the specifications are similar to the T1 (North America) specs above.