What are you using for calls coming into the central location, PRI? If so you can have PRI slipage which is affecting one of my customers now. Some calls start a bit of hum which gets more pronounced and then the call drops.

When you are figuring bandwidth, you have Xk transmit, Xk receive and "overhead." If you had 23 channels at 32K you would need more than 23x32K because of "overhead." I allow at least an extra 10% bandwidth and more if possible to avoid that problem.

You can use an Adtran or Kentrox QoS router to take incoming bandwidth and guarantee adequate bandwidth to the voice section of bandwidth usage.

We are using a VOIP provider who gives us a PRI output from their server. Two options:

Data T-1 to server input, PRI output to Toshiba RPTU
Covad SDSL to server input, PRI output to Toshiba RPTU

If data bandwidth has to be split off:
Data T-1 to Adtran, QoS output to server input, PRI output to Toshiba RPTU and non-QoS output to data router and switch.

THE Bracha, old blond specialist in Rube Goldberg solutions.