McDewey

Note: Since queuing delay and the variable component of the Network delay is already accounted within the de-jitter buffer calculations, the Total delay is effectively only the sum of all the Fixed Delay plus the de-jitter buffer delay. In this case the total delay is 258.1 ms. If you use the PBX at the central site as a switch, it increases the one-way connection delay from 206 ms to 255 ms. This is close to the ITU limits for one-way delay. This type of network configuration requires the engineer to pay close attention to design for minimum delay.
The worst case is assumed for variable delay (although both legs on the public network do not see maximum delays simultaneously). If you make more optimistic assumptions for the variable delays, it only minimally improves the situation. However, with better information about the fixed and variable delays in the frame relay network of the carrier, the calculated delay can be reduced. Local connections (for instance intra-State) can be expected to have much better delay characteristics, but carriers are often reluctant to give delay limits.
Two-Hop Connection over a Private Network with a PBX Tandem Switch
Figure 6-4: Two Hop Private Network Example with PBX Tandem