McDewey

Example 4.3 shows that, with the assumption of worst case delays, it is very difficult to keep the calculated delay under 200 ms when a branch-to-branch connection includes a PBX tandem hop at the central site with public frame-relay network connections on either side. However, if the network topology and traffic is known, it is possible to substantially reduce the calculated figure. This is because the figures generally given by carriers are limited by the worst case transmission and queuing delay over a wide area. It is much easier to establish more reasonable limits in a private network.
The generally accepted figure for transmission delay between switches is of the order of 10 σ2
Network Delay (Public Frame), ω2
40 25 De-jitter Buffer Delay, Δ2
40

Totals
258.1 58.1 Page 14 of 18 Cisco - Understanding Delay in Packet Voice Networks 7/31/2008 http://kbase.cisco.com/paws/servlet/ViewFile/5125/delay-details.xml?convertPaths=1