Switching to VoIP

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Chapter 12: PSTN Trunks

their timing is critical. Timing is especially important when “new” PSTN connec-

tions are displacing the old ones—that is, if you’re replacing an old PRI with a new

one in a different building or if you’re consolidating a bunch of POTS trunks into a

new PRI.

Major changes to trunk connections are often called switchovers. Once you’ve

designed your VoIP topology, and you know the proposed location of every phone,

every media gateway, and every PSTN connect point, you’ve got to map out a

switchover plan. This is a schedule for your trunk moves from one PBX system to

another, from one voice mail system to another, from one PSTN connect point to

another, or possibly all of these.

If possible, coordinate the switchover with the phone company so that any major

failures can be discovered immediately and the CO reverted back to its prior state

until the switchover can be attempted again. (Third-party implementers of PBX sys-

tems are experienced at managing interaction with the phone company.)

Plan to do your switchover during off-hours—not an hour before the start of busi-

ness on a Monday. Allow plenty of time for testing of the internal dial-plan after the

switchover is done, too. Even if your shiny new PRIs are working right, there may be

flaws in your call-flow ...