Switching to VoIP

This is the Title of the Book, eMatter Edition

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Dial-Plan and PBX Design

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or voice mail port, but most don’t. Fortunately, VoIP is not as geared around exten-

sion numbers as legacy PBX systems are.

Extensions “just because”

Some users may request a particular extension because it’s the extension number

they had on their former employer’s system or because it’s easy to remember. Other

extension numbers may be baggage from generations of phone system upgrades.

There may even be a hodgepodge of geography or legacy issues and special number

requests cluttering your dial-plan today, before you’ve even had a chance to add

VoIP to the dial-plan mix. Fortunately, VoIP networks can be eminently more pro-

grammable than the old PBX system.

Dial-Tone Trunks

Dial-tone trunks are the PSTN pathways of a PBX. Outbound or PSTN-bound traffic

flows to the dial-tone trunks, and inward traffic flows across them to the PBX. Tradi-

tional dial-tone trunks can be POTS, Centrex, BRI channels, or PRI DS0 channels.

Chapter 12 discusses the impact of voice applications on the selection

of PSTN trunk technologies and sizing.

It could make sense to have a very large dial-tone trunk group to make sure the rest

of the world never gets a busy signal when calling in to your phone system. But the

cost of phone lines—or T1 circuits—adds up quickly. There’s an easy ...