Switching to VoIP

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Chapter 12: PSTN Trunks

other for dial-tone service from the CO. So, it’s possible to have a T1 trunking your

PBX to the CO with, say, 12 channels and linking your IP network to the Net with

the other 12. This could save you money, because most LECs are also ISPs, and they

sell Internet access at a discount if you’re willing to bundle their local dial-tone ser-

vice on the same circuit.

When connecting a T1 circuit from the smart jack to your DSU/CSU,

router, or PBX, don’t use a CAT-5 cable! Standard CAT-5 cables don’t

have the shielding needed by a T1. T1s will behave better if you use

individually shielded twisted-pair cables instead. You can get these

from any telecom supply catalog. Ask for a plain T1 cable.

Using the PSTN for Intraorganization Calls

Leverage Centrex groups

Calls between lines on the same Centrex group are usually cheaper than calls made

to destinations outside the Centrex group. If you have a couple of offices in the same

vicinity, close enough to be members of the same Centrex billing arrangement (the

same area code and phone company), you can use Centrex signaling to your advan-

tage to connect them seamlessly. Have your users reach one another by Centrex four-

dialing, which is “in-group,” rather than having them use seven-digit dialing, which

is “out-of-group.” ...