Switching to VoIP

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Chapter 4: Circuit-Switched Telephony

Outboard analog media gateway

A device that serves the same purpose as an ATA, but allows more than one ana-

log phone to be used. Some analog media gateways are highly expandable and

can support dozens of analog endpoints. Analog media gateways may also have

some built-in call-routing functionality.

Onboard analog media interface

An interface port on the softPBX server itself that allows for direct connection of

a single analog phone.

Of course, analog endpoints are more than just phones. Sometimes they are

modems, fax machines, answering machines, burglary or fire alarm systems, or those

automated dialers with prerecorded telemarketing messages that sometimes call and

interrupt your dinner. Generally, analog endpoints can be connected to a VoIP net-

work using one of the three mechanisms listed.

But many data transmission protocols used by faxes and modems are broken by the

voice digitization process used on VoIP networks. Quantization, as described in the

earlier section “Time Division Multiplexing,” has a knack for screwing up the analog

sound wave signals used by modems and faxes to represent data. But don’t fret—

there’s a solution to this problem, and it’s covered in Chapter 14.

Digital Endpoints

Digital phones are functionally similar to