Switching to VoIP

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Installing Legacy Interface Cards

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39

The TDM400P Card

The Digium TDM400P card (Figure 3-3) is a more powerful interface card, and it is

not required for any of the projects in this book.

Like the X100P, the TDM400P is a PCI card that allows connections to the PSTN

through a POTS line, as well as connections to an analog telephone using a regular

two-wire phone cord. Unlike its simple cousin, the TDM400P has four modular

ports, so you can use up to four POTS lines and/or analog phones.

These ports accept one of the two Digium proprietary hybrid interface modules, FXS

signaling for analog trunks (POTS lines) and FXO signaling for analog phones. The

card can host them in any combination. This card also has a Molex power connector,

like a hard drive, for supplying analog phones with the line power they’re accustomed

to. Don’t forget to connect it.

Multiple TDM400P cards can be used in the same computer simultaneously. Since

they have four ports per card, they are better than the X100P for high-density appli-

cations. Due to capacity issues on the PCI bus, however, you shouldn’t use more

than two TDM400P cards. A T1 interface is a great alternative, though: it allows you

to connect two dozen phones at a time using a device called a channel bank. More

on this later.

Figure 3-3. The TDM400P interface ...