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How to Choose an IP-PBX or VoIP Card

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An IP-PBX card, also known as a VoIP card, is a simple way to add ports for connecting analog devices such as telephones or fax machines to an IP-PBX. Some cards let you connect digital lines to the IP-PBX. These cards connect the lines and devices to your VoIP network.

When choosing an IP-PBX card, there are only three questions to ask:

  • What kind of ports do you need?
  • What bus type does your IP-PBX require?
  • Do you want echo cancellation?

IP-PBX cards can come either with the ports and echo cancellation modules already installed, or with a base card that you can add modules to.


The ports on an IP-PBX card determine what equipment can be connected. They can be broken down into two groups:

  • Analog
    • FXO
    • FXS
  • Digital
    • T1
    • E1

Analog Ports

There are two of ports for integrating analog devices via an IP-PBX card.

FXS ports connect the IP-PBX to internal devices like telephones or fax machines.

FXO ports connect the IP-PBX to the service provider. You can remember what they do, because the FXO port connects to the Outside (the O actually stands for Office).

VoIP cards with FXS ports let you connect analog equipment to your IP-PBX. VoIP cards with FXO ports let your IP-PBX connect to the PSTN.

Digital Ports

In North America, there is only one type of port for integrating digital lines via an IP-PBX card: T1 ports.

You may see E1 ports mentioned. This is a European standard. Just like power outlets look different and have different specifications in Europe or in North America, digital phone lines are different between the two locations.

If your phone lines are digital, then you’ll need an IP-PBX card with either a T1 or E1 port: whichever is appropriate to your location.

Bus Type

Bus is a technical term for a system of transferring data between computers or parts of computers. It’s what the B in USB stands for: Universal Serial Bus. An IP-PBX card needs to transfer data, so it needs have a particular bus type. There are only two standard bus types in use with VoIP cards:

  • PCI
  • PCI-Express (abbreviated PCIe)

The differences between them are technical, but the upshot is that PCIe is a newer and much faster version of PCI. That’s why it’s called “express.” Many IP-PBXs still in use, however, have PCI slots and require PCI IP-PBX cards.

Make sure the IP-PBX card you buy comes with the appropriate bus type: PCI or PCIe.

Echo Cancellation Modules

Some IP-PBX cards come with integrated echo cancellation modules, which provide a hardware solution for reducing echo.

What they do is obvious: they cancel the echo that might result from connecting an analog or digital endpoint to a VoIP system. The reasons for echo are technical, and generally the result of delay or latency somewhere in the system. Not every deployment requires echo cancellation, and software-based echo cancellation might also provide an answer.

If you’re looking for hardware-based echo cancellation, make sure your IP-PBX card has an echo cancellation module.