The ATA, Its Features and Functions

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What is an ATA?

An ATA is a device which acts as a hardware interface between a PSTN analog phone system and a digital network or VoIP service. Using an ATA, you can merge your PSTN phone system and VoIP service, or connect a LAN to your phone network.

An ATA normally has two sets of outlets: one for your VoIP service or LAN and another one for your conventional phone. Obviously, on one side, you can connect and RJ-45 jack (VoIP or Ethernet cable) and on the other, a RJ-11 (phone line cable) jack.

An ATA links with the remote VoIP Service Provider’s service using a VoIP Protocol such as SIP or H.323. The encoding and decoding of voice signals are done using a voice codec. ATAs communicate directly with the VoIP service, therefore there is no need for software, and hence no need for a computer, although you can connect one to a computer or a softphone.

Features of an ATA

The most common features of an ATA are:

Ability to support VoIP protocols

The more protocols one can support, the better it is. SIP and H.323 are supported on all new ATAs today.


An ATA should provide at least one LAN (RJ-45) port and one RJ-11 port, so as to make the interface between the phone network and the VoIP service. Some ATAs even provide additional ports, like for example, a RJ-45 port to connect to a computer. You can use this to do phone-to-PC calls.

Some ATA’s have USB ports which allow them to more easily connect to computers and other devices.

Call Switching

Many people use PSTN and VoIP interchangeably. The call switching features in the ATA allows you to easily switch between these two.

Standard Service Features

It is common and practical today to have several service features like Caller ID, Call Waiting, Call Transfer, Call Forwarding etc. A good ATA should support all these.

3-Way conferencing

Many ATA’s come with 3-way conferencing support, which allows you to talk to more than one person at the same time. This proves to be very useful especially in a business context.

Power failure tolerance

The ATA runs on electric power. It normally stops working in case of a power cut. This should not mean that your communication should be completely paralyzed. A good ATA should automatically switch to PSTN line default in case there is a power failure.

ATA manufacturers are sharpening their saws day after day. Some ATAs provide superb hi-fidelity voice quality with enhanced technologies like Digital Signal Processing (DSP).


In a company context, an ATA may be part of an already-complex hardware structure. For this reason, a good ATA should be compliant and interoperable to a maximum with other hardware devices.

These are only the most common features that should make a good ATA. Modern ATAs come with a large number of additional features. Have a close look before you buy.

Figure 1 shows what a typical ATA looks like.