Analog telephone adapters (ATAs) are devices that can be used to connect regular phones to voice over Internet protocol (VOIP) networks. This can allow phone calls to be made without the use of a traditional analog telephone system. It is possible for an analog telephone adapter to be built into a phone, though most are standalone units. These standalone adapters can either connect to a computer via a universal serial bus (USB) port or directly to the Internet by means of a broadband or dial-up connection. Units that plug into a computer can allow a phone to function as a USB handset, while an analog telephone adapter that connects to a modem or router will typically contain hardware that is capable of interfacing directly with a VOIP network.
There are a number of different types of analog telephone adapters, though they all share a few basic components. The foreign exchange station (FXE) is an interface that telephones rely on for power and dial tones, so each analog telephone adapter must have at least one. For standalone units, the FXE is typically connected to a standard registered jack (RJ) type port. Analog telephone adapters tend to have some type of external power source as well and must also contain either an Ethernet port or an additional telephone jack for dial-up units.
A standalone analog telephone adapter can be designed for use with or without a computer. These devices can also operate on broadband or dial-up connections. Units designed to be used without a computer are capable of connecting directly to a modem or router by using an Ethernet connection. When a phone is plugged into one of these devices, the internal firmware can initiate a connection with a remote VOIP network. The phone can then be used to make calls that are automatically routed through the VOIP network instead of the local analog system.
Most standalone adapters are made to work with broadband Internet connections, though dial-up versions also exist. These adapters function in a similar way, though they have to be connected to a local phone line to work. This will result in a traditional phone call to a local dial-up service provider, after which the VOIP network can be used to make long distance calls.
Other units are designed to connect a phone to a computer through a USB connection. When this kind of analog telephone adapter is used, the phone is turned into a USB handset. Software located on the computer can then connect to a VOIP network and place calls.
Analog telephone adapters can also be built in to handsets. Units that contain these adapters are sometimes referred to as Internet protocol (IP) phones. Some of them are designed for use with broadband Internet and others for dial-up, though models that have dual connectivity also exist. These phones can be connected directly to a modem, router or phone jack and seamlessly used to make VOIP calls.