Analog telephony adapter

An analog telephony adapter, or analog telephone adapter, (ATA) is a device used to connect one or more standard analog telephones to a digital and/or non-standard telephone system such as a Voice over IP based network.

Form

An ATA usually takes the form of a small box with a power adapter, one Ethernet port, one or more FXS telephone ports and may also have a FXO link. Users can plug one or more standard analog telephone devices into the ATA and the analog device(s) will operate, usually transparently, on a VoIP network.

Purpose

ATAs are used by many VoIP companies selling a telco-alternative VoIP service, where the device is used to replace a user's connection to a traditional telephone company. When sold in connection with a VoIP service, the ATA is often locked so it cannot be used with a competing service, and the user can only partly change its configuration. Some providers do sell devices that are not locked and can be used with any compatible provider.

FXS to Ethernet gateways

The most common ATA is a box with at least one Foreign eXchange Station (which includes a telephone jack), used to connect a conventional telephone, and an Ethernet jack used to connect the adapter to a LAN. Using such an ATA, it is possible to connect a conventional telephone to a remote VoIP server. The ATA communicates with the server using a protocol such as H.323, SIP, MGCP, SCCP or IAX, and encodes and decodes the voice signal using a voice codec such as G.711, G.729, GSM, iLBC or others. Since the ATA communicates directly with the VoIP server, it does not require any software, such as a softphone, to be run on a personal computer.