Analog telephony adapter
Encyclopedia
An analog telephony adapter, or analog telephone adapter, (ATA) is a device used to connect one or more standard analog telephones to a digital telephone system (such as Voice over IP
Voice over IP
Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

) or a non-standard telephone system.

An ATA usually takes the form of a small box with a power adapter, one Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 port, one or more FXS telephone ports and may also have a FXO link. Users can plug one or more standard analog telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 devices into the ATA and the analog device
Analog device
Analog device is an apparatus that measures continuous information. The measured analog signal has an infinite number of possible values. The only limitation on resolution is the accuracy of the measuring device. Such apparatus operates with variables which are constituted by continuously measured...

(s) will operate, usually transparently, on a VoIP
Voice over IP
Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

 network.

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
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....

. 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
H.323
H.323 is a recommendation from the ITU Telecommunication Standardization Sector that defines the protocols to provide audio-visual communication sessions on any packet network...

, SIP
Session Initiation Protocol
The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...

, MGCP, SCCP
Skinny Client Control Protocol
The Skinny Call Control Protocol is a proprietary network terminal control protocol originally developed by Selsius Systems....

 or IAX, and encodes and decodes the voice signal using a voice codec such as G.711
G.711
G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...

, G.729
G.729
G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...

, GSM, iLBC
ILBC
Internet Low Bitrate Codec is an open source royalty-free narrowband speech codec, developed by Global IP Solutions formerly Global IP Sound . It was formerly licensed as a freeware with limited commercial use, but since 2011 it is available under an open source license as a part of the open...

 or others. Since the ATA communicates directly with the VoIP server, it does not require a personal computer or any software such as a softphone
Softphone
A softphone is a software program for making telephone calls over the Internet using a general purpose computer, rather than using dedicated hardware. Often a softphone is designed to behave like a traditional telephone, sometimes appearing as an image of a phone, with a display panel and buttons...

. It uses approximately 3 to 5 watts of electricity, depending on model and brand.

Purpose

An ATA is connected between an IP network (such as a broadband connection) and an existing telephone jack in order to provide service nearly indistinguishable from PSTN
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

providers on all the other telephone jacks in the residence. 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. This type of service, which is fixed to one location, is generally offered by broadband Internet providers such as cable companies and telephone companies as a cheaper flat-rate traditional phone service.
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