A terminal adapter or TA is a device that connects a terminal device – a computer, a mobile communications device, or other – to a communications network.

ISDN

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

terminology, the ''terminal adapter'' connects a ''terminal'' (computer) to the ISDN network. The TA therefore fulfills a similar function to the ones a

modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...

has on the POTS network, and is therefore sometimes called an ISDN modem. The latter term, however, is partially misleading as there is no modulation or demodulation performed. There are devices on the market that combine the functions of an ISDN TA with those of a classical modem (with an ISDN line interface). These combined TA/modems permit connections from both ISDN and analog-line/modem counterparts. In addition, a TA may contain an interface and

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

for one or more analog telephone lines (aka ''a/b line''), allowing an existing POTS installation to be upgraded to ISDN without changing phones. Terminal adapters typically connect to a

basic rate interface Basic Rate Interface (BRI, 2B+D, 2B1D) or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone servi ...

( S0, sometimes also U0). On the ''terminal'' side, the most popular interfaces are

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such ...

serial and

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

; others like V.35 or

RS-449 The RS-449 specification, also known as EIA-449 or TIA-449, defines the functional and mechanical characteristics of the interface between data terminal equipment, typically a computer, and data communications equipment, typically a modem or term ...

are only of historical interest. Devices connecting ISDN to a network (e.g.

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...

) commonly include routing functionality; while they technically include a TA function, they are referred to as (ISDN) routers.

Mobile networks

mobile network A cellular network or mobile network is a communication network where the link to and from end nodes is wireless. The network is distributed over land areas called "cells", each served by at least one fixed-location transceiver (typically thre ...

s, the ''terminal adapter'' is used by the

terminal equipment In telecommunication, the term terminal equipment has the following meanings: * Communications equipment at either end of a communications link, used to permit the stations involved to accomplish the mission for which the link was established. * I ...

to access the mobile termination, using AT commands (see

Hayes command set The Hayes command set (also known as the AT command set) is a specific command language originally developed by Dennis Hayes for the Hayes Smartmodem 300 baud modem in 1981. The command set consists of a series of short text strings which can be ...

). In 2G (such as

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...

CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

), the terminal adapter is a theoretically optional while in 3G (such as

W-CDMA The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Int ...

), the terminal adapter is mandatory and is part of the mobile termination.

Automation industry

In the

automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...

industry, a ''terminal adapter'' is a ''passive'' device that converts a connector like the 8P8C (RJ-45)

modular connector A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed fo ...

or 9 pin D-Sub into a

terminal block A screw terminal is a type of electrical connection where a wire is held by the tightening of a screw. Description The wire may be wrapped directly under the head of a screw, may be held by a metal plate forced against the wire by a screw, or ...

to facilitate wiring. It is often used when

daisy chain Daisy chain may refer to: * Daisy chain, a garland created from daisy flowers * Daisy chain (climbing), a type of strap * Daisy chain (electrical engineering), a wiring scheme * Daisy chain (fishing), a type of fishing lure * Daisy chain (knot), ...

wiring is necessary on a multi-node serial communication network like

RS-485 RS-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The s ...

RS-422 RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. It was meant to be the foundation of a suite of standards that ...

ISDN

Mobile networks

Automation industry

See also