The Common ISDN Application Programming Interface (short CAPI) is an ISDN-conformant standardized software interface. With the help of CAPI,

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

software intended for the use with ISDN can be provided, without knowledge of the deployed, proprietary

ISDN card 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 ...

. CAPI was designed from 1989 by German manufacturers ( AVM, Systec, Stollmann). Since 1991, CAPI is being developed further by ''CAPI Association e.V.'' Implementations exist for different operating systems, including Linux and

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

. Through the

ETSI The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...

, CAPI 2.0 was introduced as standard ETS 300 324 (Profile B). Primarily, CAPI was designed for data transfer over ISDN. The specification has been extended multiple times, thereby it became important to the area of voice and fax communication. Because pure data transfer over IP-based networks is dominant in modern times, CAPI is being used primarily in the scope of voice applications (voice mail, IVR, call center, voice conference systems, etc.), for fax servers and combined systems ( UMS). The CAPI Interface in its current release (CAPI 2.0) supports a variety of signaling protocols ( D channel protocols), e.g. DSS1 and FTZ 1 TR 6. The interface operates in the OSI model between layer 3 and 4, but only controls layers 1 to 3. Besides popular signaling protocols for ISDN, implementations of CAPI for ATM, GSM and VoIP (

H.323 H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, m ...

and SIP) exist, thus CAPI applications can be used directly on communications infrastructure. Special extensions for protocol-specific features were defined several years ago for ATM.

External links

capi.org

CapiSuite
A Python scriptable ISDN telephony suite with an answering machine. Integrated Services Digital Network