Common ISDN Application Programming Interface
Encyclopedia
The Common ISDN Application Programming Interface (short CAPI) is an ISDN
-conform standardized software interface
. With the help of the CAPI-Interface computer
software intended for the use with ISDN can be provided, without knowledge of the deployed, proprietary ISDN card.
CAPI was designed from 1989 by German
manufacturers (AVM
, Systec, Stollmann). Since 1991 CAPI is being developed further by CAPI Association e.V. Implementation
s exist for different operating system
s like Linux
and Microsoft Windows
.
Through the ETSI
CAPI 2.0 was introduced as standard ETS 300 324 (Profile B).
Primary 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 protocol
s (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
and SIP
) exist, thus CAPI applications can be used directly on cutting edge communications infrastructure. Special extensions for protocol-specific features where defined several years ago for ATM. Specification extensions for VoIP (codec negotiation, advanced addressing etc.) are already sophisticated and will be available shortly.
Integrated Services Digital Network
Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...
-conform standardized software interface
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...
. With the help of the CAPI-Interface computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
software intended for the use with ISDN can be provided, without knowledge of the deployed, proprietary ISDN card.
CAPI was designed from 1989 by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
manufacturers (AVM
AVM GmbH
AVM is a German electronics company founded in 1986 in Berlin, that produces DSL, ISDN, Wireless and VoIP products. It had sales of € 240 million in 2006 with 460 employees. It is the producer of the popular FRITZ!Box series.-Products :...
, Systec, Stollmann). Since 1991 CAPI is being developed further by CAPI Association e.V. Implementation
Implementation
Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy.-Computer Science:...
s exist for different operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s like Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
and Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
.
Through the ETSI
European Telecommunications Standards Institute
The European Telecommunications Standards Institute is an independent, non-profit, standardization organization in the telecommunications industry in Europe, with worldwide projection...
CAPI 2.0 was introduced as standard ETS 300 324 (Profile B).
Primary 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
Interactive voice response
Interactive voice response is a technology that allows a computer to interact with humans through the use of voice and DTMF keypad inputs....
, call-center, voice conference systems etc.), for fax-servers and combined systems (UMS
Unified messaging
Unified Messaging is the integration of different electronic messaging and communications media technologies into a single interface, accessible from a variety of different devices....
).
The CAPI Interface in its current release (CAPI 2.0) supports a variety of signaling protocol
Signaling protocol
A signaling protocol is a type of protocol used to identify signaling encapsulation. Signaling is used to identify the state of connection between telephones or VOIP terminals . The following is a list of signaling protocols:...
s (D channel
D channel
D channel is a telecommunications term which refers to the ISDN channel in which the control and signalling information is carried.The bit rate of the D channel of a basic rate interface is 16 kbit/s, whereas it amounts to 64 kbit/s on a primary rate interface.For DSS1 signalling, the D channel...
protocols), e.g. DSS1
Digital Subscriber System No. 1
Digital Subscriber Signalling System No. 1 , also known as Euro-ISDN or E-DSS1 , is a digital signalling protocol used for the ISDN. The interface is also called NET3 for BRI and NET5 for PRI lines. Can also be called CTR4. It is defined by ITU-T I.411...
and FTZ 1 TR 6
FTZ 1 TR 6
FTZ 1 TR 6 is the standard for the obsolete German national digital signalling protocol used for the ISDN...
. The interface operates in the OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
between layer 3 and 4 but only controls layers 1 to 3.
Besides popular signaling protocols for ISDN
Integrated Services Digital Network
Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...
implementations of CAPI for ATM
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
, GSM and VoIP (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...
and 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...
) exist, thus CAPI applications can be used directly on cutting edge communications infrastructure. Special extensions for protocol-specific features where defined several years ago for ATM. Specification extensions for VoIP (codec negotiation, advanced addressing etc.) are already sophisticated and will be available shortly.
External links
- capi.org
- capisuite.org Website of CapiSuite, an implementation for Linux (not maintained since 2006)