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Since its introduction it has been updated several times and several different versions now exist. As of version 3.0, from 1999, the interface has also supported IP telephony and access video and audio streams, in addition to traditional telephone services. Part of the interface is the TAPI32.DLL, which provides standard functions for developing telephony applications. In turn, TAPI32.DLL communicates via the TSPI interface with the TAPI Service Provider, which translates the desired functions into a language that the hardware can interpret and then passes that on to the telephony hardware. ### TAPI's functions The main functions that TAPI can enable are the basics required for setting up calls, conducting conference calls and forwarding calls. In addition, typical office functions, such as database access, are made possible via [Computer Telephony Integration (CTI)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/cti). TAPI can be used for [ISDN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn), analogue telephony, mobile telephony and voice over IP. ### TAPI and Computer Telephony Integration As part of the integration of telephony applications on computers, the TAPI can initiate calls from a PC, view data on incoming calls or indicate the status of extensions. In the Windows environment TAPI is the central component of Computer Telephony Integration, exchanging data with the [telephone system](/gb/en/products/cloudya). Communication with the telephone system is managed by the TAPI Service Provider (TSP). For example, email programs, such as Microsoft Outlook or IBM Notes, often use the TAPI to access software phone functions from within the software. One example of this is the function that allows stored contacts to be called directly with just a mouse click. Journal functions allow the person dealing with the call to directly enter contact data into a system during a call. This enables other users to immediately see the complete call history of a customer. This helps call centres to work much more efficiently. ### Related Articles ### Integrated Services Digital Network (ISDN) In telecommunications technology, the abbreviation ISDN stands for the technical term "Integrated Services Digital Network" and refers to a digital standard for telephone networks. As the name implies, various types of communication services can be transmitted through this kind of network. In addition to voice calls, ISDN allows packet-switched or circuit-switched data transmission and fax transmission. In some countries, ISDN technology has taken over from analogue telephone networks, integrating all types of services into a common network for the first time. This digitisation has also enabled digital ISDN phone lines to be made available to end users. In comparison to an analogue connection, an ISDN subscriber line offers a whole range of advantages. The basic ISDN line allows multiple phones or communication [devices](https://web-production.nfon.com/gb/products/devices), with different numbers ([MSNs](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/msn)), to operate and use two parallel connections simultaneously. In addition, the ISDN connection also offers higher data transfer rates to an analogue connection using a modem, for example, when accessing the Internet. To utilise the ISDN line, end users need special ISDN-capable phones or faxes. The use of so-called [A/B converters](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/a-b-interface), linking analogue devices to a digital connection, is common. Meanwhile, other techniques such as DSL or cable connections are used for connecting to the internet. 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