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Computer Telephony Integration, also known as Computer Telephony Integration or CTI, is a general term for any technology that enables the integration and coordination of interactions via telephone and computer. The term is mainly used to describe desktop-based interaction, which offers users greater efficiency, but can also refer to server-based functions such as automatic call forwarding.

Usual functions

By application type

  • EDP controls telephone system
    CTI enables, from computer programs, the automatic setup, the acceptance and termination of telephone calls, the establishment of telephone conferences, the sending and receiving of fax messages, telephone book services, as well as the forwarding of calls. CTI applications usually run either on the user's desktop or on an unattended server. Common desktop functions provided by CTI applications:
    • Dialog boxes - Display with caller information (ANI=Automatic Number Identification), dialed number (DNIS = Dialed Number Identification Service) and dialog box on answering the call, with or without the connection data. This function is generally used to search for more information about the caller using a business application.
    • Dial - Automatic dial-in and computer-controlled dial-in (power dialing, preview dialing, predictive dialing).
    • Telephone Control - Includes call control (answer, hang up, hold, conference call etc.) and function control (DND (do not disturb), call forwarding etc.).
    • Transferring calls - Coordinated transfer of calls and data between two call participants (i.e. forwarding the dialog box with the call).
    • Call Center - Allows users to log in as a call center agent and control their agent status (Ready, Busy, Not Ready, Pause, etc.).

  • Telephone system controls EDP
    By means of an automatic caller identification the suitable data record with customer data can be brought from a database to a screen. Furthermore, CTI programmes (depending on the provider) can keep a journal of the discussions held. This technology is mainly used by call centers. Common server functions provided by CTI applications:
    • Call forwarding - Automatic forwarding of calls to a new destination connection is based on criteria that usually include a database call of the caller's number (ANI) or the dialed number (DNIS).
    • Advanced call reporting features - The detailed data from the CTI application provides superior call reporting.
    • Voice Recording Integration - The detailed data from the CTI application enriches the data stored from the recorded calls.


Computer Supported Telecommunications Applications (CSTA) is the name of a protocol specification standardized by the ECMA that is used for data traffic between a PBX and computer programs. Like many other protocols in telecommunications, this specification is written in ASN.1. The CSTA protocol defines only the transferred data, not the transport layer. Basic encoding rules (CSTA phases I, II, and III) and XML encoding rules (CSTA phase III) are used to encode the data streams. The CSTA protocol can be transported via various media (serial, ISDN, TCP/IP).

The latest variant is uaCSTA (ECMA Technical Report TR/87). This variant, introduced for so-called user agents, was created with a limited scope, which uses XML exclusively for coding.