An API developed jointly by AT&T and Novell in the early phases (1994) of computer telephony (CT). Strongly oriented toward PC platforms, the TSAPI specification is a lesser protocol stack that does not require that the switch manufacturer fully open the switch interface.Although a number of PBX manufacturers supported TSAPI, the cost of TSAPI PBX drivers was quite high and, as a result, its widespread use has been discouraged. See also computer telephony, driver, PBX, and TAPI.