Common ISDN Application Programming Interface
Work on CAPI began in 1989, focussing on the German ISDN protocol, and was finished in 1990 by a CAPI working group consisting of application providers, ISDN equipment manufacturers, large customers, user groups and DBP Telekom, resulting in COMMON-ISDN-API Version 1.1. Following completion of the international protocol specification, almost every telecommunication provider offers BRI and PRI with protocols based on Q.931 / ETS 3009 102. Common-ISDN-API Version 2.0 was developed to support all Q.931 protocols.
[Why not CIAPI?]