A public switched telephone network (PSTN) that, at a minimum, provides for the switches to consult centralized, service- and customer-specific databases for routing instructions and authorization code verification. Intelligent Network Version 1 (IN/1) was conceived at Bell Labs and unveiled in 1976 with the introduction of INWATS (800) services and the first common channel signaling (CCS) system. IN/1 services included INWATS, calling card verification, and voice virtual private networks (VPNs). IN is dependent on the service creation element (SCE), a set of modular programming tools permitting services to be developed independently of the switch, thereby divorcing the servicespecific programmed logic from the switch logic.This enables the service to be developed independently and be made available to all switches in the network. IN/1 was succeeded by the advanced intelligent network (AIN), developed by Bell Labs in the early 1980s. See also AIN, Bell Labs, CCS, database, PSTN, routing, SCE, switch, and VPN.