Cisco first introduced the concept of Network Admission Control back around 2004. This type of functionality was really in response to a wave of Internet worms in the early 2000s that were infecting and clogging up corporate networks. Todays NAC has a somewhat different role than NAC circa 2006, as it is really being used for things like granular access control and risk-based authentication. The new NAC may not attract Sand Hill Road money or hyperbole, but it is finally in the right place at the right time driven by the dangerous threat landscape, mobile computing, and the need to control network access at a granular level.”]
Source: https://www.csoonline.com/article/2859949/nac-renaissance.html