In 2006, wireless networking based upon 802.11 was transforming from a novelty to the preferred technology for network access. NAC was seen as a solution to this problem by providing point-to-point PC inspection and authentication over Layer 2 before systems were granted Layer 3 network access access. SDP assumes NAC functionality such as device authentication and health checking, but it also adds things: Broad device support. It can be used to authenticate mobile and IoT devices. SDP can make or change access policies based upon real-time identity attributes, such as the device type, user location and time of day.”]
Source: https://www.csoonline.com/article/3141930/goodbye-nac-hello-software-defined-perimeter-sdp.html