The Network Control Program (NCP) is a program that runs on SNA controllers such as the IBM 3704 or 3705 and is responsible for opening sessions between each physical unit (PU) and the central mainframe
. NCP sessions refer exclusively to a subarea and not to the entire SNA network. Virtual Telecommunications Access Method (VTAM) is responsible for monitoring the NCP sessions. The NCP program supports route determination between an SNA controller and other network facilities. and provides terminal sessions and file transfer as services.