In a minicomputer or mainframe environment, the network control program is software that manages the traffic between terminals and the central computer. It resides in the communications controller or front end processor. IBM's SNA network control program is called precisely that: "network control program" (NCP).
In a LAN, the network control program is the operating system in the server. The "network operating system" (NOS) manages requests from the user's workstations. See front end processor
and network operating system