The original IBM Network Control Program ran on the 3705-I and supported access to older devices by application programs using Telecommunications Access Method (TCAM). With the advent of Systems Network Architecture (SNA), NCP was enhanced to connect cluster controllers (such as the IBM 3270) to application programs using TCAM and later to application programs using Virtual Telecommunications Access Method (VTAM).
On the ARPANET, the protocols in the physical layer, the datalink layer, and the network layer used within the network were implemented on separate InterfaceMessage Processors (IMPs). The host usually connected to an IMP using another kind of interface, with different physical, data link, and network layer specifications.
Example of usage – “In 2005 IBM introduced Communications Controller for Linux (CCL), a software product that allows an unmodified NCP to run on the mainframe, eliminating the need for a separate communications controller in some cases.”