IBM Network Control Program
The IBM Network Control Program, or NCP, was software that ran on a 37xx communications controller and managed communication with remote devices. NCP provided services comparable to the Data Link Layer and Network Layer functions in the OSI model of a Wide area network.
A subsequent version also supported access to Systems Network Architecture (SNA) networks, initially only by application programs using VTAM and later by application programs using Telecommunications Access Method (TCAM). This was the basis for the subsequent versions that ran on an IBM 3704, 3705, IBM 3725. IBM 3720, or 3745. It caused the machine to become an SNA Physical Unit Type 4 (PU4). A PU4 usually had SDLC links to remote cluster controllers (PU1/PU2) and optional SDLC links to other PU4s. Polling and addressing of the cluster controllers was performed by the NCP without mainframe intervention.
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.
A remote NCP had no direct connection to a mainframe. Instead a connection was made through a local NCP via SNA packet switching.
- However, if NCP was generated with Partitioned Emulation Program (PEP), then the Emulator Program (EP) has its own block of I/O addresses, normally on a different channel from that used by the NCP proper.
- Microsoft. "SNA Functional Layers". Retrieved Sep 7, 2012.
- W. S. Hobgood (1976). The role of the Network Control Program in Systems Network Architecture. Vol 15, No 1. IBM Systems Journal. Retrieved 2006-08-26.