IBM Network Control Program
The original IBM Network Control Program (NCP) ran on the 3705 and supported access to older devices by application programs using Virtual Telecommunications Access Method (VTAM). A subsequent version also supported access to SNA networks, initially only by application programs using Virtual Telecommunications Access Method (VTAM) and later by application programs using Telecommunications Access Method (TCAM), and 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 IBM Systems Network Architecture (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.
A local NCP connected to a System/370 channel via single[NB 1] address. A remote NCP had no direct connection to a mainframe. Instead a connection was made through a local NCP via SNA packet switching. NCP provided the link control and Network layer functions of a Wide area network.
Notes
- ^ However, if NCP was generated with Partitioned Emulator 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.
Further reading
- W. S. Hobgood (1976). "The role of the Network Control Program in Systems Network Architecture" (PDF). Vol 15, No 1. IBM Systems Journal. Retrieved 2006-08-26.
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