Systems Network Architecture

Systems Network Architecture (SNA) is an IBM data communication architecture that specifies common conventions for communicating among a wide variety of hardware and software data communication products. This architecture consists of two kinds of definitions: formats that define the layout of messages exchanged by network components, and protocols that define the actions that network components take in response to messages.

An SNA network is a collection of computers that are linked together and communicate using SNA.

Originally, SNA was designed to enable communications with a host computer. Each network or sub-network was controlled by the host; other computers communicated directly with the host, but not with each other. This older, host-controlled style of network is often referred to as subarea SNA. SNA has since developed to support direct peer-to-peer communications between computers in the network, without requiring a host. This newer, peer-level networking is APPN.

Many SNA networks have elements of both subarea and peer-to-peer networking. As networks migrate from subarea SNA to APPN, an APPN-capable host may act to control older systems while also acting as a peer to newer systems. Similarly, a single computer may access both peer computers (in an APPN network) and an older host; its communications with the host are controlled by the host, but its communications with other computers are peer-to-peer and do not involve the host.