1 SNA Terms and Concepts

This chapter defines Systems Network Architecture (SNA) terms and concepts that are important to understanding and using SNAP-IX. For information about SNAP-IX and its capabilities, see Introduction to SNAP-IX. If you are already familiar with SNA and SNAP-IX, you can begin with Administering SNAP-IX.

This chapter is divided into the following parts:

Systems Network Architecture provides a definition of SNA.
Basic SNA Concepts explains terms and concepts that apply to any SNA network.
Basic APPN Concepts explains terms and concepts that apply only to SNA networks that support Advanced Peer-to-Peer Networking (APPN).
Accessing Subarea Networks from APPN Networks introduces terms and concepts that apply to networks that combine SNA and APPN.

Note

This chapter is not intended as a complete reference to SNA concepts. Detailed information about SNA can be found in the SNA publications listed in Related Publications.

1.1 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 subnetwork 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 been extended 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.