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SNA (Systems Network Architecture)

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SNA is an IBM architecture that defines a suite of communication protocols for IBM systems and networks. SNA is an architecture like the OSI model. There is a protocol stack and various architectural definitions about how communication takes place at the various levels of the protocol stack.

SNA was originally designed for IBM mainframe systems. One could refer to this original SNA as "legacy SNA." The "new SNA" is APPN (Advanced Peer-to-Peer Networking). Legacy SNA is based on the older concept of centralized processing, where the mainframe was the central computing node. Dumb terminals attached to the central processor and did two things: accepted keyboard input from users, and displayed calculated results or query replies from the mainframe.

As desktop computers and LANs started to appear in the 1980s, it became obvious that personal computing (i.e., running programs on a local computer rather than a central computer) was the wave of the future. This was not so obvious to IBM engineers. There were attempts to maintain the legacy SNA architecture by integrating these new systems as dumb terminals, even though they had their own processing power.

Eventually, IBM saw the benefits of allowing these "smart terminals" to handle some of the processing load. It created APPN to support client/server computing and it began to recognize PC-based applications as being important for the enterprise. APPN is very similar to TCP/IP, and, for a while, many people thought that APPN would eventually supersede TCP/IP. In other words, TCP/IP was the experimental model and APPN would be the working model. Today, APPN is considered a legacy architecture.

By the 1990s, IBM's mainframe systems changed roles from being central processing systems to being just another server on the network-but a very fast server. IBM's high-powered systems can provide the kind of processing power, high availability, and fault tolerance that is needed to keep up with growing traffic at Web sites and corporate data centers. Most important, a vast amount of legacy data is still available on IBM systems. SNA and APPN are still critical in these environments.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.