SNA is a proprietary IBM architecture and set of implementing products for network computing within an enterprise. It existed prior to and became part of IBM's Systems Application Architecture (SAA) and it is currently part of IBM's Open Blueprint. With the advent of multi-enterprise network computing, the Internet, and the de facto open network architecture of TCP/IP, IBM is finding ways to combine its own SNA within the enterprise with TCP/IP for applications in the larger network.
SNA itself contains several functional layers and includes an application program interface called the Virtual Telecommunications Access Method (Virtual Telecommunications Access Method), a communications protocol for the exchange of control information and data, and a data link layer, Synchronous Data Link Control (SDLC). SNA includes the concepts of nodes that can contain both physical units that provide certain setup functions and logical units, each associated with a particular network transaction.