IBM Systems Network Architecture

SNA is a computer networking architecture developed by IBM to provide a network structure for IBM mainframe, midrange, and personal computer systems. SNA defines a set of proprietary communication protocols and message formats for the exchange and management of data on IBM host networks.

SNA defines methods that accomplish the following:

• Terminal access to mainframe and midrange computer applications.

• File transfer of data between computer systems.

• Printing of mainframe and midrange data on SNA printers.

• Program-to-program communications that allow applications to exchange data over the network.

SNA can be implemented in the following two network models:

Hierarchical    The hierarchical SNA networking model, also called subarea networking, provides geographically disparate terminal users access to centralized mainframe processing systems. In the hierarchical networking model, centralized host-based communication systems must provide the networking services for all users on the network.

Peer-to-Peer    The more recently developed Advanced Peer-to-Peer Networking (APPN) model makes use of modern local area network (LAN) and wide area network (WAN) resources and client/server computing. APPN networking enables a form of distributed processing by allowing any computer on the network to use SNA protocols to gain access to resources on any other computer on the network. Computers on an APPN network do not have to depend on mainframe-based communication services.

Because of the large installed base of legacy applications that run on IBM mainframe and midrange systems, both of these SNA networking models continue to be widely used in enterprise networks.

Note

SNA is gradually evolving into a more of a peer-to-peer networking structure. As part of that evolution, APPN networking is often combined with hierarchical SNA networking. APPN is described in "Advanced Peer-to-Peer Networking" later in this appendix.