Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

IBM's APPN was introduced by IBM in 1985 and integrated into SNA (Systems Network Architecture). It provides peer-to-peer networking services similar to but not quite the same as TCP/IP. One of the main reasons IBM introduced APPN was to provide distributed client/server computing services to users who might have moved to TCP/IP or other services. APPN is basically link-layer independent. It can run over token ring, Ethernet, FDDI, frame relay, ISDN, X.25, SDLC, and ultra high-speed networks such as B-ISDN and ATM.

APPN is based on the concept that computers on the network have enough processing power of their own to handle session management and routing. APPN moves various services from central control (such as that provided by a host mainframe computer) to decentralized control points that operate in a peer-to-peer relationship. In the old SNA model, a mainframe was required to control sessions. In the APPN model, user stations set up and maintain their own sessions.