APPC, also known as LU 6.2, was introduced by IBM in 1982 to address the exchange of data between two peer programs that are located either in the same computer or in two systems connected by the network.

APPC is an architecture that defines a set of networking protocols and an application programming interface (API). Because APPC is a networking protocol, it does not address the individual programming language syntax.

The APPC API is described as an abstract presentation of the various API functions called verbs. The verbs define the sequence and order an application program has to follow in order to communicate with peer application programs. The implementation of APPC in the various programming language converts the abstract API to functions or callable subroutines that conform to the syntax of the programming language.

To avoid the hierarchical nature of the mainframe SNA, and allow "small" computers like programmable workstations and iSeries to use APPC, the type 2.1 node (T2.1) was introduced. A type 2.1 (T2.1) node is a peer-oriented peripheral node that attaches to a mainframe, a communication controller, or another peripheral node.

APPN was designed to support APPC in T2.1 nodes and the exchange of control information between two APPN nodes uses APPC protocol.