advanced program to program communication (SNA) (APPC)

Advanced Program to Program Communication (APPC) is a transaction interface between equal working units, mostly within the SNA architecture. The interface is implemented in such a network by a program code, which is called LU6.2 (Logical Unit of type 6.2) within the SNA terminology. This program code is supported by Physical Units of type 2.1 (PU2.1).

An APPC node can control itself in a network and initiate, perform and terminate connections to other nodes of the same type by itself. The LU6.2 code is also referred to as the System Node Control Point(SNCP) in analogy to the System Services Control Point ( SSCP) in the hierarchical SNA architecture.

However, APPC is a general interface and may well be implemented in a completely different way. IBM would like APPC to become the basic application-oriented service for distributed transaction processing based on OSI layer 7. In fact, in the absence of alternatives, this could happen. APPC is today an ideal interface for communication from the PC world to a host.