Advanced Program-to-Program Communication IBM Systems Network Architecture (SNA) system software that allows high-speed communication between programs on different computers in a distributed computing environment. APPC establishes and tears down connections between communicating programs, and consists of two interfaces. A programming interface and a data-exchange interface. The former replies to requests from programs requiring communication, the latter establishes sessions between programs. APPC runs on LU 6.2 devices. See also LU 6.2.