LU 6.2 is an SNA communications architecture. APPC (Advanced Program-to-Program Communication) is a language based on the LU 6.2 architecture. A developer of SNA transaction programs may choose from many different implementations of APPC. Even though each implementation of APPC adheres to the LU 6.2 architecture, two implementations of APPC might not be the same. Therefore, programs that rely on one vendor's APPC implementation might not work with another vendor's implementation. CPI-C (Common Programming Interface-Communications) is a standard, common programming interface that solves this problem.
CPI-C is a programming interface that implements the APPC verb set. Therefore, applications that require the APPC verb set can be written using CPI-C to achieve SNA vendor independence. QMF for Windows is written using CPI-C.