Pronounced lap ef. A bit-oriented protocol that is part of the frame relay protocol suite, LAPF is a subset High-level Data Link Control (HDLC) and runs at Layer 2, the Data Link Layer, of the OSI Reference Model. The LAPF frame comprises a header and trailer that frame the user payload. Figure L-3 illustrates the LAPF frame and its component fields. The fields in the LAPF frame are as follows.