The LAP-F protocol (Link Access Protocol-Frame) was born with frame relay, designed to improve the performance of networks from the X.25 recommendation UITT. The latter has proved too heavy and therefore unable to increase rates, it took in search for a simplification.
The idea implementation was to remove the package level and down to the functionality of this level in the frame level. The LAP-B protocol has evolved become the LAP-F protocol, characterized by replacement of the address area an area to accommodate a switching reference, the DLCI (Data Link Connection Identifier).
Base DLCI field was extended by the addition of a second byte and then a third, in which bits 6 and 7 are vested in the lengthening of the DLCI field. Structure of the LAP-F frame is illustrated in figure.