This is a cumulative count of frames received on this port since the last reset, the frame-level counterpart to the packet and character counters on the same port. Frames represent the link-layer encapsulation around the packets counted elsewhere, so tracking this separately lets an admin spot a mismatch, such as a frame count growing much faster than the packet count, which would suggest small or fragmented frames. For example, a sudden surge in FrameInTot without a matching surge in PktInTot on the same port could indicate excessive frame fragmentation on that circuit.