When a frame corresponding to the lower edge arrives, both edges are advanced by one. Frames outside the window are discarded. Frames inside the window but higher than the lower edge are buffered until all lower frames arrives
When a frame corresponding to the lower edge arrives, both edges are advanced by one. Frames outside the window are discarded. Frames inside the window but higher than the lower edge are buffered until all lower frames arrives
The next slide shows the operation of a sliding window protocol