SLIDING WINDOW FLOW CONTROL
Sliding window flow control is potentially more efficient then stop and wait flow control because in sliding window flow control, the transmition is treated as pipe line that field with frame.
FOR EXAMPLE: WXMODEM.
The actual window size not to be maximum possible size for a given sequence number length for example: using a three bit sequence number a window size of four could be configure for station using sliding window control protocol.
Go-back-N ARQ is a specific instance ARQ protocol in which sending process continues to send a number of frame specified a window size even without receiving an acknowledgement packet from the receiver. It is a special case of sliding window protocol with the transmitted window size of N receiving window size of 1.
The receiver process keeps trace of sequence number of next frame it expect to receiver & sends that number with every acknowledgement it sends. The receiver will ignore any frame that does not have the execte sequence number it expect.
Once the sender has send all of the frame in its window, its detect all of the frame since the first lost frame are outstanding, will go-back-N ARQ sequence number of last acknowledgement it receive from the receiver.