Go-Back-N is one of the automatic repeat-request (ARQ) techniques. With go-back-n the sender sends a number of frames specified by a window size even without the need to wait for individual ACK from the receiver as in stop-and-wait. The receiver includes with each ACK the sequence number of the next expected frame. The receiver ignores any out-of-order frames. The window size at the sender shrinks with every sent frame and increases with every ACK it receives. If the sender does not receive an ACK for a frame after a timeout, the sender will go back and retransmit all frames starting from that frame.