Go Back N Protocol (With Animation) - Computer Networks

Go-Back-N ARQ is a specific instance of the Automatic Repeat-reQuest (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an ACK packet from the receiver. Learn this from this perfect animation.

The receiver process keeps track of sequence number of the next frame it expects to receive, and sends that number with every ACK it sends. The receiver will ignore any frame that does not have the exact sequence number it expects -- whether that frame is a "past" duplicate of a frame it has already ACK'ed, or whether that frame is a "future" frame past the lost packet it is waiting for. Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to sequence number of the last ACK it received from the receiver process and fill its window starting with that frame and continue the process over again.

Three cases are covered: 
1. All Packets reach the receiver and send acknowledgements back to the sender.
2. Some Packets a lost on their way to destination. 
3. Some Acknowledgements are lost on their way back to sender.

                View the animation to understand The Protocol

(Click the Play Button to start)