This illustration uses a familiar structure of a sender-here labeled "Sender window (after receipt)"-and receiver-here labeled "Receiver window (after receipt)"-positioned side-by-side, with dotted lines extending vertically downwards from each to indicate the respective timelines and send and receive operations depicted with blue arrows going back and forth between the two timelines. However, in this version an angled gray rectangle appears between the sender and receiver, representing a curtain that prevents one from being able to see the actions taken by the other. This illustration also incorporates sequence numbers for every step of each operation; each sequence appears as 0123012, and different groups of numbers are highlighted in blue for each step.

Operations begin at the topmost portion of the sender's timeline, where a blue arrow extends horizontally from left to right, passes through the curtain, and intersects with the receiver's timeline. The arrow is labeled "pkt0." The number sequence 012 is highlighted in blue. In response to pkt0, the receiver sends ACK0, represented by a blue arrow that extends diagonally downward to the left, passes through the curtain, and terminates in an X. Sequence numbers 123 is highlighted. Beneath pkt0 on the sender's timeline, we see pkt1, also represented by a horizontal arrow and also including the number sequence 012. In response to pkt1, the receiver sends ACK1, which also passes through the curtain and then terminates. Number sequence 230 is highlighted. Below pkt1 on the sender's timeline, we see pkt2, also represented by a horizontal arrow and also including the number sequence 012. In response to pkt2, the receiver sends ACK2, which also passes through the curtain and then terminates. Number sequence 301 is highlighted.

Further down the sender's timeline, we arrive at a point labeled "timeout, retransmit pkt0." The number sequence 012 is highlighted. An arrow extends horizontally to the receiver's timeline, to a point labeled "receive packet with seq number 0."