04 Try it yourself Interactive
The same scene in both modes. Eight frames numbered 0 to 7, three-bit sequence numbers, a sender window of 4, and frame 2 is lost the first time it is sent. Its retransmission always gets through, so the only difference you see is the recovery strategy. The upper lane is the sender, the lower lane is the receiver, and the indigo bar under each lane is that side’s window. Watch the receiver lane: under Go-Back-N frames 3, 4 and 5 turn rose because they arrived perfectly and were thrown away, and under Selective Repeat they turn amber because they were kept. The window selector stops at 4 because with three-bit sequence numbers 4 is the largest window Selective Repeat may legally use. Nothing plays on its own: Next, Back and Reset, or the arrow keys.