Is it 3 or 4? Is 2 enough? Let’s say the last message in your example is dropped B would have 3 acks from A while A only has 2 acks from B. Will A attack? If

Is it 3 or 4? Is 2 enough? Let’s say the last message in your example is dropped B would have 3 acks from A while A only has 2 acks from B. Will A attack? If not, B is left attacking on their own. Similarly, what if none of Bs messages make it back to A? How does B know to attack?