I am learning about TCP control flow and came across a question about how much data is carried by the 4th segment. The answer is supposed to be 1200 (2230 - 1030) but I don't quite understand why.
By definition, I know that the acknowledgement number is telling the other side what is next expected from it. Thus 5 is the server acknowledging everything up to 2230 and telling the client that the server is expecting 2230 next, while 3 is the client acknowledging everything up to 3848 and telling the server that it next expects 3848. But I still don't understand why we're considering segment 5 and segment 2? If it's only "expecting" then how do we know how much data is being carried?