at https://xiaolincoding.com/network/3_tcp/tcp_feature.html#%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3 > SND.UNA（Send Unacknowledged）： <img width="981" height="427" alt="Image" src="https://github.com/user-attachments/assets/c6463d20-9f6b-4934-aee9-b25b5a8f2b49" />
at https://xiaolincoding.com/network/3_tcp/tcp_feature.html#%E6%BB%91%E5%8A%A8%E7%AA%97%E5%8F%A3