In discussing connection termination with reference to Figure 15.8, it was stated that in addition to receiving an acknowledgement of its FIN and sending an acknowledgement of the incoming FIN, a TCP entity must wait an interval equal to twice the maximum expected segment lifetime (the TIME WAIT state). Receiving an ACK to its FIN assures that all of the segments it sent have been received by the other side.

Sending an ACK to the other side’s FIN assures the other side that all its segments have been received. Give a reason why it is still necessary to wait before closing the connection.