TCP improves upon stop-and-wait flow control by allowing the receiver to indicate a "window size" with every acknowledgment. The window size is the amount of data the receiver is capable of processing. This is the amount of data that the sender may send without waiting for an acknowledgment from the receiver. Using the window-size information, the stop-and-wait flow control may be improved. If a receiver begins by announcing a window size of 700 bytes. Assuming that the sender has 620 bytes of data to send; it sends of the data, without waiting for an acknowledgment from the receiver for the first datagram. The receiver acknowledges the data by sending a datagram, labeled ACK which indicates the amount sent has been received successfully