Data Loss and Retransmission When TCP at the source host has not received an acknowledgement after a predetermined amount of time, it goes back to the last acknowledgement number that it received and retransmits data from that point forward. Flow Control Uses the Window Size field in the TCP header to specify the amount of data that can be transmitted before an acknowledgement must be received. Adjusts the effective rate of data transmission to the maximum flow that the network and destination device can support without loss. Manages the rate of transmission so that all data is received and retransmissions are minimized.