TCP Sliding Windows
TCP sliding windows control the flow and efficiency of communication.
The size of the TCP sliding window determines the number of acknowledgements sent for a given data transfer because it constrains how much the source is willing to send before it requires an acknowledgement.
Once the window fills with data, the destination host sends an acknowledgement for all the packets received in that window. Then, the window slides over in order to accept new packets.
In general, networks that perform large data transfers should use large window sizes.