Why does tuning TCP Receive Window improve throughput?
TCP is a reliable communication protocol. As a result, sender expects Acknowlegement (ACK) packets from receiver to make sure packets are delivered to destination and are free of errors. However, as sending one packet and waiting for ACK is rather inefficient, a window is implemented. In this scheme, receiver advertises its RWIN size during TCP connection setup and sender keeps sending as many packets as allowed by receive window of receiver. In other words, each packet sent closes the window a little and each ACK received opens it up a little again. On a high bandwidth or high delay (or both simultaneously) TCP connection, sender may transmit a number of packets before the first packet reaches the receiver. Even if the receiver were to send ACK immediately, it takes some more time for the ACK packet to get back to the sender. To optimize the throughput, the pipe must be filled at all times and to do this sender should never stall waiting for ACK.This is only possible if Receive Window
