How large should the TCP Receive Window be?
Receive Window should be larger than bandwidth delay product (also known as pipe capacity). For example, for 170ms delay on a 768Kbps link, RWIN = 768000 bits/sec * 0.170 sec = 130560 bits = 16320 bytes. Note that if either available bandwidth or the delay is doubled, RWIN would double as well. On LAN links the delay is very small. Therefore, a small RWIN would be sufficient. However, effect of insufficient RWIN size become particularly noticeable on WAN links. Due to relatively small default RWIN size (8KB) Windows 95, 98, NT 3.51 and NT 4.0 throughput would suffer in above 768Kbps connection during file transfer via FTP. Windows 2000 uses a more realistic 16KB default for RWIN. However, that too would need to be increased depending on pipe capacity. Well, that looks rather simple but latency (delay) is actually not constant. It varies from connection to connection and even during the lifetime of one connection as some IP packets may follow different routes and the heavy load on a rou
