TCP Receive Window: This is where you set RWIN (RcvWindow). RWIN is the single most important tweak. Raising Rwin from default (8760 for Win95/98/98SE/NT and 17520 for WinME/2K/XP), can greatly improve download speeds. Why? Here is my kindergarten analogy: Default RWIN for broadband, is like having a tiny straw in a thick milk shake, only so much can get through the straw (line), so fast. By putting a larger straw (higher RWIN) in that same thick shake, you allow more shake (data) to come through faster, to a point that is. After which, there is no more improvement, and shake (data) can start spilling all over (packet loss). So the key is, to find an RWIN that fits your line just right. This is blank before changing from default.

Come puoi vedere dal test fatto in precedenza, con quel valore di RWIN (Default Receive Window (RWIN) = 8592) la tua connessione era limitata a
Your RcvWindow limits you to: 343.68 kbps (42.96 KBytes/s) @ 200ms
Your RcvWindow limits you to: 137.472 kbps (17.184 KBytes/s) @ 500ms