The default TCP/IP configuration of many operating systems will prevent you from realizing the true potential of your high speed Internet connection (e.g. Cable modem, xDSL, and especially satellite). The most critical parameter is the setting of TCP Receive Window size (RWIN). When you connect to a server, your advertised RWIN tells the remote server how much data it is allowed to send before requiring an acknowledgement.
If there is a high delay between you and the server and your RWIN is set too low, the remote server will only send small bursts of data and the rest of the time it will be idle, waiting to receive your acknowledgements.
The optimal RWIN setting for any given connection can be easily determined by calculating its bandwidth*delay product. This is simply the bandwidth of the slowest link between you and the server (likely your Internet connection) multipled by the latency between you and the server (as measured by a ping).
The following table shows the typical BDPs for LAN, dialup, and high-speed Internet connections:
| Connection Type | Bandwidth (Bytes/s) | Typical delay (s) | b*d (Bytes) |
| Dialup | 7,000 | 0.300 | 2,100 |
| LAN | 1,250,000 | 0.002 | 2,500 |
| Cable/xDSL | 182,000 | 0.200 | 37,500 |
| Satellite | 62,500 | 1.000 | 62,500 |
Microsoft Windows utilizes a default RWIN of 8760 bytes. This is perfectly adequate for both LAN and dialup connections which have a b*d=~2KB. However, the default RWIN is completely inadequate for high speed Internet connections which have a b*d=32-64KB.
