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Performance - Transfer Buffers

Auto Tune Receive Buffer 
Windows 2000, Windows XP, Windows 2003
If this option is enabled SmartFTP measures the bandwidth and delay during the transfer and automatically increases the Send Buffer Size to the optimal size. The optimal size can be calculated from the Bandwidth x Delay Product (BDP).
Windows Vista, Windows 2008 or higher
If this option is enabled the Auto Tuning of the TCP Receive Window feature from the Windows kernel is used and not the Auto Tune feature from SmartFTP. In this case the Receive Buffer Size has no effect.
Default: Enabled

Receive Buffer Size
Sets the size of the socket receive buffer (SO_RCVBUF). This value directly affects the TCP window size. If the Auto Tune Send Buffer Size option is enabled this is the initial value used before the connection is established. 
Default: 128 KB 

Auto Tune Send Buffer Size
If this option is enabled SmartFTP measures the bandwidth and delay during the transfer and automatically increases the Send Buffer Size to the optimal size. The optimal size can be calculated from the Bandwidth x Delay Product (BDP).
Default: Enabled

Send Buffer Size
Sets the size of the socket send buffer (SO_SNDBUF). This value directly affects the TCP window size. If the Auto Tune Send Buffer Size option is enabled this is the initial value used before the connection is established. 
Default: 128 KB

References
- Technet: TCP Receive Window Auto-Tuning
- MSDN: TCP Receive Window Size and Window Scaling (Applies to Windows XP and Windows 2003)
- MSDN: Very technical article about Auto Tuning on Windows Vista and higher
- MSDN: setsockopt Function (Windows)
- RFC1323: TCP Extensions for High Performance (TCP Window Scaling, SACK, etc)

キーワード
performance, transfer, slow, auto-tuning

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How To change Transfer Buffer Sizes