Solved TCP RACK and SACK

I download a file using a server in Germany from a server in USA.

Good speed (15-24MB/s):


sysctl net.inet.tcp.functions_default=rack
sysctl net.inet.tcp.sack.enable=1


Good speed (15-24MB/s):


sysctl net.inet.tcp.functions_default=freebsd
sysctl net.inet.tcp.sack.enable=1


It starts with 200KB/s, slowly increases and after 15-20 seconds the speed is 24MB/s):


sysctl net.inet.tcp.functions_default=rack
sysctl net.inet.tcp.sack.enable=0


It starts with 2MB/s and after few seconds it decreases to 15KB/s:


sysctl net.inet.tcp.functions_default=freebsd
sysctl net.inet.tcp.sack.enable=0


If I enable RACK then net.inet.tcp.sack.enable shouldn't play any role, right?

But with RACK enabled and SACK disabled I don't get good speed.
 
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