I am trying to start TCP slow start congestion algoritham in my raspberry device. As it documented in RFC 2581, it needs to set ssthresh value greater than the congestion window (cwnd). So I have chnaged /sys/module/tcp_cubic/parameters# sudo nano initial_ssthresh value to 65000 and cwnd was set to 10 ( checked with ss -i). After this settings I tried to send big packet from raspberry of size 19000 bytes. According to slow start it first needs to send to the destination device 2 packtes and then 4, then 8 ..etc.
But its not happening at raspberry. it sending me 10 packtes. Did I do something worng ?. In this case How can i start slow start algoritham.
Thanks
When CWND is less than ssthresh, the connection is in slowstart. When the CWND becomes greater than the ssthresh, the connection goes into congestion avoidance.
What you're seeing is that newer versions of linux have the initial congestion window set to 10. Before it was the default setting, you could change your initial congestion window from 3 through an ip route command. I haven't tried it, but I'm guessing you can do the opposite here.
Long story short, your machine is doing slow start. It is just starting with a larger initial congestion window.