Visualizing how kernel 3.0’s initial congestion window increase is lowering response times

When the recent IETF internet draft matures to an RFC, it’ll be the first increase in initial window (cwnd / TCP_INIT_CWND)  increase since 2002. The implementation has already made its way into 2.6.39 earlier this year and I thought I’d take 3.0 for a spin and demonstrate the increase in small object acceleration it yields.  I’m testing using a VPS node 100ms RTT away and loading objects ranging from 4kB to 128kB :

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The head start the large congestion window offers favors smaller objects and in the 8kB range, the entire content can be sent in a single round trip:

 

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