[Cerowrt-devel] BBR congestion control algorithm for TCP in net-next

Mikael Abrahamsson swmike at swm.pp.se
Wed Sep 21 06:15:15 EDT 2016

On Wed, 21 Sep 2016, Dave Taht wrote:

> I dunno, I'm just reading tea leaves here!
> can't wait for the paper!


I would like to understand how BBR interacts with a window-fully-open 
classic TCP session and FIFO induced delay that is in steady-state before 
the BBR session starts.

So let's say I have 100ms of lightspeed-in-fiber RTT, and I am then 
running a file transfer with some other TCP algorithm which is sitting 
there, window fully open, creating an additional 100ms of 
stupid-router-FIFO-buffering delay.

So new BBR TCP session comes along, sees 200ms of RTT, and starts sending. 
I guess the classic TCP algorithm still keeps its window fully open, and 
doesn't care that RTT now increased to 210ms by the BBR flow packets.

Now what? BBR flow sees increased latency, and backs off, right? So how 
much of the bandwidth will each flow get? How do these interact?

Mikael Abrahamsson    email: swmike at swm.pp.se

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