[Bloat] the future belongs to pacing

[Jonathan Morton]

> On 4 Jul, 2020, at 8:52 pm, Daniel Sterling <sterling.daniel at gmail.com> wrote:
> 
> could someone explain this to a lay person or point to a doc talking
> about this more?
> 
> What does BBR do that's different from other algorithms? Why does it
> break the clock? Before BBR, was the clock the only way TCP did CC?

Put simply, BBR directly probes for the capacity and baseline latency of the path, and picks a send rate (implemented using pacing) and a failsafe cwnd to match that.  The bandwidth probe looks at the rate of returning acks, so in fact it's still using the ack-clock mechanism, it's just connected much less directly to the send rate than before.

Other TCPs can use pacing as well.  In that case the cwnd and RTT estimate are calculated in the normal way, and the send rate (for pacing) is calculated from those.  It prevents a sudden opening of the receive or congestion windows from causing a huge burst which would tend to swamp buffers.

 - Jonathan Morton