Re: [Bloat] when does the CoDel part of fq_codel help in the real world?

["Bless, Roland (TM)" <roland.bless@kit.edu>]

Hi Luca,

Am 28.11.18 um 11:48 schrieb Luca Muscariello:

> And for BBR, I would say that one thing is the design principles another
> is the implementations
> and we better distinguish between them. The key design principles are
> all valid.

While the goal is certainly right to operate around the optimal point
where the buffer is nearly empty, BBR's model is only valid from either
the viewpoint of the bottleneck or that of a single sender.

In BBR, one of the key design principle is to observe the
achieved delivery rate. One assumption in BBRv1 is that if the delivery
rate can still be increased, then the bottleneck isn't saturated. This
doesn't necessarily hold if you have multiple BBR flows present at the
bottleneck.
Every BBR flow can (nearly always) increase its delivery rate while
probing: it will simply decrease other flows' shares. This is not
an _implementation_ issue of BBRv1 and has been explained in section III
of our BBR evaluation paper.

This section shows also that BBRv1 will (by concept) increase its amount
of inflight data to the maximum of 2 * estimated_BDP if multiple flows
are present. A BBR sender could also use packet loss or RTT increase as
indicators that it is probably operating right from the optimal
point, but this is not done in BBRv1.
BBRv2 will be thus an improvement over BBRv1 in several ways.

Regards,
 Roland