[Cake] Why are target & interval increased on the reduced bandwidth tins?

[Jonathan Morton]

> On 25 Jun, 2020, at 4:40 pm, Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:
> 
> So the scenario I have in my head says that BK traffic could burst at full bandwidth rate (or higher) filling upstream ISP buffers and thus inducing delays on all other traffic because "we think it’s a slow link and have high interval and target values” delaying our response to the burst.  Whereas if we retain the default interval & target from the true link capacity calculation we’ll jump on it in time.

You might be forgetting about ack clocking.  This gives the sender information about how quickly data is reaching the receiver, and normally the sender will generate either one or two packets for each packet acked.  So even without an immediate AQM action, there is still *some* restraint on the sender's behaviour within approximately one RTT.

This is one of the many subtle factors that Codel relies on.

 - Jonathan Morton