Re: [Cake] [Bloat] dslreports and inbound rate shaping

[Kathleen Nichols <nichols@pollere.com>]

It sounds like you are defining congestion as packets experiencing 5ms of
delay over a period of 5ms.

When you evaluate this, what metrics do you use to evaluate the effect on
the applications using this buffer?

	Kathie

On 5/21/15 8:26 AM, Jonathan Morton wrote:
> When Codel is applied on the upstream side of a link, a burst arrives in
> it almost instantly, and thus it only takes 5ms to detect that 5ms of
> queue has developed. The interval parameter then delays action on that
> detection until it is certain that it's a standing queue and not simply
> a burst.
> 
> When applied on the downstream side of a link, however, it takes longer
> for a burst to filter through to where Codel can see it. If the shaper
> is set to 90% of the link rate, it takes at least 45ms to build a 5ms
> queue, during which the receiver is acking data without any clue that
> congestion is in place. At 95%, it requires at least 95ms. The delay in
> detection might be even longer under some circumstances.
> 
> This means Codel has to be more aggressive at responding to a detected
> 5ms queue on ingress in order to provide control of the flow comparable
> to egress. I'm proposing using a reduced interval parameter to do that.
> A drawback is that the response will be stronger than designed, and this
> may have an impact on throughput, but the same is true (and more
> definitely so) of a policer.
> 
> On the one hand, this might lead to an interim solution while Bobbie
> gets fleshed out. On the other, it should provide more information on
> whether Bobbie is likely to work.
> 
> - Jonathan Morton
>