[Cake] [Bloat] benefits of ack filtering

Dave Taht dave.taht at gmail.com
Wed Nov 29 13:48:48 EST 2017

On Wed, Nov 29, 2017 at 10:28 AM, Juliusz Chroboczek <jch at irif.fr> wrote:
>> Recently Ryan Mounce added ack filtering cabilities to the cake qdisc.
>> The benefits were pretty impressive at a 50x1 Down/Up ratio:
> If I read this posting right, you're only measuring bulk performance.
> What about interactive traffic, when there's only one or two data segments in
> flight at a given time

In this design, you can only filter out an ack when you have a queue of them.

I am thinking saying "filter" has been misleading. Tho plenty
stateless ack filters exist.


>> I'd rather like to have a compelling list of reasons why not to do
>> this!
> I haven't looked at Cake in detail, and I haven't put much thought into
> ACK filtering, but off the top of my head:
>   - not risking breaking any of the TCP-related algorithms that depend on
>     ACKs arriving in a timely manner (AIMD, Nagle, Eifel, etc.),
>     especially in the case of just one segment in flight;
>   - not contributing to the ossification of the Internet by giving an
>     unfair advantage to TCP over other protocols;
>   - limiting the amount of knowledge that middleboxes have of the
>     transport-layer protocols, which leads to further ossification;
>   - avoiding complexity in middleboxes, which leads to a more brittle
>     Internet;
>   - not encouraging ISPs to deploy highly asymmetric links.

I'll add these to my list!

> This is not my area of expertise, and therefore I don't feel competent to
> have an opinion, but I think that before you deploy ACK filtering, you
> really should consider the worries expressed above and whatever other
> worries more competent people might have.

been worrying ever since I touched the wet paint!

> -- Juliusz


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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