Re: [aqm] I-D Action: draft-ietf-aqm-recommendation-04.txt

[John Leslie <[e-mail]>]

Simon Barber <[e-mail]> wrote:
> 
> I have a couple of concerns with the recommendations of this document as 
> they stand. Firstly - implementing AQM widely will reduce or even 
> possibly completely remove the ability to use delay based congestion 
> control in order to provide a low priority or background service.

   I agree that if AQM succeeds in reducing delay, that will reduce
the delay variation that "low priority" services depend upon.

   However, that strikes me a a problem that delay-based congestion-
control services will have to deal with regardless of AQM.

   Wouldn't we be better off to figure out how AQMs could signal what
these delay-based services actually care about?

> I think there should be a recommendation that if you are implementing
> AQM then you should also implement a low priority service using DSCP,
> e.g. CS1.

   I don't follow how that could help in practice, except for the case
where the AQM is implemented _very_ near the sender. (DSCP gets lost
pretty quickly at Autonomous System boundaries.)

> This will enable these low priority applications to continue to 
> work in an environment where AQM is increasingly deployed. Unlike
> DSCPs that give higher priority access to the network, a background
> or low priority DSCP is not going to be gamed to get better service!

   (I wish I believed we could get agreement to do this!)

> Secondly, there is a recommendation that AQM be implemented both within 
> classes of service, and across all classes of service.

   I'm not finding this in the document: "Quality of Service" is found
in Section 2.1; but that's not "class of service". "Traffic class" is
found in Sections 2.1 and 4.4, neither of which mentions "across all
classes."

   ???

> This does not make sense.

   Agreed.

> If you are implementing AQM across multiple classes of service, then you
> are making marks or drops while ignoring what class the data belongs to.

   Alas, that doesn't make sense either. :^(

> This destroys the very unfairness that you wanted to achieve by
> implementing the classes in the first place.

   That's a funny way to phrase it...

--
John Leslie <[e-mail]>