Subject: Re: Adaptive Applications

From: Francois Toutain <[email-masked]>
Date: Thu, 14 Aug 1997 18:10:15 +0200

> if all applications use the same tos and one is more demanding than
> another, then the weigth of that applications should be higher, which
> would also result in higher share of the excess bandwidth.
> (...)
> this problem can be solved by having different tos for each
> application type and doing weighting/fairness within each tos.
> (...)
> as i said, a highly demanding application can ask for a higher weigth
> (via a higher minimum rate as in case of my pbe proposal) and also then
> pay for it.

OK, it seems then that my memory didn't serve me right, since what
you're talking about here is not max/min fairness, but proportional
one, where proportions are given by minimum rates. Then if you assess
that minimum rates actually depict the users' needs (w.r.t. excess
BW), that's all right (and quite close to the kind of fairness that is
enforced by WFQ-like schedulers). Except that, to be more general, you
may want to avoid coupling minimum requirement and excess requirement.
For instance consider an application with a min requirement of zero,
and the ability to make use of several Mb/s. Then you'd force this
app. to declare a non zero and presumably large min req in order to
get access to the excess BW. If CAC is exercised based on these min.
requirements (as was the case for PBE), you're wasting resources.
Or you can define another service for those apps. which do not need
non-zero min req, in which case you'll have to somehow distribute
excess BW between the (at least) two classes.

-ft.

---

From: Juha Heinanen <[email-masked]>
Date: Thu, 14 Aug 1997 19:19:24 +0300

Except that, to be more general, you
   may want to avoid coupling minimum requirement and excess
   requirement.

decoupling those two would certainly be nice to have, but not so easy to
implement with wfq scheduler.  it looks to me that you would need to wfq
schedulers: the first one guarantees the minimum and the second that
operates after the first would guarantee the excess according to another
set of weights.  i have not yet seen such schedulers in current
equipment, but it doesn't mean that there ain't any.

-- juha