Am Donnerstag, 2. März 2006 20:54 schrieb Adam James:
> Hi,
>
> On Thu, 2006-03-02 at 15:49 +0000, Andy Furniss wrote:
> > Russell Stuart wrote:
> > > The following patch to tc allows it to perform an exact
> > > ATM / ADSL rate calculation.
> >
> > I probably haven't read the patch properly - but I don't think you
> > can do it exactly without patching net/sched/sched_htb.c aswell.
> > Specifically you need to add overhead - 1 before htb shifts the
> > length to get the slot num (-1 because you need to get 48 and 49
> > payload length to map to different slots 47 and 48 do). The table
> > should be filled according to this.
>
> As Markus mentioned in another post on this thread, Jesper Dangaard
> Brouer (http://www.adsl-optimizer.dk) has already written an iproute2
> and Linux kernel patch that implements the above. ATM cell alignment
> is done in tc_core.c, and the per packet overhead is passed to the
> relevant kernel modules.

once again i have thought about this topic and tried to built a rate 
table with exactly the same behaviour as the htb-overhead patch from 
Jesper. But now as static patch for iproute's tc, without need for 
patching htb or other kernel modules.

But in all my experiments i can't calculate an equivalent rate table.
It differs in behaviour from per packet calculated overhead. But i don't 
see the difference in mathematics in both calculations. I think it must 
be possible, but can't see my fault. With a rate table of at least one 
entry from zero (or 40b) to <mtu> it is possible. But, is it possible 
with only 256 rate table entries?

I've attached a simple program, which implements three versions of 
calculations. Two of them use a rate table, at first the static version 
(without htb-overhead patch), second one with "simulated" kernel patch 
(like Jesper's one) and at least a "realtime calculation" as a 
reference value.

The second rate table is 100% equivalent to realtime calc. But the 
static version differs for some ip-length values from it. And i don't 
understand why. 
Perhaps someone can point me to the difference?
The program is only for testing rate tables calculations.

It would be nice to do it without a htb or other qdisc module patch. And 
i think it should be possible :)

-- 	
Markus Schulz