[LARTC] HTB and ATM patch

[Andy Furniss]

Edouard Thuleau wrote:
> Hi all,
> 
> I patch my kernel (2.6.17) and my tc (iproute2-2.6.18-061002) utilitie for
> an accurate packet scheduling on an ATM link.
> I configure my HTB hierarchy on the upload of the link and try with
> differents flows.
> 
> It works correctly but in some of case I lose about 50% of my bandwith.

That's what dsl/atm is like for some packet sizes, eg. an empty windows 
ack = 40 byte IP packet, but 2 ATM cells = 106 bytes on the wire.

> I use the overhead (42) configuration for my link (PPPoE, VC/LLC) indicate
> in the documentation.
> My question is, how this hoverhead value is calculate ?

http://ace-host.stuart.id.au/russell/files/tc/tc-atm/

> 
> I try to separate the streams with the lentgh of the packet in differents
> classes and put a specific overhead for each one, but I don't know how
> calculate it. Do you think it's a good solution ?

You don't need a different overhead just 42 for all classes  (assuming 
you are shaping on the ppp device - you can take 14 from the 42 if the 
ppp terminates elsewhere any you are shaping on eth)

> 
> Is it necessary to put the atm, nohyst options and configure the overhead
> 
> for the mother class ?
> 

I would put overhead 42 atm nohyst after every rate - so yes.

Andy.