Dummynet cascade of pipes

[John Mok]

Luigi Rizzo wrote:
> On Sat, Mar 03, 2007 at 09:50:43AM +0800, John Mok wrote:
>> Hi,
>>
>> I am new to Dummynet. I would like to setup a FreeBSD QoS box to replace 
>> the one using Linux IMQ. However, I have the following questions :-
>>
>> 1. Is it possible to cascade pipes, such that the bandwidth management 
>> could be easier by hierarchical control rather than flat-out? For instance,
>> pipe 100 is the total bandwidth 2Mbps of the serial link to Internet
>> pipe 110 cascade pipe 100 with a weight 8Kbps and ceiling 16 Kbps
>> pipe 120 cascade pipe 100 with a weight 32Kbps and ceiling 256 Kbps
>> pipe 130 cascade pipe 100 with a weight 384Kbps and ceiling 2Mbps
>> pipe 140 cascade pipe 100 with a weight 224Kbps and ceiling 2Mbps
> 
> no. hierarchical bandwidth management means inheritance
> and this leads to inefficient algorithms.
> 
> WFQ does a decent job in most cases where you would want
> inheritance, it's just a slightly different way of modeling things.
> 

Without hierarchical control, would it be possible to make a dummynet 
model for the example situation to work? If separate pipes are used to 
set the bandwidth limit :-

ipfw pipe 110 config bw 16 Kbps
ipfw pipe 120 config bw 256 Kbps
ipfw pipe 130 config bw 2048 Kbps
ipfw queue 130 config weight 384 pipe 130 ....
ipfw queue 140 config weight 224 pipe 130 ....

and when the traffic is fully loaded, then the traffic 2320 Kbps (16 + 
256+ 2048) will exceed the available bandwidth 2 Mbps and would result 
in uncontrollable packet drop due to queue overflow.

Thank you,   John Mok