Pipe queues

[Stephen Clark]

Luigi Rizzo wrote:

>On Mon, Dec 10, 2007 at 11:22:33AM -0800, Chuck Swiger wrote:
>  
>
>>On Dec 10, 2007, at 8:56 AM, rihad wrote:
>>    
>>
>>>Hi,
>>>
>>>I'm having a hard time to understand what pipe queues are with  
>>>respect to bandwidth limitation. ipfw(8) and dummynet(4) manuals  
>>>didn't help me much.
>>>      
>>>
>>Pipes and queues are two different things; a pipe simulates a network  
>>link, and a queue is used to hold packets which are backlogged because  
>>they are arriving faster than the outbound link (ie, a pipe) can  
>>transmit them.
>>
>>    
>>
>>>How does dummynet's traffic shaping function?
>>>      
>>>
>>It uses a variant of weighted fair queuing.
>>    
>>
>
>actually the shaping uses a leaky bucket algorithm.
>The weighted fair queuing is the queue management scheme used
>when you have multiple queues attached to the same pipe
>
>cheers
>luigi
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>  
>
Pipes are used to limit bandwidth. Queues are used to assign priority to 
different classes of traffic. As an example
suppose you wanted to limit bandwidth for a specific ip to 2mbs. You set 
up a pipe to do this and use ipfw to put traffic
from this ip into the 2 mbs pipe. If you then wanted to prioritize ftp 
traffic at higher than priority than all other traffic for
this same user you would create 2 queues to feed the 2mbs pipe. You 
would send the ftp traffic into the higher priority queue
and all other traffic for this user into the other queue.

hth,
Steve

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