Pipe queues

[rihad]

Stephen Clark wrote:
> 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.
> 

And if I _only_ want to shape IP traffic to given speed, without 
prioritizing anything, do I still need queues? This was the whole point.