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 From:  "Ignacio Verona" <iverona at estudio dash verona dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Misunderstanding the QoS feature in m0n0
 Date:  Mon, 19 Mar 2007 17:42:02 +0100
Thank you all for your replies. I'm planning to buy a WRAP box
somewhere this month, and I just wanted to clarify some things before
doing it. Now I have a better understanding of the queues and pipes
concepts.


2007/3/19, Bob Gustafson <bobgus at rcn dot com>:
> On Mon, 2007-03-19 at 14:41 +0100, Klaus Stock wrote:
> > > For example. Let's say I've a DSL connection, 1Mb download, 512
> > > upload. What I ideally would want to have is QoS for VoIP (I've a PBX
> > > in my network). So I want VoIP to always have priority in the network.
> > > But I do not want to "waste" bandwidth. For what I understand, the
> > > "pipe" is always reserved, and if VoIP is not being used, other
> > > traffic will not be able to use all the available bandwidth.
> > >
> > > Sorry if the explanation is a little confusing... What I mean is: Is
> > > for example my p2p client able to use all the available bandwidth (if
> > > no VoIP connection is alive), and in the moment that a VoIP call is
> > > being started "prioritize" the VoIP packets, so they arrive on time?
> >
> > The pipe is not being reserved in the way you mean it. At least not in a
> > typical set-up, as the one whihc is produced by the "magic shaper wirzard".
> > You use queues for the priorization of the traffic. The traffic is then
> > allowed to use the pipe accoridng to it's priority. If no other traffic
> > occurs, P2P trffic gets the whole bandwidth of the pipe.
> >
> > However, the pipe needs to be configured in a way that the buffer of the DSL
> > modem never gets filled. Because as soon as packets get to the modem, they
> > are out of reach of the m0n0wall. And the modem will sequentially process
> > it's buffer, regardless of any QoS demands. For that reason, the pipes are
> > typically configured with 10% less bandwidth that the "native" bandwidth of
> > the modem/DSL line.
> >
> > Note that you'll most likely need NO traffic shaping for the downstream,
> > since your LAN has most likely significantly more bandwidth than your DSL
> > downlink. As there's no danger of some network buffer filling up, you can
> > set the corresponding pipe to a bandwidth value which exceeds the DSL
> > downstream bandwidth. No waste of bandwidth there!
> >
> > On the upstream however, you'll need the loss of 10% of the bandwidth. In
> > return you receive a *much* better latency!
> >
> > Best regards, Klaus
>
> The idea of QoS is that high priority packets are plucked from the queue
> ahead of lower priority packets.
>
> The worst case comes when the queue holds only big low priority packets
> and just after one is picked, a high priority packet enters the queue.
> This shows the value of smaller packets for multi-priority flows. ( for
> example, 53byte cells (packets) used in the ATM protocol).
>
> Best regards Bob G
>
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