QoS Theory on CCME

Unanswered Question
Apr 25th, 2007

Hi there,

I have a query about QoS. I guess this is more the theory of QoS than any actual implementation.

Say we have a CME system with QoS setup to give priority to all phone traffic, this CME system uses a SIP trunk to receive incoming and make outgoing calls. My collegue believes that because QoS is setup for the outgoing queue, what is to stop somone starting off a big download and throttling the downstream from our internet connection.

I was thinking that because acknowledgments sent for the download would be in the queue behind the voice traffic, that this would in effect, alleviate our problem to an extent.

Is our thinking correct? Is there any other way to minimise downloads effecting voice traffic?

Many thanks,


I have this problem too.
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Paolo Bevilacqua Wed, 04/25/2007 - 04:58


your friend is correct. In theory a large download, or even worst, savage p2p activity can saturate the link in downstream direction and disrupt voice traffic.

Fortunately, unless people tries to cause that by purpose, that just doesn't happen much in most situations.

There are partial remedies like limiting the bandwidth on the LAN interface, however none is guaranteed to work.

The only real solution is to work with an ISP that has set QoS on the router facing your circuit. Surprisingly this is often the case because voip is everywhere.

Hope this helps, please rate post if it does!


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