QoS Theory on CCME

Unanswered Question
Apr 25th, 2007

Posted by: d.bigerstaff - Apr 25, 2007, 5:50am PST

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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lagos Wed, 04/25/2007 - 06:30

I understand your SIP trunk is going across your internet connection?

Unfortunately, your collegue is correct. There is no way to control what has already been received. It's easy to initiate a big download that causes the inbound RTP/audio to be delayed/dropped.

The outbound queue will ensure VoIP gets priority outbound. You'll need a similar policy on the other end to prioritize traffic that is being sent to you.



tgrisham Wed, 04/25/2007 - 10:29

I would suggest including how you are classifing the voip traffic into your queue's. If outbound to the ISP you classify non-voip into a non-LLQ/RT queue and then rate-limit/police the non-VOIP traffic to an acceptable bit-rate, then the return ACK's would be paced back to you from the ISP.

d.bigerstaff Fri, 04/27/2007 - 04:10

I've not done a QoS course so my knowledge on it is basic. I have been on the IPTX course so thats where my knowledge level is. We've not got any systems set up with it yet, we were just discussing it. The QoS that i was going to use, was the AutoQoS feature, that was the only QoS that we covered in IPTX.


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