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Voice Quality on Voice IP Trunk

Hi Guru's

I am in the process of implementing IP trunking between 3 sites. The PBX's have E1 cards installed and we've currently got the internal extensions traversing the WAN fine.

Users are complaining that they sometimes find it hard to hear, seems to be quite a bit of noise (hiss and crackling) from time to time, generally it's not as clear as I would expect and sometimes there is loss. The WAN is provided by an ISP and is unmanaged, i.e. no QoS, but it's very high bandwidth (2 sites at 10Mbps and 1 at 100Mbps)

I'm unsure as to how best to diagnose, measure and resolve this.

Where would the noise be originating from?

I've implemented QoS on the routers - would the tagged packets get priority on the WAN routers?

Any advice would be appreciated


Re: Voice Quality on Voice IP Trunk

Lots of things to look at, but I would start with verifying the E1 clocking between the routers and the PBXs. Crackling is often a symptom of clock slips. Which side is the master clock and which side is slave?

What model routers are you using? Posting your config would be useful.


Re: Voice Quality on Voice IP Trunk

first off, NO, your QoS tagged packets would not get priority on the WAN as those routers do not perform QoS as you've indicated.

this could very well be a big part of your problem.

some other reasons for such symptoms could be the physical media itself, signalling, the router/switch hardware or the 'heat' of the signal from the telco.

first things first, i would do as much as possible to guarantee the quality of service for your calls, end-to-end.

if you still have issues, verify your media along all legs that you can. replace any cables that seem suspect. if you still have issues, see if you can get your telco to assist in testing/troubleshooting where this 'noise' could be coming from.

(may require intrusive testing which will impact availability, so after hours or non user times would be best)

New Member

Re: Voice Quality on Voice IP Trunk

Thanks for the replies. I checked the clocking and it's clocking from the line.

I've run the ip sla to check the jitter and I'm getting an MOS score of 4.6, which ain't bad. I'm not sure how far I can go with this as there can be no end to end QoS with the existing environment

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