Conference Call Issues

[scooter817]

Hi Everyone

I wanted to know if anyone could point me in the direction that I should start to work on this issue that I have. The issue is that we have users in various cities who when they join a conference call they sound robotic. We have moved all of our users from a distributed call processing model to a centralized call processing model. We didn't have the issues before we moved everyone so I was wondering what could be causing this to happen.

Eric

[shh5455 · Accepted solution]

That is usually either a QOS issue or a DSP issue.  Based on what you wrote, I would say it's a QOS issue.  Do you have end to end QOS on your network?  Are your WAN links big enough to handle the number of calls (at a specific codec) that are being sent?

A bad DSP would likely be another suspect, but that's much less common.

Are the callers using hardware media resources (DSPs on routers) or software (CUCM) for conferencing?

[scooter817]

Hi

I think that your right about the QOS issue, we are currently using G.771 on everything OnNet as well as Offnet. Do you think if I changed it to G.729 it would clear up the issue? We do have CUCM conference bridges but we are using the router with DSP's for the conferences.

[Dennis Mink · Accepted solution]

Even if you would use a lower bandwidth codec, you would still need to have QoS in place. G729 just reduces the chance of overutilisation, it does nothing itself to guarantee that it is actually sends from A to B with proper prioritisation

[scooter817]

Dennis

Do you think if I enabled Auto-QoS that would be enough or would I have to go more in-depth with the QOS?

[shh5455]

Scooter,

While Dennis is right about QOS, it really depends on what is causing the congestion.  If it's instantaneous congestion that causes short issues with call quality, only QOS will fix that.  If it's a matter of too many calls for the WAN pipe, then you need to look at changing the codec and using Call Admission Control in CUCM.

Best practice is to use G.729 across the WAN (between regions) and G.711 (or better) on the LAN.  It is roughly 24k per G.729 call and 80k per G.711 call.  You can use those values to set your Call Admission Control settings.

Auto-QOS on your switches probably won't fix what you describe.  You really need L3 QOS on your WAN links.  By changing the codec across the WAN, you may be able to get away with not doing L3 QOS for a while, but it really needs to be done anyway if you want to do it right.

[scooter817]

Thanks for the info I will definitely change the codec and then I'm going to have to tap into some of the CCIE voice engineers I know. Because I never had to deal with QOS so I'm going to need some help setting it up.