Customer compalints about "hollow sounding calls"

[netswork]

We have a customer with polycom ip 550/650 phones. The customer is "complaining" that calls sound like they are in a "hollow well". I am guessing this is because of the g722 codec on extension to extension calls. Has anyone experienced customers asking about the voice quality on g722 calls? I can just take the g722 codec out of the provisioning template but wanted to see if anyone else has seen this first.

 

[leejor]

Have you confirmed that it is indeed the use of that Codec that is causing the issue? The hollow sound might indicate a slight delay that is not being dealt with well enough by current echo suppressor settings.

Is this happening on extension to extension calls, as well as outside calls?

 

[AlexDBarrett]

I would also look at your network.
How many devices do you have, PCs etc and how many extensions?
Is it 10 or 100.
Can you VLAN your phones?
What switches do you have in your network?

I suggest running up a lab install and see if you get the same problem if so investigate Codecs if not look at above.

 

[netswork]

This is 5 systems bridged together in a mesh setup across an MPLS network. Total of about 110 phones. Voice is VLAN'ed at each site and we are using either Dell 5500 or 6200 switches at each site. QOS on the switches is configured. Each location has their own PRI and patton gateway.

QOS is configured on the cisco routers for voice calls across the bridges.

One thing i did notice yesterday was on a bridge call the phone was showing to be using G.711 but the bridge is set to only use GSM-FR.

 

[leejor]

One thing i did notice yesterday was on a bridge call the phone was showing to be using G.711 but the bridge is set to only use GSM-FR.

So there may be some transcoding, involved?

 

[netswork]

Unless 3cx does the transcoding...there is nothing else between the two phones across the bridge. The polycom phones are only configured for 4 codecs.

<!--voice.codecPref.G722="1"-->
<!--voice.codecPref.G711_Mu="2"-->
<!--voice.codecPref.G711_A="3"-->
<!--voice.codecPref.G729_AB="4"-->

 

[sigma1]

It is clear that the 3CX server is doing transcoding if GSM is the only allowed bridge codec. I would switch that to iLBC (far better sound) but why the need for a low BW codec?

By your post I assume that your customer is compaining about hollow sound between two local phones at G722, and that sounds rather incredible as we never had such an issue. But I can agree with the bridged calls w. GSM involved (I would avoid GSM at all costs)

 

[netswork]

Thanks for your reply.

The need for a low bandwidth codec is because some of these locations only have 1.5mb of bandwidth and the pipe is already saturated with Data traffic.

We were using GSM-FR because that was the codec in the bridge by default in 3cx. I can give ILBC a shot. I have read a little bit about it. I did confirm with 3cx support that there are 3 calls involved in a bridge call. Each phone to its pbx and the PBX's to each other. So I may see a different codec between the phone and 3cx then between the two PBX's.

The initial discussion with the customer over emails made me think it was g722...but it may not be. I am not used to a customer asking about "hollow" sounding calls when bandwidth/latency is the issue. Usually I would hear issues with Choppy calls, voice cutting in and out or the caller sounding under water.