[Asterisk-Users] GXP-2000 Audio Quality

[Gareth Blades]

G729 uses 8kbps but with the IP overhead it actually uses 30kbps so for
256k upstream you should be able to handle 8 calls but this is in ideal
conditions.

If you were to use IAX and enable trunking then you would use 30kbps for
the 1st call and 10kbps for each additional call.
See http://www.voip-info.org/wiki/index.php?page=Asterisk+bandwidth+iax2

On Wed, 2006-06-14 at 04:17, Daniel Salama wrote:
> I have a client with about 16 GXP-2000. They complain that the audio  
> quality is terrible after 2 or 3 simultaneous conversations. They are  
> behind DSL 1.5Mbps down and 256Kbps up. Because they are using G711.u  
> codec, I know they upstream bandwidth is the limiting factor and they  
> most likely won't be able to have more than 3 simultaneous  
> conversations, and if they're surfing the net and/or checking email,  
> things will only get worse.
> 
> So, I purchased some g729 codec licenses and forced their sip peer  
> configuration to g729 codec. We made sample test calls and were able  
> to make 8 simultaneous calls. On the eighth call, the audio started  
> to sound choppy. Then we dropped the eighth call and tested with 7.  
> We could hear just fine on the GXP-2000 but the remote end heard us a  
> bit choppy and/or with a robot-like voice. So, we kept dropping calls  
> until they were of acceptable quality.
> 
> My question is, if they were using g729 which, in theory uses 8kbps  
> plus overhead, they should have been just fine handling eight calls.  
> All the computers were turned off on the network, so there shouldn't  
> have been any other traffic but VoIP. Does anyone have any ideas?
> 
> How can I improve their audio quality? I requested BellSouth to  
> upgrade their capacity but because of where they are located, the  
> best they can get is 900Kbps/256Kbps, so the upstream continues to be  
> the limiting factor.
> 
> I purchased a Dlink-1226G switch to allow me to control QoS on the  
> LAN. I also upgraded their Netopia DSL router to the latest firmware  
> which allows me to configure VLANs and DiffServ. All the computers  
> are connected to the PC port on the phone because there is no  
> available second wiring. Can anyone suggest how to configure the QoS  
> settings on the phones, the Dlink and the Netopia?
> 
> While there was "no traffic" on the wire, pinging from/to the  
> Asterisk box gave me about 47ms latency. When we went passed the 4th  
> call, the latency started increasing significantly and when we got to  
> 8 calls, the latency was up in the 2000ms. Obviously, if anything I  
> did in the QoS configuration gave VoIP a priority, then ICMP packets  
> would have the lowest priority and I could understand that to be the  
> reason for such result. However, I'm not sure I configured QoS  
> properly and that's why I'm asking for help.
> 
> Thanks,
> Daniel
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