[asterisk-users] Diagnosing poor call quality

[Eric "ManxPower" Wieling]

Chris Bagnall wrote:
> Greetings list,
> 
> We have an issue with call quality at 2 sites where the users (4 Elmeg
> IP290s at one site, 2 SPA942s at the other) do not have an asterisk box
> on-site. Each site has an 8mb down/448k up ADSL connection and the phones
> connect via SIP to an asterisk box in a datacentre using g729.
> 
> The asterisk box in the datacentre connects to our other asterisk boxes
> providing pstn connectivity via IAX2. Latency between these boxes is between
> 1 and 2ms. The ADSL connections to the client sites are all consistently
> delivering latencies of sub-25ms to the datacentre and there is traffic
> shaping on that connection to give priority to any traffic from the phones'
> IPs.
> 
> Comments from the users at these sites are as follows:
> "call sounded like a dalek and I couldn't make out anything the caller was
> saying"
> "the phone on my desk is breaking up so badly it's virtually unusable"
> "calls sound like they're breaking up with metallic background noises"
> 
> We have quite a few customers with asterisk boxes on-site (with phones
> connected to them via the LAN) using ADSL connections from the same
> supplier, and are not having these issues with them.
> 
> canreinvite=no and nat=yes are set on all these devices, since they are
> behind NAT. Each device re-registers with asterisk every 5 minutes to
> prevent any possible NAT state timeouts.
> 
> Any pointers/places to look for potential problems would be much
> appreciated.

This should be a FAQ. Set the RTP packet size on the SPAs to .2 instead 
of .3