asterisk users - Jun 2006 - RTA, jitter, MOS et al over the internet

I have been in the process of trying to troubleshoot a phone system that is
doing IAX trunking to a provider. The average RTA is 75ms with spikes from
time to time and jitter from time to time as well. My question is this; How
much can one trust this types of samples when going over the internet? I
mean who knows who is doing what kind of ICMP rate limiting or dropping ICMP
all together? What is a good measurement or troubleshooting step for
intermittent bad quality when dealing with links that you have no control
over or is that even relevant? Here is our setup:

 

All outbound calls are going out POTS unless that line is congested. All
inbound (even from the POTS as it is forwarded directly to an IP DID) are
over the IAX trunk. We are not seeing any issues on outbound calls. On
inbound, however, we are getting intermittent choppy voice, echo and cutting
out. This is heard by the person coming in, i.e when someone is calling they
hear these symptoms of the users on the asterisk server. From our side the
issue doesn't seem to exist or it is so much less that it is really
irrelevant. 

 

As I have mentioned I have seen spikes of ping times and times of jitter but
this is recognized by tools utilizing ICMP so I don't know how much I can
trust them. 

 

Thanks for the help!

 

Curt

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