I am deffinately going to try pingplotter, at least the freeware version. I love having a large arsenal of tools. Most are based on some type of ping or traceroute.
It is very common for Toshiba and vendors to say it is the connection. In most cases that is where the problem is at. Sometimes the internet connect just won't support a VoIP calls because of the delays or jitter.
Packet loss of 25% is pretty bad. There is definately a problem there. Sometimes I wll open another window and ping google.com as a baseline to see if the connection problem is closest to the side I am on. You can also ping the remote gateway. Since the system is on it's own internet it sould not be a problem with data traffic fighting for internet, unless you are downloading windows updates at the phone side while trying to talk.
Sometimes updating the firmware will help. The latest LIPU firmaware is 02_05D. It may be a bit much for the end user to update the firmware. That is why it is recommended for a Toshiba dealer to do it. If things go bad then they can call tech supoprt, while you can not.
I am a little puzzled about your Toshiba guy not wanting to disable Difserv. In your setup I see no benefit. If the devices on the network do not support QOS, the header is usually ignored, but there are rare occations where it can cause problems.
This type of troubleshooting is never easy.
