My company has recently opened a new branch office in another city that is 15 miles away. The new location's phone system was added by a company that we have always contracted to manage our phones. I am not sure of the exact terminology used for some of the equipment so you'll have to excuse me if I am using vague terms. The main location has a combination of VOIP phones and regular wired ones. The equipment that manages the extensions is behind a firewall that only allows connections from the remote branch IP address for only the necessary ports. At the remote location, there are no VOIP phones and the hardware that manages the extensions are directly connected to the internet which it uses to connect back to the main location.
The workers at the main location have had non stop problems using the phones since this was implemented. Their calls are always dropped after a couple of minutes and when they are called from the main location, the extension has to be dialed a couple of times to get through. Calls also fade in and out while they are talking. The company that installed them is blaming the internet connection for this problem. One of their techs performed a ping test overnight where a ping was sent every second and their was about 1% failed attempts. I am not sure if that is bad for this type of setup. Of course, the two separate Internet Service Providers say that their connection is good and the problem must be the phone equipment.
What are some good free tools to help isolate the problem or at least rule out the internet connection as the problem? I have tried several online test and they all say that the connection speed is good. It is about 30-35 Mbps at both locations. Also they say that the packet loss, latency, and jitter are also acceptable. I am looking for the thresholds for these and a way to test them myself.