Voice quality

The voice quality is low, distorted or subjected to variable quality. 

In case you experience voice quality degradation, distortion or general low quality, 95% it is due to some network issues and the remaining 5% to server overload.

Here are some explanations of each network assessment point and what you can do to improve your results:

Upload and Download Speeds:

Bandwidth speeds can vary widely based on your LAN, your Internet connection (cable modem, DSL, T1, etc.) or your Internet providers network.

Verify you are receiving the Internet service purchased from your provider. In order to carry voice traffic over your Internet connection it may require you to upgrade your connection or change providers in some circumstances.

Latency (Delay):

Delay occurs when there is a higher than normal latency on your network. Latency is the amount of time it takes between one person saying something and the other person hearing what was said.

Latency doesn’t typically cause audio quality issues, but when the latency is over about 150ms, the delay is noticeable to your users. If you have a latency issue, simple network tuning can solve the issue.

Packet Loss:

Packet loss is the failure of one or more transmitted packets to arrive at their destination. This event can cause noticeable effects in all types of digital communications. With audio calls, packet loss can provide jitter and silent gaps in communication.

Jitter:

Jitter occurs when voice packets arrive with varying delays. This is typically caused with changes in network traffic, and can usually be fixed by using QoS, or reducing the amount of traffic on your network equipment is handling. Your users will often report jitter as poor audio quality. If jitter is too high, you’ll have to fix the network underneath to improve the call quality.

Quality of Service (QoS):

QoS is a feature available in quality managed network switches that allows you to prioritize your voice traffic.

This allows you to ensure that your phone calls are going to get the bandwidth needed regardless of what else is happening on the network. QoS is a very important feature to quality and reliability of IP phone systems.
Server performance: check your CPU usage is under 70% and you HDD use is under 90%