Overview

When using voice over IP, there are many considerations which can affect the quality of phone calls, and identifying the source of the issue can sometimes be difficult. This topic is designed to describe the different types of call quality issues, the general causes, and a likely solution to each type of issue.

Step By Step Guide

One-way or No Audio

This may be caused by improper NAT settings or improper handling of SIP/RTP by the firewall. Troubleshoot it as follows:

1. Avoid NAT: Bypass the firewall by connecting Kerio Operator directly to the WAN.
2. Attaching a second network interface to the local network.
3. Verify the NAT settings in Kerio Operator and the connected SIP device.
4. check the Kerio forums or other resources for known SIP handling issues with the brand of the firewall in front of Kerio Operator. The firewall should be configured to allow TCP/UDP port 5060 and 5061, and UDP ports 10000 ~ 20000.

Garbled or Incomprehensible Voice Transmission

This may be caused by a bad codec. Solve this issue by identifying and removing the bad Codec from the selected codecs in the call route.

Troubleshooting Tip: During a call, review Status > Calls and check the used Codec. Compare it to calls that don't have the issue.

Choppy Voice Quality

Some words or parts of the conversation are lost or cut off. This may be caused by:

1. Insufficient or jittery Internet bandwidth.
2. Local networking issue (bad cable, overloaded switch, bad NIC, overloaded WiFi).
3. High CPU usage or insufficient hardware resources.

To solve this:

1. Set GSM as the only selected Codec on the call route.
2. Research options for allocating more bandwidth or incorporating QoS.
3. Update firmware of the phone, replace the cable to the phone, change the Codec of the extension, replace the phone.
4. Upgrade hardware to a faster storage device (e.g. SSD) or add RAM. 

Troubleshooting Tip: Enable extension 81 for the echo test. Dial from various locations and phones to isolate the conditions under which the choppiness occurs. From a browser on that network, go to pingtest.net and check the line quality. Check the status > system health to make sure the CPU/Memory is not overloaded. Check settings for call recording and logging to ensure reduced File I/O.

Capture the Network Communication (Capture or Dump a Packet)

If the previously mentioned steps were not helpful, it may be necessary to capture the network communication for analysis. To do this:

1. In the administration interface, go to Configuration > Network.
2. Select the network interface which is linked to the network where the issue is observed.
3. Click the 'Packet Sniffer...' button to the right of the interfaces dialog.
4. Start the capture, then attempt to reproduce the problem.
5. Once the issue has been observed, stop the capture and download the capture file.
6. If you have an open case with technical support, they may request this file.

Confirmation

If the above troubleshooting solved the issue, your call quality should be restored to normal.

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