VoIP Troubleshooting Checklist

Voice over IP is very robust and reliable when set up properly. There are only four key areas to set up and check for issues. I have compiled the below list as things to check when an issue occurs. All of the steps are pretty basic and are known by every VoIP professional; however, it is handy to have to show a non-technical person or somebody who has little knowledge on VoIP systems.


  • Ensure the phone is compatible with the PBX you selected
  • Ensure voice is on the voice vlan and data is on the data vlan
  • Ensure the audio codec being used on the phone is supported by the server
  • Ensure the codec you want to use is listed first in the settings
  • Switch codecs to see if voice quality improves or declines in quality


  • Ensure voice traffic is on a separate vlan
  • Ensure the voice vlan has priority on the network (QoS)
  • Ensure there are no faulty Ethernet lines and that all 8 wires go to a single port (for PoE and best practice)
  • Ensure switches are voice vlan capable
  • Ensure the switch has enough voltage to power the amount of phones connected to it (if using PoE)


  • Ensure it is powered on
  • Ensure services are running
  • Check call quality between internal-to-internal extension
  • Check call quality between internal-to-internal extension on separate PBX host (if clustered)
  • Check inbound call routing rules
  • Check outbound call routing rules

PBX-to-Service Provider

  • Ensure you have phone service and it is turned on
  • Ensure the service provider allows self-managing of the Caller ID
  • Ensure voice traffic is not being sent out on the public internet (on-net) if using SIP trunking