# Troubleshooting

- [Calls are failure](/troubleshooting/calls-are-failure.md)
- [Change Q850 in 4xx/5xx](/troubleshooting/change-q850-in-4xx-5xx.md)
- [One-way Audio with SIP Client Testing](/troubleshooting/one-way-audio-with-sip-client-testing.md): How to Overcome NAT Issues When Connecting a SIP Client to a Class 4 Switch
- [Using Zoiper to resolve NAT issue](/troubleshooting/one-way-audio-with-sip-client-testing/using-zoiper-to-resolve-nat-issue.md)