Most VoIP problems fall into a small number of categories. If you can diagnose quickly, you spend less time in downtime and more time on calls.
- One-sided audio (you can hear them, they can't hear you — or vice versa)
Almost always a NAT traversal issue. Your router isn't forwarding SIP and RTP ports correctly. Solution: enable STUN on your SIP client, or configure your router to forward ports 5060 (SIP) and 10000–20000 (RTP) to your PBX.
- Echo on calls
Usually caused by acoustic echo (mic picking up speaker sound) or electrical echo (impedance mismatch in the audio path). Solutions: use a headset instead of speakerphone, enable echo cancellation on your PBX, reduce microphone sensitivity.
- Choppy or robotic audio
This is a jitter and packet loss problem. Your network is dropping or reordering audio packets. Solutions: enable QoS on your router to prioritize VoIP traffic, reduce network congestion, check for packet loss with a ping test. Loss above 1% will affect call quality noticeably.
- Calls dropping after exactly 30 or 60 seconds
Almost always a SIP timeout issue — your firewall is closing the SIP session thinking the connection is idle. Solution: enable SIP ALG on your router (or disable it — depending on the router, either can cause this), or set SIP keep-alive intervals.
- Can't receive incoming calls
Usually a firewall or port forwarding issue preventing inbound SIP from reaching your system. Solution: confirm your SIP provider's IP ranges are whitelisted on your firewall.
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