No audio or one-way audio is the most frequently reported VoIP issue. Follow this checklist in order to quickly identify and resolve the problem.
Step 1: Check Your Audio Devices
In iTel Dialer, go to Settings → Audio. Confirm the correct microphone and speakers/headset are selected. Make a test call to the echo test number (*47) to confirm local audio is working.
Step 2: Disable SIP ALG on Your Router
SIP ALG (Application Layer Gateway) rewrites SIP headers incorrectly, causing one-way or no audio. Log in to your router admin panel and look for SIP ALG, SIP Helper, or SIP Pass-through. Disable it and reconnect your VoIP client.
Step 3: Configure STUN
Set your STUN server to stun.itelvoip.com:3478 in your dialer settings. STUN allows the client to discover its public IP for correct SDP negotiation.
Step 4: Open RTP Ports
Ensure UDP ports 10000–20000 are open outbound on your router/firewall. These ports carry the actual audio streams (RTP). Blocked RTP results in silence even when the call connects.
Step 5: Check VPN Interference
VPN software can interfere with RTP routing. Try disabling your VPN and making a test call. If audio works without VPN, configure a split-tunnel exclusion for the RTP port range.
Step 6: Contact Support
If the above steps do not resolve the issue, contact our support team with the following information: your external IP address, your router model, your dialer version, and whether the issue is outbound, inbound, or both directions.