When you encounter issues with your 3CX SIP trunk, such as no calls going through or missing audio in calls, it can be frustrating. This guide helps you systematically diagnose and resolve common problems like failed registration, incoming calls not working, one-way audio, or RTP issues.

Diagnosis: Check Trunk Status in 3CX Admin

  1. Step 1: Log in to the 3CX Management Console

    Open your web browser and navigate to your 3CX server. Log in with administrative privileges.

  2. Step 2: Go to SIP Trunks

    In the left menu, click on SIP Trunks.

  3. Step 3: Check trunk status

    Check the status of your Internetport SIP trunk. If the trunk is not registered or if there are any warnings, click on the trunk name to view details.

Registration Fails (401/403/408 Errors)

  1. Step 4: Check SIP credentials

    Go to the Customer Portal on Internetport and retrieve the most current SIP credentials. Ensure that the username, password, and trunk ID are correctly entered in 3CX.

  2. Step 5: Check server address

    The SIP server address should be sip.internetport.se. Make sure ports 5060 (UDP) or 5061 (TLS) are open in the firewall.

No Incoming Calls Despite Registered Trunk

  1. Step 6: Check DID numbers

    Ensure that DID numbers are correctly configured in both Internetport and 3CX. Make sure the numbers match.

  2. Step 7: Check incoming rules

    In 3CX, go to Inbound Rules and ensure there is a valid rule for incoming calls on your DID number.

One-way Audio or No Audio at All (RTP/NAT Issues)

  1. Step 8: Check RTP ports

    In 3CX, go to Settings > Network and ensure that the RTP port range is correctly configured. Open these ports in the firewall.

  2. Step 9: Configure STUN server

    Configure the STUN server stun.internetport.se in 3CX to handle NAT traversal. Go to Settings > Network > External Access.

Calls Drop After 30 Seconds (SIP ALG)

  1. Step 10: Disable SIP ALG on the router

    SIP ALG can interfere with SIP signals. Log in to your router's web interface and look for SIP ALG or VoIP ALG settings. Ensure these are disabled.

Check 3CX Logs and SIP Trace

  1. Step 11: Review logs in 3CX

    Go to Tools > Logs to review the logs. Look for any error messages that may indicate issues.

  2. Step 12: Enable SIP trace

    In 3CX, enable SIP trace by going to Tools > Trace SIP. This helps you get a detailed view of the communication between 3CX and Internetport.

Open Support Ticket with Correct Diagnostic Information

  • Include logs from 3CX, especially the SIP trace log.
  • Describe the problem in detail and which steps you have already attempted to perform.

For more help, visit Internetport's support and open a new ticket with diagnostic information.