This article provides a step-by-step guide to troubleshoot common issues with SIP trunks, including registration failures, dropped calls, and one-way audio problems. By following these steps, you can systematically identify and resolve the underlying causes of these issues.

1. Verify SIP Trunk Credentials

The first step in troubleshooting SIP trunk issues is to ensure that your SIP credentials are correct and up-to-date.

  1. Log into your Internetport customer portal or contact support for the latest SIP trunk details.
  2. Compare the provided credentials with those configured on your PBX system.
  3. Ensure that the username, password, and domain are correctly entered in your PBX settings.

2. Check Firewall and NAT Settings

Firewall rules or Network Address Translation (NAT) issues can prevent SIP trunks from registering properly.

  1. Verify that the necessary ports are open on your firewall: typically UDP 5060 for SIP signaling and a range of higher ports (e.g., UDP/TCP 10000-20000) for RTP media traffic.
  2. If you have a NAT device, ensure it is configured to allow SIP traffic through. This may involve setting up port forwarding or configuring ALG settings.

Disable SIP ALG on Router

SIP Application Layer Gateway (ALG) can interfere with SIP signaling and should be disabled if present.

  1. Access your router's configuration interface via a web browser.
  2. Navigate to the settings related to firewall or advanced NAT options.
  3. Look for an option labeled "SIP ALG" and disable it.

3. Resolve Codec Mismatch Issues

A codec mismatch occurs when the audio codecs supported by your PBX do not match those offered by Internetport's SIP trunk.

  1. Check the list of codecs configured on your PBX system.
  2. Compare this list with the codecs supported by Internetport, which can be found in your service agreement or support documentation.
  3. Adjust the codec settings on your PBX to match those offered by Internetport. Typically, G711 (PCMA/PCMU) is widely supported and recommended.

4. Perform Packet Capture Analysis

If you continue to experience issues, performing a packet capture can help identify the root cause of the problem.

  1. Use network monitoring software such as Wireshark to capture SIP and RTP traffic between your PBX and Internetport's SIP trunk.
  2. Analyze the captured packets for any errors or anomalies, such as failed registrations, dropped calls, or one-way audio.

Basic Packet Capture Commands (Wireshark)

To capture SIP traffic using Wireshark, you can use the following command:

tshark -i eth0 port 5060 -w sip_capture.pcap

This command captures all traffic on port 5060 (SIP) and saves it to a file named sip_capture.pcap.

Troubleshooting Summary

  • Credentials: Double-check SIP trunk credentials in your PBX settings.
  • Firewall/NAT: Ensure necessary ports are open and NAT is configured correctly.
  • SIP ALG: Disable SIP ALG on your router if present.
  • Codecs: Verify codec compatibility between your PBX and Internetport's SIP trunk.
  • Packet Capture: Use Wireshark or similar tools to analyze network traffic for issues.

If you have followed these steps and are still experiencing problems, please contact Internetport support with detailed information about the issue, including any error messages or packet capture files. Our technical team will be happy to assist you further.