Setting up SIP Trunk connections with Fonio

Last updated: May 15, 2026

To connect your phone AI with a SIP trunk from your telephone provider, you'll need to set up a static SIP trunk connection with your telephone provider. Here's what you need to know:

Requirements for SIP Trunk Setup

The key requirement for SIP trunk connection is setting up a static SIP trunk with your telephone provider. This static trunk must then be linked to one of Fonio's available IP ranges.

Available IP Ranges

When configuring your SIP trunk, use one of these IP ranges:

  • 143.223.88.0/21

  • 161.115.160.0/19

After setting up the static SIP trunk with your provider, you'll need to enter the SIP trunk URL in the Fonio Assistant configuration.

When to Use Static IP Ranges

You should use these static IP ranges when you need to:

  • Whitelist SIP traffic in firewalls or Session Border Controllers (SBCs)

  • Work in restrictive or security-critical networks

  • Ensure a stable and predictable SIP connection

Network Configuration

Important: Make sure that both UDP and TCP protocols are enabled for these IP ranges to allow proper SIP signaling and RTP media transmission.

Setup Process

  1. Contact your telephone provider to set up a static SIP trunk

  2. Configure the trunk to work with one of Fonio's IP ranges

  3. Enter the SIP trunk URL in your Fonio Assistant settings

  4. Ensure your network allows UDP and TCP traffic for the specified IP ranges

Troubleshooting Connection Issues

Diagnosing '404 No trunk found' Errors

If you receive a '404 No trunk found' error on outbound calls, verify these configuration requirements:

  1. IP Authentication: Ensure your PBX is sending from a public IP address that has been added and allowed on your SIP trunk configuration. The trunk must be IP-authenticated (no registration required).

  2. Domain and Transport: Point the INVITE to your Fonio org domain exactly as configured in your SIP Number/Trunk settings. Use the transport protocol (TCP or UDP) as specified in your trunk configuration.

  3. SIP Number Configuration: Ensure at least one SIP Number is created and assigned to the trunk. Verify you are dialing the number in E.164 format or using the SIP URI format shown in your SIP Number configuration.

  4. Number Field: Verify the 'number' field inside the trunk configuration is correctly set, as this is a common cause of 404 errors.

Gathering Diagnostic Information

When troubleshooting SIP trunk connection problems, gather the following diagnostic information:

  • The public source IP address your PBX uses for SIP traffic

  • The exact Request-URI you're attempting to reach (including domain and number)

  • Whether you're sending via TCP or UDP transport

  • SIP trace logs showing the INVITE and response messages

For more detailed information about SIP trunks, you can refer to the SIP phone numbers documentation.