SIP Trunk Configuration and Troubleshooting

A SIP trunk connects your PBX to the public telephone network through an Internet Telephony Service Provider (ITSP). Without a SIP trunk, your VoIP system can only call internal extensions. Configure the trunk in the PBX admin panel under SIP Trunks or VoIP Providers. Required settings from your ITSP: SIP server/proxy address, port (usually 5060), authentication username and password, and the outbound caller ID (DID number). Some providers use IP-based authentication instead of username/password — whitelist your static IP on the provider's portal. Troubleshooting trunk issues: if the trunk shows as unregistered, check credentials and ensure the PBX can reach the SIP server (firewall rules). If outbound calls fail with '403 Forbidden,' check the authentication credentials. If outbound calls fail with '488 Not Acceptable Here,' there's a codec mismatch — ensure G.711 (PCMU/PCMA) is enabled in the trunk settings. Use the PBX's SIP trace/debug log to see the SIP messages exchanged during a failed call.