Unable to receive inbound calls. Outbound calls terminate within seconds.

This scenario proves to be common in newly setup SIP Trunks.

What happens is our switch sends a SIP 'keep alive' every 30 seconds to make sure the call is still active. It does this by sending a SIP re-invite for the live call, in which we expect a 200 OK response, that we then ACK back. If we receive no response within 30s of the SIP options requests, the switch turns the SIP trunk state to disabled and will not send further SIP invites until the keep alive gets a response by aggressively sending out options requests every 4 seconds.

This could be caused by:

  • A SIP aware firewall that is mangling packets sometime with a feature referred to as SIP ALG. This should be disabled.

  • NAT issues on your router and does not support SIP properly. Some routers are just not compatible with SIP. This can sometimes be resolved with a firmware upgrade to the latest version.

  • Your firewall is not configured to allow SIP UDP on port 5060 and our switch considers the trunk to be down and not responding to SIP keep alive.

  • Your IP address is different than what we have configured on the switch. Either your IP has changed, and you've not contacted us to update the address, or the IP was entered in the switch incorrectly.

  • You PBX is behind NAT but configured to use the wrong proxy. If behind NAT the correct proxy is vp.thinktel.ca - If not being NAT, the correct proxy is eico.thinktel.ca -

We hope this info was a help. If you have any problems or questions, please let us know.
You can open a support ticket or contact us atphone-icon-blue 1-888-852-2381 for additional assistance.