External SIP leg remains connected ~16–18 seconds after voicemail detection

Support Help
1

Hi,

We are using Retell for outbound calls with an external SIP trunk.

We have identified a consistent discrepancy on voicemail calls:

Call ID: call_5b0c61b093316521499c5fa1a90
Destination: +5492974738463
Retell duration: 2 seconds
Disconnection reason: voicemail_reached

Retell Data Log:
2026-09-29 17:38:45.148 Starting call
2026-09-29 17:39:04.876 Ending call

Our telephony provider confirms that the SIP leg and phone leg were disconnected at 20:39:21, with the hangup initiated by the SIP side.

So there appears to be approximately a 16–18 second delay between Retell ending the AI session and the SIP leg actually being disconnected.

We have matched this pattern across many voicemail calls. Most of the duration discrepancy between Retell and the telephony provider comes from voicemail calls.

Our settings are:

  • Voicemail Detection: enabled
  • Hang up if reaching voicemail: enabled
  • IVR Hangup: enabled

Retell’s documentation states that the call should disconnect immediately when voicemail is detected.

Could you please check the backend/SBC SIP trace for this Call ID and confirm:

  1. The exact timestamp when Retell sent the SIP BYE
  2. Whether there is any delay between voicemail_reached / internal call end and SIP BYE transmission
  3. Whether there is any known issue or configuration affecting teardown timing with external SIP trunks

The extra connected time is billable by our telephony provider, so this is materially affecting our call economics.

Thanks.

2

Hey @tornike_777

Thanks for providing the detailed information and the Call ID. I’ve noted the SIP teardown timing discrepancy you’re seeing on voicemail calls.

We’ll review this further and get back to you as soon as we have more information.

Thank you!

3

Hey @tornike_777

Just to confirm, the call ended after 2s on Retell, but the provider shows it lasted over 16s. Could you share the PCAP file from your side?

Best Regards.