Outbound call continues after user hangs up - delayed hangup detection

[hasanberat03]

Hi, We are running outbound calls using Retell AI with a SIP trunk.
The issue: When the customer hangs up, Retell does not detect the disconnect immediately. The call keeps running for up to 1 minute before the system realizes the call has ended.

Any help appreciated, thank you!

[support2]

Thank you for reaching out to Retell AI Support. We’ve received your ticket and our team will respond within 8 hours.

[support2]

Hi Retell,

Hello,
To assist you with your SIP trunk integration and ensure optimal setup, please explore the following resources:

• Video Tutorials: Access introductory videos for integration setup at Retell AI Docs: https://docs.retellai.com/videos/introduction
• Webinars: Watch detailed webinars on integration best practices at Retell AI YouTube Playlist: https://www.youtube.com/watch?v=A9H3a33gM2M&list=PLGrX1_bbFSHrD6DnoHnQw08nmAH_B3efs
• Forum Community: Join the community for real-time support at Retell AI Forum: https://community.retellai.com/invites/wzFwjPvch9
• Discord Community/Office Hours: Chat live with our experts on Discord: https://discord.com/invite/wxtjkjj2zp
• Hire A Developer Program: Connect with professional developers for personalized assistance at Retell AI Developer Form: https://retellai.retool.com/form/888fc4e3-fdd3-4de3-8434-d8ae68d35fc8

Best,
Evy AI
AI Support Agent @ Retell AI

[support2]

Hello,

Please provide the Call ID(s) where this issue is occurring so we can investigate this further.

Regards,
Retell Support Team

[hasanberat03]

call_fffe7d9979f4424d7608593a7a7
call_8948c57d7c80cf4238f29bd67d9
call_8948c57d7c80cf4238f29bd67d9

[support2]

Hello,

We have investigated the calls you shared and found the following:

Retell detects CLIENT_INITIATED (the SIP BYE) within milliseconds. The delay occurs in Netgsm’s infrastructure between when the PSTN subscriber hangs up and when Netgsm relays the BYE to Retell.

We recommend:

1. Contact Netgsm support to configure their SIP/Asterisk infrastructure to propagate PSTN disconnect signals (BYE) immediately instead of waiting for RTP/session timeout.

2. Workaround: Reduce the time to end the call after silence from 11s to 5–6 seconds. This will make Retell end the call sooner on its own when the user goes silent, before Netgsm’s 60-second timer fires. Note that with the current remind behavior (agent sends a reminder message after silence, then waits another full silence window), the effective hang-up tolerance before Retell self-terminates is already ~25–28 seconds — so reducing it to 5s would cut that to ~15–18 seconds total.

3. If the agent doesn’t need to send a reminder: You could remove the remind/re-prompt behavior entirely so the call is terminated directly on first trigger (~5-6 seconds of silence → hang up).

Regards,
Retell Support Team