routing rather than the Twilio-Retell integration itself.

### Answer Audio quality issues like glitching and cutting out can stem from several factors when using Twilio numbers with Retell AI [(1) ]() . Key Configuration Steps: When using Twilio with Retell AI, ensure your termination SIP URI is configured correctly [(2) ]() . You should use a localized termination URI that's near your region for better performance . You can expand and view your localized URIs in the Twilio console . Transport Protocol: The transport method you're using matters. Retell AI supports TCP (Recommended) , UDP, and TLS [(1) ]() . For inbound calls using different transports, you need to append the transport method to the SIP server URL : - For TCP:

sip:sip.retellai.com;transport=tcp

- For UDP:

sip:sip.retellai.com;transport=udp

- For TLS:

sip:sip.retellai.com;transport=tls

IP Whitelisting: Make sure you've whitelisted Retell's SIP SBC CIDR block

18.98.16.120/30

in your Twilio termination settings [(2) ]() . This ensures proper traffic routing between Retell and Twilio [(1) ]() . Common Issues to Check: If you're experiencing outbound issues specifically, verify there are no spaces in your Termination SIP URI [(2) ]() . Also confirm you're using the correct username and credentials (not the friendly name) if you set up authentication . For toll-free numbers, specify the transport protocol by using the format with transport parameter [(3) ]() . If these configurations don't resolve the issue, the problem may relate to network conditions, call concurrency limits, or regional

​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Twilio](https://docs.retellai.com/deploy/twilio) [[3] How to Choose the Right Telephony System in 2024 | Retell AI](https://www.retellai.com/blog/how-to-choose-the-right-telephony-system-in-2024) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.