Summary
The intermittent SIP 400 Bad Request failures between Twilio SIP Trunk and OpenAI gpt-realtime have caused a significant increase in failed calls, with no apparent configuration changes on Twilio, OpenAI, or the application. The successful calls work as expected with the same configuration, and the issue seems to be specific to the Twilio ↔ OpenAI SIP connection.
Root Cause
The root cause of the issue is still unknown, but possible causes include:
- SIP header validation issues
- SDP / codec negotiation problems
- Twilio routing changes that affect the SIP connection
- Intermittent SIP endpoint rejections without configuration changes
Why This Happens in Real Systems
In real-world systems, SIP signaling and codec negotiation can be complex and prone to errors. The intermittent nature of the failures makes it challenging to diagnose and fix the issue. Possible reasons for this behavior include:
- Network congestion or packet loss that affects SIP signaling
- Incompatible SIP implementations between Twilio and OpenAI
- Changes in Twilio’s routing or infrastructure that impact the SIP connection
Real-World Impact
The intermittent SIP 400 errors have a significant impact on the application, causing:
- Failed calls that never reach the webhook
- Unreliable service that affects user experience
- Increased support requests and debugging efforts
Example or Code
No code is required to illustrate this issue, as it is related to SIP signaling and configuration.
How Senior Engineers Fix It
Senior engineers would approach this issue by:
- Analyzing SIP ladder traces from Twilio to understand the SIP signaling flow
- Verifying SIP header validation and SDP / codec negotiation between Twilio and OpenAI
- Testing different SIP configurations to isolate the issue
- Collaborating with Twilio and OpenAI support to resolve the issue
Why Juniors Miss It
Junior engineers may miss this issue due to:
- Lack of experience with SIP signaling and codec negotiation
- Insufficient understanding of Twilio and OpenAI SIP implementations
- Inadequate debugging skills to analyze SIP ladder traces and identify the root cause
- Failure to consider the intermittent nature of the failures and the complexity of the SIP connection