Understanding timeouts and retries for the Amazon Chime SDK PTSN audio service

The PSTN audio service interacts with AWS Lambda functions synchronously. Applications wait 5 seconds for AWS Lambda functions to respond before retrying an invocation. If no response is received after 20 second the PSTN Audio service will issue a hang up. When a function returns an error with one of the 4XX status codes, then by default the SIP media application only retries the invocation once. If you run out of retries, calls terminate with the 480 Unavailable error code. For more information about AWS Lambda errors, see Troubleshoot invocation issues in AWS Lambda.