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Prepare a SIP response-code change test

A SIP response code describes a signalling result at a particular hop. It does not identify the complete cause without the request, sequence and responding system.

A SIP response-code change test

  1. Record the current route, endpoint and trunk. Choose a call that should succeed and a safe negative test that should be rejected.
  2. Save the current policy and identify who will read the trace. Agree on the acceptable final response and whether audio must follow a successful setup.

Do not treat a provisional 1xx response as call completion or a single 4xx as proof the handset is at fault.

Check the wider path

Choose the expected response for each test before making the change. A busy destination may correctly return a failure-class response, while an accepted INVITE can still fail to establish audio. Include the user-visible outcome with the code.

Use the SIP response codes: a practical troubleshooting guide to confirm terms and settings before the change.