MS-721 Question #53: Real Exam Question with Answer & Explanation

Question

Your company has a Microsoft Teams Phone deployment that uses Direct Routing and a single carrier. You deploy a new Session Border Controller (SBC) that shows as healthy in the Microsoft Teams admin center. You place a test call over the new SBC, and the call succeeds. When you attempt to transfer the call, the transfer fails. A portion of the SIP ladder is shown in the exhibit. (Click the Exhibit tab.) What is a possible cause of the issue?

Options

• AThe SSL certificate of the SBC is incorrect.
• BThe Refer on the SBC is misconfigured.
• CNOTIFY is enabled in the SIP options of the SBC.
• DThe carrier rejects the format of the forwarded FROM number.

Explanation

{"question_number": 9, "question": "A new SBC shows as healthy and initial calls succeed, but call transfers fail. A SIP ladder is shown. What is a possible cause?", "correct_answer": "B", "explanation": "Call transfer in SIP is accomplished with the REFER method. If the SBC's handling of SIP REFER is misconfigured - for example, the SBC is not correctly forwarding or generating REFER requests - the transfer will fail even though the original call succeeded. The SIP ladder in such a scenario would show the REFER being sent but not properly processed. An incorrect SSL certificate (A) would prevent the SBC from appearing healthy in the admin center. A correctly configured initial call rules out NOTIFY issues (C) as the transfer-blocking cause. If the carrier rejected the FROM number format (D), the original outbound call would also have failed, which did not occur.", "generated_by": "claude-sonnet", "llm_judge_score": 4}

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