Collaboration Communications Systems Engineer — Question 229

You have a Teams Phone deployment that uses Direct Routing on a single Session Border Controller (SBC).
Users report that outbound PSTN calls are failing, but inbound PSTN calls are successful.
When you review the SBC logs, you discover that Microsoft is responding to SIP option requests, but is NOT sending SIP option requests.
What is the cause of the issue?

Answer options

• A. The online PSTN gateway is disabled.
• B. An SBC certificate is expired.
• C. An external DNS entry is missing from the FQDN of the SBC.
• D. The phone numbers of the users are defined by running the New-csTeamsUnassignedNumberTreatment cmdlet.

Correct answer: C

Explanation

The correct answer is C because an external DNS entry is essential for the SBC to properly route outbound calls. Without this entry, the SBC cannot communicate effectively with the PSTN for outbound calls. Options A and B are irrelevant since inbound calls are functioning, and option D does not relate to SIP option requests.