300-070 · Question #273
300-070 Question #273: Real Exam Question with Answer & Explanation
The correct answer is B: Configure Phone NTP References in Cisco Unified CM Administration. SIP phones rely on NTP for accurate time synchronization, which is required for correct SIP registration, certificate validation, and call processing. In CUCM, there are two separate NTP-related configurations: the OS-level NTP server (configured in Cisco Unified OS Administratio
Question
Options
- AConfigure the NTP server in Cisco Unified CM Administration
- BConfigure Phone NTP References in Cisco Unified CM Administration
- CConfigure the NTP server in Cisco Unified OS Administration
- DRestart the Unified Communications Manager services for the publisher and subscribers on the
Explanation
SIP phones rely on NTP for accurate time synchronization, which is required for correct SIP registration, certificate validation, and call processing. In CUCM, there are two separate NTP-related configurations: the OS-level NTP server (configured in Cisco Unified OS Administration) keeps the CUCM server's own clock accurate. However, for SIP phones specifically, CUCM must advertise an NTP server address to the phones via the SIP profile or device pool - this is done by configuring Phone NTP References under System > Phone NTP Reference in Cisco Unified CM Administration (Option B). Without Phone NTP References, SIP phones do not know which NTP server to use for time sync. Option C (OS Administration NTP) is needed for the server itself but is insufficient alone for SIP phone support. Options A and D do not directly address SIP phone NTP requirements.
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