Using NTP to Set the Correct Time and Date for Devices

Topic Last Modified: 2011-01-26

Network Time Protocol (NTP) is the default time synchronization protocol used by the Windows Time Service in Windows Server operating systems. NTP is a fault-tolerant, highly scalable time protocol and is the protocol used most often for synchronizing computer clocks by using a designated time reference. Microsoft Lync 2010 Phone Edition requires NTP to set the correct time and date for phones running Lync 2010 Phone Edition.

The NTP provider in the Windows Time service consists of the following two parts:

NtpServer output provider. This is a time server that responds to client time requests on the network.
NtpClient input provider. This is a time client that obtains time information from another source, either a hardware device or an NTP server, and can return time samples that are useful for synchronizing the local clock.

Although the actual operations of these two providers are closely related, they appear independent to the time service. By default, when a computer that is running Windows Server is connected to a network, it is configured as an NTP client.

Lync Phone Edition searches for an NTP server in Domain Name System (DNS) by searching for the following:

NTP SRV record (User Datagram Protocol, or UDP, port 123)
_ntp._udp.<SIP domain> pointing to NTP Server

If Lync Phone Edition cannot find the NTP SRV record, it will attempt to use http://time.windows.com as an NTP server by searching for the following:

NTP A record
time.windows.com

To set Group Policy for Windows Time Service global configuration settings

From the Microsoft Management Console (MMC), click Active Directory Users and Computers.
Right-click the domain that contains your NTP server, and then click Properties.
Click the Group Policy tab, make sure the Default Domain Policy is highlighted, and then click Edit.
Click Computer Configuration, click Administrative Templates, click System, and then click Windows Time Service.
Click Time Providers, double-click Enable Windows NTP Server in the right pane, click the Enabled button, and then click OK.
From the Group Policy Object Editor menu, click File, and then click Exit.