All PC's have internal Real Time Clocks (RTC) that maintain time and date information. PC real time clocks are battery backed so that they can maintain time even when the PC is powered off. The PC Real Time Clock provides time and date information to operating system processes and user applications. Often this is adequate, however, for many applications PC time may need to be synchronised with other PC's on the network.

For transaction processing in a networked environment or for scheduling purposes, the system time and date may need to be synchronised with every other PC on the local network. Microsoft Windows 2003 has an integrated time service that provides synchronisation between PC's in a domain.

This article describes how the Windows 2003 Time Service synchronises time and date information on servers to a domain controller. It also describes how the Windows Time Service utilises the Network Time Protocol (NTP) to achieve network time synchronisation of servers in a domain.

Networked computers require an automated time synchronisation service which can automatically synchronise time on each client to an accurate master clock. The Microsoft Windows 2003 time synchronisation service was developed to fulfill this function. The service is installed by default on any Windows 2000, XP and Server 2003 machine.

On power-up, the Windows 2003 time service starts automatically and attempts to synchronise time and date information with a domain controller using the NTP protocol. NTP is an Internet protocol developed for the transfer of accurate time. The protocol provides time offset information along with round-trip delay information in order to accurately synchronise time.

A domain controller can be configured as either a trusted or an un-trusted time reference. A Windows Time Client will always attempt to synchronise time periodically with a trusted domain controller. In this manner networked Windows 2003 servers maintain synchronisation with a domain controller and each other.

The Windows 2003 time synchronisation service configuration settings are contained in a global group policy. The settings are obtained from registry entries, which are located in HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Time. Below is a description of some of the more useful configuration settings.

The ‘AnnounceFlags' registry entry indicates whether the server is a trusted time reference. This flag should be set to the value 5 indicating that this PC is a trusted time source. The ‘Type' registry entry specifies which network peers to accept synchronisation. Set the ‘Type' registry entry to ‘NTP' to specify synchronization to a NTP time server.

The ‘SpecialPollInterval' entry defines the period in seconds that the Windows 2003 operating system should poll the time server. A recommended value is 900, which equates to a polling period of every 15 minutes. The ‘NtpServer' parameter is used to provide domain names or IP addresses of NTP time servers that the operating system can synchronize to. Each domain name or IP address should be separated by a space.

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