Computers have integral Real Time Clock chips (RTC) that provide time and date information. The real time clock chips are battery backed so that even during power outages, they can maintain time. The function of the Real Time Clock is to provide accurate time and date information to operating system processes and user applications. For many applications, this is adequate, however, quite often applications may need time 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 discuses how the Windows 2003 time synchronisation service uses NTP to synchronise 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 Network Time Protocol provides accurate time information along with network transmission delay information, so that a precise time can be obtained.

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. A breif description of the more useful time service configuration settings is contained below.

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' registry entry defines how often the Windows 2003 operating system should poll the time server, the value should be specified in seconds. 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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