Time synchronisation in modern computer networks is essential. It not only provides the only frame of reference between all devices, it is critical in everything from securing, planning and debugging a network to providing a time stamp for applications such as data acquisition or email.

Microsoft Windows XP has a time synchronisation utility built into the operating system called Windows Time (w32time.exe) which can be configured to operate as a network time server. It can be configured to both synchronise a network using the internal clock or an external time source.

For many applications, an internal clock can be quite adequate, although, on a network, problems can arise with applications such as sharing network files or in some environments even fraud, so it is vital for security reasons to use an accurate timing source for your network.

NTP (Network Time Protocol) is a protocol already installed on Windows XP and is used by Windows Time to keep machines synchronised to the single time source. There are several timing sources available on the Internet but Microsoft and others strongly recommend that you configure a time server with a hardware source rather than from the Internet where there is no authentication.

Specialist NTP servers are available that can receive a reliable time source via the GPS signal or specialist radio transmissions that get their time from atomic clocks.

If you wish to configure Windows XP to operate as a time server then first thing is to locate the Windows Time subkey. To do this: Run Regedit (Click start/run/then type REGEDIT/and click enter.

Note: editing your system registry can cause problems with your system. It is advisable to back up your system before editing the registry.

Now locate the following subkey: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeparameters Right click the right-hand side and click Modify. In the Edit Value box, under Value Data, type NTP and then click OK. Now go to the Config folder and right-click AnnounceFlags, Modify and in the Edit DWORD Value box, under Value Data, type 5, and then click OK.

Locate this subkey: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpClient

Right-click in the right-side window and Modify. Edit the DWORD value box and type the number of seconds you want for each poll under Value data, i.e.: 900 will equal 15 minutes. The poll field represents the polling interval between NTP poll packets.

To enable the NTP server locate the subkey: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpServer Right click enabled (in the right-hand window) then Modify. Edit the DWORD Value and type 1. Right-click NtpServer, then Modify and in the Edit DWORD Value under Value Data type Peers, then click OK.

Locate: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig In the right pane, right-click MaxPosPhaseCorrection, then Modify, in the Edit DWORD Value box, under Base, click Decimal, under Value Data, type a time in seconds such as 3600 (an hour) then click OK. This adjusts the connection settings.

Now go back and click: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig

In the right pane, right-click MaxNegPhaseCorrection, then Modify. In the Edit DWORD box under base, click Decimal, under value data type the time in seconds you want to poll such as 3600 (an hour).

Exit Registry then restart windows time service by clicking Start/Run then typing: net stop w32time && net start w32time. on each computer, other than the domain controller, type: W32tm/resync/rediscover. The time server should be now up and running.