Common NTP Server Time Reference Problems

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The NTP server (Network Time Protocol) is one of the most used but least understood computer networking hardware items.

A NTP Server is just a time server that uses the protocol NTP. Other time protocols do exist but NTP is by far the most widely used. The terms ‘NTP server’, ‘time server’ and ‘network time server’ are interchangeable and often the terms ‘radio clock’ or ‘GPS time server’ are used but these simply describe the method which the time servers receive a time reference.

NTP servers receive a time source that they can then distribute amongst a network. NTP will check a devices system clock and advance or retreat the time depending on how much it has drifted. By regularly checking the system clock with the time server, NTP can ensure the device is synchronised.

The NTP server is a simple device to install and run. Most connect to a network via an Ethernet cable and the software included is easily configured. However, there are some common troubleshooting problems associated with NTP servers and in particular with receiving timing sources:

A dedicated NTP server will receive a time signal from various sources. The Internet is probably the most common sources of UTC time (Coordinated Universal Time), however, using the Internet as a timing source can be a cause for several time server problems.

Firstly Internet timing sources can’t be authenticated; authentication is NTP’s in-built security measure and ensures that a timing reference is coming from where it says it is. On a similar note to use an Internet timing source would mean that a gap would have to be created in the network firewall, this can obviously cause its own security issues.

Internet timing sources are also notoriously inaccurate. A survey by MIT (Massachusetts Institute of Technology) found less than a quarter of Internet timing sources were any where near accurate and often those that were, were too far away from clients to provide a reliable timing source.

The most common, secure and accurate method for receiving timing source is the GPS system (Global Positioning System). While a GPs signal can be received anywhere on the planet there are still common installation issues.

A GPS antenna has to have a good clear view of the sky; this is because the GPs satellite broadcast their signal by line of sight. He signal can not penetrate buildings and therefore the antenna has to be situated on the rood. Another common issue with a GPS time server is that they need to be left for at least 49 hours to ensure the GPS receiver gets a good satellite fix. Many users find that they are receiving an intermittent signal this is normally due to impatience and not letting the GPS system obtain a solid fix.

The other secure and reliable method for receiving a timing signal is the national radio transmissions. In the UK this is called MSF but similar systems exist in the US (WWVB), Germany (DCF) and several other countries. There are usually less problems faced when using the MSF/DCF/WWVB signal.

Although the radio signal can penetrate buildings it is susceptible to interference from topography and other electrical appliances.  Any issues with a MSF time server can normally be resolved by moving the server to another locale or often just angling the server so its ib-built antenna is perpendicular to the transmission.


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Richard N Williams is a technical author and a specialist in the NTP Server and Time Synchronisation industry. Richard N Williams on Google+