Time Synchronisation

This article explores how to use national time and frequency radio transmissions for network time synchronisation.

The importance of an authenticated timing reference to synchronise a computer network to, cannot be stressed highly enough.

While there are hundreds and quite possibly thousands of internet based timing sources these can’t be authenticated leaving a system open to viruses, malicious hackers or malware.

Furthermore, a survey by MIT (Massachusetts Institute of Technology) found that nearly half of internet timing sources were offset by over ten seconds and only a third could be regarded as being ‘useful ’ also it was discovered that many were too far away from peers to provide any useful accuracy.

Most dedicated network time servers are designed to receive a timing signal from the GPS (Global Positioning System), primarily because it is the most accurate and can be received from anywhere on the globe.

However, there are situations where it may not be practical to use a GPS time server. A GPS antenna has to be situated on a rooftop and have a clear view of the sky which may prove difficult if the server is on the ground floor of a multi-storey sky-scraper. Many administrators also dislike the hassle and expense of having to run a cable up a building and install an antenna or if there are possibilities the server room maybe relocated and the process has to be repeated.

Fortunately many countries’ national physics laboratories broadcast a time and frequency signal from a radio transmitter. In the US the signal is referred to as WWVB and is broadcast by NIST (National Institute for Standards and Technology) in Colorado. In the UK the National Physical Laboratory (NPL) broadcasts the MSF signal from Cumbria and similar systems are broadcast in Germany (DCF-77), Japan (JJY) and France (TDF).

Unfortunately not every country transmits a national time and frequency broadcast so if a time server is to be located outside of the US, Germany, UK, France or Japan it may be doubtful that a signal could be received (although many of the these transmissions can be received in neighbouring countries).

Radio signals are also easily susceptible to atmospheric interference and can be blocked by mountains, sky-scrapers or other topography. However, an upside to using a radio receiver is that it will receive a signal inside a building.

While a radio transmission is not as accurate as a GPS time signal a dedicated network time server receiving a radio signal can still provide accuracy between 1 – 20 milliseconds (a millisecond is 1/1000 of a second) which is more than adequate for the needs of network synchronisation.

Most businesses these days rely on a computer network. Computers in most organisations conduct thousands of tasks a second, from controlling production lines; ordering stock; preparing financial records and communicating with computers on other networks – often from the other side of the world.

Computers use just one thing to keep track of all these tasks: time. Timestamps are the computers only reference for when an event or task occurs in relation to other events. They receive time in the form of timestamps and they measure time in periods of milliseconds (thousandth of a second) as they may conduct hundreds of processes each second.

A global timescale known as UTC (Coordinated Universal Time) has been developed to ensure computers from different organisations all over the world can synchronise together. So what happens if the clocks on computers don’t coincide with each other or with UTC?

The consequences of running a network with computers that are not synchronised can be disastrous. Here are five reasons why all businesses need adequate network synchronisation using a NTP server (Network Time Protocol) or other network time server device.

1. Tasks fail to happen:

When computers are running at different times, events on different machines can fail to happen as often a PC may assume an event on another machines has already happened if the time for that event has passed according to its own clock. And what is worse, when one task fails it has a knock-on effect with other tasks failing to happen and in turn causing further tasks to fail.

2. Loss of Data:

When tasks fail to happen it soon gets noticed but when networks are not synchronised data that is meant to be kept can quite easily be lost and it can go unnoticed for quite a while. Data can be lost because storage as and retrieval is also reliant on time stamps.