Archive for January, 2010

Using GPS as a source of Accurate Time

Thursday, January 28th, 2010

The Global Positioning System (GPS) is an increasingly popular tool, used throughout the world as a source of wayfinding and navigation. However, there is much more to the GPS network than just satellite navigation as the transmissions broadcast by the GPS satellites can also be used as a highly accurate source of time.

GPS satellites are actually just orbiting clocks as each one contains atomic clocks that generate a time signal. It is the time signal that is broadcast by the GPS satellites that satellite navigation receivers in cars and planes use to work out distance and position.

Positioning is only possible because thee time signals are so accurate. Vehicle sat navs for instance use the signals from four orbiting satellites and triangulate the information to work out the position. However, if there is just one second inaccuracy with one of the time signals then the positing information could be thousands of miles out – proving useless.

It is testament to the accuracy of atomic clocks used to generate GPS signals that currently a GPS receiver can work out its position on earth to within five metres.

Because GPS satellites are so accurate, they make an ideal source of time to synchronise a computer network to. Strictly speaking GPS time differs from the international timescale UTC (coordinated Universal Time) as UTC has had additional leap seconds added to it to ensure parity with the earth’s rotation meaning it is exactly 18 seconds ahead of GPS but is easily converted by NTP the time synchronisation protocol (Network Time Protocol).

GPS time servers receive the GPS time signal via a GPS antenna which has to be placed on the roof to receive the line of sight transmissions. Once the GPS signal is received the NTP GPS time server will distribute the signal to all devices on the NTP network and corrects any drift on individual machines.

GPS time servers are dedicated easy to use devices and can ensure millisecond accuracy to UTC without any of the security risks involved in using an internet time source.

Using the WWVB Signal for Time Synchronization

Tuesday, January 26th, 2010

We all rely on the time to keep our days scheduled. Wristwatches, wall clocks and even the DVD player all tell us the time but on occasion, this is not accurate enough, especially when time needs to be synchronized.

There are many technologies that require extremely accurate precision between systems, from satellite navigation to many internet applications, accurate time is becoming increasingly important.

However, achieving precision is not always straight forward, especially in modern computer networks. While all computer systems have inbuilt clocks, these are not accurate time pieces but standard crystal oscillators, the same technology used in other electronic clocks.

The problem with relying on system clocks like this is that they are prone to drift and on a network consisting of hundreds or thousands of machines, if the clocks are drifting at a different rate – chaos can soon ensue. Emails are received before they are sent and time critical applications fail.

Atomic clocks are the most accurate time pieces around but these are large scale laboratory tools and are impractical (and highly expensive) to be used by computer networks.

However, physics laboratories like the North American NIST (National Institute of Standards and Time) do have atomic clocks which they broadcast time signals from. These time signals can be used by computer networks for the purpose of synchronization.

In North America, the NIST broadcasted time code is called WWVB and is transmitted out of Boulder, Colorado on long wave at 60Hz. The time code contains the year, day, hour, minute, second, and as it is a source of UTC, any leap seconds that are added to ensure parity with the rotation of the Earth.

Receiving the WWVB signal and using it to synchronize a computer network is simple to do. Radio reference network time servers can receive this broadcast throughout North America and by using the protocol NTP (Network Time Protocol).

A dedicated NTP time server that can receive the WWVB signal can synchronize hundreds and even thousands of different devices to the WWVB signal ensuring each one is to within a few milliseconds of UTC.

Common Issues in Time Synchronisation

Sunday, January 24th, 2010

Time synchronization is essential in modern computer networking especially with the amount of time sensitive transactions conducted over the internet these days. Without adequate synchronization computer systems will:

  • Be vulnerable to malicious attacks
  • Susceptible to data loss
  • Unable to conduct time sensitive transactions
  • Difficult to debug

Fortunately ensuring a computer network is accurately synchronized is relatively straight forward. There different methods of synchronizing a network to the global timescale UTC (Coordinated Universal Time) but occasionally some common issues do arise.

My dedicated time server is unable to receive a signal

Dedicated NTP time servers receive the time from either long wave transmissions or GPS networks. If using a GPS NTP server then a GPS antenna needs to be situated on a roof to obtain a clear view of the sky. However, a NTP radio receiver does not need a roof mounted aerial although the signal can be vulnerable to interference and the correct angle toward the transmitter should be attained.

I am using a public time server across the Internet but my devices are not synchronised.

As public time servers can be used by anyone they can receive high levels of traffic. This can cause problems with bandwidth and mean that your time requests can’t get through. Public NTP servers can also fall victim to DDoS attacks and some high profile incidents of NTP vandalism have occurred.

Internet time servers are also stratum 2 devices, in other words they themselves have to connect to a time server to receive the correct time and because of this some online time references are wildly inaccurate.

*NB – internet time servers are also incapable of being authenticated to allow NTP to establish if the time source is coming from where it claims to be, combined with the problem of ensuring the firewall is open to receive the time requests, can mean that internet time servers present a clear risk to security.

The time on my computer seems to be off by a second to standard UTC time

You need to check if a recent leap second has been added to UTC. Leap seconds are added once or twice a year to ensure UTC and the Earth’s rotation match. Some time servers experience difficulties in making the leap second adjustment.

Atomic Clock Synchronization made easy with a NTP Time Server

Friday, January 22nd, 2010

Atomic clocks are the ultimate in timekeeping devices. Their accuracy is incredible as an atomic clock will not drift by as much as a second within a million years, and when this is compared to the next best chronometers, such as electronic clock that can drift by a second in a week, an atomic clock is incredibly more precise.

Atomic clocks are used the world over and are the heart of many modern technologies making capable a multitude of applications that we take for granted. Internet trading, satellite navigation, air traffic control and international banking are all industries that rely heavily on

They also govern the world’s timescale, UTC (Coordinated Universal Time) which is kept true by a constellation of these clocks (although UTC has to be adjusted to accommodate the slowing of the Earth’s spin by adding leap seconds).

Computer networks are often required to run synchronized to UTC. This synchronisation is vital in networks that conduct time sensitive transactions or require high levels of security.

A computer network without adequate time synchronization can cause many issues including:

Loss of data

  • Difficulties in identifying and logging errors
  • Increased risk of security breaches.
  • Unable to conduct time sensitive transactions

For these reasons many computer networks have to be synchronized to a source of UTC and kept as accurate as possible. And although atomic clocks are large bulky devices kept in the confines of physics laboratories, using them as a source of time is incredibly simple.

Network Time Protocol (NTP) is a software protocol designed solely for the synchronisation of networks and computer systems and by using a dedicated NTP server the time from an atomic clock can be received by the time server and distributed around the network using NTP.

NTP servers use radio frequencies and more commonly the GPS satellite signals to receive the atomic clock timing signals which is then spread throughout the network with NTP regularly adjusting each device to ensure it is as accurate as possible.

MSF Outages for 2010

Wednesday, January 20th, 2010

Users of the National Physical Laboratory’s (NPL) MSF time and frequency signal are probably aware that the signal is occasionally taken off-air for scheduled maintenance.

NPL have published there scheduled maintenance for 2010 where the signal will be temporarily taken off-air. Usually the scheduled downtimes lasts for less than four hours but users need to be aware that while NPL and VT Communications, who service the antenna, make every effort to ensure the transmitter is off for a brief amount of time as possible, there can be delays.

And while NPL like to ensure all users of the MSF signal have advanced warning of possible outages, emergency repairs and other issues may lead to unscheduled outages. Any user receiving problems receiving the MSF signal should check the NPL website in case of unscheduled maintenance before contacting your time server vendor.

The dates and times of the scheduled maintenance periods for 2010 are as follows:

* 11 March 2010 from 10:00 UTC to 14:00 UTC

* 10 June 2010 from 10:00 BST to 14:00 BST (UTC + 1 hr)

* 9 September 2010 from 10:00 BST to 14:00 BST (UTC + 1 hr)

* 9 December 2010 from 10:00 UTC to 14:00 UTC

As these scheduled outages should take no longer than four hours, users of MSF referenced time servers should not notice any drop off in accuracy of their network as their shouldn’t be enough time for any device to drift.

However, for those users concerned about accuracy or require a NTP time server (Network Time Server) that doesn’t succumb to regular outages, they may wish to consider investing in a GPS time server.

GPS time servers receive the time from the orbiting navigational satellites. As these are available anywhere on the globe and the signals are never down for outages they can provide a constant accurate time signal (GPS time is not the same as UTC but is easily converted by NTP as it is exactly 17 seconds behind due to leap seconds being added to UTC and not GPS).

Why a GPS Time Server is the Number One Choice for Time Synchronization

Monday, January 18th, 2010

When it comes to synchronizing a computer network there are several choice to ensure each device is running the same time. NTP (Network Time Protocol) is the preferred choice of time synchronization protocols but there are a multitude of methods in how NTP receives the time.

The NTP Daemon is installed on most operating systems such as windows and applications such as Windows Time are quite capable of receiving a source of UTC time (Coordinated Universal Time) from across the internet.

UTC time is the preferred time source used by computer networks as it is kept true by atomic clocks. UTC, as the name suggests, is also universal and is used by computer networks all over the world as a source to synchronize too.

However, internet sources of UTC are to recommended for any organisation where security and accuracy are a concern. Not only can the distant from host (internet time server) to the client (your computer network) can never be accurately measured leading to a drop in precision. Furthermore, any source of internet time will need access through the firewall (usually through the UDP 123 port). And by leaving this port open, malicious users and hackers can take advantage and gain access to the system.

Dedicated NTP time servers are a better solution as they receive the time from an external source. There are really two types of NTP server, the radio reference time server and the GPS time server.
Radio reference time servers use signals broadcast by places like NPL (National Physical Laboratory in the UK) or NIST (National Institute of Standards and Time). While these signals are extremely accurate, precise and secure they are affected by regular maintenance on the transmitters that broadcast the signal. Also being long wave they are vulnerable to local interference.

GPS time servers on the other hand receive the time directly from GPS satellites. This GPS time is easily converted to UTC by NTP (GPS time is UTC – 17 seconds exactly as no leap seconds have been added.) As the GPS signal is available everywhere on the earth 24 hours a day, 365 days a week, there is never a risk of a loss of signal.
A single dedicated GPS time server can synchronize a computer network of hundreds, and even thousands of machines to within a few of milliseconds of UTC time.

How to Synchronise a Computer Network using the Time Protocol (NTP)

Saturday, January 16th, 2010

Synchronisation of modern computer networks is vitally important for a multitude of reasons, and thanks to the time protocol NTP (Network Time Protocol) this is relatively straightforward.

NTP is an algorithmic protocol that analyses the time on different computers and compares it to a single time reference and adjusts each clock for drift to ensure synchronisation with the time source. NTP is so capable at this task that a network synchronised using the protocol can realistically obtain millisecond accuracy.

Choosing the time source

When it comes to establishing a time reference there really is no alternative than to find a source of UTC (Coordinated Universal Time). UTC is the global timescale, used throughout the world as a single timescale by computer networks. UTC is kept accurate by a constellation of atomic clocks throughout the world.

Synchronising to UTC

The most basic method of receiving a UTC Time source is to use a stratum 2 internet time server. These are deemed stratum 2 as they distribute the time after first receiving it from a NTP server (stratum 1) that is connected to an atomic clock (stratum 0). Unfortunately this is not the most accurate method of receiving UTC because of the distance the data has to travel from host to the client .

There are also security issues involved in using an internet stratum 2 time source in that the firewall UDP port 123 has to be left open to receive the time code but this firewall opening can, and has been, exploited by malicious users.

Dedicated NTP Servers

Dedicated NTP time servers, often referred to as network time servers, are the most accurate and secure method of synchronising a computer network. They operate externally to the network so there are no firewall issues. These stratum 1 devices receive the UTC time direct from an atomic clock source by either long wave radio transmissions or the GPS network (Global Positioning System). Whilst this does require an antenna, which in the case of GPS has to be placed on a rooftop, the time server itself will automatically synchronise hundreds and indeed thousands of different devices on the network.

Five Reasons why your Network needs a NTP Server

Thursday, January 14th, 2010

Accurate timekeeping if quite often overlooked as a priority for network administrators yet many are risking both security and data loss by not ensuring their networks are synchronised as precisely as possible.

Computers do have their own hardware clocks but these are often just simple electronic oscillators such as exist in digital watches and unfortunately these system clocks are prone to drift, often by as much as several seconds in a week.

Running different machines on a network that have different times – even by only a few seconds – can cause havoc as so many computer tasks rely on time. Time, in the form of timestamps, is the only reference computers use to distinguish between different events and failure to accurately synchronize a network can lead to all sorts of untold problems.

Here are some of the major reasons why your network should be synchronised using Network Time Protocol, prefasbly with a NTP time server.

Data Backups – vital to safeguard data in any business or organization, a lack of synchronisation can lead to not only back ups failing but older versions of files replacing more modern versions.

Malicious Attacks – no matter how secure a network, somebody, somewhere will eventually gain access to your network but without accurate synchronisation it may become impossible to discover what compromises have taken place and it will also give any unauthorised users extra time inside a network to wreak havoc.

Error logging – when faults occur, and they inevitably do, the system logs contain all the information to identify and correct problems. However, if the system logs are not synchronised it can sometimes be impossible to figure out what went wrong and when.

Online Trading – Buying and selling on the internet is now commonplace and in some businesses thousands of online transactions are conducted every second from seat reservation to buying of shares and a lack of accurate synchronisation can result in all sorts of errors in online trading such as items being bought or sold more than once.

Compliance and legality – Many industrial regulations systems require an auditable and accurate method of timing. A unsynchronised network will also be vulnerable to legal issues as the exact time an event is alleged to have taken place can not be proved.

Did you Remember the Leap Second this Year?

Tuesday, January 12th, 2010

When you counted down on New Year’s Eve to mark the beginning of the next year did you start at 10 or 11? Most revelers would have counted down from ten but they would have been premature this year as there was an extra second added to last year – the leap second.

Leap seconds are normally inserted once or twice a year (normally on New Year’s Eve and in June) to ensure the global timescale UTC (Coordinated Universal Time) coincides with the astronomical day.

Leap seconds have been used since UTC was first implemented and they are a direct result of our accuracy in timekeeping. The problem is that modern atomic clocks are far more accurate timekeeping devices than the earth itself. It was noticed when atomic clocks were first developed that the length of a day, once thought to be exactly 24 hours, varied.

The variations are caused by the Earth’s rotation which is affected by the moons gravity and tidal forces of the Earth, all of which minutely slow down the earth’s rotation.

This rotational slowing, while only minuscule, if it is not checked then the UTC day would soon drift into the astronomical night (albeit in several thousands of years).

The decision on whether a Leap Second is needed is the remit of the International Earth Rotation Service (IERS), however, Leap Seconds are not popular with everybody and they can cause potential problems when they are introduced.

UTC is used by NTP time servers (Network Time Protocol) as a time reference to synchronise computer networks and other technology and the disruption Leap seconds can cause is seen as not worth the hassle.

However, others, such as astronomers, say that failing to keep UTC in line with the astronomical day would make studying of the heavens nearly impossible.

The last leap second inserted before this one was in 2005 but there have been a total of 23 seconds added to UTC since 1972.

Using NTP to Synchronise a Digital Signage System

Sunday, January 10th, 2010

Digital signage is advancing quite rapidly for such a burgeoning new industry. Fantastic new innovations and content styles are being developed all the time and there are some really fantastic campaigns out there and more and more adventurous implementations are springing up all the time.

One of a growing number of trends is the use of complicated, scheduled and synchronised campaigns on multiple machines. These are incredibly eye-catching especially when the content is synchronised to provide passers-by with an almost interactive experience.

Synchronised content can be really challenging to implement and this sort of content is certainly not for the beginner as setting up such a sophisticated campaign can be really difficult.

One of the essential aspects of these types of scheduled digital signage campaigns is to ensure all displays are synchronized together. Synchronization is perhaps the most crucial aspect of these types of sophisticated digital signage campaigns. There are multiple methods of synchronising this type of campaign.

One solution is to a network time server which receives a single time source and distributes it amongst all devices on that network using the time protocol NTP (Network Time Protocol).

NTP servers receive the time from an external source (normally GPS or long wave radio) so there is no need to have the network connected to the internet although it is just as possible to synchronise to an internet time source although this can be problematic if there is any disturbance in the internet connection.

Any large network of digital signage displays also need to be protected, especially if media players or PCs are being used to generate content. The best option for ensuring total security is to place both the screen and media device in a display enclosure, often referred to as an LCD enclosure.