Category: advanced NTP

New Waterproof GPS Mushroom Antenna

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Galleon Systems’ new mushroom GPS antenna provide increased reliability in receiving GPS timing signals for NTP time servers.
The new Exactime 300 GPS Timing and Synchronization Receiver boasts waterproof protection, anti-UV, anti-acidity and anti-alkalinity properties to ensure reliable and continual communication with the GPS network.

The attractive white mushroom is smaller than conventional GPS antennas and sits just 77.5mm or 3.05-inch in height and is easily fitted and installed thanks to the inclusion of a full installation guide and CD manual.

Whilst an ideal unit for a GPS NTP time server this industry standard antenna is also ideal for all GPS receiving needs including: Marine Navigation, Control Vehicle Tracking and NTP synchronisation
The main features of the Exactime 300 mushroom antenna are:

• Built-in patch antenna • 12 parallel tracking channels • Fast TTFF (Time to first fix) and low power consumption • On-board, rechargeable battery sustained Real-Time Clock and control • parameters memory for fast satellite acquisition during power-up • Interference filter to major VHF channels of marine radar • WAAS compliant with EGNOS support • Perfect Static Drift for both of speed and course •  Magnetic Declination compensation • Is protected against reverse polarity voltage • Support RS-232 or RS-422 interface, Support 1 PPS output.

2008 Will be a second longer Leap Second to be added to UTC

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New Year’s celebrations will have to wait another second this year as the International Earth Rotation and Reference Systems Service (IERS) have decided to 2008 is to have Leap Second added.

IERS announced in Paris in July that a positive Leap Second was to be added to 2008, the first since Dec. 31, 2005. Leap Seconds were introduced to compensate for the unpredictability of the Earth’s rotation and to keep UTC (Coordinated Universal Time) with GMT (Greenwich Meantime).

The new extra second will be added on the last day of this year at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time — 6:59:59 pm Eastern Standard Time. 33 Leap Seconds have been added since 1972

NTP server systems controlling time synchronisation on computer networks are all governed by UTC (Coordinated Universal Time). When an additional second is added at the end of the year UTC will automatically be altered as the additional second. #

Whether a NTP server receives a time signal fro transmissions such as MSF, WWVB or DCF or from the GPS network the signal will automatically carry the Leap Second announcement.

Notice of Leap Second from the International Earth Rotation and Reference Systems Service (IERS)


61, Av. de l’Observatoire 75014 PARIS (France)
Tel.      : 33 (0) 1 40 51 22 26
FAX       : 33 (0) 1 40 51 22 91
e-mail    :

Paris, 4 July 2008

Bulletin C 36

To authorities responsible for the measurement and distribution of time

on the 1st of January 2009

A positive leap second will be introduced at the end of December 2008.
The sequence of dates of the UTC second markers will be:

2008 December 31,     23h 59m 59s
2008 December 31,     23h 59m 60s
2009 January   1,      0h  0m  0s

The difference between UTC and the International Atomic Time TAI is:

from 2006 January 1, 0h UTC, to 2009 January 1  0h UTC  : UTC-TAI = – 33s
from 2009 January 1, 0h UTC, until further notice       : UTC-TAI = – 34s

Leap seconds can be introduced in UTC at the end of the months of December

How a GPS Time Server Works

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A GPS time server is really a communication device. Its purpose is to receive a timing signal and then distribute it amongst all devices on a network. Time server s are often called different things from network time server, GPS time server, radio time server and NTP server.

Most time servers use the protocol NTP (Network Time Protocol). NTP is one of the Internet’s oldest protocols and is used by the majority of machines that use a time server. NTP is often installed, in a basic form, in most operating systems.

A GPS time server, as the names suggests, receives a timing signal from the GPS network. GPS satellites are really nothing more than orbiting clocks. Onboard each GPS satellite is an atomic clock. The ultra-precise time from this clock is what is transmitted from the satellite (along with the satellite’s position).

A satellite navigation system works by receiving the time signal from three or more satellites and by working out the position of the satellites and how long the signals took to arrive, it can triangulate a position.

A GPS time server needs even less information and only one satellite is required in order to receive a timing reference. A GPS time server’s antenna will receive a timing signal from one of the 33 orbiting satellites via line of sight, so the best place to fix the antenna is the roof.

Most dedicated GPS NTP time servers require a good 48 hours to locate and get a steady fix on a satellite but once they have it is rare for communication to be lost.

The time relayed by GPS satellites is known as GPS time and although it differs to the official global timescale UTC (Coordinated Universal Time) as they are both based on atomic time (TAI) GPS time is easily converted by NTP.

A GPS time server is often referred to as a stratum 1 NTP device, a stratum 2 device is a machine that receives the time from the GPS time server. Stratum 2 and stratum 3 devices can also be used as a time servers and in this way a single GPS time server can operate as a timing source for an unlimited amount of computers and devices as long as the hierarchy of NTP is followed.

How an Atomic Clock Works

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Atomic clocks are used for thousands of applications all over the world. From controlling satellites to even synchronising a computer network using a NTP server, atomic clocks have changed the way we control and govern time.

In terms of accuracy an atomic clock is unrivalled. Digital quartz clocks may keep accurate time for a week, not losing more than a second but an atomic clock can keep time for millions of years without drifting as much.

Atomic clocks work on the principle of quantum leaps, a branch of quantum mechanics which states that an electron; a negatively charged particle, will orbit a nucleus of an atom (the centre) in a certain plain or level. When it absorbs or releases enough energy, in the form of electromagnetic radiation, the electron will jump to a different plane – the quantum leap.

By measuring the frequency of the electromagnetic radiation corresponding to the transition between the two levels, the passage of time can be recorded. Caesium atoms (caesium 133) are preferred for timing as they have 9,192,631,770 cycles of radiation in every second. Because the energy levels of the caesium atom (the quantum standards) are always the same and is such a high number, the caesium atomic clock is incredibly precise.

The most common form of atomic clock used in the world today is the caesium fountain. In this type of clock a cloud of atoms is projected up into a microwave chamber and allowed to fall down under gravity. Laser beams slow these atoms down and the transition between the atom’s energy levels are measured.

The next generation of atomic clocks are being developed use ion traps rather than a fountain. Ions are positively charged atoms which can be trapped by a magnetic field. Other elements such as strontium are being used in these next generation clocks and it is estimated that the potential accuracy of a strontium ion trap clock could be 1000 times that of the current atomic clocks.

Atomic clocks are utilised by all sorts of technologies; satellite communication, the Global Positioning System and even Internet trading is reliant on atomic clocks. Most computers synchronise indirectly to an atomic clock by using a NTP server. These devices receive the time from an atomic clock and distribute around their networks ensuring precise time on all devices.

Synchronising to an Atomic Clock

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Atomic clocks are the pinnacle of time keeping devices. Modern atomic clocks can keep time to such accuracy that in 100,000,000 years (100 million) they do not lose even a second in time. Because of this high level of accuracy, atomic clocks are the basis for the world’s timescale.

To allow global communication and time sensitive transactions such as the buying of stacks and shares a global timescale, based on the time told by atomic clocks, was developed in 1972. This timescale, Coordinated Universal Time (UTC) is governed and controlled by the International Bureau of weights and Measures (BIPM) who use a constellation of over 230 atomic clocks from 65 laboratories all over the world to ensure high levels of accuracy.

Atomic clocks are based on the fundamental properties of the atom, known as quantum mechanics.  Quantum mechanics suggest that an electron (negatively charged particle) that orbits an atom’s nucleus can exist in different levels or orbit planes depending if they absorb or release the correct amount of energy. Once an electron has absorbed or released enough energy in can ‘jump’ to another level, this is known as a quantum jump.

The frequency between these two energy states is what is used to keep time. Most atomic clocks are based on the caesium atom which has 9,192,631,770 periods of radiation corresponding to the transition between the two levels. Because of the accuracy of caesium clocks the BIPM now considers a second to be defined as 9,192,631,770 cycles of the caesium atom.

Atomic clocks are used in thousands of different applications where precise timing is essential. Satellite communication, air traffic control, internet trading and GPs all require atomic clocks to keep time. Atomic clocks can also be used as a method of synchronising computer networks.

A computer network using a NTP time server can use either a radio transmission or the signals broadcast by GPS satellites (Global Positioning System) as a timing source. The NTP program (or daemon) will then ensure all devices on that network will be synchronised to the time as told by the atomic clock.

By using a NTP server synchronised to an atomic clock, a computer network can run the identical coordinated universal time as other networks allowing time sensitive transactions to be conducted from across the globe.

Where to Find a Public NTP server

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NTP servers are used by computer networks as a timing reference for synchronisation. An NTP server is really a communication device that receives the time from an atomic clock and distributes it. NTP servers that receive a direct atomic clock time are known as stratum 1 NTP servers.

A stratum 0 device is an atomic clock itself. These are highly expensive and delicate pieces of machinery and are only to be found in large scale physics laboratories. Unfortunately there are many rules governing who can access a stratum 1 server because of bandwidth considerations. Most stratum 1 NTP servers are set-up by universities or other non-profit organisations and so have to restrict who accesses them.

Fortunately stratum 2 time servers can offer decent enough accuracy as a timing source and any device receiving a time signal can itself be used as a time reference (a device receiving time from a stratum 2 device is a stratum 3 server. Devices that receive time from a stratum 3 server are stratum 4 devices, and so-on)., is the official home of the NTP pool project and by far the best place to go to find a public NTP server. There are two lists of public servers available in the pool; primary servers, which displays the stratum 1 servers (most of which are closed access) and secondary which are all stratum 2 servers.

When using a public NTP server is important to abide by the access rules as failure to do so can cause the server to become clogged with traffic and if the problems persist possibly discontinued as most public NTP servers are set-up as acts of generosity.

There are some important points to remember when using a timing source from over the Internet. First, Internet timing sources can’t be authenticated. Authentication is an in-built security measure utilised by NTP but unavailable over the net. Secondly, to use an Internet timing source requires an open port in your firewall. A hole in a firewall can be used by malicious users and can leave a system vulnerable to attack.

For those requiring a secure timing source or when accuracy is highly important, a dedicated NTP server that receives a timing signal from either long wave radio transmissions or the GPs network.

Arranging a NTP Server Stratum Tree

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NTP (Network Time Protocol) is the most widely used time synchronisation protocol on the Internet. The reason for its success is that is both flexible and highly accurate (as well as being free). NTP is also arranged into a hierarchical structure allowing thousands of machines to be able to receive a timing signal from just one NTP server.

Obviously, if a thousand machines on a network all attempted to receive a timing signal from the NTP server at the same time the network would become bottlenecked and the NTP server would be rendered useless.

For this reason, the NTP stratum tree exists. At the top of the tree is the NTP time server which is a stratum 1 device (a stratum 0 device being the atomic clock that the server receives its time from). Below the NTP server, several servers or computers receive timing information from the stratum 1 device. These trusted devices become stratum 2 servers, which in turn distribute their timing information to another layer of computers or servers. These then become stratum 3 devices which in turn can distribute timing information to lower strata (stratum 4, stratum 5 etc).

In all NTP can support up to nine stratum levels although the further away from the original stratum 1 device they are the less accurate the synchronisation. For an example of how a NTP hierarchy is setup please see this stratum tree

The WWVB Time Signal

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The WWVB time signal is a dedicated radio broadcast providing an accurate and reliable source of United States civil time, based on the global time scale UTC (Coordinated Universal Time), the WWVB signal is broadcast and maintained by the United States’ NIST laboratory (National Institute for Standards and Time).

The WWVB time signal can be utilised by anyone requiring accurate timing information although its main use is as a source of UTC time for administrators synchronising a computer network with a radio clock. Radio clocks are really another term for a network time server that utilises a radio transmission as a timing source.

Most radio based network time servers use NTP (Network Time Protocol) to distribute the timing information throughout the network.

The WWVB signal is broadcast from Fort Collins, Colorado. It is available 24 hours a day across most of the USA and Canada, although the signal is vulnerable to interference and local topography. Users of the WWVB service receive predominantly a ‘ground wave’ signal. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere and is much stronger at night; this can result in a total received signal that is either stronger or weaker.

The WWVB signal is carried on a frequency of 60 kHz (to within 2 parts in 1012) and is controlled by a caesium atomic clock based at NIST

The signal’s field strength exceeds 100 µV/m (microvolts a meter) at a distance of 1000 km from Colorado – covering much of the USA.

The WWVB signal is in the form of a simple binary code containing time and date information The WWVB  time and date code includes the following information: year, month, day of month,  day of week,  hour, minute, Summer Time (in effect or imminent).

Keeping Time with Network Time Protocol

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NTP (Network Time Protocol) is the most flexible, accurate and popular method of sending time over the Internet. It is perhaps the Internet’s oldest protocol having been around in one form or another since the mid 1980’s.

The main purpose of NTP is to ensure that all devices on a network are synchronised to the same time and to compensate for some network time delays. Across a LAN or WAN NTP manages to maintain an accuracy of a few milliseconds (Across the Internet, time transfer if far less accurate due to network traffic and distance).

NTP is by far the most widely used time synchronisation protocol (somewhere in the region of 95% of all time servers use NTP) and it owes much of its success to its continual updates and its flexibility. NTP will run on UNIX, LINUX, and Windows based operating systems (it is also free, another possible reason for its huge success).

NTP uses a single time source that it distributes among all devices on a network; it also checks each device for drift (the gaining or losing of time) and adjusts for each.  It is also hierarchical in that literally thousands of machines can be controlled using just one NTP server as each machine can in itself be used by neighbouring machines as a time server.

NTP is also highly secure (when using an external time reference not when using the Internet for a timing source) with an authentication protocol able to establish exactly where a timing source comes from.

For a network to be really effective most NTP time servers use an atomic clock as a basis for their time synchronisation. An international timescale based on the time told by atomic clocks has been developed for this very purpose. UTC (Coordinated Universal Time).

There are really two methods to receive a secure UTC atomic clock time signal to be utilised by NTP. The first being the time and frequency transmissions that several national physics laboratories broadcast on long wave around the world; the second (and by far the most readily available) is by using the timing information in the GPS satellite transmissions. These can be picked up anywhere on the globe and provide safe, secure and highly accurate timing information.

Importance of Preventing NTP Time Server Abuse

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NTP time server (Network Time Protocol) abuse is quite often unintentional and fortunately thanks to the NTP pool is less frequent than it was although incidents still happen.

NTP server abuse is any act that violates the access rules of a NTP time server or an act that damages it in any way. Public NTP servers are those servers that can be accessed from across the Internet by devices and routers to use as a timing source to synchronise a network to. Most public NTP time servers are non-profit and set up as acts of generosity, mostly by University’s or other technical centres.

For this reason access rules have to be set up as huge amounts of traffic can generate giant bandwidth bills and can lead to the NTP time server being turned off permanently. Access rules are used to prevent too much traffic from accessing stratum 1 servers, by convention stratum 1 servers should only be accessed by stratum 2 servers which in turn can pass the timing information on down the line.

However, the worst cases of NTP server abuse have been where thousands of devices have sent requests for time, where in the hierarchical nature of NTP only one is needed.

Whilst most acts of NTP abuse are intentional some of the worst abuses of NTP time servers have been committed (albeit unintentionally) by large companies. The first large firm discovered to have been guilty of NTP abuse was Netgear, who, in 2003 released four routers that were all hard coded to use the University of Wisconsin’s NTP server, the resulting DDS (Distributed Denial of Service) reached nearly 150 megabits a second.

Even now, five years on and despite the release of several patches to fix the problem and the University being compensated by Netgear the problem still continues as some people have never patched their routers.

Similar incidents have been committed by SMC and D-Link. D-Link in particular caused controversy as when the matter was drawn to their attention they decided to bring the lawyers in. Only after it was discovered that they violated nearly 50 NTP servers did they attempt resolve the problem (and only after scathing press coverage did they relent).

The easiest way to avoid such problems is to use a dedicated external stratum 1 time server. These devices are relatively inexpensive, simple to install and far more accurate and secure than online NTP servers. These devices receive the time from atomic clocks either from the GPS network (Global Positioning System) .