Common Time Synchronization Pitfalls Finding UTC

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Time synchronization can be a headache for many network administrators attempting to synchronize a network for the first time. There are many pitfalls that an unaware network administrator can fall into when attempting to get every machine on a network to synchronize to the same time.

The first problem many network administrators make is the selection of the time source. UTC (Coordinated Universal Time) is a global timescale and is used throughout the world as a basis for time synchronization as it doesn’t rely on time zones enabling the global community to base itself on one timescale.

UTC is also controlled by a constellation of atomic clocks which ensures its accuracy; however, it is regularly adjusted to ensure that it matches mean solar time by the addition of leap seconds which are added to counter the natural slowing of the Earth’s rotation.

UTC is readily available as a time reference from a number of sources. The Internet is a popular location to receive a UTC time source. However, an Internet time source is located through the network firewall and security issues can arise from having to leave the UDP port open to receive the time requests.

Internet time sources can also be inaccurate and as NTP’s own security system known as NTP authentication cannot work across the Internet further security issues can arise.

A far better solution for getting a source of UTC is to use either the Global Positioning System (GPS) or the long wave radio transmissions broadcast by several national physics laboratories such as NIST in the USA and the UK’s NPL.

Dedicated NTP time servers can receive these secure and authenticated signals and then distribute them amongst all devices on a network.

How Satellite Navigation Works

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Satellite navigational systems, or sat navs, have changed the way we navigate our way around the high roads. Gone are the days when travellers had to have a glove box full of maps and gone too is the need to stop and ask a local for directions.

Satellite navigation means that we an now go from point A to point B confident our systems will take us there and while sat nav systems are not fool proof (we must have all read the stories of people driving over cliffs and into rivers etc), it has certainly revolutionised our wayfinding.

Currently there is only one Global Navigational Satellite System (GNSS) the American run Global Positioning System (GPS). Although, a rival European System (Galileo) is set to go online sometime after 2012 and a both a Russian (GLONASS) and Chinese (COMPASS) system are being developed.

However, all these GNSS networks will operate using the same technology as employed by GPS, and in fact, current GPS systems should be able to utilise these future systems without much alteration.

The GPS system is basically a constellation of satellites (currently there are 27). These satellites each contain onboard an atomic clock (actually two are on most GPS satellites but for the purpose of this explanation only one need be considered). The signals that are transmitted from the GPS satellite contain several pieces of information sent as one integer:

* The time the message was sent

* The orbital position of the satellite (known as the ephemeris)

* The general system health and orbits of the other GPS satellites (known as the almanac)

A satellite navigation receiver, the kind found on the dashbopard of your car, receives this information and using the timing information works out the exact distance from the receiver to the satellite. By using three or more of these signals the exact position can be triangulated (four signals are actually required as height above sea level has to be worked out too).

Because the triangulation works out when the time signal was sent and how long it took to arrive at the receiver, the signals have to be incredibly accurate. Even a second of inaccuracy could see the navigational information out but thousands of kilometres as light, and therefore radio signals, can travel nearly 300,000 km each second.

Currently the GPS satellite network can provide navigational accuracy to within 5 metres which goes to show just how accurate atomic clocks can be.

The Way an Atomic Clock Works

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Atomic clocks are the most accurate chronometers we have. They are millions of times more accurate than digital clocks and can keep time for hundreds of millions of years without losing as much as a second. Their use has revolutionised the way we live and work and they have enabled technologies such as satellite navigation systems and global online commerce.

But how do they work? Strangely enough, atomic clocks work in the same way as ordinary mechanical clocks. But rather than have a coiled spring and mass or pendulum they use the oscillations of atoms. Atomic clocks are not radioactive as they do not rely on atomic decay instead they rely on the tiny vibrations at certain energy levels (oscillations) between the nucleus of an atom and the surrounding electrons.

When the atom receives microwave energy at exactly the right frequency, it changes energy state, this state is constant an unchanging and the oscillations can be measured just like the ticks of a mechanical clock. However, while mechanical clocks tick every second, atomic clocks ‘tick’ several billion times a second. In the case of caesium atoms, most commonly used in atomic clocks, they tick 9,192,631,770 per second – which is now the official definition of a second.

Atomic clocks now govern the entire global community as a universal timescale UTC (Coordinated Universal Time) based on atomic clock time has been developed to ensure synchronization. UTC atomic clock signals can be received by network time servers, often referred to as NTP Servers, that can synchronize computer networks to within a few milliseconds of UTC.

Benefits of Accurate Network Time Synchronization

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Your computer probably does hundreds and thousands of tasks a day. If that is part of a network then the number of tasks could be millions. From sending emails to saving data, and everything else your computer is tasked to do, they are all logged by the computer or server.

Computers use timestamps to logo processes and indeed, timestamps are used as the only method a computer has to indicate when and if a task or application has been conducted. Timestamps are normally a 16 or 32 bit integer (one long number) that counts back the seconds from a prime epoch – normally 01 January 1970.

So for every task you computer does it will be stamped with the number of seconds from 1970 that the transaction was conducted. These timestamps are the only piece of information a computer system has to ascertain what tasks have been completed and what tasks have yet to be instigated.

The problem with computer networks of more than one machine is that the clocks on individual devices are not accurate enough for many modern time sensitive applications. Computer clocks are prone to drift they are typically based on inexpensive crystal oscillator circuits and can often drift by over a second a day.

This may not seem much but in today’s time sensitive world a second can be a long time indeed especially when you take into account the needs of industries like the stock exchange where a second can be the difference in price of several percent or online seat reservation, where a second can make the difference between an available seat and one that is sold.

This drift is also accumulative so within only a few months the computer systems could be over a minute out of sync and this can have dramatic effects on time sensitive transactions and can result in all sorts of unexpected problems from emails not arriving as a computer thinks they have arrived before they have been sent to data not being backed up or lost completely.

A NTP time server or network time server are increasingly becoming crucial pieces of equipment for the modern computer network. They receive an accurate source of time from an atomic clock and distribute it to all devices on the network. As atomic clocks are incredibly accurate (they won’t drift by a second even in a 100,000 years) and the protocol NTP (Network Time Protocol) continually checks the devices time against the master atomic clock time – it means the computer network will be able to run perfectly synchronised with each device within a few milliseconds of the atomic clock.

Life Without the Atomic Clock

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When we consider the most important inventions of the last 100 years, very few people will think of an atomic clock. In fact, if you ask somebody to come up with a top ten of inventions and innovations its doubtful if the atomic clock would figure at all.

Its probably not hard to imagine what people think of as the most life-changing inventions: the Internet, mobile phones, satellite navigation systems, media players etc.

However, nearly all theses technologies rely on accurate and precise time and they would not function without it. The atomic clocks lies at the heart of many of the modern innovations, technologies and applications associated with them.

Let’s take the Internet as an example. The Internet is, in its simplest form, a global network of computers, and this network spans time zones and countries. Now consider some of the things we use the Internet for: online auctions, Internet banking or seat reservation for example. These transactions could not be possible with precise and accurate time and synchronisation.

Imagine booking a seat on an airline at 10am and then another customer tries to book the same seat after you on a computer with a slower clock. The computer only has the time to go on so will consider the person who booked after you to have been the first customer because the clock says so! This is the reason any Internet network that requires time sensitive transactions is connected to a NTP server to receive and distribute an atomic clock time signal.

And for other technologies the atomic clock is even more crucial. Satellite navigation (GPS) is a prime example. GPS (Global Positioning System) works by triangulating atomic clock signals from satellites. Because of the high velocity of radio waves an inaccuracy of 1 second could see a sat-nav device out by 100,000 km.

Other technologies too from mobile phone networks to air traffic control systems are completely reliable on atomic clocks demonstrating how underrated this technology is.

Parking Tickets and the NTP Server

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There is nothing worse than returning to your car only to discover that your parking meter time limit has expired and you’ve got a parking ticket slapped on to your windscreen.

More-often-than-not it’s only a matter of being a couple of minutes late before an over eager parking attendant spots your expired meter or ticket and issues you a fine.

However, as the people of Chicago are discovering, whilst a minute may be the difference between getting back to the car in time or receiving a ticket, a minute may also be the difference between different parking meters.

It seems the clocks on the 3000 new parking meter pay boxes in Cale, Chicago have been discovered to be unsynchronized. In fact, of the nearly 60 pay boxes observed, most are off at least a minute and in some cases, nearly 2 minutes from what is “actual” time.

This has posed a headache to the firm in charge of parking in the Cale district and they could face legal challenges from the thousands of motorists that have been given tickets from these machine.

The problem with the Cale parking system is that while they claim they regularly calibrate their machine there is no accurate synchronization to a common time reference. In most modern applications UTC (Coordinated Universal Time) is used as a base timescale and to synchronize devices, like Cale’s parking meters, a NTP server, linked to an atomic clock will receive UTC time and ensure every device has the exact time.

NTP servers are used in the calibration of not just parking meters but also traffic lights, air traffic control and the entire banking system to name but a few applications and can synchronize every device connected to it to within a few milliseconds of UTC.

It’s a shame Cale’s parking attendants didn’t see the value of of a dedicated NTP time server – I’m sure they are regretting not having one now.

Which time signal? GPS or WWVB and MSF

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Dedicated NTP time server devices are the easiest, most accurate, reliable and secure method of receiving a source of UTC time (Coordinated Universal Time) for synchronizing a computer network.

NTP servers (Network Time Protocol) operate outside the firewall and are not reliant on the Internet which means they are highly secure and not vulnerable to malicious users who, in the case of Internet time sources can use the NTP client signals as a method of accessing the network or penetrating the firewall.

A dedicated NTP server will also receive it’s time code direct from an atomic clock, this makes it a stratum 1 time server as opposed to online time servers which are stratum 2 time servers, that is they get the time from a stratum 1 server and so are not as accurate.

In using a NTP time server there is only really one decision to make and that is how the time signal is to be received and for this there is only two choices:

The first is to make use of the time standard radio transmissions broadcast by national physics laboratories such as NIST in the USA or the UK’s NPL. These signals (WWVB in the US, MSF in the UK) are limited in range although the USA signal is available in most parts of Canada and Alaska. However, they are vulnerable to local interference and topography as other long wave radio signals are.

The alternative to the WWVB/MSF signal is to utilise the GPS satellite network (Global Positioning System). Atomic clocks are used by GPS satellites as the basis for navigational information used by satellite receivers. These atomic clocks can be used by using a NTP time server fitted with a GPS antenna.

Whilst the GPS time signal is strictly speaking not UTC- it is 17 seconds behind as leap seconds have never been added to GPS time (as the satellites are unreachable) but NTP can account for this (by simply adding 17 whole seconds). The advantage of GPS is that it is available anywhere on the planet just as long as the GPS antenna has a clear view of the sky.

Duel systems that can utilise both types of signal are also available.

Using Atomic Clocks to Synchronize a Network

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Most computer networks have to be synchronized to some degree. Allowing the clocks on computers across a network to all be telling different times is really asking for trouble. All sorts of errors can occur such as emails not arriving, data getting lost, and errors get unnoticed as the machines struggle to makes sense of the paradoxes that unsynchronized time can cause.

The problem is computers use time in the form of timestamps as the only point of reference between different events. If these don’t match then computers struggle to establish not only the order of events but also if the events took place at all.

Synchronizing a computer network
together is extremely simple, thanks largely to the protocol NTP (Network Time Protocol). NTP is installed on most computer operating systems including Windows and most versions of Linux.

NTP uses a single time source and ensures that every device on the network is synchronized to that time. For many networks this single time source can be anything from the IT manager’s wrist watch to the clock on one of the desktop machines.

However, for networks that have to communicate with other networks, have to deal with time sensitive transactions or where high levels of security are required then synchronization to a UTC source is a must.

Coordinated Universal Time (UTC) is a global timescale used by industry all over the world. It is governed by a constellation of atomic clocks making it highly accurate (modern atomic clocks can keep time for 100 million years without losing a second).

For secure synchronization to UTC there is really only one method and that is to use a dedicated NTP time server. Online NTP servers are used by some network administrators but they are taking a risk not only with the accuracy of the synchronization but also with security as malicious users can imitate the NTP time signal and penetrate the firewall.

As dedicated NTP servers are external to the firewall, relying instead on the GPS satellite signal or specialist radio transmissions they are far more secure.

The Sat Nav How it Works

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The ‘sat-nav’ has revolutionised the way we travel. From taxi drivers, couriers and the family car to airliners and tanks, satellite navigation devices are now fitted in almost every vehicle as it comes off the production line. While GPS systems certainly have their flaws, they have several uses too. Navigation is just one of the main uses of GPS but it is also employed as a source of time for GPS NTP time servers.

Being able to pin point locations from space has saved countless lives as well as making travelling to unfamiliar destinations trouble free. Satellite navigation relies on a constellation of satellites known as GNSS (Global Navigational Satellite Systems). Currently there is only one fully functioning GNSS in the world which is the Global Positioning System (GPS).

GPS is owned and run by the US military. The satellites broadcast two signals, one for the American military and one for civilian use. Originally, GPS was meant solely for the US armed forces but following an accidental shooting down of an airliner, the then President of the US Ronald Reagan opened the GPS system to the world’s population to prevent future tragedies.

GPS has a constellation of over 30 satellites. At any one time at least four of these satellites are overhead, which is the minimum number required for accurate navigation.

The GPS satellites each have onboard an atomic clock. Atomic clocks use the resonance of an atom (the vibration or frequency at particular energy states) which makes them highly accurate, not losing as much as a second in time over a million years. This incredible precision is what makes satellite navigation possible.

The satellites broadcast a signal from the onboard clock. This signal consists of the time and the position of the satellite. This signal is beamed back to earth where your car’s sat nav retrieves it. By working out how long this signal took to reach the car and triangulating four of these signals the computer in your GPS system will work out exactly where you are on the face of the world.  (Four signals are used because of elevation changes – on a ‘flat’ earth only three would be required).

GPS systems
can only work because of the highly precise accuracy of the atomic clocks. Because the signals are broadcast at the speed of light and accuracy of even a millisecond (a thousandth of a second) could alter the positioning calculations by 100 kilometres as light can travel nearly 100,00km each and every second –currently GPS systems are accurate to about five metres.

The atomic clocks onboard GPS systems are not just used for navigation either. Because atomic clocks are so accurate GPS makes a good source of time. NTP time servers use GPS signals to synchronize computers networks to. A NTP GPS server will receive the time signal from the GPS satellite then convert it to UTC (Coordinated Universal Time) and distribute it to all devices on a network providing highly accurate time synchronization.

Do I Really Need an NTP Time Server?

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The NTP time server is a much misunderstood piece of equipment. They are quite simple devices in the sense that they are used for the purposes of time synchronisation, receiving an external source of the time which is then distributed throughout a computer network using NTP (Network Time Protocol).

However, with a myriad of ‘free’ time servers available on the internet many network administrators take the decision that NTP time servers are not necessary pieces of equipment and that their network can do without it. However, there are a huge number of pitfalls in relying on the internet as a time reference; Microsoft and the USA physics laboratory NIST (National Institute of Standards and Time) highly recommend external NTP time servers rather than internet providers.

Here is what Microsoft says:
“We highly recommend that you configure the authoritative Time Server to gather the time from a hardware source. When you configure the authoritative Time Server to sync with an Internet time source, there is no authentication.”

Authentication is a security measure implemented by NTP to ensure that the time signal that is sent comes from where it claims to come from. In other words authentication is the first line of defence in protecting against malicious users. There are other security issues too with using the internet as a time source as any communication with an internet time source is going to require the TCP/IP port to be left open in the firewall this could also be manipulated by malicious users.

NIST too recognise the importance of NTP time server systems for prevention and detection of security threats in their Guide to Computer Security Log Management they suggest:
“Organizations should use time synchronization technologies such as Network Time Protocol (NTP) servers whenever possible to keep log sources’ clocks consistent with each other.”