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) .

The importance of time synchronisation in the modern world

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Time has always played an important part in civilisation. Understanding and monitoring time has been one of the pre-occupations of mankind since prehistory and the ability to keep track of time was as important to the ancients as it is to us.

Our ancestors needed to know when the best time was to plant crops or when to gather for religious celebrations and knowing the time means making sure it is the same as everyone else’s.

Time synchronization is the key to accurate time keeping as arranging an event at a particular time is only worthwhile if everybody is running at the same time. In the modern world, as business has moved from a paper-based system to an electronic one, the importance of time synchronisation and the search for ever better accuracy is even more crucial.

Computer networks are now communicating with each other from across the globe conducting billions of dollars worth of transactions every second, millisecond accuracy is now part of business success.

Computer networks can be comprised of hundreds and thousands of computers, servers and routers and while they all have an internal clock, unless they are synchronised perfectly together a myriad of potential problems could occur.

Security breaches, data loss, frequent crashes and breakdowns, fraud and customer credibility are all potential hazards of poor computer time synchronisation. Computers rely on time as the only point of reference between events and many applications and processes are time dependent.

Even discrepancies of a few milliseconds between devices can cause problems particularly in the world of global finance where millions are gained or lost in a second. For this reason most computer networks are controlled by a time server. These devices receive a time signal from an atomic clock. This signal is then distributed to every device on the network, ensuring that all machines have the identical time.

Most synchronisation devices are controlled by the computer program NTP (Network Time Protocol). This software regularly checks each device’s clock for drift (slowing or accelerating from the desired time) and corrects it ensuring the devices never waver from the synchronised time.

The MSF Time Signal

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The MSF time signal is a dedicated radio broadcast providing an accurate and reliable source of UK civil time, based on the global time scale UTC (Coordinated Universal Time), the MSF signal is broadcast and maintained by the UK’s National Physical Laboratory (NPL).

The MSF time signal can be utilised by anyone requiring accurate timing information its main use however 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 MSF signal is broadcast from Anthorn Radio station in Cumbria by VT communications under contract to the NPL.  It is available 24 hours a day across the whole of the UK and beyond, although the signal is vulnerable to interference and local topography. Users of the MSF 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 MSF 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 the radio station.

The antenna at Anthorn is at 54° 55′ N latitude, and 3° 15′ W longitude. The signal’s field strength exceeds 100 µV/m(micro volts a metre) at a distance of 1000 km from Anthorn, covering the whole of the UK, and can even be received throughout some of northern and western Europe.

The MSF transmits a simple binary code containing time and date information The MSF time and date code includes the following information: year, month, day of month,  day of week,  hour, minute, British Summer Time (in effect or imminent),  DUT1 (a parameter giving UT1-UTC)

Five Reasons Why You Should Never Use an Internet Timing Source

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Time synchronisation is now an integral part of network administration. Networks that are not synchronised to UTC time (Coordinated Universal Time) become isolated; unable to process time sensitive transactions or communicate securely with other networks.

UTC time has been developed to allow the entire globe to communicate under a single time-frame and it is based on the time told by atomic clocks.

To synchronise to UTC time many network administrators simply connect to an Internet timing source and assume they are receiving a secure source of UTC time. However, there are pitfalls to this and any network that requires security should NEVER use the Internet as a timing source:

1.    To use an internet timing source a port needs to be forwarded in the firewall. This ‘hole’ to allow the timing information to pass through can be utilised by anybody else too.
2.    NTP (Network Time Protocol) has an inbuilt security measure called authentication that ensures a timing source is exactly who it says it is, this can’t be utilised over the Internet.
3.    Internet timing sources are wholly inaccurate. A survey by Nelson Minar of MIT (Massachusetts  Institute of Technology) discovered less than half were close enough to UTC time to be described as reliable (some where minutes and even hours out!).
4.    Distance across the Internet can render even an extremely accurate Internet timing source useless as the distance to client could cause delay.
5.    A dedicated time server will use a radio of GPS timing signal which can be audited to guarantee its accuracy, providing security and legal protection; internet timing sources cannot.

Dedicated NTP time servers not only offer greater protection and security than Internet time sources. They also offer unbridled accuracy with both the GPS and time and frequency radio transmissions (such as MSF, DCF or WWVB) accurate to within a few milliseconds of UTC time.

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.

Time Server FAQ on British Time

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Time servers are used throughout UK industry. Many of which receive the MSF signal from the National Physical Laboratoruy in Cumbria. Here are some FAQ’s about British time and the MSF signal:

Who decides when clocks should go forward or back for summer time?

If you live in Europe, the time at which summer time begins and ends is given in the relevant EU Directive and UK Statutory Instrument as 1 a.m. Greenwich Mean Time (GMT).

Does ‘midnight’ belong to the day before or the day after?

The use of the word midnight is heavily dependent on its context but 00.00 (often called 12 am) is the start of the next day. There are no standards established for the meaning of 12 a.m. and 12 p.m. and often a 24 hour time is less confusing.

Is there an approved way to represent dates and times?

The standard notation for the date is the sequence YYYY-MM-DD or YY-MM-DD although in the USA it is the convention to have days and months the other way around.

When did the new millennium really begin?

A millennium is any period of a thousand years. So you could say that the next millennium begins now. The third millennium of the Christian Era began at the start of the year 2001 A.D.

How do you know atomic clocks keep better time?

If you look at several atomic clocks all set to the same time you’ll find that they still agree within ten millionths of a second after a week.

What is the accuracy of the ‘speaking clock’?

Even allowing for the delay in the telephone network, you can probably expect the starts of the seconds pips to be accurate seconds markers within about one-tenth of a second.

Why did my radio-controlled clock move to summer time at 2 a.m., one hour late?

Battery powered radio-controlled clocks typically check the time only every hour or two, or even less, This is to conserve the battery.

Why does my radio-controlled clock receive the MSF signal less well at night?

Users of the MSF 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.

Is there a permanent one-hour difference between MSF time and DCF-77 time?

Since 1995 October 22 there has been a permanent one-hour difference between British time (as broadcast by MSF) and Central European Time, as broadcast by DCF-77 in Germany.

What does MSF stand for?

MSF is the three-letter call sign used to designate the UK’s 60 kHz standard-frequency and time signal.

Thanks to the National Physical Laboratory for their help with this blog.

Time Server Manufacturers

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Time servers come in several shapes and sizes. The primary difference between most dedicated time servers is in the way they receive  a timing source.

Some time servers utilise national time and frequency transmissions that are broadcast on long wave while other use the GPS network.

Some time servers are designed to be rack-mountable perfect for the average U system of racks allowing the sever to be snugly fitted into your existing rack.

Other time servers are nothing more than small boxes that can be discretely hidden.

Here is a list of top time server manufacturers:

Galleon Systems

Elproma

Symmetricom

Meinberg

Time Tools

Next Generation of Atomic Clocks Accurate to a Second in 200 Million Years

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Atomic clocks have been around since the 1950’s. They have provided incredible accuracy in timekeeping with most modern atomic clocks not losing a second in time in a million years.

Thanks to atomic clocks many technologies have become possible and have changed the way we live our lives. Satellite communication, satellite navigation, internet shopping and network communication are only possible thanks to atomic clocks.

Atomic clocks are the basis for the world’s global timescale Universal Coordinated Time (UTC) and are the reference that many computer networks use as a time source to distribute amongst its devices using NTP (Network Time Protocol) and a time server.

Atomic clocks are based on the atom caesium -133. This element has been traditionally used in atomic clocks as its resonance or vibrations during a particular energy state, or extremely high (over 9 billion) and therefore can provide high levels of accuracy.

However, new types of atomic clocks are on the horizon that will boast even more accuracy with the next generation of atomic clocks neither gaining nor losing a second in 200 million years.

The next generation of atomic clocks no longer rely on the caesium atom but use elements such as mercury or strontium and instead of using microwaves such as the caesium clocks these new clocks use light which has higher frequencies.

Strontium’s resonance also exceeds over 430 trillion which is vastly superior to the 9.2 billion vibrations that caesium manages.

Currently atomic clocks can be utilised by computer systems by using either a radio or GPS clock or dedicated NTP time server. These devices can receive the time signal transmitted by atomic clocks and distribute them amongst network devices and computers.

However, the National Institute for Standards and Technology (NIST) have revealed a miniature atomic clock that measures just 1.5 millimetres on a side and about 4 millimetres tall. It  consumes less than 75 thousandths of a watt, and has a stability of about one part in 10 billion, equivalent to a clock that would neither gain nor lose more than a second in 300 years.

In the future these devices could be integrated into computer systems, replacing the current real time clock chips, which are notoriously inaccurate and can drift.

UTC Radio References from Around the World

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UTC (Coordinated Universal Time) is the global civil timescale used by millions of people, businesses and authorities across the globe. UTC is based on the time told by caesium atomic clocks. These clocks are the most reliably accurate chronometers on Earth, able to maintain accurate time for several millions of years whilst neither losing nor gaining a second.

Unfortunately caesium clocks are far too expensive and delicate pieces of machinery to make it practical for us all to have one but fortunately the time that they tell is transmitted by several countries. These nation’s national physics laboratories tend to broadcast the UTC time from these clocks by long-wave.

In the UK the 60 kHz transmission is broadcast by the National Physical Laboratory from a transmitter in Anthorn in Cumbria (it was based in Rugby until 2007). NPL constantly maintain the transmissions and assess its accuracy. Whilst the MSF signal is a British based transmission is possible to receive the signal in some parts of northern Europe and Scandinavia.

However, in mainland Europe, the strongest time and frequency signal is the German transmission broadcast from Frankfurt in Germany. This signal known as the DCF is controlled and maintained by the German National Physics Laboratory. While Switzerland also has its own time and frequency signal, the German DCF signal is by far the most widely used in Europe.

In the USA a similar system is maintained by NIST (National Institute for Standards and Time) and is broadcast from Fort Collins, Colorado. This signal is known as WWVB and is available in most parts of Northern America (including Canada).

Japan maintains its own timing broadcast (JJY) also which is popular in the south pacific and several other countries (such as France) maintain their own signals too although these tend to have only minor coverage.

All these times signals operate in a similar fashion. The strength of the signal is either reduced by between 6 and 10 dB or switched off for a specific amount of time before being restored at the start of each second. The amount of time the signal is reduced indicates a stream of binary numbers with positioning markers.
The signals operate on a 60 kHz frequency and carry a time and date code which relays the following information in binary format: Year, month, day of month,  day of week,  hour,  minute,  DUT1 (the difference between UTC and UT1 which is based on the Earths rotation). The signals also relay information about local time such as British Summer Time.