MSF Outage 11 December No MSF signal
| By Richard N Williams
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Posts by: Richard N Williams
Arranging a NTP Server Stratum Tree
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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
| By Richard N Williams
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.
