The NTP Server and Accurate Time

Accurate time on a network is essential for all businesses and institutions. Without an accurately synchronised system a computer network can be vulnerable to all sorts of problems, from malicious hackers and other security threats to fraud and data loss.

Network Time Protocol is the key to keeping accurate time it is a software algorithm that has been constantly developed for over two decades. NTP takes a single time source that is received by the NTP server and distributes it across a network ensuring all machines in that network are running to exact same time.

Whilst NTP can maintain synchronisation of a network to within a few milliseconds it is only as good as the time source it receives. A dedicated NTP server will use a time signal from an external source and so keep the network secure as the firewall will not have to be disturbed.

The two preferred methods for most users of NTP servers is the GPS network (Global Positioning System) or specialist time and frequency transmissions put out be several national physics labs such as the UK’s NPL.

These time signals are UTC (Coordinated Universal Time) which is the world’s civil timescale. A NTP server receiving time source from either a frequency transmission or the GPS network can realistically provide accuracy to within a few milliseconds of UTC

The NTP Server – Selecting a Time Source Check List

In selecting a timing source to synchronise a computer network to using a NTP server (Network Time Protocol) it is important that the time source is accurate, secure and a source of UTC (Coordinated Universal Time). UTC is a global timescale used by computer networks, business and commerce across the globe.

Whilst UTC is freely available across the Internet it is neither accurate nor secure (being as it is external to your firewall).  Also Internet time sources cannot be authenticated which is NTP’s own method of ensuring a time source is what it says it is. There are two secure, accurate and reliable methods for receiving UTC via a NTP server and both come with their own advantages and drawbacks.

The first method is to use the GPS network (Global Positioning System).The main advantage of using the signals transmitted from a GPS satellite’s onboard atomic clock is that a signal is available anywhere on the planet. However it does come with a downside. As the signals are all line-of-sight it means that the GPS antenna needs to be placed on a roof to ensure connectivity with a satellite.

An alternative to the GPS signal but equally as accurate and reliable is to make use of the long wave radio transmissions broadcast by several national physics laboratories. These signals, such as the UK’s MSF, Germany’s DCF-77 and the United States’ WWVB transmissions, can often be picked up inside buildings making them ideal for a solution if a rooftop is unavailable for a GPS antenna. It must be noted that not every country broadcasts such a signal and whilst most transmissions can be picked up in neighbouring countries the signals are vulnerable to interference and local geography.

MSF signal interruption – Notice from the National Physical Laboratory

For users of MSF time server or other NTP related devices:

Notice of Interruption MSF 60 kHz Time and Frequency Signal – NPL
The MSF 60 kHz time and frequency signal broadcast from Anthorn Radio Station will be shut down over the period:

11 December 2008 – from 10:00 UTC to 14:00 UTC

The interruption to the transmission is required to allow scheduled maintenance work to be carried out in safety.

If you require any additional information, please contact NPL

Or alternatively please see the NPL time website.

Free NTP server checker – available for download

Galleon’s free NTP Server Checker allows you to check the following items
* IP address – the time server you are checking.
* NTP Version
* Reference timestamp (the prime epoch ) used by NTP to work out the time from this set point
* Round trip delay (the time it takes request to arrive and come back in milliseconds)
* Local clock offset – time difference between host and client
* Leap indicator (if there is to be a leap second that day – normally only on 31 December)
* Mode 3 – indicates a client request
* Stratum level – which stratum level the NTP server is (a stratum 1 server receives the time from an atomic clock source a stratum 2 server receives the time from a stratum 1 server)
* Poll Interval (Will be 1 as only 1 requests is made by the SNTP client)
* Precision – how accurate in milliseconds
* Root Delay – This is a signed fixed-point number indicating the total roundtrip delay to the primary reference source at the root
* Root dispersion (in milliseconds)- The root dispersion is the maximum (worst case) difference between the local system clock and the root of the NTP tree (stratum 1 clock)
* Ref ID – the host name
* Originate time stamp (time before synchronisation request)
* Receive timestamp – the time the host got request
* Transmit timestamp – the time the host sends back to us
* Is response valid – synchronised or not

Please download from Galleon Systems

NTP Server – Using Stratum

NTP (Network Time Protocol) is the most prevalent time synchronisation software available. On of the reasons NTP is so successful is the way it organises its clients into a hierarchy.

The hierarchy of NTP is divided into stratum with each strata representing the distance from the original reference clock.  For instance an atomic clock that generates a UTC (coordinated universal time) signal is referred to as a stratum 0 device.

A NTP server that receives a stratum  1 time signal is referred to as a stratum 1 device and a device that receives a time source from a NTP server is a stratum 2 device. NTP can support up to 16 strata although the further away from the reference clock you get (stratum 0) the less accurate the device will be.

However, by arranging the network into stratum and allowing stratum 2 devices to pass on the time to a stratum 3 device (and so on) it reduced the demand on the NTP server and the network. By using a stratum based network, realistically thousands of machines can be synchronised to just one NTP server.

NTP Server –Telling the NTP Time

Network Time Protocol (NTP) is an Internet based protocol designed to distribute and synchronise time across a network.

NTP is in fact one of the oldest Internet protocols having been developed in the late 1980’s at Delaware University when the Internet was still in its infancy. It was devised by Professor David Mills and his team when they realised the need for accurate time synchronisation if computers were needed to communicate with each other.

A NTP server is a dedicated device that receives a single timing source and then distributes it amongst all network devices. A NTP server will receive the timing information through a number of ways but normally it is a UTC source (coordinated universal time) a global timescale based on the time as told by atomic clocks.

NTP handles the time in a different way to how humans perceive and deal with it. While we may split a time into seconds, minutes, hours, days, months and years; NTP regards time  as a single number which is the number of seconds since the ‘prime epoch’.

The prime epoch is a date set for when NTP began counting seconds. For NTP the prime Epoch is 00.01 on 1 January 1900 so that means on 1 January 2008 the time according to NTP will be 3405888000, which is the number of seconds since 1900.

The NTP Server – Trust in Time

Time synchronisation is vital for the modern computer network particularly when computer networks across the globe need to communicate with each other.

A lack of synchronisation would make impossible many online activities such as Internet auctions, seat reservation and trading in stocks and shares. It can also leave a system open to security threats and even fraud.

The NTP server (Network Time Protocol) can provide the most secure and accurate method of synchronising a network.  Many NTP servers are rack-mountable devices that can connect to a network and distributes time information between all devices on that system.

They work by using a single time reference, most commonly a source of UTC (Coordinated Universal Time), which NTP then checks all the system clocks to ensure all devices are keeping the same time. When it finds a computer or device that is drifting it advances or retreats the system clock until it matches UTC.

A NTP server will receive a timing source from either across the Internet (although not very secure or accurate), a specialist long-wave radio transmission or from the GPS network (global positioning system).

By utilising dedicated NTP server, not only can all devices on a network be synchronised together but also by using UTC the network will be synchronised with millions of computer networks all over the world.

What is a NTP server?

A NTP server is really just a time server that utilises Network Time Protocol (NTP). Whilst other time protocols do exist, NTP is by far the most commonly used and is utilised in over ninety percent of time servers.

NTP server and time server are therefore interchangeable terms but describe the same thing: a device used to receive and distribute a timing signal.

The timing signal utilised by most NTP servers is a UTC time source. UTC (Coordinated Universal Time) is a global time scale based on the time told by atomic clocks. By utilising UTC a NTP server can in affect, synchronise a network to the same time as millions of other computer networks from around the world. This has made possible many online global transactions that just simply wouldn’t be possible without UTC.

The timing signal is received by the NTP server (or time server) via a number of ways; the Internet, national time and frequency transmission (long wave) or the GPS (global positioning system) network. Once received the time server (NTP server) checks the authenticity of this signal (except from Internet sources where authentication is not possible), evaluates its accuracy then distributes it amongst the network.

To prevent a possible overload of time requests to the time server, machines that receive a time signal from the NTP server, can themselves be used as a time reference and the machines that receive a time signal from those can again be used as a reference. This hierarchy is called stratum levels. A NTP server is a stratum 1 device, a machine that receives a signal directly from the time server is a stratum 2 device and if a machine receives a signal from that it becomes stratum 3.

The NTP Server – a Beginners Guide

Computer networking is one of the most difficult aspects of information and communications technology (ICT). The logistics of connecting terminals, routers, printers and all the other devices can leave many administrators with a constant headache.
One of the most important aspects that often gets overlooked and can have disastrous consequences is that of time synchronization.

It is imperative that all devices on a network are telling the same time as timestamps, the format a computer relays time to each other, are the only form of reference a computer can use to establish a sequence of events. If different machines on a network are telling different times then unforeseen consequences such as emails arriving before they have technically been sent and other anomalies will make the administrator’s headache even worse.

What’s more a computer network that is not synchronized is open to security threats and even fraud. Fortunately the NTP time server has been around for many years and can ease the headache of time synchronization .

NTP (Network Time Protocol) is one of the oldest protocols used by computer networks. Developed nearly three decades ago NTP is a protocol that checks the time on all devices on network and adds or subtracts enough time to ensure they are all synchronized.

NTP requires a time reference to synchronise the network’s clocks to. Whilst NTP can synchronize a network to any time an authoritative time source is obviously the best solution. UTC (Coordinated Universal Time) is a globally used timescale based on the time told by atomic clocks. As atomic clocks lose less than a second of time in over a thousand years, UTC is by far the best timing source to synchronize a network to. Not only will your network be perfectly synchronized together but also your network will be synchronized to the same time as millions of computer networks all from around the world.

A NTP server can receive a UTC time reference from several sources. The Internet is the most obvious source, however Internet timing sources are notoriously inaccurate and those that are not can be relatively useless if the distance is too far away. Also having placed your NTP server securely behind your firewall it does seem pointless to have to keep a hole open in it to allow the NTP server to poll the timing reference from across the web and leave the entire network vulnerable, particularly as NTP authentication (NTP’s own security measure) is not possible over the Internet.

There are two far more secure and accurate methods of receiving a UTC timing reference. The first is to utilise the national time and frequency transmissions that several countries broadcast from their national physics laboratories. These are usually broadcast via long wave which has an advantage of being able to be picked up inside a server room although many countries do not have such a signal.

However, many NTP servers can utilize the timing signal broadcast by the onboard atomic clocks of the GPS (Global Positioning System) satellites.  This signal is available everywhere but a GPS antenna is required that can get a clear view of the sky.

By utilizing a UTC timing source either through the GPS network of radio transmission a computer network can be synchronized to within a few milliseconds of UTC time.

NTP Server and the Atomic Clock

Many network administrators boast that there networks are perfectly synchronised because they have an atomic clock as an NTP server. In actual fact as atomic clocks cost several millions of pounds and are quite vast in size it is doubtful the average server room contains such a timepiece.

What in fact they are referring to is that they have an NTP server that receives a timing source from an atomic clock. However, just because atomic clocks are the most accurate chronometers in the world, accurate to a few nanoseconds (billionth of a second) it doesn’t necessarily mean that a network using one as a timing source is receiving the same sort of accuracy

Atomic clocks work on the principle that certain atoms (in most atomic clocks the caesium -133 atom) oscillates at an exact frequency at certain energy levels. In the case of the caesium atom it resonates at exactly 9,192,631,770 every second.  Because of this exact resonance, atomic clocks lose less than a second in millions of years. In fact, the resonance of the caesium atom is so precise that the International System of Units has defined the second as exactly that number of oscillations of the caesium atom.

NTP servers can receive the time from an atomic clock through several sources. Obviously the Internet contains thousands of timing servers, some of which are hooked up to an atomic clock, others however, can be over ten seconds out of sync.

Furthermore, using an Internet timing source can leave a system open to abuse as the timing references cannot be authenticated. Also, the distance from a host, client and server can make dramatic differences in the accuracy.

The most accurate and effective way of receiving a timing source from an atomic clock is to use the national time and frequency broadcast that several country’s national physics laboratories transmit. Alternatively the American GPS (Global Positioning System) transmits the time from its own satellite’s atomic clocks. both methods can provide perfect synchronisation and accuracy to within a few milliseconds.