Archive for the 'network time' Category

NTP Server the German DCF 77 signal

The NTP server is a tool for keeping computer networks synchronised. Without adequate synchronisation networks can be left vulnerable to security threats, data loss, fraud and may find it impossible to interact with other networks across the globe.

Computer networks are normally synchronised to the global timescale UTC (Coordinated Universal Time) enabling them to communicate effectively with other networks also running UTC.

In Europe there are several methods of receiving UTC time. The Internet is an obvious choice but as these time signals are external to the network firewall they can prove a security risk. Internet time sources can also be unreliable in their precision or too far away to make any useful synchronisation.

The GPS network is available everywhere on the planet as long as there is a good clear view of the sky and many NTP server devices are designed to receive such a signal.

In Europe there is another alternative, however, to provide accurate and reliable time. The National Physics Laboratory near Frankfurt, Germany broadcast a long wave frequency time signal based on a constellation of atomic clocks. This time signal is known as the DCF-77 signal and is available across much of Europe (as far as Portugal during the evening).

DCF 77 is an reliable and secure method of receiving UTC and as it is derived from a constellation for atomic clocks is highly accurate.  A NTP server received a DCF time signal can provide accuracy to within a few milliseconds of UTC.


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 – common acronyms explained:

NTP – Network Time Protocol

SNTP – Simple Network Time Protocol

GPS – Global Positioning System

UTC – Coordinated Universal Time

MSF – Radio Time Signal for United Kingdom

WWVB – Radio Time Signal for American

DCF – Radio Time Signal for Germany

LAN – Local Area Network

UDP – User Datagram Protocol

TCP – Transmission Control Protocol

IP – Internet Protocol

TDF – Radio Time Signal for France

CHU – Radio Time Signal for Canada

JJY – Radio Time Signal for Japan

HBG – Radio Time Signal for Switzerland

USB – Universal Serial Bus

RTC – Real Time Clock

AM – Amplitude Modulation

APM – Automatic Power Management

DES – Data Encryption Standard

ESD – Electrostatic Discharge

FM – Frequency Modulation

IETF – Internet Engineering Task Force

IRIG – Inter-Range Instrumentation Group

MD5 – Message Digest

PPM – Part Per Million

PPS – Pulse Per Second

RFC – Request For Comments

SA – Selective Availability

TAI – International Atomic Time

SI – International System of Units

Finding a Public NTP Server

A public NTP Server is a time server on the Internet that, as the name suggests, members of the public can use as a timing source. The best location on the Internet to find a list of public NTP servers is the home of NTP –

There are two lists of public NTP servers on, one for primary servers and one for secondary servers. Primary servers have up to several hundred clients each. However, many primary servers are ‘closed access’ meaning that only agreed clients can access them. This is because if there is too much traffic attempting to receive a timing source from a primary source then it will clog the network making the server useless.

Primary servers are known as a stratum 1 server in that they get their timing source direct from an atomic clock often using the GPS or national time and frequency transmissions. Secondary NTP servers tend to be stratum 2 time servers, that is a time server that receives its timing source from a stratum 1 server.

Most users that require a public NTP server will find that most primary servers are closed access and that they will have to use a secondary NTP server. When using a public NTP server it is important that access policies are adhered to as many institutions require on these servers for timing information.

The Radio Referenced NTP Server

Using a long wave time and frequency transmission is perhaps the simplest and most efficient way of receiving an accurate and secure UTC timing reference (coordinated universal time). Dedicated NTP servers are available that receive a time code this way and distribute the timing information to a network. Often these time servers are referred to as radio clocks, although this title is a little misleading.

The long wave transmissions are usually broadcast at 60 khz but are not available everywhere. Only certain countries have these broadcasts and most come from their country of origin’s national physics laboratory.

In the UK the signal is known as MSF as is broadcast by the NPL (National Physical Laboratory) in Cumbria. The USA signal, WWVB, is broadcast Near Fort Collins in Colorado while the signal in Germany is known as DCF and is broadcast near to Frankfurt. Other nations such as Switzerland, Japan and Finland also have their own signals.

These transmissions are not however, available everywhere. While in many neighbouring countries it is possible to receive one of these transmissions, the long-wave signal is finite in range and susceptible to interference from topography and other electrical devices

However, where they are available, these time and frequency signals make an ideal source for a NTP server to synchronise a network too making them a logical choice for securing 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.