Time server – Synchronisation Methods

A time server is an essential piece of equipment responsible for ensuring all devices on a computer network are running the same time. Most time servers are dedicated devices that receive a time signal, normally UTC (Coordinated Universal Time), and distribute it to all devices on a network.

Most time servers use the Internet protocol NTP (Network Time Protocol) to synchronise all devices and are often referred to as NTP servers. NTP distributes a single time source throughout the network which is normally a UTC source (Coordinated Universal Time).

There are several places a time server can receive a time signal from. The internet is an obvious source for many although online time sources are not very accurate, can be too far away to give any useful precision, and more importantly are not secure being as they are external to the firewall.

As a dedicated time server is an external device they are extremely secure and impossible for malicious users to tamper with. Dedicated time server can receive a time signal from two sources the GPS network (Global Positioning System) , a highly accurate method and available everywhere on the globe with a good view of the sky; or the specialist long wave radio transmissions broadcast by national physics laboratories.

In Europe the two main radio transmissions are the UK’s MSF signal broadcast by NPL (National Physical Laboratory) in Cumbria, England and the German DCF-77 broadcast near Frankfurt.

These long wave signals are also highly accurate and can be picked up in most neighbouring countries too. The USA has a similar system called WWVB,  transmitted by the National Institute for Standards and Technology (NIST) from Boulder, Colorado.

Time Servers and NTP

Time servers are incredibly important but an often overlooked part of a computer network. They are essential devices ensuring that all computers and devices connected to the network are synchronised to the same time. This prevents any problems from occurring when networks run sporadic time such as emails arriving before they were sent or even more serious security issues.

Time servers are similar to other servers but their sole role is to receive the time from a trusted source and distribute it amongst the network. The network time server can receive this time source from several places but in doing so one must have in mind two questions: How accurate is the time reference supplying the time? And how secure is it?

There are two highly accurate and completely secure methods of receiving the time for a time server. Both methods supply UTC (Coordinated Universal Time) which is a global timescale maintained by highly accurate atomic clocks. The first is to utilise the Global Positioning System (GPS) whose satellites all have onboard an atomic clock or the second is to use the national physics’ laboratories time and frequency transmissions.

Once a timing reference is received it is distributed to machines on a network using the protocol NTP (Network Time Protocol). NTP is based on an algorithm that not only corrects the time on any device but also ensures that the UTC time being received is secure, stable and precise.

NTP is one of the oldest Internet based protocols having been around since the 1980’s yet it is a testament to its developers that over twenty years on it is not only still in use but is by far the most common time protocol in use.

Time Server and Atomic Clocks

A time server is an integral part of any network system. It ensures all machines on a network or keeping the exact same time, failure to do so could lead to all sorts of problems, particularly with time sensitive transactions.

Most computer networks are synchronised to UTC (coordinated Universal Time). UTC is a global time scale and used throughout the world. It is also highly precise as it is based on the time told by atomic clocks.

Atomic clocks are ideal sources of time as they do not drift whilst the standard electrical oscillators on our PC clocks can drift by a second every week. This drift can cause untold problems which is why most networks are synchronised to a time server that receives a time signal from an atomic clock.

Atomic clock time signals can be received from a myriad of sources. The Internet is an obvious choice but unless security and precision is not an issue then it is not recommended for any commercial networks as using an Internet times source can leave a system open to security threats.

For security and accuracy there are two options to synchronise to an atomic clock. One is to use a GPS time server that receives the time-code from the GPS system. The other method is to use a time server that can receive the long wave radio transmissions broadcast from several national physics laboratories.

Time Server Information – Sources of Radio UTC Time

Physics laboratories across the globe transmit UTC (Coordinated Universal Time) radio broadcasts that can be received using a radio referenced time server. These time signals are an accurate and secure method of receiving UTC time.

Whilst many of these signals only have a limited range and are only available for certain periods several most notably the USA’s WWVB, Germany’s DCF and the UK’s MSF signals -provide a continuous and widespread broadcast that can be received 24 hours a day and even in neighbouring countries.

Here is alist of many of the World’s radio time server signals:

Frequency (MHz)	Callsign	Location	Comments/Broadcast Time
0.0205	RAB99	Khabarovsk, Russia	02:06-02:47 and 06:06-06:47 UTC, 01:06-01:47 and 05:06-05:47 UTC summer
0.0205	RJH69	Maladziecna, Belarus	07:06-07:47 UTC, 06:06-06:47 UTC summer
0.0205	RJH77	Arkhangelsk, Russia	09:06-09:47 UTC, 08:06-08:47 UTC summer
0.0205	RJH99	N. Novgorod, Russia	05:06-05:47 UTC, 04:06-04:47 UTC summer
0.0230	RAB99	Khabarovsk, Russia	02:06-02:47 and 06:06-06:47 UTC, 01:06-01:47 and 05:06-05:47 UTC summer
0.0230	RJH69	Maladziecna, Belarus	07:06-07:47 UTC, 06:06-06:47 UTC summer
0.0230	RJH77	Arkhangelsk, Russia	09:06-09:47 UTC, 08:06-08:47 UTC summer
0.0230	RJH99	N. Novgorod, Russia	05:06-05:47 UTC, 04:06-04:47 UTC summer
0.0250	RAB99	Khabarovsk, Russia	02:06-02:47 and 06:06-06:47 UTC, 01:06-01:47 and 05:06-05:47 UTC summer
0.0250	RJH66	Bishkek, Kyrgyzstan	04:06-04:47, 10:06-10:47 UTC
0.0250	RJH69	Maladziecna, Belarus	07:06-07:47 UTC, 06:06-06:47 UTC summer
0.0250	RJH77	Arkhangelsk, Russia	09:06-09:47 UTC, 08:06-08:47 UTC summer
0.0250	RJH99	N. Novgorod, Russia	05:06-05:47 UTC, 04:06-04:47 UTC summer
0.0251	RAB99	Khabarovsk, Russia	02:06-02:47 and 06:06-06:47 UTC, 01:06-01:47 and 05:06-05:47 UTC summer
0.0251	RJH69	Maladziecna, Belarus	07:06-07:47 UTC, 06:06-06:47 UTC summer
0.0251	RJH77	Arkhangelsk, Russia	09:06-09:47 UTC, 08:06-08:47 UTC summer
0.0251	RJH99	N. Novgorod, Russia	05:06-05:47 UTC, 04:06-04:47 UTC summer
0.0255	RAB99	Khabarovsk, Russia	02:06-02:47 and 06:06-06:47 UTC, 01:06-01:47 and 05:06-05:47 UTC summer
0.0255	RJH69	Maladziecna, Belarus	07:06-07:47 UTC, 06:06-06:47 UTC summer
0.0255	RJH77	Arkhangelsk, Russia	09:06-09:47 UTC, 08:06-08:47 UTC summer
0.0255	RJH99	N. Novgorod, Russia	05:06-05:47 UTC, 04:06-04:47 UTC summer
0.0400	JJY	Ohtakadoyayama, Japan	Continuous
0.0600	JJY	Haganeyama, Japan	Continuous
0.0600	MSF	Rugby, UK	Continuous
0.0600	WWVB	Fort Collins, Colorado, USA	Continuous
0.0666	RBU	Moscow, Russia	Continuous
0.0750	HBG	Prangins, Switzerland	Continuous
0.0775	DCF77	Mainflingen, Germany	Continuous
0.1620	—	Allouis, France	Continuous
1.5100	HD2IOA	Guayaquil, Ecuador	Continuous
2.5000	BPM	Linshan, China	09:00-01:00 UTC
2.5000	WWV	Fort Collins, Colorado, USA	Continuous
2.5000	WWVH	Kekaha, Hawaii, USA	Continuous
3.3300	CHU	Ottawa, Canada	Continuous
3.8100	HD2IOA	Guayaquil, Ecuador	19:00-07:00 UTC
4.9960	RWM	Moscow, Russia	Continuous
4.9980	EBC	Cadiz, Spain	10:00-11:00 UTC Monday-Friday
5.0000	BPM	Linshan, China	Continuous
5.0000	BSF	Chungli, Taiwan	Continuous
5.0000	HD2IOA	Guayaquil, Ecuador	12:00-13:00 UTC
5.0000	HLA	Daejeon, South Korea	Continuous
5.0000	LOL	Buenos Aires, Argentina	11:00-12:00, 14:00-15:00, 17:00-18:00, 20:00-21:00, 23:00-24:00 UTC
5.0000	WWV	Fort Collins, Colorado, USA	Continuous
5.0000	WWVH	Kekaha, Hawaii, USA	Continuous
5.0000	YVTO	Caracas, Venezuela	Continuous
7.3350	CHU	Ottawa, Canada	Continuous
7.6000	HD2IOA	Guayaqil, Ecuador	13:00-24:00 UTC
9.9960	RWM	Moscow, Russia	Continuous
10.0000	BPM	Linshan, China	Continuous
10.0000	LOL	Buenos Aires, Argentina	11:00-12:00, 14:00-15:00, 17:00-18:00, 20:00-21:00, 23:00-24:00 UTC
10.0000	WWV	Fort Collins, Colorado, USA	Continuous
10.0000	WWVH	Kekaha, Hawaii, USA	Continuous
14.6700	CHU	Ottawa, Canada	Continuous
14.9960	RWM	Moscow, Russia	Continuous
15.0000	BPM	Linshan, China	01:00-09:00 UTC
15.0000	BSF	Chungli, Taiwan	Continuous
15.0000	WWV	Fort Collins, Colorado, USA	Continuous
15.0000	WWVH	Kekaha, Hawaii, USA	Continuous
15.0060	EBC	Cadiz, Spain	10:00-11:00 UTC Monday-Friday
20.0000	WWV	Fort Collins, Colorado, USA	Continuous

Table courtesy of the World Radio and TV Handbook.