Time Synchronisation

UTC – Coordinated Universal Time (from the French: Universel Temps Coordonné) is a global timescale based on Greenwich Meantime (GMT – from the Greenwich Meridian line where the sun is above at 12 noon). But accounts for the natural slowing of the Earth’s rotation. It is used globally in commerce, computer networks via a NTP server, air-traffic control and the World’s stock exchanges to name but a few of its applications.

UTC is really the only solution for time synchronisation needs. While it is just as possible to synchronise a computer network with an NTP server to a time other than UTC it is pointless. As UTC is utilised by computer networks all across the globe by using a UTC time source that means your network can synchronise with every other network in the world that is synchronised to UTC.

UTC is most commonly received from across the Internet, however, this can only be recommended for small network users where either accuracy or security is an issue. An Internet based UTC source is external to the firewall so will leave a potential hole for malicious users to exploit.

Two secure methods of receiving UTC are commonly available. These are either the GPS network (Global Positioning System) or specialist radio transmission broadcast on long wave from several of the world’s national physics laboratories. The two methods have both advantages and disadvantages which need to be ascertained before a method is selected.

A radio transmission such as the UK’s MSF, the German DCF-77 or the USA’s WWVB signal are vulnerable to local topography although many of these signals can be picked up indoors. Whilst not every country transmits a UTC radio signal around the neighbouring countries that do it is possible to still receive it.

GPS on the other hand is available literally anywhere on the globe. The signal comes directly from above and as long as the antenna has a good clear view of the sky it can be received anywhere. However, as the antenna has to be on a roof looking up this can have logistical problems (particularly for very tall buildings).

Specialist dedicated network time servers are available that can actually receive both methods of UTC but whether using GPS or a radio transmissions synchronisation of a network to within a few milliseconds is possible.

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.

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

The NTP server is an essential network tool. Whilst other protocols do exist, NTP is by far the standard time synchronisation protocol and is utilised in the majority of time servers.

A NTP server is reliant on a single time source it is this time reference that it uses to distribute amongst the network and synchronise to. This timing reference tends to be a UTC time source (coordinated universal time) which is a global time source based on the time told by atomic clocks.

There are only two viable options for receiving a UTC timing source. Although the Internet can be used, the signal can’t be authenticated this is a security measure used by NTP to ensure the reference is what it says it is. Also by using an Internet time source a hole must be left open in the network firewall to allow for communication to the server, this has its own security risks.

The only two secure methods for receiving a UTC time signal is to either use the GPS network or national time and frequency transmissions that are broadcast by several countries’ national physics laboratories.

In selecting a timing source for a NTP server, location is the key consideration. The national time and frequency transmissions are not available in every country. Whilst the USA, UK, Germany, France, Japan and Finland have a signal there are many countries that do not. Furthermore being a long wave radio transmission it can easily be blocked by local topography, although the radio aerial can pick op a signal indoors which is something a GPS NTP server can’t do.

GPS antennas have to be situated on a roof. This can have logistical problems if the server room is in the basement of a high storey building but on the plus inside the GPS signal can be received literally anywhere in the world.

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.

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.

Synchronising a network is often considered a headache by network administrators who fear that getting it wrong can lead to disastrous results and while there is no deny that a lack of synchronisation can cause unforeseen problems particularly with time sensitive transactions and security, perfect synchronisation is simple if these steps are followed:

1. Use a dedicated NTP server. The NTP server is a device that receives a single time source then distributes it amongst a network of computers using the protocol NTP (Network Time Protocol) one of the oldest Internet based protocols and by far the most widely used time synchronisation software. NTP is often packaged with modern operating systems such as Windows or Linux although there is no substitute for a dedicated NTP device.

2. Always use a UTC time source (Coordinated Universal Time). UTC is based on GMT (Greenwich Meantime) and International Atomic Time (TAI) and is highly accurate. UTC is used by computer networks all over the world ensuring that commerce and trade are all using the same timescale.

3. Use a secure an accurate time signal. Whilst time signals are available all over the Internet they are unpredictable in their accuracy and while some may offer decent enough precision an Internet time server is outside a networks firewall which if left open to receive a timecode will cause vulnerabilities in the security of the network. Either GPS (global positioning system) or a dedicated radio signal such as those transmitted by national physics laboratories (such as MSF – UK, WWVB – USA, DCF –Germany) offer secure and reliable methods of receiving a secure and accurate time signal.

4. Organise a network into stratum, levels. Strata ensure that the NTP server is not inundated with time requests and that the network bandwidth doesn’t become congested. A stratum tree is organised by a few select machines being stratum 2 devices in that they receive a time signal from the NTP server (stratum 1 device) these in turn distribute the time to other devices (stratum 3) and so on.

5. Ensure all machines are utilising UTC and the NTP server tree. A common error in time synchronisation is to not ensure all machines are properly synchronised, just one machine running inaccurate time can have unforeseen consequences.

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.