How Does NTP Work ?

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NTP or Network Time Protocol is a standard protocol for the transfer of time between computers. Typically, GPS time server’s use the network time protocol to synchronise large networks of computers to the correct time. Synchronisation of time is very important in large distributed networks in order to ensure events occur in an ordered manner.

NTP is used to ensure that the time on computers is synchronised to a single accurate reference clock. All the computers can then be provided with a synchronised time from which to operate.

In fact not only computers can use NTP, many other networks products use it to get accurate time, such as; routers, switches, telephone systems, CCTV systems, digital video recorders (DVR’s) and networked clocks, amongst others.

NTP operates in a hierarchical manner. At the highest level, stratum-1, a NTP time server device obtains accurate time from a hardware time source such as GPS. It uses the accurate time reference to synchronise its internal clock. Precise time is then passed on to stratum-2 NTP servers, who in turn use it to synchronise their internal clocks and so on down the line. Each lower level, or stratum, sees a slight decline in accuracy. The hierarchical system allows the load of a large number of clients to be shared between a number of lower-level stratum devices, rather than all trying to access the higher-level device.

A NTP client synchronises by periodically requesting time from a NTP server. The server responds by providing an accurate time stamp. Each NTP request and response is time-stamped, so that round-trip delay calculations can be performed to further improve accuracy.

GPS or Radio Timing?

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GPS and radio are the two most common time references used for network synchronisation. Both have advantages and disadvantages.

Radio time references can often be received indoors, but can be prone to interference. Also metal structures can cause problems. If you happen to be located in a valley or near hills, radio reception can prove difficult. Radio signals also have a finite range, so you need to be reasonably close to the transmitter to receive the signal. Radio transmitters are generally located to serve a particular region or nation. Radio time references generally consist of continous time and date information followed by an accurate pulse marking the start of the minute. Radio transmitters are located in a number of countries: UK, Germany, USA. They are referenced by their call sign: MSF in UK, DCF-77 in Germany and WWVB in USA.

GPS is a satellite based system – originally developed for positioning and navigation. However, it also has a very accurate timing component. GPS has the big advantage that it can be received any where in the world. Provided a GPS antenna can be shown a good view of the sky, you will get a good consistent signal lock. Also, modern GPS time servers can operate with a much reduced view of the sky – or even in many instances indoors. GPS is also much more accurate that radio time references, making it the reference of choice for network timing applications.

NTP Server Manual Time Adjustments

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Many NTP servers, including TimeTools SR series will only synchronize to an external time reference, such as GPS, if its system time is close to the supplied reference time. If there’s too great a difference between the devices system time and the reference clock time, the reference clock time stamps will be rejected.

TimeTools SR series uses a 20 minute window. If the devices system time is more than 10 minutes different from the reference clock time, timestamps are rejected. If this is the case, ‘GPS BAD’ or ‘LF BAD’ will displayed on the LCD and status pages.

This is used a fail-safe to prevent any potential (albeit unlikely) large automatic adjustments of system time taking place.

The devices systems time can be adjusted from a telnet sessions using the setclock command. The system time should be set to UTC time rather than local time.

This applies to all TimeTools LF and GPS NTP Server models.

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Why use GPS for Accurate Time

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There are a number of sources of accurate time available – GPS, Radio, CDMA. They all have their own advantages and disadvantages. The most popular has to be GPS for a number of reasons.

GPS is much more accurate than other time references. It can provide synchronisation down to nanosecond level. It is also a global system – it can also be received anywhere in the world. Provided a GPS antenna can be positioned with a reasonably good view of the sky – a good consistent signal lock is virtually guaranteed.

However, with an externally mounted GPS antenna, ideally, you should also fit some sort of surge suppression. This will protect expensive network equipment from lightning strikes and other potential voltage surges.

If you need a stratum 1 NTP server, GPS is the ideal solution, no matter where your located.

How To Choose a NTP Server

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Choosing a NTP server for your organisation can be bewildering. The list of features and options can seem overwhelming. However, by reviewing your organisations requirements, the choice can be made quite simple.
Most appliances can be divided into basic groups: NTP or SNTP, enclosure type, single or multi-port LAN, accuracy and throughput, reference clock type, backup reference clock and monitoring.
Most NTP servers provide full NTP capability, which is also compatible with SNTP. However, a few appliances are much simpler devices that only utilise the SNTP protocol.
Generally, NTP servers are housed in a 19-inch rack-mountable enclosure – usually, 1U high. Alternative options include, desktop and DIN-rail mounting devices.
Does your organisation need to sync a single or multiple independent LAN’s? If synchronisation of multiple isolated networks is required, choose a device with multiple Ethernet ports.
Accuracy and throughput is generally a function of processing power. The greater the processing power of the NTP server, the more accurate it is, and the more clients it can service. However, even the lowest spec device can usually support thousands of time clients.
GPS, radio and CDMA reference clocks are available to synchronize a stratum 1 server. GPS is by far the best and most popular option. GPS is available worldwide and is more reliable and accurate than other time references.
Some low-cost NTP servers do not provide backup clocks, so they so unsynchronized when their main reference clocks is lost. TCXO, OCXO and Rubidium backup clocks maintain accurate time during temporary signal loss.
SNMP alarms are generally used to monitor the functionality of a NTP server. However, remote syslogging and web-browsers can also be used.

The Measurement of Time

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The passage of time is an abstract notion that we all take for granted.  We all eat, sleep and go to work at about the same time every day.  Very few of us give little thought about it but it is an essential part of all our everyday lives.  This is why, for thousands of years, humans have continuously developed more and more sophisticated ways of measuring the passage of time.  People have for generations aimed to accurately measure the passage of time firstly by using sundials and now by computer time servers and atomic clocks.  This article will describe the fundamental nature of time, how it is measured by movement, and how it is closely related to the concept of space.  It will also aim to highlight the advancements of high technology time references, such as GPS NTP servers, and International time standards.

For centuries, people have measured time with reference to movement. The hands of a clock moving around a clock-face denotes the passage of hours, minutes and seconds. The Earth orbiting around the Sun describes a year.  The moon orbiting around the Earth describes a month.  A day is described by the rotation of the Earth itself.  In fact time and space are closely related.

Einstein’s General Theory of Relativity suggests time is closely linked with the concept of space.  He suggested that both space and time began with the Big Bang and the creation of the Universe some 14 Billion years ago.  At the moment just before the Big Bang, all matter was tightly packed into an incredibly dense, infinitely small, hot state.  It is hard for us to comprehend but the universe, planets, stars and all matter contained within them emerged in a split second from this infinitely small dot.

Einstein’s theory also suggested that eventually in many billions of years, the Universe would reach a maximum size and begin to collapse back in on itself.  It would shrink, becoming denser and hotter and return to a similar state to that from which it emerged.  However, some of the latest observations of the Universe, using modern telescopes, have shown that the galaxies are actually moving away from each other at an ever-increasing rate. These observations imply that the Universe will continually accelerate, expand and cool.

Horology is the study of the measurement of time.  Human history is littered with a large variety of devices developed to measure time.  One of the earliest examples of ancient time measurement devices was the sundial.  It uses the sun to cast a shadow on markings that indicate the hour of day.  Later, mechanical clocks, regulated by the movement of a pendulum, were developed to accurately measure the passage of time. Today, we mainly use electronic clocks, which are based on the resonance, or movement, of a precisely cut crystal oscillator.

Modern technology has seen the introduction of caesium atomic clocks.  They are based on frequency reference masers, which can measure the passage of time to an astonishing degree.  These clocks are typically accurate to one second in one million years. Atomic clocks form the basis of the Global Positioning System, GPS, which can provide positioning information for any location on the planet.  The Internet is synchronised using NTP servers which reference atomic clocks to ensure the synchronisation of computers across the globe.

The precise measurement of time is essential to our modern lifestyles.  So much so that International standards exist to coordinate the measurement of time across all continents of the world.  It is known as Coordinated Universal Time or UTC.  World time is split into a series of longitudinal time zones and are generally one hour apart and their local time is referenced as an offset from UTC time.

Finally, time is an abstract concept that is inextricably linked to the creation of the Universe and the concept of space.  For millennia, humans have aimed to maintain precise time references. Today, modern technology allows us to maintain highly precise time references of astonishing accuracy.  Atomic clock technology has resulted in the creation of many modern high-technology tools such as Internet time servers and the GPS system.

Keeping Accurate Time On Your Computer

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Computers use real time clock chips to maintain system time. These timing devices rely on relatively cheap components, which are generally poor at keeping accurate time. A computer systems time can typically drift by minutes every day.  This article will discuss several methods of keeping a computers system time accurate, from utilising Internet based time references to using GPS NTP servers.  It will  attempt to shed light on how to keep your computer synchronised.

One of the most accurate and cost-effective ways to obtain precise time is to use an Internet based time server.  They use the NTP protocol to distribute accurate time. NTP is an acronym for the Network Time Protocol and has been an important part of the Internet for over 25 years.  It was introduced through the need to provide synchronisation of time critical processes across the Internet.

Many operating systems, including LINUX/UNIX machines, Microsoft Windows servers and workstations have the ability to synchronise time with a NTP Server without any additional software.  Often all they need is to be configured correctly. There are a host of subscription-free public time servers across the internet, many of them are provided by Government departments and agencies.  As long as your computer has access to the Internet, the chances are that you can sync to one of these servers.

Windows NTP Server: XP has a pre-installed SNTP, Simple Network Time Protocol, client service called ‘Windows Time’.  SNTP is effectively a simplified subset of NTP.  The Windows XP time service uses SNTP to sync time with NTP time servers. It is achieved by simply entering the domain name or IP address of an Internet based server in the time properties tab.  The host computer will then, periodically, contact the server and synchronise its system time to the specified reference.

UNIX and LINUX systems also utilise the NTP protocol.  The protocol was, in fact, originally developed for the Linux operating system.  If it has not been pre-installed, the NTP software distribution is freely available from the NTP website under the GNU public licence.  The application runs as a daemon, constantly monitoring and synchronising to a specified list of NTP time references.

If an Internet connection is not available, you may need to consider a hardware time reference.  These devices have computer interfaces and use external reference clocks, such as radio and GPS to provide accurate time.

The GPS system is primarily intended for navigation purposes; however, few people realise that it can also act as an extremely accurate time reference.  GPS devices with USB or serial interfaces can provide accurate time and positioning information to computers.  Software drivers periodically obtain time from the GPS device to synchronise the system time of the host computer.  Sometimes, reference clock drivers are available that interface to the NTP distribution to provide your own dedicated time server.

Radio time receivers use time and frequency transmissions generated by national physics laboratories.  They have the ability to receive a radio signal indoors, therefore potentially reducing installation costs.  There are a number of world-wide radio time broadcasts available: MSF transmitted from Anthorn, Cumbria, UK; WWVB transmitted from Colorado, USA; DCF-77 transmitted from Frankfurt, Germany; TDF transmitted from France and CHU transmitted from Canada.  These signals can often be received up to a few 1000 kilometres away from the radio transmitter.

Internet based dedicated Stratum 1 NTP servers utilise GPS and radio hardware clocks for synchronisation.  Undoubtedly, by using the NTP protocol and a hardware reference clock, you can easily maintain your own network time server.

Ten Reasons Your Organisation Needs a Time Server

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Synchronisation of computers and processes on a computer network is a very important and often over-looked issue. Computers do not generally keep good time when left to their own devices. This can have serious implications for many applications, such as transaction processing, billing services, and security systems. Presented here are the top ten reasons your organisation needs to implement network time synchronisation using a local dedicated GPS NTP server.

1. Synchronisation of Servers and Workstations. Computers utilise relatively low-cost components to maintain time. As a result they are notoriously poor at keeping accurate time. If left unsynchronised each computer on a network will slowly drift away from the correct time to varying degrees. After a relatively short period of time, each computer will have a significantly different time. This can have catastrophic effects for many applications. Typically, transactions could have incorrect time-stamps and become ordered incorrectly; backups could start at inappropriate times, to name but a few issues. Accurate system-wide time ensures servers and workstation process events in an orderly pre-determined manner.

2. Synchronisation of Network Infrastructure. It isn’t just servers and workstations that befit from accurate time. Many devices that form your network infrastructure such as routers, switches and telephone systems benefit from an accurate time reference. Automated backup devices also need accurate time to allow them to schedule backups correctly and not interfere with other important tasks.

3. Internet Time References. There are many internet based NTP servers available that can be freely used as a time reference. Often, these services are provided by universities or scientific departments. They have the advantage of providing a free service without the need for any special hardware. However, as discussed below, they can have associated problems.

4. Provision of Service. Internet time references, of which there are many, often provide a free service. However, the providers of the service are under no obligation to guarantee availability of the service. Servers may be taken down at any time for unscheduled maintenance or configuration purposes. Additionally, restrictions may be applied to the service during certain times. The lack of guarantee of provision may result in loss of synchronisation of your network – which can have very expensive repercussions.

5. Accuracy. The accuracy of timing systems over a network degrades considerably as the distance between server and client increases. Internet NTP servers are by their very nature a long way from any clients, with many complex network paths in-between. Precision is profoundly degraded due to the asymmetric latency of packets generated by a client compared to when they are received from the server. Round trip delays of timing packets can be irregular, thus impacting on the accuracy of synchronisation. A local time server has much reduced network latency. Packets of information are transferred much quicker and more consistently between server and client. Clients can often synchronise to within a couple of milliseconds of a local time reference.

6. Reliability. Dedicated local time servers are designed specifically for the task of providing a network with an accurate time reference. They tend to utilise industrial grade components with much improved reliability when compared to desktop PC’s. Reliability is also increased by the fact that these devices often run at much lower temperatures than desktops. Internet based time references often use standard desktop PC’s to provide a service with their inherent reduced reliability. Additionally, there is much more network hardware utilised to access Internet systems due to complex network paths.
 
7. Configuration and Control. A recent survey of Internet based NTP servers indicated that as many as 78% were configured incorrectly. This leaves only a minority of servers that are actually useful as timing references. You have complete control over the configuration of a local time server ensuring that it is set up correctly for your organisations needs. A local time reference also generally provides monitoring systems to warn of out of tolerance or error conditions so that they can be swiftly acted upon.

8. Security. Internet based time references require contact to be established from servers within your firewall. It requires ports to be left open in the firewall to allow communication of timestamps. This introduces an inherent security risk that can be exploited by hackers.  A local time reference is installed inside your firewall, thus allowing firewalls to be completely locked down – preventing malicious activity. Additionally, complete synchronisation of networked systems can help prevent fraudulent activity by malicious users within an organisation.

9. Traceability. The time provided by a local time reference can be traced by an unbroken chain of calibrations back to a precise reference such as GPS. The resulting reference time can be accurately stated to be within a specified tolerance. Demonstrable traceability is often required by a court of law in legal proceedings.

10. Law. Most local time servers provide detailed logs of information specifying the accuracy of time reference over any given period. Recordkeeping such as this is often required in a court of law to prove legal traceability of time at a given period. Such records can be used to convince a jury of absolute time in a court of law.

To summarise, a network time server is an important but often overlooked resource in an organisations network infrastructure. The importance of time synchronisation in a networked environment cannot be overstated. Internet time references provide a freely available source of time but there is no continuous guarantee of service. The availability of a local time reference is paramount to the correct functioning of many organisations systems.