Rubidium Oscillators Additional Precision for NTP Serve (Part 1)

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Oscillators have been essential in the development of clocks and chronology. Oscillators are just electronic circuitry that produces a repetitive electronic signal. Often crystals such as quartz are used to stabilise the frequency of the oscillation,

Oscillators are the primary technology behind electronic clocks. Digital watches and battery powered analogue clock are all controlled by an oscillating circuit usually containing a quartz crystal.

And while electronic clocks are many times more accurate than a mechanical clock, a quartz oscillator will still drift by a second or two each week.

Atomic clocks of course are far more accurate. They still, however, use oscillators, most commonly caesium or rubidium but they do so in a hyper fine state often frozen in liquid nitrogen or helium. These clocks in comparison to electronic clocks will not drift by a second in even a million years (and with the more modern atomic clocks 100 million years).

To utilise this chronological accuracy a network time server that uses NTP (Network Time Protocol) can be used to synchronise complete computer networks. NTP servers use a time signal from either GPS or long wave radio that comes direct from an atomic clock (in the case of GPS the time is generated in a clock onboard the GPS satellite).

NTP servers continually check this source of time and then adjust the devices on a network to match that time. In between polls (receiving the time source) a standard oscillator is used by the time server to keep time. Normally these oscillators are quartz but because the time server is in regular communication with the atomic clock say every minute or two, then the normal drift of a quartz oscillator is not a problem as a few minutes between polls would not lead to any measurable drift.

To be continued…

Dealing with Time across the Globe

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No matter where we are in the world we all need to know the time at some point in the day but while each day lasts for the same amount of time no matter where you are on Earth the same timescale is not used globally.

The impracticality of Australians having to wake up at 17.00 or those in the US having to start work at 14.00 would rule out suing a single timescale, although the idea was discussed when the Greenwich was named the official prime meridian (where the dateline officially is) for the world some 125 years ago.

While the idea of a global timescale was rejected for the above reasons, it was later decided that 24 longitudinal lines would split the world up into different timezones. These would emanate from GMT around with those on the opposite side of the planet being +12 hours.

However, by the 1970’s a growth in global communications meant that a universal timescale was finally adopted and is still in much use today despite many people having never heard of it.

UTC, Coordinated Universal Time, is based on GMT (Greenwich Meantime) but is kept by a constellation of atomic clocks. It also accounts for variations in earth’s rotation with additional seconds known as ‘leap seconds’ added once of twice a year to counteract the slowing of the Earth’s spin caused by gravitational and tidal forces.

While most people have never heard of UTC or use it directly its influence on our lives in undeniable with computer networks all synchronised to UTC via NTP time servers (Network Time Protocol).

Without this synchronisation to a single timescale many of the technologies and applications we take for granted today would be impossible. Everything from global trading on stocks and shares to internet shopping, email and social networking are only made possible thanks to UTC and the NTP time server.

Radio Controlled Clocks Atomic Clocks on Shortwave

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Atomic clocks are a marvel compared to other forms of timekeepers. It would take over 100,000 years for an atomic clock to lose a second in time which is staggering especially when you compare it to digital and mechanical clocks that can drift that much in a day.

But atomic clocks are not practical pieces of equipment to have around the office or home. They are bulky, expensive and require laboratory conditions to operate effectively. But making use of an atomic clock is straightforward enough especially as atomic time keepers like NIST (National Institute of Standards and Time) and NPL (National Physical Laboratory) broadcast the time as told by their atomic clocks on short wave radio.

NIST transmits its signal, known as WWVB from Boulder, Colorado and it is broadcast on an extremely low frequency (60,000 Hz). The radio waves from WWVB station can cover all of the continental United States plus much of Canada and Central America.

The NPL signal is broadcast in Cumbria in the UK and it is transmitted along similar frequencies. This signal, known as MSF is available throughout most of the UK and similar systems are available in other countries such as Germany, Japan and Switzerland.

Radio controlled atomic clocks receive these long wave signals and correct themselves according to any drift the clock detects. Computer networks also take advantage of these atomic clocks signals and use the protocol NTP (Network Time Protocol) and dedicated NTP time servers to synchronise hundreds and thousands of different computers.

NTP or SNTP That is the Question?

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While there are several protocols available for time synchronisation the majority of network time is synchronised using either NTP or SNTP.

Network Time Protocol (NTP) and Simple Network Time Protocol (SNTP) have been around since the inception of the Internet (and in the case of NTP, several years beforehand) and are by far the most popular and widespread time synchronisation protocols.

However, the difference between the two is slight and deciding which protocol is best for a ntp time server or a particular time synchronisation application can be troublesome.

As its name suggests, SNTP is a simplified version of Network Time Protocol but the question is often asked: ‘what exactly is the difference?’

The main difference between the two versions of the protocol is in the algorithm that is used. NTP’s algorithm can query multiple reference clocks an calculate which is the most accurate.

SNTP use for low processing devices – it is suited to less powerful machines, do not require the high level accuracy of NTP. NTP can also monitor any offset and jitter (small variations in waveform resulting from voltage supply fluctuations, mechanical vibrations or other sources) whilst SNTP does not.

Another major difference is in the way the two protocols adjust for any drift in network devices. NTP will speed up or slow down a system clock to match the time of the reference clock coming into the NTP server (slewing) while SNTP will simply step forward or backward the system clock.

This stepping of the system time can cause potential problems with time sensitive applications especially of the step is quite large.

NTP is used when accuracy is important and when time critical applications are reliant on the network. However, its complex algorithm is not suited to simple machines or those with less powerful processors. SNTP on the other hand is best suited for these simpler devices as it takes up less computer resources, however it is not suited for any device where accuracy is critical or where time critical applications are reliant on the network.

Atomic Clocks the Key to Network Synchronisation

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Sourcing the correct time for network synchronisation is only possible thanks to atomic clocks. Compared to standard timing devices and atomic clock is millions of times more accurate with the latest designs providing accurate time to within a second in a 100,000 years.

Atomic clocks use the unchanging resonance of atoms during different energy states to measure time providing an atomic tick that occurs nearly 9 billion times a second in the case of the caesium atom. In fact the resonance of caesium is now the official definition of a second having been adopted by the International System of Unit (SI).

Atomic clocks are the base clocks used for the international time, UTC (Coordinated Universal Time). And they also provide the basis for NTP servers to synchronise computer networks and time sensitive technologies such as those used by air traffic control and other high level time sensitive applications.

Finding an atomic clock source of UTC is a simple procedure. Particularly with the presence of online time sources such as those provided by Microsoft and the National Institute for Standards and Time (windows.time.com and nist.time.gov).

However, these NTP servers are what are known as stratum 2 devices that mean they are connected to another device which in turn gets the time from an atomic clock (in other words a second-hand source of UTC).

While the accuracy of these stratum 2 servers is unquestionable, it can be affected by the distance the client is from the time servers, they are also outside the firewall meaning that any communication with an online time server requires an open UDP (User Datagram Protocol) port to allow the communication.

This can cause vulnerabilities in the network and are not used for this reason in any system that requires complete security. A more secure (and reliable) method of receiving UTC is to use a dedicated NTP time server. These time synchronisation devices receive the time direct from atomic clocks either broadcast on long wave by places like NIST or NPL (National Physical Laboratory – UK). Alternatively UTC can be derived from the GPS signal broadcast by the constellation of satellites in the GPS network (Global Positioning System).

Network Time Protocol For When Time Matters

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There is a certain irony that the computer that sits on your desktop and may have cost as much as month’s salary will have a clock onboard that is less accurate than a cheap wristwatch bought at a petrol or gas station.

The problem is not that computers are in particularly made with cheap timing components but that any serious timekeeping on a PC can be achieved without expensive or advanced oscillators.

The onboard timing oscillators on most PCs are in fact just a back up to keep the computer clock synchronised when the PC is off or when network timing information is unavailable.

Despite these inadequate onboard clocks, timing on a network of PC’s can be achieved to within millisecond accuracy and a network that is synchronised to the global timescale UTC (Coordinated Universal Time) shouldn’t drift at all.

The reason this high level of accuracy and synchronicity can be achieved without expensive oscillators is that computers can use Network Timing Protocol (NTP) to find and maintain the exact time.

NTP is an algorithm that distributes a single source of time; this can be generated by the onboard clock of a PC – although this would see every machine on the network drift as the clock itself drifts – A far better solution is to use NTP to distribute a stable, accurate source of time, and most preferably for networks that conduct business across the internet, a source of UTC.

The simplest method of receiving UTC – which is kept true by a constellation of atomic clocks around the globe – is to use a dedicated NTP time server. NTP servers use either GPS satellite signals (Global Positioning System) or long wave radio broadcasts (usually transmitted by national physics laboratories like NPL or NIST).

Once received the NTP server distributes the timing source across the network and constantly checks each machine for drift (In essence the networked machine contacts the server as a client and the information is exchanged via TCP/IP.

This makes the onboard clocks of the computers themselves obsolete, although when the machines are initially booted up, or if there has been a delay in contacting the NTP server (if it is down or there is a temporary fault), the onboard clock is used to maintain time until full synchronisation is again achievable.

Time Servers and the Internet

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Timing is becoming increasingly crucial for computer systems. It is now almost unheard of for a computer network to function without synchronisation to UTC (Coordinated Universal Time). And even single machines used in the home are now equipped with automatic synchronisation. The latest incarnation of Windows for instance, Windows 7, connects to a timing source automatically (although this application can be turned off manually by accessing the time and date preferences.)

The inclusion of these automatic synchronisation tools on the latest operating systems is an indication of how important timing information has become and when you consider the types of applications and transactions that are now conducted on the internet it is of no surprise.

Internet banking, online reservations, internet auctions and even email can be reliant on accurate time. Computers use timestamps as the only point of reference they have to identify when and if a transaction has occurred. Mistakes in timing information can cause untold errors and problems, particularly with debugging.

The internet is full of time servers with over a thousand time sources available for online synchronisation however; the accuracy and usefulness of these online sources of UTC time do vary and leaving a TCP/IP open in the firewall to allow the timing information through can leave a system vulnerable.

For network systems where timing is not only crucial but where security is also a paramount issue then the internet is not a preferred source for receiving UTC information and an external source is required.

Connecting a NTP network to an external source of UTC time is relatively straightforward if a network time server is used. These devices that are often referred to as NTP servers, use the atomic clocks onboard GPS (Global Positioning System) satellites or long wave transmissions broadcast by places such as NIST or NPL.

Atomic Clocks and Gravity

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We couldn’t live our lives without them. They affect almost every aspect of our daily lives and many of the technologies that we take for granted in today’s world, just couldn’t function without them. In fact, if you are reading this article on the Internet the there is a chance you are using one right now.

Without knowing it, atomic clocks govern all of us. From the Internet; to mobile phone networks and satellite navigation, without atomic clocks none of these technologies would be possible.

Atomic clocks govern all computer networks using the protocol NTP (network time protocol) and network time servers, computer systems around the world remain in perfect synchronisation.

And they will continue to do so for several million years as atomic clocks are so accurate they can maintain time to within a second for well over 100 million years. However, atomic clocks can be made even more accurate and a French team of scientists are planning to do just that by launching an atomic clock into space.

Atomic clocks are limited to their accuracy on Earth because of the effects of he gravitational pull of the planet on time itself; as Einstein suggested time itself is warped by gravity and this warping slows down time on Earth.

However, a new type of atomic clock named PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbit) is to be placed aboard the ISS (international space station) out of reach from the worst effects of Earth’ gravitational pull.

This new type of atomic clock will allow hyper accurate synchronization with other atomic clocks, here on Earth (which in effect will make synchronization to an NTP server even more precise).

Pharao is expected to reach accuracies of around one second each 300 million years and will allow further advances in time reliant technologies.

IEEE 1588 Time Protocol Promises More Accurate Time Synchronisation

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Despite being around for over twenty years, the current favoured time protocol by most networks, NTP (Network Time Protocol) has some competition.

Currently NTP is used to synchonise computer networks using network time servers (NTP servers). Currently NTP can synchronise a computer network to a few milliseconds.

The Precision Time Protocol (PTP) or IEEE 1588 has been developed for local systems requiring very high accuracy (to nano-second level). Currently this type of accuracy is beyond the capabilities of NTP.

PTP requires a master and slave relation ship in the network. A two-step process is required to synchronise devices using the IEEE 1588 (PTP). First, determination of which device is the master is required then the offsets and natural network delays are measured. PTP uses the Best Master Clock algorithm (BMC) to establish which clock on the network is the most accurate and it becomes the master whilst all other clocks become slaves and synchronise to this master.

IEEE (Institute of Electrical and Electronic Engineers) describes IEEE 1588 or (PTP) as designed to “fill a niche not well served by either of the two dominant protocols, NTP and GPS.  IEEE 1588 is designed for local systems requiring very high accuracies beyond those attainable using NTP. It is also designed for applications that cannot bear the cost of a GPS receiver at each node, or for which GPS signals are inaccessible.” (quoted in Wikipedia)

PTP can provide accuracy to a few nano-seconds but this type of accuracy is not required by most network users however, the target use of PTP appears to be mobile broadband and other mobile technologies as PTP supports time-of-day information, used by billing and service level agreement reporting functions in mobile networks.

Secrets of Time Synchronization Software

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Time synchronization is a crucial aspect of computer networking. Ensuring all machines on a network are synchronised to the global timescale, UTC (Coordinated Universal Time), otherwise time sensitive transactions with other networks would be impossible.

Time synchronization is made easy thanks to the Network Time Protocol (NTP) which was devised in the early days of the Internet for that very purpose. It works be utilising a single time source (usually UTC) which is then distributed amongst all devices on the NTP network.

The UTC time source is often taken from the Internet on networks where security is not a great issue but as this involves leaving an open port in a network firewall for many networks the vulnerability this can leave isn’t worth the risk.

Dedicated network time servers (often referred to as NTP servers) are used by many networks as a secure and even more accurate method of receiving UTC. These devices receive the UTC time direct from an atomic clock source.

Furthermore, these dedicated time servers operate external to the firewall and network and use sources such as GPS or radio frequencies to pick up the time codes.

For ease of synchronisation there are various time synchronisation software packages that run hand-in-hand with NTP and allow, through browser interfaces, easy configuration of the time synchronization throughout the network.

Whilst these time synchronisation software packages aren’t essential in using most NTP servers, the standard software installed in operating systems is often lacking or quite complicated.

Most specialist producers of dedicated network time servers will produce a times service client to allow configuration and these are probably best suited for the device from that suppler. However, there are many freeware and open source time synchronisation software packages that are mostly compatible with many NTP servers.