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Computer Network Time Synchronization

samzenpus posted more than 7 years ago | from the ticking-away-the-moments-that-make-up-a-dull-day dept.


Ben Rothke writes "For most people, having their clocks accurate to within a few millionths of a second is excessive. Yet there are plenty of reasons to ensure that clocks on networks and production systems are that accurate. In fact, the need for synchronized time is a practical business and technology decision that is an integral part of an effective network and security architecture. The reality is that an organizations network and security infrastructure is highly dependent on accurate, synchronized time." Read the rest of Ben's review.

From a practical perspective, nearly every activity requires synchronized time to operate at peak levels, from plane departures and sporting events, to industrial processes, IP telephony, GPS and much more. Within information technology, technologies from directory services, collaboration, to authentication, SIM and VoIP all require accurate and synchronized time to work effectively.

Computer Network Time Synchronization: The Network Time Protocol is a valuable book for those that are serious about network time synchronization. David Mills, the author of the book, is one of the pillars of the network time synchronization community, and an original developer of the IETF-based network time protocol (NTP). The book is the summation of his decades of experience and a detailed look at how to use NTP to achieve highly accurate time on your network.

While network time synchronization is indeed crucial to corporate networks, this is only the second book on the topic. Last year saw Expert Network Time Protocol: An Experience in Time with NTP, which is a most capable title. But this book is clearly the indisputable reference on the subject, given its extraordinary depth and breadth. While Expert Network Time Protocol gets into the metaphysics of time, Mills's book takes a much more rationalist and pragmatic approach, which explains the myriad mathematical equations.

Mills is an electrical engineer by training and a significant part of the books 15 chapters involve advanced mathematics. But even for those who can't manage such equations, there is enough relevant material to make the book most rewarding.

Chapters 1 and 2 provide an excellent overview of the basics of network timekeeping and an overview of how NTP works. We often take for granted that network computers have the capabilities to set their internal clock. But while the capabilities are there, the reality is that these clocks are rarely accurate and subjected to many externalities that affect their ability to provide accurate time. The book shows how highly accurate time is easily achievable; often without the need for additional hardware. The goal of book is to show the reader how they can use NTP to synchronize the time on their network hosts to within a few milliseconds.

Chapters 3 - 11 detail the internals of NTP and time synchronization. Topics such as clock discipline algorithms, clock drivers and more are detailed. For many readers, the information may be overkill, but remember that this is not a For Dummies book.

Chapters 13 - 15 ease up on the abstract mathematics and are much more readable to newbie to the world of time synchronization. Chapter 13 is quite readable and details the metrology and chronometry of how NTP measures time as opposed to other time scales.

One of the key differences is the notion of absolute vs. relative time. Relative or astronomic time is based on the earth's rotation. Since the earth's rotation is not absolute, leap seconds are added to keep UTC (Universal Coordinated Time) synchronized with the astronomical timescale.

So what exactly is this legendary thing called the second? In 1967, the 13th General Conference on Weights and Measures defined the International System unit of time, the second, in terms of atomic time rather than the motion of the Earth. Specifically, a second was defined as the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of cesium-133 atoms in their ground state undisturbed by external fields.

Since the 17th century, time has for the most part been measured astronomically via the solar day. But in the 1940s, it was established that the earth's rotation is not constant, as the earth is spinning slower than it did years ago.

Part of what NTP provides is coordination to UTC. UTC provides operating systems and applications with a common index to synchronize events and prove that events happened when timestamps state they did. UTC is a 24-hour clock system and that any given moment, UTC is the same no matter where you are located.

For the purist, UTC really stands for Coordinated Universal Time, but both terms are used. Mills somewhat humorously notes that we follow the politically correct convention of expressing international terms in English, and their abbreviations in French.

Chapter 15 concludes the book with a fascinating look at the technical history of NTP. As of mid-2006, NTP has been in use for over 25 years and remains one of the longest, if not longest running, continuously operating application protocols in use on the Internet. Currently in version 4.2.1, NTP is a well-developed, stable protocol.

For those that are simply interested in how time synchronization works, or are responsible for time synchronization in their organization, Computer Network Time Synchronization: The Network Time Protocol is the most comprehensive guide available to using NTP.

For those that need an exhaustive tome on all of the minutiae related to NTP and synchronization, this is the source. Short of a vendor and product analysis, the book covers every detail within NTP and is the definitive title on the subject.

Two new books on the subject in a year demonstrate the importance of time synchronization. While this is not likely indicative of a flood of new books on time synchronization, this book should be considered the last word on the topic."

You can purchase Computer Network Time Synchronization from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

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OMG (0, Funny)

Anonymous Coward | more than 7 years ago | (#15338099)

I'm n'sync here!

Finally, an NTP book for the masses (5, Funny)

Giant Ape Skeleton (638834) | more than 7 years ago | (#15338139)

It's about time!

Re:Finally, an NTP book for the masses (3, Funny)

From A Far Away Land (930780) | more than 7 years ago | (#15338225)

"It's about time!"

I clocked your pun doing 110 in a 100 pun zone. If convicted, the punishment is setting VCR clocks in your state, each to within a fraction of a second of each other.

Re:Finally, an NTP book for the masses (3, Insightful)

Seraphim1982 (813899) | more than 7 years ago | (#15338794)

Just cut the power for a few minutes. Then they'll all be blinking '12:00'.

Re:Finally, an NTP book for the masses (1)

fm6 (162816) | more than 7 years ago | (#15339098)

Not possible any more -- they stopped making VCRs with external clock displays. Can't imagine why!

Summary of the book (1)

alexhs (877055) | more than 7 years ago | (#15338596)

apt-get install ntp ntp-server ntp-doc ntpdate

NTP gurus wanted... ? (2, Insightful)

crazyjeremy (857410) | more than 7 years ago | (#15338157)

Seriously... about how many people out there actually need to know NTP to this degree? Anyone have a rough estimate? I can't imagine any one organization would have to dedicate an individual to this sort of thing or would they?

Re:NTP gurus wanted... ? (1)

ejdmoo (193585) | more than 7 years ago | (#15338182)

Indeed. Once you know a few basics (like those D-Link didn't), NTP tends to "Just Work."

Re:NTP gurus wanted... ? (1)

jacksonj04 (800021) | more than 7 years ago | (#15338386)

On newer OSes, it just works without needing even the basics. XP, I think W2K-SP4, OS X, and the vast majority of 'ready to go' linux flavours (Such as Ubuntu, and not Gentoo).

Microsoft's version of NTP (4, Informative)

AB3A (192265) | more than 7 years ago | (#15339161)

Actually, having set up the NTP servers in our network, I have to say that the Windows version of NTP draws very substantial vacuum. It's not nearly as easy to configure. It can't be queried about what it thinks of the configured time standards, and I'm not exactly sure how they expect you to manage keys.

As long as you don't give a damn about sub-second accuracy (in our SCADA system, we like to stay in sync within 7 milliseconds or less) and as long as you don't care about traceability, then I guess it's better than nothing. However, the NT version of Mills' NTP is free, it is very stable on all versions I've tested it on from NT through 2003 server, and the configuration is exactly the same as most POSIX systems.

Having been there and tried it, I have to say that Microsoft did a piss poor job with their version of NTP. Get the GNU version. It Just Works Better.

Re:NTP gurus wanted... ? (3, Interesting)

Just Some Guy (3352) | more than 7 years ago | (#15338234)

Seriously... about how many people out there actually need to know NTP to this degree?

Oh, about 10. But how many weird things do you know that not many others would value?

Some people are really, really into keeping time. It's a hobby for them. This book is for that sort of person. Besides, although my company didn't need to hire a person to do nothing but NTP, they certainly needed at least one person on staff with that skillset (hint: Active Directory, Kerberos, "clockskew") to keep everything else working. How fortunate for me that my boss needs the skills that I picked up out of personal curiosity!

Re:NTP gurus wanted... ? (2, Funny)

schon (31600) | more than 7 years ago | (#15338491)

Some people are really, really into keeping time.

Yeah, it's called OCD. :o)

Re:NTP gurus wanted... ? (1)

drewzhrodague (606182) | more than 7 years ago | (#15338516)

I read about NTP via O'Reilly's crab-book, I think. Either that, or it was the de facto Systems Administration Handbook, which I keep giving away to people. For keeping a set of servers in sync. Generally, I just populate /etc/ntp/step-tickers and restart, but it has been made easy over the years.

I understand that I can have a GPS, and plug it into my host, that I can use NTP to distribute the time from there to my local network. I haven't had a GPS to dedicate to that purpose yet, but I found NTP interesting. I don't do any realtime things yet. This book would be interesting to read, and to brandish from the office bookshelf.

Re:NTP gurus wanted... ? (1)

Firehed (942385) | more than 7 years ago | (#15338262)

I'd wager the only thing they need to dedicate someone to doing is going around once a week to everyone's machine and hit "update now" under the Internet Time tab (granted an XP system, naturally). Over the week you might lose a couple seconds, but if you need that much precision, there's a reason we invented cell phones.

Re:NTP gurus wanted... ? (4, Interesting)

Raul654 (453029) | more than 7 years ago | (#15338291)

Mills told me he was rather popular back around the year 2000 ;) {to the point of being called to the White House for a series of meeting about Y2K complaince)

More interestingly, Mills said that he fears a potential DOS against the entire internet would be to use an NTP hack to advance the clocks on all the caches, thus expiring their contents and causing the root servers to be flooded. This would effectively bring down DNS until the caches could be fixed.

Re:NTP gurus wanted... ? (0)

Anonymous Coward | more than 7 years ago | (#15338311)

my company is still in seventeent century you insensitive clod

Re:NTP gurus wanted... ? (0)

Anonymous Coward | more than 7 years ago | (#15338469)

My experience is that most organizations do not need to be in sync with UTC per se. However, having all time-critical services synchrnoized to a reliable central time source is important. Since many governments and colleges offer time-sync with their UTC-coordinated clocks, however, it makes sense to use an existing service instead of trying to re-invent the wheel. When I was administering NDS on Netware 5 back in the day, keeping servers with locally cached partitions synced to a central time source was critical. Otherwise the partitions of the directory stored on those servers became completely hosed and rebuilding the partitions was a huge PITA.

Later on, as a developer, having time-synced computers became essential to the accuracy of synchronizing data between several different systems. Fortunately a small margin of error was OK, and did not kill everything, but accurate timekeeping to establish a sequence of events as they actually occurred (as accurately as possible) helped to maintain the integrity of our data and keep things humming along. I can't count the number of arguments I had with Manglement (oops Management) over how important an accurate timeline is under some circumstances. Just as important is the ability to accurately establish a sequence of events for troubleshooting purposes. Hard to do when clocks are off.

Re:NTP gurus wanted... ? (2, Informative)

jimwelch (309748) | more than 7 years ago | (#15338480)

>>about how many people out there actually need to know NTP to this degree?

NTP or acurate time?

I am sure you can find the answer to acurate time on Google or by reading the book.
But just to get us started:

  * network file sharing with central backup
  * ditto with CVS type system.
  * network databases.

Re:NTP gurus wanted... ? (1)

Detritus (11846) | more than 7 years ago | (#15338575)

It's useful information if you are going to design time distribution networks, troubleshoot them, or evaluate their performance. NTP's algorithms are much more exposed to the user than those in protocols like TCP. It lets you twist many of the knobs.

Re:NTP gurus wanted... ? (1)

Prof.Phreak (584152) | more than 7 years ago | (#15338894)

Seriously... about how many people out there actually need to know NTP to this degree?

None. In fact, at wr0k, I setup NTP on all boxes in a matter of 20 minutes (without -ever- having used/configured NTP). It's just a matter of reading the man page, changing servers in config files, and... well.. starting NTP server. That's it.

One would have to be pretty thick headed to need a 300 page book to explain it.

Re:NTP gurus wanted... ? (1)

fm6 (162816) | more than 7 years ago | (#15339181)

Seriously... about how many people out there actually need to know NTP to this degree?
Roughly speaking? Nobody. Most NTP features are designed to allow large scale-sharing of a few expensive precision time devices. Nowadays, anybody who cares that much about accurate time keeping can afford a GPS or CDMA device. The rest of us can just poll pool.ntp.org occasionally. NTP software is helpful for both strategies — but you'll never need most of it.

Re:NTP gurus wanted... ? (2, Informative)

DerekLyons (302214) | more than 7 years ago | (#15339221)

Seriously... about how many people out there actually need to know NTP to this degree? Anyone have a rough estimate? I can't imagine any one organization would have to dedicate an individual to this sort of thing or would they?
Anyone writing hard real time distributed applications will need to know NTP this deep, or deeper. So figure, at least a couple of dozen or more individuals in the brokerage sub section of the financial world *alone*.

All you need to know about NTP (5, Funny)

Just Some Guy (3352) | more than 7 years ago | (#15338168)

1. Operate a stratum 1 ticker.
2. Get D-Link to use you as the non-configurable time source for a line of disposable networking gear.
3. Profit!

Congrats to PHK for finding the elusive middle step!

Re:All you need to know about NTP (4, Funny)

Tackhead (54550) | more than 7 years ago | (#15338283)

> 2. Get D-Link to use you as the non-configurable time source for a line of disposable networking gear.

The man who uses one NTP server always knows what time it is. The man who uses two NTP servers is never sure.

The man who wrote the firmware for D-Link is why nobody's sure anymore.

Re:All you need to know about NTP (0)

Anonymous Coward | more than 7 years ago | (#15338645)

Coulda been a woman. They *do* make mistakes too. ...lets see how the mods take this one.... flamebait? informative? insightful? troll? I bet they just leave it alone....


Question about the D-Link Guy (1)

wsanders (114993) | more than 7 years ago | (#15339081)

Was he a member of "the pool"? TFA I saw didn't really say,

These are the [0-3].north-america.pool.ntp.org lines you put in your conf files these days, unless you are D-Link.

The 4 IPs are set up to round robin to a big bunch of volunteer servers.

ieee 1588 is where it is at (5, Informative)

cxbrx (737647) | more than 7 years ago | (#15338176)

NTP is somewhat coarse, IEEE 1588 [nist.gov] gives much tighter timing. IEEE 1588 can be used for industrial automation.

From the intro [nist.gov]:

Measurement and control systems are widely used in traditional test and measurement, industrial automation, communication systems, electrical power systems and many other areas of modern technology. The timing requirements placed on these measurement and control systems are becoming increasingly stringent. Traditionally these measurement and control systems have been implemented in a centralized architecture in which the timing constraints are met by careful attention to programming combined with communication technologies with deterministic latency. In recent years an increasing number of such systems utilize a more distributed architecture and increasingly networking technologies having less stringent timing specifications than the older more specialized technologies. In particular Ethernet communications are becoming more common in measurement and control applications. This has led to alternate means for enforcing the timing requirements in such systems. One such technique is the use of system components that contain real-time clocks, all of which are synchronized to each other within the system. This is very common in the general computing industry. For example essentially all general purpose computers contain a clock. These clocks are used to manage distributed file systems, backup and recovery systems and many other similar activities. These computers typically interact via LANs and the Internet. In this environment the most widely used technique for synchronizing the clocks is the Network Time Protocol, NTP, or the related SNTP.

Measurement and control systems have a number of requirements that must be met by a clock synchronization technology. In particular:

  • Timing accuracies are often in the sub-microsecond range,
  • These technologies must be available on a range of networking technologies including Ethernet but also other technologies found in industrial automation and similar industries,
  • A minimum of administration is highly desirable,
  • The technology must be capable of implementation on low cost and low-end devices,
  • The required network and computing resources should be minimal.

In contrast to the general computing environment of intranets or the Internet, measurement and control systems typically are more spatially localized.

IEEE 1588 addresses the clock synchronization requirements of measurement and control systems.

Origination of abbreviation UTC (5, Informative)

flooey (695860) | more than 7 years ago | (#15338179)

In case anyone's interested, one of the reasons that the abbreviation is UTC is because there are a series of Universal Time time references: UT0, UT1, etc. Despite being officially "Coordinated Universal Time", it's abbreviated as UTC partly to continue the UTx notation.

Re:Origination of abbreviation UTC (0)

DuBois (105200) | more than 7 years ago | (#15338302)

Not so. From Wikipedia:

'The International Telecommunication Union wanted Coordinated Universal Time to have a single abbreviation for all languages. English speakers and French speakers each wanted the intials of their respective languages' terms to be used internationally: "CUT" for "coordinated universal time" and "TUC" for "temps universel coordonné". As a compromise, a variation of the English term was used, with the verbal adjective trailing as in French. "UTC" can thus be read as "universal time coordinated", although that is not the correct name in English.'

So, it's English words in the French order.

Re:Origination of abbreviation UTC (2, Informative)

flooey (695860) | more than 7 years ago | (#15338413)

Not so. From Wikipedia:

The very next paragraph in that article says:

"UTC" also has the benefit that it fits in with the pattern for the abbreviations of variants of Universal Time. "UT0", "UT1", "UT1R", and others exist, so appending "C" for "coordinated" to the base "UT" is very satisfactory for those who are familiar with the other types of UT.

Re:Origination of abbreviation UTC (4, Funny)

jpetts (208163) | more than 7 years ago | (#15338868)

Also, so nobody suggests using Coordinated Universal Network Time.

I've always wondered... (5, Interesting)

SenorAmor (719735) | more than 7 years ago | (#15338212)

It's been proven that the Earth is rotating slower than it used to be, and the definition of a second was changed so that the length of a second remains constant. The day, however, remains the same as it always has been: one full rotation of the Earth. Eventually there will be conflict between the two. If the rotation of the Earth continues to slow, there will be more seconds (and, in turn, more minutes, and then more hours) in a given day. To that end, I've always wondered what would be more disruptive to the human populace: longer days or longer seconds?

Re:I've always wondered... (2, Insightful)

Just Some Guy (3352) | more than 7 years ago | (#15338263)

To that end, I've always wondered what would be more disruptive to the human populace: longer days or longer seconds?

Longer seconds. The change in length of a day is extremely gradual ("glacial" is fast by comparison), but as seconds are defined in terms of physical constants, a changing second means that our physics have ripped and we're fixin' to die.

Re:I've always wondered... (1)

pclminion (145572) | more than 7 years ago | (#15338602)

Changing the size of the fundamental units merely changes the value of the various physical constants. Physics works just fine no matter what units you use. However, a redefinition of the physical constants would open the possibility of accidentally mixing old and new units in a calculation (and NASA has shown us what sorts of things can happen in that event).

Re:I've always wondered... (2, Informative)

hubie (108345) | more than 7 years ago | (#15338287)

and the definition of a second was changed so that the length of a second remains constant
This isn't my field of study, but I believe the second is defined as a certain number of oscillations between two hyperfine levels of the cesium-133 atom. This was done in the late sixties to get the definition of the second away from earth rotations and tie it to something more reliable and easy to measure.

Re:I've always wondered... (4, Funny)

mOdQuArK! (87332) | more than 7 years ago | (#15338632)

"easy to measure" being one of those relative terms that make normal people roll their eyes when thinking about engineers & scientists :-)

Re:I've always wondered... (2)

iggymanz (596061) | more than 7 years ago | (#15338294)

leap seconds are added to the "civil" day to solve that problem roughly every year at present. And there's more than one type of "day", there's mean solar day, which in 1820a.d. was 86,400 atomic seconds, and now is about 2 milliseconds longer.

Re:I've always wondered... (1)

Architect_sasyr (938685) | more than 7 years ago | (#15338415)

Longer days... if it was longer seconds than 3/4's of the slashdot population would be getting more sex for the 30 second's of pleasure ;) Not a problem I am concerned about...


Ingolfke (515826) | more than 7 years ago | (#15338492)

AHHH!!! What have we done!? I blame Bush and the American obsession with fast cars. Each time we peel out a light we slow the Earth just a little bit more.

Re:GLOBAL SLOWING!!! (2, Funny)

Urusai (865560) | more than 7 years ago | (#15338620)

Just jackrabbit your starts to the west, and let the engine brake you going east. Do your part to stop global slowing!

About the author (4, Interesting)

Raul654 (453029) | more than 7 years ago | (#15338253)

Mills is a prof in my department and was my advisor back when I was an undergrad. He is a very smart guy (A bit of trivia about him - he was asked to consult for the Chinese government on the Great Firewall and turned down the offer for ethical reasons). He also prides himself on the fact that NTP has never had a serious (any?) security issue despite being around damn-near forever. One very neat observation he described during a seminar on NTP was that high CPU load increases CPU heat, and CPU heat increases clock drift. Thus, NTP can, in effect, be used to measure CPU loads remotely. Another thing is, assuming CPU load is constant, it can be used as a thermometer, and in practice he has used it to detect fan failures.

Re:About the author (0)

Anonymous Coward | more than 7 years ago | (#15338430)

There was a remote root exploit in 2001 - Advisory [iss.net].

Re:About the author (0)

Anonymous Coward | more than 7 years ago | (#15338654)

Even the lower grade of the crystals would only have a frequency drift well within their overall accuracy of +/-100ppm (lowest grade) or +/- 50ppm (common). Typically you are looking at +/-10ppm or so for temperature drift within the operating range of the working computer system.

Let say 10ms is what your NTP can resolve. You'll need to be measuring over the time span of 1000 seconds for any observable frequency change of +/-10ppm.

time joke (1)

ch-chuck (9622) | more than 7 years ago | (#15338260)

These prisoners were hanging out in the cell when the new guy asks, "Anybody know what time it is?", and one of the older inmates says, "Oh, it's about 2006".

Offtopic, but sig related (1, Informative)

Anonymous Coward | more than 7 years ago | (#15338711)

You don't by chance happen to be a nudist?

Re:time joke (2, Funny)

one2go (829439) | more than 7 years ago | (#15338936)

Here's another one (from Zowie [chronocentric.com])

A rather confident 007 walks into a bar and takes a seat next to a very attractive woman. He gives her a quick glance, then casually looks at his watch for a moment. The woman notices this and asks, "Is your date running late?" "No", he replies, "I am here alone. Q has just given me this state-of-the-art watch and I was just testing it." The intrigued woman says, "A state-of-the-art watch? What's so special about it?" "It uses alpha waves to telepathically talk to me," he explains. "What's it telling you now?" "Well, it says you're not wearing any panties..." The woman giggles and replies, "Well it must be broken because I am wearing panties!" 007 taps his watch, ...and says "Bloody thing must be an hour fast..."

Duh (2, Interesting)

0racle (667029) | more than 7 years ago | (#15338284)

a second was defined as the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of cesium-133 atoms in their ground state undisturbed by external fields.

Well of course, I mean, what took them so long? Seriously though it's things like this that make me ask, what on earth lead them to define it like that? Its not 9 million cycles, not 9.5 million, not an obvious number of cycles at all. How did 9,192,631,770 cycles become it, not 9,192,631,771, thats too long, not 9,192,631,769 thats too short. Only 9,192,631,770 was good enough.

Re:Duh (2, Informative)

PatrickThomson (712694) | more than 7 years ago | (#15338365)

They took the pre-existing definition of a second, and measured how many cycles happened in that second, then rounded that to the nearest integer and said "new definition which is only dependant on quantum mechanics".

Re:Duh (0)

Anonymous Coward | more than 7 years ago | (#15338432)

They probably matched it to whatever was the best time reference at that point.

Re:Duh (1)

cnettel (836611) | more than 7 years ago | (#15338968)

To maintain the illusion that it didn't change from the previous definition, perharps (to within the accuracy of measurements at the time)? Of course, the final decimals were probably a bit of a hack, but a serious attempt to make the match as good as possible.

Synchronization is important in the military (1)

Aaron England (681534) | more than 7 years ago | (#15338296)

Our General raised hell over the fact that our wall clock (which is a set of LED clocks of local time, zulu time, Baghdad and Kabul) in one conference room was two minutes faster than the wall clock in another conference room. I'm not really sure why so much vitrol was spent over a clock discrepency (the clocks aren't used to conduct operations with, just to give rough situational awareness of what time it is in different parts of the world) but that day our systems guys learned the importance of synchronized clocks. Although I think their solution wasn't anything elaborate (like syncing to a central database), just adjusting the slower clock two minutes forward.

Re:Synchronization is important in the military (1)

Ingolfke (515826) | more than 7 years ago | (#15338548)

Maybe the other conference room was in a different sub-quadrant timezone or it could have been some type of spatial anomaly.

To paraphrase a real-world support incident (1)

wsanders (114993) | more than 7 years ago | (#15338559)

Big LED displays aren't cheap. Usually they have serial data input, so you can scroll random stuff on them.

Anyway, I used to work in support at <company that used to build really fast, big, expensive supercomputers>. Just for the hell of it, a user wanted to hook up their $30 Epson dot matrix printer up to their new supercomputer, and we didn't really have a decent cheapo Epson printer driver.

"I just paid $15 million for this damn computer and what do you mean the serial port doesn't work?"

We fixed the serial port driver...

Re:Synchronization is important in the military (1)

BenSchuarmer (922752) | more than 7 years ago | (#15338597)

During the Napoleonic wars, the Russians and Austrians agreed to meet up on a certain date for a coordinated attack. The Austrians waited, the date came and went, but the Russians didn't show up. Napolean saw that he had an advantage against the Austrians and defeated them. A few weeks later he beat the Russians too. When they tried to figure out why the Russians army was late the Russians insisted that they weren't late. The problem was that the Russians were still using the Julian calendar (instead of the Gregorian calendar).

I propose a new standard! (0)

Anonymous Coward | more than 7 years ago | (#15338336)

I propose a new standard:


Accurate time useful in computer security (2, Interesting)

SecureTheNet (915798) | more than 7 years ago | (#15338351)

Accurate time is very useful in computer security work. For one, it's needed to accurately correlate log file entries from one computer to another in case of a breach, to identify means of access and creating an accurate picture of what happened and when.

Of Phones and Networks (2, Interesting)

nbannerman (974715) | more than 7 years ago | (#15338393)

I run the network and phone system in a college, and whilst I appreciate NTP is great, it does have drawbacks.

The biggest problem is keeping computer systems synched to 'real life' systems, such as analogue clocks and college bells. These systems have a mind of their own, and are seemingly set to random times.

A prime example; my computer at work synchs from the web, as do the servers, which in turn means all the Cisco VoIP phones are synched as well. The bells however, are never quite spot on, nor are the many analogue clocks in offices and classrooms.

Does anyone have a method of keeping everything in synch, because centralised and synchronised systems fall apart when dealing with 'real life' systems that are out of my hands.

Re:Of Phones and Networks (1)

dgatwood (11270) | more than 7 years ago | (#15338512)

I once wrote a bell controller app for the Apple II (using the switchable joystick outputs to close a relay). You could do something similar and run it on a UNIX box hooked up to a cheaply available USB prototyping kit. Tie it across the existing manual trigger switch for the bell system, then set the bell system to "silent" mode.

The problem is not one of keeping yourself in sync with a poorly designed system. The problem is one of the poorly designed system needing to be improved to stay in sync with the rest of the planet.

Re:Of Phones and Networks (1)

nbannerman (974715) | more than 7 years ago | (#15338545)

I honestly never would've thought of setting something up like that. Excellent idea; I'll investigate the inner-workings of the system tomorrow and see if I can throw something together along those lines. Many thanks! :)

Re:Of Phones and Networks (1)

QuesarVII (904243) | more than 7 years ago | (#15339109)

You can even skip the usb kit and just use a parallel port. A simple c app can toggle the data pins (2-9) on and off on a parallel port, triggering a relay.

I have the pin going through an fet (with 5v sys power feeding it) to bump up the juice enough to flip the relay in my setup. You may or may not need it with your relay and parallel port.

I have my personal server monitor it's cable modem connection (ping tests) and cut the power via a relay to reset it if needed.

Kind of offtopic, I know, but here is the c code to do it if you're interested:

#include <stdio.h>
#include <unistd.h>
#include <sys/io.h>

int main(int argc,char *argv[]){
int duration;
fprintf(stderr,"Usage: flip-relay <duration>\n");
/*defaults to relay on - swap the 255 and the 0 in
the outb calls to reverse it*/
return 0;

Re:Of Phones and Networks (1)

wkk2 (808881) | more than 7 years ago | (#15339014)

If your application doesn't need a lot of current, an old modem can act as a switch.
Just send it an AT command to go off hook and back on hook.

Re:Of Phones and Networks (1)

jackbarnett (940094) | more than 7 years ago | (#15338550)

You can buy "real life" clocks that syncs with UTC (via NTP or otherwise). We have LED wall clocks at work that sync via Sattelie. They work great (untill a cloud storm that is :P ). Just search google for "wall clock sync" and it returns a bunch. Some sync via wireless, sattelie, dialup, ethernet, other... Just depends on if you really need to be within a second on your "real life" clocks and if so, are you willing to pay up for them?

Re:Of Phones and Networks (1)

Ingolfke (515826) | more than 7 years ago | (#15338573)

Have you gone off your meds? I mean seriously... it isn't healthy to worry about things like this.

Re:Of Phones and Networks (0, Flamebait)

nbannerman (974715) | more than 7 years ago | (#15338604)

Personally, I'm not too fussed. I'm not *that* bothered, but it'd be nice to put something in place that'll stop the complaints from support staff.

Re:Of Phones and Networks (-1, Troll)

Gothmolly (148874) | more than 7 years ago | (#15338667)

Sounds like all your fault, for being British, having a high Slashdot user number, and being a homo.

Re:Of Phones and Networks (2, Funny)

k12linux (627320) | more than 7 years ago | (#15338674)

Easy. Get payroll to set all punch-clocks to the NTP time. You'll find that most manual clocks will "magically" adjust themselves shortly after.

Have to get in an OSX burn... (0, Troll)

WiFireWire (772717) | more than 7 years ago | (#15338456)

...while the burnin' is good

My client recently purchased 40K Apple iBook G4 Laptops. Once deployed, the machines were curiously setting themselves to 1969. Found out that there was a bug in the systems' BIOS, (not sure if that is the traditional term for the MAC firmware) that would loose its time setting. Similar to a PC when the BIOS battery goes south.

So from a 'time sync' security standpoint, this bug may potentially need patched?

-- I like the above 'naked' sig...gonna steal it next forum...

Clock wisdom (2, Funny)

Copid (137416) | more than 7 years ago | (#15338457)

"A man with one clock knows what time it is. A man with two clocks is never quite sure."

Re:Clock wisdom (0)

Anonymous Coward | more than 7 years ago | (#15338510)

Unless one of them is an atomic clock.

Re:Clock wisdom (0)

Anonymous Coward | more than 7 years ago | (#15338953)

"A man with one clock knows what time it is. A man with two clocks is never quite sure."

Man with watch have tiny clock. Man with two watch holding someone else clock.

screw this! (1)

sc0p3 (972992) | more than 7 years ago | (#15338497)

screw this! bring on metric time!

Re:screw this! (1)

askegg (599634) | more than 7 years ago | (#15338849)

Aren't you on metric time already? If not, please set your clocks to 97 past 8 on the 63rd day of August to fall in line with the rest of us.

NTP is great, except if you need it in Windows (5, Interesting)

Circuit Breaker (114482) | more than 7 years ago | (#15338508)

For various reasons, I'm trying to synchronize a clock to millisecond accuracy among ~50 Microsoft Windows stations, and it's nearly impossible -- No NTP client for Windows (including AboutTime, 2000's internal client, XP's internal client, and a port of the standard NTP client) appears to be able to keep time reasonably synchronized.

Part of the problem is the Windows Kernel counting time in 10ms or 15ms (depending on whether or not you use an SMP kernel), which automatically says you can't get more than ~30ms precision. But it seems so much worse, with every machine drifting up to ~1 second daily unless they are syncrhonized very frequently -- I get somewhat reasonable results synchronizing them every minute.

On Linux and FreeBSD, this is so trivial it's not even funny; My linux machines manage to keep synchronization to ~0.5 ms over months. Please wake me up when Windows is ready for the enterprise. And, yes, the "enterprise" I work in does need millisecond precision time-of-day synchronization among machine, as does any place that seriously tries to correlate network events (especially those related to security) collected at different points in the network.

Re:NTP is great, except if you need it in Windows (2, Interesting)

ldspartan (14035) | more than 7 years ago | (#15338702)

If its synchronizing on a schedule ("synchronizing them every minute"), you don't have an NTP client, you have an SNTP client. Real NTP doesn't have a concept of a synchronization interval, the clock is either synchronized or it isn't.

I think.

This [meinberg.de] appears to be a port of real-deal NTP code to windows. I've never used it, just found it in a few minutes of googling, but its worth a shot.


Re:NTP is great, except if you need it in Windows (1)

Circuit Breaker (114482) | more than 7 years ago | (#15338760)

NTP does have a "next check" concept, or at least every NTP client I've used does (usually some form of exponential backoff when things look ok).

The "synchronizing on a schedule" was the only solution that was somewhat close to being reasonable. No "real" NTP client I used seems to work. I didn't try this specific build, but I did try one compiled from the same sources, and it had lousy performance.

Thanks for the link, though.

The solution my "enterprise" finally used, btw, is to write a high precision clock synchronizer that is linked to any of our apps that need it; Thankfully, we _are_ in a position to shove the accurate clock everywhere we need. Our own code manages to keep ~0.5ms of accuracy within our network. It's not truly a general purpose solution though.

Re:NTP is great, except if you need it in Windows (1)

russotto (537200) | more than 7 years ago | (#15338845)

Sounds like you need the book. Seriously, real NTP does more that synchronize the clock periodically; it also determines the difference between the client clock frequency and the reference clock frequency, and the first derivative of the client clock frequency (wander), and uses those values to both determine how often to poll the reference sources, and to keep the clock well-synchronized between polls.

A question (1)

toadlife (301863) | more than 7 years ago | (#15339240)

When I connect to our site's DC from my Windows workstation here are work, the times are indentical to the second. I also have my OpenBSD machines get their time from our Windows DC.

But i realize, "to the second" doesn't mean "to the milisecond". How do you even find out how far off your clock is from another machine in Windows? `net time` sure as hell doesn't do it.

CNTS - Best Price at eCampus (0, Troll)

roblambert (230731) | more than 7 years ago | (#15338517)

Re:CNTS - Best Price at eCampus (0)

Anonymous Coward | more than 7 years ago | (#15338590)

Nice way to hide a referral link in there, bub.

Hasn't this already been written? (2, Funny)

Ryan Amos (16972) | more than 7 years ago | (#15338651)

man ntpd

Re:Hasn't this already been written? (2, Informative)

Antique Geekmeister (740220) | more than 7 years ago | (#15338731)

I agree with you in general: the man pages for NTP are quite good. However, there are a few vagaries that I certainly hope this book covers: why you always want at least 3 upstream NTP servers and at least 3 local ones if you're maintaining them (so that the 2 good ones can outvote the confused one), how to gracefully monitor the state of the NTP servers (the Nagios plugins are quite good!), etc.

I am into accurate time. (4, Interesting)

JavaManJim (946878) | more than 7 years ago | (#15338797)

For my computer I am testing an old Heath Most Accurate Clock II* with its RS232 attachment that goes to the serial port on my HP Pavilion. The only problem is the brick sized power transformer gets very hot because its supplying two amp heavy circuits. Use ThinkGeek's KillAWatt to measure power consumption. AWK the transformer is hungry. I guess for real use eventually I will peek at time once a day or so.

*Heath Most Accurate Clock II, synchronizes with WWV at 10 meters.

I think that the network, with all its erratic latency, is not really the best source to use as a timing transport.

Some people have occasionally picked up old cesium clocks from ebay to set the PC's time. Most are from labs and after purchase, probably gather dust in the garage.
http://tycho.usno.navy.mil/cesium.html [navy.mil]

For my wrist, myself and lots of us geeks, use a Casio G-Shock (GW-700a) that updates its time from WWV three times a night. Its more accurate than the clocks at our local public DART train station. They are always four seconds slow.

I also have a great little Nixie clock kit that gets its info, not from WWV via radio, but from satellite GPS time. Its the dinky one at the bottom of the page. Looks fantastic though.
http://www.amug.org/~jthomas/clockpage.html [amug.org]

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