Computer Network Time Synchronization: The Network Time Protocol

Computer Network Time Synchronization: The Network Time Protocol

By David L. Mills

Publisher: CRC
Number Of Pages: 286
Publication Date: 2006-03-24
Sales Rank: 409888
ISBN / ASIN: 0849358051
EAN: 9780849358050
Binding: Hardcover
Manufacturer: CRC
Studio: CRC
Average Rating: 5

What started with the sundial has, thus far, been refined to a level of precision based on atomic resonance: Time. Our obsession with time is evident in this continued scaling down to nanosecond resolution and beyond. But this obsession is not without warrant. Precision and time synchronization are critical in many applications, such as air traffic control and stock trading, and pose complex and important challenges in modern information networks. Penned by David L. Mills, the original developer of the Network Time Protocol (NTP), Computer Network Time Synchronization: The Network Time Protocol takes a broad look at the architecture, protocols, and algorithms involved in time dissemination, distribution, and synchronization. Focused on the fourth generation of NTP, Mills' magnum opus gives an in-depth configuration and performance analysis of typical deployed NTP networks as well as a detailed error budget showing the influence of network and computer delay variations on accuracy. Mills demonstrates the algorithms used to select measurements accessed via diverse pathways to achieve the best accuracy, addresses security issues in depth, and describes the engineering principles underlying NTP architecture and timestamping exchange procedures. Opening the door to highly precise time synchronization in both public and private networks, Computer Network Time Synchronization offers in-depth analysis, theory, and practical concerns in a unified and authoritative reference.

Review:

The Bible of NTP

It is interesting that the so called 'Atomic' clocks you can buy in supermarkets or WalMart/Target are more accurate than anything you could have gotten only a few years ago and for a very little money. But when it comes to computers, they tend to use very inexpensive clocks and on a network there is normally no effort made to synchronize the individual machines.

'This book,' to quote the opening sentence. 'is all about wrangling a herd of network computers so that all display the correct time.' It is specifically is about the Network Time Protocol (NTP), a twenty year old standard that is now well defined, robust, and heavily used. Heavily used means some 25 million clients getting the time from the National Institute for Science and Technology (NIST). A properly set up network can have all participating computers synchronized to less than a millisecond with a time check every fifteen minutes or so.

This book is the Bible of the subject. It is suitable for a network administrator, or if you want to go deeper into the subject it contains enough information to take you just as far as you want to go.

You might miss it if you don't read it carefully, but Dr. Mills is the original developer of NTP. He can take you down into the mathematics of the algorithms in one chapter, and write casually like he does in the opening sentence.

Review:

A must for NTP Administrators

This is the Bible of NTP. Having administered NTP for several years I am pleased to see this work has been completed and published. It is a valuable reference. Setting up NTP is a very simple task but to understand the nuts of bolts of NTP requires patients and devotion to the subject matter and this text greatly aids in that process. The book is also very lightweight which is nice because it doesn't weigh down my backpack and I can take it wherever I go. Long story short if you administer NTP this book is must.

Review:

The definitive reference on how to deploy and use NTP

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.

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.pass: gigapedia.org

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