Archive for August, 2009

Reasons for Atomic Clock Timing

Wednesday, August 26th, 2009

Atomic clocks have, unbeknown to most people, revolutionised our technology. Many of the ways we trade, communicate and travel are now solely dependent on timing from atomic clock sources.

A global community often means that we have to communicate with people on other areas of the world and in other time zones. For this purpose a universal time zone was developed, known as UTC (Coordinated Universal Time), which is based on the time told by atomic clocks.

Atomic clocks are incredibly accurate, losing only a second in every hundred million years, which is staggering when you compare it to digital clocks that will lose that much time in a week.

But why do we need such accuracy in timekeeping? Much of the technology we employ in modern times is designed for global communication. The Internet is a good example. So much trade is done across continents in fields such as the stock exchange, seat reservation and online auctioning that exact time is crucial. Imagine you are bidding for an item on the Internet and you place a bid a few seconds before the end, the last and highest bid, would it be fair to lose the item because the clock on your ISP was a little fast and the computer therefore thought the bidding was over. Or what about seat reservation; if two people on different sides of the globe book a seat at the same time, who gets the seat. This is why UTC is vital for the internet.

Other technologies too such as global positioning and air traffic control are reliant on atomic clocks to provide accuracy (and in the case of air traffic is paramount for safety). Even traffic lights and speed cameras have to be calibrated with atomic clocks otherwise speeding ticket may not be valid as they could be questioned in court.

For computer systems NTP time servers are the preferred method for receiving and distributing a source of UTC time.

Time Server Basic Questions Answered

Wednesday, August 5th, 2009

What is a time server?

A time server is a device that receives and distributes a single time source across a computer network for the purposes of time synchronization. These devices are often referred to as a NTP server, NTP time server, network time server or dedicated time server.

And NTP?

NTP – Network Time Protocol is a set of software instructions designed to transfer and synchronize time across LANs (Local Area Network) or WANS (Wider Area Network). NTP is one of the oldest known protocols in use today and is by far the most commonly used time synchronization application.

What timescale should I use?

Coordinated Universal Time (UTC) is a global timescale based on the time told by atomic clocks. UTC doesn’t take into account time zones and is therefore ideal for network applications as in principle by synchronizing a network to UTC you are in effect synchronizing it to every other network that utilises UTC.

Where does a time server receive the time from?

A time server can utilise the time from anywhere such as a wrist watch or wall clock. However, any sensible network administrator would opt to use a source of UTC time to ensure the network is as accurate as possible. UTC is available from several ready sources. The most used is perhaps the internet. There are many ‘time servers’ on the internet that distribute UTC time. Unfortunately, many are not at all accurate an in using an internet time source you could be leaving the network vulnerable as malicious users can take advantage of the open port in the firewall where the timing information flows.

It is far better to use a dedicated NTP time server that receives the UTC time signal external to the network and firewall. The best methods for doing this is to either use the GPS signals transmitted from space or the national time and frequency transmissions broadcast by several countries in long wave.

Using NTP Networks

Monday, August 3rd, 2009

Network Time Protocol is by far the most widely used application for synchronizing computer time across local area networks and wider areas networks (LANs and WANs). The principles behind NTP are fairly simple. It checks the time on a system clock and compares it with an authoritative, single source of time, making corrections to the devices to ensure they are all synchronized to the time source.

Selecting the time source to use is perhaps the fundamentally most important thing in setting up a NTP network. Most network administrators opt, quite rightly to use a source of UTC time (Coordinated Universal Time). This is a global timescale and means that a computer network synchronized to UTC is not only using the same timescale as every other UTC synchronized network but also there is no need to worry about different time zones around the globe.

NTP uses different layers, known as strata, to determine the closeness and therefore accuracy, to a time source. As UTC is governed by atomic clocks, any atomic clock giving out a time signal is referred to as stratum 0 and any device that receives the time directly from an atomic clock is stratum 1. Stratum 2 devices are devices that receive the time from stratum 1 and so on. NTP supports over 16 different stratum levels although accuracy and reliable decrease with each stratum layer further away you get.

Man network administrators opt to use an internet source of UTC time. Apart from the security risks of using a time source from the internet and allowing it access through your firewall. Internet time servers are also stratum 2 devices in that they are normally servers that receive the time from single stratum 1 device.

A dedicated NTP time server on the other had are stratum 1 devices in themselves. They receive the time directly from atomic clocks, either via GPS or long wave radio transmissions. This makes them far more secure than internet providers as the time source is external to the network (and firewall) but also it makes them more accurate.

With a stratum 1 time server a network can be synchronized to within a few milliseconds of UTC without risk of compromising your security.