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LCD, Liquid Crystal Display or Liquid Crystal on Silicon, has been around for some time. This technology can be commonly found in popular HDTVs, computer or laptop monitors and Sony's new PSP. But the downside to LCD screens is the dreaded "dead pixel" or "hot pixel" phenomenon. Dead pixels or "hot pixels" are defined as "a pixel on an LCD monitor that remains unlit, or black, when it should be activated and displaying a color.

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Articles

Network Time Synchronisation The Importance of an Accurate Time Server

Each PC has an integral real-time clock that maintains internal system time. PC clocks have low-cost crystal oscillators that are notoriously prone to drift. With time each computer in an organisation drifts at different rates. After a relatively short period of time, there can be large differences between the system times of each computer on the network. Unsynchronised computer time can lead to many problems.

This article discusses the importance of network time synchronisation and of having an accurate network time server resource in an organisation. Computer Time Computer system time is maintained by low-cost real-time clock and crystal oscillator components. Crystal oscillators are manufactured with relatively low tolerance; each one oscillates at a slightly different rate. Additionally, crystals change frequency slightly with temperature variance. This all has the effect that computers are notoriously poor at maintaining an accurate time.

Each computers time in an organisation will drift at slightly different amounts unless they are synchronised in some way. Network Synchronisation Issues Poor network time synchronisation can cause a number of problems. In a transaction-processing environment, transactions generated from various PC's may have an irregular time-stamp. Unsynchronised computers may be vulnerable to fraud, particularly in an environment where transaction time is an important issue. Additionally, problems can arise with shared network files, if computers with unsynchronised system times are using the same resource. Network Time Servers Network time servers obtain accurate time from an external time reference and offer an accurate time resource to network time clients.

Time servers utilise the Network Time Protocol (NTP), which is a UDP based protocol over TCP/IP. A number of external time references are available, such as GPS and regional radio frequency transmissions. The GPS (Global Positioning System) is a subscription free service that offers highly accurate time. GPS antennas require a good view of the sky in order to obtain timing information.

Regional time and frequency transmissions include: MSF transmitted from Rugby (UK) with coverage of the British Isles and North-Western Europe; DCF-77 transmitted from Frankfurt (Germany) with coverage of much of Central Europe; WWVB transmitted from Colorado (US) with coverage of much of the US and Canada. Other regional radio time reference include: TDF (France); CHU (Canada); JJY (Japan) and HBG (Switzerland). Internet Time Servers There are many Internet based NTP time server resources available that can be utilised for network time synchronisation.

However, utilising an Internet time server can have a number of issues. The time server is located outside of the firewall, so a port must be left open in order to access the time server. This obviously has security implications. Additionally, time server accuracy, reliability and provision of service may be problematic. Local Dedicated Network Time Server A local dedicated network time server overcomes many of the issues associated with Internet based references.

A local time server is located inside the security firewall and so requires no external access, negating security issues. Additionally, a local time server will have improved accuracy due to consistent network paths between clients and server. Also there is no provision of service issues since the time server is owned by the organisation where it is installed. Summary Network time synchronisation is an important factor in modern computer network installations. Internet based network time servers may provide a solution to network synchronisation, but there are security issues that arise with there use.

Local dedicated network time servers overcome the security and accuracy issues with internet based services by providing a secure, accurate and reliable network time synchronisation solution.

The author, Dave Evans, is a Software Engineer who is involved in the development of Radio and GPS NTP time server synchronization solutions that ensure accurate time on computer networks. Click here to find out more about Radio and GPS NTP and Time Server solutions.



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