How Can I Synchronise My LAN
Most PC’s have internal real-time clocks that maintain system time. However, many of the components used to implement time keeping are low-cost devices and, hence, do not keep good time. In fact, PC’s are notorious for providing inaccurate time and can drift my many seconds or even minutes each day. This has serious repercussions for distributed computer systems and applications. Each computer on a network can have wildly differing system time and for transaction processing, event logging and many other applications, this is totally unacceptable.
There is a solution, however. Time servers allow all the servers, workstations and other network infrastructure on a network to synchronise to a single precise reference. A Time Server obtains accurate timing information from an external time reference and maintains a precise internal time. This precise time is then made available to network clients for synchronisation purposes.
The Network Time Protocol (NTP) is the standard means of network time synchronisation. NTP defines a number of messages, or packets of information, that are passed between a Time Server and a client in order to achieve synchronisation. Many modern operating systems have integrated NTP client software. Alternatively, NTP client software is often freely downloadable from Internet sites dedicated to network timing.
Configuration of NTP client software is very simple. Generally, the client only requires the IP address of the Time Server that the client is to utilise.
There are many NTP Servers freely available on the Internet for synchronisation. However, there are a number of advantages to having a local server on your network. Firstly, a local server will reside inside your firewall and pose less of a security risk than an Internet based server. Additionally, local servers tend to be more accurate by having a direct connection to an external timing reference. Also, many Internet based servers are configured incorrectly and can provide inaccurate time.
There are a number of external reference clocks available to time servers, the most common and most accurate being the Global Positioning System (GPS). GPS can provide time accurate to within a few nanoseconds. However, a GPS antenna is required that needs to have a good view of the sky, ideally on a rooftop. Therefore, installation costs can be an inhibiting factor. An alternative solution is a radio time reference. Radio time and frequency broadcasts can generally be received indoors close to the host server. Installation costs are therefore significantly reduced. However, weather and other forms of interference can affect radio broadcasts. Also, radio time references are not as accurate as time sourced from GPS.
To summarise, it is very straightforward to synchronise PC’s and network infrastructure to a single precise reference. NTP Time Servers are widely available as off-the-shelf solutions to the problems of maintaining accurate time on networked computers.