The Five Elements – Part 1: An Accurate Time Source
In fact, the same is true for most organizations—accurate time needs to be pervasive on the network. It’s hard to imagine a company would knowingly tolerate only some of its processes running on time or only some of its timestamps being accurate—especially if they realize how easy and inexpensive good network timekeeping can be to accomplish. To make time both pervasive and accurate, five essential elements must be present:
• An accurate and reliable time source
• A timekeeping architecture that fits the organization
• Robust server management
• Robust network time management
• A secure, verifiable audit trail
Element 1: An Accurate Time Source Ultimately, accurate time must come from reliable source. How accurate that time needs to be depends on the applications and operations performed. Most network operations (e.g., online security, log file updates) require accuracy on the order of 1 to 10 milliseconds. Depending on the specific application, electric utilities may require time measured in microseconds. Most financial and general business applications require accuracy in the 100 millisecond to 10 second range—even if only to accurately establish the order of events.
Even if set to an absolutely accurate time reference, a PC clock may still be off by 50 milliseconds at the very instant when it is set. Then, once set, the clocks in computers will start to drift, some by as much as several minutes a day. It is possible for a workstation to achieve consistent accuracy of half-a-millisecond, but only if its clock is reset repeatedly over the course of a day. The challenge is to reset the clock before it drifts too far, and to do so using a time source that is accurate.
Most organizations, unfortunately, are unaware of the importance of maintaining accurate time on their networks. Those that are aware will typically acquire time in one of two ways: 1) over the Internet from the National Institute of Standards and Technology, NIST, or a third-party time service; 2) from GPS satellites. If time is acquired over the Internet, organizations almost always use NTP (Network Time Protocol), an internationally recognized protocol for synchronizing the clock on client machines with clocks on network time servers. NTP is available on virtually all computing platforms—either as a built-in service of the operating system (Unix, Mac OS) or as widely available client software (Windows).
When evaluating the accuracy of the time source, organizations must also take into account the asymmetric path delays between the time clients and the time server, as well as the security of the time source. Of the methods listed above, GPS is the only one that offers a direct, accurate and secure connection from UTC to inside the security of the organization’s network firewall. There are no intervening WAN infrastructures or routing tables to cause uneven delays between the client requests and server responses—as can happen with internet based NTP time sources.
On a WAN, NTP client time accuracy can be as good as 10 to 50 milliseconds on average, whereas individual time corrections can frequently vary by quite a bit more. However, if UTC is provided via GPS to the LAN, NTP can usually distribute UTC locally with an accuracy of one to two milliseconds to the clients. (GPS time stamp accuracy inside the time server is typically about a few microseconds to UTC). That means for most organizations, and for most applications, a GPS referenced time server is sufficient to deliver time to the local net and distribute time to client machines once available.
There are also other reasons to use GPS besides just performance. GPS avoids keeping the networking port (#123) open in the firewall, which NTP uses, and which can be a potential point of entry for an intruder.
Microsemi provides synchronization services that assist customers with the planning, deployment and maintenance of synchronization infrastructure. Services are designed to lower costs, streamline processes, ensure quality, and deliver the highest level of performance from your synchronization network. Visit Timing & Synchronization Systems and learn how we can help provide you with comprehensive solutions across a wide range of applications.
In the next article in this series, I’ll write about Element 2: A Timekeeping Architecture. Be sure and read the first and second articles in this series, “5 Essential Elements of Network Time Synchronization – Part 1” and “The Importance of Network Time Synchronization – Part 2.”
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