NTP Or SNTP - That is the Question?

While there are several protocols available for time synchronisation the majority of network administrators are selecting either NTP or SNTP. This article will look at each in turn.

At the moment, the two most popular, and alike, protocols are SNTP and NTP. Over time, other protocols have begun to surface, but the two above are the most popular.

Compare an IP Server to a NTP Server

An NTP server is a device that synchronises a computer network to an atomic clock source. A stratum 1 NTP server will synchronise all computers to timing reference over the Internet Protocol (IP) - however, a stratum 2 device may only synchronise to a stratum 1 server.

A number of external timing references are available, most commonly the GPS network (Global Positioning System) or national radio time references. While external timing references are less trusting than Internet sources, it is better to have some say in the accuracy of the time on your network.

Synchronisation with a secure network time server is far more reliable than computer networks synchronising to just any previous time.

Internet

There are a number of secure external timing references available, most commonly the GPS network (Global Positioning System) or national radio time references.

However, as with external timing references, it is possible to synchronise to a time server that displays an inaccurate time.

The GPS network is a real-time network. The time on board the GPS device is constantly updated by the onboard crystal oscillator. The time displayed on the device is accurate to within one millisecond of the atomic clock time.

Thus, to summarise, to synchronise a computer network to a precise UTC time, there is much less required accuracy the lessening the danger of computer network downtime.

dTPTUT

Another potential problem with computer networks is that of time transmission. If a computer believes it is time to communicating with another computer it may assume that the other device is displaying the time with an accurate representation.

This assumption is not always correct. The best way to ensure that the time on your network is being received is by using a dTPTUT. A dTPTUT is a synchronisation to UTC time device. UTC time transmitters are available that can receive a recording of UTC time. These devices then convert the recording to the Universal Coordinated Time (UTC).

A GPS NTP Server

A GPS NTP server is a network device that receives a recording of UTC time from a GPS satellite. The signal is plugged into the GPS antenna and transmitted to the GPS NTP server where it is converted into local time. The time is displayed on a GPS NTP Server or GPS NTP handheld computer device.

GPS is also a location data device that receives a time signal from an atomic clock. The GPS antenna contains a very small crystal oscillator that frequently emits a time signal. This signal is measured by the GPS NTP server and convert the signal to UTC.

A NTP Server

A NTP server is a network device that receives a time signal from a GPS NTP server and converts the signal into UTC. The time signal is utilised to enable a computer to synchronise it's internal system clocks with the external NTP server. Both the GPS and atomic clock time signals are commonly used as timing sources for NTP servers.

There are a number of commercial off the shelf (KTB) NTP servers available that can synchronise a whole network to within a few milliseconds of UTC.

NTP is a hierarchical protocol. At the top of the tree are stratum levels. Stratum 0 is timing reference, while stratum 1 is a server connected to a stratum 0 timing source and a stratum 2 server connected to a stratum 1 server.

The precision of a NTP server is estimated to be somewhere between 1-50 nanoseconds (a nanosecond is 1 billionth of a second).