NTP, or Network Time Protocol, is one of the oldest Internet protocols still in use today. It is used to distribute accurate time around the Internet and computer networks to network time clients. SNTP, or Simple Network Time Protocol, is a simplified version of the Network Time Protocol lacking many of its complex synchronisation algorithms. SNTP is ideal for implementation on small computers.

This article describes the differences between NTP and SNTP. The article also discusses when SNTP can be safely used in place of the full-blown NTP protocol. It also outlines the differences between a NTP serverclient and a SNTP serverclient.

NTP protocol packets transferred between a NTP server and client are identical to SNTP packets. Each field in a NTP packet of information has a corresponding field in a SNTP packet. NTP protocol packets are entirely interchangeable with SNTP protocol packets. Indeed a NTP server cannot differentiate a request for time originating from a NTP client or SNTP client.

The difference between the NTP and SNTP protocols lie in the algorithms used to implement the protocols. NTP has complex algorithms designed to query multiple NTP servers or external reference clocks and decide on the most accurate time reference. NTP constantly monitors multiple time references for jitter and offset and decides which is the best one to synchronise. NTP corrects time by slewing the system clock. The system clock is speeded up or slowed down in order to bring it slowly into sync with a time reference. Large stepped time adjustments are avoided. NTP has complex synchronisation algorithms that calibrate the system clock to match the frequency of an accurate reference clock.

SNTP is a simplified sub-set of the algorithms used by the NTP protocol. SNTP does not slew the host computers system time instead it steps forwards or backwards to the correct time. Adjusting the system time in steps can cause time critical applications problems. SNTP also lacks the functionality to monitor multiple NTP server reference clocks and decide on the optimal source of time. Instead it utilises a list of references and in the event of failure of a reference it moves on to the next.

SNTP is ideal for synchronising computers at the leaves of a network. It is ideally suited to less powerful processors, such as micro-controllers and embedded systems, which do not require the accuracy of NTP. The complex algorithms of NTP may not be practically implemented on small computers. NTP is ideal for use in dedicated NTP server systems and synchronising large networks of computers. Here, time may be critical and the added complexity of NTP will help maintain accurate synchronisation.