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 describes when the SNTP protocol can be safely implemented in place of NTP. The article also descibes the differences between a NTP server and a SNTP server.

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. Infact a NTP server has no way of telling if a time request originated from a NTP or SNTP client.

The difference between the NTP and SNTP protocols is contained within the sophisticated routines 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 host's system clock is accelerated or decelerated to slowly bring it into line with an accurate external 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 steps the host computers system time rather than slowly slewing it towards 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.

The SNTP protocol is best suited to synchronizing computers at the extremities of a computer 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.