SNTP (Simple Network Time Protocol)

With the spread of networks and cross-system processes, it has become necessary to find a uniform solution for synchronizing system-time. The official standard was the network time protocol (NTP), which uses various algorithms to correct deviations and uses official world time as a reference clock. The release of a simplified version called simple network time protocol (SNTP) at the beginning of the 1990s is primarily due to the limited computing power of the computers available at that time. The processing power is used a lot less during synchronization via SNTP than with the basic protocol, NTP, which frees up the processor for other tasks – however, most modern devices have a processing power which can accommodate the complexity of NTP.

The simple network time protocol (SNTP) is a time synchronization protocol of the TCP/IP protocol family. It is based on the connectionless user datagram protocol (UDP) and can be used on all supporting devices to synchronize system time in IP networks (IPv4 and IPv6). The basis is a client-server structure in which the individual clients obtain the time information from a selected time server in the same network. In the event that this is not available, additional time servers are available as backup. The first version of SNTP dates from 1992 and is specified in RFC 1361. This describes the protocol as a simplified variant of the network time protocol, which is also used to adjust the system time in networks.

After several revisions, the protocol, developed by a working group at the University of Delaware, is now available in its fourth version (SNTPv4). This version was published by the university in 2006 in RFC 4330.

Like NTP, SNTP is used to synchronize the system time of all devices in a network easily. For this purpose, a client-server model is used and the official world time (“coordinated universal time”) as reference time. So-called time servers act as “distributors” of time for the SNTP clients, i.e. the respective devices, the system time which is to be synchronized using the simple network time protocol. The IP packets required for this function through UDP port 123, and since SNTP is very similar to NTP, NTP servers are often used for the synchronization process.

The transmission of the IP packets can be handled either via simple direct connections (unicast) between a client and a server, or via multipoint connections between a server and several clients (broadcast and multicast).

SNTP and NTP can be differentiated according to the two following points:

• The number of servers used for the synchronization process
• The number of algorithms used to make up for time deviations and ensure the most accurate results possible

In contrast to the more complex NTP protocol, the simple network time protocol prioritizes simplicity. The SNTP specification recommends that the time information should only be obtained from a single server, and any further client-server dependency should be avoided. Furthermore, the server-side use of SNTP is only intended if no other synchronization source is available. Synchronization via NTP, on the other hand, relies on a complex construct of different servers that pass on the information in a hierarchical layer system. Depending on the positioning in the chain, the systems involved in the process can be both clients and servers.

SNTP does not use some algorithms that are provided as standard in the NTP specification. These algorithms serve the purpose of making up for deviations in the local system time to always be able to provide the best possible relation to world time. As a result, SNTP offers a lower level of accuracy than NTP, making the simplified protocol unsuitable for applications and processes that require incredibly accurate time synchronization. Thanks to the combination of fewer algorithms and client-server communication, SNTP synchronization requires significantly fewer resources, which is particularly helpful for simple devices or systems with low computing power.