PresenTense Time Client is a multi protocol time client. This means PresenTense Time Client can acquire accurate time from various different time sources using a number of protocols. Because time protocols differ in the degree of accuracy they facilitate, they each serve different
Many UNIX servers traditionally offer time on port 37 via UDP and TCP, but the accuracy of the time protocol (RFC 868) is limited to the nearest second. See also Time Protocols & Accuracy. However, the time protocol
according to RFC 868 is insufficient for all but the most rudimentary local area network time synchronization needs as it makes no provision to account for network delays or other network errors to facilitate its limited one second accuracy. For this reason, we will focus
on newer, more sophisticated network time protocols: the Simple Network Time Protocol (SNTP) & the Network Time Protocol (NTP).
SNTP and NTP both use port 123 and share a common packet format. Because of this, SNTP hosts may interoperate with NTP hosts. Both NTP and SNTP compensate for network delays and other network errors. Using SNTP a theoretical precision of microseconds can be achieved. However, NTP distinguishes
itself from SNTP in several important ways. NTP effects synchronization of a computer to an accurate time source in a more elegant fashion. Rather than simply correcting the local system time to bring it into agreement with the time source in an "ad hoc" fashion, NTP aims to gradually bring the
local clock into step with the accurate time source via small, incremental adjustments to the system time or by tiny adjustments to the system clock frequency. Further, NTP employs a range of sophisticated error mitigation methods and performs statistical averaging of time samples it
collects. Because of this, NTP facilitates a much greater degree of accuracy than SNTP and thus minimizes clock hopping and other erratic clock behavior.
Versions prior to version 3.5 shipped with their own, built-in error mitigation and statistical averaging facilities. Starting with version 3.5, PresenTense Time Client also includes a plug-in, distributed as a DLL, which employs the code base of UNIX XNTPD and supports NTP version 3 &
4 according to RFC 1305. This plug-in is distributed with PresenTense Time Client free of charge. If you require the newest, industry standard version of NTP, the use of the NTP version 4 plug-in is recommended.