A number of time protocols are widely used to synchronize computer clocks with a network time server. These are:
NTP (Network Time Protocol)
"Network Time Protocol". NTP has the ability to synchronize computers across multiple time servers while compensating for network jitter and other statistical errors. Because of this ability, it is generally suitable for the synchronization of a corporate time server to an atomic clock on the global internet to within tens of milliseconds. This protocol is defined in the Internet standard RFC 1305. The NTP4 protocol plugin supplied with PresenTense Time Server is also able to synchronize to local GPS time sources via the COM port or USB port. This is the most accurate time synchronization as it removes all network jitter and other delays. Fallback to a network based time source is supported in the event that a GPS source becomes unavailable.
SNTP (Simple Network Time Protocol )
"Simple Network Time Protocol". SNTP is a subset of the Network Time Protocol. SNTP is able to compensate for network round trip delay and takes account of nominal dispersion to the root time source. It normally depends on a single time server at any given time and as a result is generally suitable for synchronization of clients to a known time source on a corporate intranet.
Accurate synchronization between client and server to the order of microseconds is attainable on local area networks using SNTP. This protocol is defined in the internet standard RFC 2030.
The UDP/TIME protocol permits synchronization of clients approximately to the nearest second. It provides no mechanisms to compensate for network round trip delay or similar sources of error. This protocol is defined in the internet standard RFC 868.
The TCP/TIME protocol is a variant of UDP/TIME which utilizes the Transmission Control Protocol (TCP) for delivery of data between client and server. While the use of TCP as a communications protocol provides no general enhancements to the synchronization between client and server, it is generally held to be more reliable than UDP. This protocol is defined in the internet standard RFC 868.