timesync

Timesync, or time synchronization, is the process of aligning the clocks of computers and devices to a common reference time. Accurate timekeeping enables correct ordering of events, reliable logging, and consistent timestamps across distributed systems and security protocols.

Most timesync relies on reference clocks and a hierarchy of time servers. The Network Time Protocol (NTP) and its Simple variant (SNTP) are the most widely used. In NTP, clocks are organized into strata: stratum 0 is a high-precision reference clock (such as a GPS receiver); stratum 1 servers connect to stratum 0, and higher strata serve clients. Clients exchange timestamps to estimate offset and network delay and discipline their local clocks toward selected servers. Over the public Internet, NTP typically achieves tens of milliseconds of accuracy; on controlled networks, accuracy improves significantly.

Another widely used standard is the Precision Time Protocol (PTP), defined by IEEE 1588. PTP can achieve sub-microsecond to microsecond accuracy in local networks that provide hardware timestamping and specialized network support, making it suitable for financial, telecom, and industrial applications.

Timesync faces challenges in virtualized and cloud environments, where guest clocks can drift relative to the host. Solutions often involve coordinated daemons and shared time sources to keep many guests aligned. Leap seconds and clock discipline mechanisms also affect timekeeping, sometimes requiring gradual slewing (smearing) rather than abrupt adjustments.

Security considerations include protecting time sources from spoofing and tampering. Authentication and redundancy are common practices to ensure trust in time data and to prevent timing-based attacks or data inconsistencies in logs and transactions.