Clock Synchronization to a Trusted Time Source and beyond RFC 3161 Time-Stamping (PDF)
Description: A Network Time Server is a device that uses radio frequency signals such as GPS, GLONASS or CDMA to calculate the correct time.  It then uses a standard network protocol such as NTP (Network Time Protocol) or PTP/IEEE-1588 (Precision Time Protocol) to keep all workstations on your network synchronized to within 1/2 millisecond of each other for NTP and within 100 nanoseconds for PTP (with hardware slaves).  When you own a Network Time Server you can put it inside your firewall to avoid the many problems associated with wandering computer clocks AND to avoid the security problems associated with using an Internet Time Server.