ABSTRACT
This chapter provides an overview of the current Network Time Protocol (NTP) Version 4 public software distribution for Unix, VMS, and Windows. The NTP packet header follows the User Datagram Protocol and Internet Protocol headers and the physical header specific to the underlying transport network. It consists of a number of 32-bit words, although some fields use multiple words, and others are packed in smaller fields within a word. The clock adjust process amortizes the time and frequency corrections to provide smooth, monotonic adjustments for the system clock. The peer process includes the receive, packet, and clock filter routines. The main function of the state machine is to react to bogus time, handle relatively large time steps, suppress outliers, and directly compute frequency corrections at initial startup. A bogus time step is any over PANIC, which causes the program to exit with a message sent to the system log requesting the time be set manually within 1.000 s.
