Figure G.2-1 Maintain Time
NTP/SNTP Client Maintains client clock
NTP Servers External time servers. These may have connections to other time servers, and may be synchronized with national time sources.
G.1.2.3 Referenced Standards
G.1.2.4 Basic Course of Events.
All the full detail is in RFC-1305 and RFC-2030. The most common and mandatory minimum mode for NTP operation establishes a ping pong of messages between client and servers. The client sends requests to the servers, which fill in time related fields in a response, and the client performs optimal estimation of the present time. The RFCs deal with issues of lost messages, estimation formulae, etc. Once the clocks are in synchronization these ping pong exchanges typically stabilize at roughly 1000 second intervals.
The client machine typically uses the time estimate to maintain the internal operating system clock. This clock is then used by applications that need time information. This approach eliminates the application visible difference between synchronized and unsynchronized time. The RFCs provide guidance on proper implementations.