3-3Figure 3-1 Basic work flow of NTPIP networkIP networkIP networkIP networkDevice BDevice ADevice BDevice ADevice BDevice ADevice BDevice A10:00:00 am 11:00:01 am10:00:00 amNTP message 10:00:00 am 11:00:01 am 11:00:02 amNTP messageNTP messageNTP message received at 10:00:03 am1.3.2.4.The process of system clock synchronization is as follows:z Device A sends Device B an NTP message, which is time stamped when it leaves Device A.The time stamp is 10:00:00 am (T1).z When this NTP message arrives at Device B, it is time stamped by Device B. Thetimestamp is 11:00:01 am (T2).z When the NTP message leaves Device B, Device B time stamps it. The timestamp is11:00:02 am (T3).z When Device A receives the NTP message, the local time of Device A is 10:00:03 am (T4).Up to now, Device A has sufficient information to calculate the following two parameters:z The roundtrip delay of NTP message: Delay = (T4–T1) – (T3-T2) = 2 seconds.z Time difference between Device A and Device B: Offset = ((T2-T1) + (T3-T4))/2 = 1 hour.Based on these parameters, Device A can synchronize its own clock to the clock of Device B.This is only a rough description of the work mechanism of NTP. For details, refer to RFC 1305.NTP Message FormatNTP uses two types of messages, clock synchronization message and NTP control message.An NTP control message is used in environments where network management is needed.Because it is not a must for clock synchronization, it is not described in this document.
