1-3Figure 1-1 Implementation principle 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 procedure of synchronizing the system clock is as follows:z Device A sends an NTP message to Device B, with a timestamp 10:00:00 am (T1) identifying whenit is sent.z When the message arrives at Device B, Device B inserts its own timestamp 11:00:01 am (T2) intothe packet.z When the NTP message leaves Device B, Device B inserts its own timestamp 11:00:02 am (T3)into the packet.z When Device A receives the NTP message, the local time of Device A is 10:00:03am (T4).At this time, Device A has enough information to calculate the following two parameters:z Delay for an NTP message to make a round trip between Device A and Device B:Delay = (T4 -T1)-(T3 -T2).z Time offset of Device A relative to Device B:Offset = ((T2 -T1) + (T3 -T4))/2.Device A can then set its own clock according to the above information to synchronize its clock to that ofDevice B.For detailed information, refer to RFC 1305.NTP Implementation ModesAccording to the network structure and the position of the local Ethernet switch in the network, the localEthernet switch can work in multiple NTP modes to synchronize the clock.
