H3C Technologies H3C S5120 Series Switches - Manual (Page 551)

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z The clock stratum determines the accuracy, which ranges from 1 to 16. The stratum of a reference
clock ranges from 1 to 15. The clock accuracy decreases as the stratum number increases. A
stratum 16 clock is in the unsynchronized state.
z The local clock of an S5120-SI Ethernet switch cannot operate as a reference clock. It can serve as
a NTP server only after synchronized.
Advantages of NTP
z NTP uses a stratum to describe the clock precision, and is able to synchronize time among all
devices within the network.
z NTP supports access control and MD5 authentication.
z NTP can unicast, multicast or broadcast protocol messages.
How NTP Works
Figure 1-1 shows the basic workflow of NTP. Device A and Device B are interconnected over a network.
They have their own independent system clocks, which need to be automatically synchronized through
NTP. For an easy understanding, we assume that:
z Prior to system clock synchronization between Device A and Device B, the clock of Device A is set
to 10:00:00 am while that of Device B is set to 11:00:00 am.
z Device B is used as the NTP time server, namely, Device A synchronizes its clock to that of Device
B.
z It takes 1 second for an NTP message to travel from one device to the other.