H3C S5500-EI series Operation Manual page 1154

Operation Manual – NTP
H3C S5500-EI Series Ethernet Switches
NTP message
Switch A
1.
Switch A
2.
Switch A
3.
NTP message received at 10:00:03 am
Switch A
4.
Figure 1-1 Basic work flow of NTP
The process of system clock synchronization is as follows:
Switch A sends Switch B an NTP message, which is timestamped when it leaves
Switch A. The time stamp is 10:00:00 am (T1).
When this NTP message arrives at Switch B, it is timestamped by Switch B. The
timestamp is 11:00:01 am (T2).
When the NTP message leaves Switch B, Switch B timestamps it. The timestamp
is 11:00:02 am (T3).
When Switch A receives the NTP message, the local time of Switch A is 10:00:03
am (T4).
Up to now, Switch A has sufficient information to calculate the following two important
parameters:
The roundtrip delay of NTP message: Delay = (T
Time difference between Switch A and Switch B: Offset = ((T
hour.
Based on these parameters, Switch A can synchronize its own clock to the clock of
Switch B.
This is only a rough description of the work mechanism of NTP. For details, refer to RFC
1305.
10:00:00 am
IP network
NTP message
IP network
NTP message 10:00:00 am
IP network
IP network
1-3
Chapter 1 NTP Configuration
Switch B
10:00:00 am 11:00:01 am
Switch B
11:00:01 am 11:00:02 am
Switch B
Switch B
–T ) – (T -T
4 1 3
) = 2 seconds.
2
-T ) + (T -T ))/2 = 1
2 1 3 4