Huawei AR150/200 Series Configuration Manual page 120

Huawei AR150&200 Series Enterprise Routers
Configuration Guide - Network Management
Principles of NTP
Figure 5-1
They both have their own system clocks. NTP implements automatic synchronization of their
clocks.
Suppose:
l
l
l
l
Figure 5-1 NTP basic principle diagram
Step1:
Step2:
Step3:
Step4:
The process of synchronizing system clocks is as follows:
1.
2.
3.
Issue 02 (2012-03-30)
shows the principles of NTP. Router A and Router B are connected through a WAN.
Before the system clocks of Router A and Router B are synchronized, the clock of Router
A is set to 10:00:00 am and the clock of Router B is set to 11:00:00 am.
Router B functions as an NTP time server. That is, Router A synchronizes its clock with
that of Router B.
One-way transmission of data packets between Router A and Router B takes one second.
Processing of data packets on the Router A or the Router B takes one second.
NTP packet 10:00:00am
RouterA
RouterA
RouterA
NTP Packet received at 10:00:03
RouterA
Router A sends an NTP packet to Router B. The packet carries the originating timestamp
when it leaves Router A, which is 10:00:00 am (T1).
When the NTP packet reaches Router B, Router B adds its receiving timestamp to the NTP
packet, which is 11: 00:01 am (T2).
When the NTP packet leaves Router B, Router B adds its transmitting timestamp to the
NTP packet, which is 11:00:02 am (T3).
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Network
NTP packet
Network
NTP packet 10:00:00am
Network
Network
5 NTP Configuration
RouterB
10:00:00am 11:00:01am
RouterB
11:00:01am
11:00:02am
RouterB
RouterB
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