Huawei Quidway S3500 Series Operation Manual page 626

Operation Manual - System Management
Quidway S3500 Series Ethernet Switches
1. 1. 1. 1.
2. 2. 2. 2.
3. 3. 3. 3.
4. 4. 4. 4.
Figure 7-1 Basic operating principle of NTP
In the figure above, Ethernet Switch A and Ethernet Switch B are connected via the
Ethernet port. They have independent system clocks. Before implement automatic
clock synchronization on both switches, we assume that:
Before synchronizing the system clocks on Ethernet Switch A and B, the clock on
Ethernet Switch A is set to 10:00:00am, and that on B is set to 11:00:00am.
Ethernet Switch B serves as an NTP time server. That is, Ethernet Switch A
synchronizes the local clock with the clock of B.
It takes 1 second to transmit a data packet from either A or B to the opposite end.
The system clocks are synchronized as follows:
Ethernet Switch A sends an NTP packet to Ethernet Switch B. The packet carries
the timestamp 10:00:00am (T
When the NTP packet arrives at Ethernet Switch B, Ethernet Switch B adds a local
timestamp 11:00:01am (T
When the NTP packet leaves Ethernet Switch B, Ethernet Switch B adds another
local timestamp 11:00:02am (T
When Ethernet Switch A receives the acknowledgement packet, it adds a new
timestamp 10:00:03am (T
Now Ethernet Switch A collects enough information to calculate the following two
important parameters:
NTP Packet NTP Packet NTP Packet NTP Packet 10:00:00 am 10:00:00 am
10:00:00am 10:00:00am
Network Network Network Network
LS_A LS_A LS_A LS_A
Network Network Network Network
LS_A LS_A LS_A LS_A
NTP Packet NTP Packet NTP Packet NTP Packet 10:00:00 am 10:00:00am 10:00:00am 10:00:00 am
Network Network Network Network
LS_A LS_A LS_A LS_A
NTP Packet received at 10:00:03 NTP Packet received at 10:00:03 am NTP Packet received at 10:00:03 am NTP Packet received at 10:00:03
Network Network Network Network
LS_A LS_A LS_A LS_A
) to it.
2
) to it.
4
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LS_B LS_B LS_B LS_B
NTP Packet NTP Packet NTP Packet NTP Packet 10:00:00 am 10:00:00am 10:00:00 am 10:00:00am 11:00:01am 11:00:01am 11:00:01 am 11:00:01 am
LS_B LS_B LS_B LS_B
11:00:01am 11:00:01am 11:00:01 am 11:00:01 am 11:00:02 am 11:00:02 am 11:00:02am 11:00:02am
LS_B LS_B LS_B LS_B
LS_B LS_B LS_B LS_B
) that tells when it left Ethernet Switch A.
1
) to it.
3
7-2
Chapter 7 NTP Configuration