Huawei Quidway S3500 Series - Page 626

Operation Manual - System Management
Quidway S3500 Series Ethernet Switches Chapter 7 NTP Configuration
Huawei Technologies Proprietary
7-2
Network
Network
NTP Packet 10:00:00am
Network
Network
11:00:01am
10:00:00am 11:00:01am 11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Network
Network
NTP Packet 10:00:00 am
Network
Network
11:00:01 am
10:00:00 am 11:00:01 am 11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Network
Network
NTP Packet 10:00:00am
Network
Network
11:00:01am
10:00:00am 11:00:01am 11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Network
Network
NTP Packet 10:00:00 am
Network
Network
11:00:01 am
10:00:00 am 11:00:01 am 11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
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:
z 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.
z Ethernet Switch B serves as an NTP time server. That is, Ethernet Switch A
synchronizes the local clock with the clock of B.
z 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:
z Ethernet Switch A sends an NTP packet to Ethernet Switch B. The packet carries
the timestamp 10:00:00am (T
1
) that tells when it left Ethernet Switch A.
z When the NTP packet arrives at Ethernet Switch B, Ethernet Switch B adds a local
timestamp 11:00:01am (T
2
) to it.
z When the NTP packet leaves Ethernet Switch B, Ethernet Switch B adds another
local timestamp 11:00:02am (T
3
) to it.
z When Ethernet Switch A receives the acknowledgement packet, it adds a new
timestamp 10:00:03am (T
4
) to it.
Now Ethernet Switch A collects enough information to calculate the following two
important parameters: