3Com 4210 PWR Configuration Manual page 371

NTP Implementation
Modes
When the message arrives at Device B, Device B inserts its own timestamp
■
11:00:01 am (T ) into the packet.
2
When the NTP message leaves Device B, Device B inserts its own timestamp
■
11:00:02 am (T ) into the packet.
3
When receiving a response packet, the local time of Device A is 10:00:03 am
■
(T4)
At this time, Device A has enough information to calculate the following two
parameters:
Delay for an NTP message to make a round trip between Device A and Device
■
B:
Delay = (T -T )-(T -T
4 1 3
Time offset of Device A relative to Device B:
■
Offset = ((T -T ) + (T
2 1
Device A can then set its own clock according to the above information to
synchronize its clock to that of Device B.
For detailed information, refer to RFC 1305.
According to the network structure and the position of the local Ethernet switch in
the network, the local Ethernet switch can work in multiple NTP modes to
synchronize the clock.
Server/client mode
Figure 110 Server/client mode
Client
Filters and selects a clock
and synchronizes the local
clock to that of the preferred
server
).
2
-T ))/2.
3 4
Network
Clock synchronization
request
Response
Introduction to NTP
Server
Works in server mode
automatically and sends
a response packet
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