Ntp Implementation Modes - 3Com WX3000 Series Operation Manual

Figure 1-1 Implementation principle of NTP
NTP message
Device A
1.
Device A
2.
Device A
3.
NTP message received at 10:00:03 am
Device A
4.
The procedure of synchronizing the system clock is as follows:
Device A sends an NTP message to Device B, with a timestamp 10:00:00 am (T
it is sent.
When the message arrives at Device B, Device B inserts its own timestamp 11:00:01 am (T
the packet.
When the NTP message leaves Device B, Device B inserts its own timestamp 11:00:02 am (T
into the packet.
When receiving a response packet, Device A inserts a new timestamp 10:00:03 am (T
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:
Time offset of Device A relative to Device B:
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.

NTP Implementation Modes

According to the network structure and the position of the local device in the network, the local Ethernet
device can work in multiple NTP modes to synchronize the clock.
10:00:00 am
IP network
NTP message
IP network
NTP message 10:00:00 am
IP network
IP network
Delay = (T
Offset = ((T
Device B
10:00:00 am 11:00:01 am
Device B
11:00:01 am 11:00:02 am
Device B
Device B
-T )-(T -T ).
4 1 3 2
-T ) + (T -T ))/2.
2 1 3 4
1-3
) identifying when
1
) into
2
)
3
) into it.
4