Ntp Message Format - 3Com MSR 50 Series Configuration Manual

NTP Message Format

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When this NTP message arrives at Device B, it is timestamped by Device B. The
■
timestamp is 11:00:01 am (T
When the NTP message leaves Device B, Device B timestamps it. The timestamp
■
is 11:00:02 am (T ).
3
When Device A receives the NTP message, the local time of Device A is
■
10:00:03 am (T ).
4
Up to now, Device A has sufficient information to calculate the following two
important parameters:
The roundtrip delay of NTP message: Delay = (T
■
Time difference between Device A and Device B: Offset = ((T
■
1 hour.
Based on these parameters, Device A can synchronize its own clock to the clock of
Device B.
This is only a rough description of the work mechanism of NTP. For details, refer to
RFC 1305.
NTP uses two types of messages, clock synchronization message and NTP control
message. An NTP control message is used in environments where network
management is needed. As it is not a must for clock synchronization, it will not be
discussed in this document.
All NTP messages mentioned in this document refer to NTP clock synchronization
messages.
A clock synchronization message is encapsulated in a UDP message, in the format
shown in Figure 611.
).
2
-T ) - (T
4 1
NTP Overview 2051
-T ) = 2 seconds.
3 2
-T ) + (T -T ))/2 =
2 1 3 4