Ntp Message Format - HP 5500 EI Series Configuration Manual

• When the NTP message leaves Device B, Device B timestamps it. The timestamp is 1 1:00:02 am
(T3).
• When Device A receives the NTP message, the local time of Device A is 10:00:03 am (T4).
Up to now, Device A can calculate the following parameters based on the timestamps:
The roundtrip delay of NTP message: Delay = (T4–T1) – (T3-T2) = 2 seconds.
•
Time difference between Device A and Device B: Offset = ((T2-T1) + (T3-T4))/2 = 1 hour.
•
Based on these parameters, Device A can synchronize its own clock to the clock of Device B.
This is a rough description of how NTP works. For more information, see RFC 1305.

NTP message format

NTP uses two types of messages: clock synchronization and NTP control messages. All NTP messages
mentioned in this document refer to NTP clock synchronization messages. NTP control messages are
used in environments where network management is needed. Because NTP control messages are not
essential for clock synchronization, they are not described in this document.
A clock synchronization message is encapsulated in a UDP message in the format shown in
Figure 6 Clock synchronization message format
The main fields are described as follows:
LI (Leap Indicator)—A 2-bit leap indicator. If set to 1 1, it warns of an alarm condition (clock
•
unsynchronized). If set to any other value, it is not to be processed by NTP.
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Figure 6.