3Com 7757 Configuration Manual page 755

NTP Implementation
Mode
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.
To accommodate networks of different structures and switches in different
network positions, NTP can operate in multiple modes, as described in the
following.
Client/Server mode
Figure 193 NTP implementation mode: client/Sever mode
Client
Filters and selects a clocks
and synchronize the local
clock to that of the preferred
server
Peer mode
Figure 194 NTP implementation mode: peer mode
Active peer
In peer mode, both sides
can be synchronized to
each other
).
2
-T ))/2.
3 4
Network
Clock synchronization
request packet
Response packet
Passive peer
Network
Clock synchronization
request packet
Response packet
Synchronize
Introduction to NTP
Server
Works in server mode
automatically and send
a response packet
Works in passive peer
mode automatically
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